query: which of the allotrope of carbon is a constituent of a lead pencil

pos: Allotropes of carbon that diamond is so strong. Although graphite is the most stable allotrope of carbon under standard laboratory conditions (273 or 298 K, 1 atm), a recent computational study indicated that under idealized conditions ("T" = 0, "p" = 0), diamond is the most stable allotrope by 1.1 kJ/mol compared to graphite. Graphite, named by Abraham Gottlob Werner in 1789, from the Greek γράφειν ("graphein", "to draw/write", for its use in pencils) is one of the most common allotropes of carbon. Unlike diamond, graphite is an electrical conductor. Thus, it can be used in, for instance, electrical arc lamp electrodes. Likewise,

pos: Chaoite Chaoite Chaoite, or white carbon, is a mineral described as an allotrope of carbon whose existence is disputed. It was discovered in shock-fused graphite gneiss from the Ries crater in Bavaria. It has been described as slightly harder than graphite, with a reflection colour of grey to white. From its electron diffraction pattern, the mineral has been considered to have a carbyne structure, the linear acetylenic carbon allotrope of carbon. A later report has called this identification, and the very existence of carbyne phases, into question, arguing that the new reflections in the diffraction pattern are due to clay impurities.

pos: Chaoite Edited by Franco Cataldo, CRC Press 2005, Pages 339–370, Print eBook Contents link Chaoite Chaoite, or white carbon, is a mineral described as an allotrope of carbon whose existence is disputed. It was discovered in shock-fused graphite gneiss from the Ries crater in Bavaria. It has been described as slightly harder than graphite, with a reflection colour of grey to white. From its electron diffraction pattern, the mineral has been considered to have a carbyne structure, the linear acetylenic carbon allotrope of carbon. A later report has called this identification, and the very existence of carbyne phases, into question, arguing

pos: Carbon allotrope of carbon, fullerene, that was discovered in 1985 includes nanostructured forms such as buckyballs and nanotubes. Their discoverers – Robert Curl, Harold Kroto and Richard Smalley – received the Nobel Prize in Chemistry in 1996. The resulting renewed interest in new forms lead to the discovery of further exotic allotropes, including glassy carbon, and the realization that "amorphous carbon" is not strictly amorphous. Commercially viable natural deposits of graphite occur in many parts of the world, but the most important sources economically are in China, India, Brazil and North Korea. Graphite deposits are of metamorphic origin, found in association

pos: Nonmetal Graphite, the standard state of carbon, has a lustrous appearance and is a fairly good electrical conductor. The diamond allotrope of carbon is clearly nonmetallic, however, being translucent and having a relatively poor electrical conductivity. Carbon is also known in several other allotropic forms, including semiconducting buckminsterfullerene (C). Nitrogen can form gaseous tetranitrogen (N), an unstable polyatomic molecule with a lifetime of about one microsecond. Oxygen is a diatomic molecule in its standard state; it also exists as ozone (O), an unstable nonmetallic allotrope with a half-life of around half an hour. Phosphorus, uniquely, exists in several allotropic forms that

pos: Allotropes of carbon that diamond is so strong. Although graphite is the most stable allotrope of carbon under standard laboratory conditions (273 or 298 K, 1 atm), a recent computational study indicated that under idealized conditions ("T" = 0, "p" = 0), diamond is the most stable allotrope by 1.1 kJ/mol compared to graphite. Graphite, named by Abraham Gottlob Werner in 1789, from the Greek γράφειν ("graphein", "to draw/write", for its use in pencils) is one of the most common allotropes of carbon. Unlike diamond, graphite is an electrical conductor. Thus, it can be used in, for instance, electrical arc lamp electrodes. Likewise,

pos: Allotropes of carbon and cytokine removal. Lonsdaleite is a hexagonal allotrope of the carbon allotrope diamond, believed to form from graphite present in meteorites upon their impact to Earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice. Hexagonal diamond has also been synthesized in the laboratory, by compressing and heating graphite either in a static press or using explosives. It can also be produced by the thermal decomposition of a polymer, poly(hydridocarbyne), at atmospheric pressure, under inert gas atmosphere (e.g. argon, nitrogen), starting at temperature . A one-dimensional carbon polymer with the

pos: Standard state to a total pressure of 10 Pa. For most elements, the reference point of Δ"H" = 0 is defined for the most stable allotrope of the element, such as graphite in the case of carbon, and the β-phase (white tin) in the case of tin. An exception is white phosphorus, the most common allotrope of phosphorus, which is defined as the standard state despite the fact that it is only metastable. For a substance in solution (solute), the standard state is the hypothetical state it would have at the standard state molality or amount concentration but exhibiting infinite-dilution behavior. The

pos: Chemical element cubic centimeter (g/cm). Since several elements are gases at commonly encountered temperatures, their densities are usually stated for their gaseous forms; when liquefied or solidified, the gaseous elements have densities similar to those of the other elements. When an element has allotropes with different densities, one representative allotrope is typically selected in summary presentations, while densities for each allotrope can be stated where more detail is provided. For example, the three familiar allotropes of carbon (amorphous carbon, graphite, and diamond) have densities of 1.8–2.1, 2.267, and 3.515 g/cm, respectively. The elements studied to date as solid samples have eight kinds

pos: Carbon monofluoride are formed. With increasing fluorine content the colour changes from dark grey to cream white indicating the loss of the aromatic character. The fluorine atoms are located in an alternating fashion above and under the former graphene plane, which is now buckled due to formation of covalent carbon-fluorine bonds. Reaction of carbon with fluorine at even higher temperature successively destroys the graphite compound to yield a mixture of gaseous fluorocarbons such as tetrafluorocarbon, CF, and tetrafluoroethylene, CF. In a similar fashion the recently found carbon allotrope fullerene, C reacts with fluorine gas to give fullerene fluorides with stoichiometries up to

pos: Allotropes of carbon Graphenylene is a single layer carbon material with biphenylene-like subunits as basis in its hexagonal lattice structure. It is also known as biphenylene-carbon. AA'-graphite is an allotrope of carbon similar to graphite, but where the layers are positioned differently to each other as compared to the order in graphite. Amorphous carbon is the name used for carbon that does not have any crystalline structure. As with all glassy materials, some short-range order can be observed, but there is no long-range pattern of atomic positions. While entirely amorphous carbon can be produced, most amorphous carbon actually contains microscopic crystals of graphite-like,

pos: Allotropes of carbon Allotropes of carbon Carbon is capable of forming many allotropes due to its valency. Well-known forms of carbon include diamond and graphite. In recent decades many more allotropes are forms of carbon have been discovered and researched including ball shapes such as buckminsterfullerene and sheets such as graphene. Larger scale structures of carbon include nanotubes, nanobuds and nanoribbons. Other unusual forms of carbon exist at very high temperatures or extreme pressures. Around 500 hypothetical 3-periodic allotropes of carbon are known at the present time according to SACADA database. Diamond is a well known allotrope of carbon. The hardness and high

pos: Carbon nanofoam Carbon nanofoam Carbon nanofoam is an allotrope of carbon discovered in 1997 by Andrei V. Rode and co-workers at the Australian National University in Canberra. It consists of a cluster-assembly of carbon atoms strung together in a loose three-dimensional web. The material is extremely light, with a density of 2–10 mg/cm (0.0012 lb/ft). A gallon of nanofoam weighs about a quarter of an ounce. Each cluster is about 6 nanometers wide and consists of about 4000 carbon atoms linked in graphite-like sheets that are given negative curvature by the inclusion of heptagons among the regular hexagonal pattern. This is the

pos: Allotropes of carbon extremely unstable, but it is an intermittent product used in the creation of carbenes. Diatomic carbon can also be found under certain conditions. It is often detected via spectroscopy in extraterrestrial bodies, including comets and certain stars. Carbon nanofoam is the fifth known allotrope of carbon, discovered in 1997 by Andrei V. Rode and co-workers at the Australian National University in Canberra. It consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web. Each cluster is about 6 nanometers wide and consists of about 4000 carbon atoms linked in graphite-like sheets that are given negative

pos: Carbon the plane of each covalently bonded sheet. This results in a lower bulk electrical conductivity for carbon than for most metals. The delocalization also accounts for the energetic stability of graphite over diamond at room temperature. At very high pressures, carbon forms the more compact allotrope, diamond, having nearly twice the density of graphite. Here, each atom is bonded tetrahedrally to four others, forming a 3-dimensional network of puckered six-membered rings of atoms. Diamond has the same cubic structure as silicon and germanium, and because of the strength of the carbon-carbon bonds, it is the hardest naturally occurring substance measured

pos: Amorphous carbon other allotrope of carbon. It also contains a high concentration of dangling bonds; these cause deviations in interatomic spacing (as measured using diffraction) of more than 5% as well as noticeable variation in bond angle. The properties of amorphous carbon films vary depending on the parameters used during deposition. The primary method for characterizing amorphous carbon is through the ratio of "sp" to "sp" hybridized bonds present in the material. Graphite consists purely of "sp" hybridized bonds, whereas diamond consists purely of "sp" hybridized bonds. Materials that are high in "sp" hybridized bonds are referred to as tetrahedral amorphous carbon,

pos: Graphene Graphene Graphene is an allotrope (form) of carbon consisting of a single layer of carbon atoms arranged in a hexagonal lattice. It is a semimetal with small overlap between the valence and the conduction bands (zero bandgap material).<ref name="10.1002/adma.201502544 p.6519-6525"></ref> It is the basic structural element of many other allotropes of carbon, such as graphite, diamond, charcoal, carbon nanotubes and fullerenes. Graphene has many uncommon properties. It is the strongest material ever tested, conducts heat and electricity efficiently, and is nearly transparent. Graphene shows a large and nonlinear diamagnetism, greater than that of graphite, and can be levitated by neodymium

pos: Fullerene Fullerene A fullerene is an allotrope of carbon in the form of a hollow sphere, ellipsoid, tube, and many other shapes. Spherical fullerenes, also referred to as Buckminsterfullerenes or buckyballs, resemble the balls used in association football. Cylindrical fullerenes are also called carbon nanotubes (buckytubes). Fullerenes are similar in structure to graphite, which is composed of stacked graphene sheets of linked hexagonal rings. Unless they are cylindrical, they must also contain pentagonal (or sometimes heptagonal) rings. The first fullerene molecule to be discovered, and the family's namesake, buckminsterfullerene (C), was manufactured in 1985 by Richard Smalley, Robert Curl, James Heath,

pos: Graphene graphene proceeded rapidly once commercial scale production was demonstrated. By 2017, 13 years after creation of the first laboratory graphene electronic device, an integrated graphene electronics chip was produced commercially and marketed to pharmaceutical researchers by Nanomedical Diagnostics in San Diego. Graphene Graphene is an allotrope (form) of carbon consisting of a single layer of carbon atoms arranged in a hexagonal lattice. It is a semimetal with small overlap between the valence and the conduction bands (zero bandgap material).<ref name="10.1002/adma.201502544 p.6519-6525"></ref> It is the basic structural element of many other allotropes of carbon, such as graphite, diamond, charcoal, carbon nanotubes

pos: Material properties of diamond to a very large kinetic energy barrier, diamonds are metastable; they will not decay into graphite under normal conditions. Material properties of diamond Diamond is the allotrope of carbon in which the carbon atoms are arranged in the specific type of cubic lattice called diamond cubic. Diamond is an optically isotropic crystal that is transparent to opaque. Diamond is the hardest naturally occurring material known. Yet, due to important structural weaknesses, diamond's toughness is only fair to good. The precise tensile strength of diamond is unknown, however strength up to 60 GPa has been observed, and it could be as

pos: Metalloid oxyacid salts, such as a basic selenate 2TeO·SeO and an analogous perchlorate and periodate 2TeO·HXO. Tellurium forms a polymeric, amphoteric, glass-forming oxide TeO. It is a "conditional" glass-forming oxide—it forms a glass with a very small amount of additive. Tellurium has an extensive organometallic chemistry (see Organotellurium chemistry). Carbon is ordinarily classified as a nonmetal but has some metallic properties and is occasionally classified as a metalloid. Hexagonal graphitic carbon (graphite) is the most thermodynamically stable allotrope of carbon under ambient conditions. It has a lustrous appearance and is a fairly good electrical conductor. Graphite has a layered structure. Each

pos: Pencil sharpener pencil in position, although they then sharpen them to the usual conical point as for a round pencil, abandoning some distinctive aspects of the carpenter's pencil. Sharpeners with a single blade for use on wax crayons are available, and sometimes included in boxes of crayons. These often have plastic blades, which are adequate for the soft wax. Mechanical pencils dispense the graphite lead progressively during use and thus do not require sharpening; such pencils are sometimes called "self-sharpening". A type of mechanical pencil has a rotating gear mechanism which rotates the lead slightly every time the lead is lifted off

pos: Mechanical pencil Mechanical pencil A mechanical pencil (US English) or propelling pencil (UK English), also clutch pencil, is a pencil with a replaceable and mechanically extendable solid pigment core called a "lead" . The lead, often made of graphite, is not bonded to the outer casing, and can be mechanically extended as its point is worn away. Other names include microtip pencil, automatic pencil, drafting pencil, technical pencil, click pencil, pump pen, pump pencil, leadholder, pen pencil (Indian English), and lead pencil (Bangladeshi and American English). Mechanical pencils are used to provide lines of constant width without sharpening in technical drawing and

pos: Graphene a crystalline allotrope of carbon with 2-dimensional properties. Its carbon atoms are packed densely in a regular atomic-scale chicken wire (hexagonal) pattern. Each atom has four bonds: one σ bond with each of its three neighbors and one π-bond that is oriented out of plane. The atoms are about 1.42 Å apart. Graphene's hexagonal lattice can be regarded as two interleaving triangular lattices. This perspective was successfully used to calculate the band structure for a single graphite layer using a tight-binding approximation. Graphene's stability is due to its tightly packed carbon atoms and a sp orbital hybridization – a combination

pos: Allotropes of carbon and becomes what is known as pyrolytic carbon, a useful material in blood-contacting implants such as prosthetic heart valves. Graphite is the most stable allotrope of carbon. Contrary to popular belief, high-purity graphite does not readily burn, even at elevated temperatures. For this reason, it is used in nuclear reactors and for high-temperature crucibles for melting metals. At very high temperatures and pressures (roughly 2000 °C and 5 GPa), it can be transformed into diamond. Natural and crystalline graphites are not often used in pure form as structural materials due to their shear-planes, brittleness and inconsistent mechanical properties. In its

pos: Richard Smalley can be cited for a Nobel Prize, graduate students James R. Heath, Yuan Liu, and Sean C. O'Brien participated in the work. Smalley mentioned Heath and O'Brien in his Nobel Lecture. Heath went on to become a professor at California Institute of Technology (Caltech) and O'Brien joined Texas Instruments and is now at MEMtronics. Yuan Liu is a Senior Staff Scientist at Oak Ridge National Laboratory. This research is significant for the discovery of a new allotrope of carbon known as a fullerene. Other allotropes of carbon include graphite, diamond and graphene. Harry Kroto's 1985 paper entitled "C60: Buckminsterfullerine", published

pos: Mechanical pencil applied at an angle. When excess vertical pressure is applied on the lead, the lead is automatically retracted inwards. Higher-end mechanical pencils often feature a lead hardness grade indicator and sometimes feature a retractable lead guide pipe. This allows the lead guide pipe to retract back into the pencil body, which will keep it protected in storage and during transit and makes it 'pocket-safe'. In spite of the name, pencil leads do not contain the toxic chemical element lead, but are typically made with graphite and clay, or plastic polymers. Compared to standard pencils, mechanical pencils have a smaller range

pos: Mechanical pencil leads in a limited range of diameters (0.5 mm, 0.7 mm, or 2 mm) for their own products. Koh-i-Noor makes mechanical colored pencils with replaceable leads in 2.0, 3.15 and 5.6 mm sizes. Mechanical pencil A mechanical pencil (US English) or propelling pencil (UK English), also clutch pencil, is a pencil with a replaceable and mechanically extendable solid pigment core called a "lead" . The lead, often made of graphite, is not bonded to the outer casing, and can be mechanically extended as its point is worn away. Other names include microtip pencil, automatic pencil, drafting pencil, technical pencil, click

pos: James R. Heath problems in cancer and infectious diseases. When Heath was a graduate student at Rice University, he ran the experimental apparatus that generated the first C molecules and, ultimately, won the Nobel Prize in Chemistry for the three senior members of the collaboration: Robert F. Curl and Richard E. Smalley of Rice University and Harold Kroto of the University of Sussex. This research is significant for the discovery of a new allotrope of carbon known as a fullerene. Other allotropes of carbon include graphite, diamond and graphene. James R. Heath's 1985 paper entitled "C60: Buckminsterfullerine", published with colleagues Harry Kroto, S.

pos: Harry Kroto concept had provided a clue to the likely structure of the new species. In 1985, the C discovery caused Kroto to shift the focus of his research from spectroscopy in order to probe the consequences of the C structural concept (and prove it correct) and to exploit the implications for chemistry and material science. This research is significant for the discovery of a new allotrope of carbon known as a fullerene. Other allotropes of carbon include graphite, diamond and graphene. Harry Kroto's 1985 paper entitled "C60: Buckminsterfullerine", published with colleagues J. R. Heath, S. C. O'Brien, R. F. Curl, and

pos: Linear acetylenic carbon was claimed to be carbyne rather than graphite. Finally, the oxidation of copper acetylide in ammoniacal solution (Glaser's reaction) produces a carbonaceous residue that was claimed to consist of "polyacetylide" anions capped with residual copper(I) ions, On the basis of the residual amount of copper, the mean number of units "n" was estimated to be around 230. In 2004, an analysis of a synthesized linear carbon allotrope found it to have a cumulene electronic structure—sequential double bonds along an "sp"-hybridized carbon chain—rather than the alternating triple–single pattern of linear carbyne. In 2016, the synthesis of linear chains of up to

pos: Carbon group tetraethyllead, but this application has been discontinued due to concerns of toxicity. Carbon's allotrope diamond is produced mostly by Russia, Botswana, Congo, Canada, and South Africa. 80% of all synthetic diamonds are produced by Russia. China produces 70% of the world's graphite. Other graphite-mining countries are Brazil, Canada, and Mexico. Silicon can be produced by heating silica with carbon. There are some germanium ores, such as germanite, but these are not mined on account of being rare. Instead, germanium is extracted from the ores of metals such as zinc. In Russia and China, germanium is also separated from coal deposits.

pos: Benzene derivatives are phenol, toluene, and aniline, abbreviated PhOH, PhMe, and PhNH, respectively. Linking benzene rings gives biphenyl, CH–CH. Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene and anthracene. The limit of the fusion process is the hydrogen-free allotrope of carbon, graphite. In heterocycles, carbon atoms in the benzene ring are replaced with other elements. The most important variations contain nitrogen. Replacing one CH with N gives the compound pyridine, CHN. Although benzene and pyridine are "structurally" related, benzene cannot be converted into pyridine. Replacement of a second CH bond with N gives, depending on the location of

pos: Pencil sharpener of 6 cuts and takes practice to master without breaking the lead. Specialized sharpeners are available that operate on non-standard sizes of pencil, such as crayons used in primary schools. Sharpeners that have two openings, one for normal pencils and one for larger crayons, are fairly common. An artist's or draftsman's pencil sharpener leaves the graphite untouched and sharpens only the wood (some models can switch from standard to wood-only by an adjustment). The graphite lead is then honed to a sharp point with a lead pointer, which sharpens only the lead without wood. Lead pointers are also used with

pos: Pencil "plumbago" (Latin for "lead ore"). Because the pencil core is still referred to as "lead", or a "lead", many people have the misconception that the graphite in the pencil is lead, and the black core of pencils is still referred to as "lead", even though it never contained the element lead. The words for pencil in German ("bleistift"), Irish ("peann luaidhe"), Arabic (قلم رصاص "qalam raṣāṣ"), and some other languages literally mean "lead pen". The value of graphite would soon be realised to be enormous, mainly because it could be used to line the moulds for cannonballs; the mines were

pos: Chemiresistor the other materials graphene chemiresistor sensors are relatively new but have shown excellent sensitivity. Graphene is an allotrope of carbon that consists of a single layer of graphite. This versatile material has been used in sensors to detect vapour-phase molecules, pH, proteins, bacteria, and simulated chemical warfare agents. The first published report of nanotubes being used as chemiresistors was made in 2000. Since then there has been research into chemiresistors and chemically sensitive field effect transistors fabricated from individual single-walled nanotubes, bundles of single-walled nanotubes, bundles of multi-walled nanotubes, and carbon nanotube–polymer mixtures. It has been shown that a chemical

pos: AA'-graphite That is, MWNTs are composed of AA’ stacked graphene helices rather than concentric tubes (to be linked later). attribution This article contains content copied from https://www.nature.com/articles/srep39624 licensed under CC-BY-4.0 license AA'-graphite AA'-graphite is an allotrope of carbon similar to graphite, but where the layers are positioned differently to each other as compared to the order in graphite. AA’ stacking of graphene planes is another crystalline form of graphite (orthorhombic, Fig. 1) which is metastable for Bernal AB graphite (hexagonal) (Fig. 2) and reveals a nanocrystalline feature. Dr. Jae-Kap Lee discovered the new crystalline form of graphite in 2008 when he

pos: Pencil sharpener wood and graphite tip of the pencil, while the shavings emerge through a slot along the blade edge. It is important that the cylindrical alignment hole closely fit the diameter of the pencil, to keep the pencil from wobbling, which would cause stepped or lurching cut-depths and point breakage. Another important feature is a larger clearance hole at the end of the cone allowing sections of the pencil lead which break away to be removed with only minor inconvenience. Prism sharpeners can be bare or enclosed in a container to collect the shavings, while some enclosed sharpeners may be harder

pos: AA'-graphite AA'-graphite AA'-graphite is an allotrope of carbon similar to graphite, but where the layers are positioned differently to each other as compared to the order in graphite. AA’ stacking of graphene planes is another crystalline form of graphite (orthorhombic, Fig. 1) which is metastable for Bernal AB graphite (hexagonal) (Fig. 2) and reveals a nanocrystalline feature. Dr. Jae-Kap Lee discovered the new crystalline form of graphite in 2008 when he grew graphite onto diamond. He realized that graphene layers comprising graphite grew on diamond (111) plane with stacked in the sequence of AA', due to the crystallographic feature of diamond.

neg: Carbon group a third allotrope of carbon; it is a component of soot. Another allotrope of carbon is a fullerene, which has the form of sheets of carbon atoms folded into a sphere. A fifth allotrope of carbon, discovered in 2003, is called graphene, and is in the form of a layer of carbon atoms arranged in a honeycomb-shaped formation. Silicon has two known allotropes that exist at room temperature. These allotropes are known as the amorphous and the crystalline allotropes. The amorphous allotrope is a brown powder. The crystalline allotrope is gray and has a metallic luster. Tin has two allotropes:

neg: Silicyne silicyne is analogous to the carbon allotrope graphyne, and similar to the silicon allotrope silicene, being a sheet of silicon atoms. In this form, the silicyne chains that link the silicene hexagons use disilyne bonding alternating with disilane bonding, analogous to polyyne. Silicyne Silicynes are allotropes of silicon. 1-dimensional silicyne is analogous to the carbon allotrope carbyne, being a long chain of silicons, instead of carbons. It is amorphous silicon with "sp" hybridization of the valence electrons. Silicyne is a single linear molecule composed of just silicon atoms. One of the manners they are bonded to each other in a

neg: Chalcogen reactive paramagnetic molecule that is ubiquitous to aerobic organisms and has a blue color in its liquid state. Another allotrope is O, or ozone, which is three oxygen atoms bonded together in a bent formation. There is also an allotrope called tetraoxygen, or O, and six allotropes of solid oxygen including "red oxygen", which has the formula O. Sulfur has over 20 known allotropes, which is more than any other element except carbon. The most common allotropes are in the form of eight-atom rings, but other molecular allotropes that contain as few as two atoms or as many as 20

neg: Linear acetylenic carbon this allotrope were made in 1960 and repeated in 1978. A 1982 re-examination of samples from several previous reports determined that the signals originally attributed to carbyne were in fact due to silicate impurities in the samples. Absence of carbyne crystalline rendered the direct observation of a pure carbyne-assembled solid still a major challenge, because carbyne crystals with well-defined structures and sufficient sizes are not available to date. This is indeed the major obstacle to general acceptance of carbyne as a true carbon allotrope. The mysterious carbyne still attracted scientists with its possible extraordinary properties. In 1984, a group at

neg: Sulfur allotrope again, turning from β-octasulfur to γ-sulfur, again accompanied by a lower density but increased viscosity due to the formation of polymers. At higher temperatures, the viscosity decreases as depolymerization occurs. Molten sulfur assumes a dark red color above . The density of sulfur is about 2 g/cm, depending on the allotrope; all of the stable allotropes are excellent electrical insulators. Sulfur burns with a blue flame with formation of sulfur dioxide, which has a suffocating and irritating odor. Sulfur is insoluble in water but soluble in carbon disulfide and, to a lesser extent, in other nonpolar organic solvents, such

neg: Q-carbon Q-carbon Q-carbon is an allotrope of carbon, discovered in 2015, that is ferromagnetic, electrically conductive, and glows when exposed to low levels of energy. It is relatively inexpensive to make, and some news reports claim that it has replaced diamond as the world's hardest substance. As of 2018, only the discoverers themselves have reported successfully making Q-carbon. According to researchers, Q-carbon exhibits a random amorphous structure that is a mix of 3-way (sp) and 4-way (sp) bonding, rather than the uniform sp bonding found in diamonds. Carbon is melted using nanosecond laser pulses, then quenched rapidly to form Q-carbon, or

neg: Superdense carbon allotropes have dissimilar band gaps compared to the others. For example, SC4 is supposed to be a metallic allotrope while st12, m32, m32*, t32, t32* have band gaps larger that 5.0 eV. These new materials would have structures based on carbon tetrahedra, and represent the densest of such structures. On the opposite end of the density spectrum is a recently theorized tetrahedral structure called T-carbon. This is obtained by replacing carbon atoms in diamond with carbon tetrahedra. In contrast to superdense allotropes, T-carbon would have very low density and hardness. Superdense carbon allotropes Superdense carbon allotropes are proposed configurations of carbon

neg: Allotropes of carbon centimeters in length. There are two main types of nanotubes: single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). Carbon nanobuds are a newly discovered allotrope of carbon in which fullerene like "buds" are covalently attached to the outer sidewalls of the carbon nanotubes. This hybrid material has useful properties of both fullerenes and carbon nanotubes. For instance, they have been found to be exceptionally good field emitters. Schwarzites are negatively curved carbon molecules. (A negatively curved object bends inwards like a saddle rather than bending outwards like a sphere.) The team that first created schwarzites did not recognize them as such.

neg: Carbon nanofoam is perhaps carbon nanofoam's most unusual feature: it is attracted to magnets, and below −183 °C can itself be made magnetic. Carbon nanofoam Carbon nanofoam is an allotrope of carbon discovered in 1997 by Andrei V. Rode and co-workers at the Australian National University in Canberra. It consists of a cluster-assembly of carbon atoms strung together in a loose three-dimensional web. The material is extremely light, with a density of 2–10 mg/cm (0.0012 lb/ft). A gallon of nanofoam weighs about a quarter of an ounce. Each cluster is about 6 nanometers wide and consists of about 4000 carbon atoms linked

neg: Hennig Brand Na) in the form of microcosmic salt, and various carbon-based organics. Under strong heat the oxygen atoms from the phosphate react with carbon to produce carbon monoxide CO, leaving elemental phosphorus P, which comes off as a gas. Phosphorus condenses to a liquid below about 280°C and then solidifies (to the white phosphorus allotrope) below about 44°C (depending on purity). This same essential reaction is still used today (but with mined phosphate ores, coke for carbon, and electric furnaces). Brand's process yielded far less phosphorus than it could have done. The salt part he discarded contained most of the phosphate.

neg: Filamentous carbon research efforts. These studies included studies of the thermodynamic properties of the formation of the allotrope. The most significant study that took place during that time was conducted by Terry Baker in the 1970s and concerned keeping filamentous carbon from growing inside the cooling pipes of nuclear reactors. Filamentous carbon Filamentous carbon is a carbon-containing deposit structure that refers to several allotropes of carbon, including carbon nanotubes, carbon nanofibers, and microcoils. It forms from gaseous carbon compounds. Filamentous carbon structures all contain metal particles. These are either iron, cobalt, or nickel or their alloys. Deposits of it also significantly disrupt

neg: Carbon This carbyne is of considerable interest to nanotechnology as its Young's modulus is 40 times that of the hardest known material – diamond. In 2015, a team at the North Carolina State University announced the development of another allotrope they have dubbed Q-carbon, created by a high energy low duration laser pulse on amorphous carbon dust. Q-carbon is reported to exhibit ferromagetism, fluorescence, and a hardness superior to diamonds. Carbon is the fourth most abundant chemical element in the observable universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the Sun, stars, comets, and in the atmospheres

neg: Buckypaper Buckypaper Buckypaper is a thin sheet made from an aggregate of carbon nanotubes or carbon nanotube grid paper. The nanotubes are approximately 50,000 times thinner than a human hair. Originally, it was fabricated as a way to handle carbon nanotubes, but it is also being studied and developed into applications by several research groups, showing promise as vehicle armor, personal armor, and next-generation electronics and displays. Buckypaper is a macroscopic aggregate of carbon nanotubes (CNT), or "buckytubes". It owes its name to the buckminsterfullerene, the 60 carbon fullerene (an allotrope of carbon with similar bonding that is sometimes referred to

neg: Penta-graphene Penta-graphene Penta-graphene is a carbon allotrope composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling. Penta-graphene was proposed in 2014 on the basis of analyses and simulations. Further calculations showed that it is unstable in its pure form, but can be stabilized by hydrogenation. Owing to its atomic configuration, penta-graphene has an unusually negative Poisson’s ratio and very high ideal strength believed to exceed that of a similar material, graphene. Penta-graphene contains both "sp" and "sp" hybridized carbon atoms. Contrary to graphene, which is a good conductor of electricity, penta-graphene is an insulator with an indirect band gap

neg: Dirac matter Fermionic quasiparticles, the Dirac velocity is identical to the Fermi velocity; in bosonic systems, no Fermi velocity exists, so the Dirac velocity is a more general property of such systems. Graphene is a 2-dimensional crystalline allotrope of carbon, where the carbon atoms are arranged on an hexagonal lattice. Each carbon atom forms formula_30-bonds to the three neighboring atoms that lie in the graphene plane at angles of 120formula_31. These bonds are mediated by three of carbon's four electrons while the fourth electron, which occupies a formula_32 orbital, mediates an out-of-plane -bond that leads to the electronic bands at the Fermi

neg: Filamentous carbon used as a catalyst to decompose acetylene. Filamentous carbon is also one of up to seven allotropes of carbon to form during coke formation on reactor tubes and catalysts. The allotrope has the ability to destroy catalyst support structures, thus blocking reactors. It also forms during stream reforming, along with other varieties of carbon. Filamentous carbon can also be synthesized by cracking methane. The product is then gasified by hydrogen. In the experiment that discovered this, a nickel particle was used as the metal particle for the filament. The filament precipitates on the nickel particle's "support side". Filamentous carbon can

neg: Compounds of lead asymmetry). Thanks to the similarity, both allotropes can exist under standard conditions (beta with small (10 relative) impurities, such as Si, Ge, Mo, etc.). PbO reacts with acids to form salts, and with alkalies to give plumbites, [Pb(OH)] or [Pb(OH)]. The dioxide may be prepared by, for example, halogenization of lead(II) salts. The alpha allotrope is rhombohedral, and the beta allotrope is tetragonal. Both allotropes are black-brown in color and always contain some water, which cannot be removed, as heating also causes decomposition (to PbO and PbO). The dioxide is a powerful oxidizer: it can oxidize hydrochloric and sulfuric acids.

neg: Filamentous carbon the deviation is based on the formation of an intermediate phase of carbides. This theory was proposed by De Bokx "et al." and Manning "et al.". However, it is unlikely if the central metal atom is nickel because in that case, since carbides decompose at , and carbides formation was not observed during such a reaction. A difference between the solubities of metal and filamentous carbon also allows carbon diffusion to occur. When the allotrope engages in a gasification reaction below , the reaction's activation energy is approximately 178 kilojoules per mole. Filamentous carbon is mesoporous and has unusual textural

neg: Austenite Austenite Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron, with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K (727°C); other alloys of steel have different eutectoid temperatures. The austenite allotrope is named after Sir William Chandler Roberts-Austen (1843–1902).; it exists at room temperature in stainless steel. From alpha iron undergoes a phase transition from body-centred cubic (BCC) to the face-centred cubic (FCC) configuration of gamma iron, also called austenite. This is similarly soft and ductile but can dissolve considerably more

neg: Superdense carbon allotropes work of R. Biswas et al. MP8, OP8, SC4, BC-8 and (9,0) carbon allotropes belong to the second group - they are hypothetically quasi-stable at the high pressure. BC-8 carbon is not only a superdense allotrope but also one of the oldest hypothetical carbon structure - initially it was proposed in 1984 in the work R. Biswas et al. The MP8 structure proposed in the work J. Sun et al., is almost two times denser than diamond - its density is as high as 7.06 g/cm and it is the highest value reported so far. All hypothetical superdense carbon allotropes

neg: Compounds of lead plumbates. Lead also has an oxide with mixed +2 and +4 oxidation states, red lead (), also known as "minium". Lead readily forms an equimolar alloy with sodium metal that reacts with alkyl halides to form organometallic compounds of lead such as tetraethyllead. There are three oxides known: PbO, PbO (sometimes called "minium"), and PbO. The former has two allotropes: α-PbO and β-PbO, both with layer structure and tetracoordinated lead. The alpha allotrope is red-colored and has the Pb–O distance of 230 pm; the beta allotrope is yellow-colored and has the Pb–O distance of 221 and 249 pm (due to

neg: Austenite visible spectrum, this glow increases in brightness as temperature increases, and when cherry-red the glow is near its lowest intensity and may not be visible in ambient light. Therefore, blacksmiths usually austenize steel in low-light conditions, to help accurately judge the color of the glow. Austenite Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron, with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K (727°C); other alloys of steel have different eutectoid temperatures. The austenite allotrope is named after Sir William

neg: Alloy a certain temperature (usually between and , depending on carbon content). This allows the smaller carbon atoms to enter the interstices of the iron crystal. When this diffusion happens, the carbon atoms are said to be in "solution" in the iron, forming a particular single, homogeneous, crystalline phase called austenite. If the steel is cooled slowly, the carbon can diffuse out of the iron and it will gradually revert to its low temperature allotrope. During slow cooling, the carbon atoms will no longer be as soluble with the iron, and will be forced to precipitate out of solution, nucleating into

neg: Chalcogen five known allotropes. The gray allotrope, commonly referred to as the "metallic" allotrope, despite not being a metal, is stable and has a hexagonal crystal structure. The gray allotrope of selenium is soft, with a Mohs hardness of 2, and brittle. The four other allotropes of selenium are metastable. These include two monoclinic red allotropes and two amorphous allotropes, one of which is red and one of which is black. The red allotrope converts to the red allotrope in the presence of heat. The gray allotrope of selenium is made from spirals on selenium atoms, while one of the red

neg: Paddlane and "p" + 2 carbons, counting them. The chemical formula is therefore CH. When "p" = 0, the compounds are propellanes. The best known paddlane is [1.1.1.1]paddlane which can be seen as a precursor to octahedrane (C), an allotrope of elemental carbon. The American chemist Philip Eaton, famous for being the first to synthesize the "impossible" cubane molecule, has conducted studies for the synthesis of [2.2.2.2]paddlane. The first mention of paddlane goes back to 1973. Paddlane In organic chemistry, paddlane is any member of a class of tricyclic saturated hydrocarbons having two bridgehead carbon atoms joined by four bridges. The

neg: Linear acetylenic carbon behavior can be attributed to a local charge transfer from the inner tubes to the carbon chains, counterbalancing quenching mechanisms induced by the outer tubes. Carbyne chains can take on side molecules that may make the chains suitable for energy and hydrogen storage. The material is stable at room temperature, largely resisting crosslinks with nearby chains. The rods' stiffness prevents them from coming together in a second location, at least at room temperature. Linear acetylenic carbon Linear acetylenic carbon (LAC), also called carbyne, is an allotrope of carbon that has the chemical structure (−C≡C−) as a repeating chain, with alternating

neg: Linear acetylenic carbon Linear acetylenic carbon Linear acetylenic carbon (LAC), also called carbyne, is an allotrope of carbon that has the chemical structure (−C≡C−) as a repeating chain, with alternating single and triple bonds. It would thus be the ultimate member of the polyyne family. This polymeric carbyne is of considerable interest to nanotechnology as its Young's modulus is – forty times that of diamond. It has also been identified in interstellar space; however, its existence in condensed phases has been contested recently, as such chains would crosslink exothermically (and perhaps explosively) if they approached each other. The first claims of detection of

neg: Carbon group use of tin; 50% of all tin produced goes into this application. 20% of all tin produced is used in tin plate. 20% of tin is also used by the chemical industry. Tin is also a constituent of numerous alloys, including pewter. Tin (IV) oxide has been commonly used in ceramics for thousands of years. Cobalt stannate is a tin compound which is used as a cerulean blue pigment. 80% of all lead produced goes into lead–acid batteries. Other applications for lead include weights, pigments, and shielding against radioactive materials. Lead was historically used in gasoline in the form of

neg: Carbon resemble the structure of fullerenes. The buckyballs are fairly large molecules formed completely of carbon bonded trigonally, forming spheroids (the best-known and simplest is the soccerball-shaped C buckminsterfullerene). Carbon nanotubes are structurally similar to buckyballs, except that each atom is bonded trigonally in a curved sheet that forms a hollow cylinder. Nanobuds were first reported in 2007 and are hybrid bucky tube/buckyball materials (buckyballs are covalently bonded to the outer wall of a nanotube) that combine the properties of both in a single structure. Of the other discovered allotropes, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consists

neg: Partial pressure partial pressure rapidly increases, and could lead to panic or incapacitation of the diver. The partial pressures of particularly oxygen (formula_20) and carbon dioxide (formula_20) are important parameters in tests of arterial blood gases, but can also be measured in, for example, cerebrospinal fluid. Partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas mixture is the sum of the partial pressures of the gases

neg: Material properties of diamond Material properties of diamond Diamond is the allotrope of carbon in which the carbon atoms are arranged in the specific type of cubic lattice called diamond cubic. Diamond is an optically isotropic crystal that is transparent to opaque. Diamond is the hardest naturally occurring material known. Yet, due to important structural weaknesses, diamond's toughness is only fair to good. The precise tensile strength of diamond is unknown, however strength up to 60 GPa has been observed, and it could be as high as 90–225 GPa depending on the crystal orientation. The anisotropy of diamond hardness is carefully considered during diamond

neg: Q-carbon University of California, Berkeley, and Professor James Chelikowsky's group at the University of Texas, Austin. These discoveries have been also confirmed experimentally by Professor Paul Chu and his research group at the Texas Center for Superconductivity at the University of Houston, and Professor Elisa Riedo's group at Georgia Tech and New York University. Q-carbon Q-carbon is an allotrope of carbon, discovered in 2015, that is ferromagnetic, electrically conductive, and glows when exposed to low levels of energy. It is relatively inexpensive to make, and some news reports claim that it has replaced diamond as the world's hardest substance. As of

neg: Silicyne Silicyne Silicynes are allotropes of silicon. 1-dimensional silicyne is analogous to the carbon allotrope carbyne, being a long chain of silicons, instead of carbons. It is amorphous silicon with "sp" hybridization of the valence electrons. Silicyne is a single linear molecule composed of just silicon atoms. One of the manners they are bonded to each other in a succession of double-bonded silicons, analogous to the situation of carbon found in cumulene. The other manner they may be bonded to each other is a succession of alternating single and triple-bonded silicons, analogous to the situation of carbon found in polyyne. 2-dimensional

neg: Forge welding its allotrope changes from gamma iron (face-centered cubic) to delta iron (body-centered cubic). Since the critical temperatures are affected by alloying agents like carbon, steel welds at a lower temperature-range than iron. As the carbon content in the steel increases, the welding temperature-range decreases in a linear fashion. Iron, different steels, and even cast-iron can be welded to each other, provided that their carbon content is close enough that the welding ranges overlap. Pure iron can be welded when nearly white hot; between and . Steel with a carbon content of 2.0% can be welded when orangish-yellow, between and .

neg: Allotropes of phosphorus characteristic garlic smell, and samples are commonly coated with white "diphosphorus pentoxide", which consists of PO tetrahedral with oxygen inserted between the phosphorus atoms and at their vertices. White phosphorus is only slightly soluble in water and can be stored under water. Indeed, white phosphorus is safe from self-igniting only when it is submerged in water. It is soluble in benzene, oils, carbon disulfide, and disulfur dichloride. The white allotrope can be produced using several different methods. In the industrial process, phosphate rock is heated in an electric or fuel-fired furnace in the presence of carbon and silica. Elemental phosphorus

neg: Allotropes of iron changes to a face centered cubic (FCC) crystalline structure. In this form it is called gamma iron (γ-Fe) or Austenite. γ-iron can dissolve considerably more carbon (as much as 2.04% by mass at 1,146 °C). This γ form of carbon saturation is exhibited in stainless steel. Beta iron (β-Fe) are obsolete terms for the paramagnetic allotrope of iron. The primary phase of low-carbon or mild steel and most cast irons at room temperature is ferromagnetic α-Fe. As iron or steel is heated above the critical temperature A or Curie temperature of 771 °C (1044K or 1420 °F), the random thermal

neg: Platonic hydrocarbon lack of readily available decomposition paths. Angle strain would make an octahedron highly unstable due to inverted tetrahedral geometry at each vertex. There would also be no hydrogen atoms because four edges meet at each corner; thus, the hypothetical octahedrane molecule would be an allotrope of elemental carbon, C, and not a hydrocarbon. The existence of octahedrane cannot be ruled out completely, although calculations have shown that it is unlikely. Dodecahedrane (CH) has been synthesized, and has almost zero angle strain. The tetravalency (4-connectedness) of carbon excludes an icosahedron because 5 edges meet at each vertex. True pentavalent carbon is

neg: Penta-graphene of 4.1–4.3 eV. Its hydrogenated form is called penta-graphane. It has a diamond-like structure with "sp" and no "sp" bonds, and therefore a wider band gap (ca. 5.8 eV) than penta-graphene. Chiral penta-graphene nanotubes have also been studied as metastable allotropes of carbon. Penta-graphene Penta-graphene is a carbon allotrope composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling. Penta-graphene was proposed in 2014 on the basis of analyses and simulations. Further calculations showed that it is unstable in its pure form, but can be stabilized by hydrogenation. Owing to its atomic configuration, penta-graphene has an unusually negative Poisson’s

neg: Negro (lead pencil) what they call Nero pencils, which are similar in composition. Prismacolor also manufactures a lead-based black pencil that is very close in composition. Negro (lead pencil) Negro is the name of an artist's drawing medium, consisting of black pencil lead often encased in a wooden or paper tool. Its history and uses are common knowledge among illustrators and historians interested in illustrative art. The word "Negro", translates to "black" in Spanish and Italian, and is a term commonly used to describe artists' media and pigments that are black or dark in color. Negro lead was originally composed of a mixture

neg: Nanofoam Nanofoam Nanofoams are a class of nanostructured, porous materials (foams) containing a significant population of pores with diameters less than 100 nm. Aerogels are one example of nanofoam. In 2006, researchers produced metal nanofoams by igniting pellets of energetic metal bis(tetrazolato)amine complexes. Nanofoams of iron, cobalt, nickel, copper, silver, and palladium have been prepared through this technique. These materials exhibit densities as low as 11 mg/cm, and surface areas as high as 258 m/g. These foams are effective catalysts. Carbon nanofoam is an allotrope of carbon discovered in 1997. It consists of a cluster-assembly of carbon atoms strung together in

neg: Mechanical pencil collar that, when depressed as the lead is worn away, extends out again when pressure is released. An advanced ratchet type has a mechanism that rotates the pencil lead 9° counter-clockwise every time the lead is pressed on to the paper (which counts as one stroke), to distribute wear evenly. This "auto-rotation" mechanism keeps the lead 50% narrower than in the common propelling mechanical pencils, resulting in uniform thickness of the lines written onto the paper. The design was first developed by Mitsubishi Pencil Company, and named "Kuru Toga" under the Uni brand. This type of pencil is most suited

neg: Buckminster Fuller Fuller also helped to popularize the concept of Spaceship Earth: "The most important fact about Spaceship Earth: an instruction manual didn't come with it." His concepts and buildings include: Among the many people who were influenced by Buckminster Fuller are: Constance Abernathy, Ruth Asawa, J. Baldwin, Michael Ben-Eli, Pierre Cabrol, John Cage, Joseph Clinton, Peter Floyd, Medard Gabel, Michael Hays, David Johnston, Robert Kiyosaki, Peter Jon Pearce, Shoji Sadao, Edwin Schlossberg, Kenneth Snelson, Robert Anton Wilson and Stewart Brand. An allotrope of carbon, fullerene—and a particular molecule of that allotrope C (buckminsterfullerene or buckyball) has been named after him. The

neg: Dr. Grip Grip is available, which is the same pencil, but using 0.5mm lead with a knock system. The pencils are available in 0.5mm and 0.7mm depending on the style of pencil. Dr. Grip Dr. Grip is a brand of mechanical pencil made by Pilot Pens based in Japan. The Dr. Grip style also comes in a pen variety. It is well known for its "deflection-deflection/knock system." For its ergonomic features, the Dr. Grip pencil has been awarded the Arthritis Foundation's "Commendation for Ease-of-Use." The deflection-deflection system is a special form of lead advancement. A pencil using this system is also commonly

neg: Graphyne Graphyne Graphyne is a theorized allotrope of carbon. Its structure is one-atom-thick planar sheets of sp and sp-bonded carbon atoms arranged in crystal lattice. It can be seen as a lattice of benzene rings connected by acetylene bonds. Depending on the content of acetylene groups, graphyne can be considered a mixed hybridization, sp, where 1 < n < 2, and thus differs from the hybridization of graphene (considered pure sp) and diamond (pure sp). The existence of graphyne was conjectured before 1960, and attracted attention after the discovery of fullerenes. Although not yet synthesized, periodic graphyne structures and their boron

neg: Phagraphene Phagraphene Phagraphene ["fæ’græfiːn"] is a proposed graphene allotrope composed of 5-6-7 carbon rings. Phagraphene was proposed in 2015 based on systematic evolutionary structure searching. Theoretical calculations showed that phagraphene is not only dynamically and thermally stable, but also has distorted Dirac cones. The direction-dependent cones are robust against external strain with tuneable Fermi velocities. Higher-energy allotropes named Haeckelite contained penta- hexa- and hepta-carbon rings. Three types (rectangular, oblique and hexagonal) were proposed as early as 2000. These metastable allotropes have a trival intrinsic metallic behavior. Phagraphene is predicted to have a potential energy of 193.2 kcal/mol. The bond order is

neg: Cubane-type cluster RLi molecules are not observed. The four lithium atoms and the carbon from each alkyl group bonded to them occupy alternating vertices of the cube, with the additional atoms of the alkyl groups projecting off their respective corners. Octaazacubane is a hypothetical allotrope of nitrogen with formula N; the nitrogen atoms are the corners of the cube. Like the carbon-based cubane compounds, octaazacubane is predicted to be highly unstable due to angle strain at the corners, and it also does not enjoy the kinetic stability seen for its organic analogues. Cubane-type cluster A cubane-type cluster is an arrangement of atoms

neg: Fullerene 1966 column for "New Scientist", David Jones suggested that it may be possible to create giant hollow carbon molecules by distorting a plane hexagonal net by the addition of impurity atoms. On 4 September 2010, Google used an interactively rotatable fullerene C as the second 'o' in their logo to celebrate the 25th anniversary of the discovery of the fullerenes. Fullerene A fullerene is an allotrope of carbon in the form of a hollow sphere, ellipsoid, tube, and many other shapes. Spherical fullerenes, also referred to as Buckminsterfullerenes or buckyballs, resemble the balls used in association football. Cylindrical fullerenes are

neg: Mechanical pencil do not need a rubber retainer. In one type of ratchet-based pencil (developed by Tombow Pencil Co.), shaking the pencil back and forth causes a weight inside the pencil to operate a mechanism in the cap. A button may be present on the top or side of the pencil, to allow the user to advance the lead manually when necessary. Another variation advances the lead automatically. In this design, the lead is advanced by a ratchet but only prevented from going back into the pencil, just held from falling by a small amount of friction. The nib is a spring-loaded

neg: Graphyne van der Waals radius of the helium atom, graphdiyne could behave as an ideal two-dimensional membrane for helium chemical and isotopic separation. The application of a graphdiyne based membrane as an efficient two-dimensional sieve for water filtration and purification technologies has been proposed. Graphyne Graphyne is a theorized allotrope of carbon. Its structure is one-atom-thick planar sheets of sp and sp-bonded carbon atoms arranged in crystal lattice. It can be seen as a lattice of benzene rings connected by acetylene bonds. Depending on the content of acetylene groups, graphyne can be considered a mixed hybridization, sp, where 1 < n

neg: Phagraphene 1.33, the same as for graphene. An unrelated material called PHA/graphene is a polyhydroxyalkanoate graphene composite. Phagraphene Phagraphene ["fæ’græfiːn"] is a proposed graphene allotrope composed of 5-6-7 carbon rings. Phagraphene was proposed in 2015 based on systematic evolutionary structure searching. Theoretical calculations showed that phagraphene is not only dynamically and thermally stable, but also has distorted Dirac cones. The direction-dependent cones are robust against external strain with tuneable Fermi velocities. Higher-energy allotropes named Haeckelite contained penta- hexa- and hepta-carbon rings. Three types (rectangular, oblique and hexagonal) were proposed as early as 2000. These metastable allotropes have a trival intrinsic metallic

neg: Tetranitrogen into harmless gas, in the process releasing large amounts of chemical energy. This is in contrast to carbon containing compounds which have lower energies of formation for an equivalent number of single or double bonds than for a C≡C triple bond, allowing for the thermodynamically favorable formation of polymers. It is for this reason that the only allotropic form of nitrogen found in nature is molecular nitrogen () and why novel strategies of synthesizing polynitrogen allotropes in a cost-efficient manner are so highly sought after. Tetranitrogen Tetranitrogen is a neutrally charged polynitrogen allotrope of the chemical formula ' and consists

neg: Graphene chemistry nickel ions can be coordinated with graphene ligands. Graphene chemistry Graphene is the only form of carbon (or solid material) in which every atom is available for chemical reaction from two sides (due to the 2D structure). Atoms at the edges of a graphene sheet have special chemical reactivity. Graphene has the highest ratio of edge atoms of any allotrope. Defects within a sheet increase its chemical reactivity. The onset temperature of reaction between the basal plane of single-layer graphene and oxygen gas is below . Graphene combusts at . Graphene is commonly modified with oxygen- and nitrogen-containing functional groups

neg: Graphene chemistry Graphene chemistry Graphene is the only form of carbon (or solid material) in which every atom is available for chemical reaction from two sides (due to the 2D structure). Atoms at the edges of a graphene sheet have special chemical reactivity. Graphene has the highest ratio of edge atoms of any allotrope. Defects within a sheet increase its chemical reactivity. The onset temperature of reaction between the basal plane of single-layer graphene and oxygen gas is below . Graphene combusts at . Graphene is commonly modified with oxygen- and nitrogen-containing functional groups and analyzed by infrared spectroscopy and X-ray photoelectron

neg: Terraforming of Venus space in the Venusian atmosphere. If made from carbon nanotubes or graphene (a sheet-like carbon allotrope), then the major structural materials can be produced using carbon dioxide gathered "in situ" from the atmosphere. The recently synthesised amorphous carbonia might prove a useful structural material if it can be quenched to Standard Temperature and Pressure (STP) conditions, perhaps in a mixture with regular silica glass. According to Birch's analysis, such colonies and materials would provide an immediate economic return from colonizing Venus, funding further terraforming efforts. Increasing the planet's albedo by deploying light-colored or reflective material on the surface (or at

neg: Austenite shrink more, causing it to be under tension and thermal staining. At high cooling rates, the material will transform from austenite to martensite which is much harder and will generate cracks at much lower strains. The volume change (martensite is less dense than austenite) which can generate stresses as well. The difference in strain rates of the inner and outer portion of the part may cause cracks to develop in the outer portion, compelling the use of slower quenching rates to avoid this. By alloying the steel with tungsten, the carbon diffusion is slowed and the transformation to BCT allotrope

neg: Osmium tetroxide TEM. OsO is an intermediate in the extraction of osmium from its ores. Osmium-containing residues are treated with sodium peroxide (NaO) forming Na[OsO(OH)], which is soluble. When exposed to chlorine, this salt gives OsO. In the final stages of refining, crude OsO is dissolved in alcoholic NaOH forming Na[OsO(OH)], which, when treated with NHCl, to give (NH)[OsOCl]. This salt is reduced under hydrogen to give osmium. OsO allowed for the confirmation of the soccer ball model of buckminsterfullerene, a 60 atom carbon allotrope. The adduct, formed from a derivative of OsO, was C(OsO)(4-"tert"-butylpyridine). The adduct broke the fullerene's symmetry, allowing

neg: Mechanical pencil the lead falls out freely when the jaws are opened, its forward movement cannot be controlled except by external means. This can be easily done by keeping the tip of the pencil a few millimeters above a work surface or the palm of one's hand. Some clutch pencils do have mechanisms which incrementally advance the lead, such as the Alvin Tech-Matic leadholder, but these are not normally considered to be in the same category as most pencils with propelling mechanisms. Ratchet-based pencils are a variant of the clutch pencil, in which the lead is held in place by two or

neg: Hotchkiss v. Greenwood largely gainers?" In the 1875 decision "Reckendorfer v. Faber", the Court considered and reaffirmed the "Hotchkiss" decision. The Court described the invention in these terms: The claim is simply of the combination of the lead and india-rubber in the holder of a drawing-pencil; in other words, the use of an ordinary lead pencil, in one end of which, and for about one-fourth of its length, is inserted a strip of india-rubber, glued to one side of the pencil. Like Hotchkiss's doorknob, the eraser glued to a pencil was the product of mere mechanical skill and therefore unpatentable: An instrument or

neg: Nonmetal nonmetals have a diverse range of individual physical and chemical properties. In periodic table terms they largely occupy a position between the weakly nonmetallic metalloids to the left and the noble gases to the right. Physically, five are solids, one is a liquid (bromine), and five are gases. Of the solids, carbon, selenium, and iodine are metallic-looking, whereas sulfur has a pale-yellow appearance. Ordinary white phosphorus has a yellowish-white appearance but the black allotrope, which is the most stable form of phosphorus, has a metallic-looking appearance. Bromine is a reddish-brown liquid. Of the gases, fluorine and chlorine are coloured pale

neg: Silicon has a high melting point of 1414 °C, as a lot of energy is required to break the strong covalent bonds and melt the solid. It is not known to have any allotropes at standard pressure, but several other crystal structures are known at higher pressures. The general trend is one of increasing coordination number with pressure, culminating in a hexagonal close-packed allotrope at about 40 gigapascals known as Si–VII (the standard modification being Si–I). Silicon boils at 3265 °C: this, while high, is still lower than the temperature at which its lighter congener carbon sublimes (3642 °C) and silicon

neg: Allotropes of iron the solid parts of planetary cores. The inner core of the Earth is generally assumed to consist essentially of a crystalline iron-nickel alloy with ε structure. The outer core surrounding the solid inner core is believed to be composed of liquid iron mixed with nickel and trace amounts of lighter elements. As molten iron cools down, it solidifies at 1,538 °C (2,800 °F) into its δ allotrope, which has a body-centered cubic (BCC) crystal structure. δ-iron can dissolve as much as 0.08% of carbon by mass at 1,475 °C. As the iron cools further to 1,394 °C its crystal structure

neg: Negro (lead pencil) Negro (lead pencil) Negro is the name of an artist's drawing medium, consisting of black pencil lead often encased in a wooden or paper tool. Its history and uses are common knowledge among illustrators and historians interested in illustrative art. The word "Negro", translates to "black" in Spanish and Italian, and is a term commonly used to describe artists' media and pigments that are black or dark in color. Negro lead was originally composed of a mixture of wax and charcoal and was often used in combination with heavily textured coquille paper. The intention was to create sturdy pencil line