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Lonsdaleite
Lonsdaleite (named in honour of Kathleen Lonsdale), also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice, as opposed to the cubical lattice of conventional diamond. It is found in nature in meteorite debris; when meteors containing graphite strike the Earth, the immense heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice. Lonsdaleite was first identified in 1967 from the Canyon Diablo meteorite, where it occurs as microscopic crystals associated with ordinary diamond. It is translucent and brownish-yellow and has an index of refraction of 2.40–2.41 and a specific gravity of 3.2–3.3. Its hardness is theoretically superior to that of cubic diamond (up to 58% more), according to computational simulations, but natural specimens exhibited somewhat lower hardness through a large range of values (from 7–8 on Mohs hardness scale). The cause is sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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. It is a crystal that is transparent to opaque and which is generally isotropic (no or very weak birefringence). Diamond is the hardest naturally occurring material known. Yet, due to important structural brittleness, bulk diamond's toughness is only fair to good. The precise tensile strength of bulk diamond is little known; however, compressive strength up to has been observed, and it could be as high as in the form of micro/nanometer-sized wires or needles (~ in diameter, micrometers long), with a corresponding maximum tensile elastic strain in excess of 9%. The anisotropy of diamond hardness is carefully considered during diamond cutting. Diamond has a high refractive index (2.417) and moderate dispersion (0.044) properties that give cut diamonds their brilliance. Scientists classify diamonds into four main types according to the nature of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allotrope Of Carbon
Carbon is capable of forming many allotropes (structurally different forms of the same element) due to its valency ( tetravalent). Well-known forms of carbon include diamond and graphite. In recent decades, many more allotropes 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 the Samara Carbon Allotrope Database (SACADA). Atomic and diatomic carbon Under certain conditions, carbon can be found in its atomic form. It can be formed by vaporizing graphite, by passing large electric currents to form a carbon arc under very low pressure. It is extremely reactive, but it is an intermediate product used in the creation of carbenes. Diatomic car ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexagonal Crystal System
In crystallography, the hexagonal crystal family is one of the six crystal family, crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal system and the rhombohedral lattice system are not equivalent (see section hexagonal crystal family#Crystal systems, crystal systems below). In particular, there are crystals that have trigonal symmetry but belong to the hexagonal lattice (such as α-quartz). The hexagonal crystal family consists of the 12 point groups such that at least one of their space groups has the hexagonal lattice as underlying lattice, and is the union of the hexagonal crystal system and the trigonal crystal system. There are 52 space groups associated with it, which are exactly those whose Bravais lattice is either hexagonal or rhombohedral. __TOC__ Lattice systems The hexagonal crystal family consists of two lattice systems: hexagonal and rhom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canyon Diablo Meteorite
The Canyon Diablo meteorite refers to the many fragments of the asteroid that created Meteor Crater (also called Barringer Crater), Arizona, United States. Meteorites have been found around the crater rim, and are named for nearby Canyon Diablo, which lies about three to four miles west of the crater. History The impactor fell about 50,000 years ago. Initially known and used by pre-historic Native Americans, Canyon Diablo meteorites have been collected and studied by the scientific community since the 19th century. Meteor Crater, from the late 19th to the early 20th century, was the center of a long dispute over the origin of craters that showed little evidence of volcanism. That debate was largely settled by the early 1930s, thanks to work by Daniel M. Barringer, F.R. Moulton, and Harvey Harlow Nininger. In 1953, Clair Cameron Patterson measured ratios of the lead isotopes in samples of the meteorite. Through U-Pb radiometric dating, a refined estimate of the age of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wurtzite (crystal Structure)
In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal system and the rhombohedral lattice system are not equivalent (see section crystal systems below). In particular, there are crystals that have trigonal symmetry but belong to the hexagonal lattice (such as α-quartz). The hexagonal crystal family consists of the 12 point groups such that at least one of their space groups has the hexagonal lattice as underlying lattice, and is the union of the hexagonal crystal system and the trigonal crystal system. There are 52 space groups associated with it, which are exactly those whose Bravais lattice is either hexagonal or rhombohedral. __TOC__ Lattice systems The hexagonal crystal family consists of two lattice systems: hexagonal and rhombohedral. Each lattice system consists of one Bravais lat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Staggered Conformation
In organic chemistry, a staggered conformation is a chemical conformation of an ethane-like moiety abcX–Ydef in which the substituents a, b, and c are at the maximum distance from d, e, and f; this requires the torsion angles to be 60°. It is the opposite of an eclipsed conformation, in which those substituents are as close to each other as possible. Such a conformation exists in any open chain single chemical bond connecting two sp3- hybridised atoms, and is normally a conformational energy minimum. For some molecules such as those of ''n''-butane, there can be special versions of staggered conformations called ''gauche'' and ''anti''; see first Newman projection diagram in conformational isomerism. Staggered/eclipsed configurations also distinguish different crystalline structures of e.g. cubic/hexagonal boron nitride, and diamond/lonsdaleite. See also * Alkane stereochemistry * Eclipsed conformation In chemistry an eclipsed conformation is a conformation in w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diamond
Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Diamond is tasteless, odourless, strong, brittle solid, colourless in pure form, a poor conductor of electricity, and insoluble in water. Another solid form of carbon known as graphite is the Chemical stability, chemically stable form of carbon at Standard temperature and pressure, room temperature and pressure, but diamond is metastable and converts to it at a negligible rate under those conditions. Diamond has the highest Scratch hardness, hardness and thermal conductivity of any natural material, properties that are used in major industrial applications such as cutting and polishing tools. Because the arrangement of atoms in diamond is extremely rigid, few types of impurity can contaminate it (two exceptions are boron and nitrogen). Small numbers of lattice defect, defects or impurities (about one per million of lattice atoms) can color ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eclipsed Conformation
In chemistry an eclipsed conformation is a conformation in which two substituents X and Y on adjacent atoms A, B are in closest proximity, implying that the torsion angle X–A–B–Y is 0°. Such a conformation can exist in any open chain, single chemical bond connecting two sp3- hybridised atoms, and it is normally a conformational energy maximum. This maximum is often explained by steric hindrance, but its origins sometimes actually lie in hyperconjugation (as when the eclipsing interaction is of two hydrogen atoms). In the example of ethane, two methyl groups are connected with a carbon-carbon sigma bond, just as one might connect two Lego pieces through a single "stud" and "tube". With this image in mind, if the methyl groups are rotated around the bond, they will remain connected; however, the shape will change. This leads to multiple possible three-dimensional arrangements, known as conformations, conformational isomers (conformers), or sometimes rotational isome ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Miller Index
Miller indices form a notation system in crystallography for lattice planes in crystal (Bravais) lattices. In particular, a family of lattice planes of a given (direct) Bravais lattice is determined by three integers ''h'', ''k'', and ''ℓ'', the ''Miller indices''. They are written (''hkℓ''), and denote the family of (parallel) lattice planes (of the given Bravais lattice) orthogonal to \mathbf_ = h\mathbf_1 + k\mathbf_2 + \ell\mathbf_3 , where \mathbf_i are the basis or primitive translation vectors of the reciprocal lattice for the given Bravais lattice. (Note that the plane is not always orthogonal to the linear combination of direct or original lattice vectors h\mathbf_1 + k\mathbf_2 + \ell\mathbf_3 because the direct lattice vectors need not be mutually orthogonal.) This is based on the fact that a reciprocal lattice vector \mathbf (the vector indicating a reciprocal lattice point from the reciprocal lattice origin) is the wavevector of a plane wave in the Fouri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diamond Type
Diamond type is a method of scientifically classifying diamonds by the level and type of their chemical impurities. Diamonds are separated into five types: Type IaA, Type IaB, Type Ib, Type IIa, and Type IIb. The impurities measured are at the atomic level within the crystal lattice of carbon atoms and so, unlike inclusions, require an infrared spectrometer to detect. Different diamond types react in different ways to diamond enhancement techniques. Different types can coexist within a single stone; natural diamonds are often mixes of Type Ia and Ib, which can be determined by their infrared absorption spectrum. Types of diamond Type I Type I diamonds, the most common class, contain nitrogen atoms as their main impurity, commonly at a concentration of 0.1%. Type I diamonds absorb in both the infrared and ultraviolet region, from 320 nm. They also have a characteristic fluorescence and visible absorption spectrum (see Optical prope ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diamondoid
In chemistry, diamondoids are generalizations of the carbon cage molecule known as adamantane (C10H16), the smallest unit cage structure of the diamond crystal lattice. Diamondoids also known as nanodiamonds or condensed adamantanes may include one or more cages (adamantane, diamantane, triamantane, and higher polymantanes) as well as numerous isomeric and structural variants of adamantanes and polymantanes. These diamondoids occur naturally in petroleum deposits and have been extracted and purified into large pure crystals of polymantane molecules having more than a dozen adamantane cages per molecule. These species are of interest as molecular approximations of the diamond cubic framework, terminated with C−H bonds. Examples Examples include: * Adamantane (C10H16) * Iceane (C12H18) * BC-8 (C14H20) * Diamantane (C14H20) also ''diadamantane'', two face-fused cages * Triamantane (C18H24), also ''triadamantane''. Diamantane has four identical faces available for anchoring a n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
