Chemistry
Diamond
Diamond is a form of carbon that is known for its hardness and high thermal conductivity. It is a transparent material that is often used in jewelry and cutting tools due to its durability and ability to refract light. Diamond is formed under high pressure and temperature deep within the Earth's mantle.
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10 Key excerpts on "Diamond"
- Mukunda Prasad Das(Author)
- 1999(Publication Date)
- World Scientific(Publisher)
These notes have been written in an informal style to match the tone of the lectures which were delivered at the 10th Physics Summer School held at the Australian National University in January 1997. Readers are invited to contact the author for clarification and/or more detailed references. 2. Diamond 2.1 Properties: Diamond is an extreme material. It has the highest atomic density, thermal conductivity, Young's modulus and hardness of any material known to man. It displays optical transparency all the way from the infra-red to the ultraviolet part of the spectrum, very high electrical breakdown strength, and very high electron and hole mobilities. It is also biocompatible. Importantly it has a wide band gap of 5.5eV (but can be effectively p-type doped with boron). Lastly Diamond surfaces display the intriguing property of negative electron affinity. This property means that electrons in the conduction band have a higher energy than those in the vacuum and hence electrons can leave the Diamond surface with little or no applied electric field, i.e. Diamond can act as a very efficient cold cathode. Tables of properties of Diamond can be found in many texts 1 . However, to give a qualitative feel for the remarkable properties of Diamond; Diamond is twice as strong as tungsten carbide, and three times more thermally conducting than silver. 2.2 Applications: This combination of interesting and extreme properties has made Diamond a very attractive material for technological applications (apart from its more romantic attraction as a gemstone). Some of the well known common uses for Diamond are in grinding, polishing and cutting applications. For example, Diamond knives are still used in eye and coronary surgery because the strength of Diamond allows it to be shaped into a much sharper edge than other materials. The sharper the edge the less damage is done to tissue during cutting and hence the faster the healing.
eBook - PDFCarbon Nanomaterials
Synthesis, Structure, Properties and Applications
- Rakesh Behari Mathur, Bhanu Pratap Singh, Shailaja Pande(Authors)
- 2016(Publication Date)
- Taylor & Francis(Publisher)
1 1 Introduction to Carbon and Carbon Nanomaterials 1.1 Introduction Carbon is the fifteenth most abundant element in the earth’s crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon is also present as a major component in large masses of carbonate rocks, including limestone, dolomite, and marble. Coal is the largest commercial source of mineral carbon, accounting for nearly 8 billion tons or almost 80% of fossil carbon fuel. In its elemental form, carbon (C, atomic number 6) has a valency of 4 and is therefore placed in group IV of the periodic table along with Si, Ge, Sn, and Pb. Carbon can exist in both crystalline and amorphous forms. Figure 1.1 shows the three crystalline allotropes of carbon, that is, with same chemical properties but with different physical forms. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form. In reality all the allotropes of amorphous carbons are made of microcrystals of graphite arranged in an irregular fashion. Diamond, graphite, and fullerenes are crystalline allotropes of carbon. The carbon atoms in Diamond have a three-dimensional (3D) tetrahedral network of covalent bonds, which causes the electrons to be held tightly. Diamonds are therefore very hard and have high melting and boiling points. The structure is a closely packed structure and causes Diamond to be denser than graphite. Since all its electrons end up in forming the covalent bonds, therefore it does not conduct electricity. In graphite only three of the four valence electrons of each carbon atom are used in bonding, leaving the fourth valence electron as free. Therefore graphite is a good conductor of electricity. Diamond is transparent because it has no free electron to absorb radiations and make a transition in the optical region.
eBook - PDFHandbook of Carbon, Graphite, Diamonds and Fullerenes
Processing, Properties and Applications
- Hugh O. Pierson(Author)
- 2012(Publication Date)
- William Andrew(Publisher)
Diamond has two such struc-tures, one with a cubic symmetry (the more common and stable) and one with a hexagonal symmetry found in nature as the minerallonsdaleite (see Sec . 2.5). 248 Carbon, Graphite, Diamond, and Fullerenes Figure 11.2. The Diamond tetrahedron. Structure of Cubic Diamond. Cubic Diamond is by far the more common structure and, in order to simplify the terminology, will be referred to as simply Diamond. The covalent link between the carbon atoms of Diamond is characterized by a small bond length (0.154 nm) and a high bond energy of 711 kJ/mol (170 kcal/mol) J2] Each Diamond unit cell has eight atoms located as follows: 1/8 x 8 at the corners, 1/2 x 6 at the faces and 4 inside the unit cube. Two representations of the structure are shown in Fig. 11.3, (a) and (b).£2][3] The cubic structure of Diamond can be visualized as a stacking of puckered infinite layers (the{111} planes) or as a two face-centered interpen-etrating cubic lattices, one with origin at 0,0,0, and the other at 1/4,1/4,1/4, with parallel axes, as shown in Fig. 11.3(c). The stacking sequence of the {111} planes is ABCABC, so that every third layer is identical. Density of Diamond. With its fourfold coordinated tetrahedral (Sp 3) bonds, the Diamond structure is isotropic and, except on the (111) plane, is more compact than graphite (with its Sp2 anisotropic structure and wide interlayer spacing). Consequently Diamond has higher density than graph-ite (3.515 g/cm 3 vs. 2.26 g/cm 3 ) . Structure and Properties of Diamond 249 A--B--c--(b) (c) Note ABC sequence Figure 11.3. Schematics of the structure of cubic Diamond)2][3] Diamond has the highest atom density of any material with a molar density of 0.293 q-atom/crn. As a result, Diamond is the stiffest, hardest and least compressible of all substances.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Orange Apple(Publisher)
In particular, Diamond has the highest hardness and thermal conductivity of any bulk material. Those properties determine the major industrial application of Diamond in cutting and polishing tools. Diamond has remarkable optical characteristics. Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron and nitrogen. Combined with wide transparency, this results in the clear, colorless appearance of most ________________________ WORLD TECHNOLOGIES ________________________ natural Diamonds. Small amounts of defects or impurities (about one per million of lattice atoms) color Diamond blue (boron), yellow (nitrogen), brown (lattice defects), green, purple, pink, orange or red. Diamond also has relatively high optical dispersion (ability to disperse light of different colors), which results in its characteristic luster. Excellent optical and mechanical properties, combined with efficient marketing, make Diamond the most popular gemstone. Most natural Diamonds are formed at high-pressure high-temperature conditions existing at depths of 140 to 190 kilometers (87 to 120 mi) in the Earth mantle. Carbon-containing minerals provide the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years (25% to 75% of the age of the Earth). Diamonds are brought close to the Earth surface through deep volcanic eruptions by a magma, which cools into igneous rocks known as kimberlites and lamproites. Diamonds can also be produced synthetically in a high-pressure high-temperature process which approximately simulates the conditions in the Earth mantle. An alternative, and completely different growth technique is chemical vapor deposition (CVD). Several non-Diamond materials, which include cubic zirconia and silicon carbide and are often called Diamond simulants, resemble Diamond in appearance and many properties.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
By demonstrating that burning Diamond and graphite releases the same amount of gas he established the chemical equivalence of these substances. The most familiar use of Diamonds today is as gemstones used for adornment, a use which dates back into antiquity. The dispersion of white light into spectral colors is the primary gemological characteristic of gem Diamonds. In the 20th century, experts in gemology have developed methods of grading Diamonds and other gemstones based on the characteristics most important to their value as a gem. Four characteristics, known informally as the four Cs , are now commonly used as the basic descriptors of Diamonds: these are carat , cut , color , and clarity . A large, flawless Diamond is known as a paragon. ________________________ WORLD TECHNOLOGIES ________________________ Material properties Theoretically predicted phase diagram of carbon ________________________ WORLD TECHNOLOGIES ________________________ Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in structure. A Diamond is a transparent crystal of tetrahedrally bonded carbon atoms (sp 3 ) that crystallizes into the Diamond lattice which is a variation of the face centered cubic structure. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity (900–2,320 W·m −1 ·K −1 ), as well as wide bandgap and high optical dispersion. Above 1,700 °C (1,973 K / 3,583 °F) in vacuum or oxygen-free atmosphere, Diamond converts to graphite; in air, transformation starts at ~700 °C. Naturally occurring Diamonds have a density ranging from 3.15–3.53 g/cm 3 , with pure Diamond close to 3.52 g/cm 3 . The chemical bonds that hold the carbon atoms in Diamonds together are weaker than those in graphite.
eBook - PDF- Anthony C. Fischer-Cripps(Author)
- 2011(Publication Date)
- CRC Press(Publisher)
Diamond is a good heat conductor due to the free passage of phonons . relatively f is resp o graphite electrical c o a lence electrons and is the first element h e other elements in this group become The Chemistry Companion n creasing atomic number. At room e r t . At high temperatures, it can form othe r elements. Carbon compounds are n teresting to note that silicon , the next w ith four valence electrons, is the basis e Earth’s minerals. o n has the choice of either losing or o ble gas configuration but in practice, it c ovalen t bonds. On the other hand, tin Group IV, with more loosely bound y favourable to share these electrons in carbides: e.g. silicon carbide SiC; with u nds: e.g. methane CH 4 ; with oxygen to b on dioxide CO 2 ; and with nitrogen to e structures found naturally: Diamond , a re allotropes . These have significantly e ctrical properties and differ only in the m s in the crystal structures. y favourable to share these electrons in has a two-The fullerene form of a l hexagonal t ure with the n de d together by van der o rces . Each om has three . Thus, three lectrons are in covalent while the lef t in a carbon consists of a three-dimensional arrangement of C atoms in a pentagon which together form a sphere or tube. The most famous is the C 60 molecule, often referred to as a buckyball . f ree state and o nsible for being an o nducto r . 11.2 Carbon Compounds Carbon forms a great number of com p hydrocarbons . In addition, h y dro c 11. Carbon Chemistry other atoms in addition to hydrogen be Central to this remarkable abili t compounds is the formation of chai n simple hydrocarbon methane CH 4 : C H H H H This molecule can be easily expande d C C H H And so on for propane , C 3 H 8 , and b u C C C H H Other possibilities abound, including bond such as in ethylene and the tripl e C C H H H H H H H H H = Compounds with single bonds b etw are saturated hydrocarbons .
eBook - PDFDetonation Nanodiamonds
Science and Applications
- Alexander Vul', Olga Shenderova, Alexander Vul', Olga Shenderova(Authors)
- 2014(Publication Date)
- Jenny Stanford Publishing(Publisher)
and Fig. 1.1b the structures of the cubic crystal lattice of Diamond and graphite, the principal macroscopic allotropic forms of carbon. Table 1.1 lists relevant information on the main properties of “macro” Diamond. Other elements of the fourth group of the periodic system of elements, for instance, Si and Ge, manifest sp 3 electronic shell hybridization only. Because these chemical elements contain only the occupied core p atomic orbitals, repulsion between the valence electrons and the p electrons of the core shell specifies the direction of the hybridized orbitals and, thus, makes hybridization less labile. For instance, if we assume the core p orbitals to be oriented along the x -, y -, and z -axes, the hybridized orbitals in Si and Ge should be aligned with < 111 > type directions. No such directions of “hampered” hybridization exist in the carbon atom [4]. It is the numerous possibilities of different hybridizations of electronic shells that culminate in the immense variety of isomeric forms of carbon—about 95% of known organic compounds (about 10 million of them) contain carbon atoms in their structure. 4 Carbon at the Nanoscale In the recent decades, a great number of new carbon nanos-tructures, including the already well known ones (fullerenes, nanotubes, graphene, onions, and nanoDiamond (ND)), and more exotic structures, such as nanohorns, nanobells, nanopeapods, and nanofoams [2], have been discovered. Consider now in more detail the methods employed in the classification of these nanostructures. 1.2 Classification of Carbon Nanostructures There are several methods used in the classification of carbon nanostructures. One could, for instance, proceed from the topolog-ical dimension [3, 4], with the fullerenes and ND particles being assigned to zero-dimensional structures, nanotubes and Diamond nanorods to one-dimensional, graphenes and Diamond nanoplates to two-dimensional, and ultrananocrystalline Diamond films to three-dimensional ones.
- Peter Capper(Author)
- 2005(Publication Date)
- Wiley(Publisher)
14 Crystal Growth of Diamond HISAO KANDA National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan 14.1 INTRODUCTION Diamond is one of the most attractive materials because of its superior properties such as hardness, thermal conductivity, optical transparency and wide bandgap, etc. Interests in Diamond industries may be in three fields, i.e. jewelry, mechanical engineering, and electronics. Gemmologists are interested in the size of a single crystal, colors and the origin of natural Diamonds. Hardness and toughness may be important in the mechanical engineering industry. Semiconducting properties and thermal properties are important for electronic applications. Attempts to make Diamond have a long history, more than 100 years, but reproducible success was only achieved in 1955 [1], with lift-off Diamond science and technology. Today, two methods for Diamond synthesis have been established, which are the high-pressure method and the chemical vapor deposition (CVD) method, and a variety of Bulk Crystal Growth of Electronic, Optical and Optoelectronic Materials Edited by P. Capper © 2005 John Wiley & Sons, Ltd ISBN: 0-470-85142-2 14.1 Introduction 407 14.2 Diamond synthesis 408 14.2.1 Phase diagram of carbon 408 14.2.2 Direct transformation 408 14.2.3 Agents for Diamond formation 409 14.2.4 Carbon source 411 14.2.5 High-pressure apparatus 412 14.2.6 Diamond growth methods 412 14.3 Properties of Diamond single crystals made with high-pressure methods 417 14.3.1 Morphology 417 14.3.2 Surface morphology 419 14.3.3 Inclusions 421 14.3.4 Atomic impurities, color and luminescence 422 14.3.5 Color control 423 14.4 Summary 428 References 428 408 BULK CRYSTAL GROWTH OF E, O, AND EO MATERIALS Diamonds are being made in laboratories and factories across the world; large crystals, fine powder, polycrystalline aggregates, thin films and colored crystals as well as color-less ones.
- Karen Smit, Steve Shirey, Graham Pearson, Thomas Stachel, Fabrizio Nestola, Thomas Moses(Authors)
- 2025(Publication Date)
- De Gruyter(Publisher)
The most familiar carbon allotropes are the crystalline phases of graphite and Diamond. The hexagonal form of graphite consists of sheets of sp 2 hybridized carbon atoms in a hexagonal array, with each atom bonded to three equidistant nearest neighbor atoms. The layers are attracted to each other by weak van der Waals forces and may be arranged in a hexagonal, or rarely rhombohedral, stacking sequence. Meanwhile, the carbon orbitals in Diamond are sp 3 hybridized, with each atom covalently bonded to four nearest neighbors in a tetrahedral arrangement. The prevalent Diamond structure is cubic, though the hexagonal lonsdaleite form also exists. Figure 1 illustrates the pressure and temperature (P, T) phase and transition diagram for pure carbon. Theoretically and experimentally determined conditional phase boundary lines separate the Diamond and graphite stability fields. The high cohesive and activation energies associated with the different carbon phases mean that other metastable forms can occur under conditions at which they are not thermodynamically stable. For instance, Diamond exists at room temperatures and pressures, whereas graphite can survive pressures well into the Diamond stability field (Bundy 1980; Bundy et al. 1996). High quality single crystal Diamonds can be synthesized using either the high pressure, high temperature (HPHT) or chemical vapor deposition (CVD) techniques. In the former, growers use an HPHT press to crystallize Diamond from a carbon source such as graphite either by direct or indirect (catalytic) conversion methods (Fig. 2), applying temperatures and 690 D’Haenens-Johansson et al. pressures at which Diamond is the dominant phase. The latter technique is instead based on gas-phase chemical reactions involving hydrocarbon and hydrogen gases to deposit metastable Diamond at low pressure in a CVD reaction chamber (Fig. 3). Though thermodynamically unstable, under the selected conditions Diamond growth is kinetically favorable.
No longer available |Learn more- Stuart A. Rice(Author)
- 2008(Publication Date)
- Wiley-Interscience(Publisher)
The table also lists some physical properties of Diamondoids mostly compiled by ChevronTexaco. Diamondoids, when in the solid state, melt at much higher temperatures than other hydrocarbon molecules with the same number of carbon atoms in their structures. Since they also possess low strain energy, they are more stable and stiff, resembling Diamond in a broad sense. They contain dense, three- dimensional networks of covalent bonds, formed chiefly from first and second row atoms with a valence of three or more. Many of the Diamondoids possess structures rich in tetrahedrally coordinated carbon. They are materials with superior strength-to-weight ratio. It has been found that adamantane crystallizes in a face-centered cubic lattice, which is extremely unusual for an organic compound. The molecule therefore should be completely free from both angle strain (since all carbon atoms are perfectly tetrahedral) and torsional strain (since all C—C bonds are perfectly staggered), making it a very stable compound and an excellent candidate for various applications, as will be discussed later. At the initial growth stage, crystals of adamantane show only cubic and octahedral faces. The effects of this unusual structure on physical properties are interesting [5]. Many of the Diamondoids can be brought to macroscopic crystalline forms with some special properties. For example, in its crystalline lattice, the pyramidal-shaped [1(2,3)4]pentamantane (see Table I) has a large void in comparison to similar crystals. Although it has a Diamond-like macroscopic structure, it possesses the weak, noncovalent, intermolecular van der Waals Figure 3. Molecular structure of (peri-condensed) cyclohexamantane (C 26 H 30 ). Darker spheres represent carbon atoms while lighter spheres are hydrogen atoms. Diamondoid molecules 209
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