Diamonds hardness

N. Dubrovinskaia, V. L. Solozhenko, N. Miyajima, V. Dmitriev, O. O. Kurakevych, and L.Dubrovinsky, Superhard Nanocomposite of Dense Polymorphs of Boron Nitride Noncarbon Material has Reached Diamond Hardness , Appl. Phys. Lett., 90,101912 (2007). 

What are the reasons that cause iron to be solid, water to be liquid and hydrogen to be a gas at room temperature Why is diamond hard while wax is soft Why do some solids melt at low temperatures while others melt at high temperatures ... 

Cubic BC2N. Hetero-diamond B C—N compounds have recently received a great interest because of their possible applications as mechanical and optical devices. The similar properties and structures of carbon and boron nitrides (graphite and hexagonal BN, diamond, and cubic BN) suggested the possible synthesis of dense compounds with all the three elements. Such new materials are expected to combine the best properties of diamond (hardness) and of c-BN (thermal stability and chemical inertness). Several low-density hexagonal phases of B,C, and N have been synthesized [534] while with respect to the high-density phases, different authors report contradictory data [535-538], but the final products are probably solid mixtures of c-BN and dispersed diamonds [539]. 

Fig. 6.4.4. Diamond hardness reduction and growth of lattice spacings with temperature.

Laladze T. N., Bokucharova G. V., Davidova R. E., 1967, Izmerenie tverdosti almaza pri vysokikh temperaturakh (Measuring of Diamond Hardness at High Temperatures), Zavod. Lab. 33 (8), 1005-1008. 

Their landscape paintings had a glassy rigidity, diamond hardness, and cold, gemlike strangeness. 

The combination of the diamond films beneficial mechanical properties with their biocompatibility (Section 6.6.3) renders them an ideal material for coating implants and prostheses. The wear of such parts is markedly decreased, and diamond hardly evokes rejection reactions of the surrounding tissue. 

Mohs hardness. Based on an empirical scale for determining the relative hardness of mineral or mineral-like materials. The scale is based on the ability of one crystal to scratch another and ranges from a value of 1 (talc, soft) to 10 (diamond, hard), molality (molal concentration). A concentration in which the amount of solute is stated in moles and the amount of solvent in kilograms, molarity. The concentration of a solution in moles per liter. 

Knoop indenter n. Pyramidal diamond of prescribed dimensions used for testing the indentation hardness of organic coatings. In a more restricted sense, a type of diamond hardness indenter having edge angles of 172°, 30°, and 130°. www.astm.org. Brown R (1999) Handbook of physical polymer testing, vol 50. Marcel Dekker, New York. 

This new procedure illustrates the nature of uncertainty of the diamond hardness measurement using the diamond indenter [16-18]. The scratching of the diamond face with a diamond indenter is accompanied by the appearance of numerous cracks (Figure 16.14) (as shown in [16], cracks lead to a wrong hardness value), whereas the scratching with the U-Ceo tip causes the plastic deformation of diamond without fracture (Figure 16.15). This depends upon the fact that the hardness of U-Ceo is enough to create a sufficient pressure at the contact point for the plastic... 

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