Titanium diboride

B-B distance is 1.746 A. In pure B,it is 1.75 A. Therefore, covalent B-B bonds may be expected. During the complex deformation in an indentation, these strong bonds must be broken. They are the principal barriers to dislocation kink motion in the diborides. 

Hardness values for the prototype diborides are listed in Table 10.1. Most hardness measurements for diborides have been made for sintered specimens thus, they vary from one author to another. The values listed are the highest ones reported. Average values have little meaning in this case. 

Perhaps the best known diboride is TiB2, so it will be discussed in somewhat more detail. 

It has been found by Will (2004) from X-ray scattering measurements that valence electrons concentrate along the lines connecting the boron atoms, confirming that the boron layer is a covalently bonded network. The titanium layers are metallic. However, the layers are not characteristic of either pure Ti, or pure B, so the bonding is quite complex. 

The mechanical behavior of TiB2 is characterized by its lattice parameters, valence electron density, elasticity tensor, plasmon tensor, and its heat of 

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Boron nitride and titanium diboride coatings are used on graphite for the evaporation of Hquid aluminum. 

The most important of these is the diboride, TiB2, which has a hexagonal stmeture and lattice parameters of a = 302.8 pm and c = 322.8 pm. Titanium diboride is a gray crystalline soUd. It is not attacked by cold concentrated hydrochloric or sulfuric acids, but dissolves slowly at boiling temperatures. It dissolves mote readily in nitric acid/hydrogen peroxide or nitric acid/sulfuric acid mixtures. It also decomposes upon fusion with alkaU hydroxides, carbonates, or bisulfates. 

Titanium diboride, typically 96—98% pure, may also be made by the electrolysis of mineral mtile dissolved in mixed electrolytes,... 

Ti02/Na2C02/Na2AlF2/NaCl/Na2B40, at 1050°C (20). Very fine titanium diboride may be made by a gas-phase plasma process in which titanium tetrachloride and boron trichloride are reacted in a hydrogen gas heated by a d-c plasma (21). 

Supphers of titanium diboride include Micron Metals, Atomergic Chemmetals, Cerac, and Noah Technologies, in the United States, and ElektroschmeUwerk Kempten, Herman C. Starck, and RTZ Chemicals in Europe. 

Ceramics (qv) such as those in Table 12 find high temperature use to over 800°C (32). Advanced ceramics finding interest include alumina, partially stabilized zitconia, siUcon nitride, boron nitride, siUcon carbide, boron carbide, titanium diboride, titanium carbide, and sialon (Si—Al—O—N) (33) (see... 

Uses. In spite of unique properties, there are few commercial appUcations for monolithic shapes of borides. They are used for resistance-heated boats (with boron nitride), for aluminum evaporation, and for sliding electrical contacts. There are a number of potential uses ia the control and handling of molten metals and slags where corrosion and erosion resistance are important. Titanium diboride and zirconium diboride are potential cathodes for the aluminum Hall cells (see Aluminum and aluminum alloys). Lanthanum hexaboride and cerium hexaboride are particularly useful as cathodes ia electronic devices because of their high thermal emissivities, low work functions, and resistance to poisoning. 

Titanium diboride Titanium dioxide o-Tolidine based dyes Toluene... 

Another means of strengthening ceramics is to create a composite material. Flakes of very strong, tough materials such as titanium diboride, TiB2, are distributed throughout the ceramic material. Even if a crack did form, it would be unable to propagate past the first flake that it encountered. 

A demonstration of the feasibility of a reaction is illustrated in the following example regarding the formation of titanium diboride using either diborane or boron trichloride as a boron source, as shown in the following reactions ... 

The deposition of a binary compound can be achieved by a coreduction reaction. In this manner, ceramic materials such as oxides, carbides, nitrides, borides, and silicides can be produced readily and usually more readily than the parent metal. A common example is the deposition of titanium diboride ... 

Titanium diboride whiskers by the hydrogen co-reduction of TiCl4 and BBr3 in the presence of a platinum catalyst. 

Bouix, J., Vincent, H., Boubehira, M., and Viala, J. C., Titanium Diboride-Coated Boron Fibre for Aluminum Matrix Composites, J. Less Common Metals, 117(l-2) 83-89 (Mar. 1986)... 

Fibers of titanium diboride can be prepared by reaction (a) at 400°C in an electrical discharge. Adherent layers of certain metal borides on metal substrate surfaces are obtained by thermal decomposition of metal (Mo, W, Nb, Ta) halides and BBr3 on a metallic substrate using a solar furnace or induction heating ... 

Magnesium diborate Magnesium perborate Boron oxide Titanium diboride Boron carbide... 

G. Will, Electron Deformation Density in Titanium Diboride Chemical Bonding in TiB2, Jour. Sol. St. Chem., 177, 628 (2004). 

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