Titanium boride properties

Table 3. Physical Properties of Titanium Borides, Carbides, and Nitrides ...

Borides are inert toward nonoxidizing acids however, a few, such as Be2B and MgB2, react with aqueous acids to form boron hydrides. Most borides dissolve in oxidizing acids such as nitric or hot sulfuric acid and they ate also readily attacked by hot alkaline salt melts or fused alkaU peroxides, forming the mote stable borates. In dry air, where a protective oxide film can be preserved, borides ate relatively resistant to oxidation. For example, the borides of vanadium, niobium, tantalum, molybdenum, and tungsten do not oxidize appreciably in air up to temperatures of 1000—1200°C. Zirconium and titanium borides ate fairly resistant up to 1400°C. Engineering and other properties of refractory metal borides have been summarized (1). 

Titanium anodes, 15 591 Titanium aryloxides, 25 78 Titanium beach-sand mining, 24 847 Titanium borides, 25 5-6 physical properties of, 25 7 Titanium bromide... 

Thermal Evaporation The easiest way of evaporating metal is by means of resistance evaporators known commonly as boats . Boats, made of sintered ceramics, are positioned side by side at a distance of approximately 10 cm across the web width (Fig. 8.1). Titanium boride TiB2 is used as an electrically conductive material with boron nitride BN (two-component evaporator) or BN and aluminum nitride AIN (three-component evaporator) as an insulating material [2]. By combination of conductive and insulating materials, the electrical properties of evaporators are adjusted. 

Kecskes, L. Kottke, T., and Niiler, A., Microstructural properties of combustion-synthesized and dynamically consolidated titanium boride and titanium carbide. J. Am. Ceram. Soc., 73, 1274 (1990). 

Influence of Alloying on the Constitution and Properties of Titanium-Boride Eutectic Alloys... 

Before the present work, insufficient data were available in the literature for phase equilibria of systems based on Ti-B. There is a large body of data in literature on the properties of titanium-boride materials, but there is no systematic information regarding the specific role(s) of candidate alloying elements. Thus, the present effort was undertaken to explore the role of alloying additions through the study of phase equilibria and alloy properties, as well as their interrelation, from the binary Ti-B system to the Ti-rich portions of ternaries Ti-Al-B and Ti-B-X, further to quaternaries Ti-10 at.% Al-B-X (where X = Si, Ge, Sn, Zr, V, or Nb) and to some multi-component alloys. 

Modijication and grain rejining For aluminium alloys this usually involves the addition of small amounts of metal to the melt. These additions control the grain size and modify the microstructure of the solidifying metal and thus enhance the casting mechanical properties. Sodium or strontium are used for the modification, while grain refinement is achieved with titanium, titanium boride, zircon or carbon. This treatment is mostly performed in combination with degassing in a dedicated metal treatment station... 

In addition to the aforementioned whiskers, there are many others whiskers, such as graphite (C) whiskers, barium titanate (BaTiOj) whiskers, titanium boride (TiB2) whiskers, titanium oxide (Ti02) whiskers, Si02-Mg0-Ca0 (SMC) whiskers, and so forth. Table 3.12 shows the chemical and physical properties of different whiskers. 

Brodkin, D., Zavaliangos, A., Kalidindi, S. R., Barsoum, M. W. (1999). Ambient- and high-temperature properties of titanium carbide-titanium boride composites fabricated by transient plastic phase processing. Journal of the American Ceramic Society, 82, 665-672. doi 10.1111/j.ll51-2916.1999.tb01815.x. 

In addition to being of use as a boron nitride precursor, polyborazylene has proven to serve as a useful reagent for the formation of new composite metal-nitride/metal-boride materials that have improved properties over the individual pure phase metal boride or nitride. For example, titanium-boride/titanium-nitride composites have been made (eq 4) by dispersing titanium powder into polyborazylene... 

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. 

Although few applications have so far been found for ceramic matrix composites, they have shown considerable promise for certain military applications, especially in the manufacture of armor for personnel protection and military vehicles. Historically, monolithic ("pure") ceramics such as aluminum oxide (Al203), boron carbide (B4C), silicon carbide (SiC), tungsten carbide (WC), and titanium diboride (TiB2) have been used as basic components of armor systems. Research has now shown that embedding some type of reinforcement, such as silicon boride (SiBg) or silicon carbide (SiC), can improve the mechanical properties of any of these ceramics. 

Titanium diboride is an advanced ceramic material with properties similar to those of metals such as high thermal and electrical conductivity. The other distinguishing features of this material are its excellent oxidation resistance and chemical corrosion resistance at elevated temperatures. It can be used as an abrasive and oxidation protection coating as well as the electrode material in aluminium refining. In addition, like other borides it can also be used as a neutron absorber. 

Other interesting directions are hardening with intermetallics, quasi-crystals, borides, silicides, discrete fibres, creation of natural composites. Conscious regulation of structure and properties of such materials requires studying phase equlibria in multi-component systems, in particular on the basis of light metals like aluminum, magnesium, titanium. The important direction is also a creation of specially organized porous structures. To some extent these directions are presented in a number of papers of the present book. 

Key words Titanium in-situ composites, discontinuous reinforcement, silicide reinforcement, boride reinforcement, mixed silicide-boride reinforcement, ductile reinforcement, microstructure, a -phase, (3-phase, mechanical properties, fracture mechanisms. 

Taking into account that the volume content, size, distribution and properties of the reinforcing boride phase practically do not change with the alloying studied here, the strengthening of the ternary and quaternary eutectic alloys should be attributed practically in full to solid- solution strengthening of the titanium alloy matrix. 

In this section and the next three, the properties and characteristics of the covalent carbides are reviewed and compared whenever appropriate with those of the parent elements and of the refi tory compounds of titanium. For comparison with other carbides, nitrides, or borides, see the appropriate tables in Chs. 4-6. Reported property values often vary considerably and the values given here are a general average. 

Gerasimov et have provided a reference book on the thermodynamic properties of tungsten, molybdenum, titanium, zirconium, niobium, and tantalum, and their more important compounds, viz. oxides, sulphides, halides, carbides, nitrides, silicates, borides, and hydrides. 

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