Mechanical borides

The mechanism of boride formation is not always well known. However, many studies have sought to understand the chemical processes involved in fused-salt electrolysis. 

A thorough review of the intermetallic compounds of mechanical interest has been written by Westbrook (1993). The borides, carbides, and nitrides will be considered separately in Chapter 10. 

Tetrasubstituted viodinitro compounds have been converted to olefins by treatment with amalgamated calcium.3214 Various functional groups, such as CN and COOR, did not affect the reaction. Other reagents that have been used include sodium sulfide in DMF,32V nickel boride and ultrasound,330 Bu3SnH,331 and SnCI2.332 Radical-ion mechanisms are likely in all these cases. 

In earlier work, it was found for borides, silicides and nitrides that specific activity, expressed as total rate of methane consumption per unit surface area, plummeted with increasing surface area of the catalyst samples.1718 The same relationship was also found for transition metals carbides (Figure 16.4). It should be noted the dependence of specific activity on surface area rather than catalyst composition is unusual for heterogeneous catalytic reactions. In addition, it can be found that the reaction order in the oxidant is perceptibly in excess of 1 (Tables 16.8 and 16.9). Such an order is hard to explain in terms of common mechanism schemes for heterogeneous catalytic oxidative reactions. 

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. 

Sodium hydrogen telluride reacts with epoxides 41 by a Sn2 mechanism giving the respective telluroalcohols. These intermediates are easily converted into the corresponding alcohols 42 by treatment with nickel boride.97 In contrast, epoxides suffer deoxygenation when treated with alkali 0,0-dialkyl phosphorotellurolates, to give the corresponding olefins 43 (Scheme 21).98,99... 

A root-growth mechanism has been proposed for the growth of BN nanotubes, wherein the nanotubes nucleate on the nickel boride catalyst particle often with irregular initiation caps and... 

Boron fibers, like any CVD fiber, have inherent residual stresses which originate in the process of chemical vapor deposition. Growth stresses in the nodules of boron, stresses induced due to diffusion of boron into the W core, and stresses generated due to the difference in the coefficient of expansion of the deposited boron and the tungsten boride core, all contribute to the residual stresses, and thus can have a considerable influence on the fiber mechanical properties. 

Many borides can be synthesized by novel synthetic methods, inclnding shock-induced chemical reactions, mechanical alloying by ball milling, and self-propagating high-temperature synthesis. In these methods, intimately mixed elemental powders are brought to react by a rapid pressure increase, mechanical deformation including local... 

In recent years, there has been a growing interest in the electrochemical synthesis of composite materials consisting of metal matrix with embedded particles of oxides, carbides, borides, etc. Metal-matrix composites offer new possibilities in fabrication of ftmctional coatings with radically improved durability and performance [1], However, in spite of the efforts of many researches, the overall picture of the processes occurring during co-deposition of metal with dispersed phase and mechanism of particle-induced modification of mechanical and chemical properties still remain unclear. In this study, we focused on the kinetics and mechanism of the electrochemical co-deposition of nickel with highly dispersed oxide phases of different nature and morphology. 

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