Boron polycrystalline

A wide range of cutting-tool materials is available. Properties, performance capabilities, and cost vary widely (2,7). Various steels (see Steel) cast cobalt alloys (see Cobalt and cobalt alloys) cemented, cast, and coated carbides (qv) ceramics (qv), sintered polycrystalline cubic boron nitride (cBN) (see Boron compounds) and sintered polycrystalline diamond tbin diamond coatings on cemented carbides and ceramics and single-crystal natural diamond (see Carbon) are all used as tool materials. Most tool materials used in the 1990s were developed during the twentieth century. The tool materials of the 1990s... 

The ceramic, polycrystalline siHcon carbide [409-21-2], SiC, is processed using P-siHcon carbide and boron (9). The boron is a sintering aid used at... 

Finally, the presence of ultrasound in the electrodeposition of metals can produce both massive metal and metal colloid [75]. The reduction of AuCLt- at polycrystalline boron-doped diamond electrodes follows two pathways forming... 

Next, the alkali-resistance of SA fiber is described in detail compared with other type of SiC polycrystalline fiber using boron instead of aluminum as the... 

Cubic Phase of Boron Nitride c-BN. The cubic phase of boron nitride (c-BN) is one of the hardest materials, second only to diamond and with similar crystal structure. It is the first example of a new material theoretically predicted and then synthesized in laboratory. From automated synthesis a microcrystalline phase of cubic boron nitride is recovered at ambient conditions in a metastable state, providing the basic material for a wide range of cutting and grinding applications. Synthetic polycrystalline diamonds and nitrides are principally used as abrasives but in spite of the greater hardness of diamond, its employment as a superabrasive is limited by a relatively low chemical and thermal stability. Cubic boron nitride, on the contrary, has only half the hardness of diamond but an extremely high thermal stability and inertness. 

In the sol-gel process, ceramic polymer precursors are formed in solution at ambient temperature shaped by casting, film formation, or fiber drawing and then consolidated to furnish dense glasses or polycrystalline ceramics. The most common sol-gel procedures involve alkoxides of silicon, boron, titanium, and aluminum. In alcohol water solution, the alkoxide groups are removed stepwise by hydrolysis under acidic or basic catalysis and... 

Several fiber types have been mentioned so far, and several other types have been neglected that have been worked on over the past few years. Some of those not discussed may become important fibers for reinforcement in the years ahead. To date though, they have not been available in sufficient quantity for thorough evaluation in composite specimens. Included in this group are boron carbide, spinel, polycrystalline alumina and silica, titanium diboride, and miscellaneous silicides and intermetallics. Ten years from now as we look back on the 70s we no doubt will have an entirely different view of some of these materials. 

Fig. 11.1. Topographical AFM image of boron-doped polycrystalline diamond grown for 8h. Scan size was 10 pm x 10 pm.

Wilson NR, Clewes SL, Newton ME, Unwin PR, Macpherson JV (2006) Impact of grain-dependent boron uptake on the electrochemical and electrical properties of polycrystalline boron doped diamond electrodes. J Phys Chem B 110 5639-5646... 

Similar conclusions on the character of conductance in the polycrystalline diamond films were derived in [33], The resistive intercrystallite boundaries can involve nonlinear resistance in polycrystalline diamond films moderately doped with boron [34]. Later, more sophisticated analysis [35-37] of the frequency dependence of impedance of polycrystalline diamond films resulted in a conclusion that at higher temperatures, in addition to the aforementioned electric conductance caused by the motion of free holes in the valence band, a second component of conductance manifests itself. The second component is due to the hopping of charge carriers between local traps possibly associated with the intercrystallite boundaries. 

Fig. 28. Anodic O3 evolution plots for polycrystalline diamond thin-film electrodes (top) and PbC>2 electrodes exposed to 10 vol. % H2SO4 solution. The boron/carbon ratio in the source gas during the films growth shown on the figure [119]. Reproduced by permission of The Electrochemical Society, Inc.

Fig. 8.2 Oxygen tracer diffusivities and oxygen permeabilities through liquid boron oxide, fused silica, and a polycrystalline alumina with a grain size of 5 nm. Tracer diffusivity values for B203 and Si02 were obtained from Refs. 9 and 19, respectively. Tracer diffusivity values for A1203 were obtained from data reported in Ref. 18 using a grain size of 5 /im (Ref. 13). Oxygen permeability constants were obtained using the procedure outlined in the text.2...

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