Borides formation

Borides of Al, Ti, Zr and Hf are prepared according to reaction (a), although even with careful measuring of reactants it is not always possible possible to form the metal boride in stoichiometric ratio, and free metal B may be deposited . This method is not suitable when the free metal deposits at T below those required for boride formation, as in the cases of Nb, Ta, Mo and W. 

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. 

Rapidly solidified in-situ metal matrix composites. A design project for alloys based on the Fe-Cr-Mo-Ni-B system, and produced by rapid solidification, was undertaken by Pan (1992). During processing a mixture of borides is formed inside a ductile Fe-based matrix which makes the alloys extremely hard with high moduli. These alloys provide a good example of how phase-diagram calculations were able to provide predictions which firstly helped to identify unexpected boride formation (Saunders et al. 1992) and were ultimately used in the optimisation of the modulus of a shaft material for gas turbines (Pan 1992). 

What is interesting to note here is that the catalyst that facilitates the conversion of the borohydride to borate can be an acid, metal, or metal boride. So, as this reaction proceeds, it is producing the very catalyst that degrades the starting reactant. It is possible to control the boride formation with the use of borohydride esters such as lithium triethoxyborohydride, commonly referred to as superhydride. 

C—C Borid Formation with the Allyl System as the Nucleophile 862... 

Boron W + B (amorphous) powder mixture compacts SOO C inHj/l hour 800-1200 °C in Ar/2 hours Individual boride formation depends on W/B ratio W2B, WB, W2B3, WB4... 

Only scant evidence of lead boride formation exists. Borides of lead are unlikely in view of the high second ionization potential of Pb. ... 

With allowances for the actual metal content of zirconium (a small correction is also necessary for the hafnium content of about 2 /2%) and postulation of barium zirconate formation (see Table 27), reasonable accord between calculated and measured caloric output is established. However, the situation is more complex with boron mixtures where one encounters increase of heat output with increase of the percentage of boron in the mixtures much beyond the amounts of Equation (la). Thus, even with the reasonable assumption of secondary barium borate formation, the stoichiometry and heat output of the mixtures with more than about 10% of technical boron theoretical 8%) is obscure. Chromium boride formation may be a fector. 

The region tj -12 is distinguished by a sharp decrease in the B2O2 partial pressure with the increased temperature of the combustion front, judging by the ion current of Zn, which increases to a maximum. This unexpected effect can occur only due to B2O2 consumption in the reaction for molybdenum boride formation ... 

This process proceeds with the effective rate coefficient k2 - 10 s and activation energy E = 0 19). The latter indicates that the rate of molybdenum borides formation is limited by either formation of B202(g) or its diffusion to the metal surface but not by reactive diffusion in the solid. 

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