Boron phase transformation

Riter J R Jr 1973 Shock-induced graphite.far.wurtzite phase transformation in boron nitride and implications for stacking graphitic boron nitride J. Chem. Phys. 59 1538... 

Ca3(BN2)2 is readily formed when (distilled) calcium metal is melted in the presence of (layer-type) boron nitride. This reaction provides some insight on how alkaline-earth metals like calcium may act as a catalyst in the phase transformation of layered a-BN into its cubic modification. Instead of metals, nowadays alkaline-earth (Ca, Sr, Ba) nitridoborates can be used as a flux catalyst in high-pressure and high-temperature transformation reactions to produce cubic boron nitride [15]. 

A correlation between the total momentum of impinging ions per deposited boron atom and the c-BN deposition has been observed. In this model, c-BN formation is correlated with the momentum-drive process, such as the formation of point defects in conjunction with the stress-induced phase transformation. 

Turan, S. and Knowles, K.M., (1996b), Effect of boron nitride on the phase stability and phase transformations in silicon carbide , J. Am. Ceram. Soc., 79 (12), 3325-3328. 

Sluggish reactions are often met with in boride systems even at high temperatures, especially at boron-rich compositions. This often hinders phase equihbria to be established and phase transformations under equihbrium conditions to be investigated. 

Owing to sluggish phase transformations, the temperature regions of stability for the different modifications are not known with certainty. The S-rh. modification is, however, stable from the melting point of boron, 2573 K, down to 1473 to 1673 K. The -tetr. modification (also denoted tetr. II boron) is stable in the intermediate range down to approximately 1300 K. a-rh. boron is a low-temperature modification, stable up to approximately 1300K. 

A. V. Kurdyumov and A. N. Pilyankevich, Phase Transformations in Carbon and Boron Nitride, Naukova Dumka, Kiev, 1979. 

This includes single crystal silicon [15], germanium [22] and alumina [10] fibers. Polycrystalline fibers can grow either by a VLS or a VS phase transformation when the incident laser power (focal temperature) is intermediate, and supports the growth of a fiber with a semisolid tip. This includes polycrystalline silicon [15], boron [5] and silicon carbide fibers [23]. Amorphous fibers are obtained by a VS phase transformation when the incident laser (focal temperature) is low, and supports the growth of a fiber with a hot but solid tip. This includes amorphous silicon [15], boron [12], carbon [13] [16], silicon carbide [23], and silicon nitride [17] fibers. 

While the direct conversion of a-BN to p-BN is of high interest for the preparation of p-BN semiconductors, large scale production of p-BN is performed by catalyst-aided procedures under careful control of the amount of the catalyst [36]. The catalyst material has to be removed after the end of the phase transformation process by treatment with base (sometimes acid) in order to dissolve unreacted a-BN and the catalysts, since they are not included in the lattice of the resultant p-BN. Under the high pressure and temperatures required for the phase transformation, the catalysts and their reaction products with boron nitride form a melt from which p-BN crystallizes. The temperature for the process is lowered by eutectic formation between the catalyst and BN (see discussion by [1]). 

Gasgnier M, Szwarc H, Ronez A (2000) Low-eneigy ball-milling tiansformations of boron nitride powders. Crystallographic and chemical characterizations. J Mater Sci 35 3003-3009 Batsanov SS (2011) Features of phase transformations in boron nitride. Diamond Relat Mater 20 660-664... 

Batsanov SS (2011) Features of phase transformations in boron nitride. Ditimond Relat Mater 20 660-664... 

Batsanov SS, Gavrilkin SM, Bezduganov SV, Romanov PN (2008) Reversible phase transformation in boron nitride imder pulsed mechanical action. Inorg Mater 44 1199-1201... 

The c-BN phase was first obtained in 1957 [525] by exposing hexagonal boron nitride phase (h-BN) to high pressures and low temperatures. A pressure of more than 11 GPa is necessary to induce the hexagonal to cubic transformation, and these experimental conditions prevent any practical application for industrial purposes. Subsequently, it has been found that the transition pressure can be reduced to approximately 5 GPa at very high temperature (1300-1800°C) by using catalysts such as alkali metals, alkali metal nitrides, and Fe-Al or Ag-Cd alloys [526-528]. In addition, water, urea, and boric acid have been successfully used for synthesis of cubic boron nitride from hexagonal phase at 5-6 GPa and temperature above 800-1000°C [529]. It has been... 

Farrall and Frechet recognized the possibility of forming polymer-bound boronic acids in 1976.66 Supported pnra-benzeneboronic acid groups were generated by direct lithiation of polystyrene, giving a para-lithio intermediate that could be used to generate a host of other resins also (Scheme 27). Conversion to the boronic acid was one of the more successful transformations. The purpose of this transformation was to allow the attachment of sugars to the solid phase via the boronate. 

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