Pressure-assisted-reaction-sintering

X = 1.33 to X = 1.50), Takeshita et al. (1985) reaction-sintered a mixture of powders of stoichiometric LazSj and LaHs in a hot press. This pressure-assisted reaction sintering (PARS) method is quite effective in obtaining the desired composition with densities of 97% of theoretical. But because of the reactivity of LaHj it must be handled in glove boxes. 

Different processing routes have been applied to synthesize this class of composite material. Besides the classical method of powder mixing using submicron SiC, B4C and carbon or carbon-containing precursors, followed by forming and subsequent heat treatment ]313], the infiltration of boron carbide preforms with organic precursors such as PCS, followed by heat treatment [400, 401] or the pressure-assisted reaction sintering of silicon borides with elemental carbon [423], have been used. 

To a suspension of sodium tetrahydroborate (7.6 g. 0.2 mol) in 125 ml. of anhydrous tetrahydrofuran, trimethyl-ammonium chloride (9.5 g. 0.1 mol) is added and the mixture is allowed to stir for 2 hours. A moderate evolution of hydrogen occurs. The reaction is then refluxed overnight. After filtering the mixture through a sintered-glass funnel in vactw directly into a 200-ml. flask to remove the sodium chloride and excess sodium tetrahydroborate, the filtrate is concentrated in a rotatory evaporator (or simple Kjeldahl bulb and take-off) under aspirator vacuum. Ether and low-boiling petroleum ether may be added to assist in the removal of the tetrahydrofman. A white solid is collected, which yields the trimethylamine-borane upon sublimation at 40 to 60 mm. pressure and 60 to 70°. The yield is 4.9 g. (67%), m.p. 93 to 95° reported m.p. 93°, b.p, 171°. Anal. Calcd. for (CH3)3N-BH3 C, 49.45 H, 16.48 N, 19.22. Found C, 49.55 H, 16.44 N, 19.04. 

---