Hexagonal boron nitride-aluminum nitride (h-BN-AlN, 75-25 wt%) ceramic composites are synthesized by reaction bonding. Metallic component-free, relatively dense composites are obtained by using h-BN and Al as starting materials and by optimizing sintering conditions. In comparison with reaction-bonded BN, higher bending strength, 98 MPa, and higher thermal conductivity, 66 W/(m·K), are attained for a Y2O3-added BN-AlN composite. A low thermal expansion coefficient of 2.6×10-6/K is also achieved.

The electrooxidation of sulfur in molten AlCl3‐normalNaCl (63‐37 mole percent) has been investigated by means of u.v.‐visible and electron spin resonance spectroelectrochemistry in the temperature range 132°–250°C. The electrode reaction sequence for the oxidation of S8 to SCl3+ that was proposed previously based solely on electrochemical results has been modified to include several other intermediates, such as S192+ , S5+ , S42+ , and S (II).

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The oxidation of sulfur in chloroaluminate melts in the composition range 53-47 to 49.9-50.1 mol percent A1C13-NaC1 (pC1 of 5.4-1.5 at 175~ was investigated by visible spectrophotometry, and ring-disk, differential pulse, and cyclic voltammetry. The oxidation process undergoes a significant change in this narrow melt composition region. Low oxidation states of sulfur, such as Ss § and Ss ~+, were found to be stable only atpC1 >-3.8. The other main oxidation products are $2C12, stable over the entire pC1 range studied, and SC13 +, stable only in acidic melts. ABSTRACTThe electrochemical oxidation of hydrazine has been examined on tetrasulfonated phthalocyanines of Fe, Co, Ni, and Cu, adsorbed on ordinary pyrolytic graphite electrodes and substantial catalytic effects have been observed on the Co and Fe derivatives. Tafel plots give slopes of 40 and 60 mV/decade for Fe-TSP and Co-TSP, respectively. The chemical orders in OH-and N2H4 have been determined and possible mechanisms for the reaction are proposed.