THERMOGRAVIMETRIC STUDY OF GaAs CHLORINATION BETWEEN -30 AND 900 °C

FERNANDO M. TUNEZ; JORGE A. GONZALEZ; M. DEL C. RUIZ

THERMOCHIMICA ACTA

ELSEVIER SCIENCE BV

Año: 2010

0040-6031

GaAs is at present an essential part of electronic devices, and the recovery of this element from electronic wastes is fundamental for the metallurgic industry. In this work, with the aim of recovering Ga by chlorination the following reaction was investigated: GaAs + 3Cl2(g)  GaCl3(s, l ó g) + AsCl3(s, l ó g) A thermogravimetric study of the previous was carried out, and the following variables were investigated: chlorine partial pressure, in the range between 0.2 and 1 atm, by dilution with N2 and reaction temperature in the –29°C to 900°C interval. The thermodynamic calculations predict that the reaction is feasible during the entire analyzed temperature interval, and the experimental results are in agreement with the thermodynamic estimations. The results show that the rate of chlorination did not change significantly with temperature, but it increased with the chlorine partial pressure. It was found that AsCl3 was partially evaporated at temperatures above 20°C, while the GaCl3 started to be evaporated at 100°C. The experimental observations show that the mechanism originating the reaction is different in each temperature interval ranging between -30 and 160ºC, 200 - 400ºC, and above 500ºC, respectively. In the first case the reaction is caused by adsorption of Cl2 on the solid surface. In the second case, the solid starts reacting when little quantities of GaCl3 and AsCl3 vapor are injected in the entrance of the system, indicating that the chlorination kinetics responds to an autocatalytic mechanism. Above 500ºC, the reaction is caused without adding chlorination products. The results of the analysis by scanning electron microscopy and X-ray diffraction show a preferential attack on one of the crystal planes of GaAs. Besides, the formation of Ga2O3 and GaAsO4 was observed as a consequence of the presence of small quantities of oxygen accompanying Cl2. The results obtained showed that chlorination is a selective and economic methodology for the recovery of gallium from electronic wastes.