Study On Vacuum Thermal Decomposition Of Gallium Arsenide

With the pressure of gallium continuing to use up, energy shortage and environmental protection, it would be particularly important for us to recover valuable metals comprehensively from secondary resource containing gallium. A novel technique was developed to remove gallium and arsenic effectively by thermal decomposition of GaAs scraps under vacuum, with advantages over conventional techniques, including simple operation, little reagent consumption and environmental friendliness.Thermodynamics analysis of GaAs scraps to recover Ga and As by thermal decomposition under vacuum were conducted. The results of thermodynamic analysis indicate that Ga and As2are produced firstly at1203K when the system pressure is10Pa. As3and As4are produced at1322K and1454K, respectively. The saturated pressure of pure substances of As are bigger than Ga, and the difference of β is bigger than106. Therefore, it’s easy to separate As and Ga, as As volatilizes into gas phase and Ga remains in liquid. It is known from binary phase diagram that solid GaAs is stable and it’s not easy to separate Ga and As when the temperature is lower than1083.15K.While, it is likely to separate them at higher temperature. By analyzing pressure-temperature equilibria diagram for the Ga-As system,we knew that As2was easier to volatilize as it’s saturated vapor pressure was much larger than Ga’s when the temperature was higher than700K. But the gasous contents of Ga increased remarkably at1373K or above.The theoretical calculations of GaAs energy band structure, density of states, Mulliken overlap population and electron density difference were carried out by density functional theory (DFT) at a chamber pressure of10Pa when the temperature was1273K. The dynamics simulations of GaAs about the process of thermal decomposition were performed. The calculated results showed that most of Ga-As bonds was easy to break and Ga andAs2produce, as their length increased; bond population decrease; and interatomic strength weaken. Ga-As bonds break step by step. It was interesting that we discovered that bond lengths of part of Ga-As bonds diminished; their bond population were rather large; interatomic strength enhanced. Therefore, we thought small clusters,such as GaAs, Ga2As(a), Ga2As2(b). could produce in the progress of GaAs thermally decomposed under vacuum. What is more, they were very stable and their diffusion coefficients were a bit large, and they would volatilize into gas phase. So, it could explain the appearance of GaAs in the condensate.Finally, according to the theoretical analysis, the separation possibility and effect of GaAs scraps thermally decomposed under vacuum, which was influenced by distillation temperature and distillation time were evaluated.Under the favorable conditions, highly pure Ga can be extracted with advantages over conventional techniques, including simple operation and environmental friendliness For example, the metallic gallium obtained is good and the content of which is larger than99.99%at1273K for3h when the system pressure is3to8Pa. And arsenic obtained was existed in the form of simple substance which was little damage.