On the chemical vapor transport of ternary transition metal- and earth alkaline tungstates MWO4 with chlorine

The chemical vapor transport of transition metal tungstates MWO4 (M=Mn, Co; Ni, Cu, Zn, Cd) was investigated in dependence on mean transport temperature (923 K to 1223 K) and amount of transport agent Cl-2. All tungstates migrate in a temperature gradient Delta T = 100 K from the region of higher temperature to the lower temperature with migration rates of 0.5 to 8 mg/h depending on experimental conditions. The transport behaviour was determined by continuous measurement of mass change during the transport experiments. The results were compared to thermo chemical calculations and the influence of moisture content discussed in detail. MgWO4 migrates under the influence of Cl-2 in a temperature gradient 1273 K to 1173 K (migration rate 0.7 mg/h), Ca WO4.: and SrWO4 in a temperature gradient 1423 K to 1323 K (migration rate <0.1 mg/h).

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