Thermoanalytical investigation of calcium chromate |
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| Authors: | Robert P Clark Patrick K Gallagher Beverly M Dillard |
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| Institution: | Sandia Laboratories, Albuquerque, New Mexico 87185 U.S.A.;Bell Laboratories, Murray Hill, NJ 07974 U.S.A.;General Electric Neutron Devices Department, St. Petersburg, FL 33733 U.S.A. |
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| Abstract: | Thermoanalytical methods have been used to study calcium chromate (CaCrO4) samples. Thermal decomposition temperatures determined by TG in vacuum and by DTA in air could not be successfully used for screening purposes. Other thermogravimetry studies in air indicate that TG can be an effective quality control tool in screening out samples which have an assay value below 97.0% CaCrO4. More complete analyses using TG in an argon atmosphere gave good results for CaCO3 and H2O content as well as for total CaCrO4. Reliable measurement of Ca(OH)2 was not achieved. Effluent gas analysis—mass spectrometry was used to identify gaseous products as a function of temperature, in order to verify interpretation of TG curves.Thermogravimetry, differential scanning calorimetry, nuclear magnetic resonance, and mass spectrometry have been used in an effort to explain the unusual weight loss observed between 400 and 600°C for many CaCrCO4 samples. Ca(OH)2 decomposition is not the primary cause of this weight loss, as originally suspected, but instead the loss appears to be due to volatization of H2O trapped in the CaCrO4 crystal. |
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