Combined dilatometry and mass spectrometry of sintering and evolved gases of barium titanate and zirconium diboride with sintering additives

The system components, improvements, and procedures of a combined dilatometer mass spectrometer system (CDMS) are described in detail. The CDMS is used to monitor the gas phase species and sintering progress in real time during the heating of barium titanate and ultra high temperature ceramics (UHTCs), including zirconium diboride and sintering additives. For loose powder and pressed samples of barium titanate heated at different rates, two families of signals were observed by mass spectrometry at mass to charge (m/z) ratios of 44 and 64 prior to the onset of sintering, which initiated at 1150°C. The assignment of these signals as carbon dioxide and sulfur dioxide was accomplished using reference cracking patterns, natural isotope abundances, a carbon dioxide gas reference, and comparison to the gases evolved from the model compounds barium carbonate and barium sulfate. The sources for carbon dioxide evolution at low temperatures below 500°C include organic impurities arising from processing, exposure to ambient organic material, and adsorbed carbon dioxide. The sources for the higher temperature above 600°C evolution of carbon dioxide and sulfur dioxide are likely from residual unreacted or surface barium carbonate and barium sulfate, respectively.;The UHTCs and common sintering aids heated in the CDMS individually and in mixtures include zirconium diboride, boron carbide, silicon carbide, boron oxide, zirconium oxide, zirconium disilicide, boron nitride spray, and organic binder, dispersant, and surfactant. Low temperature signals below 660°C for these UHTCs are attributed to the decomposition of organics present in the boron nitride spray, binder, dispersant, and surfactant. The high temperature signals above 900°C were determined to be CO and CO2 using reference cracking patterns and natural isotope abundances. The carbon sources are identified as arising from unreacted carbon from the synthesis methods for some of the powders and from the carbon inherent in the chemical formula. The oxygen sources were attributed to synthesis reactions for the powders and to the presence of surface oxides. An additional source for CO and CO 2 production at high temperature for the powders in mixture is the reactive sintering that occurs. Zirconium disilicide was the only additive that decreased the sintering temperature of zirconium diboride below the maximum hold temperature of 1648°C, thereby allowing sintering to occur.