The Pressureless Sintering Behavior And Master Sintering Curve At Constant Heating Rate For Titania

Thermal Dilatometer, X-ray Diffraction(XRD), Scanning Electron Microscope(SEM),Transmission Electron Microscope (TEM) and Atom Force Microscope (AFM) were usedto investigate the sintering behavior and microstructure evolution. The Master SinteringCurve (MSC) ofnano rutile was constructed and validated.Based on Coble's sintering theory, the sintering curves of nanometer anatase and rutileand submicrometer anatase titania were compared. It was found that the intermediatesintering stage of nano rutile happened in the range of 765℃～995℃, nano anatase at490℃～1000℃and submicrometer anatase at 975℃～1065℃. The temperature ofsintering shrinkage onset and maximum densification rate appearance was 750℃and920℃for nano rutile. However, that of nano anatase was 450℃and 880℃for the phasetransformation. The SEM images of sample fracture and the AFM images of etchedsurface showed that the grain growth before 1000℃was induced by the adhesionbetween small granules in the aggregate, and after 1000℃it was caused by the grainboundary motion.The sintering behaviors of TiO₂ with different grain sizes and heating rates wereinvestigated. Two peaks appeared in the densification rate vs relative density curve, phasetransformation and shrinkage peak. The influence of grain size on the relationship ofdensification rates with the relative density was analyzed. It was found that the maximumdensiflcation rates of the nanometer and submicron anatase titania sample occurred at therelative density of 66.8ï¼…and 73.1ï¼…respectively. The lower the heating rate, the higherthe relative density.Based on the combined-stage sintering model of Hansen James D, the master sinteringcurve (MSC) for the rutile was constructed for sintering in air with constant pressure andusing a constant heating rate in a dilatometer. The relative density of the sample wasmeasured using the Archimedes method. The MSC curve of the rutile TiO₂ samples wasconstructed and validated under different thermal histories. The MSC, in which thesintered density is a unique function Of the integral of a temperature function over time, isinsensitive to the heating path. According to the MSC of TiO₂, it is possible to predict thesintering shrinkage and final density and calculate the activation energy (105kJ/mol).With one temperature dependent parameter determined experimentally, it becomespossible to describe accurately the densification behavior of TiO₂ from the initial to finalstages during the sintering period.