Influence of temperature on the spark plasma sintering of calcium fluoride ceramics

The commercially abundant low purity calcium fluoride powder was directly loaded for spark plasma sintering (SPS). In a vacuum atmosphere with a constant pressure held at 70 MPa the sintering temperature was systematically varied in the range of 500–850 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) techniques were used to characterize the raw powder; and for studying the microstructural properties and in-line transmittance of the finalized ceramics, SEM and Fourier transform infrared spectroscopy (FTIR) were used. Digital images of the 700 °C sintered translucent CaF2ceramic were taken along with transmittance recordings. The grain growth mechanisms and activation energy values were determined; and the influences of temperature on the relative density, grain size, and optical transmittance were demonstrated. Furthermore, for the first time, a plausible predominant mechanism was proposed for describing the different sintering stages of calcium fluoride ceramics.