Spark plasma sintering (SPS) is a remarkable method for synthesizing and consolidating a large variety of both novel and traditional materials. One controversial SPS enhancement mechanism put forth in the literature involves the presence of momentary plasma generated between powder particles. This study attempts to ascertain the presence or absence of plasma using: in-situ atomic emission spectroscopy, direct visual observation and ultra-fast in-situ voltage measurements. Using a wide variety of powders and SPS conditions, no evidence of plasma was found using these techniques.

By using SPS ultra-fine grained polycrystalline alumina (PCA) was sintered to full density. This PCA had near theoretical transmittance (of around 85%) in the mid-infrared bands of the electromagnetic spectrum. In addition, the PCA was found to be transparent in the visible spectrum. The Rayleigh-Gans-Debye model was found to accurately predict the transmission of PCA across a wide range of grain sizes and wavelengths.

Yttria–Magnesia nanocomposites were consolidated via SPS using powders prepared from flame spray pyrolysis and plasma spraying. Obtaining fully dense compacts by using the plasma sprayed powders proved challenging. As such, the maximum mid-IR transmittance values obtained are quite low ranging from 10% to 30%. By contrast, the nanocrystalline compacts sintered from the flame spray pyrolysis showed excellent mid-IR transmittance of approximately 80%. In addition, these nanocomposite compacts exhibit hardness values approximately 35% higher than either parent phase.