Local fluctuation of the relative density of glass powders over the entire viscous sintering process

Using high-resolution X-ray computed tomography and 3D image analysis, the global relative density was determined and fluctuations in relative density were localized and quantified in a series of sintered glass bodies made of 80 μm glass spheres over the entire sintering process. A representative volume element (RVE) in the sintered body was divided into cubic volumes of 500, 250 and 125 µm edge length by an automatic segmentation routine. It was found that the expected decrease in coarseness C from the initial to the final sintering stage is interrupted by an intermediate stage with highest C and a characteristic bimodal density distribution. The bimodality of the intermediate stage is due to spatially separated denser arrangements within the RVE with closed pores and less dense arrangements with a network of interconnected or open pores. The spatial heterogeneity is biased in the z-direction due to friction caused by adhesion with the substrate.