I-Corps: Commercialization of a Decontamination Process for Powders for Transparent Ceramics

Lehigh University, Bethlehem PA

Investigators

Abstract

A novel purification process has been developed and patented to reduce unwanted impurity content in ceramic powders. This process removes impurities such as sulfur and chlorine which have largely been neglected and cannot be removed by traditional purification processes utilized commercially. As a result, even the 'ultra-high purity' powders that are commercially available often contain significant amount of such impurities. The proposed purification process has been successfully applied to magnesium aluminate spinel (MgAl2O4), a material of choice for NASA and DOD for various defense and aerospace applications for which highly transparent and high strength materials are required. In comparison to the ballistic glasses, which are currently utilized for such applications, an improved ballistic performance at half the weight and thickness can be potentially achieved utilizing spinel. This will have a significant beneficial effect in various ways such as reducing the cost of maintenance and increasing the life-time of the components, energy/fuel savings and increase payload capacity of vehicles/spacecraft where spinel parts can be utilized. The proposed patented process has been successfully utilized in laboratories to consistently produce powders with impurity content that is sufficiently low for further processing, irrespective of impurity content in the starting powder. It is believed that the patented process will invigorate the commercialization of spinel by providing a cost-effective, scalable solution for the mass production of large monolithic bodies of spinel and other ceramics. This would benefit a large number of industrial manufacturers serving this market. The novel purification process involves treating as received powders in ultra-high vacuum with or without concurrent heating for extended periods of time. The process does not modify the physical characteristics of the powders such as tap density or particle size distribution that are already optimized for specific applications. Utilizing the processed powders, it is possible to achieve near theoretical density and transparency in the spinel samples by hot-pressing only without the addition of any sintering aids. Current processing strategies involve use of sintering aids to achieve theoretical density and transparency that invariably lead to degradation of mechanical properties because of abnormal grain growth. Another processing step in the current processing strategies involves a post hot-pressing hot-isostatic pressing step at high temperatures to remove residual porosity. Although this step produces near theoretical transparency in the parts, it results in abnormal grain growth at the processing temperatures and significantly increases the production cost of the spinel parts significantly. The patented process can potentially avoid such complicating factors, but needs further evaluation to be efficient and viable at a commercial scale.