Effect of evacuation parameters on hot isostatically pressed samples titanate wasteform

Abstract

One of the methods for consolidation of titanate ceramic wasteforms (synroc) is that of Hot Isostatic Pressing (HIPing). This involves the powdered wasteform sealed in a metallic canister and heated to appropriate temperatures and pressures. If there are residual volatile gases being evolved during the HIPing process an internal pressure build up can result in residual porosity of the product within.

A typical process for encapsulating wasteforms is to heat up the sample in the metal canister (bake out) to remove excess gas and moisture and seal under vacuum to prevent the previously mentioned failure. This study evaluates the effect of the vacuum level required before sealing the metal canister as well as the influence of additives into the wasteform on this level.

It has previously been shown that an addition of 2wt % Ti added as a redox buffer to Synroc-C results in a dense durable wasteform when subjected to the standard bake out process. It was found in this study that on a small scale no can breach occurred when the powder comes directly from the calcination process and the can was sealed without pulling a vacuum. However the wasteform composition and its performance were affected by the reaction with excess oxygen sealed in the can. To further replicate a true production environment, these investigations were also carried out on larger scale samples.