Development of a Technology for the Obtainment of Fine Grain Size, Transparent MgAl2O4 Spinel Parts

The objective of the work was the establishment of a procedure allowing the obtainment of high-optical-transparency MgAl2O4 polycrystalline parts that exhibit a fine microstructure (average grains size lower than 5 mu m). The technology had to be relevant for industrial-scale production. A nano powder, commercially available in large quantities, at a reasonable price, was used as raw material. It was determined that by applying a suitable combination of powder processing and green-bodies-forming procedure, a configuration favorable for advanced densification can be derived from the selected powder. It was also found that the pore-closing ability of HIPing was best exploited when the specimens subjected to this treatment (predensified by pressureless sintering, in air) exhibited an optimal tradeoff between densification level and microstructural configuration. Specimens combining an average grain size of 2.5 mu m with an in-line transmission of 77 % (lambda = 750 nm; thickness similar to 2 mm) were obtained; such parts possess a Vickers hardness of 13.8 GPa and a transverse rupture strength of similar to 200 MPa. Because the technology developed generates transparent spinel exhibiting properties acceptable for some of the existent applications, at reasonable cost, it may be of interest to industry.