Fabrication of Transparent Spinel Honeycomb Structures by Methyl Cellulose-Based Thermal Gelation Processing

摘要

Transparent MgAl_2O_4 spinel of flat as well as honeycomb structure was fabricated by employing thermally induced gel casting of the slurry with 56 wt% solid loading containing 0.2 wt% of methylcellulose. The green specimens were pres-sureless sintered to 98%-99% of theoretical density with no open porosity at an optimum temperature of 1700℃. Final densiflcation by hot isostatic pressing of both the specimens at the optimum temperature of 1800℃ and 195 MPa pressure enabled further elimination of residual porosities and full densi-fication resulting in theoretical density of 3.58 g/cc. The design of the honeycomb was such that it exhibited a surface area to volume ratio of 0.65 cm~2/cm~3 and a relative density of 0.69. The hardness of the honeycomb specimens has been found to be 13 GPa, which is at par with the solid specimens processed under identical conditions. Solid specimens of around 4 mm thickness exhibited a transmission of＞80% in the visible (0.4-0.8 μm) region. Specimens were also tested according to ASTM procedures and have shown a flexural strength (σ_f) of 195 MPa and plane-strain fracture toughness (K_(IC)) of 1.87 MPa·m~1/2 as reported in this study.