Influence of Surface Condition on the Strength of Polycrystalline MgO

The mechanical behavior of high‐purity (greater than 99.9%) polycrystalline MgO, with relative density exceeding 9875, is described. By fracto‐graphic techniques, it was determined that inter‐granular cracks initiate fracture. These cracks originate from the extension of surface flaws into the MgO and are particularly severe in areas of high, localized, intergranular porosity. Ceramic machining techniques, such as diamond sawing and lapping with coarse abrasives, induce these surface flaws and limit the strength of MgO. The effectiveness of lapping, thermal conditioning, and chemical polishing techniques in removing these flaws and producing a substantial increase in mechanical strength is shown to be dependent on grain size and porosity.