PRESSURE SINTERING AND TRANSFORMATION TOUGHENING OF ZINC-SULFIDE

Several techniques to increase the fracture toughness of ZnS, including pressure sintering, transformation toughening and pressure bonding to a diamond film, were evaluated. The primary method used was pressure sintering, i.e. room temperature compaction followed by sintering at a relatively low temperature (less than Tm/2 where Tm is the melting point). Pressure sintering produces superior ZnS compacts with a hardness of 2.89 GPa and a fracture toughness of 1.59 MPa m1/2 compared with 2.17 DPa and 0.87 MPa m1/2 for conventionally produced chemical-vapour-deposited material. The hardness and fracture toughness of CdY2S4, GaP-doped zinc sulfide and selenide compacts processed by pressure sintering were also evaluated. In order to calculate the fracture toughness of CdY2S4, Young's modulus was determined by X-ray diffraction to be 87 GPa. NiS, TlI and TlGaSe2 were evaluated as transformation-toughening agents for ZnS. Only the mineral form of NiS (millerite) significantly toughens ZnS, but the ZnS-NiS compact is no longer transparent in the infrared region. Preliminary experiments to pressure bond ZnS to a diamond film indicate that 1.9<P≤5.5 GPa is required at T=600°C. © 1990.