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Abstract Phosphate materials based on Turquoise composition CuAl6(PO4)4(OH)8•4H2O were prepared using aqueous solutions. The light blue or green powders were obtained by heating at 500 or 700 ºC. To obtain artificial Turquoise pellets, these were sintered by the hydrothermal hot press method at 150 ºC. The amount of water, pressure, and milling as pretreatment were studied. Molded pellets were also prepared using oil as the solvent. The resulting pellets were evaluated in terms of density and hue. In addition, the effects of post-treatment, such as heating and beeswax coating, were also examined. There were several methods to improve the density of the molded product, including increasing the amount of solvent, increasing the pressure, using castor oil, and powder refining as a pretreatment. Castor oil and beeswax coating were also methods to improve product brightness. The pellets obtained in this study showed water resistance.

Abstract Spark plasma sintering (SPS) is an advanced process of sintering materials at low temperatures and short time by creating spark plasma at very high temperatures in the small points and short times, by which materials with high sintering temperature can sinter at lower temperatures. In this study, alumina-nickel-cobalt composites were sintered by SPS and RHP (rapid hot press) methods to investigate the effects of electric pulse on their microstructure and mechanical properties. To this end, sample powders containing alumina, nickel-cobalt aluminate spinel, and aluminum were sintered at 1380 °C under 30 MPa pressure for 10 min by SPS and RHP and then investigated. The densities of both samples were about 98% of theoretical density. Also, hardness and fracture toughness of both samples were about 11 GPa and 14 MPa.m0.5, respectively. The bending strengths of the SPS and RHP samples were 380 and 336 MPa, respectively.