Development of Cr-free aluminum phosphate binders and their composite applications

Environmentally friendly Cr-free aluminum phosphate (AP) binders were produced by mixing the dissolved Al(OH)(3) in H3PO4 with fillers (Al2O3 or/and Cr2O3) and with AlN, NH4F, MgO, Cu2O, and ZrO2 singly or combination, as curing promoters. The effect of various additive combinations on the curing behavior and the thermal stability of AP matrixes were comparatively evaluated using TGA/DSC and XRD measurements. The woven ceramic fiber reinforced composites fabricated from the developed AP binders showed the dependent characteristics on additive type, fabric reinforcement, and thermal history. Flexural strength exhibited only 65-74 MPa for single additive matrixes whereas 138-150 MPa for combinational additive matrixes. Thermal conductivity of the composites was in range of 0.57-1.08 W/mK. However, composite strengths were significantly degraded to different extents depending on reinforcement type when exposed to temperatures of 500 degrees C and 800 degrees C in air. (c) 2006 Elsevier Ltd. All rights reserved.