Curing effect of MgAl2O4 spinel to aluminum dihydrogen phosphate.

MgAl₂O₄ spinel powders were first applied for aluminum dihydrogen phosphate hydrosol curing reaction. The solidification of spinel powders to phosphate hydrosol was studied in middle and low temperature condition. Besides, composites were prepared with quartz textile as reinforcing part, aluminum hydrogen phosphate hydrosol as matrix and spinel MgAl₂O₄ as firming agent. Curing temperature of phosphate hydrosol and the additive content of spinel MgAl₂O₄ powders were measured by thermogravimetric analysis and differential scanning calorimeter. At the same time, the crystalline phase of curing products was identified by X-ray powders diffraction. Microstructures of the composites were observed by scanning electron microscope. Moreover, the mechanical and resistant moisture absorption properties of phosphate composites were investigated. The results showed that aluminum dihydrogen phosphate resin had occurred dehydration reaction and formed into cross-linkage net in the temperature near to 170 °C, while the resin was added spinel MgAl₂O₄ powders. And it was contributed to reduce original pores and flaws in the matrix with mild reaction process. Owing to the promoting effect of spinel, the mainly reaction products were aluminum phosphate with the style of quartz and magnesium phosphate with monoclinic structure. Meanwhile, the reaction that aluminum dihydrogen phosphate changed into aluminum polyphosphate was prevented, which was benefit to enhance the resistant moisture absorption property of the composite. When the content of spinel MgAl₂O₄ powders arrived at 18wt%, the composite obtained the highest properties, which the flexual strength at room temperature and at 800 °C were about 165 MPa and 75 MPa. And dielectric properties of the composite were remained stably during long time storage, which dielectric constant was about 3.5 to 3.6 and loss tangent was less than 0.01 at room temperature respectively. [ABSTRACT FROM AUTHOR]