Effect of Al:P ratio on bonding performance of high-temperature resistant aluminum phosphate adhesive

Abstract A series of high-temperature resistant aluminum (Al) phosphate (P) adhesives with different Al:P ratios were prepared using Si as the sole additive. The influence of Al:P ratio on the temperature-dependent composition and structural evolution of the adhesives and their bonding performance were systematically analyzed. The conversion of aluminum metaphosphate to aluminum orthophosphate during the heating process from 700 °C to 900 °C decreased with increasing Al:P ratio, which reduced the generation of micro cracks inside the adhesive. Higher Al:P ratios (≥1:1) were favorable for the generation of alumina, which then reacted with silicon oxide to form mullite phase at high temperatures. No mullite phase was generated for Al:P ratios lower than 1. Accordingly, increasing Al:P ratio effectively improved the bonding performance and thermal shock resistance of the adhesive. The bonding strength of adhesive with an Al:P ratio of 1:0.85 after calcination at 1300 °C was 35.7% and 112%, respectively, higher than those of adhesives with Al:P ratios of 4:5 and 1:2. Besides, the retention rates of their bonding strength were 48.8%, 28.6% and 7.9%, respectively, after 15 thermal shocks based on air-cooling from 1300 °C to RT.