Improving the water resistance and adhesion strength of a mixed alkali silicate adhesive by optimizing the molar ratio and curing conditions

It is important to eliminate the use of organic adhesives that are harmful to humans and cause environmental pollution. Environmentally friendly, harmless inorganic adhesives are being actively studied. Here, we found that optimized curing was possible when the curing time was controlled via temperature adjustment. We first prepared basic alkali silicate solutions, containing sodium, potassium, and lithium silicate, and compromised them in terms of water resistance. Adhesive strength was measured according to ASTM D3165 using a universal testing machine. The target material, a stainless steel (SUS) specimen, was prepared as described by ASTM D3165. Moreover, to develop fast thermal curing, the effects of two parameters were investigated: curing time and temperature. The temperature range tested was 80–140 °C for 2–36 h; we assessed adhesive strength. The maximum shear strength was obtained after thermal curing at 80 °C for 36 h, 120 °C for 12 h, and 140 °C for 2 h. However, when thermal curing proceeded past the maximum shear strength, the shear strength decreased, attributable to a reduction in the adherent area.