Active media (such as water, acids, alkalis, and certain salts) have two effects on the glass surface: one is that the infiltration crack propagates like a wedge (the crossbow) to expand the microcrack; the other is to chemically destroy the structure with the glass (for example) Disconnect the silicon oxide bond). Therefore, the strength of the glass in the active medium is lowered. Water causes the greatest decrease in strength. The strength of the glass in the alcohol is 40% higher than in water, and the higher the water content in the alcohol or other medium, the closer it is to the strength in the water. In the acid or alkali solution in the range of pH = 1 to 11.3 (both acid and alkali are below 0.1 mol / L), the strength is independent of the pH value (same as in water, at a concentration of 1 mol / L, the intensity is slightly The effect is reduced in acid and increased in alkali, and each increase or decrease is about 10% at 6 mol/L.
Dry air, non-polar media (such as kerosene, etc.), hydrophobic silicone, etc. have little effect on strength, so it is best to measure the strength of the glass in vacuum or liquid nitrogen to protect it from the active medium. Conversely, annealing the glass in an SO2 atmosphere produces a layer of hoarfrost (Na2SO4) on the surface of the glass, which is easily washed away, resulting in a reduction in the alkali metal oxide content of the glass surface, which not only increases chemical stability. It also increases the strength of the glass.