微波硬化表面包覆低共熔体锂盐水玻璃砂抗吸湿性初步研究

Preliminary Study on Humidity Resistance of Sodium Silicate Sand Hardened by Microwave Heating Coated with Eutectic Lithium Salts

介绍了一种在水玻璃砂型表面生成低共熔体锂盐包覆层的方法。首先在水玻璃砂型表面喷涂0．38LiOH-0．62LiNO，混合锂盐饱和水溶液，再将喷涂后的砂型放入微波炉加热硬化，因为配比的混合锂盐共熔点温度只有175．7℃，饱和水溶液中的溶质在微波加热时迅速析出，溶质在微波作用下在砂型表面形成低共熔体。经过低共熔体锂盐表面包覆处理的砂型微波硬化温度能达到370℃，远高于普通微波硬化砂型（110℃），因而包覆处理的砂型强度更高；在相对湿度为98％~100％恒湿条件下存放4h后，表面包覆处理的砂型强度较未处理的提高了将近2倍。SEM分析表明，混合锂盐在砂型表面和内层之间的过渡层上生成了一层致密低共熔体物质，该物质阻挡了水分的入侵而保护了内部高强度的粘结桥。

A coating method of eutectic lithium salts on the surface of sodium silicate sand was introduced. The eutectic lithium salts （0.38LiOH-0.62LiNO3） were sprayed on the surface of sodium silicate sand and then sintered by microwave energy to obtain glassy membrane for its lowest eutectic point of 175.7 ℃, so the humidity resistance of sodium silicate sand hardened by microwave heating was improved greatly. The results show that the hardening temperature of coating sand mold was about 370℃, which was higher than that of uncoated one （110 ℃） by microwave heating, and the strength of coating sand mold was higher than the uncoated one. After 4 h storage in humidistat with relative humidity of 98%-100%, strength of coating sand mold increased by two times comparing with the uncoated microwave hardening one. The SEM photos show that there was a layer of compact glassy membrane between the surface and inner to protect the inner high strength sand mold from the humidity erosion.