不同水质下铜表面CaCO_3污垢初始阶段生长特性

Initial Growth Characteristics of the CaCO_3 Fouling on Copper Surfaces of a Heat Pump Water Heater Under Various Water Qualities

紫铜和黄铜是热泵热水器中制冷剂与水换热的常用材料,在60℃时结垢严重。为研究CaCO3析晶污垢在表面的生长特性,分别在0.5和1.0 mmol/L的CaCO3溶液中,通过静态反应,分别用称重法和SEM获得不同浸入时间的结垢重量和微观形貌。结果表明:紫铜表面结垢量大于黄铜且更早形成污垢层。前期结垢量当Ca2+浓度较高时少于较低时,而浓度较高时最终结垢量则会多于较低时;Ca2+浓度并不影响晶型种类及比例,但浓度较高时大尺寸晶体出现较早较多且较小。pH值较高时使溶液体系能量较高,提高杂质和表面分子活性以及改变CaCO3电离平衡,产生更多晶核并促进文石转变为方解石。析晶污垢形成主要机理是难溶盐分子先在溶液内形成污垢颗粒,而后通过沉积到表面上,而不仅通过表面反应和吸附直接形成。

Red copper and brass are deemed as the commonly used materials for the heat exchange between coolants and water in heat pump water heaters.The fouling will be serious at 60 ℃.To study the growth characteristics of the CaCO3 precipitation crystal fouling on metal surfaces,in 0.5 and 1.0 mmol/l CaCO3 solution respectively,the weight and microscopic morphology of the fouling were obtained through static state reactions by using weight weighing and SEM(scanning electronic microscopy) method at various immerging time durations.It has been found that the fouling quantity on the red copper surface is bigger than that on the brass surface and red copper is earlier to form a fouling layer than brass.The fouling quantity in the earlier period at a relatively high concentration of Ca2+ is less than that at a relatively low concentration of Ca2+,however,the final fouling quantity at a relatively high concentration is larger than that at a low concentration.The concentration of Ca2+ will not influence the kind of the crystal and its proportion but the crystal in large sizes will emerge earlier and more but relatively small when the concentration is relatively high.A relatively high pH value will result in a relatively high energy level of the solution system,increase the impurities,heighten the molecular activity of the metal surface,change the ionization balance of CaCO3,produce more nuclei and promote aragonite to be turned into calcite.The main mechanism governing the formation of the precipitation crystal fouling lies in that the fouling particles will be first formed in the solution from the difficultly dissolved salt molecules and then deposited on the metal surface through deposition but not only formed directly through the surface reactions and adsorption.