硫酸钡混悬剂中反絮凝剂的热稳定性及其对粘度的影响

本文对硫酸钡混悬剂中所用反絮凝剂的热稳定性及其对制剂粘度的影响进行了研究。褐藻淀粉硫酸酯钠所配混悬剂(100%W/V)为牛顿流体,粘度低(14cp)。在100℃加热30 min以上即很快分解产生游离的硫酸基团,同时粘度增高,变为膺塑性流体,有触变性,分解率与粘度的增加是相平行的。如加热80 min时分解率为64%,粘度增至202 cp。六偏磷酸钠所配制剂(100%)粘度较低(15 cp)。在100℃加热后分解产生正磷酸盐,同时粘度随之增高,如加热160 min时为206 cp,并有触变性。枸橼酸钠所配混悬剂粘度较大(40 cp),有触变性,但对热稳定,在100℃加热120 min其粘度仅略有升高(40～52 cp)。证明正磷酸盐和硫酸盐的生成,是混悬剂产生絮凝和粘度增高的原因。

THERMOSTABILITY OF DEFLOCCULATING AGENTS AND ITS INFLUENCE ON VISCOSITY OF BARIUM SULFATE SUSPENSION

Heating at 100℃ for more than 30 min caused a marked increase in viscosity of barium sulfate suspensions (100% w/v) containing 0.5% sodium laminarin sulfate (formula No. 1) or 0.6% sodium hexametaphosphate (formula No. 2). The rheological property of these suspensions were also changed from a Newtonian flow of the formula No. 1 and dilatant flow of the formula No. 2 to a pseudoplastic flow with thixotropic character.Quantitative determination of sulfate ion formed from heated solution samples showed that the rate of increase in concentration was parallel to the rate of increase in viscosity. The same studies on hexametaphosphate containing suspensions gave similar results except that its decomposition rate was lower.Sodium phosphate and sodium sulfate were experimentally shown to flocculate barium sulfate suspension upon incorporation. It is concluded that the formation of phosphate and sulfate ions by thermodegradation of laminarin sulfate and hexametaphosphate was the cause for increase in viscosity. Suspensions (100% w/v) containing 3% sodium citrate (formula No. 3) exhibited a dilatant flow with thixotropic property and was more viscous than that containing other deflocculating agents. It was noted that sodium citrate containing suspension was more thermostable. The original viscosity (40 cp) did not change much after heating at 100℃ for 120 minutes (52 cp).