STUDIES OF WHOLE CRAWFISH SHELLS FOR THE REMOVAL OF CHROMIUM,LEAD, AND SELENIUM IONS IN SOLUTION

The objective of this work was to investigate the absorption characteristics, primarily with lead but also chromium and selenium ions in solution, of whole crawfish shells. An increase in the lead concentration in spiked water showed an increase in the lead absorption level. Lead absorbed by 0.5 g of whole crawfish shells was far less when compared to absorption by 0.5 g of ground crawfish shell powder due to particle size. Some of the lead is most likely being precipitated and collected along with the powder. With increase in the volume of lead spiked water, absorption of lead by whole crawfish shells also increased. Results obtained from the pH studies indicated that basic conditions (pH 9.5) are favorable for absorption of lead by both whole crawfish shells and chitin. Crawfish shells exhibited more absorption of lead compared to commercially available (shrimp) chitin at pH 9.5.

Crawfish shells absorbed more lead, selenium, and chromium from analyte spiked water when compared to chitin. However, the amount of metal added was not always equal to the amount of metal dissolved. A higher amount of lead was absorbed when compared to chromium and selenium. If comparison was done in micrograms of analyte absorbed, then the absorption order can be given as lead>chromium>selenium. If comparison was done in micromoles of analyte absorbed, then the absorption order is as follows: chromium>lead>selenium. Results from the last experiment indicated that formation of lead precipitate increased proportionately with increase in the concentration of spiked water.     

不同温度下15CrMoR循环塑性实验研究及低周疲劳寿命预测

在20℃,200℃,300℃和400℃下对15CrMoR进行了循环塑性行为和棘轮效应—疲劳交互作用的实验研究。不同温度下全寿命内循环塑性实验表明,非对称循环加载的大部分时段棘轮应变率基本保持稳定,后期接近失效阶段才急速增大。各温度下棘轮应变随平均应力、应力幅的增大而增大。低周疲劳寿命受平均应力和应力幅的共同影响,但应力幅的影响更大。与Coffin-Manson模型及Morrow修正模型相比,各温度下MSRS模型对材料疲劳寿命的预测更为准确。采用含温度参数的MSRS模型可较方便地预测不同温度下材料的疲劳寿命。