一例进口“铜精矿”的属性分析研究

采用X射线荧光光谱、X射线衍射等技术,结合超景深显微镜、扫描电镜、化学分析等手段,对一例申报为“铜精矿”的样品进行外观形貌、元素组成、物相组成、微观等进行分析。结果表明：样品含有黄铁矿、石英、孔雀石、硅锌矿、滑石等天然矿物,还含有大量的微米级球状氧化锌、玻璃态的钠钙硅铝酸盐、疏松的胶态硅酸盐以及条状、片状的金属铜屑等。样品的特征与天然铜矿浮选得到的铜精矿有显著差别,呈现出天然矿物和多种冶炼加工产物的混合物特征。     

化学概念的多重表征及教学建构——基于“氧化还原反应”概念的调查研究

从心理表征的角度看,“化学概念的理解”就是学习者对化学概念形成了恰当的心理表征。通过调查高三学生“氧化还原反应”概念的表征发现,学生对化学概念存在多重外部表征,但并非关于概念的真正理解。本文运用DeFT(Design,Functions,Task)概念框架建构教学,设计多重媒体学习环境以促进学生对抽象概念的理解。     

Comparison of direct sampling and emulsion analysis using a filter furnace for the determination of lead in crude oil by graphite furnace atomic absorption spectrometry

The determination of trace elements in crude oil is difficult due to the complex nature of the sample and the various different chemical forms in which the metals can occur. The advantage of graphite furnace atomic absorption spectrometry is that only a minimum of sample pretreatment is required. In this work two techniques have been compared to establish a fast and reliable method for lead determination in crude oil. In the first one the crude oil samples were weighed directly onto solid sampling (SS) platforms and introduced into the graphite tube for analysis. In the second one the samples were prepared as oil-in-water emulsions and analyzed in a filter furnace (FF). Twenty μL of a mixture of 0.5 mg L^− 1 Pd + 0.3 mg L^− 1 Mg + Triton X-100 has been used as the modifier, and calibration against aqueous solutions has been used for both methods. The sensitivity obtained with the FF was more than a factor of two better than that with SS; however, as a larger sample mass could be introduced in the latter case, so that the limits of detection for both techniques were 0.004 mg kg^− 1. Seven crude oil samples were analyzed using the two procedures, and all results were in agreement at a 95% confidence level using a paired Student's t-test. For validation purposes, three crude oil samples have been mineralized using an open-vessel acid digestion, and the results were in agreement with those found with direct sampling and with emulsion sampling using FF according to ANOVA test. Both methods are simple, fast and reliable, being appropriated for routine analysis; however, the direct method using SS technology should be preferred because of its simplicity, speed and commercial availability.