| Aluminium lithium alloy, a very promising light metallie structural material, is widely used in aerospace field. It is not only density weight savings, but also provides excellent corrosion resistance, a good strength, high elastic modulus, fatigue resistance as well as the advantage of appropriate ductility. The content monitoring of Ag and Li in aluminium lithium alloy is the key to ensure the performance of alloy. Aluminium lithium alloys are complex sample with multiple coexistence elements, the sample digestion, interference elimination and analysis method, is the premise and foundation of accurate analysis, therefore, it is meaningful to develop high sensitive and high precise analysis methods and study on pretreatment technology.In this study, inductively coupled plasma atomic emission spectrometry(ICP-OES), flame atomic absorption spectrometry(FAAS) were applied to determination of argentum and lithium in aluminium lithium alloy standard sample and test sample, and ultraviolet and visible(UV) spectrophotometric was used to determinate silver in lithium aluminium alloy with tannic acid as chromogenic reagent. Meanwhile, a new polarographic analysis method was established to determinate lithium. Related research is as following.1. Three different methods, dissolution standard alloy with aqua regia or HCl and H2O2 or hydrochloric acid and nitric acid mixture respectively, were applied to digest 2195 standard aluminium lithium alloy. The argentum and lithium concentration of samples from different disgestion methods were analyzed by ICP-OES and FAAS. It was found that a minimum relative error for determining of lithium by FAAS would get by dissolving standard alloy with chloroazotic acid. It was more accurate to digest standard alloy with HCl and H2O2 while determining of Ag and Li by ICP-OES simultaneously, and determining Ag by FAAS.2. The interference from co-existing elements: Ti、Zr、Mg、Cu and aluminium matrix was investigated. The result showed that determination of Ag by FAAS was disturbed by titanium, and determination of Li by FAAS was disturbed by Mg and Cu. The pretreatment technology and eliminate interference method for different analysis methods were detailedly discussed, and disodium hydrogen phosphate solution, ammonium hydroxide, and 8-hydroxyquinoline solution was added to separate co-existing elements, respectively. The interference from co-existing elements in the sample was eliminated successfully, and met the requirements of analysis. The accuracy of measurements for argentum content of standard sample was conspicuously improved which confirms the efficient of the method to eliminate interference in this study. The optimal digestion method and eliminate interference method were applied to aluminium lithium alloy samples. The recovery of samples was from 99.50% to 102.29%by ICP-OES for the determination of Ag, and from 99.66% to 101.07% by ICP-OES for the determination of Li. The recovery ranged from 98.04% to 103.66% by FAAS for the determination of Ag, and ranged from 99.59% to 100.00% by FAAS for the determination of Li. The analysis results all meet the analysis requirement.3. Spectrophotometric determination of Ag with tannic acid was improved in this study, and the improved method was applied to the determination of Ag content in the aluminium lithium alloy samples. After optimization, tannic acid was reacted with silver, a luminous yellow complex was formed in the medium of pH 8.00~9.00, the absorbance reaches its maximum within 30 min, the absorption peak was located at 404 nm. Beer’s law is obeyed in the range of 0.6~10.0 μg/mL. The linear regression equation was: y = 0.1159x-0.055,R=0.999. The interference from co-existing elements in the sample was eliminated successfully by adding ammonium hydroxide and 8-hydroxyquinoline solution, adding excess of nitrate and heating to release Ag+ from silver chloride complex. The recovery was from 97.83% to 100.33% by VS determination for Ag. It is a convenient 、 sensitive and accurate UV-vis spectrophotometric method for the determination of silver, which can be applied to the determination of silver in aluminium lithium alloy with satisfactory results.4. A versatile method for the determination of Li was described. Carboxylic acid calcium indicator reacted with H2O2 in Britton-Robinson buffer solution(pH=10.5), a complex was formed, which produced a sensitive reductive polarographic wave the peak potential(Ep) was at-0.580 V(vs. SCE) with initial potential at 0.000 V(vs. SCE), the peak current of this polarographic wave for the complex may be inhibited by Li+. The reduction second derivative peak current was proportional to the Li+ concentration in the range of 4.0~100.0 μg/mL,the linear regression equation is: Ip’(mA)=20.13 ln(C)( μg/mL)-3.65, R=0.990, the detection limit of lithium was only 0.779 μg/mL. This method is rapid, accurate, and sample in operation is simple, but the sample pretreatment technology has not yet perfect, so this method is temporarily cannot be applied to the analysis of lithium in alloy samples. |
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