The Measurment Of Silicon Isotope And The Research Of Moisture Reference Materal

Kilogram is one of the seven basic unit of measurement in international regulations. That exactly measuring Avogadro constant (NA) is an effective way to redifine kilogram by atom mass. AND exactly measuring the silicon atom mass is one important task of measuring NA, and measuring silicon isotop abundance is the premise of exactly measuring the silicon atom mass. This study had make a in-depth research in measuring silicon isotop abundance by two different meathod.This paper systematically studies the preparation methods for silicon isotope ratio measurements:the means of measuring silicon isotope of SiF4 prepared with BrF5 method, and the means of measuring silicon isotope of SiF4 prepared with mixture acid. Experimental methods were explored and sample preparation procedures were optimized. Additionally, analysis precision of mass spectrometry wrere investigated, and the advantages and disadvantages of each method were compared.Our reaserch on the means of measuring silicon isotope of SiF4 prepared with BrF5 method indicates that we have successfully set up the SiF4 preparation system which has well stability and high repeatability, meeting the requirement for the accurate measurement of silicon molar mass. After etaching contaminations on the surface of silicon single crystal sample, the silicon single crystal sample react with BrF5 in high vacuum reactor at 300℃for 15h, and after purifing by trap three times, the SiF4 was deposited in incept tube with liquid N2. We measured the silicon isotope ratios with gas mass spectrometer compared with standard SiF4 produced by AIR PRODUCTS Co.. The result show the SiF4 gas is very pure prepared by this method, the standard windage between the SiF4 samplesδ30Si/28Si (‰) is no more than 0.036%o, has reached international advanced level and this method has a good reappearance and precision.Our reaserch on the means of measuring silicon isotope of SiF4 prepared with mixture acid indicates that it is feasible to exactly measure silicon isotope abundance with this method. After etaching contaminations on the surface of silicon single crystal sample,50mg sample dissolving with appropriate of 1.8ml 48% HF and 0.2ml 65% HNO3 mixture acid. Then the H2SiF6 solution was diluted to 0.2 m mol/g.BaSiF6 precipation was getted by adding 0.1% BaCl2 solution to the silicon sample solution with excess of 6%, and then, decomposing BaSiF6 to SiF4 at 600℃in vacuum system and measuring the silicon isotope ratios with gas mass spectrometer compared with standard SiF4 produced by AIR PRODUCTS Co.. The result of measuring with gas mass spectrometer showed the SiF4 of sample is pure and the standard windage between the SiF4 samplesδ30Si/28Si (‰)is no more than 0.067‰, has reached international advanced level and this method has a good reappearance and precision. The study had make a good preparative work for exactly mesuring silicon molar mass in next work.Finally, we made a compare with this two meathods. The result show the technics to prepared SiF4 by this two methods is reappearance and the precision is high. Relatively, the BrF5 method got purer SiF4 gas.But the difference is small,the results with all the two methods have reached international advanced level.Our country has made Level 2 moisture reference material and the rules for calibrating Karl·Fischer, but we lack Level 1 moisture reference material.The paper shows the water saturated n-Octanol certified reference material and the water saturated Decanol certified reference material made by our lab,which will solve the traceability of the Karl·Fischer moisture instrument,and meet the need to calibrating moisture instrument in our country.The reaserch have prepared the water saturated n-Octanol certified reference material with water content 38.2 mg/g,and the material has good stability and uniformity,with expanded uncertainty 0.9 mg/g (k= 2).The duplicated saturated Decanol certified reference material has good repeatability, with water content 47.5 mg/g, expanded uncertainty 1.2 mg /g (k= 2).The continuous investigation in 18 months indicates that only if the saturated Decanol certified reference material would be stored, kept and used under stated conditions,it would keep good stability.The water content technical indicators of both the water saturated n-Octanol certified reference material and the water saturated Decanol certified reference material Reaching the international advanced level of similar standard substance,which meet the need to calibrating moisture instrument in our country.