Occupational Exposure Limits And Determination Methord For Silicon Tetrahydride In The Air Of Workplace

Silicon tetrahydride is a gaseous substance and common industrial raw material whichprovides silicon. It can be used to produce high purity monocrystal silicon, polycrystallinesilicon, heterogeneous silicon, microcrystalline silicon, amorphous silicon, silicon nitride,oxidation silicon and other various silicides. When environment temperature reach17Kand with extremely high pressure (96or120GPa), silicon tetrahydride can be used assuperconductor[1]. Silicon tetrahydride has become an imporment silicon-source special gasthat other silicon sources can not replace because its characteristic is high-purity[2-3]. Silicontetrahydride is widely used in the electronics industry, the energy industy, the glass industry,the chemical industry and the high-tech fields[4]. Silicon Tetrahydride’s main toxicity isstimulation. Some researches showed that it causes health damage to workers by irritatingskin, eyes and respiratory tract strongly[5-6]. Currently, there is no national occupationalexposure limits and standard determination methord for silicon tetrahydride in China. Toprotect workers from damage of silicon tetrahydride, it is important to provide reasonableexposure limit for this substance. The objective of this study is to provide occupationalexposure limit for silicon tetrahydride through literature reading and analysing; and toexplore methord for silicon tetrahydride determination in workplace. There are two parts inthis study:Part Ⅰthe Occupational Exposure Limits for Silicon Tetrahydridein the Air of WorkplaceAt present, occupational exposure limits for silicon tetrahydride are published in about20countries, such as American, Cananda, Australia, Japan, and so on. The value of7mg/m~3(PC-TWA) is recommended by nearly two thirds of these countries. The value of0.7mg/m~3(PC-TWA) is used in others. Through reviewing the literature, and combiningwith the chemical properties, toxicity data, human epidemiological data, and occupationalexposure levels of silicon tetrahydride in the air of workplaces,7mg/m~3(PC-TWA) was recommended for occupational exposure to silicon tetrahydride in this study.Part Ⅱ Determination Methord for Silicon Tetrahydride in the Airof WorkplaceThere are several methods reported to determine silicon tetrahydride. They includeatomic absorption spectrophotometer, gas chromatography, UV spectrophotometry, directreading instrument to determine silicon tetrahydride. Each methtod has some limitations.There is no national standard determination methord for silicon tetrahydride in China. Theobjective of this part is to explore methord for silicon tetrahydride determination inworkplace.The theory of this methord is that silicon tetrahydride in the air is collected by alkalineresin matrix globular active carbon. Then active carbon is desorpted by hot water. Thesilicon tetrahydride translates into sodium metasilicate. In the acidic solution, sodiummetasilicate is translated into metasilicic acid. After that metasilicic acid reacts withammonium molybdate, and generates silicon-molybdenum heteropoly acid. Add14-trichlorobenzene alpha-naphthol amino sulfonic acid，the silicon-molybdenum heteropolyacid is restored ioto silicon molybdenum blue. Measure absorbance under the680nmwavelength.The main steps of this methord include: silicon tetrahydride in the air is collected byalkaline resin matrix globular active carbon. Then active carbon is taken out and desorptedby hot water. Absorb right amount desorption liquid into15mL polyethylene pipe, anddilute it. Add the hydrochloric acid solution and ammonium molybdate, fully shake andthen put the pipe into the hot water10min. Add oxalic acid, fully shake, placed2min~15min. Add14-trichlorobenzene alpha-naphthol amino sulfonic acid, fully shake.5min later,measure absorbance under the680nm wavelength with reagent blank.In this methord, average of sampling efficiency is97.53%, average of desorption rateis94.94%, through capacity is higher than0.84mg/300mg, detection limit is0.054μg/mL,quantitative lower limit is0.18ug/mL, and minimum detection concentration is1.2mg/m~3(sampling3.0L). The conversion rate of silicon tetrahydride tends to decrease over time when prolong storage time of alkaline resin matrix globular active carbon. The decscentrate of sample is <10%when it is kept7days under seal in the room temperature,.This methord is validated by Wuhan Occupational Disease Prevention, Tongji MedicalCollege HUST, and Wuhan Occcupational disease hospital. In the meantime, we used thismethord to determine silicon tetrahydride in the air of workplace in one company. Theresults showed that this methord is repeatable well, simple, accurate, and can be used in thefield.Conclusions:Through the study of the occupational exposure limits and determination methord forsilicon tetrahydride, drow the following main conclusions:1. The occupational exposure limits for silicon tetrahydride in the air of workplace isadvised7mg/m~3(PC-TWA) in our country.2. When sampling silicon tetrahydride, the active carbon would be better be used inthe first day or saved in vacuum condition when the active carbon impregnated in the baseis dried in vacuum condition. And the sample can be kept for one week under seal in theroom temperature.3. The methord to determine silicon tetrahydride by spectrophotometer could be usedin monitoring works. This method satisfied the requirements of “developed norms ofpoison detection methords in the air of workplace”(GBZ159-2004).