Study On The Purity Controlling Technology Of High Purity Fused Silica

Quartz as a kind of important mineral resources are widely distributed in nature, theproducts which produced with quartz as raw material to produce are widely used in glass,ceramic, refractory, metallurgy and chemical industry, etc. Used for solar energy polysiliconcasting, the purity of fused silica materials have an important influence on performance offused silica ceramic crucible and the photoelectric conversion of solar cell. This thesismaterial is vein quartz which is mined in Donghai area, Jiangsu Province. Combined withfused silica powder material production process, this thesis carries on a study from threerespects which include control of the quartz material purity, purity control in the meltingprocess and purity control of fused silica machining process. The best purity control methodis defined in the production process of high purity fused silica materials.There is some clay impurities attached on the surface of mining quartz, putting quartzore through4mm vibrating screen, rinsing with water, then removing sieve residue, removingclay at the same time reducing the grade of iron and aluminum.To meet the requirement of acid treatment process and melting process, the quartz oreshould be broken. The paper uses hammer crusher, jaw crusher and counterattack crusher forcrushing experiments. The results show that compared to the other two kinds of crushingequipment, the most of quartz particles after crushing of hammer crusher are spherical, theyield of quartz particle size from4to25millimeter is higher and up to89.11%; The Ironincreasing rate is9.15%. Synthesizes the crushing effect on production efficiency offollow-up processing and the purity of product, hammer crusher is the best crushingequipment of vein quartz run of mine ore.The paper puts to use acid treatment to remove iron impurity from the vein quartzmineral raw materials, contrast the effect of single acid treatment and mixed acid treatmentand study the iron removal effect of vein quartz ore by adjusting mixed acid composition,formulation, dosage, acid leaching temperature and acid dipping time. The results of the studyshow that the iron removal effect of mixed acid is superior to single acid treatment, and thebest conditions for acid treatment is: mixed acid composition is hydrochloric acid andhydrofluoric acid, acid mixture ratio for hydrochloric acid︰hydrofluoric acid is95%︰5%, mixed acid dosage is500kg/t, acid-soaking temperature is50℃, acid-soaking time is24h.The paper use the homemade quartz melting furnace as the smelting unit of high purityquartz raw materials, study the operation process influencing purity of the fused silica productand analyses the main fused products. The results of the study show that the graphite rod mustinstall in the central of the furnace and the loading must be evenly, otherwise the graphite rodwill break because of stress inequality and the melting process will be defeated; In the meltingprocess, current should be stabilize in2700A to ensure the temperature in the furnace is notlower than2000℃, melting time must be more than5hours to guarantee quartz raw materialfully melting. Among the melting products, the “expected level” is the major product and itsmain impurities element content accord the requirements of the fused quartz ceramic crucible;Microstructure of the “flocculence” and “rawish” are analyzed by SEM and XRD, which arecrystallization products of glass melt, but the proportion of crystal in “flocculence” is small,so “flocculence” can be used as raw material of the fused quartz ceramic crucible. However,the proportion of crystal in “rawish” is large, so “rawish” can not be used as raw material ofthe fused quartz ceramic crucible. During the melting products,“dark spot” should becontrolled strictly because its major element is Fe.The paper use sorting and wind subtraction equipment which is homemade to removevisible purity from the fused quartz material; And improving structure of rotor of thecentrifugal crusher, fixing wear-resistant liner which is hard alloy steel on the left passage andthe edge of push plate, the iron content increasing rate of fused silica powder which crushedby the centrifugal crusher after improving lowered to4.48%from14.97%; The results ofmagnetic separation experiment shows that both the magnetic separation effect and theproductivity are high when the feedrate is1.2t/h and the magnetic field strength is16000gauss.The components of the fused silica powder which produced through the study aboutpurity control technology of high purity fused silica material is SiO2≥99.99％, and the totalcontent of impurities less than80ppm, the content of Fe less than10ppm.The fused silica powder can meet the purity requirements for fused silica raw material of thefused quartz ceramic crucible.