Research On Synthesis Of Mn⁴⁺-activated Fluoride Phosphors And Silicon Carbide Ceramics From Silicon Sawdust

Solar energy has been developing rapidly in recent years as a clean energy sources.Crystal silicon ingots for silicon-based solar photovoltaics generate large amounts of silicon sawdust powder during the cutting process.According to the survey,in the photovoltaic industry,the silicon sawing waste generated by wire cutting accounts for forty percent of the cutting crystal silicon ingots.If not recycled,the pure and active silica powder will not only increase the cost of the enterprise,and also cause pollution to the environment.To this end,in this paper,the silicon powder generated from crystal silicon ingots was recycled,and the recovered silicon sawdust powder was pretreated and used as raw material to prepare Mn⁴⁺-activated potassium fluorosilicate(K₂Si F₆:Mn⁴⁺)red phosphor and silicon carbide ceramic,and their relationship between preparation process and properties were studied systematically and deeply.The main research contents are as follows:（1）The recovered silicon waste powder was first characterized by XRD（X-ray diffraction）,SEM（scanning electron microscope）,and EDS（energy dispersive spectroscopy）.The phase,microscopic morphology,and composition of the silica sawing waste powder was investigated.The phase identification shows that,the recovered silica sawing waste powder is pure with elemental silicon as the main component.The particle size distribution of silica powder is around 0.55-2μm and the average value is about 1μm.EDS results shows the elements in the silicon powder are mainly Si followed by a small amount of Al,Fe and O.（2）The silicon sawdust powder was pretreated and used as the raw material to prepare K₂Si F₆:Mn⁴⁺phosphor.The pretreated elemental silicon was dissolved and K₂Si F₆:Mn⁴⁺red phosphor was prepared by a two-step synthesis method.The effects of Mn⁴⁺doping concentration,solution PH and precipitant on the luminescence properties of the phosphor were studied.When Mn⁴⁺doping concentration x=6%,solution p H=1,and solid precipitant KF·2H₂O is used,the obtained K₂Si F₆:Mn⁴⁺phosphor has the best luminescence performances.Finally,the LED device prepared by phosphor sample has the parameters of CCT=3472 K,Ra=89.2,η=125.41lm/w,which is comparable to the LED device fabricated by commercially available phosphor KSF:Mn（CCT=3498 K,Ra=88.2,η=140.3 lm/w）.（3）The pretreated silicon powder was used as the raw material to prepare silicon carbide ceramic.The effects of the ratio of silicon powder to graphite powder,reaction atmosphere,sintering temperature and sintering aids on the porosity,flexural strength and microscopic morphology of silicon carbide ceramic samples were investigated.Covered with carbon powders,at a silicon-carbon ratio of 1.08 and a sintering temperature of 1650°C,the porosity was around 40%and the flexural strength was around 6 MPa.In the presence of 5%sintering aid at a silicon-carbon ratio of 1.0,under argon atmosphere at 1350°C,the flexural strength reaches 50.66 MPa and the open porosity is 47%.Using the sucrose foaming method,the porosity reached 80%at 1500°C under argon atmosphere with the addition of 5%sintering aid.