Preparation And Application Of Calcium Sulfate Whisker

With the increasing demand for power supply in China,the annual output of flue gas desulfurization gypsum（FGD）,which is an industrial waste generated by power generation in thermal power plants,is increasing.The large accumulation of FGD gypsum not only occupies a large amount of land but also causes environmental pollution.Traditional utilization methods such as producing building gypsum and using it as a cement retarder are not a high added value method to handle the large accumulation of FGD gypsum.Therefore,the high added value utilization of FGD gypsum is currently an urgent issue to be addressed.Ca SO₄ wisker（CSW）is a kind of inorganic wisker material.Currently,the relatively mature CSW preparation process is based on natural gypsum as raw material,and the commercially available CSW has a large diameter and a small aspect ratio.Therefore,this article studies the hydrothermal process of CSW preparation using solid waste desulfurized gypsum hemihydrate and desulfurized gypsum dihydrate as raw materials,hoping to prepare CSW with small diameter,large aspect ratio,and excellent morphology and apply it to property fields.Firstly,the effects of factors such as the amount of catalyst,slurry concentration,solution p H value,reaction temperature,and reaction time on the morphology and aspect ratio of CSW prepared by hydrothermal method using semi aqueous desulfurization gypsum as raw material were explored;Secondly,the effects of four crystal catalysts:sodium dodecyl sulfonate,citric acid,potassium chloride,and potassium sulfate on the preparation of CSW compared in the hydrothermal process of preparing CSW using solid waste gypsum from thermal power plants as raw material;And the raw material of dihydrate desulfurization gypsum was subjected to ball milling and drying treatment,and the phase composition of the dried desulfurization gypsum raw material was analyzed and used to prepare CSW.The obtained CSW products were characterized using testing methods such as SEM,XRD,and aspect ratio analysis software.In the application research,four surface modifiers including KH550,KH560,stearic acid and sodium stearate were selected for surface modification of CSW.The CSW before and after modification was added into epoxy resin material to study its enhancement effect on the tensile and bending properties of epoxy resin materials.The significance of the influence of modifier type,modifier dosage and modified CSW dosage on the tensile and bending properties of epoxy resin was analyzed through orthogonal experiments,and characterization of the interface bonding between CSW and epoxy resin matrix was explored through SEM.Research results shows that CSW products with average diameter of 1-2μm and average aspect ratio of about 100 can be prepared from hemihydrate desulfurization gypsum under the hydrothermal process with slurry concentration of 5%,solution p H of 5,sodium dodecyl sulfate dosage of 2%,reaction temperature of 140℃and reaction time of 2.5 h.The resulting CSW has excellent morphology with smooth surface and no defects.The preparation of CSW directly using dihydrate desulfurization gypsum as raw material by K₂SO₄ as the crystal modifier cannot obtain CSW with excellent morphology and aspect ratio.The distribution of ratio of the obtained samples is uneven,and the shape is not needle-like.By ball milling and drying pre-treatment of dihydrate desulfurization gypsum,CSW can be prepared from the pretreated raw materials,resulting in an average diameter of1-2μm.CSW products with an average aspect ratio of around 100 and excellent morphology.The addition of modified and unmodified CSW significantly improves the bending performance of epoxy resin,but it is limited to the improvement effect on tensile performance.When the unmodified CSW content reaches 3%,its bending strength reaches a maximum value of 102.88 MPa,which is 66%higher than that of pure resin specimens;When the content of unmodified CSW is 9%,the maximum tensile strength reaches 68.4 MPa,which is15.5%higher than that without whiskers.Orthogonal experiments shows that KH560 has the best modification effect on CSW.When the content of CSW modified by KH560 is 9%,the bending strength of the composite material reaches a maximum value of 108.05 MPa,which is74.3%higher than that of pure resin specimens;When the content of CSW modified by KH560 is 6%,its tensile strength reaches a maximum of 68.73 MPa,which is 16.0%higher than that without whiskers.