Preparation,Surface-modification And Insulating Properties Of MgO Powders

Uhvdc transmission has put forward more and more high requirement to the reliabilityof the electrical insulating materials. Adding highly insulating fillers in electricalinsulating materials is main process for improving its quality. There are many problems inexisting insulating fillers such as high cost,complex process, weak adhesion and poormechanical properties. So it is of practical application value to develop insulatingpowders as fillers with lower cost and better performance.Magnesium oxide (MgO) is insulating material with wide forbidden band, and it hasbeen widely concerned in applications of the improvement of the low denditypolyethylene(LDPE), cross linked polyethylene(XLPE), etc. due to its excellent dialectricproperties and adsorption properties. It is significant to study the insulating properties ofMgO powders scientifically.In this paper, the preparation technology and conditions of MgO powders withexcellent insulating properties were investigated, the physical properties of MgO powderson its insulating properties were also analysised, and the preparation process conditions ofMgO powders with excellent insulating properties were determined. On this basis,technical route of preparing highly insulating performance MgO/EP composite materialshas been put forward with paragenetic mineral of mirabilite and bloedite at Gaxiongnorand brine of Salt Lake at Jilantai in Inner Mongolia as raw materials, combined withresearch results of predecessors. The main research contents and conclusions are asfollows：1. First, MgO powders were synthesized by direct precipitation method with analyticreagents, and the factors influencing on the volume resistivity of MgO such as the reactiontemperature, the reaction time, the concentration of ammonia, different types of dispersantand the dosage of dispersant were discussed. MgO powders were characterized by XRD,and the particle size distribution and the volume resistivity of MgO powders weremeasured.The research results showed that there was no direct relation between the inslutingproperty and the crystallinity of MgO powders. The smaller the particle size was and the more honogeneous the particle size distribution was, the better the insluting property ofpowders was.2. In order to abtain MgO powders with narrow particle size distribution, thepreparation of MgO powders by homogeneous precipitation method was investigated toimprove the particle size distribution and particle size of powders on the basis of directprecipitation method. The effects of the calcinating temprature and the calcinating time onthe insulating property of MgO powders were studied.The research results showed that the homogeneous precipitation method effectivelyreduced the width of MgO particle size distribution. Through the analysis of PL andvolume resistivities, it can be considered that there was no direct relation between theinsulatiing properties of MgO powders and the Schottky defect in MgO crystal.3. To improve the dispersing properties of MgO powders in organic phase, MgOpowders were modificated with surfactants by wet modification method. The factorsinfluencing on the volume resistivity of MgO powders such as the kinds of modifier, themodification temperature, the modification time and the the dosage of modifier werestudied.The research results showed that modification can improve the insulating propertysignificantly. The volume resistivity of MgO powders increased to a higher value and thenreduced with the increase of the modification temperature, the modification time and themodifier addition quantity. The insulating property of MgO powders modified by sodiumstearate was the best, and its volume resisitivity reached17711M·m. Through theanalysis of FT-IR and the volume resisitivites, It can be considered that the influence ofsodium stearate on insulating properties of MgO powders was mainly due to its goodinsulating property and strong adsorption to MgO particles.4. EP/MgO composite materials was prepared with paragenetic mineral of mirabiliteand bloedite at Gaxiongnor and brine of Salt Lake at Jilantai in Inner Mongolia as rawmaterials, according to the suitable preparation and modification process obtained.EP/MgO was characterizated by the tests of the bending properties and the volumeresistivities.The research results showed that the technical route of preparing highly insulatingMgO powder had realized by the natural minerals combinde with research results of previous researchers. The highly insulating MgO powders effectively improved theinsulating poroperty of EP.