| Molybdenum,a refractory metal,which possesses exceptional strength and stiffness at high temperature,high melting point,good thermal conductivity,low coefficient of thermal expansion and high corrosion resistance,is experiencing an increasing demand as electrode materials in glass industry.But the major drawback of molybdenum electrodes is its low oxidation resistance at high temperature.When the temperature is higher than 600℃,the product of MoO3 causes rapid volatilization.So the usage of molybdenum electrodes is greatly restricted in the furnace.To improve the working life of molybdenum electrodes,the coating technique can be effective in preventing high-temperature oxidation.A ZrO2-Glass coating is prepared used for protecting molybdenum electrodes from oxidation.The coating is made by adding a slurry consisted of a barium silicate glass power as a continuous phase,ZrO2 as a difficult melting filler, adhesive and terpineol,and then it is obtained after the adoption of drying.This method has some advantages,such as simple preparation process,low cost and better protective effect.Based on the analysis of previous studies,according to protective mechanism and design rules,the major components of the coating were selected by means of comparing the standard free energy of formation of MoO2 with those of the other oxides.The standard free energy was obtained through thermodynamics computation on the basis of the relationship of free energy and temperature.The base glaze is prepared by solid phase reaction method.During the preparation of the base glaze,the components of base glaze,high temperature melting process,cold ration and ball milling process were investigated in detail.The preparation of molybdenum glaze and coating process were explored,and the preparation of the coating process was determined.The coating has been found to influece by some factors in the formaiton,such as thermal expansibility,main components and their contents,spread ability,and coating heating process. Through the DTA test,the base glaze,the softening point of which is low,can be softened before catastrophic oxidation of molybdenum,and the density is high.By SEM analysis,the good surface spreading of the coating and adhesion of coating and substrate were found.But thermal expansion match beween coat and matrix was most important.The subject has founded composition with anti-oxidizability which matched with the thermal expansibility of Mo material matrix,which is putting an appropiate amount of ZrO2.In Chapter four,it mainly reported the influence of ZrO2 additions on anti-oxidant effect.By adding 10%,20%and 30%ZrO2,after 1000℃,2h sinering,the surface morphology of these coatings was observed by SEM.The results showed the surface of the coat spreaded smoothly and the pore rate of the coat is low by adding 20%ZrO＿2.According to the calculation of the thermal expansion coefficient,the CTE of the coating was 7.4×10-6/℃,and the mismatch value of the CTE of the molybdenum substrate(CTE 6.7×10-6/℃)with the coating was only 4.34%.The anti-oxidant test indicated that the weight loss of the specimen for 31.13mg/cm2,less than the other two kinds of coatings,after 1000℃,2h.In Chapter five,the subject emphasized on coating anti-oxidized effect and two important influence factors:presintering time and presintering temperature.According to SEM and anti-oxidation test,the coating of the higher density and better anti-oxidation could be obtained through the effective control of the presintering time and presintering temperature.After the presintering in 1300℃,20min,the surface of the coating was the continuous glass-phase and the pores of the coating were closed to prevent the entry of oxygen.The anti-oxidant test indicated that the weight loss of the specimen was 83.89mg/cm2 after 1200℃,20h.It showed the coating had good oxidation resistance.The application of this coating can effctively protect the high temperature oxidation of molybdenum subsrate and reduce the loss of molybdenum.The research achievements have important practical significance.
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