Heterogeneousnucleation Coating Technique Of Graphite And Its Application

Heterogeneousnucleation method applied in coating graphite are studied in this paper. It discusses the effect of technical conditions on the coat layer forming, such as pH value, treating temperature, concentration of premonitory matter solution and so on. And then, the coated graphite is added in MgO-C castables , and the properties of the castables is investigated.Originally, Heterogeneousnucleation is a kind of surface modification way applied in coating nanometer powder successfully. In this paper , two kinds of Heterogeneousnucleation technics are used for reference in treating graphite , namely hydrolyze coating way and deposition coating way.In the view of hydrolyze coating way , pH value , treating temperature , concentration of premonitory matter solution , buffer solution amount and premonitory matter amount affect the coat layer forming mainly. According to the results of experiments , the best technical condition is that pH=6.5, [Al3+]=0.064mol/l, T=343K , Vbugersoiution=40ml. Under the best technical condition, graphite surface can be coated by A1(OH)3 nanometer particles equably .In addition , with the increase of premonitory matter amount , coat layer particle grow up and thicken . Treated by hydrolyze coating way , the surface electric potential of graphite moves and IEP changes from 2-3 to 8-9 , reach the one of A1(OH)3; Moreover , the wetting angle of treated graphite decreased 10 , and the oxidation ratio decreased 20% when Al(OH)3/graphite(wt%) =10 , compared with untreated graphite under the same condition .That is to say, the wetting and anti-oxidation ability of graphite is improved, after treated by hydrolyze coating way .In regard of the deposition coating way, the results of experiments show that pH value have no influence on the coat layer forming. Under different pH value in these experiments, graphite surface can't be coated mostly. Just on some surface of graphite, is there the flaky coat layer deposited. All hi all , the coat layer distribute unevenly . With the increase of Al2(SO4)3.18H20 amount , the flaky coat layer grow up and thicken . Compared with untreated graphite under the same condition, the surface electric potential of treated graphite changes in part, but unlike A1(OH)3, the oxidation ratio decreases 10% when A1(OH)3/ graphite(wt%)=10 , and the wetting angle of treated graphite hold the line , namely the wetting ability is not improved . Contrasted with the hydrolyze coating way, the deposition coating way has simple technical process, lower cost, and its disadvantage, for instance, coatlayer distributes unevenly, the wetting ability is not improved .Furthermore ,the effect of treated graphite applied in MgO-C castables are investigated . The results indicate that the properties of castables containing the graphite treated by hydrolyze coating way are better than the one containing the untreated graphite, but the properties of castables containing graphite by deposition coating way is same as one containing the untreated graphite. And with the increase of the coat layer content, the properties of castables can be enhanced. The little of graphite treated by hydrolyze coating way, the better are properties of castables.