Preparation Of Graphene/Al₂O₃Composite Powders And Their Application In Castable

Carbon-containing castable has excellent corrosion resistance and thermal shock resistancewith an uniformly distribution and sufficient amout of graphite.However, graphite’s lowwettbility to water and poor dispersion severely restricts the application and development ofcarbon-containing castable.In this work,graphene was selected as the carbon source ofcarbon-containing castable due to the outstanding electrical,thermal and mechanical properties ofgraphene and the low carbonization trend of carbon-containing refractory.Al₂O₃modifiedgraphene sheets and composite powders of α-Al₂O₃and graphene oxide were prepared for thepurpose to improve the dispersion of graphene oxide/graphene sheets in castable using self-madegraphite oxide as the precusor.And the structure and performance of these two powders wereanalyzed and characterized.After then,effects of graphene oxide/graphene sheets and theirintroduced forms on the performance of MgO-C castables were discussed.The main conclusionsare as follows:In this work, graphite oxide was prepared by a modified Hummers method using expandedgraphite as raw material and graphene oxide aqueous dispersion was obtained by ultrasonictreatment of graphite oxide in distilled water.Graphene oxide sheets can stablily disperse inneutral or weak alkaline aqueous medium because of the plentiful surface oxygen-containingfunctional groups and Zeta potential of the graphene oxide dispersion approaches zero whenpH=6.With the increasing of solid contents,the dispersion transform from a Newtonian fluid to apseudo-plastic fluid.With the introduction of sodium citrate,the absolute value of Zeta potentialincrease simultaneously,while the viscosity of the dispersion decrease.And in this work, theoptimal addition contents of sodium citrate is0.4%in weight.α-Al₂O₃/GO composite powders with different graphene oxide ratios were prepared by adrying treatment of the hybrid suspensions of graphene oxide and α-Al₂O₃at a70℃water bathcombined with electromagnetic stirring,and the structure and properties of the compositepowders were analyzed and characterized.The results show that,graphene oxide sheets disperseuniformly between α-Al₂O₃particles at a transparent platelet morphology when graphene oxideto α-Al₂O₃ratio is less than1/30.However,with the increase of graphene oxidecontents,graphene oxide sheets ramarkably agglomerate.The investigation on rheologicalproperties of AG30and α-Al₂O₃slurry demonstrate that this two kinds of slurry are in a similarflow properties.In order to improve the dispersity of graphene in aqueous medium,Al₂O₃modified graphenewas synthesised by a homogeneous symbiosis method using graphene oxide and AlCl₃·6H₂O as raw materials.The structure and performance of Al₂O₃modified graphene and the correspondingprecusor were analyzed and characterized.The results show that,after treated at300℃for3hours,the precusor is transformed to amorphous Al₂O₃modified graphene.When the heattemperature reaches to1000℃,the amorphous Al₂O₃is translated into α-Al₂O₃and graphitizedcarbon can be detected.Owing to the Al₂O₃coating on graphene surface,Al₂O₃modifiedgraphene possesses an excellent dispersibility in water medium and a significantely enhancedoxidation resistance of graphene sheets.Effects of graphene and its introduction forms on properties of MgO-C castable wereinvestigated.The results show that,graphene is inappropriate to introduce into the castable by agraphene oxide dispersion,which may cause an increasing water adding and a weakeningstrength. However,when graphene is introduced by α-Al₂O₃/GO composite powders and Al₂O₃modified graphene,water adding of the castable shows little change,and leads to an increasedmechanical strength of the samples after treated at1500℃for3h.