Effect Of Dispersants On Rheology,Hardening And High Temperature Properties Of Al₂O₃-SiC-C Castables

Al₂O₃-SiC-C（ASC）castables are widely used in blast furnaces for their excellent resistance to iron scouring,slag erosion and thermal shock.SiC,as its main raw material,is not easily dispersed in the castables due to its non-wetting nature with water,which affects the rheology,hardening process and high temperature performance of ASC castables.In addition,the current research on the combination of calcium aluminate cements,hydratable alumina and silica gel is significantly influenced by factors such as maintenance temperature,maintenance time and the nature of the raw material during hydration,hardening and service.To this end,the paper investigates the effect of the introduction of different dispersants on the rheology,hardening and structure and properties of the ASC castables by introducing different types of dispersants.The main findings of the paper are as follows:（1）The series of dispersants studied showed the same pattern of action for each of the two particle sizes of SiC slurry:they changed the surface charge of the SiC particles and the p H of the slurry,increased the zeta potential of the slurry,reduced the viscosity at different shear rates,and improved the flowability.In contrast,the cationic charge generated by the ionisation of polyethyleneimine adsorbs onto the surface of the SiC particles,increasing the zeta potential of the slurry,while its long molecular chain has a spatially dislocated effect,synergistically improving the slurry dispersion stability;the polycarboxylate contains a comb-like structure-COOH,which adsorbs onto the SiC particles under alkaline conditions,significantly reducing the viscosity of the SiC slurry and improving the rheology through spatial dislocation.The polycarboxylate contains a comb-like structure-COOH,which adsorbs to the SiC particles under alkaline conditions,significantly reducing the viscosity and improving the rheology of the slurry through spatial site resistance.（2）The study of the influence of a series of dispersants on the rheological properties of SiC composite slurry showed that polycarboxylates have the most significant impact on the rheological properties of the slurry.In the composite slurry of SiC alumina micropowder silica micropowder,polycarboxylates are simultaneously adsorbed on the surface of SiC and oxide powder particles.The adsorbed COOH on the surface of these particles was conducive to opening the interlocking structure between particles under shear action,and had a spatial steric effect,improving the fluidity of the slurry.In the composite slurry containing calcium aluminate cement,the adsorption of COOH contained in polycarboxylates on the surface of cement particles reduced the friction between particles and improved the fluidity of the slurry;In the composite slurry containing hydrated alumina,the adsorption of COOH contained in polycarboxylates on the surface of hydrated alumina particles was beneficial to reducing its hydration rate,thereby reducing the viscosity of the slurry and improving its fluidity.（3）The study on the hardening behavior of the composite paste composed of SiC and binder showed that the composite use of polycarboxylates and different additives had different effects on the hydration and hardening of the paste.Using calcium aluminate cement as a binder,and adding polycarboxylates and naphthalene based water reducing agents in combination,could help regulate the formation process of hydration products.With the increase of curing temperature（20-40℃）and time,it promoted the conversion of CAH₁₀to C₃AH₆,significantly improving the strength of the hardened paste.Using hydrated alumina as a binding agent,polycarboxylates and aluminum lactate were added in a complex manner.The lactic acid ions in aluminum lactate produced a complexation effect,and they ionize to form aluminum ions,which were partially adsorbed on the surface of hydrated alumina to inhibit hydration,facilitating the formation of boehmite.Using silica sol as a binding agent,polycarboxylate and silane coupling agent were added in combination.The hydrolysis product of silane coupling agent,silicanol,and methanol,undergo a polycondensation reaction,promoting the condensation of colloidal particles,and contributing to the hardening of silica sol series pastes at different temperatures.（4）In calcium aluminate cement combined with ASC castables,the composite introduction of polycarboxylates and naphthalene based water reducing agents reduced the viscosity of the castables,and reduced the content of closed pores within the castables,was conducive to uniform particle distribution of the castables,and improved the mechanical properties at room temperature and high temperature flexural strength of ASC castables.In hydrated alumina combined with ASC castables,the composite introduction of polycarboxylates and aluminum lactate reduced the hydration rate of hydrated alumina,promoted the formation of boehmite,improved the flow value of the castables,and improved the resistance to cracking.In silica sol bonded ASC castables,the composite introduction of polycarboxylates and silane coupling agent promoted the hardening of the castables at room temperature and the in-situ formation of mullite at high temperatures,which was beneficial to improving the mold release strength and thermal shock resistance of the castables.