Effect Of Dispersant On The Change Of Chemical Bond Of Colloidal Silica-bonded Castables During The Curing Process

The low demoulding strength of colloidal silica-bonded refractory castables limited the range of application of these materials.Other researchers usually use dispersants to improve the fluidity,room-temperature physical properties and high temperature performance of colloidal silica-bonded castables,while few studies delt with the impact of dispersant on the chemical bond changes of the colloidal silica and the demoulding strength of colloidal silica-bonded castables.Two types of dispersants,inorganic anionic dispersants?SHP and STP?and polycarboxylate amphoteric surfactants?FS10,FS20,FS60,FS65?were selected for this experiment.The effect of dispersants?SHP or STP?on the conductivity of colloidal silica were studied.The microstructures of two different types of dispersants added to the colloidal silica were observed.FTIR spectroscopy and XPS spectroscopy analysis were used to investigate the effect of dispersant addition and curing time on the change of chemical bond between the surface of colloidal silica particles.The effect of dispersant addition on the demoulding strength of colloidal silica-bonded castables was investigated.At the same time,the relationship between the demoulding strength of castables and the change of chemical bond of colloidal silica was investigated.The results show that the conductivity of colloidal silica increased with the addition of dispersant?SHP or STP?.With the increase of SHP addition,the conductivity of colloidal silica changed from 4.3 ms/cm to 14.7 ms/cm.With the increase of STP addition,the conductivity of colloidal silica changed from 4.3 ms/cm to 21.8 ms/cm.The reason is the difference in the amounts of Na⁺and anionic groups which are ionized by SHP or STP.FTIR spectrum analysis show that the relative content of Si-OH and Si-O-Si changed with the addition of dispersant to colloidal silica,and new weak vibration peak appeared.This may be the addition of above dispersants affect the charge environment of colloidal silica particles,because of the Na⁺and anionic groups ionized by SHP or STP,and the charged main chain and uncharged side chains of polycarboxylic acid dispersant molecules.As a result,the change of chemical bond of colloidal silica is affected,and the degree of adhesion between colloidal silica particles was changed.SEM results show that the higher the temperature,the more SiO₂ particles adhere in the pure colloidal silica.After adding two types of dispersants to the colloidal silica,more SiO₂ particles agglomerate.The change is consistent with the microstructure.XPS spectrum analysis show that the electron binding energy of O 1s and Si 2p decreased after the SHP,STP or FS10 were added to the colloidal silica,the samples were cured at 50°C for 48 h.And after the addition of SHP and STP,characteristic peaks of Na KLL and Na 1s of about 1069.84 eV appeared in the full spectrum of XPS.This may be the Na⁺ionized by the SHP or STP participate in the condensation of colloidal silica.The Na⁺ionized by SHP or STP may exist in the state of Si-O-Na,which is beneficial to the condensation process of colloidal silica.The result of fitting the corresponding O 1s spectrum also verifies this possibility.The results show that the demoulding strength of castables increased with the increase of curing temperature?10°C?30°C?50°C?.When the amount of SHP or STP is 0.05%,the demoulding strength is the highest.When the amount of SHP or STP?0.05⁰.2%?increases,the demoulding strength of castables gradually decreased.The addition of polycarboxylate dispersant reduced the demoulding strength of the colloidal silica-bonded castables,and the demoulding strength decreased more significantly with the increasing of dispersant.The reason is the stability of colloidal silica does not change significantly when the amount of SHP or STP is 0.05%,and the condensation of Na⁺favors the formation of Si-O-Si bonds in the colloidal silica.With the increase of the amount of SHP or STP,it is possible that Na⁺participated in the condensation reaction of colloidal silica in favor of the formation of Si-O-Si bonds.At the same time,the stability of colloidal silica is reduced and the particles are aggregated,which is unfavorable condensation of colloidal silica.With the increase of the amount of polycarboxylate dispersant,the steric hindrance to colloidal silica is greater than electrostatic force.Therefore,the stability of colloidal silica is reduced,and the dehydration condensation reaction of colloidal silica is affected,which is not conducive to the formation of Si-O-Si chemical bonds in colloidal silica.When the two types of dispersants were added,the demoulding strength of castables and chemical bond of colloidal silica were similarly changed.Therefore,it can be inferred that the demoulding strength of colloidal silica-bonded castable is related to the change of the chemical bond of the colloidal silica.