| Resin bonded Al-Al2O3 refractories have achieved good results in the application of sliding plates and RH furnaces.Its excellent high temperature performance comes from the reaction of Al to form high melting point non-oxides at high temperatures,which transforms the refractory into oxide and non-oxide composite refractory.Currently,the researches on resin-bonded Al-Al2O3 refractories are mainly focused on the following aspects:improving the phase and structural stability of the refractory after the aluminum is melted,improving the alkali corrosion resistance of the refractory,and broadening the scope of application.In this project,we optimize the performance of resin-bonded Al-Al2O3 refractories by introducing Ti-containing oxides and MgO into the refractory,and systematically explore the effects of Ti-containing phases in the brown fused alumina,rutile TiO2 and fused magnesia on the phase,structure,and performance of the refractory under high-temperature and nitrogen conditions.China is the world's largest producer and user of brown fused alumina.However,no consensus has been reached on the existence of Ti-containing phases in brown fused alumina.In this project,we explore the existence of Ti-containing phases in brown fused alumina and their evolution under high temperature(1400,1600 and 1700?)and nitrogen conditions.Results show that the Ti-containing phases in the brown fused alumina include:Ti2O3,Ti(C,N,O),TiFeSi2,Ca0.95Mg0.9Al10.1(Ti)O17 and Ca3Al2Si3(Mg,Ti)O12.The presence of Ti-containing phases in brown fused alumina at high temperatures is affected by the partial pressure of oxygen around the material.When there is C(s)-O2(g)or Al(l)-O2(g)oxygen-consuming reaction under nitrogen conditions,the Ti-containing components in the brown fused alumina will continuously migrate to the low-melting phase and react at the position in the low-melting phase in contact with the ambient gas to form Ti(C,N)solid solution.Using rutile-type TiO2 as the Ti source and phenolic resin as the carbon source,the in-situ synthesis of Ti(C,N)solid solution in resin-bonded Al-TiO2-Al2O3 refractories was achieved under high temperature and nitrogen conditions,and the synthesis process and mechanism were also explored at 800?-1600?.Results showed that the reaction between Al(1)and TiO2 had already started at 800?,and a continuous distribution of Ti(C,N)solid solution was formed in the refractory after heat-treated at 1200?.The reaction mechanism can be expressed as followed:Under the action of Al(l),TiO2 is gradually deoxidized and transformed into TiOx and free Ti;Tifree and Al(l)together form an Al-Ti mixed melt to realize the flow and mass transfer of Ti element in the refractory,and then convert the continuously distributed carbon produced by the resin into TiC;Phenolic resin is used as a carbon source to build a Ti-rich reactant system in the refractory,then the remaining Tifree and the TiO(g)formed in the Ti(l)-TiOx(s)system react with N2(g)and TiC to form a Ti(C,N)solid solution.The reaction can be written as:TiC(s)+TiAl-Ti(l)/TiO(g)+N2(g)?Ti(C,N)ss(s).The addition of TiO2 transforms the Al(l)into an Al-Ti mixed melt at high temperatures,which improves the structural stability of the refractory,and at the same time forms Tifree that can be actively diffused in the refractory to transform carbon and the already formed Al4C3/AIN into Ti(C,N)with stronger thermodynamic stability,thereby reducing the risk of hydration of the refractory.By introducing fused magnesia into the refractory,the resin-bonded Al-TiO2-MgO-Al2O3 refractory was successfully transformed into a non-oxide composite refractory with Mg-Al spinel solid solution and Ti(C,N)solid solution as the reinforcing phase under high temperature and nitrogen conditions.After heat treatment at 1600 0C,a dense layer with MgA12O4ss,MgAlONss,Ti(C,N),plate-like and granular AIN polymorphs as the main components was formed in the outer part of the Al(15%)-TiO2(8%)-MgO-Al2O3 refractory.The formation mechanism can be expressed as:First,the reaction between Al and TiO2 rearranges the structure of the refractory and simultaneously generates Al-Ti mixed melt and tiny particles such as TiOx,TiC,Al2O3;The generation of tiny particles hinders the flow of the Al-Ti mixed melt,thereby realizing the uniform distribution of the molten phase in the refractory;Then,the evenly distributed Al-Ti melt prevents gas from penetrating into the refractory through physical barriers and reactive absorption,so that the active gases such as Al2O(g)and Mg(g)diffuse outward along the pores,and deposit in the outer part of the refractory with sufficient gas to form a dense layer;The deposited products Al2O3,AIN and MgO react with corundum to form Mg-Al spinel,MgAlON and AlN polytypoids,while Ti element transforms the carbon and carbides in the refractory into Ti(C,N)solid solution through the liquid reaction mechanism.Resin-bonded Al-TiO2-MgO-Al2O3 refractory heat-treated at 1500? in N2-flowing shows excellent hydration resistance,oxidation resistance and corrosion resistance to molten iron and slag.The reason for the excellent hydration resistance of the refractory after heat treatment can be explained by TiO2 to form Al-Ti melt and Ti-containing Mg-Al spinel solid solution to realize the transformation of the Al4C3 and AlN:Al-Ti melt transforms the Al4C3 and AlN formed by liquid reaction mechanism into Ti(C,N),while the Ti-containing Mg-Al spinel solid solution absorbs the AlN formed by the gas reaction mechanism and transforms it into Ti-containing MgAlON solid solution.The reason for the excellent oxidation resistance of the refractory after heat treatment can be attributed to the fact that the original dense layer in the outer part of the heated refractory becomes more dense through the crystal growth caused by the oxidation of the non-oxides and mass transfer of the active gases produced by the metal phase in the refractory to block the pores,which hinders the infiltration of the ambient gases into the refractory.The dense layer in the outer part of the refractory after heat treatment also gives the refractory excellent resistance to molten iron corrosion.When encountering molten slag,the continuously distributed Ti(C,N)in the refractory is transformed into Ti(C,N,O)and stably exists between the refractory and the slag,thereby protecting the refractory from corrosion.The boundary between the original brick and the molten slag on the hot face of the corroded refractory is clear,and the slag layer is composed of cacoclasite,uniformly distributed Ti(C,N,O)and Mg-Al spinel particles. |
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