Study On Influence Of Alkaline Oxides On The Microstructure And Macroscopical Properties Of Aluminate Slag

To solve the problem of steel-slag reactivity in the casting process of high aluminum steel,aluminate slag with Al2O3 as the main network forming body has become a hot research topic.But because Al2O3 is a kind of amphoteric oxide with complex structure,the influence of each component on the macroscopic properties of aluminate slag is different from that of traditional slag.Since the microstructure and macroscopic properties are the characterization forms of materials at different scales,the viscosity,melting temperature,crystallization property and other macroscopic properties of slag are essentially determined by its microstructure.Therefore,this paper firstly studies the influence mechanism of the alkaline oxides（Na2O,K2O,Mg O,Ba O）on the microstructure characteristics of ternary aluminate slag,it provides theoretical guidance for obtaining a stable component range for the Al-O network structure.Then,on this basis,some flux was added to study the influence mechanism of Ca O/Al2O3（C/A）ratio and alkaline oxides on the microstructure and macroscopic properties of aluminate slag.Some results can be drawn as below:Molecular dynamics simulation were employed to study the influence of Na2O,K2O,Mg O,and Ba O on the microstructural characteristics of ternary aluminate slag,When the Mx O mass fraction was 4 wt.%,compared with alkaline earth metal oxides,adding alkaline metal oxides can stabilize the Al-O bond and Al-O coordination better.The sequence of M^x+close to the[Al O₄]^5-tetrahedron was Mg²⁺<Ca²⁺<Ba²⁺<Na⁺<K⁺,and M⁺primarily compensates for the[Al O4]^5-tetrahedron charge,while more Al^Vwas formed in two-valence alkaline aluminate to balance the excess negative charge.As the Mx O mass concentration increased,in the KAC、NAC and BAC systems,the M^x+replaced Ca²⁺in the[Al O₄]^5-tetrahedron and approached O_t to balance the excess negative charge,while in the MAC system,Mg²⁺replaced Ca²⁺in O_nb and approached Ot to form non-bridging Al-O-Mg.Combined with the synergistic effect of M^x+,Al^V,and Ot,the melt structure complexity followed the trend of MAC<NAC<KAC<BAC with a certain mass fraction of Mx O.Through the analysis of spectroscopy,with the increase of C/A ratio,the structure of aluminate slag was first polymerized and then depolymerized.When the C/A ratio is 1.1,on increasing alkaline oxides content,the complex aluminate network structure decreases first and then increases,but the minimum content of each system is different.When the C/A ratio is 1.3,the polymerization degree decreases with the increase of the content of alkaline oxides.With the increase of C/A ratio,the melting temperature increases first and then decreases.When the C/A ratio is 1.1,the melting temperature decreases with the increase of the content of alkaline oxides.When the C/A ratio is 1.3,on increasing Na2O and Ba O content,the melting temperature decreases,and on increasing K2O and Mg O content,the melting temperature decreases first and then increases.In addition,all melting temperatures have a small decrease,indicating that the superheat is small,viscosity change is mainly affected by the degree of polymerization,so the composition of the slag viscosity and degree of polymerization are basically consistent.When the C/A ratio is 1.1,the viscosity-temperature curve shows the characteristics of acidic slag,and when the C/A ratio is 1.2,it shows the characteristics of alkaline slag,and on increasing C/A ratio,the break temperature increases.When the C/A ratio is 1.1,Na2O content is 0-6 wt.%,K2O and Mg O content is 0-2 wt.%,Ba O content is 0-8 wt.%,the viscosity-temperature curve shows the characteristics of acidic slag.When the content of Na2O exceeds 6 wt.%,K2O and Mg O exceeds 2 wt.%and Ba O exceeds 8 wt.%,the viscosity-temperature curve tends to the characteristics of alkaline slag,and on increasing alkaline oxide content,the break temperature increases.Furthermore,with the increase of Ba O content,the phase and proportion of crystallization do not change.With the increase of Mg O content,the phase of crystallization does not change significantly,but the proportion of crystallization increases greatly.When the content of Na2O and K2O exceeds 6 wt.%,the phase and proportion of crystallization increase greatly.When the C/A ratio is 1.3,the viscosity-temperature curves are all alkaline,and on increasing Ba O content,the break temperature decreases,on increasing Na2O,K2O and Mg O content,the break temperature decreases first and then increases,but the minimum values of each system are different.In addition,with the increase of Ba O and Mg O contents,the crystallization types of all systems remain unchanged,but the addition of Ba O can effectively reduce the crystallization temperature,while the addition of Mg O can increase the crystallization temperature.