Wetting And Corrosion Penetration Properties Of Alkali Metals On Refractory Surfaces

The alkali metal slag generated during the alkali recovery process of black paper liquor will adhere to the surface of refractory materials inside the alkali recovery furnace to form a molten coating layer,causing corrosion and spalling of the refractory materials inside the furnace and affecting the service life of the refractory materials.It is essental to study the wetting and cladding characteristics of alkali metal slag on the refractory surface and the mechanism of corrosion penetration of alkali metal salts inside the refractory.This paper investigated alkali metal slag and three refractory materials(dense corundum,magnesium oxide and magnesia-alumina spinel).First,the seat-drop method investigated the wetting and coating characteristics of the alkali metal molten column on the refractory surface.The apparent contact angle and slag column height variation processes were measured by Image J software,the apparent porosity and bulk density variation of the refractory were analyzed,and the influence of different heating conditions on the wetting process of the molten column on the refractory surface was obtained.Subsequently,the corrosion penetration mechanism of alkali metal slag on refractory was analyzed using the static crucible method.The microstructure,fundamental changes and compound composition of the fused and interfacial layers was analyzed by SEM-EDS and XRD to probe the mechanism of corrosion penetration of slag on refractory.Finally,Factsage7.3 software was used to simulate the reaction process between molten slag and refractory to provide guidance for the experiments and analysis.The main conclusions are as follows:(1)The alkali metal molten column has good wettability on the dense corundum refractory surface.The thermal hysteresis causes the wetting of the molten column to be inhibited as the heating rate increases.Changing the heating atmosphere changes the wetting characteristics,with the reducing atmosphere lagging the wetting temperature by about 50℃ compared to the oxidizing atmosphere.As the inclination of the refractory increases to 15° and 20°,the effect of gravity on the adhesion effect of the molten column increases and can lead to poor wetting properties.During heating,the molten slag undergoes penetration and dissolution reactions in the corundum material,generating high melting point compounds such as NaAlO2,3Al2O3-2SiO2(mullite),KNa3Al4Si4O16(chalcocite)and Na1.75Al1.75Si0.25O4(mullite type).Combined with thermodynamic simulation,it is found that the reaction interface layer generates high melting point compounds,which will fill the pores and cracks on the material surface and stop the erosion of slag.(2)The high porosity property of magnesia refractory directly affects the wetting characteristics of the molten column,resulting in the rapid penetration of the molten column into the refractory during the heating process.The molten column is more easily penetrated into the magnesia refractory in an oxidizing atmosphere;combined with thermodynamic simulation,it is found that the magnesia olivine(Mg2SiO4)generated in the reducing atmosphere is 2.5 times more than in an oxidizing atmosphere,and the generation of large amount of Mg2SiO4 is the reason to inhibit the wetting of molten column.Meanwhile,the study showed that magnesia refractories have good resistance to dissolution.The generation of Mg olivine changes the microstructure and physicochemical properties of the interfacial layer of magnesia refractory,fills the pores of the material and forms a dense structure of the isolation layer,which in turn will inhibit slag penetration and erosion of the refractory.(3)The alkali metal molten column has good wettability on the surface of the magnesia-alumina spinel refractory.The change of the tilt angle had less effect on the wettability of the molten column.The wettability process of the molten column in the reducing atmosphere was inhibited,and the generation and transformation of high melting point compounds led to a deformation temperature lag of about 90℃ in the reducing atmosphere than in the oxidizing atmosphere.The microscopic morphology of the molten cladding layer and matrix of the magnesia-alumina spinel refractory changed significantly after the corrosion penetration experiments.Under the same heating time,the molten slag was more likely to penetrate into the matrix at 900℃ than at 1100℃ to generate substances such as NaAlO2.After using EDS layer-by-layer analysis,it was found that magnesia-alumina spinel has good resistance to dissolution.Combining experiments with thermodynamic simulations,it was found that MgSiO3 and NaAlO2 generated after contact between the molten slag and the surface of the refractory would strengthen the denseness of the refractory surface and form a reactive interface layer,which could effectively prevent the molten slag from penetrating into the interior of the refractory.