QIN Huiqing^a，XIA Yufeng^a，HUANG Qing^a，YUAN Wenjie^a，b，c

a. State Key Laboratory of Refractories and Metallurgy， Wuhan University of Science and Technology， b. National-provincial Joint Engineering Research Center of High Temperature Materials and Lining Technology， c. Joint International Research Laboratory of Refractories and Metallurgy， Wuhan University of Science and Technology， Wuhan 430081， China

Abstract

Objective Owning to their advantages， including easy production， simple construction， no need for firing， and fewer joints that can lead to lower corrosion， monolithic refractories such as castable have replaced traditional shaped refractories in most application fields. The use of a large amount of micro powders makes the dispersion of castable crucial for construction. Zirconia-containing micro silicas， a by-product of the desilication process in zirconium production， boasts enhanced dispersibility and favorable rheological properties. These characteristics can reduce the required amount of dispersant， lower construction costs，and exhibit promising application potential. To fully utilize its potential to improve the construction and service performance of castable， the rheological properties of zirconia-containing micro silicas slurries were systematically investigated. The effects of powder characteristics and dispersant on their rheological properties were analyzed. The results can provide practical guidance for the development and utilization of castable with zirconia-containing micro silicas.

Methods In this paper， three grade zirconia-containing micro silicas powders （SIF-A， B， C） produced by Imerys Fused Minerals Yingkou Co. ， Ltd. were selected. The phase of zirconia in micro silicas was identified by X-ray diffraction （XRD）. The microstructure of zirconia-containing micro silicas was observed using transmission electron microscopy （TEM）. Functional groups of zirconia in micro silicas were identified by Fourier transform infrared spectroscopy （FTIR）. The particle size distribution of micro silicas was tested by a laser particle size analyzer. A 5% mass fraction slurry was prepared and the Zeta potential of the solution was measured at different pH values. The rheology of zirconia-containing micro silicas micro powders slurries containing 0. 2% sodium tripolyphosphate （STPP），0. 2% sodium hexametaphosphate （SHMP）， and 0. 1% FS20-type polycarboxylate dispersant in mass fractions was measured using a cylindrical coaxial rotational rheometer. The shear stress-shear rate relationship of zirconia-containing micro silicas slurries with different dispersants was fitted using the Herschel-Bulkey model. Rheological parameters were investigated using gray correlation analysis combined with weighting analysis.

Results and Discussion Tetragonal zirconia in micro silicas was detected by XRD. It was observed that large spherical particles contained numerous smaller zirconia particles. The median particle size D₅₀ of micro silicas A and the grading accuracy D₇₅/D₂₅ were the largest. All three saturated solutions of zirconia-containing micro silicas were strongly acidic， with pH values in the order A<B<C due to the high content of soluble acidic oxide P₂O₅ in micro silicas. The absolute value of the Zeta potential of the slurries increased with the increase of pH in the acidic environment. According to the grey correlation analysis， the correlation between the pH of the slurry and the D₅₀ of the powders， and the rheological properties of the zirconia-containing micro silicas slurries at a shear rate of 0. 13 s^-1 were 0. 975 3 and 0. 9427， respectively， consistent with the calculated values of the weighting. There was a positive correlation between the particle size of zirconia-containing micro silicas and the rheological properties of its slurries. With the addition of different dispersants， the zirconia-containing micro silicas slurries exhibited shear thinning characteristics. The addition of sodium tripolyphosphate （STPP） and sodium hexametaphosphate （SHMP） dispersants brought the zirconia-containing micro silicas slurry close to Newtonian fluid. The improvement of slurry rheology by STPP and SHMP was greater than that of the polycarboxylate FS20. For micro silicas A， the dispersion effect of STPP was the highest. The most effective dispersant was SHMP for micro silicas B and C. This was because the hydroxyl groups on the surface of the zirconia-containing micro silicas interacted more effectively with water molecules under the action of proper amount of phosphate. The phosphate content of STPP was lower than that of SHMP. For micro silicas A with more surface hydroxyls， STPP was the best dispersant， whereas for samples B and C containing fewer surface hydroxyls， SHMP provided more phosphate for better dispersion. In addition， an increase in pH inhibited the adsorption of phosphate. Therefore， the phosphate dispersant was more significant for micro silicas A.

Conclusion The zirconia particles are located on the surface of silica or encapsulated in larger silica particles. The saturated solutions of three selected zirconia-containing micro silicas for this study all exhibit strong acidity， with pH values A<B<C. In acidic environment， the absolute value of the Zeta potential of the slurry increases with the increase of pH value. The influence of the characteristics of zirconia-containing micro silicas on its rheological properties was analyzed using the grey correlation analysis method. The pH value of the slurry and the D₅₀ particle size have the greatest impact on its rheological properties. For larger micro silicas particles and lower pH values of the slurry， the rheological properties are better. Zirconia-containing micro silicas slurries with different dispersants exhibit shear thinning characteristics. The slurries are approximately Newtonian fluid when STPP and SHMP were added as dispersants. The effects of STPP and SHMP on their rheological properties are more significant than those of polycarboxylate superplasticizers. At a certain shear rate， weak intermolecular forces between particles in the slurry are disrupted， weakening the adsorption of polymer structures. Therefore， under shear force， the dispersion effect of ionic surfactants is stronger than that of polycarboxylate dispersants. Zirconia-containing micro silicas with a larger range of particle size distribution and more surface hydroxyl groups shows the best dispersion with STPP. Zirconia-containing micro silicas with slightly higher pH values requires the addition of SHMP to obtain slurries with minimized viscosity， as their adsorption of phosphate is inhibited.

Get Citation: QIN Huiqing， XIA Yufeng， HUANG Qing， et al. Rheological properties of zirconia-containing micro silicas slurries［J］. China Powder Science and Technology，2024，30（6）：1−11.

Received:2023-11-09.Revised:2024-05-22,Online:2024-10-18.

Funding Project:国家自然科学基金项目，编号：52172023；湖北省科技创新人才计划科技服务人才专项，编号：2023DJC124。

First Author:覃慧清（2000—），女（侗族），硕士生，研究方向为耐火材料。E-mail：qhq20001125@163. com。

Corresponding Author:员文杰（1980—），男，教授，博士，博士生导师，研究方向为耐火材料和高温陶瓷复合材料。E-mail：yuanwenjie@wust. edu. cn。

DOI：10.13732/j.issn.1008-5548.2024.06.010

CLC No:TQ175.4； TB4                Type Code:A

Serial No:1008-5548（2024）06-0001-11