Low-temperature ceramics of the 3Y-TZP-Al2O3 system, containing sintering additives

In this work, we studied the effect of complex additives containing Na2Si2O5 and Ni, Zn oxides on the properties and sintering temperature of a ceramic material 3Y-TZP- Al2O3 with an aluminum oxide (Al2O3) content of 5 wt %. It was shown that the introduction of complex additives promoted an increase in the flexural strength of ceramic materials. The greatest strength (445±22 МПа) was achieved by sintering at 1250 °C on the composition with 5 wt % Na2Si2O5 and 0.33 mol % Zn.

Determination of melt composition in an open-arc ore-thermal furnace

The aim of the study is to improve the technical and economic performance of the normal electrocorundum production process in an ore-thermal furnace by automated control of the melt composition at the final stage. The essence of the research is to exploit the valve effect of an AC arc. The expression for the Al2O3 content in the melt was obtained from the electrical characteristics of the melt. Studies have shown a fairly high degree of accuracy in the convergence of the results of the proposed method with laboratory data.

Pyrophyllite: An Economic Mineral for Different Industrial Applications

Pyrophyllite (Al2Si4O10(OH)2) is a phyllosilicate often associated with quartz, mica, kaolinite, epidote, and rutile minerals. In its pure state, pyrophyllite exhibits unique properties such as low thermal and electrical conductivity, high refractive behavior, low expansion coefficient, chemical inertness, and high resistance to corrosion by molten metals and gases. These properties make it desirable in different industries such as refractory; ceramic, fiberglass, and cosmetic industries; as filler in the paper, plastic, paint, and pesticide industries; as soil conditioner in the fertilizer industry; and as a dusting agent in the rubber and roofing industries. Pyrophyllite can also serve as an economical alternative in many industrial applications to different minerals as kaolinite, talc, and feldspar. To increase its market value, pyrophyllite must have high alumina (Al2O3) content, remain free of any impurities, and possess as much whiteness as possible. This paper presented a review of pyrophyllite’s industrial applications, its important exploitable properties, and the specifications required for its use in industry. It also presents the most effective and economical techniques for enriching low-grade pyrophyllite ores to make them suitable for various industrial applications.

Production of corundum armored ceramics

The purpose of this study was to develop the compositions and technology of corundum armored ceramics with high ballistic characteristics based on aluminum oxide with an α-Al2O3 content of more than 99 wt.%. The results of the study of the physicochemical processes of obtaining corundum ceramics modified with complex additives consisting of magnesium - aluminosilicate eutectic mixture and oxides of magnesium, yttrium, titanium, zirconium are presented. The introduction of complex additives into the composition of corundum ceramics provides a significant reduction (100-150°C) of the sintering temperature of the product. In this case, additives of yttrium and zirconium oxides contribute to the formation of a uniform-grained microstructure of ceramics, and in the case of adding titanium oxide, a collective recrystallization of corundum grains is noted. The use of small additives (0.3-0.5 wt.%) of magnesium and yttrium oxides together with a eutectic mixture in the compositions of corundum ceramics based on high-quality alumina contributes to the formation of a uniform-grained, dense structure of the material and giving it a high level of physical and mechanical properties as a result of directional the action of each component of the additive on the physicochemical processes of phase formation of the crystalline matrix. A model idea of the mechanism of action of additives on the formation of the microstructure of ceramics during stage-by-stage heating from 1350 to 1650°C in the sintering mode of products is presented. The developed compositions and technologies of corundum armored ceramics have a production focus and implementation in practice.

Analysis of Rational Proportion of Raw Materials Based on Biomass

Most of the air pollutants in the steel industry come from the sintering process, and the air pollutants produced by the sintering process mainly come from the sinter fuel (coke breeze). The S and N content of biomass fuel is low; therefore, biomass fuel is used instead of coke breeze for sintering to reduce the emission of the sinter flue gas pollutants. However, the use of biomass fuel reduces the sintering layer temperature, which results in the deterioration of the sinter properties. In order to ensure the quality of sintering base on biomass fuel, the thermodynamic calculation and related experiments were carried out, the effects of different basicity, MgO and Al2O3 content on the formation of low melting point minerals in sintered mixture were studied, and the suitable composition of sintered mixture was determined in this paper, so as to reduce the liquid phase formation temperature of sinter and increase in biomass fuel addition, which provided theoretical support for the application of biomass fuel in sintering. Experimental results indicate that the suitable conditions for the low-temperature sintering were a basicity of 2.0, and MgO and Al2O3 contents of 1.0% and 1.8%, respectively. Under this condition, more biomass fuel can be used to replace coke breeze, and the emission of flue gas pollutants can be greatly reduced.

Process Mineralogy Characteristics and Flotation Application of a Refractory Collophanite from Guizhou, China

A refractory phosphate ore obtained from Guizhou, China, contains high amounts of detrimental metal impurities (e.g., Fe, Al, and Mg) which affect the deep wet processing of phosphorus products before use. In this study, mineralogy parameters of the ore such as mineral composition, disseminated particle size, mineral liberation degree, and intergrowth relationship were investigated using X-ray fluorescence spectrometer (XRF), X-ray powder diffractometer (XRD), and advanced mineral identification and characterization system (AMICS). The mechanism for flotation separation was also discussed. The results showed that the ore was a fine-grained calcareous-siliceous collophanite with high P2O5 grade. The gangue minerals such as quartz, sericite (muscovite), pyrite, and dolomite were finely disseminated and encapsulated by fluoroapatite particles in a rather complex relationship. A double reverse flotation process was carried out based on the separation principle of less flotation and more inhibition. A phosphorous concentrate with a P2O5 grade of 35.53%, SiO2 content of 5.88%, MgO content of 0.91%, sesquioxide (Fe2O3+Al2O3) content of 1.98%, MER value of 8.13%, and phosphorus recovery of 75.04% was obtained. Based on the flotation test results and the analysis of process mineralogy parameters, we concluded that the main causes of difficulty in separation of collophanite are fine disseminated particle size, poor mineral liberation degree, and serious argillization. The selection of foam-controlled collectors, efficient dispersing inhibitors and classified desliming process will be necessary for improving flotation index. These results provide a technical reference for subsequent development and utilization of collophanite resources.

Influence of Al2O3 content on mechanical properties of silica-based ceramic cores prepared by stereolithography

Silica ceramic cores have played an important part in the manufacture of hollow blades due to their excellent chemical stability and moderate high-temperature mechanical properties. In this study, silica-based ceramics were prepared with Al2O3 addition by stereolithography, and the influence of Al2O3 content on mechanical properties of the silica-based ceramics was investigated. The Al2O3 in silica-based ceramics can improve the mechanical properties by playing a role as a seed for the crystallization of fused silica into cristobalite. As a result, with the increase of Al2O3 content, the linear shrinkage of the silica-based ceramics first decreased and then increased, while the room-temperature flexural strength and the high-temperature flexural strength first increased and then decreased. As the Al2O3 content increased to 1.0 vol%, the linear shrinkage was reduced to 1.64% because of the blocked viscous flow caused by Al2O3. Meanwhile, the room-temperature flexural strength and the high-temperature flexural strength were improved to 20.38 and 21.43 MPa with 1.0 vol% Al2O3, respectively, due to the increased α-cristobalite and β-cristobalite content. Therefore, using the optimal content of Al2O3 in silica-based ceramics can provide excellent mechanical properties, which are suitable for the application of ceramic cores in the manufacturing of hollow blades.

Estimation of Iron Ore Pellet Softening in a Blast Furnace with Computational Thermodynamics

In blast furnaces it is desirable for the burden to hold a lumpy packed structure at as high a temperature as possible. The computational thermodynamic software FactSage (version 7.2, Thermfact/CRCT, Montreal, Canada and GTT-Technologies, Aachen, Germany) was used here to study the softening behavior of blast furnace pellets. The effects of the main slag-forming components (SiO2, MgO, CaO and Al2O3) on liquid formation were estimated by altering the chemical composition of a commercial acid pellet. The phase equilibria for five-component FeO-SiO2-CaO-MgO-Al2O3 systems with constant contents for three slag-forming components were computed case by case and the results were used to estimate the formation of liquid phases. The main findings of this work suggested several practical means for the postponement of liquid formation at higher temperatures: (1) reducing the SiO2 content; (2) increasing the MgO content; (3) reducing the Al2O3 content; and (4) choosing suitable CaO contents for the pellets. Additionally, the olivine phase (mainly the fayalitic type) and its dissolution into the slag determined the amount of the first-formed slag, which formed quickly after the onset of softening. This had an important effect on the acid pellets, in which the amount of the first-formed slag varied between 10 and 40 wt.%, depending on the pellets’ SiO2 content.