Refractories and Industrial Ceramics

Results are provided for an experimental study of the effect of deoxidation on the composition of nonmetallic inclusions in pipe steels melted in a vacuum induction furnace with a periclase lining. Thermodynamic calculations are made for oxygen activity within melts with lanthanum, cerium, aluminum, and yttrium for the metal of four melts. Conditions are evaluated for magnesium spinel inclusion formation in relation to deoxidant used and the extent of deoxidation. The effect is demonstrated of reduced aluminum concentration during metal ladle treatment on nonmetallic inclusion composition and the possibility of modifying them in the course of an industrial pipe steel melt.

Results are provided for refractory materials developed on basis of both secondary resources (broken chamotte refractory, mullite-containing waste, and aluminum melting slag), fireclay, and phosphoric acid. A relationship is established for physicochemical and strength properties of the materials on additive content, filler fractional composition, and also firing temperature. It is stablished that the optimum aluminum melting slag and mullite-containing waste contents are 5% and 15% respectively. The material produced with a firing temperature up to 1200°C has density of 1785 – 1795 kg/m³, open porosity of 20 – 23%, ultimate strength in compression of 40 – 50 MPa, and thermal shock resistance of 30 – 50 thermal cycles (1000°C – water).

The effect of natural additives on aluminosilicate sintering capacity is studied. It is demonstrated that addition of natural alkaline aluminosilicates with predicted viscosity and amount of melt makes it possible to prepare stronger ceramic materials.

Results are provided for a study of the structure and composition of composites based on red-burning kaolinite clay and calcium carbonate heat treated at 500°C during acid activation. It is shown that during reaction with 12% H₂SO₄ there is leaching of iron and aluminum ions and formation of calcium sulfate with retention of the kaolinite structure. Introduction into the material composition of water glass leads to breakdown of the kaolinite structure that facilitates an increase in in the rate of aluminum ion extraction during subsequent acid activation. Ca²⁺- and Fe³⁺-containing components entering into the composite composition in the presence of water glass are passivated by active amorphous silica formed during reaction of water glass with air CO₂.

The effect of annealing and sintering temperature on phase transformation of ZrO₂ is studied in relation to REE concentrate content using differential thermal analysis, Raman spectroscopy and x-ray diffraction. It is shown that introduction of REE concentrate in an amount of more than 15 wt.% stabilizes ZrO₂ tetragonal phase solely at below 1200 °C. A further increase in temperature leads to destabilization of the tetragonal phase with formation of the monoclinic and cubic phases of the Ln₂Zr₂O₇ type isostructural compounds (n = La, Nd, ...) with a pyrochlore structure.

It is established that addition of nano-dispersed iron oxide pigment in an amount of 0.25 – 0.50% provides intentional control of the chemisorption reaction of binder and filler during mixing facilitating an increase in carbon refractory density. It is shown that during addition of nano-additive to a carbon composition it is necessary to adjust the weight for binder in the direction of a reduction in its content. The principle of selecting the optimum binder content as a result of the plastifying effect of nano-dispersed iron oxide pigment for maximum torsional moment in the mixer shaft corresponds to a high level of expended mechanical energy and correspondingly intensification of the mixing process, and also provides an increase in mix sintering capacity during firing.

A slip casting method was used to produce samples of BeO-based composite ceramics with additions of 5 – 30 wt.% of nanocrystalline TiO₂ powder. It was established that slip casting does not provide the maximum density of ceramic samples. This may cause some effect on its thermophysical properties. A microstructure of (BeO + TiO₂)-ceramics was studied, as well as variations in its specific heat capacity at constant pressure, thermal diffusivity and thermal conductivity depending on the amount of additive at room temperature and in the range of 300 – 800 K. The established patterns will help designing more powerful absorbers of scattered microwave radiation based on (BeO + TiO₂ )-ceramics.

The properties of traditional refractory concrete modified by means of microsilica and the deflocculant, including the different types of chamotte filler are studied. It is established that refractory concrete with chamotte filler Bos145 (containing 44% of has lower open porosity, and both high density and ultimate strength in compression compared with the properties of concrete with fillers Bos125 and Bos135 (containing ~26 and ~37 % Al₂O₃ respectively). It is also established that that independent of the type of chamotte filler supplementary addition of SiO₂-based additive facilitates an increase concrete alkaline resistance by a factor of five and more. It is shown that this additive is effective at temperatures up to 1100°C, and at 1200 °C chamotte concrete porosity increases and the material resistance to molten alkali falls significantly.

The composition and structure of periclase-chromite refractories contacting the coal–gas atmosphere of copper-sulfide-ore smelting furnaces were studied. Combined effects of high-temperature suspensions of enriched copper concentrate and SO₂ altered the chemical composition of the refractory surface and inner layers. The impurity contents (wt%) reached Fe 54.0, Cu 7.2, Zn 6.4, and S 1.8. Saturation of the surface layer with iron and nonferrous-metal oxides decreased its porosity and promoted the formation of low-melting compounds and eutectics. The periclase-chromite refractories were decomposed by exfoliation of layers with filled pores during alternating heat—cool cycles because of the different linear thermal expansion coefficients of the phases. The surface layer of spent refractories should be mechanically removed for recycling. The remaining part is suitable for producing refractory powders for various purposes.

The technique is presented for the determination of chemically bound water in metakaolin (with the mass fraction of water being within 0.5 and 5 %) by IR spectrometry at 900°C using the ELTRA (Germany) CW-800M infrared spectrometer. A single sample can be tested within 5 – 6 min, allowing for quality control of incoming metakaolin samples keeping defective samples out of production. The possibility of water determination at 600°C was shown, in which case analysis time increases to 20 – 22 min. The developed technique for the determination of chemically bound water in metakaolin provides results with sufficient accuracy and precision.

The possibility of obtaining a porous ceramic composite with a low heat conductivity and high heat reflecting ability based on a mixture of raw materials including potassium polytitanate and different silicon oxide modifications is investigated. It is shown that the introduction of silicon oxide favors the formation of the potassium silicate glass phase acting as a binding agent and promoting the formation of a ceramic composite structure consisting of interwoven high-strength fibrous K₂Ti₆O₁₃ crystals bound by the evenly distributed glass phase.

We seek constructive solutions aimed at the improvement of the efficiency of dust capture for an open-type local exhaust and at decreasing the dust losses into an aspiration network by a closed-type local exhaust (shelter) caused by the use of a vertical rotating cylindrical exhaust. We study exhausts in the form of slit-type gaps along the generator of the cylinder and exhausts with drains from the end of the cylinder. We proposed improvements that enable one to increase the efficiency of entrainment of the air flow by rotating cylinders. The accumulated results can be useful for the design of aspiration hoods with a function of dust-collecting chamber.

The Acknowledgement on page 105 should read

The work was financially supported by the Ministry of Education and Science of the RF under a State Task for Scientific Activity, Project No. 9.1372.2017/4.6.

The Acknowledgement on page 289 should read

The work was financially supported by the Ministry of Education and Science of the RF under a State Task for Scientific Activity, Project No. 9.1372.2017/4.6.