Properties dependence of the lightweight alumina products obtained by a semi-dry pressing method on the alumina type

Lightweight materials are widely used in industry for thermal insulation of various thermal units. The choice of lightweight material depends on the specific conditions of service. For the lining of high-temperature units operating in reducing environments, alumina lightweight products are used that contain a minimum amount of Fe2O3 impurities and free (unbound in compounds) SiO2. In JSC “URIR named after A. S. Berezhnoy” a technology of alumina lightweight products of grades KLA-1.1 and KLA-1.3 by a semi-dry pressing method with an application temperature of up to 1550 °C has been developed. These products are made from a mixture of ground and no-milled γ-form alumina of grade 0 and α-form alumina of grade S with additives of pitch coke and chalk. The work purpose was improvement of the alumina lightweight products technology and search for new alternative raw materials along with the currently used alumina grade S. The properties dependence of alumina lightweight products, obtained by the semi-dry pressing method, on the type of alumina α-form, was investigated. As a result of the studies, it was found that, for the manufacture of alumina lightweight products of grades KLA-1.1 and KLA-1.3 by the semi-dry pressing method, alumina grades N and NR can be used as an alternative alumina-containing raw material along with alumina grade S. The phase composition of alumina lightweight products of grades KLA-1.1 and KLA-1.3, which are manufactured using alumina grades S, N and NR, was represented mainly by corundum and calcium hexaluminate. The alumina lightweight products, which were manufactured using alumina grades S, N and NR, were characterized by similar high properties and correspond the technical requirements for grades KLA-1.1 and KLA-1.3.

Influence of an addition amount of a new type of alumina on the properties of ramming mullite-corundum mixes and samples from them

Effect investigation of an addition amount of spherical alumina on the properties of ramming mullite-corundum mixes of the MMK-90 (on a binder of an aqueous solution of orthophosphoric acid) and MMKPBF (with a MgO addition on a borophosphate binder) brands, as well as samples from them, have been carried out. As a result of the carried out studies, it was found that the use of an optimal amount (4 %) of spherical alumina in the composition of ramming mullite-corundum mixes provides an increase in by 30 % in the cold crushing strength of samples made from them, fired at a temperature of 1580 °C, while maintaining at sufficiently high level indicators of their thermal shock resistance and slag resistance. The indicated alumina use in the composition of the MMK-90 mix during high-temperature firing of samples leads to an intensification of the mullite synthesis process. In fired samples from the MMKPBF mix, the spherical alumina forms a dense intergrowth of "felt-like" structure, which reinforces the structure, increasing the strength and thermal shock resistance of the samples. Indicators of physical and chemical properties of ramming mullite-corundum mixes of improved composition and samples made from them (for MMK-90 and MMKPBF mixes, respectively): chemical composition, wt. %: Al2O3 — not less than 90.0 and 85.0; SiO2 — within 3.2-5.0 and no more than 2.5; Fe2O3 — no more than 1.0 and 0.6; P2O5 — in the range of 2.5-3.5 and 0.5-1.0; grain size composition, mm — 3-0; cold crushing strength after firing at a temperature of 1580 °С — 110 and 70 N/mm2; thermal shock resistance — > 20 thermal cycles 950 °С — water. Ramming mullite-corundum mixes of improved composition are recommended for use in various heating units with high specific mechanical loads on the lining.

Researches on development of alumina-chromia-zirconium silicate refractories containing 60 % Cr2O3

Researches of a branch composition and firing atmosphere influence on structure and properties of pressed alumina-chromia-zirconium silicate refractories with 60 % Cr2O3 content were carried out. The optimal branch composition which after firing in oxidizing atmosphere provides obtaining of samples with open porosity 24.8 %, apparent density 3.46 g/cm3, cold crushing strength 78 N/mm2 and thermal shock resistance by 950 ºС — water — 7 thermal cycles was established. The phase composition of samples was determined. It has been shown that, firing in a reducing atmosphere, as well as titanium oxide addition, have no significant effect on samples properties. Corrosion resistance comparative researches of alumina-chromia-zirconium silicate refractories with 60 % Cr2O3 content and refractory brand KHTSS-30 with 30 % Cr2O3 content to glass «E» and basalt melts by crucible method at a temperature of 1580 °C with an exposure time of 8 hours were carried out. It has been established that, glass «E» and basalt impregnate refractories, moreover for samples with the developed optimal composition the impregnation depth was the smallest in comparison with samples of other compositions. The corrosion mechanism has been established, which consists in the penetration of glass «E» and basalt melts into refractory with further dissolution of corundum grains in them. Sintered Cr2O3 and solid solutions based on it in the composition of samples prevent corrosion, reducing the interaction area of melts with corundum grains, and when exposed to basalt melt, also forming spinelid with its components, which slows down further penetration of melt into refractory structure, thereby reducing its corrosive effect on the refractory. Based on the obtained results, a technology of a new domestic type of product (alumina-chromia-zirconium silicate refractories with 60 % Cr2O3 content manufactured by semi-dry pressing method) was developed.

High alumina refractory concretes bonded with calcium aluminate phosphate binder

For many industries, further progress is possible provided that more efficient refractories of new types are created. The refractory concretes bonded by calcium aluminate phosphate binders in comparison with conventional refractories continue to gain in popularity because of the following advantages: quick installation and low construction costs; reduced and simplified furnace maintenance; good thermal-shock resistance; monolithic (no joints); linings of the units done need not be cured to develop initial strength. The longevity of refractory is essentially increasing provided structure is forming under conditions of the service site. That is why developing of new refractory materials must be carried out by means of its structure design. These principles have been realizing in the refractory concretes technology under the limited conditions of refractory lining installation and industrial unit final heat up. The present paper identifies the phosphate phases responsible for developing mechanical-strength properties of high alumina concretes bonded with calcium aluminate phosphate binders. It sets out the colloid and crystalline phases resulted from interphase interaction that provides the basis for calcium aluminate phosphate binders (suspensions) useful to the refractory industry. The concretes obtained retain their volume integrity after 30 cycles of heating and cooling; can be used for refractory applications > 1700 °С; exhibit sufficient strength of lining 40 MPa.

Effect study of an amount of active alumina addition on the properties of alumina refractories with a complex additive of chromium oxide and zirconium dioxide

An effect of active alumina amount introduced into a batch (7.5 - 22.0 %) on the properties of alumina samples containing a complex additive of chromium oxide (10 %) and zirconium dioxide (3 %) was studied. The optimal amount of introduced active alumina (12.5 %) was established, which ensures the production of samples fired at a temperature of 1580 ºС, with the lowest open porosity (18.2 %), the highest apparent density (3.25 g/cm3) and the highest cold crushing strength (117 N/mm2), refractoriness under a load of 0.2 N/mm2 > 1700 ºС, thermal shock resistance (in the mode of 1300 ºС — water) not less than 7 thermal cycles.The results of carried out studies were used in the development of production technology of domestic refractory products based on fused corundum, α-form alumina, active alumina, containing the complex addition of chromium oxide and zirconium dioxide, by semi-dry pressing method. These refractory products characterized by high properties and intended for service at a temperature of 1850 ºС in the combustion chamber of carbon black production reactors.The use of these refractories in the lining of above mentioned high-temperature industrial units will allow to increase a duration of their operation due to an increase in the refractory durability in service, as well as to save material and energy resources associated with a relining of the reactors.

Control of the work quality of chemical and analytical departments of the refractory industry enterprises of Ukraine in 2019

Control of the work quality of chemical and analytical departments of the refractory industry enterprises of Ukraine is one of the activity areas of JSC "The URIR named after A. S. Berezhnoy" and helps to increase the competitiveness of products manufactured by enterprises.The comparison of work quality of chemical-analytical units of refractory enterprises (JSC "KDZ", PJSC "Chasovoyarsk Refractory Plant", JSC "Velikoanadol Refractory Plant") and JSC "The URIR named after A. S. Berezhnoy" was carried out. The discrepancy between the average results of chemical analysis in the chemical-analytical unit of refractory enterprises and in the laboratory of chemical-analytical and structural-phase research of JSC "The URIR named after A. S. Berezhnoy" does not exceed the permissible value of γ in terms of SОU-N МPP 77.080-012:2004. The work quality of chemical-analytical units of central refractory laboratories of all the above mentioned refractory enterprises is satisfactory. Recommendations for improving the accuracy of the chemical analysis results in the refractory enterprises laboratories that participated in the tests are not required.

Thermodynamic studies in the MgO – FeO – Al2O3 system

Prediction of the phase composition is one of the most important tasks in the development of new refractory materials and their operation in thermal units. The most complete information on phase interactions and thermodynamic stability of phase combinations is contained in the phase diagrams. The article presents thermodynamic studies of the three - component system MgO – FeO – Al2O3, which is of great interest for the production of refractory materials with high performance characteristics. Based on the analysis of binary systems of this system, it was found that, the stable phases are MgO, FeO, Al2O3 and MgAl2O4, FeAl2O4. The results analysis of calculating the Gibbs energy for the reaction (FeO + MgAl2O4 = MgO + FeAl2O4) indicates the thermodynamic stability of the phases combination of MgO, FeAl2O4 to a temperature of 1141 K. Above the temperature of 1141 K FeO and MgAl2O4 are stable phases. Thus, in the system MgO – FeO – Al2O3 up to the temperature of 1141 K, the phases MgO – FeAl2O4 and MgAl2O4 – FeAl2O4 coexist, above this temperature — FeO – MgAl2O4 and MgAl2O4 – FeAl2O4. The data obtained make it possible to predict thermally stimulated phase changes that give the effect of thermoplasticity and will be important for obtaining refractory materials with high performance characteristics based on the MgO — FeO — Al2O3 system.

Influence research of an α–form alumina type on the properties of samples from vibrocasting mullite corundum granular masses

The technology of refractories vibrocasting was developed by JSC "URIR named after A. S. Berezhnoy" in particular highly refractory mullite corundum crucibles for melting of heat-resistant alloys in induction furnaces. At manufacturing of highly refractory vibrocasting mullite corundum refractories a-form alumina, as a dispersion binder, which milling to a particles size of less than 10 μm (the content of particles less than 4 μm in such alumina is more than 50 %) is used. For improvement the casting characteristics of vibrocasting masses dispersants are used. At research milling kinetics alumina of all brands was milling in a vibration mill for a specified time. For this research a certain amount of the investigated alumina of each brand was loaded into a vibration mill, and after a specified grinding time (30, 45, 60, 75 and 90 min), a sample of alumina after milling was taken in a specified amount. In this work, the kinetics of changes the dispersion of alumina (S, N and NR brands) during their milling was studied. The dispersion of alumina which were needed (the content of particles less than < 10 μm in such alumina is not less than 90 %, the content of particles less than < 4 μm — not less than 50 %) was achieved in almost the same milling time was found (~ 45 min). With a further increase of milling time to 60, 75 and 90 minutes, the dispersion of alumina N and NR brands increases in comparison with alumina S brand and after 90 minutes of milling, the content of particles < 4 μm in alumina, respectively, is ~ 60, ~ 75 and ~ 80 %. After fired at a temperature of 1580 °C the properties of vibrocasting mullite corundum samples, which contain alumina S, N and NR brands, are characterized by a high level of apparent density (above 3 g/cm3), open porosity (less than 16 %) and cold crushing strength (above 140 N/mm2). The high properties make it possible to use a-form alumina N and NR brands along a-form alumina S brand in the technology of vibrocasting mullite corundum refractories, including the highly refractory mullite corundum crucibles.

Alumina silicate glass-ceramic materials for electrical purposes

The prospects for use of glass-ceramic materials as electrical products were analyzed. The priority of a self-organized macro- and nanostructure formation of the glass-ceramic materials under conditions of low-temperature heat treatment to ensure their high physical and chemical properties was shown. The choice of an alumina silicate system of materials for obtaining high-strength glass-ceramic materials with improved electrical properties was substantiated, taking into account the aspects of energy saving. The technological modes of cooking, forming and heat treatment of glass-ceramic materials were determined. Resistance, dielectric constant and dielectric loss tangent at 106 Hz were measured using an E6-13A teraometer on a trielectrode system at a temperature of +29 °C and a DE-5000 RLC meter. Electric strength (Em) and cold crushing strength were determined according to GOST 24409-80. Tensile strength according to GOST 32281.1-2013 (EN 1288-1: 2000). The decisive influence on the electrical properties of glass-ceramic materials the crystalline phases of α-cordierite, β-spodumene or lithium disilicate, as well as the residual glass phase composition has been established. The structure influence of the alumina silicate glass-ceramic materials on the provision of their electrical (tgδ∙104 = 70 ÷ 80; ε = 8.0 ÷ 9.3 (at f = 106 Hz); lg ρv = 12.9 ÷ 15.0 (ρv, Ohm·cm at Т = 20 °C) and mechanical (K1C = 3.15 ÷ 4.3 МPа∙м1/2; σ comp = 630 ÷ 700 МPа, σbend = 300 ÷ 350 МPа; KCU = 4.8 ÷ 5.9 kJ/m2) properties. It was found that, the defining condition for the developed glass-ceramic materials use as insulating materials under repeated exposure to high-temperature operations is their high breakdown strength Em = 37 ÷ 42 MV/m and thermal shock resistance due to low TCLE (α∙107 = 21.5 ÷ 31.8 deg-1). The influence of phase composition and structure of the alumina silicate glass-ceramic materials on their electrical and mechanical properties was analyzed. A comparative assessment of the known ceramic and glass-ceramic materials for electrical purposes has made it possible to establish the feasibility of using the developed materials as substrates in the design of a hybrid integrated circuit, vacuum-tight shell and capacitor dielectrics.

Effect investigation of a thinning additive on the physical and mechanical properties of celsian ceramics obtained by slip casting

The article discusses the physical and mechanical regularities of ceramics formation based on the BaO—Al2O3—SiO2 system by slip casting into gypsum molds, and also investigates the rheological properties of a slip based on сelsian and the physicochemical properties of products made from it. The samples were made according to the following technology: the first stage is synthesis of celsian in a muffle furnace at a temperature of 1200 °C with a maximum temperature holding for 2 hours. The synthesis products were ground in a planetary mill to a residue on the № 0063 sieve of no more than 0.2 %. Then, slips with different moisture content without additives and with the addition of 0.10, 0.15 and 0.20 wt. % thinning additive Dolapix PC 67 were made. The second stage is to obtain samples by casting slip into gypsum molds. Firing of products took place in a muffle furnace at a temperature of 1350 °C with a two-hour holding. The optimal amount of thinning additive in the celsian slip was determined, which corresponds to 0.10 wt. %. It was found that, in the studied area of technological parameters, the material acquires the best properties at a sample firing temperature of 1350 °C and is characterized by the following indicators: water absorption — 10.20 %, apparent density — 2.15 g/cm3, open porosity — 21.04 %.