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 investigation of the type and amount of the new active aluminas addition on the properties of products from low-cement corundum chromium-containing castable mass

The influence of new active aluminas addition (NABALOX NO 635 and NABALOX NO 713-10 MF) and its amount on the properties of non-burning and fired at 1580 оC samples has been studied. It was established that, the compressive strength of non-burning samples, depending on the type and amount of the active alumina addition, is maximal when 5 % of the active alumina NABALOX NO 635 is added. After high-temperature firing, the densest structure is formed in the samples of this composition, as evidenced by their indices properties: open porosity of 23.3 %, apparent density of 3.03 g/cm3, compressive strength of 115 N/mm2. As a result of the carried out researches, the technology of products manufacturing by vibrocasting method from the low-cement corundum chromium-containing castable mass has been improved by adding the new active alumina of NABALOX NO 635 instead alumina grade of CTC-40. This technology provides manufacturing of products with higher compressive strength (115 vs. 104 N/mm2) and a larger apparent density (3.03 vs. 3.02 g/cm3) with substantially equal open porosity values compared to those of earlier manufactured products containing of active alumina addition grade of CTC-40. Based on the economic feasibility, as well as the availability and the possibility of purchasing NABALOX NO 635 alumina in small batches on the domestic raw materials market (“Nabaltec AG”, Germany, has a representative office in Ukraine), its use for manufacture of the low-cement corundum chromium-containing castable mass is more preferable compared to with the previously used active alumina grade of CTC-40 produced by “Almatis GmbH” (Germany). As a result of the carried out researches, normative documentation has been developed. According to this documentation, in the conditions of PJSC “UKRNIIO NAMED AFTER A. S. BEREZHNOY” full-scale samples of products characterized by high properties were produced: compressive strength after hardening in humid conditions for 7 days of 63 N/mm2, open porosity of 23.3 %, an apparent density of 3.03 g/cm3, compressive strength after firing at a temperature of 1580 оC of 94 N/mm2.