Guniting the lining of heating furnaces of rolling mills

Conclusions Guniting mass compositions and a procedure for guniting worn brickwork of continuous heating furnaces of rolling mills have been developed. At a number of metallurgical factories the worn brickwork of eight continuous heating furnaces of rolling mills have been repaired by guniting. The use of guniting enables the period between furnace lining repairs to be doubled (from 1 to 2 years), the volume of brickwork repair and the length of the repair work to be reduced, and a saving of 5000 rubles per annum per furnace to be obtained (merely by reducing the amount of repair work).Using IR spectroscopy the authors have investigated hydration and dehydration in alumina and high-alumina cements and aluminosilicate guniting masses with additives of these cements. They have shown that during guniting by the semidry method, hydration of the cements included in the composition of the gunite coatings does not go to completion and ends in the stage of formation of CaO·Al₂O₃·10H₂O; dehydration of the gunite coatings is completed below 300°C.Translated from Ogneupory, No. 5, pp. 30–35, May, 1980.     

Fusion diagram for the pseudosystem CaO·Al2O3-MgO·Al2O3-MgO

Conclusions The use of statistical methods will considerably reduce the number of experiments needed to construct fusion diagrams, and yield good results.We constructed a calculation fusion diagram for the pseudosystem CaO·Al₂O₃-MgO·Al₂O₃-MgO in which we determined the region of optimum compositions for the cements of the highest refractoriness, which is interesting in relation to producing highly refractory cements with prescribed properties.Translated from Ogneupory, No. 4, pp. 27–28, April, 1989.     

Influence of CuO on the formation and coexistence of 3CaO·SiO2 and 3CaO·3Al2O3·CaSO4 minerals

The influence of CuO on the formation and coexistence of 3CaO·SiO₂ and 3CaO·3Al₂O₃·CaSO₄ minerals in Portland cement containing 3CaO·3Al₂O₃·CaSO₄ mineral is reported in this paper. The results show that a suitable amount of CuO can lower the clinkering temperature and improve the burn-ability of clinkers. It can also promote the formation of 3CaO·SiO₂ and 3CaO·3Al₂O₃·CaSO₄ minerals and facilitate the coexistence of the two minerals in the clinkers. But adding 1% CuO to the raw material can cause the decomposition of 3CaO·3Al₂O₃·CaSO₄.     

Resistance of corundum refractories to basic electric steel slags

Conclusions Upon reaction with slag corundum specimens exhibit a substitution of corundum by calcium hexa and di-aluminates. This process occurs most intensely in the bond part of the refractory and over the periphery of the fragment of fused corundum.The temperature of the eutectic between CaO·2Al₂O₃ and CaO·6Al₂O₃ is 1730 ± 10°C, and corresponds to the operating temperature of refractories in the slag belt of electric furnaces.The formation of calcium aluminates around the fragments of corundum and in the bonding part tends to reduce the refractories of the altered zones of material and the wear by fusion. Therefore corundum refractories are not reccomended for lining the slag belt of electric steel smelting furnaces.Translated from Ogneupory, No.5, pp. 41–44, May, 1970     

Influence of MgO on the formation of Ca3SiO5 and 3CaO·3Al2O3·CaSO4 minerals in alite-sulphoaluminate cement

The influence of MgO on the formation of Ca₃SiO₅ and 3CaO·3Al₂O₃·CaSO₄ minerals in alite-sulphoaluminate cement is reported in this paper. The results show that adding a suitable amount of MgO can lower the clinkering temperature, promote the formation of Ca₃SiO₅ and 3CaO·3Al₂O₃·CaSO₄ minerals, and help in the coexistence of the two minerals in the clinker. MgO may obviously decrease the formation of Ca₃Al₂O₆, and increase the SiO₂ content incorporated into the interstitial phase.     

Fuel mixture approach for solution combustion synthesis of Ca3Al2O6 powders

Single-phase 3CaO·Al₂O₃ powders were prepared via solution combustion synthesis using a fuel mixture of urea and β-alanine. The concept of using this fuel mixture comes from the individual reactivity of calcium nitrate and aluminum nitrate with respect to urea and β-alanine. It was proved that urea is the optimum fuel for Al(NO₃)₃ whereas β-alanine is the most suitable fuel for Ca(NO₃)₂. X-ray diffraction and thermal analysis investigations revealed that heating at 300 °C the precursor mixture containing the desired metal nitrates, urea and β-alanine triggers a vigorous combustion reaction, which yields single-phase nanocrystalline 3CaO·Al₂O₃ powder (33.3 nm). In this case additional annealing was no longer required. The use of a single fuel failed to ensure the formation of 3CaO·Al₂O₃ directly from the combustion reaction. After annealing at 900 °C for 1 h, the powders obtained by using a single fuel (urea or β-alanine) developed a phase composition comprising of 3CaO·Al₂O₃, 12CaO·7Al₂O₃ and CaO.     

Molten cast materials of the Al2O3-MgO system

Molten cast alumomagnesia refractory materials containing up to 28.3% MgO (MgAl₂O₄) are investigated. It is shown that materials with 10–15% MgO have a complex structure and phase composition. The latter can be interpreted as a solid solution of corundum and spinel or as a combination of MgO · 2.5Al₂O₃. The behavior of these materials in molten TK16 and K8 glass is investigated.     

Changes in high alumina brick used in hot air stoves

Conclusions Aluminous brick made by the Semiluks Refractories Plant containing 60% Al₂O₃ sinters intensely, with sharp changes in properties and reductions in refractoriness from 1810 to 1750°C when used at temperatures of 1500–1600°C.The least-change zone and working zone of the refractory consist mainly of mullite and glassy substance. The amount of mullite increases in the direction from the least-change to the working zone.It is necessary to use high alumina refractories with a higher content of Al₂O₃ (70–72%), preferably with increased density, in order to increase the life of the linings in hot air stoves.Translated from Ogneupory, No. 6, pp.29–32, June, 1968.     

PhreeqC modeling of Friedel's salt equilibria at 23±1 °C

A series of slurries containing Friedel's salt (3CaO·Al₂O₃·CaCl₂·10H₂O) in equilibrium with other solids that include Al(OH)₃, Ca(OH)₂, and 3CaO·Al₂O₃·6H₂O were produced at room temperature (23±1 °C). The liquid phases were analyzed for calcium, aluminum, and chlorine, and the speciation program PhreeqC was used to model the equilibria that were established between the solid and liquid phases. By matching closely, the experimentally determined solution parameters with those calculated using PhreeqC, important information concerning equilibria in the CaO-Al₂O₃-CaCl₂-H₂O system was obtained. For example, it was shown that the stable phase pair, Friedel's salt/3CaO·Al₂O₃·6H₂O, acts to buffer against rising chloride concentrations by acting as a chloride sink. PhreeqC calculations have estimated the solubility product of Friedel's salt to fall within the range −28.8<log K_sp<−27.6.     

The solubility of selenate-AFt (3CaO·Al2O3·3CaSeO4·37.5H2O) and selenate-AFm (3CaO·Al2O3·CaSeO4·xH2O)

The Se(VI)-analogues of ettringite and monosulfate, selenate-AFt (3CaO·Al₂O₃·3CaSeO₄·37.5H₂O), and selenate-AFm (3CaO·Al₂O₃·CaSeO₄·xH₂O) were synthesised and characterised by bulk chemical analysis and X-ray diffraction. Their solubility products were determined from a series of batch and resuspension experiments conducted at 25 °C. For selenate-AFt suspensions, the pH varied between 11.37 and 11.61, and a solubility product, log K_so=61.29±0.60 (I=0 M), was determined for the reaction 3CaO·Al₂O₃·3CaSeO₄·37.5H₂O+12 H⁺⇔6Ca²⁺+2Al³⁺+3SeO₄²⁻+43.5H₂O. Selenate-AFm synthesis resulted in the uptake of Na, which was leached during equilibration and resuspension. For the pH range of 11.75 to 11.90, a solubility product, log K_so=73.40±0.22 (I=0 M), was determined for the reaction 3CaO·Al₂O₃·CaSeO₄·xH₂O+12 H⁺⇔4Ca²⁺+2Al³⁺+SeO₄²⁻+(x+6)H₂O. Thermodynamic modelling suggested that both selenate-AFt and selenate-AFm are stable in the cementitious matrix; and that in a cement limited in sulfate, selenate concentration may be limited by selenate-AFm to below the millimolar range above pH 12.     

Large-scale fine structural alumina matrix ceramic guideway materials improved by diopside and Fe2O3

Diopside and Fe₂O₃ were introduced in alumina matrix ceramic materials. Large-scale fine structural alumina matrix ceramic guideway materials were fabricated by the technology of pressureless sintering, during which liquid phase sintering took place and new phases such as 3Al₂O₃·2SiO₂, CaO·Al₂O₃·2SiO₂ and CaO·6Al₂O₃ were produced by the chemical reactions taking place among alumina and the additives. The hardness, the fracture toughness and the bending strength of the guideway products were tested. The influences of diopside and Fe₂O₃ additions were studied by microstructural observations and mechanical properties evaluations. Meanwhile, the expected improvement of mechanical properties compared with pure alumina was indeed observed. The fracture mechanism and porosity of large-scale fine structural alumina matrix ceramic guideway materials were analyzed.     

Thermal Expansion and Glass Transition Temperature of Calcium Borate and Calcium Aluminoborate Glasses

The thermal expansion (the temperature coefficients of linear expansion for solid glasses and the structural temperature coefficients of linear expansion) and the glass transition temperatures are studied for glasses in the CaO–B₂O₃ and CaO–B₂O₃–Al₂O₃ systems. The results obtained are compared with the available data for barium borate and barium aluminoborate glasses. The revealed dependences are interpreted within the concepts of the borate glass structure.     

Thermoanalytical and infrared spectroscopy investigations of some mineral pastes containing organic polymers

The interaction in the presence of water between organic polymers [two polyvinyl alcohol acetate (PVA1 and PVA2)-, one polyvinyl acetate (PVAc)-, and one acryloethyl-metacrylomethyl (R)-type copolymers] and inorganic materials (3CaO·Al₂O₃+CaSO₄·2H₂O, 12CaO·7Al₂O₃, and CaO·Al₂O₃) was investigated using complex thermal analyses and infrared (IR) spectroscopy. The DTA curves of the 1-to 28-day-hydrated organo-mineral composite samples showed some significant differences in comparison with those of the hydrated inorganic materials. The most important differences consist in the presence of some exothermic peaks that are not attributable to the pure organic polymers. More than that, none of the specific effects of the pure organic polymers are evidenced on the DTA curves of the hydrated organo-mineral composite materials. This, in connection with their IR spectra, which clearly evidence the disappearance of some investigated polymers specific IR bands, can be considered as an indirect evidence of the cross-linking of polymer chains via metal ions.     

Thermomechanical properties of ceramics in the systems Al2O3-TiO2 and Al2O3-TiO2-mullite

Conclusions We studied certain properties of ceramics in the systems Al₂O₃-TiO₂ and Al₂O₃-TiO₂-mullite, obtained by the use of the double-stage synthesis of aluminum titanate.We established the nature of the change in the high-temperature strength in relation to the ratio of Al₂O₃ and aluminum titanate. The maximum high-temperature strength (bending) at 1200°C is possessed by ceramic with a corundum matrix and a volume proportion of aluminum titanate equal to 40–45%.It is established that the addition of CaO + SiO₂ made in amounts of up to 1.0–1.5% contributes to the partial breakdown of the aluminum titanate in the compositions Al₂O₃-TiO₂ and the production of a ceramic with a bending strength of 160–190 N/mm² at 20–200°C, thermal-shock resistance 650–800°C, and thermal conductivity of 1.9–2.1 W/(m·K).We studied the effect of the mullite concentration on the properties of the ceramic in the system Al₂O₃-TiO₂-mullite. The introduction of mullite in amounts of not more than 50%, containing up to 3% of impurities, contributes to an increase in the ceramic's strength in the range 20–1300°C and in the thermal shock resistance.Translated from Ogneupory No. 2, pp. 22–26, February, 1988.     

Utilization of borogypsum as set retarder in Portland cement production

Boron ores are used in the production of various boron compounds such as boric acid, borax and boron oxide. Boric acid is produced by reacting colemanite(2CaO·3B₂O₃·5H₂O) with sulphuric acid and a large quantity of borogypsum is formed during this production. This waste causes various environmental problems when discharged directly to the environment. Portland cement is the most important material in the building industry. This material is produced by adding about 3-5% gypsum (CaSO₄·2H₂O) to clinker as a set retarder. The aim of this study was to stabilize borogypsum, and to produce cements by adding borogypsum instead of natural gypsum to clinker. Concrete using cement produced with borogypsum was tested to find the mechanical properties and the test values were compared with those of concrete from cement with natural gypsum. Compressive strength of concrete from cement produced with borogypsum was found to be higher than that of natural gypsum. Also, the setting time of cement with borogypsum was longer than that of the Portland cement.     

Hydration characteristics of waste sludge ash utilized as raw cement material

In this study, the hydration characteristics and the engineering properties of three types of eco-cement pastes, including their compressive strength, speciation, degree of hydration, and microstructure, were studied and compared with those of ASTM type I ordinary Portland cement. The results indicate that it is feasible to use sludge ash and steel-making waste to replace up to 20% of the mineral components of the raw material of cement. Furthermore, all the tested clinkers met the toxicity characteristic leaching procedure requirements. The major components of Portland cement, C₃S (i.e., 3CaO·SiO₂), C₂S (i.e., 2CaO·SiO₂), C₃A (i.e., 3CaOAl₂O₃) and C₄AF (i.e., 4CaO·Al₂O₃·Fe₂O₃), were all found in the waste-derived clinkers. All three types of eco-cements were confirmed to produce calcium hydroxide (Ca(OH)₂) and calcium silicate hydrates (CSH) during the hydration process, increasing densification with the curing age. The thermal analysis results indicate that the hydration proceeded up to 90 days, with the amount of Ca(OH)₂ and CSH increasing. The chemical shift of the silicates, and the resultant degree of hydration, and the increase in the length of the CSH gels with the curing age, were confirmed by ²⁹Si NMR techniques. Compressive strength and microstructural evaluations confirm the usefulness of eco-cement.     

Effect of phosphoric acid concentration on some properties of finely milled refractory materials

Conclusions The concentration of phosphoric acid seriously affects the setting, weakening, and sintering of the finely milled refractory materials.Increasing the acid concentration boosts the setting rate of alumina, MgO·Al₂O₃, chromite, electrocorundum, dunite, and dinas, but hardly affects the setting of MgO, Cr₂O₃, magnesite, zircon, and quartzite.The materials that were studied are almost unaffected at 800°C. Increasing the concentration of H₃PO₄ improves the sintering of alumina, MgO·Al₂O₃, chromite, zircon, and dinas, but impairs the sintering of MgO, Cr₂O₃, magnesite, electrocorundum, dunite, and quartzite.Translated from Ogneupory, No.3, pp. 40–43, March, 1968.     

Mortars for zirconia refractories

Conclusions The composition was developed for a mortar based on zirconium dioxide and orthophosphoric acid intended for laying zirconia refractories. The filler should be stabilized ZrO₂ powder of a particle size below 0.5 mm with 10% monoclinic fine-grain ZrO₂ mixed with orthophosphoric acid added in the proportion of 2–4% in terms of P₂O₅.The mortar was tested with zirconia refractory linings and gave satisfactory results.Owing to its low water retention capacity and short setting time Ca₇Al₆ZrO₁₈ cement cannot be recommended for a zirconia base mortar.Translated from Ogneupory, No. 8, pp. 52–59, August, 1973.     

The effect of fluoride ions on the structure and crystallization kinetics of La2O3-containing diopside based oxyfluoride glasses

Oxyfluoride glasses in the system CaO–MgO–BaO–SiO₂–Al₂O₃–La₂O₃–CaF₂ were obtained by adding CaF₂ (3–8 wt%) to a parent diopside based glass composition, Ca_0.8Ba_0.1MgAl_0.1La_0.1Si_1.9O₆. The characterization of the glasses has been made by density, dilatometry and FTIR measurements. Non-isothermal crystallization kinetic studies in conjunction with XRD and SEM have been employed in order to investigate the effects of fluoride ion additions on crystallization behaviour and mechanism of glasses.     

Cast refractories of the Al2O3-Cr2O3-CaO system

Conclusions In order to develop stable materials for glassmaking, we studied the physical and technological properties of the refractories belonging to the Al₂O₃-Cr₂O₃-CaO system that contain 5–20% CaO, 15–35% Cr₂O₃ and 45–80% Al₂O₃.The glass resistance of the refractories of the experimental systems (compositions) exceeds that of the BKCh-33 baddeleyite-corundum products by 3–5 times and their thermal shock resistance is superior to that of the well known chromium-containing refractories at comparable levels of mechanical properties.The developed refractories are recommended for the top or the bottom structures of the glassmaking furnaces depending on their glass resistance and thermal shock resistance and for making the refractory components of ferrous metallurgical units that are in contact with highly basic slags.Translated from Ogneupory, No. 3, pp. 23–26, March, 1989.