Effect of chromite additives on the properties of a high-alumina tamping mass

Conclusions The physicochemical properties of a high-alumina tamping mass with the addition of chromite have been studied. The optimum grain composition of the batch has been checked.It is shown that the addition of 10% chromite helps to produce a tamping mass with optimum characteristics in relation to strength, porosity, density, and thermal-shock resistance.Translated from Ogneupory, No. 3, pp. 42–44, March, 1981.     

Corundum wash for repairing carbon reactor linings

Conclusions We developed a body composition from electrocorundum and phosphoric acid. The body is well bonded to high-alumina refractories, and after heat processing has a high thermal-shock resistance and strength.The use of this body as a wash for the high-alumina (62% Al₂O₃) lining of reactors used in carbon production increases the service life by not less than 60%.Translated from Ogneupory, No. 3, pp. 27–33, March, 1969.     

Gas-flame guniting of the lining of intermediate continuous steel-casting ladles

Conclusions As a result of laboratory investigations and rig testing of the flame guniting of intermediate ladles for continuous steel-casting plant we recommend the following bodies: 90% corundum, 10% sodium tripolyphosphate; 80–90% corundum, 20–10% chamotte; 80–90% high-alumina chamotte, 20–10% chamotte. The particle size of the corundum body is <0.088 mm, high-alumina <0.25 mm.The optimum guniting cycle is: consumption of natural gas 60 m³/h, oxygen 100 m³/h, gunite body 150–200 kg/h, guniting distance 450–550 mm, rate of moving the burner 1.0 m/min.In the case of chamotte, the coefficient of gunite body utilization equals 0.75, for high-alumina 0.70, and for corundum 0.40, with an open porosity in the gunite coating of 10–15, 8–10,and 4–6%, respectively.Using the experimental equipment the body made from 90% corundum and 10% sodium tripolyphosphate was used to gunite the side surface of the lining of an intermediate ladle. The wear of the gunite section of the lining was 1.3–2.5 mm per heat.Translated from Ogneupory, No. 4, pp. 37–42, April, 1973.     

Scale resistance of some refractory concretes

Conclusions The scale resistance of refractory concretes when the latter interact with molten scale varies, and is primarily determined by the composition of the concretes. The highest scaleresistance is found in the dunite concretes and the lowest in the high-alumina; the chromemagnesite, chromite, and corundum concretes occupy the intermediate position.The scale in the solid state hardly interact with the concretes at all.The wear of the high-alumina and corundum concretes by molten scale occurs as the result of the formation of FeO·Al₂O₃ hercynite which forms a low-melting eutectic with the iron oxides (hercynite-wustite eutectic at 1330°C); hercynite is next replaced by magnetite and hematite which, after changing into FeO, form low-melting fayalite 2FeO·SiO₂ with SiO₂. The process of hercynite-formation and its replacement by iron oxides are accompanied by an increase in volume of roughly 16% and this leads to the swelling and deformation of the concretes.The wear of the chrome-magnetite and chromite concretes is accompanied by the appearance of new formation of the magnomagnetite and high-iron chrome-spinel type.Translated from Ogneupory, No. 1, pp. 43–47, January, 1979.     

Effect of binder type and other parameters in synthesis of magnesite chromite refractories from process waste

Recycling of the process waste in basic refractory production will not only make it possible to put the waste substances to use but also help to solve the problems of environmental pollution and storing. This paper is the first part of a study on using the magnesite and chromite dusts in refractory production, accumulated in −10⁻³ m and finer particle fraction as process waste at the Konya Chrome-Magnesite Plant. In this work, three different MgO and Cr₂O₃ compositions were studied. Magnesite ore is added to the mixture without any thermal process. The type and proportion of the bond to be used, particle size distribution of the magnesite and chromite ores and the influence of compaction pressure on the refractory properties were examined. Consequently the influence of the changes in the mixture composition and sintering temperature on refractory properties was studied. The results of the experiments revealed the optimum type and content of the bond as MgSO₄·7H₂O and 8%, and optimum pressing pressure of the materials containing raw magnesite at 250 MPa. It was observed that when the chromite content of the material composition increased from 10 to 28% and 50%, the cold crushing strength (CCS) of the material has decreased, yet its porosity (P%) increased. This improves when the sintering temperature increased from 1450 to 1550 °C and 1750 °C. The optimum sintering temperature was found at 1750 °C     

Production and properties of high-alumina ceramic concrete

Conclusions A high-alumina ceramic concrete containing ACBS based on the waste products of the high-alumina products industry and on a filler with D _s ^gr =2.5–15.0 mm of an analogous chemical composition has been obtained. The combination of studied properties suggests that new ceramic concrete shows promise for use in heat assemblies of various designs.Translated from Ogneupory, No. 2, pp. 54–56, February, 1982.     

A high-alumina mass for gunniting the lining of steel-casting buckets

Conclusions The composition for a high-alumina gunniting mass with an Al₂O₃ concentration of 65% was developed on the basis of chamotte obtained by firing the natural raw material. The production of the high-alumina gunniting mass was organized at the Semiluksk Refractory Plant.The process for gunniting 180-ton steel-casting buckets using the new gunniting mass has been mastered and introduced at the Novolipetsk Metallurgical Plant. An increase by 2.88 smeltings was achieved in the average resistance of the bucket linings with a once-only gunniting during the campaign.Translated from Ogneupory, No. 3, pp. 15–18, March, 1982.     

Changes in the magnetic properties of chromite ore heated with scale

Conclusions Chrome spinel and gangue of Kimpersarski chromite ores has a low and scarcely distinguishable magnetic susceptibility which does not alter after heating at temperatures from 400° to 1300°C. The magnetic susceptibility of the ores fired with additions of iron oxide or scale at 1000–1300°C increases from (20–120)×10^–6 to (1650–3400)×10^–6 cm³/g. The increase in the magnetic properties of chromite ores after firing occurs on account of the increase in the magnetic susceptibility of the gangue from (50–120)×10^–6 to (6000–8000)×10^–6 cm³/g. Thus after firing of chromite ores with iron-containing additives the gangue acquires ferromagnetic properties. The magnetic susceptibility of the gangue is 50–115 times greater than chrome-spinel which permits us to use highly productive magnetic separators with low and medium magnetic field forces for their treatment.     

Thermoreactive compaction of an alumina — Polymethylsiloxane composition

Conclusions An investigation was carried out of the thermoreactive compaction of a composition of alumina with polymethylsiloxane, the technological parameters being varied. Before a heat treatment the open porosity of specimens containing 20% PMS is 0.8%, the bending strength 260 kgf/cm², and the cold-crushing strength 1070 kgf/cm².Firing at 1700°C gave a high-alumina composition ceramic with an open porosity of 2%, a bending strength of 1000 kgf/cm², a cold-crushing strength up to 5000 kgf/cm², and a thermal-shock resistance of 14–20 reversals from 1300°C into water (in tests with specimens).Translated from Ogneupory, No. 5, pp. 47–50, May, 1978.     

Investigation of TiO2-added refractory brick properties from calcined magnesite raw material

This paper is the second part of a study on recycling magnesite and chromite ore (in the 0–10⁻³ m fraction) powder, which remains as a production process waste. In this work, 90% magnesite-10% chromite composition was used as a brick composition. Compaction pressure, sintering temperature, ratio of TiO₂ addition, and influence of bonding type on refractory properties were examined. In refractory brick production, one of the most important parameters that affects the properties of the product is the particle size distribution of the blend. Experiments show that using a magnesite particle size of −10⁻³ m and a chromite particle size of −63×10⁻⁶ m affects the properties of the product in a positive way. Experiment blends with the particle sizes selected above were used. Magnesite ore was used in experiments after calcination at 1200°C for four hours. In the experiments we mention, MgCl₂ and MgSO₄ solutions were used as a bonding agent, as a result of which a 6% bonding ratio of MgCl₂ and MgSO₄ solutions was determined as optimum. The effect of compacting pressure on the refractory properties was studied, and the optimum compacting pressure was determined as 180 MPa. For bricks prepared using calcined magnesite, the optimum sintering temperature was found to be 1750°C. The positive effect of TiO₂ addition on the magnesite chrome refractory brick structure has been reported in the literature. Thus, 1, 3, 5, and 7 wt.% TiO₂ ratios were used in the blend, and the refractory properties were positively affected by the 3% TiO₂ addition. Taking the result of the MgCl₂ and MgSO₄ bonding solution into consideration, it is clear that the refractory properties of brick can be improved by using a mixture of MgCl₂ and MgSO₄ bonding solutions. In light of the above concept, bonding mixtures with 1:3, 1:5, and 1:10 ratios were prepared, and these bonding mixtures were studies as a bonding material. The experimental results show that the cold crushing strength (CCS) and volume density of bricks increase, whereas the porosity decreases when a 1:5 ratio of MgCl₂ and MgSO₄ in the bonding mixture and 3% TiO₂ addition were used. Microstructural study of the produced bricks was done using scanning electron microscope (SEM). In addition to this, the phases forming the structure of brick were examined via x-ray diagrams of the material. In bricks where a mixture of a 1:5 MgCl₂: MgSO₄ bonding solution was used as bonding agent and 3% TiO₂ was added, spinel (magnochromite (MgCr₂O₄)), magnesium orthotitanate (Mg₂TiO₄), monticellite (CaMgSiO₄), and forsterite (Mg₂SiO₄) phases were found. The perovskite phase was not observed during the experimental study. Translated from Novye Ogneupory, No. 7, pp. 56–60, July 2008.     

Electrofused refractory based on tumanyan stoney clay and commercial alumina

Conclusions A technology was developed for making fused-cast refractories of mullite composition from stone-like Tumanyan clays and commercial alumina for the structures of the lower courses of the walls of glass tank furnaces. The experimental refractories are 50–100% more glass resistant than normally used fireclay and high-alumina refractories made by the ceramic technology. The introduction into the composition of the batch of up to 10% ZrO₂ does not greatly improve their properties.According to approximate calculations, the use of electrofusion cast mullite experimental refractories is economically desirable.Translated from Ogneupory, No. 3, pp. 21–25, March, 1967.     

Properties of compositions based on the system Al2O3-Mg(Al1−x,Crx)2O4

Conclusions Magnesia-alumina spinel and highly chromic spinel MgAl_0.4Cr_1.6O₄ and MgCr₂O₄ retard the grain growth of corundum during firing of the product. Low-chromic spinel MgAl_1.6Cr_0.4O₄ and MgAlCrO₄ added in small quantities intensify the corundum recrystallization.Small (5–10% by weight) additions of spinel Mg(Al_1–x, Cr_x)₂O₄ increase the strength of the corundum specimens, but only the high-alumina spinel improves their sintering.The sintering of mixtures of Al₂O₃ and Mg(Al_1–x Cr_x)₂O₄ is impaired during the substitution of magnesia-alumina spinel by magnesia chromite, and with an increase in the quantity of spinels from 5 to 30%.A small addition (5–10%) of high-alumina spinel of the composition Mg(Al_1–x, Cr_x)₂O₄ where x 0.5 to the alumina precalcined at 1450°C enables us to obtain dense, strong, and thermally shock-resistant corundum products.Translated from Ogneupory, No. 3, pp. 53–56, March, 1972.     

Methane combustion over copper chromite catalysts

A study of the activity and durability of two different copper chromite catalysts in methane combustion is presented. The catalysts, a massive (CAT-E) and a supported (CAT-I) copper chromite, were characterized by different techniques in order to investigate morphological properties (N₂ adsorption), crystalline structure (X-ray diffraction, XRD) and surface composition (X-ray photoelectron spectroscopy, XPS). Among the different crystalline phases identified, CuCr₂O₄ spinel represented the common phase in both the catalysts. The Cr^VI/Cr^III surface ratio was almost the same for the two catalysts, while the Cu^II/Cu^I surface ratio was much higher on the massive catalyst than on the supported one. The activity for CH₄ combustion was studied in the temperature range 300-700°C at constant CH₄:air ratio of 1:30 and constant methane content, 1.2%. The activity was higher for CAT-I and CAT-E showed better stability. A kinetic study from the catalytic data, collected at different contact times in the interval 0.047-0.315 s as a function of temperature, provided a value of about 110 kJ/mol for the activation energy. This value was obtained for various degrees of methane converted for the two catalysts. The reaction rates were between 10^-3 and 10^-4 (mol_CH4)_conv/(g h) in the temperature interval 550-700°C, for both the catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnesite refractory with a high CaO content

Conclusions Chromite, added in amounts of 10% to dolomitic magnesite containing 8.35% CaO by bonding with it completely during firing, is an effective stabilizer.An increase in the chromite content of the batch of more than 10% lowers the quality of the refractory.The hydrothermal treatment of the calcined dolomitic magnesite with 10% chromite accelerates the process of hydrating the free CaO and disperses the material, which helps the refractory to sinter during firing.The proposed technique provides for combined grinding and firing of a mixture of dolomitic magnesite with chromite, excludes aging of the body, reduces the firing temperature of the body and increases the quality of the refractory compared with the periclase-spinel technique.The calcium oxide in dolomitic magnesite with the addition of 10% chromite is bonded mainly with theCr₂O₃ into calcium oxychromite 9CaO · 4CrO₃ · Cr₂O₃ and the ferric oxide is introduced into the lattice of the periclase with the formation of a solid solution. With 30% chromite in the batch 3CaO · 2CrO₃ · 2Cr₂O₃ is formed, and the ferric oxide enters the magnesio-ferrite.Calcium oxychromite, existing in the refractory with 10% chromite and being a secondary phase, at its fusing temperature (>1250–1290°C) reversibly converts to calcium monochromite with a fusing temperature of 2170°C, which explains the increase in the refractoriness under load.     

High-temperature stable inverse opal photonic crystals via mullite-sol-gel infiltration of direct photonic crystals

Three-dimensionally ordered macroporous materials for photonic or refractory applications have been developed by an innovative approach based on mullite sol-gel infiltration of direct photonic crystals followed by burn-out and calcination. Direct photonic crystals were obtained using polystyrene spheres templates either by vertical convective self-assembly or by drop casting. The samples were then infiltrated by spin coating with mullite sol-gels prepared with two different compositions (74 wt.% Al₂O₃, 26 wt.% SiO₂ and 80 wt.% Al₂O₃, 20 wt.% SiO₂). The inverse opal photonic crystals prepared with both sol-gels presented a highly ordered porosity and the high-alumina composition showed stability up to 1500°C. After inversion of the structure (polymeric template burn-out), the high-alumina composition showed roundness of the PS templated pores closer to an ideal sphere (Ø = 0.967) when compared to the low-alumina composition (Ø = 0.954). Although the inverse opal photonic crystals did not present a photonic bandgap, they showed structural stability at high temperatures, which enable their application as refractory materials.     

Research in the production of periclase-chromite refractories from beneficiated raw materials

Conclusions Laboratory and technological investigations of periclase-chromite refractories produced from beneficiated starting materials were carried out for the purpose of defining more precisely the required grainsize distribution of the starting components of the mix. The structural characteristics (the nature of the porosity, the development of a fragmented macro- and microstructure, and the formation of a direct intergranular bond) were analyzed in relation to the composition and grain-size distribution of the mix.The process of the formation of direct chrome-spinel-periclase bonds depends primarily on the firing temperature. The degree of the development of direct bonds can be regulated, however, by varying the composition of the mix in addition to which the process can be intensified by adding some of the chromite to the fine-ground part of the mix and increasing the proportion of coarse-grained chromite. An increase in the molding pressure and a decrease in the upper limit of the coarseness of the granular chromite also contribute to the formation of direct bonds.To ensure that the properties of the refractories, more particularly the thermal-shock resistance, are as required and that the standard specifications for the Cr₂O₃ content are met the proportion of the granular chromite in the mix must be 10–15% and that of the fine-ground component 5–10%. It will be necessary to verify the compositions in production conditions and to investigate the durability of the refractories in service.Translated from Ogneupory, No. 7, pp. 30–38, July, 1978.     

Dispersing (Deflocculating) Aluminas

The rheological properties of aqueous suspensions of a reactive alumina and high-alumina cements have been studied, and a method for evaluating the thinning effect due to agents used to deflocculate ceramic casting systems has been developed; a classification of thinning agents is proposed. Alumina dispersants make it possible to decrease the moisture content of Al₂O₃ suspensions by 50 – 60 rel.% and increase their volume concentration from 0.50 to 0.65. The characteristics of dispersing aluminas used for the thinning (deflocculation) of new refractory castables containing Al₂O₃ (76 – 96%) and organic deflocculants are given. Suspensions based on four types of dispersants (with a moisture content of 19 – 25%) exhibiting a thixotropic flow behavior are considered.     

Experimental casting of multichamotte refractories from slip

Conclusions The possibility of casting refractories from multichamotte slip with a maximum moisture content of 15% has been investigated; a preliminary treatment of the slip under vacuum is recommended as well as a brief vibration of the gypsum molds within a certain period after pouring.The high rate of moisture loss and solidification of multichamotte slip castings allow production on an industrial scale.Multichamotte kaolin mixtures yield castings up to 100 × 80 × 80 mm which acquire the following properties after firing at 1470° C: bulk density –2.17–2.26 g/cm³; porosity –12 to 18%; compressive strength –420 to 800 kg/cm²; loss on ignition –2. 7 to 4. 3; total shrinkage in relation to the size of gypsum molds –4 to 5%.The casting process is of practical value for the manufacture of multichamotte products (including high-alumina refractories) since molding the latter by means of pressing is either impossible or extremely difficult.Industrial tests are conducted for the verification and more accurate determination of technological parameters and the technical and economic effectiveness of the method.     

Effect of reaction of periclase and iron-chrome spinel on the properties of periclase-spinel refractories

Conclusions Using a typical composition of the type MgO-Mg(Al_1–x–yCr_xFe_y)₂O₄ a study was made of the effect of the processes involved in the processing and decomposition of solid solutions of periclase and spinels on the technical properties of the fired products.During cooling from 1600–1750°C decomposition occurs in the solid solutions of periclase and spinel; the crystals of spinel separating under these conditions are able to grow to large sizes which inevitably should lead to the development of stresses inside the periclase grains.The decomposition of the solid solution of periclase and spinel adversely affects the strength and thermal-shock resistance of the fired specimens.The best technical properties are possessed by combinations of periclase with small (up to 15%) quantities of high-alumina (x=0.16 and 0.46) spinels.The use of compositions of periclase with high-alumina spinels of the type x=0.16 and 0.46 enables us to obtain denser and more thermal-shock resistant refractories.Translated from Ogneupory, No.6, pp. 44–47, June, 1970.     

Study of the service of high-alumina and kaolin refractories in the checkers and structure of blast-furnace stoves

Conclusions The structure of kaolin brick in the high-temperature zone of the stove after 6.7–7.2 years service at subcupola temperatures of 1300°C underwent substantive external and structural changes.In the structure of the stove made from high-alumina brick VGO-62 after six years service we detected substantially less change.In the kaolin brick of the upper rows of the checker three clearly defined zones are formed: working (slag), impregnated with alkalis, the transition zone (porcelain-type), and the least-changed zone. During the service of high-alumina refractories mullite crystallizes, which confirms the results of work carried out previously.Owing to the creep of kaolin and high-alumina refractories 4–5% shrinkage of the brick occurs in the upper rows of the checker, and at a depth of 2.5–6.0 m — 1.5–2.0%. The height of the checker diminishes under these conditions by 0.8–1.0 m.The densification of the structure of the upper rows of the checker corresponds to a reduction in porosity and an increase in the density of the brick.The temperature of initial deformation under load of 2 kg/cm² of the slagged kaolin refractories taken from the upper rows of the checker diminishes by 150–200°C, and in the lower layers of the checker it does not alter. This factor for high-alumina refractories in service increases by 160–190°C. In the high-temperature zone of the stoves it is desirable to test dense, high-alumina refractories containing 72–75% Al₂O₃.Translated from Ogneupory, No. 5, pp.14–19, May, 1972.