Krasnoufimsk dolomites as raw materials for metallurgical powder and tar-bonded dolomite products

Conclusions The chemical composition of Krasnoufimsk dolomite satisfies the requirements of GOST-10375-63 for dolomite raw material metallurgical class 1. The features of the dolomite are low SiO₂ content and low sesquioxide content.In its microstructure the dolomite is finely crystalline with a large amount of fauna residues substituted by finely grained dolomite.The dolomite in lumps and grains without additions will not sinter at 1600 and 1700°C. Adding 4% clinker yields a satisfactorily sintered product 5–20 mm in size.Preliminary fine grinding reduces the sintering temperature of the dolomite. A well-sintered product resistant to hydration, is obtained at a firing temperature of 1350°C after wet grinding and at 1450°C after dry grinding. The low SiO₂ and sesquioxide content and the high calcium-oxide and magnesia contents suggest that it is possible to use this dolomite as a raw material for making tar-bonded dolomite refractories.In connection with this it is necessary to arrange wide and detailed investigations of Krasnoufimsk dolomites as a technological material for making metallurgical powders and refractory products.     

Tar-bonded dolomite magnesite brick based on alekseev dolomite

Conclusions Raw dolomite from the Alekseev source has a relatively low silica content, and its chemical composition completely satisfies the requirements of MRTU 14-06-28-63 as a raw material for the production of unfired tarred dolomite refractories.Alekseev dolomite can be considered a well-sintered raw material for industrial use. Its firing under industrial conditions at 1700°C yields a well-sintered dense powder.During the tests of the prepared unfired tarred dolomite-magnesite products using Alekseev dolomite in a 50-ton oxygen converter, the life exceeded that obtained in converters of the same capacity at the Krivoi Rog Metallurgical Factory.The Alekseev dolomite can be used as a raw material for the production of unfired tarred dolomite refractories.Translated from Ogneupory, No.2, pp. 18–21, February, 1967.     

Limestones and dolomites from crimean deposits in the production of magnesium oxide from brines

Conclusions Laboratory and industrial tests have been made on eight representative samples of carbonate raw materials from Crimean deposits.To lower the impurity content in the starting raw material it is necessary to use preliminary enrichment by washing, with subsequent wet-screening, in use of the total raw material.The optimum calcining temperature for carbonate raw material with Crimean deposits is 1100–1200°C, and the slaking time of the calcined raw material is 15 min.Milk of lime obtained from samples of Balaclava limestone has the highest purity. The deposit is recommended as a source of auxiliary raw material in the production of magnesium oxide from brines. For use in the production of magnesium oxide from brines, the most promising of the Crimean dolomites investigated is the dolomite from the Pervomaisk deposit. The deposit is recommended for industrial tests aimed at exploring the possibility of replacement of limestones by dolomite.Translated from Ogneupory, No.4, pp. 19–23, April, 1968.     

Experimental study on a mortar. Temperature effects on porosity and permeability. Residual properties or direct measurements under temperature

This study is a part of a large experimental program intended to characterize the effects of increasing temperature upon the hydraulic properties of cement based materials. Initial gas permeability and porosity values of the used material, a normalized mortar with a water / cement ratio of 0.5, clearly show the material homogeneity after a drying phase at 60 °C. The initial permeability is moreover insensitive to confining pressure variation which is evidence of the absence of significant initial micro-cracking in which the flow could occur. Residual properties (at room temperature) were measured after thermal treatments at 150 or 250 °C. These heating phases lead to a clear increase in porosity and permeability being sevenfold its initial value after a 250 °C treatment. This increase in permeability comes from two distinct effects that can be experimentally highlighted: a pore widening observed with the Klinkenberg effect being lower and a micro-crack closure occurring with the increase in confining pressure. Permeability was also measured with gas injection in samples submitted to thermal loading and slightly confined (at 4 MPa). Three levels of temperatures were used: 25, 105 and 200 °C; in a first stage the permeability remained almost constant to finally significantly increased at 200 °C. At 105 °C there is a widening of pores observed with the Klinkenberg effect but not sufficient to vary the permeability. At 200 °C micro-cracks have occurred but their influence upon permeability is lower than for treated material. This is an effect of the confining pressure applied on the material during heating.     

Biodiesel production through transesterification over natural calciums

Transesterification of palm kernel oil (PKO) with methanol over various natural calciums, including limestone calcite, cuttlebone, dolomite, hydroxyapatite, and dicalcium phosphate, has been investigated at 60 °C and 1 atm. The study showed that dolomite, mainly consisting of CaCO₃ and MgCO₃, is the most active catalyst. The calcination temperature largely affected the physicochemical properties, as evidenced by N₂ adsorption-desorption measurement, TGA, SEM and XRD, and the transesterification performance of the resultant catalysts. It was found that the calcination of dolomite at 800 °C resulted in a highly active mixed oxide. CaO was suggested to be the catalytically active site responsible for the methyl ester formation. Under the suitable reaction conditions, the amount of dolomite calcined at 800 °C = 6 wt.% based on the weight of oil, the methanol/oil molar ratio = 30, and the reaction time = 3 h, the methyl ester content of 98.0% can be achieved. The calcined dolomite can be reused many times. The analyses of some important fuel properties indicated that the biodiesel produced had the properties that meet the standard of biodiesel and diesel fuel issued by the Department of Energy Business, Ministry of Energy, Thailand.     

Dolomite of the Skursk deposits

Conclusions Analyses were carried out of samples of dolomite from the Skursk deposits in the form of white, pale-gray, and gray rock of fine-grained, medium-grained, and consertal structures.Dolomite samples Nos. 1, 2, 5, 7, and 8 and T-1 conform to the specifications of raw dolomite intended for the production of tar-bonded dolomite refractories, and samples Nos. 3, 4, and 6 to those of the State Standard for raw metallurgical dolomite.The dolomite is not readily sintered. It can be sintered to apparent density 3 g/cm³ and over by firing the material in granular form, grain size 5–15 mm, at 1780°C without added scale and at 1700°C with added scale, or by firing it in briquets of fine-ground or caustic dolomite at 1750°C.Translated from Ogneupory, No. 4, pp. 22–24, April, 1978.     

Effects of Chinese dolomites on tar cracking in gasification of birch

To minimize tar in the producer gas from birch gasification at 700, 750 and 800 °C, four Chinese dolomites (Zhenjiang, Nanjing, Shanxi, Anhui) and a Swedish dolomite (Sala) used as reference were studied in a laboratory-scale atmospheric fluidized bed gasifier. The gasifier was equipped with a downstream fixed catalyst bed. The results imply that all dolomites but Anhui dolomite effectively decompose tar into gases. Anhui dolomite showed a low catalytic capacity to crack tar produced at 700 and 800 °C. The influence of various ratios of steam to biomass on tar content in the producer gas after passing over dolomite was studied. The tar cracking efficiency of the dolomites did not improve significantly with the ratio of steam to biomass in the region 0.11-0.52.     

Dolomite used as raw material to produce MgO-based expansive agent

In this paper, the manufacture of MgO-based expansive agent using dolomite as raw material was studied. The decomposition of dolomite was discussed at first by DTA-TG analysis and on the crystalline view. On the characteristics of decomposition of dolomite, the authors think it is possible to use dolomite as raw material, but the silica-bearing mineral is considered to combine the CaO released from dolomite to form silicate. The phases of MgO-based expansive agent are mainly MgO, C₂S and a little amount of CaO. The expansion of resulting expansive agents by autoclaving testing and hot water curing at 80 °C shows that the MgO-based expansive agents have desired expansion. If the burning temperature and burning time, dosage in cement are controlled according to the requirement of concrete construction, the MgO-based expansive agent can be used to compensate the shrinkage as designed.     

Obtaining a high-density clinker based on natural dolomite and magnesite

Conclusions The main parameters for the production from natural dolomite and magnesite of high-density synthetic periclase-lime clinker containing 20% CaO have been determined under laboratory conditions.It is shown that this clinker may be obtained by firing at relatively low temperatures ( 1500°C) briquettes based on a hydrated mixture of previously decarbonated and milled dolomite and magnesite. This technology should make it possible to produce a material with a uniform distribution of components and an apparent density of 3.3 g/cm³.Translated from Ogneupory, No. 4, pp. 52–56, April, 1979.     

The influence of calcination parameters on free calcium oxide content in natural hydroxyapatite

Effect of calcining temperature and time on the content of free CaO in hydroxyapatite of natural origin is presented. Hydroxyapatite was obtained from pork bones in the course of a three-stage process: hydrolysis with the application of lactic acid, pre-calcination at 600 °C and main calcination stage within the temperature range of 750-950 °C. Calcination was conducted in an electrically heated stationary chamber oven in air atmosphere and in a laboratory scale rotary kiln equipped with a gas burner. The FT-IR spectra confirmed that all organic substances were removed during the calcination process. An increase in free calcium oxide content in hydroxyapatite from 0.003% to 0.023% was caused by the increase of calcining temperature from 750 °C to 950 °C respectively. Calcining time at 950 °C gave a distinct impact upon free CaO content ranging from 0.014% (2 h) to 0.023% (3 h). Hydroxyapatite calcined in the rotary kiln contained the lowest amount of free calcium oxide: 0.002% (750 °C) and 0.003% (950 °C). A method of neutralizing of free calcium oxide, present in calcined hydroxyapatite powders of natural origin, through CaO transformation into hydroxyapatite by application of diluted thermic phosphoric acid has been developed.     

Cyclic calcination/carbonation looping of dolomite modified with acetic acid for CO2 capture

The dolomite modified with acetic acid solution was proposed as a CO₂ sorbent for calcination/carbonation cycles. The carbonation conversions for modified and original dolomites in a twin fixed-bed reactor system with increasing the numbers of cycles were investigated. The carbonation temperature in the range of 630 °C–700 °C is beneficial to the carbonation reaction of modified dolomite. The carbonation conversion for modified dolomite is significantly higher than that for original sorbent at the same reaction conditions with increasing numbers of reaction cycles. The modified dolomite exhibits a carbonation conversion of 0.6 after 20 cycles, while the unmodified sorbent shows a conversion of 0.26 at the same reaction conditions, which is calcined at 920 °C and carbonated at 650 °C. At the high calcination temperature over 920 °C modified dolomite can maintain much higher conversion than unmodified sorbent. The mean grain size of CaO derived from modified dolomite is smaller than that from original sorbent with increasing numbers of reaction cycles. The calcined modified dolomite possesses greater surface area and pore volume than calcined original sorbent during the multiple cycles. The pore volume and pore area distributions for calcined modified dolomite are also superior to those for calcined unmodified sorbent during the looping cycle. The modified dolomite is proved as a new and promising type of regenerable CO₂ sorbent for industrial applications.     

Electric insulating material for thermoelectrodes working in vacuum

Conclusions Yttrium oxide possesses better properties than alumina, zirconia, and magnesia, which means it can be recommended as an electric insulating material for high temperature thermocouples or as a construction material for high-temperature insulations, for instance, as a material for making sectors for protecting the inductor in vacuum electric furnace.In order to save material the yttrium oxide can be recommended for use only in the hottest zone with contact on the coolest side with the refractory components made from alumina, zirconium dioxide, and magnesia at temperatures up to 1700°C.The yttrium oxide can be successfully used as a stabilizing additive for zirconium dioxide in making heat-resistant components or vacuum-tight protective sheaths. This additive reduces the rate of volatilization of the solid solution of zirconia-yttria in vacuum at temperatures above 2000°C.Translated from Ogneupory, No. 5, pp. 50–53, May, 1970.     

Dolomites from the Alekseev deposits

Conclusions Two samples of Alekseev dolomite that were studied can be classified as DK-2 grade as specified by TU-14-2-232-77, and two samples DSM-1 as specified by OST 1484-82. Lime-periclase powder for converter refractories from sample 1T can be obtained by firing in a rotary kiln at 1720–1750°C; from sample 4T at 1750°C; and standard metallurgical dolomite grade DOM-1 as specified by OST 1485-82 from samples 2T, 3T — at 1700–1720°C.Sintering can be accelerated by finely grinding the dolomite with pelletizing and firing the pellets, or by adding about 2% iron slag to the fired lump dolomite.Translated from Ogneupory, No. 6, pp. 16–19, June, 1992.     

The effect of natural dolomite admixtures on calcium zirconate–periclase materials microstructure evolution

The reaction sintering mechanism of dolomite–zirconia mixtures was investigated using fine grounded dolomite raw material and zirconium powder. The used dolomite raw materials differed by the content of impurities (SiO₂, Al₂O₃ and Fe₂O₃ oxides). The microstructure evolution of MgO–CaZrO₃ and CaZrO₃ sintered materials was presented as a temperature function. One- and two-step firing processes of calcium raw materials powder mixed with chemically pure zirconium oxide were applied. The kinetics of reaction of CaZrO₃ synthesis was estimated by determining the “free” calcium oxide by chemical and XRD analysis. The densification process was evaluated by firing shrinkage, apparent density, pore diameter and pore size distribution measurements. The microstructure of sintered materials was observed by SEM. It was observed that CaZrO₃ synthesis was definitely finished at temperature of 1500 °C in the both applied ways of the synthesis (one- or two-step process). The only phase present in the model material synthesized from chemically pure reagents (CaCO₃ and ZrO₂) after firing at temperature of 1500 °C was calcium zirconate.In the materials synthesized from natural dolomites and ZrO₂ two main phases were present—calcium zirconate and periclase. During firing of CaZrO₃–MgO materials at lower temperatures the presence of transient phases was detected (mainly ferrites and calcium aluminates, 4CaO·Al₂O₃·Fe₂O₃ or 2CaO·Fe₂O₃). These phases disappeared at higher temperatures. This is probably related to the dissolution of impurities in the main phases of CaZrO₃–MgO.The material obtained from the mixture of zirconium oxide and natural dolomite with the high impurities content has the highest densification level (～95% theoretical density of CaZrO₃–MgO) at 1500 and 1600 °C.     

X-ray absorption spectroscopy studies of nickel oxide thin film electrodes for supercapacitors

Nickel oxide films were synthesized by electrochemical precipitation of Ni(OH)₂ followed by heat-treatment in air at various temperatures (200-600 °C). Their structure and electrochemical properties were studied by cyclic voltammetry, X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). XRD results showed that the nickel oxide obtained at 250 °C or above has a crystalline NiO structure. The specific capacitance of the oxide depends on the heat-treatment temperature, showing a maximum value at 300 °C. XAS results revealed that the non-stoichiometric nickel oxide (Ni_1−xO) approached the stoichiometric NiO structure with increasing heat-treatment temperature due to the defect healing effect. The defective nature of the nickel oxide could be utilized to improve its specific capacitance for supercapacitor application.     

Some features of tar-bonded dolomite refractories

Conclusions Bloating and cracking of tar-bonded dolomite refractories during storage, especially in summer, is apparently due mainly to internal hydration of free lime in the body by water formed as a result of the reaction of the lime with organic acids in the pitch-anthracene bond.Keeping freshly pressed tar-dolomite products at 5–8°C for 12–24 h increases their resistance to cracking, due to the internal hydration of the lime. Therefore, it is desirable to test this variant of processing the products in the summer and to compare the results with those from preparing tar-dolomite goods with bodies which have been stored for a long time before pressing at 20°C. This makes it possible to assess the technical and economic factors of producing tar-dolomite brick.Converters should be lined with an edge structure which gives denser wetting of the brick in the ring on account of bloating and a reduction in the thickness of the joints between the rings of the structure owing to the lower variation over the thickness of the brick which results from the constant dimensions of the press mold.A discussion.     

Suitability of Zavadov deposit dolomites for use as raw material

Conclusions Investigations of raw Zavadov deposit dolomite showed that in strength it belongs to the dense varieties of dolomite with a fine crystalline structure. The weight % of the basic component (dolomite) is 88–98%. The impurities are calcite, quartz, clay particles, and iron oxides.By firing the dolomite in the form of the previously separated 5–25-mm fraction at 1700–1750°C it is possible to provide sintering of practically all of the samples. The use of preliminary grinding and briquetting improves sintering but does not provide significant advantages in comparison with firing in granular form. The addition of scale causes an improvement in sintering and an increase in the resistance to hydration.The resistance of hydration after firing at 1750°C in storage in air of samples Nos. 4–17 was satisfactory while the dolomite of samples Nos. 1–3 hydrated significantly more rapidly. With the addition of 1% scale and firing at 1700°C in storage in air the resistance is significantly greater.As the result of the investigation it was established that the dolomite, with the exception of individual samples, meets the requirements of Industry Standard 14-84-82 for raw metallurgical dolomite for patching and filling the sills of hearth furnaces and also for firing for metallurgical dolomite. A further improvement in dolomite quality is pssible with selective mining and benefication of it.Translated from Ogneupory, No. 2, pp. 36–40, February, 1987.     

Use of calcium zirconate as stabilizer when making zircon parts

Conclusions The method of casting from aqueous suspensions using calcium zirconate as a stabilizer was used to make zircon parts close in the nature of the green material, fired material and shrinkage during firing to parts made from prestabilized zirconium dioxide.The operation requires one high-temperature firing and a single grinding for the bulk of the mateial (about 80%).The addition of a calcium zirconate additive makes it possible to cast from acid dross characterized by greater resistance to particle aggregation and demixing of the suspension, and to obtain stronger and easy to process green material which is less liable to deform during firing.The use of calcium zirconate with a synthesizing temperature of 1200° produces good grindability and almost complete stabilization of the zirconium dioxide in the parts.The research was carried out by the Technology of Ceramics and Refractories Department of the Mendeleyev MKHTI in collaboration with the Industrial Silicates Laboratory of the Institute of Silicate Chemistry of the Academy of Sciences of the USSR and with the Podol'sk Refractory plant.     

Rational firing cycle for converter lining

Conclusions The firing of linings in converters made from tar-bonded refractories should be done with portion loading of coke in amounts of 200 kg, with careful control of the oxygen consumption. The temperature relationship with the rate of discharge of volatiles from the tar should be taken into account.The rational temperature cycle for firing tarred dolomite linings in converters is: raising the temperature to 300–350°C at a rate of 30–40 deg/min, from 300–350 to 700–800°C at a rate of 1.5–2.0 deg/min, and from 700–800° to 1000°C at a rate of 15–20 deg/min. The total firing time is 4.5 h, the coke consumption 2.8 ton, and the oxygen consumption about 4500 m³. The use of this cycle allows excellent preparation of the lining for service, practically excluding loss of brick due to spalling, and increasing the resistance of the lining.Translated from Ogneupory, No. 6, pp. 21–27, June, 1971.     

Investigation of oxide film formation on 316L stainless steel in high-temperature aqueous environments

Oxide films were grown on the surface of 316L stainless steel subjected to high temperatures and a high-pressure aqueous environment (250 °C and 7 MPa). The morphology, chemical compositions and corrosion properties of oxide films were investigated by scanning electron microscopy (SEM), auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The results indicated that oxide films formed at 250 °C were more corrosion resistant and thicker than were oxide films formed in air at room temperature (25 °C). These distinctions are correlated with the structure and chemical compositions of oxide films. It was found that both films contained a double-layer structure comprised of mixed iron–nickel oxides and chromium oxides. Iron was present as FeO, Fe₂O₃ and FeOOH; Cr was present as Cr₂O₃, Cr(OH)₃ and CrO₃; and Ni existed as Ni(OH)₂ within the oxide films formed at 250 °C.