Investigation of Taimyrsk graphites for producing periclase-carbon ladle refractories

Conclusions The investigations showed that Taimyrsk graphite corresponds in chemical composition to foundry and crucible graphite.The content of crystalline graphite equals 13.0–26.3%. The characteristics of periclase carbon goods based on foundry and Taimyrsk graphites correspond to the demands placed on ladle refractories. The wear factors of these products in the slag belt of the lining of 350-tonne steel ladles are on practically the same level.Taimyrsk graphites may be used for the production of periclase-carbon ladle refractories in place of crucible or foundry graphite.L. N. Kurlyandskaya (Urals Geology Planning Association) and L. Ya. Osipova (All-Union Institute of Refractories) took part in this research.Translated from Ogneupory, No. 1, pp. 15–17, January, 1991.     

Fabrication Of Periclase-Carbon Refractories With An Antioxidant And Their Testing In A Lining Of A 370-ton Converter

Periclase-carbon refractories based on electrofused periclase with an additive of passivated aluminum have been tested in service in the top cone of a 370-ton converter of the Magnitogorsk Metallurgical Works. The lining with experimental refractories withstood 1501 heats whereas the endurance of commercial periclase-carbon refractories of grades PUPK-6 and PUPK-8 equals 1185–1416 heats. It was concluded that the periclase-carbon articles with an aluminum antioxidant have good prospects for lining converters.     

Unfired periclase-carbon refractories with a thermoreactive polymer binder

Elevated environmental requirements necessitate the development of new binders with a high carbon residue, heat treatment of which does not result in emission of toxic or carcinogenic substances. Such binders should have adequate technological properties. It is shown that it is possible to use a thermoreactive polymer binder based on a resorcinol oligomer for production of periclase-carbon refractories. The binder is soluble in water and organic solvents and possesses a high carbon residue (> 60%). Specimens of periclase-carbon refractories with the suggested binder and 5–12% graphite exhibit good ceramic and mechanical properties. Translated from Ogneupory i Tekhnicheskaya Keramika, Nos. 1–2, pp. 19–24, January–February, 1999.     

Properties of periclase-carbon refractories containing metal powders

Conclusions The effect of the metallic additives (Al, Cr, and FeSi) on the properties of unfired periclase-carbon products was studied. It was shown that their presence decreases the degree of oxidation of graphite without decreasing the strength properties of the refractory. When heat treating the periclase-carbon specimens up to 1000°C, the effectiveness of the additives decreases in the following order: Al, Cr, FeSi. At 1400°C, the effectiveness of all the additives is virtually identical.Translated from Ogneupory, No. 8, pp. 7–9, August, 1989.     

Increasing the Durability of the Lining of 385-Ton Steel-Teeming Ladles

Data on the durability of the lining of steel ladles in service at an MISW ISC oxygen-converter shop are reported. The best stability of the lining under severe operating conditions was achieved using periclase-carbon refractories (since 2000, available from an in-home manufacturer at the MISW). The highest lining durability is found in periclase-carbon components composed of fused periclase (with MgO content not less than 96%) and coarse-grained graphite (7 – 10%).     

Development of optimum composition of a batch for periclase-carbon lining of steel-teeming ladles of AFM shops

Results of a study of the effect of antioxidant additives, i.e., metallic aluminum and titanium diboride, on the quality parameters of periclase-carbon ladle refractories are presented. Laboratory studies have shown that the addition of the studied antioxidants into the batch increases the strength and lowers the porosity of the specimens. The size of the decarburized layer due to the addition of metallic aluminum and titanium diboride is virtually the same, but the use of TiB₂ adds additional strength to the decarburized and transition layers of the specimens. It is recommended that pilot tests be performed for joint introduction of the additives. __________ Translated from Novye Ogneupory, No. 11, pp. 56–58, November, 2007.     

Production of high-quality graphite crucibles for metallurgy

Processes for the manufacture of crucible graphite with high performance characteristics are considered. Among these processes are the use of highly graphitized needle coke as a filling agent, the vibromolding of a starting coke-pitch mixture, the use of medium-temperature coal-tar pitch impregnation-burning cycles, the burning of molding compounds in metal containers, and the graphitization of burnt materials in graphite cylinders. The latter two techniques decrease a temperature drop across the bulk raw material in the course of thermal treatments and, consequently, minimize the appearance of cracks due to a decrease in thermal stresses. All of the recommended techniques can be implemented at current electrode plants, and they can considerably improve the quality of the manufactured crucible graphite. In this case, the quality of the resulting materials can correspond to world standards.     

Synthesis and Mechanism of Nanosized AlN from an Aluminum Oleic Emulsion Using Carbothermal Reduction at Low Temperatures

Nanosized Al₂O₃ particles homogeneously dispersed in a matrix of amorphous carbon (a-C) were prepared by decomposition of an aluminum oleic emulsion at 600°C in Ar. Nanosized aluminum nitride (AlN) grains were prepared by carbothermal reduction and nitridation (CRN) of this Al₂O₃–a-C mixture in NH₃ using graphite, BN, and alumina crucibles or boats. The phases formed by CRN were identified by X-ray diffraction analysis. The morphology and grain size of the AlN were determined by transmission electron microscopy. The formation of single-phase AlN was achieved at temperatures as low as 1150°–1200°C in NH₃ using a cylindrical graphite crucible with holes in its two flat faces. Mass spectroscopy (MS) showed that a significant amount of HCN and a minor amount of C₂H₂ are formed at 500°C by reaction of NH₃ with carbon at the decomposition temperature of NH₃. A most probable formation mechanism of the AlN from nanosized Al₂O₃ and a-C in NH₃ is discussed on the basis of MS results and thermodynamic considerations.     

Properties and behavior of periclase-carbon systems during the firing-process under oxidizing conditions

Conclusions It is not advisable to introduce more than 20% graphite into the composition of the periclase-carbon refractories because, in this case, the strength of the products decreases significantly and their porosity increases.The temperature corresponding to the beginning of carbon depletion (burn off) does not depend on its content in the body and amounts to 550–560°C.Caustic periclase introduced for achieving additional low-temperature densification of the strucutre with reduced degree of carbon depletion did not give the expected effect: the temperature at which carbon depletion begins does not depend on its content in the body.When fired under oxidizing conditions, a reducing atmosphere is created within the periclase-carbon products which actively reacts with periclase; at and above 1650°C, one observes reduction of MgO up to Mg vapor with its subsequent oxidation and redeposition in the form of a dense layer of secondary MgO; a relict polygonized grain structure of MgO forms in the products and is accompanied by the development of a layered texture exhibiting cyclic recurrence.Translated from Ogneupory, No. 6, pp. 8–12, June, 1987.     

Antioxidants in carbon-bearing refractories

A study of boron-bearing additives to periclase-carbon refractories is described. The special features of their oxidation and phase formation in heating of periclase-carbon compositions are investigated. It is shown that some of them can be used successfully as an antioxidant component that improves the operational characteristics of periclase-carbon ceramics. It is shown that the imported antioxidant boron-2000 is analogous to amorphous-boron (95–85%) preparations, and the latter are recommended for the creation of domestic grades of thermally stable periclase-carbon refractories. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 2, pp. 2–5, February, 2000.     

Use of aluminum phosphate as a bond for refractory corundum products and washes

Summary The use of aluminum phosphate is desirable for preparing corundum products and washes based on commercial calcined alumina.A composition was developed ensuring strong bonding of corundum refractories and also of corundum refractories with steel and graphite.The bonded refractory components (corundum) are tightly held on graphite components of thermocouples after 15 h operation in the walls of electric arc furnaces at 2000°C.Aluminophosphate bond increases the spalling resistance of corundum products and also raises their strength.     

Carbon black pastes as coatings for improving thermal gap-filling materials

Carbon black pastes were found to be effective as coatings for improving the performance of thermal gap-filling materials, including flexible graphite, aluminum and copper. The thermal contact conductance across copper mating surfaces was increased by up to 180%. A fluidic form of carbon black paste (based on polyethylene glycol) was more effective than a thixotropic form (based on polyol esters). The carbon black pastes were much more effective as coatings than a commercial silver paste. With a carbon black paste coating, aluminum foil (7 μm thick) was a superior gap-filling material compared to similarly coated flexible graphite (130 μm thick). However, without a coating, flexible graphite was superior to aluminum. Commercial silicone-based gap-filling materials were inferior to flexible graphite or aluminum (whether coated or not).     

电磁分离高硅铝硅合金制备低硅铝硅合金

在不考虑杂质元素的情况下研究了含铝45wt%的铝硅合金熔体电磁分离过程中电流频率、下拉速度、保温温度及坩埚材质对初晶硅相分离效果的影响. 结果表明,在电流频率3 kHz、保温温度1000℃、下拉速度10 ?m/s的条件下,以石墨坩埚为容器,可使合金的硅铝质量比降至0.0939. 保温温度对合金中硅的去除影响最大,相同条件下1500℃时合金硅铝质量比为0.11439;低频交变电流能强化电磁搅拌从而加强传质,降低下拉速度对降低合金中硅含量有一定作用,且可使分离界面更平坦.     

低碳MgO-C材料的抗热震性研究

以电熔大结晶镁砂、天然鳞片石墨、纳米炭黑、酚醛树脂、铝粉等为主要原料制备w(C)=3%的低碳MgO-C材料,以其抗热震性为考核指标,选取颗粒级配、复合抗氧化剂、石墨粒度和复合结合剂4个因素,进行了四因素三水平正交试验。结果表明:在本试验范围内,颗粒级配是影响低碳MgO-C材料抗热震性的主要因素,复合抗氧化剂次之,石墨粒度和复合结合剂的影响基本相当;通过极差分析确定,镁砂颗粒级配(3～1、1～0.088和≤0.088mm的镁砂的质量比)采用50:23:27,复合抗氧化剂采用Al2.5+Mg-Al0.5+B4C0.5,石墨粒度采用10μm的,复合结合剂采用炭黑N220+沥青+酚醛树脂,可制备出抗热震性最佳的低碳MgO-C材料。     

Effect of antioxidants on the properties of unfired carbon-bearing refractories

The effect of antioxidants on the properties of periclase-carbon and aluminum-periclase-carbon refractories is considered. It is shown that the introduction of aluminum and crystalline silicon into the composition of the refractory mixture decreases the degree of burning-out of silicon in 3-h heat treatment at 1200°C. In addition, the thermoreactive binder based on a resorcinol oligomer used for the production of refractory specimens has a favorable effect on the preservation of carbon in the refractory due to the activation of the oxidation of the coke formed in polymerization of the oligomer. These factors should improve the slag-and metal-resistance of the refractory, its service parameters, and the quality of the final product.     

Determination of Trace Nickel in Hydrogenated Cottonseed Oil by Pressurized Bomb Acid Digestion and Graphite Furnace Atomic Absorption Spectrometry Detection

A pressurized polytetrafluoroethylene (PTFE) bomb method for the digestion of trace nickel in hydrogenated cottonseed oil prior to its determination by graphite furnace atomic absorption spectrometry (GFAAS) has been developed. Currently, the methods outlined in United States Pharmacopeial 28 (USP28) and British Pharmacopeial (BP2003) methods are recommended as the official methods for analyzing nickel in hydrogenated cottonseed oil. However, when using these methods, the samples were easily tarnished during sample pretreatment when using a silica crucible. In contrast, when using a platinum crucible, hydrogenated cottonseed oil acting as a reducing material may react with the platinum and destroy the crucible. In order to avoid the tarnish with a silica crucible and the risk when using platinum, the technology of a pressurized PTFE bomb method was applied in the digestion of nickel in hydrogenated cottonseed oil. The results showed that hydrogenated cottonseed oil can be digested completely by the optimal combinations of HCl (0.1 mL) and HNO₃ (0.5 mL). The digested solution was investigated using graphite furnace atomic absorption spectrometry.     

Refractories for the Taphole of Converters

A range of refractory materials for the converter's taphole lining commercially available from the Kombinat Magnezit Joint-Stock Co. and major aspects of the processing technology are considered. The effective use of antioxidant additions is confirmed by thermal analysis. Results of operational tests of refractory materials are discussed. The advantages of an innovative design of the taphole unit composed of blocks of variable diameter and assembled on a metal template are emphasized. An economic feasibility analysis of the use of periclase-carbon taphole blocks is given. The newly designed refractory material are shown to conform with the requirements of modern converter technology.     

Thermal Expansion of Magnesian Materials

Results for periclase-carbon materials with different proportion of the finely dispersed fraction tested for linear expansion at 20 – 1420°C under argon are reported. The composition of finely dispersed fraction (varying in proportion from 100% periclase to 100% alumomagnesian spinel) and the carbonization regime are factors that determine the thermal expansion of the materials studied. A hysteretic behavior of the linear expansion curves is established and shown to be related to sintering processes and volumetric phase transformations. The data obtained can be used to optimize the composition and heat treatment of periclase-carbon refractory materials.     

Factors of large graphite crucible life

Production methods used to prepare graphite crucibles with high operating properties are considered: use as a filler of good graphitizing acicular coke, vibration molding of the original coke mix, use of production cycles for impregnation with medium temperature coal-tar pitch — firing, firing of compacted billets in metal containers, graphitization of fired billets in graphite cylinders. The last two production methods make it possible to reduce the temperature drop throughout the volume of a billet during heat treatment, and as a consequence to reduce crack development to a minimum as a result of reducing thermal stresses. All of the production methods recommended may be entirely accomplished in existing electrode plants and may be used to increase markedly the quality crucible graphite. It is possible to achieve a quality for these materials at the best world level. Translated from Novye Ogneupory, No. 8, pp. 28–33, August 2008.     

Effects of graphitization degree of crucible on SiC single crystal growth process

Effects of graphite crucible on mass transport and crystal growth process has been investigated in the fabrication of SiC single crystal by the seeded sublimation growth method. Different graphitization degrees of the crucibles were obtained by heat treatment at various temperatures between 2100 and 2300 °C. The crucibles were subjected to SEM and XRD in which the graphitization degree was determined quantitatively. The experimental results indicate that the graphite crucible plays an important role in the SiC crystal growth by providing carbon. High crystal growth is obtained by using the untreated crucibles (corresponding to low graphitization degree), which contributes to the reaction activity between Si and graphite of the crucible. Increasing the graphitization degree results in degradation in crystal growth, even in the graphitization of the SiC seed crystal.