Possibility of using fibrous thermal-insulation materials for lining electric furnaces containing a reducing atmosphere

Conclusions A study has been made of the possible use of fibrous thermal-insulation materials for the lining of furnaces operating with a reducing gas. The results of the study make it possible to recommend the use of ShVP-350 tiles at the maximum working temperature of 1200°C and products made from mullite-silica fiber and mineral wadding over the same interval of temperatures as in air, i.e., up to 1150 and 600°C, respectively. The use of fibers made from rocks with a high concentration of iron oxides is ruled out because of their low stability in a reducing atmosphere.The thermal conductivity of the fibrous materials in a reducing atmosphere is 25–40% higher than its value in an air atmosphere.The lowering of the thermal conductivity of fibrous linings in a reducing atmosphere makes it preferable to use them rather than normal linings of equal thickness because of their thermal-insulation properties. The use of the fibrous linings, moreover, helps to keep stable the specified composition of the furnace atmosphere. The time taken to restore this after the door has been opened is 1.5–2.0 times faster than that required for furnaces with the normal lining materials.Translated from Ogneupory, No. 2, pp. 8–11, February, 1984.     

On thermal conductivity of micro‐ and nanocellular polymer foams

Many theoretical and empirical models exist to predict the effective thermal conductivity of polymer foams. However, most of the models only consider the effect of porosity, while the pore size effect is ignored. The objective of this study is to understand the effect of pore size on the thermal conductivity of polymer foams, especially when it reduces to the micro and nanometer scales. A wide range of pore sizes from 1 nm to 1 mm were studied in conjunction with the porosity effect using finite element analysis and molecular dynamics simulation methods. Experimental data was used to validate the modeling result. It is shown that the pore size has significant effect on thermal conductivity, even for microcellular and conventional foams. The contribution of heat conduction through air is negligible when pore size is reduced to the micrometer scale. The extremely low thermal conductivity of nanofoams is attributed to extensive diffusive scattering of heat carriers in the solid phase of polymer matrix, instead of air. This study provides quantitative understanding of the pore size effect on thermal conductivity of polymer foams. It is also shown that polyetherimide (PEI) nanofoams could have a thermal conductivity as low as 0.015 W/m‐K. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Problem of the thermal conductivity of coking Dinas

Conclusions Dinas in service in the wall regions of coking furnaces acquire a zoned structure with different thermal conductivity levels in the zones. The thermal shock resistance of the hot zone is about four times less than that of the remaining zones. The thermal conductivity of the hot zone is determined by the extent of the tridymite crystals in the direction of the thermal current and the degree of development of the direct bond of crystal-crystal. In the zone arranged on the coking side the Dinas is carbonized, preventing growth of crystals of tridymite. The porosity in the range 15–25% does not have any decisive influence on the thermal conductivity of the coking Dinas.To increase the thermal conductivity of the coking Dinas we recommend the incorporation during the production process of additives which control the growth of tridymite crystals, develop a direct bond between them, and remove the carbon during service.An increase in the thermal conductivity of the Dinas is economically effective. An increase in the thermal conductivity of the wall Dinas of 1 kcal/(m · h · deg) reduces the coking time by about 1.8 h, which is equivalent to increasing the output of the coking batteries by 15%.Translated from Ogneupory, No. 2, pp. 48–52, February, 1973.     

Effects of silica fume, latex, methylcellulose, and carbon fibers on the thermal conductivity and specific heat of cement paste

Due to their poor conductivity, latex (20–30% by weight of cement), methylcellulose (0.4–0.8% by weight of cement), and silica fume (15% by weight of cement) decreased the thermal conductivity of cement paste by up to 46%. In addition, these admixtures increased the specific heat of cement paste by up to 10%. The thermal conductivity decreased and the specific heat increased with increasing latex or methylcellulose content. Short carbon fibers (0.5–1.0% by weight of cement) either did not change or decreased the thermal conductivity of cement paste, such that the thermal conductivity decreased with increasing fiber content due to the increase in air void content. The fibers increased the specific heat due to the contribution of the fiber-matrix interface to vibration.     

The thermal conductivity of periclase and periclase — Spinel refractories

Conclusions It was established that it is possible to vary the thermal conductivity of periclase and periclase- spinel refractories within fairly wide limits by varying their phase composition and structure.Translated from Ogneupory, No. 3, pp. 48–50, March, 1975.     

Gunited coating with high thermal conductivity for water-cooled structures in steel works

Conclusions The authors have devised a composition for gunited coatings with high thermal conductivity for protection of water-cooled structures in the linings of steel smelting systems at the points of contact with the slag. They show that addition of 20 or 40 wt. % of a heat-conductive filler, consisting of cast iron pellets measuring 2–5 mm, to magnesia guniting material increases the thermal conductivity of the gunited coatings by an average factor of 1.3 or 1.6, respectively.The dependence of the thermal conductivity of the coatings on the bulk concentration of pellets is satisfactorily represented by the equations of Euchen and Odelevskii, which were derived for a two-phase system consisting of a continuous matrix with randomly distributed inclusions of spherical particles. High-thermal-conductivity gunited coatings were tested in service in a water-cooled screen in a vertical channel of a 500-ton open-hearth furnace at the Zaporozhstal' works.Translated from Ogneupory, No. 2, pp. 31–36, February, 1979.     

Low density and low thermal conductivity chrome oxide refractories for glass-melting furnaces for fiber production

Conclusions Studies have been carried out on the production of chromic oxide refractories with lower density and thermal conductivity. The connection between the strength and thermal conductivity, on the one hand, and the porosity, gas permeability, and average pore size, on the other, have been studied for chromic oxide refractories.It is shown that when a small amount of soot is added, high-density and high-porosity chromic oxide refractories can be obtained with an ultimate compressive strength of >10MPa, a low thermal conductivity, and high glass resistance.Translated from Ogneupory, No. 4, pp. 45–49, April, 1981.     

Fibrous heat-insulation materials use of the hot wire method to determine thermal conductivity of fibrous heat-insulation materials

Conclusions It is desirable to determine the thermal conductivity of materials in the form of plates 30–40 mm thick or of a layer of wool of the same thickness by the hot wire method throughout their service temperature range, beginning at room temperature.Translated from Ogneupory, No. 1, pp. 21–23, January, 1980.     

Graphene layers from thermal oxidation of exfoliated graphite plates

Graphite platelets of 1–5 μm in diameter consisting of a few graphenes were generated from commercially available exfoliated graphite by ultrasonic treatment in benzene (1 mg material in 20 ml solvent) for 3 h. Droplets from the suspension were dispersed on silicon wafer. The graphite platelets were characterized by atomic force microscopy (AFM). Successive oxidation of the sample was carried out at 450–550 °C in air. AFM measurements showed that the thermal oxidation removed 2–3 graphenes from the platelets and it left behind single graphene layers.     

Vermiculite — a Promising Material for High-Temperature Heat Insulators

Vermiculite, a mineral of natural occurrence of the group of hydromicas, when heated to above 300°C, expands to become a highly efficient heat-insulating material. The expanded vermiculite, owing to its unique properties – low bulk density, low heat conductivity, relatively high melting point, chemical inertness, endurance, and environmental safety – can be used as a filler for heat-insulating materials. Heat insulators based on expanded vermiculite can be used in thermal power units with the hot-wall temperature not exceeding 1150°C as replacement for lightweight chamotte components and fibrous heat insulators.     

Effect of thermal aging on the defectiveness of ultrastrong para-aromatic armos and SVM fibres

The change in the defectiveness of ultrastrong para-aromatic Armos and SVM fibres during thermal aging in air was investigated based on the scale dependences and coefficients of variation of the breaking characteristics: strength, elongation, and strain energy at break. The increase in the defectiveness of ultrastrong para-aromatic fibres during thermal aging can be more objectively assessed by the change in the scale dependences and coefficients of the strain characteristics (elongation and strain energy at break) than with the change in the scale dependences and scale coefficients of the strength and the coefficients of variation of the breaking characteristics. The defectiveness of Armos fibres in thermal aging changes less significantly than for SVM fibres. The data obtained show the sufficiently high working capacity of Armos and SVM fibres in extreme temperatures — up to 300°C — for up to 10 h.Translated from Khimicheskie Volokna, No. 1, pp. 34–38, January–February, 1995.     

Electrospun flexible calcium zirconate fiber membrane with excellent thermal stability and alkali resistance

Ceramic fibrous membranes have promising application in gas solid filtration and in areas requiring high thermal insulation, as well as catalyst supports, owing to their high porosity and low thermal conductivity. However, achieving flexible ceramic fibrous membranes that are stable at high temperatures remains a challenge. In the present work, a CaZrO₃ fibrous membrane with excellent stability at 1200 °C and good flexibility at 1100 °C was achieved using a combination of sol-gel and electrospinning methods. The thermal decomposition process and microstructure evolution of CaZrO₃ precursor fibers at high temperatures were discussed. The single orthorhombic phase of CaZrO₃ fibers was stable up to 1400 °C. Furthermore, the CaZrO₃ fibrous membrane exhibited excellent alkaline resistance. The excellent thermal stability and flexibility of the CaZrO₃ fibrous membrane make it a promising candidate for high-temperature applications.     

Influence of thermal fixation on the photochemical transformation of triacetate fibres

Conclusions It has been shown that the thermal fixation of the fibre with hot air at 195°C leads to the optimum results. Under these conditions the highest light-fastness of the triacetate fibre is achieved, the tensile strength and elongation at break do not decrease so markedly, and practically no chemical changes take place.Kaunas Polytechnic Institute. Translated from Khimicheskie Volokna, No. 3, 37–39, May–June, 1969.     

Thermal conductivity of magnesite refractories in the range 500–1800°C

Conclusions An experimental setup was developed for studying the thermal conductivity of refractories up to 2300°C on the hot face of the specimen.In the average temperature range of 500–1800°C a study was made of the thermal conductivity of magnesite refractories of different porosity. The experimental data obtained satisfactorily agree with well-known literature and calculated values for the thermal conductivity coefficients.Translated from Ogneupory, No. 1, pp. 17–21, January, 1972.     

Macrokinetics of thermal and thermooxidative destruction of organic-reinforced plastic on heating in a gas flow

The thermochemical failure of organic-reinforced plastic in a high-temperature gas flow (nitrogen, air) is studied experimentally. The activation energy, preexponential factors, thermal effects, and orders of the solid-phase and heterogeneous oxidation reactions are determined by methods proposed previously.Scientific Research Institute of Polymer Mechanics and Materials, 634050 Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 3, pp. 54–59, May–June, 1994.     

Large-scale and ultra-low thermal conductivity of ZrO2 fibrofelt/ZrO2-SiO2 aerogels composites for thermal insulation

The large-scale fibrous/aerogels composites are prepared by using zirconia fibrofelt (ZFF) as skeleton to give high strength and ZrO₂-SiO₂ aerogels (ZSA) as filler to give excellent thermal insulation through vacuum impregnation. The ZFF/ZSA with a low density of 0.302?g/cm³ and a high porosity (89%) exhibits large size of 180?mm in length, 180?mm in width and 25?mm in height which is larger than other fibrous aerogels. Meanwhile, the ZFF/ZSA exhibits high compressive strength of up to 0.17?MPa which is approximately six times higher than that of ZFF (0.028?MPa). The ZFF/ZSA shows a much lower thermal conductivity of 0.0341?W?m^?1 K^?1 at room temperature and 0.0460–0.096?m^?1 K^?1 during 500?°C and 1100?°C which are lower than that of conventional fibrous materials, indicating its excellent thermal insulation property in a wide temperature range, and the thermal insulation mechanism is analyzed. Thus, the large-scale, low density, high strength, and low thermal conductivity of ZFF/ZSA composites show enormous potential application in the fields of architecture, engineering pipes and aerospace for thermal insulation and protection.     

Selection of the structures of tunnel kiln suspended roof thermal insulation

Conclusions A method has been developed for thermal calculation of suspended roofs taking into consideration the three-dimensional geometric configuration of the roof, the temperature relationship of the thermal conductivity of the materials, and the mutual irradiance of the projecting elements of the structure. An engineering program for calculation of suspended, and, as a particular case, of nonsuspended roofs was developed for Fortran IV algorithm language.With use of the program for thermal calculation of the roof at temperatures in the working channel from 1100 to 1900°C variations were developed of structures of the thermal insulation of tunnel kiln suspended roofs making it possible to substantially (up to 30%) reduce heat losses in comparison with those observed in existing kilns.Translated from Ogneupory, No. 6, pp. 40–44, June, 1983.     

Thermal conductivity of insulating refractories measured by the standard method and by the cylinder method

Conclusions The coefficients of thermal conductivity of insulating refractories measured by the method prescribed in GOST 12170-66, using the recommended thermometers with a scale division of 0.1°C and thermal insulation made from firebrick with an apparent density of 1.0 g/cm³, are appreciably higher than data obtained by the cylinder method. At average temperatures of 200–500°C (400–1000°C on the hot face) the discrepancy comes within the range 50–200%; when T_mean=600–700°C (1200–1300°C on the hot face) the discrepancies diminish to 0–30%.The maximum apparatus error in determining the thermal conductivity according to GOST 12170-66 with the use of Beckmann thermometers and low thermal-conducting linings is 10–30% for – 0.2–1.0 kcal/(m·h·deg), which greatly exceeds that indicated in the standard, ±10%. The maximum proportion in the error comes from the measurement of the drop in water temperature as it passes through the calorimeter. Consequently, the use of the standard recommended thermometers with scale divisions of 0.1°C is unacceptable for measurements on materials with a low thermal conductivity, since it may lead to errors of about 100%.Detailed comparison of the results of measuring this factor on standard equipment using the Beckmann thermometers, and on the improved instrument designed by the Ukrainian Institute (the cylinder method), showed that the mean square deviation of the experimental values for thermal conductivity for identical specimens with respect to the interpolation curves in the case of standard determinations is 2–3 times greater than the corresponding deviation for the cylinder method.In most experiments the interpolation curves =f(T) for the standard method is different by ±15–25% from the curves obtained with the cylinder method. This displacement apparently is due to certain constant errors connected with the unaccounted-for sources of error in the standard methods.The proposed method of determining the coefficient of thermal conductivity is of interest for scientific-research work. The use of the cylinder method is industry is associated with difficulties in preparing the specimens — Editors.Translated from Ogneupory, No. 8, pp. 45–52, August, 1971.     

Effect of thermal aging on the defectiveness of thermostable aromatic arimid and togilen fibres

The effect of thermal aging in air on the defectiveness of thermostable heteroaromatic Arimid-T and Togilen fibres was investigated based on the change in the scale dependences and coefficients of variation of the breaking characteristics: strength, elongation at break, and arbitrary deformation energy to break. The change in the scale dependences and scale coefficients of the deformation characteristics (elongation and deformation energy to break) more significantly and objectively reflect the increase in the defectiveness of thermostable fibres during thermal aging than the change in the scale dependences and scale coefficients of the strength and the coefficients of variation of the breaking characteristics. In thermal aging, the change in the defectiveness of Arimid-T fibres is smaller than for Togilen fibres. The data obtained indicate the elevated workability of thermostable heteroaromatic fibres at temperatures of 300°C: 300 h and more for Arimid-T fibres and up to 100 h for Togilen fibres.St. Petersburg State University of Design and Technology. Translated from Khimicheskie Volokna, No. 3, pp. 27–30, May–June, 1995.     

Infrared spectroscopic study of thermal transformations of polyacrylonitrile in gas media

Conclusions Optical densities of the main absorption bands have been compared in the IR spectra of specimens of polyacrylonitrile fibre which have been treated in the presence of SO₂ by keeping them at constant temperature for 30 min and by rapid (15 min) elevation of temperature to higher values. It has been found that no fundamental differences are observed in the processes which take place in the fibre.From a comparison of the changes in optical density of the main absorption bands in the IR spectra of fibres which have been treated in air, in nitrogen, and in SO₂ under otherwise equal conditions, it follows that treatment in air is characterized mainly by oxidation reactions. Treatment in SO₂ is characterized by the generation of absorption bands at 1130 and 1680 cm^–1, which are assignable to sulfur-containing functional groups.The suggestion has been made that sulfur-containing bridge bonds are the main reason for the thermal stability of fibres treated in SO₂.It has been shown that stretching loads accelerate many reactions which take place in the fibre on heating in various media, and can therefore be used to accelerate the thermal stabilization process.Translated from Khimicheskie Volokna, No. 2, pp. 21–24, March–April, 1989.