© 2020 Springer Nature Switzerland AG. The high melting point and excellent chemical properties of zirconia would suggest its use as a refractory. Also, these metals are highly resistant to factors like thermal shock. E. R. Begley and P. O. Herndon, Am. Soc. White, Trans. Bull. Cold modulus of rupture and deformation modulus – Due to the thermal stress, generally combined with altered physical- chemical conditions because of infiltrations, strain conditions occur in the refractory brickwork which can lead to rupture and crack formation. Milena Pavlíková, Ph.D. K123, D1045. Hence, the ratio of rupture stress to rupture deformation has been introduced as the modulus of deformation. It should be able to withstand high temperatures generated in the furnace. V. S. Bakunov, E. S. Lukin, and D. N. Poluboyarinov, Tr. Am. Porosity is a measure of the effective open pore space in the refractory into which the liquid metal, slag, fluxes, gasses, and vapours etc. Physical & Chemical Properties of Tungsten. Porosity is a significant factor in heat flow through refractories. L. J. Trostel, Jr., Am. Refractory Properties Qtories co The physical and chemical properties of a refractory product, as shown on data sheets, are characteristics which give an indication of the product's performance under specific operating conditions (i.e., slagging, load bearing, fluctuating high temperatures, etc. In order to determine the magnitude of the rupture stress, the resistance to deformation under bending stress, i.e. Soc. This comprehensive reference details the technical, chemical, and mechanical aspects of high-temperature refractory composite materials for step-by-step guidance on the selection of the most appropriate system for specific manufacturing processes. Brit. The tests for refractoriness under load serve to evaluate the softening behaviour of fired refractory bricks at rising temperature and under constant load conditions. The cold crushing strength is determined by the methods described in various standards. The apparent porosity includes only those holes which can be infiltrated by water and not the closed holes. The following formula gives the heat stored (W) in one square meter of refractory wall of thickness‘s’. The contraction or expansion of the refractories can take place during service. The method of determination of slag resistance is described in various standards. The main component of the acid refractory is silicon oxide, and the common bricks are silica bricks and fireclay bricks. The book surveys a wide range of lining system geometries and material combinations and covers a broad The porosity of refractory is expressed as the average percentage of open pore space in the overall refractory volume. High porosity materials tend to be highly insulating as a result of high volume of air they trap, since air is a very poor thermal conductor. Chemical properties of glass, ceramics, and refractories Ing. An increase in bulk density increases the volume stability, the heat capacity, as well as the resistance to abrasion and slag penetration. It is added to alumina for use in the sliding gate valves which are an integral part of the continuous casting … In general, a good refractory must have low porosity. Bulk density is by far one of the most important characteristics and serves, together with the density, to calculate the true porosity and, together with water absorption, to calculate the apparent porosity. Hot modulus of rupture – Hot modulus of rupture is the resistance to bending stress at high temperature. As the refractories hardly ever consist of a single compound, reference is made, not to a specific melting point, but to a softening region. /* 300x250, created 1/18/11 */ Ed. The gas flow can be carried out by means of a pressure or suction pump. Through the ispatguru.com website I share my knowledge and experience gained through my association with the steel industry for over 54 years. Bull. The test samples are bars which are heated in electric chamber kilns. Abstract. Insulating refractories have lower densities (0,06 to 1,12 gr/cm3) and provide insulating properties, while offering resistance to corrosion and chemical reactions with the operating environment. The test is conducted as described in the various standards. However, the tetragonal-monoclinic phase transformation and the associated volume change preclude the use of unstabilised zirconia in the bulk form. In the water quenching method, the test piece is a standard cylinder which is heated to 950 deg C and then quenched in running cold water. One major identifying factor of refractory metals is heat resistance. If a refractory brick has very strong after shrinkage then the joints get enlarged and the brickwork is loosened and no longer tight. Soc. This factor indicates the amount of energy (joules) required to raise the temperature of 1 gram of a material by 1 degree kelvin. 9. Soc. Ceram. It is a measure of the weight of a given volume of the refractory. J. Refractory refers to the mechanical strength of the material at high temperatures. The term bulk density describes the measure of mass and volume including the pore space. Dimensional accuracy and size is extremely important to enable proper fitting of the refractory shape and to minimize the thickness and joints in construction. They are typically composed of oxides or non oxides like carbides, nitrides etc. These keywords were added by machine and not by the authors. The following is the discussion of the outstanding characteristics of the various types of refractories : Ceram. Progressive deformation up to rupture is outside the purely elastic region with the deformations on the less resistant fines content and for this reason the stress increases more slowly relative to the deformation. Chemical composition of refractories Thanks to its wide range of analytical instruments, Stazione Sperimentale del Vetro is capable of determining with precision and reliability both the concentrations of the main components present in refractory materials (e.g. Melting point – Melting temperatures (melting points) specify the ability of materials to withstand high temperatures without chemical change and physical destruction. In opposite case, after expansion is also dangerous since this can cause the destruction of the brickwork through pressure. B. Mitchell and R. M. Spriggs, J. This is determined with the help of comparative ceramic samples of known softening behaviour usually known as ‘Seger cones’ (Fig 1). However, under actual service where the bricks are heated only on one face, most of the load is carried by the relatively cooler rigid portion of the bricks. These properties are frequently among those which are used as ‘control points’ in the manufacturing and quality control process. (adsbygoogle = window.adsbygoogle || []).push({}); Properties of the refractories can be classified to resist four types of service stresses namely (i) chemical, (ii) mechanical, (iii) thermal, and (iv) thermo-technical. Download preview PDF. The unit of the thermal conductivity of refractories is W/K*m. The determination of thermal conductivity is carried out by the plate, ball, hollow cylinder or hot wire method. At higher temperatures, titanium can react with many elements and compounds. E. M. Passmore and T. Vasilos, J. Resistance towards Acid Attack test showed that the refractory samples present good resistance, as well as, the alumina powder ARobtained from waste of sil- ica-alumina bricks proves to be efficient for an eventual use. Some chemical origins of mechanical behavior and corrosion lifetime are illustrated. usually, the environment in most furnaces are either acidic or basic. It is, however, fairly common practice to use zirconia in a finely divided dispersed form to enhance the thermal shock resistance of other ceramic materials. Porosity and density – Low porosity of the refractory brick is desirable since it improves the mechanical strength and other properties of the refractories. In addition, processing of these minerals with the goal of upgrading their quality was done. For many refractories, the bulk density provides a general indication of the product quality. Part of Springer Nature. by A. M. Alper, Academic Press, New York, 1970. M. L. Van Dreser, Blast Furnace and Steel Plant, April, 1964. Resistance to slag, glass melts, gasses, and vapours – The slag resistance characterize the resistance of refractories to chemical attack of any type, including that of glass and vapours. Am. Cold crushing strength – The cold crushing strength determines the ability to withstand the rigorous of transport and handling before the installation of refractories in the furnace. All - Basic Furnace Sub-Committee Report, J. Service Temperature) Wear & Attack Mechanisms of Refractory Materials; Testing of Refractories: Physical, Chemical, Thermomechanical (PCE, RUL, etc.) M. L. Van Dreser and R. H. Cook, Am. Abrasion resistance – The mechanical stress of refractories is not caused by the pressure alone, but also by the abrasive attack of the solid charge materials as they slowly pass over the brickwork inside the furnace. 4. Not logged in open and closed pores) of a body to its volume and is expressed in volume percent. The compression of the sample, after maximum expansion has been attained, is given in relation to the test time as a measure of creep at a specified test temperature. Stanford Libraries' official online search tool for books, media, journals, databases, government documents and more. Ceram. Refractoriness under load – Refractoriness points to the resistance of extreme conditions of heat (temperature more than 1000 deg C) and corrosion when hot and liquid materials are contained while being transported and/or processed. Ceram. The most straightforward way to produce these refractories is to use with 50 % or 60% Al2O3 aggregates (i.e., bauxitic kaolin or andalusite). the test data is quite significant. It is not recommended to employ Acid refractory in contact with an alkaline (basic) product or vice-versa. In case of refractories this modulus is smaller than or at the most equal to the modulus of elasticity. True porosity of a refractory brick is the ratio of the total pore space (i.e. Overview Terminology Silicates and aluminates Glass Ceramics Refractories. The bulk density is generally considered in conjunction with apparent porosity. For many refractories, the bulk density provides a general indication of the product quality. The used refractory properties required for each kiln/furnace varies based on the application. This is normally measured dynamically by means of ultrasonic or resonance frequency. They are strong under extremely high temperatures and are innately hard, making these metals perfect for drilling and cutting tools. According to the chemical properties, the types of refractory materials are acid refractory materials, neutral refractory material, and alkaline refractories. properties and behaviour of refractory materials in the wide variety of hostile environments to which they are sub- jetted and" the so far poorly developed state of refractories engineering. 12 Properties of Refractories (contd.) M. L. Van Dreser and W. H. Boyer, J. So different refractories are used to provide unique properties. google_ad_width = 300; Refractory materials with high porosity are usually not chosen when they are to be in contact with liquid slag since they can be penetrated as easily. The refractoriness under load test provides an indication of the temperature at which the refractory bricks collapse, in service conditions with similar load. Reheat change (after shrinkage and after expansion) – After heating to high temperature and subsequent cooling, a permanent change in the dimension (permanent linear change) often occurs which is described as after expansion or after shrinkage. There is a negative temperature gradient of thermal conductivity in bricks which consist almost exclusively of crystalline components. The ratio of stress of deformation within this purely elastic initial region, where the deformation is still reversible, is described as the modulus of elasticity. The mechanical stress can also be due to the impingement of the fast moving gasses loaded with fine solid dust particles. by V. F. Zackay, John Wiley and Sons, Inc., New York, 1965. of the following materials: silicon, aluminium, magnesium, calcium, and zirconium. J. R. Kreglo and W. J. Smothers, J. Am. Therefore, the service conditions considerably affect the structure and properties of the refractory castables. The cone values reported for refractories are based on a defined standard time – temperature relationship, so different heating rates result in different PCE values. The resistance to bending stress of refractory products provides information on their deformation behaviour at high temperatures. The refractory castables have generally complex heterogeneous microstructures and their physical and thermomechanical properties are highly temperature-dependent because of the complex hydration and dehydration processes. A good refractory material should have the following properties: 1. T. Vasilos, J. In this article, we are going to see all types of refractories available in the industry. R. L. Coble; p. 706 in High - Strength Materials. Chemical and mechanical properties of these materials were investigated and correlated with their microstructure. 224 354 688, milena.pavlikova@fsv.cvut.cz. Refractories are inorganic, nonmetallic, porous, and heterogeneous. Bricks with high expansion are very susceptible to thermal shock. Enter your e-mail address and your password. 50 216 (1966). Based on the behaviour during contact reactions, the refractories can be categorized as (i) acid refractories (silica, silicon carbide, zircon cristobalite, and zircon silicate etc. True porosity of refractory bricks is composed of closed pores and open pores. With this method, temperature values are obtained by differential measurements in an oxidizing atmosphere and these values are considerably lower than the refractoriness under load values. The formula for true porosity is as follows. Am. S. I. Warshaw and F. H. Norton, J. Some metals with melting points >1850oC like niobium, chromium, zirconium, tungsten rhenium, tantal… The destructive agents coming into contact with refractories are of different composition and the destruction processes are correspondingly many. The Delta Chem® is a range of chemically bonded refractory products. If not done, then edge pressure and premature spalling of the bricks take place. Inst. This means that they will not experience cracking, expansion or stress w… All five metals under this class are characterized with a melting point higher than 3,632°F (2,000 °C). The relationship between service stresses and important properties of the refractories are at Tab 1. google_ad_client = "ca-pub-7057920448327527"; Ceram. ). The general requirements of refractories include (i) ability to withstand high temperatures and trap heat within a limited area such as a furnace, (ii) ability to withstand action of liquid metal, hot gasses and liquid slag by resisting erosion and corrosion etc. Refractoriness under load (differential) – In order to eliminate errors as a result of the inherent expansion of the test equipment when the refractoriness under load is being tested, and to enable tests to be carried out in an oxidizing atmosphere, a different method has been developed to determine the resistance at rising temperature and constant load which is the refractoriness under load (differential) test. 2. Not affiliated Air quenching method is used for bricks which are susceptible to hydration. 49 (7) 633 (1970). (iii) ability to withstand load at service environment, (iv) ability to resist contamination of the material with which it comes into contact, (v) ability to maintain necessary dimensional stability at high temperatures and after/during repeated thermal cycling, and (vi) ability to conserve heat. The powders were characterized for their chemical and physical properties. Aluminates and silicates {Silica dioxide SiO 2 {Aluminium oxide Al 2 O 3. 13. As a result, low porosity materials are generally used in hotter zones, while the more porous materials are usually used for thermal backup. Tungsten is one of the important strategic resources. Khim.-Tekhnol. The open pores can be either permeable or impermeable. Chemical Properties of Titanium – The Chemical Reaction. The abrasive stress is quite well simulated by Bohme’s grinding machine, but the results normally cannot be applied to the conditions existing in the furnaces being operated at high temperatures, especially when the strength of the refractory brick is getting changed due to the chemical influences. Thermal expansion under load (creep) – Refractory materials must maintain dimensional stability under extreme temperatures (including repeated thermal cycling) and constant corrosion from very hot liquids and gases. Impurity components: there are a certain amount of impurities in refractory materials or raw materials. Such materials, however, do not work with higher temperatures and direct flame impingement, and are likely to shrink when subjected to such conditions. There is presently no approved measuring method available for measuring abrasion resistance, and the abrasion factor according to Bohme is still being used as a reference value. This process is experimental and the keywords may be updated as the learning algorithm improves. Thermal shock resistance – Thermal shock resistance is one of the most important service properties. Pyrometric cone equivalent – Refractories due to their chemical complexity melt progressively over a range of temperature. Silica bricks, however, have an irregular and strong thermal expansion in the temperature range of up to 700 deg C.  By changes in structure or in firing methods of refractory bricks, the expansion curve can be influenced within certain limits. Am. Important properties of refractories include chemical composition, bulk density, apparent porosity, apparent specific gravity and strength at atmospheric temperatures. Then the modulus of elasticity is no longer sufficient to calculate the stress which occurs. The test is repeated till the destruction of the sample but not more than 30 times. Here are some advantages and disadvantages of high porosity. T. S. Busby and M. Carter, Trans. The density is the quotient of mass and volume excluding pore space and is determined on finely crushed material. The chemical industry itself provides a con- siderable variety of environmental conditions, the effects of these have generally been well studied and the most important of them are discussed. Categories of Refractories in Modern Industry: Pre-formed, Monolithics; Design Properties: Thermal and Mechanical, based on ASTM Standards; Characteristics of Working Refractories: (Max. Soc. Refractory materialsare characterized by a high melting point, and when exposed to high temperatures they do not lose their strength and of form. Cite as. Those refractories which retain their quenching resistance even after higher firing temperatures or service temperatures are the most useful in practice. Some chemical origins of mechanical behavior and corrosion lifetime are illustrated. can penetrate and thereby contribute to eventual degradation of the structure. chemical compositions, fumes, dust, and gases. In the first method a polarizing microscope or a scanning electron microscope is used to identify the crystal structure while in the second method the crystalline phases are examined by X-ray examination or by X-ray diffraction analysis. Soc. Thermal expansion is important in service, as the effects of expansion are to be taken into account during the installation of refractory lining. Such permanent changes in dimensions may be due to (i) the changes in the allotropic forms which cause a change in specific gravity, (ii) a chemical reaction which produces a new material of altered specific gravity, (iii) the formation of liquid phase, (iv) sintering reactions, and (v) may happen on account of fluxing with dust and slag or by the action of alkalis on fireclay refractories, to form alkali-alumina silicates, causing expansion and disruption. It is a measure of the weight of a given volume of the refractory. Specific heat – Specific heat is a temperature and material related energy factor and is determined with the help of colorimeters. It is usually considered that refractories with higher bulk density (low porosity) are better in quality. Hence, both the pore size as well as distribution of pores is important. Pore size distribution and types of pores – The mechanical strength of refractories is largely determined by the true porosity. rupture strength is measured. B. Jackson and J. Laming, Refractories J. J. E. Neely, W. H. Boyer and C. A. Martinek, Jr., Am. S. C. Carniglia; pp. Aggregate of small crystals can be dissolved and transformed more rapidly by infiltrating substances than closed crystalline materials. Over 10 million scientific documents at your fingertips. Bulk density – In order to know the stored heat, it is necessary to know the bulk density of the refractories. https://doi.org/10.1007/978-1-4684-3141-4_26. 3 Ed. Ceram. The content of open pores is determined by water absorption while the pore size distribution is determined by forcing mercury in the brick sample with the help of a pressure porosimeter. The physical and chemical origins of these properties are given together with ISO, ASTM, and DIN standards to measure them. Its main composition can be oxide and can also be an element or a non oxide compound.According to the chemical property of the principal components, refractory can be classified to acidic refractory, neutral refractory, and alkaline refractory. checker work,  not only the thermal conductivity of the refractories is of interest but also the ratio of the thermal conductivity to the thermal capacity (known as temperature conductivity), is important for the progression of the temperature changes.