THE THERMAL CONDUCTIVITY OF SOME REFRACTORIES1

The problem of measuring the thermal conductivity of materials up to high temperatures has been studied, especially in regard to the sources of error. This investigation has shown that many of the previous determinations of thermal conductivity may have had little precision due to a lack of appreciation of the errors involved. The values of thermal conductivity for a number of refractories are given, as obtained by a new type of apparatus designed to eliminate to a considerable extent the errors of measurement. However, it is believed that these values may have an error as high as ± 25 % for the better heat conductors; so there is still much work to be done in developing a method for measuring thermal conductivity with the precision usual in other physical measurements.     

THE THERMAL CONDUCTIVITY OF CARBORUNDUM REFRACTORIES1

Thermal conductivity measurements up to 1350°C of silicon carbide refractory materials have been made, using the water calorimeter method. Data were secured on furnace walls such as those commonly used in practice and results are believed to be accurate to within about 1%. Conductivity measurements were made on seven carborundum single walls and on eight carborundum-fire-clay composite walls. The relation of the thermal conductivity to temperature, chemical composition, and porosity was investigated, as well as the magnitude of the surface and joint effects. The conductivity of carborundum was found to vary with the quantity of heat energy transmitted through the wall. Tables are given showing the coefficients of thermal conductivity and heat flow through various types of walls with a temperature of 1500°C in the combustion chamber. Temperature gradient charts and heat flow curves for various walls are also given together with the practical application of the results in the design of commercial furnaces.     

THE THERMAL EXPANSION OF SOME REFRACTORY OXIDES1

The thermal expansion of crystals of alpha-alumina, magnesia, chromite, mullite, and zircon and of a mass of fused zirconia has been measured up to 1000°C. The results are exhibited in tables and in graphical form.     

MEASUREMENT OF THE THERMAL CONDUCTIVITY OF FIRELAY REFRACTORIES*

Thermal conductivity determinations have been made on superduty fire-clay, silica, and kaolin refractories, using the Globar-heated, water calorimeter apparatus previously described. The arrangement, which is satisfactory for insulating firebrick, gives considerable error when firebrick samples are tested. Results obtained by different arrangements of the guard samples and heating elements are shown as well as a final arrangement which gives a satisfactory condition of parallel heat flow.     

SECONDARY EXPANSION OF HIGH-ALUMINA REFRACTORIES*

Several mixtures of raw and calcined diaspore and bauxite with raw and calcined fire clays were prepared and fired at 2700°F. Specimens were refired at higher temperatures, and the linear changes were determined. Bodies composed of high-alumina grog and fire clay expand in the refire, whereas specimens of fire-clay grog that are bonded with ground raw diaspore exhibit shrinkage. The cause of the secondary expansion and shrinkage of these bodies is discussed.     

THE REVERSIBLE THERMAL EXPANSION OF REFRACTORY MATERIALS

The reversible thermal expansion from 15–1000°C was measured for kaolin, siliceous and aluminous fire clays, quartzite, alumina, magnesia, and carborundum, after preliminary burnings at cones 06, 9, 14 and 20, and as well as for English commercial silica bricks before and after use in a coke oven and the roof of a steel furnace. Kaolin and bauxitic fire clay after calcination have a regular reversible thermal expansion which does not vary much with the temperature of calcination. Siliceous fire clays, after calcination at cone 06 (980°C) or cone 9 (1280°C) display irregularities (departures from uniformity) in their expansion. Between 500° and 600°C they show a large expansion due to contained quartz and on cooling the contraction in that region is larger than the corresponding expansion. Moreover, the expansion between 100° and 250°C after being fired to cone 9 (1280°C) exceeds the average. After calcination at higher temperatures, cone 14 (1410°C) or cone 20 (1530°C). these materials gradually lose these peculiarities until on incipient vitrification a linear expansion similar to that of kaolin is attained. This change is due to the destruction of quartz by its interaction with the clay material and fluxes; it takes place most easily in a fine-grained, rather friable clay such as ball clay. The previous thermal treatment necessary for a particular clay in order to obtain regular expansion in use can only be determined by trial. It can be stated with confidence that in such a piece of apparatus as a glass pot or crucible, a distinct gain will result from maintenance at a high temperature for some time before use, but that the red heat of an ordinary pot arch is useless for the purpose. An increase in the porosity of a fire clay was accompanied by a corresponding decrease in expansion between 15° and 1000°C until a porosity of 50% was attained. Further increase in porosity produced very little change in the expansion. No irregularities in expansion were shown by magnesia brick, carborundum, or alumina bonded with 10% of ball clay. Welsh quartzite with lime bond, either unfired or after burning at cone 06, had a large expansion to 550 °C and a much larger expansion from 550–600 °C due to the inversion of α to β quartz while from 600–1000°C a slight contraction took place. Firing to cone 9 converted part of the quartz into cristobalite, thus increasing the expansion from 200–250°C. This conversion was considerably increased on burning for two hours at cone 14, which greatly reduced the expansion from 550–600°C with a corresponding increase of that from 200–250°C. The conversion of the quartz into cristobalite was completed by a further heating for two hours at cone 20. Determinations of refractive indices and specific gravities confirmed these results. Flint inverted to cristobalite with greater ease than quartz. Commercial silica brick consisted chiefly of cristobalite and unconverted quartz and showed a large expansion up to 300°C, followed by a considerably smaller but regular expansion to 550°C. From 550° to 600°C the rate of expansion was considerably increased, but above 600°C the change in dimensions was small. The innermost exposed layer of a silica brick after use in a coke oven was an impure glass with a steady expansion, but only half as large as that of the layers of brick behind, which was made for shelling away. A silica brick after use in a steel furnace was divided into four layers. The layer exposed to the furnace heat was practically all cristobalite and silicates, the next layer the same, the third layer showed some α to β quartz expansion as well as the α to β cristobalite expansion, while the fourth (outermost) layer exposed to air was similar to the brick before use. In these bricks exposure to high temperature had evidently completed the change from quartz to cristobalite which had been largely effected in the kiln during manufacture. Little or no tridymite had formed. The reversible thermal expansion from 15–1000°C of the commercial silica brick examined was 1.1 to 1.3%, about double that of fire clay brick.     

RELATIONSHIP BETWEEN CHEMICAL COMPOSITION AND THE THERMAL EXPANSION OF GLASSES1

Thermal expansion data on soda-silica, soda-lime-silica, soda-magnesia-silica, soda-lime-magnesia-silica, soda-alumina-silica, soda-lime-alumina-silica, and other glasses, over the range of 25° to 90°C are presented and compared. The relations existing between thermal expansion and chemical composition of the glasses, with the exception of boric oxide glasses, is approximately linear. New so-called expansion factors calculated by the authors give calculated values for expansion coefficients closer to those observed than do Winkelman and Schott factors.     

高精度热膨胀仪的设计

提出一种基于单片机8098和集成化测量电路的高精度热膨胀仪的设计方法。重点论述了温度控制算法、精密位移测量机构。     

THE THERMAL EXPANSION OF SHEET-IRON GROUND-COAT ENAMELS*

The thermal expansions of sheet-iron ground-coat enamels were determined by use of the interferometer. The results showed that the calculated expansions based on the factors of Mayer and Havas were close to the actual expansions. It was also shown that variations of borax, feldspar, and quartz resulted in a fairly uniform change in the expansion. It was possible to interpolate between values for these constituents. The softening of the enamels in the interferometer test proved to be a characteristic change depending on the fusibility of the enamel. These data showed promise as a test for fusibility.     

THERMAL EXPANSION OF SILICA BRICK AND MORTARS1

Thermal expansion from 20 to 950°C and physical data of silica brick from various producing districts in the United States and Europe are presented. The variations in thermal expansion of brick from various parts of kilns are given for plants in the United States. The magnitude of variation of the thermal expansion of silica brick is quite small, the expansion ranging between 1.15% and 1.30% at the highest point of expansion. The expansion of the silica mortars varied between 1.30 to 1.52% depending upon variations in clay, quartzite, and bats. The variations in thermal expansion of silica mortars from various producing plants are also shown. Data on the effect of size of grain, clay content, and P.C.E. on the thermal expansion of mortars are given. An extensive bibliography on thermal expansion of silica brick appears with the paper.     

THE RELATION OF STRUCTURE AND COMPOSITION TO THERMAL EFFICIENCY OF REFRACTORIES WHEN USED IN REGENERATORS1

This study shows the relative rates of heat transmission in typical clay, silica, diaspore, fused alumina and silicon carbide refractories, when used as checker brick. It is shown that by lowering the porosity of checker brick an increase in efficiency is obtained by virtue of its greater heat capacity, which is a function of the weight and specific heat of the material. The glazing of a clay brick does not appreciably impair its efficiency in regeneration, as is sometimes thought, as shown by experiment and as explained by the fact that the greatest part of the heat leaves the surface of the brick by convection and this is affected only by the surface area, which is not appreciably changed by glazing.     

耐火材料抗热震疲劳行为评价的研究

提出了热震条件下的强度衰减方程,用多种耐 试验结果对该方程进行了拟合,强度衰减速率和残余强度两者的对数值间存在或人段存在直线上此可将材料分成３种类型,并可更精确评价其抗热震性。     

THE ELECTRICAL RESISTIVITY OF REFRACTORIES1

The electrical resistivities of flint fire clay, kaolin, magnesite, sillimanite, silica, diaspore, Maryland, Italian and Indian talcs were determined at temperatures up to 1500°C. Tests were made in an atmosphere of nitrogen, by the Wheatstone bridge method, using 45-volt 1000 cycle alternating current. With the exception of magnesite, the rate of decrease of resistivity decreases with an increase in temperature. The investigation indicates that the resistivity of a complex ceramic body, especially if it is open and porous, is not constant for a given temperature above the temperature at which its most fusible mixture melts. Resistivity is affected by the amount of impurities present, decreasing with an increase of impurities. As was shown in the tests of Italian talc, the resistivity is not only dependent upon the amount of impurities, but also upon their distribution. Within the limits of the voltage used, the resistivity is independent of the potential applied.     

玻璃钢管道系统中的热膨胀分析

在玻璃钢管道系统铺设中选用合理的安装措施,不设置膨胀接头,也能保证管线长期安全使用。     

THE LABORATORY TESTING OF ALUMINOUS REFRACTORIES1

Eight brands of high alumina refractories and two brands of fire clay refractories, which are used by the trade under conditions of service requiring resistance to the corrosive action of lime and cement clinker at high temperatures, were subjected to standard and modified laboratory tests for high grade refractories. Data obtained indicate the results which may be expected in the technical examination of this type of product.     

APPARATUS FOR MEASURING THERMAL CONDUCTIVITY OF REFRACTORIES*

An apparatus for measuring the thermal conductivity of refractories, is described in detail, and results are shown for several types of insulating refractories. Comparisons are madc from data which were obtained on a low-temperature plate tester, and the effect of several variables on measured heat flow are discussed.     

THE TRANSVERSE BREAKING STRENGTH OF REFRACTORIES1

A furnace has been designed which has the following characteristics: (1) The possibility of running a4-hour day testing schedule. (2) The feasibility of measuring the modulus of rupture at temperatures up to 1500°C.     

THE LABORATORY TESTING OF PLASTIC REFRACTORIES1

Twelve brands of plastic refractories, representing the products of nine manufac- turers, were subjected to standard and modified laboratory tests for high grade refractories. The data obtained show the chemical and physical characteristics of the material now furnished to the trade and indicate the results which may be expected from a technical examination of this type of product.