VARIATION IN HEAT TREATMENT OF A SILICA BRICK IN THE CROWN OF A TUNNEL KILN1

It is possible through microscopic investigation of a silica brick to ascertain approximately the heat treatment to which it has been subjected. In this way the temperature difference between the inner and outer ends of a silica brick which had seen service in the arch of a Dressler tunnel kiln was estimated to be at least 200°.     

USE OF ALUMINUM METAL IN THE CERAMIC INDUSTRY I,PROPERTIES OF REFRACTORIES PRODUCED WITH MIXTURES OF ALUMINUM,FIRE CLAY,AND GROG*

The addition of aluminum metal powder to fire-clay-grog mixtures greatly increased the strength of the fired brick as a result of an aluminothermic reaction between the metal and the silica in the clay and grog. Because the reaction takes place at 930°C. and causes the temperature to rise rapidly, it is necessary to heat these refractories only to 930°C. to produce hard, well-fired brick. Such products have a high load-carrying capacity at furnace temperatures and also a fair spalling resistance.     

OUTLINE OF REFRACTORY REQUIREMENTS FOR THE IRON AND STEEL INDUSTRY1

One of the greatest obstacles to the development of better refractories for the iron and steel industry has been the failure of the iron and steel men to give refractory manufacturers accurate detailed analysis of chemical, physical and thermal conditions to which the refractories are to be subjected. This paper summarizes briefly some of the conditions to be encountered in the major processes. Blast furnace refractories may be divided according to requirements as follows: Hearth and Bosh brick should withstand the scouring action of molten iron and acid slag at temperatures around 1800°C. Inwall brick should be impervious to hot, reducing gases, should resist the sand blast action of the from particles of ore carried by the gas, should have a low coefficient of thermal expansion and should possess sufficient compressive strength to support the weight of the upper part of the furnace. Top brick should be as dense and resistant to abrasion as possible. Downcomer, Dustcatcher and Gas Line brick should be dense and resist sand blast action of gas heavily laden by particles of charge. Hot Blast Main and Bustle Pipe brick should be of low heat conductivity. Hot Blast Stove brick should not vitrify at 900°C, should have maximum capacity for absorbing and giving off heat, and be of high compressive strength. The by-product coke oven is becoming a big factor in the refractory fields and has major requirements as follows: Canals and Ovens require brick of high thermal conductivity which will resist sudden changes in temperature and will not be affected by reducing gases at high temperatures. Checker brick should have great capacity for absorbing heat. Bessemer converters require brick resistant to slag at temperatures from 1600° to 1700°C, the nature of the slag being determined by whether the process is acid or basic. Requirements for open hearth furnaces are as follows: Roof brick (both acid and basic furnaces) must not only be capable of maintaining an arch but should withstand as much as possible the action of iron oxides at temperatures of 1800°C. Checker brick (both acid and basic furnaces) should possess a maximum capacity for absorbing and giving off heat, and a minimum chemical affinity for oxides from charge. Ports (both acid and basic) must withstand the action of slag splashes, also direct action of flame. The hearth of the furnace consists of several courses of brick (acid or basic depending on the process) upon which is built the hearth proper by means of many layers of crushed refractory of the same nature. This crushed material must frit together at high temperatures without excessive softening.     

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.     

PROGRESS REPORT ON INVESTIGATION OF FIRECLAY BRICK AND THE CLAYS USED IN THEIR PREPARATION1

This is a progress report of an extensive study of fire clays and fireclay brick. It includes the results of a preliminary study of clays representative of those used in the manufacture of refractories throughout the United States. Chemical analyses and a summary of physical tests are given of both fire clays and the brick manufactured from them. The thermal expansion behavior of the fire clays fired at 1400°C and those of the fire brick “as received” from the manufacturer and also after firing at 1400°C, 1500°C, and 1600°C were studied and the materials classified into groups having characteristic thermal expansions. The moduli of elasticity and rupture were determined at 20°C, 550°C, and 1000°C. The resistance of the brick to spalling in a water-quenching test is expressed in an empirical relation correlating the elasticity, strength, coefficient of expansion, and percentage of grog used in compounding the brick batches. Data are presented on individual bricks made by the same manufacturer showing probable reasons for great differences in the number of quenchings required to cause spalling in the water-dip test.     

THE COMMERCIAL DEVELOPMENT OF A KAOLINIC FIRE BRICK1

The development of a kaolinic brick from Georgia clay is described. The high and continued shrinkage of this clay makes it necessary to fire the brick a t a very high temperature. A temperature of over 3000°F was required. The development of a kiln for the firing of the grog and brick was a problem that was satisfactorily solved. A light weight brick for use in marine boilers and a dense refractory for use in glass tanks were developed. The following physical properties of these two refractories are given and compared with other high grade bricks: (1) start of deformation under 25 Ibs. per sq. in. load, (2) 10% deformation under 25 Ibs. per sq. in. load, (3) start of permanent volume change without load, (4) mean coefficient of expansion, (5) cycles in 2900°F air-spalling test, (6) melting point, (7) thermal conductivity a t 1000, 2000 and 2750°F. Various successful applications of this type of brick are described.     

ELASTIC BEHAVIOR AND CREEP OF REFRACTORY BRICK UNDER TENSILE AND COMPRESSIVE LOADS*

Specimens cut from 9-in, brick of nine brands of firebrick, including two high-alumina, four fire-clay, two siliceous fire-clay, and one silica, were subjected to tensile and compressive creep tests at eleven temperatures from 25° to 950°C., inclusive. The duration of each test was approximately 240 days. Small length changes, independent of stress direction (that is, compressive or tensile), occurred at the lower temperatures. The lowest temperatures at which creep was significant were (a) high-alumina brick, 700° to 850°C.; (b) fire-clay brick, 600° to 700°C.; and (c) siliceous and silica brick, 950°C. Creep results under compressive stress could not be correlated with results under tensile stress. Specimens of different brands, at 950° C. showed greatly different capacities to carry load. Repeated heatings caused growth of silica brick of approximately 0.27%. Moduli of elasticity at room temperature were determined before and after the various heat-treatments and resultant changes were recorded. The changes in moduli were 15% or greater for silica and siliceous brick and 4% or less for the fire-clay brick. The moduli of elasticity at room temperature were approximately 2.7–4.3 × 10⁶ for high-alumina brick, 0.6–1.9 × 10⁶ for fire-clay brick, 0.3–1.7 × 10⁶ for siliceous fire-clay brick, and 0.4 × 10⁶ for silica brick.     

EFFECT OF REDUCING GASES ON THE TRANSVERSE STRENGTH OF FIRECLAY BRICKS1

It was reported that fireclay brick, when heated in the presence of carbon monoxide, were disintegrated by the progressive deposition of finely divided carbon at the “iron spots” in the brick. The conditions necessary for the occurrence of this phenomenon were not definitely known, although the known reversibility of the catalytic reaction around 650°C and the outcome of small scale experiments indicated that disintegration would not occur above this temperature. To obtain more definite information on this score, the effect of city gas at 550°C and 1100°C on the transverse strength of three brands of fireclay brick was determined. No significant changes in strength occurred at 1100°C. At 550°C two of the brands suffered very significant decreases in strength, but the other brand was unaffected, although it had the highest iron content.     

INVESTIGATION OF THE EFFECT OF LOW-FIRED GROGS ON PROPERTIES OF SOFT-MUD BRICK*

Soft-mud brick were made from various mixtures of Hudson River clay and grog prepared by calcining the clay at 500°, 700°, and 900°C., and rate of drying tests were carried out. The brick were fired to cones 012, 08, and 04, and a special fast fire to cone 08 was also run. The various properties were compared with those of regular mix brick and all-clay brick. Brick made of a mixture of clay with 35% of 900°C. grog had particularly satisfactory properties such as to afford definite advantages as regards faster drying and accelerated firing.     

新型三维脉动热管的性能

把传统脉动热管冷却段改进成双螺旋结构,形成新型三维脉动热管,并建立实验平台,考察了以丙酮为工质,在充液率54%、冷却水温度22℃的条件下,不同加热功率（20~700W）、不同倾斜角度（0°、50°、90°）对新型三维脉动热管的启动以及传热性能的影响,通过加热段以及冷却段管壁温度变化判断脉动热管启动运行特性,通过总热阻评价热管传热效果。实验结果表明,脉动热管在0°、50°和90°倾斜角度下均可以启动,但90°倾斜角时更有利于新型脉动热管的启动和稳定运行。90°倾斜角时,脉动热管在加热功率40W时启动,100W达到稳定运行状态,700W时到达传热极限,脉动热管的总热阻呈现先减小后增大的趋势,总热阻最小可达0.117℃/W。脉动热管在90°和50°倾斜角度下传热总热阻没有明显差异,但在0°倾斜角时,极易达到传热极限且在整个过程中热阻要比50°和90°倾斜角条件下高很多,加热功率180W达传热极限。     

A CONE FUSION MUFFLE FURNACE FOR HIGH TEMPERATURE WORK1

A laboratory type muffle furnace in which the muffle (inside dimensions 9 by 6 inches) was built of standard “Refrax” brick and heated by means of two slotted graphite electric resistors, has been in use for over a year in the Research Laboratory of The Carborundum Company at Niagara Falls. Although specifically designed for cone fusion studies, in which work it is very successful, it can be used for other laboratory work especially at high temperatures (up to at least 1600°C)such as small fusions, heat treatment, etc.     

TRANSVERSE TESTING FURNACE*

An electric furnace is described, designed for determining the transverse strength of 9-in. brick to temperatures as high as 1500°C. It is especially useful when a large number of brick are to be tested because the samples, which have been preheated in a second furnace, may he easily introduced and withdrawn while the furnace is held at breaking temperature.     

Calcium sulphate scaling in falling film evaporators

The formation of calcium sulphate scale in Vertical Tube Evaporators (VTE) of the falling film type has been investigated in a single tube experiment using fluted tubes. It was found that the scaling threshold is dependent not only on the brine concentration and temperature, but also on the heat flux to the evaporating film. With normal sea water concentrations and a high heat flux, scale was observed at 240°F (115°C), whereas with a low heat flux scale-free operation was possible at 266°F (130°C). The effect of heat flux is attributed to the presence of local areas of high concentration in the falling film which form as a result of uneven evaporation from the film. A simple model has been developed to explain the results.     

RELATION OF CRUSHING STRENGTH OF SILICA BRICK AT VARIOUS TEMPERATURES TO OTHER PHYSICAL PROPERTIES*

The failure at elevated temperatures under constant load for silica brick is reported using the Iupuy load test apparatus. The crushing strength at 1500°F, 1800°F. 2100°F, and 2400°F is recorded, as well as the crushing strength at room temperature. The size of test piece utilized normally was 1 by 1 by 2′/2 inches. A definite relationship is shown to exist between the strength at room temperature and that at elevated temperatures. The effect of variation in lime content, bats content, and fluxes is also reported. Data were obtained on brick made from three different quartzites. Additional physical data are reported to give information concerning the properties of the brick tested.     

THE WATER SMOKING OF CLAYS1

Experimental Method. —The water smoking behaviors of two plastic brick clays, one shale and one fire-clay were studied by heating 4-in. cubes at different rates, two thermo-elements being buried in the brick and two others placed against the exterior surface. Results of Conclusions. —To save time in water smoking, the ware should be previously dried not far from 100°C, good circulation should be provided in the kiln and the temp. of the interior of the product should not lag appreciably behind that of the kiln. It should be possible to water smoke heavy clay products in 15 hours with heating rate of 20°C per hour.     

CONSTITUTION AND THERMAL EXPANSION OF SILICA COKEOVEN BRICK AFTER SERVICE*

Two silica brick which were in service in a coke oven for over ten years have been examined under the petrographic microscope. At the fluc sidc the brick were almost completely converted to cristobalite, next comes a relatively thick layer which is mainly tridymite, and finally near the coke side quartz is found in addition. Measurements on small specimens taken from one of the brick show that the several layers have very different expansions. It is concluded that in cooling a battery of ovens great care should be taken to cool slowly through the temperature range 200 to 300°C.     

FACTORS INFLUENCING THE STAINING OF SILICA BRICK*

The staining of silica brick was found to occur in a critical temperature range of 900°‘ to 1000°C. Concurrently the brick had to be “soaked“ in this temperature range and exposed to an oxidizing atmosphere. Stained brick could be “cleaned up” or staining prevented by manipulation of the foregoing set of conditions as well as by additions of 4.5% or more of lime. The experimental data examined in the light of the system CaO-Fe₂O₃-SiO₂ suggest that the colorant is the mineral dicalcium ferrite.     

Evaluation of the morphology and pore characteristics of silica refractory using X-ray computed tomography

Silica refractory has excellent high-temperature performance, but its apparent porosity is relatively high. In this work, samples obtained before and after creep testing of silica brick (1550 °C, 50 h), from used silica checker brick (existing only tridymite and amorphous) and from used dome brick (existing only cristobalite and amorphous) were investigated using a three-dimensional structure model based on X-ray computed tomography (CT). The results show that the porosity of silica brick was high but consisted mainly of interconnected pores, with a very small proportion of closed pores (smaller after long-term use). During the use of silica brick, the morphology and phase transformation caused large particles to rupture, and the mineralizer became liquid at high temperature. The broken particles and interconnected pores provided channels for the migration of the liquid in the brick at high temperature. The silica brick presented a homogeneous ceramic structure during long-term operation. Tridymite or cristobalite presented a solid frame leading to an excellent creep performance of the silica brick (the creep rate of the checker brick was ?0.16% at 1550 °C for 50 h). Results were discussed, compared with literature and a model for the transformation of the silica brick from a refractory structure to a homogeneous ceramic structure was established in this paper.     

LIGHTWEIGHT SUPERDUTY KYANITE-TOPAZ REFRACTORY*

Standard-size 9-in. brick with a weight of 5 lb. were successfully processed. Some of these brick had linear shrinkages of less than 1% in the A.S.T.M. load test at 1450°C. and less than 2% volume shrinkage in the 1600°C. A.S.T.M. reheat test. The pyrometric cone equivalent was 37 or above.     

THE THERMAL EXPANSION OF REFRACTORIES1

The thermal expansion or contraction of a number of typical refractories has been measured up to 1700°C in a neutral or slightly oxidizing atmosphere. In nearly every case the expansion curve has been carried to a higher temperature than given by previous data. In a few cases the expansion curve has been obtained for materials that have not been studied in this way before. It is believed that the expansion curve of a brick, if carried to the softening point, gives valuable information as to the performance of that brick in service.