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.     

SOME OBSERVATIONS OF SURFACE DEPOSITS FORMED IN GLASS FURNACE REGENERATORS1

Two high alumina refractory brick which had been used in glass furnace regenerators were examined with the petrographic microscope. The deposits formed on the surface of the brick through reaction with the dusts and gases of the furnace atmosphere were found to be composed principally of nephelite, carnegieite, and corundum. Nephelite and carnegieite probably can form only in those parts of glass furnaces where the temperature is considerably lower than that required to melt the glass, but corundum may be formed at melting temperatures.     

SPLITTING OF SOFT-MUD BRICK*

A study was made of the cause and methods of preventing the splitting of Hudson River soft-mud brick. The splitting occurred in the kiln and paralleled the 8- by 4-in face of the brick and was found to be associated with black coring. Tests made on various portions of the brick showed that the black portions were more vitreous and had lower thermal expansions than the outer, more oxidized portions. On cooling, the stresses resulting from the difference in thermal expansion were such as to tend to split the brick Modification of brick mixes and method of setting are recommended to overcome black coring.     

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.     

A Discussion on Stability of Mg-Al-spinel Crown of Glass Melters

In order to understand the failure mechanism of magnesia-alumina spinel crown of glass melters,a discussion on the stability of Mg-Al-spinel crown of glass melters was given in this paper.The discussion focused on the weight balance in the crown arch made of spinel or silica bricks,the creep of spinel crown bricks at high temperatures,the thermal stress distribution in crown bricks as well as at brick joints,and the displacement behavior of crown arch during heat-up of glass melter.It is believed that the tangential stress in spinel crown is much higher than that in silica crown due to the large differenee in their densities,and that the thermal stresses in the crown brick result in opening of a part of the brickto-brick joints at the cold side of the crown,and increase of the tangential stress needed for balancing the weight of the crown.Both defect migration in lattice or along grain boundary and viscous flow in glass phase at grain boundary contribute to the creep of crown bricks at high temperatures.The creep of the matrix of spinel brick is more significant than that of coarse grains because impurities,such as silica and calcia,are concentrated in it.For keeping the crown stable during heat-up period it is important to adjust properly the horizontal positions of each skew brick as temperature increasing based on correctly evaluating the thermal expansion according to the thermal expansion coefficient of the crown brick.     

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.     

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.     

A STUDY OF THE FACTORS INVOLVED IN THE SPALLING OF FIRE CLAY REFRACTORIES WITH SOME NOTES ON THE LOAD AND REHEATING TESTS AND THE EFFECT OF GRIND ON SHRINKAGE1

Of the three factors, elasticity, coefficient of expansion and rate of temperature change, which affect spalling, the former is by far the most important. Only small differences are found between fire clay mixtures of widely varying structure and composition in the rate at which they change in temperature under like conditions of heating. The coefficient of expansion varies directly with the silica content and differences in this respect of large order were found. However, the spalling on the particular mixtures tested varied almost inversely as the coefficient of expansion. This apparent discrepancy is explained on the basis of greater elastic properties of the brick which had high expansions. The elasticity may be varied between wide limits and is sufficiently important as to overbalance the effect of greater expansion. This property is accordingly the one upon which efforts directed toward the development of non-spalling brick should be centered. It was discovered that a plastic deformation could be obtained at as low a temperature as 635°C. This gives the effect of elasticity and undoubtedly has considerable influence on spalling at the higher temperature ranges. Results are given for a number of load tests which show clearly the importance of hard firing. The secondary expansion of brick made from Pennsylvania flint clay is shown to be influenced by the temperature of reheating, as well as its rate. Detailed results showing the effect of grind and firing on the finished size of the brick included in the investigation are also given.     

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.     

熔融石英砖的蚀变过程及特点

由于熔融石英砖的热膨胀系数小,它在玻璃熔窑上被作为热修补材料使用,从而也存在和其它耐火材料一样被侵蚀,引起蚀变,并在玻璃液中产生疵点的现象.本文从几个典型的侵蚀样品的岩相分析中,试图揭示其变化过程及特点.     

架状硅酸盐矿物的Raman光谱研究

分别测定了架状硅酸盐天然矿物正长石、方钠石和霞石的Raman光谱,利用Materials Studio 3.0软件对上述3种矿物的Raman振动频率进行计算,分析他们的简正振动模式,确定了3种矿物的Raman特征谱峰的归属,分析了铝对架状硅酸盐Raman光谱的影响.结果表明:在架状硅酸盐结构中,700～800cm~(-1)区间内出现的谱峰是Al-O 振动的表现,800～1 200 cm~(-1)区间的谱峰是硅氧四面体Q~4结构单元振动的反映,随着结构中n(Al)/n(Si)(摩尔比)由正长石的1:3变化至方钠石和霞石的1:1,800～1 200 cm~(-1)波数区间的振动频率有明显的降低(从1 126 cm~(-1)降至992 cm~(-1)),在霞石和方钠石中n(Al)/n(Si)相同,其振动频率稍有变化.说明随着硅氧四面体结构中Al~Ⅳ含量的增加,800～1 200 cm~(-1)波数区间的振动频率向低频方向迁移,而金属阳离子的种类会影响Raman光谱的振动频率.     

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 MAKING OF DOLOMITE BRICK AND A STUDY OF THEIR PROPERTIES1

This investigation deals with the making and the properties of dolomite brick. A thorough review of the literature shows that there are many improvements possible in the making of dolomite brick and some of the principal faults are pointed out. In this investigation it was shown that 200-mesh dolomite mixtures of a composition 9–0–6M (9% Fe₂O₃–0% Al₂O₃–6% SiO₂–85% dolomite); 6–3–6M (6% Fe₂O₃–3% Al₂)₃–6% SiO₂–85% dolomite); and 2–4–4M (2% Fe₂O³–4% Al₂O₃–4% SiO₂–90% dolomite) can, if calcined to cone 20 down, be made into better brick than any previously described. The advantages of this higher fired material are (1) it has been more completely shrunk than that fired at lower temperatures and therefore does not shrink as much when refired in the form of brick, (2) in the use of aqueous binders less trouble is encountered due to slaking than with the lower fired material. In a continuation of the binder studies a thorough investigation was made of molasses, tar, epsom salts, water and carbonated water. No conditions were found where water, carbonated water, bindex or epsom salts, could be satisfactorily used. Using 20-mesh (2–4–4M) calcine and 15 and 20% of molasses as a binder it was found that the brick always squatted considerably at about cone 15 down. This was shown to be inherent in the material itself and not due to a migration of any part of the material or a softening of the molasses. The most successful brick were made using 20-mesh D9-0-6M composition (9% Fe₂O₃–0% Al₂O₃–6% SiO₂–85% dolomite 200-mesh calcined to cone 20 down), plus 13% of a one to three dextrin-water mixture as binder, and 20-mesh S6–3–6M (6% Fe₂O₃–3% Al₂O₃–6% SiO₂–85% dolomite 200-mesh calcined to cone 20 down), plus 12% of a 5% solution of sodium silicate and in each case fired to cones 16 to 18 down. These brick are dense, well shaped and refractory. Cone fusion temperatures of calcines 9–0–6M, 6–3–6M and 2–4–4M were made in an especially constructed oxyacetylene furnace. The results of the tests show that the above compositions have cone fusion temperatures above cone 40 (2010°C) down. In connection with this work it was also shown that an electric induction furnace, where graphite is used as the resistor, is not reliable for cone fusion tests due to the strong reducing atmosphere. In a load test on brick D9–0–6M and S6–3–6M it was found that when they are heated to 1350°C and held at 1350°C for one hour under a load of twenty-five pounds per square inch they show only a small compression. Brick D9–0–6M shows a compression of 3% while S6–3–6M shows a compression of 0.9% neither brick showing any tendency to crack or squat. In a spalling test these brick (D9–0–6M and S6–3–6M) were shown to possess the characteristic fault of magnesite in that they do not withstand sudden heat change without spalling. On heating one hour a t 1350°C and then exposing to room temperature they crack badly. The use of less flux was unsuccessful as the material thus prepared shows strong hydration which is fatal in that it causes the material to disintegrate. Dolomite compositions 9-0-6M, 6-3-6M and 2 4 4-M, flux violently with silica and fire brick but are inactive toward magnesia and chrome brick. It is, however, possible to burn the dolomite on fire clay brick if a thick layer of magnesia brick grog is used. Since it is necessary to grind the dead-burned dolomite before it can be made up into brick i t is necessary to know the relative tendency toward slaking of the various size particles. It was found that the finer the calcined dolomite is ground the more rapidly the slaking takes place and that it is in some cases very appreciable for 20-mesh material as used in making brick.     

焚硫炉设计的改进

总结焚硫炉使用中出现的问题，对焚硫炉结构的设计和选材进行了改进和完善。针对保温材料选用不合格致使焚硫炉壳体温度过高，调整炉墙 厚度，保温层同耐火层一样设为114mm和230mm两层。随着硫磺制酸不断大，粘土质耐火砖的高温机械性能达到极限，建议焚硫炉内层迎火面、挡墙选用高铝砖砌筑，次内层仍用粘土砖，以保证焚硫炉稳定操作。以砂改用槽钢代替角钢加强，并缩短槽钢间距，增加预留膨胀缝量，解决封头的变形。     

Al2O3对硼硅酸盐玻璃热膨胀和分相的影响

通过红外光谱分析了Al2O3取代SiO2后硼硅酸盐玻璃结构的变化,测试了玻璃的热膨胀系数和膨胀软化温度,通过扫描电子显微镜分析硼硅酸盐玻璃的分相,并结合X射线能谱分析了富硅相的组成.结果表明:硼硅酸盐玻璃中引入Al2O3后,随着Al2O3取代量的增加,玻璃结构中[BO3]增多,[BO4]减少;玻璃的热膨胀系数增大,转变温度和软化温度提高;硼硅酸盐玻璃中引入Al2O3后对玻璃的分相没有明显的改善作用.     

使用后铝镁炭砖的显微结构分析

对宝钢电炉盛钢桶用铝镁炭砖使用后的显微组成和结构进行了分析 ,研究了用后铝镁炭砖的相组成和显微结构变化。结果表明 ,铝镁炭砖在使用过程中组成相的烧结反应产物产生的微膨胀使制品结构进一步致密 ,尤其是越靠近工作面 ,尖晶石晶粒尺寸越大 ,最终在工作面与蚀变铝酸钙一起形成致密层 ,有效地减缓和阻止了铁水和熔渣向砖内的侵蚀与渗透。     

PROPERTIES OF SANDSTONES AS A REFRACTORY MATERIAL*

Sandstories from Chungking were tested for their properties as a refractory material. Chemical, petrographical, rational, and sieve analyses were made; properties, such as porosity, refractoriness, specific gravity, thermal expansion, and resistance to spalling. were determined; and studies were made on changes in firing up to 1550°C. No inversion of the quartz grains in the rock into tridymite or cristohalite could be detected. The interstitial clay substances fused first, and the quartz grains then dissolved gradually into the glassy matrix on firing at high temperatures. Being free from mineralogical and structural changes, unusually low in thermal expansion and porosity, and good in spalling resistance after firing at high temperatures, sandstones are shown to be an excellent refractory if properly employed. Of the two kinds of rocks, the dense and the porous, the former was found much better in test for refractoriness under load. Prefiring of the material before lining in a furnace structure is desirable to eliminate the permanent expansion and to improve the resistance to spalling in the raw state.     

Reaction of Vaporized Sodium Sulfate with Aluminous Refractories

A method was devised and tested whereby the action of an alkali salt, in the vapor or in the liquid state, on refractory materials may be studied under controlled conditions of temperature and pressure. Using Na₂SO₄, the progress of reaction was followed by (1) change of weight, (2) determination of SO₃ by precipitation, and (3) determination of Na₂O by flame photometer. The materials studied were a commercial-grade high-alumina brick (88% Al₂, 11 % SiO₂) * and fused crystalline alumina (99.5% Al₂O₃).
The dissociation of sodium sulfate, reacting in contact with high-alumina refractory materials, is speeded more by the presence of SiO₂, probably as the compound mullite, than by crystalline alpha-alumina. The ultimate product in the commercial brick is probably nephelite, NaAl-SiO₄; in the alumina, sodium alumina, NaAlO₄.
Exposure at 1200°C. in a vacuum of 150 μ of mercury approximately doubles the rate of deposition of sodium sulfate on the brick studied and adds one-third to the rate on fused alumina, as compared with the rate in air at atmospheric pressure.     

A GENERAL THEORY OF SPALLING

A theory is proposed whereby certain physical properties of a material are combined such a way as to give a measure of its resistance to rapid temperature changes. The important physical properties are the coefficient of expansion, the flexibility in shear and diffusivity. These quantities have been measured for a number of types of refractories and the theory checked by actual spalling results on these same refractories. The theory applies mainly to a single brick free from external stresses.