CORRECTION OF AN EXTREME CASE OF CRACKING IN THE DRYING OF BRICK1

I. In the manufacture of stiff-mud brick from a highly colloidal clay of low permeability to water, drying breakage was extremely high even though the drying was conducted at a very slow rate under high humidity conditions. Laboratory investigation yielded two methods of correcting the faults: (1) Preheating the clay for half an hour at a temperature between 400 °C and 500 °C increased the permeability to such an extent that brick made from the preheated clay could be dried rapidly without cracking. (2) Coagulating chemicals, such as aluminium chloride, ferric chloride, sodium chloride, and hydrochloric acid, in conjunction with moderate additions of grog, increased the permeability and thus improved the drying properties of the clay. II. Plant scale tests using ferric chloride, sodium chloride, and grog resulted in the production of brick which could be dried safely in a reasonable time. The fired brick were improved in quality as to strength and color. III. The chemical treatment of the clay using 1% ferric chloride and 0.5% sodium chloride with 10 to 15% grog was adopted for plant operation and resulted in increased production, lower cost of manufacture, and improved quality of product.     

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.     

SUBSTITUTION OF DOMESTIC MINERALS FOR INDIA KYANITE: VI,REFRACTORY PROPERTIES OF GEORGIA MASSIVE KYANITE*

The massive kyanite of Georgia is similar in structure to India kyanite, but it contains quartz with only occasional small amounts of corundum; sericite between the kyanite crystals is common. Excellent coarse grog (67% through 6- on 35-mesh) can be produced from this kyanite. Maximum expansion of the rock during calcining occurs at 1400°C. with slight shrinkage thereafter. Brick were made of the kyanite grog with 3% and 10%, respectively, of EPK (Florida) clay; both had excellent resistance to load at elevated temperatures and met the reheat specifications of the Navy Department and the A.S.T.M. In the panel spalling test, Georgia kyanite brick showed approximately 20% loss, whereas India kyanite brick of the same grain size and clay content showed only 0.3% loss. Intensive prospecting is necessary and the unusual mining and cleaning operations with present known deposits make large-scale commercial operation questionable.     

SOME EXPERIMENTS WITH ZIRCON AND ZIRCONIA REFRACTORIES*

This is a record of the results of five years' research on refractory uses for a chemically purified grade of zircon and electrically fmed zirconia of high purity. The products investigated included semi-permanent foundry molds, refractory brick and cements, ladle nozzles, and crucibles. Electric firing and a small oil-fired tunnel kiln are described. Sintered zircon grog was found superior to electrically fused grog. Zircon brick made with 50% grog, using 20% milled zircon for the permanent bond and fired at 1600°C for an hour, showed no firing shrinkage, very slight volume change, and high compressive strength at 1600°C. They were extremely resistant to spalling but did not resist basic slags or metallic oxides very well a t high temperature. Zircon-bonded magnesite brick were more refractory than ordinary magnesite, more resistant to spalling, and had about the same slag resistance magnesite. Zirconia was more refractory than zircon and had better slag resistance. Lime-bonded zirconia crucibles of good spalling resistance were made, but the cost was higher than that of zircon. The effects of various binders are discussed.     

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.     

THE USE OF PLASTIC CLAY GROG IN PREVENTING SPALLING1

Effect of calcined clay grog on the properties of fire-brick .—A medium dense-burning clay was calcined at cone 8, then ground and mixed with plastic clay in various proportions up to 40 per cent. An air spalling test of the burned bricks showed that the grog increased the resistance to spalling about 5 per cent for each per cent of grog added. The results for other physical properties agreed with those found by previous observers; the bricks with grog were more porous and weaker mechanically but showed less drying and burning shrinkage.     

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 PROPERTIES OF REFRACTORIES IN THE METALLURGY OF ZINC1

A study has been made of some of the properties of clays, grogs, and body mixtures used by various zinc smelters for the manufacture of zinc retorts. Only minor differences were observed in the properties of the clays. No attempt has been made to offer any of the results as conclusions. The investigation tends to confirm the following points; that the use of reclaimed retort material in the grog for new retorts is of doubtful economy; that, if old bricks or shapes are used as grog, care should be taken that they were originally made of good quality clay and that they are free from slag; that some flint clay of good quality and properly calcined is advisable for at least a part of the grog; and that zinc in a clay or body mixture markedly affects the refractoriness by lowering the deformation value.     

COMPARATIVE SERVICE TESTS OF GROSS ALMERODE AND DOMESTIC CLAY POTS1

Glass-drawing pots made from Gross Almerode clay proved to be superior in a service test to pots made from a synthetic siliceous domestic clay mixture. When removed from service the faces of the Gross Almerode pots are pitted. The faces of domestic clay pots are surface cracked. The blistering of the glass caused by this cracking is eliminated by substituting silica brick grog for fire clay grog.     

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 INVESTIGATIONS OF A NEBRASKA CLAY1

A brief review of the literature on the fluxing action of different metallic oxides on clays is given. A series of mixtures of what seemed to be the “dirtiest” clay of four obtained, with varying amounts of pure calcium carbonate which passed a 150-mesh screen was made up into briquets and physical properties were studied on the unfired and fired specimens. The firing was done at four temperatures, 1800°F, 1900°F, 1950°F, and 2000°F. Properties observed were fusion point, drying and firing shrinkage, crushing strength, and porosities of the fired specimens. The principle of the Armstrong volumeter used for porosity determinations is explained. The results obtained indicate possibilities of materially improving qualities of brick now being produced from so-called ordinary clays but only after a very considerable amount of further work is done.     

OBSERVATION ON THE EFFECT OF SILICON CARBIDE IN CLAY BODIES1

In these studies the distinction is made between silicon carbide in a clay body and clay-bonded silicon carbide. An increase of strength by replacement of grog particles was noted. Tests were made on various bodies containing as little as 10% Sic by weight and up to 67% by weight. Comparison of clay and grog bodies, clay grog, and SiC bodies, and clay and SiC bodies were carried out under the load-span test at various temperatures. The resistance of bodies containing SiC to the corrosion effect of various slags, particularly iron oxides with alkalis and alkaline earths, is given. A comparison is made with clay-grog bodies. The increase of conductivity of bodies containing SiC is apparent. Commercial application of SiC and clay bodies is discussed.     

Firing arkalyksk clays into grog and obtaining products from it

Conclusions We obtained heat-technical and technological factors for the firing of Arkalyksk clays in rotary furnaces.On the basis of grog made from these clays we obtained class-A articles.Ladle brick made on the basis of grog from Arkalyksk clay shows a resistance of 1–3 heats greater than ordinary ladle brick.Translated from Ogneupory, No. 7, pp. 33–40, July, 1966.     

Effect of heat treatment and zircon addition on the properties of low-cement castables based on recycled alumina grog

In this investigation, low-cement castables were prepared using 70% alumina grog aggregates obtained from crushed alumina brick waste. The aggregates were thermally treated at 1550 °C for 3 h. Four types of low-cement castables were prepared with various types of aggregates (alumina grog with or without thermal treatment) and fillers (with or without zircon addition), and they were evaluated in terms of their physical, thermal, and chemical properties. Microstructural analysis via scanning electron microscopy (SEM) was performed on the castables before and after slag attack. Compared to the other fabricated castables, the thermally treated alumina grog castables with zircon showed better physical properties, such as a higher bulk density, cold crushing strength, and modulus of rupture and a lower apparent porosity and water absorption. In addition, they had a higher positive linear thermal expansion, refractoriness under load, permanent linear change, and hot modulus of rupture. The results of the SEM with energy dispersive X-ray analysis of the prepared castables confirmed that the mullite and anorthite phases were predominant when zircon was not added and the zircon–mullite phase additionally appeared upon the incorporation of zircon. A quantitative elemental analysis via X-ray fluorescence spectroscopy was employed to determine the composition of the castables. X-ray diffraction analysis showed that the alumina grog castables had a high mullite and low anorthite content, and the thermally treated alumina grog had a high anorthite, low mullite, and high zircon content. The improvement in the mechanical and thermo-mechanical properties of the castables with thermally treated alumina grog and added zircon can be attributed to the formation of the zircon–mullite phase with a low mullite phase content.     

SOME EXPERIMENTS ON THE FIRECRACKING OF TERRA COTTA1

Firecracking .—occurs on terra cotta under certain conditions and is characterized by the appearance of sharp, hair-line cracks extending into the body. The experiments were made by firing large typical pieces of terra cotta made from various clays and grogs and cooling them at different rates. The tendency to firecrack was observed after weathering. The absorption, porosity and transverse strength of the various bodies were determined. Rate of Cooling .—All bodies similar to those used in practice showed a tendency to firecrack when cooled rapidly and all were free from cracks when cooled slowly. The rate of cooling has a much greater effect on the tendency to firecrack than the composition or physical properties of the body. Effect of Clay .—Three of the four sandy clays showed a decided tendency to firecrack, due to the difference in the expansion and contraction behavior of sand and clay in heating and cooling. The sandy clays showed more tendency to firecrack than the non-sandy, vitrifying clays. The tendency of a clay to develop firecracks in a body depends to a very large extent upon the character of the clay itself, regardless of the impurities it contains. The presence of sandy material and the character of the clay appear to have a much greater effect on the tendency to firecrack than the absorption, porosity or transverse strength of the body. No relation was found to exist in these experiments between the porosity and transverse strength of a body and its tendency to firecrack. Effect of Grog .—The greatest tendency to firecrack was found on a body with all grog finer than 40-mesh, but a body with all grog coarser than 40-mesh did not appear to have much less tendency to firecrack than the average. Increase of grog reduced the tendency to firecrack. The kind or source of the grog used does not have as much effect on the tendency to frecrack as the size and amount. The kind of grog is of much less importance in this respect than the kind of clay.     

A STUDY OF THE EFFECT OF GROG ON PRESSURE TRANSMISSION IN DRY PRESSING1

A study of the dry-pressing characteristics of several fire brick and building brick clays was made by compressing them, at high and low pressures, into large shapes with a hydraulic press The clays do not effectively transmit the pressure into the interior. The finest grained clays are morc deficient in this respect. The result is a porosity gradient as high as 15% of the interior porosity between center and surface. Such a variation may account, in part, for the defects in dry-press ware. The addition of fired grog increases the pressure transmission. Some clays require more than 50% grog and some less for maximum pressure transmission and optimum results. Fireclay shapes as much as ten inches in thickness and of substantially uniform physical properties can be formed if the proper amount of grog is used.     

PROGRESS REPORT ON INVESTIGATION OF SAGGER CLAYS. V. Preparation of Experimental Sagger Bodies According to Fundamental Properties1

This is a Fifth Progress Report giving the results obtained in a preliminary study of sagger bodies, which is a continuation of an extensive investigation of sagger clays for the purpose of determining the properties of clays and bodies best suited for sagger purposes. The report contains data on the modulus of elasticity, transverse breaking strength, plastic flow, thermal expansion, and resistance to failure due to heat shock of 55 sagger mixes representing 39 different bodies fired at either 1230°C or 1270°C. The 16 bodies prepared in duplicate were tested both after firing at 1230°C and 1270°C. All of these bodies were compounded with two clays whose properties are given in earlier progress reports, and a mixture of graded grog. The grog was graded into sizes so as to result in two types of bodies, those having (1) a coarse and open-grained structure and (2) a dense and fine-grained structure. The data on the fired bodies show that those containing the fine sizes of grog have the higher modulus of elasticity, transverse strength, and in the majority of cases, thermal expansion. Very little difference in total porosity of the two types of bodies is indicated although the rate of absorption shows large differences. The data obtained in this preliminary study indicate that those bodies having (1) a porosity of less than 25% (2) a low modulus of elasticity, (3) as high transverse strength as is compatible with the low modulus of elasticity, and (4) low thermal expansion below 250°C are the most desirable for sagger purposes.     

Development of fly ash cenosphere-based composite for thermal insulation application

Cenosphere-based composite was developed with addition of clay and other additives, by dry processing route. The performance of cenosphere as high-temperature insulating material was studied. Cenosphere stands unique among the constituents found in fly ash due to its hollow spherical structure. Cenosphere is utilized in numerous modern applications due to its unique properties such as lightness, high compressive strength, enhanced flow characteristics, less water absorption, chemical inertness, and good thermal resistance. Keeping cenosphere as major component, three different mix recipes for insulating brick were made. The recipes were blended and shaped by pressing, followed by drying and sintering at 1000°C. The prepared samples were analyzed for their physical, mechanical, and thermal properties. The surface and pore distribution are analyzed by scanning electron microscope. Results from the analysis shows that cenosphere can be used as high temperature insulating material.     

Ural clays for building brick production

The chemical-mineral composition and technological properties of two varieties of low-melting clays used in production of building brick are investigated. It is found that based on the blend of these types of clay and using metallurgical slag as an additive, it is possible to obtain a ceramic mixture with minimum drying sensitivity and mechanical strength after firing at a temperature of 950°C at least equal to 12.5 MPa. Translated from Steklo i Keramika, No. 5, pp. 25 – 27, May, 1998.     

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.