THE EFFECT OF STEAM ON THE TRANSVERSE STRENGTH OF FIRECLAY BRICKS1

In connection with an investigation of checker brick for carbureters of water-gas machines, it was considered desirable to find out whether or not fireclay brick suffered an appreciable decrease in transverse strength when exposed to the action of steam at a high temperature. Except for occasional references to the “destructive action” of steam, no information on this score was found in the literature. This paper describes experiments in which standard straight bricks at 11,00°C were subjected to the action of steam at the same temperature and the resulting change in transverse strength measured. No significant decrease in strength due to the action of steam alone was found.     

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.     

Fireclay refractories in pyrometallurgical processes

In primary liquid metal production, the temperature of processing and the composition of the slag phase largely determine the selection of the refractories used to line the furnace. The objective of this work was to study the effect of temperature and FeO content on the dissolution rate of a clay refractory.50-g samples of synthetic, prefused iron oxide and silica were poured into slip cast crucibles of a high-duty fireclay. These were then placed in a preheated silicon carbide-element furnace and held at the required temperatures for known times. The cooled crucibles and their contents were broken and the amount of crucible wall thinning which had taken place at the slag-refractory interface was measured using a low-power microscope and a calibrated graticule.The study of the effect of process temperature was carried out over the temperature range 1100°–1400°C at 50°C intervals. Only two compositions, 65 and 75 wt.% FeO, were chosen for this part of the work.The effect of slag composition was next studied at 1300°C, the range of slag compositions being 60–80 wt.% iron oxide at 5% intervals in the iron oxide-silica system. Only one high-duty fireclay composition was studied throughout the tests.The outcome of the work was to show that for the iron oxide-silica compositions studied a high-duty fireclay refractory can be used to contain the melts if the temperature of the process is maintained below 1300°C and when the slag composition is less than the orthosilicate composition (2FeO.SiO₂).     

THE PREVENTION OF DISINTEGRATION OF BLAST FURNACE LININGS1

Theories and observations on the causes of disintegration of fireclay refractories in blast furnaces are given and a process is developed for improving high iron clays for this use. The disintegration of refractories in blast furnace linings is initiated by alteration in the iron spots. Ferric oxide is reduced to ferrous oxide at 500°C and hastens the cracking of 2CO to CO₂+C₁ the carbon being retained by the lining. When Fe₂O₂ is converted to Fe₃O₄ the brick will not disintegrate.     

SPALLING AND LOSS IN COMPRESSIVE STRENGTH OF FIRE BRICK1

A preliminary report of the loss of compressive strength when fireclay brick from the Pacific Northwest were subjected to a series of heat treatments to 1350° and 1250°C. It illustrates some of the variations of heat treatment in the manufacturer's kilns and the differences between the high siliceous type of fire brick and the vitrifying clay type with lower free silica content. It is possible that a satisfactory spalling test may be developed in this direction.     

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.     

SOME EFFECTS OF COAL ASH ON REFRACTORIES1

The action of coal ash on the following types of refractories was studied: (1) high diaspore brick, (2) fireclay refractories with very little quartz, (3) fireclay refractories with considerable quartz, (4) refractories containing a mixture of diaspore and fireclay, and (5) andalusite refractories. The tests were carried out in a rotary test furnace at temperatures ranging from 1500 to 1600°C. The phases present in the coal-ash refractory slag were identified by means of the petrographic microscope and consisted of magnetite, mullite, and glass. The effects of time of slag action and slagging temperature were studied.     

METALLURGICAL REQUIREMENTS FOR REFRACTORIES IN THE ELECTROTHERMIC METALLURGY OF ZINC1

Refractory brick for lining electrothermic dry distillation furnaces must have a melting point of not less than 1600°C, must retain their strength at temperatures of 1400–1500°C, must be non-porous, and of uniform size. For lining electrothermic smelting furnaces, in which a liquid slag is produced, they must in addition to having these qualities be resistant to the corrosive action of highly heated slags which may be either strongly acid or strongly basic. The condensers are similar for both types of furnace. The brick for lining them need not have a high melting point but must be dense and of uniform size and must be very low in free iron oxide to withstand the disintegrating effect of carbon monoxide in the cooler portion of the condenser.     

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.     

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.     

COMPARISON OF REPEATED REHEAT TESTS OF VARIOUS GRADES OF FIREBRICK WITH SERVICE RESULTS

Representative brands of Navy-approved class A brick (60% alumina), class B brick (superduty), and special firebrick (in a price group above the 60% alumina brick) were installed in a naval boiler operating continuously at the Naval Boiler and Turbine Laboratory. The permanent volume change of the various brands, subjected to repeated reheat tests at 2912°F., is compared with their service life.     

THERMAL SHOCK EFFECT ON THE TRANSVERSE STRENGTH OF CLAY BODIES1

Test specimens of twenty commercial shale and fireclay bodies, ranging in softening point from cones 7 to 30, were fired in laboratory kilns to cones 04, 2, and 6. Comparisons of transverse strength before and after thermal shock were made, thermal shock h a i h g been produced by eight cycles of heating in a furnace at 1100°F for 15 minutes and cooling over an air blast for an equal length of time. Results indicate that as initial strength increases, per cent reduction in strength increases and strength after thermal shock increases to a maximum and then declines. Curves are fitted to the data and the mathematical relationships are shown. The results of other investigators are discussed.     

Kinetics of carbon combustion in claydite based on montmorillonite clay and coal-enrichment wastes

On heating porous fillers to 600°C, hydrocarbons are released from the granules. The only carbon remaining in the granules is graphite, which is stable at high temperatures. At 1050–1100°C, the reduction of iron is greatly accelerated. At 1100°C, there are practically no organic compounds in fired ceramic.     

Insight into the corrosion failure of mullite thermal insulation materials in carbon monoxide

The service condition of mullite thermal insulation materials is complicated, the effects of carbon deposition are always considered the primary cause of damage to mullite ceramic in carbon monoxide atmosphere. In the present study, mullite thermal insulation material was subjected to a carbon monoxide atmosphere at 1100°C–1400°C. The thermodynamics stability, phase composition, and microstructure of the mullite thermal insulation material were analyzed. Furthermore, the effects of carbon monoxide corrosion on thermal shock resistance and compressive creep behavior at high temperatures were evaluated. The carbon content in the mullite-based insulation material is below 0.02% after treatment at 1100°C–1400°C. After treatment at 1400°C, most areas in the specimen comprised corundum and glass phase, and K, Na, Ca, Mg, and Fe were detected as impurities, leading to the improvement of cold crushing strength after 20 thermal shocks but a remarkable recession in high-temperature compressive creep.     

The effect of pre-carbonization on the properties of PAN-based carbon fibers

A continuous stabilization and two-stage carbonization process was used to prepare polyacrylonitrile (PAN)-based carbon fibers, The effect of pre-carbonization (300 to 550°C) on the final properties and microstructure of carbon fibers was measured. Experimental results using an X-ray diffractometer indicated the presence of a less ordered structure at 2Θ from 5 to 18° in the pre-carbonized fibers and the final carbon fibers. This study found that the pre-carbonization process strongly affects the microstructure of the resulting carbon fibers. The results also showed that a suitable pre-carbonization was very conducive to improvement in tensile strength or in Young's modulus of the final carbon fibers. When the final carbon fiber was pre-carbonized at 300 and 550°C, respectively, these fibers had a higher tensile strength and higher Young's modulus than carbon fibers pre-carbonized at other conditions.     

Effect of transient creep on compressive strength of geopolymer concrete for elevated temperature exposure

The strength and transient creep of geopolymer and ordinary Portland cement (OPC)-based material (paste and concrete) were compared at elevated temperatures up to 550 °C. The strength properties were determined using an unstressed hot strength test and unstressed residual strength test for paste and concrete, respectively. At 550 °C, compared with the original strength, the strength of geopolymer was increased by 192% while the strength of OPC paste showed little change. However, after exposure to 550 °C, the residual strength percentage of both geopolymer and OPC concretes was similar. Transient creep data show that geopolymer had little change in transitional thermal creep (TTc) between 250 and 550 °C while OPC paste developed significant TTc in this temperature range. In comparison with OPC concrete, a higher strength loss of geopolymer concrete is thus believed to be due to the absence of TTc to accommodate nonuniform deformation during thermal exposure.     

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.     

Structure and properties of iron containing glassy carbons

Glassy carbons containing iron were prepared from copolymers of furfuryl alcohol and ferrocene derivatives at heat-treatment temperatures from 500°C to 2500°C. The copolymerization produced a highly dispersed state of iron in carbonaceous matrices at least in the early stage of pyrolysis. Above 500°C, the homogeneously dispersed iron separated into irregularly spaced domains consisting of cementite, pure iron and iron compounds of unknown composition. Addition of iron resulted in a local graphitization of the glassy carbon at heat-treatment temperatures above 1000°C. At heat-treatment temperatures between 500°C and 800°C, electrical resistivities of the iron-doped carbons were much smaller than those of unmodified polyfurfuryl alcohol carbons but followed more or less the behavior of the latter for heat-treatment temperatures above 800°C.Measurements of mechanical properties indicated a remarkable increase in tensile strength of the low temperature carbons (500°C) with increasing iron content but the strength of the iron containing carbons decreased at higher carbonization temperatures.     

Combustion of carbon in the firing of ceramic heat insulation based on fuel-shale wastes

The firing of ceramic heat insulation based on fuel-shale wastes without traditional materials is investigated. On heating insulation in the range 400–600°C, most of the volatiles are removed. Above 800°C, pyrolytic forms of carbon (coke and semicoke) are produced. In the range 1050–1100°C, the reduction of iron is markedly accelerated. At 1100°C, there are practically no organic compounds in the fired ceramic.     

CAUSE OF DEFECTS IN ENAMEL FIRED ON CAST IRON AT TEMPERATURES ABOVE 725°C., I*

A previous investigation on enameling cast iron is continued. Various wet-process enamels were fired at temperatures above 725 °C. (1335°F.). Blistering and pinholing, even at high temperatures, were found to be caused principally by hydrogen contained in the iron and not by carbon oxides. If carbon oxides form, they do not occur in sufficient quantities to deface the enamels. Dehydrogenized cast iron may be fired as high as 790°C. (1455°F.) with a direct application of sheet-steel white cover coat and at 840°C. (1545°F.) with sheet-steel ground coat without incurring defacement. The moisture content of certain constituents in wet-process enamels at higher temperatures causes an important gas effusion by reacting with the metal. The characteristics of the behavior of hydrogen in cast iron during enameling are compared with those of hydrogen in steel.