THERMAL AND MOISTURE EXPANSION OF KAOLINS AND BODIES FIRED TO DIFFERENT TEMPERATURES*

Thermal-expansion and moisture-expansion determinations were made on four kaolins of the Georgia, Florida, North Carolina, and English types alone and on typical semivitreous, hotel china, and electrical porcelain bodies embodying each of these kaolins after being fired at cones 6, 9, and 11. The Georgia and Florida kaolins and bodies showed surprisingly similar expansion characteristics. The general order of decreasing thermal expansion and increasing moisture expansion of the kaolins at all three firing treatments was Georgia, Florida, North Carolina, and English china. The semivitreous bodies at cones 6 and 9 showed the same order of expansion as the kaolins alone, but at cone 11 the thermal expansion of the English china clay body was the highest and the North Carolina kaolin body next in order. Moisture expansion of the bodies at cone 11 was found to be a function of the absorption, regardless of the kaolin used with no expansion obtaining at zero absorption. Mixtures of clay, flint, and feldspar, given an autoclave treatment after being fired to cones 6 and 9, showed that feldspar additions increased moisture expansion. When these mixtures were dehydrated at different temperatures, the data obtained were insufficient to confirm any theory on the nature of moisture expansion in a porous ceramic body.     

THE RESISTANCE OF SINGLE CLAY BODIES TO THE ACTION OF STEAM1

Twelve whiteware bodies were made, consisting of 51.41%, clay, 10.69% North Carolina feldspar, and 37.9% flint, one clay being used in each body. Twelve clays were studied. The specimens made from these bodies were fired in the regular tunnel bisque kiln to cone 9, glazed on one side, and fired to cone 4 in the glost kiln. The trial pieces were then subjected to the autoclave test, with the steam at a pressure of 100 pounds per square inch, maintained for a period of 3 hours. Of three American ball clays none was found to have caused crazing. In the case of four domestic kaolin bodies, one crazed in part, two were noncrazing, and one shivered. Of five imported kaolins, one of the bodies was noncrazing. While lower absorptions bring about a craze-resisting condition, it was shown that of two single clay bodies with practically the same absorption, one may resist the steam action and one may not. The structure of the clay is an important factor in this connection.     

USE OF THE PHOTRONIC CELL AND SPECTROPHOTOMETER FOR MEASURING TRANSLUCENCY OF WHITEWARE*

A method has been developed for measuring the translucency of whiteware by means of the photronic cell, and a modified formula has been derived to express the relationship between translucency and thickness of ware. Bodies containing mixtures of feldspar and lepidolite were translucent over a greater range of temperatures than those which contained feldspar or lepidolite alone, although the translucency of the feldspar bodies was greater than that of the lepidolite bodies having equivalent absorptions. The spec-trophotometer gives a more complete record of the translucency of porcelain because it may be used to measure the transmittance of ultraviolet, visible, and infrared light.     

MOISTURE EXPANSION OF GLAZES AND OTHER CERAMIC FINISHES1

Research for ascertaining why some glazes are more resistant to “moisture crazing” than others revealed the fact that certain glazes expand, because of the action of water, similarly to some of the ceramic bodies t o which they are applied. Although a control of this type of expansion is very important in fitting glazes to bodies, it has not been previously considered. Its importance should be evident at once when it is considered that a large “moisture expansion” in a glaze or other finish is in many cases an indication that the glaze will not be so liable to craze when the ceramic ware or material on which it is used is exposed to moisture. This follows since the glaze and the body on which it goes and which is ordinarily very susceptible to this kind of expansion will then increase in size simultaneously and more nearly at the same rate. Such conditions lessen the tendency of the body expansion to cause tensile stresses in the glaze. In this investigation specimens of various finishes were subjected to steam at 150 pounds per square inch for an hour because it was known that this treatment of such materials produces effects similar to those caused by long exposure to weather. This artificial weathering treatment caused in lustrous glazes an average expansion of 0.004%, in mat glazes 0.011%, in vitreous slip finishes 0.005%, and in porous slip finishes 0.033%. The moisture expansion of one of the mat glazes was 30% of the average obtained for a ceramic body having an absorption of approximately 12%. This proclivity of ceramic finishes to expand by the absorption of moisture can be controlled in their manufacture.     

EFFECTS OF AUTOCLAVE TREATMENTS ON CERAMIC BODIES AND CLAYS1

It has been found that porous ceramic bodies increase in volume and weight due to an autoclave treatment in which the ware is subjected to steam at a pressure of 150 pounds per square inch. The change is rapid at first but decreases as the time of treatment is increased. Typical American and English china clays also increase in volume but ball clays when fired to the same temperature as the china clays do not increase in volume. The effect of prolonged drying treatments after the autoclave treatment is also studied. Data given indicate that the changes in volume are not necessarily caused by rehydration of the clay within the body. Bodies containing clay, feldspar, and flint show a greater increase in volume than do the pure clay constituents. It is shown that the composition is a more important factor than absorption in determining the reaction of ceramic products to the autoclave treatments.     

EFFECT OF ADDITIONS OF DIOPSIDE ON PROPERTIES OF WALL-TILE BODY *

Diopside was substituted for both talc and feldspar in a typical wall-tile body. It was found to lower the fusion temperature and to lower thermal expansion when compared with talc and to raise thermal expansion when compared with feldspar. Its effects on firing shrinkage, fired absorption, and moisture expansion were somewhat similar to those of talc.     

INFLUENCE OF FLUXES OF SPODUMENE AND FELDSPAR MIXTURES ON PROPERTIES OF CHINAWARE BODIES*

The most fusible spodumene-feldspar mixture used in these studies was composed of 30% of spodumene, 10% of potash feldspar, and 60% of soda feldspar. In semi-vitreous bodies and vitreous hotel chinaware bodies, however, the most effective fluxes were made up of 30 to 40% of spodumene, 40 to 60% of potash feldspar, and 10 to 20% of soda feldspar. Such fluxes lowered the maturing temperature of these bodies and improved their strength at lower temperatures. When they were fired at cones 6 to 9, their resistance to impact was equal to or higher than that of the feldspar bodies.     

THE EFFECT OF CALCINED CYANITE IN PORCELAIN BODIES1

A study was made of the physical properties of porcelain bodies containing varying amounts of calcined cyanite (mullite), feldspar, and flint with a constant content of 50% clay. All bodies were made up under uniform conditions and fired to their proper maturing temperatures which varied from cones 8 to 20. Moduli of rupture for correctly fired bars varied from 5100 to 12,100 Ibs. per square inch, those bodies high in mullite being the strongest. The coefficients of linear expansion between 30 and 844° C varied from 4.3 × 10⁻⁶ to 6.6 × 10 ×⁻⁸ 6, those bodies high in mullite having the lower expansion. Thirty per cent or more calcined cyanite (50% or more total mullite as figured from chemical composition) must be present to obtain a marked effect on either of these properties. Triaxial diagrams show the position of various typical porcelain bodies and how they might be affected by additions of this material.     

Recycling and Utilization of some Waste Clays for Production of Sintered Ceramic Bodies

The recycling of industrial waste clays for production of an interesting ceramic product is the main goal of the present research work. Ceramic bodies were prepared using Feeders or Cyclons waste clays, sand and feldspar. 0.0, 15, 20, and 25 wt.% of sand were added at the expanse of kaolin (75-50 wt.%). Constant mass percent (25 wt.%) of feldspar was added for all ceramic compositions. The designed batches were sintered at 1200–1400 °C. Physical properties were determined by water displacement method. Phase composition and microstructure were investigated by x-ray diffraction and scanning electron microscope, respectively. The compressive strength was also determined. The results indicated that the ceramic bodies prepared from Cyclons’ waste clay exhibited higher physical and mechanical properties than that prepared from Feeders’ clay after sintering at 1400 °C. The addition of sand enhances the porosity, water absorption, bulk density and mechanical strength after sintering at 1400 °C due to the formation of mullite network and glassy phases.

     

The effects of fine fire clay sanitaryware wastes on ceramic wall tiles

In the last decade, environmental preservation has become an important issue. Specifically, recycling of sanitaryware fine fire clay (FFC) waste is important for reducing costs. In this study, the use of FFC waste as an alternative raw material in the production of ceramic wall tiles was investigated. Five ceramic wall tile bodies were prepared by substituting kaolin (max. 15 wt%) with FFC wastes. All formulations were mixed, pressed into pellets and sintered at 1145 °C. The sintering behaviour was evaluated using an optical dilatometer. Water absorption, linear shrinkage and bending strength were also measured. This study revealed that FFC wastes are good alternative raw materials, and the corresponding formulations were shown to be viable in the manufacturing of ceramic tiles. The most remarkable conclusion from this study was that the addition of FFC waste decreased moisture expansion.     

EFFECT OF REPEATED WETTING AND DRYING ON PHYSICAL PROPERTIES OF A CLAY BODY*

Specimens of fine-grained, red-firing clay, which had been fired to temperatures corresponding to various stages of vitrification, were subjected to 200 cycles each of wetting at 100°F. and drying at 100°F. and 60% of relative humidity. This treatment, simulating weathering in mild climates, caused (1) a permanent gain in weight which was greater for the softer specimens; (2) a moisture expansion for the softer specimens but none for those near vitrification; (3) a fairly uniform decrease in modulus of elasticity for all specimens; and (4) a decrease in modulus of rupture for the softer specimens but an increase in strength for those that were completely vitrified. The data indicate that moisture expansion and a decrease in strength of soft-fired clay bodies, caused by repeated wetting and drying, may be eliminated by proper vitrification.     

晶相组成与中铝瓷机械强度关系的研究

本研究以粘土 ,长石和石英为基本原料 ,并引入煅烧铝矾土以满足配方中的Al2 O3 含量 ,制造出了中铝质高强度陶瓷材料 ,材料的抗折强度达到 14 0MPa。通过对中铝质陶瓷材料的XRD分析 ,研究了材料晶相组成与强度之间的关系 ,并探讨了其机理     

Effect of particle size and alkali activation on coal fly ash and their role in sintered ceramic tiles

We focus on fly ashes of different sizes and their alkali-activation on ceramic products. Backscattered electron imaging-energy dispersive X-ray spectroscopy was used to classify coal fly ash particles according to particle size and to study the pre-activation of particles with different sizes. Secondary electron imaging-energy dispersive X-ray spectroscopy was used to study the role of coal fly ash particles of different sizes in ceramic bodies before and after alkali-activation. Ash particles can be divided into three classes based on size: clay-, quartz- and feldspar-like particles, which act as clay, quartz and feldspar, respectively, in ceramic bodies. The pre-activation process contributes to the plasticity of ash particles, the crystal skeleton role of clay-like particles and the fluxing agent role of feldspar-like particles, so preprocessing can improve the performance of ash-based ceramic tiles significantly. This research provides a new pretreatment method for coal fly ash in ceramic fields.     

Moisture Expansion of Clay Products

The phenomenon of moisture expansion as related to structural clay products was studied to obtain information on the magnitude of expansion in commercial brick and to determine the phases in the fired body which are responsible for the expansion. Many commercial brick were tested and analyzed, and the results were expanded by laboratory tests on specimens prepared from the crude clays. Pure kaolin specimens, with and without controlled additions of impurities, were employed to study the mechanism and causes of moisture expansion. Information was gathered to substantiate the theory of moisture expansion proposed by Smith in 1955. The results produced considerable doubt about the reliability of an accelerated autoclave test as a measure of moisture expansion under service conditions. At the end of this study, several factors came to light which would assist the brick manufacturer in producing a more stable product with respect to moisture expansion.     

THE CAPILLARY SUCTION OF SOME CERAMIC MATERIALS1

The forces which act when clay is mixed with water and when water is removed from wet clay by evaporation have received little study. For this reason, very little definite information regarding the internal mechanism of the drying of clayware is available. In this paper, the writer reviews the experiments and theories of Pukall, Terzaghi, Dixon, etc., lists some of the forces which may act when ware is drying, and defines an important force which he calls “capillary suction.” A simple experiment is described, by means of which this force can be readily demonstrated. The development and final form of an apparatus for measuring the capillary suction of ceramic materials is described and data obtained from measurements on a ball clay, a kaolin, flint, feldspar and mixtures of these substances are reported. Capillary suction decreases rapidly with increase in the flint and feldspar of a ceramic body. By utilizing the capillary suction produced by evaporation of water from a clay surface, water at atmospheric pressure has been made to enter a steel bomb in which the gas pressure was maintained at 200 lbs. per square inch.     

FELDSPARS AND THEIR PECULIARITIES AS CERAMIC SOLVENTS1

Data are presented to combat the fallacy that the chemical composition of a feldspar is a definite indication of its behavior as a vitrifying agent in ceramic bodies. A general presentation of data on the pure feldspar types and their constitution and mode of occurrence in commercial deposits is made. The effect of solid solution vs. associated or mixed feldspars on the physical properties of feldspars of similar compositions is outlined and the character of associated quartz and muscovite (white mica) is considered. A proposed basis of classification depending on the fusion behavior of the feldspar in the presence of quartz, kaolin, and ball clay is made.     

THE SOLUBILITY OF QUARTZ AND CLAY IN FELDSPAR1

The literature on the subject is completely reviewed. The method used involved the addition of increasing amounts of kaolin to fixed amounts of feldspar and the addition of increasing amounts of quartz to fixed amounts of feldspar. All compositions were examined microscopically and the presence of undissolved kaolin was shown by the appearance of mullite needles, while the presence of undissolved quartz was shown by the presence of cristobalite. Soda feldspar is a better solvent for both quartz and clay than potash feldspar. The solution of quartz in soda feldspar starts at about 1350°C and increases with the temperature until at 1425°C. 32 parts of quartz per 100 of feldspar are dissolved. The solution of quartz in high potash feldspar does not start until 1400°C and only 4 parts are soluble at 1425°C to every 100 parts of feldspar. The solution of clay in soda feldspar starts at 1225°C and increases with the temperature until at 1425°C thirty-six parts are soluble. The solution of clay in high potash feldspar starts at 1250°C and at 1425°C the solubility is 20.5 parts per 100 of feldspar. The solution of quartz in porcelain bodies starts at the same temperature as it does in the pure feldspar which the body contains. The amount of solution per unit of feldspar is much greater. The general trend of one of the boundary lines in the ternary system K₂O-A1₂O₃-SiO₂ has been found.     

METHOD OF MEASURING STRAINS BETWEEN GLAZES AND CERAMIC BODIES1

A new test was developed for comparing the strains existing between different glazes or other ceramic finishes and the bodies to which they are applied. By its use these strains may be so adjusted that the finishes will be in suflicient compression to prevent crazing from subsequent expansion of the body without causing initial shivering. The new test is particularly valuable because the measuremen & are made on combinations of glaze and body prepared and treated almost exactly like those intended for regular use and because of the simplicity and cheapness of the apparatus required. A modification of the test provides a comparison of the moisture expansions of different bodies.     

Feldspar and firing cycle effects on the evolution of sanitary-ware vitreous body

This work is focused on the study of macroscopic and microscopic properties of traditional sanitary-ware vitreous bodies as a function of feldspar flux and firing time-temperature profile, using a fixed slip formulation (50 wt.% clay, 25 wt.% quartz and 25 wt.% feldspar). Two flux particle sizes (45 and 75 μm), three flux compositions (Na-based feldspar, K-based feldspar and a mix of them) and three firing cycles with the same soaking temperature (i.e. 1240 °C) have been combined to evaluate their effects on the relevant industrial properties of water absorption and thermal expansion. The micro-scale observables, phase composition and micro-morphology, have also been investigated. Despite a general similarity exhibited by the ceramic samples, qualitative and quantitative differences in terms of feldspar dissociation temperature, phase-composition and densification trends have been observed. In particular, for a fixed firing cycle, the combination of the sodium based feldspar with the smallest flux particle size leads systematically to a water absorption value that is below the 0.5 target value and to a glass amount that approaches 70 wt.%. Thermal expansion coefficients below the quartz α–β transition are found in the 6.2–6.9×10⁻⁶ °C⁻¹ range; the highest values seem to be favoured by incorporation of potassium based.     

无锆乳浊釉的研制

本文以粘土、钾长石、石英、硅灰石、氧化锌、滑石、硼钙石等为原料,形成K2O-CaO-MgO-ZnO-B2O3-Al2O3-SiO2系统釉料,运用四角配料的方法进行配制,获得釉面平整、白度和光泽度高的无锆乳浊釉。采用XRD、SEM等测试手段,研究了该釉的微观结构和乳浊机理。