Clay Raw Materials Research Articles

Quantitative determination of pyrite in, ceramic clay raw materials by DTA

Abstract The thermal oxidative decomposition in air of 0–1.5 wt% of pyrite added to two traditional powdered clays was investigated by non-isothermal DTA. It emerged that the first step of the exothermic oxidation of pyrite, in the 350–500°C range, partly overlapped the endothermic dehydroxylation of clay minerals, centred at 590°C, and the result was dependent on the pyrite contents. Based on the values of the area of the oxidative peak and of the corresponding oxidation heat, it is possible to calculate quantitatively the amount of pyrite present in the industrial clay bodies and therefore to inform the technicians of the factories so they can avoid the negative effects of reducing reactions that could occur during firing of ceramic raw materials.

Special effects of quartz, calcite and coal on the drying properties of ceramic mixtureS

The method of dispersion analysis and experiments are used to establish the possibility of using coal concentration waste, which contains a clay component close to conventional clay raw materials and quartz, calcite and coal impurities. The results of an experimental study of the physicochemical properties of model mixtures are presented together with some practical recommendations.

Fly ash in Polish building ceramics—threat or proecology?

Fly ash from the combustion of bituminous coals extracted in some Polish collieries (e.g. from “Wesoła” colliery in the Upper Silesian Coal Basin) can be characterized by the moderate contents of subordinate and trace elements as well as by acceptable radioactivity. Hence, the fly ash can be used successfully for the production of building ceramic materials. The increase in the amount of fly ash (60–70 wt.% and more) in the raw materials for building ceramics can be considered as a proecologic solution. On the one hand it results in the utilization of this waste material and on the other it contributes to a decrease in the consumption of unrestorable clay raw materials.

Clay and man: clay raw materials in the service of man

Clay has always played a major role in human life. Clay raw materials are used and their value recognized in many economic branches, agriculture, civil engineering and environmental studies. This is largely because of their wide-ranging properties, high resistance to atmospheric conditions, geochemical purity, easy access to their deposits near the earth's surface and low price.Clay minerals, the essential constituents of argillaceous rocks, can be classified in seven groups according, to their crystal structure and crystal chemistry. Clay raw materials are divided in the same way into seven groups. An eighth group covers clay ochres and pigments. Further classification is based on the purpose-made technological application. Some examples show relations between the crystal structure or crystal chemistry of the dominant phyllosilicate and the technological properties. The chapter “Utilization of clay raw materials in industry and other human activities” is the most extensive. It gives information on the application of clay raw materials or individual clay minerals: in the production of foods, feedstuffs, beverages, paper, rubber, plastics, artificial leather, protective coatings for interior and exterior use, pharmaceutics, cosmetics, paints, pencils, pastels, porcelain, electro-porcelain and other fine ceramics, coarse ceramics and sialon ceramics; in the foundries, various branches of the chemical, petroleum and cement industries, agriculture and forestry; in the preparation of agrochemicals and special fertilizers, lubricating oils and gels, lightweight ceramics and effective sorbents; in the manufacture of mineral wool, in briquetting and pelletizing processes; as ingredients in grinding and polishing pastes, in the insulations of dumps of various kinds of waste (including toxic and radioactive waste), in thermally, electrically, acoustically and chemically resistant insulations, and in filters for the treatment of industrial, agricultural and similar outflows.The earth sciences use the clay minerals in the earth crust: (1) as indicators of the environment during weathering, allothi- and authigenesis in the sediments and in the study of the source areas of the detrital supply; (2) as pH indicators and indicators of processes in micro- and mega-environments and of changes in the course of diagenesis and metamorphosis. Mineralogical, petrological, geological and geochemical investigations directed to clay minerals serve as one of the correlation methods, in the recognition of processes in the petroleum-bearing sediments, coal-bearing formations, origin of riverine, lacustrine, marine and oceanic sediments and in the climatic, geodynamic, paleogeographical, stratigraphic and weathering rate interpretations.

The drying of clay minerals and mixed clay minerals

In natural plastic clays used on ceramic compositions, the presence of certain minerals is frequently observed in the mineralogical composition. In this study, the drying ability of five different clay minerals was examined. All experiments were conducted under steady-state drying conditions. The sorption isotherm of the samples was determined by measurement of the mass of water absorbed at a fixed temperature versus the relative partial water pressure. The shrinkage of pastes was measured under the same experimental conditions. From the experimental data the heat of water sorption was calculated using a model which comes from the interpretation of a sorption reaction. The specific behaviour of the five clay minerals studied was observed; this can explain the behaviour of common plastic clays during the drying process. In particular, some investigations were conducted on mixed minerals. The results should support the possibility of obtaining a correlation between the heat of water sorption of certain clay raw materials and their mineralogical composition.

Thermal analysis — including evolved gas analysis — of clay raw materials

Thermal analysis is important for both compositional determinations of clay raw materials for ceramics and technological control of firing processes (Sladek, 1985 ). The main techniques of thermal analysis are listed in Table 1. Developments in instrumentation and computer software now allow reactions to be followed in greater detail, leading to powerful new approaches such as controlled transformation rate thermal analysis (Ortega et al., 1993 ) and closely related techniques such as stepwise isothermal analysis (Sorensen, 1992 ). In this approach, the heating or cooling programme is controlled by the rate of reactions taking place in the sample. The sample is heated at a constant rate until the reaction rate exceeds a pre-set limit, at which point the

Clay raw material of Berezovka deposit

Berezovka Deposit clays represented by the investigated samples are a basic aluminosilicate clay kaolinite-type raw material, medium plastic, and medium and highly dispersed. They may be widely used in refractory production.

CHARACTERIZATION OF CLAY RAW MATERIALS IN NEPAL AND THEIR APPLICABILITY FOR PORCELAIN RAW MATERIAL

Some clay raw materials in Nepal were characterized and their aptitude for porcelain raw material was studied. The main constituent minerals in the samples were identified to be halloysite(7A), mica, quartz, feldspar, and gibbiste by X-ray powder diffraction (XRD), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The chemical composition of the bulk sample showed very low Fe 2 O 3 and TiO 2 contents, and therefore, the whiteness of sintered body is on a very good level. The vitrification temperature was around 1200°C and high bulk density still maintained in the temperature range from 1200 to 1350°C

Abundance of chromium and other transition metals in ceramic clays from Westerwald (GFR)

Ten commercial clay samples, coming from the Westerwald deposit, have been selected to represent practically all the compositional variety of the raw materials used to obtain white ceramic bodies for pottery. For each sample, the concentration of chromium and some other trace elements has been determined and examined with reference to the main chemical and mineralogical composition. The fraction less than 2 μm from two clay samples have been investigated in the same way. Kaolinite, quartz and illite in different proportions are the principal mineral constituents of the samples, while abundant smectite is contained in only one sample; little amounts of feldspars have been found in a lot of cases. The chromium content ranges between about 40 and 210 ppm, but its variations do not show a good correlation with those of any other principal chemical or mineralogical parameters of the samples. It is concluded that chromium is contained in mineral of its own which is present in trace amounts; that mineral, probably a chromium oxide or hydroxide, is quite uniformly dispersed in the clay fraction and in the coarsest one. From a practical point of view, the results suggest that it is possible to select clay raw materials with low chromium content to avoid the appearance of yellow blots on the glazed surface of ceramic articles made of an earthenware-type body.

Firing characteristics of Sinai calcareous clays

Ceramic bodies have been prepared using the clay deposits from Sinai and Suez localities, either of straight clay or with 20% sand additions by the extrusion method. Briquettes were dried and fired at different temperatures. The properties of the fired bodies were thoroughly determined and correlated with their phase composition as elucidated by I.R. spectroscopy and X-ray diffraction. Results indicate that the clay bodies, fired at 900°C, contain detectable amounts of wollastonite, gehlenite, plagioclase and quartz with minute cristobalite and enstatite phases. Sinai clays gave bodies with moderate bulk density and compressive strength, high water absorption and porosity. Those made of straight Suez clay were unsuccessful. Sand addition increased the bulk density of the clay bodies with increasing porosity, water absorption and compressive strength. Thus Suez clay/sand bodies revealed outstanding high bulk density and compressive strength along with low porosity and water absorption. As the firing temperatures were increased an improvement in properties along with an increase in the crystalline phases evidenced in the bodies fired at temperatures up to 1050°C followed by a marked disappearance of the crystalline phases with a reduction in strength. The maturing temperature of the studied clays is around 1050°C. These properties recommend the clay raw materials for the production of various heavy-clay products; in this respect Suez clay/sand mixture ranks higher.

Un four de potier médiéval à Saint-Georges-de-Rouelley (Manche), les premiers grès bas-normands

A rescue dig carried out at Saint Georges de Rouelley (Manche), in the «La Potterie » locality, provided the opportunity to bring to light the remains of a medieval kiln, and several sherd piles. The paleomagnctic survey of the kiln floor situates chronologically the last firing to the first half of the fourteenth century. The pottery, which consisted mainly of the first roman protostoneware to be foud in it's production context, included cooking pots, large pots with lugs, pitchers, large basins, and a few more specific types. The mineralogical and chemical approach shows the addition of a local granitic arcnite temper, in variable quantities according to the type, to the clay raw material. Fragments of «œil de perdrix » (partridge eye) mortars found on the site were the object of a particular interest. The origin of their manufacture, if not at Saint Georges itself, at least in the Domfront area, was established chemically, thus adding a fifth centre of production to the four already known.

THE MINERALOGY OF BRICKMAKING AT BROOMFLEET, NORTH HUMBERSIDE.

SUMMARY The mineralogy and chemistry of three clay raw materials and three types of brick product have been examined by transmitted light and scanning electron microscopy, X-ray diffraction and X-ray fluorescence analysis. The clays contain varying proportions of illite, kaolinite, vermiculite, quartz, calcite, rutile and hematite. The bricks consists of mullite, cristobalite, quartz, feldspars, spinel, rutile, illite and glass. The calcium-rich brick also contains wollastonite and gehlenite. Electron microprobe analyses of relict feldspars, new pyroxenes and matrix have been made, leading to an estimation of the glass composition. Examination of heated test pieces of each clay has shown the sequences of mineralogical change. This preliminary appraisal provides a basis for further work to elucidate the mineralogical reactions taking place in brickmaking.

Sialon based on natural clay raw materials

Conditions were worked out for the synthesis of β'-sialon on the basis of natural clay raw materials. It was established that the maximum yield of sialon is obtained from nitriding nonbriquetted mixtures of Novoselitsk kaolin and graphite. It was found that the yield of sialon is increased with a rise in the Al2O3∶SiO2 ratio in the clay material.

Baza surowcowa południowej Zamojszczyzny oraz perspektywy jej rozwoju

Przedstawiono charakterystyke wlasności Iitologiczno-surowcowych kenozoicinych osadow okruchowych, ilastych i weglanowych poludniowej cześci wojewodztwa zamojskiego. Oceniono stan rozpoznania i wykorzystania zloz oraz perspektywy rozwoju bazy zasobowej. Wskazano rejony perspektywiczne dla poszukiwan zloz piaskow dla budownictwa i przemyslu materialow budowlanych oraz surowcow ilastych dla przemyslu ceramiki budowlanej i ceramicznych kruszyw lekkich, a takze podano sugestie dotyczące ukierunkowania badan surowcowych i przyszlego wykorzystania zloz. RAW MATERIAL BASIS IN THE SOUTHERN ZAMOŚC REGION AND POSSIBILITIES OF ITS DEVELOPMENT The southern part of the Zamośc region, situated within the area of the Carpathian Foredeep, is perspective from the point of view of development of resource basis of rock raw materials for building and building industry. This is especially the case of sand and clay materials, the deposits of which are known to be widely distributed here (Figs. 1, 2). Up to the present,7 deposits were recognized here (see Table I for their resources and the present use) whereas quality and resources of building sand deposits still require surveying. Carbonate raw materials are here represented by limestones and sandy biodetrital limestones (see Table 2). They are used for production of aggregates for road and railway building and in local building. The group of natural aggregate deposits comprises Tertiary quartz sands (Fig. 3) and Quaternary river (Fig. 4), fluvioglacial (Fig. 5), dune (Fig. 6) and glacial (Fig. 7) sands. Miocene sands are fine- to medium-grained, highly uniform in mineral composition (over 99% of quartz). Quaternary sands are more diversified in mineral composition (Table 3). They are usually fine-grained and not much varying in granulation, except for fluvial and glacial sands which sometimes yield an admixture of gravel-size grains (Figs. 4, 7). Marine, river, fluvioglacial and dune sands occurring in that region may be used for production of silicate bricks and chambered concrete and in building industry. Their use in building industry is, however, impeded by too fine and uniform granulation. Miocene sands may be also used for production of moulding sands and filters. Clay raw materials of economic value include clay-silts, known as Krakowiec Clays (Miocene - Lower Sarmatien), occurring under Quaternary cover throughout the major part of that region (Fig. 2). The are characterized by low differentiation in chemical composition (Fig. 4) and good technological properties (Fig. 8, Table 5), which makes them suitable for automatized production of building ceramics and in light aggregate industry. At present, they are used for production of ordinary full bricks and Gothic bricks (in Tarnogrod and Markowicze brickyards, respectively). The perspectives of finding new deposits of sands and clays are fairly high in that region. Resources of sands in several perspective areas (Fig. 1) are estimated at 96 m. m 3 and those of clays and clay silts (Krakowiec Clays) - at 2,005 m. m 3 . It follows that a new center of exploitation and processing of mineral raw materials and production of building materials may be created here.

Determining the mineralogical composition of raw clay materials using an electronic computer

Determining the mineralogical composition of raw clay materials using an electronic computer

On thermal colour test

A new and simple method ‐ the thermal colour test (TCT) ‐ for investigation of pottery and raw clay material is suggested. The method is based on colour changes of clays during firing. The Munsell Color Chart System is used as a standard colour reference. TCT is expected to be widely used for research on ceramics.

‘Shigaraki’ Clay and Its Clay Minerals and also Generating Environment of Clay Deposit

Excellent clay raw materials such as the ‘Gaerome’ and ‘Kibushi’ clays lie in the lower part of ‘Shigaraki’ clay stratum overlying basal granite. The ‘Gaerome’ clay contains mainly coarser grains of quartz and weathered feldspar, and the ‘Kibushi’ clay is stained into dark brown by organic matter. The ‘Gaerome’ and ‘Kibushi’ clays mostly contain the kaolinite and are accompanied with hydrated halloysite. Under electron-microcopic observation, we can find that the large flakes of kaoline minerals have curled shape and the small particles appear to be rolled into tube-like forms. The white clay (Shirae) that is weathering product of volcanic ash generally contains the hydrated halloysite of lettuce- or cabbage-like forms, tubular and curled shapes. The clays in the upper part of ‘Shigaraki’ sand-silt stratum have a small quantity of montmorillonite.The clay stratums of ‘Shigaraki and Iga’ districts were deposited (first), under warm climate condition, on the basement rocks and ‘Shigaraki’ sand-silt stratum and ‘Shigaraki’ mud stratum accumulated on it. The original formation of present geographical features in the ‘Shigaraki’ plateau was constructed by abrupt compression of E-W direction in the middle period of Diluvial epoch. Considering the history of later basal movement and erosion, we can understand the formation of main faults and the variety of clay deposit in ‘Shigaraki’ district.

Geology and Clay Deposits in the Shigaraki District, Shiga Prefecture

The Shigaraki district, south of lake Biwa, is located at the southern part of Shiga prefecture. ‘Shigaraki’ is well-known as one of the six old kilns in Japan, where has a history since about 1, 200 years ago. The present writers have carried out geological field survey and mineralogical study of the clays by using the technique of X-ray diffraction, electron-microscope and thermo-analysis.The lower part of the Pliocene sediments in the Shigaraki district, lower stratum of Paleo-Biwa group, is abundant in the commercial clays such as ‘gaerome’ clay, ‘kibushi’ clay and white clay (Shirae). They are considered as sediments in the present Shigaraki plateau in the northern part of the Iga tectonic basin. The irregularity of clay deposits and the variation of quality as raw clay material in the three sections of Sangoyama-Makiyama, Hosohara-Nakazato-Shimode and Kumoi were able to be considerably explained by the geological full survey.

Investigation of fireclay dust from rotary furnaces

Dust removed during the firing of clay raw materials into grog in rotary furnaces consists mainly of dehydrated material with a low plasticity and bonding capacity. The temperature of vitrification of the dust is higher than for the original raw materials. Therefore, with the use of dust for firing into grog it is necessary to densify it before firing (for example briquetting) and to increase the temperature in the kiln.

Efflorescence Resulting from Sulfates in Clay Raw Materials

An attempt has been made to isolate the effects of sulfates in clay raw materials on efflorescence from the effects of sulfides and sulfurous fuels. A low‐sulfur shale was used and sulfates were added in different amounts and particle sizes. It was found that sulfates react with clays between 1800° and 1900°F. with the result that efflorescence is reduced. Sulfates were not considered as a serious source of soluble salts causing efflorescence. Recommendations are given for minimizing efflorescence when sulfates occur in the raw material.