Kiln Firing Research Articles

Effect of firing atmosphere and soaking time on heavy clay ceramics with addition of Bayer's process bauxite residue

Ceramics were developed using Bayer's process bauxite residue and a clay mixture in a weight ratio 1 : 1. Firing was performed in a propane firing kiln at 1000°C for 1 or 4 h soaking. For oxidising atmosphere, water absorption varies between 18⋅9 and 19⋅5% and bending strength between 25⋅9 and 27⋅9 MPa. The crystalline phases identified are haematite Fe2O3, quartz SiO2, plagioclase [anorthite (Ca,Na)(Al,Si)2Si2O8], clinopyroxene [augite Ca(Mg,Fe+3,Al)(Si,Al)2O6] and corundum Al2O3. The microstructure is comprised of Si rich vitrified areas that contain quartz and have closed, round pores and an assemblage of particles creating a mass with open and interlinked pores and no signs of glassy phase. For reducing atmosphere and 1 or 4 h soaking, water absorption varies between 18⋅2 and 18⋅7% and bending strength is ∼29⋅5 MPa. The crystalline phases identified are qualitatively the same as for the oxidising atmosphere. The microstructure is comprised of two concentric zones due to the reduced gas permeability in the core of the body. The outer shell is highly vitrified with closed and rounded pores. The microstructure in the core of the body resembles that of samples fired in oxidising atmosphere; however, the average pore size is higher and the vitrified regions are more extensively formed. The build-up of compressive stresses in the outer shell may also account for the increase in the bending strength; however, cracks were developed in few occasions. In all cases, quartz participates in the development of liquid phase and dissolves in the melt. Increase in the soaking time results in a decrease in the quartz content in the body and an increase in the vitreous phase.

Development and approval of a mathematical model of a brick firing kiln

A mathematical model that can be used to maintain the process parameters in real time as a function of the amount of brick manufactured is examined.

Effective lining of tunnel kiln cars made of aluminosilicate ceramoconcrete

Aluminosilicate ceramoconcrete lining for cars used in ceramic plant firing kilns was developed and introduced. The first cars with this lining have already operated for more than 50 cycles.

Variação da cor e propriedades cerâmicas com o aumento da temperatura de queima de uma argila proveniente da formação Corumbataí, região de Piracicaba, SP)

Objetivando compreender a influência do ferro contido na illita, presente na formação Corumbataí, na cor de queima de produtos cerâmicos selecionou-se uma amostra de cor cinza esverdeado claro, dominantemente illítica e com porcentagem de óxidos e hidróxidos de ferro relativamente baixo, com base em estudos petrográficos, mineralógicos e químicos. Para os testes cerâmicos, os corpos de prova foram queimados em forno de queima rápida de laboratório nas temperaturas de 900 ºC, 950 ºC, 1000 ºC, 1050 ºC, 1075 ºC e 1100 ºC, com taxa de aquecimento de 40 ºC/min, sendo um conjunto de corpos de prova queimado a 950 ºC, porém com taxa de aquecimento de 20 ºC/min, com o intuito de verificar a influência do tempo de queima na coloração das peças cerâmicas. O tempo de queima mostrou não interferir significativamente na alteração da cor e os corpos de prova apenas apresentaram alterações significativas a partir da temperatura de 1000 ºC, adquirindo, respectivamente os matizes: laranja, vermelho e marrom escuro. A mudança de cor foi acompanhada em intensidade equivalente pela retração linear de queima, pela absorção de água e módulo de ruptura por flexão.

Low temperature process to create brick

The making of durable alkali-activated aluminosilicate brick can be accomplished on a small or industrial scale according to the needs of the community. Brick made with this technology can be obtained in a few hours using a pressurized vessel and elevated curing temperatures (⩾100°C) or after three to four weeks if the brick is cured under a tarp or in a solar heated enclosure in areas where energy is unavailable. The process is less expensive than conventional kiln firing of brick, because the development of strength vis à vis sintering is a result of a chemical reaction that takes place at a relatively low temperature. Starting materials available in Senegal consist of highly leached aluminosilicate soils (laterites) and tuffs that primarily contain kaolin, and/or or certain by-product materials now considered to be industrial waste (e.g. aluminum refining sludge). The dry ingredients are mixed with just enough concentrated caustic solution to form a thick paste, compacted in a mold, and allowed to cure. Caustic can consist of sodium hydroxide mixed with sodium silicate and water/seawater. The bricks produced in this fashion are durable and relatively inexpensive to make, thus the technology should appeal to those living in villages in less industrialized nations such as Senegal, because the technology uses locally available materials and solar heating that are available almost everywhere.

明治・大正期におけるセメントの生産管理について : 小野田セメント製造株式曾社を例として

The resources left in Onoda Cement Company, such as its history, documents, and letters, were examined in order to explore the transition of the cement production management between 1883 and 1925. The study specifically focuses on the company's manufacturing as well as quality control items for a variety of firing kilns. The findings are as follows: 1) The process control items initially included only "the amount of both fuel and raw materials" and "the cement production volume." A few years later, "the operating time of the main manufacturing devices" were added to the original process control items. Furthermore, while the measurement of the pressure in the kilns began to be conducted by the end of the Taisho era, the firing condition of the cement was only being discerned. 2) The outline of the quality control items was formed between 1898 and 1899 and it was completed in the Taisho era. The completed list of the items is similar to the one adopted today. 3) For the chemical analysis (one of the quality control items), the existence of CaCO_3 in both the limestone and the raw materials was measured and confirmed first, and then the analysis of the cement powder was followed. 4) The diameter of the raw materials and the cement powder became smaller as the time proceeded. By the beginning of the Taisho era, the size of the mesh of the sieve used for measuring the diameter became almost the same as the one used today. 5) When the cement production originally started in the early Meiji era, the physical test of the cement included only "the verification of possible cracks and the strength test on the cement paste" and the stiffness of the cement was being measured only roughly. Approximately ten years later, "the tensile and compressive strength of the cement mortar" were included in the physical test. In another ten years, morever, "the specific gravity of the cement powder" became one of the items and started to be measured. By the end of Thaisho era, after the careful consideration the completed list of control items was refined and became almost the same as the one employed today.

Archaeological calibration of remagnetized volcanic rocks from pottery firing kilns in Cuentepec, Morelos, Mexico

Investigaciones etnoarqueológicas en Cuentepec incluyen experimentos durante la producción de cerámica, de donde es posible extraer conocimientos sociales a partir de la aplicación de técnicas arqueométricas. En este caso, el experimento trata sobre la confiabilidad de técnicas de fechamiento en arqueología. En Cuentepec, se usan pequeños hornos a cielo abierto para la fabricación de cerámica (comales de barro). Se tomaron muestras de roca volcánica que conformaban los hornos para verificar la confiabilidad de la dirección magnética registrada por las mismas y compararla con datos del Observatorio Geomagnético de Teoloyucan localizado cerca a la ciudad de México. Con el objeto de medir sus propiedades magnéticas se perforaron/obtuvieron en el laboratorio 47 núcleos pertenecientes a ocho muestras de bloque orientadas. Las curvas continuas de susceptibilidad magnética con altas temperaturas resultaron en muchos casos razonablemente reversibles, con puntos de Curie sugiriendo titanomagnetita de rica a pobre en titanio. Los parámetros de histéresis indican que todas las muestras caen en la región de tamaño de grano pseudo-dominio-simple, indicando probablemente una mezcla de granos multidominio más una cantidad significante de granos de dominio simple. Las curvas de adquisición de magnetización remanente isotermal fueron muy similares para casi todas las muestras. La saturación se alcanzó en campos moderados del orden de 100-120 mT, lo cual indica algunas espinelas como portadores de la remanencia. Concluimos que las muestras obtenidas de la parte interna de los bloques que forman los hornos, las más cercanas al fuego, guardan los registros más confiables del campo geomagnético. Esto significa que el calor producido por el fuego probablemente sólo remagnetizó las partes internas de los bloques.

Heat losses in a tunnel kiln for brick firing

The results of experimental studies of heat losses via the enclosing structures of an operating brick-firing kiln using a thermal imager are described.

New refractory materials for the aluminum industry

A technology for production of andalusite-based refractory components for the lining of anode firing kilns is described. The formulation for a low-cement castable resistant to attack by molten aluminum is proposed.

明治・大正時代におけるセメント製造方式の変遷 : 焼成窯形態に伴う製造方式の変遷

The purpose of this study was to clarify a part of Japan's modernization by retracing the transition in the Portland cement production system. The study examined the resources, including the histories of a several cement corporations, which were left in Onoda Cement Company (OCC). Its focus was on the transitions in the cement production system employed in the cement corporations in the Meiji and Taisho eras and the transitions in the cement production process and the kilns' types and numbers that were found in OCC. The outcomes are as follows: 1) Although thirty-five cement manufacturing companies existed in the Meiji era, only eighteen remained at the end of the Taisho era due to the hard social conditions. 2) In spite of the advent of kilns such as Dietzsch's and Hoffman's Ring kilns, the bottle kilns became popular in Meiji era, and have been replaced by rotary ones since 1908 for its high productivity. 3) The cement production system of law material changed from wet to dry process since 1897. 4) Along with the transitions in kilns, the cement manufacturing process as well as the equipments for firing kilns were improved in OCC. 5) The fundamentals of cement production system was established by the end of the Taisho era, and the equipments before and after manufacturing process were almost the same as the ones that are currently used in general.

小野田セメント製造株式會社におけるセメント焼成窯の種類と操業状況

Throughout the changes of cement manufacturing techniques in the Meiji and Taisho eras, the history of Onoda Cement Corporation, the resources and material left with them were examined in order to find out a part of Japan's modernization. The material includes the transition of the amount of cement, manufacturing process, energy cost, operating term etc. according to the change of kiln types between 1883 and 1923. The following findings were obtained: 1) Although the cement manufacturing process in bottle kilns, batch system, was consisted of 1) filling raw materials into the kiln, 2) firing, and 3) taking cement clinker out of the kiln, there was not precise manufacturing process in Dieztsch's ones and the revolving ones which systems were continuous. 2) While the operating cycle of Bottle kilns was about ten days, Dieztsch's ones run approximately half a year. Rotary ones paused four days a month for mechanical repairs in 1912. 3) By the end of the Taisho era, along with the changes of firing kiln, the cement manufacturing productivity increased sixty times, and the labor productivity for each person improved rapidly seven times as those of the establishment. 4) The fuel and labor cost accounted for a majority of all the manufacturing cost. 5) The manufacturing capacity, the productivity, and the cost were improved with the times.

Eco-efficiency of fabric filters in the Italian ceramic tile industry

Italy is an important producer of ceramic tiles, with a high production share in Europe (50%) and worldwide (16%). Since early 1990s, fabric filters have been installed to reduce emissions of dust, lead, fluorine, etc. from firing kilns. Such end-of-pipe technologies can increase energy consumption and production costs. This paper presents a simplified LCA to assess the overall environmental effects of fabric filters in Italian ceramic tiles production. We also calculate the eco-efficiency of such filters, the additional cost per unit reduction of emissions. The results indicate that the environmental drawbacks of the filter are small and that, in comparison to existing eco-efficiency reference values, this air pollution abatement technique can be seen as an eco-efficient technique. These results can be useful in the identification of best available techniques (BAT), which is required under environmental regulations such as EC directive 96/61 (IPPC directive).

Influence of firing conditions on ceramic products: Experimental study on clay rich in organic matter

The effect on ceramic products of firing conditions in the presence of abundant organic matter is assessed here experimentally by reproducing two ancient firing techniques: pit firing, characterised by a high heating rate and short residence time in a reducing atmosphere; kiln firing, with a low heating rate and long residence time in an oxidising atmosphere. As expected, pit firing conditions produced uniformly reduced ceramics, and gehlenite, diopside and spinel occurred at suitable temperatures (above 900 °C). Interestingly, in kiln firing conditions, sandwich structures formed in the ceramics, in which mineral assemblages and Fe oxidation state turned out to be different in the black core with respect to the margin. Spinel, cordierite and metallic Fe formed in the core, whereas hematite and spinel, in addition to gehlenite and diopside, crystallised in the margin at suitable temperatures (above 800 °C). Therefore, despite the oxidising atmosphere of the firing, reducing conditions occurred in the core, suggesting sluggish oxygen diffusion within the pottery. In addition, decomposition of reactant mineral phases and crystallisation of new mineral products in pit firing conditions occurred at temperatures about 50 °C higher than in kiln firing conditions, indicating that residence time strongly controlled reaction kinetics, as higher temperatures (i.e., a higher degree of reaction overstepping) are required when residence time is lower. On the contrary, illite broke down at a lower temperature than expected in both sets of firing conditions. This is interpreted as the effect of reduced water fugacity caused by burning of the organic matter.

Present and Application of Microwave Firing Kilns

Present and Application of Microwave Firing Kilns

Utilization of Bagbagotot (Phyllantus reticulatus) and Atswete (Bixa orellana) Dyes as Ceramic Colorants

This study determined the effects of bagbagotot (Phyllantus reticlatus) berry dye and atswete (Bixa orellana) seed dye as colorants of white wares constituting transparent base DT 24 at low firing temperature. The results ofthis study showed that atswete dye can be used as colorant on pre-fired white clay ceramics but such dye decolorized at a temperature of 750C in electric kiln firing. The addition of transparent base DT24 to atswete dye did not affect the coloration of the dyes on white ware ceramics.

03/01933 Influence of mineral precipitation and dissolution on hydrologic properties of porous media in static and dynamic systems: Freedman, V. L. et al. Applied Geochemistry, 2003, 18, (4), 589–606

The effect on ceramic products of firing conditions in the presence of abundant organic matter is assessed here experimentally by reproducing two ancient firing techniques: pit firing, characterised by a high heating rate and short residence time in a reducing atmosphere; kiln firing, with a low heating rate and long residence time in an oxidising atmosphere. As expected, pit firing conditions produced uniformly reduced ceramics, and gehlenite, diopside and spinel occurred at suitable temperatures (above 900 °C). Interestingly, in kiln firing conditions, sandwich structures formed in the ceramics, in which mineral assemblages and Fe oxidation state turned out to be different in the black core with respect to the margin. Spinel, cordierite and metallic Fe formed in the core, whereas hematite and spinel, in addition to gehlenite and diopside, crystallised in the margin at suitable temperatures (above 800 °C). Therefore, despite the oxidising atmosphere of the firing, reducing conditions occurred in the core, suggesting sluggish oxygen diffusion within the pottery. In addition, decomposition of reactant mineral phases and crystallisation of new mineral products in pit firing conditions occurred at temperatures about 50 °C higher than in kiln firing conditions, indicating that residence time strongly controlled reaction kinetics, as higher temperatures (i.e., a higher degree of reaction overstepping) are required when residence time is lower. On the contrary, illite broke down at a lower temperature than expected in both sets of firing conditions. This is interpreted as the effect of reduced water fugacity caused by burning of the organic matter.

Kiln Firing Groups: Inter-Household Economic Collaboration and Social Organization in the Northern American Southwest

AbstractRecent research on trench kilns from the Mesa Verde region of the northern American Southwest (Blinman and Swink 1997) suggests that trench kilns represent collaborative firings by groups of potters. This study presents a method for estimating the sizes of these proposed kiln firing groups. A comparative analysis between firing group sizes and the size of other contemporaneous social units provides insights into socioeconomic relationships between Mesa Verde households in both dispersed and aggregated settlement contexts. This study demonstrates that different stages of a production process may involve different production groups and highlights the utility of examining each production stage individually. It further suggests the importance of searching for archaeological evidence of production beyond residential areas to other production contexts, such as firing features, if the organization of all stages of production is to be understood.

Processing Technical Ceramics with Maltodextrins: Crosslinking by Acetalation

Technical ceramics are made by a sequential process of: (i) mixing ceramic powder with an organic carrier liquid (e.g., organic solvents, polyethylene wax) to form a plastic slurry, (ii) molding the plastic slurry into a three-dimensional shape, (iii) thermal treatment to evaporate or pyrolyze the organic carrier, and (iv) kiln firing. In this paper, the use of aqueous polysaccharide solutions is examined as environmentally-friendly, economically-viable substitutes for organic carrier liquids in ceramic molding. The central focus of the present study is to examine optimum conditions for crosslinking model slurries of maltodextrin and colloidal aluminum oxide by acetalation of maltodextrin. Crosslinking is needed to prevent the common problem of cracks that form in ceramic shapes during thermal treatment (stage iii above). Experiments involving rheology and differential thermal analysis revealed that glyoxal and glutaraldehyde are effective crosslinkers, whereas formaldehyde and pyruvic acid did not exhibit measureable changes in slurry rheology over a wide range of concentrations. Glutaraldehyde reacted faster than glyoxal, however, glyoxal produced the strongest gels. Basic conditions catalyzed acetalation. The sequence of blending the slurry components had no significant effect on slurry rheology.

Environmental Issues and Kiln Firing

AbstractIt is not necessary to repeat the well known concerns about environmental issues and how they affect the design and operation of combustion processes. In this paper I wish to describe recent experiences in this area and how engineers can react to the associated issues. A UK content will be used and discussions will be made about how this relates to the global situation.

Kiln emissions and potters' exposures.

Some ten thousand British Columbia potters work in small private studios, cooperative facilities, educational institutions, or recreation centers. There has been considerable concern that this diffuse, largely unregulated activity may involve exposures to unacceptable levels of kiln emissions. Pottery kiln emissions were measured at 50 sites--10 from each of 5 categories: professional studios, recreation centers, elementary schools, secondary schools, and colleges. Area monitoring was done 76 cm from firing kilns and 1.6 m above the floor to assess breathing zone concentrations of nitrogen dioxide, carbon monoxide, sulfur dioxide, fluorides, aldehydes, aluminum, antimony, arsenic, barium, beryllium, boron, cadmium, chromium, cobalt, copper, gold, iron, lead, lithium, magnesium, manganese, mercury, nickel, selenium, silver, vanadium, and zinc. Personal exposures to the same metals were measured at 24 sites. Almost all measured values were well below permissible concentrations for British Columbia work sites and American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit values (TLVs) with the following two exceptions. A single firing duration (495 minute) acrolein measurement adjacent to an electric kiln (0.109 ppm) exceeded these guidelines. One 15-minute sulfur dioxide measurement collected adjacent to a gas kiln (5.7 ppm) exceeded the ACGIH short-term exposure limit. The fact that concentrations in small, ventilated kiln rooms ranked among the highest measured gives rise to concern that unacceptable levels of contamination may exist where small kiln rooms remain unventilated. Custom designed exhaust hoods and industrial heating, ventilating, and air-conditioning systems were the most effective ventilation strategies. Passive diffusion and wall/window fans were least effective.