Firing Shrinkage Research Articles

CHARACTERIZATION OF CLAYS FROM “MINES MARITSA IZTOK” AS RAW MATERIALS FOR CERAMIC INDUSTRY

The chemical and phase compositions of the clays from coal mining were evaluated by XRF and powder XRD method, respectively. Hot Stage Microscope was used to estimate the thermal behaviour. In addition, the thermal losses of the clays after 1 h thermal treatment at different temperatures were measured. This preliminary analysis elucidates potential prospects for using some of clays as raw materials for ceramic industry. It seems that samples which are montmorillonite type are more plastic, while the others, where higher sand content is observed, and the drying shrinkage is negligible could be characterized as less plastic. The initial results for the thermal behaviour and the structure of a brick sample (obtained by mixing two types of clays) and a foamed geopolymer are also reported. The first sample shows a beginning of the firing shrinkage at about 1000°C, while the second demonstrates intensive bloating after 950°C, leading to specimen with about 56 % closed porosity. Finally, X - ray Computed Tomography and SEM was used to highlight the structure of some test samples.

A new proposal to reduce microplastics from cigarette butts: Production of eco-friendly fired clay bricks

It is estimated that approximately 1.2 million tons of cigarette butts (CBs) are introduced into the environment annually. The aim of this work is to analyze the incorporation of shredded CBs into bricks making by extrusion, for recycling and waste recovery purposes. Samples were prepared in compositions of 0 %, 1 %, 2.5 % and 5 % w/w CBs and fired at 700 ºC, 900 ºC and 1000 ºC. Density, water absorption, apparent porosity, linear firing shrinkage, flexural strength, compressive strength, thermal conductivity, diffusivity and sound transmission loss (TL) were determined. A total of 180 samples were taken, and a Weibull statistical analysis was performed for compressive strength. The results showed a decrease in density and an increase in water absorption and apparent porosity of the clay bricks produced by mixing 1–5 % CBs compared to the control bricks. Firing shrinkage decreased with 1 % CBs and up to 2.5 %, its was lower than standard samples. Samples with CBs showed fewer cracks than standard samples. Compressive strength increased with 1 % CBs incorporation for firing temperatures of 900ºC and 1000ºC compared to standard samples. It gradually decreased with larger amounts of waste. For flexural strength, up to 2.5 % CBs, the strength increased in most cases. In addition, there was an improvement in the thermal conductivity of bricks prepared with 5 % CBs and fired at 700ºC and 900ºC (0.46–0.58 W/mK) compared to the reference samples (0.51–0.76 W/mK). All waste samples showed higher TL than the reference pieces. Above 2.5 % CBs, TL decreased, but remained larger than the reference. Thus, the results showed that the use of CBs in fired clay bricks in amounts of up to 5 % w/w is capable of forming porosity in the samples, making the part lighter, in addition to possibly reducing thermal conductivity and sound transmission, being an economical and sustainable alternative for the final disposal of CBs.

Production and Characterization of Porous Anorthite Ceramics Using Sugar Process Solid Waste, Chamotte and Coal Powder Additives

Press filter cake is a solid waste produced during sugar production process and includes carbonates and organic components. In this study, coal powder in different percentages (from 10 wt.% to 50 wt.%) was mixed with 35 wt.% press filter cake and 65 wt.% chamotte composition to produce porous anorthite ceramic products with different apparent porosity percentages. The anorthite phase was observed as the dominant crystalline phase in all fired samples. The firing shrinkage values sharply increased after adding higher than 40 wt.% coal powder to composition. In addition, apparent porosity values were changed from 49% to 70%. Compressive strength values reduced from 18 MPa to 1.73 MPa while percentages of ground coal were increasing. Microstructural analysis also showed that the porosity values of the sintered samples showed important changes depending on the amount of coal additive. The thermal conductivity values showed a reduction from 0.113 W/mK to 0.064 W/mK while increasing the percentage of ground coal. Micro-computed tomography (Micro CT) analysis was performed for 40wt. % coal powder added composition and the total porosity value was found as 60.2%.

Evaluating pumice as a sustainable raw material in porcelain tile production: impact on technical properties

AbstractPumice, a porous rock resulting from the rapid cooling of tuff fragments during volcanic activity, exhibits a spongy texture and light color due to its low density. Found predominantly in Central Anatolia and Eastern Anatolia, it has drawn interest for industrial applications. This study delved into utilizing micronized pumice within the porcelain tile manufacturing process. Comparative analyses were conducted between formulations incorporating micronized pumice and the standard ceramic tile recipe. In place of feldspar, micronized pumice was introduced at concentrations of 3%, 5%, and 7%, while clay was substituted with micronized pumice at concentrations of 3%, 5%, 7%, and 10% by weight. The prepared bodies were fired in an industrial kiln at 1210 °C for 54 min, and various physical and mechanical properties were evaluated. These included viscosity, sieve residue, green strength pre-firing, firing shrinkage, water absorption, firing strength, and firing color after-firing. The results indicated that the samples incorporating micronized pumice closely matched the physical and mechanical properties of the standard porcelain tile. Phase and microstructural analyses revealed the presence of mullite and quartz phases. Notably, micronized pumice demonstrated promise as a substitute for clay or feldspar, with the optimal usage rate determined to be 7% in the porcelain tile recipe. This indicates that pumice has the potential to be an alternative raw material in the production of porcelain tiles.

Upcycling process of mill scale waste into high-value ceramic products

Ceramic industry consumes large amounts of raw materials, including costly and environmental impact iron based-pigments. Steel rolling (SR) and wire drawing (WD) waste, rich in iron (>67 wt %), present a viable alternative. This study aims to develop high value stoneware pastes for tableware products by substituting commercial pigments with SR and WD. The influence of incorporation content (3, 5 and 10 wt %) and pre-treatments (sieving at 250, 150 and 63 μm, and grinding followed by sieving at 63 μm) on the samples properties was assessed including weight loss, firing shrinkage, apparent density, flexural resistance, and water absorption. The laboratory scale results revealed that darker hues, ranging from grey to reddish, were obtained when SR and WD were incorporated in the stoneware paste (beige colour). The smaller the particle size, more homogeneous is the developed colour, which is intensified as higher is the incorporation level.The prototypes (plates) were characterized in terms of thermal shock, edge impact, cracking and microwaves resistance, water absorption, and leaching behaviour, demonstrating that they met the industrial requirements. Thermal shock resistance was enhanced and the levels of leached Fe, Pb, Cd, Ni, Cr, Mo, V, Zn, and Cu, were below permissible limits (EU Ceramic Directive 84/500/EEC, Decree-Law n°152/2017, Decree-Law n°236/98 and WHO Guidelines for Drinking-Water Quality) confirming their effective immobilization. Concluding, this work shows the viability of using mill scale waste as a valuable secondary raw material in stoneware pastes acting as a chromophore agent. Dark colours are obtained while preserving the product technical characteristics, promoting sustainable production and reducing landfilled waste.

Enhancing Mechanical Properties of Clay Brick by Using Stone Powder

Abstract Hundreds of studies have been written in the last several decades on the advantages of using stone powder as a raw material in the production of fired clay bricks. The durability and long-term behavior of the finished product, however, have received very little attention in the literature. Clay bricks are generally fired at high temperatures in developing countries, which reduces the mechanical performance of the bricks. This is especially evident in extreme environmental settings where weathering leads to significant damage. The evaluation of concrete waste (stone powder) used to make fired clay bricks is the main topic of this study. There are two sections: the first evaluates how adding stone powder to clay bricks improves their physical characteristics such absorption, efflorescence, density, and firing shrinkage. The impact of stone powder on the mechanical characteristics of specimens of burned clay bricks, such as compressive and flexural strengths, is covered in the second section. The percentages of stone powder in the clay bricks are 0 %, 5 %, 10 %, 15 %, and 20%. While the ratio of dry soil to water content remains is 0.3. In this work three fire phases are used untel to the maximum temperature is reached. The first one is 300 °C, the second phase is 600 °C, and 900 °C for the third phase. The water absorption of specimens decreased as the quantity of stone powder increased, and efflorescence also decreased, according to the results for the physical attributes. The density does, however, somewhat rise with the amount of stone powder. Additionally, when the amount of stone powder was increased, the experimental results indicated that firing shrinkage decreased. Mechanically considered, clay brick specimens with 20% more stone powder showed stronger compressive flexural capabilities.

Alternative material recommendation for facade cladding: High silica-containing stonepaste ceramics

This study investigated the potential of using stonepaste ceramics, which were widely preferred as a coating and decoration material on the facades of architectural buildings in ancient times and continues to be produced on a workshop scale today as a cladding material on building facades. Stonepaste ceramics, made from a mixture prepared with a high amount of crystalline quartz as well as frit, plastic clay, and bentonite raw materials, were hand-shaped and sintered at 930 °C after glazing. The physico-mechanical properties of stonepaste ceramics, their behaviour under various environmental conditions (resistance to chemicals, frost, and thermal shock), and their microstructures have been characterized. The characterization results were compared with the properties of commonly used facade cladding materials. It was determined that stonepaste ceramics had a very low firing shrinkage value (2.84 %) compared to that of other ceramic cladding materials, a higher water absorption value (11.79 %) than that of porcelain tiles and floor tiles, and close to wall tiles, and a flexural strength value (33.64MPa) higher than wall tiles and close to porcelain tiles despite the high-water absorption value. Ten cycles of thermal shock resistance showed that the body and glaze layer of the stonepaste ceramic material are well bonded to each other, and there is no significant thermal expansion mismatch between them. One hundred cycles of freeze-thaw conditions indicated that the stonepaste ceramic had good adhesion and thermal expansion compatibility between the glaze and the body but only chipping damage under the action of tensile forces caused by the freezing of water entering the pores of the body. In terms of behaviour against various chemicals, stonepaste ceramics were found to be highly resistant to high and low concentrations of household chemicals, swimming pool salts, and alkalis but less resistant to low concentrations of HCl and citric acid and high concentrations of HCl and lactic acid compared to other chemicals. The results show that stonepaste ceramics, despite their high-water absorption potential, have properties close to those of traditional ceramic tiles and, like these materials, can serve for significant periods in various environmental conditions when used as facade cladding. Consequently, it has been revealed that stonepaste ceramics can be used as a facade cladding material in sustainable, long-lasting, contemporary architectural facades thanks to their technical and protective properties.

EFFECT OF RICE STARCH CONTENT ON TUBULAR ALUMINA MEMBRANE SUPPORT FABRICATED BY AGAR GELCASTING

This study addresses the challenge of fabricating cost-effective tubular ceramic membranes through agar gelcasting. The addition of rice starch as the pore-forming agent in the ceramic membrane support layer, with varying contents from 0 to 6 wt%, was focused on improving the permeability of the tubular ceramic membrane. Scanning electron microscopy (SEM) revealed the co-existence of large pores from starch decomposition and small pores in the form of interparticle voids. When the rice starch was enhanced, the firing shrinkage and apparent porosity increased, and the bulk density decreased. Notably, the tubular ceramic membranes with 6 wt% of the rice starch addition exhibited a permeability of 0.17 Lh⁻¹m⁻²bar⁻¹ under a pressure of 2.5 bar.

Development of bio-based lightweight and thermally insulated bricks: Efficient energy performance, thermal comfort, and CO2 emission of residential buildings in hot arid climates

This study explores the viability of using industrial wastewater sludge (IWWS), generated by the mycelium treatment of dyeing wastewater, for the fabrication of lightweight and thermally insulating bricks. The pulverized IWWS was used at various replacement ratios of 0, 5, 10, 15, and 20 wt% of clay. The mixture was subjected to firing temperatures of 700, 800, and 900 °C. The effect of applying IWWS to the brick characteristics is assessed through an examination of the physico-mechanical and thermal properties. The utilization of IWWS resulted in a significant enhancement in apparent porosity (34.4 %), cold water absorption (25.6 %), boiling water absorption (28.5 %), linear drying shrinkage (5.1 %), and linear firing shrinkage (7.9 %) using 20 % IWWS at 900 °C. Furthermore, the density, compressive strength, and thermal conductivity were reduced as the substitution IWWS ratio increased, reaching up to 1662.9 kg/m3, 11.56 MPa, and 0.198 W/m.K., respectively, using 20 wt% IWWS at 900 °C. The effect of fabricated fired bricks (FBs) on the thermal insulation, CO2 emissions, and energy consumption of residential buildings was tested. This is accomplished by using energy modeling tools, such as Honeybee, Ladybug, and Climate Studio (Grasshopper plugins), in addition to Galapagos for optimizing wall design. The suggested wall design is being used in a communal residential building located in two distinct climatic regions, namely Cairo in Egypt and Jazan in Saudi Arabia. According to the projected mean vote (PMV) and anticipated percentage of discontent (PPD) measures, the utilization of fabricated FBs as wall materials exhibits significant improvements in thermal comfort. Furthermore, they lead to a 6 % and 7 % drop in CO2 emissions in Cairo and Jazan cities, respectively, as well as a significant 38.8 % and 39 % reduction in energy consumption in Cairo and Jazan cities, respectively. Therefore, the use of fabricated FBs demonstrates itself as a feasible and environmentally friendly choice for building construction.

Fast-drying of red ceramics: A new evaluating approach based on the combined use of optical dilatometry and thermogravimetric analysis

This study aimed to evaluate the effects of composition and heating rate on the fast-drying (∼60 min) of red ceramics obtained by extrusion using optical dilatometry and thermogravimetry to obtain the drying curve. Three different plastic clays were used in the four formulations investigated, as well as three heating rates with a total time of 60 min and a maximum drying temperature of 200 °C: 5.83, 3.89, and 2.92 °C/min. Based on the results obtained from the modified Bigot curves, a fast-drying curve (3 °C/min) was established in a static laboratory dryer with a total cycle of 60 min and a maximum temperature of 160 °C. The samples were characterised in terms of compressive resistance and visual aspects related to drying cracks. Formulation F5, containing 50 wt% AM clay and 50 wt% AV clay, exhibited the worst performance in fast-drying with drying cracks, whereas formulation F7, containing 33.3 wt% AC clay, 33.3 wt% AM clay and 33.3 wt% AV clay, exhibited the best performance. Formulations F7 and F8 (16.7 wt% of AC clay, 66.6 wt% of AM clay and 16.7 wt% of AV clay) were fired at 900 °C in an electric kiln, with a heating rate of 1.5 °C/min and a 2 h holding time, and then characterised in terms of firing shrinkage, water absorption and compressive strength. The results showed that Formulation F7 presented suitable behaviour in the fast-drying process at 160 °C for 60 min in a laboratory dryer at a heating rate of 3 °C/min, 0.9 wt% a residual moisture. It exhibited no drying cracks and a dry compressive strength of 0.94 ± 0.09 MPa. However, the combined analysis of optical dilatometry and thermogravimetry indicated that the drying conditions could be optimised for a residual moisture of 2 wt%, using a thermal cycle of 138 °C for 19 min (heating rate of 5.83 °C/min) if adequate control of the humidity of the chamber atmosphere in the first drying stage is employed to avoid drying cracks. The results also showed that the specimens of formulations F7 and F8 met the technological requirements defined by the Brazilian standard ABNT NBR 15270-1, demonstrating the feasibility of producing red ceramic bricks by extrusion with fast-drying. The combined optical dilatometry and thermogravimetry techniques used to obtain the Bigot curve applied to fast-drying showed very good agreement with those obtained in the laboratory dryer. These combined techniques represent promising approaches for studying the fast-drying of red ceramics.

Assessment of Some Clay Deposits from the Gercus Formation (Middle Eocene) for Brick Manufacturing in the Dokan Area, NE Iraq

The objective of this research is to evaluate the suitability of some clay deposits from the Gercus Formation (Middle Eocene) in the Dokan area, Northeastern Iraq for brick manufacturing. Physical properties of the raw material including grain size analysis and Atterberg limits showed that composed mostly of sand and silt with a minor proportion of clay and classified as muddy sand. According to the plasticity chart, the studied sample plotted on the field of silt and organic clay with low plasticity. The geochemical analysis by X-ray fluorescence revealed that composed of a low percentage of silica and alumina and a high percentage of calcium oxide and magnesium oxide. The mineralogical analysis by X-ray diffraction showed that the studied samples were composed of non-clay minerals (dolomite, quartz, hematite, albite, anatase, and orthoclase) and clay mineral (montmorillonite, kaolinite, and illite). Twelve ceramic briquettes were prepared from the clay sample by semi-dry pressing method and pressed by 200 kg/cm² pressure with 14 – 15 % moisture content and fired at 880, 900, and 920 °C for evaluation tests of linear firing shrinkage, apparent porosity, water absorption, bulk density, efflorescence, and compressive strength. Results of physical and mechanical properties of the studied ceramic briquettes compared with the specification of Iraqi standard (1993) for clay brick manufacture, according to this specification the studied sample was not suitable for brick manufacturing due to a high percentage of water absorption and low compressive strength.

Effect of milling and compaction on sintering of porcelain stoneware tiles

The present study aims to provide a deeper understanding of how different particle size distributions and degrees of powder compaction affect the densification process of porcelain stoneware tiles. For this purpose, three different batches underwent a laboratory simulation of the industrial tilemaking process, at growing grinding time or increasing forming pressure, with technological characterization of both unfired and fired products. Sintering behaviour was determined by hot-stage microscopy. Phase composition was determined by XRD-Rietveld allowing the estimation of the chemical composition and physical properties of the liquid phase. The results illustrate the impact of too fine (or too coarse) grain size on powder compaction, firing shrinkage, water absorption, efficiency of densification, sintering rate, stability at high temperature, and risk of anticipated overfiring (and similarly for too high or too low forming pressure). Simultaneous variation of particle size and forming pressure beyond usual standards induced changes in technological behaviour that in most cases compensate each other. Phase composition is moderately influenced by particle size and little by powder compaction. The vitreous phase mainly suffered from a decreasing degree of polymerization as the particle size became finer or the dry bulk density decreased. In case of insufficient grinding, too much residual feldspars caused improper composition and properties of the glassy phase, which resulted in lower efficiency of densification and slower sintering rate. Both the sintering kinetics and degree of densification depend on the timescale, i.e. the ratio of surface tension to viscosity (melt) and median particle size. Nevertheless, a low powder compaction can trigger a microstructural effect on sintering (improving both densification rate and efficiency) that may outweigh the timescale effect.

Mineralogical, geochemical and physical properties assessment of clay deposits in Umuoke Obowo Southeastern Nigeria for industrial applications

This study assessed the suitability of clay deposits from Umuoke, Obowo in southeastern Nigeria as local raw materials for industrial applications. Ten samples were collected from different mining pits across the locality. X-ray fluorescence, X-ray diffraction and physical property tests characterized the clays based on geochemical composition, mineralogy and key attributes. The clays showed high silica (56.41%) and alumina (32.82%) contents typical of aluminosilicate clays. Iron oxide levels were moderately elevated (3.34% Fe2O3). Clay minerals kaolinite (18.9-37.0%) and illite (0.5-4.15%) occurred predominantly alongside non-clay minerals like quartz, feldspars and metal oxides. The clays exhibited high plasticity (avg. plasticity index 26.61%) enabling easy moulding and shaping. Porosity averaged 21.33% appropriate for refractories. Firing shrinkage (6.5-19.2%) and density (1.54-1.76 g/cm3) were in acceptable ranges. Strength post-firing reached the 15 N/mm2 minimum standard. Estimated refractoriness was 1680.22°C. Overall, the Umuoke clays demonstrate favourable chemistry, mineralogy and physical properties for refractories and structural ceramics applications pending some processing adjustments. Locally exploiting these deposits can promote import substitution, rural industrialization and sustainable development in Nigeria. Further pilot testing can optimize formulations and processes for targeted ceramic products. Comprehensive nationwide clay deposit prospecting is also recommended. The clays are suitable for refractory bricks, ceramic tableware, architectural ceramics, wall tiles, pottery items.

Utilizing machine learning to integrate silica-based production waste material in ceramic tiles manufacturing: Progressing toward sustainable solutions

The production of ceramic tiles is an intricate process of combining modern technology with ancient craftsmanship, which creates versatile and durable finished surfaces for various construction applications. The manufacturing of ceramic tiles causes the production of significant waste during different production stages such as shaping, firing, and finishing leading to environmental degradation and depletion of resources. Therefore, this research work was planned to investigate the possibility of utilizing ceramic waste in the manufacturing of ceramic tiles. Two types of ceramic waste, namely glaze waste and body waste were used with 5–10% replacement of different materials in the production of ceramic tile. The results revealed that up to 10% of the waste produced during the manufacturing of ceramic tiles can successfully be reused in the manufacturing of ceramic tiles. The ceramic tiles produced with 10% replacement of feldspar satisfied the minimum criteria of flexural strength, shrinkage, and water absorption supported by scanning electron microscopy findings. Moreover, a machine learning model was developed using six input variables, i.e., feldspar (F), three different types of clays (C1, C2, and C3), body waste (BW) and glaze waste (GW), while three variables, i.e., firing shrinkage (SF), flexure strength (FS) and water absorption (WA), as output. Applying a machine learning approach to data revealed that the model, i.e., artificial neural network (ANN), exhibited strong and consistent performance, displaying notable generalization capabilities (with an R2 greater than 0.95 on the test set). This study aims to shape sustainable waste management approaches and establishes a blueprint for harnessing ceramic waste with the potential to be a primary resource in the production of ceramic tiles.

Porous refractory ceramics using agrowastes and some kaolinitic clays

In the purpose of making low cost porous refractories bricks, two kaolin named MY3 and KG from the locality of Foumban in Cameroon are used together with a rice husks (Br) and coffee residues (Rc). The formulations made of mixture of chamotte, raw clay as a binder and agricultural wastes in varying proportions, are fired at 1200 °C for 4 h. The addition of chamotte from 10 to 60 % in the studied clays, contributes to a reduction of firing shrinkage. The mineralogy of the products is made of mullite (34–38 %) which is associated to cristobalite (10–19 %), quartz (14–20 %) and amorphous phase (23–39 %). The addition of 10–20 % of agrowastes causes a reduction in the apparent density of 13 % and an increase in the open porosity of 14 %.

The recycling of demolition roof tile waste as a resource in the manufacturing of fired bricks: A scale-up to the industry

This study illustrates the utilization of roof tile waste as a resource in the manufacturing of fired bricks. Although commonly referred to as demolition waste, it is technically classified as construction and demolition waste (C&D). This demolition waste was used as a partial replacement of two soils (alluvial and laterite soil) at three firing temperatures that were considered economical (700, 850, and 900 °C). The waste considered was obtained from roof tiles previously fired at a low temperature below 800 °C, thus containing residual carbonates and clay minerals. The increased waste input resulted in higher firing shrinkage, bulk density, and water absorption while decreasing loss on ignition. An increase in firing temperature led to higher firing shrinkage, loss on ignition, and bulk density, but lower water absorption. The bricks met both Indian and ASTM standards for 2nd and 3rd class by adding 20–35 wt% of roof tile waste and firing at 850–900 °C in laboratory and industrial settings. The minimum acceptable quality for the produced bricks was achieved with an addition of 35 wt% waste, resulting in a water absorption of approximately 19% and a compressive strength ranging from 6 to 9 MPa. The study suggests that incorporating waste from demolished roof tiles into the production of burned bricks can be advantageous. It can partially replace the need for soils, reduce natural resource usage, lower energy consumption during production, and decrease the carbon footprint.

Characterization and properties of Chinese red clay for use as ceramic and construction materials.

This study involves the characterization and analysis of a Chinese red clay obtained from Hunan province to determine its suitability for manufacturing ceramic products. X-ray fluorescence analysis showed the clay has high silica (63.25 weight percent) and alumina (21.38 weight percent) content along with iron oxide, alkalis, and calcium acting as fluxes. X-ray diffraction (XRD) confirmed the presence of quartz, kaolinite, illite, and hematite as the major mineralogical phases. Scanning electron microscopy revealed loosely stacked, plate-shaped kaolinite particles exhibiting pseudohexagonal morphology. Particle size distribution shows a d50 of 12.7 μm and specific surface area is 21.3 m2/g. Differential thermal analysis-thermogravimetric analysis showed mass losses between 450-600°C and 950-1050°C corresponding to dehydroxylation and formation of a liquid phase, respectively. Dilatometry traced the onset of viscous flow sintering around 1000°C. Test bars produced from the clay were fired at 800°C, 900°C, 950°C, 1000°C, and 1050°C. The firing shrinkage increased from 2.5% at 800°C to 12.8% at 1050°C. Strength improved from 11.2 megapascals at 800°C to 42.3 megapascals at 1050°C due to densification and mullite formation. Hematite content caused the color to change from orange-red at 950°C to dark red at 1050°C. XRD analysis of fired specimens confirmed the presence of hematite and newly formed mullite and cristobalite phases. The results indicate the suitability of the clay for manufacturing bricks, roof tiles, and wall tiles using appropriate firing temperatures and cycles.

Technology and Peculiarities of Production of Large-format Ceramic Stones Based on Opoka-like Rocks

Introduction. One of the urgent tasks of the wall ceramics industry at present is the production of large-format ceramic stones with compressive strength of 10–15 MPa and thermal conductivity less than 0.12 W/(m·оС), while the market cost per 1 m3 should be competitive with gas-concrete blocks and be in the range of 5–6 thousand rubles per 1 m3. This problem can be solved by developing modern energy-efficient production technology and using opoko-like rocks and coal processing wastes as the main raw material as fuel and burnout additive.Materials and Methods. The opoka-like rocks — opokas from the deposits of southern Russia — Nagolnovskoye, Bakanskoye, Shakhtinskoye, Avilo-Fyodorovskoye, and coal cake produced by Pyramida LLC were used for research. The study of chemical and mineral composition was carried out by standard methods on prepared samples. The study of ceramic and technological properties (plasticity, molding moisture, degree of crushing, air and fire shrinkage, compressive strength, water absorption) of raw materials was carried out according to generally accepted methods on samples precrushed to a certain grain composition, since opokas, depending on the type, do not soak or slowly soak in water.Results. Pre-firing technological properties of opokas and their differences from traditional clay raw materials soaked in water were confirmed: increased molding moisture, small air shrinkage, low sensitivity to drying. The dependence of density and strength of samples on the degree of pulverization of opoka, firing temperature and the amount of carbon cake in the raw material mixture has been established. The influence of coal preparation wastes and their optimal amount on physical and mechanical properties of fired samples has been determined. The introduction of carbon cake allows to exclude the use of gas for firing or minimize its introduction. On the basis of the obtained results a simplified technological scheme for the production of large-format stones with minimum production cost has been developed.Discussion and Conclusion. The proposed technological scheme consists of two units of the main mass preparation equipment, molding of products is carried out by semi-rigid extrusion, drying of products is carried out directly on kiln cars, and for firing coal cake is used, which is introduced into the raw mix. These factors and technological methods allow to obtain products with low thermal conductivity, but with strength 3–5 times higher than that of aerated concrete blocks of similar density. The prime cost of ceramic stones will amount to 3–3.5 thousand rubles per 1 m3 of products. Rostov region, possessing opoka-like rocks and unclaimed reserves of technogenic coal raw materials, can become a center of production of large-format ceramic stones with low cost and provide the south and central part of the country with highquality wall materials.

Upcycling glass wool and spodumene tailings in building ceramics from kaolinitic and illitic clay

With concerns related to the high cost and environmental footprint of energy, reducing the sintering temperature in the ceramic industry remains a key challenge. This study investigates the effect of glass wool waste on the sintering properties of kaolinitic and illitic clays, two types of clay commonly used in the ceramic industry. Both clays were substituted with 20 and 40 wt% glass wool, and the effect on sintering at 850, 950, and 1050 °C was investigated. The properties of the sintered materials were assessed with several techniques, including X-ray diffraction, scanning electron microscopy, bulk density, water absorption, dilatometry, and compressive and flexural strength. The water absorption of the prepared ceramics varied from 0 to 30 %, while compressive and flexural strength were in the ranges of 10–60 MPa and 2–15 MPa, respectively, depending on the glass wool content and sintering temperature. The addition of glass wool induced more glass formation, microstructure densification, and higher firing shrinkage at lower temperatures, which contributed to an increase of more than 100 % strength at 850 °C. The addition of 10–20 parts spodumene tailings was observed to mitigate the firing shrinkage at 950 °C with no significant effect on the mechanical properties.

Ultra-reduction of drying and firing shrinkage on pottery slip casting by adding mullite fiber

Slip casting is a popular method for producing ceramics. However, during the drying and firing processes, the molded bodies shrink and deform considerably, developing cracks and fractures. This reduces the product yield, limits the range of possible shapes and sizes, and reduces dimensional accuracy. This study proposes a slurry consisting of firing-nonshrinkage clay, mullite fiber, dispersant, and water. The results of slip casting a molded body using the proposed slurry indicated that the total shrinkage is significantly reduced owing to the addition of mullite fiber, particularly ≥ 10 mass%. Therefore, it is inferred that the fiber forms a rigid, bulky three-dimensional network structure in the molded body, which is retained even after dehydration and firing. This technique is expected to be useful in the creation of new ceramic industrial products and works of art involving high-precision dimensions and complex, linear, and thick-walled shapes.