Effect of specimen geometry on kinetics of thermal decomposition of minerals in porous ceramic tiles

Porous ceramic tiles are used as covering for indoor vertical surfaces in buildings. Clay and limestone are the starting raw materials. The firing step consolidates the product's properties in the manufacturing process. In this step several reactions occur, among them are the dehydroxylation of the clay minerals and decomposition of the carbonates. This study determined the kinetics parameters associated with the decomposition of these 2 minerals. Two different methods of samples preparation were investigated. In the first method, 60 mg of a spray-dried powder was submitted to analysis in traditional thermogravimetric equipment. In the second method, compacted specimens with dimensions of 80 × 20 × 2.5 mm³ and a mass of 7 g, compacted at 25 MPa, were submitted to analysis using customized thermogravimetric apparatus. The curves were obtained for 6 different heating rates between 2.5 and 20 K min⁻¹. The activation energy, the pre-exponential factor of the specific velocity equation, and the reaction mechanism were determined. Depending on the methods and compaction degree the activation energy varies from 177.0 to 224.7 kJ mol⁻¹ and from 188.5 to 230.2 kJ mol⁻¹ for kaolinite and calcium carbonate, respectively. For accurate measurement of the activation energy, the heat transfer needs to be considered for each particular experimental configuration.     

Phase composition,microstructure, and properties of ceramic tile prepared using ceramic polishing waste as raw material

Polished ceramic products are currently the most popular in architectural decoration, but a significant amount of ceramic polishing waste (CPW) is produced during the preparation process. Determining how to handle the CPW is a pressing task for enterprises. This work investigated the feasibility of recycling CPW in porcelain tile, and its influence on the phase composition, microstructure, and properties of the ceramic body. The CPW was found to have a similar composition to the traditional ceramics and worked as a flux. The SiC within CPW began to decompose into SiO₂ with CO₂ generation at about 1100°C, resulting in a porous structure. Microstructure observation indicated that a high CPW sample produced sufficient liquid phase when fired at temperatures ≤1100°C, which was not only beneficial for mullite growth but also for matrix densification by the viscous flow mechanism. But a high-content CPW caused the body to foam or even expand at temperatures >1100°C, thus significantly reducing mechanical properties. Finally, a series of porcelain tiles were successfully prepared with a CPW content of ≤30 wt% at a firing temperature of 1125-1200°C. The results of this study are considered to be valuable for the utilization of CPW.     

陶瓷过滤机在电石渣脱水中的应用

介绍了一种利用陶瓷过滤机处理电石法生产PVC时产生的电石渣的新方法,该工艺稳定,故障率低,效果良好,可得到清澈的滤液和水分较低的电石渣料。     

Effect of calcium carbonate on the preparation of glass ceramic foams from water-quenched titanium-bearing blast furnace slag and waste glass

ABSTRACT

Glass ceramic foams were fabricated with powder sintering technology at a low temperature (900°C), using water-quenched titanium-bearing blast furnace slag (WTS) and waste glass as the primary raw materials. Additionally, calcium carbonate, sodium borate and sodium phosphate were chosen as sintering aids to form excellent performance products. The effects of calcium carbonate additions on foaming process, crystal content, morphology and properties of the prepared samples were systematically researched. The research indicates that increasing the calcium carbonate content made the foaming process harder and the pore size got more uniform. Consequently, the compressive strength and bulk density increased, while the porosity and water absorption decreased. The homogenous porous structures and optimal comprehensive properties were achieved with 5–7?wt-% CaCO₃ addition, including a bulk density of 0.79–0.82?g?cm^–3, porosity of 73.13–75.28%, water absorption of 3.29–3.75% and compressive strength of 13.13–13.85?MPa.     

Pore size distribution and porosity influence on Sorptivity of ceramic tiles: From experimental data to fractal modelling

The Sorptivity is a coefficient very important to characterize porous materials. It is associated to principal properties such as mechanical durability, thermal and electrical conductivity, etc. In this work, the Sorptivity coefficient of several systems of porous ceramics has been measured following the experimental procedure. In different situations, this very simple test could be not performed; in cultural heritage or during an optimised industrial process. Major reasons for this inability include that it would demand great quantitates of materials impossible to withdraw from the protected building, as well as the experimental test can last for several days, which reduces the possibility to correct/improve the industrial production process. In this regards, being very useful to have analytical formulas in order to calculate Sorptivity coefficient, an Intermingled Fractal Units model has been proposed. Starting from its capability to reproduce entirely the pore size distributions of porous materials, IFU is used to simulate water absorption process and to estimate the Sorptivity coefficient. The obtained results are in good agreement with experimental data and others two models predictions. This fact allows considering IFU model as a future tool for design materials and to predict their service life.     

Effect of processing on the microstructure and crystalline phase composition of wood derived porous SiC ceramics

Pine (Pinus silvestris) wood samples were dried and impregnated with a SiO₂ sol from a sol–gel process. The impregnation involved a two step process in a custom-made apparatus. Impregnated samples were dried and pyrolised at 500 °C under an oxygen-free atmosphere. SiC synthesis was performed in a high-temperature furnace in an argon atmosphere at a temperature of 1600 °C for 2, 4 and 8 h. The samples were investigated with X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The changes in the SiC synthesis time at the maximum temperature lead to changes in the microstructure and crystalline phase composition. An increase in the synthesis time opens up the possibility to produce mainly α-SiC crystalline modification containing porous SiC ceramics.     

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.     

Effect of waste glass and zircon on ceramic properties and microstructure of porcelain tiles

Abstract

The possibility of using waste glass as a flux in porcelain tiles without deterioration in mechanical properties has been assessed. Waste glass was added to a typical porcelain tile body, replacing feldspar by up to 15%. Zircon was also added at 5% in partial replacement of quartz. The prepared batches were fired at temperatures of 1160 to 1240°C with 20 min soaking time. Addition of 5% zircon in the presence of 5% waste glass resulted in unusual mechanical and physical characteristics. Further additions of waste glass enhanced vitrification and consequently some surface and mechanical properties, but worsened modulus of rupture (MOR) and toughness. Generally specimens containing zircon had better physicomechanical properties.     

微孔陶瓷过滤装置及其在火电厂冲渣水治理工程上的应用

简述了微也陶瓷过滤装置的原理、结构特点;着重介绍了采用此装置处理锅炉冲渣水悬浮物的工艺过程和运行实况。     

Influence of Al2O3 and SiO2 nanoparticles addition on the microstructure and mechano-physical properties of ceramic tiles

The effect of adding nano-alumina and nano-silica on the microstructural and physical properties of ceramic tiles was investigated. Samples are fabricated from typical raw materials by uniaxial pressing under 10 MPa and firing at 1160 °C. The microstructures and crystalline phases are studied using scanning electron microscopy and X-ray diffraction, respectively. The mechanical-physical properties are reported in terms of compressive strength, water absorption, bulk density and apparent porosity. Image software analysis is used to determine the total porosity and the size distribution of the porosity. The results show that samples with nanoparticles present increases in density and reductions in porosity. The best results correspond to the highest addition of nanoparticles. The formulation with 1 wt% nano-alumina shows the highest density associated with a reduction in porosity and an increment in the mullite phase. The sample with 1 wt% nano-silica exhibits the lowest water absorption, apparent porosity and total porosity.     

Effect of thermal exposure on the microstructure and strength of an alumina-silica ceramic fiber

The microstructure and mechanical properties of an alumina-silica ceramic fiber after thermal exposure at 1100–1300°C were investigated by X-ray diffraction, nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy analyses and room temperature tensile strength test. The results showed that the fiber was composed of γ-A1₂O₃ and amorphous SiO₂. A phase reaction of γ-A1₂O₃ and amorphous SiO₂ occurred when thermal exposure temperature exceeded 1150°C, and a new mullite phase formed. The grain size of the newly formed mullite increased with the increase of exposure temperature. Both the phase transition and grain growth of mullite had a significant impact on the mechanical properties of the fiber. Tensile strength of the fiber decreased slightly when thermal exposure temperature was below 1150°C, while the strength retention of the fiber decreased sharply to 65.36% as exposure temperature rose to 1200°C. A higher dispersion of tensile strength was also observed at higher exposure temperatures, as revealed by the Weibull statistical model.     

Effect of polymerization conditions on the microstructure of a liquid crystalline copolyester

The melt polycondensation of mixtures of sebacic acid (S), 4,4′‐diacetoxybiphenyl (B), and 4‐acetoxybenzoic acid (H), carried out for the synthesis of semiflexible liquid–crystalline copolyesters referred to as SBH 1 : 1 : x, has been studied with the aim of clarifying the effect of the reaction conditions on the microstructure and the thermal properties of the products. It has been shown that the segregation of a liquid–crystalline phase within the polymerizing mixture, coupled with the thermodynamic tendency of the two phases to undergo compositional differentiation as polymerization proceeds, is responsible for the formation of blocky, rather than ideally random, copolyesters with poor processibility, when the mole ratio of H to the other two monomers is higher than x ≈ 1.90. The results of this study have shown that this unwanted effect can be considerably limited by carrying out the polycondensation at a relatively high temperature from the very beginning, rather than by the standard technique involving progressive heating of the reaction mixture, thus allowing the production of SBH copolyesters with a higher degree of aromaticity. The results are discussed in terms of the relative rates of the condensation reactions, which are responsible for chain growth, and of the concurrent acidolysis and esterolysis reactions leading to copolyester sequence reorganization. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 141–150, 2000     

Preparation of glass-ceramics with diopside as the main crystalline phase from low and medium titanium-bearing blast furnace slag

Because of the low content of TiO₂, the utilization of low and medium Ti-bearing blast furnace slag is a difficult problem. In this study, glass-ceramics with diopside as the main crystalline phase was made by using TiO₂ in the blast furnace slag as the nucleating agent and adding additional elements of TiO₂, Fe₂O₃ and Cr₂O_3. The effects of these three nucleating agents on the phase composition and structural properties of the prepared glass-ceramics were evaluated by DSC, XRD, and SEM to determine their optimal dosage. Research results show that the suitable mass percentages of the TiO₂, Fe₂O₃ and Cr₂O₃ crystal nucleation agents of the glass-ceramics are 7.69%, 0.96%, and 2.88%, respectively. The prepared glass-ceramics have excellent physical and chemical properties, e.g., a bending strength of 114.74 MPa, a bulk density of 2.77 g/cm³, a water absorption rate of 0, and a mass-loss rate of only 0.085%.     

Influence of composition and microstructure on transparency and diffusivity in ion-exchangeable spinel glass-ceramics

Ion-exchangeable, transparent spinel glass-ceramics are presented and discussed here for the first time. To retain transparency with increasing crystallinity, spinel glass-ceramics must have uniform crystallization of small (~9 nm) crystallites, not large spherulitic structures comprised of small crystallites. To obtain such a uniform microstructure, the amount of total nucleating agents (ZrO₂ + TiO₂) in the precursor glass composition must be greater than 5 mol%. With small changes in composition and significant differences in microstructure, the demarcation between transparent and opaque glass-ceramics is distinct as is the decrease in K diffusivity during ion-exchange from the transparent (14.7 microns²/h) to the opaque (11.2 microns²/h) compositions. Understanding how to retain transparency during ceramming and increase diffusivity during chemical strengthening is critical in designing materials for many real-world applications. Ion-exchangeable, transparent spinel glass-ceramics are presented and discussed here for the first time. To retain transparency with increasing crystallinity, spinel glass-ceramics must have uniform crystallization of small (~9 nm) crystallites, not large spherulitic structures comprised of small crystallites. To obtain such a uniform microstructure, the amount of total nucleating agents (ZrO₂ + TiO₂) in the precursor glass composition must be greater than 5 mol%. With small changes in composition and significant differences in microstructure, the demarcation between transparent and opaque glass-ceramics is distinct as is the decrease in K diffusivity during ion-exchange from the transparent (14.7 microns²/h) to the opaque (11.2 microns²/h) compositions. Understanding how to retain transparency during ceramming and increase diffusivity during chemical strengthening is critical in designing materials for many real-world applications.     

陶瓷抛光砖废料和磷石膏对硅酸盐水泥熟料煅烧及其岩相结构的影响

试验研究了陶瓷抛光砖废料和磷石膏配料对硅酸盐水泥熟料烧成的影响,并通过XRD、岩相分析和性能测试等手段探讨了其对熟料岩相结构与性能的影响及其机理.结果表明,通过优化配料方案和工艺条件,陶瓷抛光砖废料和磷石膏代替部分原料配料可烧制出合格的硅酸盐水泥熟料.     

Effect of shrinkage-reducing admixtures on the properties of alkali-activated slag mortars and pastes

The effect of a shrinkage-reducing admixture (SRA) based on polypropylenglycol on the dimensional stability of waterglass-activated slag mortars was studied. The analysis also showed the effect of the admixture on pore structure of the mortars as well as on the mineralogical composition and microstructure of the alkali-activated slag pastes.The SRA reduced the shrinkage by up to 85 and 50% when the alkali-activated slag mortar specimens were cured at relative humidities of 99 and 50%, respectively. The mechanism primarily involved in shrinkage reduction is the decrease in the surface tension of pore water prompted by the admixture. The SRA also modified the pore structure - under both curing conditions - increasing the percentage of pores with diameters ranging from 1.0 to 0.1 μm. Capillary stress is much lower in these pores than in the smaller capillaries prevailing in mortars prepared without admixtures.Microstructurally, the SRA occasioned a slight increase in the proportion of Si units Q² in the CSH gel and a decrease in the percentage of Al replacing the Si in the gel structure. The admixture did not, however, modify the mineralogical composition of the pastes.Finally, the SRA admixture retarded the alkaline activation of the slag, more intensely at higher admixture dosages. While the admixture did not significantly alter the degree of reaction in pastes cured for 7 days at RH = 99%, the value of this parameter dropped by 7% in the presence of the admixture in pastes cured at 50% relative humidity.     

Reticulated open-cellular aluminum nitride ceramic foams: Effect of sintering aids on microstructural,thermal, and mechanical properties

Open-celled aluminum nitride ceramic foams were prepared by the polymer sponge replication technique involving aqueous dispersions of passivated AlN. The amount of the Y₂O₃ and Dy₂O₃ as sintering aid was varied, and the effects on the densification, microstructure formation, phase composition, and finally, the thermal conductivity were investigated. A typical thermal conductivity of 1.1 W m⁻¹ K⁻¹ was determined for foams at a porosity level of 94.3 vol.%, on average. This measured foam thermal conductivity was subsequently modeled using different porosity ↔ thermal conductivity relations considering the different hierarchical levels of porosity in these foams. From these models, the thermal conductivity of the bulk AlN strut material was determined, correlated with the strut microstructure and the phase composition, and compared to literature data.     

工业废渣-阴离子团多元复合掺杂对高C3S水泥熟料烧成及性能的影响

利用某些工业废渣并复合一些阴离子(团),以一定比例配入生料中,采用高饱和比、高硅率、高铝率配料,在实验室于正常烧成温度下烧成了3d和28d抗压强度分别达42MPa和84MPa、其它性能正常的高C3S水泥熟料(ARPC),实现了熟料的高胶凝性。废渣-阴离子多元复合掺杂通过改善C3S形成的动力学过程改善了生料的易烧性。熟料的高胶凝性一方面是由于熟料中C3S的含量高,另一方面是由于不同的离子以一定量固溶到C3S晶格,会稳定不同的晶型,杂质离子还会改变液相性质,调整CS晶貌,使得水泥熟料具有良好的微观结构。