ABSTRACT Use of waste or by-products from different industries and the agricultural sector has received increasing attention in the scientific, technology, ecological, economic and social spheres in recent years. Rice husk (RH) is a by-product of rice milling and rice husk ash (RHA) is generated by combustion in a separate boiler. Both RH and RHA are abundantly accessible in rice growing countries such as China, India, Brazil, the USA, and Southeast Asia. RH has therefore been recycled by burning it for energy production. This generates RHA, which contains a huge quantity (85–95%) of amorphous silica. Over the past two decades, RHA has been used extensively in numerous fields for manufacturing of different silicates, zeolites, catalysts, nanocomposite, cement, lightweight construction materials, insulators, and adsorbents. This paper presents a comprehensive overview on the processing of nano-silica from RH/RHA. It tries at the same time, to present a critical review of the application of RHA as an ingredient for the production of various ceramic materials, e.g. refractory, glass, whiteware, oxide and non-oxide ceramics, silica aerogel and SiO2/C composites. In summary, amorphous silica derived from RHA or RH provides a potential alternative to conventional silica sources (e.g. quartz) for the manufacture of value-added ceramics for practical applications.
Abstract Geopolymers are mostly produced with main-stream precursors such as fly ash and slag. These precursors are successfully used and competitively demanded by the cement industry. Development of geopolymers from alternative precursors is appealing. The main aim of this work is the development of geopolymers with construction and demolition waste-based precursors including masonry units (red clay brick, roof tile, hollow brick) and glass. Different curing temperatures (50, 65, 75, 85, 95, 105, 115, 125 °C), curing periods (24, 48, 72 h), and Na concentrations (10, 12, 15%) of alkaline activator (NaOH) were employed. Compressive strength testing and microstructural investigations were performed including X-ray diffraction, thermogravimetry and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Results showed that depending on the type of precursor (hollow brick), curing temperature/period (115 °C/24 h) and concentration of alkaline activator (12%), it is possible to obtain compressive strength results more than 45 MPa. Hollow brick is the most successful precursor resulting in higher compressive strength results thanks to a more compact microstructure. The strength performance of red clay brick and roof tile is similar. The compressive strength results of geopolymers with glass precursor are lower, most probably due to significantly coarser particles of glass used. The main reaction products of red clay brick-, roof tile- and hollow brick-based geopolymers are sodium aluminosilicate hydrate (N-A-S-H) gels with zeolite-like structures while they are sodium silicate gels in the case of glass-based geopolymers. Our findings showed that CDW-based materials can be used successfully in producing geopolymers. Current research is believed to help raise awareness in novel routes for the effective utilization of such wastes which are realistically troublesome and attract further research on the utilization of CDW-based materials in geopolymer production.
Antonia del Rocío López Guemez, Adrián Cordero García, José Luis Cervantes López
et al.
The increase in pollution, using photocatalytic materials to degrade organic pollutants remains in force. ZnO is the most used semiconductors for photocatalytic applications. The oriented growth of nanostructures on substrates or seed layers (SL) improves the physical and chemical properties compared to the bulk-grown material. In this work, the photocatalytic efficiency of ZnO nanorods and nanoflowers was evaluated, obtained by hydrothermal growth (HG) over SL deposited by the spin-coating technique (SCT). The characterizations results showed two types of growth: 1D nanostructures with a dimension in the range of 400–1000 nm and diameters of 70–100 nm, and 1D microstructures with approximate 5–11 μm length and diameters of 1–2 μm. However, in the 7 SL system, micro prisms were generated, which led to the formation of 3D nanostructures (micro flowers) of ZnO with a maximum of 6 μm in diameter. The system with 1D and 3D ZnO nanostructures, grown in 7 SL, was the most efficient methylene blue degradation. Achieving 100% transformation in 120 min, with a rate constant of 2.98 × 10−2 min−1. The results show that the SCT deposit combined with the sol–gel method and HG produces 1D and 3D structures with high potential in photocatalytic degradation. Resumen: El aumento de la contaminación, el empleo de materiales fotocatalíticos para degradar contaminantes orgánicos continúa vigente. El óxido de zinc (ZnO) es el semiconductor más utilizado para aplicaciones fotocatalíticas. El crecimiento orientado de nanoestructuras sobre capas semillas (SL) mejora las propiedades físicas y químicas comparado con el material crecido en bulto. En este trabajo se evaluó la eficiencia fotocatalítica de nanovarillas y nanoflores de ZnO obtenidas por crecimiento hidrotérmico (HG) sobre SL depositadas por la técnica spin coating (SCT). Los resultados de las caracterizaciones mostraron dos tipos de crecimiento: nanoestructuras 1D con dimensiones en el rango de 400 a 1.000 nm y diámetros de 70 a 100 nm, y microestructuras 1D con longitud aproximada de 5 a 11 μm y diámetros de 1 a 2 μm. Sin embargo, en el sistema de 7 SL se generaron microprismas orientados, generando nanoestructuras 3D (microflores) con un diámetro máximo de 6 μm. Este sistema fue el más eficiente en la degradación de azul de metileno. Degradando de 100% en 120 min, con una constante de velocidad de 2,98 x 10-2 min-1. Los resultados indican que la SCT combinada con el método sol-gel y el HG produce estructuras 1D y 3D con alto potencial de degradación fotocatalítica.
Piezoelectricity offers an electromechanical coupling that is widely utilized in transducer applications. There has been a consistent demand for transparent piezoelectric materials for optoelectrical applications. Therefore, despite the inherent tradeoff between the transparency and the piezoelectricity, numerous strategies have been explored to develop the transparent piezoelectric materials. Nonetheless, the most transparent piezoelectric materials developed to date is either a single crystal or materials that achieve transparency via hot-press sintering, limiting its industrial applicability. Therefore, we introduce a novel piezoelectric material that ensures transparency through co-doping and pressureless sintering of polycrystalline ceramics. In this study, we employed a compositional optimization approach to enhance the synergistic effect between the transparency and the piezoelectric properties of 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (PMN–0.29PT) ceramics. By utilizing the tape casting process for mass production and large-area manufacturing, our Pb0.913La0.0145Sm0.0145(Mg1/3Nb2/3)0.71Ti0.29O3 (TP2.9) ceramics exhibited over 60% transparency and large piezoelectric coefficient (d33) of 1104 pC/N. This material holds considerable promise for a wide range of industrial applications in both the optical and electronic domains.
The introduction of oxygen vacancies into zirconia is an effective strategy for enhancing its light absorption ability and photocatalytic performance. However, the cost-efficient preparation of oxygen-deficient zirconia (ZrO2−x) remains challenging, which severely limits its broad application. In this study, flash sintering treatment was used to fabricate ZrO2−x bulk in very short time of 90 s. Oxygen vacancies were introduced into ZrO2 bulk through electrochemical reduction reactions. The as-prepared black ZrO2−x exhibited excellent optical absorption capability, a small band gap (2.09 eV for direct and 1.67 eV for indirect), and a reduced conduction band energy, which is ascribed to the generation of oxygen vacancies and reduction of Zr cations. The as-prepared ZrO2−x showed remarkable photocatalytic activity due to excellent solar light absorption and low recombination rate of electron‒hole pairs. Flash sintering treatment provides a cost-efficient approach for rapidly fabricating ZrO2−x bulk materials with high concentrations of oxygen vacancies, which can also be applied to other materials.
Mullite (3Al2O3·2SiO2) is an aluminosilicate characterized by excellent physical properties, which makes it an important ceramic material. In this way, ceramics based on mullite find applications in different technological fields as refractory material (metallurgy, glass, ceramics, etc.), matrix in composite materials for high temperature applications, substrate in multilayer packaging, protective coatings, components of turbine engines, windows transparent to infrared radiation, etc. However, mullite is scarce in nature so it has to be manufactured through different synthesis methods, such as sintering, melting-crystallization or through a sol-gel route. Commonly, mullite is fabricated from pure technical grade raw materials, making the manufacturing process expensive. An alternative to lowering the cost is the use of mining waste as silica (SiO2) and alumina (Al2O3) feedstock, which are the necessary chemical compounds required to manufacture mullite ceramics. In addition to the economic benefits, the use of mining waste brings out environmental benefits as it prevents the over-exploitation of natural resources and reduces the volume of mining waste that needs to be managed. This article reviews the scientific studies carried out in order to use waste (steriles and tailings) generated in mining activities for the manufacture of clay-based ceramic materials containing mullite as a main crystalline phase.
Abstract Clays from the Saïss basin (northern Morocco) used traditionally in the ceramic industry in the Fez area were studied using mineralogical and physicochemical techniques to evaluate their potential suitability as raw materials for ceramics manufacture. X-ray diffraction was used to determine their mineralogical composition. The physical properties determined were particle-size distribution and consistency limits. The chemical composition was determined using X-ray fluorescence analysis and Fourier-transform infrared spectrometry. The structural changes of the mineral phases in the raw materials during firing were studied over a temperature range of 500–1000°C. In the pottery site from Fez, generally potters use a mixture of 25% fine clay (ARFS) from the upper part of the Miocene marls and 75% sandy clay (ARFR) from the lower part of the Miocene marls. The ARFS clay yielded very rigid specimens after firing that artisan potters would find difficult to handle so as to produce desired shapes and sizes. However, the specimens obtained from ARFR clay show signs of faltering. The mixture of these two clayey materials from this pottery site is therefore necessary to obtain the optimal paste for ceramics purposes. The chemical compositions indicated that SiO2, Al2O3, CaO and Fe2O3 are the major minerals, with trace amounts of K2O and MgO. Quartz, feldspars and clay minerals prevail in all samples. Kaolinite, illite and smectite are the dominant clay mineral phases, with traces of chlorite and interstratified illite–smectite. The classification of these samples using appropriate ternary diagrams showed that the proportions used in the mixture produce a new material with adequate characteristics for the production of traditional ceramics.
Mariane Costalonga de Aguiar, M. C. Gadioli, Maria Angélica Kramer Sant’Ana
et al.
The ornamental stone industry is growing and has a large production in Brazil, mainly in Espírito Santo, where the largest production in the country is concentrated. Brazil is part of the group of countries that produce the most ornamental stones in the world; however, the generation of waste in this sector is very large. These ornamental stone wastes when used for the manufacture of new materials, such as red ceramics, contribute to the reduction in the raw material clay and to the reduction in the environmental impact. The objective of this work was to incorporate fine wastes from the processing of ornamental stones called FIBRO in red ceramics and later, to contribute to the standardization of the use of these wastes in the ceramic industry, contributing to the manufacture of more economical and sustainable products. Wastes were incorporated in the proportion of 0 to 50% by mass that were prepared by extrusion and fired at 900 °C, 950 °C, and 1000 °C. After firing, the physical and mechanical properties of the ceramic material were evaluated. Specific mass apparent, water absorption, porosity, and flexural strength by three points tests were carried out. The results showed that from 30% at the lowest temperature, tile is already fabricated within the values stipulated by the standards, thus saving energy. The analyzed waste is a material with excellent chemical characteristics to be used in the ceramic mass, in addition to having improved the technological properties of the material, such as less water absorption and greater flexural strength.
The kinetics of the thermally induced glass / crystal phase transformation of chalcogenide glasses plays an important role in determining their candidacy for optical phase change memory applications. The rate of crystallization and the corresponding activation energy are the two crucial kinetic parameters that reflect the durability and quality (i.e., storage properties) of phase change materials. This script deals with metal-induced effects on thermally regulated non-isothermal crystallization in a new glass alloy of Se-Te-Sn using calorimetric measurements. The elements Antimony (Sb), Cadmium (Cd) and Indium (In) have been used as structural modifiers for this purpose. The crystallization and glass transition kinetics of these glass alloys have been investigated by thermal analysis of several kinetic parameters such as the parameter of order n, the maximum crystallization temperature Tc, the crystallization rate K and the consequent activation energy Ec). A DSC is used in non-isothermal mode for the present studies. The values of the activation energy Ec are determined using the data obtained from the displacement of the exothermic peaks of crystallization in non-isothermal DSC plots at various heating rates. The role of the additives Sb, Cd and In in the variation in the rate of crystallization K of and the Avrami index (n) for each glass alloy is also examined. Detailed thermal analysis of the kinetic data confirms the superiority of Cd over the other two additives (In and Sb) for optimization of the kinetic properties of the main SeTeSn glass. Resumen: La cinética de la transformación de fase vidrio/cristal inducida térmicamente de los vidrios calcogenuros desempeña un papel importante en la determinación de su candidatura para las aplicaciones de memoria óptica de cambio de fase. La tasa de cristalización y la energía de activación correspondiente son los dos parámetros cinéticos cruciales que reflejan la durabilidad y la calidad (es decir, las propiedades de almacenamiento) de los materiales de cambio de fase.El presente guión trata de los efectos inducidos por metales sobre la cristalización no isotérmica regulada térmicamente en una nueva aleación vítrea de Se-Te-Sn, utilizando mediciones calorimétricas. Los elementos antimonio (Sb), cadmio (Cd) e indio (In) se han empleado como modificadores estructurales para este propósito. La cinética de cristalización y transición vítrea de estas aleaciones de vidrio se ha investigado mediante el análisis térmico de varios parámetros cinéticos como el de orden n, la temperatura máxima de cristalización (Tc), la velocidad de cristalización (K) y la energía de activación consiguiente (Ec). Se usa un DSC en modo no isotérmico para los presentes estudios. Los valores de la energía de activación Ec se determinan utilizando los datos obtenidos del desplazamiento de los picos exotérmicos de cristalización en gráficos de DSC no isotérmicos a diversas velocidades de calentamiento. También se examina el papel de los aditivos Sb, Cd e In en la variación en la K y el índice de Avrami (n) para cada aleación vítrea. El análisis térmico detallado de los datos cinéticos confirma la superioridad del Cd sobre los otros dos aditivos (In y Sb) para la optimización de las propiedades cinéticas del vidrio principal Se-Te-Sn.
Two novel garnet-type ceramics Ca3MZrGe3O12 (M = Co and Zn) with pure phase were prepared through a solid-state reaction method. Structure–property relationships were studied by the Rietveld refinement and Raman spectra. The appearance of two weak symmetric stretching vibrational peaks in Ca3ZnZrGe3O12 might be due to the lower ordering. Higher Q × f value in Co-analogue was related to the larger packing fraction and the lower FWHM of A1g mode. The smaller oxygen bond valence in Ca3CoZrGe3O12 indicates a smaller τf value. At the optimized sintering temperature of 1280 °C, Ca3CoZrGe3O12 shows desirable microwave dielectric properties with εr of 10.37, Q × f value of 60,100 GHz, and τf value of −28.5 ppm/oC. The Ca3ZnZrGe3O12 ceramic sintered at 1200 °C has the best microwave dielectric properties with εr of 10.48, Q × f value of 49,700 GHz, and τf value of −35.8 ppm/oC.
Scaling or precipitation fouling involves crystallization of hard and chalky solid salts from a solution. Scaling results in significant production and energy losses and is a major concern in many industries. Here we investigate the scalephobicity of rare earth oxide (REO) ceramics (particularly CeO2, Gd2O3, and Er2O3) in comparison with glass and stain-less steel. We quantify the surface energy and its polar and apolar components for these materials using the Van Oss-Chaudhury-Good approach and show a direct correlation between surface energy and scale deposition. We also show that the polar component of surface energy is the main contributor to scale deposition; hence, REOs with minimal polar component represent high barrier to scale deposition. Moreover, we study the weight gain due to calcium sulfate dihydrate (gypsum) scale accumulation on these materials and show 55% and 77% reduction on REOs in comparison with bare glass and stainless-steel, respectively. We also evaluate the adhesion forces between salt and test materials using atomic force microscopy with a gypsum microparticle adhered onto a tipless cantilever. We show adhesion force between salt particles and REO surfaces is about half of that of bare glass and stainless-steel because of lower surface energy and polar component. We expect REO ceramics would find widespread applicability as robust scale-phobic surfaces in various industries.
Direct ink writing technique, an extrusion based additive manufacturing process, has been used to fabricate kaolinite clay based-ceramics with several inexpensive ceramic powders: lime, fly ash and talc. All the above materials are commonly used in the traditional ceramics industry, in both small and large industries, and therefore available worldwide. This research shows the simplicity of the process feasible not only for companies but also for individual users. The samples were fabricated with water to clay ratios (W/C) between 0.68 and 0.72. Additives were tested in 3.0, 5.0 and 7.0wt.% with respect to the clay contents, although 3 wt.% of additives worked best. Cylindrical samples were fabricated with 20mm in diameter and 20mm in height in order to test their compressive strength and density. Measurement samples were previously cured for three days at room temperature and then exposed to 1100?C for 1 h. The powdered additives and their corresponding mixtures with clay were characterized with scanning electron microscopy, X-ray fluorescence and X-ray diffraction techniques. Results showed that samples with 0.70 W/C ratio and using fly ash as an additive were the best in terms of workability, mechanical properties and surface finishing.
We investigated the use of waste glass fiber-reinforced plastic (GFRP) to remove dye from industrial wastewater. The dye adsorbent material, based on GFRP/clay ceramics, was produced by mixing crushed GFRP with clay and firing the resulting mixture. Several types of ceramics were produced by adjusting the mixing ratio of clay, crushed 40% GF/GFRP, and firing atmosphere. Adsorption tests with methylene blue (MB) dye were performed by mixing the ceramics into an MB solution while controlling the stirring speed and measuring the decrease in MB dye concentration over time. These results showed that GFRP/clay ceramics reductively fired at 1073 K had a higher MB dye adsorption ability than that of the clay ceramic. The MB dye absorptivity of the reductively fired ceramics increased as we increased the mixing ratio of GFRP. We attribute this result to the high plastic carbide content in the ceramic, which has excellent dye absorbability. Furthermore, these particles had a comparatively high specific surface area and porosity.
Nanostructured zinc oxide (ZnO) thin films were deposited on glass substrates using various molar concentrations of zinc acetate dihydrate as the starting precursor at 400°C by the spray pyrolysis technique. The structural, morphological, and optical properties of the samples were investigated. X-ray diffraction studies showed thin films with a polycrystalline nature of the hexagonal wurtzite phase type. The preferred orientation was observed along the (002) direction. The crystallite size increased from 16.18nm to 20.42nm with increases in the molar concentration from 0.1M to 0.3M and then decreased further to 17.85nm at a molar concentration of 0.4M. SEM micrographs showed significant changes in the zinc oxide thin films with increases in the molar concentration of the precursor. Room-temperature Raman spectra confirmed typical electron-phonon coupling in the ZnO thin films. The optical band gap of the zinc oxide thin films was calculated using the Tauc plot. The sensitivity and selectivity of such toxic volatile organic vapors as benzene, toluene, ethylbenzene, and xylene (BTEX) were studied at room-temperature and reported.
Co0.5Zn0.5Fe2O4/Ba0.8Sr0.2TiO3 (CZFO/BST) composite ceramics with different molar ratios (1:3, 1:2, 1:1, 2:1 and 3:1) were prepared by combining chemical co-precipitation and sol-gel method. Effects of molar ratio on the microstructure, dielectric and multiferroic properties were investigated. The formation of the individual phases and the composites was confirmed by XRD results and small amount of secondary phase (Ba2Fe2Ti4O13) was observed. The grain sizes of magnetic (CZFO) and ferroelectric phase (BST), measured by SEM, were about 5 µm and 0.5 µm, respectively. The sample with molar ratio (1:2) has the largest dielectric constant, while the sample with molar ratio (3:1) shows the lowest dielectric constant. A distinct loss peak can be observed for all the samples. Both the peak position and peak intensity increase with the frequency, indicating relaxation polarization process generated by space charge or interface polarization. The ceramics with molar ratio (1:1) shows the smallest leakage current (∼ 10−7 A/cm at 1.5 kV/cm), while the leakage current (∼ 10−5 A/cm at 1.5 kV/cm) of the sample with molar ratio (3:1) is the largest. The ferroelectric hysteresis loop is not apparent due to the low Curie temperature of the ferroelectric phase, but the sample with molar ratio (2:1) shows the best ferroelectric properties. It was found that with the increase of CZFO content, the values of saturation (Ms) and remnant (Mr) magnetization increase at first and then decrease. The sample with molar ratio (3:1) has the maximum Ms value (about 50.34 emu/g), while the sample with molar ratio (1:2) shows the minimal Mr value (about 0.46 emu/g). This anomalous magnetic property is induced by the interface interaction between the two phases.
Laminated glass provides safety in an impact or explosion event by way of a polymer interlayer to which glass fragments adhere upon fracture. The mechanical deformation of the interlayer defines how the impact energy can be absorbed to prevent calamities by flying glass debris, penetration of a blast wave, lacerations, etc. The PVB interlayer used in safety glass shows highly nonlinear viscoelastic material behaviour, with a great sensitivity to temperature and deformation rate. Although various material models for PVB can be found in literature, few publications discuss the full range of its mechanical behaviour and none are found to describe a material model that is valid in a wide range of deformation rates and up to high elongations. Such material model is necessary for the numerical study of the post-fracture response in a dynamic event. The article describes the mechanical behaviour of PVB interlayer and the constitutive models by which the polymer can be represented under different load cases. Tensile experiments of Saflex® PVB are presented for a wide range of deformation rates and up to tearing of the specimens. Subsequently, a method to calibrate a hyper-viscoelastic material model for the interlayer by numerically simulating the tensile tests is developed. The resulting material models are valid up to the tearing strain of the interlayer and are accurate within a specified range of deformation rates and temperatures.