Improvement in Char Strength with an Open Cage Silsesquioxane Flame Retardant

Different characterization techniques were used to study the hydrolysis and condensation reaction kinetics of 3-methacryloxypropyltrimethoxysilane (MAPTMS) to obtain open cage silsesquioxane oligomers. The formation of hydrogen bonds, which condition the chemical structures of the resulting products, was identified. Improved thermal and fire resistant behavior of unsaturated polyester (UP) composites prepared with aluminium trihydroxide (ATH) and the synthesized oligomer were registered. Opened silsesquioxane structures also showed an improvement in the mechanical properties of the char formed after firin

Síntesis del pigmento de hierro-circón: Propuesta de un índice de mezclado para mezclas de materias primas

Iron zircon coral pigments are very interesting from an industrial point of view because of their high colouring power and their stability at high temperatures. However, the pigment's synthesis is particularly troublesome due to its specific reaction mechanism. As an encapsulated pigment it becomes very important how the raw materials are distributed in the reaction mixture. To evaluate the effectiveness of the mixing process, it would be convenient to define a parameter, that is the mixing index, to estimate the degree of homogeneity of the system. In the current investigation, a mixing index is proposed derived from the power spectrum of Fourier transform of scanning electron microscope (SEM) images of the raw material mixture. Concretely, the number of pixels in a certain range of values in the image of the power spectrum, seems to behave relatively well as mixing index. This index allows us to distinguish between samples with different zirconia and iron oxide used as precursors. The proposed mixing index seems to be related to the colouring power of the final pigment when the synthesis generates enough zircon to encapsulate hematite particles.Los pigmentos coral de hierro-circón son muy interesantes desde el punto de vista industrial ya que n un alto poder colorante y estabilidad a altas temperaturas. Sin embargo, la síntesis del pigmento es particularmente problemática debido a su mecanismo de reacción. Al tratarse de un pigmento encapsulado, resulta fundamental cómo se encuentran distribuidas las materias primas en la mezcla de reacción. Para evaluar la efectividad del proceso de mezclado, es conveniente definir un parámetro, que es el índice de mezclado, para estimar el grado de homogeneidad del sistema. En el presente trabajo de investigación se propone un índice de mezclado basado en el espectro de potencia de la transformada de Fourier de imágenes obtenidas con el microscopio electrónico de barrido de las mezclas de materias primas. Concretamente, el número de píxeles en un cierto rango de valores en la imagen del espectro de potencia parece funcionar relativamente bien como índice de mezcla. Este índice permite distinguir entre muestras con diferentes circonas y óxidos de hierro uitilizados como precursores. El índice de mezcla propuesto se relaciona con el poder colorante del pigmento final cuando durante la síntesis se genera suficiente cantidad de circón para encapsular las partículas de hematites

Effects of composition and furnace temperature on (Ni, Co) (Cr, Al)2O4 pigments synthesized by solution combustion route

The effects of composition and furnace temperature on Ni1-ΨCoΨCr2−2ΨAl2ΨO4 (0≤Ψ≤1) pigments prepared by Solution Combustion Synthesis were studied. As-synthesized samples showed spinel-like spongy structure, very easy to grind. However, important differences on crystallinity, crystal size, and microstructure were observed depending on composition and furnace temperature. All pigments developed intense tones, covering a wide color palette because of composition influence, although little effect was observed with furnace temperature. Stable crystalline structures, suitable grain size, and high resistance against synthesizing variables and ceramic glazes make SCS pigments perfect candidates to be used in the ceramic ink-jet decoration

Effect of secondary thermal treatment on crystallinity of spinel-type Co(Cr, Al)2O4 pigments synthesized by solution combustion route

The effect of a post-synthesis thermal treatment on CoCr2−2ΨAl2ΨO4 (0.0 ≤ Ψ ≤ 1.0) ceramic pigments synthesized by Solution Combustion Synthesis (SCS) has been studied. As-synthesized SCS pigments were treated at two different calcination temperatures (800 °C and 1000 °C) to study changes in mineralogy, microstructure and thermal behaviour, as well as their effect over the colouring power. Spinel-type Fd-3m crystalline structure was developed in all cases. Nevertheless, crystallinity parameters were highly affected by both analysed processing parameters: composition (Ψ) and post-synthesis calcination temperature (Tc). A Cr(III) enrichment along with Tc increase favoured ion rearrangement to promote sample crystallization and crystallite growth. Fast kinetics of SCS makes Al-rich spinels with transition metals difficult to be synthesized. The application of a secondary thermal treatment resulted in a favourable evolution towards a well-crystallized structure. Lattice parameter did not seem to be affected by Tc, although it evolved indeed with composition. From a microstructural point of view, as-synthesized pigments were foamy, with a very low bulk density and nanometric grain size. After the thermal treatment, larger grain sizes were obtained, especially for the samples richer in Al and treated at higher Tc. All pigments developed intense colours in a transparent glaze without showing heterogeneities, indicating a stable behaviour against glazing process. Glaze colour evolved from green to perfectly blue shades, indicating an important dependence on composition. Nevertheless, colouring power seemed to be rather affected by calcination process

Solution combustion synthesis of (Co,Ni)Cr2O4 pigments: Influence of initial solution concentration

Initial solution concentration effect was studied on the synthesis of mixed spinels Co1-ΨNiΨCr2O4 (0≤Ψ≤1) obtained by Solution Combustion Synthesis. Fd-3m spinel structure was developed in all range of compositions analysed, regardless of the concentration. However, structural characteristics such as ion rearrangement and crystal size showed a noticeable dependence on the initial concentration, being the spinel network more ordered and with higher crystallite size as the concentration increased. Cell parameter, however, presented dependence on composition but not on initial solution concentration. All as-synthesized pigments showed a significant colouring power in ceramic glazes without any significant influence of initial solution concentration. Therefore, a second thermal treatment was not needed. The coloured glazes covered a broad range of tones in the green section of colour space, which evolved as a function of composition

Characteristics reproducibility of (Fe, Co)(Cr, Al)2O4 pigments obtained by solution combustion synthesis

Synthesis reproducibility of mixed spinels Fe1−ΨCoΨCr2−2ΨAl2ΨO4 (0≤Ψ≤1), obtained by Solution Combustion Synthesis using urea as fuel, has been studied. Pigments with spinel structure Fd-3m have been obtained for all the compositional range analysed. Characteristics such as crystallinity, cell parameter, crystal size and specific surface area show a noticeable dependence with Ψ, but some of them present a low reproducibility, indicating a pronounced dependency with process conditions in each batch. Colouring power of synthesized pigments is highly significant, so they can be directly integrated in ceramic glasses without introducing a second thermal treatment. However, the generated colour also suffers from a limited reproducibilityThe authors thank Universitat Jaume I for their support in the development of this research (Project Nr. P11B2015-04)

Influence of starch content on the properties of low-cost microfiltration ceramic membranes

The use of starch as pore former is frequent in the fabrication of porous ceramic membranes, since starches are cheap, innocuous and environmentally friendly. A study has been conducted to evaluate the influence of potato starch content (0–30 wt%) and sintering temperature (1100 and 1400 °C) on low-cost ceramic microfiltration membranes. The raw materials were a mixture of kaolin, alumina and starch, from which membrane specimens were shaped by uniaxial dry pressing. The results indicated that the percentage of potato starch did affect the properties of the membrane. Thus, an increase of starch content provoked a reduction of bulk density (an increase of porosity) a rise of water permeability and a substantial modification (coarsening) of the pore size distribution. This effect deals with the role as pore former of starch, which burns out when fired. More interestingly, it was experimentally observed that the effect of starch was particularly effective for starch percentages higher than 10 wt% once a connected coarse pore network is developed. On the other hand, an increase in sintering temperature from 1100 to 1400 °C also influenced membranes׳ characteristics but the effect was much less significant than that of starch content. A percolation analysis based on the Effective Medium Approximation (EMA) contact model allowed to conclude that the critical porosity calculated corresponds to a starch content of 10.2 wt%, which agrees quite well with the estimation from experimental results. Finally, tortuosity was calculated with a simple model derived from the Hagen–Poiseuille equation. The obtained data showed that tortuosity factor decreased as the starch content or sintering temperature increased. These findings are consistent with SEM analysis and pore size determination.The authors thank Spanish Ministerio de Economía y Competitividad their support for the development of this research (Plan Nacional de I+D, ref. CTQ2012-37450-C02-02

Post-deposition heat treatment effect on microstructure of suspension plasma sprayed bioactive glass coatings

This research addresses a simple and easy method to improve the microstructure of suspension plasma sprayed bioactive glass coatings. Based on previous research of the group, a SPS bioactive glass coating was deposited under optimised variables employing a stable suspension feedstock. After the microstructural characterisation, the coatings were subjected to a heat treatment at 400, 500 and 600 ºC peak temperatures. These temperatures have been chosen according to the shrinkage curve of the working glass which results from a hot stage microscope. Results show an improvement of the coatings microstructure (reduction in both porosity and thickness and increment of the adhesion) after a heat treatment at 500 ºC with respect to the original coating. However, for a temperature of 400 ºC the coating microstructure is not altered (porosity, thickness and adherence are the same as those of the original sample) while at 600 ºC the entire coating is completely delaminated

Valorización de residuos de diferentes industrias en la fabricación de baldosas cerámicas

Ponència presentada al IX Simposio Iberoamericano de Ingeniería de Residuos, Panamá, del 20 al 24 de setembre de 2021En el marco de la economía circular y la valorización de residuos, el presente trabajo trata sobre la posibilidad de fabricar azulejos cuyos soportes incluyen residuos en su formulación. Los azulejos son baldosas cerámicas indicadas para el revestimiento de paredes que se caracterizan por porosidades y absorciones de agua elevadas. Los residuos seleccionados para formar parte de los soportes sostenibles porosos son tiesto triturado de baldosas cocidas defectuosas, residuos de polvo de mármol y cenizas volantes de central térmica. Los residuos de baldosas cocidas son materiales de interés para la reutilización por su semejanza en composición con el producto a desarrollar. El polvo de mármol, proveniente de la manufactura y manipulación mecánica de bloques de mármol, tiene utilidad como fuente de óxido de calcio en sustitución del carbonato cálcico comúnmente utilizado para generar porosidad. Las cenizas volantes, provenientes de la combustión de carbón en centrales térmicas, son materiales de naturaleza vítrea que han sufrido un proceso térmico a elevada temperatura y por ello son susceptibles de poder integrarse en composiciones de soportes cerámicos. Los resultados obtenidos ponen de manifiesto la correcta formulación de soportes sostenibles porosos a partir de estos residuos en combinación con otros materiales arcillosos en distintas proporciones. De este modo, es posible fabricar soportes porosos para azulejo utilizando un porcentaje de residuos superior a 50 %, obteniéndose unas propiedades en cocido (densidad aparente, contracción lineal y absorción de agua) y unas propiedades mecánicas adecuadas para esta tipología de producto.Within the framework of the circular economy and waste recovery, this work deals about the possibility of manufacturing ceramic wall tiles whose bodies include wastes in their formulation. These wall tiles are characterised by high porosity and water absorption. The wastes selected to form part of the sustainable porous bodies are crushed scraps of defective fired tiles, marble dust residues and fly ash from thermal power stations. Fired tile waste is a material with interest for reuse due to its compositional similarity to the product to be developed. Marble dust, from the manufacture and mechanical handling of marble blocks, is useful as a source of calcium oxide, replacing the calcium carbonate commonly used to generate porosity. Fly ash, from the combustion of coal in thermal power stations, is a vitreous material that has undergone a thermal process at high temperature and, therefore, it can be integrated into ceramic body compositions. The obtained results show a correct formulation of sustainable porous bodies from these wastes in combination with other clay materials in different proportions. In this way, it is possible to produce porous bodies for wall tiles using a percentage of waste higher than 50 %, obtaining suitable firing properties (bulk density, linear shrinkage and water absorption) and notable mechanical properties for the final product

Residual stresses in porcelain tiles. Measurement and process variables assessment

This research addresses the residual stresses phenomenon taking place during the manufacture of porcelain tiles. Residual stresses were quantified by the strain relaxation slotting method. The method is based on the fact that stresses are released when a slot is made leading to a curvature change. Once the method was validated, the impact of process variables such as starting body composition, temperature and cooling rate of firing cycle was investigated. Findings showed that cooling rate was the most influencing variable whereas Young’s modulus of fired specimens also play a significant role. Symmetry of the parabolic residual stress profile denoted homogenous cooling on upper and lower tile surfaces during the cooling step. In addition, it was observed that polishing of a stressed tile gives rise to a decreasing of deformation as a consequence of stress release by mechanical grinding