Boletin de la Sociedad Espanola de Ceramica y Vidrio最新文献

SrZrO₃-structured perovskite particles were prepared under hydrothermal conditions in a KOH (5 M) solution using Zr-gel and SrSO₄ mineral precursors. The treatments were conducted between 150 and 240 °C for different reaction intervals (1–96 h), and the KOH solution volume varied between 7.5 and 30 mL. To evaluate the effect of the Zr-gel precursor, the treatments were preliminarily conducted with a coprecipitated pasty Zr-gel (Zr(OH)₄·9.64H₂O) and subsequently with a lyophilized Zr-gel Zr(OH)₄ powder. Generally, SrZrO₃ particles were produced by a single-step reaction following the simultaneous bulk dissolution of the Zr⁴⁺ gel precursor and the SrSO₄ powder. However, in the preliminary experiments, a dehydration reaction of the pasty Zr-gel preceded the ultimate single-step reaction, resulting in complete SrZrO₃ particle formation taking place over a longer interval of 96 h at 240 °C. In contrast, when using the dried Zr-gel powder, complete feedstock dissolution occurred more rapidly, producing SrZrO₃ particles at 200 °C over 48 h. The SrZrO₃ particle sizes varied significantly depending on whether the pasty gel or dried powder Zr precursor was used. Particles prepared with the pasty gel exhibited a bimodal size distribution with mean particle sizes of 25 and 65 μm with pseudocubic and star-shaped cuboidal morphologies, respectively. In contrast, particle growth resulting from the rapid dissolution of solid powder feedstock produced cubic-shaped particles, monomodally distributed with an average particle size of 10 μm. Furthermore, byproduct (SrCO₃) formation occurred predominantly under earlier stages together with SrZrO₃ particle irrespective of the 5 M KOH filling volume; however, at a volume of 15 mL spontaneously achieved in situ the SrCO₃ dissolution at intermediate stages of reaction. This reaction pathway did not proceed at small (7.5 mL) and large (30 mL) volumes of the alkaline fluid. A kinetic study indicated that the activation energy required to produce the SrZrO₃ cubic-shaped particles was low in both cases, i.e., 15.05 and 22.27 kJ mol⁻¹ between the powder and pasty Zr⁴⁺ precursors, respectively.

Eight samples of Portland cement and a clinker provided by the Brazilian Association of Portland Cement were analysed with different laboratory diffractometers and a synchrotron instrument to determine the statistical variability in the determination of the mass percentage of the main crystalline phases. Five laboratories participated in the experiment. Data collection was performed by each laboratory following its own internal procedures for a standard Rietveld analysis of mineral phases. Both Cu and Mo radiations were used. Reflection geometries—with and without sample rotation—and transmission geometries were also used. The synchrotron diffraction pattern was acquired from a rotating capillary and a wavelength of 0.41290 Å. Analysis of all diffraction patterns was performed with the help of TOPAS Academic v. 6 with the specific purpose of determining the proportions of polymorphs M1 and M3 of alite, since their ratio must be taken into account for the subsequent development of the mechanical properties of concrete.

This research consists of the fabrication of synthetic gels of hydrated calcium silicate (C-S-H gel) and hydrated calcium aluminate silicates (C-A-S-H gel) in aqueous solution oversaturated in calcium hydroxide. These gels were fabricated using nanomaterials with different specific surface area; two nanosilicas (NS), OX50 and A200 (50 and 200 m²/g respectively) and two nanoaluminas (NA), A65 and A130 (65 and 130 m²/g). Mixtures were carried out maintaining a Ca/Si = 2 ratio and variable Al/Si ratios of 0.1, 0.5 and 1. The effect of aluminium incorporation in the C-S-H gel was studied using the nuclear magnetic resonance technique (²⁹Si MAS-NMR), and the information obtained was further processed using the mathematical deconvolution method. Chemical shift bands were delimited to identify the structures. From the results obtained, modifications of the tetrahedral (Q_n) in the dreierketten structure were observed in the different combinations, as well as the modification of the bridging tetrahedral (Q₂b) due to the presence of aluminium replacing the silica bridging tetrahedron Q₂b(1Al). High Q₄ values were detected in the C-S-H gel with NS OX50 and this could be associated to a double chain formation very similar to a perfect tobermorite. The length of the mean chains (MCL) was very variable in each blend, but some trends were observed as the Al/Si = 1 ratio and the Al/Si = 0.1 ratio maintain or increases the MCL respectively. The results are interesting and concrete case mixtures with NS OX50 show original trends that have not yet been reported in the literature.

This work aims to contribute to reducing environmental damage caused by the manufacturing of Portland cements (PC), through in-depth exploration into the durability of two mortars manufactured from blast furnace slag: an alkaline-activated one (AAS) and a hybrid cement (HS) with less than 20% clinker. The carbonation resistance of these eco-friendly mortars is compared to that of a mortar based on Portland IV cement. From a mineralogical point of view, DTA-TG and confocal Raman microscopy (CRM) tests have been carried out, along with measurement of pH changes, compression strength and total porosity. Böhme tests have been performed to evaluate changes due to carbonation in the wear behavior of the mortars under study. Using the CRM technique, it has been possible to establish a relationship between the carbonation of the systems with the unbound carbon content, as well as identify the different polymorphic phases of CaCO₃ formed. The results obtained reveal that alternative AAS and HS mortars are more difficult to carbonate than Portland cement mortars, and that the effect of this process on the porosity depends on the nature of the hydroxides previously present in the pore solution. The carbonation of the surfaces also improves the abrasive wear resistance of the mortars under study.

Superficial cracks are one of the common defects in the manufacturing of traditional ceramic tiles. Such defects do not only damage the appearance of the product, but also affect their mechanical behavior. Understanding the correlation between superficial cracks and deflection is key for the traditional ceramic tile industry. However, the related bibliography is very rare, and its importance is systematically ignored during design and manufacturing. In this work, we investigate the impact of the location and size of superficial cracks over the deflection of traditional ceramic tiles. A technique based on FEA (finite element analysis) is validated through experimental data and used to undertake a statistical, parametric research. The study shows that location and depth of the defect have an exponential cross-correlation over deflection and could be characterized together through a single surface. On the contrary, the width and sharpening of the defect barely interfere.

A series of glasses with chemical composition (50−x−y) TeO₂–30ZnO–10YF₃–10NaF–xHo₂O₃–yYb₂O₃ (x = 0.5 and y = 0.5, 1.0, 3.0, 5.0 mol%) were prepared by melt-quenching procedure. The absorption spectra, excitation, down conversion emission spectra, up-conversion (UC) emission spectra and decay time measurements were analyzed. In down conversion, the visible emission transition intensity associated with ⁵F₄ → ⁵I₈ (547 nm), ⁵F₅ → ⁵I₈ (657 nm), and ⁵F₄ → ⁵I₇ (755 nm) of Ho³⁺ ions decreased with Yb³⁺ concentration due to the energy transfer (ET) process from Ho³⁺ to Yb³⁺ ions. In up-conversion, on exciting with 980 nm diode laser beam, we observed a strong green (543 nm) and red (657 nm) UC emissions, that refers to the energy level transitions; ⁵F₄ (⁵S₂) → ⁵I₈ and ⁵F₅ → ⁵I₈ of Ho³⁺. The influence of excitation power on UC intensities studies revealed that the population at ⁵F₄ (⁵S₂) and ⁵F₅ levels of Ho³⁺ ion occurs due to two-photon absorption process associated energy transfer from Yb³⁺ to Ho³⁺. The influence of Yb³⁺ doped concentration on UC was studied, and it is observed that both the green and red UC intensities improved significantly on increasing Yb³⁺ ions concentration.

The need for biodegradable bone graft biomaterials in orthopedic surgeries is more often each day due to the promotion of natural tissue regeneration. One option is calcium phosphate cements (CPC), that are also osseconductors. However, their low mechanical properties restrict their application to low mechanical requirement areas of the body. The CPC mechanical resistance depends on the entanglement grade of the calcium deficient hydroxyapatite (CDHA), one option to improve it is trough incorporation of nucleating agents (e.g., stoichiometrically hydroxyapatite). This work proposes the use of a biodegradable nucleating agent, as it is Type B carbonated Hydroxyapatite (CHA-B), to improve the CPC performance. It was formulated compositions of alpha tricalcium phosphate (α-TCP) with variations on the amount of CHA-B (0–5–10–15 wt.%). The compression resistance was evaluated and results indicated that 5% CHA-B increases the strength (7.8%) and the elastic modulus (6.16%), while the other additions diminished such values. Besides, the effect on the setting time, the in vitro degradation and in the physicochemical properties was determined through scanning electron microscopy, X-ray diffraction and infrared spectroscopy.

The nucleation and growth of ZnO nanorods by hydrothermal method onto seed layer deposited onto an ITO/PET substrate. Concentrations of 10 and 15 mM were used for the synthesis of the seed layer solution, as well as 10 and 15 mM for the hydrothermal treatment, it is noted that the entire process was carried out at low temperature (<100 °C). The synthesis of ZnO nanorods was carried out in two stages: (i) A nucleation process, using the sol–gel method to obtain a seed layer; and (ii) a growth process, using the hydrothermal process to promote the perpendicular growth of ZnO nanostructures. The X-ray diffraction (XRD) ZnO results revealed a preferential orientation along the (002) axis, with a wurtzite hexagonal structure. The crystallite size (27 nm) and Gibbs free energy of the films were calculated, which exhibited a minimum diameter for the nucleation of ZnO nanorods (22 and 30 nm of the core diameter). The thickness layer is between 200 and 500 nm. These results indicate that ZnO nanorods with an average diameter between 50 and 195 nm are obtained, oriented perpendicularly to the ITO/PET substrate, synthesized by a low temperature process. Their potential applications are in power generators and sensors.