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

The current approach in bone tissue engineering requires resorbable biomaterials that enhance bone formation while maintaining sufficient mechanical stability. In this work, the influence of three levels of B-type carbonate substitution in hydroxyapatite lattice on mechanical strength and degradation rate is analyzed. The inverse aqueous route has been selected as a synthesis method of four powders with carbonate substitution between 4 and 6 wt.%. X-ray fluorescence (XRF), (C-S)-Analysis, FT-Infrared, X-ray diffraction, DTA-TG and TEM were used to investigate chemical composition, type of substitution, thermal behaviour, and morphology of the powders. Disc shaped specimens were processed by uniaxial pressing and sintering in argon/CO₂ flow. Maximum temperatures of thermal treatment between 750 and 850 °C were selected to obtain similar porosity levels for the different compositions. The highest carbonate substituted material (5.3 wt.%) presented higher compressive strength and dissolution rate than the other materials showing the beneficial effect of B-type substitution in hydroxyapatite materials for bone repair.

This study investigated the transformation of cancrinite-type zeolite, together with secondary phases, in a hydrothermal system. The mineral kaolin and NaOH were used as precursors under self-generated pressure at 140 °C, varying the reaction time at intervals of 0 to 10 hours. The kaolin, the main precursor, was subjected to X-ray diffraction (XRD), elemental chemical composition (XRF) and Fourier Transform IR Spectroscopy (FT-IR) analyses. The resulting solids were characterized by XRD. Initially, crystalline phases such as Na-P2 zeolites, gismondine, analcime, natrolite and sodalite were formed, but with time they became unstable and dissolved to form new phases. At 8 hours of reaction, the cancrinite zeolite predominated, fulfilling the main objective of the study. The solid material was analyzed by scanning electron microscopy (SEM) and FT-IR. The behavior of Na, Si and Al in the solutions was evaluated over time by inductre coupled plasma (ICP). It was conclusively demonstrated that kaolin from Hidalgo is a feasible precursor to synthesize zeolites, cancrinite type as predominant phase in 8 hours at 140 °C, using moderate concentrations of NaOH.

The impact of graphene oxide (GO) on the hydration process, calcium silicate hydrate (CSH) gels structure, and macro-mechanical properties were systematically researched by combinatorial techniques. Findings from ²⁹Si MAS-NMR and nitrogen adsorption (BET) revealed that the effect of GO on the hydration degree of the cement paste, and the main chain length (MCL) is more pronounced at advanced ages (from 28 days), due to its act as a nucleation site. Moreover, the results of Raman spectroscopy tests showed that GO has a strong interaction with the cement matrix. Due to the increase in the degree of hydration, the lengthening of the chain length (MCL), and the formation of strong bonds, both compressive and flexural strength tests also improved. Therefore, the effect of GO as a nucleation site has a positive effect on the cement paste nano-properties at advanced ages.

The use of natural zeolites as precursors offers a valuable alternative in the search for new materials applied to zeolite synthesis. Each study focused on the interzeolitic conversion method plays a fundamental role in understanding the evolution from one zeolite to another. In this study, a natural zeolite containing the crystalline phases of clinoptilolite and mordenite, with HEU and MOR topologies, respectively, as per the coding assigned by the IZA, was employed as a precursor. Combined with potassium–aluminum hydroxide solutions at two different concentrations, followed by a conventional hydrothermal process with durations of 50 and 90 h, characterization of both the precursor and resulting zeolite was performed. A conversion mechanism was proposed based on the structural similarity between the initial and target zeolites. To support these conclusions, characterization techniques such as X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, Fourier-transform infrared spectroscopy, inductively coupled plasma optical emission spectroscopy, and nitrogen adsorption were utilized. This process represents a potential pathway for the synthesis of merlinoite-type zeolites, MER.

Geopolymer composite production has become an indispensable product to reduce carbon dioxide emissions, which have become an important problem today, and to provide green sustainability. Concerns about the global climate change problem have also accelerated geopolymer studies. This research investigated the mechanical and durability characteristics of low-calcium fly ash (LCFA) based geopolymer mortars with different curing temperatures and times. Two forms of curing conditions were applied; the first one was standard curing at room temperature (20 ± 3 °C and RH 65 ± 10%) and the second one was cured in the hot air at 40 °C, 60 °C, and 80 °C for 24 h, 48 h, and 72 h followed by standard curing. After all curing processes, compressive strength, flexural strength, water absorption, void ratio, resistance to elevated temperatures, and freeze–thaw conditions were determined experimentally. In addition, SEM analysis was performed before and after durability tests for comparison purposes. Also, XRD and TGA analyzes were performed. According to test results, curing specimens at longer times and higher temperatures has been shown to increase compressive strength results. The highest compressive strength value was reached at 80 °C after 72 h of curing. Geopolymer specimens subjected to elevated temperatures (600 °C and 900 °C) lost a significant part of their strength value. After the freeze–thaw test, LCFA-based geopolymer specimens showed more than 70% resistance. The freeze–thaw resistance of geopolymer samples was positively affected on long-term curing at high temperatures, but high-temperature resistance was impacted negatively.

Bioactive glasses are mainly used to repair bone defects since they stimulate the natural healing of damaged tissues, allowing the adhesion and proliferation of bone-forming cells. On the other hand, tantalum is known to have good chemical resistance and biocompatibility, with no adverse biological response in organisms. In the present work, 45S5 bioglass systems undoped and doped with Ta₂O₅ were prepared according to the following stoichiometric molar relationship (46 − x)SiO₂ − 26.9CaO − 24.4Na₂O − 2.6P₂O₅ − xTa₂O₅ (x = 0, 0.1, 0.5) by the conventional melt quenching technique. Subsequently, scaffolds from these glassy systems were prepared using the combined method of powder technology and polymer foaming. Both, glass powders and scaffolds, were physicochemical characterized. The results showed that the 0.5 mol% Ta₂O₅-doped scaffolds exhibited less contraction (36.53%) and higher porosity (84.24%) during sintering, with interconnected porosity, pore size in the range of 19–260 μm, and a greater surface area (17.431 ± 0.846 m²/g) than the scaffolds with no Ta₂O₅. Furthermore, the tantalum oxide promoted the formation of a sodium tantalum phosphate phase, along with the combeite and silicorhenanite present in the undoped-glass scaffolds. The maximum compressive strength of scaffolds ranged from 0.42 to 1.40 MPa and the elastic modulus (E) from 0.19 to 0.47 GPa.

Image analysis techniques can be used to detect and interpret the degradation processes that a material undergoes and to help identify the causes and mechanisms of degradation. Structures and morphological changes are also analysed to establish hypotheses about physical changes. Together with complementary analytical techniques, chemical and mineralogical changes can be evaluated.

The methodological process consists of a sequential simplification of the initial micrograph: segmentation of the image, cleaning and isolation of the crack from associated elements, and crack skeletonisation. This method allows the previous image to be processed, thus successfully isolating the microcracks. It is also valid for their quantification.

Cold winter temperatures at high latitudes in coastal regions lead to prolonged exposure of offshore concrete structures to freeze–thaw (F–T) damage, which significantly reduces the mechanical and durability properties of concrete. To improve the durability of concrete under F–T damage, this study investigated the combined effects of fly ash (FA) and bentonite on the frost resistance of polyvinyl alcohol fiber reinforced geopolymer concrete (PFRGC). The study comprehensively analyzed the effect of fly ash and bentonite content on the rate of mass change and compressive strength under various F–T damage conditions. In addition, uniaxial compressive tests were carried out at different stages of F–T damage and the resulting stress–strain curves and compressive properties were analyzed. Correlations between peak stress, peak strain, modulus of elasticity and deterioration time of the concrete were developed. SEM microscopy tests were also used to investigate the evolution of the internal microstructure and the morphological characteristics of the erosion products under freeze–thaw conditions. The results indicated that the change in concrete mass with a growing number of F–T cycles can be divided into two periods: a gentle increase and a faster increase. A continuous increase in the rate of mass increase was observed for the specimens containing fly ash and bentonite, while the compressive strength of these specimens continued to decrease. During F–T damage, the maximum stress decreased slightly and the maximum strain increased gradually as the volume of bentonite and fly ash increased. This study provides a theoretical basis and technical basis for the development of fly ash and bentonite to improve the frost durability of offshore structures.