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

A large amount of waste glass (WG) and rice husk ash (CCA) is produced yearly. This paper evaluated the effect of incorporating waste glass in concrete prepared with rice husk ash (RHA) as a partial substitute for cement, considering differences in the mechanical and thermal behavior of concrete based on the proportions of WG and CCA. A 5% replacement of cement by ashes of rice husk and waste glass was considered in this work. Concrete samples were prepared with several RHA:WG ratios namely 1:0, 1:1, 1:2, and 1:3 (RHA + WG = 5%). For these concrete samples, the mechanical, thermal, and environmental properties were evaluated, the latter measured in CO₂ emissions. Results showed that workability (i.e. slump) and density increased as long as WG content increased. The value of compressive strength of 1:3 mixture was 14% higher than the 1:0 concrete mixture. Moreover, the thermal conductivity was increased by 380% and CO₂ emissions were dropped by 5.5%, in comparison to 1:0 concrete mixture. The incorporation of WG improves mechanical and thermal properties and reduces the environmental impact of rice husk ash concrete.

Lithium silicate-based glass-ceramics are widely employed dental materials, showing superior aesthetics (determined by translucency) but poorer wear resistance under severe contact conditions than alternative, artificial crown materials. This work investigates possible correlations between the level of translucency and resistance to wear (in vitro) under sliding contact against hard zirconia antagonists in commercial lithium disilicate and zirconia-reinforced lithium silicate dental glass-ceramics. Wear rates are quantified, and mechanisms responsible for material removal are analyzed. Results are discussed in terms of the materials’ microstructure and mechanical properties within the framework of a fracture mechanics model. Finally, implications for materials selection in dentistry are briefly discussed.

The synthesis of glass–crystalline materials in the system Na₂O/CaO/SiO₂/Fe₂O₃ with high concentrations of Fe₂O₃ (20, 25 and 30 mol%) by applying the melt-quenching technique is reported. The melts spontaneously crystallize during pouring and the formation of magnetite (Fe₃O₄), hematite (α-Fe₂O₃) and ɛ-Fe₂O₃, as identified by X-ray diffraction (XRD) is observed. The microstructure and the elemental composition of the prepared materials are further investigated by scanning electron microscopy (SEM) and two different morphological types of Fe-containing crystals – needle-like and dendrite-shaped are detected. Mössbauer spectroscopy showed the presence of Fe³⁺ and Fe²⁺, as well as the existence of iron ions both in tetrahedral and octahedral coordination and the precipitation of hematite, ɛ-Fe₂O₃ and magnetite. The magnetic measurements on the prepared samples reveal ferrimagnetic properties with well defined hysteresis curves, although due to relatively small volume fraction of the iron-rich crystalline phases, the net magnetic moment is quite low compared to the bulk values for magnetite.

Plasma electrolyte oxidation was used to modify the surface of different Ti alloys: c.p. Ti (α hcp structure), Ti–15Nb (α′ + β structure) and Ti–33Nb–33Zr (stable β cubic structure) and the influence of elements and microstructure in the TiO₂-based ceramic layer formed as well as the surface properties was analyzed. The XRD patterns confirmed the presence of TiO₂ (anatase and rutile) in the c.p. Ti. For Ti–15Nb (wt.%) indicated the presence the same oxides also of pentoxide niobium (Nb₂O₅). For Ti–33Nb–33Zr (wt.%) indicated just the presence of rutile as the stable oxide one at room temperature and dioxide zirconium (ZrO₂). In addition, the formation of calcium carbonate CaCO₃ and calcium phosphate Ca₃(PO₄)₂ was detected in all 3 materials. The ceramic-like layer was more homogeneous for c.p. Ti and Ti–15Nb and more irregular hole like-pores for Ti–33Nb–33Zr. Bioactive ions used were detected in all alloys and the roughness for Ti–15Nb was higher compared to c.p. Ti. and Ti–33Nb–33Zr. The contact angle for the three samples was higher than 100°.

Ceramic-based bone graft substitutes have been extensively studied for bone tissue engineering, due to their biocompatibility and osteoconductivity. Additionally, several studies have shown how graphene and its derivatives, due to their unique properties, can strongly promote cell adhesion, by enhance cellular adherence, proliferation, and osteoblast differentiation, and how graphene-based materials can promote spontaneous osteoblastic differentiation. The aim of this study was the use of a calcium silicophosphate ceramic, previously prepared in our laboratory, that presents excellent in vitro bioactivity, optimizing its operation by rGO coating. After coating with rGO any significant differences were observed in diffraction peaks from starting calcium silicophosphate ceramic, and SEM analysis showed a rough and undulating surface that favored a high specific surface area for promoting cell adhesion, proliferation and differentiation of cells. It could be confirmed by in vitro cell cultured with ahMSCs, showing adhesion and growing for cells with interconnected filaments extending over the surface, covering it after 7 days.

Hybrid organic–inorganic aerogels are highly hydrophobic porous solids that avoid the brittleness and moisture adsorption of the standard silica aerogels. Superhydrophobic porous materials have attracted great interest because of their ability for selective absorption of organic solvents while repelling water, as excellent candidates for remediation techniques. This work shows a comparative of three drying procedures of DEDMS/TEOS (diethoxydimethylsilane/tetraethylorthosilicate) gels, namely, by supercritical CO₂, by supercritical ethanol, and dried at ambient conditions. Supercritical CO₂ and ambient drying produced superhydrophobic aerogels (θ > 150°), while supercritical ethanol drying produces denser aerogels with smaller both porous volume and specific surface area. Regarding the absorption of organic liquids, swelling is observed in all cases. Hexane had faster diffusion that obeyed Fick's law (∝t^0.5) whereas liquid polydimethylsiloxane exhibited slower non-Fickian diffusion process (∝tⁿ, n < 0.5).

This research focused on the synthesis and characterization of Faujasite-Na zeolites from fly ash (FA). The FA was subjected to pretreatment processes, washings with hydrochloric acid solutions and heat treatments at 700 °C for 3 h, to remove unburned carbon that would affect the synthetic process. After a fusion with NaOH at 550 °C for 3 h, the resulting material was disposed in a hydrothermal reactor at 100 °C for 12 h to obtain the corresponding zeolite. The products were characterized by XRD analysis, where quartz, mullite, sillimanite and lime phases were identified for the fly ash; quartz, mullite and in higher proportion Faujasite-Na for the synthesized material. The average size of the crystals of the fly ash and zeolite Faujasite-Na was 35.0 and 38.7 nm respectively, while the FTIR results allowed the identification of vibrational bands, characteristic of SiOSi and SiO bonds. The TGA-DTA analysis, allowed the identification of signals associated with exothermic and endothermic processes related to water removal and Faujasite-Na formation, while the EDX analysis coupled to SEM allowed verifying that the composition of the samples is consistent with the results sought and that the morphological characteristics validate the proposed methodology. The XRF results confirm the composition of the fly ash and the obtained Faujasite in accordance with some previous results and an improved composition. Surface area analyses (BET) showed that synthesized Faujasite possess an active area of 460 m² g⁻¹ while the fly ash for its physicochemical properties just an area of 6 m² g⁻¹. The overall results confirmed the efficiency of Faujasite-Na synthesis from FA by the proposed fusion-hydrothermal method.

Graphite–molybdenum–titanium powders prepared by colloidal processing technique were sintered by Spark Plasma Sintering (SPS). This material is proposed in this manuscript due to its potential interest as heat sink. The influence of the molybdenum content (2.5, 5.0 and 10.0 vol.%) on the thermal, electrical, and mechanical properties of the composite are studied to define the composite with the best properties. Thermal, electrical, and mechanical properties of the composite graphite–10 vol.% Mo–1 vol.% Ti (that are composites of graphite with molybdenum and titanium carbides after sintering) are significantly better than those of the composites with lower molybdenum contents (2.5 vol.% and 5 vol.%). This way, flexural strength, electrical conductivity, and thermal conductivity are 1.5, 7.8 and 18 times greater, respectively, than in the composite graphite–2.5 vol.% Mo–1 vol.% Ti. In the case of comparing with the composite graphite–5 vol.% Mo–1 vol.% Ti, flexural strength, electrical conductivity, and thermal conductivity are 1.2, 5.1 and 3.2 greater in the composite graphite–10 vol.% Mo–1 vol.% Ti, respectively.

Multicomponent oxide with pyrochlore structure (A₂B₂O₇), containing 7 different A-site cations and 3 B-site cations in equiatomic amounts, was synthesized. Powders with nominal composition (La_1/7Sm_1/7Nd_1/7Pr_1/7Y_1/7Gd_1/7Yb_1/7)₂(Sn_1/3Hf_1/3Zr_1/3)₂O₇ were fabricated through a reaction of metal nitrates (A-site) and metal chlorides (B-site) with sodium hydroxide during the solid state displacement reaction. Room temperature synthesis initially resulted in the obtainment of amorphous powders, which crystallized after subsequent calcination to form single crystalline compounds. Crystalline high-entropy ceramic powders formation took place at temperatures as low as 750 °C. During calcination, defective fluorite (F-A₂B₂O₇) and crystal pyrochlore (Py-A₂B₂O₇) structures coexist. A large number of cations induce the obtainment of stable high-entropy pyrochlores. Results showed that sintering at 1650 °C lead to pure crystalline single-phase pyrochlore formation. High-density ceramic, free of additives, was obtained after powders were compacted and subjected to pressureless sintering at 1650 °C. Multicomponent pyrochlore structure was investigated using the theoretical and experimental multi-methodological approach.