169,984 research outputs found
Influence of the binder composition on the water debinding properties of a PVB-PEG-alumina feedstock for the fused deposition of ceramic process
No full textThe study investigates the influence of several binder compositions on the solvent debinding characteristics of highly filled thermoplastic alumina feedstocks at different temperatures. All feedstocks contain the same powder volume fraction but vary in the repartition of the binder components: polyvinyl butyral (PVB), polyethylene glycol (PEG), and a plasticizer (3G8). The weight loss, debinding speed, volumetric changes, and the microstructure were analyzed. The water temperature was set to room temperature -RT- (23 degrees C) and 40 degrees C. SEM micrographs were taken on as-processed and solvent-debinded samples fractured after dipping in liquid nitrogen. Water debinding of the compositions with high proportions of low molecular weight components PEG and 3G8 helps to reduce the remaining polymer amount and to achieve an open porosity, which should ease the following thermal debinding
Mine clay washing residues as a source for alkali-activated binders
No full textThe aim of this paper is to promote the use of mine clay washing residues for the preparation of alkali activated materials (AAMs). In particular, the influence of the calcination temperature of the clayey by-product on the geopolymerization process was investigated in terms of chemical stability and durability in water. The halloysitic clay, a mining by-product, has been used after calcination and mixed with an alkaline solution to form alkali activated binders. Attention was focused on the influence of the clay’s calcination treatment (450–500–600◦C) on the geopolymers’ microstructure of samples, remaining in the lower limit indicated by the literature for kaolinite or illite calcination. The mixtures of clay and alkali activators (NaOH 8M and Na-silicate) were cured at room temperature for 28 days. The influence of solid to liquid ratio in the mix formulation was also tested in terms of chemical stability measuring the pH and the ionic conductivity of the eluate after 24-h immersion time in water. The results reported values of ionic conductivity higher for samples made with untreated clay or with low temperature of calcination (≥756 mS/m) compared with values of samples made with calcined clay (292 mS/m). This result suggests that without a proper calcination of the as-received clay it was not possible to obtain 25◦C-consolidated AAMs with good chemical stability and dense microstructure. The measures of integrity test, pH, and ionic conductivity in water confirmed that the best sample is made with calcined clay at 600◦C, being similar (53% higher ionic conductivity of the eluate) or equal (integrity test and pH) to values recorded for the metakaolin-based geopolymer considered the reference material. These results were reflected in term of reticulation and morphology of samples through the analysis with scanning electron microscope (SEM) and X-ray diffraction (XRD), which show a dense and homogeneous microstructure predominantly amorphous with minor amounts of quartz, halloysite, and illite crystalline phases. Special attention was dedicated to this by-product to promote its use, given that kaolinite (and metakaolin), as primary mineral product, has a strong impact on the environment. The results obtained led us to consider this halloysite clay very interesting as an aluminosilicate precursor, and extensively deepening its properties and reactivity for the alkaline activation. In fact, the heart of this work is to study the possibility of reusing this by-product of an industrial process to obtain more sustainable high-performance binders
Lanthanum glass infiltrated alumina/alumina composites for dental prosthetic applications
No full textLanthanum glass frits suitable for infiltration in pre-sintered alumina were developed in order to obtain innovative alumina–glass composites, which are promising materials for all-ceramic dental prosthetic restorations, such as single crowns and fixed partial dentures. Glass compositions belonging to the lanthanum-silicate-borate system were synthesized in order to reinforce and give an improved esthetic appearance to the pre-sintered Al2O3.
Fifteen formulations, defined by using a mixture design approach, were melted and quenched in water at room temperature in order to obtain the frits. Those exhibiting the lower melting temperatures were tested for infiltration into Al2O3 to obtain Al2O3/glass composites. The frits and the composites were characterized by X-Ray diffraction, differential thermal analyses, hot stage microscopy, colorimetry (Hunter color scale) and scanning electron microscopy. The mechanical properties of the composites, in terms of flexure strength, were evaluated using a three-point bending tests
Preparation and characterization of glass ceramic frits with high solar reflectance
No full textThe temperature of cities increases due to the UHI phenomenon and climate change. Among the mitigation strategies, high solar reflectance materials make an important contribution, in particular ceramic materials on which studies have shown that the functionalization of the ceramic engobe allows to increase solar reflectance (SR). This study attempted to improve the SR of ceramic tiles, starting from studies correlating the heat treatment temperatures of glass-ceramic frits with SR, because frit is fundamental for the preparation of an engobe, which plays, as some studies have shown, an increasingly important role in solar reflectance. Five glass-ceramic frits have been analysed: four of these are commercial frits, while one has been obtained and optimized experimentally
Vanadium doping in CaO-ZrO2-SiO2 glasses
No full textStructural and colour changes induced by increasing amounts of vanadium oxide. V2O5, are presented for a near formulation of glass with composition 37CaO, 6ZrO(2), 57SiO(2) (mol%). Property changes were evaluated by measuring density, chemical durability and microhardness of glasses with increasing amount of vanadium oxide. Vanadium oxide imparts to tire glass a light green colour, not dissimilar to that from chromium, at low content, while at higher concentration the colour changes to dark brown. Spectroscopic technique, VIS-NIR and ESR were rued to identify tire chromophore centres in terms of vanadium oxidation state and coordination which there subsequently correlated to property changes. Experimental evidence is reported for an equilibrium between two species. V5+-tetrahedral and V4+ tetragonally distorted octahedral
Wheat husk: A renewable resource for bio-based building materials
No full textThe huge annual production of wheat husk in Europe (10 million tons) creates management problems. Valorization options are thus sought. Here, insulting lime concrete was designed using native wheat husk as lightweight aggregate. Physical-chemical and technological properties of both particles and concretes were determined. Comparisons with hemp concrete manufactured with the same process were made. Similar thermal conductivities for the two types of concretes were obtained (ca. 0.09 W/(m·K)), whereas slightly lower compressive strength was found for wheat husk concrete due to weaker particle-binder interface. Nevertheless, results highlight the high potential of raw wheat husk for development of bio-based materials with interesting performances
differential Anomalous Wide Angle Scattering and X-Ray Absorption Spectroscopy experiments to investigate the formation of glass ceramics in the CaO-SiO2-ZrO2 system
No full textDifferential anomalous wide-angle X-ray scattering and X-ray absorption experiments to investigate the formation of glass ceramics in the CaO-SiO2-ZrO2 system
No full textThe structure of a CaO-SiO2-ZrO2-based glass ceramic has been investigated by X-ray diffraction, X-ray absorption spectroscopy and differential anomalous scattering techniques as a function of the thermal treatment of the sample. The microstructure of the glass has been investigated at room temperature, before the recrystallization of the glass ceramic, and on two samples annealed at 1073 and 1273 K for 1 h to follow the early stages of nucleation of the quartz and wollastonite crystalline phases. Indications on the roles of Ca, Si and Zr during the devitrification process are given
Structure and luminescence properties of Dy2O3 doped bismuth-borate glasses
No full textIn this work heavy bismuth-borate glasses were studied as host matrices of Dy2O3 rare earth, for potential application as scintillator materials in high energy physics experiments and in general radiation detection systems. Glass matrices were prepared from 20BaO-xBi2O3-(80-x)B2O3 (x = 20, 30, 40 mol%) ternary systems and synthesized by the melt-quenching method at different temperatures in order to obtain high density and high transparency in the UV/Vis range. Particularly, the glass manifesting the higher transparency and with sufficiently high density was doped with Dy2O3 (2.5 and 5 mol%) in order to induce the luminescence characteristics. The effects of Bi2O3 and Dy2O3 on density, thermal behaviour, transmission as well as luminescence properties under UV excitation, were investigated. The experimental results show that the synthesized glasses can be considered promising candidate materials as dense scintillators, due to the Dy3 + centres emission
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