High-temperature mechanical behavior of polycrystalline yttrium-doped barium cerate perovskite

The high-temperature mechanical properties of the mixed ionic-electronic conductor perovskite BaCe0.95Y0.05O3-δ with average grain size of 0.40μm have been studied in compression between 1100 and 1300°C in air at different initial strain rates. The true stress-true strain curves display an initial stress drop, followed by an extended steady-state stage. As the temperature decreases and/or the strain rate increases, there is a transition to a damage-tolerant strain-softening stage and eventually to catastrophic failure. Analysis of mechanical and microstructural data revealed that grain boundary sliding is the primary deformation mechanism. The strength drop has been correlated with the growth of ultrafine grains during deformation, already present at grain boundaries and triple grain junctions in the as-fabricated material.Ministerio de Ciencia e Innovación MAT2009-13979-C03-0

Fracture characteristics of 6 AL-4V titanium alloy forgings containing alpha stringer microstructure Final report, 10 Sep. 1968 - 24 Jan. 1969

Fracture characteristics of 6Al-4V titanium alloy forgings containing alpha stringer microstructur

Vacuum infiltration of copper aluminate by liquid aluminium

This paper studies attained microstructures and reactive mechanisms involved in vacuum infiltration of copper aluminate preforms with liquid aluminium. At high temperatures, under vacuum, the inherent alumina film enveloping the metal is overcome, and aluminium is expected to reduce copper aluminate, rendering alumina and copper. Under this approach, copper aluminate toils as a controlled infiltration path for aluminium, resulting in reactive wetting and infiltration of the preforms. Ceramic preforms containing a mixture of Al2O3 and CuAl2O4 were infiltrated with aluminium under distinct vacuum levels and temperatures, and the resulting reaction and infiltration behaviour is discussed. Copper aluminates stability ranges depend on vacuum level and oxygen partial pressure, which determine both CuAl2O4 and CuAlO2 ability for liquid aluminium infiltration. At 1100 °C and 0.76 atm vacuum level CuAl2O4 is stable, indicating pO2 above 0.11 atm. Reactive infiltration is achieved via reaction between aluminium and CuAl2O4; however, fast formation of an alumina film blocking liquid aluminium wicking results in incipient infiltration. At 1000 °C and 3.8 × 10−7 atm vacuum level, CuAlO2 decomposes to Cu and Al2O3 indicating a pO2 below 6.0 × 10−7 atm; infiltration of the ceramic is hindered by the non-wetting behaviour of the resulting metal alloy. At 1000 °C and 1.9 × 10−6 atm vacuum level CuAlO2 is stable, indicating pO2 above 6.0 × 10−7 atm. Extensive infiltration is achieved via redox reaction between aluminium and CuAlO2, rendering a microstructure characterised by uniform distribution of alumina particles amid an aluminium matrix. This work evidences that liquid aluminium infiltration upon copper aluminate-rich preforms is a feasible route to produce Al–matrix alumina-reinforced composites. The associated reduction reaction renders alumina, as fine particulate composite reinforcements, and copper, which dissolves in liquid aluminium contributing as a matrix strengthener.The authors are grateful to Teresa Marcelo (LNEG) for helpful discussions and use of lab facilities, and to Paulo Machado (EST/IPS) for assistance in experimental issues. MG acknowledges FCT for financial support under contract SFRH/BD/25711/2005

Processing and properties of large-sized ceramic slabs

Large-sized ceramic slabs - with dimensions up to 360x120 cm2 and thickness down to 2 mm - are manufactured through an innovative ceramic process, starting from porcelain stoneware formulations and involving wet ball milling, spray drying, die-less slow-rate pressing, a single stage of fast drying-firing, and finishing (trimming, assembling of ceramic-fiberglass composites). Fired and unfired industrial slabs were selected and characterized from the technological, compositional (XRF, XRD) and microstructural (SEM) viewpoints. Semi-finished products exhibit a remarkable microstructural uniformity and stability in a rather wide window of firing schedules. The phase composition and compact microstructure of fired slabs are very similar to those of porcelain stoneware tiles. The values of water absorption, bulk density, closed porosity, functional performances as well as mechanical and tribological properties conform to the top quality range of porcelain stoneware tiles. However, the large size coupled with low thickness bestow on the slab a certain degree of flexibility, which is emphasized in ceramic-fiberglass composites. These outstanding performances make the large-sized slabs suitable to be used in novel applications: building and construction (new floorings without dismantling the previous paving, ventilated fa?ades, tunnel coverings, insulating panelling), indoor furnitures (table tops, doors), support for photovoltaic ceramic panelsSe han fabricado piezas de gran formato, con dimensiones de hasta 360x120 cm, y menos de 2 mm, de espesor, empleando m?todos innovadores de fabricaci?n, partiendo de composiciones de gres porcel?nico y utilizando, molienda con bolas por v?a h?meda, atomizaci?n, prensado a baja velocidad sin boquilla de extrusi?n, secado y cocci?n r?pido en una sola etapa, y un acabado que incluye la adhesi?n de fibra de vidrio al soporte cer?mico y el rectificado de la pieza final. Se han seleccionado piezas en verde y cocidas, caracteriz?ndolas desde el punto de vista tecnol?gico, composicional (FRZ, DRX) y microestructural (MEB). Los productos semiacabados muestran una destacada uniformidad microestructural y estabilidad dimensional, dentro de un amplio margen de temperaturas de cocci?n. La composici?n de las fases y la compacidad de la microestructura, son muy semejantes a las que presentan las baldosas de gres porcel?nico convencionales. Los valores de la capacidad de absorci?n de agua, densidad aparente, porosidad cerrada, propiedades funcionales as? como las propiedades tribol?gicas y mec?nicas se sit?an en los mejores valores de las piezas de gres porcel?nico. No obstante las grandes dimensiones, unidas al reducido espesor dotan a las piezas de una cierta flexibilidad, que refuerza el empleo de la capa de fibra de vidrio. Estas destacadas propiedades hacen utilizables, a los grandes formatos, en nueva s aplicaciones, construcci?n y edificaci?n (sin desmontar los pavimentos preexistentes, fachadas ventiladas, revestimiento de t?neles, paneles aislantes etc.) muebles ( encimeras y puertas), soporte de paneles fotovoltaico

Development of a new glass–ceramic by means of controlled vitrification and crystallisation of inorganic wastes from urban incineration

This paper reports the results of a study of the feasibility of recycling the solid residues from domiciliary waste incineration by producing a glass-ceramic. The major components of the raw material (TIRME F+L), which was from a Spanish domiciliary incinerator, were CaO, SiO2 and Al2O3 but nucleating agents, such as TiO2, P2O5, and Fe2O3 were also present in reasonable amounts. It was found that a relatively stable glass with suitable viscosity could be obtained by mixing 65 wt% TIRME F+L with 35 wt% glass cullet. The heat treatment required to crystallise the glass produced from this mixture, designated TIR65, was nucleation at 560°C for 35 min followed by crystal growth at 100°C for 120 min. The resulting glass-ceramic contained a number of crystalline phases, the most stable being clinoenstatite (MgSiO3), or perhaps a pyroxenic phase which incorporates Ca, Mg and Al in its composition, and åkermanite (Ca2MgSi2O7). The microstructure contained both fibre-like and dendritic crystals. The mechanical properties were acceptable for applications such as tiles for the building industry.Peer reviewe

Predicting the initial rate of water absorption in clay bricks

The effect of product characteristics and processing conditions on the initial rate of water absorption of fifteen clay bricks was investigated and the influence of porosimetric parameters (amount, size and tortuosity of pores) as well as of phase composition (amount of calcium-silicates and amorphous phase) was established. The suction behaviour of bricks, which may be brought back to the models of Gummerson et al. (1981) and Hoffman and Niesel (1988), was also evaluated on the basis of both the product microstructure and the liquid physical properties. According to the model of Beltran et al. (1988), which reveled to be sufficiently reliable, the values of the capillary coefficient Ks were calculated and their correlation with the experimental ones has been provided. For a given liquid and in the same experimental conditions, the results indicate that varying in a controlled way the product microstructure (i.e. decreasing the pore size, increasing the pore tortuosity and/or controlling the amorphous/new formed phases ratio) should allow to design materials having a most suitable behaviour

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

Phase evolution in reaction sintered zirconium titanate based materials

11 páginas, 17 figuras.-- El pdf del artículo es la versión post-print.Zirconium titanate materials are proposed for structural components for which fully reacted and relatively large pieces are required. In this work the phase evolution in slip cast compacts constituted by equimolar mixtures of TiO2 and ZrO2 stabilized with 3 mol% of Y2O3 at high temperature is studied, to establish the basis to design suitable thermal treatments for ZrO2(Y2O3)–TiO2 materials. The temperatures at which the processes involved in the reaction sintering occurred were identified by constant heating rate experiments. Phase and microstructure analyses have been performed on specimens treated at the identified temperatures and air quenched. Then the adequate temperature range to get fully reacted and dense materials has been deduced. Materials treated at 1500 ◦C to 2 h were constituted by Zr5Ti7O24 as major phase, a solid solution of TiO2 and Y2O3 in c-ZrO2 as secondary phase and a ZrO2–TiO2–Y2O3 non-stoichiometric compound with pyrochlore structure as minor phase. Pyrochlore was demonstrated to be a metastable phase at 1500 ◦C.This work has been supported by the Spanish Ministry of Education and Science under contracts MEC MAT2006- 13480 C02-01 and MAT2007-64486 C07-02. E. López-López acknowledges to Community of Madrid (Spain) and European Social Fund for economical support by CPI/0552/2007 contract.Peer reviewe