Castable systems designed with powders reclaimed from dismantled steel induction furnace refractory linings

Despite environmental pressures and intrinsic recycling potential, spent refractories waste is generally considered an economically unattractive waste stream. This work proposes an upgraded view of the debris recovered from dismantled spinel-bonded high-alumina linings of steel induction furnaces, demonstrating that it can be reused in the form of vibratable and self-flowing castable systems. The recovered material retains the microstructural distribution of in situ spinel formation without the corresponding disruptive expansion, mirroring the use of pre-formed spinel without the onus of a pre-firing. The mechanical performance after firing was found to be always best for the self-flowing system, which is also less affected by changes in added-water content. There is potential for large usages of cleaned waste (50–60 wt%), which helps reducing the supply risk for major refractory primary raw materials as well as landfilling costs.info:eu-repo/semantics/publishedVersio

Designing particle sizing and packing for flowability and sintered mechanical strength

In this work, alumina powders in five different commercially available size ranges were used to prepare various refractory castable mixtures, defined using the statistical design of mixture experiments (STATISTICA, StatSoft Inc.) and the EMMA 3.3 software (Elkem Materials). Those mixtures were characterized for packing density, Andreasen particle size distribution modulus (q), flowability and after sintering properties, in order to investigate the relationships between these variables. The optimization of matrix and aggregate sizes and matrix-aggregate proportion, subjected to different property requirements, brought to light the relationships between q, specific surface area (SSA) and maximum paste thickness (MPT). Those relationships were investigated for three fundamental processing steps, namely, dry powders, fresh paste and consolidated dried and sintered bodies. The optimized all-alumina castable was found to require 47.5wt.% of a fine size matrix with high flowability, which provides the necessary flow bed for 52.5wt.% of coarse aggregates, resulting in a gap-sized particle size distribution, and presented a fresh paste flowability index above 130% with minimum added water (28mg/m2) and sintered modulus of rupture above 50MPa.info:eu-repo/semantics/publishedVersio

Thermomechanical evaluation of self-flowing refractory castables with and without the addition of aluminate cement

Much has been discussed about the advantages regarding the thermomechanical performance of self-flow refractory castables (SFRC), with very little or no addition of calcium aluminate cement (CAC) when compared to conventional composites with cement. Previous works demonstrated that a 100% alumina SFRC with optimized particle size distribution simultaneously results in high-flowability fresh paste and high mechanical strength. In this work, the thermomechanical behaviour of zero-cement ceramic matrix is compared to that of the equivalent composite with 1% CAC content. The results show that the differences in performance can be related to differences in hydration mechanisms, namely the formation sequence of calcium aluminate hydrates, which results in increased open porosity. With lower dried strength, the all-alumina castable presents lower porosity, higher mechanical strength and uncompromised thermal shock resistance, being a valuable option when fast drying or rough green handling can be avoided.info:eu-repo/semantics/publishedVersio

Manufacturing and characterization of epoxy resin with Fe3O4 and SiO2 particles

Thermosetting polymers are very popular in the automotive and aeronautic industry, in particular epoxy resin is widely used as matrix thermoset in carbon and glass  fibre reinforced composites. The properties of these epoxy-based polymers can be improved with the addition of particulate or small fibre materials in order to construct a lightweight material with enhanced mechanical and structural response. This work aimed to manufacture and characterize epoxy resin reinforced composites with iron (II, III) oxide (magnetite, Fe3O4) in amounts of 0.25, 0.5 and 1 wt%, and 2 and 4 wt% of fumed silicon dioxide (silica, SiO2). Mechanical properties were investigated by three-point bending flexural test, fracture toughness, flexural stress relaxation. In addition, apparent porosity, apparent density and Differential Scanning Calorimetry tests were performed. The results showed that the addition of Fe3O4 does not contribute significantly to the improvement of mechanical properties. However, fumed SiO2 promotes a considerable improvement in the mechanical properties.   Keywords: Composite, epoxy resin, Fe3O4, SiO2, mechanical propertie

Young’s modulus and hardness of multiphase CaZrO3 -MgO ceramics by micro and nanoindentation

The aim of this work is to determine the values of the hardness and elastic modulus of the phases present in CaZrO3-MgO-ZrO2 composites and to analyse their contribution to the composite properties. Two materials previously developed with the same major phases (CaZrO3, MgO and c-ZrO2) present in different volume fractions and grain size have been analysed. The hardness and Young´s modulus of each phase determined by nanoindentation are independent from the specific composite and coincident with nanoindentation values for single phase bulk materials. The contribution of the individual phases to Young´s modulus of the multiphase materials is in agreement with calculations using the nanoindentation values and the Voight upper limit of the “rule of mixtures”. Scale dependence due to microcracking has been observed for microhardness values of the composites and differences between calculations and experimental values are related to this effect.This work was performed in the frame of the CYTEDnetwork HOREF(312RT0453)and was supported by the Spanish Government underprojectMAT2013-48426-C2-1-R.AbílioP.Silvaacknowledges thefinancialsupportofJECSTrustthroughmobilityContract201597 and Instituto de Cerámica y Vidrio–CSIC.info:eu-repo/semantics/publishedVersio

Hygrothermal Effect on the Impact Response of Carbon Composites with Epoxy Resin Enhanced by Nanoclays

This paper presents the results of the hygrothermal effect on the impact response of carbon/epoxy composites and the benefits gained from doping the epoxy resin with nanoclays previously subjected to a silane treatment appropriate for the resin. The nanoclay reinforcement increased the maximum load and the elastic recovery of the composites. The thermal degradation caused by exposure to 60°C for 10 days was insignificant, while the immersion in water at 60ºC for 30 days led to a continuous reduction in the maximum load and the elastic recovery. Multiple impacts resulted in a continuous and nearly linear degradation of the impact response both of dry and environmentally assisted specimens.info:eu-repo/semantics/publishedVersio

Young’s modulus and hardness of multiphase CaZrO3 -MgO ceramics by micro and nanoindentation

The aim of this work is to determine the values of the hardness and elastic modulus of the phases present in CaZrO3-MgO-ZrO2 composites and to analyse their contribution to the composite properties. Two materials previously developed with the same major phases (CaZrO3, MgO and c-ZrO2) present in different volume fractions and grain size have been analysed. The hardness and Young´s modulus of each phase determined by nanoindentation are independent from the specific composite and coincident with nanoindentation values for single phase bulk materials. The contribution of the individual phases to Young´s modulus of the multiphase materials is in agreement with calculations using the nanoindentation values and the Voight upper limit of the “rule of mixtures”. Scale dependence due to microcracking has been observed for microhardness values of the composites and differences between calculations and experimental values are related to this effect.This work was performed in the frame of the CYTEDnetwork HOREF(312RT0453)and was supported by the Spanish Government underprojectMAT2013-48426-C2-1-R.AbílioP.Silvaacknowledges thefinancialsupportofJECSTrustthroughmobilityContract201597 and Instituto de Cerámica y Vidrio–CSIC.info:eu-repo/semantics/publishedVersio

Potential for reuse of tungsten mining waste-rock in technical-artistic value added products

Mining and quarrying activities in Europe generate approximately 55% of total industrial wastes, according to a recent Eurostat report. Most of these wastes are directly dumped on land or deposited in landfill sites. The first solution may lead to negative environmental impacts on land (removal of vegetation, deforestation, land slope changes and increased risk of erosion), water (pollutant transport through surface runoff, soil infiltration and contamination of water resources), may lead to the contamination of agricultural goods and may impose risks on human health. In Portugal, about 20% of industrial waste produced originates from mines and quarries, particularly from Panasqueira mining, one of the largest tungsten mines in the world. Currently, Panasqueira mining generates almost 100 tonnes of waste-rock, per day. Such waste-rock have accumulated over a number of years into very large heaps and it is desirable to seek new economic solutions that can contribute towards their reuse. In this context, this work discusses the potential for reuse of waste-rock piles of Panasqueira tungsten mine, which may be a case statement to be followed. The proposed solution described in this paper consists in developing innovative polymer-based composite materials, obtained from non-contaminated waste-rock tailings. Such materials must have suitable properties for technical-artistic value added applications, such as conservation, restoration and/or rehabilitation of historic monuments, sculptures, decorative and architectural intervention, or simply as materials for building revetments.info:eu-repo/semantics/publishedVersio

Effect of particle size distribution and calcium aluminate cement on the rheological behaviour of all-alumina refractory castables

Previous works based on statistical design of experiments (DoE) defined a model all-alumina self-flow refractory castable (SFRC) with optimized particle size distribution for simultaneous high flowability index (FI) and superior post-sintering performance. This work compares the SFRC rheological behaviour and setting time with those of alternative all-alumina castables with different Andreasen aggregate particle size distribution modulus, and of the equivalent castables containing calcium aluminate cement. The model castable showed Bingham behaviour with low yield stress, viscosity and thixotropy, guaranteeing easier casting and less wear in the casting and/or projection equipment. However, as the coarse particle fraction increases, the castable flow tends to be non-linear and changes from Bingham to Herschel–Bulkley. The cement containing castables quickly loose flowability despite the applied shear. This work confirmed previous conclusions based on FI measurements and demonstrates the adequacy of the use of FI values in the calculation of FI response surface by DoE.info:eu-repo/semantics/publishedVersio

Aplicação de métodos estatísticos na otimização da densidade de empacotamento de distribuições de pós de alumina

Fatores como a distribuição granulométrica e a morfologia condicionam as propriedades físicas de sistemas particulados (e.g. misturas de pós, pastas, concretos refratários), entre as quais a densidade de empacotamento. Podem ser encontrados, na literatura, vários modelos para a otimização da distribuição de tamanhos de partículas que maximiza o empacotamento, todos desenvolvidos para sistemas de esferas perfeitas (e.g. Furnas, Andreasen, Alfred). Neste trabalho, pós de alumina comercial (reativa e tabular) foram separados em nove frações granulométricas e, recorrendo a dois procedimentos distintos, construíram-se seis sistemas ternários diferentes e complementares de tamanhos de partículas. Usando a metodologia das superfícies de resposta e técnicas de análise estatística afins (programa de cálculo Statistica) obteve-se, em ambos os casos, a distribuição granulométrica que maximiza a densidade de empacotamento. Por comparação com as distribuições granulométricas teóricas, ficou demonstrada a validade do modelo teórico de Alfred para esferas perfeitas. Os resultados obtidos demonstram, assim, que o efeito prejudicial da não esfericidade das partículas pode ser, na realidade, compensado pela otimização da distribuição granulométrica global.Particle size distribution and morphology are among the factors that affect the physical properties of particulate systems (e.g. powder mixtures, pastes, castable refractories). One such property is packing density. There are, in the literature, models that optimise particle size distributions for maximum packing density, all of them derived for spherical particles (e.g. Furnas, Andreasen, Alfred). In this work, commercial alumina powders (reactive and tabular) were divided into nine particle size classes. Following two different approaches, the latter were used to build six different ternary systems of complementary particle sizes. Using the response surface methodology and related statistical techniques (software Statistica), the particle size distribution that maximises the packing density was obtained in both cases and, by comparison with theoretical particle size distributions, the validity of Alfred’s theoretical model for perfect spheres was demonstrated. These results clearly show that the harmful effect of the nonspherical shape of real particles can, in fact, be compensated by the optimization of the overall particle size distribution.info:eu-repo/semantics/publishedVersio