Preliminary analysis of physical and chemical phenomena occurring in droplet at solution precursor plasma spraying of zirconia coatings

International audienc

Microestrutura e distribuição de Weibull da resistência à ruptura de cerâmicas de argila-talco

International audienceThe mechanical properties of clay-talc ceramics containing 0 to 10 wt% of talc fired at 1100 °C were obtained by flexural measurements. With the average value of flexural strength of 23.1 MPa, the sample with 5 wt% of talc (G5) was the strongest and it had the lowest value of interconnected pore (64%). The scattering of strength values was described with the Weibull distribution model. For all samples, Weibull plots showed either a typical linear behavior or a multi-stage response and the Weibull modulus varied in a large range of 3 to 14, depending on the ceramic type and on the applied load. Interconnections between pores formed a network of possible failures under the stress field, resulting in a change of Weibull plots. Reducing the grain size range and the pore interconnectivity led to a reduced strength distribution. The flaw size range had a unimodal distribution for sample G5 with homogeneous microstructure and correspondingly a Weibull modulus m=9.79. © 2019 Associacao Brasileira de Ceramica. All rights reserved.As propriedades mecânicas das cerâmicas de argila-talco contendo 0 a 10% em massa de talco sinterizadas a 1100 °C foram obtidas por medidas de flexão. Com o valor médio de resistência à flexão de 23,1 MPa, a amostra com 5% de talco (G5) foi a mais forte e apresentou o menor valor de poro interconectado (64%). A dispersão dos valores de resistência foi descrita com o modelo de distribuição de Weibull. Para todas as amostras, os gráficos de Weibull mostraram um comportamento típico linear ou uma resposta de múltiplos estágios e o módulo de Weibull variou em uma ampla faixa de 3 a 14, dependendo do tipo de cerâmica e da carga aplicada. Interconexões entre poros formaram uma rede de possíveis falhas sob o campo de tensão, resultando em uma mudança nos gráficos de Weibull. Reduções da faixa de tamanho dos grãos e da interconectividade dos poros levaram a uma redução na distribuição da resistência. A faixa de tamanho de defeito apresentou uma distribuição unimodal para a amostra G5 com microestrutura homogênea e correspondentemente um módulo de Weibull m=9,79

Microstructure and Weibull distribution of rupture strength of clay-talc ceramics

International audienceThe mechanical properties of clay-talc ceramics containing 0 to 10 wt% of talc fired at 1100 °C were obtained by flexural measurements. With the average value of flexural strength of 23.1 MPa, the sample with 5 wt% of talc (G5) was the strongest and it had the lowest value of interconnected pore (64%). The scattering of strength values was described with the Weibull distribution model. For all samples, Weibull plots showed either a typical linear behavior or a multi-stage response and the Weibull modulus varied in a large range of 3 to 14, depending on the ceramic type and on the applied load. Interconnections between pores formed a network of possible failures under the stress field, resulting in a change of Weibull plots. Reducing the grain size range and the pore interconnectivity led to a reduced strength distribution. The flaw size range had a unimodal distribution for sample G5 with homogeneous microstructure and correspondingly a Weibull modulus m=9.79. © 2019 Associacao Brasileira de Ceramica. All rights reserved.As propriedades mecânicas das cerâmicas de argila-talco contendo 0 a 10% em massa de talco sinterizadas a 1100 °C foram obtidas por medidas de flexão. Com o valor médio de resistência à flexão de 23,1 MPa, a amostra com 5% de talco (G5) foi a mais forte e apresentou o menor valor de poro interconectado (64%). A dispersão dos valores de resistência foi descrita com o modelo de distribuição de Weibull. Para todas as amostras, os gráficos de Weibull mostraram um comportamento típico linear ou uma resposta de múltiplos estágios e o módulo de Weibull variou em uma ampla faixa de 3 a 14, dependendo do tipo de cerâmica e da carga aplicada. Interconexões entre poros formaram uma rede de possíveis falhas sob o campo de tensão, resultando em uma mudança nos gráficos de Weibull. Reduções da faixa de tamanho dos grãos e da interconectividade dos poros levaram a uma redução na distribuição da resistência. A faixa de tamanho de defeito apresentou uma distribuição unimodal para a amostra G5 com microestrutura homogênea e correspondentemente um módulo de Weibull m=9,79

Thermal behaviour and microstructural evolution of metakaolin and meta-halloysite-based geopolymer binders: a comparative study

Two calcined clays (halloysite and kaolinite clays at 700 °C) were used as solid precursors for geopolymer synthesis. This study compares the physicochemical properties of the both resulting geopolymer series heated at 200, 400, 600 and 800 °C. The end specimens were characterized using Optical Dilatometer, XRD, FTIR, MIP and SEM analyses. Results revealed that the flexural strengths were 18.10 and 21.74 MPa for meta-halloysite- and metakaolin-based geopolymers, respectively. After subjected to high temperatures, the flexural strength drastically decreased from 18.10 ± 1.06 to 6.7 ± 0.23 MPa and 21.74 ± 1.20 to 4.63 ± 0.24 MPa, respectively. The maximum shrinkage recorded on metakaolin and meta-halloysite-based geopolymers was 14 and 16% around 950 °C, respectively. The thermal conductivities decreased with increase in heating temperature from 0.78 to 0.19 Wm−1 K−1 and 0.96 to 0.26 Wm−1 K−1, respectively. This reduction is linked to the additional voids and microcracks that occurred within the geopolymer network. The cumulative intrusion in both geopolymers increased with increase in heating temperature up to 600 °C, leading to the degradation of geopolymer network that affected the mechanical strength evolution. Both synthesized geopolymer series are potential candidates for insulation materials or refractory applications

About the thermal transformations and sintering of a Ghassoul clay from Morocco

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Refractory ceramics bonds from potassium-based inorganic polymer for advanced applications: Crystalline phase changes and descriptive microstructure

Understanding the structural and meso-scale properties of alkali activated matrices subjected to high temperature treatment, provides useful information on the stability of their self-life service or, fire resistance in extreme environments. The current project focuses on the transformation of phase and structural bonds within kyanite-reinforced refractory geopolymer. After being exposed to temperatures ranging from 1050 °C to 1250 °C, the micro-structural and macro-scale properties of the resulting matrices were evaluated using X-ray diffraction, chemical bond analysis, SEM-EDS, and resistance to flexural strengths. The fineness of the kyanite powder played an important role in the geopolymer composites' bonding system, as well as the crystallization of the cordierite phase during the sintering process. Further decomposition of kyanite minerals limited the thermal expansion to less than 0.8%, suggesting the formation of new and stronger bonds between the particles, which result in the formation of crystalline phases such as: cordierite, mullite, leucite and enstatite. These phases render the matrices compact and dense. Based on the findings, kyanite particles were discovered to be refractory components and fillers in the formation of refractory alkali-bonds ceramics, with environmental and eco-friendly benefits

Characterization and performance evaluation of laterite based geopolymer binder cured at different temperatures

Abstract This paper presents the results of experimental evaluation of curing conditions on the microstructure and performance of geopolymer binders developed from iron-rich laterite soils. Two calcined iron-rich laterites namely LB600 and LY600 were used as solid precursors in the preparation of geopolymer binders. The geopolymer samples were cured at 20, 60 and 80 °C. FTIR, XRD, EDS and DTA/TG were used to evaluate the microstructural properties of the prepared products. The performance of the binder was evaluated in terms of the compressive strengths, water absorption, porosity, bulk density and thermal conductivity. The findings from this study showed that the dissolution of the calcined laterites in 8 M NaOH increased the dissolution of Al, Si and Fe elements with increasing temperature from 20 to 80 °C. This higher dissolution of the monomers further resulted to an increase in the compressive strength of the binders at 7 and 28 days. It was also found out that curing the geopolymer in the dry state resulted in higher compressive strength at all ages compared to those cured in the wet and wet-dry state. Drying shrinkage evaluation of the geopolymer samples cured between 60 and 80 °C exhibited a lower linear shrinkage due to a high degree of geopolymerization. Microstructural investigation of the geopolymer samples cured at 80 °C showed a heterogeneous compact and dense structure resulting from high polycondensation. This densified microstructure also induced an increase in the thermal conductivity from 0.65 to 0.90 W/mK and 0.75 to 0.91 W/mK for LB600 and LY600, respectively. Nonetheless, both geopolymer binders made of LB600 and LY600 laterite powders performed well in dry, wet and wet-dry conditions, and can be used for various construction applications especially in the precast industry