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The necessity to accelerate green and low carbon technologies, to mitigate the pending energetic crisis, potentiates the urgent search for alternative energy transfer methods. In this regard, Proton Ceramic Membrane Reactors (PCMRs) have shown great potential as a clean alternative for both energy production and the electrochemical synthesis of a wide range of chemical products. One of the most important is that of ammonia, where recent literature has demonstrated the potential use of PCMRs to either synthesize this chemical product or to use it as a fuel, and where suitable new electrodes must be developed. Hence, this work investigates the use of niobium (oxy)nitride (NbNxOy) in combination with proton ceramic conducting materials, as a new category of composite electrode for PCMRs applications. To achieve this goal, firstly, the chemical compatibility of the NbNxOy phase with the well-known proton conducting perovskite, yttrium-doped barium cerate (BaCe0.9Y0.1O3-δ, BCY10), was assessed. By X-ray powder diffraction, BaCe0.7Zr0.1Y0.2O3-δ (BCZY712) was shown to be chemically stable with the NbNxOy phase, surviving up to 850 °C, thus, facilitating the production of an electrolyte supported composite electrode film based on BCZY712-NbNxOy (40–60 vol%). Thermogravimetric experiments combined with X-ray diffraction were also made to assess the thermal stability of the NbNxOy material in both N2 and 2 % H2/N2 atmospheres, revealing that NbNxOy decomposes into its parent oxide in N2, while retaining the pure (oxy)nitride phase in the more reducing conditions. The polarization behavior of the BCZY712-NbNxOy composite electrode was evaluated by electrochemical impedance spectroscopy under different gaseous conditions of H2/N2 and NH3 atmospheres. The overall electrode mechanism was tentatively explained by three main steps, including i) proton incorporation/water release or adsorption/desorption of water, ii) gaseous hydrogen adsorption/desorption, and iii) interfacial transfer reaction of either protons or oxygen-ion vacancies. To the best of our knowledge, this is the first work that reports a detailed chemical compatibility study of niobium (oxy)nitride with a protonic ceramic matrix, while also outlining a detailed electrode mechanism under prospective conditions of hydrogenation/de‑hydrogenation of ammonia. published

Mullite is one of the preferred aluminosilicates for both traditional and advanced ceramics. This paper reports the use of simplex-centroid mixture design to prepare mullite–glass ceramics by reactive sintering. The phase composition and technological properties of formulations containing kaolinitic clay, kaolin waste and alumina were investigated after sintering at 1400 °C. The sintering behavior was assessed by dilatometry. Microstructural analysis indicated the crystalline phases mullite, residual quartz, cristobalite, and α-alumina. A glassy phase was also identified as a matrix embedding mullite grains (as seen by X-ray diffractometry and scanning electron microscopy). In kaolin waste-rich formulations, a liquid phase sintering mechanism favored the densification process and the mechanical resistance. Highly significant statistical models allow correlating the concentrations of raw materials with linear firing shrinkage, water absorption and apparent porosity. Overall results stand out for the potential of using kaolin waste in the preparation of mullite–glass ceramics.

In this work, we report a comparative study of Ni-based anode compositions, made of Cu and Co (40 and 80 mol%) and gadolinia-doped ceria (CGO) matrices, for application the dry reforming of methane (DRM) reaction using Solid Oxide Fuel Cells (SOFCs). The new compositions are synthesized by a one-step synthesis route, using citric acid as chelating agent, and characterized at three different stages: i) after synthesis, ii) after reduction, and iii) after DRM. X-ray diffraction (XRD) analysis combined with thermodynamic calculations is used to understand phase evolution along the different stages, revealing that complete solid solutions of NiCo- and NiCu-based alloys are formed after DRM reaction. Transmission Electron Microscopy (TEM) shows the formation of nanocrystalline powders, while surface area (SBET) measurements show higher values in the case of the NiCo-based samples. Moreover, the Co-containing compositions exhibit higher reducibility and stronger metal-ceramic interactions than the Cu-containing samples, according to the Temperature Programmed Reduction (TPR) results. Finally, DRM results demonstrate higher CO2 and CH4 conversions in the case of the Co-containing samples, as well as increased resistance towards carbon deposition, as confirmed by Thermogravimetric and Differential Scanning Calorimetry analyses (TG-DSC). Overall, the Co-based compositions are highly beneficial for their use as anodes for the CO2 reforming of methane in SOFCs.

Cordierite is one of the compounds in the MgO–Al2O3–SiO2 system which has the lowest thermal expansion coefficient. Despite this advantage, which results in high resistance to thermal shock, monophasic cordierite is difficult to prepare due to its narrow sintering temperature range and the existence of secondary phases that increase its thermal expansion coefficient. Fluxing agents are generally used to stimulate the sintering of cordierite precursor powders as well as to modify the microstructures and properties of these ceramics. In this context, this work aims at studying the structural, microstructural and physical properties of cordierite-based ceramics with small amounts of coffee husk ash residue as fluxing agent. Sintered samples were prepared from a standard formulation (containing clay, alumina and talc) with controlled additions of coffee husk ash residue (a natural source of K2O) aiming to investigate the effects of the sintering temperature and amount of residue on the phase composition and properties. Quantitative phase analysis of samples sintered between 1350 and 1450 °C was determined by Rietveld refinement of XRD data. Physical properties were estimated by the Archimedes methodology. The microstructure of sintered samples was inspected by scanning electron microscopy. The results indicated that the addition of residue amounts as low as 1 wt% accelerates the reaction between cristobalite and spinel, originating the cordierite phase. The formation of liquid phase with increasing the residue content explained the decrease in the apparent porosity and water absorption.

Calcium cobaltites have emerged as an attractive alternative to be used in Solid Oxide Cells (SOCs), due to their excellent thermal compatibility with standard electrolytes that may privilege these compounds among state-of-the-art SOC electrodes. Nonetheless, their electrochemical performances have been strongly limited by poor oxygen ion transport. Hence, we report a new composite electrode containing the misfit calcium cobaltite [Ca2CoO3-δ]0.62[CoO2] (C349) phase combined with Ce0.8Pr0.2O2-δ (CPO). A comparative study is presented between this composite and the standard La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), in terms of their microstructures, number of depositions, and resultant electrochemical properties. Such tailoring permits the best C349/CPO composite electrode to attain high levels of electrochemical performance that rival with the standard LSCF material. This successful result is highly relevant, as it can provide insight into the most critical optimisation factors for similar SOC electrodes that intrinsically suffer from similarly low levels of ionic transport.

Ca-doped ceria (CCO) electrolytes were prepared using two processing approaches, proteic sol-gel synthesis using gelatin (SG) and solid-state reaction (SSR). Mollusk shell powder was used in the SSR method as the main source of Ca. Materials sintered at 1350–1450 °C exhibited relative density above 95% and different microstructural features regarding grain size and morphology. Impedance spectroscopy in air revealed a comparatively better total electrical response of materials prepared by the proteic sol-gel route. CCO ceramics prepared by the SG route have bulk conductivity four times higher than the highest conductivity of samples processed by the SSR route. Electrical properties of the grain boundaries of both series of materials reveal distinct oxygen vacancy concentration profiles and space charge potentials. The role of processing route and sintering schedules was discussed taking into consideration the distinct impact of Ca interaction in the grain boundaries.

Nanocrystalline Fe-based spinels (MFe2O4, where M = Cu, Co or Ni) were synthesized by a proteic sol-gel method. The effect of metal cation swap on the battery-type behavior was evaluated at room temperature in a three-electrode cell configuration in alkaline medium (3 M KOH). Raman spectroscopy was performed to assess the cationic distribution of divalent Cu, Co and Ni at the tetrahedral and octahedral sites, establishing a correlation with oxygen vacancies. X-ray photoelectron spectroscopy (XPS) was used to confirm oxygen vacancies and oxidative states of metal elements. Rietveld refinement analysis combined with FESEM inspection reveals the attainment of mixed spinel ferrites with nanosized crystallites (39–77 nm) and particle sizes (44–92 nm). Cyclic voltammetry and discharging curves of spinel-based electrodes indicate an improved performance for CuFe2O4 (Qs = 183 C g−1), followed by CoFe2O4 (Qs = 79 C g−1) and NiFe2O4 (Qs = 32 C g−1) at a specific current of 0.5 A g−1. The remarkable electrochemical stability for CuFe2O4 is confirmed by retention capacity of 98% after 1000 charge-discharge cycles at a specific current of 1 A g−1. The enhanced electrochemical performance of CuFe2O4 is due to an increase in Faradaic reactions boosted by a higher fraction of surface defects (determined by Raman and XPS spectroscopies) combined with a grain boundary-dependent effect responsible for a smaller charge transfer resistance as measured by electrochemical impedance spectroscopy.

In this work, brownmillerite-type calcium ferrite (Ca2Fe2O5) ceramics were prepared by two distinct routes, namely by a proteic sol-gel synthesis using commercial flavorless gelatin, and by a solid-state reaction method using mollusk shells. XRD analyses revealed single phase brownmillerite-type calcium ferrites in both cases. SEM-EDS analysis of sintered Ca2Fe2O5 ceramics revealed larger grain sizes for the samples prepared via the solid-state reaction. All samples possessed a p-type conduction mechanism, with the largest power factor of ~2 ​μW ​m-1 K−2 at 450 ​°C observed for the samples obtained via the solid state reaction. The charge transport mechanism was found to depend on the preparation route. The obtained results demonstrated that the proposed synthesis routes can be successfully employed for the preparation of single-phase brownmillerite-type materials.

This work reports the microstructural and thermoelectric characterization of the misfit [Ca2CoO3-δ]0.62[CoO2] compound obtained by a solid-state synthesis using mollusk shells and a proteic sol-gel method, which uses gelatin as a polymerizing agent. The results clearly demonstrate the capability of these routes to produce pure Ca3Co4O9 with plate-like morphology. Sintered ceramic samples show randomly oriented grains and relative densities in the range of 63–67%. The obtained microstructures provide reasonable electrical properties and result in competitive thermoelectric performance for the material prepared by the proteic sol-gel synthesis (P.F. of 205 μW/K2 m at 700 °C).

2021-04 Alumina-based composites were prepared by solid-state synthesis of mixtures containing kaolin clay + alu- minum hydroxide and kaolin waste + aluminum hydroxide. The starting raw materials were characterized by X- ray diffraction (XRD) and quantitative phase analyses of fired samples were performed by Rietveld refinement of the XRD data. The effects of the applied pressing pressure (60–320 MPa) and firing temperature (1400–1500 °C) on volumetric firing shrinkage and apparent density were studied through a 22 factorial design. Mullite/alumina and alumina/glass composites were obtained from kaolin clay and kaolin waste processed ceramics, respectively. Overall results suggest the densification processes of mullite/alumina composites with up to 70.1 wt% mullite and alumina/glass composites with up to 59.7 wt% alumina were dominated by solid-phase and liquid-phase sintering mechanisms, respectively.

This work reports the effects of crystallographic changes due to the secondary phases, in particular sigma (&sigma, ), on the mechanical properties and electrochemical behavior of thermally aged duplex stainless steel (DSS). Structural, morphological, mechanical, and electrochemical characterizations were performed. Sigma phase content increased with increasing aging treatment time. It had a lamellar-like shape, as observed by electron backscatter diffractometry (EBSD). Its presence directly damaged mechanical properties. The corrosion assessment included electrochemical impedance spectroscopy (EIS) in 1 M NaCl solution at temperatures of 25, 40, and 65 &deg, C. EIS results demonstrate that an increase in the &sigma, phase content decreased the corrosion resistance (21.1&ndash, 0.8, 3.5&ndash, 0.3, and 3.1&ndash, 0.2 kΩ cm2 at 25, 40, and 60 &deg, C, respectively).

Gd-doped ceria (Ce1−xGdxO2-δ; x = 0, 0.1 and 0.2) is one of the best ceramic electrolytes for application in solid oxide electrochemical devices. This work reports an innovative and environmentally friendly route known as “proteic sol–gel synthesis” using gelatin for their preparation. Materials are characterized via thermogravimetric analysis, X-ray diffractometry, scanning electron microscopy, Raman and X-ray photoelectron spectroscopies, and electrochemical impedance spectroscopy. The proposed method allows to produce pure phase nanosized powders at 400 °C that exhibit excellent sinterability at 1350 °C. Significant differences are found in the bulk at lower temperatures, with estimated defect association enthalpies of 0.45 and 0.56 eV for the compositions containing 10 and 20 mol% Gd, respectively, leading to an increased bulk conductivity in the first case. In contrast, identical grain boundary Schottky barrier height values of around 0.2 V are a possible result of the relatively low sintering temperature, decreasing the extent of the acceptor dopant segregation to the grain boundaries due to insufficient cation mobility. This leads to similar specific grain boundary characteristics in both doped compositions. Overall, this work provides a rational understanding of a novel route for the synthesis of CGO ceramics with competitive performance and decreased sintering temperature.

In this study, the influence of the surface oxygen vacancies on the energy storage performance of electrodes based on nickel oxide (NiO) nanoparticles was investigated. NiO samples were synthesized by three facile and low-cost syntheses routes: nitrate calcination, citrate, and combustion methods. The concentration of surface defects in NiO powders was determined using XPS analyses, which showed a higher amount of oxygen vacancies for the sample obtained by nitrate calcination. According to the cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) curves, NiO-based electrodes were classified as battery-like. CV results suggest that redox reactions are diffusion-controlled processes with a faster diffusion rate for the sample obtained by the nitrate calcination method. This is in accordance with the GCD and electrochemical impedance spectroscopy (EIS) results, with higher specific capacity and higher electrical conductivity (lower equivalent series resistance) for the sample obtained by nitrate calcination. The results indicate that oxygen vacancies play an important role in the electrochemical performance of battery-type NiO electrodes

Among the most promising electrode choices for solid oxide cells, the misfit calcium cobaltite, with the nominal composition [Ca2CoO3-δ]0.62[CoO2] (C349), is gaining special relevance due to its ability to provide good performance in oxidizing conditions, and also for possessing a thermal expansion coefficient similar to that of the standard electrolytes. In this work, we investigate the electrochemical behavior of the misfit C349 with the addition of an active interlayer made of Ce0.8Pr0.2O2-δ (CPO, + 2 mol% Co), compared to the electrode mechanism of an interlayer-free C349 electrode. A combination of three different approaches for the distribution function of relaxation times analysis permits a careful analysis on the characteristic time constants associated with the surface-exchange processes, revealing the existence of parallel reaction paths at higher temperatures, where the pathway through the C349 electrode may take on an important role. Conversely, at lower temperatures, due to the poor ionic conductivity of the C349 compound, the interlayer pathway may become predominant, since the CPO + Co provides much higher ionic conductivity than the C349. These results highlight the competition between an increased electroactive area and the role of the surface-exchange on the CPO + Co interface, where the latter becomes more relevant on decreasing temperature.

An in situ one step synthesis route based on the polymeric precursor method was used to produce dual phase CuO-samaria doped ceria (SDC) nanocomposite powders. This chemical route allowed to obtain composite powders with reduced particle size and uniform distribution of Cu, Ce and Sm elements. The particulate material was characterized by powder X-ray diffraction (XRD) combined with Rietveld refinement. CuO-SDC sintered in air between 950 to 1050 °C and subsequently reduced to Cu-SDC cermets were further characterized by XRD and scanning electron microscopy. The open porosity was measured using the Archimedes’ principle. Suitable microstructures for both charge transfer and mass transport processes (30 to 45% porosity) were attained in Cu-SDC cermets previously fired at 1000 to 1050 °C. Overall results indicated that CuO-SDC composites and Cu-SDC cermets with potential application as anodes for solid oxide fuel cells (SOFCs) can be obtained by microstructural design. An anode supported half-cell was prepared by co-pressing and co-firing gadolinia doped ceria (CGO) and the herein synthesized CuO-SDC nanocomposite powder. Resumo Uma rota de síntese em uma etapa baseada no método dos precursores poliméricos foi usada para produzir pós do nanocompósito contendo as fases CuO e céria dopada com samária (SDC). Esta rota química permitiu obter pós compósitos com reduzido tamanho de partícula e uniforme distribuição dos elementos Cu, Ce e Sm. O material particulado foi caracterizado por difração de raios X (DRX) combinado com refinamento Rietveld dos dados de difração. Compósitos CuO-SDC sinterizados em ar entre 950 e 1050 °C e em seguida reduzidos a Cu-SDC foram caracterizados por DRX e microscopia eletrônica de varredura. A porosidade aberta foi medida usando o princípio de Arquimedes. Microestruturas adequadas para os processos de transferência de carga e transporte de massa (30 a 45% de porosidade) foram obtidas em cermets Cu-SDC previamente sinterizados a 1000 a 1050 °C. Os resultados indicaram que compósitos CuO-SDC e cermets Cu-SDC com potencial aplicação como anodos de células a combustível de óxido sólido (CCOS) podem ser obtidos por projeto microestrutural. Meia célula suportada no anodo foi preparada por coprensagem e cossinterização de céria dopada com gadolínia (CGO) e o nanocompósito obtido neste trabalho.

CuO-Ce 0.9 Gd 0.1 O 1.95 (CuO-CGO) nanocomposite powders obtained by in situ one-step synthesis were used to prepare Cu-CGO cermet anodes for solid oxide fuel cells (SOFCs). The effects of the CuO content (varying from 40 to 60 wt.%) on the lattice parameter and crystallite size of CuO and CGO phases were investigated by X-ray diffraction (XRD) with Rietveld refinement of the XRD data. CuO-CGO composites were screen-printed on both faces of ceria-based substrates, fired at 1150 °C, reduced to Cu-CGO cermets, and electrochemically characterized by impedance spectroscopy in hydrogen and synthetic biogas atmospheres. One-step Cu-CGO anodes with 40 wt.% CuO showed area specific resistances of 0.15 Ω.cm 2 (in hydrogen) and 2.30 Ω.cm 2 (in biogas) at 800 °C. The anode performance is deteriorated by increasing the CuO content to 60 wt.%.

Mullite-glass composites were obtained by solid-state reactive sintering of kaolinite clay and kaolin waste mixtures with waste additions up to 100 wt%. The structural and microstructural analysis of starting powders and sintered samples were evaluated by X-ray diffractometry (XRD) and field-emission scanning electron microscopy (FESEM). The mechanical properties were evaluated by measuring the flexural strength of sintered bodies. Electrical properties of the composites were assessed by impedance spectroscopy (at 30 °C and from 400 to 700 °C) in air. A viscous flux mechanism resulting from the glassy phase filled up the open porosity and increased the mechanical strength. Electrical conductivity, dielectric constant and dielectric loss were strongly dependent on the microstructural features, namely glassy phase and porosity. The activation energies (0.89–0.99 eV) for electrical conduction were lower than typical literature values of mullite-based materials. The results indicated that the herein synthesized mullite-glass composites with up to 53.6 wt% mullite are promising low-cost materials for electronics-related applications.

NiO, CeO2 and respective composites are extensively used in energy storage devices due to mostly their high electrochemical activity. However, the assessment of battery-like behavior of Ni-ceria based systems comprising (Ni or Gd)-doped ceria combined with NiO seems to be neglected in the literature. In this work, NiO and ceria-based solid solutions composite powders were obtained by a co-precipitation synthesis method. The structure and particle size of the calcined powders were investigated by X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM), respectively. Oxidative states of composites were inspected by X-ray photoelectron spectroscopy (XPS). The electrochemical performance of powders was evaluated by cyclic voltammetry, galvanostatic charge-discharge and impedance spectroscopy. Refinement of the XRD patterns showed that powders have nanosized crystallites and mean size of particles within 20 – 70 nm were revealed by FESEM. The improved specific capacity of the NiO-CeO2 electrode material (about 2.5 times higher than that of NiO-CGO at 5 mV s−1) is due to an increase in Faradic reactions taken place on its surface with a higher fraction of defects (namely Ni3+, Ce3+ and oxygen vacancies), as determined by XPS. The superior electrochemical performance of the NiO-CeO2 electrode is also confirmed by electrochemical impedance spectroscopy.

NiO-Ce0.9Gd0.1O1.95 (NiO-GDC) composites (30, 40 and 50 wt% NiO) were obtained by a “one-step” synthesis method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were applied to the calcined compositions, revealing powders in the nanometer range. NiO-GDC composites were sintered at 1450–1550 °C and the respective Ni-GDC cermets were produced in a 10%H2-N2 atmosphere at 800 °C. A factorial design tool allowed to establish a regression equation that correlates the effects of Ni content and sintering temperature on the porosity of Ni-GDC cermets. Impedance spectroscopy was used to analyse the electrical properties of the solid oxide composites in air (at 500–650 °C) and of the Ni-GDC cermets in 10%H2-N2 (at 650 °C). The impedance analysis in reducing conditions revealed an improved in the electrical properties for the Ni-GDC cermet derived from the composite with 50 wt% NiO and sintered at 1450 °C. The electrical resistivity values are among the best ones reported for Ni-based cermets produced by different conditions.

Reversible Solid Oxide Cells (r-SOCs) are promising devices for energy production and management, with the misfit calcium cobaltite electrode ([Ca2CoO3−δ]q[CoO2], commonly designated as Ca3Co4O9, C349), being proposed as a potential oxygen electrode for these devices. To be able to correctly assess this possibility, the processes that limit its polarisation behaviour need to be clarified under relevant conditions of reversible operation. In the current work, we assess the electrochemical characteristics of the C349 electrode by electrochemical impedance spectroscopy using a 3-probe cell configuration. The impedance data is analysed by the use of an equivalent circuit model (EQM) including a Gerischer element to describe the diffusion and surface-exchange properties of the C349 electrodes under applied polarisation, in both cathodic and anodic modes of operation. This analysis is complemented by distribution function of relaxation times (DFRT) and Kramers-Kronig (KK) analyses, revealing that two major processes dominate the total polarisation resistance. Under cathodic polarisation, surface diffusion is rate-limiting upon moderate applied potentials, while, under anodic polarisation, bulk diffusion is rate-limiting. Overall, the performance of C349 was found to not be prevented by the diffusion limiting characteristics of this material, due to compensation of this feature by very fast oxygen exchange. Moreover, the performance of C349 was found to be enhanced under anodic polarisation, due to the easier removal of electrons during oxygen evolution. This work, therefore, provides the first full description of the electrochemical behaviour of the C349 electrode under applied polarisation conditions for r-SOC applications and highlights the high potential of this material for this application.

Large-size Ca3Co4O9 microplates in the range of 10 μm to 18 μm, were prepared by using molten salt synthesis method. The piezoelectric properties of Ca3Co4O9 were reported in the first time. The crystal structure was characterized by X-ray diffractometry along with Rietveld refinement of lattice parameters. In situ piezoresponse force microscopy (PFM) measurements demonstrated that a maximum piezoelectric strain coefficient d*33 of 95.1 pm/V was obtained, rooting in the non-centrosymmetric and anisotropic crystalline structure. This work suggests that the misfit-layered cobaltite oxides can be considered to be a promising alternative lead free piezoelectric material.

Minimizing the impact of fossil fuels has led to intense research for the development of new devices and components for energy applications. In this work, we have fabricated NiO, CeO2 and NiO-CeO2 hollow micro/nano fibers by Solution Blow Spinning (SBS) and evaluated their performance as electrodes for electrochemical energy storage. The electrochemical performance analysis based on cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectra (EIS) revealed a battery-like behavior for the electrodes. Morphological aspects, diffusive process limitations and electron conductivity are the reasons for the performance of electrodes of different compositions, according to Warburg impedance values of 14.37, 128.3 e 258.1 Ω s−0.5 and, charge transfer resistance of 1.03, 37.45 and 119.9 Ω for NiO, CeO2 and NiO-CeO2, respectively. However, hollow fiber electrodes of nickel and cerium-based oxides show better performance than literature reports for electrodes of same composition derived from conventional synthetic routes, which is understandable since battery-like electrodes involve diffusion-controlled processes.

Granite waste has been studied as an eco-friendly raw material in red clay processed-ceramics. However, its influence on the technological properties of industrial porcelain tile formulations has been little discussed, which leaves gaps in this field. This work aims to understand the effects of granite waste content on the physico-mechanical properties of silicate based-ceramics (red clay and porcelain tile). Starting materials were characterized by X-ray fluorescence (XRF), X-ray diffractometry (XRD), particle size distribution, and thermal analyses (DTA and TG). The effects of granite waste addition on the technological properties of sintered samples were evaluated by measuring water absorption, apparent density, and flexural strength. XRD pattern revealed that the granite waste consists of quartz, muscovite, potassium feldspar, anorthite, cordierite, calcite, and dolomite, which is similar to that of raw materials used in the ceramic industry. The characterization of the raw materials showed that granite waste is a promising material to be used in the ceramic industry, without impairing mechanical strength of porcelain tile for additions of up to 12 wt.%. This study reports a high mechanical strength of 40 MPa for samples with 3 wt.% waste content sintered at 1150 oC. Granite waste additions showed values of water absorption ( 7.3 MPa, for samples with up to 38 wt.% granite waste) in good agreement with the range established by the Brazilian standard for perforated bricks and roof tiles.

Cermet compositions based on Nickel–Copper alloys with gadolinium doped ceria as the ceramic matrix, Ni1-xCuxO (x = 0, 0.4 and 0.8 mol%) with 50 wt% CGO (Ce0.9Gd0.1O1.95), are assessed as possible anodes for SOFCs operating in H2 and biogas fuels. Equivalent circuit modelling is employed to evaluate the total polarisation resistance of cermet anodes with correction of data for electronic short-circuiting that may arise when using Ce0.9Gd0.1O1.95 (CGO) electrolytes under reducing conditions. Data analysis highlights that presence of electronic leakage in CGO electrolyte can lead to severe underestimation of total polarisation resistance in the case of H2 fuel, with this deviation becoming more serious with increasing temperature. In contrast, less significant effects are noted under biogas in similar conditions, due to a less reducing nature of this fuel. The results underscore that anode characteristics are highly dependent on the effective oxygen partial pressure of working gas atmosphere and that suitable correction of data is imperative before discussion. Corrected values for polarisation resistance in each fuel reveal the Nickel–Copper alloy cermet with copper content of x = 0.4 to be beneficial under the biogas atmosphere, while, conversely, the pure Ni-cermet is shown to be the peak performing composition in H2 fuel.

This work deals with the synthesis, processing and characterization of NiO/Ni-CGO composite materials as potential solid oxide fuel cell (SOFC) anodes. The particulate materials were obtained by a one-step synthesis method and characterized by thermal analysis (prior to calcination) and X-ray diffraction (calcined powder). The ceramic processing of samples containing from 30 to 70 wt% NiO was carried out by factorial design. Besides the NiO content controlled during the chemical synthesis, the impacts of the pore-former content (citric acid, used in proportions of 0, 7.5 and 15 wt%) and the sintering temperature (1300, 1350 and 1400 °C) were also investigated. The open porosity of NiO-CGO composites and reduced Ni-CGO cermets was modeled as a function of factors (NiO content, citric acid content and sintering temperature) and interaction of factors. The electrical conductivity of a selected NiO-CGO composite was compared to that of a gadolinia doped ceria electrolyte.