Pre-firing Temperature Research Articles

ETHNOGRAPHIC CERAMICS FROM BANKIM (ADAMAWA, CAMEROON / WEST CENTRAL AFRICA): MINERALOGICAL AND THERMAL CHARACTERIZATION

The study investigates mineralogical characteristics and thermal threshold at successive steps of Tikar pottery production chaine-operatoire from Bankim (Adamawa, Cameroon). It is a pilot study relying on X-ray diffraction (XRD), thermal analysis (DSC/TG) and Fourier Transform Infrared Spectroscopy (FTIR). The ceramics were collected in the drying and firing stages of the production chain. The work aimed to estimate the drying and firing temperature of the studied pottery sherds. Due to the mineralogical change occurring during the drying or pre-firing and firing stages, the correlation between the three analytical methods suggested that the pre-firing temperature were below 450°C whereas the firing temperature was between 650-800°C in a simple bonfire.

Studies on the effects of pre-firing and sintering temperature on NSDC nanocomposite electrolytes

Solid oxide fuel cells (SOFCs) technology, with fuel flexibility, is one of the most promising power generation technology. However, the high operating temperature of SOFCs has hindered their commercial applications. As a crucial requirement to enhance its performance, SOFCs electrolytes should operate at a low temperature. Carbonate/ceria composites are developed as electrolytes for low operating temperature SOFCs, and a better understanding of the mechanism of its ionic conductivity serves this purpose. In this work, ceria-carbonate composite electrolyte, Na2CO3/samarium doped ceria (NSDC) were synthesized by the co-precipitation method. The synthesized electrolytes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV–Vis spectroscopy. The XRD and SEM results showed that the sintered NSDC nanocomposite comprised a single-phase dense electrolyte structure. The crystallite size of the NSDC nanocomposite was greatly affected by the different pre-firing temperatures and different sintering temperatures. Also, the ionic conductivity of the prepared NSDC nanocomposite electrolytes was strongly dependent on the pre-firing and sintering temperatures. The NSDC nanocomposite electrolytes were pre-fired at 950 ​°C and 650 ​°C and sintered at 1200 ​°C and 900 ​°C respectively, had ionic conductivity in H2 and air high as 0.36 ​S/cm and 0.3 ​S/cm.

Effects of andalusite aggregate pre-fired at different temperatures on volume stability and oxidation resistance of Al2O3–SiC–C castables

In the present work, the effects of the pre-firing temperature of andalusite aggregates (5–3 mm) on the conversion of andalusite as well as the volume stability and oxidation resistance of the Al2O3–SiC–C castables were investigated. The phases of the andalusite aggregates were tested via X-ray diffraction, and their microstructures as well as those of the castables were characterized via scanning electron microscopy. The linear expansion of the castables decreased with increase in the pre-firing temperature of andalusite, as less residual andalusite in the pre-fired aggregates lowered its transformation in the castables during firing at high temperatures. Moreover, the higher amounts of SiO2-rich glass produced by andalusite pre-fired at high temperatures and secondary mullite generated between andalusite and the matrixes were both favorable to the production of castables with denser structure. This prevented the diffusion of O2 into the castables and improved their oxidation resistance.

Processing temperature tuned interfacial microstructure and protonic and oxide ionic conductivities of well-sintered Sm0.2Ce0.8O1.9- Na2CO3 nanocomposite electrolytes for intermediate temperature solid oxide fuel cells

Well-sintered SDC-NC (Sm0.2Ce0.8O1.9-Na2CO3) nanocomposites have been prepared through a rare-earth/sodium complex carbonate precipitation, powder prefirings at the temperatures 400, 500 and 600 °C and sintering at 800 °C. Their sintering performances, phase components and microstructures have been characterized by Archimedean method, XRD and FESEM techniques. In particular, the influence of the interfacial interactions between the phases of SDC and NC on the microstructures and electrical conductivities of SDC-NC nanocomposites have been investigated by AC impedance and Raman spectroscopies. It has been found that on the basis of the fitting analysis of AC impedance data, the oxide ionic and protonic conductivities of interfacial and non-interfacial phases in the SDC-NC nanocomposites are found to be strongly dependent upon their prefiring temperatures with the sample of SN-600 showing the highest values of 73.2/33.7 and 51.1/105.4 μS/cm at 300 °C, respectively. The single cell based on the electrolyte of SN-600 presents an OCV of 0.992 V and peak power density of 421 mW/cm2 at 550 °C. The interfacial interactions between the phases of SDC and NC inside SDC-NC nanocomposites are considered responsible for their differences in microstructure and electrical conductivity.

Fracture behaviour and microstructure of refractory materials for steel ladle purging plugs in the system Al2O3-MgO-CaO

Abstract This paper completes the investigations performed on cement- and no-cement bonded refractory materials for steel ladle purging plugs. In addition to the thermodynamic evaluations and detailed material descriptions given in a previous paper, this paper focuses on the fracture behaviour of the materials. The influence of low and high pre-firing temperatures on the fracture behaviour is investigated. Differences in the microstructure of cement- and hydratable alumina-bonded castables with and without spinel can explain their different mechanical properties and fracture behaviour especially after pre-firing at elevated temperatures. When comparing cement- with no-cement bonded materials for applications in steel ladle purge plugs, both concepts have advantages and disadvantages. The much higher hot modulus of rupture of the cement bonded materials, especially in combination with spinel, is advantageous for the required erosion resistance in this application. With regard to corrosion resistance against the iron oxide-rich slag created during the oxygen lancing of the purging plugs, the calcia-free no-cement bonded materials would be advantageous. The more ductile, less brittle fracture behaviour of the no-cement system even after high temperature pre-firing should provide advantages with respect to the cracking and spalling behaviour of the hot face during use. Based on this investigation it would appear to be worthwhile testing hydratable alumina bonded corundum-spinel materials in industrial applications for steel ladle purging plugs.

Chemical and mineralogical characterization of portuguese ceramic tiles in the historic center of São Luís do Maranhão (Brazil): an approximation of the mineralogy and firing temperature of the raw materials

This work involved the first-ever characterization of antique Portuguese ceramic wall tiles in the Historic Center of São Luis do Maranhão, Brazil. The tiles were characterized by optical microscopy, X-ray diffraction (XRD) and chemical analysis to identify the possible raw materials used in the fabrication process, as well as the firing temperature of these materials. The results indicate that the microstructure of these materials consists of pores of varying sizes with calcite incrustations and quartz grain sizes smaller than 500 µm distributed in a pinkish yellow matrix, which were identified by XRD as calcite, gehlenite, wollastonite, quartz, and amorphous mineral phases. Based on this information, it can be inferred that the original raw materials probably consisted of a mixture of kaolinitic clays (Al2O3·2SiO2·2H2O) rich in calcium carbonates and quartz, or mixtures of kaolinitic clays, quartz and calcite, which did not reach the pre-firing temperature of 950ºC.

Sol-gel Synthesis and Characterization of YAG:Ce3+ Phosphors by Various Pre-firing Temperatures

AbstractCeria doped-yttrium aluminum garnet (Y3Al5O12:Ce3+, YAG:Ce), which is known as an efficient phosphor, have been widely used in optical display and lighting applications. Improved wet chemical method, sol-gel, has been studied, since conventional solid-state reaction requires a high-temperature and prolonged heating to obtain the pure phase. However, there has been little information, such as on pre-firing temperature, concerning high-quality powder formed by the wet chemical process. In this work, YAG:Ce was synthesized with a salted sol-gel process in which a water solution of inorganic salt with citric acid as additive. Transparent starting sol was pre-fired at 200 ˜ 300°C for 2 hrs in air and final annealing to obtain phase-pure YAG:Ce particles was performed at 1100°C for 2 hrs in argon. The effects of pre-firing temperatures on the crystal structure, morphology and luminescence were investigated. Effects of residual organics in the pre-fired gel on the properties of finally annealed phosphors will be fully discussed on the basis of the results of thermal analysis and chemical structure.

Microstructures and electrical properties of La 0.8Sr 0.2MnO 3 films synthesized by sol–gel method

La 0.8Sr 0.2MnO 3 (LSMO) thin films were fabricated on alumina substrates by an improved sol–gel dip-coating process. It was found that multiple dip-coating process could not be performed until the pre-firing temperature reached 600 °C. Different amounts of LSMO powders were added to precursor solution with an aim to avoid cracks in LSMO thin films during calcining caused by the shrinkage mismatch between the film and the substrate. The structure and surface morphology of the films prepared from precursors with and without LSMO powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the addition of 56.4 wt.% LSMO powders into the sol–gel precursor solution significantly modified the microstructure of films. A single LSMO perovskite phase was obtained on alumina substrate after calcining at 800 °C for 4 h by the improved sol–gel method. The sheet resistance of the films prepared with different processing parameters was measured by four-point dc method. Results indicated that the sheet resistance of films decreased with increasing the number of coating applications and the amount of LSMO powders.

Structure of kaoline–alumina based foam ceramics for high temperature applications

Light weight refractory materials were developed applying the aerated concrete technology. Kaolinite based suspensions were agitated with Al powders or Al pastes. Under release of hydrogen gas, foams were formed at pH values from 7 to 9, stabilised, dried and fired at temperatures up to 1600 °C. Loading fractions of alumina up to 80 vol.% were demonstrated. The porosity varies with the amount of the metal precursor Al. A macro porosity of 0.2–1 mm was formed which was characterised by image analysis and X-ray tomography. The working temperature of the produced refractory materials depends on the prefiring temperature, the filler character and content and the macroscopic structure. Silica free pure porous mullite or mullite-corundum ceramics were obtained. Thermal analysis shows that the porous refractories meet the ASTM requirements for application temperatures up to 1550 °C.

Fabrication of an Anode Supported Tubular SOFC System

Tubular SOFC systems have many desirable characteristics compared to their planar counterparts, however there are many obstacles and difficulties that must be met to achieve a successful and economically viable manufacturing process and stack design. Anode supported tubes provide an excellent platform for individual cells. They allow for a thin electrolyte layer, which helps to minimize polarization losses, to be applied to the outside of the tube, thus avoiding the difficulty of coating the inside of an electrolyte or cathode supported tube, or the stack design problem of having a fuel chamber if the anode is on the outside of the tube. This paper describes the fabrication of a traditional (Ni-YSZ) anode tube via extrusion of a plastic mass through a die of the required dimensions. The anode tubes were dried before firing, and tests performed on the tubes to determine the effects of pre-firing temperature on porosity. The porous tubes had a vacuum applied to the inside while being submerged in aqueous electrolyte slurry. Various parameters were examined, including vacuum pressure, submergence time, and drying conditions, and studied using light microscopy. Cathode coatings were applied using a brush painting technique, and optimized as a function of paint consistency, drying conditions, and firing temperatures.

Sintering Distortion of Barrier Ribs Formed via Capillary Molding

Various closed-cells of plasma display panel were prepared via capillary moldingof paste containing ceramic powders of barrier ribs. The cells include meander, honeycomb, waffle and SDR. In this study, the sintering behaviors of such barrier ribs were investigated. The effects of pre-firing temperature, solid content in the paste, and type of cells on morphologies of the ribs were examined. The results indicated that cells with asymmetric geometry such as SDR and meander results in severe distortion after the sintering. The cells with symmetric geometry such as waffle and honeycomb, on the other hand, the distortion was negligible. Using the waffle type cells, the luminance characteristics of PDP device were evaluated.

Microwave firing of MnZn-ferrites

Microwave firing is evaluated in comparison to conventional firing for MnZn-ferrites. For otherwise identical conditions, microwave firing results to higher densities and coarser microstructures. Initial magnetic permeability values (25 kHz, 25 °C, <0.1 mT) after conventional firing are approximately 5000, but the corresponding values after microwave firing are approximately 6000. Unlike the conventional firing process, the final density after microwave firing is increased by increasing the prefiring temperature. As appears from the results of this study, microwave firing could be in principle a promising MnZn–ferrite firing technology for materials to be used in high magnetic permeability applications. No advantages of microwave firing are evident for materials intended to be used in high field power applications.

Microstructure and NO decomposition behavior of sol–gel derived (La 0.8Sr 0.2) 0.95MnO 3/yttria-stabilized zirconia nanocomposite thin film

(La 0.8Sr 0.2) 0.95MnO 3 and (La 0.8Sr 0.2) 0.95MnO 3/YSZ gel films were deposited by a spin-coating technique on scandium-doped zirconia (ScSZ) substrate using the precursor solution prepared from La(O i-C 3H 7) 3, Sr(O i-C 3H 7) 2, Mn(O i-C 3H 7) 2 and 2-methoxyethanol. By heat-treating the gel films, the membrane reactors, (La 0.8Sr 0.2) 0.95MnO 3|ScSZ|Pt and (La 0.8Sr 0.2) 0.95MnO 3/YSZ|ScSZ|Pt were fabricated. It was found that the pre-firing temperature affected the microstructure evolution of (La 0.8Sr 0.2) 0.95MnO 3 and (La 0.8Sr 0.2) 0.95MnO 3/YSZ thin films. Pre-firing at low temperature resulted in high porosity and large grain size of the thin films. NO decomposition characteristics of the obtained membrane reactors were investigated at 600 °C in reactant gas, 1000 ppm of NO and 2% of oxygen. By applying a direct current to the membrane reactors, NO can be decomposed at the (La 0.8Sr 0.2) 0.95MnO 3 and (La 0.8Sr 0.2) 0.95MnO 3/YSZ composite cathode. By incorporating YSZ into (La 0.8Sr 0.2) 0.95MnO 3, the required consuming power to decompose NO could be reduced.

Furnaces: Improving low cement castables by non-wetting additives

Aluminosilicate castables, which are widely used in aluminum transformation furnaces, are susceptible to chemical reactions between molten aluminum and the furnace refractory lining. To prevent those reactions, commercial additives such as BaSO4, CaF2, and AlF3 are generally added in castables. This article presents and analyzes the effect of various amounts of the above additives as well as the influence of pre-firing temperatures on the corrosion behavior of an aluminosilicate low cement castable matrix in contact with liquid Al-5%Mg alloy.

High-pressure synthesis of diamond from phenolic resin

Two kinds of phenolic resin, novolak and resols, have been studied with an addition of cobalt at pressures between 2 and 4 GPa and at temperatures from 1300 to 1900 °C, all under thermodynamically graphite-stable conditions. Diamond was synthesized from these resins which had been pre-fired at 500–1000 °C. From such resins, carbon precursors carrying a great number of radicals, being nearly free of hydrogen and oxygen, and turbostratic in structure, can be constructed. The pressure–temperature conditions suitable for the diamond synthesis were dependent on the pre-firing temperatures. The cobalt served as a catalyst–solvent, similar to the case of conventional diamond synthesis from graphite under diamond-stable conditions. Well-defined single crystals cubo-octahedral in shape, measuring 0.3–0.7 mm across and classified as type Ib were obtained.

The effect of Bi&amp;lt;sup&amp;gt;3+&amp;lt;/sup&amp;gt;on the behavior of V&amp;lt;sup&amp;gt;5+&amp;lt;/sup&amp;gt;of CaVIG in the solid state reaction process

It was found from the curves of reduced magnetization (σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> /(σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> versus the prefiring temperature Tp of Bi <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Y <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.2-x</inf> Ca <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.8</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</inf> V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf> Ge <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.7</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> (x=0, 0.4, 0.8, 1.2) that some of these curves showed a peak value larger than 1, with the maximum value 1.2 for x=0. The σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> -T curves for materials with x=0 at different Tp have much higher Tc than that of the sintering samples, and are not smooth, suggesting a superposition of many phases. The results demonstrate that the garnets with high σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> and high Tc were first formed at lower temperature, and V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5+</sup> , Sn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> , Ge <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> ions gradually occupy d or a site only at higher temperature. It can also be seen from plot of (σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> /(σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> -Tp that (σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> /(σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> >1 died away with increasing x and vanished at x=1.2, The σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> -T curves of prefiring samples with x=0.4 show a major phase (Tc=150°C) and a minor phase(Tc>200°C) and the curves of the prefiring samples with x=1.2 are smooth and give a common Tc (165 °C) equal to that of the sintering samples. The results show that Bi substitution is favourable for V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5+</sup> Sn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> , Ge <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> . ions to enter the garnet lattices.

The Effect of Milling and Firing Conditions on Density and Oxygen Content of Microwave Magnesium Manganese Ferrites

Microwave ferrites were prepared and the effect of aqueous and non-aqueous media on milling, the influence of milling period pre-firing and sintering temperatures on bulk density and oxygen content were studied. It has been found that oxygen content is dependent on the bulk density of the ferrite, i.e. with increasing bulk density, oxygen content decreases. Ferrites milled in non-aqueous media and pre-fired before final sintering gave satisfactory results. The effect of quenching and slow linear cooling on oxygen content was also studied. In the former process the ferrites are deficient in oxygen, whereas the latter results in excess oxygen ferrites.