Function Of Firing Temperature Research Articles

AC conductivity of C130 type electroporcelain as a function of firing temperature and compaction pressure

Dependence of the AC conductivity of the C-130 type electroporcelain on the compaction pressure was measured. The samples were manufactured from spray-dried mixtures using isostatic compaction in vacuum at 5 different pressures (70 MPa to 110 MPa, 10 MPa step size). AC conductivity measurements were performed at 25 different frequencies ranging from 50 Hz to 3 MHz at room temperature on samples with dimensions 10 × 10 × 3 mm3. In addition to the compaction pressure, the effect of different firing temperatures was studied (1100°C and 1200°C). The highest values of AC conductivity were observed in the case of the raw samples, due to an amount of physically and structurally bound water. Conductivity relaxation was observed after firing at 1200°C in all samples at 2.5 MHz. A small effect of the compaction pressure was observed for the raw samples and samples fired at 1200°C.

The investigation of the physical properties of an electrical porcelain insulator manufactured from locally sourced materials

Abstract The work aims to evaluate the effect of temperature and composition on the physical properties of ceramic electrical porcelain insulators, produced from locally sourced materials in Nigeria. The basic raw materials of triaxial porcelain (Kaolin, feldspar, and quartz) were pulverized, milled for 22 h, and sieved using a 200 μm mesh size. The chemical composition and characterization of the raw materials were obtained using X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis. The mixtures were formulated using sodium silicate as a deflocculant to help produce the ceramic porcelain samples. The green samples were weighed and fired at temperatures of 1200 °C and 1250 °C. The samples were subjected to 1 h of boiling plus 2 h of soaking. The slip casting technique was used in the production of porcelain insulators. The linear shrinkage, water absorbance, apparent porosity, and bulk density were measured and studied as a function of firing temperature. The apparent porosity and water absorption decreased as the firing temperature increased. The bulk density increased gradually from 1200 °C to 1250 °C and the percentage of moisture remained fairly unaffected by the temperature increase. The linear shrinkage was also found to increase as the firing temperature increased. Despite having the same composition, the average physical properties of the locally manufactured insulators revealed that those manufactured at higher temperatures provided a better insulating effect than those manufactured at lower temperatures. In other words, it shows that excellent ceramic porcelain insulators can be manufactured from locally sourced materials using the appropriate composition and firing temperature.

Influence of firing temperature on the ceramic properties of illite-chlorite-calcitic clays

The influence of firing temperature on the ceramic properties of illite-chlorite-calcitic clays has been investigated. Three samples of the same clay deposit have been selected. Weight loss, dimensional changes, water absorption, bulk density, open porosity, flexural and compressive strengths, initial capillary water absorption rate and thermal conductivity have been determined as a function of firing temperature in the range 900-1200 °C with 1 h of soaking time. The microstructures of the fired samples have been examined by SEM and the phase evolution studied by XRD. The water absorption capacity decreased from ∼ 22% at 900 °C/1 h to a maximum of 12% at 1200 °C/1 h with a maximum linear shrinkage of ∼ 2.7%. The open porosities decreased from ∼ 36% at 900 °C/1 h up to ∼ 20% at 1200 °C/1 h as an effect of progressive sintering with higher densification degree of the ceramic bodies. The flexural strength reached a maximum value of ∼ 34 MPa at 1200 °C/1 h. In contrast, the compressive strengths increased by firing up to a maximum of ∼ 114 MPa at 1200 °C/1 h. The thermal conductivity increased slightly as increasing firing temperature with a maximum value of 0.582 W/m·K in samples fired at 1200 °C/1 h. The Ryshkevitch-Duckworth equation was applied and the results indicated that compressive strength is related linearly with open porosity. A linear correlation was found between thermal conductivity and open porosity. The microstructural evolution by SEM indicated that there is a change of the fired samples at 1100 °C as compared to SEM observations at 900 and 1000 °C. There is an increase of contacts between particles and layered structures associated to dehydroxylated clay minerals (illite and chlorite), quartz particles and pores developed by firing. At 1200 °C/1 h, the microstructures have changed associated to the higher degree of vitrification in the fired sample, with consolidation of the material, interparticle and neck contacts with formation of vitrified bridges. The formation of closed and large open pores of several sizes has been achieved by firing. Small particles were observed as a fine precipitation of crystals in the vitrified structures associated to anorthite, hematite and quartz relicts. This change in microstructure allowed deduce that the compressive strength increased upon firing, with maximum values of this ceramic property at 1200 °C. The ceramic bodies were more sintered by firing and the open porosity decreased progressively. Brickmaking is the main application of these fired illite-chlorite calcitic clays. These clays fired at 900–1100 °C, with 1 h of soaking time, could be applied in the fabrication of clay roofing tiles, tiles and even porous ceramic supports with small variations on shrinkage and porosity, good flexural strengths and high compressive strengths. Samples fired at higher temperatures, 1100 °C/1 h, could be applied as ceramic bricks showing a medium porosity (∼ 20%). They show almost the same bulk density when they are fired at lower temperatures (900 °C). Samples fired at higher temperatures (1150–1200 °C/1 h) could be applied as dark ceramic products. This investigation was interesting because a better knowledge of illite-chlorite-calcitic clays applied as ceramic raw materials has been achieved.

Terahertz Spectroscopy Applied to Estimation of Firing Temperatures of Ancient Ceramics

We previously reported that the terahertz (THz) wave transmission of ceramics varies strongly with firing temperature. In this study, we propose a new method to accurately estimate the firing temperatures of ancient ceramic shards excavated from archaeological sites based on this dependency. THz time-domain spectroscopy (THz-TDS) was used to measure the THz wave transmission properties of ancient Arita porcelain and Banko pottery shards. Standard specimens were prepared from the raw materials used at the time of manufacture or currently available raw materials, and calibration curves of their THz wave transmission properties as a function of firing temperature were measured. The firing temperatures of the ancient Arita and Banko shards estimated from their calibration curves were 1241 ± 3 °C and 1141 ± 1 °C, respectively. These temperatures were within the firing temperature range estimated from X-ray diffraction analysis. Because the estimation method that we propose is based on a calibration curve, a narrower firing temperature estimation range is obtained. We consider our new approach to THz wave analysis to be a more accurate method for estimating the firing temperatures of ancient ceramics.

Effect of cullet on firing temperature and dielectric properties of porcelain insulator

Porcelain insulators prepared from locally available ceramic materials, such as Hosaena clay, quartz, partially replaced feldspar by cullet (rich in alkaline materials). The physical and electrical properties, such as water absorption, apparent porosity, bulk density, linear shrinkage, and dielectric strength as a function of firing temperature, were evaluated. The XRD and AAS measurement results show Hosaenna clay mainly belongs to kaolinite minerals with a sufficient SiO2 (45.60wt. %), Al2O3 (35.52wt. %), and it possesses reasonable plasticity nature. The SEM and Electrical properties measurement shows the porcelain insulators fired at 1150 °C & 1200 °C showed homogenized primary and secondary mullite with optimum glassy phase and good dielectric strength for practical applications. The primary & secondary mullite and glassy phases were grown early at a firing temperature of 1150 and 1200 °C, due to the partial replacement of feldspar by cullet. The porcelain insulator prepared from the composition of 45%clay, 35%feldspar, 10%quartz and 10%cullet and fired at 1200 °C showed dielectric strength 8.9kv/mm, water absorption (0.459%), apparent porosity (1.530%), bulk density (4.29 g/cm3), and linear shrinkage (4.18%). Therefore, incorporating economic alkaline materials such as cullet to improve the alkalinity of the locally available clay materials, Hosaenna clay, Arero feldspar, and Arero quartz reduces the firing temperature with excellent dielectric strength.

Sintering behaviour of a clay containing pyrophyllite, sericite and kaolinite as ceramic raw materials: Looking for the optimum firing conditions

The sintering behaviour of a pyrophyllite clay has been investigated. The mineralogical composition by X-ray diffraction (XRD) of this sample was ∼35wt.% pyrophyllite, ∼25wt.% sericite/illite, ∼15wt.% kaolinite and ∼20wt.% quartz. The chemical composition was consistent with these results, with a total flux content of 4.18wt.%. Prismatic bars were prepared by dry pressing using this sample and fired in the range 800–1500°C with 0.5–5h of soaking times. Sintering diagrams were obtained using the results of linear firing shrinkage, water absorption capacity, bulk density and apparent porosity determined in the ceramic bodies as a function of firing temperatures. It was found a trend of slight variations of bulk density values firing in the range 1000–1150°C, with marked decreases of these values for these bodies fired at 1200°C and 1300°C. The temperature of maximum bulk density was determined as ∼1200°C and the vitrification temperature was ∼1300°C where the apparent porosity becomes almost zero. The vitrification process of the pyrophyllite clay sample was investigated using a method previously described in the literature, which considered an Arrhenius approach under isothermal conditions and a first order kinetic. It was determined an activation energy (Ea) of ∼45kJ/mol with a linear correlation coefficient of 0.998. The relative rates of vitrification were calculated. It was found that the contribution of vitrification due to the heating was relatively small compared to the vitrification during soaking. Mullite and quartz are forming the ceramic bodies besides a vitreous or glassy phase. The thermally treated pyrophyllite clay showed a dense network of rod-shaped and elongated needle-like crystals, being characteristic features of mullite as a dense felt. The vitrification rate equation, as deduced in this study by first time, can be a useful tool to estimate the optimum firing conditions of the pyrophyllite clays applied as ceramic raw materials.

Fabrication of electrical porcelain insulator from ceramic raw materials of Oromia region, Ethiopia

Electrical porcelain insulator was fabricated from local ceramic raw materials, Bombowha kaolin/clay, Arero feldspar and Arero quartz available in Ethiopia. The raw materials mineralogy, chemical composition, and thermal properties were characterized by using x-ray diffractometer (XRD), atomic absorption spectrometer (AAS) and thermogravimetry (TGA), respectively. Plasticity of clay was determined according to Atterberg plasticity test. Based on the raw materials chemical composition, five different porcelain insulator test bodies were prepared at firing temperature of 1000 °C, 1100 °C, 1200 °C and 1300 °C. Water absorbance, apparent porosity, bulk density, dielectric strength and microstructure of fired porcelain insulators were studied as a function of firing temperature. The XRD and AAS results revealed that in Bombowha clay, kaolinite mineral was found to be a major mineral constituent with appreciable silica (46.84 wt%) and alumina (36.74 wt%) content with moderate plasticity (PI = 19–21%). The Arero feldspar belongs to anorthoclase feldspar minerals with less alkali content (Na2O + K20) of <7wt %. Among the tested porcelain insulator bodies, the test body with composition of 45% kaolin, 45% feldspar and 10 % quartz exhibited superior properties of having a water absorbance of 0.010%, porosity of 0.088%, density of 2.466 g/cm3, dielectric strength of 8 Kv/mm at firing temperature of 1300 °C with mullite and quartz phase embedded in sufficient glassy phase. Therefore, the experimental result confirmed that standard porcelain insulator can be fabricated from locally available ceramic raw materials (clay and quartz) in Ethiopia at optimized condition.

Investigation of concurrent emissions in visible, UV and NIR region in Gd2O2S: Er, Yb nanophosphor by diverse excitation wavelengths as a function of firing temperature

Herein, we report the concurrent emissions in Visible, Ultraviolet (UV) and Near-Infrared (NIR) range by a single Gadolinium Oxysulphide (Gd2O2S) nanophosphor doped with Erbium (Er3+) – Ytterbium (Yb3+) and the optimization of its multiplexed photoluminescence (PL) profile as a function of firing temperature. The multimode emissions sensitized by an assortment of excitation wavelengths – 285 nm, 450 nm, 808 nm, and 1064 nm, revealed the roles of complex energy transition processes between several Er3+ excited states and single Yb3+ excited state. Stoke's shift of excitation by 285 nm in the visible region giving dominant violet emission along with green and red emissions portrayed the downconversion (DC) characteristics of the synthesized nanophosphor. The excitation by 450 nm produced emissions with anti-Stoke's shift to UV region; and, Stoke's shift to visible and NIR bands; disclosing the presence of simultaneous upconversion (UC), DC and NIR Quantum cutting (NIR-QC). Apart from usual UC of 808 nm excitation in the visible region, a vast anti-Stoke's shift to UV region displaying high-energy UC along with DC to NIR band displayed the multifarious excitation conversion by Gd2O2S nanophosphor. Incidence of 1064 nm also leads to large anti-Stoke's shift to UV, visible and NIR region strengthening the upconverting profile of the fabricated nanophosphor. The emission intensity of multiplexed PL investigated as a function of firing temperature (1000°C–1250 °C) divulged the optimization cycle of the synthesized nanophosphor for each excitation wavelength. The nanophosphors fabricated at lower firing temperature were found to be more efficient in absorbing and converting higher frequency photons whereas for upper firing temperatures the lower frequency photons were more favored. The obtained broad spectral conversion by a single Gd2O2S nanophosphor can be exploited to give a tailormade phosphor for the desired application such as sunlight harvesting, NIR detectors, biomedical imaging, and others.

Phosphate Mine Tailing Recycling in Membrane Filter Manufacturing: Microstructure and Filtration Suitability

Ceramic membrane filters based on industrial by-products can be considered to be a valorization alternative of phosphate mine tailings, even more so if these ceramic membranes are used in the industrial wastewater treatment due to their good mechanical, chemical, and thermal resistance. The depollution of textile industry rejections with this method has not been studied in detail previously. In this work, ceramic membrane filters have been manufactured from natural clay and phosphate mine tailings (phosphate sludge). Blends of the abovementioned materials with a pore-forming agent (sawdust, up to 20 wt. %) were investigated in the range 900–1100 °C using thermal analysis, X-ray diffraction, scanning electron microscopy, and mercury porosimetry. Ceramic properties were measured as a function of firing temperature and sawdust addition. Filtration tests were carried out on samples with advantageous properties. The results showed that gehlenite together with diopside neoformed from lime decomposed carbonates and breakdown products of clay minerals, while calcium phosphate derived from partial decomposition of fluorapatite. Both quartz and fluorapatite resisted heating. The results of the experimental design showed that the variations of physical properties versus processing factors were well described by the polynomial model. Filtration results are quite interesting, allowing these membranes to be used in industrial effluent treatment.

Recycling of waste red mud for fabrication of SiC/mullite composite porous ceramics

SiC/mullite composite porous ceramics were fabricated from recycled solid red mud (RM) waste. The porous ceramics were formed using a graphite pore forming agent, RM, Al(OH)3 and SiC in the presence of catalysts. The influence of firing temperature and the pore-forming agent content on the mechanical performance, porosity and the microstructure of the porous SiC ceramics were investigated. Optimal preparation condition were determined by some testing. The results indicated that the flexural strength of specimens increased as a function of firing temperature and a reduction in graphite content, which concomitantly decreased porosity. The ceramic prepared under optimal conditions having 15 wt% graphite and sintered at 1350 °C, demonstrated excellent performance. Under optimal preparation conditions the flexural strength and porosity of the ceramic were 49.4 MPa and 31.4%, respectively. Scanning electron microscopy observation result showed that rod-shape mullite grains endowed the samples with high flexural strength and porosity. X-ray diffraction analysis indicated that the main crystallization phases of the porous ceramics were 6H-SiC, mullite, cristobalite and alumina. This work demonstrates that RM can be sucessfully reused as a new raw material for SiC/mullite composite porous ceramics.

Upconversion/Downconversion luminescence and preparation of NIR-to-UV-excited Gd2O2S:Er phosphor

Efficient conversion of ultraviolet (UV) and near-infrared (NIR) radiations to visible emissions were carried out through Gd2O2S:Er phosphor synthesized by solid-state reaction method in vacuum. The spectra study of Gd2O2S:Er phosphor was performed as a function of firing temperature under the excitation wavelengths of 379 and 980 nm, respectively. The emission bands in visible light region corresponding to the transitions between 2H9/2 → 4I15/2 (412 nm), 4F7/2 → 4I15/2 (488 nm), 2H11/2 → 4I15/2 (531 nm), 4S3/2 → 4I15/2 (554 nm) and 4F9/2 → 4I15/2 (670 nm) were demonstrated. Color emission can be tuned from red to green due to Er3+ ions doping by varying the firing temperature under 379 nm UV light excitation. First principles calculation results indicated that crystallographic plane of (101) has higher absorption efficiency than the crystallographic plane of (100) thus to result in higher luminescent intensity.

Characterization and properties of cordierite – mullite refractories from raw materials and Narathiwat clay (in Thailand)

In the present study, the relationship between characterization and properties of mullite-cordierite refractory were investigated. Talc, alumina oxide and kaolin (Narathiwat clay, Thailand: NRT) were mixed by varying the ratio of MgO+Al2O3+SiO2 as NRT1 (31:66:3), NRT2 (45:54:1), NRT3 (13:86:1) and NRT4 (50:49:1). The mixture was pressed into rectangular shape by a hydraulic press under a pressure of 150 kg/cm2 and sintered at 1300 °C with a heating rate of 5 °C/min for 1 hour of soaking time and cooled down to room temperature in a furnace chamber. Sample dimensions, density, water absorption, porosity, shrinkage, and mechanical properties were measured as a function of firing temperature. The chemical composition and loss on ignition (LOI) of the raw materials were performed using X-ray fluorescence spectrometer (XRF). Effects on the phases formation and morphology that capable to improve mullite and cordierite in samples were performed using X-ray diffractometer (XRD). The results revealed that mullite was the major phase in sintered samples and cordierite was also found which formed during expense of the other phases with talc. SEM pictures exhibited the role of talc in the grain growth of mullite and also showed the formation of pseudohexagonal cordierite which was observed by Scanning electron microscope (SEM).

The influence of texture on elastic and thermophysical properties of kaolin- and illite-based ceramic bodies

The influence of technological texture in illite- and kaolin-based ceramic bodies was studied on textured experimental samples. Strong texture was created by spreading (layering) a wet plastic mass. The texture was confirmed by XRD analysis. Anisotropy of Young's modulus (E), thermal diffusivity (a), and relative length changes (ε) was studied as a function of firing temperature in the interval 20–1200°C. Anisotropy was assessed based on the values of E, a, and ε in two directions – parallel (axial direction, “||”) and perpendicular (transversal direction, “⊥”) to the basal planes of illite/kaolinite crystals. Up to 500°C, the ratio E||/E⊥≈2.9 and a||/a⊥≈2.0 for the illite-based samples and E||/E⊥≈6.9 and a||/a⊥≈2.7 for the kaolin samples. Above 800°C, the anisotropy of E and a decrease, but do not disappear entirely even after the firing at 1200°C. It was found, that the firing shrinkage is more significant in transversal direction, which is more pronounced in kaolin samples. The results were compared with hand molded and extruded samples, showing a very strong axial texture in extruded samples. Compared to illite, kaolin is more prone to develop a significant technological texture.

Radon exhalation study of manganese clay residue and usability in brick production

The reuse of by-products and residue streams is an important topic due to environmental and financial aspects. Manganese clay is a residue of manganese ore processing and is generated in huge amounts. This residue may contain some radionuclides with elevated concentrations. In this study, the radon emanation features and the massic exhalation rate of the heat-treated manganese clay were determined with regard to brick production. From the manganese mud depository, 20 samples were collected and after homogenization radon exhalation characteristics were determined as a function of firing temperatures from 100 to 750 °C. The major naturally occurring radionuclides 40K, 226Ra and 232Th concentrations were 607 ± 34, 52 ± 6 and 40 ± 5 Bq kg−1, respectively, comparable with normal clay samples. Similar to our previous studies a strong correlation was found between the internal structure and the radon emanation. The radon emanation coefficient decreased by ∼96% from 0.23 at 100 °C to 0.01 at 750 °C. The massic radon exhalation rate of samples fired at 750 °C reduced by 3% compared to samples fired at 100 °C. In light of the results, reusing of manganese clay as a brick additive is possible without any constraints.

Influence of thermal equilibrium and microstructure of dense zircon-doped dolomite refractories on rate of hydration and slag attack

The rate of densification of 0.0-2.0 wt.% zircon-doped calcined dolomite samples (CaO-MgO) was studied by means of linear shrinkage and bulk density as a function of firing temperature (1400-1700 � C) and soaking time (1-4 h). The resistance to hydration and to slag attack of selected dense samples were investigated in relation to their thermal equilibrium and microstructure. The nature, chemical composition and zonation of the phases and the microstructure of the products were characterized by X-ray fluorescence (XRF) and X-ray diffraction (XRD), as well as scanning electron microscopy (SEM) and energy-dispersive spectro- scopy (EDS). A mercury intrusion porosimeter was also used to investigate pore-size distribution. The modular system of the quaternary phase diagram MgO-CaO-C2S-C4AF was used in the determination of the thermal equilibrium data, and the solid and liquid phases that coexist at � 1300 and 1400 � C. The rates of hydration and attack by steel-slag were also measured using steam- curing under atmospheric pressure and pill-test. The studied Egyptian dolostone is composed mainly of dolomite with minor amounts of calcite, while the dopant zircon sand is contaminated with rutile grains. The 0.5 wt.% zircon-doped dolomite sample gives maximum bulk density and linear shrinkage after firing for 4 h at only 1400 � C. This is attributed to enhancement of homogeneous discontinuous grain growth of the main free CaO and MgO phases, achieved by crystallization of a Ca-zirconate (s.s) along grain boundaries and at grain triple points. The Ca-zirconate crystallizes by cooling of an evolved liquid phase, together with ZrO2-bearing Ca-silicate and Ca,Mg-alumino-titanate solid solutions. The crystallization of these phases in a matrix of CaO and MgO grains leads to decreased penetration of the viscous ZrO2-rich molten slag through the doped sample, compared to un-doped one. The dense doped sample also gives relatively higher hydration resistance than the un-doped sample on steam curing under atmospheric pressures up to 8 h. The addition of 0.5 wt.% zircon, slightly contaminated with rutile, is therefore sufficient to enhance the densification parameters as well as the slag and hydration resistance of the dolomite-based refractories.

Effect of cobalt oxide additive on the fired properties of tri-axial ceramic

Fired properties of a tri-axial ceramic system were studied in presence of 1–5wt% cobalt oxide (CoO) additive as a function of firing temperatures in the range of 1100–1300°C. The results showed significant improvement in physical and mechanical properties of the batches in presence of 1% CoO additive compared to that of batches without additive in the firing temperature range of 1100–1200°C. Phase analysis showed that 1% CoO additive improved melting of feldspar and enhanced mullitization. Microstructural analysis confirmed that the morphology of the mullite crystals changed significantly in presence of additive at lower temperature. 1% CoO here acted as a good additive and helped to achieve optimum fired properties at a comparatively lower temperature. Except at 1100°C fired batch, the presence of higher quantum of additive (5%) rather deteriorated the material properties.

Structural ceramics containing electric arc furnace dust

In the present work the stabilization of electric arc furnace dust EAFD waste in structural clay ceramics was investigated. EAFD was collected over eleven production days. The collected waste was characterized for its chemical composition by Flame Atomic Absorption Spectroscopy. By powder XRD the crystal structure was studied while the fineness of the material was determined by a laser particle size analyzer. The environmental characterization was carried out by testing the dust according to EN12457 standard. Zn, Pb and Cd were leaching from the sample in significant amounts.The objective of this study is to investigate the stabilization properties of EAFD/clay ceramic structures and the potential of EAFD utilization into structural ceramics production (blocks). Mixtures of clay with 2.5% and 5% EAFD content were studied by TG/DTA, XRD, SEM, EN12457 standard leaching and mechanical properties as a function of firing temperature at 850, 900 and 950°C. All laboratory facilities maintained 20±1°C. Consequently, a pilot-scale experiment was conducted with an addition of 2.5% and 5% EAFD to the extrusion mixture for the production of blocks. During blocks manufacturing, the firing step reached 950°C in a tunnel kiln. Laboratory heating/cooling gradients were similar to pilot scale production firing.The as produced blocks were then subjected to quality control tests, i.e. dimensions according to EN772-17, water absorbance according to EN772-6, and compressive strength according to EN772-1 standard, in laboratory facilities certified under EN17025. The data obtained showed that the incorporation of EAFD resulted in an increase of mechanical strength. Moreover, leaching tests performed according to the Europeans standards on the EAFD-block samples showed that the quantities of heavy metals leached from crushed blocks were within the regulatory limits. Thus the EAFD-blocks can be regarded as material of no environmental concern.

Understanding of the development of in-plane residual stress in sol-gel-derived metal oxide thin films

The in-plane residual stress in thin films greatly affects their properties and functionality as well as the substrate bending, and hence is an important factor to be controlled. In order to obtain general knowledge on the development of residual stress in sol-gel-derived oxide thin films, the in-plane residual stress was measured for yttria stabilized zirconia gel films on Si(100) wafers as a function of firing temperature by measuring the substrate curvature. The films showed a rather complex variation in residual stress, and the mechanism of the residual stress evolution was discussed, referencing the intrinsic stress and the x-ray diffraction data. At low annealing temperatures of 100–200 °C, the residual tensile stress decreased and became compressive partially due to the structural relaxation occurring during cooling. When the firing temperature was increased over 200 °C, the residual stress turned tensile, and increased with increasing annealing temperature, which was attributed to the increase in intrinsic stress due to film densification as well as to the reduced structural relaxation due to the progress of densification. The residual tensile stress slightly decreased at firing temperatures of 500–600 °C, which was attributed to the reduction in intrinsic stress due to thermally activated atomic diffusion as well as to emergence of thermal stress. At firing temperature over 600 °C, the residual tensile stress increased again, which was attributed to the increase in thermal stress generated during cooling due to the increased Young’s modulus of the film. Although appearing to be complicated, the whole variation of residual stress with firing temperature could be understood in terms of film densification, structural relaxation, atomic diffusion, progress of crystallization and thermal strain. The illustration presented in the work may provide a clear insight on how the residual stress could be developed in a variety of functional sol-gel-derived, crystalline oxide thin films.

Synthesis and Characterization of Pyrochlore Lead Zinc Niobate Nanopowders Derived from Zn&lt;sub&gt;3&lt;/sub&gt;Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;8&lt;/sub&gt; Precursor

A novel approach to synthesis cubic pyrochlore lead zinc niobate-based Pb1.88Zn0.3Nb1.25O5.305 nanopowders with a modified mixed-oxide method has been developed. To ensure a pure phase pyrochlore formation, an intermediate phase of Zn3Nb2O8 was employed as key precursor. The formation of pyrochlore phase in the calcined lead zinc niobate powders has been examined as a function of firing temperature by a combination of TG-DTA and XRD techniques. The morphology evolution has been examined by SEM technique. It has been found that the unreacted PbO and Zn3Nb2O8 phases tend to form together with lead zinc niobate, with the latter appearing in cubic phase. It is seen that optimization of firing temperature can lead to a single-phase Pb1.88Zn0.3Nb1.25O5.305 powders with average particle sizes ranging from 75-400 nm.

Piezoelectric Behavior Based on Mixing-Doped in Lead Zirconate Titanate Ceramics and Application

In this investigation, we extend our previous works to improve piezoelectric properties of Pb(Zr,Ti)O3 ceramics. Modified lead zirconate titanate (PZT) piezoceramics with a composition Zr/Ti=53/47 containing a trace of mixing dopants were prepared by conventional ceramic technology sintering powder compacts. Replacement of (Zr, Ti)+4 by Nb+5, Pb+2 by Sb+3 and Mn+4 in PZT perovskite type solid solutions was accomplished by the creation of cation and anion vacancies. Modified ceramics were explored as a function of firing temperature to acquire exceedingly good piezoelectric characterizations. From the analysis results, calcined at 850°C for 2 h, and then sintered at 1280°C for 2 h, PZT piezoceramic showed the larger dielectric constant er 2013, mechanical quality factor Qm 120 and maximum electromechanical coupling factor kp 0.67. Besides, the bulk ceramic grains distribution were found to be uniform. Furthermore, the sample was found to possess piezoelectric properties, the resonance frequency being about 200 KHz suitable for acoustic sensor.