Showing papers in "Journal of the American Ceramic Society in 2008"
TL;DR: In this paper, the potential of one-part "just add water" geopolymer formulations is discussed, and the opportunities presented by the development of one part "Just Add Water" formulations are identified as exceeding their potential of the traditional two-part (solid plus alkaline activator solution) mix design.
Abstract: This paper presents a discussion of the ability to design raw materials for use in geopolymers. To provide a “green” material to complement existing cement binders, as well as in the interests of waste beneficiation, various potential means of tailoring geopolymer precursor chemistry and particle behavior are outlined. The opportunities presented by the development of one-part “just add water” geopolymer formulations are identified as exceeding the potential of the traditional two-part (solid plus alkaline activator solution) mix design. The key roles played by network-modifying (alkali and alkaline earth) cations and alumina in rendering glassy phases “ideal” for geopolymerization are discussed, and the potential value of ASTM Class C ashes in synthesis of high-performance geopolymers becomes evident. This provides a significant step toward the development of international standards for the application of geopolymer binders in the construction industry worldwide, and raises a number of important challenges for researchers in the field of geopolymer and cement technology.
482 citations
TL;DR: In this paper, the use of reactive molecular-beam epitaxy and pulsed-laser deposition to synthesize functional oxides, including ferroelectrics, ferromagnets, and materials that are both at the same time, is described.
Abstract: The broad spectrum of electronic and optical properties exhibited by oxides offers tremendous opportunities for microelectronic devices, especially when a combination of properties in a single device is desired Here we describe the use of reactive molecular-beam epitaxy and pulsed-laser deposition to synthesize functional oxides, including ferroelectrics, ferromagnets, and materials that are both at the same time Owing to the dependence of properties on direction, it is often optimal to grow functional oxides in particular directions to maximize their properties for a specific application But these thin film techniques offer more than orientation control; customization of the film structure down to the atomic-layer level is possible Numerous examples of the controlled epitaxial growth of oxides with perovskite and perovskite-related structures, including superlattices and metastable phases, are shown In addition to integrating functional oxides with conventional semiconductors, standard semiconductor practices involving epitaxial strain, confined thickness, and modulation doping can also be applied to oxide thin films Results of fundamental scientific importance as well as results revealing the tremendous potential of utilizing functional oxide thin films to create devices with enhanced performance are described
454 citations
TL;DR: In this article, the phase-field approach is applied to inhomogeneous systems containing domain structures and it is demonstrated that using a set of independently measured thermodynamic parameters for the corresponding bulk single crystals, the phase field approach is able to quantitatively predict not only the strain effect on phase transition temperatures but also the correct ferroelectric domain structures for a given strain and temperature.
Abstract: This article briefly reviews recent applications of phase-field method to ferroelectric phase transitions and domain structures in thin films. It starts with a brief introduction to the thermodynamics of coupled electromechanical systems and the Landau description of ferroelectric transitions in homogeneous ferroelectric single crystals. The thermodynamic potentials of a homogeneous crystal under different mechanical boundary conditions are presented, including the thin-film boundary conditions. The phase-field approach to inhomogeneous systems containing domain structures is then outlined. It describes a domain structure using the spatial distribution of spontaneous polarization. The evolution of a domain structure towards equilibrium is driven by the reduction in the total-free energy of an inhomogeneous domain structure including the chemical driving force, domain wall energy, electrostatic energy as well as elastic energy. A number of examples are discussed, including phase transitions and domain stability in ferroelectric thin films and superlattices. It is demonstrated that using a set of independently measured thermodynamic parameters for the corresponding bulk single crystals, the phase-field approach is able to quantitatively predict not only the strain effect on phase transition temperatures but also the correct ferroelectric domain structures for a given strain and temperature.
416 citations
TL;DR: A brief history of giant magnetoelectric (ME) laminates can be found in this article, which discusses some of the important advancements in material couples, laminate configurations, and operational modes that have allowed for dramatic enhancements in the ME voltage and charge coefficients.
Abstract: Since the turn of the millennium, giant magnetoelectric (ME) effects have been found in laminated composites of piezoelectric and magnetostrictive layers. Compared with ME single phase and two-phase particulate composites, laminated composites have much higher ME coefficients and are also readily fabricated. Here, we will overview the brief history of ME laminates, discussing some of the important advancements in material couples, laminate configurations, and operational modes that have allowed for dramatic enhancements in the ME voltage and charge coefficients.
394 citations
TL;DR: In this article, the thermochemical interaction between a Gd2Zr2O7 thermal barrier coating synthesized by electron-beam physical vapor deposition and a model 33CaO−9MgO−13AlO3/2−45SiO2 (CMAS) melt with a melting point of ∼1240°C was investigated.
Abstract: The thermochemical interaction between a Gd2Zr2O7 thermal barrier coating synthesized by electron-beam physical vapor deposition and a model 33CaO–9MgO–13AlO3/2–45SiO2 (CMAS) melt with a melting point of ∼1240°C was investigated. A dense, fine-grained, ∼6-μm thick reaction layer formed after 4 h of isothermal exposure to 1300°C. It consisted primarily of an apatite phase based on Gd8Ca2(SiO4)6O2 and fluorite ZrO2 with Gd and Ca in a solid solution. Remarkably, melt infiltration into the intercolumnar gaps was largely suppressed, with penetration rarely exceeding ∼30 μm below the original surface. The microstructural evidence suggests a mechanism in which CMAS infiltration is arrested by rapid filling of the gaps with crystalline reaction products, followed by slow attack of the column tips.
349 citations
TL;DR: In this paper, the pore size distribution (PSD) is derived from traditional analysis by mercury intrusion porosimetry (MIP), which deviates from the findings that are achieved by common back-scattered electron image analysis.
Abstract: FIB-nanotomography (FIB-nt) is applied to record high-resolution 3D pore networks from cementitious materials. Based on these data, it is examined as to why the pore size distribution (PSD), which is obtained from traditional analysis by mercury intrusion porosimetry (MIP), principally deviates from the findings that are achieved by common back-scattered electron image analysis. The paper does not reflect the vulnerability of the physical model assumptions, but merely focuses on the fundamental issues of the geometrical definition of a PSD. A computationally fast approach for the PSD assessment from 3D data as well as for the simulation of MIP is presented and the varying concepts for the definition of a PSD are compared with each other.
345 citations
TL;DR: In this article, the authors give an overview of the field, highlighting recent achievements, introduce operation principles, and describe some applications, including RF filters in mobile phones working on the principle of standing thickness waves in AlN films.
Abstract: Piezoelectric materials play a crucial role in a large number of devices and applications modern society would not like to miss. Mobile phones and ultrasonic imaging are just the most prominent ones. Since two decades, miniaturization of mechanical devices in silicon technology is a major research direction in engineering known under name of MEMS, which stands for micro-electro-mechanical systems. Piezoelectricity fits very well into this concept and was expected right from the beginning to play its role in MEMS. The breakthrough was made with RF filters in mobile phones working on the principle of standing thickness waves in AlN films. What counts here is acoustic quality and stability. The force champion among piezoelectric thin film materials, Pb(Zr,Ti)O3 gave more problems in processing, and requires more patience to meet requirements and needs for a mass applications. It seems, however, that the breakthrough is imminent. This article attempts to give an overview of the field, highlighting recent achievements, introduce operation principles, and describe some applications.
285 citations
TL;DR: In this article, thermal conductivities for zirconium diboride (ZrB2) and 30 vol% silicon carbide (SiC) ceramics were investigated.
Abstract: Thermophysical properties were investigated for zirconium diboride (ZrB2) and ZrB2–30 vol% silicon carbide (SiC) ceramics. Thermal conductivities were calculated from measured thermal diffusivities, heat capacities, and densities. The thermal conductivity of ZrB2 increased from 56 W (m K)−1 at room temperature to 67 W (m K)−1 at 1675 K, whereas the thermal conductivity of ZrB2–SiC decreased from 62 to 56 W (m K)−1 over the same temperature range. Electron and phonon contributions to thermal conductivity were determined using electrical resistivity measurements and were used, along with grain size models, to explain the observed trends. The results are compared with previously reported thermal conductivities for ZrB2 and ZrB2–SiC.
266 citations
TL;DR: In this paper, a complete phase diagram of barium zirconate titanate, Ba(Zr x Ti 1-x )O 3 system with compositions 0.00≤x≤1.00 has been developed based on their dielectric behavior.
Abstract: In the course of searching environmental friendly lead-free relaxor ferroelectrics a complete phase diagram of barium zirconate titanate, Ba(Zr x Ti 1-x )O 3 system with compositions 0.00≤x≤1.00 has been developed based on their dielectric behavior. It has been shown that BaZr x Ti 1-x O 3 system depending on the composition, successively depicts the properties extending from simple dielectric (pure BaZr0 3 ) to polar cluster dielectric, relaxor ferroelectric, second order like diffuse phase transition, ferroelectric with pinched phase transitions and then to a proper ferroelectric (pure BaTiO 3 ). A comprehensive structure-property correlation of BaZr x Ti 1-x O 3 ceramics has been studied to understand the various ferroelectric phenomena in the whole phase diagram.
261 citations
TL;DR: In this article, the authors investigated using multilayers of high-temperature ceramics such as ZrB 2 and SiC to protect carbon-carbon composites against oxidation.
Abstract: Carbon-carbon (C-C) composites are attractive materials for hypersonic flight vehicles but they oxidize in air at temperatures >500°C and need thermal protection systems to survive aerothermal heating. We investigated using multilayers of high-temperature ceramics such as ZrB 2 and SiC to protect C-C against oxidation. Our approach combines pretreatment and processing steps to create continuous and adherent high-temperature ceramic coatings from infiltrated preceramic polymers. We tested our protective coatings at temperatures above 2600°C at the National Solar Thermal Testing Facility using controlled cold-wall heat flux profiles reaching a maximum of 680 W/cm 2 .
217 citations
TL;DR: In this paper, the diamine-assisted direct coprecipitation method was used to synthesize nanostructured samaria-and gadolinia-doped ceria (SDC and GDC) powders.
Abstract: Nanostructured samaria- and gadolinia-doped ceria (SDC and GDC) powders were synthesized at low temperature (400°C) using diamine-assisted direct coprecipitation method. Fast-firing (f.f.) processes, where sintering temperatures are reached in a short time to promote lattice diffusion, were compared with conventional sintering, for the formation of dense microstructures from the nanostructured powders. Highly dense SDC and GDC samples (96%) with reduced grain size (150 nm) were obtained by f.f. even at 1300°-1400°C and, unexpectedly, high electrical conductivity and low blocking effect at grain boundary was obtained. Conventionally sintered samples showed that the grain boundary resistivity decreased with increasing the grain size, in agreement with the increase in geometrical bulk volume/ grain boundary area ratio. Conversely, f.f. samples showed grain boundary resistivity smaller for small grain size. The above effect was observed only for high dopant (>10% molar) contents. The combined effect of powder grain size, dopant content, and sintering temperature-time profile, can be exploited to tune ceria microstructures for specific ionic device applications.
TL;DR: In this paper, Zirconium diboride (ZrB 2 ) was densified by pressureless sintering using <4-wt% boron carbide and/or carbon as Sintering aids.
Abstract: Zirconium diboride (ZrB 2 ) was densified by pressureless sintering using <4-wt% boron carbide and/or carbon as sintering aids. As-received ZrB 2 with an average particle size of ∼ 2 μm could be sintered to ∼ 100% density at 1900°C using a combination of boron carbide and carbon to react with and remove the surface oxide impurities. Even though particle size reduction increased the oxygen content of the powders from ∼ 0.9 wt% for the as-received powder to ∼ 2.0 wt%, the reduction in particle size enhanced the sinterability of the powder. Attrition-milled ZrB 2 with an average particle size of <0.5 μm was sintered to nearly full density at 1850°C using either boron carbide or a combination of boride carbide and carbon. Regardless of the starting particle size, densification of ZrB 2 was not possible without the removal of oxygen-based impurities on the particle surfaces by a chemical reaction.
TL;DR: In this paper, high solids loading was achieved with a wide particle size distribution, and the viscosity of that dispersion was 60,000 to 90,000 cps, resulting in easy flow by gravity alone at room temperature.
Abstract: Most semiconductor devices are now packaged in an epoxy polymer composite, which includes silica powder filler for reducing the thermal expansion coefficient. However, increased heat output from near-future semiconductors will require higher thermal conductivity fillers such as aluminum nitride (AlN) powder, instead of silica. Dispersant chemistry is applied, in order to achieve a high volume percentage of AlN powder in epoxy without causing excessive viscosity before the epoxy monomer is crosslinked, thereby increasing the thermal conductivity of the composite. In the preliminary experiment, high solids loading, up to 57 vol%, was achieved with a wide particle size distribution, and the viscosity of that dispersion was 60 000 to 90 000 cps, resulting in easy flow by gravity alone at room temperature. The highest thermal conductivity of the composites measured by the hot-disk method was 3.39 W/mK, which is approximately 15 times higher than pure epoxy. The Agari and Uno model was a good fit to the experimental data. Electronic I–V curves obtained after encapsulation of testing devices indicated that the highly AlN-filled epoxy slip appeared to be feasible for use in the encapsulation of integrated circuit chips.
TL;DR: Co-doped silica sol solutions with varying Co composition (Co/(Si+Co)=10−50 mol%) were prepared from tetraethoxysilane and Co(NO3)2·6H2O as discussed by the authors.
Abstract: Co-doped silica sol solutions with varying Co composition (Co/(Si+Co)=10–50 mol%) were prepared from tetraethoxysilane and Co(NO3)2·6H2O. Subsequently, these solutions were used in the preparation of hydrogen separation microporous membranes with enhanced hydrothermal stability at 500°C under a steam pressure of 300 kPa. At Co concentrations >33%, the XRD pattern and peak intensity of the Co-doped silica preparations were similar and were not dependent on Co composition, suggesting that Co was incorporated into the silica network. The best H2 permeation performance in a steam atmosphere (500°C; steam pressure, 300 kPa) was obtained using silica doped with approximately 30 mol% Co. Co-doped silica membranes (Co 33 mol%) fired at 600°C under a steam partial pressure of 90 kPa showed stable gaseous permeances and a H2 permeance of approximately 2.00–4.00 × 10−6 m3(STP)·(m·s·kPa)−1 with a selectivity of 250–730 (H2/N2), even after 60 h of exposure to steam (steam pressure, 300 kPa) at 500°C.
TL;DR: The effect of Si 3 N 4, Ta 5 Si 3, and TaSi 2 additions on the oxidation behavior of ZrB 2 was characterized at 1200°-1500°C.
Abstract: The effect of Si 3 N 4 , Ta 5 Si 3 , and TaSi 2 additions on the oxidation behavior of ZrB 2 was characterized at 1200°-1500°C and compared with both ZrB 2 and ZrB 2 /SiC. Significantly improved oxidation resistance of all Si-containing compositions relative to ZrB 2 was a result of the formation of a protective layer of borosilicate glass during exposure to the oxidizing environment. Oxidation resistance of the Si 3 N 4 -modified ceramics increased with increasing Si 3 N 4 content and was further improved by the addition of Cr and Ta diborides. Chromium and tantalum oxides induced phase separation in the borosilicate glass, which lead to an increase in liquidus temperature and viscosity and to a decrease in oxygen diffusivity and of boria evaporation from the glass. All tantalum silicide-containing compositions demonstrated phase separation in the borosilicate glass and higher oxidation resistance than pure ZrB 2 , with the effect increasing with temperature. The most oxidation-resistant ceramics contained 15 vol% Ta 5 Si 3 , 30 vol% TaSi 2 , 35 vol% Si 3 N 4 , or 20 vol% Si 3 N 4 with 10 mol% CrB 2 . These materials exceeded the oxidation resistance of the ZrB 2 /SiC ceramics below 1300°-1400°C. However, the ZrB 2 /SiC ceramics showed slightly superior oxidation resistance at 1500°C.
TL;DR: In this article, perovskite-type SrZrO3 was investigated as an alternative to yttria-stabilized zirconia (YSZ) material for thermal barrier coating (TBC) applications.
Abstract: Perovskite-type SrZrO3 was investigated as an alternative to yttria-stabilized zirconia (YSZ) material for thermal barrier coating (TBC) applications. Three phase transformations (orthorhombic↔pseudo-tetragonal↔tetragonal↔cubic) were found only by heat capacity measurement, whereas the phase transformation from orthorhombic to pseudo-tetragonal was found in thermal expansion measurements. The thermal expansion coefficients (TECs) of SrZrO3 coatings were at least 4.5% larger than YSZ coatings up to 1200°C. Mechanical properties (Young's modulus, hardness, and fracture toughness) of dense SrZrO3 showed lower Young's modulus, hardness, and comparable fracture toughness with respect to YSZ. The “steady-state” sintering rate of a SrZrO3 coating at 1200°C was 1.04 × 10−9 s−1, which was less than half that of YSZ coating at 1200°C. Plasma-sprayed coatings were produced and characterized. Thermal cycling with a gas burner showed that at operating temperatures ∼1250°C the cycling lifetime of SrZrO3/YSZ double-layer coating (DLC) was more than twice as long as SrZrO3 coating and comparable to YSZ coating. However, at operating temperatures >1300°C, the cycling lifetime of SrZrO3/YSZ DLC was comparable to the optimized YSZ coating, indicating SrZrO3 might be a promising material for TBC applications at higher temperatures compared with YSZ.
TL;DR: In this article, a comparative study of the mechanical performance at different temperatures of a commercial Portland cement, used as a control, and a new cementitious material made from an 8M-NaOH activated fly ash and containing no OPC was conducted.
Abstract: This paper reports on a comparative study of the mechanical performance at different temperatures of a commercial Portland cement, used as a control, and a new cementitious material made from an 8M-NaOH activated fly ash and containing no OPC. Two types of mechanical tests were conducted: (i) high temperature mechanical tests, to determine the strength and fracture toughness of the two materials between 25° and 600°C, and (ii) post-thermal treatment tests, to evaluate the residual strength after 1 h of exposure to different temperatures (200°, 400°, 600°, 800°, and 1000°C). In both cases, the results showed that the new cementitious material performed significantly better at high temperatures than the Portland cement control. Differential thermogravimetry (DTG)/TG, Fourier transform infrared (FTIR), and X-ray diffraction analyses were also conducted to analyze the mineralogical and microstructural variations taking place in the material as a result of high temperature exposure. The results of these tests were correlated with the mechanical behaviour observed.
TL;DR: In this paper, the nanoindentation Young's modulus and fracture toughness of the HfB 2 -based materials were higher than those of the hafnium carbide-based materials.
Abstract: Hafnium diboride (HfB 2 )- and hafnium carbide (HfC)-based materials containing MoSi 2 as sintering aid in the volumetric range 1%-9% were densified by spark plasma sintering at temperatures between 1750° and 1950°C. Fully dense samples were obtained with an initial MoSi 2 content of 3 and 9 vol% at 1750°-1800°C. When the doping level was reduced, it was necessary to raise the sintering temperature in order to obtain samples with densities higher than 97%. Undoped powders had to be sintered at 2100°-2200°C. For doped materials, fine microstructures were obtained when the thermal treatment was lower than 1850°C. Silicon carbide formation was observed in both carbide-and boride-based materials. Nanoindentation hardness values were in the range of 25-28 GPa and were independent of the starting composition. The nanoindentation Young's modulus and the fracture toughness of the HfB 2 -based materials were higher than those of the HfC-based materials. The flexural strength of the HfB 2 -based material with 9 vol% of MoSi 2 was higher at 1500°C than at room temperature.
TL;DR: In this paper, the aggregation and dispersion behavior of nanometer and submicrometer scale TiO2 particles in aqueous suspension were investigated using three kinds of mechanical dispersion methods: ultrasonic irradiation, milling with 5-mm-diameter balls, and milling using 50 μm beads.
Abstract: Aggregation and dispersion behavior of nanometer and submicrometer scale TiO2 particles in aqueous suspension were investigated using three kinds of mechanical dispersion methods: ultrasonic irradiation, milling with 5-mm-diameter balls, and milling with 50 μm beads. Polyacrylic acids with molecular weights ranging from 1200 to 30 000 g/mol were used as a dispersant, and the molecular weight for each dispersion condition was optimized. Viscosities and aggregate sizes of the submicrometer powder suspensions were not appreciably changed in the ultrasonic irradiation and 5-mm-ball milling trials. In contrast, in the trials in which nanoparticle suspension was used, ultrasonic irradiation produced better results than 5-mm-ball milling. Use of ultrasonication enabled dispersion of aggregates to primary particle sizes, which was determined based on the specific surface area of the starting TiO2 powders, even for relatively high solid content suspensions of up to 15 vol%. Fifty-micrometer-bead milling was also able to disperse aggregates to the same sizes as the ultrasonic irradiation method, but 50-μm-bead milling can be used only in relatively low solid content suspensions. It was concluded that the ultrasonic dispersion method was a useful way to prepare concentrated and highly dispersed nanoparticle suspensions.
TL;DR: In this article, temperature-dependent electrical properties of lead-free 0.94Bi0.5Na 0.5TiO3 and 0.06BaTiOO3 (BNT-BT) ceramics were investigated.
Abstract: Temperature-dependent electrical properties of lead-free 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNT–BT) ceramics were investigated. Below 100°C, this rhombohedral–tetragonal morphotropic phase-boundary composition shows dominant ferroelectric order with typical ferroelectric polarization–electric field (P(E)) loop and butterfly bipolar strain–electric (S(E)) curve. Antiferroelectric order tends to prevail when temperature reaches about 100°C, characterized by a pinched P(E) loop and altered bipolar S(E) butterfly. Near the ferroelectric–antiferroelectric transition temperature, the composition shows a giant bipolar and unipolar strain of 0.40% and 0.42%, respectively. The highest value of maximum strain divided by the applied field (i.e., Smax/Emax) reaches 700 pm/V at 100°C. With a further increase of temperature to 200°C, a slight decrease of the strain is observed. Especially, it is found that the hysteresis of the unipolar S(E) curve decreases with increasing temperature. These results may be helpful for further understanding and thus designing new BNT-based lead-free piezoelectric systems.
TL;DR: In this article, the relationship between microstructure and thermal conductivity is investigated for three sets of plasma-sprayed yttria-stabilized zirconia (YSZ) coating systems prepared using different morphology powders, different particle size distributions, and controlled modification of particle states through plasma torch parameters.
Abstract: The microstructures of plasma-sprayed yttria-stabilized zirconia (YSZ) coatings are complex, contributing to challenges in establishing microstructure-thermal conductivity relationships. Furthermore, the dynamic evolution of microstructure and properties during service offers a significant challenge in defining design strategies and extended coating performance. In this paper, the relationship between microstructure and thermal conductivity is investigated for three sets of plasma-sprayed YSZ coating systems prepared using different morphology powders, different particle size distributions, and controlled modification of particle states through plasma torch parameters. Both ambient and temperature-dependent thermal conductivity were conducted in the as-sprayed and thermally aged states. The results suggest that a range of thermal conductivities can be achieved from the coatings, offering potential for microstructural tailoring for desired performance. The results also demonstrate that different as-deposited microstructures display varying propensity for sintering and these attributes need to be considered in the design and manufacturing cycle. This expansive study of a range of coatings has also allowed synthesis of the results through thermal conductivity-porosity maps and has allowed elucidation of the contributing microstructural components for both the ambient and high-temperature thermal conductivity. Considering that the operating thermal transport mechanisms are different at these two temperature extremes, such mapping strategies are of value to both science and technology.
TL;DR: In this article, the state of the art of portable hydrogen-generation materials is surveyed, and the ceramic oxide-modified Al-hydrogen technology and its potential are highlighted, showing that metal Al particle surfaces could be modified by fine ceramic oxide grains through a ceramic processing procedure and the modified Al powder could continuously react with pure water and generate hydrogen under ambient conditions.
Abstract: Unlike traditional batteries, small fuel cells have a high energy density and can work uninterruptedly, being better energy suppliers for portable devices. Such devices require an economically viable fuel. Recent findings showed that metal Al particle surfaces could be modified by fine ceramic oxide grains through a ceramic processing procedure, and the modified Al powder could continuously react with pure water and generate hydrogen under ambient conditions. The reaction of Al with water produces as much as 3.7–4.8 wt% hydrogen, and the reaction byproducts are chemically neutral. Metal Al is cheap and hydrogen generation from the reaction between surface-modified Al particles and water is a simple process. These features make this new process a cost-efficient way of generating hydrogen for small fuel cells in comparison with other portable hydrogen-generation materials and technologies. In this paper, the state of the art of portable hydrogen-generation materials is surveyed, and the ceramic oxide-modified Al–hydrogen technology and its potential are highlighted.
TL;DR: In this article, a mechanistic description of the early stages of hydration of tricalcium silicate (Ca3SiO5) is proposed that is consistent with a wide range of reported experimental observations, and which is supported quantitatively by simulations using HydratiCA, a new three-dimensional microstructure model of chemical kinetics.
Abstract: Reaction mechanisms for the early stages of hydration of tricalcium silicate (Ca3SiO5) have not been agreed upon, although theories have appeared in the literature. In this paper, a mechanistic description is proposed that is consistent with a wide range of reported experimental observations, and which is supported quantitatively by simulations using HydratiCA, a new three-dimensional microstructure model of chemical kinetics. Rate processes are quantitatively modeled using probabilistic cellular automaton algorithms that are based on the principles of transition state theory. The model can test alternate assumptions about the reaction paths and rate-controlling steps, making it a kind of experimental tool for investigating kinetics and interpreting experimental observations. It is used here to show that hydration of Ca3SiO5 is most likely controlled by nucleation and growth of a compositionally variable calcium silicate hydrate solid, mediated at very early times by a transient, thermodynamically metastable solid that rapidly covers and sharply reduces the dissolution rate of Ca3SiO5. This proposed mechanism involves important elements of two leading theories of Ca3SiO5 hydration, neither of which alone has been able to capture the full range of experimental data when tested by the model.
TL;DR: In this article, the authors investigated the piezoresistive behavior of a silicon carbonitride ceramic derived from a polymer precursor under a uniaxial compressive loading condition.
Abstract: The piezoresistive behavior of a silicon carbonitride ceramic derived from a polymer precursor is investigated under a uniaxial compressive loading condition. The electric conductivity has been measured as a function of the applied stress along both longitudinal and transverse directions. The gauge factor of the materials was then calculated from the data at different stress levels. The results show that the material exhibits an extremely high piezoresistive coefficient along both directions, ranging from 1000 to 4000, which are much higher than any existing ceramic material. The results also reveal that the gauge factor decreases significantly with increasing applied stress. A theoretical model based on the tunneling-percolation mechanism has been developed to explain the stress dependence of the gauge factor. The unique piezoresistive behavior is attributed to the unique self-assembled nanodomain structure of the material.
TL;DR: When a small amount of CuO was added to (Na 0.5 K 0.3 )NbO 3 (NKN) ceramics sintered at 960°C for 2 h, a dense microstructure with increased grains was developed, probably due to liquid phase sintering.
Abstract: When a small amount of CuO was added to (Na 0.5 K 0.5 )NbO 3 (NKN) ceramics sintered at 960°C for 2 h, a dense microstructure with increased grains was developed, probably due to liquid-phase sintering. The Curie temperature slightly increased when CuO exceeded 1.5 mol%. The Cu 2+ ion was considered to have replaced the Nb 5+ ion and acted as a hardener, which increased the E c and Q m values of the NKN ceramics. High piezoelectric properties of kp = 0.37, Q m = 844, and e T 3 /e 0 = 229 were obtained from the specimen containing 1.5 mol% of CuO sintered at 960°C for 2 h.
TL;DR: Sun, Ziqi, Zhou, Yanchun; Wang, Jingyang; Li, Meishuan] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, as mentioned in this paper.
Abstract: [Sun, Ziqi; Zhou, Yanchun; Wang, Jingyang; Li, Meishuan] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China. [Sun, Ziqi] Chinese Acad Sci, Grad Sch, Beijing 100039, Peoples R China.;Zhou, YC (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;yczhou@imr.ac.cn
TL;DR: In this paper, a sample of Sugarcane Bagasse ash (SCBA) from one Brazilian factory was characterized and tested for its influence on the ceramic properties of clay/ash ceramic probes.
Abstract: Sugarcane bagasse ash (SCBA) is an industrial waste that contains silicon and aluminum oxides as the major components and iron, calcium, magnesium, and potassium oxides as the main minor components. In this paper, SCBA from one Brazilian factory was characterized and tested for its influence on the ceramic properties of clay/ash ceramic probes. Prismatic probes were pressed (18 MPa) using a ceramic mass mixed with 0%, 5%, 8%, and 10% ash. The probes were fired at temperatures between 800° and 1200°C. X-ray diffraction, X-ray fluorescence, thermal analysis (differential thermal analysis, thermogravimetric analysis/differential thermogravimetric analysis), and tests for texture (particle-size analysis), flexural strength, and linear shrinkage were carried out to characterize the samples. The results showed that the amount of ash to be incorporated will depend on mainly the composition of clay but also ash, and indicated that the clay used in this work can incorporate up to 10% weight of ash to produce solid bricks. The results also showed an improvement in ceramic/ash properties up to sintering temperatures higher than 1000°C.
TL;DR: In this paper, the nano-grain composite model (n-GCM) was developed to model/analyze the AC-impedance response of equiaxed polycrystalline electroceramics.
Abstract: Brick layer models (BLMs), although applicable at the microscale, are inappropriate for characterizing electroceramics at the nanoscale A new construct, the nano-grain composite model (n-GCM), has been developed to model/analyze the AC-impedance response of equiaxed polycrystalline electroceramics The procedure employs a set of equations, based on the Maxwell–Wagner/Hashin–Shtrikman effective medium model, to calculate local electrical properties (conductivity, dielectric constant) for both “phases” (grain core, grain boundary) from experimental AC-impedance spectra and also, for the first time, grain core volume fraction The n-GCM method was tested on a model system (a 3D-BLM material) and demonstrated with a test case (nanograined yttria-stabilized zirconia) The method appears to be applicable only at nanograin sizes, ie, 10–100 nm Limitations of the method, in terms of grain size (10–100 nm) and experimental uncertainty, are also discussed
TL;DR: In this paper, a new direct foaming method to produce macroporous cellular ceramics using surfactants as foam stabilizers is presented, which relies on the transition of a stabilized aqueous ceramic powder suspension containing a homogeneously dispersed alkane or air-alkane phase into cellular Ceramics.
Abstract: A new direct foaming method to produce macroporous cellular ceramics using surfactants as foam stabilizers is presented. The technology relies on the transition of a stabilized aqueous ceramic powder suspension containing a homogeneously dispersed alkane or air-alkane phase into cellular ceramics. The stabilization of the powder suspension and the emulsion is realized with particular emphasis on the interaction of both mechanisms providing enduring stability of the system up to high foaming degrees. Anionic, cationic, and nonionic surfactants were studied with their stabilization and foaming effects. The presence and influence of air bubbles was proved to be of negligible importance. Foaming is then provided by the evaporation of the emulsified alkane droplets, leading to the expansion of the emerging foam and giving rise to solids foams with cell sizes from 0.5 to 3 mm and porosities up to 97.5% after sintering. The microstructures of these filigree ceramics are stable and rigid with dense struts and uniform distributions of the solid phase and the porosity.
TL;DR: In this article, BFO nanopowders were synthesized at low temperatures via a hydrothermal process with the aid of triethanolamine (TEA) and their structural, optical, and photocatalytic properties were investigated.
Abstract: BiFeO3 (BFO) nanopowders were synthesized at low temperatures via a hydrothermal process with the aid of triethanolamine (TEA) and their structural, optical, and photocatalytic properties were investigated. As a result of a strong reaction between TEA and Fe ions, pure BFO nanopowders without any secondary phases could be synthesized at temperatures as low as 130°C. BFO nanopowders exhibited a strong absorption in the visible-light regime, which resulted in the efficient photocatalytic activity for decomposition of organic compounds.