This paper describes a new mechanism for boundary migration, namely the mixed control mechanism (either diffusion or interface reaction), and the principle of microstructural evolution in polycrystals. The basis of the mechanism and the microstructural prediction of the principle are explained, including key experimental results that support the mechanism and the principle. The solid state single crystal growth method, a new technique of single crystal fabrication, is described as an application example of the microstructural evolution principle. Future research directions in the subject areas are also given.
Templated and reactive-templated grain growth is a convenient preparation method for textured ceramics. In this method, green compacts composed of aligned template grains and randomly oriented matrix grains are sintered. The matrix grains must be eliminated to obtain highly textured materials and an understanding of the growth behavior for both template and matrix grains is essential to the design of the conditions for effective elimination of matrix grains. This review paper addresses the microstructure development in BaBi4Ti4O15 and Bi4Ti3O12 prepared by the templated grain growth method and in Bi0.5(Na1−xKx)0.5TiO3 and K0.5Na0.5NbO3 textured by the reactive-templated grain growth method. The grains of these materials are faceted, and critical driving force is required for the growth of faceted grains. It is illustrated that the relative magnitude of the driving force of the template grains and the critical driving force determines the mode of grain growth behavior and the microstructure of the final products. A discussion on the grain growth behavior is presented to give the criteria for designing the preparation conditions.
A flash sintering experiment can be carried out by applying an electric field and heating the specimen at a constant rate. The flash event occurs at a specific temperature that depends on the strength of the electric field. Alternatively, the furnace can be held at a constant temperature and the voltage applied as a step function; after an incubation time there is a highly non-linear rise in conductivity. This incubation step is called Stage I. The non-linearity is constrained by switching the power supply to current control. This short transient, during which the sample sinters nearly instantaneously, is the second stage. Under current-control, the (essentially dense) sample remains in a highly excited state indefinitely, which we call Stage III. In this state, the samples are often brightly electroluminescent emitting a green glow; unusual phase transformations occur and the rate of chemical reactions is greatly enhanced. We infer that these manifestations are evidence of a defect catastrophe that includes unusual generation of electrons, holes and point defects, which can produce sintering, electronic conductivity, electroluminescence, and phase transformations, all at the same time. We hypothesize that both Joule heating and electric field are necessary for this catastrophe.
Sintering of powder mixtures is one of the widely used production methods of composite materials. The distribution of the reinforcement phases in these composites is a function of both initial powder structure and sintering conditions. Based on the recent literature and experimental results obtained by the authors, this article discusses a specific type of reinforcement distribution—the network distribution—in composites produced by sintering of powder mixtures. Examples of the influence of networks of different nature on sintering of metal and ceramic matrices are presented for continuous structures composed of carbon nanotubes and quasi-continuous structures of smaller particles located at boundaries between larger particles. The principles of the microstructure formation in composites with networks formed by ceramic particles, particles of metallic glass and carbon nanotubes are analyzed. Unusual properties of composites with metal and ceramic matrices achieved by organizing reinforcements in networks are discussed.
Using TiO2 as a model system, the effects of different doping (un-doped, V-doped vs. N-doped) and starting phases (anatase vs. rutile) on the flash sintering of TiO2 are investigated. The doping and starting phase not only alter the onset flash sintering temperatures via changing the temperature-dependent electric conductivities of the green specimens, but also significantly affect the densification and microstructural development during the flash sintering. In all six cases, the coupled thermal and electric runaway temperatures predicted from measured specimen conductivities agree well with the observed onset flash temperatures (with less than 5°C in differences), supporting a recently-developed quantitative model.
Based on various deformation mechanisms occurring during solid state sintering (pressureless and pressure assisted), a multitude of sintering models have been developed and presented in literature. As reported in literature, most of the simulation results line up well with experimental data. Unfortunately, none of them can be used arbitrarily and none of them are applicable to a generalized case. This paper focuses on a comparative study of three commonly applied models. The first model is based on a physical approach (Riedel) and the other two are phenomenologically based models (the modified Skorohod–Olevsky Viscous Sintering (SOVS) model and a modified Abouaf model). The material models have been implemented through FORTRAN Subroutines used for the FE-Software ABAQUS. The simulation results demonstrate their advantages and disadvantages based on sintering simulations of an aluminum oxide based ceramic cylinder and a bilayer laminate. A guideline to select a suitable model and the adjustment of input parameters under different sintering conditions for general usage is also discussed.
Highly transparent Lu2O3 ceramics with and without Nd3+ and Eu3+ dopants were fabricated by spark plasma sintering using a two-step pressure profile. A transmittance at 1080 nm for the Lu2O3 ceramics sintered by as-received powders at a pressure of 100 MPa was 57%. By sintering ball-milled Lu2O3 powders with 0.2 mass % LiF at a preloading pressure of 10 MPa, final pressure of 100 MPa, heating rate of 0.17 K s−1, and sintering temperature of 1723 K, the transmittance at 1080 nm of the Lu2O3 ceramics reached 80–82% after annealing in air, i.e., nearly 100% of the theoretical value for no scattering. Finally, laser oscillation was demonstrated using 1 at.% Nd3+:Lu2O3 transparent ceramics at 1076 and 1080 nm wavelengths, e.g., laser output of 0.2 W and slope efficiency of 14% for straight-cavity configuration.
Flash sintering experiments were performed, for the first time, on sodium potassium niobate (KNN) ceramics. A theoretical density of 94% was achieved in 30 s under 250 V/cm electric-field at 990°C. These conditions are ∼100°C lower and faster than the conventional sintering conditions. Grains tended to grow after 30 s. flash sintering duration under constant electric-field. Detailed microstructural and chemical investigations of the sample showed that there was inhomogenous Na, K distribution and it resembles a core–shell structure where K is more in the shell and Na is more in the core region. The inhomogenous distribution of Na and K was correlated with the doubling of the unit cell within the grain along 002 direction. Compositional equilibrium is achieved after a heat treatment at 1000°C for 4 h. The compositional variations appeared to have been linked to grain boundary melting during flash and consequent recrystallization as the sample cooled.
During final stage sintering, a complex interplay of densification and grain growth dominates microstructural evolution. Grain growth starts, when pore drag effects become less important due to pore shrinkage. This grain growth then decreases the driving force available for sintering. Accordingly, the interplay of pores and grain boundaries needs to be considered in detail. A phase-field model was extended to treat pore dynamics under consideration of pressure stability. To study pore attachment and detachment at moving interfaces, an idealized hexagonal microstructure with a constant driving force relationship for pore migration is constructed. Additionally, realistic polycrystalline microstructures were used. The model is in good agreement with experiments and analytic equations. Three different cases were observed in the realistic microstructure: pore attachment at the moving interface, partial and total pore detachment. However, in the partial case, the initial location of pores was found to be important: pores tend to migrate from quadruple junctions over triple junctions to grain boundary planes, where they eventually detach. This results in a variation of pore detachment, which is not captured in analytic equations. Therefore large simulation setups are required to reflect the impact of initial pore location on pore drag effects.
The modelling of processes involving powder needs taking into account the particulate nature of the materials involved. The Discrete Element Method (DEM) is well suited for this task. It allows the macroscopic behavior of an assembly of particles to be calculated from the contact forces generated between each particle. Particle rearrangement, a significant signature of powder materials, is explicitly taken into account. We show that DEM has demonstrated use and significant potential for understanding the link between defect formation and initial microstructure. We present diverse examples of application on free and constrained sintering.
The microstructural evolution of undoped and iron doped SrTiO3 is analyzed during sintering at 1280°C in air and reducing atmosphere. The focus is on densification and grain growth during different holding times investigated by dilatometric studies and microstructural analysis. The sintering equations developed by Coble are used to characterize sintering. The influence of point defects on diffusion, densification and grain growth is evaluated using basic defect chemistry equations. A space charge concept at the grain boundaries is added to bulk defect chemistry concepts to understand sintering of perovskites, since the major part of mass transport during sintering occurs in this region. The extension of the defect chemistry concept allows to explain the change in diffusion mechanism during sintering (grain boundary diffusion or bulk diffusion) as well as grain growth stagnation observed in iron doped SrTiO3. The results are used to separate the complex interplay of densification and grain growth. While grain growth decreases with increasing defect concentration, no clear trend is observed for the densification kinetics, since both grain growth and diffusion are relevant. The results show that grain growth during sintering provides comparable results to grain growth experiments in dense SrTiO3 and, thus, pore drag seems not to be important. The calculated diffusion coefficients are in good agreement with literature data and show a strong dependency on the concentration of strontium vacancies.
Micrometer-sized porosity, which cannot be recognized by typical density measurement method, was observed inside transparent polycrystalline alumina prepared by pulsed electric current sintering (PECS). The pores derive from hard agglomerates in starting powder and appear as black dots inside transparent bulk samples. In this study, porosity coming from the agglomeration was studied to degrade by chemical and mechanical treatments. Starting alumina powder was mixed with some surfactants as aqueous solutions. The slurries were ball-milled in 1 d, followed by drying and heat treatment to obtain treated alumina powders. Sintering of those alumina powders was carried out by two-step PECS technique. Transparent alumina specimens were evaluated by the density of black dots and the apparent transmittance. In summary, their treatments of alumina powder can break agglomerates and dramatically reduce the total density of black dots within transparent polycrystalline alumina. Consequently, the transmittance of polycrystalline alumina increased, from 68% for untreated sample to 72–74% for treated samples.
Micro-tubular SOFCs (Solid Oxide Fuel Cells) with internal conduction layer were fabricated by controlling the shrinkage of the inner anode layer to avoid the delamination or breakage of the cell during sintering. In order to fabricate these cells, pre-sintering of anode tubes were examined in a temperature range of 1000–1350°C. Micro close end tubular cells were successfully prepared by using this pre-sintering at 1100°C. The micro-tubular cells with close end show good tolerance to repeating thermal cycles due to their unique shape. Because of one end connection, the polarization of them was larger than the common tubular cells with two end connection and needed to be improved, which was solved by the application of internal porous conduction layer. As demonstrated by this work, maximum power density of 0.6 W/cm2 at 600°C was obtained after application of a thin nickel conductive layer, which was as thin as 20 µm.
A solid-state crystal growth (SSCG) method has been utilized to prepare (K0.45Na0.55)0.94Li0.06NbO3 (KNLN) lead-free piezoelectric single crystals. The effects of different kinds of seeds and additives on K0.5Na0.5NbO3 (KNN)-based crystal growth were studied. It was found that 〈100〉-oriented SrTiO3 seed was inappropriate for growing KNLN single crystal, while 〈100〉-oriented KTaO3 one could act as a good seed. The inverse pole figure (IPF) showed that the epitaxial layer was indeed single crystal and oriented in the same 〈100〉 direction as the seed. Addition of 0.5 mol % ZnO, CuO and MnO2 brought liquid phase in the samples and increased the diffusion rate of the atoms. This would finally enhance both the single crystal and the matrix grain growth. Among all the sintering additives, CuO could increase the matrix grain growth remarkably due to the assistance of the largest amount of the Na-deficient liquid phase, whose composition was time-independent. However, CuO was not the most effective one that can promote the single crystal growth. The reasons might be as follows: (1) the liquid accumulation at the interface of the single crystal/matrix lead to the liquid phase content exceeding the critical value in the CuO-added samples, which increased the diffusion distance and partly offset the enhanced diffusion rate; (2) the large matrix grains brought low driving force for crystal growth.
Highly homogeneous bismuth doped cubic-YSZ was prepared using reverse-strike co-precipitation from nitrates. The dopant reduced the sintering temperature for effective fabrication of fully dense pellets within 5 min using fast firing procedure at 1300°C. Delta-Bi2O3 second phase was observed at the boundaries and caused enhancement of grain boundary conductivity, while decreasing activation energy for bulk transport. Longer sintering times (up to 4 h) lead to grain boundary cleaning by evaporation of the Bi phase, consequently reducing the grain boundary conductivity and making the bulk transport activation energy similar to undoped YSZ. No changes in polymorphism were observed during the various processing steps, and only cubic polymorph existed. The findings are expected to have positive impacts on the strategies for manufacturing of more efficient solid oxide fuel cells (SOFC).
We propose a new master sintering curve (MSC) theory for liquid phase sintering in consideration of grain rearrangement and solution-precipitation in order to analyze the sintering behaviors of silicon nitride (Si3N4) powder compacts. We found that the MSC for liquid phase sintering is theoretically the same expression as that for solid-state sintering. Very fine high-purity powders of Si3N4 Y2O3, Al2O3, AlN, and TiO2 were used as the raw materials to make powder compacts. The degree of sintering shrinkages of the powder compacts, which contained different amounts of the sintering aids, were measured directly by the laser displacement measurement method using a dilatometer. Based on the displacements and the specimen dimensions, the shrinkage ratios and rates could be calculated. The sintering shrinkage behavior depended on the sintering aid used and the heating rate. The MSCs were obtained for shrinkage ratios of 0–2 and 2–15% corresponding to grain rearrangement and the solution-precipitation process, respectively. Finally, the apparent activation energies of sintering of Si3N4 for grain rearrangement and the solution-precipitation process were found to be 251–294 and 345–430 kJ/mol, respectively, depending on the sintering aid used.
TaC–NbC with and without the addition of 5 vol.% B4C and 5 vol.% Si nano-powders as sintering aids were consolidated by spark plasma sintering at 1850°C. The effect of sintering aid addition on the densification and mechanical properties is evaluated along with secondary phase formations. Relative density >99% is achieved with a hold time of just 3 min for the addition of Si and 10 min for the addition of B4C as sintering additives. High load instrumented indentation was performed and projected area of residual damage is compared to estimate relative fracture toughness. The addition of 5 vol.% Si as a sintering additive resulted in a 46% reduction in projected residual damage area and 14.5% more energy dissipation during indentation than the sample with 5 vol.% B4C as the sintering additive resulting in a higher overall toughness.
The microstructure of the damaged area created during a flash sintering event in BaTiO3 was examined by high resolution transmission electron microscopy (HRTEM) and electron energy loss spectrometry (EELS) measurement. A DC electric field of 133 V/cm was applied to a fully-densified BaTiO3 body prepared by conventional sintering, and the specimen temperature was elevated at a constant heating rate. The flash sintering event, at which the electric current in the specimen abruptly increases at the threshold field and temperature, took place at 890°C. After the flash event, tunnellike physical damage was observed in the direction of the field through the specimen. Formation of grain boundary second phase layers around the damaged area was confirmed by HRTEM observations. The grain boundary second layer was a crystalline phase with a low Ba/Ti atomic ratio of less than one. The temperature in some of the grain boundaries must increase by Joule heating during the flash event, thus the chemical composition in the vicinity of the grain boundaries changed due to vaporization of the Ba cations, resulting in the formation of the grain boundary second phase layers.
Zirconium diboride based ceramics, owing to their superior high temperature properties are potential materials for use as leading edge components in hypersonic space vehicles. However, the difficulty in sintering these ultra high temperature ceramics limit their applications to some extent. Sintering of such materials is usually accomplished by resorting to advanced sintering techniques such as Spark Plasma Sintering (SPS) accompanied by sinter aids to improve the sinterability. In this backdrop, the current work investigates the effect of Ti addition on the mechanical properties and sinterability of ZrB2–based ceramic composites. Tailored addition of Ti to ZrB2–18 wt. % SiC baseline composites not only improves the densification but also increases hardness and indentation toughness, when sintered using Multi Stage Spark Plasma Sintering technique. Microstructure and X-ray diffraction analysis reveals the presence of ultrafine grains of ZrB2 and SiC, which is found to be effective in obtaining a good hardness (up to 29 GPa) and reliable indentation toughness (up to 9 MPa·m1/2).
Spark Plasma Sintering (SPS) of silicon nitride is affected by temperature non-uniformities within the powder compact, resulting in density and microstructure inhomogeneities. A double-pyrometer experimental setup reveals a temperature disparity of 100–200°C between the overheated outer surface of the die and the bottom of the upper punch, as a consequence of the electric current concentration through the die’s wall characterizing the SPS of non-conductive powders utilizing conventional SPS tooling. A novel tooling design, consisting in the tailored drilling of axial cylindrical or ring-shaped holes within the punch, is individuated and optimized through a campaign of fully-coupled thermal, electrical and mechanical finite element simulations. The analysis of the numerical results, experimentally assessed, allows for a comprehensive understanding of the phenomena underlying radial temperature distributions in SPS and leads to the development of a technological solution for the uniformization of temperature distribution.
Synthesis and sintering behavior of Cr2AlC compounds were investigated using two sintering techniques: pressureless sintering and field assisted sintering technology/spark plasma sintering. Both processes—synthesis and sintering—were carried out simultaneously in one or two different steps. Pure Cr2AlC bulk materials but with relative density below 90% can be obtained by pressureless sintering, whereas highly dense compounds with secondary phases were achieved by FAST/SPS. The optimized processing route to obtain highly pure and dense (98.9%) Cr2AlC materials is based on the synthesis of the pure phase by pressureless calcination followed by FAST/SPS densification.
The representative volume element (RVE) is a basic concept in the continuum mechanics of sintering of random heterogeneous porous materials. A quantitative determination of its size was performed by using synchrotron X-ray microtomography data of constrained sintering of thin glass film on a rigid substrate. A RVE size is associated with a property of interest; we determined it for relative density, specific surface area, and hydrostatic component of sintering stress. The RVE size was estimated to be from 11 to 17 times larger than the average initial particle size. The RVE size was associated with a given precision of the property. It depended on the volume fraction of porous structure, or, relative density, so that it varied with microstructural evolution.
Translucent alumina ceramics with high strength and reliability were fabricated through dry pressing of industry-grade granules and subsequent vacuum-sintering prior to hot isostatic pressing (HIP). The raw materials consisted of two types of granules, containing acrylic binder with and without 500 ppm MgO. The internal structures of samples in each manufacturing step were evaluated by the liquid immersion method using an optical microscope. Large defects and their transitions were observed in the samples after each processing step. The fabricated ceramics had high relative density (>99.6%) and very fine microstructures with grain sizes smaller than 1 µm. In the granule system with the binder non-uniformly distributed, interstices in the granules were observed in the powder compacts and samples after vacuum sintering. Alumina ceramics derived from the granule system with uniformly distributed binder and MgO additive exhibited high translucency with 50% in-line transmittance and strength greater than ∼700 MPa. This result suggests that characteristics of the granules considerably affect not only the packing structures in powder compacts but also the microstructure and properties of the sintered ceramics.
Textured α-alumina ceramics were prepared by mixing different ratios of three-sized plate-like α-alumina particles and fine equiaxed particles without the use of sintering aids. The plate-like particles have developed a-b planes and were incorporated as an aligned template. Mixed powders were formed into a green sheet using a doctor blade technique and sintered under various conditions (temperature, duration and atmosphere). The development of microstructure and texture in the sintered bodies was examined and correlated with the preparation conditions. The addition of plate-like particles to the fine equiaxed powder suppressed densification and grain growth during sintering. The plate-like particles tend to grow with a lower aspect ratio at high temperatures, especially under vacuum sintering conditions. The addition of 30% plate-like particles produced sintered bodies with the highest uniaxial 〈001〉 orientation, but with residual porosity. The addition of 5% plate-like particles resulted in sintered bodies with almost full density but texture development was inferior to that of 30%. The vacuum-sintered specimens with larger amounts of platelets exhibited pseudo-isotropic grain growth and high-to-medium uniaxial 〈001〉 orientation, which suggests that anisotropic grain growth is not essential to achieve a high degree of orientation.
Al2O3–SiO2 aerogel was prepared through mixed sol–gel process and ethanol supercritical drying technology using aluminum chloride hexahydrate (AlCl3·6H2O) and tetraethoxysilane (TEOS) as precursors. Under the condition of the propylene oxide used as gelation initiators, during the process, a kind of Al2O3–SiO2 aerogel with porous and large specific surface area were achieved in our experiments. Structures and properties of Al2O3–SiO2 aerogel are investigated by means of X-ray Diffraction, Nitrogen adsorption/desorption analysis, Scanning Electron Microscopy, Fourier Transform Infrared Spectroscope, and Thermogravimetry-Differential Thermal analysis. The results showed that the Al2O3–SiO2 aerogel with the mole ratio of Al/Si = 3/1 possessed better heat-insulation performance and high-temperature stability. And it possessed a porous network structure made up of leaf shape particles. At the same time, Al2O3–SiO2 aerogel showed a low density of 0.071 g/cm3 at room temperature, specific surface areas of 708 m2/g at 600°C, as well as 255 m2/g at 1200°C. The Al2O3–SiO2 aerogel is the polycrystalline boehmite (γ-AlOOH) phase at room temperature. As the temperature growing, it transferred to γ-Al2O3 at 600°C, and mullite phase at 1200°C.
The surface roughness in moving and stationary blades of steam turbines is known to become rougher through steam oxidation during plant operation, resulting in the degradation of the turbine performance. The formation of an Al2O3–SiO2 based coating film on high chromium steel, which is used in moving and stationary blades, through chemical solution deposition (CSD) is attempted to suppress the increase of surface roughness. The arithmetic average roughness Ra and maximum height Rz after an oxidation test in a steam atmosphere at 873 K for 1,000 h were equal to 3.0 and 19.4 µm, respectively, for high chromium steels without coating, while those for high chromium steel with an Al2O3–SiO2 based coating were 0.10 and 1.0 µm, respectively. Therefore, the formation of a coating film is proven to significantly suppress the roughening of the surface. The observation of the cross-section texture near the high chromium steel substrate surface of both specimens showed that a two-layer oxide film forms on the surface of the non-coated specimen; the outer layer consists of Fe3O4, whereas the inner layer comprises (Fe,Cr)3O4 and CrO2. This film forms a very coarse texture. On the other hand, the oxide film does not form on high chromium steel with an Al2O3–SiO2 based coating film deposited using CSD; the Al2O3–SiO2 based coating film remains as the topmost surface after testing. A thin intermediate layer with a thickness smaller than 0.1 µm forms between the high chromium steel substrate and the coating film. Its thickness increases with increasing the temperature and reaches approximately 0.5 µm with heat treatment at 973 K for 1,000 h. This layer consists of Cr, Mn, Al, Si, and O.
The self-compensation mode and dielectric properties of the nominal (Ba1−xTbx)(Ti1−xTbx)O3 (0.05 ≤ x ≤ 0.20) ceramics (BTTT) were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-dependent Raman spectroscopy and electron paramagnetic resonance (EPR), dielectric and electrical measurements. The solid solution limit of Tb in BTTT was determined to be x = 0.12 by XRD. The variation in unit cell volume (V0) with x satisfied Vegard’s law. In the case of Ba/Ti = 1, a complete self-compensation mode of Tb3+ in BaTiO3 could not be formed like Eu3+ or Dy3+ because Tb ions in BTTT coexisted in the mixed-valence states of Ba-site Tb3+ and Ti-site Tb4+. The room-temperature resistivity decreased with increasing x owing to a gradually enhanced Tb3+ donor effect. An X5S specification with medium dielectric stability was achieved at x = 0.05. This ceramic is a promising dielectric for a higher room temperature permittivity (ε′RT = 1190), a very low dielectric loss (tan δ < 0.02), and a nearly invariant ε′ in the frequency range of 102 to 105 Hz.
High-quality (1 − y)(Mg0.95Co0.05)2(Ti0.95Sn0.05)O4–y(Ca0.61Nd0.8/3)TiO3 ceramics were prepared by solid-state reaction. The products were characterized by scanning electron microscopy, X-ray diffraction, and network analyzer. (Mg0.95Co0.05)2(Ti0.95Sn0.05)O4 (MCTS) has a dielectric constant (εr) of ∼14.7, a high quality factor (Q×f) of ∼330, 134 GHz, and a temperature coefficient of resonant frequency (τf) of ∼ −46 ppm/°C. 0.48 MCTS −0.52CNT has an excellent combination of microwave dielectric properties: εr ∼ 28.58, Q×f ∼ 208027 GHz (at 9 GHz), and τf ∼ −4.38 ppm/°C sinter at 1325°C, and can be utilized in the fabrication of microwave devices. Therefore, a band-pass filter is designed and simulated using the proposed dielectric to study its performance.
6% BaTiO3-doped Na0.5Bi0.5TiO3 (BNT–BT) lead-free piezoelectric thin films with the composition around morphotropic phase boundary (MPB) were spin-coated via an economical water-based sol–gel method on Pt(111)/Ti/SiO2/Si substrates. High-quality BNT–BT thin films with the thickness ranging from 120 to 560 nm were synthesized by stepwise crystallization process, and the thickness effect on structures and electric properties were investigated. Two theoretical models are used to analyze the ferroelectric results. Intrinsic contribution and extrinsic contribution alternatively dominates under different conditions in the BNT–BT thin film. The piezoelectric properties of BNT–BT thin films were found to change monotonically with the increase of the thickness. The largest effective piezoelectric constant (d33) of the BNT–BT thin films can reach the value of 97.7 pm/V for the film with the thickness of 560 nm.
The lateral sealing method of vacuum sealing used to fabricate Low-E vacuum glazing. The optical performance and surface morphology of the film at each sealing temperature were tested. The heat transfer rate to the central vacuum glazing was also tested. High-temperature sealing treatment may increase the density of the Low-E film surface. The visible spectral transmittance of the film and the far infrared spectral reflectance were significantly increased, Whereas the near-infrared spectral absorption ratio decreased slightly. The lowest rate of central heat transfer of vacuum glazing was 0.9 W/(m2·K) when the sealing temperature was 500°C. However, above 500°C, after the Ag film breakage and reunion to form a polymer film, the film performance degrades.
Without surfactants or templates, CaTiO3 with various morphologies had been synthesized via a simple hydrothermal route. Effects of optical properties and photocatalytic activities of the CaTiO3 nanostructures with various morphologies were investigated. The results found that the optical reflectance, absorption and photocatalytic properties of the samples were found to be significantly dependent on their morphologies. Three-dimensional CaTiO3 butterfly–like structures with nanoflakes showed lower reflectance, more efficient light harvesting, higher surface area and higher photocatalytic activities compared with that of other dendrites and prism. It can be ascribed to the unique butterfly–like structure in which the interspace between ordered nanoflake units acts as a light–transfer path for introducing incident light into the inner surface of CaTiO3. This allows UV light waves to penetrate deep inside the CaTiO3. The nanoflake units also offer multiple reflective and scattering effects of UV light, preventing the incident waves from bouncing back to the free space. Due to microstructure with nanometer-scale unit, they are much easier to store and be separated from the solution as photocatalysts compared with traditional nanometer-scale powders, which might offer opportunities for fundamental study and industrial applications to explore CaTiO3 nano-structure under effective morphology control.
Silica glass films were coated on polypropylene (PP) microporous membrane separators by a dip coating method, in which polysilazane diluted with xylene was used as precursor material for the silica glass. Scanning electron microscopy (SEM) observation showed that the silica glass films were uniformly coated on the separator surfaces, while Fourier transform infrared spectroscopy (FTIR) measurements revealed that almost all polysilazane in the as-prepared films was converted to silica after heating at 100°C in a steam oven. In addition, the thermal shrinkage properties of the PP microporous membrane separators were significantly improved after coating. Electrochemical studies of an Al ion-doped lithium manganese oxide cathode were conducted to evaluate the coating effect on the properties of the PP microporous membrane separator. The results revealed that rechargeable capacity, cycle stability, and rate performance of the lithium-ion batteries were not changed by the silica glass coating.
The adsorption of poly(acrylic acid) [PAA] on the surface of commercial ball clay was studied. The adsorption isotherm of PAAs with different molecular weights was determined at pH 6 and 9. The results showed that the amount of PAA adsorbed on clay was independent of molecular weight. Also, the adsorption amount was decreased with increased pH. However, the overall adsorption amount was lower than the range predicted by a model based upon the mineralogy of kaolinite. A kinetic study of PAA adsorption presented plausible displacement of initially adsorbed PAA. PAA adsorption on clay particles decreased the viscosity of suspensions. Clay suspensions showed the minimum viscosity with a sufficient coverage of particles with PAA necessary for stable suspensions. Optimum chain length of PAA was revealed for effective dispersion.
In this work, iron oxide nanoparticles with various morphologies were synthesized by the precipitation method from aqueous solutions of iron oxide chlorides and urea in the absence or presence of chitosan. Synthesis conditions were selected to yield magnetite nanoparticles with three different morphologies. By adding chitosan, we were able to change the morphologies of the Fe3O4 nanoparticles from cubo-octahedral, flower-like, and rod-like structures to cubic, quasi-spherical, and rice-seed-like structures, respectively. The size of these iron oxide structures were in the range of 28–125 nm, while the longitudinal sizes of the rod-like and rice-seed-like structures were 110–1000 and 75–290 nm, respectively. Transmission electron microscopy (TEM) results showed that the magnetite nanostructures synthesized in the presence of chitosan have a mesoporous structure and are composed of many nanocrystals. The mechanisms responsible for the formation of differently shaped iron oxides in the presence or absence of chitosan are analyzed and discussed. We observed that the growth mechanism changed from the classical route to the reverse growth mechanism, when chitosan was added to the synthesis solution.