Microstructure Of Ceramic Materials Research Articles

Effects of frequency on the AC flash sintering behavior and microstructure of Ga-LLZO

In this paper, the effects of frequency on the flash sintering behavior and microstructure of Li6.4Ga0.2La3Zr2O12(0.2Ga-LLZO) were investigated. The results showed that an increase in frequency had little effect on the onset temperature, but this increase reduced the duration of the weak current stage the incubation stage. Moreover, this phenomenon led to a decrease in the power loss during the constant current stage. Scanning Electron Microscope images showed that the microstructure was symmetrically distributed, and the uniformity increased with increasing frequency. Finite element simulations and an IR thermocamera were used to analyze the temperatures of the specimens. The symmetric distribution of temperature during the flash sintering process was the root cause. The results of AC impedance spectroscopy showed that when the frequency of flash sintering was ≥ 400 Hz, the ionic conductivity of Ga-LLZO was greater than that of conventional sintering. The results of this work demonstrated the important role of frequency in controlling the microstructures of ceramic materials in flash sintering.

Microstructure and performance optimization of Al2O3/TiC/TiB2/h-BN@Al2O3 self-lubricating ceramic tool materials

Based on the classical Monte Carlo (MC) model and grain growth theory, the model of h-BN@Al2O3 coated solid lubricant was designed and introduced into the simulation system. The Al2O3/TiB2/h-BN@Al2O3 self-lubricating composite ceramic tool model was designed, and the microstructure evolution of tool materials during hot pressing sintering was simulated. The effects of TiB2 and h-BN@Al2O3 content on the microstructure of ceramic materials were studied, and finally the optimized composition parameters were obtained. The effects of sintering temperature and sintering pressure on the microstructure of tool materials were studied, and reasonable sintering parameters were obtained. The experimental results show that under the sintering temperature of 1650℃ and sintering pressure of 32Mpa, the ceramic material with 10%volTiB2 and 5%volh-BN@Al2O3 has the best mechanical properties, that is, the bending strength is 610MPa, the hardness is 17.9GPa, and the fracture toughness is 5.17 MPa·m1/2. SEM analysis shows that the grain growth of the material is uniform, the solid lubricant is well combined with the matrix, and the material has a good microstructure. Comparing the simulation results with the previous experimental results, it is found that the results are in good agreement, which indicates that the designed MC model reliably reflects the physical process of material grain growth, and has certain guiding significance for further research on the mechanism of grain growth.

Low Temperature Thermal Properties of Nanodiamond Ceramics

The temperature dependence of thermal conductivity and specific heat for detonated nanodiamond ceramics is investigated on specially designed experimental setups, implementing the uniaxial stationary heat flow method and the thermal relaxation method, respectively. Additionally, complementary studies with a commercial setup (Physical Property Measurement System from Quantum Design operating either in Thermal Transport or Heat Capacity Option) were performed. Two types of samples are under consideration. Both ceramics were sintered at high pressures (6–7 GPa) for 11–25 s but at different sintering temperatures, namely 1000 °C and 1600 °C. The effect of changing the sintering conditions on thermal transport is examined. In thermal conductivity κ(T), it provides an improvement up to a factor of 3 of heat flow at room temperature. The temperature dependence of κ(T) exhibits a typical polycrystalline character due to hindered thermal transport stemming from the microstructure of ceramic material but with values around 1–2 W/mK. At the lowest temperatures, the thermal conductivity is very low and increases only slightly faster than linear with temperature, proving the significant contribution of the scattering due to multiple grain boundaries. The specific heat data did not show a substantial difference between detonated nanodiamond ceramics obtained at different temperatures unlike for κ(T) results. For both samples, an unexpected upturn at the lowest temperatures is observed—most likely reminiscent of a low-T Schottky anomaly. A linear contribution to the specific heat is also present, with a value one order of magnitude higher than in canonical glasses. The determined Debye temperature is 482 (±6) K. The results are supported by phonon mean free path calculations.

Optical and Mechanical Properties of Highly Translucent Dental Zirconia.

The aim was to evaluate the translucency, opalescence, and fluorescence of highly translucent zirconia, lithium disilicate, and bovine teeth. One mm-thick specimens of five monolithic zirconia systems, two glass-ceramics, and bovine enamel/dentin were investigated. A spectrophotometer (Ci7600) was used to measure the CIELab color coordinates, and the translucency and opalescence values were obtained. For evaluating the fluorescence emission, the differences in spectral reflectance by the UV component of illumination were calculated. The microstructures of ceramic specimens were examined with a scanning electron microscope and the chemical compositions were determined with an X-ray fluorescence spectrometer. Mechanical properties were appraised with three-point bending strength, indentation fracture toughness, and Vickers hardness. Data were analyzed using a one-way ANOVA, followed by Tukey’s multiple comparison test (α = 0.05). A higher yttria content (5 mol%) significantly improved the translucency of zirconia ceramics, while they were less translucent than lithium disilicate (p < 0.05). Lowering the alumina content below 0.05 wt.% enhanced the translucency (p < 0.05), but a small amount of alumina was still required to obtain full densification. 0.05 wt.% Fe was used to increase the chroma of zirconia specimens without compromising their mechanical properties. The Er-containing zirconia specimen showed a maximal fluorescence emission at 430 nm. The degree of opalescence was affected by the microstructures of ceramic materials. The microstructure, incorporation of a secondary phase, and sintering behavior can have a strong impact on the final mechanical and optical properties of dental ceramics. Addition of small amounts of metal oxides can affect the translucency, opalescence or fluorescence qualities of zirconia

Influence of rare earth elements on the structure and properties of powders based on zirconium dioxide during consolidation

Zirconium oxide powders with different contents of REE concentrate (La, Nd, Pr) in an amount from 25 to 35 mol. % were synthesized by the method of reverse chemical deposition. The effect of the annealing temperature in the range of 600–1200 ° C on the phase transformations of the synthesized powders has been investigated by Raman spectroscopy. It was found that the formation of REE zirconates with a pyrochlore structure occurs after annealing at a temperature of 1000 ° C. At higher annealing temperatures, the presence of tetragonal ZrO2 was noted in the samples with a lower concentrate content in the phase composition. A study of the influence of the sintering temperature of 1400-1600 °C on the densification processes, phase composition and microstructure of ceramic materials based on REE zirconates has been carried out. It has been shown that the densification processes proceed most slowly in a ceramic material with 35 mol.% of rare-earth oxides, and at all sintering temperatures it has a stable phase composition, consisting mainly of rare-earth zirconates with a pyrochlore structure.

RETRACTED: Mechanical properties analysis and microstructure of ceramic materials of mullite ceramic material

Two unique multiphase volume elements were developed in this paper against the mechanical performance analysis problem of mullite ceramic material. They realized consideration of multiple materials...

Effect of porosity on the electrical conductivity of LAMOX materials

Porous La2Mo1.5W0.5O9 (LMW05) samples with different levels of densification were obtained by varying the sintering temperature in the range of 750 to 1100°C. Impedance spectroscopy was used to evaluate the effect of porosity on the electrical response of LMW05-type compounds. The bulk conductivity was found to depend on the microstructure and the pore volume fraction. Effective medium theories (Bruggeman and Maxwell–Garnett approximations) were used to predict the macroscopic properties of the heterogeneous medium. The Bruggeman approximation proved to be better suited to predicting the bulk electrical response of porous LMW05 samples in the pore volume fraction range of 0 to 0.22. Compared with other ceramic materials, LMW05 was found to have a low blocking factor (αR). This characteristic of LMW05 could be related to the microstructure of ceramic materials. Two porous YSZ model samples with the same porosity but different pore morphologies were used to explain why microstructural defects (MD) have a small impact on the electrical properties of LMW05.

Effect on Wollastonite on the Structure of Porous Ceramic Tiles Based on Wastes From Nonferrous Metallurgy and Power Generation

Analysis of experimental data obtained by diffuse small-angle x-ray scattering (SAS) shows that even though it increases the total number of pores ranging in size from 10–5 to 10–4 m the wollastonite in ceramic face tiles secures the uniformity of the microstructure of ceramic materials.

Effect of acid-etching protocols on 3D microstructure of ceramic materials

Effect of acid-etching protocols on 3D microstructure of ceramic materials

Numerical and experimental analysis of crack propagation behaviour for ceramic materials

The study of crack growth in microstructure of ceramic materials is important for establishing the relationship between homogeneous microstructures and mechanical properties. This paper has modelled the fracture behaviour of Al2O3/ZrB2/ZrO2 ceramic materials, and the cracking propagation and fracture resistance are investigated by numerical and experimental analysis. The crack propagation in AZ20 ceramic materials becomes more tortuous as the addition of reasonable reinforced phase, and the deflection occurs in the crack propagation. AZ20 ceramic composites are superior to the AZ40 ceramic composite materials in absorption of crack propagation energy. Comparison between the numerical and experimental results shows that the present numerical results are in good agreement with the experimental ones.

Evaluation of potential applications of recycled moulding and core sands to production of ceramic building materials

This study summarises the properties of ceramic materials containing used moulding sand, from processed and recycled mould and core mixes. The sand preparation procedure involves crushing and separation of metallic parts. Thus obtained substance acts as a substitute for natural quartz sand, commonly used as a leaning agent in ceramic plastic bodies to be formed into ceramic-based construction materials. The study summarises the basic functional parameters, structure and microstructure of ceramic materials made from plastic bodies containing variable qualitative proportions of used sand. The issues addressed in the paper include the potential threats associated with manufacturing and disposal of these types of materials. Potential hazards include atmospheric emissions of hazardous gaseous substances in the form of polycyclic aromatic hydrocarbons (PAHs) as derivatives of organic binders used for manufacturing of moulding and core sand mixes. These substances are formed in the process of combustion of ceramic products or can be produced when heavy metals are released from the ceramic matrix. This process can occur throughout the entire service life of ceramic products under the specific conditions. Applicability of used sand in this disposal scheme is well proved by good parameters of thus obtained ceramic materials and positive test results evidencing the absence of atmospheric emissions of hazardous substances and low-level leaching of heavy metals.

Applications of the electron backscatter diffraction technique to ceramic materials

A technique with a relatively high spatial resolution is required for an effective analysis of the microstructure of ceramic materials. The recently developed electron backscatter diffraction (EBSD) technique, which works within a scanning electron microscope, enables a spatially highly resolved study of crystallographic orientations while recording Kikuchi patterns on a user-defined grid. However, such an EBSD texture analysis was until now not often performed on ceramic materials – in contrary, the technique is widely employed in the analysis of metallic materials, including the investigation of various types of steels. The use of ceramics possesses a variety of problems for EBSD investigations like: (i) complicated crystal structure, (ii) difficult surface preparation, and (iii) problems arising from a low conductivity of the ceramic materials. Here, we discuss these problems and present solutions in order to obtain high-quality Kikuchi patterns from such ceramics.

Densification and Microstructural Evolutions during Reaction Sintering of SiC-Si-C Powder Compacts

Porous SiC-Si-C ceramics were produced by reaction sintering (RS) of silicon carbide, silicon, and carbon powder compacts in the temperature range of 1400–1600°C. The effects of chemical composition of the starting powder, initial SiC particle size, and reaction sintering temperature and duration on the densification and microstructure of ceramic materials were studied. The results showed that increasing the amount of Si and/or C powders in the starting powder mixture had a detrimental influence on the densification of ceramic material as a result of higher amount of remained silicon and carbon phases in the ceramic specimen. Increasing the RS temperature also degraded densification due to the melting of Si and coming out of it from compact during heating. Nevertheless, densification was improved by increasing the RS duration. Using nanometric SiC particles in the starting powder mixture improved the densification compared to that of micrometric ones especially at longer RS processing duration.

Phase transformations in t-ZrO2-Al2O3 nanoprecursors and formation of the microstructure of related ceramic materials

The phase transformations in nanosized precursors (precipitation products) prepared by the sol-gel processing and the formation of the microstructure of ceramic materials in the t-ZrO2-Al2O3 system are investigated. It is demonstrated that the phase transformation occurring during the precipitation depends on the precrystallization state that is governed by a sequence of precipitation of the components in the Al2O3-ZrO2-CeO2 system in the course of the synthesis of precursors. The nascent metastable phases of solid solutions based on t-ZrO2 and θ-Al2O3 subsequently have a substantial effect on the sizes of grains in the microstructure of the corresponding ceramics.

NMR techniques: A non-destructive analysis to follow microstructural changes induced in ceramics

Magnetic resonance relaxation (MRR) and magnetic resonance imaging (MRI) of water 1H nuclei confined in high-surface-to-volume ratio systems are important tools to investigate pore-space properties such as connected porosity and pore-size distribution in a non-destructive way. In the present work, MRR and MRI techniques were applied to study the microstructure of ceramic materials used for the production of tiles, with different compositions and fired at different temperatures, in terms of porosity distribution and pore-size distribution. Relaxation analysis of samples saturated with water gave a clear characterisation of the pore space of the materials, with high resolution power. Actually, the decay of the nuclear magnetization was turned into pore-size distribution, the relaxation rates depending on local surface-to-volume ratios. MRI has been applied to visualize in a non-destructive way internal sections of ceramics saturated with water, in order to check the spatial homogeneity. It was also possible to evaluate parameters connected to the local structure in the inside regions. The effects of different firing temperatures and compositions were distinguished. The results were compared with microstructural studies carried out by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). SEM analysis confirmed the outcomes of MRR and MRI, and the comparison with MIP made it clear that a higher temperature allows the formation of larger pores connected by smaller channels. MRR and MRI proved to be particularly useful to assess, in a non-destructive way, the effects of different fluxes on the final microstructures.

Retardation of Recrystallization in the TiC – SiC System

Silicon carbide, introduced into titanium carbide matrix via gas-phase mass transfer and subsequent deposition in the intergranular contact zone, acts as a shield for TiC grains. This results in a sharp retardation of the collective recrystallization and thus provides a means of controlling formation of the composite ceramic microstructure under sintering and hot-pressing conditions. By varying the composition and processing parameters in the TiC – SiC system, one can control the microstructure of ceramic materials to optimize their electrophysical and physicomechanical properties

Synthesis and properties of in situ Al 2TiO 5/Al 2O 3 composite

A novel route to simple processing of an in situ aluminum titanate–alumina composite is described. This process offers a simple means of tailoring the composition and microstructure of ceramic material. The process involves and equimolar mixture of Al 2O 3–TiO 2 mixed with a varying equal proportion of FeTiO 3+Fe 2O 3 (1–10 wt.%, 50/50 mixture). It is known that the kinetic transformation of the aluminum titanate is slow, leaving unreacted Al 2O 3 and TiO 2 after the Al 2TiO 5 transformation, besides the iron pseudobrookite: Fe 2TiO 5 grows at the expense of hematite–ilmenite solid solution at 1100 °C which is isostructural with Al 2TiO 5 and forms a complete solid solution, the obtained structure over 5% addition was Al 2TiO 5 with dispersed unreacted Al 2O 3. The XRD patterns did not show the presence of FeTiO 3, TiO 2 or Fe 2O 3 signals that makes to believe that they enter completely in solid solution with the aluminum titanate. The variation in composition allows an increase in the aluminum titanate Vickers hardness: 10 GPa partly due to the additive strengthening and to the alumina reinforcement.

Synthesis and properties of in situ layered and graded aluminium titanate/alumina composites

A novel route to simple processing of an in situ layered and graded aluminum titanate (AT)/alumina composite is described. This process offers a simple means of tailoring the composition and microstructure of ceramic materials. The processing involves partial infiltration of a porous alumina preform with titanium ethoxide to yield a homogeneous surface layer of alumina and a heterogeneous graded layer of AT/alumina. Analysis of the graded layer by X-ray diffraction shows the existence of concentration gradients, the AT content decreasing with depth. Depth profiling of the graded layer also shows gradual changes in elastic modulus, thermal expansion coefficient, and microhardness. This novel process has the potential to fabricate other material systems and architectures.

Infiltration-processed, functionally graded aluminium titanate/zirconia–alumina compositePart I Microstructural characterization and physical properties

A novel route for processing aluminium titanate (AT)/(alumina–zirconia (AZ)) with graded microstructure and properties is described. This process offers a simple means of tailoring the composition and microstructure of ceramic materials. The processing involves infiltrating porous AZ preforms with a solution of TiCl4, followed by sintering at 1550°C for 3 h. The resultant material has a homogeneous core encased with a graded and heterogeneous layer of AT/AZ. Analyses by X-ray diffraction and energy-dispersive spectrometry have revealed the existence of concentration gradients, the AT content decreasing with increasing sample depth. The presence of both AT and zirconia inhibits the growth of alumina grains through a pinning mechanism. The existence of microcracking in AT and zirconia grains has been revealed by scanning electron microscopy. The graded material displays gradual changes in thermal expansion values due to the presence of AT which gradually reduces in amount from the surface to the core. The inclusion of zirconia has a favourable effect on the thermal stability of AT against phase decomposition. © 1998 Kluwer Academic Publishers

Ceramic sensors for humidity detection: the state-of-the-art and future developments

The possible applications of humidity sensors in automated systems for environmental control encompass many industrial and domestic fields. Very different operating temperatures and a variety of humidity ranges are needed for these purposes. The different humidity-sensing mechanisms and operating principles identified for ceramics are reviewed. Ceramic humidity sensors are divided into ionic, electronic, solid-electrolyte and rectifying-junction types. Examples of the performance of some ceramic sensors are presented. The correlation between the microstructure of ceramic materials and their humidity-sensitive electrical response is discussed. The improvement of the performance of ionic-type humidity sensors by the addition of alkali ions is explained in terms of influence on the microstructure and on the intrinsic impedance. The recent trend towards the miniaturization and integration of sensors on a single chip requires the production of ceramic films. Ceramic thin films prepared by sol-gel or sputtering processes are investigated. The results obtained on the humidity sensitivity of pn semiconducting oxide heterocontacts are also reported.