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The paper studies ceramic samples prepared using traditional ceramic technology also knows as conventional sintering. Samples were prepared from Eu3+ activated fine powders of gadolinium niobate-tantalates GdNb1−yTayO4 (y = 0, 0.7, 1); Eu3+ concentration was x = 0.01, 0.2 and 0.4. Powders were synthesized using nitrate solutions Gd and Eu and niobium and tantalum hydroxides. The hydroxides were coprecipitated from hydrofluoric acid solutions. Full-profile analysis (Rietveld refinement) of XRD (X-ray diffraction) patterns of polycrystals determined the phase composition and refined the parameters of the structure of solid solution phases depending on the Eu concentration. Morphological features of the microstructure have been studied for gadolinium niobate-tantalate ceramics Gd1−xEuxNb1−yTayO4 where y = 0, 0.7, 1 and x = 0.01, 0.2, 0.4. Their mechanical properties have been studied; strength characteristics (Young's modulus, microhardness) and critical stress intensity factor for mode I KIC have been estimated. The compositions and modes for producing ceramics with optimal mechanical properties have been determined. The photoluminescence (PL) has been studied in ceramic solid solutions in the visible range upon excitation by near UV (376 nm). The features of energy transfer between the host of ceramic GdNb1−yTayO4:Eu solid solution (y = 0; 0.7; 1) and 4fn-4fn levels of Eu in concentrations x = 0.01, 0.2 and 0.4 have been established. We have established that concentration quenching of PL in single-phase ceramics Gd1−xEuxNbO4 occurs above Eu concentration x > 0.01 and in ceramics Gd1−xEuxTaO4—at Eu concentration x > 0.2. The sample with the composition Gd0.99Eu0.01NbO4 demonstrated the maximal PL intensity among all other studied samples. The least PL intensity is observed in Gd0.99Eu0.01Nb0.3Ta0.7O4 relative to individual compounds of gadolinium niobates and tantalates, activated with Eu in the same concentration x = 0.01. The significant difference in Stark splitting of levels has been shown for solid solutions based on niobium (Gd1−xEuxNbO4) and tantalum (Gd1−xEuxTaO4). The compositions of ceramic GdNb1−yTayO4:Eu solid solution have been established which have maximum luminance. We have determined that the luminance of some of the studied samples exceeded the luminance of an industrial phosphor based on Y2O3:Eu3+. [ABSTRACT FROM AUTHOR]

SiC-TiB2 composite ceramics of the solid-state has stable property in high temperature with wide application. In the paper, SiC-TiB2 composite ceramics was prepared by spark plasma sintering with 50 MPa pressure and heat preservation for 10 min at 1750 ℃, and the effect of TiB2 content (0 vo l%-20 vol%) on microstructure and mechanical properties of SiC composite ceramics by solid-state spark plasma sintering was investigated. The experimental results show that the grain growth of SiC is inhibited with the increase of TiB2 content. When TiB2 content is 20 vol%, TiB2 promotes the decomposition of SiC into Si, which is located in the grain boundaries of SiC and TiB2 to reduce mechanical properties of composite ceramics. SiC-15 vo l%TiB2 composite ceramics have the preferable comprehensive mechanical properties with relative density, Vickers hardness, bending strength and fracture toughness of 98.8%, 27.2 GPa, 431 MPa and 5.24 MPa • m1/2, respectively. [ABSTRACT FROM AUTHOR]

This paper presents the experimental investigation of the effect of Nb2O5 content on the phase composition, microstructure, and physical and mechanical performance of the zirconia-toughened alumina (ZTA) ceramics, aimed to optimize the additional amount of Nb2O5, refine the ceramic grains, and improve the densification, hardness and fracture toughness. ZTA ceramics with various Nb2O5 contents were prepared using the spark plasma sintering method. The addition of trace amounts of Nb2O5 did not produce a new Nb-rich phase; the Nb atoms were dissolved in the ZrO2 grains. The addition of trace amounts of Nb2O5 led to grain refinement and an increase in density, but the addition of excessive Nb2O5 resulted in grain growth and a decrease in relative density. Furthermore, the addition of Nb2O5 promoted uniformity of the microstructure. The sample with 0.25 wt.% Nb2O5 had the maximum Vickers hardness and indentation fracture toughness, which were 1228.40 HV and 9.17 MPa √m, respectively. Mechanical properties of the composite mainly depended on the grain size, which was influenced to some extent by the relative density. [ABSTRACT FROM AUTHOR]

Microwave dielectric materials with low permittivity and high quality factor are the cornerstone of high-speed data transmission. This paper prepared a new low-permittivity microwave dielectric ceramic Sr3MgSi2O8 (SMS) by a solid-state reaction method. SMS ceramics belonged to the monoclinic system (space group: P21/a) at 1375 °C ~ 1475 °C, accompanied by the formation of small amount of Sr2SiO4 second phase (space group: P21/n). SMS ceramics has the lowest damping at 1450 °C. With the increase in sintering temperature, the relative density of ceramics increases firstly and then decreases, reaching the maximum value (95.82%) at 1450 °C. The SMS ceramics sintered at 1450 °C for 4 h have the best microwave dielectric properties of εr = 11.06, Q × f = 25,375 GHz, and τf = − 57.41 ppm/°C. [ABSTRACT FROM AUTHOR]

In this paper, nanocrystalline Nd[(Zn0.925Co0.075)1/2Ti1/2]O3 (NZCT75) powders were synthesized through glycine–nitrate combustion method with the intent of reducing the sintering temperature and improving the microwave dielectric properties of NZCT75 ceramics. Phase composition, structure, and morphology of the powders were analyzed by thermogravimetric analysis–differential thermal analysis (TG–DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The XRD results showed that the as-synthesized powder after rapid self-propagating combustion was highly crystallized and was mainly composed of NZCT75 phase and small amount of unknown phase. The unknown phase could be vanished through the calcination process of 600 °C. Compared to solid-state reaction route, a reduction of about 600 °C in the synthesis temperature for pure phase NZCT75 was realized. A large amount of pores with inhomogeneous distribution in size and shape was found from the SEM image of the as-synthesized powder due to the rapid combustion reaction between glycine and nitrates. The TEM study revealed that the average particle size of the calcined powder is around 31.9 nm. The bulk sample prepared by the nanosized powder could be sintered to 98.8% of the theoretical density at 1250 °C, reducing about 160 °C more than the solid-state reaction method. Meanwhile, excellent microwave dielectric properties of NZCT75 ceramics presented a dielectric constant of 37.17, a quality factor of 257,600 GHz, and a temperature coefficient of resonant frequency of – 29.48 ppm/oC. This study develops a facile approach to synthesize nanocrystalline powder for a promising application in microwave dielectric ceramics. [ABSTRACT FROM AUTHOR]

The paper deals with the thermal plasma synthesis of anorthite (CaO·Al2O3·2SiO2). It is shown that the optimum synthesis parameters include 100 A current, 110 V voltage, 14 nL/min gas rate, and 25–30 s exposure time. According to the X-ray diffraction analysis, the initial mixture melting provides the silicate melt formation followed by its cooling and the anorthite phase formation. For the synthesis of the anorthite phase enriched with the calcium-containing CaO·Al2O3·2SiO2·nCaO compound, it is necessary to increase the calcium oxide content up to 38%. For synthesis of the anorthite phase enriched with silicon-containing CaO·Al2O3·2SiO2·nSiO2 compound, the silicon oxide content must be increased up to 67%. Idiomorphism of anorthite acicular crystals is observed. The practical implication of synthesized anorthite is the ceramics production. [ABSTRACT FROM AUTHOR]

In this paper, the sintering behavior, microstructure and microwave dielectric properties of Al2O3 ceramics co-doped with 1.5wt%CuO-3wt%Nb2O5 (CN) and 1.5wt%CuO-3wt%Nb2O5-0.5wt%ZrO2 (CNZ) were systematically studied. The results show that the sintering temperature of Al2O3 ceramics could be effectively decreased by adding 5 wt% CNZ. After sintered at 1000 °C for 5 h, Al2O3 ceramics with high density (3.91 g/cm3), uniform microstructure and good microwave dielectric properties (εr = 9.79, Q × f = 15,541.5 GHz) could be obtained by adding 5 wt% CNZ. Higher temperature can further increase the density of the sample, but it will also lead to abnormal grain growth and decrease of Q × f value. Besides, the effect of CNZ on the low temperature densification, the changing of microstructure and dielectric properties of ceramics samples were also discussed. [ABSTRACT FROM AUTHOR]

The partial substitution of Sb5+ on the Ti site for giant dielectric constant material CaCu3Ti4O12 (CCTO) has been done in the present paper, and the effect of Sb substitution on the microstructural, dielectric and electrical property of the material is investigated. The main objective of this paper is to minimize high loss tangent (tan δ) which has restricted the practical applications of CCTO. XRD analysis carried out on the as-synthesized powders confirms formation of single phase material accompanied by dopant-induced lattice constant shrinkage. Scanning electron microscope images demonstrate that the grain size of sintered ceramic samples decreases with the increasing Sb content. The dielectric response of sintered CaCu3Ti4−xSbxO12 samples studied by precision LCR meter suggests that Sb doping is an effective way for maintaining a high dielectric constant and low loss over a broad range in temperature and frequency. Room temperature complex impedance spectroscopy analysis suggests that all compounds are electrically heterogeneous consisting of semiconducting grains and insulating grain boundaries establishing internal barrier layer capacitance model. These results indicate that Sb-doped CCTO ceramics have a favorable prospect to be able to stimulate practical applications. [ABSTRACT FROM AUTHOR]

Piezoelectric properties of the recently developed lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 (BCZT) ceramics have been improved by suitable additives. In this paper, Bi0.5Na0.5TiO3 (BNT) was synthesized to precursor through the molten salt method. Then, these precursors were introduced into BCZT and prepared for samples. The electrical properties of prepared samples were compared to the sample prepared through traditional solid-state sintering. Also, the influence of precursor synthesizing temperature of molten salt method on the microstructure, electrical properties, and dielectric relaxation behavior of prepared samples was also investigated. Experimental results indicated that the ceramics of molten salt-synthesized BNT-modified BCZT have optimum performances at 820 °C, where d33 ~ 450 pC/N, kp ~ 53%, εr ~ 4013, and tanδ ~ 0.017. Moreover, the XRD patterns and TEM results prove that all the samples are mainly with perovskite structure, and the SEM figures show that the average grain size of the ceramic prepared by the precursor method is slightly increased compared with the ceramic prepared by the solid-phase method. Furthermore, the temperature-dependent dielectric performance results present that all the samples perform obvious relaxation behavior. [ABSTRACT FROM AUTHOR]

In this paper, through thermal analysis of the melting process of foamed ceramics, the microstructure evolution of foamed ceramics and the effect mechanism of the appearance of gas–solid interface on the evolution of pore wall structure are studied. A new method for regulating the microstructure of pore wall based on gas–solid interface is proposed. The results show that after the initial melting temperature point, the appearance of the gas–solid interface provides a large number of heterogeneous nucleation sites, which promotes the precipitation of anorthite in the pore wall. Within the soaking time of 0–50 min, the gas–solid interface showed a decreasing trend, which resulted in a significant decrease in the anorthite content on the pore wall and eventually disappeared. The addition of alkali metal oxide-Na2O not only reduces the melting point of the raw material, but also increases the number of gas–solid interfaces, thereby increasing the content of anorthite in the pore wall. When the Na2O content reaches 2.1 mass%, the effect of the gas–solid interface is significantly reduced. Na2O reacts with quartz to form a sodium silicate melt, at the same time, the addition of Na2O provides excess O2−. The Mg2+ and Al3+ in the raw material combine with free O2− to form spinel, which promotes the spinel precipitation in the pore wall, leading to the main crystalline phase from anorthite to spinel. This research has important guiding significance for enriching and precisely controlling the preparation process of porous materials. [ABSTRACT FROM AUTHOR]

The paper studies the possibility of changing the properties of piezoceramic materials of various functional groups. The aim of this work was to vary the properties of piezoceramics at the stage of production by changing the technological factors with a constant chemical composition. The microstructure of piezoceramics is formed during its sintering, and also are the most important mechanical properties – density and hardness – which affect electrophysical properties. Therefore, by correcting the microstructure formation process, it is possible to change the electrophysical properties of piezoceramics. Methods of hot pressing and spark plasma sintering allow us to effectively correct the forming process of the sintered piezoceramics microstructure. The aim of this study was to use these methods for the sintering of piezoceramic materials of various functional groups and variations of their parameters. The study confirmed the effectiveness of the proposed methods for a wide-range changing piezoceramic functional parameters. [ABSTRACT FROM AUTHOR]

The influence of different dispersants on the dispersion of Y2O3 sintering aid in B4C powder and the microstructure and performance of the subsequently hot-pressed ceramics were studied in this paper. The results indicated that ammonium polycarboxylate (APC) could effectively enhance the distribution of Y2O3 in B4C powder, and further improve the distribution homogeneity of the formed second phase YB4 in the fabricated ceramics. Polyethyleneglycol (PEG) 600 was beneficial to breaking the Y2O3 agglomeration in B4C powder and improving the distribution of YB4. The remaining PEG 600 in the mixed powder would react with B4C and Y2O3 particles to form the dendritic-structure second phase in the sintering process, which comprised some whisker-like branches and a layer of film. The distribution of YB4 in the fabricated ceramics was slightly improved by adding sodium citrate (SC) dispersant. Y2O3 reacted with B4C to form the intergranular and intragranular YB4, and liquid phase was formed in the sintering process, facilitating the rearrangement of B4C grains and improving the densification. The dispersant APC could improve the homogeneity of YB4, promoting the densification and strength of the ceramics. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the effect of Nb element doping on the microstructure and electrical properties of lead zirconate stannum titanate (PZST) ceramic and to improve phase transition properties of PZST. Nb-doped Pb(Zr,Sn,Ti)O3 ceramic samples were prepared by the conventional mixed oxide method. Phase transitions induced by temperature, pressure, and electric field were measured with electric dielectric permittivity, hydrostatic pressure, and hysteresis. The microstructure of the samples was observed by electron scanning microscope to discuss the effect of Nb doping on PZST ceramics. The experiment results indicated that the remnant polarization (Pr), dielectric constant, phase transition, and microstructure were strongly dependent on Nb doping content. [ABSTRACT FROM AUTHOR]

The paper presents the results of an experimental study of the microstructure and microhardness of a functionally gradient material fabricated from 316L stainless steel and tungsten carbide (WC) ceramic particles by the selective laser melting method. High-quality defect-free cermet coatings with different ceramic contents were obtained. Optical and scanning electron microscopy and energy dispersive analysis show that laser processing leads to dissolution of WC ceramic particles. The produced coating has a dendritic structure and contains iron- and chromium-based carbides. The coating microhardness is in the range HV0.3 = 280 – 430. [ABSTRACT FROM AUTHOR]

Thermal energy storage (TES) has been identified as a breakthrough concept in development of renewable technologies. However, the main challenges are related to the development of competitive heat storage materials. Despite the number of studies on heat storage materials, the determination of new alternatives for next generation technologies is still open. In this regard, this paper presents the results of an experimental study of the physical, thermal and mechanical properties of SiC-doped ceramics as potential materials for TES applications. Two kinds of SiC additives (high and low densities) were incorporated with different percentages into the clay matrix in order to produce ceramics via the extrusion process. The addition of low-density SiC (true density 3.16 g cm−3) led to the increasing of porosity with large pore sizes and the decreasing of bulk density. Therefore, the thermal and mechanical properties are decreased up to − 50% for flexural strength and − 15% for thermal conductivity when 20 mass% of low-density SiC was used. On the other hand, when high-density SiC (true density 3.42 g cm−3) was used, properties of the clay ceramic were strongly improved: i.e., increase in the bulk density, decrease in the porosity, increase in the thermal conductivity and increase in the flexural strength. The best material was found with the addition of 20 mass% of high-density SiC which had a thermal conductivity of 1 W m−1 K−1, a specific heat capacity of 0.62 kJ kg−1 K−1 and a mechanical strength of 19.6 MPa. It also showed a high thermal stability after 20 successive heating/cooling cycles. Hence, this study provided a useful insight into how the SiC modified the microstructure and properties of fired clay ceramics. Thus, the current results suggest that clay ceramics with high-density SiC addition are promising materials for thermal energy storage applications. [ABSTRACT FROM AUTHOR]

Lithium tantalite (LiTaO3) is an excellent single crystal, only a few studies focused on polycrystalline LiTaO3 ceramics, because it is difficult to sintering densification in fabrication process by common sintering. In this paper, LiTaO3 composite ceramics with added 3 wt% MnO2 were obtained by hot-pressing sintering at different temperatures from 1200 to 1350 °C. The sinterability, microstructure and dielectric properties of LiTaO3 ceramics fabricated at sintering temperatures were investigated. The relative density of the LiTaO3 ceramics was significantly enhanced as the sintering temperature increases first and then decreased. The LiTaO3 ceramics achieved the highest relative density (98.6%) and shown homogeneous microstructure when sintered at 1300 °C. The LiTaO3 and manganese oxide phases were observed in the MnO2/LiTaO3 ceramics fabricated at different sintering temperatures. The dielectric properties of MnO2/LiTaO3 ceramics were significantly influenced by the sintering temperatures. The study of dielectric properties revealed that the specimen had excellent dielectric properties when sintering temperature was 1300 °C and the dielectric constant was 78, as it tends to stay invariable at room temperature. [ABSTRACT FROM AUTHOR]

In this paper, a sol-spray pyrolysis route was employed to fabricate (Cs, Ba)-hollandite ceramic waste forms. The high-phase purity (Cs0.8−xBa0.4+x)(Al1.6+xTi6.4−x)O16 (0 ≤ x ≤ 0.4) ceramics were synthesized at 1050 °C using the produced powders by sol-spray pyrolysis. The results show that all samples show tetragonal hollandite with rod morphology. Additionally, the sintered (Cs, Ba)-hollandite ceramics exhibit a good chemical durability. The normalized release rates of Cs and Ba were < 10−2 g m−2 d−1 after 14 days. These results indicate that hollandite ceramics are promising candidate for immobilizing radioactive cesium. [ABSTRACT FROM AUTHOR]

The paper examines the production of Si-modified biogenic hydroxyapatite ceramics. The introduction of methylsilicic acid hydrogel in amounts converted to 2 and 5 wt.% Si and subsequent sintering at 600°C increase the specific surface area by 10 times, from 6.1 to 59.8 m/g. The porosity of ceramics increases from 43.0 to 62.3% when the modifying addition reaches up to 5 wt.%, the compressive strength being equal to 27-33 MPa. The modifying addition also influences the structure and reduces the minimum grain size of the material from 0.65 to 0.1μm [ABSTRACT FROM AUTHOR]

This paper studies the microwave dielectric properties, microstructure, vibration and densification of Li2ZnTi3+xO8+2x (-0.04≤x≤+0.06) ceramics, manufactured via a conventional mixed oxide route. The X-ray diffraction and Raman spectroscopy revealed the unit cell parameter and cation ordering in LZT non-stoichiometry in their vibrational modes. The densification and phase composition were characterized by the EDX and SEM methods. It was found that a slight Ti vacancy can improve the relative density to the maximum value (96.2%). The XRD results showed that the second phase of TiO2 in the Li2ZnTi3.06O8.12 composition is formed. The sintered samples were detected in the microwave frequency range by using the resonance technique. The τf values of the ceramics within Ti excess adjusted to near zero. The Li2ZnTi2.96O7.92 ceramic showed the best relative density, single phase and best microwave dielectric εr=25.98, Q × f = 61,000 GHz, τf=-17.4ppm/∘C sintered at 1100 °C for 4 h. [ABSTRACT FROM AUTHOR]

The paper describes advances in a promising area for the development of Samsonov’s scientific school at the Igor Sikorsky Kyiv Polytechnic Institute. The main results are provided to refine the mechanisms whereby crystals nucleate and grow from melts of eutectic alloys and acquire their microstructure and phase composition and the mechanisms whereby reinforced composite materials with isotropic and anisotropic microstructure are strengthened for extreme applications involving high-speed heating and cooling, impact interaction, cyclic loading, and corrosive environments. The mechanical properties of reinforced composite materials in a wide temperature range are presented. Areas for application of the reinforced ceramics are identified. [ABSTRACT FROM AUTHOR]

A glass with the nominal composition of 28Y48Si24Al83O17N (in equal percentage) was chosen as parent glass in this paper to prepare YAlO-based glass-ceramics. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to assess the crystallization process of the parent glass. YAG as the only crystalline phase appears in all glass-ceramics produced under 1250°C. A small amount of O'-Sialon secondary phase starts to precipitate from parent glass samples as heat treatment temperature increases to 1250°C. Grain size of the dendrite crystal which corresponds to YAG phase increases and the dendrite branches get thickened as heat treatment temperature increases. Moreover, grain size of YAG phase resulting from two-stage heat treatment is much smaller than that of YAG phase obtained by one-stage heat treatment. The results are relevant to developing improved crystallization treatments for glasses with potential for crystallization to YAG-based glass-ceramics and for heat treatments of YAG/ β-SiAlON materials. [ABSTRACT FROM AUTHOR]

The paper reviews the wear behaviour of oxide ceramics. Wear maps are considered and consequently mild and severe wear are defined. Since the use of ceramics in engineering applications require operation in the mild wear regime, the paper concentrates on mild wear mechanisms, but also considers factors which control the transition to severe wear. Within the mild wear regime, the formation of tribofilms are discussed and the manner in which dislocation activity leads to the wear transition is considered. The wear of so-called ceramic nanocomposites, for which no time dependent wear transition has yet been observed, is considered and the reasons for enhanced performance discussed. The role of transformation toughening in zirconia ceramics is considered in detail, and reasons for the generally poor wear response of these materials defined. [ABSTRACT FROM AUTHOR]

This paper reports the effect of BiO addition as a sintering aid to lower the sintering temperature of SrCuSiO ceramics, as well as the sintering behavior, microstructure, phase evolution and dielectric properties of SrCuSiO ceramics were investigated. The BiO addition significantly reduced the sintering temperature of SrCuSiO ceramics from 1100 to 950 °C. Small amount of BiO addition could promote the densification of SrCuSiO ceramics. However, excessive BiO addition caused the abnormal grain growth, leading to deteriorate dielectric properties. The τ constantly shifted towards the positive direction with increasing the amount of BiO additions. The SrCuSiO ceramics with 3.0 wt% BiO addition sintered at 950 °C for 6 h showed excellent dielectric properties: ε ~ 6.26, tanδ = 3.1 × 10 and τ value of 122.90 ppm/°C. [ABSTRACT FROM AUTHOR]

The evolution of knowledge and inventions that contributed to the science of materials has been studied. The development of materials science in the ancient world involved the accumulation of intuitive inventions and the development of crafts. The antiquity established natural philosophy ideas about the nature of matter and divided all existent things into organic and inorganic worlds (Democritus, Epicurus, Aristotle). In the early Middle Ages, alchemy was widespread, with an idea of transmuting elements into gold. Although alchemical ideas were erroneous, they brought some benefits, contributing to the development of scientific experiment. The New Times marked the rapid development of fundamental sciences that promoted theoretical and practical materials science. This paper presents a chronology of the most important inventions and scientific concepts in a tabular form. [ABSTRACT FROM AUTHOR]

In this paper, 0.6(NaBi)TiO-0.4NaNbO(0.6NBT-0.4NN) was synthesized by solid state reaction method. The homogenous green ceramic sheets with high density were produced by tape casting according to suitable casting parameters. Embryos of multilayered ceramic capacitors (MLCC) had been fabricated by punching, screen printing, stacking, laminating and cutting processes. And then after burning out and sintering at different conditions, the cross-sectional microstructures of components were compared. Differential scanning calorimetric analysis and the thermo-gravimetric analysis of green devices were carried out to analyze the effects of different sintering procedures on MLCCs. The dielectric properties and polarization loops of the MLCCs were investigated with dielectric constant (800-895), dielectric loss (0.004-0.007) and capacitance variation ΔC/C < 11 % in the temperature range of −55 to 205 °C, which satisfied X9R in the Electronic Industries Association standard. The breakdown strength of the capacitor was 260 kV/cm. The resistance of the capacitor was measured to be 1.873 × 10 Ω. These properties of the 0.6NBT-0.4NN ceramic capacitor indicated the potential dielectric materials for the application of MLCCs at the high temperature. [ABSTRACT FROM AUTHOR]

In this paper, the influence of MgO/NbO co-doping on the microstructure and microwave dielectric properties of AlO ceramics has been investigated. Comparing with only MgO doped samples, the introducing of NbO can further promote the densification progress and improve the microwave dielectric properties. A high Q × f value of 216,894 GHz could be obtained with 500 ppm MgO/500 ppm NbO co-doped sample. Besides, MgO/NbO co-doping could increase the stability of the Q × f value of the AlO ceramics. Charge compensation and low content of the second phase are believed to be the main reason of this high and stable Q × f value. [ABSTRACT FROM AUTHOR]

Rare earth zirconates (RE2Zr2O7) are considered as a class of potential high-temperature structural materials. In this paper, a series of Y2O3 and Ta2O5 co-doped Gd2Zr2O7 [(Gd1−xYx)2(Zr1−xTax)2O7+x, x = 0, 0.1, 0.2, 0.3, 0.4] ceramics were prepared by solid-state reaction sintering in order to clarify the influence of Y2O3 and Ta2O5 co-doped on microstructure, Young's modulus and thermal conductivity. The results showed that Y2O3 and Ta2O5 co-doped Gd2Zr2O7 exhibited a single pyrochlore structure, and a small amount of Y3+ ions were doped into the Zr4+ ions lattice. The Young's moduli of doped Gd2Zr2O7 ceramics slightly change with the increase in Y2O3 and Ta2O5 doping concentration. The minimum thermal conductivities of the specimens were obtained at 800 °C. The thermal conductivity of doped Gd2Zr2O7 with x = 0.3 is lower than that of others among the doped specimens, which is around 1.41 W m−1 K−1 at 800 °C. In addition, (Gd0.7Y0.3)2(Zr0.7Ta0.3)2O7.3 ceramic exhibits excellent phase stability from room temperature to 1550 °C. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate and compare the formation of ordered etching masks for submicron-size patterned sapphire substrates through use of the nanosphere lithography and nanoimprint lithography methods. The metal honeycomb network structure and the polymer pillar protrusion structure were obtained from these two methods. Subsequently, the inductively-coupled-plasma reactive ion etching technique was applied to etch the sapphire substrates, and the etchant mixture gases of boron trichloride and argon with the flow rate ratio of 1 to 6 were introduced into the etchant chamber. Two types of submicron -pattern structures were obtained on the sapphire substrate surface after the etching processes were completed. One type of sapphire substrate was the submicron hole array structure and another type was the submicron cone array structure. The working pressure had a considerable effect on the shape geometry and etching rate, and the possible mechanism is discussed. [ABSTRACT FROM AUTHOR]

Technological advancements in ceramic powder synthesis, shaping and sintering have made it possible to tailor the microstructural, mechanical and optical property relationships in the case of advanced transparent ceramic materials. Transparent polycrystalline alumina (TPCA) is the hardest known transparent ceramic and one of the emerging candidate materials for transparent armour applications. The prerequisites for obtaining transparency with the high hardness, is to achieve the sintered average grain sizes <1 μm in combination with density close to the theoretical value. This paper outlines the processing of TPCA by an environmentally benign methyl cellulose based thermal gel casting (MCTG) process, which is employed for the first time in shaping of the TPCA. The green specimens shaped through this technique were pressureless sintered (PLS) to >96 % density at an optimum temperature of 1350 °C. The post sintering by Hot Isostatic Pressing (HIP) at an optimum temperature of 1350 °C and a pressure of 195 MPa resulted in >99.5 % of the theoretical density and a grain size of 0.7 μm. For the sake of comparison, conventional polycrystalline alumina samples (non-transparent) were also processed by sintering at 1550 °C under PLS condition with nearly the same densities (designated as PCA). The TPCA thus developed exhibit a combination of high hardness of 21 GPa, flexural strength of 550 MPa and excellent fracture resistance properties as compared to conventional PCA samples. [ABSTRACT FROM AUTHOR]

In order to effectively improve the flexural strength and fracture toughness of ceramics, two methods can be used to control the growth rate of grain during sintering of ceramic materials by adding a certain amount of (W,Ti)C material. Therefore, on the one hand, the paper simulates the composite ceramic materials based on cellular automata (CA) to optimize the ratio of two formulations. On the other hand, in order to optimize sintering process, CA modeling is also carried out for the sintering process of composite ceramics. Finally, in order to detect the temperature of the firing zone of the ceramic kiln by using the characteristics of the flame image of the firing zone, the K-means clustering method is used for the color segmentation of the flame image of the firing zone of the ceramic kiln. The experimental results show that the size of the grains is in accordance with the actual situation of the simulation and the microstructure evolution of the composites can be simulated well by using the CA theory to simulate the composites; with the increase of simulation time, the grain size distribution is basically unchanged, which accords with the normal distribution, and the simulation process of grain growth is very stable. Based on the K-mean clustering segmentation method, the segmentation of the flame image of ceramic kiln firing zone is realized. This method also provides a good technical means for feature extraction of flame image in ceramic kiln firing zone. [ABSTRACT FROM AUTHOR]

Nanometer-scaled yttria (YO) powders were synthesized by a polymer solution route using polyvinyl alcohol (PVA) as an organic carrier. The PVA polymer contributed to a soft and porous powder microstructure, and homogeneous precursor gels containing PVA polymer were effective in making nanometer-sized yttria powders. In this process, the content of PVA and the calcination temperature strongly affected the microstructure and crystallization behavior of the yttria powders. The homogeneous precursors were crystallized to a stable yttria phase at 600 °C for 1 h. In this paper, a simple solution technique for the fabrication of nanometer-sized yttria powders is introduced. The effects of PVA on the powder morphology and on powder specific surface area were studied. The characterization of the synthesized powders was examined by using XRD, DTA/TG, SEM, TEM, a particle size analyzer and nitrogen gas adsorption. The yttria powder synthesized from PVA with a content ratio of 4:1 revealed a crystallite size of about 15 nm with a high surface area of 34.71 m/g. [ABSTRACT FROM AUTHOR]

The research on materials and systems for tunable microwave devices has gained attraction within the last years. The radio frequency characterization and the component design of tunable microwave components based on dielectric ceramics especially barium-strontium-titanate (BST) are presented in this second part, whereas the basic material properties are discussed in detail in the first part. After a short introduction to the processing technology used for the fabrication of tunable components based on a BST thick film, the relations between microwave properties and material properties as well as the microstructure are presented in detail. The design process for tunable microwave components based on BST thick films is described. Especially the considerations related to micro- and macrostructure and their connection are highlighted. The paper closes with two different application examples: a reconfigurable array antenna for satellite communication and varactors for high power applications. [ABSTRACT FROM AUTHOR]

This paper examines the effect of milling on the morphology and properties of ultrafine ZrO + 3 wt % MgO powder and on the microstructure and strength of the ceramics produced from it. Low-energy milling enables a marked decrease in the degree of aggregation of the powder, which in turn reduces the grain size and increases the density and strength of the ceramics. [ABSTRACT FROM AUTHOR]

Abstract  This paper presents a micro roller embossing process for patterning large-area substrates of laminated green ceramic tapes. The aim of this research is to develop a large-area microstructure formation technique for green ceramic substrates using a thermal roller laminator, which is compatible with screen printing apparatus. A thin film nickel mold was developed via photolithographic patterning and nickel electroplating on a 75-μm-thick nickel film. The mold had an effective panel size of 150 mm × 150 mm with the height of plated protrusive patterns being about 38 μm. Formation of micro patterns was successfully demonstrated over the whole panel area on laminated green ceramic tapes using roller embossing. Micro patterns for inductors, heaters as well as interconnection with 50 μm line-width were embossed on green ceramic substrates. By means of tuning process parameters including roller temperature, applied pressure and feeding speed, we have demonstrated that micro roller embossing is a promising method for patterning large-area green ceramic substrates. [ABSTRACT FROM AUTHOR]

Ceramic technology has had an important role in microelectronics since 1960s and ceramic seems to be a continuously developing, mature technology. Recently, development of low temperature co-fired ceramic technology (LTCC) has been geared up due to the huge demand of miniaturisation of electronic components. New materials are being developed for extending the demand of wide range of dielectric properties of LTCC, minimization of shrinkage, cambering of LTCC, high quality of conductors and patterning etc. This paper deals with formulation of silver conductor inks for LTCC and the effect of ink organics on the LTCC in particular to cambering/warpage, microstructure development were studied and presented. [ABSTRACT FROM AUTHOR]

Designing tissue engineering scaffolds with the required mechanical properties and favourable microstructure to promote cell attachment, growth and new tissue formation is one of the key challenges facing the tissue engineering field. An important class of scaffolds for bone tissue engineering is based on bioceramics and bioactive glasses, including: hydroxyapatite, bioactive glass (e.g. Bioglass®), alumina, TiO2 and calcium phosphates. The primary disadvantage of these materials is their low resistance to fracture under loads and their high brittleness. These drawbacks are exacerbated by the fact that optimal scaffolds must be highly porous (>90% porosity). Several approaches are being explored to enhance the structural integrity, fracture strength and toughness of bioceramic scaffolds. This paper reviews recent proposed approaches based on developing bioactive composites by introducing polymer coatings or by forming interpenetrating polymer-bioceramic microstructures which mimic the composite structure of bone. Several systems are analysed and scaffold fabrication processes, microstructure development and mechanical properties are discussed. The analysis of the literature suggests that the scaffolds reviewed here might represent the optimal solution and be the scaffolds of choice for bone regeneration strategies. [ABSTRACT FROM AUTHOR]

A study of the structural characteristics of the composites [Pb(Fe0.5Nb0.5)O3(PFN)] x -[Cr0.75Fe1.25O3(CRFO)]100− x ( x = 0 (CRFO100), 10, 50, 90, 100) was performed in this work. The compounds PFN100 and CRFO100 were prepared by conventional solid-state method and investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and 57Fe Mössbauer Spectroscopy techniques. The X-ray analysis shows that PFN100 is tetragonal and the CRFO100 phase has a trigonal symmetry. The refinement of all the composites was also performed and discussed in this paper. The Mössbauer spectrum for the composite samples shows a paramagnetic doublet and a sextet probably assigned to a magnetic phase associated to Fe+3. For the sample PFN100, only a magnetic field of 49.5 T (isomer shift (δ) = 0.21 mm/s) was detected. For the composite sample, the δ and Δ are typical of Fe ions at sites of octahedral coordination. [ABSTRACT FROM AUTHOR]

Gd3+ was chosen as a substitute for Bi3+ in BiNbO4 ceramics, and the substitution effects on the sintering performance and microwave dielectric properties were studied in this paper. The high temperature triclinic phase was observed only in the Bi0.98Gd0.02NbO4 ceramics when sintered at 920 °C. Both bulk densities and dielectric constant (εr) increased with the sintering temperature, while decreased with the Gd content. The quality factor ( Q) exhibited a correlation to the Gd content and the microstructures of Bi1− x Gd x NbO4 ceramics. At the sintering temperature of 900 °C, Bi0.992Gd0.008NbO4 ceramics exhibited microwave dielectric properties of εr ∼ 43.87, Q × f ∼ 16,852 GHz (at 4.3 GHz), and its temperature coefficient of resonant frequency (τf) was found to be near-to-zero. [ABSTRACT FROM AUTHOR]

The red glaze (slip) that characterizes the Terra Sigillata potteries, greatly contributed to their success during the Roman period. This feature can in fact be partially explained by the microstructure (crystalline phases and grain sizes) and the physico-chemistry (compositions) of the ceramics. In this paper, we describe how the technique of synchrotron micro scanning X-raydiffraction could contribute to the understanding of the elaboration process and origins of these ceramics. The small (micron) size of the X-raybeam coupled with the use of a sample scanning stage allows one to spatially resolve the distribution and other characteristics of the constitutive mineral phases. [ABSTRACT FROM AUTHOR]

This paper presents a new functional material for smart structure applications. Piezoelectric PZT/cement 1-3 composites that have good compatibility with civil engineering structural materials have been studied. The composites with different volume fractions of PZT ranging from 0.25 to 0.77 were fabricated by the dice-and-fill method. It was found that the 1-3 composites have good piezoelectric properties that agreed quite well with theoretical modeling. The thickness electromechanical coupling coefficient could reach 0.55 in the composite with a ceramic volume fraction of 0.25. Those composites have potential to be used as sensors in civil structure health monitoring systems. [ABSTRACT FROM AUTHOR]

This paper deals with the effects of preparation methods on the texture development and densification in textured SrBi4Ti4O15 (SBT) ceramics. The specimens were prepared by the oriented consolidation of anisotropic particles (OCAP), templated grain growth (TGG) and reactive templated grain growth (RTGG) methods. The specimens with extensive texture were obtained by all methods except for TGG with small template and large matrix particles. The origin of extensive texture development was the growth of aligned platelike particles. A characteristic of microstructure was the formation of colonies, in which platelike grains contacted face-to-face. The size of colonies was dependent on the preparation method, and determined the size of pores between colonies, which had a large effect on the sintered density. The OCAP and RTGG methods gave the green compacts composed of only platelike particles and large colonies and pores formed during sintering. The TGG method gave the green compacts composed of platelike and equiaxed particles and prevented the formation of large colonies and pores during sintering. Thus, the dense, highly-textured SBT ceramics were obtained by the TGG method. [ABSTRACT FROM AUTHOR]

From antiquity, glazes have been one of the techniques used for decorating ceramics. Potters took advantage of the optical properties of these glazes to improve the quality of the object, especially to obtain an appearance or some characteristics that had commercial success. This is why it is important to know the reasons of the visual appearance of glazes. In this paper we present some aspects of the characterization of lustre, one of the on-glaze decorations that results in a more spectacular visual effect, as a microstructure, its composition, its raw materials and some technological aspects of its production. Lustre is a three-dimensional heterogeneous structure, where copper and silver nanoparticles play the most important role, but also alkali elements in the glaze and other components of raw lustre pigments. Lustre properties are determined by copper and silver composition and by distribution and dimension of these metallic nanocrystals in the decoration layer. [ABSTRACT FROM AUTHOR]

Sialon ceramics were discovered simultaneously (but independently) in late 1971 at Newcastle University and also at the Toyota Research Laboratories in Japan. During the 30 years since their original discovery, the Newcastle laboratory has made a significant contribution to current understanding of the science and technology of these materials. Sialons are of interest as engineering materials for high temperature (>1000°C) applications because they can be pressureless-sintered to high density and be designed to retain good mechanical properties even up to ≈1350°C, whereas competing metallic materials are weaker and prone to corrosion. A characteristic disadvantage of all nitrogen ceramics is that an oxide additive is always included in the starting mix to promote densification, and this remains in the final product as a glassy phase distributed throughout the grain boundaries of the final microstructure. Since the glass melts at ≈1000°C, the high temperature properties of the final ceramic are in fact determined by the properties of the grain-boundary glass. The most common method of improving high-temperature performance is to heat-treat the material at temperatures of 1100–1350°C in order to devitrify the glass into a mixture of crystalline phases. More specifically it is desirable to convert the glass into a sialon phase plus only one other crystalline phase, the latter having a high melting point and also displaying a high eutectic temperature (max ≈1400°C) in contact with the matrix sialon phase. Previous studies have shown that there are a limited number of possible metal-silicon-aluminium-oxygen-nitrogen compounds which satisfy these requirements. The present paper gives an overall review of this subject area and then summarises recent work at Newcastle aimed at total removal of residual grain boundary glass. This has been achieved by: (1) a post-preparative vacuum heat treatment process to remove the grain boundary glass from silicon nitride based ceramics in gaseous form, (2) above-eutectic heat-treatment (AET) of sialon-based ceramics to crystallize grain-boundary liquid into five-component crystalline sialon phases. [ABSTRACT FROM AUTHOR]

Using the solid-state reaction process, we prepared (Bi,Pb)2Sr2Ca2Cu3O10-δ (Bi-2223 for brevity) ceramics with the addition of zirconium dioxide (ZrO2) nanoparticles. The proportion x of ZrO2 per the total masse of superconductor ranged from 0 wt.% to 0.2 wt.%. We report the intragrain critical current density (Jc), pinning mechanisms, and thermal fluctuations induced excess conductivity. Employing numerous characterization techniques, combining X-rays diffraction, electrical transport measurements, scanning and transmission electron microscopes (SEM and TEM), and DC magnetization hysteresis measurements, we find that the ceramic sintered with 0.1 wt.% ZrO2 nanoparticle showed the best superconducting performance. From the analysis of excess conductivity using Aslamazov–Larkin model, we assessed the crossover temperatures between different regimes of conductivity, the penetration depth, the coherence length, as well as the upper and the lower critical magnetic fields (Bc1, Bc2) at zero kelvin for all the ceramics. Critical current density versus temperature deduced from magnetization measurement is raised by NP-ZrO2 addition. Thereby, NP-ZrO2 strengthened the role of δl pinning cores and enhanced the flux pinning ability. [ABSTRACT FROM AUTHOR]

This paper concerns the thermophysical properties of high-frequency induction heat (HFIH) sintered alumina ceramic nanocomposites containing various graphene nanoplatelets (GNP) concentrations. The GNP/alumina nanocomposites demonstrated high densities, fine-grained microstructures, highest fracture toughness and hardness values of 5.7 MPa m1/2 and 18.4 GPa, which found 72 and 8%, superior to the benchmarked monolithic alumina, respectively. We determine the role of GNP in tuning the microstructure and inducing toughening mechanisms in the nanocomposites. The sintered monolithic alumina exhibited thermal conductivity value of 24.8 W/mK; however, steady drops of 2, 15 and 19% were recorded after adding respective GNP contents of 0.25, 0.5 and 1.0 wt.% in the nanocomposites. In addition, a dwindling trend in thermal conductions with increasing temperatures was recorded for all sintered samples. Simulation of experimental results with proven theoretical thermal models showed the dominant role of GNP dispersions, microstructural porosity, elastic modulus and grain size in controlling the thermal transport properties of the GNP/alumina nanocomposites. Thermogravimetric analysis showed that the nanocomposite with up to 0.5 mass% of GNP is thermally stable at the temperatures greater than 875 °C. The GNP/alumina nanocomposites owning a distinctive combination of mechanical and thermal properties are promising contenders for the specific components of the aerospace engine and electronic devices having contact with elevated temperatures. [ABSTRACT FROM AUTHOR]

New microwave dielectric ceramics Mg2CeNbO6.5 were synthesized by solid-state method. The phase, crystal structure, micro-structures and microwave dielectric properties of Mg2CeNbO6.5 ceramics had been investigated in the sintering temperature range of 1225-1325 °C. Two phases were detected by the X-ray diffraction patterns, including the main crystalline phase of CeO2 and the second phase of Mg4Nb2O9. Well-developed microstructures of the well-dense samples were obtained for samples sintered at 1225-1325 °C. As sintering temperature increased, the τf values were stable, however, the significant change in the ɛr values and Q × f values were observed. At 1275 °C, the obtained Mg2CeNbO6.5 ceramics had promising excellent microwave dielectric properties: εr = 15.38, Q × f = 17,300 GHz and τf = − 49.71 ppm/°C. [ABSTRACT FROM AUTHOR]

The incorporation of foreign nanostructure oxide phase into the YBa 2 Cu 3 O 7 - d ( Y 123 ) superconductor material is capable of producing trapping sites and upgrading the property of flux pinning (FP). Bulk ceramics with porosity around 19% ± 1% having a nominal composition Y 123 + x Dy 2 O 3 are prepared via the solid-state reaction method. Dy 2 O 3 nanoparticles ( Dy 2 O 3 - NPs ) with an average size of about 20 nm and content x = 0.0, 0.1, 0.2, and 0.5 wt% are considered in this study. The structure, microstructure, magnetic susceptibility, electrical properties, and fluctuation-induced conductivity were investigated in detail. The X-ray diffraction (XRD) patterns showed the existence of YBa 2 Cu 3 O 7 - d with orthorhombic structure as a major phase. The microstructural examination using scanning electron microscope (SEM) and energy-dispersive X-ray (EDX) spectroscopy showed that Dy -rich nano-agglomeration segregated at the grain boundaries or on the surface of Y123 grains. The volume fraction of superconductor grain ( f sg ) and Josephson energy coupling (E j) were extracted from AC susceptibility versus temperature measurements. From log–log plots of the excess conductivity versus, the reduced temperature and using the Aslamazov–Larkin model, we assessed the crossover temperatures between different regimes of conductivity, the effective thickness of the 2D layer system (d), the coherence length ( ξ co ), the penetration depth ( λ o ), the critical current density ( J c (0) ) as well as the upper and the lower critical magnetic fields ( B c2 (0) and ( B c1 (0) ) at zero kelvin for all the ceramics. ξ co and λ o decreased, while J c (0) , B c2 (0) , and B c1 (0) increased with Dy 2 O 3 -NPs addition up to 0.2 wt% results in better flux trapping. The highest values of B c 1 (0) , B c 2 (0) , and J c (0) are found to be equal to 2.6 Tesla, 120.6 Tesla, and 65.64 × 103 A/cm2, respectively. The inclusion of a suitable amount of Dy 2 O 3 -NPs into the YBa 2 Cu 3 O 7 - d superconductor is an encouraging way for developing material with good superconducting performances for practical applications such as the second-generation HTS technologies for power transmission and fault current limiters. [ABSTRACT FROM AUTHOR]

Ca1+xV2O6 (x = 0.25, 0.50, 0.75, 1.0) ceramics were synthesized via the conventional solid-state reaction method. The effects of calcium ion content on the phase composition, sintering, microstructure, and microwave properties were investigated. XRD analysis showed that in the three samples with x < 1, the CaV2O6 phase and the Ca2V2O7 phase were the main phase and the secondary phase, respectively. In the sample with x = 1, Ca2V2O7 was the only crystalline phase. EDS analysis was consistent with the above results. The results of phase content showed that the increase in Ca2+ ion content led to an increase in the Ca2V2O7 phase and a decrease in the CaV2O6 phase. The increase in the Ca2V2O7 phase content led to an increase in the εr value, but worsened the Q × f value. In addition, due to the relatively large τf value of the Ca2V2O7 phase, the increase in Ca ions also improved the τf value of the ceramics. The Ca2V2O6 sample sintered at 950°C for 4 h showed optimal microwave dielectric properties: εr = 11.9, Q × f = 38,500 GHz (at 8.9 GHz), τf = −31 ppm/°C. [ABSTRACT FROM AUTHOR]

Zirconia toughened alumina (ZTA) ceramics are commonly used in various industries. Adding suitable additives is an effective way to improve the performance of ZTA ceramics. However, the common reinforcement in ZTA, chromia (Cr2O3), tends to volatilize at high temperature in the presence of oxygen, limiting ceramic densification. Consequently, additional amounts of Cr2O3 are typically limited to below 1 wt%. In this study, spark plasma sintering was utilized to inhibit the volatilization of Cr2O3. Dense ZTA ceramics with high Cr2O3 content (from 1 to 10 wt%) were prepared at 1350 °C. The impact of the solid solution on the structure and properties of the ceramics was investigated. The findings demonstrate that the high Cr2O3 solution can regulate the grain size in the matrix, leading to an enhancement in both hardness and fracture toughness. The optimum performance of the sample was obtained with a 5 wt% dosage of Cr2O3, where the maximum values of Vickers hardness and fracture toughness were 20.66 GPa and 6.37 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

A novel hybridized magnesium-based metal matrix composite consolidated with 4wt%AlN-4wt% Y2O3-4wt%VB nano-ceramics has been developed via powder metallurgy (PM) of spark plasma sintering (SPS) process. A statistical Taguchi design was employed to examine the significant effects of the individual or the interactive sintering parametric process, namely, sintering temperature, pressure, dwell time, and heating rate on the relative density, hardness, and nanohardness of the developed composite. The outcome of the optimized process shows that all the factors contributed to the densification and hardness of the composite, but temperature was seen as the major factor that significantly influenced the process beyond 90%. The highest microhardness value of 106 HV and 2.8 GPa nanohardness was exhibited by the material sintered at 500 °C, 40 MPa of pressure, 5 min of dwell time, and a heating rate of 100 °C/min. Likewise, a minimum crystallite size of 8.87 nm and the smallest grain size of 17.68 µm were achieved at the highest sintering temperature. However, the modeling response suggested that full densification (relative density of about 99%) can be achieved at sintering temperature of 500 °C, pressure of 30 MPa, dwell time of 5 min, and heating rate of 75 °C/min. [ABSTRACT FROM AUTHOR]