Sintering Temperature Range Research Articles

$$\hbox {Bi}_2\hbox {O}_{3}\hbox {-doped}$$ $$\hbox {SnO}_{{2}}$$ varistors with low breakdown electric fields

This work presents $$\hbox {Bi}_{{2}}\hbox {O}_{\mathrm {3}}\hbox {-doped SnO}_{{2}}$$ ceramic varistors prepared through conventional ceramic processing in the sintering temperature range of 1290–1320°C. The sample sintered at 1300°C exhibits a breakdown electric field as low as 11.6 V $$\hbox {mm}^{\mathrm {-1}}$$. Scanning electron microscopy images reveal that all the samples have a compact structure, and energy dispersive spectroscopy results for the sample sintered at 1300°C indicate that Bi distributes homogeneously along the grain boundaries and aggregates inhomogeneously on the grain surfaces. With increasing sintering temperature, the grain boundary barrier height remains nearly constant at 0.80 eV. In both the dielectric loss and electric modulus spectra of the sample sintered at 1300°C, obvious relaxations were observed and the activation energies obtained from the respective spectra were 0.33 and 0.15 eV, which are expected to be related to oxygen vacancies and interstitial ions, respectively. Complex impedance spectra are employed to develop a non-typical equivalent circuit model for the $$\hbox {Bi}_{{2}}\hbox {O}_{\mathrm {3}}\hbox {-doped SnO}_{{2}}$$ ceramic varistors at low voltage that yields an excellent fit to the data.

Enhancing the crystallization phenomena and strength of porcelain stoneware: the role of CaO

Limestone was used to modify the fluxing action of two potash feldspars (a pure potash feldspar and a soda-potash feldspar) labeled P and C, respectively, in the formulation of porcelain stoneware based on Cameroonian raw materials. The effect of limestone addition (0–10 mass%) was investigated in the range of sintering temperature between 1125 and 1300 °C. Characterization of sintered samples including thermal behavior (DTA, TG and dilatometry test), phase evolution, densification parameters, flexural strength, morphology as well as pores structure was investigated in details. The maximum flexural strength (138 MPa) was obtained at 1175 °C with P series (7 mass% addition of limestone) and at 1200 °C (122 MPa) for C series. The maximum density (≈ 3.1 g cm−3) and lower water absorption (≈ 0%) were obtained at 1200 °C. Mullite and anorthite were identified as main crystalline phases. Starting from 1175 °C and mostly at 1200 °C, the two series compositions (with 7 mass% addition) presented a self-glazing phenomenon which gave them significant brightness and high aesthetic quality; these properties were accomplished only at 1300 °C for reference samples with no lime addition (P0 and C0). A proper addition of limestone (3–7 mass%) with potash feldspar significantly reduced the sintering temperature (~ 150 °C) and permits the production of high strength (122–138 MPa), low energy and sustainable porcelain stoneware.

Promoting spinel formation and growth for preparation of refractory materials from ferronickel slag

AbstractThe study provides a method for improving the quality of the refractory material prepared from ferronickel slag by promoting the spinel formation and growth in the slag which was sintered with sintered magnesia and chromium oxide in a broad sintering temperature range from 1200°C to 1500°C. According to the thermodynamic analysis, except for forsterite due to the addition of sintered magnesia, a number of high‐melting point spinel phases can also be formed in the presence of chromium oxide and this trend becomes more apparent with increasing sintering temperature, along with declined presence of low‐melting point clinopyroxene, mainly enstatite. This expectation was verified by conversion of a part of the original phase of ferronickel slag, olivine, to two main spinel phases, including magnesium aluminate spinel and donathite which was produced by the replacement of nontoxic Cr3+ ions with Fe3+ ions in the octahedral vacancies of magnesium chromate spinel. The formation and growth of these spinel phases were promoted by elevating temperature from 1200°C to 1500°C, which accelerated the transition of initially generated enstatite to a glassy phase, in favor of densification. The formation and growth of spinel during sintering contributed to high refractoriness and compressive strength of the resulting refractory materials

Crystallization and properties of high calcium glass-ceramics synthesized from ferromanganese slag

Ferromanganese slag (containing 41.7 wt% CaO and 4.5 wt% Al2O3) was used as main raw material to synthesize high calcium glass-ceramics. The amount of ferromanganese slag is 72.4-88.7 wt%. By adjusting Al2O3 content, the rapid crystallization problem in preparing high calcium glass-ceramics by using high content of ferromanganese slag was solved. Moreover, the effects of Al2O3 content on crystallization behavior, microstructure and sintering properties of high calcium glass-ceramics were investigated. The results showed that Al2O3 broadened the sintering temperature range of the powder and improved the uniformity of the grain distribution, achieving effective control of heat treatment process of high calcium glass-ceramics. With the increase of Al2O3 content, the crystallization activation energy increased from 199.7 to 236.9 kJ/mol, and the main crystalline phase changed from Ca2MgSi2O7 to Ca2Al(AlSiO7). When the Al2O3 content was at 11 wt%, the sample strength was 67 MPa and the water absorption rate was 1.8%.

Structure, infrared reflectivity spectra and microwave dielectric properties of a low-firing microwave dielectric ceramic Pr2Zr3(MoO4)9

Pr2Zr3(MoO4)9 ceramics were prepared by solid state reaction method and the microwave dielectric properties were investigated for the first time. Single-phase Pr2Zr3(MoO4)9 ceramics with a space group R-3c were obtained in the whole sintering temperature range (600–800 °C) confirmed by X-ray diffraction (XRD) and Rietveld refinement. SEM images combined with high relative density (95.7%) suggested that well-densed Pr2Zr3(MoO4)9 ceramic could formed at low sintering temperature 650 °C. The intrinsic factors affecting dielectric properties were analyzed according to chemical bonds theory of complex crystals and infrared spectra. Typically, the novel microwave dielectric ceramic Pr2Zr3(MoO4)9 sintered at 650 °C exhibited desirable dielectric properties combination: εr = 10.72, Q·f = 64,200 GHz (at 9.6 GHz) and τf = −13.0 ppm/°C.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ СТРУКТУРЫ, УПРУГИХ И ПРОЧНОСТНЫХ ХАРАКТЕРИСТИК ПОРИСТОЙ КОРУНДОВОЙ КЕРАМИКИ

This paper aims to investigate the internal structure and to evaluate the elastic and strength characteristics of the corundum ceramic samples sintered at different temperatures. The average value of porosity of the sintered samples at the temperatures of 1400, 1500, and 1600 °C is 33, 26, and 17%, respectively. Mechanical tests of the ceramic samples are performed using the threepoint bending method. The ultimate bending strength varies from 135 to 265 MPa in the studied sintering temperature range. The elastic moduli of the sintered samples are found to be in the range of 58 – 113 GPa. An analysis of the ceramic samples’ microstructure is performed using a scanning electron microscope. The dependence of the porosity, pore size, and grain size on the sintering temperature is indicated. The values of strength and elastic modulus of the samples increase nonlinearly with rising sintering temperature in the experiment. Statistical behavior of mechanical properties of the ceramic samples is described using the Weibull analysis. The strength data for the sintering temperatures of 1500 and 1600 °C are well described by the Weibull distribution, and the strength values for a sintering temperature of 1400 °C are described with a significant scatter.

Large dielectric response of 0.6PMN-0.4PZN relaxor ferroelectric ceramic for multilayer capacitors

0.6PMN-0.4PZN solid solution ceramic was synthesized employing two stage columbite route using sintering temperature range 1000–1170 °C for calcination temperature 800 °C and 850 °C, respectively. XRD and SEM characterization revealed single perovskite phase formation in ceramic between 1050 °C to 1100 °C. The highest density upto 94% was achieved for the composition under study. The excellent dielectric properties were obtained at lower sintering temperature 1000–1100 °C. Ceramics sintered between 1000 °C–1100 °C exhibit εmax≈14000 and 24000 at 1 kHz with Tc = 51–48 °C which is near room temperature. A good correlation was obtained between dielectric properties with structure, microstructure and density. The TCC values within the limit of Z5U capacitor specification reflect ceramics of composition 0.6PMN-0.4PZN is a potential candidate for MLC.

Effects of sintering temperature on mechanical properties of alumina fiber reinforced alumina matrix composites

In this study, the continuous alumina fibers reinforced alumina matrix (Al2O3/Al2O3) composites were fabricated through sol–gel method at a sintering temperature range of 900–1400 °C, and their mechanical properties were analyzed separately. To explore the effects of sintering temperature on mechanical properties of composites, the high temperature properties of fibers and matrix were studied in a comprehensive manner. Our results suggested that the composites fabricated at different temperatures exhibited two different fracture features (ductile fracture and brittle fracture). Besides, the 1100 °C fabricated composites possessed the highest flexural strength of nearly 150 MPa. Al2O3 fibers displayed excellent thermal stability, and did not undergo phase transition during the preparation process. However, the grain size of fibers increased dramatically at a sintering temperature of 1200 °C, which led to a significant decrease in the mechanical properties. In the meantime, the surface morphology of fibers became very uneven because of grain coarsening. Due to the phase transition from γ-Al2O3 to α-Al2O3 at 1200 °C, the elastic modulus and microhardness of matrix increased significantly. The higher sintering temperature not only intensified the matrix but also strengthened the interface bonding, thus making the composites prone to brittle fracture. In conclusion, the optimal temperature of composites preparation should be lower than 1200 °C.

Dependence of dielectric and energy storage properties on sintering temperature in lead lanthanum zirconate titanate antiferroelectric ceramics

The effect of sintering temperature on the phase evolution, microstructures, dielectric properties and energy-storage properties of lead lanthanum zirconate titanate antiferroelectric ceramics has been investigated. Scanning electron microscopy images showed that a gradual increase in grain size with increasing sintering temperature. The dielectric measurements revealed that the variation of sintering temperature did not lead to a systematic trend. A correlation between the dielectric properties and microstructures was established. The room temperature dielectric properties demonstrated that both the dielectric constant and saturation polarization increased with increasing sintering temperature up to 1180 °C and then slightly decreased. Furthermore, as for the sintering temperature dependence of energy storage properties, it has shown that with the increase of sintering temperature, both the charged density and discharged density first increased and then decreased. There is an intermediate optimum sintering temperature range (1180 ∼ 1200 °C) in which the samples have better energy storage performance. The dependence of released energy and power densities on the sintering temperature was also investigated. These charge-discharge measurement results were consistent with the calculated values obtained from polarization-electric field hysteresis loops.

Low temperature sintering of Zn4B6O13 based substrates, their microstructure and dielectric properties up to the THz range

Tape casting was used to prepare green tapes based on pure and doped Zn4B6O13 ceramics that are destined for LTCC high frequency substrates. In order to broaden the sintering temperature range, three additives which were based on Zn2SiO4–Li2TiO3, AlF3–CaB4O7–Li2TiO3 and Zn2SiO4–MgTiO3, were selected using heating microscope studies. Differential thermal analysis was used to establish the optimal firing profiles. The microstructure and composition of the sintered ceramics were examined by scanning electron microscopy, energy dispersive spectroscopy and the X-ray diffraction method. Owing to the low sintering temperatures and good compatibility with commercial Ag thick films, multilayer substrates based on green tapes made of the developed materials can be cofired at 900–920 °C. The dielectric properties were studied in a broad range up to the THz frequencies. The most advantageous properties for LTCC substrates, such as high densification degree, a low dielectric permittivity (6.9 at 1 THz) and a low dissipation factor (0.005 at 1 THz) were exhibited by the Zn4B6O13 ceramic to which 10% Zn2SiO4 and 5% MgTiO3 were added.

Investigation into the Influence of the Structure Dispersion and Homogeneity on the Properties of Powder Metastable Austenitic Carbide Steels and Diamond Tools

Diffusion and homogenization in “iron (5 μm–nickel (5 μm or 50 nm)” powder systems of various degrees of dispersion during sintering (900 and 1000°C), as well as spark plasma sintering, are investigated using the Matano–Boltzmann method. Calculated diffusivities in pairs of micron powders sintering without applying pressure (900°C, 6 h) and by the spark plasma method (900°C, 5 min) in these systems are equal to 7 × 10–10 cm2/s. It is shown that the use of nanodispersed nickel powder in diffusion pairs based on finely dispersed iron powder promotes a twofold increase in diffusivity at 900°C in contrast to the pair with the microdispersed nickel powder. Constants in the Ivensen sintering kinetics equation are calculated for the “iron–nickel” powder systems, by which the factors activating sintering of these systems are established. The dependences of the structural phase composition and physicomechanical properties of carbide steels of the Fe(base)–14 wt % Ni–8 wt % TiC system on the sintering temperature in range t = 900–1200°C and structure dispersity and homogeneity are determined. The dependences of the grain size, porosity, hardness, microhardness, fracture toughness, and bending ultimate strength on the sintering temperature are shown. Dependences of tribotechnical properties on the degree of homogeneity of the solid solution and volume of the phase transformation of metastable austenite into deformation martensite during abrasive friction turn out similar for carbide steels and diamond tools based on carbide steel. Optimal values of the variation coefficient of the nickel concentration in austenite and carbide steels of the same chemical composition but with different degrees of dispersity, which provide the maximal volume of the austenite decomposition and high values of the diamond-tool grinding coefficient, turn out equal to 5 in both systems, but the sintering parameters are different. It is shown that the physicomechanical properties of the studied systems depend on the structure porosity and dispersity, while tribotechnical properties depend on the structural homogeneity of steels.

Sintering of binderless cubic boron nitride and its modification by β-Si3N4 additive for hard machining applications

This study present the results of HP-HT sintering, microstructure, properties, and performance of binderless cBN tool material. Within the investigated sintering temperature range of 1900–2600 °C the optimum was found to be 2200–2300 °C. Lower temperature results in incomplete diffusion bonding between cBN grains, while higher temperature results in high degree of recrystallization of initial structure, grain growth, and even formation of hexagonal boron nitride in triple joints. Introduction of stress-inducing β-Si3N4 minor inclusions resulted in high overall mechanical and thermal properties: HK = 41 GPa; KIC = 12.6 MPa·m1/2; λ = 180 W/(m·K). Machining experiments in roughing of hardened tool steels show that binderless cBN material provides high performance in terms of resistance to tool cratering, chipping, and tool fracture.

Effect of sintering temperature on luminescence properties of borosilicate matrix blue–green emitting color conversion glass ceramics**Project supported by the Science and Technology Planning Project of Zhejiang Province, China (Grant No. 2018C01046) and Enterprise-funded Latitudinal Research Projects, China (Grant Nos. J2016-141, J2017-171, J2017-293, and J2017-243).

The color conversion glass ceramics which were made of borosilicate matrix co-doped (SrBaSm)Si2O2N2: (Eu3+Ce3+) blue–green phosphors were prepared by two-step method in co-sintering. The change in luminescence properties and the drift of chromaticity coordinates (CIE) of the (SrBaSm)Si2O2N2: (Eu3+Ce3+) blue–green phosphors and the color conversion glass ceramics were studied in the sintering temperature range from 600 °C to 800 °C. The luminous intensity and internal quantum yield (QY) of the blue–green phosphors and glass ceramics decreased with the sintering temperature increasing. When the sintering temperature increased beyond 750 °C, the phosphors and the color conversion glass ceramics almost had no peak in photoluminescence (PL) and excitation (PLE) spectra. The results showed that the blue–green phosphors had poor thermal stability at higher temperature. The lattice structure of the phosphors was destroyed by the glass matrix and the Ce3+ in the phosphors was oxidized to Ce4+, which further caused a decrease in luminescent properties of the color conversion glass ceramics.

The effect of SPS processing parameters on the microstructure and thermal conductivity of ThO2

Thorium dioxide (ThO2), is a nuclear fuel that is expected to play a vital role in the Generation IV nuclear reactors. One of the challenges to implementation of thoria for the fuel cycle has been the difficulty in fabricating dense pellets via conventional sintering techniques. In this study, the non-conventional sintering of thoria using spark plasma sintering (SPS) was explored. A systematic investigation into the influence of processing parameters on the densification, microstructure, grain size and thermal conductivity of ThO2 is presented. The range of sintering temperature, pressure, and hold time has been systematically varied between 1500 and 1800 °C, 50–70 MPa and 5–15 m, respectively. The results revealed that without the help of any sintering aid, pellets with a relative density of 95% theoretical density (TD) were fabricated at a sintering temperature of 1600 °C, sintering pressure of 50 MPa and a hold time of 10 min. Furthermore, the characterization of these specimens clearly indicates that by carefully selecting the processing parameters, the density, microstructure, grain size and the thermal conductivity of ThO2 can be suitably controlled. This study shows that the use of the SPS technique can potentially solve one of the primary concerns in the front end of the thoria fuel cycle.

Microstructure, microtexture and grain boundary character evolution in microwave sintered copper

In the present investigation, the evolution of microstructure and microtexture of commercially available copper powder during solid state sintering using microwave furnace has been studied. The powder was compacted using 300 MPa uniaxial die pressure and the green compacts were sintered at 610 °C, 880 °C and 1020 °C in argon atmosphere at 20 min and 45 min isothermal holding times using multi-mode microwave furnace which has output power of 3 kW and operated at 2.45 GHz frequency. The temperatures were selected to obtain different dominant densification processes. For sintered samples comparative analysis has been made based on densification behavior, microstructural and microtexture evolution and mechanical properties. Electron backscatter diffraction (EBSD) study indicated that there is a distinct evolution of microtexture and microstructure in terms of evolution of grain boundary character distribution, misorientation, size, shape and morphology of grains and pores. Attributed to high temperature driven volume diffusion process, 1020 °C sintered samples showed better sintering between copper particles, grain growth, grain coalescence, reduction in porosity area fraction and increased pore rounding. For all microwave sintered samples, the highest fraction of CSL boundary fraction found to be Σ3 boundary with a common (111) grain boundary plane which indicated coherent twin boundaries with low energy. More Σ3 twin population is found on intermediate sintering temperature range whereas significant reduction is observed higher temperature sintering which might be the result of grain coalescence and volume diffusion at higher sintering temperature that reduced high angle grain boundaries. Microwave sintered copper samples brought random microtexture evolution with variation of sintering temperature and holding time. This might indicate the presence of non-conventional sintering mechanisms during microwave sintering.

A novel Li1/3Sr1/3Eu1/3MoO4 red phosphor: Influences of sintering temperature on microstructures and luminescent properties

A series of novel Li1/3Sr1/3Eu1/3MoO4 phosphors have been fabricated via the conventional ceramic processing route at different sintering temperatures. The crystal structure, morphology and luminescent properties of the as-synthesized phosphors were characterized through X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and photoluminescence (PL), respectively. It is found that the sintering temperature has significant influences on the crystallinity, morphology and luminescent properties of the obtained Li1/3Sr1/3Eu1/3MoO4 phosphors. In the selected sintering temperature range (600–1000 °C), all the obtained Li1/3Sr1/3Eu1/3MoO4 phosphors possess tetragonal scheelite structure, the synthesized phosphors changed gradually from quasi-spherical to polyhedral particles with a size of 1.0–5.0 μm. All the as-synthesized Li1/3Sr1/3Eu1/3MoO4 samples are typical red-emission phosphors, which can emit 591 nm and 615 nm red light under the excitation of 393 nm ultraviolet and 464 nm blue light, respectively. Moreover, the emission intensities of the phosphors firstly increase and then decrease with increasing sintering temperature, reaching the maximum at 800 °C. All the obtained Li1/3Sr1/3Eu1/3MoO4 phosphors displayed a pure red emission, which are promising red phosphors.

A low εr and temperature-stable Li3Mg2SbO6 microwave dielectric ceramics

Li3Mg2SbO6 ceramics without dehiscence were prepared using a two-stage process. The sintering behavior, structure, and microwave dielectric performances of Li3Mg2SbO6 ceramics had been investigated. XRD and Raman results showed that nearly pure phase Li3Mg2SbO6 were obtained in the sintering temperature range of 1225–1350 °C. The quality factor (Qxf) and relative permittivity (εr) values of samples were strongly influenced by the density, grain size, and cell volume. Typically, balanced microwave dielectric properties were obtained for Li3Mg2SbO6 ceramics sintered at 1300 °C:εr∼10.5, Qxf∼84,600 GHz (at 10.6 GHz), and temperature coefficient of resonance frequency τf ∼ -9.0 ppm/oC.

Effect of Sintering Temperature on Mechanical and Electrical Properties of Lead-Free Bi<sub>0.5</sub>(Na<sub>0.4</sub>K<sub>0.1</sub>)Ti<sub>0.98</sub>Zr<sub>0.02</sub>O<sub>3</sub> Piezoelectric Ceramics

Effect of sintering temperatures on phase formation, mechanical and electrical properties of lead-free Bi0.5(Na0.8K0.2)0.5Ti0.98Zr0.02O3 or BNKTZ piezoelectric ceramics were investigated. The BNKTZ ceramics were prepared via a conventional solid-state sintering technique under various sintering temperature range 1100-1150°C for 2 h. The phase formation and microstructure of the ceramics were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM) method, respectively. XRD analysis indicated that all samples exhibited a single perovskite structure and no secondary phase. SEM microscopy study revealed an increase in grain size with increasing sintering temperature. The maximum values of density and maximum dielectric constant of the ceramics sintered at 1125 °C were 5.79 g/cm3 and 3446, respectively. In addition, the ceramics sintered at 1125 °C showed highest mechanical properties (HV = 4.32 GPa, HK = 5.87 GPa, E = 143 GPa and KIC = 1.30 MPa.m1/2). The highest values of ferroelectric and piezoelectric were found at this sintering temperature.

Low-firing and microwave dielectric properties of a novel glass-free MoO3-based dielectric ceramic for LTCC applications

A novel glass-free MoO3-based dielectric ceramic of Li2Ni2(MoO4)3 was prepared by the conventional solid-state route. The phase compositions, microstructures and microwave dielectric properties were investigated. The XRD data analysis shown that Li2Ni2(MoO4)3 belongs to an orthorhmbic lyonsite-type structure with Pmcn (62) space group during the sintering temperature range from 650 to 725 °C. The Li2Ni2(MoO4)3 ceramic could be well densification at 700 °C for 2 h with 96.8% relative density and exhibited excellent microwave dielectric properties: er = 9.2, Q × f = 41,064 GHz, τf = − 68.86 ppm/°C. Moreover, the Li2Ni2(MoO4)3 ceramic shown excellent compatible with Ag electrode, which makes it a promising candidate for advanced substrate materials in low temperature co-fired ceramic applications.

Enhanced Sintering Behaviour and Microwave Dielectric Properties of CaLa4Ti4O15 Ceramics with ZnO–B2O3 Addition

Effects of ZnO-B2O3 (ZB) addition have been investigated on the sintering behavior, structure and microwave dielectric properties of CaLa4Ti4O15 ceramics. The sintering temperature of CaLa4Ti4O15 ceramics with a very small amount of ZB addition such as 0.2 and 0.5% is obviously reduced from 1550 to 1375°C, and the sintering temperature range is significantly broadened to 1350–1450°C. With the increase of ZB addition, the secondary phases of CaLa4Ti5O17 and LaBO3 are observed in these ceramics. Not only sintering behavior but also microwave dielectric properties of CaLa4Ti4O15 ceramics have been enhanced by a small amount of ZB addition. Excellent microwave dielectric properties of e = 42.7, Qf = 46.678THz, τf = –3.5 ppm/°C are achieved for the CaLa4Ti4O15 ceramics with 0.5% ZB addition sintered at 1375°C.