Effect Of Sintering Process Research Articles

Effect of Sintering Process on Microstructure and Properties of (Zr0.2Ta0.2Ti0.2Cr0.2Hf0.2)Si2 High-Entropy Silicide Ceramics

In this study, five kinds of (Zr0.2Ta0.2Ti0.2Cr0.2Hf0.2)Si2 high-entropy ceramics were prepared by a two-step method under different vacuum pressureless pre-sintering processes, and the microstructures and mechanical properties of the ceramics under different parameters of the pre-sintering process were systematically discussed. The results show that the physical structure of the ceramic samples remains basically unchanged by changing the pre-sintering conditions; the longer the holding time of the initial pre-sintering, the higher the densification of the samples and all of them are above 95%. The hardness of the ceramics was around 10 GPa, with the best hardness of 10.11 GPa at 1300 °C for 3 h. This conclusion provides data support for the optimization of the high-entropy ceramics preparation process.

Effects of La doping on diffused ferroelectric phase transition, electric and dielectric properties of lead-free SrBi2Ta2O9 ceramics

Citric acid-assisted method was used to synthesize pure polycrystalline La-doped SrBi2Ta2O9 powders which were uniaxially pressed and sintered under different conditions. La doping of SrBi2Ta2O9 resulted in the shortening of Ta-O bond lengths, but increased the unit cell volume and decreased the crystallite size. The effect of sintering process on dielectric properties was studied in order to find optimal sintering conditions. Dielectric loss, measured at room temperature, increases when sintering temperature rises from 1100 to 1200?C, as well as when sintering time increases from 6 to 9 h. Thus, further investigation was performed on the sample sintered at 1100?C for 6 h. The obvious change in ?? around TC and diffusive phase transition, pronounced for the ceramics with higher La content, were characteristic of the doped ceramics. The diffused ferroelectric phase transition behaviour is caused by structural disorder at the Sr-sites (Sr, Bi and La cations) in the Bi2O2 layers and perovskite blocks. The electrical conductivity increases steadily at lower temperatures (below 200 ?C), but shows a strong temperature- and frequency-dependent trend at higher frequencies. La-doping decreases conductivity by hindering charge carriers? long-distance mobility.

Effects of Sintering Processes on Microstructure Evolution, Crystallite, and Grain Growth of MoO2 Powder

MoO2 micro-powders with a mean pore size of 3.4 nm and specific surface area of 2.5 g/cm3 were compacted by dry pressing, then pressureless sintered at a temperature of 1000–1150 °C for 2 h or for a sintering time of 0.5–12 h at 1050 °C in an N2 atmosphere. Then, their microstructure evolution for morphology, crystallite, and grain growth were investigated. By sintering at a certain temperature and times, the irregular shape of the MoO2 powders transformed into an equiaxed structure, owing to the surface energy, which contributed to faster grain growth at the initial stage of sintering. The crystallite and grain sizes exponentially increased with the sintering time, and the growth exponent, n, was approximately 2.8 and 4, respectively. This indicates that the crystallite growth is governed by dislocation-mediated lattice diffusion, and the grain growth is determined by surface diffusion-controlled pore mobility. The increase in sintering temperature increased both crystallite and grain size, which obeyed the Arrhenius equation, and the activation energies were determined to be 95.65 and 76.95 kJmol−1 for crystallite and grain growths, respectively.

Effect of sintering process on microstructure and properties of Al–Si alloy made by powder metallurgy for electronic packaging application

The impact of the sintering temperature on the microstructure and characteristics of Al–Si composite was investigated in this study. Al-60Si (wt%) composites were sintered at different temperatures, and the microstructural features were evaluated. Optimal microstructural characteristics were observed when the composites were sintered at 850 °C for 2 h. The resulting material exhibited a thermal conductivity, coefficient of thermal expansion, and relative density of 131.4 W/(m·K), 10.02 × 10–6 K–1, and 99.87%, respectively. Elevating the temperature facilitated better wettability of the material, which in turn aided the filling of voids within the material by liquid Al. In addition, a decrease in the total number of interfaces within the material and the establishment of a connected network by the Al matrix contributed to enhanced thermal conductivity and coefficient of thermal expansion.

Effect of sintering process on the properties of transparent Al2O3

ABSTRACT Transparent Al2O3 is the most widely used transparent ceramic. The main factors affecting the transparency of Al2O3 are porosity and impurities. It was found that increasing the sintering temperature or extending the holding time can increase the grain size and reduce the porosity. Holding at 1800°C for more than 1 h is critical for grain growth and elimination of porosity. The increase in light transmittance mainly depends on the decrease in porosity, and the increase in grain size also helps. The increase in bending strength is inversely proportional to the increase in grain size. In a comprehensive comparison, the sample held at 1800°C for 2 h can achieve 87% light transmittance based on the bending strength of 322 MPa.

UHF-RFID enabled wearable flexible printed sensor with antenna performance

Many different parameters affect the antenna performance of the wearable sensors. In this study, antenna performances of textile based sensors which have different pass numbers from 1 to 5 printed using conductive ink with pad printing method were investigated. Moreover, the effect of sintering process after printing on the RF antenna performances of wearable sensors was examined. For this, antenna impedances, and reflection coefficients of the sintered, and non-sintered printed sensors were measured using a vector network analyzer. While the frequency at the collapse point of the reflection coefficient graph of the sensors without sintering and with different pass numbers was 254 MHz, the collapse point of the reflection coefficient graph of the sensors was 943 MHz after sintering. The measurements indicate that the sintering process has a significant effect on the antenna performances of wearable sensors, and it is concluded that the sintered printed wearable sensor samples enable data transmission wirelessly in short range. In addition, bending, and gain measurements was applied to wearable sensor which has the best performance according to the impedance measurement results. Thus, these UHF-RFID enabled wearable sensors with antenna performance might be good option to form a network of passive interactive sensor architecture for RFID and wearable technologies. In addition, considering the designed wearable sensor structure, it is foreseen that the potential usage areas of this structure may be moisture sensitive areas (such as supply chains and transportation of moisture-sensitive products).

Performance of B4C/CeB6 composites fabricated via hot pressing under different processes

AbstractIn this work, CeO2 sintering additive reinforced B4C ceramic composites were prepared by hot‐pressing reaction sintering under different processes of low temperature–long holding time (1980°C, 30 MPa, 3 h, 4 wt% CeO2) and high temperature–short holding time (2050°C, 30 MPa, .5 h, 4 wt% and 6 wt% CeO2). The effect of sintering process and CeO2 content on the microstructure and mechanical properties of B4C‐CeB6 composites were investigated. The existed impurities in the obtained composites were also analyzed. Results show that CeO2 is an active sintering additive. CeB6 is formed by the reaction between CeO2, B4C and C in sintering process. The densification of B4C ceramics is enhanced, and the grains can be refined by the formed CeB6, which promotes the strength. The thermal expansion coefficient mismatch, crack deflection, and fracture mode change caused by the in situ formed CeB6 improve the toughness. The process of low temperature–long holding time is more suitable for playing the role of CeO2 additive in sintering of B4C, under which condition the relative density, flexural strength, fracture toughness, and hardness reach 99%, 417 MPa, 5.32 MPa·m1/2, and 30.66 GPa, respectively. The impurities in the composites are the kinds of Ti‐contained, C‐O‐Mg‐Ca‐contained, C‐O‐Ca‐S‐contained, and Si‐contained impurities.

Effect Of Sintering Process On Micro-structure And Properties Of Mullite Porous Ceramics Containing magnesium oxide

Mullite porous ceramics with high porosity and good mechanical properties were prepared by foaming method combined with gel casting process using kaolin and alumina as main raw materials and sodium polyoxyethylene ether sulfate as foaming agent. The effects of sintering process and magnesium oxide content on the microstructure and properties of mullite porous ceramics were investigated. The studies show that: With the addition of magnesium oxide, the amount of mullite produced and the compactness of the sample will increase. At this time, the microscopic morphology of mullite is needle-like and prismatic, and the mechanical properties are better. and the pore size distribution gradually tends to be between 0.1-0.2mm and 0.2-0.3mm. The addition of magnesium oxide, The amount of mullite phase increased, the densification degree of the sample increased, and the acicular and prismatic mullite phases with good mechanical properties were mainly formed, and the porosity of mullite porous ceramics decreased and the compressive strength increased. The pore size distribution gradually tends to be between 0.1-0.2mm and 0.2-0.3mm. As the sintering temperature increases, the porosity of mullite porous ceramics decreases and the compressive strength increases. With the extension of the holding time, the amount of mullite phase generated increases, the porosity remains basically unchanged, and the compressive strength increases.

Preparation and characterization of red mud based porous materials

China was a large country in bauxite mining and refining. One ton of alumina was produced, accompanied by 0.5 ~ 2 tons of red mud [1]. Therefore, the accumulation and pollution of red mud had been a difficult problem to be solved by enterprises and local governments. In this paper, red mud based porous materials were prepared with Bayer red mud, perlite, silicon carbide (as foaming agent) and glass powder (as flux). The effects of sintering process and iron oxide on thermal conductivity, bulk density, porosity and compressive strength of red mud based porous materials were studied by TG-DSC, XRD, SEM and XEDS. The results show that red mud based porous materials with uniform pore distribution could be obtained when the amount of red mud was 60%, perlite was 37%, SiC was 1%, glass powder was 2%, sintering temperature was 1150 °C and holding time was 120 min. The true porosity of the red mud based porous material was 70%, and the average pore diameter was 216.84 μ m. The thermal conductivity was 0.26w / (m • K) and the compressive strength was 2.31MPa.

Experimental Investigations on Microwave-Current Assisted Sintering Process and Oxidation of Graphite Die at High Temperature

In the current-assisted sintering technique, graphite is mainly used to fabricate die and other components (such as electrodes and spacers) because of its excellent thermoelectric properties, high melting point and high ratio of the tensile strength to the compressive strength. As widely known, graphite is one of the brittle materials, and the failure is difficult to be anticipated before it happens. Besides, there is a lack of information about the effects of sintering process, environment and impurity on the graphite structure of the furnace, especially the die, which is the weakest part of the graphite structure. Therefore, the effects of electrical field and oxidation on the graphite die of microwave-current assisted sintering apparatus were investigated at a high temperature of 600-1900 °C based on physical characteristics and mechanical strength. In this article, the spark discharge phenomenon was experimentally proved during the sintering process of nonconductive material. The tensile strength of the upper punch after the sintering process was 20.2% higher than the pristine one because of the transforming of micro-graphite to carbon nanotubes which increased with increasing the temperature. On the other hand, the tensile strengths of graphite lower punch and sleeve were slightly dropped. While, the oxidation of GW-6S graphite in the air caused a mass loss that led to the reduction in tensile and compressive strengths.

Effect of sintering process on the electrical properties and microstructure of Ca-doped ZnO varistor ceramics

The electrical properties of Ca-doped ZnO varistor ceramics are affected by sintering temperature. The samples exhibit excellent electrical properties and microstructure at a sintering temperature of 1050 °C. The ZnO varistor ceramics sintered at 950 °C have the best voltage gradient value, but their nonlinearity and leakage current are very poor. At different sintering temperatures, the grain boundary behavior of ZnO varistor ceramics is different. The grain boundary barrier increases with the increase in the surface state concentration, and it reaches the optimal value at the sintering temperature of 1050 °C. The electrical properties of the samples at the sintering temperature of 1050 °C are as follows: breakdown voltage E1mA = 529 V/mm, leakage current JL = 0.13 μA/cm2, and nonlinearity coefficient α = 92.

Effect of Sintering Process on Ionic Conductivity of Li7-xLa3Zr2-xNbxO12 (x = 0, 0.2, 0.4, 0.6) Solid Electrolytes.

Garnet-type Li7La3Zr2O12 (LLZO) is considered as a promising solid electrolyte. Nb-doped LLZO ceramics exhibit significantly improved ion conductivity. However, how to prepare the Nb-doped LLZO ceramics in a simple and economical way, meanwhile to investigate the relationship between process conditions and properties in Li7-xLa3Zr2-xNbxO12 ceramics, is particularly important. In this study, Li7-xLa3Zr2-xNbxO12 (LLZNxO, x = 0, 0.2, 0.4, 0.6) ceramics were prepared by conventional solid-state reaction. The effect of sintering process on the structure, microstructure, and ionic conductivity of LLZNxO (x = 0, 0.2, 0.4, 0.6) ceramics was investigated. Due to the more contractive Nb-O bonds in LLZNxO ceramics, the cubic structures are much easier to form and stabilize, which could induce the decreased preparation time. High-performance garnet LLZNxO ceramics can be obtained by optimizing the sintering process with lower calcining temperature and shorter holding time. The garnet samples with x = 0.4 calcined at 850 °C for 10 h and sintered at 1250 °C for 4 h exhibit the highest ionic conductivity of 3.86 × 10−4 S·cm−1 at room temperature and an activation energy of 0.32 eV, which can be correlated to the highest relative density of 96.1%, and good crystallinity of the grains.

Effect of sintering process on microstructure, 4-point flexural strength, and grain size of yttria-stabilized tetragonal zirconia polycrystal for use in monolithic dental restorations

Statement of problemModifications have been made in the microstructure and sintering parameters of monolithic zirconia to improve esthetics qualities and avoid chipping of 2-layer restorations. However, how these modifications affect the physical and mechanical properties of zirconia is unclear. PurposeThe purpose of this in vitro study was to compare the influence of different sintering parameters on the microstructure, 4-point flexural strength, density, and grain size of 2 commercially available zirconia advocated for the fabrication of monolithic dental prostheses and 1 commercially available zirconia for use as a core material. Material and methodsThree presintered blocks (Ceramill Zolid, Prettau, and IPS e.max ZirCAD) were used. Specimens were cut and sintered as per the manufacturer's recommendation or as per a modified heating protocol. Ceramill Zolid (Z1450) was sintered at 1450 °C, Prettau (P1600) was sintered at 1600 °C, and IPS e.max ZirCAD (I1530) was sintered at 1530 °C by following the manufacturer's heating protocol. Groups Ceramill Zolid Z1530 and Z1600 were sintered at temperatures higher than the manufacturer's recommendation. Specimens from each group (n=13) were analyzed with X-ray diffraction (XRD), density calculus, average grain size measurement, and 4-point flexural tests. Data were compared by using ANOVA (α=.05). ResultsXRD analysis showed the presence of a tetragonal metastable phase in all groups before and after sintering. No significant differences were found in relative density values for the 3 Ceramill groups (5.98 g/cm3). Groups I1530 (6.03 g/cm3) and P1600 (6.03 g/cm3) had similar density results greater than 6.00 g/cm3. The average grain size of all groups remained lower than 1 μm. P1600 had the highest grain size (0.817 μm), and Z1450 presented the lowest grain size (0.465 μm). P1600 showed the most homogeneous flexural strength and the highest Weibull modulus (m=8.22). Z1530 presented the lowest Weibull modulus (m=4.58). IPS e.max ZirCAD (I1530) had the highest flexural strength (1057.41 ±150.54 MPa), and Ceramill Zolid Z1450 had the lowest (621.01 ±138.08 MPa). ConclusionsThe flexural strength, microstructure, crystal phase, and grain size of the analyzed zirconia varied as per the sintering processing. The IPS e.max ZirCAD had the highest flexural strength (1057.41 ±150.54 MPa), followed by Prettau zirconia (864.18 ±118.21), with a statistically significant difference (P<.05). The Ceramill Zolid zirconia presented the lowest flexural strength, as well as the lowest reliability for all sintering parameters used (Z1450: 621.01 ±138.08 MPa and m=5.42; Z1530: 713.10 ±175.44 MPa and m=4.58; Z1600: 630.15 ±112.08 MPa and m=6.87). At a lower heating rate (8 °C/min), the final density increased and excessive grain growth in group Z1530 was prevented.

Grain Growth Kinetics of 0.65Ca0.61La0.26TiO3-0.35Sm(Mg0.5Ti0.5)O3 Dielectric Ceramic.

The 0.65Ca0.61La0.26TiO3-0.35Sm(Mg0.5Ti0.5)O3[0.65CLT-0.35SMT] ceramic was prepared by the solid-state reaction method. The effects of sintering process on its microstructure and grain growth behavior were investigated. The Hillert model and a simplified Sellars model were established by linear regression, and the Sellars-Anelli model with a time index was established by using a nonlinear regression method. The results show that the grain size gradually increases with the increase of sintering temperature and holding time. Meanwhile, the sintering temperature has a more significant effect on the grain growth. The grain sizes of 0.65CLT-0.35SMT ceramic were predicted by the three models and compared with the experimentally measured grain size. The results indicate that for the 0.65CLT-0.35SMT ceramic, the Hillert model has the lowest prediction accuracy and the Sellars-Anelli model, the highest prediction accuracy. In this work, the Sellars-Anelli model can effectively predict the grain growth process of 0.65CLT-0.35SMT ceramic.

The effect of the sintering process on Ag–added FeSe0.94 superconducting wire

We investigated the effect of different sintering processes on Ag–added FeSe0.94 superconducting wires. After applying different sintering procedures, we successfully obtained zero resistivity, at 350 °C for 100 h and at 700 °C for 1 h, in Ag–added FeSe0.94 superconducting wire produced using the ex-situ powder-in-tube method. The crystal structure of both wires is mainly composed of the tetragonal β–FeSe phase. Ag does not react with selenium, and it can be incorporated into the crystal structure. The transport Jc value of these wires is calculated to be 24.4, and 38 A cm−2 at 4.2 K in a self-field, respectively. The low current densities of the wires are attributed to the low core–density and the presence of porosity. The upper critical field is estimated to be 16.2 and 14.6 T from Werthamer–Helfand–Hohenberg theory, respectively.

Influence of the sintering process on microstructures and microwave properties of Ca5Ni2Mg2V6O24 ceramics

A new low-temperature sintered microwave ceramic Ca5Ni2Mg2V6O24 (CNMVO) was synthesized by a solid-state reaction method. The effect of sintering process on microstructures and microwave properties of CNMVO ceramics was investigated in detail. XRD results and EDS analyses show that CNMVO ceramics sintered at 850–925 °C are the uniform solid solution with a stable cubic garnet structure. The CNMVO ceramic sintered at 875 °C has the highest Q × f value and is accompanied by the volatilization of vanadium observed by SEM. TG curves demonstrate that the increase of heating rate weakens the vanadium loss. According to the Raman spectra, the Q × f value reaches the maximum value at a heating rate of 2 °C/min, because of the highest cation ordering degree and the densest packing fraction caused by the properly deficient vanadium. As a result, the Ca5Ni2Mg2V6O24 ceramic sintered at 875 °C with a heating rate of 2 °C/min exhibits the best microwave properties: εr = 8.07, Q × f = 60,613 GHz, and τf = −32 ppm/°C.

Synthesis and Characterization of Hollow Glass Sphere Containing Aluminum Syntactic Foam by Spark Plasma Sintering and Hot Pressing

The effect of sintering process on the microstructure and the mechanical properties of aluminum syntactic foam were investigated in this study. Two different sintering processes of spark plasma sintering and hot pressing were used. Glass hollow spheres with a size of 50–80 μm was used to fabricate the foams having various volume fractions of the spheres in the range of 10–30%. Microstructural analysis revealed that the glass hollow spheres were uniformly distributed in the aluminum matrix, both in the spark plasma sintered and hot pressed ones. As the volume fraction of the spheres increased from 10 to 30%, the density, micro-hardness and compressive strength of the foams were decreased. In comparison to the foams fabricated by hot pressing method, the spark plasma sintered foams had slightly lower density and mechanical strength. In nanoindentation study, it was found that the aluminum matrix in the foam prepared by the spark plasma sintering process had lower strength than foam prepared by the hot pressing process. This is likely because of shorter sintering time used in the spark plasma sintering process than the hot pressing.

Two-step sintering of submicro-grain Ni0.54Mn1.26Fe1.2O4 NTC ceramics with an excellent electrical performance

High temperature-sensitive Ni0.54Mn1.26Fe1.2O4 NTC ceramics were prepared by a conventional two-step sintering approach in the present work. The effect of sintering process on the microstructural and electrical properties of submicro NTC thermistors was investigated. The micromorphology results show increase of the first-step sintering temperature (1000–1180 °C) significantly reduced pores. The relative density and grain size of the materials are increased with the increase of the second-step sintering temperature (1000–1080 °C). The electrical properties results illustrate that thermal constant (B values) are in the range of 5210–5392 K. The complex impedance results demonstrated that both the grain boundary resistance and grain resistance showed a typical NTC characteristic, most of all, the latter illustrated more sensitive with temperature than that of the former, indicating that the grain resistance is dominant for the submicro-structured NTC ceramics.

Mechanical performance of GNP/PLA nanocomposite under varied SPS process parameters

The study examines the mechanical performance of GNP/PLA nanocomposite developed under varied SPS process parameters. The samples were fabricated using a novel Spark Plasma Sintering technique. In this research, the effect of sintering process in terms of sintering pressure and temperature has been studied by focusing on the mechanical properties of GNP/PLA nanocomposites. The densification of the samples was obtained via the Archimedes’ principle while hardness results was obtained using the micro hardness tester. The results show that the density and hardness increased with increasing sintering temperature and pressure. The samples were prepared under uniaxial pressure of 20 MPa and 30 MPa. The sintering temperature of 135 °C and 160 °C was used in developing the samples. The synergetic influence of these process parameters and graphene inclusion was significant in obtaining above 99% densification and with a concurrent enhancement in the hardness property of the developed composite.

Effect of sintering process on the microstructure and ionic conductivity of Li7–La3Zr2–Ta O12 ceramics

Li 7– x La 3 Zr 2– x Ta x O 12 (0 ≤ x ≤ 1) ceramics were prepared by pressureless sintering at 1230 °C in air. XRD, SEM and Impedance test were used to characterize the crystal structure, microstructure and electrical performance of Li 7– x La 3 Zr 2– x Ta x O 12 ceramics. According to XRD data, the specimens with x ≥ 0.2 sintered at 1230 °C for 1 h exhibit a cubic garnet structure without impurities. The Ta-doped specimens sintered at 1230°C for 1 h show high relative density of 91.6%–93.9%. Ta doping has a certain effect on the Li vacancy concentration, lithium arrangement, movable Li + concentration and microstructure of the LLZO ceramic. The Li 6.6 La 3 Zr 1.6 Ta 0.4 O 12 ceramic sintered at 1230°C for 1 h has the highest total conductivity of 6.01 × 10 –4 S·cm –1 at room temperature and the lowest activation energy of 0.27 eV.