Sintering Of Samples Research Articles

Improved dielectric properties of Ba0.5Sr0.5TiO3–ZnAl2O4 composite ceramics using double sintering

Ba0.5Sr0.5TiO3–ZnAl2O4 composite ceramics were prepared by double sintering and conventional sintering. The results show that the double sintering can effectively reduce the ion diffusion between Ba0.5Sr0.5TiO3 and ZnAl2O4 phases. The double sintered samples exhibit higher density and more uniform grain size distribution than the conventional sintered samples. The dielectric permittivity of double sintered samples is lower than that of conventional sintered samples. Impedance spectrum analysis shows that the oxygen vacancy content and grain boundary resistance of the double sintered samples is lower than that of the conventional sintered samples, which indicates that the Q value of the double sintered samples is higher than that of the conventional sintered samples. The optimum dielectric tunability and Q value of double sintered 60 wt%Ba0.5Sr0.5TiO3-40 wt%ZnAl2O4 sample are 23.4% at 30 kV/cm and 276 at 2.257 GHz, respectively. Therefore, double sintering is a strategy that can effectively adjust the dielectric tunability and Q value of BST-ZA composite ceramics.

Thermoelectric properties of type-I clathrate Na8Al8Ge38

To investigate the use of Na-containing clathrates as thermoelectric materials, we prepared several sintered samples of the title clathrate and studied their thermoelectric properties and electronic structure. The Na8Al8Ge38 samples had low lattice thermal conductivities, 15 mW cm−1K−1 at 300 K, because of alloy disorder scattering for phonons due to the Al–Ge framework, compared to a previously reported Na8Ga8Ge38 (21 mW cm−1K−1). Due to the s-orbital of the Na guest atoms, the Na8Al8Ge38 clathrate had a larger effective mass, 3.6me (me: free electron mass), than Ba8Ga16Ge30 (1.5me), although it was a little lower than that 4.6me of Na8Ga8Ge38. However, the Na8Al8Ge38 samples had comparable carrier mobility, 8 cm2V−1s−1 at 300 K, to that of Na8Ga8Ge38, probably because of alloy disorder scattering for electrons. The dimensionless figure-of-merit ZT of Na8Al8Ge38 was almost the same as that of Na8Ga8Ge38, and the former was higher than the latter at high temperatures. The maximum value of ZT was 0.76 at 870 K.

Granularity reconstruction and characterization of silicon carbide micronized powders

Water glass and silica-alumina sol were used as adhesives, uniformly mixed with silicon carbide powder. The effects of binder, binder concentration, sintering temperature, and sintering process on the granularity reconstruction of SiC powders were studied in detail. The results show that when water glass is used as the binding agent, vacuum sintering can effectively inhibit the oxidation of silicon carbide, and suitable granulation and sintering samples are obtained at a concentration of 5%. When silica-aluminum sol is used as the binding agent, it is discovered that the increase in engagement can effectively increase the particle size, and the best effect is achieved at a concentration of 10%. Both systems of binding agents can successfully bind silicon carbide micronized powder, enlarge silicon carbide particles, and accomplish the goal of Granularity reconstruction.

Physico-mechanical, microstructure, and chemical properties of Si/Ti/Nb additions to CoCrMoW medium entropy alloys

CoCrMoWSi, CoCrMoWTi, and CoCrMoWNb medium entropy alloys (MEAs) were manufactured by powder metallurgy technique. The MEAs were sintered in a vacuum furnace followed by a hot isostatic press (HIP) as a secondary process. Optical microscope, scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), and mapping for elemental distribution were investigated. They indicated a homogenous distribution for all the elements with each other. Both the XRD patterns and calculated thermodynamic parameters indicated the formation of new phases including Co7Mo6 and Co7W6, CoCrTi, CoCrNb, and CrSi, with a dual FCC and BCC phase during the sintering process. Density and hardness measurements recorded the highest value for the HIP-sintered samples compared to the vacuum-sintered ones. CoCrMoWSi recorded the highest density and hardness followed by CoCrMoWNb and finally CoCrMoWTi MEAs. The wear resistance results are in complete agreement with the density and hardness results for both sintering samples. The corrosion resistance of the investigated Co-based MEAs was also studied in 3.5% NaCl which recorded the highest corrosion resistance for CoCrMoWNb alloy than the other investigated ones. Uniform, localized and even galvanic corrosion in CoCrMoWTi MEA was noticed on the surface morphologies of the corroded MEA samples.

Resolving the 1886 White Terraces riddle in the Taupō Volcanic Zone

Among the Seven Wonders of the Ancient World, only the Great Pyramid of Giza survives. Yet there is another, older than the seven, that was found and then lost again in the 19th century and once more located by the research herein: the White Terraces, named Te Tarata by indigenous peoples, of the Taupō Volcanic Zone in New Zealand. The greatest geoscience and tourist attractions in the southern hemisphere were the siliceous Pink and White Terraces. European, American, and British tourists bypassed the calcareous terraces at Saturnia, Yellowstone, and Pamukkale for the long sea voyage down to New Zealand. The 1886 Mount Tarawera eruption buried the siliceous terraces, decimating their indigenous owners and their tourism. An eruption crater lake now occupies much of the Rotomahana Basin in the Taupō Volcanic Zone, leading to assumptions that the Terraces were lost. However, no evidence was produced. The indigenous Māori owners did not believe they were lost. Controversy ensued. The resolution of this controversy is of economic and cultural importance as well as scientific interest. In 2011, a joint New Zealand-American project claimed to have found the Pink and White Terraces underwater in crater lake but produced no sinter samples. Recently, their claims were refuted. In Europe, terrestrial survey documents were unearthed, including compass bearings to the terraces by the German geologist Ferdinand Hochstetter. His survey records were digitally repatriated, and the reconstruction of his 1859 survey showed that the terrace springs lay outside the eruption crater. This renewed research in the Rotomahana Basin which has resolved the controversy. By studying topography and with the aid of Māori navigation knowledge, the geographic coordinates of the White Terraces have been triangulated and lie on land, on the shoreline outside the 1886 crater. Surprisingly, this evidence demonstrates that the White Terraces could have been located after the 1886 eruption by observation of the Rotomahana Basin with mapping available since 1864. Exploration and excavation of the Terraces are now possible. Even if degraded by the 1886 eruption, the White Terraces may earn a World Heritage listing and a second life in global tourism.

Investigation of Pressing and Sintering Processes of Powder Copper Samples for Equal Channel Angular Pressing

The pressing and sintering processes of copper powders produced by different methods are studied in the paper. The main research is based on PMS-1 powders, obtained by electrolysis. To find the easiest and the most reasonable sintering mode, the process is carried out in the open air and dissociated ammonia atmosphere. The samples parameters after each processing procedure were calculated, compression tests were carried out. Basing on preliminary experiments the masses and sintering modes of rectangular shape forms used for equal channel angular pressing were figured out. The possibility in principle to carry out the process of equal channel angular pressing of porous sintered samples without metal damage was shown.

αSiC - βSiC - graphene composites

In this study, the mechanical properties of the pressureless sintered samples of α-SiC based composite containing 0–3 wt.% graphene and 0–15 wt.% nano β-SiC were investigated. Simultaneous usage of nano β-SiC and graphene and transformation of β-SiC (3C) to α-SiC (6H/4H) resulted in elongation of secondary α-SiC grains, which significantly improved the mechanical properties (e.g. fracture toughness) of SiC ceramics. According to the results, the highest Relative density of 99.04%, Young’s modulus of 537.76 GPa and fracture toughness of 5.73 MPa × m1/2 were obtained in the sample containing 5 wt.% nano β-SiC and 1 wt.% graphene (5B1G). In addition, two methods of measuring bending strength including three-point bending tests and biaxial tests (piston-on-three-ball) were compared. Strip-shaped specimens were prepared for three-point bending test and disc-shaped specimens were prepared for biaxial bending test. Each bending test was evaluated using a universal testing machine. The results showed that the biaxial bending strength is less than the three-point bending strength. Also, the maximum three-point bending strength of 582.01 MPa and biaxial bending of 441.56 MPa were obtained in 5 wt.% Nano β-SiC and 1 wt.% Graphene samples (5B1G). Studies have shown that in addition to the many advantages of using the biaxial bending method, the results have a very similar trend to the three-point bending strength. Also, the most-increased hardnesses of 28.03 GPa and 29.97 GPa were seen in the sample containing 5 wt.% nano β-SiC (5B) with forces of 10 N and 1 N, respectively. One of the effective mechanisms in improving the fracture toughness of α-SiC ceramics is crack deflection/bridging. Also, the difference in thermal expansion of the α-SiC matrix and the reinforcements, leading to the creation of residual stresses between the matrix grains and the reinforcement, is effective in improving the mechanical properties (e.g. strength and fracture toughness).

Formation and distribution of dioxins in agglomerated products and emitted dust during iron ore sintering

This study investigated the concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) in sintered products and emitted dust samples. Four types of iron ores were used in this study and tested in a sinter pot grate. The PCDD/F analysis showed that the PCDD concentrations (0.175–1.415, pg/g, 0.028–0.087 pg WHO-TEQ/g) were higher than the PCDFs (0.105–0.327 pg/g, 0.006–0.032 pg WHO-TEQ/g) in sinter. In dust samples, three of the four test experiments showed PCDDs < PCDFs in their measured concentrations. Although PCDD/F concentrations were different in sinter and dust samples, the PCBs presented similar behavior in both solid samples. The PCB analysis (pg WHO-TEQ/g) showed that non-ortho PCBs were higher in concentration than the mono-ortho PCBs. The statistical analysis showed significant correlations between low chlorinated PCDD/F congeners and high chlorinated PCDD/F congeners, as well as strong correlations between non-ortho PCBs and mono-ortho PCBs in both sinter and dust samples. However, the dust samples presented stronger and more positive correlations among the PCDD/F and PCB congeners in comparison to corresponding data in sinter samples. The differences in PCDD/F profiles and correlation matrix in sinter and dust samples suggest the dioxin formation during sintering undergos different mechanisms in the sinter and dust samples.

Multilayer co-sintered Pt thin-film strain gauge for high-temperature applications

Typical high-temperature thin-film sensors are fabricated by layer-by-layer deposition and layer-by-layer sintering, which are time and energy consuming. In this study, thin-film strain gauges (TFSGs) were fabricated on superalloy substrate by co-sintering process for the first time. The co-sintering behavior of glassy insulating layer and Pt thin-film resistance grid was studied. Compared with layer-by-layer sintering, the weak interface constraint between the top and sub layers of co-sintered TFSG allows the free in-plane shrinkage of the Pt resistance grid. In the co-sintering process, the glassy SiO2 in the insulating layer fills the pores in the Pt resistance grid, significantly improving the compactness. Further, no Pt element diffuses into the insulating layer. Owing to the remarkable advantages of the co-sintering process, the co-sintered Pt TFSG not only inherits the high-temperature insulation (2.8 MΩ at 800 °C) of the layer-by-layer sintered insulating layer, but also significantly increases the high-temperature stability of the Pt grid resistance; the resistance change rate of layer-by-layer sintered samples at 800 °C is 7.3 % h−1, while that of co-sintered samples at 800 °C is only 0.9 % h−1. Finally, the high-temperature strain response of co-sintered Pt TFSG up to 800 °C was tested.

Low-density Fe40Mn19Ni15Al15Si10C1 high entropy steel processed by mechanical alloying and spark plasma sintering: Phase evolution, microstructure and mechanical properties

The present study deals with the synthesis of a novel Fe40Mn19Ni15Al15Si10C1 low-density high entropy steel (HES) processed through mechanical alloying (MA) and spark plasma sintering (SPS). The elemental powder was milled for 35 h, leading to the formation of multiphase structures i.e., BCC phase (a = 0.286 nm; cI2), γ-brass type (a = 0.872 nm; cI52) and partially ordered B2-type (a = 0.290 nm; cP2) phases with the trace amount of Si. The milled powder was found to be thermally stable up to ∼500 °C, however, the formation of Fe5Si3-type phase was evident at ∼520 °C. The spark plasma sintered (SPSed) sample was able to retain the BCC phase (a = 0.286 nm), γ-brass type (a = 0.872 nm), B2 (a = 0.289 nm) along with the formation of Fe5Si3 type silicide phase (a = b = 0.667 nm, c = 0.468 nm; hP16). These SPSed HES sample was found to have low density (∼6.49 ± 0.3 g cm−3), high microhardness (∼7.8 ± 0.3 GPa) and good compressive strength (∼2046 ± 160 MPa) with an appreciable ductility of ∼19%. The enhanced mechanical properties of the SPSed sample can be attributed to dual-phase microstructure i.e., BCC and B2 along with finer nano-sized silicide precipitates leading to dominant strengthening mechanisms (i.e., grain-boundary and dislocation strengthening). The experimental findings on phase evolution, thermal stability and mechanical properties of non-equiatomic HES were correlated with the various thermodynamic parameters, CALPHAD modelling and strengthening mechanisms. The significance of the present study is to design a high entropy steel containing the dual phase microstructures i.e., BCC as major phase and B2 as secondary phase, for giving rise to high mechanical strength and high temperature stability.

Influence of sintering temperature on microstructure and properties of 90W-10Ti alloy targets prepared by hot oscillating pressing

The 90W-10Ti refractory alloy was sintered by the hot oscillating pressing (HOP) and hot pressing (HP) under vacuum conditions with no contamination of oxygen and hydrogen. The effects of different sintering temperatures on the microstructure, hardness, and electrochemical corrosion properties of the resulting samples were investigated. Compared to the sample made by HP at the same temperature, the relative density, microstructure uniformity (W-W grain contiguity and βTi(W) bonding phase thickness) and properties of HOP sintering samples were significantly improved. Moreover, the sintering temperature and the activation energy were effectively reduced to inhibit grain growth by HOP. The results show that W-Ti targets with high density, fine grain size, high hardness and excellent corrosion resistance could be obtained by HOP.

Joint effect of Bi2O3 and CuO additives in regulating the thermoelectric properties of (Ca0.87Ag0.1Dy0.03)3Co4O9 composite ceramics

Exploring the impact of secondary phase that modulates charge carrier transporting is crucial to achieve high thermoelectric properties of Ca3Co4O9-based ceramics. Bi2O3 and CuO phase were introduced into the Ca3Co4O9 composite. The obvious plate-like grains were observed and the components were verified. The work function of 3.71 eV was acquired to resolve the potential barrier. By the sintering samples in increasing Bi2O3-2CuO content, the gradually reduction in electrical resistivities and the enhancement in Seebeck coefficients were attributed to liquid-phase sintering. The importing of CuO phase formed a large of liquid phase. As a result, a maximum ZT value of 0.23 at 1073 K was obtained, which was 1.6 times than that of the pure Ca3Co4O9. It is an effective way to confirm an important role on the thermoelectric properties of oxides thermoelectric ceramics.

Flash Sintering Preparation and Characterizations of (M0.5Ta0.5)0.05Ti0.95O2 (M = Al, Ga, In) Colossal Dielectric Ceramics

In this paper, (M0.5Ta0.5)0.05Ti0.95O2 (M = Al, Ga, In) ceramic materials were successfully prepared by Flash Sintering (FS) under an electric field of 550 V cm−1 at 1200 °C for 18 min. The influences of different ionic radius on flash sintering behavior, crystal structure, microstructure and dielectric properties of TiO2-based colossal permittivity (CP) ceramics were systematically investigated. FS can reduce the sintering temperature by 200 °C and shorten the sintering time by more than 12 times. The results show that all flash sintering samples were pure rutile TiO2 structure. The grain size decreased with increasing ionic radius. ATTO had the lowest dielectric loss of 0.2 and ITTO had a maximum dielectric constant of 8100 at 1 kHz. XPS analysis confirms that Ti3+ content increased gradually with increasing ion radius. Impedance spectroscopy analysis shows that all flash sintering ceramics were composed of semi-conductive grains and insulating grain boundaries. The CP behavior was explained using the internal barrier layer capacitance effect. This work provides a very meaningful method for the preparation of co-doped TiO2 CP ceramic materials.

Microstructure, Phase Evolution, and Chemical Behavior of CrCuFeNiTiAlx High Entropy Alloys Processed by Mechanical Alloying

High entropy alloys (HEAs) of the type CrCuFeNiTi-Alx were processed through mechanical alloying. The aluminum concentration was varied in the alloy, to determine its effect on the HEAs' microstructure, phase formation, and chemical behavior. X-ray diffraction studies performed on the pressureless sintered samples revealed the presence of structures composed of face centered cubic (FCC) and body centered cubic (BCC) solid-solution phases. Since the valences of the elements that form the alloy are different, a nearly stoichiometric compound was obtained, increasing the final entropy of the alloy. The aluminum was partly responsible for this situation, which also favored transforming part of the FCC phase into BCC phase on the sintered bodies. X-ray diffraction also indicated the formation of different compounds with the alloy's metals. Bulk samples exhibited microstructures with different phases. The presence of these phases and the results of the chemical analyses revealed the formation of alloying elements that, in turn, formed a solid solution and, consequently, had a high entropy. From the corrosion tests, it could be concluded that the samples with a lower aluminum content were the most resistant to corrosion.

Large magnetic-field-induced strains in sintered chromium tellurides

Sintered samples of Cr3Te4 and Cr2Te3 are found to show large strains accompanied by large volume changes under a magnetic field. In Cr3Te4, volume increases of ΔV/V = 500–1170 ppm by applying a magnetic field of 9 T are observed over the entire temperature range below 350 K. At room temperature, the ΔV/V value exceeds 1000 ppm, which is considerably larger than the maximum values reported for Cr-based magnets, thus far, and is comparable to the room-temperature value of forced-volume magnetostriction in invar alloys. Cr2Te3 shows a large ΔV/V of 680 ppm when applying a magnetic field of 9 T at 200 K. Both samples display particularly large volume increases around the Curie temperature, where they also show negative thermal expansion due to the microstructural effects, suggesting that the cooperation between anisotropic lattice deformation associated with the magnetic ordering and microstructural effects is essential for the manifestation of the large magnetic-field-induced volume changes.

Essential factors that can tremendously influence the grain connectivity of ex-situ sintered MgB2 superconductor

Extending the holding time and slightly excessive Mg addition and Mg-Cu co-addition are introduced to the MgB2 superconductors prepared by ex-situ sintering method aiming to improve their grain connectivity and Jc. The influence of which on superconducting performance and microstructure of ex-situ sintered MgB2 was also systemically studied. The AF value of Mg-added samples is obviously improved, especially the AF value of the Mg-Cu co-addition sample has reached the level of the in-situ sintering samples. The Jc of two samples with Mg addition is improved by comparing to others within the entire whole field.

Investigation of forming of structural components of iron ore sinter of different basicity under heating

A high-quality iron ore sinter must have sufficient mechanical strength both in the cold and hot state. Structural components such as the binding phases of calcium and aluminum silicoferrites SFCA and modifications of dicalcium silicate directly affect the strength characteristics of the sinter. During phase transitions, the volume of phases changes, which leads to the occurrence of stresses at the phase boundaries. Then stabilized phases of SFCA are key bundles in the iron ore sinter. Understanding the mechanisms of SFCA formation can lead to an increase in the efficiency of sintering process. The phase transformations occurring in sinter with a basicity of 1.2‒2.0 under controlled heating in an inert atmosphere and an air atmosphere are investigated. The temperatures of phase transitions during heating are shown. The study of the phase composition of sinter samples with different basicities showed that the ore phase consists of magnetite Fe3O4, hematite Fe2O3, calcium and aluminum silicoferrite SFCA and dicalcium silicate modifications α-2CaO•SiO2 and β-2CaO•SiO2. With an increase in the basicity of the sinter, the amount of magnetite and SFCA increases, the amount of hematite decreases, the content of α- and β-2CaO•SiO2 increases slightly. Heating of the sinter in the air atmosphere leads to the oxidation of magnetite to hematite, a decrease in the amount of SFCA, an increase in bicalcium and the appearance of tricalcium silicate. Heating in an inert atmosphere contributes to an increase in the amount of magnetite due to the reduction of hematite and the decomposition of the SFCA phase and an increase in the amount of dicalcium silicate.

Effects of compression on magnetic properties of MnBi prepared by liquid-phase sintering

In this work, the Mn and Bi mixture prepared with and without compression were sintered in a vacuum at 325°C and cooled down naturally to obtain low-temperature phase MnBi. For non-compressed samples, the MnBi content increases with sintering time which could be described by the diffusion process. The average maximum energy product ((BH)max) values were 3.67, 3.05, and 4.77 MGOe for MnBi sintered for 24, 48, and 96 hr, respectively, consistent with their phase identifications. For the compressed samples, the MnBi phase is significantly low in the 24-hr sintered samples compared to the samples sintered for 48 and 96 hr. This resulted in an average (BH)max of 0.43, 3.90, and 3.23 MGOe for the compressed samples sintered for 24, 48 and 96 hr, respectively. The results suggest that compression of the Mn and Bi mixture affects the flow of liquid Bi during sintering and, thus, hinders the formation of MnBi. The effects of the compression were reduced for the prolonged sintered samples, suggesting changes in the internal structure as the sintering proceeded.

К вопросу о фазовой диаграмме твердых растворов Na-=SUB=-1/2-=/SUB=-Bi-=SUB=-1/2-=/SUB=-TiO-=SUB=-3-=/SUB=--xBaTiO-=SUB=-3-=/SUB=-

In solid solutions of Na1/2Bi1/2TiO3-xBaTiO3, the question of the relationship between the concentration of BaTiO3(x) and the presence of relaxor properties, as well as at what value of x these properties disappear, was studied. For this purpose, dielectric measurements of polarized and unpolarized compounds were carried out in a wide range of concentrations x 0.05&lt;x&lt;0.45. Ceramic and monocrystalline samples were studied. It was found that relaxation properties exist in the studied concentration range x and the normal ferroelectric state cannot be achieved. This contradicts a number of literature data in which relaxor properties disappear already at x=0.18. It is suggested that different values of x at which relaxor properties are lost may be associated with different sizes and numbers of polar nanoblasts in the cubic ergodic phase resulting from the synthesis of ceramics due to different sintering temperatures and sample densities. It is concluded that the value of x, at which the relaxor properties disappear, is not constant for all NBT-xBT compounds and may vary depending on the synthesis conditions

Influence of iron ore properties on dioxin emissions during iron ore sintering

Iron ores are principal input materials for iron and steel-making industries. Quality of iron ores is one of the critical parameters for formation of environmental pollutants related to the steel-making process. Dioxins are identified as one of the most toxic pollutants emitted during ironmaking, specifically during the sintering process. This study applied four types of iron ores and analyzed their moisture, density, particle size distribution and element concentrations to investigate their effect on the dioxin formation during sintering. Each type of iron ore was processed in a sinter pot grate. During each processing route, exhausted dust and generated sinter products were collected and subjected to PCDD/F and PCB analysis. Statistical analysis was applied to assess correlations between properties of iron ores and exhausted dioxin emissions, identifying key contributors to dioxin formation during sintering process. Results showed that Fe in iron ores was positively and significantly related to PCB 114 formation in dust and confirmed its co-catalytic effect on dioxin formation. Concentrations of Al, Ti and Cl in iron ores greatly increased PCDD/F and PCB emissions in the sintered products compared to dioxins in dust samples. The S levels and density of iron ores were highly related to the increasing PCDD/F and PCB emissions in both sinter and dust samples. By contrast, concentrations of Si in iron ores played a significant role in decreasing PCDD/F and PCB emissions in both sinter and dust samples. This study also confirmed the optimum size (< 1 mm–2.59 mm) for iron ores, which helps reduce dioxin emissions without affecting the quality of iron and steel-making products.