Rise Of Sintering Temperature Research Articles

Effects of sintering temperatures on the thermal conductivity and microstructural evolution of yttrium hydride monoliths by spark plasma sintering

In this study, YHx (where x represents the H/Y ratio) monoliths were fabricated using Spark Plasma Sintering (SPS), employing yttrium hydride powder as the raw material. The effects of different sintering temperatures (800 °C∼1200 °C) on the thermal conductivity and microstructural evolution of the YHx monoliths, including porosity, grain size, precipitated phases, and internal defects, were investigated. The results indicate that the sintering temperature exerts a significant influence on thermal conductivity and microstructural evolution. Notably, the thermal conductivity of these samples initially increases with rising sintering temperature, but subsequently decreases under identical testing conditions. This phenomenon is primarily attributed to the effects of porosity and precipitate phase. Furthermore, the presence of twin crystals also contributes to the reduction in thermal conductivity. The procedures provide an initial framework for understanding the relationship between thermal conductivity and the evolution of microstructure.

In situ boro-mullite phase formation in Glass–Ceramic glazes: Anatase–rutile phase transformations and microstructure properties

‘‘Boro-mullite’’ is the name for mullites produced through the synthesis of boron-rich material and playing a critical role in producing high-performance materials. Also, the stability of the anatase phase in the glaze and against temperature has been addressed and improved by many studies. In situ boro-mullite crystals generated using various glass-ceramic glaze compositions that contain TiO2 and their impact on the transformation of anatase into a rutile phase were examined in this study. Additionally, the samples' water absorption, bulk density, apparent porosity and shrinkage, Vickers hardness, and optical properties were evaluated at various Al2O3 and B2O3 amounts at 700 °C, 800 °C, 900 °C, 1000 °C and 1100 °C. X-ray diffraction analysis revealed that as the temperature and Al2O3 ratio rose, it triggered the boro-mullite phase formation. On the other hand, increasing the Al2O3 ratio led to a rise in the samples' sintering temperature and delayed the anatase to rutile phase transformation. Furthermore, the presence of corundum crystals retarded the anatase crystal size growth during the remodelling process of the conversion of anatase to rutile. While the increase in the B2O3 ratio sharpened the peaks of albite crystals, the formation of rutile crystals accelerated with the increase in temperature and caused inhibition of albite formation. The albite phase's presence facilitated the creation of the liquid phase and achieved the 0.010 % water absorption and 0 % apparent porosity values as well the highest bulk density and microhardness with 2.476 g/cm3 and 550 H V. The yellowness (+b∗) values were found to be the highest at 1100 °C where the rutile crystals reached their maximum size. The anatase-rutile conversion is postponed and the increase in the yellowness value is prevented by the glaze's formation of boro-mullite. FESEM-EDS analysis showed that the temperature was the driving force in the transformation of acicular boro-mullite crystal into highly acicular prismatic needle crystal and spherical anatase crystals into the rod shape rutile.

Cr-Diamond/Cu Composites with High Thermal Conductivity Fabricated by Vacuum Hot Pressing.

Chromium-plated diamond/copper composite materials, with Cr layer thicknesses of 150 nm and 200 nm, were synthesized using a vacuum hot-press sintering process. Comparative analysis revealed that the thermal conductivity of the composite material with a Cr layer thickness of 150 nm increased by 266%, while that with a Cr layer thickness of 200 nm increased by 242%, relative to the diamond/copper composite materials without Cr plating. This indicates that the introduction of the Cr layer significantly enhanced the thermal conductivity of the composite material. The thermal properties of the composite material initially increased and subsequently decreased with rising sintering temperature. At a sintering temperature of 1050 °C and a diamond particle size of 210 μm, the thermal conductivity of the chromium-plated diamond/copper composite material reached a maximum value of 593.67 W∙m-1∙K-1. This high thermal conductivity is attributed to the formation of chromium carbide at the interface. Additionally, the surface of the diamond particles in contact with the carbide layer exhibited a continuous serrated morphology due to the interface reaction. This "pinning effect" at the interface strengthened the bonding between the diamond particles and the copper matrix, thereby enhancing the overall thermal conductivity of the composite material.

Stability of giant dielectric properties in co‐doped rutile TiO2 ceramics under temperature and humidity

AbstractThis research investigated the influence of temperature and humidity on the giant dielectric (GD) properties of 1% indium tin oxide and 1% Ta2O5 co‐doped TiO2 ceramics sintered at different temperatures. A single phase of rutile TiO2 was obtained in all sintered samples. The mean grain size increased with higher sintering temperatures, resulting in ceramics with a relative density exceeding 98%. A uniform dispersion of dopants and major elements was achieved. Remarkably, the dielectric constant increased significantly from 2 × 103 to 3.7 × 104 with a rising sintering temperature, primarily due to the enlarged grain size. Concurrently, the authors observed low loss tangents, ranging from tanδ≈0.016 to 0.024 at 1 kHz. Slight variations in the dielectric constant were observed with temperature from room temperature up to 210°C, while maintaining remarkably low tanδ. The GD properties were attributed to space charge polarisation at internal interfaces and defect dipoles. Further research explored the impact of environmental conditions on dielectric properties. Remarkably, the ceramics exhibited minimal capacitance variations of less than 10% within the relative humidity range of 30%–95% and temperatures from 15 to 85°C, indicating excellent dielectric stability.

Photoluminescence and thermoluminescence dosimetry properties of Ag/Y co-doped ZnO nanophosphor for radiation measurements.

This work explores the thermoluminescence (TL) and photoluminescence (PL) properties of Ag/Y co-doped zinc oxide (ZnO) nanophosphor. The proposed dosimeter was prepared by the coprecipitation method and sintered at temperatures from 400°C to 1000°C in an air atmosphere. Raman spectroscopy was studied to investigate the structural features of this composition. The new proposed dosimeter revealed two peaks at 150°C and 175°C with a small shoulder at high temperature (225°C). The PL spectrum showed strong green emissions between 500 to 550 nm. The Raman spectrum showed many bands related to the interaction between ZnO, silver (Ag), and yttrium oxide (Y2 O3 ). The rising sintering temperature enhanced the TL glow curve intensity. The Ag/Y co-doped ZnO nanophosphor showed an excellent linearity index within a dose from 1 to 4Gy. The minimum detectable dose (MDD) of the Ag/Y co-doped ZnO nanopowder (pellets) equaled 0.518 mGy. The main TL properties were achieved in this work as follows: thermal fading (37% after 45 days at 1 and 4Gy), optical fading (53% after 1h and 68% after 6h by exposure to sunlight), effective atomic number (27.6), and energy response (flat behavior from 0.1 to 1.3MeV). Finally, the proposed material shows promising results nominated to be used for radiation measurements.

Microstructure, mechanical properties, and corrosion behavior of TiVNbZrHf high entropy alloys fabricated by multi-step spark plasma sintering

The primary objective of this study was to produce a TiVNbZrHf high-entropy alloy through powder metallurgy process and characterize its properties. The effect of sintering temperature on the microstructure and mechanical properties of bulk TiVNbZrHf samples was investigated. The resulting microstructure of the bulk samples included two different phase structures: a body-centered cubic (BCC) phase with a composition rich in (Ti-V-Nb)-Hf and a hexagonal close-packed (HCP) phase with a composition rich in (Hf-Zr)-Ti. The particle size and relative density of the bulk sample increased with the rising sintering temperature. The bulk TiVNbZrHf sample exhibited the highest hardness and the lowest wear rate when sintered at 1400 °C. The corrosion resistance of the bulk samples submerged in a 3.5 wt% NaCl solution steadily improved with increasing sintering temperatures. This improvement is attributed to the increased relative density and diminished grain boundaries. Our research highlights the crucial role of precise temperature control during the sintering process to achieve the desired material properties of high-entropy alloys.

Ytterbia – praseodymia co-stabilized TZP with high toughness and transformation limited strength

Tetragonal zirconia polycrystals (TZP) with high strength and toughness offer the potential to compensate for manufacturing or application related defects. In this study aiming at ultimate toughness a co-stabilized TZP was manufactured by coating of monoclinic zirconia by a wet chemical process with 1.5 mol% ytterbia and 1.5 mol% praseodymia. The powder was hot-pressed at 1300–1400 °C in 25 °C increments for 1 h by 60 MPa axial pressure. The materials exhibit an ultrafine microstructure with grain sizes ranging from 130 to 200 nm. Mechanical properties were measured in a 3-point bending setup, the material shows a combination of moderate strength (600–950 MPa) and high toughness (11–12 MPa√m). Non-linear stress strain curves and occurrence of transformation bands prior to fracture indicate transformation induced failure behaviour. The transformation stress determined from the location of transformation bands in fractured samples increases with rising sintering temperature and is about 100–250 MPa lower than the bending strength.

Effect of Temperature Sintering on Grain Growth and Optical Properties of TiO2 Nanoparticles

Titanium dioxide (TiO2) nanoparticles were prepared by the sol–gel method and the structural, morphological, and optical properties were investigated at different sintering temperatures of 500, 600, 700, 800, and 900°C. A tetragonal structure of anatase, mixed (anatase–rutile), and rutile phases are observed in the X-ray diffraction (XRD) analysis. Pure anatase phase formation occurred at 500°C, whereas anatase-to-rutile phase transformation began at 600°C, and reaching complete conversion to rutile at 800°C. The average crystallite size increased from 23 to 34 nm for anatase and 38 to 62 nm for the rutile when sintering temperature increased from 500 to 900°C. The scanning electron microscope (SEM) result presented the increase of grain size (25–100 nm) with increasing the sintering temperature. The Fourier transform infrared (FTIR) spectra demonstrated the presence of TiO2 vibrational bonds in all samples. The optical bandgaps of the sintered TiO2 nanoparticles decreased with rising sintering temperature. Photoluminescence spectra exhibited three characteristic peaks centered at 380, 450, and 550 nm. The emission intensity increased with increasing the sintering temperature. The Mie analysis was also studied to calculate scattering cross-section, forward scattering, and asymmetry for different grain sizes. The results showed that by increasing the nanoparticle diameters, the peaks of all spectra are redshifted for larger grain sizes and cross-section peaks shift to high values. In this study, the sintering temperature is observed to have a strong influence on crystalline phase transformation, microstructure, and optical properties of TiO2 nanoparticles. The TiO2 sample sintered at 900°C shows the best result to be used as luminescent material due to the low optical bandgap energy.

Optimizing the strength and electrical conductivity of graphene reinforced Cu–Cr–Zr alloy fabricated by powder metallurgy and spark plasma sintering

Copper-based Cu–1Cr-0.2Zr alloys reinforced with graphene nanosheets were fabricated via the powder metallurgy route. The alloy powders were first mechanically alloyed in a high-energy planetary ball mill up to 96 h in an argon atmosphere. Then graphene nanosheets were added (between 0 and 1 wt%) to the alloyed powder and mixed for 6 h in the milling machine. The composite powders were then consolidated in a graphite die using the spark plasma sintering (SPS) at temperatures of 650–850 °C under a vacuum atmosphere. Results showed that relative densities decreased with increasing graphene content but increased with the rising sintering temperature. The compressive yield stress of the composites increased with increasing the graphene content. The maximum yield stress was obtained with 1 wt% graphene, more than two-times increase compared with the parent alloy with no graphene addition. The contribution of the various strengthening mechanisms for the graphene-reinforced composites was calculated using a combined microstructure strengthening model based on the modified shear lag theory. The electrical conductivity enhanced as the sintering temperature was increased while it diminished with graphene addition. According to the results, the sintering temperature of 750 °C and 0.1 wt% graphene addition resulted in optimal electrical and mechanical properties.

Preparation and properties of high-strength lightweight aggregate ceramsite from nepheline tailings

Nepheline tailings (NTs) were made into pellets and then transformed to lightweight aggregate ceramsites by sintering approach, the effects of mix composition and sintering process on air-void structure and performance were studied. The results show that introducing mineralizer, rising sintering temperature and extending holding time increased air-void size, decreased density, reduced cylinder compressive strength and rose water absorption of NT-based ceramsite. Acceleration of heating rate led to the increase of density, resulting in strength enhancement, but heating rate of 20 ℃/min caused uneven air-voids, weakening strength. Dense enamel layer on surface, suitable air-void structure and well-crystallized nepheline of ceramsite contributed to preparation of high-strength lightweight ceramsite with a NT content of 93 % to 97 %, bulk density of 577 kg/m3 to 823 kg/m3, cylinder compressive strength of 4.3 MPa to 9.3 MPa and a low water absorption of 0.3 % to 0.8%

3D printing of pink bioceramic scaffolds for bone tumor tissue therapy

For therapy of tumor-induced bone defects, functional biomaterials with tumor therapy and bone regeneration are of great importance. In this study, 3D printing of calcium titanate (CaTiO3) bioceramic scaffolds was prepared for the therapy of tumor-induced bone defects. The digital laser processing (DLP) based 3D printing technology was applied to prepared CaTiO3 bioceramic scaffolds. It was found that the color of CaTiO3 (CaTi) scaffolds was deeper with the sintering temperature rising. Interestingly, CaTi scaffolds with pink color were found with optimal compressive strength (13.44 ± 0.99 MPa) and satisfactory photothermal property when exposed to NIR laser. The temperature of pink CaTi scaffolds could be over 70 ℃ under NIR laser irradiation (1.32 W/cm2). Attributing to such excellent photothermal performance, CaTi scaffolds had been used as a photothermal biomaterial for the effective therapy of the in vitro and in vivo bone tumor. Moreover, the prepared pink CaTi scaffolds possessed bone-forming in vitro and in vivo. Therefore, 3D printing of pink CaTi bioceramic scaffolds represents a promising strategy by using the bifunctional biomaterial for tumor-induced bone defect therapy.

The influence of sintering temperature on the mechanical evolution of Al2TiO5 flexible ceramics based on the acoustic emission

To explore the influence of sintering temperature on mechanical properties of Al2TiO5 (AT) flexible ceramics, the XRD/Raman, SEM and acoustic emission (AE) technology were used to estimate the phase composition, microstructure evolution and damage behaviors of AT ceramics, respectively. Results show that the diffraction peaks of AT increase before rising sintering temperature from 1300 °C to 1500 °C and then start to decrease at 1600 °C due to the decomposition of AT grains. In specimens with sintering temperature of 1300 °C and 1400 °C, intergranular fractures are more likely to occur, which controls the origination of AE events in the whole stage. And the fracture of big bodies composed by large number of fine AT grains is the main source of AE events with high energy level at initial stage. In addition, Thanks to the more transgranular fracture in specimens with sintering temperature of 1500 °C and 1600 °C, the number of AE events in these two specimens are more than that of specimens with sintering temperature of 1300 °C and 1400 °C.

Microstructure and properties of FeSi6,5 soft magnetic materials prepared by spark plasma sintering

In this paper, FeSi6,5 (6.5 wt.% Si) soft magnetic materials have been prepared Via a Spark Plasma Sintering (SPS) technique at difference sintering temperatures in the range of 1150 to 1300 °c for 15 min and a heating rate of 100 °c/min. The results show that the density of sintered samples increased with the rising sintering temperature resulted in the enhancement of Vickers hardness and magnetic properities otsintered samples. Hovvever, the highest magnetic saturation (Ms) of 209.6 emu/g and lowest coercivity (Hc) of 1.85 Oe were obtained for the SPSed sample at 1250 °c. In contrast, the sample sintered in vacuum at 1300 °c for 1h with heating rate of 20 °c/min shows the lower magnetic properties due to the lower density and high amount of pores in the structure. The results of research show that the spark plasma sintering route has a high potential of fast sintering Fe-Si soft magnetic materials and for application.

Effect of Sintering Temperature on the Interfacial and Mechanical Properties of SiC Fiber Reinforced Mullite Matrix Composites

In the present work, SiC fiber reinforced mullite matrix composites (SiCf/Mu composite) were prepared through a sol-gel process. The effect of sintering temperature on the interfacial and mechanical properties of the SiCf/Mu composite was studied comprehensively and deeply. The experimental results indicated that the micro-mechanical properties of mullite matrix and fiber/matrix interface were closely related to the sintering temperature. When sintering temperature reached 800 and 1000 °C, the matrix was composed of the γ-Al2O3 and amorphous SiO2. As the sintering temperature rise to 1200 °C, mullite phase was formed via the chemical reaction between γ-Al2O3 and amorphous SiO2, leading to significantly increased Young’s modulus and hardness of mullite matrix. It was also found that the interfacial shear strength was enhanced remarkably with sintering temperature due to the interfacial interaction between fiber and matrix. The interface controlled macro-mechanical properties of SiCf/Mu composites were sharply depressed at sintering temperature of 1000 °C, exhibiting a ductile-to-brittle fracture behavior transition.

Microwave Performance, Microstructure, and Crystallization of (Mg0.6Zn0.4)1−yNiyTiO3 Ilmenite Ceramics

The sintering behavior, microstructure analysis, crystallization, and microwave performance of (Mg0.6Zn0.4)1−yNiyTiO3 (y = 0.01–0.2) ceramics, processed with raw powders of MgO, NiO, ZnO, and TiO2 via the conventional solid-state method, are investigated. The main phases of (Mg0.6Zn0.4)1−yNiyTiO3 ceramics were obtained. With partial replacement by Ni2+, the (Mg0.6Zn0.4)0.95Ni0.05TiO3 could be well sintered at 1200 °C, and the microwave performance was shown to be positively correlated with sintering temperature. The permittivity (εr) saturated at 18.7–19.3, and the quality factor (Qf) values approached 72,000–165,000 (GHz) as the sintering temperatures increase from 1125 to 1250 °C. The temperature coefficient of resonance frequency (τf) falls in a stable range of −62.9 to −66 ppm/°C as sintering temperature rising. A permittivity (εr) of 19.3, a maximum Qf value of 165,000 (GHz), and a temperature coefficient (τf) of −65.4 ppm/°C were measured for the samples at 1200 °C/4 h. (Mg0.6Zn0.4)0.95Ni0.05TiO3 material system shows high potential for applications of high frequency-selection components in satellite communication and 5G wireless telecommunication systems.

Microstructural evolution and phase transition mechanism of Ti(C,N)-based cermets during vacuum sintering process

Ti(C,N)-based cermets were fabricated using section vacuum sintering. The density and shrinkage ratio of sintered samples were recorded and analyzed. Phase transition, microstructure and interface behaviors of cermets were examined by transmission electron microscope, X-ray diffractometer and scanning electron microscope. As the sintering temperature rising, the number of pores in cermets was decreased and the density of samples was increased. Moreover, with the progress of sintering, atoms of various elements were constantly diffusing and gathering, affecting the formation of different microstructure, and the angle and intensity of each XRD peak were also constantly changing slightly, or disappearing at a certain temperature. These relevant results indicated that the proportion of heavy element to Ti in the hard phase would affect its lattice parameter. After the appearance of liquid phase, the densification mechanism changed from surface diffusion to grain boundary diffusion, thus accelerating the densification. With the proceeding of sintering process, various microstructures were formed such as core - rim/rimless structure. Finally, the process of interface change in core rimless phase transition was discussed. This rim phase, formed in solid state sintering process while failing to develop into core-rim structure after liquid sintering, was formed by some heavy elements short-range diffusion into core phase. The orientation different and the misfit between this core and rim were relatively large. While after liquid sintering, the semi-coherency or even coherency state at the interface of core-rimless and binder was formed.

Influences of sintering temperature on the electrical conductivity of GDC-50vol%MgO composite ceramics: the role of the GDC/MgO heterogeneous interface

Magnesium oxide can be added into Gd-doped CeO2 (GDC) as a suitable sintering additive, and the continuous GDC/MgO heterogeneous interface will contribute to the promotion of the oxygen ion transmission. GDC-50vol%MgO composite ceramics were sintered at different temperatures (1350~1500 °C). The phase composition, micromorphology, and electrical conductivity of GDC-50vol%MgO were analyzed by XRD, SEM, TEM, and electrochemical impedance, respectively. There are only GDC and MgO phases in the ceramics sintered at 1350 °C, 1400 °C, 1450 °C, and 1500 °C. As the sintering temperature rises from 1350 to 1500 °C, the average grain size of GDC and MgO increases from 239/274 to 680/651 nm, respectively. The GDC/MgO heterogeneous interface is clear, and many edge dislocations form there. The grain boundary and total conductivities decrease significantly with the rising sintering temperature, and the GDC/MgO heterogeneous interface possesses a higher electrical conductivity than the GDC/GDC homogeneous interface.

Response Surface Methodology Study on Macroporous Hydroxyapatite Prepared by Protein Foaming-Consolidation Method

Macroporous hydroxyapatite have been used in biomedical application especially for bone graft. The objective of this research was to study the effect of yolk addition, rate of sintering temperature rise, and rate of stirring on the physical, chemical and mechanical properties of porous hydroxyapatite prepared using protein foaming-starch consolidation method. The slurry was made by mixing the hydroxyapatite and starch powder with Darvan 821A and yolk in a beaker glass. The slurry was stirred mechanically at rate of 150 rpm for 3 hours and it poured in cylindrical mold. Subsequently the slurry was heated in air oven at 180°C for 1 hour. The dried green bodies were burn out at 600°C ended by sintering at 1250°C. The porous hydroxyapatite with average pore size in the range of 13.7-17.9 μm, porosity of 59.3-63.6 % and compressive strength of 5.17-8.2 MPa was obtained. The calculation result of response surface methodology shows that p-value < 0.05 and lack of fit > 0.05. The most effecting factor significantly was hydroxyapatite addition that followed by mixing rate and temperature rising rate of sintering. Optimum condition hydroxyapatite addition of 22 gr, mixing rate of 150 rpm and temperature rising rate of sintering of 2.8°C/minutes with the optimum value of response for pore size by 17.665 μm, porosity by 63.475% and compressive strength 5.17 MPa.

Fabrication of Al2O3-ZrO2-Ni composites with improved toughness using nano powders prepared by mechanical alloying

It has been established that the production of structural ceramic/metal composites with improved toughness has a great of interest for industrial applications. Al2O3-10 wt % ZrO2 sintered composites reinforced with 0, 3, 6, 9 and 12 wt % of Ni were fabricated from nano powders prepared by mechanical milling method. The phase identification, crystal size, morphology and particle size of obtained powder were examined by XRD and TEM, respectively. The powder was compacted and sintered at various temperatures up to 1550 °C. Relative density and apparent porosity of fired composites were determined by water displacement method whileas their microstructure was investigated by SEM. Mechanical and electric properties of sintered specimens were also determined in details. The results revealed that nano powders were successfully prepared after milling for 20h. The particle and crystal sizes increased while lattice strain and dislocation density decreased with increasing Ni content. For the sintered composites, the microhardness, compressive strength and elastic moduli reduced when the Ni content increased while they improved with rising sintering temperature. The fracture toughness improved with increasing both Ni content and sintering temperature. For AZ12Ni composite sintered at 1550 °C, it exhibited the maximum fracture toughness (6.5 MPa m0.5). The electrical-resistivity reduced with rising both Ni quantity and firing temperature. While the dielectric constant and dielectric loss reduced with higher Ni content but they increased with rising firing temperature. The electrical resistivity, dielectric constant and dielectric loss of AZ12Ni composite sintered at 1550 °C were 8.94 × 109 Ω m, 7.47 and 2.8 × 10−5, respectively.

Transformation in the structural and optical properties with the phase change from hematite (Fe2O3) to pure spinel structure in Mn-Zn nanoferrites

In present investigation, the effect of phase change, induced via sintering, from hematite (Fe2O3) to pure spinel structure on structural and optical properties in coprecipitated Mn0.4Zn0.6Fe2O4 nanoferrites has been studied. The Mn0.4Zn0.6Fe2O4 nanoparticles have been sintered at three temperatures 700 °C, 900 °C, and 1100 °C for 3 h. The presence of hematite (Fe2O3) phase in samples sintered at temperatures 700 °C and 900 °C has been observed from XRD. The crystallite size of the sintered samples has been found to increase on increasing the sintering temperature from 700 °C to 900 °C and then decrease for 1100 °C. Pure cubic spinel structure having single-phase has been obtained at 1100 °C. A cation distribution has also been proposed. Two absorption bands in the range 445 cm−1-473 cm−1, as well as 556 cm−1-582 cm−1, have been recognized in FTIR spectra and that indicates the formation of metal ion oxygen bond in spinel structure. With the rising sintering temperature, the peak position in the absorption spectra has been noticed to shift toward lesser wavelength, i.e., from 266 nm to 261.18 nm. The optical band gap shows shrinkage with the augmentation in the crystallite size on elevating the sintering temperature from 700 °C to 900 °C, while the optical band gap shows a broadening on raising the sintering temperature to 1100 °C. Photoluminescence study on the sintered samples has also been performed to examine the impurity levels and defects in samples. Stokes shift has been observed in all three samples.