Maximum Sintering Temperature Research Articles

Mechanical measurements of pure and kaolin reinforced hydroxyapatite-derived scaffolds: A comparative study

This study describes the mechanical properties of pure hydroxyapatite (HAp) and kaolin reinforced hydroxyapatite (K-HAp) produced from non-separated animal bones using compression pressure under different sintering regimes. The HAp microparticles were synthesized separately using a facile heat treatment method and reinforced with 15 wt% of beneficiated kaolin (HAp/15 wt% BK) using the sol–gel method. The HAp and K-HAp derived scaffolds were fabricated by cold pressing with a compaction pressure of 500 Pa. Next, the scaffolds were sintered at 900 °C, 1000 °C and 1100 °C with a 2 h dwell time in air atmosphere. Subsequently, the mechanical properties of the scaffolds were examined. The effect of sintering temperature and compaction pressure on the hardness and the compressive strength of the pure and reinforced HAp showed that at all points of measurement (with and without compaction pressure), the mechanical properties increased with an increase in sintering temperature, and the most significant mechanical properties were obtained at 1100 °C. The values of hardness at the maximum sintering temperature (1100 °C) are 0.93 and 1.09 GPa with and without the application of compaction pressure, respectively, for pure HAp-derived scaffolds and 0.74 and 0.78 GPa with and without the application of compaction pressure, respectively, for K-HAp-derived scaffolds. The compressive strength for K-HAp had the value of 7.84 MPa as compared with 0.69 MPa for the non-reinforced HAp matrix with the application of compaction pressure (500 Pa). The findings show that the mechanical properties of the synthesized kaolin reinforced HAp in relation to the scaffolds produced with the low compaction pressure of 500 Pa is suitable for human trabecular bone.

The influence of synthesis modes of alumina ceramics doped with manganese on sensitivity to ionizing radiation

A temperature growth and a decrease in impurity ion concentration result in a sensitivity increase of Al2O3:Mn ceramics to the ionizing radiation. The highest sensitivity to the ionizing radiation for Mn-doped alumina ceramics is observed for minimum dopant concentration and a maximum of temperature sintering (maximum sintering temperature). A sublinear increase in a thermoluminescence intensity with a growing dose is observed in the range of 1–400 Gy for the peak at 460 K and in the range of 1–100 Gy for the peak at 620 K for the Mn-doped alumina ceramic (1 wt % of Mn in a solution) annealed under vacuum at the temperature of 1700°С for 2 h.

Dry-sliding wear of the 316L/h-BN composites produced under crack ammonia atmosphere

Wear is one of different problems in mechanical failures of moving components. When a component encounters friction force on its surface, crack initiation tends to occur and wear follows crack propagation. Thus, the moving parts of automobiles should have proper wear resistance for long-time services, in addition to having high strength and hardness for heavy load operation. A self-lubricating material with compromised tribological and mechanical properties is important for some moving components. In this work, self-lubricating composites, metal matrix composites embedded with a solid lubricant, made from 316L stainless steel powder mixed with different hexagonal boron nitride (h-BN) contents of 10%, 15% and 20% by volume. The mixed powders were compacted into green parts (according with MPIF Standard 42) with density of 6.5 g·cm-3. Then, the green parts were sintered at 1100, 1150, 1200, 1250 and 1300°C under cracked ammonia (75% H2+25% N2) atmosphere for 60 min. The experimental results revealed that increases of hardness and strength sintered 316L matrix by reduction of pore amount and size were due to the increase of sintering temperature. However, the increase of h-BN content resulted in increase of pore amount and size. Additions of h-BN content up to 20 vol. % reduced friction coefficient of the sintered composites. At sintering temperatures of equal to and higher than 1200°C, h-BN did not react with 316L stainless steel powders to form intergranular boride phase. The sintered composites produced under the maximum experimental sintering temperature of 1300°C showed low specific wear rate.

Molybdenum Oxide and Nickel Nitrate as Cooperative Sintering Aids for Yttria-Stabilized Zirconia.

The entirely accidental observation of increased sintering performance of nickel-infiltrated yttria-stabilized zirconia (8YSZ) in a molybdenum and oxygen rich atmosphere was explored. Molybdenum and nickel were found to be synergistic sintering aids for 8YSZ. However, sintering had to take place in an atmosphere of flowing oxygen. Samples sintered in air consistently burst. The sintering performance, microstructure, and crystal structure of 8YSZ with additions of both Mo and Ni together are compared to the sintering performance, microstructure, and crystal structure of pure 8YSZ, 8YSZ with only Ni added as a sintering aid, and 8YSZ with only Mo added as a sintering aid. Enhanced densification and grain growth is observed in the Mo–Ni 8YSZ samples when compared to all other sintering samples. Order of magnitude sintering rate increases are observed in the Mo–Ni 8YSZ over that of pure 8YSZ. With a maximum sintering temperature of 1200 °C and a one-hour dwell, sintered densities of 85% theoretical density (5.02 g⁄cm3) are achieved with the Mo–Ni samples: a 57% increase in density over pure 8YSZ sintered with the same sintering profile. EIS results suggest conductivity may not be negatively impacted by the use of these two sintering aids at temperatures above 750 °C. Finally, the spontaneous generation of nickel-molybdenum nano-rods was observed on the 5, and 10 mol.% Mo–Ni infiltrated 8YSZ samples after being left under vacuum in a scanning electron microscope chamber, suggesting evaporation of a possible nickel–molybdenum compound from the sample fracture surfaces.

Densification behavior and microstructure development in TiB2 ceramics doped with h-BN

This paper aims to study the impacts of h-BN additive on the microstructural features and sintering behavior of TiB2. For this objective, two different samples of monolithic TiB2 and TiB2-5 wt% h-BN were fabricated using spark plasma sintering (SPS) technique at 1900 °C. An external pressure of 40 MPa was exerted to the specimens during the sintering, and they were maintained at the maximum sintering temperature for 7 min. The characterization of as-fabricated ceramics was carried out using thermodynamical investigations, field emission SEM, and X-ray diffractometer. The thermodynamical and XRD studies revealed that the sintering process was non-reactive for both samples. However, introducing h-BN noticeably promoted the sinterability of TiB2 through activating the liquid phase sintering mechanism, and a near-fully dense composite was attained. The fractographical assessment manifested that the intergranular fracture was the dominant type in both monolithic and h-BN doped specimens. Finally, the quantitative image analysis indicated the role of h-BN in refining the microstructure of the doped TiB2 ceramic.

Effect of silver content on the wear and mechanical properties of powder metallurgical Ti-5Al-2.5Fe-xAg alloys

In the current research, the effect of Ag on the mechanical properties of Ti5Al2.5Fe alloy was investigated. The Ti5Al2.5Fe alloy, with different amounts of Ag ranged from 1 to 5 wt. % was prepared by mechanical mixing and then fabricated by hot pressing at 950?C for 15 min under 50 MPa. Three holding steps were applied to the powder compacts to restrain the liquid phases inside graphite die before reaching the maximum sintering temperature. The sintered samples were subjected to hardness, bending and wear tests to study the effect Ag on the mechanical properties of Ti5Al2.5Fe alloy. The microstructural characterization was carried out by means of optical and scanning electron microscope. The results showed that Ag played a differential role on the mechanical properties supported by microstructural constituents. The bending strength and hardness of the produced samples increased with the addition of Ag, the hardness of the alloys then tended to decrease with increasing Ag content but still remained above the hardness of Ti5Al2.5Fe alloy. Wear test also showed similar trends with hardness test results. Finally, the optimum Ag content for the Ti5Al2.5Fe alloy was determined as 1 wt.%. XRD analysis showed that undissolved Ag content was the main reason for the decrease in the mechanical properties.

Microwave sintering of 316L stainless steel: Influence of sintering temperature and time

This study deals about the influence of sintering temperature and holding time on microwave sintered PM stainless steel 316L microstructure, hardness and self-limiting characteristics. The samples exhibited increasing theoretical density upon increase in sintering temperature and superior density of 89.77% theoretical achieved at 1300 °C of 60 min holding time. Grain size distribution of microwave sintered SS316L at three different sintering temperatures (1200 °C, 1250 °C and 1300 °C) was compared, almost 68% to 75% uniformity in grain size was noticed and the largest grain (115 µm) was observed at 1300 °C with 60 min holding time. Self-limiting characteristics of microwave absorption analysed by time-temperature graph at different sintering temperatures. The effect of soaking time influenced the grain size, i.e., higher the soaking time larger the grain size. After maximum microwave absorption in core region, from outer surface region SiC susceptor play a role in contributing heat (20 °C/min) at the temperature beyond 1130 °C to achieve maximum sintering temperature.

The preparation of ZrO2-Al2O3 composite ceramic by SLA-3D printing and sintering processing

In this paper, the UV curable ZrO2-Al2O3 composite ceramic pastes based on SLA-3D printing technology were synthetized firstly, and the corresponding ceramic green bodies were 3D printed, and finally the ZrO2-Al2O3 composite ceramic parts were manufactured by a subsequent debinding and sintering process. Our work focuses on the investigation of the microstructure, hardness and fracture toughness of the printed ZrO2-Al2O3 composite ceramics sintered at different maximum sintering temperature and holding time. In case of the sintering temperature of 1500 °C and holding time of 60 min, the actual density, hardness and fracture toughness of the ceramics can reach 3.75 g/cm3, 14.1 GPa and 4.05 MPa⋅m1/2, respectively. If the sintering temperature is higher than 1500 °C, the abnormal grain growth can occur, resulting in some more reductions in the mechanical properties of ceramics; while when the sintering temperature is lower than 1500 °C, the lower driving force makes the grains not fully developed, resulting in a low density of ceramics and worse mechanical properties. With the increase of holding time, the sintering driving force is promoted, making for the grain growth. However, when holding time is more than 60 min, the actual density of ceramics almost remains unchanged, and the mechanical properties of ceramics are not able to be improved further.

Porous structure engineering of bioceramic hydroxyapatite-based scaffolds using PVA, PVP, and PEO as polymeric porogens

ABSTRACTNanobioceramic hydroxyapatite (HAp) was synthesized from golden apple snail (Pomacea canaliculata) shell and used to fabricate HAp-based scaffolds with polyvinyl alcohol (PVA), polyethylene oxide (PEO), or polyvinylpyrrolidone (PVP) as the porogen agent. The porogen was removed during the HAp sintering process. The SEM results showed increased agglomeration of HAp particles with increases in concentration of polymeric porogen used in the scaffold fabrication process. The XRD pattern showed the scaffolds to be HAp/β-TCP composites. Thermal analysis of the porogen weight loss at a sintering rate of 32°C/min showed that all the porogen had leached out before the sample attained the maximum sintering temperature. Fourier transform infrared (FTIR) spectra confirmed the absence of porogen functional groups within the scaffold after sintering. The weight concentration of the porogen plays an important role in establishing the homogeneity and interconnectivity of the pores, as well as the mechanical strength of the scaffold.

Hydrothermal synthesis, sintering and characterization of nano La-manganite perovskite doped with Ca or Sr

Two lanthanum manganite perovskite-nanostructures, namely; LaxCa(1-x)MnO3 and LaxSr(1-x)MnO3 (x = 0.1, 0.3, 0.5 and 1.0), were synthesized by hydrothermal method. To follow up the composition of formed phases, the synthesized powders were calcined at different temperatures. The obtained materials were investigated by X-ray diffraction (XRD) and transmission electron microscope (TEM). Moreover, the calcined powders were pressed at 100 MPa and sintered at variable temperatures; i.e. 1250, 1300, 1350 and 1450 °C. The phase composition and microstructural characteristics of sintered pervoskites were examined by XRD and scanning electron microscope (SEM). Furthermore, physical (bulk density and apparent porosity), electrical resistivity and magnetic properties were also determined. The results revealed that LaxCa(1-x)MnO3 and LaxSr(1-x)MnO3 nanostructures were successfully prepared by hydrothermal method. The physical properties of sintered pervoskites were strongly depended on dopant type and concentration. The maximum sintering temperature for LaxCa(1-x)MnO3 was 1400 °C while for LaxSr(1-x)MnO3 was 1450 °C, after which the materials have been fused. Materials doped with Ca or Sr exhibited lower resistivity. On the other side, the magnetic properties have been also improved after addition of Ca or Sr. This has been discussed based on the double exchange mechanism. LaxSr1-xMnO3 exhibited better magnetic properties than LaxCa1-xMnO3 and LaMnO3. La0.5Ca0.5MnO3 and La0.5Sr0.5MnO3 exhibited the highest magnetization among the other pervoskites.

Ultra‐rapid microwave sintering of pure and Y2O3‐doped MgAl2O4

AbstractMgAl2O4 samples were microwave sintered to near‐full density in rapid processes with heating rates on the order of 100°C/min and zero isothermal hold. The experiments were carried out using a gyrotron system for microwave processing of materials operating at a frequency of 24 GHz with a maximum power of 6 kW. In the regimes with a preset heating rate sustained by the automatically regulated microwave power, the maximum achieved density was about 95% of the theoretical value in pristine MgAl2O4 samples (maximum sintering temperature 1650°C) and about 97% in 1 wt.% Y2O3‐doped samples (1700°C). In the regimes with a fixed microwave power (about 3.5 kW), translucent spinel samples with a relative density above 99% were obtained at 1700°C. The duration of the high‐temperature stage of sintering was 1.5‐10 minutes. The suggested mechanism responsible for the enhanced densification involves development of a thermal instability and formation of transient liquid phases at grain boundaries. The estimated specific absorbed power in the samples during the high‐temperature stage of ultra‐rapid microwave sintering was 27‐80 W/cm3, similar to the values observed in dc field‐assisted flash sintering experiments.

Influence of Technological Parameters on Thermal Properties of Cordierite Ceramics

Porous cordierite ceramic samples have been prepared by using 33% of two carbonate-containing illite clays as substitutes for the necessary synthetic ingredients. The changes of thermal (CTE) and mechanical properties (compressive strength, modulus of elasticity), as well as phase content, apparent porosity and bulk density have been investigated in regards to gradual changes in maximum sintering temperature. It can be affirmed that these properties strongly depend on the thermal parameters of sintering as well as slightly upon differences in chemical composition of composition substitutes.

Dense zircon (ZrSiO4) ceramics by a simple milling-sintering route

In this work, a simple milling sintering route (pressure less) to process dense zircon ceramics from fine (D50 0.8 ?m) zircon powders is explored. Particularly, the milling time effect (0-120 min) and the maximum sintering temperature (1400-1600?C) were studied. The sintering grade developed microstructure and Vickers hardness (Hv) were evaluated and correlated. The dissociation of silicate into (monoclinic and tetragonal) zirconia and silica was evaluated by X-ray diffraction followed by the Rietveld method; it was found to be below 10 wt% in all the studied ranges. The sintering was enhanced by the milling pretreatment. No sintering additives were incorporated. Dense zircon (porosity below 1%) ceramics were obtained by a simple milling-sintering route of this high refractory powder at 100-200?C below the sintering temperature used with conventional processing routes to obtain equivalent final properties. The Vickers hardness reached: 9.0 GPa.

Strength analysis of small-sized thin ceramic discs obtained by spark-plasma sintering

The study develops an original method of mechanical test of thin small-size disks for determining resistance of brittle materials to rupture. Based on this method a test of ultimate flexture strenght was conducted on Al2O3 ceramics and composites of β–Si5AlON7–BN, system obtained by the method of spark-plasma sintering. The obtained test results allowed determining the optimal process parameters for sintering this ceramic materials in terms of their strength level: composition and dispersion of the starting powder mixtures, the maximum sintering temperature, etc.

Tailoring structural and electrical properties of A-site non-stoichiometric Na0.5Bi0.5TiO3 ceramic at different sintering temperature

ABSTRACTNa/Bi stoichiometry plays crucial role in determining various properties of sodium bismuth titanate-based system. In this work, we have synthesised lead free (Na0.5Bi0.5)1+xTiO3 (x = 0, 0.02 and 0.05) ceramics by sol-gel method and systematically presented structural, dielectric and ferroelectric properties at different sintering temperature. Single phase perovskite structure with rhombohedral symmetry (R3c) is obtained for all compositions from low (850°C) to maximum (1150°C) sintering temperature. The shifting of x-ray diffraction peaks and characteristic perovskite metal-oxide vibrational band (∼627 cm−1) in Fourier Transform Infra-red spectra suggests compression or expansion of crystal lattice with Na/Bi non-stoichiometry. Excess of Na/Bi comprises dense crystal growth as compared to pure Na0.5Bi0.5TiO3 composition suggesting compensation of volatile elements loss during heat treatment whose impact has also been observed in dielectric as well as ferroelectric properties. It is observed that Na0.51Bi0.51TiO3 sample with x = 0.02 exhibits better structural, dielectric and ferroelectric properties in whole range of sintering temperature.

Effect of average grain size and sintered relative density on the imaginary part – µ″ of the complex magnetic permeability of (Cu0.12Ni0.23Zn0.65)Fe2O4 system

The influence of the sintered microstructure on the electromagnetic properties of Cu-doped NiZn ferrites were investigated. Two of the main variables of the thermal cycle have been modified: the maximum sintering temperature and the dwell time at that temperature, or sintering time. The evolution of the imaginary part – µ″ of the complex magnetic permeability was studied as a function of relative density, grain size and amplitude of the grain size distribution of the sintered pieces. The results show that µ″ depends on the sintered microstructure and that there is a limiting value of the average grain size (~20–25µm) from which the electromagnetic properties of these kinds of materials worsened significantly.

Fabrication and microstructural stability of spark plasma sintered Al2O3/Er3Al5O12 eutectic

Al2O3/Er3Al5O12 (EAG) eutectic was prepared by a arc melting process under Ar atmosphere. Button shaped melts, containing fine sized irregular eutectic structures of ‘Chinese script’, with interpenetrated Al2O3 and EAG phases and primary EAG, were achieved by rapid cooling. Pulverized fine powders of eutectic were then consolidated by the spark plasma sintering (SPS) technique, applying different cooling rates (10°C, 600°C) and dwell times at 1700°C, under a uniaxial pressure of 15MPa. Coarsening of both phases was observed over a long dwell time (10min) at the maximum sintering temperature. Applying short holding times (2min) and slow cooling rates (10°C/min) led to samples retaining their starting microstructures. The measured Vickers hardness was in the range of 14.11–15.86GPa, and the fracture toughness of the samples was around 2MPam1/2. In addition, the micro-structural stability of the eutectics was investigated at 1500°C in air atmosphere for 5 and 20h. Samples sintered with a dwell time of 10min were found to be unstable at high temperatures due to grain coarsening. On the other hand, samples sintered with a dwell time of 2min preserved their main microstructural features following-after the heat treatment. The relationship between microstructural and mechanical properties was also discussed.

Spark plasma sintering of commercial and development titanium alloy powders

Emerging lower cost titanium metal powder produced via an electrolytic method has been fully consolidated using spark plasma sintering (SPS) generating microstructures comparable to those observed in Ti–6Al–4V PM product. This is the first time powder from an alternative titanium extraction method has been processed via SPS and it is benchmarked with commercial alloys (CP–Ti, Ti–6Al–4V, and Ti–5Al–5V–5Mo–3Cr). The effect of powder feedstock size, morphology, and alloy chemistry on the consolidated density and microstructure is presented. Through a design of experiments (DoE) type approach the effect of SPS processing conditions on these alloy powders, including maximum sintering temperature, pressure, heating rate, and dwell time were investigated. The SPS process is found to be largely insensitive to feedstock size and morphology, although very large or highly porous powder particles are more difficult to fully consolidate. The maximum sintering temperature and pressure have the largest contribution to achieving full consolidation, with higher pressures and temperatures increasing the final density. Increasing heating rate increases the final grain size, despite less time being spent at the higher temperature and it is thought this is due to bypassing the traditional first phase of sintering. This paper shows that SPS is a viable step for a low-cost manufacturing route, for example to produce preform billets to be finished with a one-step forging operation, especially when combined with the possibility of lower cost powder. In the long-term, SPS will allow a significant reduction in the processing cost, contributing to an increased usage of titanium powder feedstock for a range of applications. This is reinforced by the successful large scale production of a 5 kg SPS Ti-6-4 billet, demonstrating the potential industrial scalability of the process, particularly for the aerospace industry.

INFLUENCE OF CHARCOAL ON QUALITY OF AGGLOMERATE

This paper deals with assessing the impact of substitution fuel charcoal on the technological parameters of sintering and agglomerate quality. Changes in the quantity and qualitative parameters of fuel in the process of agglomeration affect the maximum sintering temperature and productivity. The maximum temperature varies with calorific value, the amount of fuel and gas-dynamic conditions in the sintered layer. When replacing fuel by solid biomass, an important parameter is also quantity of volatile substances that affect the process of agglomerate formation. Agglomerate quality is determined by its chemical composition, its physical and metallurgical properties. Effect of charcoal, as fuel substitution, on agglomerate quality indicators is evident. It was confirmed that the replacement of fuel by charcoal is only possible to a certain percentage level regarding agglomerate quality. Small amount of charcoal in the agglomeration process favorably affects the quality of agglomerate.

Heat transfer of spent ion exchange resin in iron ore sintering process

Spent ion exchange resin (SIER) is a kind of solid waste which derived from water treatment process in iron and steel industry. Utilization of SIER as a replacement of fuel in sintering process is a promising method of SIER treatment. In order to investigate the feasibility of this method, heat transfer effects of SIER in iron ore sintering process were studied in this paper via numerical simulation. A 3D unsteady numerical reference model was developed on the basis of the porous media model and local non-equilibrium thermodynamics model and verified by the data form measurement. Heat transfer effects of different SIER mass fractions (0–8%) in sintering material during the sintering process were studied on the numerical model established in this paper. The results showed that with the increasing mass fraction of SIER, the maximum combustion zone thickness and flame front speed are both increased, the heating-up point, the moment when solid temperature reached the top and the maximum temperatures were all became earlier in different location of sintering bed. When SIER content is 8%, the maximum sintering temperature exceeds the maximum limit of best sintering temperature.