Effect Of Sintering Conditions Research Articles

Effect of Sintering Parameter on Ferroelectric Properties in PZT Based Ceramics

This research was conducted to improve the ferroelectric properties of PZT based ceramics by studying the effect of sintering conditions in terms of temperature and soaking time (time of sintering) on the ferroelectric properties of ceramics in the 0.8Pb (Zr1/2Ti1/2)O3-0.2Pb (Zn1/3Nb2/3)O3 system prepared by vibro-milling mixed-oxide method. The XRD patterns of specimens showed perovskite structure for all compositions. The pyrochlore phase was not observed in this system. The sintering temperature and soaking time affects the ferroelectric properties of ceramics by the optimum sintering condition for 0.8PZT-0.2PZN ceramic is sintered at 1250°C for 2h.

Densification and Microstructural Evolution of Hierarchically Porous Ceramics During Sintering

Several technologically important ceramics are porous. One common approach to make high porosity ceramics is to use fugitive pore formers followed by partial densification. The resultant ceramic has hierarchical porosity: extrinsic large pores from the burnout of the pore former; and intrinsic small inter‐particle pores. In this study, the effect of sintering conditions and pore former on porosity and microstructure of hierarchically porous ceramics has been investigated. Pore size and pore volume fraction evolution of intrinsic and extrinsic pores were quantified as a function of sintering conditions. The effect of porosity and sintering conditions on average grain size is also investigated. It is shown that during sintering both the extrinsic and the intrinsic porosity decrease but along different trajectories. It is shown that the intrinsic pores control the grain growth. The results are discussed in terms of standard mechanisms and models available in the literature.

Effect of Sintering Conditions on Texture Formation of Si3N4 Ceramic Shaped up in a Strong Magnetic Field

Si3N4ceramics with preferential texture along a or b axis were shaped up by gel-casting in a magnetic field of 6T and then pressureless sintered. Effect of the sintering temperature and time on the texture formation of the Si3N4 ceramics was investigated. It was found that the phase transformation of αto β was completed for the Si3N4 ceramics prepared by the present process. With the increasing sintering temperature the texture formation of Si3N4 ceramics may be enhanced, i.e. of which the degree of texture increased from 0.40 at 1700℃ to 0.76 at 1800℃. The extension of sintering time at 1750℃ had few effect on texture development of Si3N4 ceramics.

Preparation of spiral porous stainless steel hollow fiber membranes by a modified phase inversion–sintering technique

The practical use of inorganic hollow fibre membranes has been limited by their brittleness. When assembled inside a membrane module for high temperature applications, the unavoidable thermal expansion or shrinkage would break the membrane. To overcome this problem, in this paper, spiral-shaped porous stainless steel (PSS) hollow fiber membranes have been developed via a modified phase inversion–sintering technique using 316L stainless steel powder as the membrane material, polysulfone as the polymeric binder and N-methylpyrrolidone as the solvent, respectively. The effects of sintering conditions on the hollow fiber properties have been investigated extensively to optimize the preparation. In order to obtain the desired porous structure, high performance and appropriate mechanical strength, the PSS hollow fiber precursors should be calcined in O2-free sintering atmosphere between 1050°C and 1100°C. Under the optimal sintering conditions, the resultant PSS hollow fibre membranes have a bimodal pore size distribution of 0.1–3μm diameter, high mechanical strength of 290–600MPa, and the nitrogen permeances ranged between 2.23×10−4 and 2.84×10−5molm−2s−1Pa−1. When two sides are fixed by sealant, such spiral hollow fiber membranes are able to flexibly expand by 20% and shrink by at most 57% of its original length, thus suitable for variable high-temperature operations as they can offset the thermal expansion and contraction caused by the temperature change.

Effects of fabrication conditions on mechanical properties and microstructure of duplex β″-Al2O3 solid electrolyte

Abstract Na-beta batteries are an attractive technology as a large-scale electrical energy storage for grid applications. However, additional improvements in performance and cost are needed for wide market penetration. To improve cell performance by minimizing polarizations, reduction of electrolyte thickness was attempted using a duplex structure consisting of a thin dense electrolyte layer and a porous support layer. In this paper, the effects of sintering conditions, dense electrolyte thickness, and cell orientation on the flexural strength of duplex BASEs fabricated using a vapor phase approach were investigated. It is shown that sintering at temperatures between 1500 and 1550 °C results in fine grained microstructures and the highest flexural strength after conversion. Increasing thickness of the dense electrolyte has a small impact on flexural strength, while the orientation of load such that the dense electrolyte is in tension instead of compression has major effects on strength for samples with a well-sintered dense electrolyte.

Electrochemical performance of intermediate temperature micro-tubular solid oxide fuel cells using porous ceria barrier layers

We describe the manufacture and electrochemical characterization of micro-tubular anode supported solid oxide fuel cells (mT-SOFC) operating at intermediate temperatures (IT) using porous gadolinium-doped ceria (GDC: Ce0.9Gd0.1O2−δ) barrier layers. Rheological studies were performed to determine the deposition conditions by dip coating of the GDC and cathode layers. Two cell configurations (anode/electrolyte/barrier layer/cathode): single-layer cathode (Ni–YSZ/YSZ/GDC/LSCF) and double-layer cathode (Ni–YSZ/YSZ/GDC/LSCF–GDC/LSCF) were fabricated (YSZ: Zr0.92Y0.16O2.08; LSCF: La0.6Sr0.4Co0.2Fe0.8O3−δ). Effect of sintering conditions and microstructure features for the GDC layer and cathode layer in cell performance was studied. Current density–voltage (j–V) curves and impedance spectroscopy measurements were performed between 650–800°C, using wet H2 as fuel and air as oxidant. The double-cathode cells using a GDC layer sintered at 1400°C with porosity about 50% and pores and grain sizes about 1μm, showed the best electrochemical response, achieving maximum power densities of up to 160mWcm−2 at 650°C and about 700mWcm−2 at 800°C. In this case GDC electrical bridges between cathode and electrolyte are preserved free of insulating phases. A preliminary test under operation at 800°C shows no degradation at least during the first 100h. These results demonstrated that these cells could compete with standard IT-SOFC, and the presented fabrication method is applicable for industrial-scale.

Effect of sintering conditions on the structural, electrical, and magnetic properties of nanosized Co0.2Ni0.3Zn0.5Fe2O4

The effect of sintering conditions (the temperature and the pressure) on the electrical/dielectric and the magnetic properties of a nanocrystalline Co0.2Ni0.3Zn0.5Fe2O4 was studied. The XRD and EDX results confirmed a single phase nanocrystalline spinel-type ferrite structure of both the as-prepared polyol-made powder and its associated ones sintered between 773 and 1273K. In addition, analysis of the integrated intensity ratios I220/I222 and I220/I422 indicated changes in the cation occupancy with sintering temperature variation. This result is supported by IR analysis. As expected, the mean particle size inferred from XRD and TEM increased with sintering temperature increase, it ranges from~2nm for the as-prepared ferrite to~83nm for the ferrite sintered at 1273K. The electrical/dielectric properties were investigated over a wide range of frequency and temperature. The sintered ferrites showed a semiconductor behavior with conductivity following the Arrhenius law. At moderately sintering temperatures, the increase of conductivity was attributed to the increase Fe2+ concentration, while, at higher temperatures, the increase is mainly due to the decrease of porosity. The loss factor of our nanoferrites was found to decrease drastically with both the pressure and temperature of sintering showing better values than reported for similar ferrites. Magnetic measurements conducted on a VSM apparatus showed a superparamagnetic behavior at room temperature. In addition, the saturation magnetization was found to increase in a continuous manner with the sintering temperature increase consequence of particle size increase. Finally, the Curie temperature was found to vary slightly between 600 and 631K, the chemical composition seems to be the main parameter influencing this feature.

Effect of Consolidation and Sintering Parameters on the Mechanical Responses of Nanocrystalline Al-Fe Alloy Processed by Mechanical Alloying

In this investigation, bulk ultra-fine grained and nanocrystalline Al-2 wt.% Fe alloy was produced by mechanical alloying (MA). The powder was mechanically milled in an attritor for 3 hours and yielded an average crystal size of ~63 nm. The consolidation and sintering was performed using a high frequency induction sintering (HFIS) machine at a constant pressure of 50 MPa. The prepared bulk samples were subjected to uniaxial compressive loading over wide range of strain rates for large deformation. To evaluate the effect of sintering conditions and testing temperature on the strain rate sensitivity, strain rate jump experiments were performed at high temperature. The strain rate sensitivity of the processed alloy increased with an increase in temperature. The density of the bulk samples were found to be between 95 to 97%. The average Vickers micro hardness was found to be 132 Hv0.1.

Thermoelectric figure of merit of bulk FeSi2–Si0.8Ge0.2 nanocomposite and a comparison with β-FeSi2

Among various thermoelectric (TE) materials, iron disilicide (FeSi2) has relatively low cost and non-toxic characteristics which make it appropriate for large scale applications. To enhance the dimensionless figure of merit (ZT) of this material, a composite of FeSi2–Si0.8Ge0.2 with high fraction of α-FeSi2 was prepared by mechanical alloying and sintering. The process was followed by thermal annealing to transform α to β phase FeSi2 through a slow peritectoid reaction (several hours). The thermoelectric properties were significantly improved upon the completion of the phase transformation. At temperatures above 900 °C, FeSi2 component rapidly changed from β to α phase (several minutes) leading to sudden increase of the thermal conductivity. For comparison, the thermoelectric alloy of β-FeSi2 was prepared through a similar process. The effect of sintering conditions and annealing time were studied and a comparison was drawn between the thermoelectric properties of β-FeSi2 and FeSi2–Si0.8Ge0.2 nanocomposite. Overall, (FeSi2)0.75(Si0.8Ge0.2)0.25 showed 170% enhancement in ZT compared with β-FeSi2 making it suitable for medium to high temperature applications (500 °C −850 °C).

Grain growth kinetics of textured-BaTiO3 ceramics

Textured BaTiO3 (BT) ceramics were fabricated by templated grain growth method. Effects of sintering conditions on the grain growth process of textured-BT ceramics were investigated. Orientation degree increased initially and then decreased with increasing soaking time. The ceramics were composed of equiaxed matrix grains and brick-like template particles. The brick-like particles aligned parallel to the casting direction by observing from SEM images. A (h00)-preferred orientation was confirmed by SAED and XRD patterns. Mechanism of grain growth in textured-BT ceramics was studied. Both consumption of matrix by templates and grain growth of templates determined the orientation degree of ceramics. The kinetic mechanism for grain orientation was also discussed by the simplified phenomenological kinetic equation. The average activation energies were 364 kJ/mol for matrix grain and 918 kJ/mol for template particle, respectively. Finally, a dense ceramic with 85% grain orientation was obtained after sintering at 1400 °C for 2 h.

Effects of Sintering Conditions on the Mechanical Properties of Alumina Particle Dispersed Magnesium SPS Compacts

To enhance the mechanical properties of Mg alloys, 0-30vol% Al2O3/Mg powders were formed by ball milling powder mixtures of pure Mg and Al2O3 particles, and then Spark plasma sintering (SPS) compacts (Al2O3/Mg discs) were made by the Al2O3/Mg powders. The effect of the cooling conditions in the SPS process on the mechanical properties of the Al2O3/Mg discs was investigated. From the results of SEM, XRD and TEM-EDS, the microstructures of the Al2O3/Mg discs were identified to consist of α-Mg solid solution, Al2O3 particles, refined MgO particles and refined needle-like Mg17Al12 ( more than 20vol% Al2O3 content). The mechanical properties of the discs were able to control by the regulation of the cooling conditions (cooling rate (vc) and applied pressure in the cooling (pc)) in SPS process, and as a result, the SPS discs possessing the mechanical properties beyond HP compacts were obtained under the cooling conditions of “vc= 0.83K/sand pc = 20MPa”. Main factor that the cooling conditions in SPS process effect on the mechanical properties of the Al2O3/Mg discs are considered to be the compresive residual stress generated in the α - Mg solid solution by the thermal stress associated with deference of the coefficients of thermal expansion between the α - Mg and ceramics particles (Al2O3 and MgO) in the discs.

Rapid synthesis of single phase Gd2Zr2O7 pyrochlore waste forms by microwave sintering

Single phase Gd2Zr2O7 pyrochlore have been successfully prepared by microwave sintering processing. The total time of sintering is less than an hour compared to several days required in the case of conventional sintering. The prepared samples are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Archimedes method. The phase purity, density and microstructure of the microwave processed samples were determined and compared with a conventionally processed material. The effects of sintering conditions on the densification, microstructure and phase purity were investigated. It was found that the microwave sintered pyrochlore show better densification, higher phase purity and more uniform grain size than conventional one. Furthermore, sintered densities and phase purity were found to increase with increase in sintering time and temperature.

Effect of Sintering Conditions on Mechanical and Optical Properties of 3Y-TZP Dental Ceramic

The use of zirconia dental ceramics has grown in recent years due to improvements in esthetics and biocompatibility. Zirconia is used in dental applications for its high strength and fracture toughness. In this research, the influence of sintering conditions on the strength and optical properties of zirconia was investigated. Spray dried granules of 3Y-TZP zirconia were die pressed into disc-shaped samples and cold isostatic pressed at 250 MPa. Sintering was conducted using either one step sintering at 1500 oC or two-step sintering, with pre-sintering at 1200 oC and final sintering at 1500 oC. Heating rates of 2 and 10 oC/min were used. The biaxial flexural strength, fracture toughness, density, microstructural characteristics and optical properties of the sintered samples were determined. It was found that the sintering conditions did appear to influence the mechanical and optical properties. The sintering conditions had no significant effect on the density. It was concluded that for the sintering conditions examined, the two-step sintering with a heating rate of 2 oC/min produced the best average mechanical and optical properties of 3Y-TZP zirconia.

Influence of sintering conditions on low-temperature degradation of dental zirconia

The effect of sintering conditions and concomitant microstructure of dental zirconia (ZrO2) ceramics on their low-temperature degradation (LTD) behavior remains unclear. ObjectivesTherefore, their effect on LTD of dental ZrO2 ceramics was investigated. MethodsThree commercial pre-sintered yttria-stabilized dental zirconia materials were sintered at three temperatures (1450°C, 1550°C and 1650°C) applying three dwell times (1, 2 and 4h). Grain size measurements and LTD tests were performed on polished sample surfaces. LTD tests were performed at 134°C in an autoclave. The amount of monoclinic ZrO2 on the exposed surface was measured by X-ray diffraction (XRD). ResultsHigher sintering temperatures and elongated dwell times increased the ZrO2 grain size. Simultaneously, a larger fraction of zirconia grains adopted a cubic crystal structure, resulting in a decreased yttria content in the remaining tetragonal grains. Both the larger grain sizes and the lower average stabilizer content made the tetragonal grains more susceptible to LTD. Overall, independent on the commercial dental zirconia grade tested, the specimens sintered at 1450°C for 1h combined good mechanical properties with the best resistance to LTD. SignificanceIn general, increased sintering temperatures and times result in a higher sensitivity to low-temperature degradation of Y-TZP ceramics.

Effects of Sintering Condition on the Trapped Magnetic Field Properties for MgB2 Bulks Fabricated by in-situ Capsule Method

We have studied the trapped field properties of MgB2 bulks which were fabricated by the in-situ capsule method under various sintering temperatures of 700-900̊C for 1-24h. The trapped field, BT (T), was 1.8-1.9 T for all the bulks approximately at 16K. The BT (T) values on the bulks sintered at 900̊C for 6h and at 800̊C for 24h were slightly lower than those of other bulks because of the decrease of critical current density, Jc, which originates from both the lower connectivity, K, and the promotion of the grain growth. The high temperature and/or the long periods sintering decrease the BT (T) value. From the obtained results, the sintering at 700-800̊C for 1-6h is the optimum condition to fabricate MgB2 bulks by the capsule method.

Effect of sintering conditions on the microstructural and mechanical characteristics of porous magnesium materials prepared by powder metallurgy

There has recently been an increased demand for porous magnesium materials in many applications, especially in the medical field. Powder metallurgy appears to be a promising approach for the preparation of such materials. Many works have dealt with the preparation of porous magnesium; however, the effect of sintering conditions on material properties has rarely been investigated. In this work, we investigated porous magnesium samples that were prepared by powder metallurgy using ammonium bicarbonate spacer particles. The effects of the purity of the argon atmosphere and sintering time on the microstructure (SEM, EDX and XRD) and mechanical behaviour (universal loading machine and Vickers hardness tester) of porous magnesium were studied. The porosities of the prepared samples ranged from 24 to 29 vol.% depending on the sintering conditions. The purity of atmosphere played a significant role when the sintering time exceeded 6h. Under a gettered argon atmosphere, a prolonged sintering time enhanced diffusion connections between magnesium particles and improved the mechanical properties of the samples, whereas under a technical argon atmosphere, oxidation at the particle surfaces caused deterioration in the mechanical properties of the samples. These results suggest that a refined atmosphere is required to improve the mechanical properties of porous magnesium.

Studies on the effect of sintering conditions on the magnetostriction characteristics of cobalt ferrite derived from nanocrystalline powders

The effect of sintering conditions on the magnetostriction characteristics of sintered cobalt ferrite derived from nanocrystalline powders is studied. It is observed that the magnetostriction coefficient as well as the slope of the magnetostriction as a function of field depends on the microstructure of the sintered product. There is a direct correlation between the magnetostriction characteristics and density as well as porosity of the sintered products. Intragranular pores are found to be strongly influencing the magnetostriction characteristics. Similarly, correlation is found between the magnetostriction parameters and the Curie temperature, indicating the role of cation distribution which affects the magnetic anisotropy. Sintering the compacts made from nanocrystalline powders at 1450 °C for a very short duration is found to give high values of magnetostriction coefficient. However, higher values of magnetostriction at low magnetic fields are obtained for samples sintered at lower temperatures for longer duration and having relatively lower density.

Transformation-assisted consolidation of Y2O3:Eu3+ nanospheres as a concept to optical nanograined ceramics

A concept is proposed to produce Y2O3:Eu3+ optical nanograined ceramics by the transformation-assisted consolidation of nanospheres under 8GPa pressure. The nanoceramics were prepared by high-pressure low-temperature sintering (~0.04–0.2Tm, where Tm is the melting temperature) accompanied by the cubic-to-monoclinic phase transition. The effects of sintering conditions upon phase composition, grain size evolution, density, morphology, optical and luminescent properties of sintered ceramics have been studied. It has been shown that Y2O3:Eu3+ nanograined ceramics consisting of individual (cubic or monoclinic) phases or their mixture can be obtained by variation of the sintering temperature. The use of transformation-assisted consolidation makes it possible to prepare Y2O3:Eu3+ nanoceramics with average grain size three times smaller (12nm) than that of the starting nanopowders (37nm), which corresponds to extremely low grain growth factor of 0.3. The grain size refinement is related to numerous nucleation events in the parent phase of cubic yttrium oxide. The preparation conditions of translucent (T=50%) composite Y2O3:Eu3+ nanograined ceramics with a relative density of 99±1 % have been determined. The obtained two-phase ceramics show high optical transparency due to negligible birefringence at extremely small (~12nm) average grain size.

Densification and grain growth during microwave sintering of titanium diboride

Dense TiB2 ceramics have been produced by microwave sintering at 1600–1700 °C under a controlled atmosphere. The effect of sintering conditions on the densification, microstructure and mechanical properties were investigated. Microwave sintering resulted in a uniform crack-free uniform microstructure; a density of 98.5%, a bending strength of 410 ± 15 MPa, a Young’s modulus of 495 ± 10 GPa, an electrical resistivity of 1 × 10−5 Ω cm, a Vickers hardness of 24.5 ± 0.5 GPa and a fracture toughness of 5.42 ± 0.20 MPa m1/2 were obtained after sintering for 30 min at 1700 °C.

Effect of sintering conditions on the magnetic and structural properties of Fe 0.6 Mn 0.1 Al 0.3 synthesized by mechanical alloying

In order to study the effect of sintering condition on the structural and magnetic behavior of prealloyed metallic powders of Fe0.6Mn0.1 Al0.3 system, two different thermal treatments were employed. All samples were previously milled and then compacted. Later, the sintering process was carried out in two cycles. For the first one, a sintering time of 2 h was followed by a cooling process governed by the inertia of the furnace. In the second treatment, a sintering time of 0.17 h with a controlled slow ramp of 1 °C/min between 500 °C and 250 °C. All samples were characterized by X-ray diffraction and Mossbauer spectroscopy. It was found that the sintering time improves the crystallinity while the magnetic behavior was modified by the changes in the cooling rate.