Influence Of Sintering Conditions Research Articles

The influence of sintering conditions on the phase purity of bulk EuTiO3 and Eu0.5Ba0.5TiO3 ceramics

EuTiO3 and Eu0.5Ba0.5TiO3 ceramics were synthesized using mechanochemical activation of oxide precursors and then calcined. The uniaxially as well as isostatically pressed samples were sintered in different kinds of reducing atmospheres, namely Ar + (7–10)%H2, respectively, 99.99%H2 in the case of pressureless sintering or in vacuum (enriched by CO vapors) in the case of pressure-assisted spark plasma sintering (SPS). The samples prepared by SPS contained the pyrochlore phase as the second phase. In contrast with SPS, pressureless sintered samples were phase pure, although thermodynamics calculations showed that CO atmosphere in SPS is more reducing than pure hydrogen. This is explained by short sintering times in SPS that do not allow establishment of the thermodynamic equilibrium. The proper choice of sintering temperature, time, and atmosphere enabled preparation of dense and phase pure samples of Eu x Ba1− x TiO3 ceramics suitable for the evaluation of “true” physical properties (e.g., infrared reflectivity), or for experimental confirmation of specific functionalities proposed from theory.

Production and structural characterization of tailored made open-cell alumina–vanadia foams

Tailored made open-cell alumina–vanadia foams were produced by employing a dissolution sintering process, using crystalline raw cane sugar as a leachable pore former material. The process parameters of the production stages were properly adjusted to optimize the quality and structure of open-cell ceramic foams. The influence of sintering conditions (temperature, time and cooling rate) on the microstructure of the resultant foam is investigated with a view to produce high-quality ceramic foams having satisfactory strength. The effects of V 2 O 5 molar addition on the microstructure of ceramics foams are described by SEM and XRD analyses. The crystal size, grain growth (appearance of texturing-preferred orientation) and X-ray intensities of phases are closely related to the cooling rate and sintering duration. V 2 O 5 addition enlarges the lattice parameters of the Al 2 O 3 phase resulting in a 4–5% increase of the actual (measured) porosity of the produced ceramic foam compared to the theoretical one.

Influence of sintering conditions in the preparation of acetate-based fluorine-free CSD YBCO films using a direct sintering method

In this paper, an intensive study is performed to elucidate the link between sinter temperature and sinter atmosphere as processing parameters in YBCO film formation, starting from an aqueous fluorine-free AWAT CSD precursor. Moreover, the results are linked to the reaction mechanism behind this non-fluorine approach. This resulted in a partial oxygen versus temperature diagram containing different zones giving rise to specific YBCO properties. It is observed that sinter temperature and sinter atmosphere should be judiciously chosen to obtain high quality superconducting films. Under a 200ppm O2 atmosphere, highly textured YBCO films are obtained when sintering took place at 815°C giving rise to an inductive Tc,onset of 92K and a Jc-value up to 1.1MAcm−2. Moreover, this paper gives a clear indication that the formation of a liquid phase strongly enhances the epitaxial growth.

Influence of sintering conditions on the electrical properties and the PTCR effect of the multilayer Ba1.005(Ti1−xNbx)O3 ceramics with Ni internal electrode

The effects of the Nb-dopant content and the sintering conditions on the electrical properties and the positive temperature coefficient of resistance (PTCR) effect of Ba1.005(Ti1−xNbx)O3 (BTN) ceramics were investigated, which were sintered at 1,070–1,220 °C for 0.5–6 h in a reducing atmosphere and then re-oxidized at 600–750 °C for 1 h. The results indicated that both the sintering temperature and sintering time affected the electrical properties and the PTCR effect of the multilayer BTN samples, whose room-temperature (RT) resistance first reduced and then increased as a function of the donor–doped concentration at all sintering temperature; moreover, the higher the sintering temperature was, the lower the critical dopant concentration. The BTN ceramics showed a remarkable PTCR effect, with a resistance jump greater by 3.3 orders of magnitude, along with a low RT resistance of 0.3 Ω at a low reoxidated temperature of 600 °C after sintering in a reducing atmosphere.

Influence of Sintering Conditions on Electric Performance of Textured 92BNT-6BT-2KNN Ceramics

0.92(Bi0.5Na0.5)TiO3-0.06BaTiO3-0.02(K0.5Na0.5)NbO3(92BNT-6BT-2KNN) is a high-stain material due to the volume change which come from antiferroelectric-ferroelectric (AFE-FE) phase transformation. Textured 92BNT-6BT-2KNN with a Lotgering factor of 67% was obtained by templated grain growth (TGG) method using plate-like (Bi0.5Na0.5)TiO3（BNT）particles as templates. The influences of sintering process on Lotgering factor and strain were investigated. It was found that the Lotgering factor increased as sintering temperature increase and then decreased with further temperature increase. The changing tendency of polar and unipolar strain did not keep the same accordance with that of Lotgering factor. The maximum of Lotgering factor (79%) and polar strain (0.36%) was obtained when the sintering temperature was 1240°C and 1220°C, respectively, due to the decrease of density when high sintering temperature was employed. Also it was found that the lotgering factor and polar strain reached its highest values when the soaking time was 4h. All these proved that the density and grain orientation codetermined the strain of 92BNT-6BT-2KNN ceramics.

Prediction of mechanical properties of Fe–Cr–Mo sintered steel in relationship with microstructure

The contribution deals with the evaluation of required thermodynamic conditions for proper sintering and prediction of tensile and yield strength of Cr–Mo-pre-alloyed sintered steel. The material used in experiment was Fe–1.5 Cr–0.2 Mo pre-alloyed water atomised steel powder with addition 0.3–0.7% of graphite. Three different sintering routes were used applying sintering at 1180 and 1250°C for 40 and 60min in 10%H2+90%N2 atmosphere of different purity. The influence of sintering conditions on the microstructure and mechanical properties of sintered Fe–1.5Cr–0.2Mo–(0.3–0.7)C steels is analyzed and mechanical properties are predicted. Results indicate that very accurate prediction of mechanical properties can be achieved for sintered steel with bainitic microstructure (higher carbon content) and higher differences were obtained for ferritic–pearlitic microstructures. High sensitivity of mechanical properties on sintering atmosphere purity for chromium prealloyed powder steel was identified. Required sintering atmosphere composition and purity for successful sintering of studied material were evaluated.

Fabrication of High-Porosity Silicon Nitride Ceramics with Excellent Mechanical Properties

High-porosity silicon nitride ceramics with excellent mechanical properties were fabricated by the carbothermal reduction of SiO2. The influences of sintering conditions on microstructure and mechanical properties were studied. The results showed that microstructure and mechanical properties of porous silicon nitride ceramics were dependent mostly on the sintering conditions. The sintered porous silicon nitride ceramics exhibited the formation of fibrous microstructure with submicrometer-sized, high-aspect ratio b-Si3N4 grains, and uniform pore structure. Porous Si3N4 ceramics with a porosity of about 70%, and a flexural strength of about 70 MPa were obtained by sintering at 1750°C, with lower rate of temperature rise and no retaining time. The high strength was attributed to fine, high-aspect ratio b-Si3N4 grains and uniform pores between grains.

Influence of sintering conditions on the electrical properties of 10% ZrO 2–10% Y 2O 3–CeO 2 (mol%)

Yttria–zirconia doped ceria, 10% ZrO 2–10% Y 2O 3–CeO 2 (mol%) (CZY) and 0.5 mol% alumina-doped CZY (CZYA), prepared through oxide mixture process, were sintered by isothermal sintering (IS) and two-step sintering (TSS) having as variable the temperature and soaking time. The electrical conductivity of sintered samples was investigated in the 250 to 600 °C temperature range by impedance spectroscopy in air atmosphere. The microstructure was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Alumina, as additive, improves the grain boundary conductivity of samples sintered at temperatures lower than 1500 °C. Concerning the sintering mode, two-step sintering (TSS) proved to be a good procedure to obtain CZYA samples with high electrical conductivity and density (> 95%) at relatively low sintering temperature and long soaking time.

Effects of Sintering Conditions on Phase Formation and Dielectric Properties of 0.8Pb(Zr1/2Ti1/2)O3 - 0.2Pb(Co1/3Nb2/3)O3 Ceramics

The influences of sintering conditions on dielectric properties of the 0.8Pb(Zr 1/2 Ti 1/2 )O 3 −0.2Pb(Co 1/3 Nb 2/3 )O 3 ceramics have been investigated with sintering temperatures of 1175, 1200°, 1225, and 1250°C and dwell times for 2, 6, and 10 hours. The crystal structure of dense specimens showed coexistence between tetragonal, rhombohedral and pseudo cubic phases in all sintering temperatures, while tetragonal-rich phase appeared with increasing dwell times. A maximum dielectric constant was observed at sintering condition of 1200°C for 2 hours, while the transition temperature slightly increased with increasing dwell time. All ceramics also showed diffused phase transition behaviors with a minimum diffusivity at sintering condition of 1200°C for 2 hours.

Influence of Sintering Conditions on Densification of YAG—ZrB2 Multi-phase Ceramics with Spark Plasma Sintering

Zirconium diboride (ZrB2) is difficult to prepare as high-density ceramics, which limits its application. To obtain high-density ZrB2 ceramics for improving its high-temperature properties, ZrB 2 particles were coated with Al2O3—Y 2O3 particles to prepare 20%YAG—ZrB2 ceramics with SPS. The optimum sintering condition is a temperature of 1700°C, a pressure of 20 MPa, and a holding time of 4 min. The relative density of prepared 20%YAG—ZrB2 multi-phase ceramics is 97.2% under optimization sintering technology, which indicate that high density YAG—ZrB 2 multi-phase ceramics are successfully prepared.

Dielectric and ferroelectric properties of 0.8PZT–0.2PCN ceramics under sintering conditions variation

The influences of sintering conditions on electrical properties of the 0.8Pb(Zr1/2Ti1/2)O3–0.2Pb(Co1/3Nb2/3)O3 ceramics have been investigated with sintering temperatures of 1175, 1200, 1225, and 1250°C and dwell times for 2, 6, and 10h. The crystal structure of dense specimens showed coexistence between tetragonal, rhombohedral and pseudo cubic phases in all sintering temperatures, while tetragonal-rich phase appeared with increasing dwell times. A maximum dielectric constant was observed at sintering condition of 1200°C for 2h, while the transition temperature slightly increased with increasing dwell time. All ceramics also showed diffused phase transition behaviors with a minimum diffusivity at sintering condition of 1200°C for 2h. In addition, the polarization–electric field (P–E) hysteresis loops of the ceramic systems also changed significantly with sintering conditions. Interestingly, the ferroelectric parameters; remnant polarization (Pr) and loop squareness (Rsq) tended to increase with increasing sintering temperatures and dwell times.

Synthesis of Magnesium Silicide Compounds by a Liquid-solid Phase Reaction Method and their Thermoelectric Properties

Dimagnesium silicide (Mg2Si) is a promising thermoelectric material for energy conversion over intermediate temperature range (300 to 600°C). This material has advantages of the constituent elements in abundance in the earth's crust and of the nontoxicity of its processing by-products as an environmental symbiosis thermoelectric semiconductor. However, there are few research reports about this material for improving thermoelectric performance because of difficulty of its synthesis. In this study, Mg2Si was synthesized from Mg and Si powders by a liquid-solid phase reaction (LSPR) method, which is effective in synthesizing a compound from the two elements having sufficiently different melting points. The powder synthesized by LSPR method was compacted and then sintered by a pulse discharge sintering (PDS) process. Influence of sintering conditions on thermoelectric properties of Mg2Si was investigated. The thermoelectric properties of each sintered sample were measured at temperature of RT to 600°C. The thermoelectric properties of the sintered sample were, however, strongly affected by the sintering temperature and/or the sample density. The sample sintered at 730°C for 30 min under 60 MPa had the maximum dimensionless figure of merit of 0.27 at 516°C. This value is higher than the previous report.

The influence of sintering conditions on the dielectric and piezoelectric properties of PbZrTiO–PbMgNbO ceramic tubes

Abstract Piezoelectric tube actuators with a composition of 0.9Pb(Zr 0.52 Ti 0.48 )O 3 –0.1Pb(Mg 1/3 Nb 2/3) O 3 (0.9PZT–0.1PMN) have been prepared using electrophoretic deposition (EPD) method. The effect of sintering temperature on the phase formation, densification, microstructure, dielectric and piezoelectric properties of the 0.9PZT–0.1PMN system was investigated. The results show that when the sintering temperature varies from 1150 to 1300 °C, the tubes exhibit single perovskite structure with coexistence of rhombohedral and tetragonal phase. The P – E hysteresis loops reveal the ferroelectric nature of 0.9PZT–0.1PMN system. The tip deflection of the tube upon the applied voltage shows typical butterfly loop, which is a feature of piezoelectric systems. It was found that both dielectric and piezoelectric constants increase with increasing sintering temperature up to 1250 °C. When exceeding 1250 °C, the evaporation of PbO degrades the dielectric and piezoelectric properties of the PZT–PMN. The sample packing technique during sintering is also critically important for obtaining good properties.

Sintering and dielectric properties of Cu 2Ta 4O 12 ceramics

In this work, Cu 2Ta 4O 12 ceramic was investigated as a promising, lead-free, nonferroelectric material with high dielectric permittivity. The results of impedance spectroscopy studies carried out at frequencies 10 Hz to 2 MHz over a wide temperature range from −55 to 700 °C were analyzed in the impedance, dielectric permittivity and electric modulus formalisms. In complex impedance plots two distinct arcs were distinguished, ascribed to the semiconducting grains and to the insulating grain boundaries. Cu 2Ta 4O 12 ceramic was found to exhibit a high dielectric permittivity exceeding 10,000 at low frequencies in the temperature range 150–740 °C. High permittivity of this material was attributed to the formation of internal (grain boundary) barrier layer capacitors. The influence of sintering conditions on microstructure, composition and dielectric properties of Cu 2Ta 4O 12 ceramics was also studied.

Biomorphic Silicon Nitride Ceramics with Fibrous Morphology Prepared by Sol Infiltration and Reduction–Nitridation

Biomorphic silicon nitride (Si3N4) ceramics with fibrous morphology were fabricated by combining sol–gel infiltration with carbothermal reduction nitridation from wood precursor. Y2O3‐incorporated silica sol was used as the infiltrated solution to promote the formation of fibrous Si3N4 grain at 1600°C under high nitrogen pressure (0.6 MPa). The influence of sintering conditions (additive and temperature) on the phase composition and microstructure of sintering bodies was analyzed, and the reaction mechanism is discussed.

Influence of sintering conditions on microstructure and electrical conductivity of yttrium-substituted SrTiO 3

The microstructure and electrical conductivity of Y-substituted SrTiO 3 ceramics (Sr 1− αx Y x TiO 3− δ , x = 0, 0.035, 0.07; α = 1.0, 1.5) sintered under both oxidizing and reducing conditions were studied in detail. In these compositions, Y 3+ ions have been found to occupy the Sr sites and act as donor substitutes. The observed interesting dependence of the microstructure and electrical property on the starting composition (cation nonstoichiometry) and the sintering or processing conditions indicates that the defect chemistry known for other donor-substituted SrTiO 3 (e.g. Sr 1− x La x TiO 3− δ ) ceramics also applies for Y-substituted SrTiO 3 ceramics. The positive charge from the Y-substitute can be compensated either electronically under reducing conditions or ionically under oxidizing conditions. Therefore, to obtain a single-phase and highly conductive yttrium-substituted SrTiO 3 material, e.g. as a candidate for an SOFC anode, a starting composition with (Sr + Y)/Ti = 1 and a high-temperature heat treatment (>1200 °C) under reducing conditions is required.

The influence of the segregation of Cu-rich phase on the microstructural and impedance characteristics of CaCu3Ti4O12 ceramics

The influence of sintering conditions on the microstructural features and impedance characteristics of the giant dielectric constant material CaCu3Ti4O12 (CCTO) was investigated. The microstructure and impedance characteristics were found to be strongly dependent on the sintering conditions. Sintering of the CCTO ceramics at elevated temperatures (>1100 °C) for prolonged durations resulted in the segregation of Cu-rich phase, mostly confined to the surface, which was in concomitance with the appearance of the additional semicircle at the low frequency end in Impedance (Z*) plots. The absence of this additional semicircle in the Cu-deficient CCTO ceramics and the appearance of the same in Cu-rich CCTO ceramics that were deliberately fabricated corroborated the above observations. Also, La2/3Cu3Ti4O12 (LCTO), a low dielectric constant member of CCTO family, which consisted of small grains without the segregation of Cu-rich phase at the grain boundary, did not reveal the presence of additional semicircle in the Z*plots.

Influence of sintering conditions and doping on the dielectric relaxation originating from the surface layer effects in CaCu 3Ti 4O 12 ceramics

Detailed investigations into the dielectric dispersion phenomenon in the giant dielectric constant material CaCu 3Ti 4O 12 (CCTO) around room temperature revealed the existence of two successive dielectric relaxations. In the temperature domain, a new dielectric relaxation was clearly observed around 250 K, in addition to the well-investigated dielectric relaxation close to 100 K. The effect of sintering and doping (La 3+) on the strength of these dielectric relaxations were studied in detail. The sintering temperature as well as its duration was found to have tremendous influence on the dielectric relaxation that was encountered around 250 K. This Maxwell–Wagner (M–W) type of relaxation was found to be originating from the surface layer containing the Cu-rich phase, which was ascribed to the difference in the oxygen content between the surface and the interior of the sample. Interestingly, this particular additional relaxation was not observed in La 2/3Cu 3Ti 4O 12, a low dielectric constant member of the CCTO family, in which the segregation of Cu-rich phase on the surface was absent. Indeed the correlation between the new relaxation and the presence of Cu-rich phase in CCTO ceramics was further corroborated by the absence of the same after removing the top and bottom layers.

Influence of sintering conditions on relaxor properties of BaBi2Nb2O9 ceramics

The main purpose of present studies is to learn the effect of sintering temperature on BaBi2Nb2O9 (BBN) ceramics properties. Grain structure analysis performed by the scanning electron microscope (SEM) exhibits differences in grain structure of the ceramics sintered at various temperatures for a constant time. Namely, the grain sizes increase with the increase of the sintering temperature. This fact is connected with changes in dielectric properties. The maximum of the real part of permittivity () and corresponding temperature (T m) shifts to higher values. The properties characteristic for the ferroelectric relaxors also yield to change. The ceramics sintered in higher temperature revealed lower frequency dispersion of and T m. It should also be noticed that the freezing temperature and the Burn's temperature have changed. These results indicate that the behaviour of the relaxor ferroelectrics is weakened by the increase in the grain size.

自動車に関連する粉体および粉末冶金技術 低合金焼結鋼の機械的特性に及ぼす２次工程の影響

Partially diffusion bonded alloy has been used for components which require high mechanical properties. Secondary operations as a carburizing are used for these materials to achieve higher strength. Pre-alloyed 3Cr-0.5Mo steel powder can have excellent mechanical properties when it is sintered at 1250°C, followed by secondary operations: carburising or shot peening. This time the fatigue strength of 520MPa has been achieved after the same shot peening process by adjusting cooling rate of Carbon/Carbon Composite Mesh Belt Furnace for 3Cr-0.5Mo steel powder. The influence of sintering conditions on chemical analysis and the effect of controlling cooling rate on fatigue strength are discussed. Pre-alloyed 1.5Cr-0.5Mo steel powder are also discussed. Finally the paper describes the simulation methods of residual stress after shot peening.