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1.
CaCu 3Ti 4O 12 (CCTO) was prepared by the solid state technique. The sample was calcined at 900 °C/12 h and sintered at 1050 °C/24 h, then subjected to XRD to ensure CCTO formation. The microstructure was observed by SEM. XRD results identified both samples as single phase CCTO, whereas the microstructure shows abnormal grain growth and large pores. Sintering was studied in the temperature range of 950–1050 °C for 3–12 h. Increasing sintering temperature enhances the density and secondary formation of Cu 2O. A clear grain boundary and dense microstructure were observed. The results show that the sample sintered at 1040 °C/10 h yields a clearly uniform grain size with the highest εr (33,210). 相似文献
2.
The lattice and total Li +-ionic conductivity of Li 0.29La 0.57TiO 3 ceramic (LLTO) sintered at 1200 °C were determined as functions of powder calcination temperature and sintering duration, and these results were correlated with the relative degrees of Li +-ordering, Li-content, grain size, and bulk density to assess the relative impact of these parameters on material performance. Under all conditions, LLTO formed with a high degree of tetragonal superstructure to its perovskite related framework, and the lattice conductivity closely followed the relative amounts of the superstructure, as evaluated via determination of the sample ordering parameter from X-ray diffraction data. LLTO powders that were calcined at 900 °C for 1 h and sintered at 1200 °C for 6 h gave lattice conductivity values (~1.14 × 10 −3 S cm −1) comparable within the highest ranges reported in the literature. This coincided with the lowest degree of tetragonal superstructure formation, and it was also found to be largely independent of the values of Li-content measured on sintered ceramic despite significant Li 2O volatilization at longer sintering times (up to 23 % after 12 h at 1200 °C). Samples of LLTO powder that were calcined at 1100 °C and sintered at 1200 °C for 12 h resulted in the highest total Li-ion conductivity value ~6.30 × 10 −5 S cm −1. The total conductivity of LLTO varied inversely with grain size when the grains were <20 μm but was insensitive to that parameter above that size threshold. The strongest influence on total conductivity was primarily the bulk ceramic density. It was estimated from measured values that as the bulk ceramic density approached the full theoretical value for LLTO the total conductivity could near the lattice conductivity of ~1.2 × 10 −3 S cm −1. 相似文献
3.
Microstructure, electrical properties and dielectric behaviour of K 1/2Na 1/2NbO 3 (KNN) and CaTiO 3-modified K 1/2Na 1/2NbO 3 (CTO-KNN) systems, were investigated. Discs doped with 0 to 0·55% mol of CaTiO 3 (CTO) were sintered at 1125°C for 2 h. Although minority phases were found in doped samples, CaTiO 3 was not detected. It was also observed that CTO changed the microstructure and grain size of KNN drastically. Also, the Curie
temperature and permittivity values decreased. Addition of CTO between 0·15 and 0·45 mol% decreases the density and dielectric
values. Samples prepared with higher content of CTO than 0·45 mol% showed better electrical properties. 相似文献
4.
Na 5GdSi 4O 12 has been prepared via conventional ball-milling technique and through spray-freezing/freeze-drying. The ball-milled materials were calcined at 700°C or 925°C and sintered at 1050°C/3.5h to 89% dense multiphase ceramics. Spray-frozen/freeze-dried powders were calcined at 530°C and sintered at 1050°C/25 min to 99 ± 1% theoretical density. The latter material was single-phase NGS nasicon with a 300°C resistivity of 3.8 Ω·cm, an activation energy for Na +-conduction of 4.4 kcal/mol, a flexural strength of 105 MPa, a duplex grain structure with average sizes 0.4 μm and 3 μm and a unique linear thermal expansion coefficient (25–540°C; α = 12.6 × 10 ?6/°C±4%). 相似文献
5.
Microstructure characteristics, phase transition, and electrical properties of (K 0.4425Na 0.52Li 0.0375) (Nb 0.8925Sb 0.07Ta 0.0375)O 3 (KNLNST) lead-free piezoelectric ceramics prepared by normal sintering were investigated with an emphasis on the influence
of sintering temperature. The microstructure and piezoelectric, ferroelectric, and dielectric properties were investigated,
with a special emphasis on the influence of sintering temperature from 1,100 to 1,140 °C. Orthorhombic phases mainly exist
in the ceramics sintered at 1,100–1,130 °C, whereas the tetragonal phase becomes dominant when sintering temperature is above
1,130 °C. Because of the existence of MPB-like transitional behavior, the piezoelectric coefficient ( d
33), electromechanical coupling coefficient ( kp), and dielectric constant ( ε) show peak values of 304pC/N, 0.48, and 1,909, respectively, which are obtained in the sample sintered at 1,120 °C, and its
Curie temperature ( T
C) is about 271 °C. 相似文献
6.
Ba(Zr 0.2Ti 0.8)O 3 (BZT) ceramics are prepared from spray-dried powder by spark plasma sintering (SPS) and by normal sintering. By the application
of SPS, ceramics with >96% relative densities could be obtained by sintering at 1,100 °C for 5 min in air atmosphere. The
pellet as sintered by SPS at 1,100 °C was black and conductive. Although SPS was carried out in air atmosphere, the samples
were deoxidized by heating the carbon die. By post-annealing at 1,000 °C for 12 h in air, the pellet was oxidized and became
white and insulating. Grain growth was suppressed in the ceramics prepared by SPS, and the average grain size was 0.52 μm.
The starting powder contained 1.90% carbon, mainly as binder, and the SPS-prepared ceramics and ordinary prepared ceramics
contained 0.15 and 0.024% carbon, respectively. The BZT ceramics obtained by SPS and the subsequent annealing at 1,000 °C
for 12 h exhibited a mild temperature dependence of their dielectric constant. The field-induced displacement of the BZT ceramics
was less hysteretic and smaller than that of the ceramics sintered by the conventional method. 相似文献
7.
In this investigation, Fe 3Mo 3C ternary carbide was synthesized from the elemental powders of 3Mo/3Fe/C by mechanical milling and subsequent heat treatment. Structural and morphological evolutions of powders were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results showed that no phase transformation occurs during milling. A nanostructure Mo (Fe) solid solution obtained after 30 h of milling. With increasing milling time to 70 h no change takes place except grain size reduction to 9 nm and strain enhancement to 0.86%. Milled powders have spheroid shape and very narrow size distribution about 2 μm at the end of milling. Fe 3Mo 3C was synthesized during annealing of 70 h milled sample at 700 °C. Undesired phases of MoOC and Fe 2C form at 1100 °C. No transformation takes place during annealing of 10 h milled sample at 700 °C. Mean grain size and strain get to 69 nm and 0.23% respectively with annealing of 70 h milled sample at 1100 °C. 相似文献
8.
BaFe12O19 (BaM) was synthesized through the co-precipitation route. Pure phase BaM was formed after calcination of precipitated powder at 900 °C. BaM was sintered at three different temperatures; 1100, 1200, and 1300 °C to study the sintering kinetics by varying the sintering time from 1 to 4 h. Apparent porosity decreased, and bulk density increased with increasing sintering temperature and period. A bulk density of about 4.6 g/cm3 was achieved after sintering at 1300 °C/4 h. The rate-controlling mechanism of BaM densification was the diffusion of oxygen, and the activation energy for the sintering process was 274 kJ/mol. The grain size of BaM increased with rising sintering temperatures. Permittivity increased from about 11 to 17 and the permeability increased from about 10 to 16 with the increase in sintering temperature from 1100 to 1300 °C. Saturation magnetization was also enhanced to about 69 emu/g after sintering at 1300 °C/4 h. Therefore, BaM ferrite synthesized through the co-precipitation route can be effectively used for high-frequency applications after sintering at 1300 °C. 相似文献
9.
Stainless steel (316) foams of varying porosities have been made through powder metallurgy route using NH 4HCO 3 as a space holder. Green compacts of stainless steel powder with NH 4HCO 3 were sintered at two different temperatures: 1100 °C and 1200 °C. At higher sintering temperatures, neighboring stainless steel powders fused together to form polycrystalline grain structure with iron–chromium intermetallic phases segregated along the grain boundaries. Whereas, the fusion of neighboring stainless steel powders was limited around the particle–particle contact only when the green compacts were sintered at 1100 °C, which resulted in a larger amount of microporosities in the cell wall. These foams exhibited strain hardening behavior in the plateau region under compressive loading. The yield stress and the flow stress (at lower strain levels) of foams, sintered at 1100 °C were higher. But, the reverse is true for the flow stress at higher strain levels. The exponents and the coefficients of the power law relationships varied with sintering temperature and strain levels. 相似文献
10.
Polycrystalline samples of Pb[(1 − x)(Zr 1/2Ti 1/2) − x(Zn 1/3Ta 2/3)]O
3
, where x = 0.1–0.5 were prepared by the columbite and wolframite methods. The crystal structure, microstructure, and dielectric properties
of the sintered ceramics were investigated as a function of composition via X-ray diffraction (XRD), scanning electron microscopy
(SEM), and dielectric spectroscopy. The results indicated that the presence of Pb(Zn 1/3Ta 2/3)O 3 (PZnTa) in the solid solution decreased the structural stability of overall perovskite phase. A transition from tetragonal
to pseudo-cubic symmetry was observed as the PZnTa content increased and a co-existence of tetragonal and pseudo-cubic phases
was observed at a composition close to x = 0.1. Examination of the dielectric spectra indicated that PZT–PZnTa exhibited an extremely high relative permittivity at
the MPB composition. The permittivity showed a ferroelectric to paraelectric phase transition at 330 °C with a maximum value
of 19,600 at 100 Hz at the MPB composition. 相似文献
11.
High-density β-calcium orthophosphate (β-Ca 3(PO 4) 2, also called β-tricalcium phosphate: β-TCP) ceramics with submicrometer-sized grains were fabricated using a pulse-current
pressure firing route. The maximum relative density of the β-TCP compacts was 98.7% at 1050 °C and this was accompanied by
a translucent appearance. The mean grain size of the β-TCP compacts increased slightly with temperature to reach 0.78 μm at 1000 °C. However, upon further increasing the firing
temperature to 1050 °C the mean grain size increased significantly to 1.6 μm. The extent of plastic deformation during tensile
testing was examined at temperatures between 900 and 1100 °C using a strain rate in the range 9.26 × 10 −5 to 4.44 × 10 −4 s −1. The maximum tensile strain achieved was 145% for a test temperature of 1000 °C and strain rate of 1.48 × 10 −4 s −1 and this was attributed to the relatively high density and small grain size. 相似文献
12.
Na 0.5Bi 0.5Cu 3Ti 4O 12 (NBCTO) ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure and dielectric properties of NBCTO ceramics sintered at various temperatures with different soaking time were investigated. Pure NBCTO phase could be obtained with increasing the temperature and prolonging the soaking time. High dielectric permittivity (13,495) and low dielectric loss (0.031) could be obtained when the ceramics were sintered at 1000 °C for 7.5 h. The ceramics sintered at 1000 °C for 7.5 h also showed good temperature stability (−4.00 to −0.69%) over a large temperature range from −50 to 150 °C. Complex impedances results revealed that the grain was semiconducting and the grain boundaries was insulating. The grain resistance ( Rg) was 12.10 Ω cm and the grain boundary resistance ( Rgb) was 2.009 × 10 5 Ω cm when the ceramics were sintered at 1000 °C for 7.5 h. 相似文献
13.
The sinterability of manganese oxide (MnO 2) doped hydroxyapatite (HA) ranging from 0.05 to 1 wt% was investigated. Green samples were prepared and sintered in air at temperatures ranging from 1000 to 1400°C. Sintered bodies were characterized to determine the phase stability, grain size, bulk density, hardness, fracture toughness and Young’s modulus. XRD analysis revealed that the HA phase stability was not disrupted throughout the sintering regime employed. In general, samples containing less than 0.5 wt% MnO 2 and when sintered at lower temperatures exhibited higher mechanical properties than the undoped HA. The study revealed that all the MnO 2-doped HA achieved > 99% relative density when sintered at 1100–1250 °C as compared to the undoped HA which could only attained highest value of 98.9% at 1150 °C. The addition of 0.05 wt% MnO 2 was found to be most beneficial as the samples exhibited the highest hardness of 7.58 GPa and fracture toughness of 1.65 MPam 1/2 as compared to 5.72 GPa and 1.22 MPam 1/2 for the undoped HA when sintered at 1000 °C. Additionally, it was found that the MnO 2-doped samples attained E values above 110 GPa when sintered at temperature as low as 1000 °C if compared to 1050 °C for the undoped HA. 相似文献
14.
The effect of heat treatment on the superconducting properties of ErBa 2Cu 3O 7−δ
(ErBCO) ceramic materials has been studied. The nano-metal oxalate precursor was prepared using coprecipitation (COP) method.
The prepared materials were subjected to calcination process at 900 °C for 12 h and then sintered under oxygen environment
for 15 h at 920 °C, 930 °C, 940 °C, and 950 °C, respectively. All samples showed a metallic behavior and single-step transition
in the R–T curves. The best zero critical current, T
C(R=0)=91.4 K, was for the sample sintered at 920 °C. XRD data showed single phase of an orthorhombic structure. As the sintering
temperature increases, the formation of nonsuperconducting phases (impurities) was observed when the samples sintered above
920 °C. The formation of nano-oxalate powders via COP method is a very efficient procedure to produce high-quality superconductors
with less processing temperature required. 相似文献
15.
A new Li 2O–Nb 2O 5–TiO 2 (LNT) ceramic with the Li 2O:Nb 2O 5:TiO 2 mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li 2TiO 3 and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave
dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li 2O–0.17V 2O 5 (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave
dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties
of ε r = 51.3, Q × f = 7235 GHz, τ
f
= 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices. 相似文献
16.
In this work, austenitic oxide dispersion strengthened (AODS) steel of composition Fe–16Cr–16Ni–1.5 W–0.21Ti–0.3Y 2O 3 (wt. %) was fabricated using two–stage ball milling followed by consolidation through spark plasma sintering (SPS). In the first–stage, mechanical alloying (MA) of ferritic powder and nano sized Y 2O 3 was carried out. This was followed by the addition of Ni in second–stage milling. SPS of the milled powder was carried out at 900, 950, 1000 and 1050 °C to explore the role of SPS temperature on density, microstructure as well as mechanical properties of the consolidated samples. A relative density of ~ 99% was obtained for samples sintered at 950 and 1000 °C. The as–sintered samples were subsequently solution annealed at 1075 °C for 2 h and water quenched. X–ray diffraction studies confirmed the presence of austenite in the consolidated and solution annealed samples. Electron back scatter diffraction analysis of solution annealed samples sintered at all the temperatures revealed a bimodal microstructure. The average grain size of 1.07 ± 0.72 µm was obtained for solution annealed samples sintered at 1000 °C. Yield strength and elongation of the same was measured as 851 MPa and 18%, respectively at room temperature. These values are the best combination of strength to elongation achieved on AODS alloys processed using MA and SPS, which makes this AODS steel much promising for high temperature applications. 相似文献
17.
The effects of La 2O 3 on the properties of (Zn, Co, Ta) doped SnO 2 varistors were investigated in this study. The samples with different La 2O 3 concentrations were sintered at 1400 °C for 2 h and their properties were characterized by XRD, SEM, I- V and impedance spectroscopy. The grain size was found to decrease from 13 μm to 9 μm with increasing La 2O 3 content. The addition of rare earth element leads to increase the nonlinear coefficient and the breakdown voltage. The enhancement was expected to arise from the possible segregation of lanthanide ion due to its larger ionic radius to the grain boundaries, thereby modifying its electrical characteristics. Furthermore, the dopants such as La may help in the adsorption of O′ to O″ at the grain boundaries characteristics. 相似文献
18.
The densification behavior of nanocrystalline Gd-doped ceria electrolyte, synthesized via mechanical alloying process, was
investigated by means of the conventional pressure less sintering and the two-step sintering methods. The effect of the heating
rate and the amounts of dopant on the sinterability of Ce 1−x
Gd
x
O (2−δ)
x = 0.2 (2GDC) and x = 0.3 (3GDC) oxides was studied, which indicated that the gadolinium retards densification and grain growth in the final
state of the conventional sintering and 2GDC samples reach 94% density at 1,550 °C. Subsequent investigation on the grain
growth in the fully densified ceramics showed that lowering of the heating rate and increasing of the soaking time reduce
the effect of dopant and cause samples to be densified to the higher theoretical density (97%) at lower temperatures (1,400 °C).
Fully dense Gd-doped ceria ceramics with finest grain size (900–1,100 nm) can be obtained by two-step sintering method. Electrical
conductivity measurement in the GDC samples was studied by impedance spectroscopy. The grain boundary conductivity in these
specimens obtained by two-step sintering method was compared with normal sintered specimens. It is concluded that the reduced
conductivity observed in the two-step sintering specimen is attributable to the microstructure changes obtained by increased
of grain boundary resistivity. 相似文献
19.
The high temperature behavior of SrSO 4, SrCO 3 and Al 2O 3 mixtures was studied. A mixture of 1:1 mole of SrSO 4 and mechanically activated SrCO 3 was mixed and characterized using thermal gravimetric analysis. Some samples were uniaxially pressed and sintered at 1100, 1200 and 1300 °C for 8 h and then analyzed using X-ray diffraction and scanning electron microscopy. Additionally, a mixture of SrSO 4:SrCO 3:Al 2O 3 was uniaxially pressed and sintered at 1500 °C. The decomposition temperature of SrCO 3 was decreased 18° by milling for 180 min. Samples sintered at 1300 °C showed a microstructure free of porosity. X-ray diffraction analysis showed the presence of SrO and SrSO 4 after sintering at 1100, 1200 and 1300 °C. The mixture containing alumina showed the formation of a strontium aluminum oxide sulfate compound in addition to strontium aluminate. 相似文献
20.
The present paper describes calcination of calcium phosphate ceramics (hydroxyapatite, HA) at 200, 400, 600, 800 and 1000 °C to observe the phase change using X-ray diffraction. HA phase was found to be stable up to 600 °C and later got dissociated into other non-stoichiometric phases like tricalcium phosphate (Ca 3(PO 4) 2 [TCP]), calcium pyrophosphate (Ca 2P 2O 7 [CPP]) and calcium hydrogen phosphate (CaHPO 4 [CHP]). TCP was found to be the major phase above 1000 °C. FTIR spectra showed the presence of various PO 43− and OH − groups present in the powder. Powders compacted and sintered at 900, 1000, 1100 and 1200 °C showed an increase in density from 2.11 to 2.95 g/cm 3 while biaxial flexural strength (BFS) was found to be higher (48.7 MPa) when the samples were sintered at 1100 °C and it decreased with further increase in sintering temperature. 相似文献
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