共查询到20条相似文献,搜索用时 31 毫秒
1.
Choon-W. Nahm 《Journal of Materials Science: Materials in Electronics》2011,22(8):1010-1015
The microstructure, electrical properties, and DC-accelerated aging behavior of the ZnO-V2O5-Mn3O4 ceramics were investigated at different sintering temperatures of 850–925°C. The microstructure of the ZnO-V2O5-Mn3O4 ceramics consisted of ZnO grain as a primary phase, and Zn3(VO4)2 which acts as a liquid-phase sintering aid, in addition to Mn-rich phase as secondary phases. The maximum value (3,172 V/cm)
and minimum value (977 V/cm) of breakdown field were obtained at sintering temperature of 850 and 900°C, respectively. The
nonlinear coefficient exhibited the highest value, reaching 30 at 925°C and the lowest value, reaching 4 at 850°C. The optimum
sintering temperature was 900°C, which exhibited not only high nonlinearity with 24 in nonlinear coefficient, but also the
high stability, with %ΔE1mA = −0.9% and %∆α = −12.5% for DC-accelerated aging stress of 0.85 E1mA/85°C/24 h. 相似文献
2.
Guo-Hua Chen 《Journal of Materials Science》2007,42(17):7239-7244
The effects of replacement of MgO by CaO on the sintering and crystallization behavior of MgO–Al2O3–SiO2 system glass-ceramics were investigated. The results show that with increasing CaO content, the glass transition temperature
firstly increased and then decreased, the melting temperature was lowered and the crystallization temperature of the glass-ceramics
shifted clearly towards higher temperatures. With the replacement of MgO by less than 3 wt.% CaO, the predominant crystalline
phase in the glass-ceramics fired at 900 °C was found to be α-cordierite and the secondary crystalline phase to be μ-cordierite.
When the replacement was increased to 10 wt.%, the predominant crystalline phase was found to be anorthite and the secondary
phase to be α-cordierite. Both thermal expansion coefficient (TCE) and dielectric constant of samples increases with the replacement
of MgO by CaO. The dielectric loss of sample with 5 wt.% CaO fired at 900 °C has the lowest value of 0.08%. Only the sample
containing 5 wt.% and10 wt.% CaO (abbreviated as sample C5 and C10) can be fully sintered before 900 °C. Therefore, a dense
and low dielectric loss glass-ceramic with predominant crystal phase of α-cordierite and some amount of anorthite was achieved
by using fine glass powders (D50 = 3 μm) fired at 875–900 °C. The as-sintered density approaches 98% theoretical density. The flexural strength of sample
C5 firstly increases and then decreases with sintering temperature, which closely corresponds to its relative density. The
TCE of sample C5 increases with increasing temperature. The dielectric property of sample C5 sintered at different temperatures
depends on not only its relative density but also its crystalline phases. The dense and crystallized glass-ceramic C5 exhibits
a low sintering temperature (≤900 °C), a fairly low dielectric constant (5.2–5.3), a low dielectric loss (≤10−3) at 1 MHz, a low TCE (4.0–4.25 × 10−6 K−1), very close to that of Si (∼3.5 × 10−6 K−1), and a higher flexural strength (≥134 MPa), suggesting that it would be a promising material in the electronic packaging
field. 相似文献
3.
P. Thomas L. N. Sathapathy K. Dwarakanath K. B. R. Varma 《Bulletin of Materials Science》2007,30(6):567-570
CaCu3Ti4O12 (CCTO) was synthesized and sintered by microwave processing at 2·45 GHz, 1·1 kW. The optimum calcination temperature using
microwave heating was determined to be 950°C for 20 min to obtain cubic CCTO powders. The microwave processed powders were
sintered to 94% density at 1000°C/60 min. The microstructural studies carried out on these ceramics revealed the grain size
to be in the range 1–7 μm. The dielectric constants for the microwave sintered (1000°C/60 min) ceramics were found to vary
from 11000–7700 in the 100 Hz–00 kHz frequency range. Interestingly the dielectric loss had lower values than those sintered
by conventional sintering routes and decreases with increase in frequency. 相似文献
4.
Strontium titanate and barium titanate ceramics prepared by a reaction-sintering process were investigated. The mixture of
raw materials of stoichiometric SrTiO3 and BaTiO3 was pressed and sintered into ceramics without any calcination stage involved. A density 4.99 g/cm3 (97.5% of the theoretic value) was found in SrTiO3 after 6 h sintering at 1,370 °C. Grains less than 1.5 μm were formed at 1,300–1,330 °C and became 2.2–3.3 μm at 1,350–1,370 °C
SrTiO3. A density 5.89 g/cm3 (97.9% of the theoretic value) was found in BaTiO3 after 6 h sintering at 1,400 °C. Merged grains were observed in BaTiO3 and were less than 10 μm after sintered at 1,400 °C. 相似文献
5.
Jianfeng Zhu Guoquan Qi Haibo Yang Fen Wang 《Journal of Materials Science: Materials in Electronics》2011,22(1):96-100
The microstructure and electrical properties of ZnO-Bi2O3-based varistor ceramics doped by Pr6O11 in the content range of 0–5.49 wt% were investigated at different sintering temperatures (1,100, 1,150, 1,175, 1,200 °C).
The increase of sintering temperature leads to more dense ceramics, which increases the nonlinear property, whereas it decreases
the voltage-gradient and leakage current. With increasing Pr6O11 content, the breakdown voltage increases because of the decreases of ZnO grain size. The improvement of non linear coefficient
together with the decrease of leakage current are related to the uniformly distribution of secondary phases along the grain
boundaries of the ZnO. The varistors sintered at 1,175 °C with the 3.37 wt% Pr6O11 doping possess the best electrical properties: the varistor voltage, nonlinear coefficient, and leakage current are 340 V/mm,
46 and 0.63 μA, respectively. 相似文献
6.
We have developed a procedure for the synthesis of phase-pure α- and β-Cu2V2O7. Thermal analysis and X-ray diffraction demonstrate that the β-phase (monoclinic structure) exists at low temperatures (stability
range 25–610°C), while α-Cu2V2O7 (orthorhombic structure) is stable in the range 610–704°C. The α-phase observed during cooling, in particular at room temperature,
is in a metastable state. The melting of the high-temperature phase γ-Cu2V2O7, which forms between 704 and 716°C, has the highest rate in the range 770–785°S and is accompanied by peritectic decomposition
and oxygen gas release. Subsequent cooling gives rise to four exothermic peaks, one of which (780.9°C) is attributable to
the crystallization of the peritectic melt, one (620.1°C) is due to the γ → α → β phase transformations of Cu2V2O7, and the other two arise from the crystallization of multicomponent low-melting-point eutectics containing α- and β-Cu2V2O7, CuVO3, and other compounds. 相似文献
7.
V. V. Sokolov I. Yu. Filatova I. V. Korol’kov V. S. Danilovich A. P. Nefed’ev A. I. Usherov P. A. Poltarak 《Inorganic Materials》2012,48(3):279-284
We have studied the effect of manganese dioxide (5–20 wt %) on the formation of calcium monoaluminate in the CaO-Al2O3 system during solid-state sintering of five oxide mixtures corresponding to the known calcium aluminates at temperatures
from 1100 to 1400°C. X-ray diffraction examination indicated the formation of calcium manganates. The mixture of the calcium
manganates melts at 1330°C, promoting the sintering process and the reaction between the calcium oxide and alumina and raising
the yield of calcium monoaluminate as the dominant phase. The calcium manganates are shown to be nonreactive with the forming
calcium aluminates. The X-ray diffraction results are supported by scanning electron microscopy data for a number of samples. 相似文献
8.
T. K. Bhattacharya A. Ghosh H. S. Tripathi S. K. Das 《Bulletin of Materials Science》2003,26(7):703-706
The sintering of lime by double calcination process from natural limestone has been conducted with La2O3 and CeO2 additive up to 4 wt.% in the temperature range 1500–1650° C. The results show that the additives enhanced the densification
and hydration resistance of sintered lime. Densification is achieved up to 98.5% of the theoretical value with La2O3 and CeO2 addition in lime. Grain growth is substantial when additives are incorporated in lime. The grain size of sintered CaO (1600°C)
with 4 wt.% La2O3 addition is 82 μm and that for CeO2 addition is 50 μm. The grains of sintered CaO in presence of additive are angular with pores distributed throughout the matrix.
EDX analysis shows that the solid solubility of La2O3 and CeO2 in CaO grain is 2.9 and 1.7 weight %, respectively. The cell dimension of CaO lattice is 4.803 %C. This value decreases with
incorporation of La2O3 and CeO2. The better hydration resistance of La2O3 added sintered lime compared to that of CeO2 added one, is related to the bigger grain size of the lime in former case. 相似文献
9.
Xiumin Yao Shouhong Tan Xiangyu Zhang Zhengren Huang Dongliang Jiang 《Journal of Materials Science》2007,42(13):4960-4966
SiC reticulated porous ceramics (SiC RPCs) was fabricated with polymer replicas method by using MgO–Al2O3–SiO2 additives as sintering aids at 1,000∼1,450 °C. The MgO–Al2O3–SiO2 additives were from alumina, kaolin and Talc powders. By employing various experimental techniques, zeta potential, viscosity
and rheological measurements, the dispersion of mixed powders (SiC, Al2O3, talc and kaolin) in aqueous media using silica sol as a binder was studied. The pH value of the optimum dispersion was found
to be around pH 10 for the mixtures. The optimum condition of the slurry suitable for impregnating the polymeric sponge was
obtained. At the same time, the influence of the sintering temperature and holding time on the properties of SiC RPCs was
investigated. According to the properties of SiC RPCs, the optimal sintering temperature was chosen at 1,300 °C, which was
lower than that with Al2O3–SiO2 additives as sintering aids. 相似文献
10.
Harim Jeon Sung Hoon Ahn Jong Hak Kim Yoon Jae Min Ki Bong Lee 《Journal of Materials Science》2011,46(11):4020-4025
Mesoporous aluminas were synthesized via a sol–gel process by templating an amphiphilic graft copolymer, PVC–g–POEM, consisting of a poly(vinyl chloride) (PVC) backbone and poly(oxyethylene methacrylate) (POEM) side chains. The mesoporous
structures of aluminas with large surface areas were confirmed by X-ray diffraction, transmission electron microscopy, and
nitrogen adsorption/desorption analysis. Aluminas synthesized with PVC–g–POEM graft copolymer exhibited higher CO2 adsorption capacities (0.7 mol CO2/kg sorbent) than aluminas synthesized without graft copolymer (0.6 mol CO2/kg sorbent). The adsorption capacity of alumina strongly depends on its structure and calcination temperature; amorphous
(400 °C) > γ phase (800 °C) > α phase (1000 °C). 相似文献
11.
Ramazan Asmatulu Annamalai Karthikeyan David C. Bell Shriram Ramanathan Michael J. Aziz 《Journal of Materials Science》2009,44(17):4613-4616
Rafts of aligned, high aspect ratio TiO2 nanotubes were fabricated by an electrochemical anodization method and their axial electrical conductivities were determined
over the temperature range 225–400 °C. Length, outer diameter, and wall thickness of the nanotubes were approximately 60–80 μm,
160 nm, and 30 nm, respectively. Transmission electron microscopy studies confirmed that the TiO2 nanotubes were initially amorphous, and became polycrystalline anatase after heat treatment at temperatures as low as 250 °C
in air. The activation energy for conductivity over the temperature range 250–350 °C was found to be 0.87 eV. The conductivity
values are comparable to those of nanocrystalline and nanoporous anatase thin films reported in literature. 相似文献
12.
A. I. Orlova A. K. Koryttseva A. E. Kanunov V. N. Chuvil’deev A. V. Moskvicheva N. V. Sakharov M. S. Boldin A. V. Nokhrin 《Inorganic Materials》2012,48(3):313-317
Ceramic materials based on Ca0.5Zr2(PO4)3 and NaFeNb(PO4)3, structural analogs of NaZr2(PO4)3 (NZP), were prepared by spark plasma sintering. At sintering temperatures of 1100–1200 and 880°C and sintering times of 12
and 3 min, the relative densities reached were 99.1 and 99.9%, respectively. According to X-ray diffraction data, the sintering
process caused no changes in phase composition. The ceramics had a dense, homogeneous microstructure and ranged in grain size
from 0.5 to 2.5 μm. 相似文献
13.
A. Beitollahi H. Hosseini-Bay H. Sarpoolaki 《Journal of Materials Science: Materials in Electronics》2010,21(2):130-136
Nanocrystalline alumina–zirconia powders were prepared by a modified chemical route using sucrose, polyvinyl alcohol (PVA)
and metal nitrates followed by a post calcination process. The process involved dehydration of Al3+–Zr4+ ions-sucrose–PVA solution to a highly viscous liquid which on decomposition process produced a black precursor material.
The obtained precursor were then calcined at various temperatures: 1,050, 1,100, 1,150, 1,200 and 1,250 °C for different soaking
times (1, 2, 4 h) in air. The formation of a nanocomposite composed of α-alumina (~20 nm) and tetragonal (t) zirconia (~19 nm) crystallites were confirmed for the sample calcined at 1,200 °C for 2 h, based on our XRD and TEM results.
However, for the samples calcined below 1,150 °C the composite formed were composed of metastable alumina (γ, δ, θ) as well as t-zirconia phases. Interestingly, the zirconia phase retained its tetragonal structure for all the samples calcined above 1,050 °C.
This is possibly related to the “size effect” and reduction of surface enthalpy of the zirconia crystallites surrounded by
Al3+ cations. 相似文献
14.
T. S. Sasikala C. Pavithran M. T. Sebastian 《Journal of Materials Science: Materials in Electronics》2010,21(2):141-144
Mg2SiO4 (Forsterite) ceramics were synthesized by solid state route. The effect of lithium magnesium zinc borosilicate (LMZBS) glass
addition on the densification temperature and microwave dielectric properties of forsterite ceramics was investigated. The
crystal structure and microstructure of ceramic–glass composites were studied by X-ray diffraction and scanning electron microscopic
techniques. The dielectric properties of the sintered samples were measured in the microwave frequency range by the resonance
method. Addition of 0.5 wt% LMZBS glass improved densification with ε
r = 7.3 and Qxf = 121,200 GHz. Addition of 15 wt% LMZBS glass lowered the sintering temperature to about 950 °C with ε
r = 6.75 and Qxf = 30,600 GHz. The reactivity of 15 wt% LMZBS glass added forsterite with silver was also studied. The result
shows that forsterite doped with suitable amount of LMZBS glass is a possible material for LTCC and microwave substrate applications. 相似文献
15.
Hiroshi Maiwa 《Journal of Materials Science》2008,43(19):6385-6390
Ba(Zr0.2Ti0.8)O3 (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
16.
M. V. Nikolić N. Obradović K. M. Paraskevopoulos T. T. Zorba S. M. Savić M. M. Ristić 《Journal of Materials Science》2008,43(16):5564-5568
Zinc-titanate ceramics were obtained by initial mechanical activation in a high-energy planetary mill for 15 min followed
by sintering at temperatures 900–1100 °C for 2 h. Room temperature far infrared reflectivity spectra for all samples were
measured in the range 100–1200 cm−1. The same ionic oscillators were present in the measured spectra, but their intensities increased with the sintering temperature
in correlation with the increase in sample density and microstructure changes. Optical parameters were determined for seven
oscillators belonging to the spinel structure using the four-parameter model of coupled oscillators. Born effective charges
were calculated from the transversal/longitudinal splitting. 相似文献
17.
Huanfu Zhou Xiuli Chen Liang Fang Changzheng Hu Hong Wang 《Journal of Materials Science: Materials in Electronics》2010,21(9):939-942
Ba5Nb4O15 powders were synthesized by molten-salt method in NaCl–KCl flux at a low temperature of 650–900 °C for 2 h, which is lower
than that of the conventional solid-state reaction. This simple process involved mixing of the raw materials and salts in
a certain proportion. Subsequent calcination of the mixtures led to Ba5Nb4O15 powders at 650–900 °C. XRD and SEM techniques were used to characterize the phase and morphology of the fabricated Ba5Nb4O15 powders, respectively. After sintering at 1,300 °C for 2 h, the densified Ba5Nb4O15 ceramics with good microwave dielectric properties of εr = 39.2, Q × f approximated as 27,200 GHz and τ
f
= 72 ppm/°C have been obtained. 相似文献
18.
Dunmin Lin Qiaoji Zheng K. W. Kwok Chenggang Xu Chun Yang 《Journal of Materials Science: Materials in Electronics》2010,21(7):649-655
Lead-free MnO2-doped K0.5Na0.5Nb0.92Sb0.08O3 ceramics have been fabricated by a conventional ceramic technique and their dielectric and piezoelectric properties have
been studied. Our results show that a small amount of MnO2 (0.5–1.0 mol%) is enough to improve the densification of the ceramics and decrease the sintering temperature of the ceramics.
The co-effects of MnO2 doping and Sb-substitution lead to significant improvements in the ferroelectric and piezoelectric properties. The K0.5Na0.5Nb0.92Sb0.08O3 ceramic with 0.5 mol%MnO2 doping possesses optimum propeties: d
33 = 187 pC/N, k
P = 47.2%, ε
r = 980, tanδ = 2.71% and T
c = 287 °C. Due to high tetragonal-orthorhombic phase transition temperature (T
O-T ~ 150 °C), the K0.5Na0.5Nb0.92Sb0.08O3 ceramic with 0.5 mol%MnO2 doping exhibits a good thermal stability of piezoelectric properties. 相似文献
19.
The Zn2SiO4 ceramics with the addition of BaO and B2O3 are fabricated by traditional solid-state preparation process at a sintering temperature of 900 °C. The introduction of BaO
and B2O3 to the binary system ZnO-SiO2 is achieved by adding 10 and 20 wt. % flux BB to the mixed ZnO-SiO2 ceramic powders pre-sintered at 1,100 °C, respectively. The chemical composition of the flux BB (50 wt.%BaO-50 wt.% B2O3) is located at a liquid phase zone with a temperature range of about 869–900 °C in the binary diagram BaO-B2O3. In addition, the introduction of BaO and B2O3 to the binary system ZnO-SiO2 is also achieved by the means of a chemical combination of H2SiO3, H3BO3, ZnO and Ba(OH)2·8H2O, which can result in the formation of the hydrated barium borates with low melting characteristics. In turn, by the liquid
sintering aid of the barium borate melts, the preparation process of the Zn2SiO4 ceramics can be further simplified. In the two preparation methods, the Zn2SiO4 ceramics with the 1.5–2.0 ZnO/SiO2 molar ratios and the addition of a 10 wt. % flux BB can show good dielectric properties whereas the bending strength mainly
depends on the microstructure of the Zn2SiO4 ceramics and SiO2 content in the composition of the specimen. 相似文献
20.
Sergio Yesid Gómez J. A. Escobar O. A. Alvarez C. R. Rambo A. P. Novaes de Oliveira D. Hotza 《Journal of Materials Science》2009,44(13):3466-3471
In this work, Y2O3-stabilized ZrO2 (YSZ) foams with low relative density were developed through the replication method, for application as porous radiant burners.
The ceramic foams were produced by impregnation of open-cell polyurethane foams with aqueous suspensions and different fractions
of raw materials: ZrO2–8% Y2O3 (8YSZ) powder, and additives. The materials were milled for 10–40 min. The impregnated foams were dried and submitted to
a heat treatment for polyurethane elimination at 1000 °C for 1 h, with subsequent sintering of the remaining ceramic structure
at 1600 °C for 2 h, which resulted in YSZ foams with low relative density (0.07). The structural analysis revealed a cellular
structure with an average mechanical strength of 95.6 kPa. The radiation efficiency (>19%) was obtained by tests with different
air/fuel ratio. The ceramic matrixes exhibited high performance and structural integrity at high operation temperatures (1400 °C). 相似文献