共查询到20条相似文献,搜索用时 31 毫秒
1.
Ahmed A. Ghani Ali I. Eatah El-Mozamel El-Faramawy 《Journal of the American Ceramic Society》1988,71(12):492-C
Magnetoresistance measurements (Δ/R) were carried out on Cu x Co1- x Fe2 O4 samples with x =1, 0.75, 0.50, 0.25 and cobalt ferrite in the range of magnetic intensity (H) from 1.0 to 4.5 kG. Linear plots were obtained between log (Δ/R) and log H for all compositions except that of cobalt ferrite. The values of n at x =0.5 do not agree with the results of some authors. The discrepancy may be attributed to the value of magnetic field intensity at which such measurements were carried out. The similarity of features of n and μD with composition leads us to believe that the magnetoresistance may arise from the scattering of conduction electrons by localized electrons involving the s-d exchange interaction. 相似文献
2.
BUICHI KUBOTA TOMOZO NISHIKAWA AKIRA YANASE EIICHI HIROTA TOSHIHIRO MIHARA YOSHIO IIDA 《Journal of the American Ceramic Society》1963,46(11):550-556
Several mixtures in the system Te-CrO2 were prepared by the decomposition of anhydrous chromic acid, CrO3 , and telluric acid (H6 TeO6 ) under high oxygen pressures; the physical and chemical properties were then studied. When Te was added, the grain size of CrO2 decreased rapidly from 5 to 10 μ to 0.1 to 1.0 μ and the magnetic coercive force increased from 20 to 120 oersteds. The magnetic Curie temperature and the lattice constants of CrO2 did not vary, however, with additions of Te up to 20 atomic %. X-ray analysis showed that the CrO2 plus Te was not a solid solution but a mixture of CrO2 and TeCr2 O6 that was nonmagnetic. 相似文献
3.
Abstract. We investigate autoregressive processes {Xn } ({Y" }) satisfying Xn+1 =Λ(Xn ) + Zn+1 ( Yn+1 =μ(Yn ) + Zn+1 ) , n = 0, 1, 2, …, where Λ and μ are odd increasing functions and the Zn 's are i.i.d. with unimodal symmetric distribution. The process {|Xn |} is then stochastically monotone on [0, ∞). If |Λ| ≤ |μ| then |Xn is stochastically dominated by |Yn | for n = 1, 2, …. Some related asymptotic properties, e.g., stationary distributions, are also discussed. 相似文献
4.
Matiur Rahman Ching C. Wang Weihua Chen Sheikh A. Akbar Cathleen Mroz 《Journal of the American Ceramic Society》1995,78(5):1380-1382
The electrical resistivities of hot-pressed samples of Ti1- x Zr x B2 ( x = 0.0, 0.3, 0.5, 0.7, 1.0) were measured by a four-point ac technique over the range 298 to 1573 K in an argon atmosphere. The hot-pressed samples for the intermediate compositions were found to be mixtures of two solid-solution phases. The resistivities for all compositions were found to increase linearly with temperature and can be described by ρ( T ) =ρ298 +φ( T - 298). The room-temperature resistivity ρ298 (μΩ cm) and the temperature coefficient of resistivity φ (nΩ·cm/K) for ZrB2 were determined to be 7.8 and 10, both of which increase with the content of TiB2 . These values for TiB2 were determined to be 20.4 and 36, respectively. 相似文献
5.
M. J. REDMAN J. H. CHEN W. P. BINNIE W. J. MALLIO 《Journal of the American Ceramic Society》1970,53(12):645-648
The compounds CaTe2 O5 , SrTe2 O5 , and CdTe2 O5 were obtained as mica-like plates by slowly cooling their melts. Dielectric properties were similar to those of mica. Optical and infrared spectra showed appreciable transmittance from 0.33 to 7 μm on with a cutoff at 10 μm. The compounds have refractive indices greater than 2. X-ray diffraction studies showed that only the calcium and cadmium compounds are isomorphous; tentative structures, accounting for the marked cleavage, are proposed for these materials on the basis of the geometric distribution of X-ray scattering. 相似文献
6.
Toshinobu Yogo Koichi Kikuta Yasuhiro Ito Shin-ichi Hirano 《Journal of the American Ceramic Society》1995,78(8):2175-2179
Highly oriented K(Ta,Nb)O3 (Ta:Nb = 65:35) (KTN) thin films of perovskite structure were synthesized successfully on Pt(100)/MgO(100) substrates from a metal alkoxide solution through reaction control. Homogeneous KTN coating solutions prepared from KOC2 H5 , Ta(OC2 H5 )5 , and Nb(OC2 H5 )5 in ethanol were analyzed by 1 H, 13 C, and 93 Nb NMR spectroscopy. The KTN precursor included a molecular-level mixture of K[M(OC2 H5 )6 ] (M = Ta, Nb) units interacting in ethanol solution. X-ray pole figure measurement showed that perovskite KTN films crystallized on Pt(100)/MgO(100) substrates had not only a (100) orientation but also a three-dimensional regularity of grains. The remanent polarization and coercive field of the KTN film (thickness, 1.0 μm) crystallized at 700°C were 1.5 μC/cm2 and 8.7 kV/cm, respectively, at 225 K. 相似文献
7.
In the present study, α-SiC powder is coated with pyridineborane (BH3 ·C5 H5 N), a liquid molecular compound, which forms a boron carbonitride (BC3.5 N) layer by heat treatment at 1000°C under argon. The precipitation method leads to an improved chemical homogeneity in the compacted powder resulting in enhanced densification and significant reduction in grain growth during subsequent sintering at temperatures exceeding 2070°C. Thus, small average grain sizes of d 50 = 1.3 μm and a narrow grain size distribution ( d 10 = 0.6 μm, d 90 = 2.2 μm) are detected in the liquid-phase-processed sample sintered at 2200°C for 0.5 h in argon. Final densities of at least 98% of theoretical could be obtained by pressureless sintering at 2100°C. These results as well as the microstructural distribution of the sintering aids in the densified samples are discussed. 相似文献
8.
Some physical properties okf phosphate glasses con-taining up to about 26 mol% Fe2 O2 were studied. Pronounced changes in properties were observed at compositions containingabout 6, 10, and 13 mol% Fe2 O3 . The X-ray diffraction spectra of devitrified (heat-treated) samples showed new compounds near these compositions. Electron spin resonance and optical studies confirmed the presence of Fe3+ and Fe2+ in both 4- and 6-coordination. An increase in total iron in these samples was associated with a decrease in the ratios Fe2+ 4-coordinated/Fe3+ 6-coordinated 6-coordinated and Fe3+ 4-coordinated/Fe3+ 6-coordinated up to about 2.0 mol% Fe2 O3 , as shown by the intensity of the optical absorption bands at about 2.0 and 1.0 μm and by the intensity of the ESR lines at g⋍4.2 and 2.0, respectively. Samples containing up to 4.3 mol% Fe2 O3 showed an increase in Fe3+ concentration and a decrease in Fe2+ concentration after gamma irradiation. The electrical conductivity and activation energy decreased sharply with increasing Fe2 O3 content. 相似文献
9.
Yuuji Mori Yukishige Kitano Akira Ishitani Takaki Masaki 《Journal of the American Ceramic Society》1988,71(7):322-C
A revised method to determine the transformation zone size in ceramics containing tetragonal ZrO2 using X-ray diffraction technique was described. The zone sizes of tetragonal ZrO2 polycrystals (TZP) and partially stabilized ZrO2 (PSZ) containing 2.0 to 5.0 mol% Y2 O3 were found to be larger than those determined by the method previously reported. The maximum zone size of TZP containing 2.0 mol% Y2 O3 was estimated to be 6.6 μm, whereas it had been determined to be 2.9 μm by the method previously reported. 相似文献
10.
Sukill Kang Amit Goyal Keith J. Leonard Noel A. Rutter Dominic F. Lee Donald M. Kroeger Mariappan Parans Paranthaman 《Journal of the American Ceramic Society》2005,88(10):2677-2680
YBa2 Cu3 O7−δ (YBCO) films with thicknesses ranging from 1.0 to 6.4 μm were deposited by pulsed laser deposition on rolling-assisted biaxially textured substrates (RABiTS). The RABiTS were of the configuration CeO2 /YSZ/Y2 O3 /Ni–3 at.% W. As the YBCO film thickness increased, I c continued to increase and reached ∼300 A/cm width for a 4.3 μm-thick YBCO film. Commonly observed mechanisms for J c decrease with increasing YBCO film thickness were not observed. Homogeneous microstructures obtained in even the thickest YBCO films, suggest that the I c /width can still be enhanced considerably. 相似文献
11.
Arnold Broese van Groenou Déanis J. C. van Oers 《Journal of the American Ceramic Society》1983,66(12):223-C
By using an instrumentation recorder with Al2 O3 tape loaded on the reverse side with an Al2 O3 sphere 4 mm in diameter, flat samples were thinned locally to a thickness of 10 μm. About 90 min is required for two-sided thinning of a ferrite sample 200 μm thick, followed by 30 h of ion-milling. Transmission electron micrographs showing details of glass gaps in magnetic recording heads were obtained. The method is also thought to be useful for making thin cross sections of complicated structures . 相似文献
12.
Yongsheng Liu Litong Zhang Laifei Cheng Yongdong Xu Yi Liu 《International Journal of Applied Ceramic Technology》2010,7(1):63-70
Silicon nitride particle-reinforced silicon nitride matrix composites were fabricated by chemical vapor infiltration (CVI). The particle preforms with a bimodal pore size distribution were favorable for the subsequent CVI process, which included intraagglomerate pores (0.1–4 μm) and interagglomerate pores (20–300 μm). X-ray fluorescence results showed that the main elements of the composites are Si, N, and O. The composite is composed of α-Si3 N4 , amorphous Si3 N4 , amorphous SiO2 , and a small amount of β-Si3 N4 and free silicon. The α-Si3 N4 transformed into β-Si3 N4 after heat treatment at 1600°C for 2 h. The flexural strength, dielectric constant, and dielectric loss of the Si3 N4(p) /Si3 N4 composites increased with increasing infiltration time; however, the pore ratios decreased with increasing infiltration time. The maximum value of the flexural strength was 114.07 MPa. The dielectric constant and dielectric loss of the composites were 4.47 and 4.25 × 10−3 , respectively. The present Si3 N4(p) /Si3 N4 composite is a good candidate for high-temperature radomes. 相似文献
13.
Youren Xu Chao M. Huang Waltraud M. Kriven Avigdor Zangvil 《Journal of the American Ceramic Society》1994,77(8):2213-2216
The microstructure of a pressureless sintered (1605°C, 90 min) O'+β' SiAlON ceramic with CeO2 doping has been investigated. It is duplex in nature, consisting of very large, slablike elongated O' grains (20–30 μm long), and a continuous matrix of small rodlike β' grains (< 1.0 μm in length). Many α-Si3 N4 inclusions (0.1–0.5 μm in size) were found in the large O' grains. CeO2 -doping and its high doping level as well as the high Al2 O3 concentration were thought to be the main reasons for accelerating the reaction between the α-Si3 N4 and the Si-Al-O-N liquid to precipitate O'–SiAlON. This caused the supergrowth of O' grains. The rapid growth of O' crystals isolated the remnant α–Si3 N4 from the reacting liquid, resulting in a delay in the α→β-Si3 N4 transformation. The large O' grains and the α-Si3 N4 inclusions have a pronounced effect on the strength degradation of O'+β' ceramics. 相似文献
14.
Zushu Li William Edward Lee Shaowei Zhang 《Journal of the American Ceramic Society》2007,90(2):364-368
Calcium zirconate (CaZrO3 ) powder was synthesized using calcium chloride (CaCl2 ), sodium carbonate (Na2 CO3 ), and zirconia (ZrO2 ) powders. On heating, CaCl2 reacted with Na2 CO3 to form NaCl and CaCO3 . NaCl–Na2 CO3 molten salts provided a liquid reaction medium for the formation of CaZrO3 from in situ -formed CaCO3 (or CaO) and ZrO2 . CaZrO3 started to form at about 700°C, increasing in amount with increasing temperature and reaction time, with a concomitant decrease in CaCO3 (or CaO) and ZrO2 contents. After washing with hot-distilled water, the samples heated for 5 h at 1050°C were single-phase CaZrO3 with 0.5–1.0 μm grain size. 相似文献
15.
Yiquan Wu Larry L. Hench Jing Du Kwang-Leong Choy Jingkun Guo 《Journal of the American Ceramic Society》2004,87(10):1988-1991
Hydroxyapatite (Ca10 (PO4 )6 (OH)2 , HA) fibers were prepared by electrospinning a precursor mixture of Ca(NO3 )2 ·4H2 O and (C2 H5 O)3 PO with a polymer additive, followed by a thermal treatment. The X-ray diffraction (XRD) analysis of the annealed composite fibers revealed that pure HA phase could be obtained by annealing at 600°C for 1 h. The scanning electron microscopy (SEM) analysis showed the surface of as-electrospun composite fibers with an average diameter of 50 μm was smooth due to the amorphous nature of the polymer. However, the surface of the calcined HA fibers was rough because of the complete removal of the polymer. The pure HA fibers obtained by electrospinning in this work were up to 10 mm in length and 10–30 μm in diameter and the hydroxyapatite grain size was ∼1 μm in the HA fibers. 相似文献
16.
Qiyi Yin Shuoguo Yuan Qiang Dong Changan Tian 《Journal of the American Ceramic Society》2010,93(1):167-170
A new type (1− x )(K0.485 Na0.485 Li0.03 )NbO3 – x Pb(Zr0.53 Ti0.47 )O3 piezoelectric ceramics was fabricated by conventional ceramics sintering technique. Their microstructure and electrical properties of the ceramics were also studied. X-ray diffraction and scanning electron microscopy patterns indicate that all ceramics samples exhibit a pure perovskite and highly dense structure, and the coexistence of the tetragonal and orthorhombic phases is formed; The ceramic with x =0.75 exhibits the following excellent properties: d 33 =363 pC/N, k p =63%, Q m =142, ɛr =1590, tan δ=1.70%, P r =28.6 μC/cm2 , E c =0.89 kV/mm, T c =295°C. These results indicate that the ceramic is a promising candidate for piezoelectric ceramics in practical applications. 相似文献
17.
Huamin Kou Jing Wang Yubai Pan Jingkun Guo 《Journal of the American Ceramic Society》2005,88(6):1615-1618
Hollow Al2 O3 spheres with ∼2 μm in diameter and ∼200 nm in wall thickness were prepared successfully via the calcination of the Al/AlOOH· n H2 O core-shell particles, prepared by wet-chemical method using commercial microscale aluminum powders as raw materials, at 900°–1100°C in air. X-ray powder diffraction, differential scanning calorimetric analysis, scanning electron microscopy, and transmission electron microscopy were used to characterize the obtained samples, and the possible formation mechanism was discussed. These hollow Al2 O3 microspheres may have promising applications in insulators, lightweight fillers, and catalyst carriers because of their unique hollow structure. 相似文献
18.
Sandeep Butee Ajit Kulkarni Om Prakash Ramnath P.R.C. Aiyar Sumesh George Mailadi Sebastian 《Journal of the American Ceramic Society》2009,92(5):1047-1053
(Ni1− x Zn x )Nb2 O6 , 0≤ x ≤1.0, ceramics with >97% density were prepared by a conventional solid-state reaction, followed by sintering at 1200°–1300°C (depending on the value of x ). The XRD patterns of the sintered samples (0≤ x ≤1.0) revealed single-phase formation with a columbite ( Pbcn ) structure. The unit cell volume slightly increased with increasing Zn content ( x ). All the compositions showed high electrical resistivity (ρdc =1.6±0.3 × 1011 Ω·cm). The microwave (4–5 GHz) dielectric properties of (Ni1− x Zn x )Nb2 O6 ceramics exhibited a significant dependence on the Zn content and to some extent on the morphology of the grains. As x was increased from 0 to 1, the average grain size monotonically increased from 7.6 to 21.2 μm and the microwave dielectric constant (ɛ'r ) increased from 23.6 to 26.1, while the quality factors ( Q u × f ) increased from 18 900 to 103 730 GHz and the temperature coefficient of resonant frequency (τf ) increased from −62 to −73 ppm/°C. In the present work, we report the highest observed values of Q u × f =103 730 GHz, and ɛ'r =26.1 for the ZnNb2 O6 -sintered ceramics. 相似文献
19.
Sunuk Kim Myong-cheol Jun Soon-cheol Hwang 《Journal of the American Ceramic Society》1999,82(2):289-296
Crack-free, undoped PbTiO3 ceramics were fabricated successfully using sol–gel-synthesized powder prepared from chelated titanium alkoxide and lead acetate. The sintered ceramics, 8.3 mm in diameter and 6–8 mm thick, were 96% dense. In the present study, PbTiO3 ceramics with excess lead (Pb:Ti = 1.1:1.0) had large grains, averaging 14.3 μm. Lower-lead ceramics (Pb:Ti = 1.0:1.0 and 0.9:1.0) had smaller grains, averaging 1.8 μm. The PbTiO3 ceramics with a high lead content cracked during sintering at 1150°C, whereas the other ceramics did not crack. Excess lead, in a more-than-stoichiometric ratio, promoted grain growth and caused disintegration of the ceramics. Therefore, uncracked PbTiO3 ceramics apparently can be fabricated by avoiding excess lead, possibly because restricted grain growth in low-lead ceramics causes low residual stress over many small grains during transition. The electrical properties measured in the present study for PbTiO3 ceramics with a Pb:Ti ratio of 1:1 are d 33 = 35 pC/N, K 3 = 64, k p = 0.59, and k t ≈ 0. 相似文献
20.
The effects of Si and ZrO2 dopants on the crystallization and phase transformation process in Li2 O · Al2 O3 · 6SiO2 glasses were investigated using differential thermal analysis, X-ray powder diffractometry (XRD), and high-resolution transmission electron microscopy (TEM) interactively. Phase separation was observed in the studied glasses prior to substantial crystallization. Elemental Si (1 mol%) significantly aided in glass devitrification. Dropletlike phase-separated regions in the as-quenched or heat-treated glass devitrified at ∼760°C, which in turn provided sites for the heterogeneous nucleation and growth of β-quartz(ss) (solid solution), which transformed to β-spodumene(ss) at higher temperature. Low-temperature surface crystallization in these glasses occurred as low as 760°C. ZrO2 has limited solubility in this glass system. Small ZrO2 crystallites (·5 nm) in the as-quenched glass acted as sites for the heterogeneous nucleation and subsequent growth of large (<5 μm) β-quartz(ss) crystals in glasses containing 1.0 mol% or more ZrO2 . The transformation from β-quartz(ss) to β-spodumene(ss) was increasingly inhibited with ZrO2 additions. The nucleating efficiency of Si was significantly greater than that of ZrO2 in this glass system. 相似文献