Showing papers by "Wuhan University of Technology published in 1994"

Magnetoelectric effect in composites of piezoelectric and piezomagnetic phases

Abstract: The magnetoelectric effect in composites of piezoelectric and piezomagnetic phases is investigated theoretically. The magnetoelectric effect is totally absent in these two constituent phases, and so it is a new property of the composites. A generalized theoretical framework based on a Green's function method and perturbation theory is proposed to treat the coupled magnetoelectric behavior in the composites. Explicit relations for determining the effective magnetoelectric effect in the composites are derived, and the different approximate expressions for the magnetoelectric coefficient of the fibrous composites with 1-3 or 3-1 connectivity of phases are given. To illustrate the technique, numerical calculations of the magnetoelectric coefficients of the BaTiO3-CoFe2O4 composites for various phase compositions and particle shapes are performed. The theoretical estimates are shown to be in agreement with available experimental results, and also show the interesting magnetoelectric behavior of the composites.

Theoretical approach to the coupled thermal-electrical-mechanical properties of inhomogeneous media.

Abstract: A generally theoretical framework for predicting the coupled thermal-electrical-mechanical properties of inhomogeneous media is developed in terms of a Green's function method and perturbation theory. Taking a tranversely isotropic fiber-reinforced composite of the 4- or 6-mm symmetry class as a practical example, I discuss the general theoretical results, and give explicit expressions for the effective coupled thermal-electrical-mechanical properties. The pyroelectricity of BaTiO3-epoxy and CdS-epoxy composites is numerically analyzed. An enhanced pyroelectricity is predicted, and the numerical results show the interesting behavior of these materials.

Glass formation in Sb2Se3MXn (metal halides)

Abstract: Glass formation in Sb 2 Se 3 MX n (metal halides) has been studied. Glass transition temperatures, crystallization temperature and infrared transmission of some of the glasses were examined. Broad glass-forming regions were found in the Sb 2 Se 3 HgI 2 , Sb 2 Se 3 HgBr 2 and Sb 2 Se 3 CuI with narrow glass-forming regions in Sb 2 Se 3 PbI 2 and Sb 2 Se 3 PbBr 2 . No bulk glass formation was found in Sb 2 Se 3 CdBr 2 , Sb 2 Se 3 AgI, Sb 2 Se 3 AgBr, Sb 2 Se 3 TiI and Sb 2 Se 3 TiBr by quenching a silica glass ampoule (inner diameter 4.5 mm, outer diameter 6 mm) in water. The glass transition temperature ranges from 110 to 180°C and the difference between crystallization and glass transition temperatures ranges from 40 to 60°C. The infrared cut-off wavelengths of the glasses extend to 22 μm. Sb 2 Se 3 -based chalcogenide-halide glasses may have capabilities applicable to infrared optical fiber materials.

Structural properties of sodium-iron phosphate glasses

Abstract: The affects of iron on the structure, physical, and optical properties of several iron phosphate and sodium-iron phosphate glasses were investigated using x-ray photoelectron spectroscopy (XPS), Mossbauer spectroscopy, and infrared spectroscopy (IR). Archimedes method, differential scanning colorimeter and Able refractometer measurements were used to determine the glass density (d), transition temperature (Tg), and refractive index (n), respectively. XPS and Mossbauer spectra showed the presence of iron in both the Fe2+ and Fe3+(4- and 6-coordinated) states. With the increase of Fe2O3 content in the iron phosphate glasses and the increase of Na2O content in the sodium-iron phosphate glasses, the Fe2+/Fe ratio decreases and the Fe3+(4-coordinated)/Fe ratio increases. The infrared measurements showed that the increase in the Fe2O3 content or the Na2O content caused a change in coordination from FeO6 to FeO4. Finally, the relationship between the properties and the Fe2+Fe3+(4-coordination) ratio is discussed briefly.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Product property between thermal expansion and piezoelectricity in piezoelectric composites: pyroelectricity

Abstract: acad sinica,int ctr mat phys,shenyang 110015,peoples r china.;nan, cw (reprint author), wuhan univ technol,adv mat res inst,hubei 430070,peoples r china

The in-situ TEM observation of microcrack nucleation in titanium aluminide

Abstract: Rice and Thomson assumed that the emissions of dislocation from a crack tip would lead to plastic blunting of the crack tip, and the materials were categorized as intrinsically cleavage if a condition for decohesion of the crystal plane ahead of the crack was reached before those for dislocation emission from the crack. For the ductile material, the TEM in-situ observation showed that a main crack tip might still be sharp after the dislocations had been emitted from the crack tip and the dislocation free zone (DFZ) had been formed; thus, the local stress near the crack tip in the DFZ was high enough to equal the cohesive strength, and then a microcrack with size of nanometers nucleated in the DFZ. The microcracks initiated in the DFZ would blunt into voids through the movement of the existing dislocation and/or those emanated from the crack tip and the nearby dislocation source. The discontinuous void resulting from the blunting of the microcracks in the DFZ would link with each other and with the main crack, resulting in ductile fracture. For brittle materials, the authors wonder whether the DFZ also exist and whether a microcrack with the size of nanometers nucleated preferably inmore » the DFZ. If such occurred, the microcrack initiated in the DFZ should propagate into a cleavage crack rather than blunt into void. The goal of the present work was to check the possibility of dislocation emissions, DFZ formation, and initiation and propagation of a microcrack in the DFZ for the brittle material. For the titanium aluminides, e.g., Ti-24Al-11Nb or TiAl, a brittle fracture occurred by slow stable crack growth characterized by a well-defined resistance curve, i.e., the resistance of the cleavage crack propagation increased with crack growth.« less

Continuous Microwave Sintering of Ceramics

Abstract: The microwave sintering technology is still at the developmental stage due to the limitation of the volume (or size) and batch of the ceramic products that can be fabricated by microwave processing. The present paper introduces a new microwave processing technique, i.e. a continuous microwave sintering, which makes it possible to sinter ceramic products with an infinite length in a microwave field. By this technique, alumina-mullite ceramic rollers of 40 mm in diameter and 2400 mm in length have been successfully microwave sintered. The exploratory results show this new technique could offer some new opportunities to scale up microwave sintering for industrial applications.

Electronic conductivity of LiMn2O4B2O3 and LiMn2O4B2O3P2O5 glasses

Abstract: A series of glasses in the pseudobinary system LiMn2O4-B2O3 and the pseudoternary system LiMn2O4-B2O3-P2O5 are prepared, and their electronic conductivity is measured. According to small polaron theory, the experimental results can be interpreted in terms of polaron-assisted hopping of small polarons. The glasses in the LiMn2O5-B2O3 system conduct in the non-adiabatic regime, and the substitution of P2O5 for B2O3 in the LiMn2O4-B2O3-P2O5 system does not change the conduction mechanism.

Sol-Gel derived PbTiO3 films on a polar glass ceramic substrate

Abstract: Sol-Gel derived PbTiO3 films were prepared with a polar glass ceramic as the substrate. The crystallization was investigated by means of X-ray diffraction. A preferential c-axis orientation in the film was observed. The grain size and the microstrain were determined by measuring the integrated width of the diffraction. The grain size increases with increasing firing temperature following an Arrhenius relation. The microstrain decreases with increasing firing temperature and it is much higher in the [001] direction than in the [100] direction.

Study of Boundary Free Tb-Dy-Fe Magnetostrictive Materials

Abstract: As a promising candidate of advanced smart materials Tb-Dy-Fe system has been studied for many years. It is well known that the boundaries (which exist in polycrystal and grain oriented crystals of magnetostrictive materials) heavily hinder the motion of domain walls. Therefore to eliminating those boundaries will improve their magnetostrictive behaviors to a large extent. A single crystal growth method (which is called: growth with magnetic levitation cold crucible in CZ technique) has been successfully developed in our lab. since a few years ago. Now bulk cubic Laves phase RFe 2 Tb x Dy 1-x Fe 1.95–2.0 single crystals with boundary free structure can be prepared. Studies have been focused on comparing the performances of polycrystal, grains oriented crystal with a single crystal of the same composition. Some results indicate that λ s and d 33 performed by the single crystal are much higher than the two former materials under the same conditions.

The relationship between the elastic modulus, resistivity and number of metal-metalloid bonds in FeSiB amorphous alloys

Abstract: The elastic modulus E and resistivity ϱ of FeSiB amorphous alloys are studied in this paper. The experimental results reveal the following: when metalloid content x E and ϱ increase with increasing x ; when x = 25 at.%, E and ϱ reach maxima; when x > 25 at.%, E and ϱ decrease with increasing x . The results can be interpreted by means of the rhomb unit structure model of amorphous alloys. The calculated n − x curve ( n is the number of metal-metalloid bonds) is similar to the E − x curve and ϱ − x curve. We can deduce from this result that E and ϱ are determined by metal-metalloid bonds in FeSiB amorphous alloys.

Preparation of Biodegradation Ceramic Implants

Abstract: In this paper, The authors present a new method to prepare porous ceramic calcium phosphate and give an investigation on the properties of this kind of material. The biodegradation behaviour of the ceramic in bone tissue and growing process of new bone are also analyzed by means of the X — Ray photography, SEM, EDAX . The ceramics Weree made by immersion shaping process and fired at 900°C. The results Show that the porous ceramic calcuim phosphate possesses superior biocompatibility and can be replaced by new bone gradually.

High Precision Actuator with Tb0.27DY0.73Fe1.95 Single Crystal

Abstract: It has been proved that the saturation magnetostrictive constant λs of Tb0.27Dy0.73Fe1.95 single crystal is greater than the polycrystal and grains oriented crystal with the terfenol compositions, especially for its large linear magnetostrictive strain. Tb0.27Dy0.73Fe1.95 single crystal also can produce large force and fast, precision motion at high efficiency and power levels. A proto-type micro positioning actuator with the single crystal was designed in our lab. The structure and performances are discussed in this paper.

Hot Corrosion Mechanism of Silicon Nitride Based Ceramics Exposed to Coal Slag Containing Potassium Sulfate

Abstract: The corrosion of three kinds of silicon nitride based ceramics by static liquid potassium sulfate-coal slag immersion was investigated at high temperatures. The reaction kinetics between silicon nitride based ceramics and coal-slag-potassium sulfate was investigated, different kinetic curves were obtained at different temperatures, it was l-(l-a)1/3=kt at 1350°C and a=kt2at 1400°C. Phase composition, microstructure of the materials before and after corrosion were studied by XRD, SEM/EDAX, and EPMA etc, which lead to the following detailed corrosion mechanism: (1) oxidation of silicon nitride based ceramics by potassium salt and oxygen in air simultaneously and formation of silicon dioxide. (2) melting of as-formed silica by potassium sulfate or K-contained silicate and resulting in a silicate melt Me-K2O·xSiO2, and (3) formation of a protective silica layer below the silicate melt.

Alloys, properties and quantum chemistry studies on intermetallic compounds of NiAl

Abstract: NiAl intermetallic compound and its alloys (added Fe, Co, Nb, Mo or B), synthesized with self-propagating high temperature synthesis (SHS), were studied with SCF-X a -DV, a quantum chemistry method. The relations between mechanics properties and chemical bonding are studied. The method to improve ductility of NiAl are discussed.