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1.
Zr---Al metallo-organic compounds (zircoaluminates), having (CH 2) 4COOH, (CH 2) 12CH 3 and (CH 2) 2NH 2 as the organofunctional groups, were treated preliminary by (1) spray-drying, (2) gelation of addition of 10% NH 4OH aqueous solution followed by spray-drying and (3) rotary evaporation under a reduced pressure. After the treatment they were heated in air to prepare ZrO 2---Al 2O 3 composite powders. The IR and DTA profiles for the treated compounds indicated that the procedures modified the structures for the zircoaluminates. The stability of tetragonal ZrO 2 for the ZrO 2---Al 2O 3 composite powder were dependent on the modification in the structure for the zircoaluminates. Balloon shaped particles, 0.5–2 μm in diameter, were obtained through procedure (1) and spherical particles, 1–4 μm in diameter, through (2). Tetragonal ZrO 2 grains, 0.1–0.2 μm in diameter, were dispersed in the particles when heated at 1400°C. 相似文献
2.
Glasses of compositions 5ZrO 2·5SiO 2(ZS), 5ZrO 2·Al 2O 3·4SiO 2(ZAS) and 5 5ZrO 2·0.5Al 2O 3·0.5Na 2O·4SiO 2(ZANS) were prepared by the sol-gel process from metal alkoxides and sintered to make glass-ceramics. Tetragonal ZrO 2 was precipitated by heat treatment at 900 to 1300°C. The activation energy for tetragonal ZrO 2 crystal growth was extremely high in Al 2O 3 containing glasses. ZAS and ZS were sintered to the near theoretical densities above 1200°C, at which the predominant phase was tetragonal ZrO 2. On the other hand, for ZANS, high densification was not attained owing to the large pores enclosed by the glass phase. Strength and fracture toughness increased with the densification and the crystal growth of tetragonal ZrO 2, reaching 450 MPa and 9 MN/m 1.5, respectively. 相似文献
3.
The glass formation of the ZrO 2---Al 2O 3---P 2O 5 system in the high phosphate region is determined. The crystallization process and the crystal types formed during heat treatment have been studied. The structure of these glasses is discussed. 相似文献
4.
The preparation of glass-lined coating mould from gels in the ternary system of SiO 2–ZrO 2–B 2O 3 has been investigated. The crystallization characterization and high temperature structure stability of this coating mould are demonstrated. We can find that the crystallization of t-ZrO 2 as well as the tetragonal to monoclinic phase transformation are, respectively, retarded and impeded owing to the encasement of SiO 2 matrix. While the inhibitive effect of B 2O 3 on crystallization of the SiO 2–ZrO 2–B 2O 3 coating mould is explained. Finally, DD3 single crystal superalloy melt can realize highly undercooled rapid solidification by adopting this coating mould, which further evinces that SiO 2–ZrO 2–B 2O 3 coating mould has an ideal nucleation inhibition for superalloy. 相似文献
5.
Since 1980 much attention has been payed to hydrothermal processing. There are several papers related to hydrothermal fine Zirconia powders by authors 1), 2), 3) and 3). The authors 3) prepared ZrO2 and Y2O3-ZrO2 powders under hydrothermal conditions. Several methods were used to prepare fine ZrO2 powders under hydrothermal conditions: hydrothermal precipatation, hydrothermal crystallization, hydrothermal oxidation, hydrothermal decomposition, hydrothermal synthesis, hydrothermal anodic oxidation, RESA (reactive electrode submerged arc) process, etc. This paper describes hydrothermal precipatation processing of ZrO2 and Y-ZrO2 powder. 相似文献
6.
Various oxide films on SiO 2 glass substrates were irradiated by a laser beam. A continuous CO 2 laser source (wavelength 10.6 μm) was used for this purpose; the composition change at the surface layer was determined by Rutherford backscattering spectrometry (RBS). All the alkaline-earth oxides as well as those of lanthanum and yttrium, entered the glass after treatment. ZrO 2 and CeO 2, however, did not enter the SiO 2 glass due to laser irradiation. It is interesting, however, that a film of ZrO 2 + Al 2O mixture easily entered into the SiO 2 glass by laser processing. The conditions and mechanism of laser-enhanced interaction of ZrO 2 or other oxide films with SiO 2 glass surfaces are discussed especially in view of their structural behaviour in glass. 相似文献
7.
The structure and thermal stability of ZrO 2 films grown on Si (1 0 0) substrates by metalorganic chemical vapor deposition have been studied by high-resolution transmission electron microscopy, selected area electron diffraction and X-ray energy dispersive spectroscopy. As-deposited films consist of tetragonal ZrO 2 nanocrystallites and an amorphous Zr silicate interfacial layer. After annealing at 850°C, some monoclinic phase is formed, and the grain size is increased. Annealing a 6 nm thick film at 850°C in O 2 revealed that the growth of the interfacial layer is at the expense of the ZrO 2 layer. In a 3.0 nm thick Zr silicate interfacial layer, there is a 0.9 nm Zr-free SiO 2 region right above the Si substrate. These observations suggest that oxygen reacted with the Si substrate to grow SiO 2, and SiO 2 reacted with ZrO 2 to form a Zr silicate interfacial layer during the deposition and annealing. Oxygen diffusion through the tetragonal ZrO 2 phase was found to be relatively easier than through the monoclinic phase. 相似文献
8.
SrTiO 3/BaZrO 3 heterofilms as buffer layers are deposited on (0 0 1) MgO substrates by an RF-sputtering technique. The atomic structure and the defect configuration at the interfaces are investigated by means of aberration-corrected high-resolution transmission electron microscopy. At the BaZrO 3/MgO interface, two types of interfacial structures, MgO/ZrO 2-type and MgO/BaO-type, are observed. Antiphase boundaries and dislocations are found at the BaZrO 3/MgO interface. The formation of these lattice defects is discussed in terms of film growth and structural imperfections of the substrate surface. At the SrTiO 3/BaZrO 3 interface, a high density of misfit dislocations is observed with different configurations. The formation of these dislocations contributes both to the relaxation of the large misfit strain and to stopping of the further propagation of lattice defects which are formed in the BaZrO 3 layer into the SrTiO 3 layer. 相似文献
9.
The oscillation of Y 2BaCuO 5 (2 1 1) particle concentration in form of bands parallel to the growth front was observed in top-seeded melt-grown (TSMG) single-grain YBa 2Cu 3O 7/Y 2BaCuO 5 bulk superconductors. The formations of these bands have been associated with temperature fluctuations at the growth front, which induce the fluctuation of the growth rate of the YBa 2Cu 3O 7 (123) crystal and consequently also the fluctuation of the amount of trapped 211 particles. We have shown that the oscillation of 211-particle concentration does not occur when the growth front is horizontal and the crystal solidifies from below upwards. In the a-growth sector (a-GS) the oscillation was observed only in the nests with very small 211 particles. 相似文献
10.
The effects of vibration ball-milling of a mixture of two gels, prepared from mixing ZrO 2 and TiO 2 sols, on crystallization processes during heating are studied in order to determine enhanced mechanochemical reactions with the aid of hydroxyl groups. Data of differential thermal analysis (DTA) and X-ray diffractometry show that TiO 2 (anatase) and ZrO 2 (tetragonal) crystallized at 698 and 712 K, respectively, when a powdered gel mixture was heated to 1023 K to 10 K min −1 in air. No reactions between the two phases were detected. After vibro-milling a powdered gel mixture at room temperature for 3 to 30 h, a new exothermic DTA peak appeared around 950 K and ZrTiO 4 (orthorhombic) was detected on heating to 1023 K. After vibro-milling, the compositional micro-homogeneity of non-heated gels was estimated from the fluctuations of elemental compositions in local areas using energy dispersive spectrometer with a 25 nm electron beam. The fraction of ZrTiO 4 crystallized on heating the gels to 1023 K, determined by Raman spectroscopy, increased linearly with increasing the micro-homogeneity for non-heated gels. It is suggested that atomic movement and short-range ordering of ZrTiO 4 rather than crystallization of individual oxides occur when applying mechanical stress to a powdered mixture of ZrO 2 and TiO 2 gels. 相似文献
11.
The La L 1 and L 3 XANES and L 3 EXAFS have been investigated for the series of glasses 10K 2O---50SiO 2--- x La 2O 3 ( x = 1, 5, 10) and (10 − x)K 2O---40SiO 2−( x/3)La 2O 3 ( x = 7.5, 5, 2.5) and model compounds La 2O 3, LaAlO 3, LaPO 4, La 2NiO 4, La 2CuO 4 and La(OH) 3. An edge resonance at 25 eV above the L 1 edge in the glass spectra is concentration-dependent, decreasing in intensity with increasing lanthanum concentration. The 2s → nd forbidden transition increases with La 2O 3 concentration, indicating a reduction in the ‘average’ site symmetry of the first coordination shell of La. Mapping X( k) space, which is a new and promising technique, was employed to extract bond distance, coordination number and thermal parameters from the EXAFS. By this method, one calculates the complete X( k) space a function of all physically reasonable values of the adjusted parameters in all possible combinations. The advantage in this method is the assurance of a global minimum. Bond lengths were comparable to those obtained by Fourier transforming the phase corrected EXAFS. The values are 2.42 Å (± 0.03 Å) for La---O. The coordination numbers ( N ≤ 7 ± 1.5) were derived by mapping and comparison to the published structures for other La compounds. X( k) mapping is compared with least-squares fitting the data, and the correlation between the Debye-Waller factor and coordination number is also discussed. 相似文献
12.
Grain size composition of precipitated Al(OH) 3 is dependent on the mechanism of decomposition process of the caustic solution which determines crystal growth process, agglomeration process and secondary nucleation. Because the literature data shows that the growth rate is very low, the agglomeration process plays an important role in increasing the initial particle size. On the other hand, the agglomeration process enables the inclusion of impurities by the grain boundary of sticking Al(OH) 3 particles, above all, the inclusion of soda Na 2O. In this paper we investigate the influence of caustic soda concentration Na2O(c), that is the supersaturation of the solution, seed charge and seed grain size on the agglomeration and secondary nucleation processes and total soda content in precipitated Al(OH)3. The results have shown that the factor which causes the increase of the agglomeration process also causes the increase of total soda content in precipitated Al(OH)3. 相似文献
13.
Clustered anatase phase TiO 2 particles were uniformly formed on the surface of glass fibers by a liquid phase deposition (LPD) method at 60 °C using TiF 4 and H 3BO 3 as the precursors. The clustered TiO 2 particles deposited on the glass fibers and as a photocatalyst these particles not only have a larger surface area than TiO 2 thin films, but also can avoid the disadvantages of using TiO 2 powders encountered in air purification or water treatment. The photocatalytic activity of the sample was evaluated by the photocatalytic oxidation of nitrogen monoxide (NO) in the gaseous phase. The deposition conditions and chemical composition of the clustered TiO 2 particles were discussed. It was found that the clustered TiO 2 particles that formed on the glass fibers obviously showed photocatalytic activity without high-temperature calcination. A formation mechanism was proposed to account for the formation of TiO 2 clustered morphology on the glass fibers. 相似文献
14.
The electrical and dielectric properties for three series of MoO 3–Fe 2O 3–P 2O 5 and one series of SrO–Fe 2O 3–P 2O 5 glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO 3 is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe 2O 3 content and Fe(II)/Fe tot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe 2O 3 content in MoO 3–Fe 2O 3–P 2O 5 glasses with O/P at 3.5 the dc conductivity, σ dc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe 2O 3 and is independent of the MoO 3 content. Also, the dielectric properties such as ′(ω), ″(ω) and σ ac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO 3. On the other hand, the dc conductivity for MoO 3–Fe 2O 3–P 2O 5 glasses with O/P > 3.5 increases with the substitution of MoO 3 which has been explained by an increase in the number of non-bridging oxygens and formation of Fe–O–P bonds that are responsible for formation of small polarons. The increase in the dielectric permittivity, ′(ω) with increasing MoO 3 content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe 2O 3–P 2O 5 glasses the conductivity and dielectric permittivity remained constant with increasing SrO. 相似文献
15.
The MoS 2 nanowires with diameters of 4 nm and lengths of 50 nm were synthesized by a hydrothermal method using 0.36 g MoO 3 and 1.8 g Na 2S as precursors in 0.4 mol/l HCl solution at 260°C. The products are characterized by XRD, XPS, TEM, HTEM and BET. Results show that the as-prepared MoS 2 nanowires consist of 1–10 sulfide layers with BET surface areas of 107 m 2/g. The possible reaction route and the formation mechanism of the MoS 2 nanowires are discussed. The effects of exterior conditions such as pH value, temperature, concentration of precursors and additives on the particle size and morphology of MoS 2 crystallites were investigated. 相似文献
16.
A novel approach for preparation of red-emitting europium-doped yttrium oxide phosphor (Y 2O 3:Eu) by using the bicontinuous cubic phase (BCP) process was reported in this paper. The BCP system was composed of anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and aqueous yttrium nitrate/europium nitrate solution. Energy dispersive spectrometer analysis revealed the homogeneous precipitation occurred in the BCP structure. Thermogravimetric analysis measurements indicated the precursor powder was europium-doped yttrium hydroxide, Y 1−xEu x(OH) 3. Scanning electron microscopy micrographs showed the precursor powder had a primary size about 30 nm and narrow size distribution. After heat treatment in furnace above 700 °C for 4 h, high crystallinity Y 2O 3:Eu phosphors was obtained. However, the primary size of particles grew to 50–200 nm and the dense agglomerates with a size below 1 μm were formed. X-ray diffraction patterns indicated the crystal structure of precursor powders and Y 2O 3:Eu phosphors were amorphous and body-centered cubic structure, respectively. The photoluminescence analysis showed that the obtained Y 2O 3:Eu phosphor had a strong red emitting at 612 nm and the quenching started at a Eu concentration of 10 mol%. This study indicated that the BCP process could be used to prepare the highly efficient oxide-based phosphors. 相似文献
17.
The corrosion of ZrO 2-containing refractories by molten glasses has been investigated experimentally in relation to the compositions of the glasses. For a zircon refractory, zircon crystals contacting the glass decomposed into ZrO 2 crystals and glassy phase at higher temperatures. The decomposition temperature was changed with the glass compositions. Alkali components in the glasses were confirmed to be most corrosive for the zircon refractory. For a ZrO 2 refractory, compositions of the glass-refractory interfaces were nearly saturated with ZrO 2. The corrosion rate of the ZrO 2 refractory was considered to be controlled by the transport rate of zirconium away from the interface. The concentration of CaO in glasses, as well as that of alkali components, was found to be very effective for increasing the corrosion rate of ZrO2 refractories. 相似文献
18.
Appropriate glass compositions of the Na 2O---Al 2O 3---SiO 2 system and glass melting technology were investigated. The dependence of some factors, such as composition of molten salts, time and temperature of ion exchange treatment on the modulus of rupture was studied. As expected, the coefficient of interdiffusion is a function of concentration and has the mixed-alkali effect. The order of the interdiffusion coefficient is 10 −6 cm 2/s. The effect of binary and ternary salt baths on the surface controlled crystallization was reported. The experimental data showed that there is a series of technological advantages from applying molten salts of the ternary system Li 2SO 4---Na 2SO 4---K 2SO 4 in comparison with the binary system Li 2SO 4---Na 2SO 4. 相似文献
19.
The surface of a TiO 2 film electrode, about 1 μm thick, prepared by the sol-gel method, was modified by being additionally coated with about 0.1 μm thick TiO 2---SiO 2, TiO 2---ZrO 2 or TiO 2---Al 2O 3 films. The effect of the additional coating on the photoelectrochemical properties of a TiO 2 film electrode was investigated in detail. On addition of the second additive to TiO 2, the flat band potential was shifted toward negative potential for SiO 2 and positive potential for ZrO 2 and Al 2O 3, which is attributed to the change in the point of zero zeta potential (pzzp), not in the electron affinity ( EA). However, enhancement in photocurrent was not observed for all the cases. 相似文献
20.
Tellurite containing vanadate (50− x)V 2O 5– xBi 2O 3–50TeO 2 glasses with different bismuth ( x=0, 5, 10, 15, 20 and 25 wt%) contents have been prepared by rapid quenching method. Ultrasonic velocities (both longitudinal and shear) and attenuation (for longitudinal waves only) measurements have been made using a transducer operated at the fundamental frequency of 5 MHz in the temperature range from 150 to 480 K. The elastic moduli, Debye temperature, and Poisson’s ratio have been obtained both as a function of temperature and Bi 2O 3 content. The room temperature study on ultrasonic velocities, attenuation, elastic moduli, Poisson’s ratio, Debye temperature and glass transition temperature show the absence of any anomalies with addition of Bi 2O 3 content. The observed results confirm that the addition of Bi 2O 3 modifier changes the rigid formula character of TeO 2 to a matrix of regular TeO 3 and ionic behaviour bonds (NBOs). A monotonic decrease in velocities and elastic moduli, and an increase in attenuation and acoustic loss as a function of temperature in all the glass samples reveal the loose packing structure, which is attributed to the instability of TeO 4 trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi 2O 3 content are more stable than with high Bi 2O 3 content. 相似文献
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