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1.
Fine-sized ZnO–B 2O 3–CaO–Na 2O–P 2O 5 glass powders with spherical shape were directly prepared by high temperature spray pyrolysis. The ZnO–B 2O 3–CaO–Na 2O–P 2O 5 powders prepared by spray pyrolysis at temperatures above 1200 °C had broad peaks at around 30° in the XRD patterns. The glass transition temperatures ( Tg) of the glass powders obtained by spray pyrolysis at preparation temperatures between 900 °C and 1400 °C were near 480 °C regardless of the preparation temperatures. The dielectric layers formed from the glass powders prepared by spray pyrolysis at preparation temperatures above 1300 °C had clean surface and dense inner structure at the firing temperature of 580 °C. The transmittance of the dielectric layer formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1400 °C was 90% at the firing temperature of 580 °C, in which the thickness of the dielectric layer was 13 μm. The UV cutoff edges gradually shift towards longer wavelength with increasing the preparation temperature of glass powders and the firing temperature of dielectric layers. 相似文献
2.
Single-crystal growth of KY(WO 4) 2 (KYW) by top-seeded solution growth technique has been investigated. The effects of seed orientation, temperature gradient experienced by the growing crystal and rate of crystallization on crystal quality are reported. The best results are obtained when the growth is seeded along the 0 1 0 direction. Minute deviations from this growth direction are found to be detrimental to crystal perfection. The differential thermal analysis shows that the amount of super-cooling required for dissolution and crystallization of KYW in the flux is only 5° and this promotes an easy formation of tiny crystallites in the solution. Consequently, the crystal rotation and the solution cooling rates are found to have pronounced effects on the growth of KYW crystal. 相似文献
3.
NaBi(WO 4) 2 (NBW) crystals have been grown for the first time by modified-Bridgman method. Influences of some factors on the crystal growth process are discussed. X-ray powder diffraction experiments show that the unit cell parameters of NBW crystal are a= b=0.5284 nm, c=1.1517 nm, and V=0.3215 nm 3. The differential thermal analysis shows that the NBW crystal melts at 923°C. 相似文献
4.
This paper reports the detail synthesis of a new kind of metal iodate, anhydrous (LiFe 1/3)(IO 3) 2, from aqueous solutions. The synthesized compound shows spinal morphology and is chemical stable up to 400°C. The iodate shows paramagnetic behavior from room temperature down to 4.2 K. At room temperature, the new compound has a hexagonal structure with the lattice parameters a=5.4632(2) Å, c=5.0895(6) Å, Z=1, space group of P6 3. 相似文献
5.
Alkoxide derived gels were prepared in the system Na 2O---B 2O 3---SiO 2. The gel compositions were situated in the liquid-liquid immiscibility area of the phase equilibrium diagram. Hydrolytic resistance tests were performed on the gels heat-treated at temperatures ranging between 120 to 850 °C. The Na2O, B2O3 and SiO2 extracted from the attack gels were analyzed. The experimental results indicate that the amount of B2O3 has a significant influence on the chemical durability of the heat-treated gels. At temperatures of 850 °C the greater the B2O3 mol% the greater are the amounts of Na2O and B2O3 extracted. Different behaviour was observed for gels heat-treated at 600 °C where the amounts of B2O3 and Na2O extracted slightly increases as the B2O3 mol% increases. Small amounts of extracted SiO2 were always observed. These results are complemented with other measurements so that an explanation of the controlling mechanism is given. 相似文献
6.
The development of microstructure during crystallisation of a glass with composition Y 15.2Si 14.7Al 8.7O 54.1N 7.4 has been studied by analytical and high resolution transmission electron microscopy. Crystal nucleation at temperatures in the range 965–1050°C occurs by the heterogeneous nucleation of lenticular-shaped yttrium, silicon and aluminium containing crystals on silicon-rich clusters that formed during glass preparation. The lenticular crystals have a wide range of composition after heat treatment at 1050°C; the yttrium cation percentage varies around that of the expected B-phase composition Y 2SiAlO 5N but the aluminium content is lower and the silicon content generally significantly higher than that. The crystals display the hexagonal crystal structure of B-phase, although the results from EDX analysis imply that the atomic arrangement of the lattice is not the previously proposed B-phase structure. Crystal growth during prolonged heat treatment at 1050°C occurs to a significant extent by coalescence. 相似文献
7.
This study demonstrates that hydrolysis should be carried out in a step manner in gel synthesis. The key to the increase in the amount of water added is the control of the hydrolysis rate of Ti(OC 4H 9) 4. The hydrolysis of Si(OC 2H 5) 4 can be carried out at about 75°C. The amount of added water (γ WI), which varied with TiO 2 content (in mol%), was about 64–88% of the total amount of added water. The hydrolysis reaction should be performed at room temperature while Ti(OC 4H 9) 4 is added. The total amount of added water (γ W) is related to the amount of solvent ( R). For example, if TiO 2 is 40mol%, γ W will vary from 3.2 to 8.0 when R varies from 0.8 to 2.0. The amount of added water was affected by the distribution of solvent in the metal alkoxides. The amount of added water can be increased when RSi(OC2H5)4 = 1, RTi(OC4H9)4 > 1. The rate of rise in temperature of the thermolysis of the dried gel should be less than 10°C per hour, and the heat treatment temperatyre is related to the TiO 2 content (in mol%). Gel glasses without devitrification can only be obtained by thermolysis at 600°C from the gel with no less than 20 mol% TiO 2. 相似文献
8.
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
9.
Cobalt ferrite (CoFe 2O 4) thin film is epitaxially grown on (0 0 1) SrTiO 3 (STO) by laser molecular beam epitaxy (LMBE). The growth modes of CoFe 2O 4 (CFO) film are found to be sensitive to laser repetition, the transitions from layer-by-layer mode to Stranski–Krastanov (SK) mode and then to island mode occur at the laser repetition of 3 and 5 Hz at 700 °C, respectively. The X-ray diffraction (XRD) results show that the CFO film on (0 0 1) SrTiO 3 is compressively strained by the underlying substrate and exhibits high crystallinity with a full-width at half-maximum of 0.86°. Microstructural studies indicate that the as-deposited CFO film is c-oriented island structure with rough surface morphology and the magnetic measurements reveal that the compressive strained CoFe 2O 4 film exhibits an enhanced out-of-plane magnetization (190 emu/cm 3) with a large coercivity (3.8 kOe). 相似文献
10.
Homogeneous, crack-free, thin films of crystalline LiNbO 3 were synthesized above 250°C on Si(100) substrates by the dip-coating method using a double alkoxide solution. The coating solution, which was prepared by the controlled partial hydrolysis of the double alkoxide, gave stoichiometric LiNbO 3 crystalline films at temperatures as low as 250°C. The concentration of the alkoxide solution influenced both of thickness and quality of films. Crystallinity of thin film top-coated directly on the substrate affected the crystallization state of films coated on the film remarkably. Films crystallized on -Al 2O 3(0001) showed preferred orientation along the c-axis, while the preferred orientation could not be observed on Si(100) substrates. 相似文献
11.
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
12.
New glasses in the PbBr 2–PbCl 2–PbF 2–PbO–P 2O 5 system have been prepared and characterized. The glass-forming regions have been explored and the stability of the glasses against crystallization studied. Results show that the PbBr 2–PbCl 2–P 2O 5 ternary system has a broad glass-forming region which extends to 30 mol% P 2O 5. Most of the glasses in this system show strong stability against crystallization and some have glass transition temperatures as low as 146°C. When 5% PbO or 5% PbF 2 is introduced into the PbBr 2–PbCl 2–P 2O 5 system, the glass-forming region becomes smaller and the glass transition temperatures increase. However, the introduction of 2.5% PbF 2 and 2.5% PbO into the ternary system increases the glass transition temperature and broadens the glass-forming region. The introduction of PbF 2 alone improves the glass-forming ability of the system while the introduction of PbO alone lowers the glass-forming ability. 相似文献
13.
Crystallization of In 2O 3 occured in closed porcelain crucibles in air at 960–1200°C by vapor phase reaction of In 2O or In vapor with the oxygen diffusing into the system. The In 2O or In vapors were thermally generated from mixtures such as graphite/In 2O 3, graphite/In, In 2O 3/In and graphite/In 2O 3/In. The graphite/In 2O 3 system at a mole ratio of 30/1 and 1000°C produced yellow, transparent needle crystals with a maximum size of 0.5 X 0.5 X 8 mm and electrical resistivity of 5.5 X 10 -2 ω cm at 25°C. 相似文献
14.
A new niobate Sr 6CrNb 9O 30 was found in the ternary system SrO---Cr 2O 3---Nb 2O 5. The transparent crystal which has a green color and a need-like shape can be grown by the flux method. The crystal structure was determined by x-ray diffraction analysis and dielectric measurement, and it belongs to the orthorhombic tungsten bronze structure at room temperature with space group Cmm2, and unit cell parameters A=1.7505(4) nm, B=1.7510(1) nm, C=7.768(4)nm, Z=4. Dielectric constant measurement show that Sr 6CrNb 9O 30 has two phase transitions, paraelectric to ferroelectric at 110°C and ferroelectric to ferroelastic at 205°C. 相似文献
15.
The hydrolysis and condensation reactions of Si(OC 2H 5) 4 (TEOS) at 80°C in the TEOS---H 2O---C 2H 5OH---HCl solutions with H 2O/TEOS molar ratios ( r) from 1.0 to 2.0 were followed by gas chromatography (GC) and measurement of molecular weight (
) of the hydrolyzates, in order to explain the viscosity change of the solutions. It has been found that the siloxane oligomers with average polymerization degree ( n) from 2 to 7 are formed in the early stage of reaction and undergo condensation to form higher polymers. The n and the number of silanol groups of the oligomers are increased with increasing r. The fact that the solution viscosity increased once rapidly around the so-called gelation point followed by a sluggish increase with the increase of reaction time for an r of 1.7, while it increased rapidly without a break till gelation for an r of 2.0, was attributed to fewer silanol groups and higher steric hindrance as a result of more −OC 2H 5 groups remaining in the oligomers for an r of 1.7. 相似文献
16.
Heavily magnesium-doped p-type-InGaAs layers on InP(100) substrates were successfully grown, for the first time, by low-pressure metalorganic chemical vapor deposition (MOCVD) using bis-ethylcyclopentadienyl-magnesium, (C 2H 5C 5H 4) 2Mg (EtCp 2Mg), as organometallic precursor for the Mg. It was experimentally verified that the room-temperature hole concentration of Mg into InGaAs increased with increase of the V/III ratio and decrease of the growth temperature. A maximum hole concentration of over 4 × 10 19 cm −3 was obtained. The diffusion coefficient of Mg in InGaAs was experimentally derived to be 10 −12 cm 2/s at 800°C, which was comparable to that of Be. Finally, InP/InGaAs heterojunction bipolar transistors (HBTs) with Mg-doped bases were fabricated successfully. Measured maximum current gain was about 320 with a 90 nm thick base and a sheet resistance of the base layer of 1.28 kΩ/sq. 相似文献
17.
Phase relation of Bi 2O 3---SiO 2 system was evaluated experimentally from DTA and XRD measurements and its stable and metastable phase diagrams were proposed. Although BSO melts near-congruently at 1025°C in the stable phase equilibrium, its melt crystallizes to form metastable phase Bi 2SiO 5 in accordance with the metastable phase diagram while cooling. Therefore, BSO couldn't nucleate and crystallize spontaneously without crystal seed and only Bi 2SiO 5 crystallized at about 850°C with significant supercooling during Bridgman growth. BSO single crystal with 20×20×100mm 3 was grown in a vertical Bridgman furnace with a BSO seed according to its phase diagram. The measuring results of scintillation properties of BSO specimen show that its decay constant is 91 ns (about 1/3 of BGO) and light output is 23% of BGO. 相似文献
18.
NdAl 3(BO 3) 4 single crystals were grown by the flux method and the TSSG technique using a K 2O/3MoO 3/B 2O 3/0.5Nd 2O 3/KF flux system. Light-violet clear crystals could be obtained. The effects of fluoride on the growth of NAB crystals were investigated. As the content of KF was gradually increased, the growth form of NAB was changed from the equant to the columnar and the primary crystalline region of NAB was shrinked. At the ratio of KF/K 2O = 0.75, NAB crystals could not be grown. 相似文献
19.
Using HCl as a transport agent, well-shaped crystals of rhombohedral Fe 2(SO 4) 3 with edge length up to 1 mm were formed in the less hot zone of a silica ampoule. The dependence of the deposition rate on the mean transport temperature for a constant concentration of the transport agent ( C = 4.5 × 10 −2 mmol HCl/cm 3) shows a distinct maximum at
= 560°C. Additionally, the influence of the concentration of the transport agent at a constant temperature gradient was investigated. On the basis of thermochemical calculations, an explanation of the observed transport behaviour is given in the present paper. 相似文献
20.
Ceramic materials with a very low thermal expansion coefficient are synthesized by the sol-gel process. The binary gel is obtained by hydrolysis and polycondensation reactions of organometallic compounds of aluminium and titanium. The thermal evolution of the amorphous powder is followed by DTA and TGA measurements. Structural evolution is followed using X-ray diffraction. The crystallization of the TiO 2 rutile and Al 2O 3 corindon starts at 700 and 900°C respectively. The transformation of Al 2O 3 and TiO 2 into Al 2TiO 5 appears between 1200 and 1300°C. The densification of the powder is performed by the hot pressing process. The shrinkage of the powder was previously followed by dilatometric measurements. The physical properties of the final material are studied as a function of pressing parameters. 相似文献
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