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1.
Yuan Lirong  Yao Guoxing 《Journal of Non》1988,100(1-3):309-315
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(OC4H9)4. The hydrolysis of Si(OC2H5)4 can be carried out at about 75°C. The amount of added water (γWI), which varied with TiO2 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(OC4H9)4 is added. The total amount of added water (γW) is related to the amount of solvent (R). For example, if TiO2 is 40mol%, γW 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 TiO2 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% TiO2.  相似文献   

2.
Glass films of pure SiO2 and TiO2 have been prepared on sodalime silica flat slide glasses by the sol-gel process using the dip-coating technique from TEOS and Ti(OC3H7)4 solutions. The various parameters such as chemicals concentrations, viscosity, type of catalyst, withdrawal speed and temperature of densification leading to the obtention of good and adherent coatings with definite film thicknesses are reported. The same technique has been used for the depositon of layers of colored films SiO2---MxOy (M = Co, Mn, Nd and Cr). Brilliant yellow coatings have been obtained with TiO2---CeO2.  相似文献   

3.
Preparation of radial gradient refractive index (r-GRIN) glass rods has been undertaken by a sol-gel process using metal alkoxides. Two binary systems, Si(OCH3)4---Ge(OC2H5)4 and Si(OCH3)4−Ti(O−n-C4H9)4 have been investigated. It has been shown that immersion of rod-shaped wet gels in neutral or acidic water gives rise to leaching of the dopants (germanium and titanium components). Since this leaching is controlled predominantly by diffusion, the dopants remaining in the gels are expected to form concentration gradients. Optical measurements of the glass rods obtained after drying and sintering of the leached gels have shown that the concentration gradients are retained in the glass rods and they give r-GRIN profiles.  相似文献   

4.
Small-angle X-ray scattering (SAXS) measurements on V2O5·nH2O sols and gels, prepared by dissolving V2O5 glass into water at room temperature, show that there are V2O5 polymeric fibers entangled like random coils in the sol of n 5000, while the deviation from the random coil behavior occurs in the dilute sol of n 6000.

A Bragg peak appears at the scattering vector h 0.02 Å−1 to be superimposed on an asymptotic h−2-course in the SAXS curve of the concentrated sol of n 680. This means that the spatial correlation between V2O5 polymeric fibers takes place even in the fluid state.

V2O5·nH2O sols completely lose fluidity at n 250 to transfer to the gel state, where V2O5 polymeric fibers begin to pile up in the parallel with a substrate surface. Such a layer structure is preserved up to the gel of n 4. However, V2O5 polymeric fibers are randomly oriented within each layer.  相似文献   


5.
A precursor prepared from a methyltriethoxysilane ((CH3)Si(OC2H5)3, MTES)-B(OC2H5)3-polyacrylonitrile (PAN) composition was used for the synthesis of boron-doped SiC by carbothermal reduction. Initially, MTES was hydrolyzed with HCl (MTES: H2O: HCl = 1 : 1 : 0.01) for 1 h in a sealed vessel. The number-average molecular weight measurement and a NMR spectrum revealed that the species in the solution were mainly oligometric. With the addition of B(OC2H5)3, no significant changes in the distribution of the Si containing species were detected. The mixing of the hydrolyzed solution with a PAN-dimethylsulfoxide solution led to a homogeneous solution. After the evaporation of the solvents and the subsequent heat treatment at 220° C, brown precursor powder was obtained. By the heat treatment at 1600° C in Ar, it was converted to boron-doped SiC powder.  相似文献   

6.
To avoid breaking of the gel during drying any organic solvent such as ethanol has not been used. When the amount of HCl is increased and the mixture is stirred vigorously, a transparent silica sol can be prepared immediately with only Si(OC2H5)4 and H2O. By adjusting the amount of HCl and the temperature, the sol may gel at any time, even in 5 min at room temperature. Such a gel may be dried without cracking under completely open conditions. The addition of glycol as a complex agent can apparently increase the pore size of the gel and decrease its capillary force and surface tension. So, large dried gels can be made in a rather short time. For example, a dried gel of diameter 68 mm and thickness 13 mm can be made in only 4 days. Because of the large pores, the dried gels can be sintered to monolithic silica glasses of practical size with a rather fast heating rate. The mechanisms in the whole process have been explored.  相似文献   

7.
Structural evolution of the solution of tetraethoxysilane hydrolyzed with [H2O]/[Si(OC2H5)4] = 2 under acidic condition has been investigated by rheological measurements. It was found that the solution behaves as a Newtonian liquid up to a highly viscous state and shows spinnability before gelation when the evaporation of the solvent is allowed during gelation reaction. On the other hand, the solution behaved as a non-Newtonian liquid in the viscous state, showing no spinnability when the evaporation of the solvent was not allowed during the reaction. It was indicated from the Casson plots that the spinnable solution prepared in the open system has no yield stress up to highly viscous states, whereas the non-spinnable solution prepared in the closed system has a yield stress at viscous states. It was proposed that the increase in viscosity of the open system solution is attributable to the concentration of the sol particles whereas that of the closed system solution is attributable to the formation of the three dimensional network in the solution.  相似文献   

8.
High-performance carbon-doped-base GaAs/AlGaAs heterobipolar transistors (HBTs) were grown by gas-source MBE using only gaseous sources including dopant sources. The AlGaAs emitter layer was doped with Si from uncracked SI2H6 (n = 9 × 1017 cm-3), and the base layer (92.5 nm) was doped with carbon from TMG (p = 4 × 1019 cm-3). From SIMS analysis it was confirmed that a well-defined emitter-base junction with sharp carbon profile was obtained. The base-current ideality factor from the Gummel plot was 1.47, and the emitter-base junction ideality factor was 1.12. A high DC current gain of 53 was obtained at a current density of 4 × 104 A/cm2. The device characteristics of our carbon-doped HBTs were found to be stable under current stress.  相似文献   

9.
The conditions under which selective epitaxial growth (SEG) is achieved in UHV-CVD with Si2H6 are determined by the amount of Si2H6 molecules being supplied, and there is a critical gas supply amount (Fc) beyond which SEG will break down and lose its selectivity. The value of Fc is itself determined by two factors, growth temperature and the material used for masking, i.e. SiO2, Si3N4. We found that this limiting factor of Fc was increased through the addition of a small amount of Cl2, and that after such addition, the resulting decrease in growth rate is minimal.  相似文献   

10.
Small-angle X-ray scattering was used to examine in situ formation of ZrO2---SiO2 structures in alcoholic solution of tetraethoxysilan (TEOS) as a function of the ratio of ZrO2 to SiO2. For the moment of the first measurement (15 min after the preparation) primary particles with Rg ≈ 1.5 nm exist in all investigated mixed gels. These particles aggregated to secondary clusters. The resulting clusters can be described by means of fractal theory, where the determining mechanism of formation is cluster-cluster aggregation (diffusion or chemical limited). The time of gelation is a function of the ZrO2 concentration. The higher the ZrO2 concentration in the solution, the faster is the aggregation to secondary clusters. Gelation times were between 170 and 970 h.  相似文献   

11.
以钛酸丁酯、聚乙烯吡咯烷酮(PVP)、无水乙醇为原料,利用静电纺丝技术制备出Ti(OC4H9)4/PVP纳米纤维,经500~1000℃高温煅烧制得TiO2纳米纤维,再通过水热法将AgBr纳米颗粒负载到TiO2纳米纤维表面.利用X射线衍射仪、场发射扫描电镜、差热-热重分析对AgBr/TiO2纳米纤维进行表征分析.利用甲基...  相似文献   

12.
A large-size silica glass was fabricated with a new sol-gel process involving the following procedures: (a) hydrolysis of Si(OC2H5)4 with HCl, (b) addition of silica powders and their high dispersion, (c) adjustment of the pH value by adding ammonia solution, (d) gellation, (e) drying to dry-gel, and (f) sintering to silica glass. With this process a dry-gel plate as large as 520 x 360 mm2 was obtained, which was sintered to a 420 x 290 mm2 sized silica glass. The effect of pH on the gelation time of the sol, and the correlation between the weight percentage of silica powder and porosity of dry-gel were examined. In addition, fiber preforms were produced by this sol-gel process.  相似文献   

13.
Raman spectra have been measured for ZnCl2---ZnX2 and ZnCl2---KX (X = Br, I) glasses to investigate the structure of the glasses with varying composition. The assignment of each band was made, and the change of the spectra with composition was explained in terms of the bridging and non-bridging states of halide ions and the change of the tetrahedral units, ZnXnCl4−n2− (n = 0–4), formed in the glasses. As the content of ZnX2 in ZnCl2---ZnX2 glasses increases (20 → 80 mol%), the peak frequency of the Zn---Cl stretching mode increases (238 → 248 cm−1 in X = I glasses, 238 → 259 cm−1 in X = Br glasses) while the Zn---I and Zn---Br stretching frequencies decrease (173 → 120 cm−1 for Zn---I, 196 → 157 cm−1 for Zn---Br). The decrease of the Zn---I and Zn---Br band frequencies was attributed to the increase of the number n of the ZnXnCl4−n2− tetrahedra. The increase of the Zn---Cl frequency suggests the existence of the bonding state of Cl ions which is intermediate between the bridging and the non-bridging states. In ZnCl2---KX glasses, the Zn---Clnon-bridging band at about 300 cm−1 was observed in addition to the bands observed in ZnCl2---ZnX2 glasses. The addition of KX produces non-bridging anions while the tetrahedral units, ZnXnCl4−n2− are also formed.  相似文献   

14.
11B (I=3/2) MAS NMR in the binary glass system xV2O5–B2O3 (x=0.053, 0.43) and the ternary glass system xV2O5–B2O3–PbO (0.1x1.5) has been investigated at room temperature. In the xV2O5–B2O3 glasses, one NMR line due to BO3 unit was observed. Meanwhile in the xV2O5–B2O3–PbO, two NMR lines which arise from BO3 and BO4 units were detected, where the appearance of BO4 units is produced by the presence of PbO. From the computer-simulation of the 11B NMR central transition line (m=−1/2↔1/2), the quadrupole parameters (e2qQ/h and η) for BO3 units in xV2O5–B2O3, and those for BO3 and BO4 units in xV2O5–B2O3–PbO were obtained as a function of x. As the V2O5 content increases in xV2O5–B2O3–PbO, the e2qQ/h and η values of the BO3 associated resonance are found to slightly decrease and increase, respectively. Meanwhile, the e2qQ/h and η values of BO4 associated resonance in xV2O5–B2O3–PbO are found to slightly increase and decrease, respectively. By comparing the intensities of the total transitions (m=−3/2↔−1/2,m=−1/2↔1/2, and 1/2↔3/2) for the 11B NMR line of BO3 and BO4 units contained in xV2O5–B2O3–PbO with those of respective standard samples of 0.053V2O5–B2O3 and NaBH4, the quantitative fractions of BO3 and BO4 in xV2O5–B2O3–PbO were obtained as a function of x.  相似文献   

15.
There has been a great demand in the field of kitchen appliances to develop transparent water repellent films which have high heat-resistance around 300°C. However, those films have not been obtained by conventional sol–gel methods. In this paper, we propose a new method for fabricating transparent water repellent films with high heat-resistance using the sol–gel method, in which silicon or germanium substrates were coated with a solution including tetraethoxysilane (Si(OC2H5)4) and (2-perfluorooctyl)ethyltrimethoxysilane (CF3(CF2)7C2H4Si(OCH3)3), followed by ‘ammonia-treatment' and annealed at 300°C. The contact angles of water on the ammonia-treated film maintained its initial value, 110° after the heat treatment at 300°C for 250 h while those on the untreated film decreased to 70°, indicating that the ammonia-treatment improves heat-resistance on the film. The mechanism of ammonia-treatment was inferred from FT-IR results; the ammonia-treatment should accelerate hydrolysis and polymerization of FAS and TEOS molecules, resulting in high density of siloxane bonds between FAS and silica glass. These bonds suppress the evaporation of FAS molecules from the film during the heat treatment at 300°C, thus the film has high heat-resistance.  相似文献   

16.
通过3,3′-((乙烷-1,2-二基双(2-甲基吡啶杂氮二基)双(亚甲基))双(2-羟基-5-甲基苯甲醛)与2-羟基-1,3-丙二胺的缩合反应得到一种具有双吡啶悬臂的双核锰配合物。通过X射线单晶衍射确定了该配合物结构,结果显示其分子式为[Mn2(C37H43N6O6)]·(ClO4)2。该配合物属于单斜晶系,P21/c空间群,晶胞参数为:a=1.096 50(19) nm, b=1.419 5(3) nm, c=3.109 4(5) nm, β=108.153(5)°。进一步分析表明两个二价锰离子分别与(Namine)2(Nimine)2O3和(Nimine)2O4体系配位,它们与配位原子形成的几何构型分别是十面体和扭曲的八面体。两个中心锰离子距离为0.331 6 nm,由酚氧原子和醋酸根共同桥联。另外,本文也利用伏安法和黏度法对该配合物与小牛胸腺DNA的结合能力进行研究,实验结果表明它们之间的结合方式为弱的插入作用。  相似文献   

17.
Gels with composition xZrO2−(100−x)SiO2, X = 10−55, were prepared in different conditions using zirconium acetylacetonate and TEOS as precursors.

Gels treated at different temperatures up to 1100°C were characterized by X-ray diffraction, IR spectroscopy and TEM. Preparation conditions determined the subsequent development of crystalline phases following thermal treatment.

Monoclinic zirconia segregation dispersed in a silica matrix occurred when the gels were prepared in a strong hydrocloric acid medium. Preparation with a lower acid content favours instead the formation of very small crystals of tetragonal zirconia.  相似文献   


18.
The La L1 and L3 XANES and L3 EXAFS have been investigated for the series of glasses 10K2O---50SiO2---x La2O3 (x = 1, 5, 10) and (10 − x)K2O---40SiO2−(x/3)La2O3 (x = 7.5, 5, 2.5) and model compounds La2O3, LaAlO3, LaPO4, La2NiO4, La2CuO4 and La(OH)3. An edge resonance at 25 eV above the L1 edge in the glass spectra is concentration-dependent, decreasing in intensity with increasing lanthanum concentration. The 2s → nd forbidden transition increases with La2O3 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   

19.
Magnesium polyphosphate glasses with molar ratios, y=n(MgO)/n(P2O5), ranging from 1.0 to 1.9 have been examined by X-ray and neutron scattering and 31P magic angle spinning nuclear magnetic resonance spectroscopy to extract information on their short-range, intermediate-range and submicroscopic structure. The depolymerization of the PO4 chains with rising MgO content is quantitatively described by the increasing concentration of Q1 and Q0 groups determined by NMR. In the pyrophosphate region the Q1 sites disproportionate to Q0 and Q2 groups, whereas there is no disproportionation of the Q2 sites at metaphosphate composition. The shortening of the real-space distances, rm, indicates that the structure of the glasses becomes more compact with progressive depolymerization which is due to the increasing connection of the MgOn polyhedra by sharing the non-bridging oxygen atoms. The Mg–O co-ordination sphere was found to change not significantly in dependence on composition. Heterogeneities about 1 nm in diameter exist in the glasses with MgO content exceeding 46.6 mol% indicated by a weak small angle X-ray scattering.  相似文献   

20.
This paper reports the detail synthesis of a new kind of metal iodate, anhydrous (LiFe1/3)(IO3)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 P63.  相似文献   

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