Flow characteristics and spinnability of sols prepared from silicon alkoxide solution

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.     

Thin SiO2---TiO2---ZrO2 films from alkoxide solutions

Different solutions containing alkoxides of silicon, titanium, and zirconium have been prepared. Some of their properties like the time dependent viscosity and the gelling time have been measured and are reported here for different H₂O, HCl, ethanol and/or formamide contents. Microscope slides have been dip coated in these solutions. After baking, film thickness and chemical durability have been determined.

In order to get good SiO₂---TiO₂---ZrO₂ glass coatings, the withdrawal speed should not exceed 5 cm/min unless the viscosities of the solutions are reduced by the addition of ethanol. By such a dilution, the film thickness could also be reduced, while the addition of formamide caused a delayed increase of the viscosity and increased gelling times. For this reason, solutions containing formamide can be used for longer periods. The chemical durability of the substrates against boiling NaOH solution is enhanced by the SiO₂---TiO₂---ZrO₂ glass coatings.     

Hydrolysis and condensation reactions of Si(OC2H5)4 related to silica fiber drawing

The hydrolysis and condensation reactions of Si(OC₂H₅)₄ (TEOS) at 80°C in the TEOS---H₂O---C₂H₅OH---HCl solutions with H₂O/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 −OC₂H₅ groups remaining in the oligomers for an r of 1.7.     

Ca(H2PO4)2-H3PO4-K2SO4体系中石膏晶型及形貌调控

为将Ca(H₂PO₄)₂制备KH₂PO₄过程中的石膏资源化利用,以H₃PO₄与CaCO₃反应制备Ca(H₂PO₄)₂溶液,并与K₂SO₄溶液反应,进行Ca(H₂PO₄)₂-H₃PO₄-K₂SO₄体系中石膏晶型和形貌调控研究。结果表明:通过改变反应时间、反应温度、SO^2-₄过量系数和CaO含量等参数可对Ca(H₂PO₄)₂-H₃PO₄-K₂SO₄体系中石膏晶型和形貌进行调控,制得短柱状α-CaSO₄·0.5H₂O。体系在温度高于95 ℃和CaO含量为3.0%~5.0%(质量分数,下同)时形成α-CaSO₄·0.5H₂O,在CaO含量为5.5%主要形成CaSO₄·2H₂O;反应时间长于20 min和SO^2-₄过量系数大于1.4将形成K₂SO₄(CaSO₄)₅·H₂O,导致石膏晶体表面缺陷增加。本实验条件下,适宜反应条件为:反应时间10 min、反应温度95 ℃、SO^2-₄过量系数1.2和CaO含量5.0%,此条件下可制得长度42~70 μm、直径13~24 μm的短柱状α-CaSO₄·0.5H₂O,其抗折和抗压强度分别可达5.61 MPa和33.74 MPa,滤液中钾收率和脱钙率分别可达94.23%和83.80%。     

Pinacoidal growth and optical properties of calcite crystals

Optical quality calcite single crystals, CaCO₃, have been grown under hydrothermal conditions in the of CaCO₃ - NH₄Br - H₂O system doped with Li ions. 24- liter autoclaves including titanium inserts were used in these experiments. Optical properties of calcite crystals were studied. The light absorption index of the crystals grown is similar to rhombohedron materials, but pinacoidai calcite have no V-shaped defects.     

添加CaSO4·2H2O为晶种制备磷石膏半水硫酸钙晶须

以固体废弃物磷石膏为原料,在传统常压醇水热法的基础上添加CaSO₄·2H₂O为晶种制备半水硫酸钙晶须。采用单因素试验法探究了晶种含量、丙三醇含量和磷石膏质量分数对晶须结构和形貌的影响,确定晶须的最佳制备工艺条件。采用SEM和XRD对样品进行表征分析,实验结果表明:添加CaSO₄·2H₂O晶种制备晶须的长径比(49.29)比只添加丙三醇的样品的长径比(30.99)提高了近60%;当丙三醇与水的体积比(V)为1、晶种含量为1%、磷石膏质量分数为5%时制备的晶须的平均直径为0.65 μm,长径比达到了62.15,晶须的尺寸均匀。这说明添加1%CaSO₄·2H₂O晶种、V为1的丙三醇和质量分数为5%的磷石膏在常压下能制备出高长径比和尺寸均匀的半水硫酸钙晶须。     

基于2,5-二溴对苯二甲酸配体的锌/钴配合物合成、晶体结构及性质

将有机物2,5-二溴对苯二甲酸(H₂L₁)和2,2′-联吡啶(L₂)作为双配体,使用溶剂热法和七水合硫酸锌(ZnSO₄·7H₂O)、六水合硝酸钴(Co(NO₃)₂·6H₂O)分别反应,得到配合物[Zn(L₁)(L₂)(H₂O)]_n(1)和配合物[Co(L₁)(L₂)(H₂O)]_n(2)。采用单晶X射线衍射、元素分析、红外光谱、紫外光谱、荧光光谱、热重分析等测试方法对这两种物质进行分析研究。单晶测试结果表明配合物1是单斜晶系,以Zn²⁺配位连接L^2-₁与L₂形成一维链状结构,各条链在分子间氢键和π…π共轭作用下有规律地堆叠形成三维网络结构。配合物2是三斜晶系,Co1离子和Co1ⁱ离子由H₂L₁上的羧酸氧原子O4和O4ⁱ连接,形成双齿螯合的配位结构单元,以Co²⁺配位连接 L^2-₁和L₂形成二维网格结构,各层在O—H…O分子间氢键和范德瓦耳斯力作用下有规律的堆叠形成三维网络结构。配合物1和2均含有芳香杂环、羧基杂环和氮杂环,具有良好的荧光性质和热稳定性,最大发射波长分别为345 nm和333 nm。     

基于5-磺基水杨酸的单、双核铜(Ⅱ)三元混配配合物的合成及晶体结构

以5-磺基水杨酸和咪唑衍生物为配体合成了单核、双核结构的三元混配Cu(Ⅱ)配合物:[Cu(H2 biim)(Hssal)(H2O)2]·H2O(1)和{[Cu(MeHbiim)(Hssal)(H2O)]·0.5H2O}2(2)(H3ssal=5-磺基水杨酸,H2biim=2,2'-联咪唑,MeHbiim=N-甲基-2,...     

Preparation and physical properties of amorphous V2O5 containing TiO2, Na2O or Li2O

V₂O₅ gels containing up to 18 mol% of TiO₂ were obtained through the simultaneous hydrolysis of alkoxides in ethanol solution. V₂O₅ gels containing Na₂O or Li₂O were obtained through the ion exchange method. The crystallization temperature, T_cr, of the gels increased and the H₂O content of the gels decreased by the addition of TiO₂ or Na₂O. These additives seem to stabilize the amorphous state of the gels. On the other hand, T_cr and the H₂O-content slightly varied with the addition of Li₂O. No ionic polarization was observed in coating films of the gels dried at temperatures below T_cr. The dc conductivity of the films was anisotropic, and increased with the addition of Li₂O or Na₂O. However, it decreased with increasing TiO₂ content. The fiber-like structure of gels was observed by TEM. The gels obtained from alkoxides were thin and short in comparison with the gels obtained through the ion exchange method.     

Rheology of sols and fiber drawing

The investigations on the viscosity of the metal alkoxide solutions in the course of hydrolysis and condensation reactions leading to the gelation of sols have been reviewed. All the solutions which gel finally show a continuous increase in viscosity with time until they gel at a certain viscosity higher than about 100 P which is dependent on the composition of the starting solution. When a metal alkoxide solution is catalyzed with an acid and its water content is small at less than 4 or 5 in the water to alkoxide mol ratio, the solution exhibits spinnability at viscosities above about 10 P and becomes drawable into gel fibers, whereas no spinnability appears when a solution contains a large amount of water or is catalyzed with an alkali like ammonia.

The investigations on the relation between the reduced viscosity and the concentration or the relation between the intrinsic viscosity and the number-averaged molecular weight have made it clear that the spinnable silicon alkoxide solutions have long-shaped siloxane particles and non-spinnable solutions have round particles.

It has been established that spinnable solutions exhibit Newtonian flow behavior up to high viscosities, where fibers can be drawn, while non-spinnable solutions exhibit marked structural viscosity and, sometimes, thixotropy. Similar behavior is confirmed in the alumina solutions prepared from inorganic salts. It has been reported that the viscosity measurements provide information on the rate of the reaction leading to gelation. It is also known that the viscosity of the alkoxide solution controls the thickness of the thin coating film made by the dip-coating technique using an alkoxide solution.     

SAXS investigations of structure of formation in alcoholic ZrO2---SiO2 solutions

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 R_g ≈ 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.     

Demko-Sharpless合成稀土四唑化合物的结构及性质

使用 Demko-Sharpless法,用氰基吡啶(4-氰基吡啶和3-氰基吡啶)与稀土硝酸盐(Ln=La, Gd, Er)在水热条件下反应,安全有效地合成了四个稀土四唑离子型化合物:[Ln(H₂O)₈·3(p-TPD)·2(p-HTPD)·7H₂O], (Ln=La(1), Gd(2), Er(3), p-TPD=4-四唑吡啶), [Ln(H₂O)₈·3(m-TPD)·6H₂O]和(m-TPD=3-四唑吡啶, Ln=Er(4))。同时,对这四个稀土四唑离子型化合物进行单晶X射线衍射、红外光谱、热重、介电性能、X射线粉末衍射等测试,并且对其介电性质进行了研究。X射线单晶结构分析显示,所得到的四个稀土四唑化合物均为离子型,稀土金属离子与配体分别处于不同的两层,[Ln(H₂O)₈]³⁺结构单元与 p-TPD 以及水分子通过氢键作用形成阳离子层,同时p-TPD与p-HTPD通过π-π堆积与氢键作用形成阴离子层,阳离子层和阴离子层交替排列形成一个规则的网络结构。介电性能测试表明化合物1,2具有较好的介电性。     

一例镉(Ⅱ)配合物的合成、结构及发光性质研究

镉配合物因其独特的结构及性质而被广泛应用于光学、医药、化学等领域,水热法因其溶剂清洁、操作简单等因素是目前合成配合物方便有效的方法之一.本文以2,6-双(2-吡嗪基)-4,4′-联吡啶(L)、对苯二甲酸和CdCl2·2.5H2O为原料,运用水热合成法合成了配位化合物[Cd2(L)2(bdc)(H2O)4](bdc),用...     

Growth and characterization of a new nonlinear optical material: Potassium p-nitrophenolate dihydrate (NO2–C6H4–OK·2H2O) with new bonding properties

Single crystals of potassium p-nitrophenolate dihydrate (NPK·2H₂O) have been grown successfully using the isothermal solvent evaporation technique. It is a new semiorganic nonlinear optical crystal, possessing a d_eff of about 1.5 times that of lithium niobate and in which the K⁺ ions are bonded to the nitro group instead of bonding with the phenolic O⁻. Large single crystals of dimension upto 20×6×4 mm³ are harvested within a period of 60 days. The grown crystals are subjected to single crystal X-ray, FTIR and DRS-UV visible spectral, thermal and microhardness analyses. Single crystal X-ray analysis confirms the molecular formula and the structure of the crystal. FTIR spectral studies verify the functional groups present in the crystal. The DRS-UV visible spectrum proved the optical transparency of the crystal in the entire visible and near infrared region. Thermal studies reveal that the crystals are stable upto 180 °C. Microhardness measurements on the cleaved plane (1 1 0) explain the strength and slip direction in the crystal. The SHG efficiency of the crystal is examined by performing the Kurtz powder test using Nd:YAG laser.     

Calculation of NMR shieldings and other properties for three and five coordinate Si, three coordinate O and some siloxane and boroxol ring compounds

Valuable information on the geometric and electronic structure of both predominant and defect species in the bulk and on the surface of amorphous SiO₂ can be obtained from solid state ²⁹Si and ¹⁷O NMR. Most previous NMR.studies have made assignments of structure types to NMR signals by relying on a comparison to crystalline reference materials. Using the quantum mechanical technique of Coupled Hartree-Fock Perturbation Theory (CHFPT) we can directly calculate NMR shielding tensors, σ, for Si and O and electric field gradients tensors, q for O in silicates. Previous CHFPT calculations on (SiH₃)₂O at Si---O---Si = 180° to 140° semiquantitatively reproduced observed trends in σ for SiO₂ polymorphs. These calculations have been improved and extended to Si---O---Si = 120° in (SiH₃)₂O and to the small siloxane rings H₄Si₂O₂, H₆Si₃O₃, H₈,Si₄O₄ which are models for the ring structures which may occur in the bulk and surface of amorphous SiO₂. Thus, predictions can be made of the ¹⁷O and ²⁹Si NMR characteristic of such species. We have also calculated NMR shieldings and other properties for three and five coordinate Si and for three coordinate O. The ²⁹Si NMR shielding increases with coordination, as expected, and five coordinate Si shows an anisotropy which although large is still smaller than that inferred from spin-lattice relaxation times in silicate melts. O q values are also calculated for (BH₂)₂O and H₃B₃O₆. The results are consistent with O EFGs and Raman frequencies observed in B₂O₃ glass, supporting a boroxol ring model.     

Hydrogenated amorphous silicon with substrate-dependent structure

Hydrogenated amorphous silicon (a-Si:H) thin films grown at 250°C on (1 0 0) crystalline substrate using plasma-enhanced chemical vapor deposition (PECVD) with SiH₄/H₂ gas flow ratio equal to 5/1 (sccm) are investigated by transmission electron microscopy. It is found that the thin film is totally amorphous when grown on a glass substrate. But when the substrate is changed to crystalline silicon, some crystalline grains are found embedded in the amorphous structure in certain regions even if the thickness of the film reaches 600 nm. It is suggested that the amorphous silicon film grown on a crystalline silicon substrate at a temperature of 250°C without heavy H₂ dilution is a mixed network of a small amount of crystalline silicon and the major portion of amorphous silicon.     

基于有机羧酸配体的Co(Ⅲ)/Cu(Ⅱ)配合物的合成、结构及表征

在溶剂热条件下,以含卤素有机羧酸3-溴-吡啶-2,6-二甲酸(H₂L)为配体,以硝酸钴、硝酸铜为金属源,合成了两例配合物:[Co(L′)₃](1)和[Cu(L′)₂]_n(2)(HL′=5-溴-吡啶-2-甲酸),通过元素分析(EA)、X射线单晶衍射(SXRD)、X射线粉末衍射(PXRD)、红外光谱(IR)和热重分析(TGA)进行结构表征。X射线单晶衍射结果表明,配体H₂L在反应过程中发生脱羧现象,生成单羧酸配体5-溴-吡啶-2-甲酸。在配合物1中,每个Co(Ⅲ)都位于略微扭曲的八面体几何构型中,不对称单元中含有两个单核单元,单核单元通过C—H…O氢键形成三维超分子结构。配合物2的不对称单元中含有一个Cu(Ⅱ),两个脱质子的L′^-配体,每个Cu(Ⅱ)都是六配位的,位于扭曲的八面体几何构型中。Cu(Ⅱ)由配体连接生成1D链结构,通过C—H…O氢键形成三维超分子结构。此外,研究了两例配合物的热稳定性能。     

Fabrication of novel urchin-like architecture and snowflake-like pattern CuS

The interesting biomimetic morphologenesis of CuS, containing urchin-like architecture and snowflake-like pattern can be separately obtained via heating different solutions. In our case, ethanol or the mixed solvent of ethanol/H₂O containing CuCl₂ and CS₂ as raw materials in the presence of the surfactant additive cetyltrimethylammonium bromide (CTAB) have been used. The products were characterized by various techniques of XRD, SEM and ED. In the process, the solvent medium and the surfactant additive CTAB played very important roles in the formation of different biomimetic morphologies and the formation mechanisms were primarily discussed, respectively.     

Synthesis of fluorine doped silica gel and its properties at high temperature

Fluorine doped silica gels were synthesized by using the sol-gel processes of (A) SiF₄(g) and H₂O(1) and (B) the mixed solution of Si(OC₂H₅)₄, C₂H₅OH, H₂O and H₂SiF₆. By the former process we obtained a gel of relatively high fluorine content (8–12 at.%F), while we could synthesize the gel of 0–12 at.% F by adjusting the F/Si ratio of the starting solution mixtures by the latter process.

The defluorination behavior and the structural change of these gels at high temperature were studied by heating-mass spectrometry, IR and ESR measurements. The results revealed the following: (1) defluorination by liberation of SiF₄(g) was admitted from temperatures at about 400°C and was controlled by the diffusion of fluorine in the gel bulk. (2) The peak separation analysis for the IR band of 1300-900 cm⁻¹, where the stretching vibrations of Si---O and Si---F appear, showed that the change of the band shape resulted from the increase or the decrease of the Si---F bonds and the change of the bond angle of Si---O---Si as well as the change of the force constant accompanied by fluorination or defluorination. (3) The defects of the Si E′ center were induced by X-ray irradiation depending on the degree of the defluorination, and were reduced by the heat treatment. However, with the heat treatment at temperatures higher than 1000°C, the E′ center increased again. The IR spectra suggest that this behavior might correspond to the gel-glass trasition.     

Vapor phase epitaxy of pure VO2 and V1−xCrxO2

The vapor phase epitaxy of thin epilayers of VO₂ and V_1−xCrxO₂ on TiO₂ transparent substrates is described. Chemical vapor deposition occurs by reacting a (VOCL₃/CrO₂Cl₂/H₂O/H₂) mixture at about 800°C using argon as a carrier gas. The preparation of pure VO₂ requires special care to make it homogeneously stoichiometric and to obtain steep concentration profiles at the TiO₂/VO₂ interface. Layers were obtained which had electrical and optical properties comparable to the best bulk crystals grown by other techniques. Homogeneous solid solutions of V_1−xCr_xO₂ epilayers were also grown for the first time in the range o < x < 0.17. Chromium concentration and homogeneity were determined by electron microprobe analysis. The separation coefficient k was also found to vary with x. It is close to unity below x = 0.001 and above this value Cr is incorporated more easily. High quality heteroepitaxial layers (1 cm² area, 1 to 30 μm thickness) of V_1−xCr_xO₂ have for the first time allowed the measurement of the optical absorption coefficient.