Ti(IV)在介孔氧化硅MCM-41中的液相移植

以钛酸丁酯为原料,通过液相移植反应,在介孔氧化硅ＭＣＭ－４１中成功地组装了Ｔｉ（ＩＶ）,利用ＸＲＤ、ＴＥＭ、ＥＤＳ、ＦＴ－ＩＲ、Ｎ_２吸附－脱附、^２９Ｓｉ ＭＡＳ ＮＭＲ等多种实验方法对材料进行了表征,并讨论了液相移植反应的机理．实验表明,通过与介孔材料骨架表面Ｑ^３硅原子中的硅醇键（Ｓｉ－ＯＨ）的反应而形成钛－氧－硅（Ｔｉ－Ｏ－Ｓｉ）键,Ｔｉ（ＩＶ）被成功地固定到介孔材料的骨架上面; ９５０～９６０ｃｍ^－１红外共振吸收的加强是Ｓｉ－Ｏ－Ｔｉ键形成的标志．     

LiNiO2热分解反应动力学研究

用ＤＴＡ和ＸＲＤ研究了ＬｉＮｉＯ_２在空气中的热分解过程为：ＬｉＮｉＯ_２（ｓ）→(６５０～７２０℃)Ｌｉ_２Ｎｉ_８Ｏ_{１０（ｓ）}＋４Ｌｉ_２Ｏ_（ｓ）＋Ｏ_２（ｇ）→(８５０～９５０℃)Ｌｉ_２Ｏ_（ｓ）＋８ＮｉＯ_（ｓ）＋１／２Ｏ_２（ｇ） →(１０００～１１５０℃)ＮｉＯ（ｓ）＋Ｌｉ_２Ｏ_（ｇ）用 Ｄｏｙｌｅ－Ｏｚａｗａ法和 Ｋｉｓｓｉｎｇｅｒ法计算了各反应阶段的表观活化能分别为 ７４７．１８±１．０ ｋＪ·ｍｏｌ^－１、９３２．４６±１．０ ｋＪ·ｍｏｌ^－１和 １１２６．９７±１．０ ｋＪ·ｍｏｌ^－１．用 Ｋｉｓｓｉｎｇｅｒ法确定了反应级数和频率因子,确定了三个阶段的动力学方程分别为 ｄα／ｄt＝１．７３６ｘ１０３９ｅ^{－９００００／Ｔ}（１－α）^{１．０５７}; ｄα／ｄｔ＝１８０６×１０^３９ｅ^{－１１１５００／Ｔ}（１－α）^{０．８４４};ｄα／ｄｔ＝４．２６２×１０４２ｅ^{－１３５０００／Ｔ}（１－α）^{１．２７５}     

疏水型SiO2气凝胶

以多聚硅为硅源,通过溶胶-凝胶、表面修饰及超临界干燥过程制备出了疏水型ＳｉＯ_２气凝胶．表面修饰后ＳｉＯ_２气凝胶孔洞由修饰前的２３．１ｎｍ减小到１８．２ｎｍ;比表面积由修饰前的 ４７７ｍ２ｇ^－１增加到 ５６３ｍ２ｇ^－１,骨架颗粒比修饰前略大,饱和水蒸汽吸附量由吸附前的０．０４（重量比）降低到０．００１２,且与水不浸润．     

快凝钛合金中硅化物的析出及长大规律

研究了热处理对Ｔｉ－５Ａｌ－０．３Ｓｉ和Ｔｉ－５ＡＩ－２Ｚｒ－０．３Ｓｉ（质量分数，ｍｇ／ｇ）析出相长大规律的影响结果表明，含硅的钛合金的快凝态和在６００℃短期（１ｈ）处理后的基体中无析出相＞６５０℃时，近球状的相大量析出热处理后析出相聚集长大速度很快．Ｔｉ－５Ａｌ－０．３Ｓｉ的析出相为四方的Ｔｉ３Ｓｉ，其长大激活能为２１９ｋＪ·ｍｏｌ－１．加入Ｚｒ后，分布更加弥散且长大速度更快的（Ｔｉ，Ｚｒ）６Ｓｉ３的长大激活能为１０５ｋＪ．ｍｏｌ－１     

Li2MnO3的柠檬酸盐溶胶-凝胶法合成及离子导电性

以Ｌｉ_２ＣＯ_３、ＭｎＣＯ_３为原料,用柠檬酸盐溶胶凝胶法合成了Ｌｉ_２ＭｎＯ_３超微粉．对合成的材料进行了ＤＴＡ、ＴＧ、ＸＲＤ和ＴＥＭ等表征,并应用交流阻抗谱技术测定了样品的电导率．结果表明,６５０。Ｃ以上生成Ｌｉ_２ＭｎＯ_３纯相超微粉,粒径在５０nｍ以下．在１８～４００℃温度范围内,产物烧结体的离子导电率为１０^－６～１０^－３Ｓ·ｃｍ^－１,其电导活化能为４４．８７ｋＪ·ｍｏｌ^－１．     

Sm-Fe-Si-C非晶合金的晶化动力学

用差热分析（ＤＴＡ）,结合Ｘ射线衍射（ＸＲＤ）研究了Ｓｍ－Ｆｅ－Ｓｉ－Ｃ非晶态合金的晶化动力学。结果表明：温度低于９００℃时,该合金晶化相为α－Ｆｅ（Ｓｉ）固溶体和Ｓｍ２（Ｆｅ,Ｓｉ）１７Ｃｘ。α－Ｆｅ（Ｓｉ）相的晶化表观激活能为４３１．５１ｋＪ／ｍｏｌ,Ｓｍ２（Ｆｅ,Ｓｉ）１７Ｃｘ相的晶化表观激活能为５１４．４３ｋＪ／ｍｏｌ。上在晶化初期活能变化不大,当α－Ｆｅ（Ｓｉ）相的体积分数大于７０％,Ｓ     

Sm8Fe83Si2C5Cu0.5Nb1.5非晶合金的晶化动力学

用差热分析（ＤＴＡ）,结合Ｘ射线衍射（ＸＲＤ）研究了Ｓｍ８Ｆｅ８３Ｓｉ２Ｃ５Ｃｕ０．５Ｎｂ１．５非晶合金的晶化动力学。结果表明：温度在０￣１０００℃范围内,该合金的晶化相为α－Ｆｅ和Ｓｍ２（ＦｅＳｉ）１７Ｃｘ,α－Ｆｅ相的晶化表观激活能力３４９．５３ｋＪ／ｍｏｌ,Ｓｍ２（ＦｅＳｉ）１７Ｃｘ的晶化表观激活能力３１６．１９ｋＪ／ｍｏｌ,两相在晶化初期激活能量小,随晶化量（ｘｃ）的增加激活能增大,当α－     

SiO2碳热还原法制备Si3N4／SiC的固相反应机理

ＳｉＯ２／Ｃ体系在氮气气氛下１５７３～１９７３Ｋ温度范围内反应所得的产物为α、β－ＳｉＣ。高的反应温度、高的升温速率以及原料碳的过量均有利于ＳｉＣ的生成。反应过程可分为三个阶段，产物分别为ＳｉＯ气体，Ｓｉ３Ｎ４和ＳｉＣ，表现活化能分别为４７０ｋＪ／ｍｏｌ，４６７ｋＪ／ｍｏｌ和４８４ｋＪ／ｍｏｌ。以非等温热重分析为主要实验方法，对ＳｉＯ２／Ｃ体系在流动的氮气中的反应机理进行了研究，探讨了体系固相反应所经历的步骤，确定了控速环节和动力学参数。     

共沉淀法制备掺杂氧化锌压敏陶瓷粉料热力学分析

本文通过对Ｍｅ^ｎ＋（Ｚｎ^２＋;Ｃｒ_３^＋,Ｍｎ^２＋;Ｓｂ^３＋,Ｂｉ^３＋,Ｃｏ^２＋）－ＮＨ_３－ＣＯ_３^２－－Ｈ_２Ｏ体系进行热力学分析的基础上,获得了Ｍｅ－ＮＨ_３－ＣＯ_３^２－Ｈ_２Ｏ体系中的ｌｇ［Ｍ］_T－ｐＨ关系图,得到了用ＮＨ_４ＨＣＯ_３和ＮＨ_３·Ｈ_２Ｏ作沉淀剂,用共沉淀法制备掺杂氧化锌压敏陶瓷粉料时,最佳共沉淀ｐＨ为７．０左右．     

新型复合钙钛矿Ba(SbⅢ,SbⅤ)O3的水热合成和表征

采用水热晶化法制备了Ｂａ（Ｓｂ^Ⅲ,Ｓｂ^Ⅴ）Ｏ_３新型钙钛矿型氧化物,并通过ＸＲＤ、 ＩＲ、ＳＥＭ和ＩＣＰ等方法对产物物相、形貌和组成等进行了表征．结果表明,产物为立方钙钛矿结构,晶胞参数为α＝０．４１５ｎｍ,粒度为１～２μｍ具有一定团聚的多晶粉末．产物中锑为三价和五价两种价态．水热条件对合成影响的研究结果表明, Ｂａ（Ｓｂ^Ⅲ,ｓｂ^Ⅴ）Ｏ_３合成的适宜碱度和ｎ_{Ｓｂ（Ⅴ)}／ｎ_{Ｓｂ（Ⅲ）}分别为 ８～１０Ｍｏｌ／Ｌ ＫＯＨ和 ０～１     

Chemically feasible hypothetical crystalline networks

Our systematic enumeration of 4-connected crystalline networks (that is, networks in which each atom is connected to exactly four neighbours) used recent advances in tiling theory to evolve over 900 topologies. The results are relevant to the structures of zeolites and other silicates, aluminophosphates (AlPOs), oxides, nitrides, chalcogenides, halides, carbon networks, and even to polyhedral bubbles in foams. Given their importance as molecular sieves, ion exchangers, catalysts and catalyst supports, we have applied the results to microporous aluminosilicates and aluminophosphates (zeolites). Zeolite chemistry has to date produced 152 distinct types of structure. However, it was always clear that although many further structures can be synthesised, only a fraction of the mathematically generated networks would be chemically feasible (many are 'strained' frameworks requiring unrealistic bond lengths and bond angles), and that an effective 'filtering' process is needed to identify the most plausible frameworks. Here, we describe the use of computational chemistry methods to calculate optimized structural parameters, framework energies relative to alpha-quartz, volumes accessible to sorption, and X-ray diffraction patterns for systematically enumerated hypothetical 4-connected crystalline frameworks. Structures were treated as silica polymorphs with the empirical formula SiO(2), and their energies were minimized.     

Electron-phonon coupling and localization of excitons in single silicon nanocrystals

We report a detailed photoluminescence (PL) study on single silicon nanocrystals produced by laser pyrolysis. The PL spectra reveal nearly homogeneously broadened zero-phonon lines coupled to Si-O-Si phonon transitions in the SiO2 shell. A systematic investigation of electron-phonon coupling is reported on the basis of single nanocrystals. The stepwise localization of electron and hole at the Si-SiO2 interface for nanocrystals smaller than d approximately 2.7 nm is driven by electron-phonon coupling. From the localization energies the effective Bohr radii of the (localized) electron and hole are estimated to be in the range of 1-2 bond lengths of Si-O and Si-Si.     

汽相转化法制备纳米晶组成的块状ZSM-5多孔沸石

在ZSM-5沸石前驱体中加入羧甲基纤维素钠并制得干胶, 然后通过蒸汽相转化制得了大块状ZSM-5沸石。由于羧甲基纤维素钠与硅铝物种之间的相互作用干扰了沸石晶体的正常生长, 这种干扰所产生的“键阻断”作用导致合成的大块状ZSM-5沸石由100~150 nm的初级ZSM-5沸石晶体组成, 在这些初级粒子之间存在2~20 nm的二次介孔结构。异丙苯催化裂化结果表明, 由于纳米沸石具有较高的外表面积和较大的介孔孔容, 比参比催化剂表现出更高的异丙苯转化率。     

On the crystal chemistry of NaP zeolites

Multiphase samples containing a series of well-crystallized gismondine-type NaP zeolites, unit cell content Na_xAl_xSi_16−xO₃₂ ·yH₂O with 3 ⩽ x ⩽ 8, were prepared at 90–95°C or 150°C from aluminosilicate glasses and aqueous sodium hydroxide. Powder X-ray diffraction using a Guinier-Hägg camera and energy dispersive X-ray microanalysis performed in a scanning electron microscope revealed three NaP phases with increasing silicon content, i.e., low-silica P (8–10 Si atoms per unit cell), orthorhombic medium-silica P (10–12 Si/cell), and tetragonal high-silica P (12–13 Si/cell). NaP1 (pseudocubic lattice geometry) probably represents an end-member low-silica P with 10 Si/cell, whereas NaP2 (pseudotetragonal lattice geometry) is identical to medium-silica P.     

Peculiarities of electron-energy structure of surface layers of porous silicon formed on p-type substrates

The atomic and electron structure of porous silicon surface layers were investigated by the methods of ultrasoft X-ray emission spectroscopy and X-ray absorption near edge structure spectroscopy. The thicknesses of the surface oxide layer and the degree of distortion of the silicon-oxygen tetrahedron in this layer were estimated. The thickness of the surface oxide layer lying on the amorphous layer, which covers the nanocrystals of porous silicon upon keeping for a year, exceeds severalfold the thickness of the natural oxidation of plates of monocrystalline silicon. The distortions of the silicon-oxygen tetrahedron??the main structural unit of silicon oxide??are accompanied by the strain of Si-O bonds and the increase in Si-O-Si bond angles.     

Microstructure and microhardness of pearlitic steel after laser shock processing and annealing

The microstructure evolution of the high carbon pearlitic steel after laser shock processing (LSP) with different laser pulse energy and high temperature annealing was investigated. After LSP, the cementite lamella were bent, fractured and broken into granules. Fragmentation and dissolution of the cementite lamella were enhanced by increasing the laser pulse energy. Results show that the ferrite lattice parameter increased due to carbon atom dissolution in the ferrite matrix, and the corresponding ferrite X-ray diffraction peaks shifted significantly towards the smaller diffraction angles. After annealing at 650°C for 30?min, an ultrafine duplex microstructure (ferrite+cementite) was formed on the surface. After LSP with a high energy, equiaxed ferrite grains were refined to 400?nm and the cementite lamella were fully spheroidised with the particle diameter of ～150?nm. The corresponding grain size of ferrite and cementite under low pulse energy was 500 and 300?nm respectively. After annealing, the ferrite peaks significantly shifted towards the higher diffraction angles, and the ferrite lattice parameter decreased. The microhardness initially increases after LSP and then slightly decreases after subsequent annealing but remained higher than without LSP.     

Ab initio calculation of the mechanical strength of the Si-O-Si bond

The theoretical mechanical strength of the Si-O-Si bond has been evaluated by means ofabinitio RHF/3-21 G^* calculations on the Si₂O₇H₆ molecule simulating the structure of the-cristobalite crystal. Deformation was applied by increasing the distance between the silicon atoms from equilibrium up to the distance of maximum force. The position of the bridging oxygen has been optimized at each step of deformation. The interatomic force, the total energy, atom charges and overlap population have been calculated as functions of the Si-Si separation. The strength of the structure appears to be equal to 1.1 mdyn, i.e. the theoretical strength of the crystal for fracture along the [0 1 1] plane is equal to 64 GPa. The model used has been found to overestimate strongly the rigidity of the Si-O-Si angle and therefore the elasticity of silica. Nevertheless, the value of the ideal strength (that is determined by the strength of the Si-O bond) may be considered as a reasonable approximation.     

HMDSO plasma polymerization and thin film optical properties

Thin films were deposited from hexamethyldisiloxane (HMDSO) in a glow discharge supplied with radiofrequency (rf) power. Actino-metric optical emission spectroscopy was used to follow trends in the plasma concentrations of the species SiH (414.2 nm), CH (431.4 nm), CO (520.0 nm), and H (656.3 nm) as a function of the applied rf power (range 5 to 35 W). Transmission infrared spectroscopy (IRS) was employed to characterize the molecular structure of the polymer, showing the presence of Si-H, Si-O-Si, Si-O-C and C-H groups. The deposition rate, determined by optical interferometry, ranged from 60 to 130 nm/min. Optical properties were determined from transmission ultra violet-visible spectroscopy (UVS) data. The absorption coefficient , the refractive index n, and the optical gap E₀₄ of the polymer films were calculated as a function of the applied power. The refractive index at a photon energy of 1 eV varied from 1.45 to 1.55, depending on the rf power used for the deposition. The absorption coefficient showed an absorption edge similar to other non-crystalline materials, amorphous hydrogenated carbon, and semiconductors. For our samples, we define as an optical gap, the photon energy E₀₄ corresponding to the energy at an absorption of 10⁴ cm⁻¹. The values of E₀₄ decreased from 5.3 to 4.6 as the rf power was increased from 5 to 35 W.     

29Si MAS n.m.r. of aluminosilicate sodalites: Correlations between chemical shifts and structure parameters

The ²⁹Si n.m.r. chemical shifts of 16 sodalites of the general composition M_6+x [SiAlO₄]₆A_x·nH₂O (M = alkali metal cation, A = OH⁻, anion) cover a range of more than 20 ppm and show linear correlations with the SiOAl bond angles and the lattice constants. As a result of the different steric and coordination requirements of the various nonframework constituents, bond-angle variations between 126 and 160° occur, and these can be calculated directly from the chemical shift data. The ²⁹Si chemical shifts and the average SiOAl bond angles of Si(4Al) environments in several other zeolites also fit the same type of correlation that has been established here for the sodalites.     

Optical Dispersion Parameters with Different Orientations for SrLaAlO4 Single Crystals

The different optical dispersion parameters of SrLaAlO4 single crystals have been studied by the transmission and reflection measurements at normal incidence for the three orientations 001,100 and 101 in the spectral range 400nm-250nm,The optical absorption data revealed the existance of allowed indirect and direct transition ,The refractive index has abnormal behaviour in the spectral region 400-900nm ,but has a normal one in the higher wavelength region .The optical dispersion parameters,the single oscillator energy Eo and the disperison energy Ed were detemined and indicated the ionic structure of the material .The high-frequency dielectric constant ,The lattice dielectric constant and the electronic polarizability were determined by the free carriers and the lattice vibration modes,The real dielectiric constant ε1,the dielectric loss tangent (tanδ),the volume(VELF) and the surface energy loss function (SELF)have also been discussed.