Preparation and stability of nanocrystalline (C6H5C2H4NH3)2PbI4-doped PMMA films

Preparation and stability of nanocrystalline (C₆H₅C₂H₄NH₃)₂PbI₄-doped PMMA films were investigated. By using spin-coating and subsequent annealing technique, nanometer-sized (C₆H₅C₂H₄NH₃)₂PbI₄ precipitates were successfully formed into a PMMA matrix. These films showed clear exciton absorption and free exciton emission at room temperature. Comparing with (C₆H₅C₂H₄NH₃)₂PbI₄ film, marked improvement of thermal- and photo-stability was observed for nanocrystalline (C₆H₅C₂H₄NH₃)₂PbI₄-doped PMMA films. The thermal-stability of these films correlates with the decomposition of the organic part. As for photo-stability, photo-irradiation induced oxidation is one of the possible reasons for the degradation of the films.     

Preparation and optical properties of nanocrystalline (C6H5C2H4NH3)2PbI4-doped PMMA films

Nanocrystalline (RNH3)2PbI4-doped PMMA films were successfully fabricated on glass substrates by the spin-coating technique and subsequent annealing. X-ray diffraction spectra revealed that the (RNH3)2PbI4 crystals dispersed as nanometre-sized crystals in the PMMA matrix. These films showed a strong exciton absorption band with narrow bandwidth, even at room temperature. The exciton absorption observed here could be attributed to the 6s to 6p transition of Pb2+. The stability of the (RNH3)2PbI4 crystal was improved by doping these crystals into a PMMA matrix. © 1998 Chapman & Hall     

Preparation of SiO2 films from Si(OC2H5)4-C2H5OH-H2O solutions without catalysts

Thin and homogeneous SiO₂ films were prepared on aluminium plates from Si(OC₂H₅)₄-C₂H₅OH-H₂O solutions which had controlled compositions and did not contain any acid as a catalyst. Aluminium with the coatings showed good corrosion resistance. However, SiO₂ films prepared from alkoxide solutions with HCI contained Cl^– ions. Aluminium with coatings including Cl^– ions corroded in a corrosion test. Alkoxide solutions without acids were necessary for use in the coating of aluminium. The transformation of gels prepared from solutions without acids to amorphous SiO₂ was investigated.     

氟表面活性剂C_8F_(17)SO_2N(C_2H_5)C_2H_4(OC_2H_4)的合成与性能

以全氟辛基磺酰氟为原料,与乙胺在异丙醚中加热反应制得N 乙基全氟辛基磺酰胺,再与2 氯乙醇在加热回流下反应得到N 乙基N 乙醇全氟辛基磺酰胺,随后在碱性条件,加热和带压下与环氧乙烷进行聚合反应,得到表面活性剂C8F17SO2N(C2H5)C2H4(OC2H4)nOH,n=8～9。该活性剂在质量浓度为0.05%时就可将表面张力降至19.2mN/m以下,具有良好的表面活性。运用IR,NMR,DSC,TG等技术对该表面活性剂进行了表征和研究。     

Analysis of C2H4 in C2H6 and C2H5D with VUV absorption spectroscopy and a method to remove C2H4 from C2H6 and C2H5D

The photoabsorption cross section of C2H4 was measured in the spectral region 107-183 nm and those of C2H6 and C2H5D were accurately determined in the spectral region 107-162 nm using radiation from a synchrotron as source of VUV light. Typically, C2H4 present as a minor impurity in samples of C2H6 and C2H5D distorted the absorption cross section in curves of C2H6 and C2H5D in the onset region. We completely eliminated C2H4 from C2H6 and C2H5D using adsorption on activated Pd/charcoal at 195 K. By this means, we detected no C2H4 in samples of C2H6 and C2H5D according to their absorption spectra. The detection limit of C2H4 in C2H6 and C2H5D is less than 0.03 ppm with VUV absorption spectroscopy.     

Geometric isomerism of layered complexes of uranyl selenates: Synthesis and structure of (H3O)[C5H14N]2[(UO2)3(SeO4)4(HSeO4)(H2O)] and (H3O)[C5H14N]2[(UO2)3(SeO4)4(HSeO4)(H2O)](H2O)

New uranyl selenates with organic cations (H₃O)[C₅H₁₄N]₂[(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)] (I) and (H₃O)[C₅H₁₄N]₂[(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)](H₂O) (II) were synthesized by evaporation of aqueous solutions and studied. Compound I has monoclinic symmetry, space group C2/c, a = 16.7572(13), b = 11.7239(12), c = 19.0490(13) Å, β = 98.875(6)°, V = 3697.6(5) ų, Z = 4. The crystal structure was solved by the direct method and refined to R ₁ = 0.085 for 2868 reflections with |F _hkl | ≥ 4σ|F _hkl |. Compound II has monoclinic symmetry, space group P2₁/n, a = 10.8252(10), b = 19.0007(10), c = 18.6463(15) Å, β = 100.324(7)°, V = 3773.2(5) ų, Z = 4. The crystal structure was solved by the direct method and refined to R ₁ = 0.084 for 5721 reflections with |F _hkl | ≥ 4σ|F _khl |. The structures of I and II are based on layered complexes [(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)]^3? formed by combination of uranyl pentagonal bipyramids and selenate tetrahedra. H₃O⁺ cations, water molecules, and protonated methylbutylamine cations are located in the interlayer space. Geometric isomerism of two-dimensional complexes [(UO₂)₃(SeO₄)₅(H₂O)] in the structures of uranyl selenates was found and described.     

Synthesis and structural study of new potassium uranyl selenates K2(H5O2)(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)4 and K3(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)5

Single crystals of new uranyl selenates K₂(H₅O₂)(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₄ (1) and K₃(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₅ (2) were prepared by isothermal evaporation at room temperature. The crystal structure of 1 was solved by the direct method [C2/c, a = 17.879(5), b = 8.152(5), c = 17.872(5) Å, β = 96.943(5)°, V = 2585.7(19) ų, Z = 4] and refined to R ₁ = 0.0449 (wR ₂ = 0.0952) for 2600 reflections with |F _o| ≥ 4σ _F . The structure of 2 was solved by the direct method [P2₁/c, a = 17.8377(5), b = 8.1478(5), c = 23.696(1) Å, β = 131.622(2)°, V = 2574.5(2) ų, Z = 4] and refined to R ₁ = 0.0516 (wR ₂ = 0.1233) for 4075 reflections with |F _o| ≥ 4σ _F . The structures of 1 and 2 are based on [(UO₂)₂(SeO₄)₄(H₂O)₂]^4? layers. The charge of the inorganic layer is compensated by potassium and oxonium ions arranged in the interlayer space. Each K ion is surrounded by seven O atoms belonging to uranyl selenate layers and water molecules, so that it binds with each other the adjacent uranyl selenate structural elements.     

Thermodynamic properties of Mn-Y-Si(Ge,Sn, Pb,C) melts

The effect of Group IVA elements on the integral enthalpy of mixing of Mn-Y-Si(Ge, Sn, Pb, C) melts has been studied using the mixing enthalpies of Mn-Y-Si(Ge) melts determined earlier by calorimetry at 1770 ± 5 K. Since the thermochemical properties of Mn-Y-C(Sn, Pb) melts are unexplored, they have been calculated by the Bonnier-Caboz method using reliable data for the constituent binary systems. To this end, we have performed critical evaluation of the phase diagrams and thermochemical data for the constituent binary systems and have compared the enthalpies of formation of solid Δ_f H and liquid Δ_mix H binary alloys. The results indicate that, among liquid Mn-Y-IVA alloys, the formation of Mn-Y-Ge melts is the most exothermic. The thermochemical properties of all the ternary alloys examined are determined by the properties of the Y-Si(Ge, Sn, Pb, C) constituent binary systems, which have the highest exothermic mixing enthalpies.     

Thermodynamic stability of silicon oxycarbide Si5C6O2 (Nicalon)

The standard entropy and heat of formation of amorphous silicon oxycarbide, Si₅C₆O₂, have been assessed to be 161.1 J K^–1 mol^–1 and — 1282.3 kJ mol^–1 respectively, based in part on the literature data of the mass-spectrometric vapour pressure of SiO(g) over a Nicalon fibre. Using the so-obtained standard Gibbs energy of Si₅C₆O₂, new phase relations (predominance diagrams) of the Si-C-O system have been computed and graphically shown for the temperature range 300–2400 K, including such condensed phases as C, Si, SiC, Si₂O, SiO, Si₂O₃, SiO₂ and Si₅C₆O₂. The thermal behaviour of Nicalon fibres can be quantified thermodynamically by use of the predominance diagrams.     

Zn2+、Ge4+的取代对Li5AlSi2O8的影响

尝试以叶腊石为基体,通过高温固相反应,合成通式为Li5+xAl1-xZnxSi2-2xGe2xO8(x=0.0～1.0)系统锂快离子导体.X射线粉末衍射表明当x≤0.3时体系仍维持原有的Li5AlSi2O8结构(正交晶系);x＞0.5时结构发生明显变化,体系转变成Li6ZnGe2O)8.红外检测显示当x≥0.1红外谱图中出现Li2CO3吸收峰,表明在室温下体系中的Ge4+吸收空气中的CO2而发生分解反应.交流阻抗技术测试交流阻抗表明当温度大于200℃时体系有较高的电导率,最高时为1.11×10-2S/cm(400℃,x=1.0),x≤0.5时离子电导率很低,且不随温度变化.     

Precise Pore Engineering of fcu-Type Y-MOFs for One-Step C2H4 Purification from Ternary C2H6/C2H4/C2H2 Mixtures

The purification of C₂H₄ from C₂H₆/C₂H₄/C₂H₂ mixtures is of great significance in the chemical industry for C₂H₄ production but remains a daunting task. Guided by powerful reticular chemistry principles, herein a systematic study is carried out to engineer pore dimensions and pore functionality of fcu-type Y-based metal–organic frameworks (Y-MOFs) through the construction of a series of eight new structures using linear dicarboxylate linkers with different length and functional groups. This study illustrates how delicate changes in pore size and pore surface chemistry can effectively influence the adsorption preference of C₂H₆, C₂H₄, and C₂H₂ by the MOFs. Importantly, clear relations between pore size/pore surface polarity and C₂ adsorption selectivities of this series of MOFs are established. In particular, HIAM-326 built on a linker decorated with trifluoromethoxy group shows notably preferential adsorption of C₂H₆ and C₂H₂ over C₂H₄, with balanced C₂H₂/C₂H₄ and C₂H₆/C₂H₄ selectivities. This endows the compound with the capability of one-step purification of C₂H₄ from C₂H₆/C₂H₄/C₂H₂ ternary mixtures, which is validated by breakthrough measurements where high purity C₂H₄ (99.9%+) can be obtained directly from the separation column. Its adsorption thermodynamics and underlying selective adsorption mechanisms are further revealed by ab initio calculations.     

Mechanochemical transformation of mixtures of Ca(OH)2 and (NH4)2HPO4 or P2O5

A detailed comparative study of the mechanochemical transformation of two mixtures: Ca(OH)₂–(NH₄)₂HPO₄ and Ca(OH)₂–P₂O₅, milled in a mortar dry grinder for different periods of time was carried out. The phase transformations obtained at each milling stage were studied by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis.The transformations taking place during the first periods of milling are very different for both mixtures. However, prolonged milling, over nearly the same period, causes amorphization of both mixtures. DSC analysis of the milled powders showed the temperature of crystallization of hydroxyapatite and tricalcium phosphate (β-TCP). Calcinations of all the different milled powders at 800 °C for 2 h, results in the formation of hydroxyapatite and β-TCP.     

Separation of H(2)SO(4) + CuSO(4) mixture by diffusion dialysis

Diffusion dialysis of aqueous solution of H(2)SO(4) + CuSO(4) has been investigated in a two-compartment cell with an anion-exchange membrane Neosepta-AFN. The experiments have proved that sulfuric acid permeates well through the membrane used, while cupric sulfate is efficiently rejected. This operation is very effective at high acid concentrations and low concentrations of cupric sulfate. Furthermore, it has been found that even at the highest concentration of CuSO(4), the rejection coefficient is higher than 0.965. The flux of CuSO(4) calculated from the time dependences of the CuSO(4) concentration is negatively influenced by increasing acid concentration.     

Preparation of YVO4 powder from the Y2O3 + V2O5 + H2O system by a hydrolysed colloid reaction (HCR) technique

Prior to the formation of YVO₄ in the Y₂O₃ + V₂O₅ + H₂O system, two intermediate, partially hydrophobic, complex colloidal mixtures with metastable characteristics can be produced at room temperature and atmospheric pressure. The ball-milled system, having both hydrophobic and hydrophilic species, transforms into the stable yttrium orthovanadate phase due to intensive hydrolysis. At room temperature an orange mixture (possessing dispersed Y₂O₃ and 4Y₂O_3–P (OH) _p ^p+ ·2VO ₃ ^– , Y₂O_3–p (OH) _p ^p+ ·6VO ₃ ^– ·xH₂O-like heteroaggregations) formed by 20 h mixing at pH ca. 4.0 transforms slowly, another red-brown heavily flocculated colloidal mixture (with dispersed Y₂O₃ and Y₂O_3–p (OH) _p ^p+ ·V₁₀O ₂₈ ^6– ·yH₂O-like aggregation) formed by 70 h mixing at pH ca. 4.5 transforms rapidly into YVO₄ in water. During additional mixing of highly diluted red-brown mixtures this transformation can be completed at room temperature. At elevated temperatures (50–95 °C) the orange mixture precipitates into a red-brown decavanadate-type precipitatium which subsequently can also rapidly hydrolyse into an orthovanadate phase in the diluted aqueous systems. Both vanadium excess meta-and decavanadate-type aggregations exhibit amorphous character by X-ray diffraction.The semi-hydrophobic colloidal structure can modify the dissociation mechanism, which prevents the system from returning to the starting oxides, and gives a new HCR technique for YVO₄ preparation with a simple hydrolysis process at low temperatures and atmospheric pressure.     

化学气相沉积制备纳米结构碳化钨薄膜

采用氟化钨(WF6)和甲烷(CH4)为前驱体,采用等离子体增强化学气相沉积(PECVD)方法制备具有纳米结构的碳化钨薄膜。采用SEM、XRD、EDS等方法表征了碳化钨薄膜的形貌、晶体结构和化学组成。通过表征,表明在前驱体混合气体中的甲烷与氟化钨气体的流量比(碳钨比)为20、基底温度为800℃的条件下得到的碳化钨薄膜是由直径为20～35nm的圆球状纳米晶构成。通过分析影响薄膜的晶体结构、化学组成的因素后,认为要得到具有纳米晶结构的碳化钨薄膜,主要应控制前驱体气体中的碳钨比以及基底温度。     

Synthesis of SiO2 glass fibres from Si(OC2H5)4-H2O-C2H5OH-HCl solutions through sol-gel method

Various factors affecting the spinnability of the Si(OC₂H₅)₄-H₂O-C₂H₅OH-HCl solutions have been investigated in order to find appropriate experimental conditions for making gel-derived SiO₂ glass fibres. The molar ratios of H₂O, C₂H₅OH and HCl to Si(OC₂H₅)₄ were changed in the range from 0.5 to 10.0, 0.5 to 7.0 and 0.001 to 0.1, respectively. The solutions were reacted at 30 and 80° C. It has been reconfirmed that the most important factor determining the spinnability of the solution in the course of the hydrolysis reaction is the molar ratio of water to Si(OC₂H₅)₄ in the solution. The rise of the reaction temperature led to the remarkable shortening of the time required for drawing fibres. The increase of the amount of HCl decreased the upper limit of the H₂O/Si(OC₂H₅)₄ molar ratio range where the spinnability is found as well as reaction temperature. The solutions with a H₂O/Si(OC₂H₅)₄ ratio larger than 2.0 gave often fibres having a circular cross-section, while other solutions gave fibres with a non-circular one. The tensile strength of the gel-derived SiO₂ glass fibres was also reported.     

Nucleation studies in supersaturated aqueous solutions of (NH4)H2PO4 doped with (NH4)2C2O4·H2O

Induction periods were measured for various supersaturated aqueous solutions of ammonium dihydrogen orthophosphate doped with ammounium oxalate monohydrate by the direct vision method. Various critical nucleation parameters were calculated based on classical theory for homogeneous crystal nucleation and the results reported and discussed. The critical nucleation parameters increased with increase in doping concentration.