Fabrication of Free-Standing Titania-Based Gas Sensors by the Oxidation of Metallic Titanium Foils

A simple method for fabricating TiO₂-based sensors of CO( g ) is demonstrated: the oxidation of Ti-bearing foils. Metallic foils (35 μm thick) were converted into free-standing, porous rutile foils (60 μm thick) by exposure to O₂( g ) at 800°—965°C. The oxidized foils contained thin (0.5—1 μm thick), regularly spaced oxide layers oriented parallel to the external surface. The exposure of such porous foils to increasing concentrations of CO( g ) resulted in a monotonic increase in the steady-state electrical resistance. Rutile foils sensitive to 50 ppm changes in CO( g ) content with response times of a few minutes were produced. The effects of oxidation conditions and copper doping on sensing performance are discussed.     

Preparation of Mesoporous Organically Modified Titanium Materials and their Activity in the Oxidation of Cyclohexene

Mesoporous organically modified Ti-MCM-41 materials were synthesised employing different Ti precursors. Materials were found to possess improved properties in terms of stability, hydrophobicity and activity compared to the parent Ti-MCM-41, preserving their mesoporous structural order. The organically modified mesoporous materials were tested in the oxidation of cyclohexene using conventional heating and microwaves. The microwave assisted protocol was found to enhance reaction rates and selectivities to the epoxide, reducing the times of reaction from 24 to less than 1 h at comparable activities (60–80% conversion).     

利用废旧高分子材料制备改性石油沥青

利用废旧高分子材料、无机填料为改性剂，采用熔融共混方法制备了一系列性能优异的新型改性石油沥青，分析了改性剂类型和用量对石油改性沥青的软化点、脆化温度、针入度和延度等性能的影响。结果表明：改性石油沥青的针入度和延度稍有降低，但其软化点明显升高，脆化温度降低，拓宽了石油沥青的使用温度范围，综合性能提高。     

Ignitability Analysis of Siding Materials Using Modified Protocol for Lift Apparatus

This paper reports on the ignitability of common siding materials that could be exposed to wildland fires. When exposed to brands or fires, structures will experience piloted ignition, which is requisite for sustained ignition involving burn-through and surface flame spread in various directions. In this study, the Lateral Ignition and Flame Spread Test (LIFT) apparatus (ASTM E1321 and E1317) was used to test various siding materials (plywoods, softwoods, and vinyl), some of which were painted, humidified, or sawed. A recently developed protocol provided useful, accurate values of the following thermophysical properties: surface emissivity, surface ignition temperature, thermal conductivity, and thermal diffusivity. Full consistency was achieved with independent literature values of these properties and can be used directly in the database of fire growth models.     

Aminoborane Polymers as Precursors of C-N-B Ceramic Materials

Aminoborane polymers were prepared via condensation reactions between polyfunctional amines and either triethylborane or tris(dimethylamino)borane. The products were characterized by chemical and spectroscopic analyses. The thermal degradation of these materials was studied to establish pyrolytic pathways and to evaluate their potential as precursors to C-N-B ceramic materials. The borane condensation products with 4,4'-methylenedipyrazole, o -phenylenediamine, and 3,3'-diaminobenzidine produced relatively high ceramic yields at 800°C, whereas that with diethylenetriamine decomposed into partially volatile oligomers.     

Metal Chelate Monomers as Precursors of Polymeric Materials

The principal advances and problems of the preparation of polymeric materials based on metal chelate monomers containing metal chelate cycle and functionality are analysed. The data are systematized according to methods for preparing polymeric materials: homopolymerization, copolymerization, living and controlled polymerization, grafting polymerization, electropolymerization, polycondensation, as well as synthesis of dendrimers and hyperbranched polymers based on metal chelate monomers. Special attention is paid to the effect of a metal on both the synthesis mechanism and properties of the products formed. The principal applications of polymeric materials based on metal chelate monomers are considered.     

Precursors for the Synthesis of Ceramic Oxide Materials

Classical techniques for solid-phase synthesis of oxide materials used in the production of ceramics and refractories are revised from the standpoint of thermodynamics and kinetics. The theoretical aspects of alternative methods for the synthesis of powdered materials involving chemical and thermochemical techniques for homogenization of precursor mixtures are discussed and routes to the efficient sintering of ceramic materials with required properties are outlined.     

Preparation of Titanium Nitride Films from Amide Precursors Synthesized by Electrolysis

A TiN precursor solution was synthesized by galvanostatic electrolysis of Ti metal and isopropylamine at a current density of 50 mA·cm⁻² at room temperature. TiN films were prepared by dip-coating of the precursor solution on a Si wafer, followed by two-stage heat treatment at 400°C and a fixed temperature of 800–1200°C in flowing N₂, N₂/NH₃, or NH₃ gas. The TiN films were characterized by XRD, chemical analysis, XPS, and electrical resistivity measurements. The TiN films were composed of uniform grains 20 to 200 nm in size with thicknesses ranging from 300 to 400 nm at temperatures of 800–1200°C. The effect of the heat treatment atmosphere (N₂ and NH₃) on the impurity content, crystallinity, particle size, and electrical resistivity is discussed.     

Consolidation of Combustion-Synthesized Titanium Diboride-Based Materials

The quasi-static consolidation in uniaxial compression of combustion-synthesized TiB₂-based materials was investigated. Consolidation was carried out in insulated containers upon completion of the combustion reaction, while the porous reaction products were ductile. Since the consolidation is not an isothermal process, the temperature change during consolidation was monitored and recorded. The effect of the addition of metallic elements to the elemental powders was established, and it was found that nickel and chromium provide the best compact integrity. The partial densification is sufficient to show significant differences between the effects of metallic additives. A phenomenological (not based on the micromechanisms of densification) constitutive model was applied to the hot and porous reaction products incorporating the temperature dependence of flow stress. The activation energy for the temperature dependence of the flow stress is established and indicates that, in addition to diffusion-induced plastic deformation, other processes occur, such as fracturing of ligaments.     

Metabolic Glycoengineering in hMSC-TERT as a Model for Skeletal Precursors by Using Modified Azide/Alkyne Monosaccharides

Metabolic glycoengineering enables a directed modification of cell surfaces by introducing target molecules to surface proteins displaying new features. Biochemical pathways involving glycans differ in dependence on the cell type; therefore, this technique should be tailored for the best results. We characterized metabolic glycoengineering in telomerase-immortalized human mesenchymal stromal cells (hMSC-TERT) as a model for primary hMSC, to investigate its applicability in TERT-modified cell lines. The metabolic incorporation of N-azidoacetylmannosamine (Ac₄ManNAz) and N-alkyneacetylmannosamine (Ac₄ManNAl) into the glycocalyx as a first step in the glycoengineering process revealed no adverse effects on cell viability or gene expression, and the in vitro multipotency (osteogenic and adipogenic differentiation potential) was maintained under these adapted culture conditions. In the second step, glycoengineered cells were modified with fluorescent dyes using Cu-mediated click chemistry. In these analyses, the two mannose derivatives showed superior incorporation efficiencies compared to glucose and galactose isomers. In time-dependent experiments, the incorporation of Ac₄ManNAz was detectable for up to six days while Ac₄ManNAl-derived metabolites were absent after two days. Taken together, these findings demonstrate the successful metabolic glycoengineering of immortalized hMSC resulting in transient cell surface modifications, and thus present a useful model to address different scientific questions regarding glycosylation processes in skeletal precursors.     

钛修饰的锆基-金属有机框架材料催化苯甲硫醚制备苯甲砜

本文以UiO-66型Zr-MOFs为基础,通过后合成修饰的方法合成了UiO-66(Zr,Ti).以水为绿色溶剂,在相对温和的条件下,UiO-66(Zr,Ti)高效绿色催化双氧水分解,进而促使苯甲硫醚选择性氧化制备苯甲砜.研究发现,当原料苯甲硫醚用量为1mmol,最佳反应温度为60℃,反应时间为12h,UiO-66(Zr...     

Studies on the Carbothermal Preparation of Titanium Carbide from Different Gel Precursors

Different mixed organic–inorganic gels as precursors for the synthesis of titanium carbide and oxycarbides have been prepared in aqueous and organic solutions starting either from rutile or titanium alkoxide. The sol–gel processes have been controlled by complexing additives such as H₂O₂, acetic acid or ethyl aceto-acetate. Upon pyrolysis up to ∼600°C, composites of finely divided particles of amorphous titania and carbon are formed. Monitoring of the high-temperature treatment by TG, XRD and nitrogen adsorption up to 1600°C revealed a three-step carbothermal reduction mechanism through lower titanium oxides and oxycarbides. The intimate mixture of titania and carbon leads to a considerable lowering of the onset of the reaction temperature in comparison with rutile/carbon black and rutile/gel mixtures. Delayed reactions in the final steps, however, may be due to the interruption of the intimate contact of the reactants by pore generation. During the high temperature processes microporous and mesoporous intermediate materials have been prepared; the final products at 1600°C are finely divided particles of oxycarbides with oxygen contents of 1·2–3·4 wt% and grain sizes lower than 1 μm.     

Organometallic Derivatives of Polyphosphazenes as Precursors for Metallic Nanostructured Materials

Co-polyphosphazenes containing anchored organometallic fragments are useful precursors for nanostructured metallic materials. Pyrolysis in air at 800°C yields metallic nanoparticles of the type, M°/M _x O _y /M _z (P _x O _y )/P₄O₇, depending on the metal used; i.e., M° when the metal is a noble metal, metal oxide when the metal is Cr, W and Ru, metallic pyrophosphate when M = Mn and Fe. The organic spacer of the polyphosphazene influences strongly the morphology of the pyrolytic product. The mechanism of formation of the nanostructured materials involves carbonization of the organic matter, which produces holes where the nanoparticles are grown. Reaction of the phosphorus polymeric chain with O₂ yield phosphorus oxide units, which act as a P₄O₇ matrix to stabilize the nanoparticles and/or P _x O _y ⁻ⁿ for the formation of metallic pyrophosphates. The method appears to be a general and versatile new route to metallic nanostructured materials. Dedicated to Professor Harry Allcock for his pioneering and persevering work on Polyphosphazene and their projection in another field as materials and recently nanomaterials.     

纳米二氧化硅改性SA P内养护水泥基材料的力学性能研究

为了研究纳米二氧化硅(NS)改性高吸水性树脂(SAP)内养护水泥基材料的力学性能,在水泥和混凝土中掺入不同掺量的SAP和NS,从宏观和微观的角度对单掺SAP、单掺NS以及复掺下的水泥胶砂强度和混凝土力学性能进行分析,结果表明:在掺量范围内,SAP对水泥胶砂抗折强度提高不大,却会降低水泥胶砂的抗压强度;NS对水泥胶砂的抗折强度和抗压强度仅略有提高;SAP会降低混凝土的抗压强度和劈裂抗拉强度,其强度随着SAP掺量的增加而降低;NS对混凝土抗压强度和劈裂抗拉强度略有提高,且都随着NS掺量的增加而提高.基于NS本身固有的特性能够较好弥补SAP所带来的负面影响,混凝土抗压强度的最佳掺量为0.16％SAP和1.5％NS,而水泥的胶砂强度和混凝土的劈裂抗拉强度的最佳掺量为0.08％SAP和1.5％NS.SAP的掺入使内部结构生成大量的钙矾石穿插于水化硅酸钙凝胶之中,且NS的掺入使内部结构更加密实.     

Lead Zirconate Titanate Prepared from Different Zirconium and Titanium Precursors by Sol-Gel

Modified sol-gel processes have been developed for the preparation of lead zirconate titanate (PZT) (52/48) powders. These processes use different starting sources to introduce the titanium and zirconium components, namely tetraethyl orthotitanate, titanium isopropoxide, or titanium diisopropoxide bis(2,4-pentanedionate) for titanium and zirconium propoxide or zirconium acetylacetonate for zirconium. To achieve stable and homogeneous precursor systems, several solvents (acetic acid, 1,2-propanediol, propanol, and distilled water) and chemical modifying additives, such as acetylacetone and nitric acid, were also introduced for the preparation processes. The influence of the different precursors on the crystallization behavior of the sol-gel-derived powders was studied. Well-crystallized single-phase PZT powders were obtained after heat treatment at 600°C for 1 h. The powders obtained sintered well at 1000°C/2 h and a homogeneous microstructure with small grain sizes was obtained.     

Synthesis of Homochiral Side-chain Precursors for Modified Vitamin D3 Metabolites

Homochiral 3-alkylated (2R,3R)- and (2R,3S)-2,3-dihydroxyalkyl p-toluenesulfonates ( 9 and 10 ) are essential building blocks for vitamin D₃ metabolites with a modified side chain. Nine of these compounds have been prepared starting from (R)-2,3-O-cyclohexylideneglyceraldehyde ( 1 ) by addition of alkylmagnesium halides, Jones oxidation of the obtained diastereomeric alcohols 2 and 3 to the corresponding ketones 4 , and a second addition of alkylmagnesium halides, followed by hydrolytic removal of the cyclohexylidene group and selective tosylation. The opposite diastereoselectivity of the two Grignard reactions is discussed.     

表面修饰的Fe~(3+)/TiO_2制备研究

采用微波水热法制备了表面包覆有硬脂酸的铁掺杂的二氧化钛纳米粒子,对其微结构进行了表征。结果表明:产物为表面包覆有硬脂酸Fe3+ /TiO2 的纳米复合粒子,粒度分布均匀且单分散性好,平均粒径约为38nm;表面为非极性,紫外透过率较低,催化活性较低。可用于防晒化妆品。