Thermal and Structural Characterization of TiO2 and TiO2/Polymer Micro Hollow Spheres

Micro hollow spheres, synthesized by the coating of tetradecane filled microcapsules with titanium dioxide, are characterized using thermal gravimetry (TG), infrared spectroscopy (IR), Hg‐porosimetry and scanning electron microscopy (SEM). The investigations show a strong dependence of the coating efficiency on the initial pH (precipitation in water or dilute sulfuric acid) as well as the specific capsule surface present in solution. Since the process is dominated by heterogeneous precipitation, the coating efficiency is governed by the counteracting processes of capsule‐TiO₂ and TiO₂‐TiO₂ agglomeration. TG‐IR analysis of the capsules shows the vaporization of tetradecane prior to the decomposition of the polymeric wall to carbon monoxide, carbon dioxide and water. After the extraction or calcination of the core microcapsules, stable inorganic and organic‐inorganic hollow spheres are obtained.     

Thermal conductivity of polymers

In this review we have concentrated on the interpretation of three essential aspects of the thermal conductivity K of polymers: the temperature dependence, the crystallinity dependence and the orientation effect. K for all amorphous polymers is approximately equal in magnitude and characterized by a T² dependence below 0.5K, a plateau region between 5 and 15K and a slow increase at yet higher temperatures. While a number of models involving different phonon scattering mechanisms are capable of explaining these features, further corroborating evidence would be needed to explain the ad hoc assumptions involved. For semicrystalline polymers K shows both strong crystallinity and temperature dependence, with a distinctive cross-over point at about 10K. These marked features can now be understood as the result of the interplay between two competing factors: the intrinsically higher conductivity in the crystalline regions, and the reduction in K due to an additional phonon scattering mechanism which becomes important at low temperature. This scattering could arise from either the correlation in the spatial fluctuation of the sound velocity in the polymer or the acoustic mismatch at the interfaces between the crystallites and the amorphous matrix.Orientation produces a very large anisotropy in semicrystalline polymers, which however decreases at low temperature and becomes insignificant below 10K. This feature can again be understood in terms of the same competing mechanisms if one realizes that the molecular chains in the crystallites are essentially lined up along the direction of orientation thus offering very little thermal resistance along this direction. For polyethylene with an extrusion ratio of 25 the thermal conductivity at 100K along the extrusion direction is 91 mW/cm K, a value extremely high for polymers and close to that of stainless steel. At this temperature the anisotropy is only about 20, yet because of the different temperature dependence of the thermal conductivity along and perpendicular to the extrusion direction, we predict an anisotropy as high as 60 at room temperature.     

Photoresponsive polymers: 2. The monolayer behaviour of photochromic polymers containing aromatic azobenzene residues

The monolayer characteristics of photochromic azo containing addition and condensationpolymers have been investigated under different conditions of illumination. Possible orientations of the polymers in the monolayers have been proposed. It was found that trans → cis photoisomerization of these materials was not always possible in the Langmuir films and photoinduced changes in monolayer area with time were followed for those polymers which showed uninhibited photoisomerization.     

Exactly alternating silarylene—siloxane polymers: 6. Thermal stability and degradation behaviour

The thermal stability and degradation behaviour of a series of twelve different exactly alternating silarylene—siloxane polymers were investigated by several different methods including thermal gravimetric analysis (t.g.a.) in air and in nitrogen, long term (up to 48 h) high temperature (600° and 900°C) isothermal degradation in nitrogen, and rapid pyrolysis in helium. No weight loss was observed by t.g.a. until about 400°C, and two distinctly different mechanisms were observed, one for degradation in nitrogen (a single step process), and the other in air (a three step process). Under nitrogen, black, insoluble, carbon-hydrogen-silicon containing degradation products were obtained, which were stable in pure oxygen to at least 1100°C. In air, pure SiO₂ was obtained after heating to above 730°C. Isothermal investigations revealed that at temperatures of 600°C and above, weight loss by thermal degradation under a nitrogen atmosphere was completed in less than an hour, and the polymeric products which remained thereafter did not change any further even after 48 h at 900°C.     

Pressure-volume-temperature behaviour of molten polymers

Summary The solubility parameter theory of Hildebrand and Scott extended for polymer blends originally has accounted for dissimilarities only between contact energies of the blend components, neglecting free volume effects which are predicted by the corresponding states theories. Biro et al., however, have shown that using expressions of the Prigogine-Flory corresponding state theories for energy and volume, effects of free volume will be implicity included in the solubility parameter approach too. The results are similar then to those derived by the corresponding state theories. In addition, it is shown that in this case the temperature and pressure dependencies of the solubility parameters are predicted qualitatively correct.We performed this procedure with the Sanchez- Lacombe EOS theory instead of the Prigogine-Flory approach, Formally, identical expressions result, and the calculated solubility parameters evaluated according to the two EOS theories are in good agreement. However, because Sanchez-Lacombe's approach is not a corresponding state theory, it is able to predict additionally qualitatively correct the dependence of the solubility parameters on chain length.     

聚酰亚胺／TiO2复合材料热性能研究

用热重法研究了纳米TiO2含量不同的聚酰亚胺（H）／TiO2复合材料热分解动力学，采用Freeman-Carroll法和最大速率法处理并计算了热分解动力学参数：活化能E、反应级数n、频率因子；并考察了其250℃和400℃热失重。结果表明：纳米TiO2质量分数为20％时，复合材料的耐热性能最好。     

Influence of TiO2 on the densification behaviour of Yb2O3

The effect of temperature and heating rate on the densification of ytterbia (Yb₂O₃), with and without titania (TiO₂) doping was investigated. It is shown that up to a certain doping level, titania doping enhances the densification behaviour of ytterbia. The effect of titania doping on crystal structure confirms that titania is substitutionally incorporated in ytterbia up to the solubility limit, which corresponds well with the densification results. The increased densification rate of titania-doped ytterbia is attributed to the formation of cation vacancy and lattice distortion. Using constant heating rate experiments, the activation energy for densification has been calculated and it is shown that in the intermediate density range (60 % to 85 %), the activation energy is independent of the density. Titania doping increases the activation energy for densification.     

PI/TiO2纳米复合材料的制备及其热稳定性

PI可与无机纳米微粒复合生成性能更加优良的复合膜材料.对以PI为基料、纳米TiO2微粒为添加物制成的PI/TiO2膜进行了研究,考察纳米粒子的用量及固化工艺对PI/TiO2膜热稳定性能的影响.实验结果表明,随着TiO2含量的增加,PAA/TiO2贮存时间变短,而固化后PI/TiO2膜的热稳定性能提高.采用阶梯升温固化,固化温度为310℃时,得到的PI/TiO2膜热稳定性能较好.     

Densification behaviour and microstructural evolution of TiO2/CAS-incorporated alumina

Densification behaviour and microstructural evolution of TiO₂/CAS (CaO-Al₂O₃-SiO₂)-incorporated alumina has been investigated systematically. The experimental results show that TiO₂ can greatly enhance the densification rates of alumina but trigger severely abnormal grain growth (AGG) at 0.60 wt%. On the other hand, small amounts of CAS can effectively inhibit abnormal grain growth, but provoke an abnormal densification owing to the formations of in situ pores left by liquid phase. With additional 0.50 wt% of CAS incorporated into 0.60 wt% TiO₂-doped sample, the aspect-ratios of anisotropic growth grains increase by reduced growth rates of flat boundaries, accomplished by basal planes much smoother and straighter. This microstructure subsequently disappears when CAS incorporation is up to 4.0 wt%, substituted by that with low aspect-ratio and fine-equiaxed grains. Such occurrences are discussed in term of levels of liquid phase and 2-dimension (2-D) nucleation processes.     

Al2 TiO5-ZrO2复相材料中ZrO2的相变特性

以α-Al2O3、TiO2、ZrO2为主要原料,以MgO-SiO2或MgO-Fe2O3为Al2TiO5的稳定剂,经1500℃2 h烧成制得Al2TiO5-ZrO2复相材料,研究了Al2TiO5对ZrO2相变及复相材料热膨胀性的影响.试验发现以MgO-SiO2稳定的Al2TiO5对ZrO2相变的影响显著,随复相材料中Al2TiO5含量增加,m-ZrO2相变为t-ZrO2的温度不断降低,Al2TiO5含量为58.8%的复相材料,ZrO2的相变开始温度由原1150℃降至500℃,相变结束温度为700℃.Al2TiO5-ZrO2复相材料具有低膨胀特性,其室温～1300℃的热膨胀系数仅为1.57×10-6℃-1,适于用作冶金浇钢系统的高抗热震性材料.     

Thermal behaviour of 2-hydroxyethyl methacrylate - methyl methacrylate- copolymers

Copolymerization of 2-hydroxyethyl methacrylate (HEMA) with methyl methacrylate (MMA) was carried out in bulk in nitrogen atmosphere at 70°C using 0.2% benzoyl peroxide as initiator. Fractionation of the copolymers was done by precipitation method. The fractions were characterized by viscosity, NMR, IR and elemental analysis. Thermal behaviour of various fractions was investigated by dynamic thermogravimetry. Thermal stability of various fractions was not significantly influenced by the change in intrinsic viscosity.     

Thermal effect of carbamates based polymer on the TiO2 growth

We investigated the growth of TiO₂ on poly((tetrahydropyran‐2‐yl N‐(2‐methacryloxyethyl) carbamate)‐co‐(methyl 4‐(3‐methacryloyloxypropoxy) cinnamate) (THP‐polymer) using thermal heating, octyl isocyanate (OIC), and glutaraldehyde. It is found that TiO₂ can be grown on surfaces terminated with ? NH₂ and ? O? groups from aqueous solution. However, TiO₂ did not deposit on ? CH₃ terminated surfaces, due to the low surface energy of these surfaces. Fourier transform infrared spectroscopy and thermogravimetric analysis data showed that the ? THP functional group can be removed and the surface functional group converted to ? NH₂ by heating the material over 180°C. OIC can then be immobilized on the surface after heating, changing the surface functional group from ? NH₂ to ? CH₃. As TiO₂ can be deposited from solution on ? NH₂ terminated, but not ? CH₃ terminated surfaces, THP‐polymer can be used to switch the surface properties by thermal activation and subsequent reaction with OIC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal degradation of some perfluoroalkylene-linked polymers

Poly (1,3-phenylenehexafluorotrimethylene) and perfluoroalkylene-linked polyanhydride, polycarbonate and polyester have been studied by thermogravimetry, pyrolysis–gas chromatography–mass spectrometery and fluoride ion analysis. The thermal stability is governed by the ease of formation of specific cyclic degradation products.     

Thermal stability of p-phenylene sulphide polymers

The thermal stability of a series of linear and branched p-phenylene sulphide polymers at 350° has been evaluated by differential thermal analysis, thermogravimetric analysis and weight-loss studies. It has been concluded that there is some indication that the thermal stability increases with the degree of branching present in the polymer and that the stability can be further improved by a preliminary heat treatment in the absence of air. The mechanism of ageing appears to involve a combination of crosslinking, chain scission and oxidation reactions.     

Thermal expansion of oriented glassy polymers

A phenomenological model of entanglement networks is developed and applied to deformed glassy polymers. Thermal expansivities and birefringence are analyzed. The model assumes a stable network of entanglements up to draw ratios of about 5. Beyond that range the entanglement structure breaks down to maintain a nearly constant drawing stress. The results are used to determine the ultimate linear expansivities of atactic polystyrene.     

Thermal analysis of nitro-substituted epoxide polymers

The thermal properties of a number of nitro-substituted and analogous nonnitro-substituted expoxide polymers were investigated. Dramatic increases in char yield and decreases in maximum rate of weight loss were observed for the nitro-substituted systems compared to their nonnitrated analogs. These effects were enhanced when highly functional and highly aromatic epoxide resins were used. The sample size and heating rate employed had pronounced effects upon the amount of char formed during thermal degradation. Analysis of char residues indicates heteroring formation for the nitro-substituted systems during pyrolysis.     

热处理对纳米TiO2光催化活性的影响

本文对纳米TiO2光催化剂在空气气氛中进行程序升温热处理,以苯酚的光催化降解反应评价光催化剂活性,以XRD、FTIR分析TiO2的晶相结构、粒子大小和表面结构随处理温度的变化情况。分析了热处理作用条件下TiO2光催化活性的变化机理。400℃条件下热处理TiO2具有最高光催化活性。适宜的表面结构、粒子大小及晶相结构是纳米TiO2光催化剂表现出较高催化活性的主要原因。     

Thermal properties of strained thermoplastic polymers

Injection moulded tensile bars of several amorphous and semi-crystalline thermoplastic polymers have been deformed uniaxially to a macroscopic strain of 40% so that they showed necked and unnecked regions. From both the necked and unnecked regions of the tensile bars the specific heat and the thermal expansion coefficient were measured. The specific heat of the necked regions decreases about 20% with respect to unstrained samples for semi-crystalline polymers at temperatures between 40°C and 60°C and for amorphous polymers at temperatures between 50°C and 70°C. The thermal expansion coefficient becomes negative at these temperatures. A smaller negative expansion coefficient is observed even in the unnecked region although nearly no change in specific heat can be observed. There is also an increase in the heat of fusion of the semi-crystalline specimens of the necked region. Strain rate dependent effects on specific heat and thermal expansion were not observed within the accuracy of thermal analysis.     

热喷涂技术在光催化TiO2涂层领域的研究与进展

通过对等离子喷涂、超音速火焰喷涂和液料热喷涂等热喷涂工艺在光催化TiO2涂层领域的应用分析,阐明了不同热喷涂方式对涂层性能有不同的影响,指出液料热喷涂可以较好地减少锐钛矿向金红石的转变,并能进一步细化晶粒,可以制备具有较好光催化性能的重要环保材料。而在涂层粉末中掺杂其他元素可以改善涂层的光催化性能,但如何选择合适的掺杂元素需要进行进一步的研究。