几种酚醛树脂热裂解的研究

采用热失重、差热分析、热机分析、裂解气体容积分析及组分的色谱分析等方法,对几种热固性酚醛树脂的热裂解进行了研究。结果表明酚醛树脂的热稳定性与二亚甲基醚键的存在很有关系,随着醚键的增多而热稳定性降低。对树脂的热裂解机理进行了讨论。     

Thermal transport coefficients for liquid and glassy water computed from a harmonic aqueous glass

We compute thermal transport coefficients for liquid and glassy water in terms of the vibrations of the quenched liquid. The thermal conductivity and thermal diffusivity are computed for H(2)O and D(2)O at densities from 0.93 to 1.2 g cm(-3). The computed thermal diffusivity of liquid water is in reasonable agreement with measured values and is found to increase with increasing temperature due largely to the thermal accessibility of delocalized librational modes. The influence of structure and density on the thermal conductivity of amorphous ices is investigated. The calculations reveal that density alone is unable to explain the measured thermal conductivity of amorphous ices, particularly low-density amorphous ices, for which the thermal conductivity decreases with increasing temperature near 100 K. To investigate the influence of structure on thermal transport in amorphous ices we have computed the thermal transport coefficients for low-density amorphous ices prepared in two different ways, one formed by quenching the liquid at 0.93 g cm(-3) and the other by distortion of cubic ice at the same density. The computed thermal conductivity of the latter is higher, but the structures of both forms are too disordered for the thermal conductivity to exhibit the unusual variation observed experimentally.     

石墨烯导热研究进展

石墨烯具有目前已知材料中最高的热导率,在电子器件、信息技术、国防军工等领域具有良好的应用前景。石墨烯导热的理论和实验研究具有重要意义,在最近十年间取得了长足的发展。本文综述了石墨烯本征热导率的研究进展及应用现状。首先介绍应用于石墨烯热导率测量的微纳尺度传热技术,包括拉曼光谱法、悬空热桥法和时域热反射法。然后展示了石墨烯热导率的理论研究成果,并总结了石墨烯本征热导率的影响因素。随后介绍石墨烯在导热材料中的应用,包括高导热石墨烯膜、石墨烯纤维及石墨烯在热界面材料中的应用。最后对石墨烯导热研究的成果进行总结,提出目前石墨烯热传导研究中存在的机遇与挑战,并展望未来可能的发展方向。     

Thermal characterization of Al2O3 and ZnO reinforced silicone rubber as thermal pads for heat dissipation purposes

Silicone rubber filled with thermally conductive, but electrically insulating Al₂O₃ or ZnO fillers were investigated to be used as elastomeric thermal pads, a class of thermal interface materials. The effect of Al₂O₃ or ZnO fillers on the thermal conductivity and coefficient of thermal expansion (CTE) of the silicone rubber were investigated, and it was found that with increasing Al₂O₃ or ZnO fillers, the thermal conductivity of the thermal pads increases, while the coefficient of thermal expansion (CTE) decreases. The thermal conductivity results obtained were also analyzed using the Agari model to explain the effect of Al₂O₃ or ZnO fillers on the formation of thermal conductive networks. Thermal gravimetry analysis (TGA) showed that the addition of either Al₂O₃ or ZnO fillers increases the thermal stability of the silicone rubber, while the scanning electron microscope (SEM) showed that at 10 vol.% filler loading percolation threshold has yet to be reached.     

Anisotropic and heterogeneous thermal expansion of polyethylene foam blocks: Effect of thermal treatments

Crosslinked closed cell polyethylene foams produced in blocks by compression moulding present an anisotropic and heterogeneous thermal expansion behaviour when the temperature is increased. This paper analyses the main reason for this particular behaviour and presents a way to reduce it by using thermal treatments.In order to perform this analysis, an experimental study on the cellular structure, lamellar distribution and thermal expansion is presented as a function of two kinds of thermal treatments. The experimental results have showed that the main factor controlling the foams thermal expansion is an anisotropic and heterogeneous cellular structure of the original foams. It has been also proved that an adequate thermal treatment allows homogenising the foams thermal expansion.     

Thermal study of calcium silicate material synthesized with solid wastes

This work focuses on the thermal characterization of a calcium silicate-based material synthesized with different solid wastes (chamotte and marble) for use as thermal insulation material. Thermal and structural changes occurring during heating were accompanied by differential thermal analysis, thermogravimetric analysis, dilatometric analysis, open photoacoustic cell technique, X-ray diffraction (XRD), and scanning electron microscopy. An endothermic event at 823.2 °C was interpreted as decomposition of carbonates. An exothermic event around 900 °C is associated with the crystallization of calcium silicate phases mainly wollastonite. The themophysical properties of the calcium silicate-based material (thermal diffusivity, thermal conductivity, specific thermal capacity, and thermal effusivity) are influenced by the synthesis temperature. The thermal analysis results agree well with the XRD. The calcium silicate pieces presented low thermal conductivity values (0.227?0.376 W m^?1 K^?1). These results suggest that the calcium silicate-based materials produced essentially with chamotte and marble wastes has high potential to be used as thermal insulation construction material.     

神府次烟煤在不同温度下的热溶产物表征

利用FT-IR、热重、GPC以及同步荧光分析等对神府次烟煤在不同温度条件下的1-甲基萘热溶物和热溶残煤进行了表征。结果表明,热溶物中含有较多的脂肪结构,灰分几乎全部转移至残煤中;热溶残煤与神府原煤的热失重特性存在明显差别;在300~360 ℃,随着温度升高,热溶物数均分子量呈增加趋势,进一步提高温度,分子量减小;热溶物缩合芳环数随着温度升高而增加。据此表明,在低于煤初始热解温度下神府次烟煤的热溶主要以溶剂化作用破坏煤中的非共价键为主,其中,酮、酯等轻质组分易于脱除;而高于煤初始热解温度的热溶过程则伴有侧链和桥键等弱共价键断裂的热解反应和自由基缩聚反应,热溶物中三环等稠环芳香结构增加。     

聚硅氧烷热稳定性研究进展

综述了聚硅氧烷的热老化机理、影响其热稳定性的因素和提高其热稳定性的途径。聚硅氧烷的热老化反应主要包括热解聚和热氧化两个反应。氧气、水或醇、酸、碱或残留催化剂、硅油、机械外力、填料、聚硅氧烷的链端基等都会影响聚硅氧烷的热稳定性。提高聚硅氧烷热稳定性的途径主要有改变聚硅氧烷的分子结构以及在体系中添加热稳定剂。     

Thermal diffusivity and electrical conductivity of electropolymerized polypyrrole films

This article presents measurement of thermal diffusivity and electrical conductivity of polypyrrole films prepared by electropolymerization. Thermal diffusivity was measured by laser radiometry (former flash radiometry). Electrical conductivity was determined by a conventional four-probe method. Increase of thermal diffusivity is observed when increasing the supporting electrolyte concentration, which is also shared with the increase of electrical conductivity. Both thermal diffusivity and electrical conductivity significantly depended on the types of counter anion incorporating into polymer bulk. Thermal diffusivity of polypyrrole film is larger than that for common nonelectrical conductive polymers. Temperature profile of thermal diffusivity for as-grown polypyrrole films shows that thermal diffusivity increases with increasing temperature (first running profile), whereas remeasured temperature profile of thermal diffusivity (second or third running profiles) shows the decrease of thermal diffusivity with increasing temperature. Electrical conductivity monotonically increases until the significant decrease of it occurs at the temperature above 130°C. Investigation of these temperature profiles of thermal diffusivity and electrical conductivity has been made by corresponding to thermal analysis data. © 1994 John Wiley & Sons, Inc.     

Dependence of thermal diffusion factor of binary mixtures to the thermodynamic state by NEMD simulation

In this paper, we investigate the dependence of thermal diffusion factor and thermal conductivity to the temperature, density and mole fraction in Lennard–Jones binary mixtures of isotopes, noble gases and SF₆–noble gases by non-equilibrium molecular dynamics simulations.The results for the isotopic mixtures indicated that the density has a crucial effect on the dependence of thermal diffusion factor on the temperature. For isotope system at low density, thermal diffusion factor increased with temperature then remains constant at higher temperatures and the slope of thermal diffusion factor vs. temperature is positive while at higher density, thermal diffusion factor decreased with temperature and then fluctuate. For noble gas mixtures, thermal diffusion factor reduces with increasing of temperature and remain constant at high temperatures. For SF₆–Ar system, thermal diffusion factor has a negative slope and reduced with increasing of temperature, but remain nearly constant at high temperatures. For Xe–SF₆ thermal diffusion factor changed sign and the slope of thermal diffusion factor vs. temperature was negative. The results also show that thermal conductivity increases with temperature for all systems.The dependence of thermal diffusion factor to mole fraction of heavier component also investigated. The inverse of thermal diffusion factor versus mole fraction of heavier component is linear for isotope mixtures at thermodynamic conditions: (a) Low temperature, large mass ratio and all densities. (b) High temperature, large mass ratio and low densities. For Ne–Kr mixture, the inverse of thermal diffusion factor shows a linear dependence to the mole fraction of heavier component in moderate temperatures and all densities. For SF₆–Ar and Xe–SF₆ mixtures, the inverse of thermal diffusion factor has linear behaviour at moderate temperatures and low density and high temperature and low density, respectively.     

Development of a thermal conductivity cell with nanolayer coating for thermal conductivity measurement of fluids

Various techniques and methodologies of thermal conductivity measurement have been based on the determination of the rate of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy of the rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude of transient thermal diffusivity along these directions. The transient hot-wire technique is broadly used for absolute measurements of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal diffusivity together with the determination of the specific heat. However, these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. Recently developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. A thermal conductivity cell for measurement of the thermal properties of electrically conducting fluids has been developed and discussed.     

Argentophilicity-dependent colossal thermal expansion in extended prussian blue analogues

The thermal expansion behavior of isostructural variants of the colossal thermal expansion material Ag3[CoIII(CN)6] has been investigated using variable temperature X-ray and neutron powder diffraction. It was found that substitution at the octahedral transition metal site did not strongly affect the thermal expansion behavior, giving Ag3[FeIII(CN)6] as a new colossal thermal expansion material. Substitution at the Ag site (by D) was shown to reduce the thermal expansion coefficients by an order of magnitude. It was proposed that this correlation between the presence of argentophilic interactions and extreme thermal expansion behavior may explain a variety of thermal effects in flexible framework materials containing metallophilic interactions.     

Thermophysical Properties of Poly(propylene)-based Composite Polymer

The thermal diffusivity and the thermal conductivity of polypropylene-based composite polymer were simultaneously measured with a temperature wave analysis method. We can measure the thermal properties under cooling process which are important to consider the polymer processing. The effect of filler in the composite was analyzed by thermal diffusivity and thermal conductivity as a function of temperature. The thermal conductivity of particle dispersed composite was confirmed as a reasonable value and was explained with a series model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Plasma Technology: Where Do We Stand and Where Are We Going?

In this overview, an attempt is made to assess the present and future research and development in thermal plasma processing of materials restricted to (1) thermal plasma coating technologies, (2) thermal plasma synthesis of fine powders, (3) thermal plasma waste destruction, and (4) thermal plasma spheroidization and densification. Since thermal plasma processing is, in general, governed by a large number of parameters, implementation of controls becomes mandatory. The lack of sufficient controls combined with economic drawbacks in some cases has been the main obstacle for the growth of thermal plasma technology. Present R&D efforts, however, address these problems.     

Hyphenated techniques of thermal analysis for characterisation of soil humic substances

Our aim was to investigate the thermal behaviour of humic substances extracted from temperate and tropical soils by means of hyphenated techniques of thermal analysis (e. g. simultaneous thermal analysis DSC/TG coupled with mass spectrometry, MS, for the analysis of evolved gas, EGA) in order (i) to verify whether the chemical composition of isolated humic substances also reflected the differences in microbial parameters previously measured in related soil samples and (ii) to identify suitable indices of thermal stability. Our results show that the investigation of humic substances by thermal methods can provide information on soil organic matter dynamics. Differences in thermal behaviour between the two groups of soils were found. The indices of thermal stability here proposed, IR (index of thermal recalcitrance), and ID (index of thermal decomposability) clearly showed that in humic substances from tropical soils the thermally recalcitrant organic fraction dominated, whilst in temperate humic substances the opposite held. This agrees with previous results on the microbial dynamics and organic matter turnover of the respective soils and indicates that these indices of thermal stability could represent a useful tool in soil environmental quality investigations.     

Effects of hydroxyvalerate contents in thermal degradation kinetic of cellulose acetate propionate/poly(3-hydroxyalkanoates) blends

Thermal stability of polymers is an important parameter that determines the application as well as the processing conditions. The green polymers have shown low thermal stability, such as the polyhydroxyalkanoates (PHAs). The PHAs with different comonomers containing hydroxyvalerate (HV) were studied. It was seen that the green polymer showed a fast thermal degradation process. The addition of the HV comonomer modified this profile and the thermal degradation kinetic. The blend prepared between the PHAs and other polymers can modify the thermal degradation process of the green polymers. In the present study, blends of cellulose acetate propionate and PHAs were prepared, and the thermal degradation kinetics of these blends were evaluated. It was observed that the cellulose acetate propionate (CAP) phase in the blends modified the thermal degradation process and kinetic profile of the PHA phase. In the blends, the thermal stability of the PHAs was slightly modified because of CAP reducing the reactivity of the PHAs. On the other hand, the thermal stability of the CAP phase in the blends is not largely modified by the PHA phase. However, the hydroxyvalerate comonomer decreases the reactivity of the CAP phase at the start of thermal degradation of the same. The interaction between the phases promotes the synergetic interaction, which slightly improves the thermal stability of the two polymers blends.     

Thermal study of sandstones from different Czech localities

Thermal analysis is a useful tool for determination of the rock‘s thermal behavior. The thermal behavior of the rock is affected by both its composition and structure. This study presents the application of thermogravimetric, differential thermal, and thermomechanical analyses for the characterization of the selected Czech sandstone samples. The detailed study of mineralogical composition was carried out by FTIR spectroscopy, X-ray diffraction, and optical microscopy. Thermal expansion during heating up to 1,000 °C, together with the coefficient of thermal expansion showed almost the same values for all the studied sandstone samples. Nevertheless, the residual thermal expansion varied depending mainly on the composition. In the case of higher content of quartz, the thermal expansion showed higher values. With increase of carbonate, glauconite, or clay mineral volume, the residual thermal expansion decreased. Factors such as grain size or shape of particles did not significantly influence the observed thermal expansion values.     

Effect of thermal decomposition processes on the thermal properties of carbon fiber reinforced cement composites in high-temperature range

Thermal conductivity, specific heat capacity, thermal diffusivity and linear thermal expansion coefficient of two types of carbon fiber reinforced cement composites are measured in the temperature range up to 800°C. Thermal conductivity and thermal diffusivity are also determined for the specimens exposed to thermal load up to 800°C before the measurement. Differential thermal analysis (DTA), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) are utilized for the assessment of thermal decomposition processes taking place in the high temperature range under consideration. The high temperature thermal properties of the studied materials are found to be positively affected by the application of the high alumina cement and in the case of the Portland cement based composite also by using the autoclaving procedure in the production process. Also, the randomly distributed carbon fibers that can reduce the damage of the pore structure by the thermal decomposition processes are identified as a positive factor in this respect. A comparison of thermal conductivity vs. temperature curves obtained for the specimens pre-heated to different temperatures is found to be a useful tool in the identification of major dynamic effects in the specimens due to the thermal decomposition reactions. The results are in a good agreement with the DTA, MIP, SEM and XRD analyses. The character of the thermal conductivity measurements that in fact includes the effects of convection and radiation into the thermal conductivity coefficient can be beneficial for a simple assessment of the influence of the fire on a dividing structure.     

Study about thermal runaway behavior of high specific energy density Li-ion batteries in a low state of charge

Lithium-ion batteries are widely used in electric vehicles and electronics, and their thermal safety receives widespread attention from consumers. In our study, thermal runaway testing was conducted on the thermal stability of commercial lithium-ion batteries, and the internal structure of the battery was analyzed with an in-depth focus on the key factors of the thermal runaway. Through the study of the structure and thermal stability of the cathode, anode, and separator, the results showed that the phase transition reaction of the separator was the key factor affecting the thermal runaway of the battery for the condition of a low state of charge.     

The use of thermal analysis to study thermal processing effects on polypropylene

The thermal stability of a polypropylene copolymer has been examined at several stages during the processing of the material into its final product in order to obtain information on the influence of processing steps such as grinding and thermal heating on the expected lifetime of the material. Mass loss kinetics in an inert atmosphere were able to detect differences in thermal stability, but oxidative differential scanning calorimetry studies proved to be a more sensitive techiique. A comparative study of a specially prepared series of samples revealed the importance of additives on measured thermal stability and indicated that both mechanical and thermal processing can cause reduction in measured thermal stability.