预氧化聚碳硅烷纤维热分解动力学及其机理

利用动态TGA分析和Coats-Redfern模型研究了预氧化聚碳硅烷(PCS)纤维的热分解动力学,用IR、XRD、SEM和HRTEM等研究了其热分解过程与机理。结果表明,预氧化PCS纤维热分解过程为一级反应,表观活化能为19.826kJ/mol;在初始分解阶段,主要为小分子PCS逸出,≡Si-H键之间以及≡Si-H与≡Si-CH3键发生了脱氢、脱CH4反应,从而导致交联程度的增加;随热分解温度进一步提高,分子的有机侧链急剧热解,分解产物从有机物转变为存在部分微晶的无机结构;热分解温度继续提高,纤维无机化结构进一步完善,β-SiC晶粒尺寸增加,纤维中出现自由碳;1250℃以上,β-SiC晶粒急剧长大,晶粒尺寸增加导致SiC纤维的力学性能下降。     

Thermal oxidation crosslinking in the blended precursors of organosilicon polymers containing polyvinylsilane with polycarbosilane

The polymer precursors containing polyvinylsilane (PVS) with polycarbosilane (PCS) in coating form were prepared. As the content of PVS increases, the onset temperature of the precursor oxidation decreases and the surfaces formed after the oxidation become smooth and hard. The role of Si–H bonds in the PCS–PVS systems during the oxidation is quantitatively analysed on the basis of the absorption of the Si–H stretching band in the precursor spectra. In the blended systems, the oxidation of the Si–H groups forms the dense crosslinked polymer layer which limits the oxygen diffusion into the precursor interior. © 1998 Chapman & Hall     

含异质元素聚碳硅烷的制备及应用研究进展

回顾了聚碳硅烷陶瓷先驱体的制备方法及其化学结构,着重对近年来几种含异质金属元素聚碳硅烷先驱体的制备、化学结构及应用的研究进展进行了综述,并提出了今后的发展方向。     

Preparation of copper-cobalt oxide spinels by thermal decomposition of copper-cobalt basic nitrate mixed crystals

Copper-cobalt oxide spinels with a common formula Cu _x Co_3–x O₄ (0x1.0) have been prepared by thermal decomposition at 350° C in air of single-phase mixed basic nitrate precursors (Cu, Co)₂(OH)₃NO₃. The formation of the oxide phase during the thermal treatment has been associated with a diffusionless mode of transformation, established for some hydroxides and hydroxysalts with a layer-type structure.     

Microstructures,thermal diffusion and decomposition studies in the two phase solution grown mixed crystals of NaCl and KCl

Mixed NaCl-KCl crystals are grown from water solution. Thermal diffusion, decomposition and microstructures studies by employing the etching technique are reported. It is shown that microstructures consisting of alternate lamellae of NaCl and KCl arranged in 〈100〉 and 〈110〉 directions in the two-phase mixed NaCl-KCl crystals observed at room temperature get converted to the one consisting of random mixture of both the phases on finer scale on heating at 300°C for 30 hr. The dissociated matrix on heating at 600°C for 15 hr regains almost all the characteristics of a single crystal transforming the material into single-phase mixed (NaK) Cl crystals. The temperature dependence of the thermal diffusion is discussed.     

Temperature-dependence of the thermal conductivity of polymers

A method is proposed for the generalization of test data pertaining to the thermal conductivity of polymers.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 4, pp. 632–638, April, 1973.     

Cu/Fe hydrotalcite derived mixed oxides as new catalyst for thermal decomposition of ammonium perchlorate

Cu/Fe mixed oxides (Cu/Fe-MOs) were prepared by calcination of Cu/Fe hydrotalcite (Cu/Fe-HT) precursors. They were used as new catalyst for thermal decomposition of ammonium perchlorate (AP) and their catalytic activity was studied by thermal gravimetric and differential thermal analysis. With the addition of 4 wt.% Cu/Fe-MOs, thermal decomposition of AP was accelerated by 104 °C. Higher catalyst addition favors further decomposition of AP. The catalytic activity order is: Cu/Fe-MOs-500 > Cu/Fe-MOs-800 > CuO·Fe₂O₃. The proposed catalytic mechanism is the presence of O₂⁻ on the surface of Cu/Fe-MOs which can simplify thermal decomposition of AP.     

Characterization of carbon thin films prepared by the thermal decomposition of spin coated polyacrylonitrile layers containing metal acetates

Polyacrylonitrile (PAN) layers were cast from dimethyl-formamide solutions onto quartz substrates by spin coating and subsequently annealed at up to 1000 °C in N₂ atmosphere. Carbonization was catalyzed by nickel or cobalt added to the solution as acetate salts. The synthesized films were approx. 970 nm thick and were characterized by Raman and infrared spectroscopy as well as thermogravimetric and electrical conductance measurements. We discuss the effects of carbonization temperature and metal concentration on the morphology, composition and electrical properties of the formed carbon layer. Increasing the amount of catalyst and the pyrolysis temperature was beneficial for the process and resulted in carbonaceous films with a higher degree of structural order as evidenced by the decreasing Raman I_D/I_G ratio and the increasing electrical conductivity of the films. Cobalt is a better catalyst for PAN carbonization than nickel as far as the structure of the product film is concerned.     

中空酚醛纤维的熔纺研究及性能表征

以提纯后的热塑性酚醛树脂为原料,用圆弧狭缝式喷丝板进行熔融纺丝,经过固化液固化和热处理一系列工艺,制备出了中空酚醛纤维.结果表明:树脂提纯后可纺性能大大提高,只有在适当的熔纺条件下圆弧狭缝式喷丝板才能纺出中空结构的酚醛纤维,改变的熔纺参数,还可以纺出C形和实心圆形另外两种截面的酚醛纤维.SEM,IR,TG-DSC和强度测试等分析结果表明,所制备的中空酚醛纤维和普通实心酚醛纤维一样,具有较高的固化交联度、分解温度和残炭率,同时具有更好的力学性能.     

Melt-spinning and semi-solid processing of bainitic steel

A steel with a chemical composition meant to form nanostructured bainite following appropriate heat treatment, was, cooled rapidly from the liquid phase (1550°C) using melt spinning and modified injection-suction methods, as well as from a semi-solid temperature (1430°C) through thixoforming. The hardness of the as-cast melt spun ribbons was ～960?HV due to a fine martensite–austenite mixture surrounded by three-dimensional skeleton-like primary carbides of length scale 0.2–0.3?µm. The suction-injection cast method led to a similar structure but less hard (780?HV) due to a lower cooling rate. The thixoformed material showed unmelted globular, fine grains and a fine eutectic mixture formed directly from the liquid phase. The variety of processed steel samples were tempered and their microstructures, examined.     

Formation and thermal decomposition of rare-earth carbonates

The preparation of carbonate-containing rare-earth compounds and their thermal decomposition in 0%–17% CO₂/N₂ gas streams has been studied. Three types of rare-earth carbonate or hydroxycarbonate were produced by precipitation; with ammonium bicarbonate as the precipitant, La₂ (CO₃)₃,CeOCO₃ and Ln (OH) _x (CO₃) _y (Sm, Tb, and Yb) were obtained, whereas with Na₂CO₃, only the normal carbonate, Ln₂(CO₃)₃ (La, Sm, Tb, Er and Yb) was found. Temperature programmed decomposition studies revealed that the normal carbonate decomposed stepwise via a dioxocarbonate, Ln₂O₂CO₃, to the oxide. In contrast, the hydroxycarbonates decomposed directly to the oxide. The presence of CO₂ during heating had minimal effect on the decomposition of Ln₂(CO₃)₃ to La₂O₂CO₃ but raised significantly the decomposition temperature of Ln₂O₂CO₃ to the oxide. As CO₂ is a major product of the rare-earth oxide catalysed oxidative coupling of methane, these observations indicate that the state of catalyst carbonation will be dependent on the reaction temperature, overall catalyst selectivity and preparative method.     

Structure-solubility relationship and thermal decomposition of furosemide

Furosemide, a high ceiling diuretic, decomposes on heating and is very sparingly soluble in water. The aim of this study was to identify the thermal decomposition product(s) of furosemide and to calculate the activation energy needed for this reaction. This was done to gain a better understanding of the unusually low water solubility of this drug. The main thermal decomposition product was identified by nuclear magnetic resonance (NMR), mass spectrometry (MS), and infrared (IR) analysis as 4-chloro-5-sulfamoylanthranilic acid (saluamine), and the activation energy, calculated from thermogravimetric analysis (TGA) measurements, for this reaction was 47.7 (±1.93) kcal/mol. The experimentally measured activation energy was well below the normal 59 ± 4 kcal/mol needed for the cleavage of the C-N bond to form saluamine. This could possibly be explained by the weakening of the C-N bond through the I-effect of the furane ring and the delocalization of the electrons of the aniline nitrogen in the chlorosulfamoyl benzoic acid entity of furosemide. This decomposition of furosemide indicates the breaking of intramolecular bonds before those of intermolecular bonds (separation of individual furosemide molecules). Strong inter- and intramolecular bonds are a probable cause for the poor water solubility of furosemide because, when some of the inter- and intramolecular bonds that form part of the hydrogen bond network disappeared, as in the structurally related decomposition product saluamine, the aqueous solubility increased.     

The thermal decomposition of dimethoate.

The thermal decomposition of dimethoate, an organophosphorus pesticide, has been studied with the aim at assessing the reaction kinetics, the energy released during the process and the decomposition products. Dimethoate shows a marked tendency to undergo thermal decomposition at temperature higher than 369 K. A moderate pressure increase has been recorded at the end of all runs. Many thiophosphoric compounds have been identified among the decomposition products.     

The thermal decomposition of ammonium paratungstate

The thermal decomposition of monoclinic, orthorhombic and freeze-dried ammonium paratungstate (APT) has been studied over the temperature range 100 to 500°C using thermogravimetry, evolved gas analysis. X-ray diffraction and electron optical techniques. The particle morphologies of the original APT have been related to the morphologies of the products of decomposition. A mechanism of decomposition which postulates the formation and subsequent decomposition of amorphous ammonium metatungstate is proposed and substantiated by X-ray diffraction analysis and evolved gas analysis.     

Kinetics of aluminum hydride thermal decomposition

The kinetics of A1H₃ decomposition were studied as a function of temperature and hydrogen pressure. Analysis of the experimental data in the formal heterogeneous kinetic approach suggests that the rate of the process is limited by the breaking of Al-H bonds.     

Copper terephthalate and its thermal decomposition products

Crystalline copper terephthalate of composition Cu[C₆H₄(COO)₂]·2H₂O has been synthesized by reacting aqueous solutions of sodium terephthalate and copper sulfate, and its dehydration has been studied in the temperature range 150–300°C. The results indicate that its dehydration behavior depends on the heating rate. Slow heating (to 200°C over a period of 24 h) removes one water molecule per formula unit near 150°C and leads to the formation of an anhydrous salt and a mixture of Cu₂O and CuO (a total of 12.41%) near 200°C. Heating to 300°C in 10 min leads to the formation of nearly phase-pure Cu₂O.     

聚丙烯的热分解与超临界水分解对比实验研究

为了寻求一种更为有效的聚合物分解回收方法，采用热分解和超临界水分解方式对聚丙烯(PP)的分解行为和分解产物进行了对比实验研究，并利用红外光谱、热分析仪等分析手段对反应残留物进行分析，用气相色谱和质谱对液相成分进行表征．结果表明：在反应温度为420℃的条件下，PP经热分解全部转化成液体油状物，而超临界水分解只有63％的分解率，反应较热分解进程缓慢；超临界水分解时，压力越高，PP分解率越低；压力的存在对于某些小分子分解产物的生成有一定的抑制作用。     

Different thallium(III) oxide nano-structures from direct thermal decomposition of two thallium(I) coordination polymers

Two thallium(I) coordination polymers, [Tl(3-np)] and [Tl(2,4-dnp)], 3-np⁻ = 3-nitrophenoxide and 2,4-dnp⁻ = 2,4-dinitrophenoxide, have been synthesized and characterized by elemental analyses and IR spectroscopy. Flower-like nano-structure and nano-powders thallium(III) oxide, Tl₂O₃, have been prepared by direct thermal decomposition of two different Tl(I) coordination polymers, [Tl(3-np)] and [Tl(2,4-dnp)]. The nano-materials were characterized by scanning electron microscopy, X-ray powder diffraction (XRD) and IR spectroscopy. The thermal stability of nano-structure Tl₂O₃ was studied by thermal gravimetric and differential thermal analyses and showed that there is no reportable loss of weight in the TGA curves that proves the existence of thallium(III) oxide. This study demonstrates that coordination polymers may be suitable precursors for the preparation of nanoscale materials with different and interesting morphologies.