非等温动力学积分-微分法研究聚苯乙烯热解反应机理及动力学参数

首次采用积分-微分相结合的方法研究了聚苯乙烯非等温热解动力学,通过比较同一机理函数的微分和积分法结果,推测了聚苯乙烯热解所遵循的机理及动力学参数。实验结果显示,在氮气中聚苯乙烯有一个失重阶段,温度范围282.9℃~398.2℃,在此范围内约有96%聚苯乙烯发生了分解,其最大失重速率发生在372.4℃。积分-微分法拟合结果表明,聚苯乙烯在氮气中的热解符合一级化学反应,其动力学模型方程式为:dα/dt=A exp(-E/RT)(1-α)。平均表观活化能E为199.2 kJ/m o l,lnA为36.56。     

玻璃纤维/环氧树脂复合材料热解特性研究

采用热重-差热分析仪研究玻璃纤维/环氧树脂复合材料在空气及氮气氛围下不同升温速率的热解特性规律。结果表明,在空气气氛下,热解分为两个阶段;氮气气氛下,热解只存在一个热分解阶段,与空气气氛相比热解初始分解温度较高,热解温度范围变窄,失重速率明显变大。在两种气氛下,玻璃纤维均不参与热解。随着升温速率的增加,热解反应各阶段的起始温度、终止温度、最大失重速率温度均向高温方向移动,热解温度范围大小都基本保持不变。氮气气氛下使用Kissinger法、FWO法和Starink法计算出玻璃纤维环氧树脂的平均表观活化能分别为106.42、123.09和119.48kJ/mol。复合材料活化能随转化率的增加而升高,表观活化能保持在一定数值范围内且数值相近,热解反应比较稳定,具有较低A值,表明其具有较强的热稳定性。     

主链含苯基均三嗪联苯型聚芳醚的热稳定性

利用热重分析(TG、DTG)研究了主链含苯基均三嗪联苯型聚芳醚在不同气氛和升温速率时的热降解动力学。比较了升温速率和气体气氛对热降解行为的影响,结果表明,该聚合物具有优异的耐热性和耐热氧化稳定性。用Flynn-Wall-Ozawa,Freeman-carroll等方法进行了动力学处理,计算得热降解反应活化能分别为291.19kJ/mol,286.83kJ/mol,与Kissinger法计算活化能值283.25kJ/mol非常接近。结合Coats-Redfern方法,推测出聚合物在氮气气氛中的热分解机理为F2机理,其机理函数积分式为g(α)=1/(1-α)。     

酚醛树脂热分解非等温动力学机理函数推测

通过热重分析法研究了S-157酚醛树脂的热分解反应。结果表明,S-157树脂耐热性较普通酚醛树脂好,起始分解温度约为615.7 K。Kissinger法、Ozawa法计算得到该树脂热分解活化能分别为210.6 kJ/mol和208.2 kJ/mol,反应频率因子约为2.81×1013。S-157树脂热分解可分为3个阶段,当转化率(αT)小于40%时,活化能(E)随着αT增大而逐渐变小;当αT在40%~55%之间时,E随着αT增大而相对快速增大;当αT大于55%以后,E随着αT增大而缓慢增大。通过Coats-Redfern非等温积分法推断出S-157树脂热分解反应初期的反应机理为扩散反应,末期时为化学反应,期间为过渡阶段。     

粘胶基炭纤维热解特性及几种动力学方法研究

利用热重分析考察了不同升温速率下粘胶纤维的热解特性,结合红外光谱对粘胶纤维热解的不同阶段生成的碳化纤维进行表征,分析了粘胶纤维的热裂解过程,结果表明,粘胶纤维的热解是一个旧键断裂挥发、新键重组的过程。采用4种不同动力学方法(等转化率微分法Friedman法、等转化率积分法Flynn-wall-Ozawa(F-W-O)法、无模式积分法Vyazovkin and Wight(VW)法以及Kissinger法)估算出热解反应的表观活化能。4种方法显示粘胶纤维的活化能主要在110~144kJ·mol-1之间。其中后3种方法获得的活化能值很接近,约为140kJ·mol-1,微分方法Friedman法估算的值较小,为110.3kJ·mol-1。4种互补的动力学方法估算得到的结果总体相差不大,因此,此结果真实可靠,可为今后粘胶纤维研究提供理论依据。     

煤沥青粉填充氯醋/聚氨酯复合材料的热特性

采用差示扫描量热分析(DSC)、热重分析(TG)研究了煤沥青粉填充氯醋/聚氨酯复合材料的玻璃化转变温度、粘流温度及热分解特性,在氮气氛下以不同升温速率讨论并计算得热解动力学相关参数及热解速率经验方程式。结果表明,煤沥青粉填充氯醋/聚氨酯弹性体复合材料的玻璃化温度为-46℃,粘流温度为145℃,其耐热特性与氯醋/聚氨酯材料基本一致。该复合材料热降解分两阶段,活化能E为(97.9±1.1)kJ/mol(、229.8±3.9)kJ/mol,反应级数n为1.2和0.9。     

聚苯基三苯乙炔基硅烷树脂的非等温热分解过程研究

借助TG-DTG技术研究了聚苯基三苯乙炔基硅烷树脂(PPTPES)在氮气气氛中不同升温速率下的热分解行为,利用模型拟合法和非模型拟合法求出了聚苯基三苯乙炔基硅烷树脂热分解反应动力学三因子及分解机理函数。计算结果表明,7种分析方法得到的PPTPES的平均热分解活化能为E=252.76kJ/mol,指前因子lgA=13.93,反应级数n=3,机理函数微分式为1f(α)=(1-a)[-ln(1-a)]-23积分式为g(α)=[-ln(1-α)]3反应遵循随机成核和随后生长机理。     

椰壳纤维的热解动力学分析

将椰壳纤维在NaOH、KOH、ZnCl2和(NH4)2HPO4溶液中进行处理,并采用耐驰STA449C-Jupiter同步热分析仪研究了椰壳纤维在不同升温速率时的热分解反应.通过积分法对椰壳纤维的热解失重曲线进行动力学分析发现,升温速率为5K/min时热解的主反应阶段的活化能最低,低温段和高温段的分别为30.52kJ/mol、56.44kJ/mol,对椰壳纤维的热解反应最有利.采用5%的碱溶液浸泡处理可以有效除去椰壳纤维中的半纤维素、果胶等易降解的成分,改变热解反应过程,从而更有利于制备活性炭纤维.     

碳化钨粉末注射成形一步热脱脂的脱脂动力学EI北大核心CSCD

采用热重分析法测定了在氮气气氛中5℃/min、10℃/min、15℃/min和20℃/min不同升温速率下的石蜡、保形聚合物(PP与HDPE的混合物)、石蜡/保形聚合物和碳化钨(WC-10%Ni)粉末注射成形专用料的热解过程,采用Kissinger法和Flynn-Wall-OZAWA法对4种专用料的热分解动力学进行分析,并用Coats-Redfern研究反应级数。结果表明,用Kissinger法分析不能很好地反映混合物的复杂的热解过程,不能支持碳化钨粉末注射成形一步热脱脂的工艺制定。用Flynn-Wall-OZAWA法分析,石蜡的热分解活化能在59~72 k J/mol,保形聚合物的热分解活化能在143~252 k J/mol,石蜡/保形聚合物的热分解活化能在60~240 k J/mol和WC-10%Ni的专用料的热分解活化能在93~220 k J/mol。用CoatsRedfern法分析,石蜡与保形聚合物的热解可用一级反应来描述,而石蜡/保形聚合物与WC-10%Ni的专用料的热解则适用3个连续一级反应来描述。     

碳化钨粉末注射成形一步热脱脂的脱脂动力学

采用热重分析法测定了在氮气气氛中5℃/min、10℃/min、15℃/min和20℃/min不同升温速率下的石蜡、保形聚合物(PP与HDPE的混合物)、石蜡/保形聚合物和碳化钨(WC-10%Ni)粉末注射成形专用料的热解过程,采用Kissinger法和Flynn-Wall-OZAWA法对4种专用料的热分解动力学进行分析,并用Coats-Redfern研究反应级数。结果表明,用Kissinger法分析不能很好地反映混合物的复杂的热解过程,不能支持碳化钨粉末注射成形一步热脱脂的工艺制定。用Flynn-Wall-OZAWA法分析,石蜡的热分解活化能在59~72 k J/mol,保形聚合物的热分解活化能在143~252 k J/mol,石蜡/保形聚合物的热分解活化能在60~240 k J/mol和WC-10%Ni的专用料的热分解活化能在93~220 k J/mol。用CoatsRedfern法分析,石蜡与保形聚合物的热解可用一级反应来描述,而石蜡/保形聚合物与WC-10%Ni的专用料的热解则适用3个连续一级反应来描述。     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Effect of Permeable Crystalline Material on Steel Reinforcement Corrosion of Concrete

Permeable crystalline materialcan permeate into pores and cracks of concrete and catalyze the reaction between Ca(OH) 2and unhydrated cement to generate a great quantity needle non-soluble crystals, which can stop up the pores and cracks of concrete, and increase the impermeability of concrete. This paper reported the results of a study conducted to evaluate steel reinforcement corrosion of concrete specimens uncoated and coated with permeable crystalline material as well as mixed with the permeable crystalline material. The properties evaluated for corrosion test were water impermeability, water absorption, compressive strength and potential. The results of water impermeability, water absorption, compressive strength clearly showed that the permeable crystalline material could prohibit water, any soluble salts and moisture from penetrating the concrete to cause corrosion, leaking, and other problems, and it did increase the compressive strength, which was favorable for protection of corrosion of reinforcing steel. Moreover, it was concluded from the potential-time curve that the steel reinforcement of uncoated specimen was in the state of activation whereas that of other specimens coated and mixed with the permeable crystalline material was in the state of inactivation. Above all, it was indicated that the permeable crystalline materialis very effective to protect the steel reinforcement of concrete from corrosion.     

The Research and Application About "Dry Peeling Off" Technology for Airplane Surface Paint Layer

In this paper, the principle of spurting take off lacquer were introduced; and with orthogonal method the unsaturate polyester was prepared ;it was easy to peel airplane paint layer off with this material and equipment.     

Quality Study of Honeycomb Core Shaping Without Wax Stabilization

Sandwich panels utilizing honeycomb cores result in lightweight, high-strength units that are very rigid. Indeed, they give honeycomb panels the best strength-to-weight ratio of any construction type available. Conventionally, the wax is poured into the cell of the core to strengthen the structure and prevent the core from being crushed during milling. Much time and labor is required to wax, mill, and clean the cores. In this study, the process of pouring wax into the core was skipped. In other words, the cutter directly milled the core. Experiments showed that the compressive strength of the core produced without wax stabilization was only 3% lower than that of cores produced using the traditional method. In addition, the drum peel strengths of cores produced without wax stabilization were 38.4% higher than cores produced using the traditional method, in which residual wax seriously polluted the adhesive. It was also found that eliminating the wax process can reduce costs.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

In-process thermal treatment of polylactic acid in fused deposition modelling

Polylactic acid (PLA) is one of the most widely used open source fused filament fabrication materials due to its ease of extrusion, biodegradability, and mechanical strength. The mechanical strength of PLA largely depends on the proper growth of its semi-crystalline structure, which can be severely impaired by a low rate of crystallization, particularly in open source printers. This can be further aggravated by the non-uniform thermal distribution of heat that causes improper curing among the extruded beads of the printing material. As a result, PLA printed on open source printers does not achieve the best mechanical properties. This research, for the first time, proposes an additive-free solution implemented through a detailed set of experimentation to improve the curing rate through in-process temperature variations to cure the joints among the beads. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy is used to confirm the improvements in the bead joints. This work is conducted in two phases of experiments. In the first phase, a full factorial ANOVA is used to investigate various process parameters and the important variables are used in the second phase to print test specimens in four different sets.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.     

Early ironwork in Biscay: Survey,excavation, experimentation and materials characterization. An integral study of the mountainside ironworks (ferrerías de monte or “haizeolak”)

ABSTRACT

The production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials.