Chemical Aging in Epoxies: A Local Study of the Interphases to Air and to Metals

The aging behavior of an epoxy adhesive (DGEBA and DETA) in the bulk surface region and in the contact region to metal substrates (Au, Cu) is studied locally. Therefore, the chemical depth profile during aging is recorded with FTIR microscopy on sample surfaces prepared with low angle microtomy. Two environmental conditions are applied at 60°C for up to 500 days to separate the role of temperature and humidity in aging.

Quantitative evaluation of the IR spectra provides the following results: in the bulk surface region, three aging mechanisms form a gradient region of more than 200 μm. Their intensity and depth profile depend on the environmental conditions. Epoxy-metal contacts are unaffected under dry conditions. Humidity is needed to form a 50 μm thick region where the copper substrate accelerates aging. Based on the experimental results, chemical aging mechanisms are discussed.     

Chemical Aging in Epoxies: A Local Study of the Interphases to Air and to Metals

The aging behavior of an epoxy adhesive (DGEBA and DETA) in the bulk surface region and in the contact region to metal substrates (Au, Cu) is studied locally. Therefore, the chemical depth profile during aging is recorded with FTIR microscopy on sample surfaces prepared with low angle microtomy. Two environmental conditions are applied at 60°C for up to 500 days to separate the role of temperature and humidity in aging.

Quantitative evaluation of the IR spectra provides the following results: in the bulk surface region, three aging mechanisms form a gradient region of more than 200 μm. Their intensity and depth profile depend on the environmental conditions. Epoxy-metal contacts are unaffected under dry conditions. Humidity is needed to form a 50 μm thick region where the copper substrate accelerates aging. Based on the experimental results, chemical aging mechanisms are discussed.     

UV—Vis光谱法与FT—IR光谱法研究聚苯乙烯老化

用紫外-可见光谱法与付里叶变换红外光谱法研究聚苯乙烯以及苯乙烯-丙烯酸酯共聚物的老化过程。在光、热、氧的作用下,这些聚合物的部分主链与侧苯基断裂,有少量苯乙酮结构生成,导致材料变色。     

Convective Drying of Wastewater Sludges: Influence of Air Temperature, Superficial Velocity, and Humidity on the Kinetics

The influence of air temperature, velocity, and humidity during convective drying of two different sludges (A and B) is investigated through a 3³ factorial design. For sludge A, a constant drying flux period is observed, while sludge B is characterized by a long decreasing drying flux phase. A sensitivity analysis shows that temperature is the main operating parameter affecting the drying kinetics. Mass and heat transfer coefficients as well as water evaporation capacities are calculated from drying curves. Transfer coefficients are related to operating conditions through dimensionless relations. For both sludges, a linear relation is found between water evaporation capacity and the maximal measured drying flux.     

Convective Drying of Wastewater Sludges: Influence of Air Temperature,Superficial Velocity,and Humidity on the Kinetics

Abstract

The influence of air temperature, velocity, and humidity during convective drying of two different sludges (A and B) is investigated through a 3³ factorial design. For sludge A, a constant drying flux period is observed, while sludge B is characterized by a long decreasing drying flux phase. A sensitivity analysis shows that temperature is the main operating parameter affecting the drying kinetics. Mass and heat transfer coefficients as well as water evaporation capacities are calculated from drying curves. Transfer coefficients are related to operating conditions through dimensionless relations. For both sludges, a linear relation is found between water evaporation capacity and the maximal measured drying flux.     

Some Effects of Structure,Composition and Cure on the Water Absorption and Glass Transition Temperature of Amine-cured Epoxies

The effect of structure, composition, and cure on the water absorption and T_g of amine-cured epoxies was investigated. Water absorption is considered to depend on the polar group concentration and type, and on the amount of free volume in the polymer network. The contribution of polar groups in terms of their hydrogen bonding capabilities is reflected by the effect of meta (with respect to the diglycidylamino group) chloro, bromo, and methyl substituents on the water absorption of bis[N,N-bis(2,3-epoxypropyl)-4-aminophenyl]methane cured with 4,4′-diaminodiphenylsulphone. The observed water absorptions are in line with the expected electronic effects of the substituents on the basicity of the amine group. Substituents in the ortho position adversely affect the hydrogen bonding capability of the amine group and limit the extent of reaction by steric interference. Examination of four O-glycidyl systems (Epon 825, Epon 1153/114, Epon 1031, and Dow XD-7342) cured with 4,4′-diaminodiphenylsulphone has revealed quite a good linear relationship between the equilibrium water absorption and T_g for a particular hardener concentration irrespective of the epoxy compound employed. Networks ranged from those of low T_g (110°C) and water absorption (1.3%) to those of high values (300°C and 6.1%) for these parameters. Differences in slope for low (50-65%) and high (100%) stoichiometric amounts of hardener are attributed to differences in the relative importance of OH/epoxy and NH₂ or NH/epoxy reactions. The theoretical polar group concentrations and polar group type are much the same for these different systems and thus, free volume is considered to be a function of T_g and to play an important part in determining the level of water absorption.     

Study of the Effects of Aging under Humidity Control on the Thermal Decomposition of NC/NG/BTTN/RDX Propellants

The effects of aging under controlled humidity on the thermal decomposition of two nitrate ester/RDX propellants are examined. Propellant samples are artificially aged at 60 °C and 70 °C at various levels of relative humidity. Differential scanning calorimetry is used to study the post aged samples to determine the activation energy of the peak exotherm and peak temperature of these events. For each humidity level, differential scanning calorimetry is conducted on an aged and an unaged sample that is conditioned to the humidity of the environment to distinguish between aging effects and residual moisture effects. Nitrate ester stabilizer depletions rates are presented as a function of aging and humidity. The results of the study show that moisture level during aging irreversibly alters the activation energy of the primary heat release events and significantly influences the stabilizer depletion rates.     

A Study of Chemical Interactions at the Stainless Steel/Polymer Interface by Infrared Spectroscopy. Part 2: Mechanical Properties and Study of the Interphase

The interaction of a thermoplastic ethylene-maleic anhydride copolymer with stainless steel has been studied by infrared spectroscopic techniques (FTIR). The aim was to improve understanding of the reaction processes at the steel/polymer interface in order to optimize the quality of assemblies in terms of adhesion and durability under the conditions which will subsequently be those of normal operation.

Steel/polymer associations have been tested after being submitted to several different conditions of treatment and aging in order to understand the various phenomena which occur at the steel/polymer interphase.

Mechanical behavior improves after heat treatment, and similar conclusions can be transposed to the structure after use, such as in domestic equipment. Modifications in interactions between stainless steel and polymer are caused first by the chemical reactivity of anhydride functions, and second by the mobility of organic chains which reorganize at the interphase.

Analysis of failure surfaces shows several correlations between the mechanical behavior and the chemical nature of residual polymer on the metal substrate. Localization of failure depends on aging conditions and can be explained by minimization of interfaical energy between the polar structure of the metal surface and the organic chains.     

Chemical interaction of D9 alloy clad with B4C in liquid sodium: Studies employing XPS,XRD, and SEM

A cell representing typical control rod subassembly of the prototype fast breeder reactor is designed to probe the liquid sodium-mediated chemical interaction of boron carbide (B₄C) control rod with the D9 alloy clad. The cell was equilibrated at 973 K for 5000 hours with liquid sodium in the annular gap. XRD shows the formation of Cr₃C₂ and Fe₂B along with oxides of Ni, Cr, and Fe. XPS studies reveal the diffusion of boron and carbon up to a depth of about 160 and 120 μm, respectively. A boron-rich region is observed up to a depth of about 40 μm which consists of B³⁺ arising from oxides and a nearly constant elemental boron region, extending up to a depth of 160 μm. The highly reacted zone extends up to a depth of about 40 μm consisting of oxides of most of the elements of D9 clad exhibiting a higher valence states. As the cell is helium leak tested, oxygen out gassed from B₄C at 973 K played a major role in chemical oxidation of the constituents of the D9 alloy which can be minimized by using high-density B₄C.     

环氧树脂及其改性树脂的低温性能分析和增韧研究(Ⅰ):低温性能分析

对环氧树脂及其改性后树脂的低温性能、动态性能进行了试验研究 ,得到环氧树脂及其增韧树脂在低温情况下材料特性 ;并对材料的断口照片进行了分析 ,得出在低温、低载荷作用下的橡胶增韧双酚A改性的环氧树脂共混体系中 ,共混体性能此时以橡胶颗粒的性能作为主导性能出现。     

化工原理和化工设备机械基础两门课课程设计结合的思考与实践

针对化工原理课程设计和化工设备机械基础课程设计中存在的现实问题,我们将两门课的学习时间调到同一学期,让学生在同一时间学习两者的相关内容。在安排课程设计时,化工原理课程设计和化工设备机械基础课程设计时间作对接安排,内容安排上将化工原理课程设计和化工设备机械基础课程设计的对象安排为同一单元操作设备,指导学生将化工原理课程设计得到的工艺参数直接用于后面的强度计算和设备设计,收到了显著的教学改革效果。     

熔剂化学组成对陶瓷薄板坯体断裂模数影响的探究

陶瓷薄板作为一种新型建筑装饰材料,其配方和工艺技术应用方面还需不断提升,陶瓷研究者们也一直致力于陶瓷薄板的探究.笔者通过对K2 O(Na2 O)-SiO2-Al2 O3体系配方中不同化学组成熔剂对陶瓷薄板坯体烧后机械强度的影响研究,开发出一种断裂模数达94.77 MPa的陶瓷薄板坯体配方.     

The Influence of Temperature and Composition on the Operation of Al Anodes for Aluminum‐Air Batteries

The influence of composition and temperature on the anode polarization and corrosion rate of pure Al and Al‐In anodic alloys in 8M NaON electrolyte has been investigated. High current density (more than 800 mA cm⁻²) and faradaic efficiency over 97% were observed for all investigated alloys at 60 °C. Lower temperature provides lower current density (200–300 mA cm⁻² at 40 °C, and less than 100 mA cm⁻² at 25 °C). Different formation of the product reaction layers was observed for pure aluminum and Al–0.41In alloy, leading to the different polarization character of the samples. The comparison of two Al‐In alloys with similar composition has been carried out. Al–0.45In alloy having a coarse‐grained structure had a more positive no‐current potential and lower value of anode limiting current (200 mA cm⁻² vs. 300 mA cm⁻²) compared with the fine‐grained Al–0.41In alloy, as well as greater parasitic corrosion rate and greater no‐current corrosion. The current‐voltage, power and discharge characteristics of the aluminum‐air cell with Al–0.41In anode and gas diffusion cathode have been investigated. Open circuit voltage of the cell is 1.934 V and the maximum power density of the cell is 240 mW cm⁻² at the voltage of 1.3 V.     

地方性高校《化学反应工程》课程的教学探索与改进

化学反应工程是化工类专业的核心课程,目的培养学生的工程意识。根据化学反应工程这门课程的特点,结合我校目前的教学状况,从教材的选择、课堂教学、教师的自身修养和专业实验等方面来实施教学改进,促进学生的学习热情和工程认知能力,增强学生的实践能力。     

Effects of Storage Temperature, Atmosphere and Light on Chemical Stability of Astaxanthin Nanodispersions

Astaxanthin, as a functional lipid, can be incorporated easily into different water-based food formulations in the form of a nanodispersion. In this study, astaxanthin nanodispersions were produced using different stabilizer systems, namely, polysorbate 20 (PS20), sodium caseinate (SC), gum arabic (GA) and an optimum combination of these three stabilizers (OPT). Since astaxanthin is sensitive to oxidative damage, its degradations kinetics in the prepared nanodispersion systems were investigated as a function of storage temperature, atmosphere and light. The results showed that astaxanthin degradation followed a first-order kinetic and, in most cases, astaxanthin was more stable in optimum-formulated three-component-stabilized nanodispersions as compared to nanodispersion systems stabilized by individual stabilizers. In addition, high storage temperature and intense illumination significantly (P < 0.05) increased the degradation of astaxanthin, while oxygen-free conditions significantly (P < 0.05) reduced the astaxanthin degradation rate.     

锅炉腐蚀的形成及化学清洗

简述了锅炉爆管事故的原因,综合分析了锅炉管束腐蚀的形成和危害。介绍了化学清洗的方法、作用及清洗效果的测试技术。     

地方高校化工原理实验教学改革初探

结合《化工原理实验》课程的特点,本文介绍了对《化工原理实验》进行的教学改革,即通过强调实验类型分类、对设计型实验进行项目化教学、增加计算机在实验数据处理中的应用和探索成绩评定方式,激励学生的学习积极性和主动性,培养学生的工程概念和工程意识,促进学生实践能力和创新能力的发展。     

Mechanistic Modeling of Pollutant Removal,Temperature, and Evaporation in Chemical Air Scrubbers

Chemical air scrubbers reduce the concentration of water‐soluble components such as ammonia from the outgoing ventilation air through absorption in water, followed by chemical conversions and removal of the end products. A mechanistic model for a countercurrent air scrubber was set up. Mass balances for ammonia, hydrogen sulfide, nitrous oxide, and methane were implemented, as well as the water mass balance and heat balances. The model was validated against experimental data from a conventional fattening pig housing facility. The effect of influent characteristics, design parameters, and control handles on the removal efficiency, the temperature profile, and the water evaporation rate were investigated through simulation. The model was able to describe the behavior of a countercurrent chemical air scrubber.     

Experimental Investigation of Air Relative Humidity (RH) Cycling Tests on MEA/Cell Aging in PEMFC Part I: Study of High RH Cycling Test With air RH at 62%/100%

The effect of high air relative humidity (RH) cycling (RH_C 62%/100%) on the degradation mechanisms of a single (5 × 5 cm²) proton exchange membrane fuel cells was investigated. The cell performance was compared to a cell operated at constant humidification (RH_C = 62%). Runs were conducted over approximately 1,500 h at 0.3 A cm^–2. The overall loss in cell performance for the high RH cycling test was 12 μV h^–1 whereas it was at 3 μV h^–1 under constant humidification. Impedance spectroscopy reveals that the ohmic and charge transfer resistances were little modified in both runs. H₂ crossover measurement indicated that both high RH cycling and constant RH test did not promote serious effect on gas permeability. The electroactive surface loss for anode and cathode during high air RH cycling was more significant than at constant RH operation. The water uptake determined by ¹H nuclear magnetic resonance within the membrane electrode assembly (MEA) after high RH cycling was reduced by 12% in comparison with a fresh MEA. Transmission electron microscopy showed bubbles and pinholes formation in the membrane, catalyst particles agglomeration (also observed by X‐ray diffraction), catalyst particles migration in the membrane and thickness reduction of the catalytic layers. Scanning electron microscopy was conducted to observe the changes in morphology of gas diffusion layers after the runs.