双氰胺及其衍生物固化环氧树脂性能的研究EI北大核心

选用甲基丙烯酸钝化 2 ,4-咪唑作为促进剂 ,研究了它促进双氰胺及苯胺甲醛改性双氰胺 (TH- 11)固化环氧树脂的反应 ,并对这一体系在低沸点溶剂中的溶解性、固化产物的力学性能及复合材料的力学性能进行了测试。结果表明 ,双氰胺在树脂及树脂溶液中具有良好的分散性是得到高性能复合材料的重要条件之一 ,改变双氰胺的结构及在固化体系中加入促进剂都会影响到体系的贮存性 。     

双氰胺及其衍生物固化环氧树脂性能的研究

选用甲基丙烯酸钝化２,４－咪唑作为促进剂,研究了它促进双氰胺及苯胺甲醛改性双氰胺（ＴＨ－１１）固化环氧树脂的反应,并对这一体系在低沸点溶剂中的溶解性,固化产物的力学性能及复合材料的力学性能进行了测试。结果表明,双氰胺在树脂及树脂溶液中具有良好的分散性是得到高性能复合材料的重要条件之一,改变双氰胺的结构及在固化体系中加入促进剂都会影响到体系的贮存性,加速固化反应的进行。     

新型改性双氰胺固化剂对环氧树脂的固化行为研究

用苯肼对双氰胺进行改性,合成得到一种新型改性双氰胺固化剂LB-A,探讨了LB-A对环氧树脂的固化行为及反应机理。红外光谱和X射线衍射分析表明,苯肼对双氰胺进行改性后,破坏了双氰胺的规整结构和强结晶性,从而较好地解决了双氰胺与环氧树脂混溶性不佳的问题,并且分子中引入了更多的活泼基团,提高了其与环氧树脂的反应活性。差热分析研究结果表明,相对于双氰胺固化E-44环氧树脂的固化条件(160～180℃/20～60min),LB-A固化环氧树脂的固化温度显著降低,其在110℃/40min或90℃/5h就可以使E-44完全固化,且固化物具有很好的力学性能。     

盐酸二甲双胍缓释胶囊质量标准提高的研究

目的：对现有的盐酸二甲双胍缓释胶囊的质量标准进行提高。方法：在原标准基础上增加了对单杂的控制：降低了双氰胺的限度。结果：有关物质的检测方法成立。双氰胺在0．005μg／ml-0．6μg／ml浓度范围内线性关系良好,（r=0．99999）。结论：所建立的方法简便、准确,能有效地控制产品质量。     

农药常用符号的识别

PC(百分浓度)表示药剂中有效成分的百分含量。EC(有效浓度)表示能将防治对象,比如害虫、病菌或杂草毒死而对作物安全无害的浓度。LG(致死浓度)能引起受试动物死亡的浓度。MED(最大有效     

几种化学药剂在解除林木种子休眠中的应用

简要介绍了浓H2SO4处理、NaOH、NaCO3处理、KNO3处理等几种主要的化学药剂在林木解除休眠中的应用，认为在林业科研与生产中应根据种子休眠的类型不同而采用相应的化学药剂，同时应严格注意处理浓度和处理时间。     

3221中温固化环氧树脂体系的固化反应

采用DSC方法研究了不同固化体系对3221环氧树脂固化体系固化反应的影响,探讨了反应机理,分析了双氰胺及双氰胺 取代脲作为固化剂的反应动力学,预测了氰胺 取代脲固化体系的固化工艺参数,并加以验证。结果表明,采用双氰胺 取代脲的复合固化体系能使3221体系的表观活化能Ea比单独使用双氰胺时降低58 kJ/m o l,前者固化温度比后者降低50℃左右,并能使反应缓和。     

双氰胺在胶膜中的分布状态及其对胶接性能的影响

一、前言双氰胺是环氧树脂较好的潜伏性固化剂。由于双氰胺在一般树脂溶液中是不溶解的,分散的微粒易沉淀析出,给胶粘剂的贮存和使用都带来困难,而且直接影响胶接强度。但是,双氰胺在膜状胶粘剂中的分布状态及其对胶接性能的影响,目前尚未见到报导。     

RO膜外壳用环氧树脂/双氰胺树脂体系的反应机理

双氰胺(DCD)是一种常用的潜伏性固化剂,环氧树脂(EP)/双氰胺树脂体系可用于分离膜外壳的生产中,对环氧树脂/双氰胺树脂体系的反应机理进行了分析.利用差示量热法得到固化反应过程曲线和固化物松弛过程曲线,对反应前后树脂体系进行红外光谱分析,采用模型拟合法研究了固化反应机理和反应行为,计算出固化反应活化能为60.2 kJ/mol,固化物松弛过程所需的活化能为12 515 kJ/mol.     

氰化钠药剂制备与自动添加技术在四方金矿的应用

通过对氰化钠药剂制备与添加系统中存在问题的分析与研究,对其进行技术改造,通过改造,稳定了制备药剂的＇浓度,更能精确控制浸出系统的CN质量浓度,稳定了生产工艺;降低了氰化钠的消耗,降低了选矿成本,实现了节支降耗的目的,取得了良好的经济效益。     

Effects of particle size of reactant on characteristics of combustion synthesis of TiC-Fe cermet

Four Ti-C-Fe powder mixtures, with a same molar ratio but a different particle size, were used for a combustion synthesis of TiC-Fe cermet to investigate effects of the particle size on the characteristics of the combustion synthesis. The results showed that the mixture with the finer Ti powder gave out a higher combustion temperature, a higher reaction velocity, a higher product density, a layer-shaped pore, and a greater size of TiC particles whether the Fe powder was finer or coarser. While in the case of the coarser Ti powder used, a small amount of residual phase remained in the product, and what is more interesting that the mixture with the finer Fe powder gave out a lower reaction velocity than that by the mixture with the coarser Fe powder. These effects were successfully explained with the previously proposed mechanisms of the combustion synthesis of TiC-Fe, and the mechanisms were proved to be valid thereby.     

Effect of different factors on coke combustion in a highly concentrated polydisperse ascending flow

A study was made of the effect of ash content, the initial concentration of oxidant, and particle interactions on the parameters of the physicochemical processes occurring in the combustion of anthracite fines in a highly concentrated polydisperse ascending flow. The possibility of regulating the temperature of the gas-dust mixture is discussed.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 60, No. 2, pp. 225–231. February, 1991.     

Radiative heat transfer in splash and dilution zones of the pressurized oxy-fuel combustion CFB considering particle-dependent scattering

Radiative heat transfer is dominant in splash and dilution zones of the oxy-fuel combustion pressurized circulating fluidized bed (PCFB). However, the particle radiation fields interact with each other due to the high particle concentration. Moreover, the particle concentration distribution, the flue gas components and pressure change drastically due to pressurized oxy-fuel combustion technology. In this paper, the radiative heat transfer in splash and dilution zones of the oxy-fuel combustion PCFB is investigated when particle-dependent scattering is considered. The results show that the maximum error of the particle radiation model is less than 1% in predicting the incident heat flux at the wall when particle-dependent scattering is considered. The particle concentration distribution has a significant impact on the radiative heat transfer in splash and dilution zones of oxy-fuel combustion PCFB. The simplified particle concentration distribution model cannot capture the zero-source term phenomenon in the core region and has a large error in the annular region. In addition, the mechanism and importance of the flue gas composition and pressure on the radiative heat transfer in splash and dilution zones of oxy-fuel combustion PCFB are analyzed.     

Excitation of acoustic vibrations upon combustion of droplets of liquid fuel at supercritical pressure

Theoretical investigation of the excitation of acoustic vibrations upon combustion of liquid fuel droplets at a supercritical pressure of a gaseous mixture is carried out. The droplets are assumed to be spherical and mono-dispersed. The combustion is assumed to run in the diffusion regime. The binary diffusion coefficients are taken equal and independent of the concentration of the components of the gaseous mixture. The Lewis number is assumed to be unity. The flow is considered to be one-dimensional; the mixing in the transverse direction is assumed to be complete, with no mixing in the longitudinal direction. The rate of combustion at supercritical pressure of the gaseous mixture is calculated on the basis of the modified quasi-stationary theory. Expressions for the frequency and excitation increment of acoustic vibrations are obtained in this paper; the properties of the fuel and the oxidizer are explicitly taken into account.     

Experimental study on flames propagating through zirconium particle clouds

To reveal the mechanisms of flame propagation through the hardly volatile metal dust clouds clearly, the flame propagating through zirconium particle clouds has been examined experimentally. A high-speed video camera was used to record the propagation process of the flame. Combustion zone temperature was detected by a fine thermocouple. Based on the experimental results, structure of flame and combustion courses of zirconium particles were analyzed, the combustion propagation in zirconium dust was investigated, and the velocity and temperature characteristics of the combustion zone were also elucidated. The combustion zone propagating through zirconium particle clouds consists of luminous particles. Particle concentration plays an important role in the combustion zone propagation process. With the increase of zirconium particle concentration, the maximum temperature of the combustion zone increases at the lower concentration, takes a maximum value, and then decreases at the higher concentration. It is also found that the propagation velocity of the combustion zone has a linear relationship with its maximum temperature.     

Extinction Threshold in Random Heterogeneous Condensed Mixtures with an Extremely Small Amount of a Combustible

A mathematical model describing the process of combustion of heterogeneous condensed mixtures with account for the randomness of the distribution of combustible particles over the system is proposed. The step dependence of the reaction rate on the temperature is used as a model of chemical kinetics. The case where the concentration of the particles is extremely low but the heat energy released in their combustion is high has been investigated. It is shown that for an adiabatic system there exists a concentration limit of combustion. The relation of this combustion limit to the geometric phase transition occurring in a heterogeneous condensed mixture with rare combustion inclusions has been demonstrated. An analytical approach to the evaluation of the threshold concentration of the combustible in such systems, based on the continual theory of percolation, is proposed.     

Effect of KCl, NaCl and CaCl2 mixture on volume combustion synthesis of TiB2 nanoparticles

Preparation of titanium diboride (TiB₂) nanoparticles was carried out by volume combustion synthesis. TiO₂, B₂O₃ and elemental Mg were mixed with 0-60% salt mixture of KCl, NaCl and CaCl₂ with increment of 15% as a low melting temperature diluent. Compressed samples were synthesized in a tubular furnace at a constant heating rate under argon atmosphere. Thermal analysis of the process showed that the addition of the low melting temperature salts mixture led to a significant decrease in ignition and combustion temperatures. Synthesized samples were then leached by nitric and hydrochloric acids to remove impurities. The samples were examined by XRD, SEM and DLS analysis. The results showed the formation of fine deagglomerated particles with the addition of the salts mixture. The results revealed that 45% salts mixture had the smallest average particle size of about 90 nm.     

Dual-solution-precipitation mechanism of combustion synthesis of TiC-Fe cermet with fine Ti powder

A Ti-C-Fe powder mixture with a finer Ti powder was used for a combustion front quenching test to investigate the effect of titanium particle size on the mechanism of the combustion reaction, and the microstructural evolution in the quenched specimen was then observed with scanning electron microscopy, and the combustion temperature was also measured. The results showed that the nature of the combustion reaction could be described with a dual-solution-precipitation mechanism and a correspondent model. The melting of the finer Ti particle prior to its reaction was attributed to a combined effect of two factors: a decrease of its size-controlled melting point, and a decrease of its composition-controlled melting point. The use of the finer Ti powder led to a more complete combustion reaction and hence a higher combustion temperature. As a result, the combustion-synthesized TiC-Fe cermet had a greater average size of TiC particles and layer-shaped pores that was confirmed to be a consequence of gathering of the evolved gases into the combustion wavefront.     

Mixture of fuels approach for the solution combustion synthesis of Al2O3-ZrO2 nanocomposite

A modified solution combustion approach was used for the first time in the preparation of nanosize zirconia toughened alumina (ZTA) composite. ZTA-1 with an average particle size of ∼37 nm was prepared using corresponding metal nitrates and urea. ZTA-2 with an average particle size of <10 nm was prepared by using mixture of fuels such as ammonium acetate, urea and glycine. The products formed were characterised by powder X-ray diffractometry, Transmission electron microscopy and BET surface area analysis. By using mixture of fuels, the energetics of the combustion reaction and eventually the properties of the combustion product have been changed. A series of combustion reactions were carried out to optimise the fuel ratio combinations required to obtain <10 nm ZTA particles. The microstructure of ZTA consisted of crystallites of Al₂O₃ and ZrO₂ both of which were nanocrystalline as evident from TEM.     

Diesel combustion of oil and refrigerant mixture during pump-down of air conditioners

Compressor-destruction accidents during the pump-down operation of air conditioners were experimentally investigated. Assuming air penetration into refrigerant tubes, the gaseous mixture of the air, refrigerant, and lubricating oil for a compressor was compressed by the compressor with different refrigerant concentrations, and the diesel combustion of the mixture was examined. The compressor was simulated by a small-scale engine. R1234yf, R32, R410A, R134a, R22, and R125 were tested as refrigerants. The mixture burned via adiabatic compression when the refrigerant concentration was low, which means that accidents during the pump-down were caused by the diesel combustion of the mixture. The refrigerant burned and caused intense pressure increase. The mixture without the oil did not burn under any refrigerant concentration, which suggests that oil is necessary for the combustion. These phenomena were observed in the results for R1234yf, R32, R410A, R134a, and R22. Thus, combustion was observed under certain conditions even for refrigerants categorized as non-flammable.