微胶囊红磷和聚苯醚对高抗冲聚苯乙烯的协同阻燃作用

利用微胶囊红磷(MRP)和聚苯醚(PPO)来提高高抗冲聚苯乙烯(HIPS)的阻燃性能, 通过熔融共混法制备了一系列不同组成的MRP-PPO/HIPS复合材料。采用水平燃烧、垂直燃烧、氧指数、锥形量热分析、高温热分解实验等方法研究了复合材料的阻燃性能。研究表明, 阻燃剂用量相同时, 在HIPS基体中同时加入MRP和PPO得到的复合材料比单独加入MRP或PPO得到的复合材料具有更好的阻燃性能。当MRP-PPO/HIPS的质量比为10:20:70时, 复合材料的氧指数为23.9%, 水平燃烧级别达到FH-1级, 垂直燃烧级别达到FV-0级, 阻燃性能达到最佳。MRP用量过多时, 复合材料的阻燃性能下降。研究认为, PPO和MRP对HIPS具有较强的协同阻燃作用。两者以适当比例并用时能够使复合材料在燃烧时的热释放速率和燃烧热大幅度减小, 降低了气相燃烧区的温度, 起到气相阻燃作用。同时, 复合材料在热分解和燃烧时能够生成连续和致密的炭层, 抑制了燃烧过程中的热量传递和物质交换, 起到凝聚相阻燃作用。因此, 复合材料的阻燃性能显著改善。     

Mg(OH)2-Al(OH)3-微胶囊红磷/高抗冲聚苯乙烯无卤阻燃复合材料

以氢氧化镁(MH)、氢氧化铝(ATH)和微胶囊红磷(MRP)为无卤阻燃剂,高抗冲聚苯乙烯(HIPS)树脂为聚合物基体,通过熔融共混法制备了一系列不同组成的MH-ATH-MRP/HIPS复合材料.采用水平燃烧、垂直燃烧、氧指数、锥形量热分析、高温热分解实验等方法研究了复合材料的阻燃性能.结果表明,阻燃剂用量相同时,在HIPS基体中同时引入MH和ATH得到的复合材料比单独加入MH或ATH得到的复合材料具有更好的阻燃性能.当MH-ATH/HIPS的质量比为70∶30∶100时,复合材料的水平燃烧级别达到FH-1级,氧指数为25.2％,但垂直燃烧无级别.在上述体系中加入极少量的MRP(占复合材料的质量分数为2.9％)就可使复合材料的火灾性能指数(FPI)提高85％,燃烧过程中热量释放和质量损失更慢、成炭能力明显增强,垂直燃烧级别达到FV-0级.当MH-ATH-MRP/HIPS的质量比为21∶9∶12∶100时,复合材料的各项阻燃性能达到最佳,可以大幅度减少阻燃剂的用量.MH、ATH和MRP对HIPS具有非常显著的协同阻燃作用.同时加入MH和ATH时不仅可以在更宽的温度范围内抑制HIPS的升温和分解,而且能够在更宽的温度范围内相继释放出水蒸气稀释氧气和可燃气体的浓度,从而起到协同阻燃作用.加入MRP后复合材料的成炭能力大大增强,进一步改善了凝聚相阻燃的效果,因此阻燃性能显著提高.     

无卤阻燃高抗冲聚苯乙烯及其增韧研究

以可膨胀石墨(EG)和微胶囊红磷(MRP)为无卤阻燃剂对高抗冲聚苯乙烯(HIPS)进行阻燃改性,通过熔融共混法制备了一系列不同组成的HIPS/EG/MRP复合材料。采用氧指数、水平燃烧和垂直燃烧方法研究了复合材料的阻燃性能,研究表明,在阻燃剂用量相同时,与单独加入EG和MRP相比,同时加入EG和MRP所制备的HIPS复合材料的阻燃性能更好,当HIPS/EG/MRP的质量比为70/20/10时,HIPS复合材料的阻燃性能最佳,氧指数可达27.4%,水平燃烧性能和垂直燃烧性能分别达到FH-1级和FV-0级。在最佳阻燃剂配比下,研究了苯乙烯-丁二烯-苯乙烯共聚物(SBS)对HIPS复合材料的阻燃性能和力学性能的影响,结果表明,SBS的加入能够有效的改善HIPS复合材料的力学性能,且几乎不影响其阻燃性能。     

Mg(OH)2-Al(OH)3-微胶囊红磷/高抗冲聚苯乙烯无卤阻燃复合材料

以氢氧化镁(MH)、氢氧化铝(ATH) 和微胶囊红磷(MRP) 为无卤阻燃剂, 高抗冲聚苯乙烯(HIPS) 树脂为聚合物基体, 通过熔融共混法制备了一系列不同组成的MH-ATH-MRP/HIPS复合材料。采用水平燃烧、垂直燃烧、氧指数、锥形量热分析、高温热分解实验等方法研究了复合材料的阻燃性能。结果表明, 阻燃剂用量相同时, 在HIPS基体中同时引入MH和ATH得到的复合材料比单独加入MH或ATH得到的复合材料具有更好的阻燃性能。当MH-ATH/HIPS的质量比为70:30:100时, 复合材料的水平燃烧级别达到FH-1级, 氧指数为25.2%, 但垂直燃烧无级别。在上述体系中加入极少量的MRP(占复合材料的质量分数为2.9%)就可使复合材料的火灾性能指数(FPI) 提高85%, 燃烧过程中热量释放和质量损失更慢、成炭能力明显增强, 垂直燃烧级别达到FV-0级。当MH-ATH-MRP/HIPS的质量比为21:9:12:100时, 复合材料的各项阻燃性能达到最佳, 可以大幅度减少阻燃剂的用量。MH、ATH和MRP对HIPS具有非常显著的协同阻燃作用。同时加入MH和ATH时不仅可以在更宽的温度范围内抑制HIPS的升温和分解, 而且能够在更宽的温度范围内相继释放出水蒸气稀释氧气和可燃气体的浓度, 从而起到协同阻燃作用。加入MRP后复合材料的成炭能力大大增强, 进一步改善了凝聚相阻燃的效果, 因此阻燃性能显著提高。     

MgO-微胶囊红磷/高抗冲聚苯乙烯复合材料的阻燃性能

通过熔融混合方法把MgO和（或）微胶囊红磷（MRP）加入高抗冲聚苯乙烯（HIPS）基体中制备了一系列不同组成的MgO-MRP/HIPS复合材料。采用极限氧指数（LOI）、垂直燃烧（UL-94）、锥形量热分析、TGA、SEM、XRD、FTIR等方法研究了复合材料的阻燃性能。结果表明,MgO和MRP单独使用时对HIPS的阻燃作用较小,但是当二者以适当比例共同使用时对HIPS有明显的协同阻燃作用。当MgO∶MRP∶HIPS的质量比为35∶15∶100时,复合材料的LOI为24.7%,UL-94级别达到V-0级,热释放速率和总热释放量显著降低,表现出良好的阻燃性能。MgO-MRP/HIPS复合材料在无氧条件下热分解时,MgO、MRP与HIPS之间无相互作用。但是,在空气中热分解或燃烧时,MgO和MRP均能够促进HIPS成炭。MgO-MRP/HIPS复合材料燃烧时能够在材料表面生成连续致密的炭层,起到防火屏障作用,提高材料的阻燃性能,燃烧残余物主要由结晶性MgO和含磷的无定形碳组成。此外,MgO-MRP/HIPS复合材料燃烧时MRP在气相也起到了一定的阻燃作用。     

环氧树脂/微胶囊红磷体系对高抗冲聚苯乙烯阻燃性能的研究

用锥形量热仪、TGA、LOI及UL94垂直燃烧研究了Novolac对MRP阻燃高抗冲聚苯乙烯(HIPS)性能的影响.结果表明,在MRP阻燃HIPS中添加适量的Novolac,可以使材料的阻燃性能满足使用要求,且随着Novolac用量的增加,材料的阻燃性能和热稳定性上升.     

水菱镁石-Mg(OH)_2协同聚乙烯阻燃复合材料的性能与分解行为

以水菱镁石(HM)和Mg(OH)_2为阻燃剂,利用双螺杆挤出机制备了一系列HM-Mg(OH)_2协同聚乙烯(PE)阻燃复合材料。采用垂直燃烧仪、极限氧指数仪、锥形量热仪和拉伸性能测试仪分别测试了HMMg(OH)_2协同PE阻燃复合材料的阻燃性能和拉伸性能,采用热重分析仪研究了HM-Mg(OH)_2协同PE阻燃复合材料的热分解行为。结果表明,HM与Mg(OH)_2以适当比例复配作为阻燃剂能在更宽的燃烧温度范围内发生分解,起到更好的阻燃效果,在极限氧指数和拉伸强度不变的前提下,HM-Mg(OH)_2协同PE阻燃复合材料的成本大幅下降。两种阻燃剂协同可以减少复合材料点燃初期的无效甚至负面分解,保留了HM分解产物对PE基体高温下分解的抑制作用,同时还可以在燃烧区域表面形成较为稳定和不易破坏的鳞片状保护层,加之复合阻燃剂总体更高的总分解释放率,多种因素共同作用,使复合材料的阻燃效果提高。当HM和Mg(OH)_2以质量比1∶2协同且用量达到复合材料总质量的60wt%时,HM-Mg(OH)_2协同PE阻燃复合材料的极限氧指数为28%,垂直燃烧级别达到UL-94V-0级,拉伸强度达到28.8 MPa。     

三聚氰胺氰尿酸盐改性PPO/PS复合材料的燃烧性能和流动性能

以无卤阻燃剂三聚氰胺氰尿酸盐(MCA)为改性剂, 采用熔体共混法制备了改性聚苯醚/聚苯乙烯 (PPO/PS)复合材料。通过XRD和SEM对MCA-PPO/PS复合材料的微观结构进行了表征, 重点研究了复合材料的燃烧性能和流动性能。研究发现: 在复合材料的制备和加工过程中MCA的微观结构并没有发生任何变化, 因此复合材料中MCA的阻燃作用不变。MCA在复合材料中分散比较均匀, 无明显团聚现象。与纯PS相比, 质量比为100:100的PPO/PS在燃烧时的氧指数增加5.4%, 热释放速率峰值降低33.1%, 但总烟释放量增加近1.5倍。在PPO/PS中加入MCA后得到的复合材料的阻燃性能随着MCA用量增加而逐渐增强, 发烟量大幅度降低, 同时熔体黏度减小, 流动性增加。在MCA-PPO/PS复合材料中加入5%、 25%和45%质量分数的MCA可分别使复合材料的总烟释放量比PPO/PS降低43.7%、 82.6%和91.6%。PPO/PS的阻燃机制为凝聚相成炭阻燃, 随着MCA用量增加, MCA-PPO/PS复合材料的阻燃机制逐渐转变为气相稀释和对聚合物基体的冷却效应。加入MCA对MCA-PPO/PS复合材料可同时起到阻燃、 抑烟和改善加工流动性的作用。     

高抗冲聚苯乙烯的无卤阻燃

采用熔融共混法制备出了高抗冲聚苯乙烯(HIPS)/高性能纳米氢氧化铝(nano-CG-ATH)/包覆红磷(ERP)/改性聚苯醚(MPPO)无卤阻燃复合材料,研究了nano-CG-ATH、ERP和MPPO对HIPS基复合材料阻燃性能、力学性能和热稳定性的影响;利用扫描电镜分析了HIPS基复合材料燃烧后的炭层形貌;利用傅里叶变换红外光谱分析了HIPS/nano-CGATH/ERP/MPPO(60/6/9/25)复合材料及其经不同温度热处理后残留物的结构。结果表明,nano-CG-ATH、ERP和MPPO之间有很好的协效阻燃效果,当nano-CG-ATH用量为6%(质量分数,下同),ERP用量为9%,MPPO用量为25%时,HIPS复合材料的极限氧指数达到27.5%,UL-94级别达到V-0级;该复合材料的拉伸强度达到30.04 MPa,弯曲模量达到2485.60 MPa;热分解后残留物质的量达到10.58%。但是该复合材料的冲击性能有待提高。     

苯并噁嗪与微胶囊红磷及丁腈橡胶对ABS的阻燃增韧

采用苯并噁嗪(BOZ)与微胶囊化红磷(MRP)复配制备了无卤阻燃丙烯腈-丁二烯-苯乙烯共聚物(ABS)。研究了BOZ/MRP质量比和用量对阻燃ABS性能的影响。然后固定BOZ和MRP的用量,考察丁腈橡胶(NBR)的添加量对BOZ/MRP/ABS阻燃体系阻燃性能和力学性能的影响。结果表明,BOZ/MRP质量比为3:2,总量为20%(质量分数)时,可制得氧指数(LOI)达24.4%,垂直燃烧达UL-94 V-0级的无卤阻燃ABS;BOZ受热产生的酚羟基与红磷燃烧产生的氧化磷等发生酯化反应减缓了ABS的分解;NBR添加量为8%时,阻燃体系垂直燃烧达V-0级,拉伸强度为30.8 MPa,缺口冲击强度达11.4 kJ/m2。     

As-cast microstructures and behavior at high temperature of chromium-rich cobalt-based alloys containing hafnium carbides

Hafnium is often used to improve the high temperature oxidation resistance of superalloys but not to form carbides for strengthen them against creep. In this work hafnium was added in cobalt-based alloys for verifying that HfC can be obtained in cobalt-based alloys and for characterizing their behavior at a very temperature. Three Co–25Cr–0.25 and 0.50C alloys containing 3.7 and 7.4 Hf to promote HfC carbides, and four Co–25Cr– 0 to 1C alloys for comparison (all contents in wt.%), were cast and exposed at 1200 °C for 50 h in synthetic air. The HfC carbides formed instead chromium carbides during solidification, in eutectic with matrix and as dispersed compact particles. During the stage at 1200 °C the HfC carbides did not significantly evolve, even near the oxidation front despite oxidation early become very fast and generalized. At the same time the chromium carbides present in the Co–Cr–C alloys totally disappeared in the same conditions. Such HfC-alloys potentially bring efficient and sustainable mechanical strengthening at high temperature, but their hot oxidation resistance must be significantly improved.     

Measurement of the thermal expansion of metal and FRPs

Thermal expansion is an important parameter for characterization of different binding forces, lattice dynamics, band and crystal structure of any solids. Many investigators have focused their attention to study this property theoretically and experimentally at different temperatures. It is one of the important properties of metals and its alloys, which helps to calculate the thermal stress. This parameter is also used to determine the compatibility of an insulator as load bearing materials. Different experimental setups have been developed to study thermal expansions of the materials using different techniques namely capacitance method, interferometric principle, LASER, optical, quartz tube etc. This paper reviews most of the experimental setups available to measure thermal expansion of metals, alloys, polymers and fibre-reinforced plastics at temperature ranging from 1 to 1100 K.     

Real gas choked flow conditions at low reduced-temperatures

Real gas choked mass flux is calculated for a frictionless stream expanding isentropically until it reaches the speed of sound and without phase changes. The other parameters associated with the choked state are the pressure, density, temperature ratios, and the speed of sound. Departure of the choked mass flux from the ideal gas model is discussed first in absolute terms and then in relative terms, using the Principle of Corresponding States, for gases with boiling points in the low temperature range. Reduced-stagnation pressures are examined up to values of 30 for hydrogen, neon, nitrogen, argon, methane, krypton, xenon, and R-14 and up to 100 for ⁴He. The corresponding reduced-stagnation temperatures go down to 1.4 and in some cases down to 1.2 for nitrogen and argon. Also discussed are the limiting values of stagnation parameters for which no phase change occurs in the choked state. Compared to the ideal gas, the mass flux may almost double and the critical pressure ratio may decrease by an order of magnitude. The relevance of results is discussed qualitatively and quantitatively for Joule-Thomson cryocooling.     

Development of No-Vent™ liquid hydrogen storage system for space applications

A number of technological advances required to store and maintain normal-boiling-point and densified cryogenic liquids, including liquid hydrogen, under zero boil-off conditions in-space, for long periods of time, have been developed. These technologies include (1) thermally optimized compact cryogen storage systems that reduce environmental heat leak to the lowest-temperature cryogen, which minimizes cryocooler size and input power, and (2) actively-cooled shields that surround the storage systems and intercept heat leak. The processes and tools used to develop these technologies are discussed. A zero boil-off liquid hydrogen storage system technology demonstrator for validating the actively-cooled shield technology is presented.     

Analysis of optimum configuration of two-stage thermoelectric modules

In this paper, the theoretical analysis and stimulating calculation were conducted for a basic two-stage thermoelectric module, which contains one thermocouple in the second stage and several thermocouples in the first stage. The study focused on the configuration of the two-stage thermoelectric module, especially investigating the influences of some parameters, such as the allocation of the junction temperature difference in the module, the length of thermocouples and the number of thermocouples, on the cooling performance of the module. The obtained analysis results indicate that changing the junction temperature difference in the second stage, the length of thermocouples and the number of thermocouples in the first stage can improve the cooling performance of the module. These results can be used to optimize the configuration of the two-stage thermoelectric module, and provide guides for the design and application of thermoelectric cooler.     

Development of a miniature cryogenic fluid circuit and a cryogenic micropump

This article presents the development of a miniaturized cryogenic fluid circuit for distributed cooling of low-temperature tracking detectors in high-energy physics (HEP). The heart of the circuit is a prototype cryogenic micropump. This volumetric pump is compatible with cooling powers of about 10-100 W, and capable of producing pressure heads of up to around 0.3 MPa. Besides detector and electronics cooling in HEP, potential applications are found in the field of superconductor technology.     

Effect of cryogenic treatment on microstructure, mechanical and wear behaviors of AISI H13 hot work tool steel

This paper focuses on the effects of low temperature (subzero) treatments on microstructure and mechanical properties of H13 hot work tool steel. Cryogenic treatment at −72 °C and deep cryogenic treatment at −196 °C were applied and it was found that by applying the subzero treatments, the retained austenite was transformed to martensite. As the temperature was decreased more retained austenite was transformed to martensite and it also led to smaller and more uniform martensite laths distributed in the microstructure. The deep cryogenic treatment also resulted in precipitation of more uniform and very fine carbide particles. The microstructural modification resulted in a significant improvement on the mechanical properties of the H13 tool steel.     

Effect of different treatments of copper surface on its total hemispherical absorptivity bellow 77 K

Total hemispherical absorptivity of copper surfaces treated with standard industrial methods was measured in dependence on the temperature of thermal radiation, varying from 25 K to 300 K. The sample temperature was typically from 5 K to 40 K and did not exceed 70 K. Usability of chemical and mechanical Cu surface finishing as well as Cu plating with Ni and Au for cryogenic design is discussed. As an example of practical application of our results, the cryogenic design of a LN₂ trap is presented.     

PU/ST/SA复合微球的制备及血液相容性研究

采用预聚—扩链—中和—分散法合成PU水溶液,将PU、ST、SA溶液按质量比1∶1∶1、1∶1∶2、1∶1∶3进行复合,通过凝聚相分离法制备复合微球。由红外光谱分析样品的化学结构,发现PU与ST和SA之间通过氢键作用复合;由SEM观测微球表面及剖面的形态结构,发现复合微球平均粒径约为2~3mm,表面光滑且内部有很多均匀致密的管状孔隙,适合用作药物释放载体材料;血液相容性测试结果表明,复合微球的动态凝血时间、溶血率以及血小板消耗率均达到了与血液接触材料的国家标准,说明PU/ST/SA复合微球具有良好的血液相容性。