γ-氯丙基三乙氧基硅烷对SiO_2-AgCl复合溶胶凝胶薄膜性能的影响

以正硅酸乙酯(TEOS)为前驱体经γ-氯丙基三乙氧基硅烷(CPTES)改性后制备硅溶胶,与以醇盐硝酸银(AgNO3)为前驱体制备的AgCl溶胶共混后形成复合溶胶,采用浸渍提拉法涂覆于PET基片表面形成SiO2-AgCl复合薄膜,采用SEM、FTIR、机械折叠、接触角测试、烘干质量法、贴膜法研究硅烷偶联剂含量对溶胶-凝胶成膜过程、成膜特性等的影响。结果表明,当摩尔比n(CPTES)∶n(TEOS)=1时可获得表面光滑膜厚均匀,具有良好膜基结合力、疏水性能、耐水性能及抗菌性能的SiO2-AgCl复合薄膜。     

纳米纤维素增强淀粉食品包装材料的研究进展

目的 为了解决纯淀粉材料力学性能低、脆性大等缺点,探索纳米纤维素对淀粉膜材料的影响,为食品包装材料领域和替代传统石油基的高分子材料方向提供新的思路。方法 通过跟进国内外纳米纤维增强淀粉相关研究和应用进展,概括3种纳米纤维素的性能,介绍淀粉食品包装材料未来将面临的挑战和机遇,重点分析纳米纤维素对淀粉膜性能的影响。结论 纤维素纳米纤维（CNF）、纤维素纳米晶（CNC）和微晶纤维素（MCC）对淀粉进行增强后,淀粉复合材料的力学性能、阻隔性能和热学性能均得到改善,纳米纤维素增强淀粉食品包装材料在未来食品包装领域将得到扩展。     

氧化微晶纤维素交联壳聚糖复合膜的制备及性能

目的 制备氧化微晶纤维素交联壳聚糖复合膜,并探索交联改性对壳聚糖复合薄膜性能的影响。方法 首先采用高碘酸钠氧化法对微晶纤维素进行氧化处理,制备氧化微晶纤维素,再通过溶液共混流延法制备不同质量分数(0%、1%、3%、5%、7%、9%)的氧化微晶纤维素交联壳聚糖复合薄膜。通过对复合薄膜组分、形貌、力学性能、光学性能、热稳定性及阻隔性能的表征,考察不同含量的氧化微晶纤维素对壳聚糖薄膜各性能的影响。结果 氧化微晶纤维素表面的醛基能与壳聚糖中的氨基发生交联反应,氧化微晶纤维素的加入可以改善壳聚糖薄膜的拉伸强度和断裂伸长率,复合薄膜的拉伸强度和断裂伸长率最大分别达到了43.07 MPa和19.42%;随着氧化微晶纤维素含量的增大,复合薄膜的紫外屏蔽性能增强,水蒸气透过系数增高,但热稳定性未见明显变化。结论 采用氧化微晶纤维素交联改性壳聚糖可以有效改善壳聚糖薄膜的力学性能和紫外屏蔽性能,有助于进一步扩大其包装应用范围。     

离子液体法微晶纤维素/聚乙烯醇共混膜的制备及性能EI北大核心CSCD

以离子液体为微晶纤维素(MCC)和聚乙烯醇(PVA)的共溶剂,采用液-固相转变法制备MCC/PVA共混膜。共混膜经红外光谱(FT-IR)、扫描电镜(SEM)、热重分析(TGA)、接触角测试和拉力试验等表征。FT-IR和SEM分析结果表明,两组分间有很好的相容性,用甲醇做沉淀剂可以制备出孔径均一的纳米共混膜。TGA和力学性能测试结果表明,共混膜具有良好的综合热稳定性、拉伸强度及尺寸稳定性。     

离子液体法微晶纤维素/聚乙烯醇共混膜的制备及性能

以离子液体为微晶纤维素(MCC)和聚乙烯醇(PVA)的共溶剂,采用液-固相转变法制备MCC/PVA共混膜。共混膜经红外光谱(FT-IR)、扫描电镜(SEM)、热重分析(TGA)、接触角测试和拉力试验等表征。FT-IR和SEM分析结果表明,两组分间有很好的相容性,用甲醇做沉淀剂可以制备出孔径均一的纳米共混膜。TGA和力学性能测试结果表明,共混膜具有良好的综合热稳定性、拉伸强度及尺寸稳定性。     

纳米材料对阔叶纤维素包装膜性能影响的研究

采用NMMO法,以阔叶纤维素为原料制备纤维素膜,通过向铸膜液中添加经硅烷偶联剂KH-550改性的纳米SiO2,钛酸酯偶联剂改性的CaCO3以及载银TiO2材料制备纳米／纤维素复合膜。对制备纳米／纤维素复合膜微观结构采用原子力显微镜（AFM）和扫描电子显微镜（SEM）进行了表征,并结合力学性能和透氧性能测试分析了纳米材料结构和含量对膜综合性能的影响。结果表明：纳米材料的加入可以改善NMMO法纤维素膜的透氧性能,当改性纳米SiO2、改性纳米CaCO3和载银TiO2添加质量分数分别为2％、1％和1．5％时制备的纤维素纳米复合薄膜的综合性能达到最优。     

疏水性硅烷复合膜修饰的铜合金表面的防腐性能

采用自组装方法,在铜合金表面首先制备了6-（3-三乙氧基硅基丙基）氨-1,3,5-三嗪-2,4-二硫醇单钠盐（TES）自组装薄膜,然后用正辛基三甲氧基硅烷（OTES）或十六烷基三甲氧基硅烷（HDTMS）对TES修饰的铜合金表面进行硅烷化处理,得到了具有疏水功能的复合自组装薄膜。通过傅里叶变换红外光谱（FT—IR）、接触角、循环伏安、极化曲线和扫描电子显微镜（SEM）对铜合金表面的自组装薄膜进行了表征。结果表明,与未处理的铜合金相比,经复合自组装薄膜修饰的铜合金表面接触角由89．4°上升到123．7°,提高了铜合金表面的疏水性;FT—IR表明了复合自组装薄膜在铜合金表面的形成;SEM测定结果表明该方法成功地在铜合金表面获得均匀致密的有机硅烷复合膜;循环伏安及极化曲线测试均表明了该复合膜有效地提高了铜合金的耐腐蚀能力。     

表面疏水纳米碳酸钙制备及表征

采用3-氨丙基三乙氧基硅烷（APTES）、3-巯丙基三乙氧基硅烷（MPTES）、3-甲基丙烯酰氧基丙基三甲氧基硅烷（KH570）3种硅烷偶联剂,对纳米碳酸钙进行表面改性,制备了具有表面疏水性能的纳米碳酸钙。采用红外光谱仪器与接触角测定仪对玫性前后的纳米碳酸钙进行了表征与比较,结果表明：硅烷偶联剂能成功连接到纳米碳酸钙表面;3种硅烷改性剂中,KH570改性后的接触角最大,改性效果最好;表面疏水改性有助于提高纳米碳酸钙在亲油相和在有机相中的分散性能。     

纳米SiO_2/纤维素包装薄膜结构形态及性能研究

采用具有活性基团的硅烷偶联剂KH550(γ-氨丙基三乙氧基硅烷)对纳米SiO2粒子的表面进行改性。以NMMO为溶剂,以纤维素为原料,并向铸膜液中添加改性纳米SiO2,制备改性纳米SiO2/纤维素膜。采用原子力显微镜(AFM)观察了改性纳米SiO2/纤维素薄膜的表面形态,结合电子显微镜(SEM)观察其断面结构,并测定了薄膜的力学性能和透氧透湿性能。实验结果表明:改性后的SiO2较好的在铸膜液中分散,当SiO2粒径为30nm,添加量为2%,偶联剂用量为5%时,纳米复合纤维素膜的各项性能达到最佳。     

单硬脂酸甘油酯改性蓖麻油基水性聚氨酯的制备与性能研究

目的 使用单硬脂酸甘油酯(GMS)对蓖麻油基水性聚氨酯进行改性,增强其防水、耐热和力学性能。方法 使用丙酮法合成不同GMS含量的蓖麻油基水性聚氨酯乳液,进行乳液粒径测定和稳定性试验;使用浇铸法制作薄膜,并进行铅笔硬度测试、力学性能测试、吸水测试、接触角测试、热重测试、DSC、FTIR测试。分析薄膜表面硬度、力学性能、耐水性能、热稳定性、耐热性能和内部结构。结果 当GMS的−OH的摩尔分数为25%时薄膜综合性能最佳,此时膜的抗拉强度为(9.37±1.28)MPa,弹性模量为(250.55±34.05)MPa,薄膜的吸水率降低到12%,薄膜的水接触角为92°。GMS的加入,增加了薄膜的玻璃态转化温度和铅笔硬度,但热稳定性有所下降。结论 GMS的加入增强了蓖麻油基水性聚氨酯的耐水、耐热和力学性能。     

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.     

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 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.     

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 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.     

Percolation and the resistive transition of the critical temperature Tc of Nb3Sn

The relationship between the distribution of the critical temperature, the percolation function, and the resistive transition of the critical temperature is explored for polycrystalline Nb₃Sn. In the neighborhood of the critical temperature, Nb₃Sn is assumed to be a random mixture of superconducting and normal grains. Percolation concepts are applied to a study of the resistivity. A general analysis is made showing that the onset and shape of the resistive transition for composite conductors are determined by the percolation function and the distribution of the critical temperature. An approximate form of the percolation function is determined based on a linear FEM analysis. Example resistive transitions are calculated for an assumed normal distribution of the critical temperature. An argument is presented that relates grain orientation and strain dependence in Nb₃Sn. It is noted that a dependence of the distribution of T_c with strain, in addition to the usual shift in T_c with strain, would be the result of a strain dependence that is a function of grain orientation. The analysis shows the extent to which the slope of the resistive transition is a measure of the distribution of the critical temperature, and therefore a measure of the grain orientation strain sensitivity. Finally, a method is described to determine the percolation function experimentally.     

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.