用于电磁波吸收的碳纳米管水泥基复合材料

采用弓形法对多壁碳纳米管(MWCNTs)水泥基复合材料的吸波性能进行了实验研究。结果表明,当MWCNTs掺量为0.6%(质量分数)时,厚度为25mm的试样在2.9GHz处获得最强吸收峰值-28dB,并能够在2～8GHz范围内对出现在吸收峰值附近的电磁波进行充分吸收;厚度为35mm的试样在8～18GHz表现出良好的宽频吸波性能。当MWCNTs掺量为0.9%(质量分数)时,水泥基复合材料在8～18GHz低于-10dB的带宽达到7.1GHz。力学强度测试结果表明MWCNTs在一定掺量范围内改善了水泥基材料的力学强度,但掺量的继续增大会导致力学强度的下降。MWCNTs掺量为0.9%(质量分数)的水泥砂浆抗压强度为60.2MPa,抗折强度为10.2MPa,虽然较空白试样有所下降,但仍有较高的力学强度。     

粉煤灰在水泥基材料中吸波性能的探索

为了研究粉煤灰在水泥基材料中的吸收电磁波性能,将Ⅲ级粉煤灰掺入水泥净浆中,制成厚度为15～30mm的试样,分别进行吸波性能测试.结果显示,粉煤灰在16GHz附近有一个14.5dB的吸收峰;掺入粉煤灰的水泥净浆,在低频率区1～4GHz范围内,有6～10dB的吸收峰;在高频率区4～18GHz内,一般只有4～6dB的吸收峰.掺量为30%、厚度为30mm的试样在17GHz附近有一个8.5dB的吸收峰.     

双层水泥基吸波材料制备及性能研究

以膨胀珍珠岩作为阻抗匹配层,以碳纳米管和铁氧体作为吸波剂制备双层水泥基吸波体,采用RCS法(radar cross section)研究水泥基吸波材料的吸波性能。实验结果表明,匹配层的透波率随着膨胀珍珠岩掺量的增加而增大,在8~18GHz频率范围内,掺有20%膨胀珍珠岩试样透波率介于20%~60%之间;以膨胀珍珠岩的水泥浆体作为匹配层制备的双层水泥基材料,其吸波性能要优于相同厚度单层吸波材料;当匹配层中膨胀珍珠岩掺量增加时,吸波性能也随着增加;以0.15%碳纳米管和10%FP型铁氧体作为复合吸波剂制备吸波层,具有优异的吸波性能,并且匹配层与吸波层的最佳厚度比为3∶1;而当吸波层复掺0.75%碳纳米管和30%FP型铁氧体时,双层吸波材料的吸波性能比相同厚度单层吸波材料要差,匹配层与吸波层的最佳厚度比为1∶3,试样反射率的峰值为-31.0dB,低于-7dB的带宽达10.6GHz。     

石墨烯/碳纳米管复合材料的微波吸收性能研究

石墨烯和碳纳米管都是新型纳米尺寸碳材料,具有极大的比表面积、良好的导电性以及优秀的机械性能等特性。通过微波膨化法在石墨烯(寡层石墨)表面空隙结构内生长了碳纳米管,制备出石墨烯/碳纳米管复合材料,碳纳米管不仅可以发挥连接石墨烯层片结构的作用,还可以与石墨烯共同发挥协同吸波效应;同时生长碳纳米管所添加的催化剂在微波状态下分解为纳米磁性颗粒,提高整体复合材料的吸波性能。通过采用SEM、EDX、XRD等对材料的形貌、化学成分进行表征,并用矢量网络分析仪测试了材料在2~18GHz频带内的复介电常数和复磁导率,利用计算机模拟出不同厚度的微波衰减性能。结果表明,材料的电磁损耗机制由电介质损耗、磁损耗共同构成,微波吸收峰随着材料厚度的增加向低频移动,当厚度为2.5mm时,在14.4GHz时最大损耗值为-28dB,并且在频带12.4~17.7GHz的范围内达到-10dB的吸收。     

石墨泡沫混凝土的吸波性能研究

多功能化和低成本有利于建筑吸波材料的应用。在频率8～18GHz范围内,采用弓形反射法测试了掺加石墨的水泥基泡沫混凝土的吸波性能,研究了石墨掺量、发泡剂用量和试件厚度对石墨泡沫混凝土吸波性能的影响。结果表明,掺加石墨后,泡沫混凝土吸波性能逐渐增强,石墨泡沫混凝土吸波材料中石墨的逾渗阈值为水泥质量的15%;随着发泡剂用量增加,石墨泡沫混凝土反射率逐渐降低。厚度为30mm时,泡沫混凝土吸波性能最佳,当石墨掺量和发泡剂用量分别为水泥质量的15%和2.5%时,反射率降低至-15.64dB,<-10.0dB的带宽可达3.0GHz,导热系数低至0.083W/(m.K)。石墨泡沫混凝土具有良好的保温和吸波性能,可以浇注施工建筑物的屋面和墙体,同时实现建筑电磁辐射防护和建筑节能的目标。     

双层雷达波吸收平板吸波特性研究

依据阻抗匹配原理与电磁波传播规律,设计了具有阻抗渐变结构的双层吸波材料。研究了以硫化锑作为匹配层填充物,炭粉作为吸收层填充物的双层吸波体的吸波性能。结果表明:面层硫化锑填充量选定为15%(ω),当底层炭粉填充量为30%(ω)时,试样总厚度为4.0mm,测试频率为8~18GHz,R<-10dB的频宽为7.6GHz,最大吸收峰值在13.8GHz(R=-20.89dB)。当底层炭粉填充量为35%(ω)时,试样总厚度为3.4mm,R<-10dB的频宽为7.2GHz,最大吸收峰值在13.8GHz(R=-15.85dB)。具有一定的工程应用价值。     

掺杂 TiO2水泥的吸波性能与力学性能研究

研究了纳米吸波材料与硅酸盐水泥复合材料的吸波性能和力学性能,讨论并分析了纳米氧化钛的用量、分散方式、试样厚度对电磁波反射衰减的关系和纳米氧化钛对水泥基复合材料的力学性能影响。实验结果表明：在8-18GHz频率范围内,纳米氧化钛与水泥制成的复合材料的反射率均小于-7dB,在16．24GHz时其反射率达-16．34(m,反射率小于-10dB的带宽达4．5GHz,且其力学性能明显优于水泥净浆。     

铁氧体与水泥复合吸波材料的研究

以碳酸锰、氧化锌和氧化铁为原料,经球磨、煅烧得到锰-锌铁氧体,然后与水泥复合制得水泥基复合吸波材料,研究铁氧体吸波剂掺量、胶凝材料品种和试样表面形状对复合材料吸波性能的影响及其力学性能.结果表明:铁氧体在水泥材料中较稳定,其用量和复合材料的表面形状对吸波性能均有较大程度的影响;在8～12.5GHz频率范围内,掺35%铁氧体的水泥基复合材料的反射率基本上都＜-6dB,而粗糙面试样的反射率均＜-7dB,最小反射率达-10.5dB;其28d强度与纯水泥样品相比约有下降.     

镍锌铁氧体的制备及其吸波性能的研究

利用溶胶直接自蔓延反应制备了镍锌铁氧体纳米粉末，采用XRD分析了其结构。以聚乙烯醇为基体（PVA）制备了炭黑，镍锌铁氧体复合材料吸波平板；采用矢量网络分析仪测量了其在2～18GHz频带上的吸波性能。结果表明：具有双层结构的炭黑，镍锌铁氧体复合材料具有较好的吸波效果，试样厚度为3mm；当面层镍锌铁氧体的质量分数为40％，底层炭粉的质量分数为20％时，在8～18GHz的测试频段范围内，复合材料最大吸收峰值为-15．7GHz，优于-6dB的有效带宽为6．4GHz；当底层炭粉的质量分数为15％时，复合材料最大吸收峰值为-13．6GHz，优于-6dB的有效带宽为8．2GHz。     

碳纳米管/镍铁氧体涂层的吸波性能及吸波机理

采用柠檬酸络合物形成的溶胶凝胶制备了镍铁氧体,并将所得镍铁氧体与碳纳米管混合均匀,得到不同碳纳米管质量分数的复合材料。采用微波矢量网络分析仪测量了复合材料的电磁参数,根据电磁参数研究了1mm厚涂层在2~18GHz频段的微波反射率。结果表明:复合材料的吸波性能明显优于单纯的镍铁氧体材料,而且复合材料中碳纳米管含量对吸波性能有明显的影响。对于厚度为1mm的薄涂层,当碳纳米管的质量分数为20%时,涂层具有最优的吸波性能,最大吸收峰值达-14.02dB,小于-10dB的有效带宽达3GHz;然后通过电损耗功率密度分析了复合材料的微波吸收机理,并给出了厚度为1mm的薄涂层,当其中的碳纳米管含量为20%时,吸波效果最佳的理论解释。     

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.     

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.     

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.     

Mechanism Study on the Wear of CrAlTiN Coated High-Speed Steel Twist Drills Under Dry Cutting Conditions

As demands about environment protection are growing up, dry cutting technology is getting more and more concerns from all over the world. Main works performed here are study on dry cutting performances and wear mechanisms of M2high-speed steel (HSS) twist drills with CrAlTiN multicomponent coatings, which was deposited using magnetron sputter ion plating system, in drilling 45 and 30CrMnSiA steel, and their comparisons to those in drilling the same steel but using monolayer CrN and commercial TiN coated drills. Drilling performances of drills are evaluated mainly through the measurements of width on outer corner flank land and the cutting forces. Results show that performances of CrAlTiN coated drills are better than those of monolayer CrN and TiN coated drills. In drilling 45 and 30CrMnSiA steel, the average tool life of the CrAlTiN coated drills are 17.2 and 11.8 times higher than those of the uncoated drills. Observing wear of the drill with scanning electronic microscope, results show that there is no crack or spallation of the CrAlTiN coatings in wear zones. Main mechanism of the wear here is adhesion.     

Study on Bond Ability of Arc-Spraying Coatings with Different Surface Pretreatment on Cast-Iron

Arc spraying coatings are widely used in various applications, but uncommon in cast iron substrate. Different surface pretreatment technology is tested on substrates of gray cast iron. Surface roughness and residual stress were measured by TR200 and X-ray diffraction analyzer. Influence of different surface pretreatment methods ( dry blasting and fusebond) on roughness and residual stress was analyzed. The arc-sprayed coatings of wire 3Cr13 (φ2mm) on gray cast iron substrate is studied. The microstructure and interface of bonding layer were observed by SEM. The bond strength was taken by tensile test. Results show that bond strength with grit blasting is higher than fuse-bond; it is feasible to make wire 3Cr13 coating with arc spraying on cast iron substrate roughened by grit blasting.     

Structural Characteristics of TiO2 Ceramic Coating by Micro-Plasma Oxidation

TiO2 ceramic coatings with thickness of 20 μm were formed on the surface of pure titanium by micro-plasma oxidation. Their micro-structures were investigated by by using X-ray diffraction and their surface images were detected by using scan electronic microscope. There were three kinds of TiO2 coatings, pure anatase type TiO2 phase, mixed phases consisted of rutile type TiO2 phase and anatase type TiO2 phase, pure rutile type TiO2 phase. The coating surface with the pure anatase type TiO2 phase is rough, while the coating surface with the pure rutile type TiO2phase is smooth. The upper coating surface with the mixed type TiO2 phases is anatase type TiO2 structure and the subsurface of the TiO2 coating is rutile type TiO2structure.     

Evaluation of fatigue life of steel using steel grain size

The insightful discussion of the relationship between the construction of metallographic and fatigue life and proposition of mathematical relationships describing this relationship was conducted in the paper. This paper presents a method for estimating the fatigue life, based on the construction of the microstructural material taking into account the grain size and the participation of ferrite and pearlite phase.