Mi Jin Koh Hae Young Hwang Deuk Ju Kim Hyeng Jun Kim Young Taik Hong
材料科学技术（英）
Polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) / clay nanocomposite membranes were prepared by phase inversion method through controlling retention time to apply for a lithium ion secondary batteries. Increased membrane porosity with macrovoids was observed at increasing retention time. Partially intercalated structures of PVdF-HFP/clay nanocomposite membranes were confirmed by X-ray diffraction (XRD) analysis. PVdF-HFP membranes containing various kind of clay showed the increase of membrane modulus compared to the pristine PVdF-HFP membrane.
关键词:
PVdF-HFP
,
Porosity
,
Mechanical properties
,
Clay
,
Separator
Chih-Chia HUANG
,
Chen-Sheng YEH
材料科学技术（英）
Porous cube-like crystalline In2O3 nanoparticles with an average diagonal length of 34.8 nm were fabricated by a laser ablation-reflux process to form In(OH)3, followed by a calcination treatment to yield porous In2O3. HRTEM (high-resolution transmission electronic microscopy), XRD (X-ray diffraction), BET (Brunauer-Emmett-Teller), and XPS (X-ray photoelectron spectroscopy) analysis were used to characterize their crystalline structures, grain sizes, surface areas, and surface compositions. The as-prepared porous indium oxides were tested for their sensing properties toward ethanol. Non-porous In2O3 nanopowder (about 40 nm) was also examined in order to compare the results with the as-prepared porous In2O3 nanomaterials. The porous In2O3 exhibited much better performance than that of non-porosus In2O3, and showed enhanced sensitivity with a lower detection limit than other reported In2O3-based materials when exposed to ethanol. Good gas sensitivity and linear behavior as a function of ethanol concentration were observed in the porous In2O3 nanoparticles.
关键词:
In2O3
,
porosity
,
nanoparticles
,
gas
,
senso
Kiyoung KIM
,
Kyongwhoan LEE
材料科学技术（英）
Porosity is a main defect in aluminum alloy castings, which is also thought to be severe in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring. Fundamental experiments were carried out to evaluate the effect of process parameters such as the melt treatment, the cooling rate and the density of expanded polystyrene (EPS) foam on porosity in A356.2 bar casting. The effect of melt treatment including degassing and refining was investigated. The effect of cooling rate was also evaluated by changing the mold packing material such as the silica sand, the zircon sand and the steel shots. Gas entrapment due to the turbulent metal flow during mold filling in conventional molding process results in porosity. Mold filling sequence in lost foam process is different from that in conventional molding process. The effect of molten metal flow was estimated by comparing the density of the casting by conventional sodium silicate molding with that by lost foam process. Density measurement was conducted to analyze the extent of porosity in the casting. Source of the porosity in lost foam process can be divided into two factors, i.e. turbulence in molten metal flow and entraining residue or gas from the pattern during pouring.
关键词:
Lost foam process
,
null
,
null
,
null
,
null
Xudong ZHANG
,
Wuzhu CHEN
,
Gang BAO
,
Lin ZHAO
材料科学技术（英）
This paper describes a way to improve the weld quality through suppressing the porosity formation and restraining the growth of columnar grains by using a weaving beam in laser welding. The experimental results show that the N2 porosity of beam-weaving laser welding low carbon steel can be remarkably reduced with increasing weaving frequency, and porosity can be eliminated when the weaving amplitude is only 0.5 mm; and the Ar porosity in the weld metal is decreased with increasing weaving frequency and amplitude when the welding speed is higher than 0.5 m/min. The beam-weaving laser welding of ultra-fine grained steel has been investigated. The experimental results show that beam-weaving laser welding with appropriate amplitude and frequency can partly restrain the growth of the columnar grain and improve the tensile strength of the weld metal.
关键词:
Welding
,
null
,
null
,
null
Yi FENG
,
Zhengang ZHU
,
Shisheng HU
,
Yi PAN
材料科学技术（英）
The dynamic mechanical properties of open-cell aluminum alloy foams with different relative densities and cell sizes have been investigated by compressive tests. The strain rates varied from 700 s-1 to 2600 s-1. The experimental results showed that the dynamic compressive stress-strain curves exhibited a typical three-stage behavior: elastic, plateau and densification. The dynamic compressive strength of foams is affected not only by the relative density but also by the strain rate and cell size. Aluminum alloy foams with higher relative density or smaller cell size are more sensitive to the strain rate than foams with lower relative density or larger cell size.
关键词:
Aluminum alloy
,
null
,
null
,
null
Young-Hwan Song
,
Hwan-Goo Seon
,
Soo-Han Parka
,
Min-Jae Jeong
,
Bo-Young Hur
材料科学技术（英）
Fabrication characteristics are unstable in direct foaming method. Therefore, most of near net-shape metallic foams are produced, and investigated by powder metallurgy. Direct foaming method, however, has many benefits (i:e. reduce the unit cost of goods and fabrication process etc.) to fabrication of metallic foams. In this article, the fabrication characteristic of near net-shape metallic foams by direct foaming method was evaluated. Al and Plaster was used for base material and mould material respectively. Ca and TiH2 were added to molten Al as thickening and blowing agent for stable condition of bubbles. Thickening time was about 10 min with a stirring speed of 600 r/min. Foaming time was 30-120 s for evaluation of the optimum foaming condition. Amount of agent was selected by pre-experimental data. Porosity of near net-shape goods was measured by Archimedes method. On the other hand, it seems that increasing poring time and thickening agent make the poor porosity
关键词:
Metal foam
,
null
,
null
张睿
,
詹亮
,
孟庆函
,
梁晓怿
,
吕春祥
,
李开喜
,
凌立成
新型炭材料
doi:10.3969/j.issn.1007-8827.2004.01.002
热固性酚醛树脂-羟甲基三聚氰胺经历聚合反应、溶胶-凝胶、超临界干燥和裂解过程生成了有机和炭气凝胶.比较了超临界石油醚干燥(240 ℃、6.0 MPa下1 h)和超临界二氧化碳干燥(60 ℃、10.0 MPa下7 d)在制备有机和炭气凝胶过程中的作用.结果发现:超临界石油醚干燥时间比超临界二氧化碳的显著短,虽然前者制备的有机气凝胶的BET比表面和中孔孔容比后者小,但前者制备的有机气凝胶在热裂解过程中的热稳定性比后者好,因此,超临界石油醚干燥制备的炭气凝胶的BET比表面和中孔孔容均比超临界二氧化碳的大.超临界石油醚干燥可以替代超临界二氧化碳干燥来制备炭气凝胶.
关键词:
有机气凝胶
,
炭气凝胶
,
超临界干燥
,
孔隙
孙天鸣
,
董利民
,
王晨
,
郭文利
,
王莉
,
梁彤祥
新型炭材料
doi:10.1016/S1872-5805(13)60087-6
依据经典流体力学理论,建立了真实密度和孔隙率对炭素材料电阻率影响规律的模型.模型计算结果表明,真实密度对炭素材料的电阻率影响较小,偏差小于3％;开孔气孔率对电阻的影响大于闭孔气孔率,开孔气孔率增加40％时电阻率增加了250％,而相同幅度闭孔气孔率的增加引起电阻率的增加值只有25％.模型计算结果与实测值偏差小于2％,表明模型具有较好的精度.
关键词:
模型
,
炭材料
,
电阻
,
气孔率
柯泽豪
,
胡宪霖
,
丁志明
,
张营煌
新型炭材料
doi:10.3969/j.issn.1007-8827.2005.04.014
主要探讨酚醛树脂为前驱物的类玻璃炭,在炭化及石墨化至2 400 ℃过程中,利用透射电子显微镜观察其微结构的变化.发现一些明显的微晶碳层平面完好地堆栈在孔洞周围,这些碳层结晶尺寸在20 nm～200 nm之间.同时,这些碳层平面排列十分整齐并延伸至孔洞的表面,这些排列完好的碳层平面主要是因在小分子物气化过程中所产生.这个气化反应会生成像石墨化应力的效果,导致在孔洞内部及边缘形成高结晶碳层平面.
关键词:
电子显微镜
,
孔隙率
,
微结构
,
类玻璃碳
,
炭化
王志平
,
梁吉勇
,
张国尚
宇航材料工艺
doi:10.3969/j.issn.1007-2330.2014.02.007
对采用不同台阶比率挖补修理的玻璃纤维增强树脂基复合材料层合板进行了吸湿实验,获得了各种台阶比率试样的吸湿规律以及损伤行为.通过面内剪切强度测试以及形貌观察,研究分析了导致吸湿试件强度降低以及层间开裂的主要因素.实验发现:玻璃纤维增强树脂基复合材料的孔隙率是影响层合板吸湿率和层间开裂的重要影响因素,孔隙率越高,吸湿率越高,但层间开裂倾向却降低;台阶比率对长时间吸湿试件的强度保持率有较大的影响,恰当选择台阶比率不但有助于提高强度恢复率,还可减小因吸湿而产生的强度降低幅度;吸湿会导致玻璃纤维增强树脂基复合材料层合板的面内剪切强度大幅度下降,导致这种结果主要原因之一是吸湿会严重劣化纤维/树脂界面粘结状态.
关键词:
复合材料
,
修补
,
吸湿
,
裂纹
,
孔隙
