Processing and characterization of porous Ti2AlC with controlled porosity and pore size

In this work, we demonstrate a simple and inexpensive way to fabricate porous Ti₂AlC, one of the best studied materials from the MAX phase family, with controlled porosity and pore size. This was achieved by using NaCl as the pore former, which was dissolved after cold pressing but before pressureless sintering at 1400 °C. Porous Ti₂AlC with samples a volume fraction of porosity ranging from ～10 to ～71 vol.% and different pore size ranges, i.e. 42–83, 77–276 and 167–545 μm, were successfully fabricated. Fabricated samples were systematically characterized to determine their phase composition, morphology and porosity. Room temperature elastic moduli, compressive strength and thermal conductivity were determined as a function of porosity and/or pore size. For comparison, several samples pressureless-sintered without NaCl pore former, or fabricated by spark plasma sintering, were also characterized. The effects of porosity and/or pore size on the room temperature elastic moduli, compressive strength and thermal conductivity of porous Ti₂AlC are reported and discussed in this work. It follows that porosity can be a useful microstructural parameter to tune mechanical and thermal properties of Ti₂AlC.     

定向凝固多孔Mg-Zn合金的制备及气孔结构

采用Bridgman型定向凝固法制备出藕状多孔Mg-Zn合金.研究了不同锌含量和氢气压力对气孔形貌的影响.通过理论计算对Mg-1Zn(质量分数,％,下同)合金的孔隙率进行了预测.结果表明,锌元素的加入会对孔结构产生重大影响.随着Zn含量从0％增加到2％,平均孔径增加.随着氢气压力从0.1 MPa增加到0.6 MPa,M...     

凝固模式对定向凝固多孔铜锰合金气孔结构的影响

采用金属-气体共晶定向凝固工艺（GASAR工艺）,制备气孔定向排列的多孔铜锰合金,并研究气孔结构的变化。结果表明：这种变化主要取决于合金的凝固模式（平面凝固、柱状胞晶凝固、柱状枝晶凝固、等轴枝晶凝固）,而合金凝固模式由合金的凝固过程决定。通过数值模拟发现,随着合金凝固的进行,合金的凝固模式从胞晶凝固向柱状枝晶凝固过渡,最终变为等轴枝晶凝固。通过升高合金熔体温度和铸型的预热温度,可以缩小等轴枝晶凝固的范围,扩大定向生长气孔的区域。     

凝固模式对Gasar多孔Cu-Cr合金结构及组织影响

在0.6 MPa纯H2气氛中,采用金属/H2共晶定向凝固(Gasar)技术制备得到Gasar多孔Cu-x Cr合金。研究了Cr含量、凝固模式以及凝固速率对Gasar多孔合金气孔结构和显微组织的影响。结果表明,当合金以平面、胞状及柱状枝晶凝固时,Gasar多孔Cu-x Cr合金能获得定向生长气孔。当凝固方式转变为等轴枝晶凝固时,定向生长气孔发生中断。Gasar多孔Cu-x Cr合金(x=0.8%、1.3%)气孔在共晶相前沿析出,与共晶组织协同定向生长。随Cr含量增加,共晶组织体积百分比增加,孔隙率和孔圆整度进一步增加;随多孔Cu-1.3 Cr合金试样凝固高度增加,凝固速率下降,界面生长方式转变为等轴晶生长方式,则无法得到定向生长气孔。     

Fabrication of tunable pore size of nickel membranes by electrodeposition on colloidal monolayer template

Large-area nickel patterned membranes with tunable pore size are prepared by the combination of self-assembly nanosphere lithography and electrodeposition. The morphology of the nickel membranes exhibits a honeycomb or egg-shell-roofed structure depending on the deposition time and the electrostatic-induced absorption effect. With an increase of electrodeposition time, the movement of polystyrene spheres caused by metal-filling gradually changes the contact evolution between the spheres and the substrate from facet contact to quasi-point contact, until complete lift from the substrate. Hence, the pore size can be controlled by varying the deposition time; i.e., by controlling the contact area between the polystyrene spheres and the substrate. Such membranes can be useful as templates for nanofabrication. The site and density control of one-dimensional nanostructures, depending on the distance and the size of the pore, is a critical issue in many potential applications, such as optical antennas, biosensors and bioprobes, and field emission devices.     

不同孔径分布多孔钛的力学性能

从生物学角度出发设计并制备2种不同孔径分布的多孔钛,并研究其力学性能。采用造孔剂烧结方法制备孔隙率为36%~63%的多孔钛,通过室温压缩测试其力学性能。多孔钛的弹性模量和抗压强度分别在2.662~18 GPa和94.05~468.57 MPa范围内,且都随着孔隙率的增加而降低。抗压强度和孔隙率的关系曲线呈现完全的线性特征,表明抗压强度主要受孔隙率的影响,几乎不受孔径的影响。Gibson-Ashby力学关系分析结果显示：常数项C值的差异说明孔径分布对多孔钛的屈服强度有一定的影响;密度指数n值均大于临界值3,表明这2种不同孔径的多孔钛的变形方式相同,为孔壁的屈曲作用。     

Influence of the method of preparation on the porous structure of perovskite oxides

The results of investigation of the textural properties of perovskite-type binary oxides corresponding to the formulae LaMeO₃ (Me ≡ Fe, Co, Ni, Cr) and La_0.85Me′_0.15CoO₃ (Me′ ≡ Ca, Ba, Ce) are presented. The texture of the samples was studied by physical adsorption and capillary condensation of nitrogen, and is discussed in relation to the method of preparation of the samples.     

渗流法制备高孔隙率多孔铝

采用负压渗流铸造法,通过控制铝熔体浇铸量,制备了高孔隙率(70%～90%)、高通孔度(25%～50%)的多孔铝;研究了渗流驱动压力、铝熔体浇铸温度及模具预热温度对渗流过程的影响;测试了多孔铝的渗透系数,并分析了孔结构对渗透系数的影响.结果表明:通过正交实验选择渗流参数,可以降低多孔铝在渗流方向上的孔隙率梯度;多孔铝的渗透系数与其孔结构密切相关:对于相同孔径的多孔铝,渗透系数随孔隙率增大而提高;在孔隙率相同的条件下,随着孔径增大,表面积减小,摩擦阻力减小,渗透系数相应增大.     

炭、石墨材料孔结构特征描述及其对综合性能的影响

随着传统行业、新兴产业的不断升级,炭、石墨材料（CGM）已成为支撑高新技术发展的重要战略资源和基础矿物原料。目前针对CGM的研究主要围绕宏观性能,对其孔结构的系统报道较少。众所周知,CGM的宏观性能取决于其微观结构,而孔结构的研究又占据了微观结构的重要一环。因为,本文回顾了CGM的应用与发展,总结了CGM的孔结构特征,进一步分析了炭、CGM孔结构特征对其综合性能的影响和内在联系。为阐述CGM物理、化学性能、材料改性、性能优化及新工艺的设计提供理论依据。     

采用循环伏安法研究微孔型多孔炭电极的电容特性

以酚醛树脂为原料,KOH为活化剂,制备出3种不同孔径分布的微孔型多孔炭(孔径≤2 nm)。在低温氮气吸附法测定BET比表面积和孔结构的基础上,采用循环伏安法考察了这3种微孔型多孔炭作电极的双电层电容器(EDLC)的电容特性。实验结果表明,微孔型多孔炭作电极的EDLC的电容特性是:在低扫描速率下,其循环伏安曲线达到电容平台后在高电压(±1.0 V)附近出现峰电容;延长在电解液中的浸渍时间,电极的比电容增大,高电位附近的峰电容减小。3种不同孔径分布的微孔型多孔炭作电极的EDLC的循环伏安特性受浸渍时间影响的程度也不同。     

小孔径通孔多孔铝合金的防风降噪性能

以降低语音系统气流噪声为目标,制备小孔径(d0.1～0.5 mm)多孔铝合金,采用自制设备研究多孔铝合金的厚度、孔径及气流速度等因素对气流噪声的影响.结果表明:相对于孔的气流噪声,多孔铝合金的气流噪声在低频段下降18 dB,降幅随频率增加而减小;材料厚度越大、孔径越小、气流速度越大,多孔铝合金的防风降噪性能越好.     

Influence of the carbonization conditions on the formation of the porous structure of activated carbon from cotton lignin

Carbonization (thermal pyrolysis) is the determining step in the formation of the porous structures and other physicochemical properties of activated carbons obtained from cotton lignin. Activation of the samples carbonized at 800°C produces carbon sorbents with the optimum parameters.     

阳极氧化法制备多孔氧化铝模板

采用阳极氧化法,以硫酸为电解液制备了多孔氧化铝模板。讨论了氧化电压和电解液温度对多孔阳极氧化铝膜的孔径的影响。试验结果表明,当氧化时间为6h时,氧化膜厚度达到最大值35．6μm。XRD分析结果证实,多孔氧化铝膜由非晶态的Al2O3组成。     

多孔金属结合剂CBN砂轮孔隙结构对磨料层胎体力学性能的影响

为解决多孔金属结合剂CBN砂轮在高孔隙率下的强度下降问题,采用球形尿素颗粒为造孔剂,制作孔径、孔形和孔隙可控的多孔金属结合剂砂轮磨料层胎体,研究不同载荷情况下的孔隙率和孔隙排布等孔隙结构因素,对多孔金属结合剂磨料层胎体力学性能的影响规律。结果表明:孔隙有序排布时的胎体弹性模量要小于孔隙无序排布的;胎体材料的屈服强度随孔隙率增大而下降;在相同孔隙率下,孔隙有序排布的胎体,在纵向受压、孔隙正向排布的情况下屈服强度更高。      

Corrosion synthesis of boron carbide with pore and hollow structure

In this study, corrosion synthesis of boron carbide particles with pore size ranging from hundreds of nanometers to several micrometers was reported. Firstly, the pristine boron carbide powders which contain free carbon have been synthesized at 350 °C in a steel autoclave. As the pristine boron carbide was refluxed by HClO₄ at 170 °C for 1–2 h, the boron carbide particles with macropores were produced. Similarly, the boron carbide nanocages can also be obtained. The corrosion of the embedded amorphous and/or low crystallinity carbon/boron carbide using HClO₄ was considered for the formation of boron carbide with macropores and hollow nanocages.     

气压对定向凝固藕状多孔镁的气孔分布影响

采用统计分析方法,通过孔径分布、气孔最邻近距离和局部气孔率定量分析定向凝固藕状多孔镁横截面上的气孔分布特征,并在此基础上分析气压对藕状多孔镁气孔分布的作用规律。结果表明:纯氢条件下气压越高,孔尺寸分布越趋于一致、孔位置和气孔结构单元分布越均匀;氢气分压一定,选择合适的氩气分压可使熔体共晶凝固时,孔尺寸、孔位置和气孔结构单元的分布最均匀。     

Study of the structure and magnetic properties of Co nanoparticles in the matrix of highly porous amorphous carbon

This paper presents the results of investigations into the structure and the magnetic properties of powders consisting of Co nanoparticles in the matrix of a high-porous amorphous carbon material. An analysis of X-ray diffraction and nuclear magnetic resonance spectra revealed the presence of hcp and fcc phases of cobalt in the particles of the powder and demonstrated the existence of a highly defective state, which could be related to a high concentration of defects of the “displaced-plane” type. The magnetometric measurements showed that the powder particles were in the ferromagnetic state and were characterized by a high field of the local magnetic anisotropy.     

模板法-脱合金制备低密度、分级多孔金及其电催化性能

本文提出了以模板法-脱合金复合方法制备低密度分级多孔金。在该方法中,以直径为700 nm的二氧化（SiO2）微球作为模板,通过化学镀的方法依次制备了Ag@SiO2和Au@ Ag@ SiO2核壳粒子,并通过冷压-烧结方法制备了Au@ Ag@ SiO2合金块材。通过连续改变腐蚀溶液,SiO2模板以及Ag元素从Au@ Ag@ SiO2合金中完全去除。将SiO2从Au@ Ag@ SiO2微球完全去除从而得到了大尺寸空心球壳（直径约为675 nm）,将Ag元素脱合金去除从而在球壳表面形成了许多小尺寸的孔结构（直径约为75nm）。TEM图像表明,块状金样品中的韧带由具有多晶特性的纳米晶粒组成。这种具有低密度1.1 g/cm3（相对密度为5.7%）和高表面积4.24 m2/g的分级纳米多孔金材料在碱性溶液中对甲醇电氧化具有优良的催化活性以及快速的传质速率,表明其在催化领域具有广阔的应用前景。     

Pitting of carbon steel in the synthetic concrete pore solution

Pitting corrosion is a possible mode of failure of the carbon steel overpack of the Belgian supercontainer concept for the isolation of high-level nuclear waste (HLNW). However, no firm experimental data are currently available to estimate the probability of failure over the extended storage time (100,000 years). Extensive work shows that passivity breakdown results from the condensation of cation vacancies (CVs) at the metal/barrier layer (m/bl) interface, in response to the absorption of Cl⁻ into oxygen vacancies at the surface of the barrier oxide layer. The CVs migrate across the bl to the m/bl interface where they condense, leading to the separation of the bl from the metal. The resulting blister prevents the growth of bl into the metal and dissolution results in blister rupture, marking a passivity breakdown event. Stabilization via differential aeration produces a potentially damaging, stable pit. We review our work on passivity breakdown and the nucleation of pits on P355 QL2 carbon steel in high-pH aqueous media typical of concrete pore solution, with emphasis on the mechanistic aspects. We conclude that failure of the carbon steel overpack containing the HLNW over a storage horizon of 100,000 years is improbable.     

Effect of pore size on the high temperature oxidation of Ni-Fe-Cr-Al porous metal

This study investigated the effect of the pore size of Ni-22.4%Fe-22%Cr-6%Al porous metal on its hightemperature oxidation. Two types of open porous metals with pore sizes of 800 μm and 580 μm were used. A 24-hour isothermal oxidation test was conducted at three different temperatures of 900 °C, 1000 °C, and 1100 °C under a 79% N₂ + 21% O₂ atmosphere. The results of the BET analysis revealed that the specific surface area increased as the pore size decreased from 800 μm to 580 μm. The high-temperature oxidation results showed that porous metals exhibited far lower levels of oxidation resistance compared with bulk metals, and that the oxidation resistance of porous metals decreased with a decreasing pore size. According to the microstructural observations of the oxide layers, the 900 °C and 1000 °C oxidation layer contained Ni, Cr, and Al oxides mainly on the strut. The 800 μm porous metal strut exhibited similar oxidation behavior at 1100 °C to that found at lower temperatures. In contrast, the 580 μm porous metal strut was found to consist of Ni and Fe oxides in the upper layer and Ni, Cr, and Al oxides in the lower layer, representing a low oxidation resistance. For powders affixed to the strut inside the porous metal, a different oxide-forming behavior from that of the strut was observed. In addition, the Ni-Fe-Cr-Al porous metal high-temperature oxidation microscopic mechanism is also discussed.