泡沫铜微孔表面池沸腾换热特性的实验研究

利用改进电镀法制备了新型的泡沫金属铜微孔表面,通过扫描电子显微镜(SEM)测定泡沫铜上微孔表面的微观结构,实验以去离子水为工质,研究了光滑表面和微孔表面的池沸腾传热特性,获得了光滑和微孔表面的池沸腾传热曲线。研究结果表明,在相同的热流密度条件下,微孔表面的汽化核心在核沸腾区密度较大,可有效降低壁面初始沸点的过热度,显著提高池沸腾的换热系数,证明该表面可用于半导体制冷系统等大型功率电子器件散热。

微孔表面髋关节假体

微孔表面髋关节假体表面材料包括金属和陶瓷两种。金属假体与骨组织结合牢固,这主要受材料种类及微孔直径影响。但是,金属材料会产生癌症、神经病变、过敏反应、应力遮挡等副作用。因此,陶瓷材料尤其是羟基磷灰石(HA)因其良好的生物相容性及传导成骨作用而受到重视。HA主要通过生物结合和化学结合两种方式与骨组织形成牢固结合,在结合过程中,HA的降解起了重要作用,纯度、结晶率、表面微孔量等几方面影响其降解速度,巨噬细胞等也介入其降解过程。微孔表面假体在临床应用中取得了优异的疗效,大大提高了患者生活质量,已被广泛接受。

超疏水低黏附微孔表面的制备及其冷凝微滴的高效自去除性能

冷凝微滴在基底材料表面的高效自去除是防结霜的一种有效手段。以硅片为基底材料,采用飞秒激光直写技术制备了微孔阵列结构,经低表面能修饰后,表面水接触角为165°,滚动角为0.6°,液滴在微孔结构表面可以实现多次弹跳。通过冷凝微滴的自去除实验,重点分析了冷凝微滴的成核、生长、合并自去除机制,发现冷凝微滴可以在微孔内部短时间内快速成核,并且微孔表面的超疏水低黏附特性能有效加速合并后液滴的弹跳自去除。通过对自去除过程中的参数分析,讨论了液滴自去除效率随时间的变化关系。制备的微孔表面在防结霜领域具有应用前景。

表面微孔方向性对润滑温升特性影响实验研究

实验研究表面倾斜方向性微孔表面润滑温升特性。采用环-环摩擦方式,分别在水润滑和油润滑实验条件下,对比分析光滑表面、圆形和倾斜椭圆微孔表面的微孔分布方式和开孔率对摩擦因数和润滑温升的影响规律。实验结果表明:微孔表面的摩擦因数和润滑温升明显小于光滑表面,且倾斜椭圆微孔表面的摩擦因数和润滑温升小于无方向性圆孔表面;微孔分布和表面开孔率对摩擦因数和润滑温升影响明显,径向局部开孔表面比径向全开孔表面具有更小的摩擦因数和润滑温升。

解剖型表面微孔钛合金椎间融合器的生物相容性

背景:传统的带螺纹水平圆柱形钛合金椎间融合器虽能改善腰椎退变疾病患者的症状,但患者预后较差、椎间融合率较低。目的:研究解剖型表面微孔钛合金椎间融合器生物相容性及在腰椎退变性疾病中的应用效果。方法:将50例腰椎退变性疾病患者随机分为两组,试验组(n=25)采用解剖型表面微孔钛合金椎间融合器进行椎间融合治疗,对照组(n=25)采用传统钛合金椎间融合器进行椎间融合治疗。治疗后随访观察融合率、椎间隙高度比、椎间孔高度比、椎体间角度活动域、融合节段前凸角、腰椎前凸角、腰椎水平角及骶骨水平角。结果与结论:随访6-29个月,试验组骨融合率显著高于对照组(92%,68%,P<0.05),试验组未出现不良反应,对照组3例出现感染、慢性脑脊液漏等并发症;治疗后3,6个月,试验组椎间隙高度比、椎间孔高度比、椎体间角度活动域(L_(3/4)、L_5及L_5/S_1)、融合节段前凸角、腰椎前凸角、腰椎水平角及骶骨水平角显著大于对照组(P均<0.05);结果表明,解剖型表面微孔钛合金椎间融合器置入治疗腰椎退变性疾病具有良好生物相容性,且融合率高。

油润滑微孔SiC表面极限PV值特性试验

为提高摩擦副材料极限PV值以避免启停等极端条件下润滑表面的剧烈磨损失效,提高零件的可靠性和使用寿命,开展油润滑微孔SiC表面极限PV值试验研究。考虑空化效应影响,分别对光滑表面、圆孔表面和椭圆微孔表面进行润滑状态分析,获得微孔试件表面的压力分布;对摩擦因数、温度和表面磨损形貌进行试验测量,获得不同载荷工况下微孔表面磨损失效的临界转速和极限PV值的变化规律。结果表明:微孔表面呈现出提高SiC摩擦副极限PV值的趋势,平均极限PV值最大提高70%以上,其中椭圆微孔最大可使摩擦副的极限PV值提高2倍以上;微孔表面的极限PV值随载荷工况的变化呈现明显的波动和不确定性。边界润滑条件下,表面微孔可能出现减摩效果,也可能出现增摩现象,试验中圆形微孔可使摩擦副的极限PV值下降超过60%。

聚合物真空绝缘子表面二级微结构

为研究绝缘子表面二级微结构的耐压提升机制,将表面二级微结构拆分为两种子结构,也即是表面微孔结构与表面微槽结构,并通过复合材料制备、激光处理、酸液选择性腐蚀等方式制备出表面二级微结构与相应的两种子结构。对三种结构分别进行沿面耐压性能测试,结果表明表面微孔与表面微槽均能有效地提升绝缘子的真空沿面耐压性能,而二者组合形成的表面二级微结构能够进一步提升绝缘子的真空沿面耐压性能。该结果表明通过将表面结构进行合理的组合能够实现对绝缘子表面闪络发展的多重、协同抑制,进一步提升绝缘子的真空沿面耐压水平。

机械密封椭圆微孔端面动力润滑性能

为了深入探讨机械密封椭圆微孔端面的动力润滑性能,应用计算流体力学软件FLUENT,基于Navier-Stokes方程,建立单一椭圆型微孔端面不可压缩牛顿流体的三维CFD动力润滑模型,分析微孔深度、倾斜角、长短轴之比以及雷诺数对液膜承载力和微孔端面摩擦因数的影响。结果表明:当其他因素不变且仅考虑单一因素的影响时,微孔深度为端面间隙的1/2时液膜承载力最大、摩擦因数最小,端面间的液体动力润滑性能最好;倾斜角为45°时,液膜承载力有最大值,摩擦因数有最小值,端面间液体动力润滑性能也达到最佳;随椭圆微孔长宽比的增加,液膜承载力增大,摩擦因数减小,液体动力润滑性能提高。

镶嵌固体润滑剂的硬质合金摩擦学性能研究

在硬质合金YT5表面利用微细电火花加工小孔,并装填MoS_2固体润滑剂以改善基体表面的摩擦磨损性能。在UMT摩擦试验机上进行摩擦磨损试验,结果表明:装填固体润滑剂MoS_2的微孔表面比光滑表面的摩擦系数显著降低,改善了摩擦表面磨损工况,表现出良好的减摩和润滑效果。结合SEM和EDX分析微孔固体润滑的机理:在摩擦过程中,存储于微孔中的固体润滑剂受到相对摩擦和挤压作用而粘着、拖覆在基体表面,形成一层固体润滑膜,从而起到减摩润滑作用。表面微孔润滑技术是提高基体表面摩擦磨损特性的有效方法,但需通过合理设计微孔结构尺寸,兼顾微孔表面的减摩润滑作用和基体的物理机械性能之间的平衡。

氧化钛和氧化铝陶瓷的骨诱导作用

蛋白质吸附、钙磷离子释放和表面生物矿化是钙磷材料诱导异位骨生成的可能材料机制。对比了非表面微孔羟基磷灰石陶瓷(HA-S)、表面微孔羟基磷灰石陶瓷(HA-R)和表面微孔生物惰性非钙磷陶瓷(TiO_2陶瓷;Al_2O_3陶瓷;两者无钙磷释放,无表面生物矿化能力)的异位骨诱导能力。研究发现,不同化学成分的陶瓷材料对蛋白质有选择性吸附。即使不吸附骨形态发生蛋白-2(rhBMP-2),具有表面微孔的非钙磷陶瓷也能诱导异位骨组织生成。结果表明,钙磷离子释放和表面生物矿化在磷酸钙生物材料骨诱导中不起关键作用,表面微孔也不一定通过蛋白质吸附而在异位骨诱导中起作用。

Surface Functionalization of Microporous Polypropylene Membrane with Polyols for Removal of Boron Acid from Aqueous Solution

Affinity membranes are fabricated for boric acid removal by the surface functionalization of microporous polypropylene membrane(MPPM)with lactose-based polyols.The affinity is based on specific complexation between boric acid and saccharide polyols.A photoinduced grafting-chemical reaction sequence was used to prepare these affinity membranes.Poly(2-aminoethyl methacrylate hydrochloride)[poly(AEMA)]was grafted on the surfaces of MPPM by UV-induced graft polymerization.Grafting in the membrane pores was visualized by dying the cross-section of poly(AEMA)-grafted MPPM with fluorescein disodium and imaging with confocal laser scanning microscopy.It is concluded that lactose ligands can be covalently immobilized on the external surface and in the pores by the subsequent coupling of poly(AEMA)with lactobionic acid(LA).Physical and chemical properties of the affinity membranes were characterized by field emission scanning electron microscopy and Fourier Transform Infrared/Attenuated Total Refraction spectroscopy(FT-IR/ATR).3-Aminophenyl boric acid(3-APBA)was removed from aqueous solution by a single piece of lactose-functionalized MPPM in a dynamic filtration system.The results show that the 3-APBA removal reaches an optimal efficiency(39.5%)under the alkaline condition(pH9.1),which can be improved by increasing the immobilization density of LA.Regeneration of these affinity membranes can be easily realized through acid-base washing because the complexation of boric acid and saccharide polyol is reversible.

Synthesis of MgO-Al_2O_3/ZSM-5 by Solid State Reaction for Propane Dehydrogenation

Solid-state grinding is a simple and effective method to introduce guest species into the channels of microporous materials through filling.The structure and the surface acidity of the materials were obtained from BET isotherms and NH3-TPD,respectively.XRD,UV-vis,UV diffuse-reflectance,and TEM were used to characterize the phases,and the morphology,respectively.The clustered layers of MgO-Al2O3phases were formed in the internal pore surface and were highly dispersed inside the channels of the ZSM-5 host.So the volume of MgO-Al2O3/ZSM-5 composite was larger than the ZSM-5 zeolite itself and some mesoporous channels appeared when Mg/Al species entered the channels.Meanwhile,new acid sites emerged in MgO-Al2O3/ZSM-5 composite and the acid amount of the sample changed.The improved Pt dispersion and the increased acid content would cause the increase of propane conversion and the modification of selectivity during the reaction.

Micromorphology of Surface Crusts in the Knersvlakte,South Africa

Soils in the Knersvlakte are particularly prone to crusting and have lower inherent infiltrability than other soils across western southern Africa. Micromorphological techniques were used to examine the structure and porosity of soil crusts in the Knersvlakte to ascertain why crusting is so intense in this region. Quantile regression using boundary lines was employed to examine the relationships between infiltrability and soil properties for all samples （n = 67）. This analysis showed that infiltrability is potentially maximal at low water- dispersible ＇clay plus silt＇ content and low silt content （r^2 = 0.72 and 0.64; respectively, n = 67） （Figure 2）. The strength of crusts, pH, EC, clay mineralogy, and water-dispersible clay, silt and ＇clay plus silt＇ content were compared, and a pore analysis using optical microscopy was undertaken on images of six soil thin sections （n = 6） （circular and parallel polarizers）. Pore analysis was further undertaken on five horizontal slices of equal dimensions taken through each soil thin section. The porosity samples with low infiltrability （〈 100 mm·hr^-1, n = 4） had greater crust strength, lower porosity （both total and in the least porous slice） and greater water-dispersible ＇day plus silt＇ and silt content than the porosity samples with high infiltrability （〉 100mm·hr^-1, n = 2）. The porosity samples with low infiltrability showed a trend of lower pH and greater water dispersible clay percentage. Porosity varied within the porosity samples due to the presence of dense clay/silt bands （〈 0.5 mm in width） with relatively few air vesicles. The porosity samples with horizontal slices of low porosity （but large numbers of air vesicles） had low infiltrability, while those without slices of low porosity （and relatively few air vesicles） had high infiltrability. We conclude that the intense crusting and resultant low infiltrability of soils in the Knersvlakte appears to be related to the formation of thin, dense clay/silt bands in the pedoderm.

Calcium phosphate deposition on surface of porous and dense TiNi alloys in simulated body fluid

Porous and dense TiNi alloys were successfully fabricated by powder metallurgy(P/M) method, and to further improve their surface biocompatibility, surface modification techniques including grind using silicon-carbide(SiC) paper, acid etching and alkali treatment were employed to produce either irregularly rough surface or micro-porous surface roughness. X-ray diffractometry(XRD), scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDX) attached to SEM were used to characterize surface structure and the Ca-P coatings. Effects of the above surface treatments on the surface morphology, apatite forming ability were systematically investigated. Results indicate that all the above surface treatments increase the apatite forming ability of TiNi alloys in varying degrees when soaked in simulated body fluid(SBF). More apatite coatings formed on TiNi samples sintered at 1050℃ and 1100℃ due to their high porosity and pure TiNi phase that is beneficial to heterogeneous nucleation. Furthermore, more uniform apatite was fabricated on the sample sintered from the mixture of Ni and Ti powders.

Capillary Rise between Parallel Perforated Plates in Microgravity

This paper presents the setup and performance of a drop tower experiment which investigates the behavior of liquid during self-driven capillary transport between two parallel perforated plates under microgravity. With the onset ofmicrogravity the liquid rises between the two parallel plates as a result of capillary pressure. Eight different sets of plates are tested in this study and the free surface height and the volume of transported liquid is subsequently analyzed. The plate sets differ in geometric properties of their perforations, distance, and width. In each set the perforations of both plates are identical and have a diameter of a few millimeters. The capillary rise velocity is influenced by the perforation diameter and the area porosity of the plates. As could be expected, the capillary transport capability increases with decreasing plate porosity.

Changes of Porosity and Roughness of Concrete Surfaces Due to Microbial Corrosion

The issue of the building materials biocorrosion has a significant economic dimension because it results in the costly repair. The start and the course of corrosion are conditioned by many factors which undoubtedly include biological effects like the influence of vegetation and microorganisms causing the so called microbial corrosion. Microorganisms have also a considerable share in the decay and degradation of different building materials. The activity of sulphuratum is the keystone of many processes in nature and in industry. The sulphuric bacteria oxidize hydrogen sulphide produced by sulphate-reducing bacteria into sulphuric acid resulting in the acid or sulphate corrosion of cement stone. The paper is aimed on evaluation of porosity and roughness of concrete samples surface as elementary characteristics of microbial corrosion. After 4 months exposure to the real conditions in sewers deposition the changes were observed by confocal laser microscopy and consequently analyzed and interpreted.

Experimental study on hydrodynamic effect of orientation micro-pored surfaces

The orientation of the dimple increases the flow distance in the dimple and produces fluid cumulative effect in the dimple length direction, which leads to obvious hydrodynamic effect as a result. In order to investigate the hydrodynamic effect of orientation dimples, a series of experiments was carried out on a ring-on-ring test. Multi-pored faces were tested with different dimple inclination angles and slender ratios. Film thickness and frictional torque were measured under different conditions of load and rotation speed. Experimental results showed that the orientation dimple could produce obvious dynamic effect by change of the flow direction and the increasing dimple orientation leads to increase of the load capability. The hydrodynamic effect strongly depends on dimple orientation parameters such as inclination angle and slender ratio. A larger load capability can be available by increasing dimple orientation and rotation speed. Experimental results agreed well with the theory that orientation micro-pores can significantly improve hydrodynamic performance of surfaces.

Localization and macroscopic instability in nanoporous metals

Ductile fracture generally relates to microscopic voiding and to strain localization in metallic materials.When the void size is reduced to the nanoscale,size effects often lead to a different macroscopic plastic behavior from that established for the same material with larger voids.For example,irradiation of metallic materials can generate a large number of voids at the nanoscale,leading to complex deformation behaviors.The present work advances the understanding of strain localization in nanoporous metallic materials,connecting both the microscopic(nano-)and macroscopic scales.To explore the physical mechanisms at the nanoscale,molecular dynamics(MD)simulations were here carried out,capturing multiple nanovoids explicitly.Then,a homogenized continuum theory based in Gurson's constitutive framework is proposed,which enables us to explore how localized behavior at the macroscopic scale evolves.The homogenized model incorporates the surface tension associated with nanosized void.The importance of this surface tension is illustrated by several parametric studies on the conditions of localization,when a specimen is subjected to uniaxial tension.Our parametric studies show that for smaller nanovoid sizes,and for a hardening matrix material,shear localization onset is delayed.Our proposed homogenization model was then used to predict localization behavior captured by our MD simulation.The yield stress and the localization strain predicted by our continuum model are in general agreement with the trends obtained by MD simulation.Moreover,based on our present study,experimental results of shear failure strain vs.dose of irradiation for several metals could be qualitatively explained rather successfully.Our model can therefore help shed light on prolonging the operation limits and the lifetime of irradiated metallic materials under complex loading conditions.

Soil Microbial Responses to Biochars Varying in Particle Size,Surface and Pore Properties

Biochars are known for their heterogeneity, especially in pore and surface structure associated with pyrolysis processes and sources of feedstocks. The surface area of biochar is likely to be an important determinant of the extent of soil microbial attachment, whereas the porous structure of biochar is expected to provide protection for soil microorganisms. Potential interactions between biochars from different sources and with different particle sizes were investigated in relation to soil microbial properties in a short-term incubation study. Three particle size （sieved） fractions （0.5-1.0, 1.0-2.0 and 2.0-4.0 mm） from three woody biochars produced from jarrah wood, jarrah and wandoo wood and Australian wattle branches, respectively, were incubated in soil at 25 ℃ for 56 d. Observation by scanning electron microscopy （SEM） and characterisation of pore and surface area showed that all three woody biochars provided potential habitats for soil microorganisms due to their high porosity and surface areas. The biochars were structurally heterogeneous, varying in porosity and surface structure both within and between the biochar sources. After the 56-d incubation, hyphal colonisation was observed on biochar surfaces and in larger biochar pores. Soil clumping occurred on biochar particles, cementing and covering exposed biochar pores. This may have altered surface area and pore availability for microbial colonisation. Transient changes in soil microbial biomass, without a consistent trend, were observed among biochars during the 56-d incubation.