电场作用下竖直板表面特性对霜层生长的影响

研究了自然对流条件下直流电场对竖直表面上霜晶初始形态的影响,拍摄了不同电场下的霜晶形态,研究发现,在成霜初期,电场越强,冷壁面上形成的水珠越小。当水珠完全冻结后,所形成的冰柱在一定时间内不断增大。在适当的电场下,亲水表面比裸铜表面能够更好地抑制霜层的厚度。对亲水表面结霜质量的研究表明,电场使结霜质量增加,并且结霜质量随着电场的增大而增大。     

自然对流条件下疏水表面与普通金属表面霜生长的对比研究

结霜是一种在低温下普遍存在的现象,可对设备造成很多危害.本文通过在自然对流条件下,竖直冷平板上疏水表面与普通金属表面霜生长过程显微动态观察实验,证明疏水表面有利于延缓霜的生长并根据相变动力学理论,分析了原因.     

铝基体超疏水表面结冰结霜特性研究

采用中性电解液,通过电化学加工技术及氟化处理方法制备出铝基体超疏水表面,接触角达160°,滚动角小于5°,并在其上进行了结冰和结霜研究.在不同实验条件下研究超疏水表面的形貌、霜高随时间的变化,并与相同条件下的普通铝表面、吸水性表面进行了对比.结果表明,该超疏水表面经过50多次结霜、除霜后,仍具有很好的超疏水性能,表现出良好的重复性和耐久性;与普通铝表面相比,铝基体超疏水表面具有明显的抗结冰结霜性能,霜晶先出现在四周边缘处并逐渐蔓延到中间,但抑霜能力随着冷表面温度的降低而减小;与吸水性表面相比,超疏水表面在抗结冰结霜的同时能有效抑制表面质量的增加.     

自然对流条件下冷表面结霜的实验研究

本文利用微观可视化观测方法,实验对比研究了裸铝(接触角78°)、疏水（接触角141°）和亲水(接触角26°)三种特性表面结霜过程。结果表明,当相对湿度为26%,表面温度为﹣10 ℃时,相比于裸铝表面,疏水表面可以延迟结霜29 min;当温度降至﹣18 ℃,疏水表面仍具有较好的抑霜效果。1 h后,疏水表面上的霜层高度仅为裸铝表面上霜层高度的68%。当表面温度为﹣26 ℃时,3种不同接触角的表面上初始霜晶的形态差异较大,疏水表面倾向于形成更加稠密的沿水平方向生长的枝状霜晶并向片状转变,而亲水表面则倾向于形成沿竖直方向生长的稀疏的针状霜晶,随着空气中水蒸气向霜晶扩散凝华,针状霜晶从顶部向底部逐渐向片状霜晶转变。     

一种新型抑霜涂料在翅片管式换热器上的应用研究

换热器表面结霜是制冷和低温设备中最常见的问题之一,它会严重影响换热器的换热效率,降低制冷系统的整体性能。用自行研制的一种新型抑霜涂料制成亲水表面,将其涂敷于换热器翅片上,厚度为0．05mm。在相同的实验条件下与没有涂层的换热器实验结果进行比较,发现有涂层的换热器能够大大延长融霜周期,在整个实验过程中没有出现结霜现象。涂层厚度对换热器出口的温度和换热器的传热性能没有明显影响。另外,还针对有涂层的翅片进行了一系列的吸水试验,测试涂层质量、厚度以及表面粗糙度随浸水时间的变化。     

水平冷面上霜晶生长规律的实验研究

对水平铜冷面上的结霜过程进行了显微实验观察，实验结果表明：结霜过程基本上都经历了水珠生成、长大、冻结、初始霜晶生成、长大以及霜层成长等过程。根据霜晶的外观形状特点将初始霜晶分成了四大类，讨论了初始霜晶形状随冷面温度和空气相对湿度的变化规律，指出冷面温度是影响霜晶形状的主要因素，而空气的相对湿度对霜晶形状也有一定影响。     

铝基体超疏水表面的抗结冰结霜效果分析

增加接触角是提高表面抗结冰结霜能力的重要方法.借助电化学加工和氟化处理获得铝基体超疏水表面,该表面具有二元微纳米复合结构,干燥时水滴在其上的接触角为160°,滚动角小于5°,处于Cassie-Baxter状态.在自制的半导体制冷台上,观测冷表面温度为-5.2 ℃时,铝基体超疏水表面的结霜过程,并将其与普通铝表面进行了对比,发现铝基体超疏水表面的四周边缘处先出现霜晶并逐渐蔓延到整个表面,与普通铝表面相比具有显著的抗结冰结霜性能.最后对铝基体超疏水表面的边缘效应和抗结冰结霜机理进行了分析.     

疏水性对竖直冷表面上自然对流结霜特性的影响

本文采用控制表面氧化法制备超疏水表面(153. 2°),并对自然对流条件下竖直放置的超疏水表面与裸铜表面进行可视化结霜实验,观察并对比实验初期有液核与无液核生成成霜时疏水性对结霜过程的影响,研究了疏水性对结霜的影响随冷表面温度(-50～-30℃)、空气相对湿度(30%～70%)的变化规律。结果表明,有液核成霜时,超疏水表面具有显著的抑霜效果;无液核成霜时,疏水表面不再具有抑霜效果,反而超疏水表面霜晶生长更为密实;疏水性对无液核成霜过程的影响随空气相对湿度的增大、冷表面温度的降低而减弱;从云物理学与核化理论角度分析了无液核生成时超疏水表面霜晶分布更密的原因,发现实验制备的超疏水表面上凹坑与CuO晶体颗粒为凝华核化提供了有利位置。     

水平阵列方微柱表面自然对流的结霜特性研究

本文制作了微机械加工的阵列方微柱金属表面,实验研究了其在环境温度Tatm=24℃,相对湿度RH=17％,不同冷表面温度(Tw=-5.2、-10.1、-15.2℃)及不同试件尺寸时,自然对流条件下的结霜特性,分析了表面温度和持续时间对霜层厚度和霜重量的影响,提出了阵列方微柱表面的抗结霜机理,并通过仿真模拟进行了验证.结果...     

自然对流条件下竖直冷平板霜生长规律的研究

本文通过在自然对流条件下,竖直冷平板上金属表面霜生长的过程显微动态观察及霜高的测量,根据实验现象和测量数据,从理论上分析了相变驱动力对结霜的作用,并可以正确解释霜生长过程中观察到的现象.     

An experimental study on minimizing frost deposition on a cold surface under natural convection conditions by use of a novel anti-frosting paint. Part II. Long-term performance, frost layer observation and mechanism analysis

In this part of study, the comparative observations of the structure and the surface temperature of the frost layer of both the coated and uncoated surfaces ware carried out and a preliminary analysis was presented. A series of the repeated cycling tests were completed that lasted for more than 2 months, and the influences of the coating thickness were also investigated. The results show that the frost layer deposited on the coating surface has a very fragile structure and can be removed easily by external force. The coating thickness has an important effect on the anti-frosting performance of the paint. The results also show that the coating of the paint on the copper surface is durable and presents a very good repeated cycling performance.     

An experimental study on minimizing frost deposition on a cold surface under natural convection conditions by use of a novel anti-frosting paint. Part I. Anti-frosting performance and comparison with the uncoated metallic surface

In this study, an experimental investigation is made of the anti-frosting performance of our newly developed anti-frosting paint. By coating the paint on a cold metal surface the onset of the frost formation may be delayed at least 15 min and the thickness of the deposited frost layer may be reduced by at least 40% and thus the weight of the deposited frost may be reduced by more than 40% compared with that on the uncoated copper surface. Under some preferable conditions (air relative humidity <60%, cold plate surface temperature >−10 °C), the coating surface can be kept free of frost at least for 3 h.     

SiC/PyC复合涂层碳纤维微观结构及氧化行为研究

采用两步法在碳纤维表面制备了碳化硅/热解碳(SiC/PyC)复合涂层,PyC内涂层的制备采用等温化学气相渗透法,SiC外涂层的制备采用碳热还原法.借助X射线衍射、场发射扫描电镜、透射电镜分析了SiC/PyC复合涂层碳纤维的物相组成以及微观结构,利用热重分析研究了SiC/PyC复合涂层、PyC涂层以及无涂层碳纤维的氧化行为.结果表明,在碳纤维表面制备的SiC/PyC复合涂层连续致密、厚度均匀,PyC内涂层厚度约为200nm,SiC外涂层厚度约为160nm,SiC层中存在大量孪晶面高度有序的SiC孪晶.SiC/PyC复合涂层能够有效地改善碳纤维的抗氧化性能,较无涂层碳纤维起始氧化温度提高了近250℃.     

Development of diamond coated tool and its performance in machining Al-11% Si alloy

An attempt has been made to deposit CVD diamond coating on conventional carbide tool using hot filament CVD process. ISO grade K10 turning inserts with SPGN 120308 geometry were used to deposit diamond coating. This diamond coating well covering the rake surface, cutting edges and flank surfaces could be successfully deposited. The coatings were characterized by SEM, XRD and Raman spectroscopy for coating quality, morphology etc. Performance of diamond coated tool relative to that of uncoated carbide tool was evaluated in turning Al-11% Si alloy under dry environment. The diamond coated tool outperformed the uncoated carbide tool which severely suffered from sizeable built-up edge formation leading not only to escalation of cutting forces but also poorer surface finish. In contrast, the diamond coated tool, owing to chemical inertness of diamond coating towards the work material, did not show any trace of edge built-up even in dry environment and could maintain low level of cutting forces and remarkably improved surface finish. It has been further revealed that success of the diamond coated tool depends primarily on adhesion of the diamond coating with the carbide substrate and this is strongly influenced by the pre-treatment of the carbide substrate surface before coating.     

Hard coatings on light-metal components under mechanical surface loading

In this work the behaviour of hard coated light-metal components was investigated when they are mechanically loaded. Three lightmetal alloys, Ti-6Al-4V, AlSi7Mg and AlMgSi0.5 and 100Cr6 steel (as a reference material) were coated by two different physical vapour deposition processes: radio frequency magnetron sputtering and electron beam evaporation. The coating materials utilised were CrN and TiN. Standard test methods with different loading conditions were used to evaluate the substrate/coating-combinations: the hardness test (applying a static normal load), the scratch test (applying a combination of a static normal and a static tangential force) and the impact test (applying a dynamic normal load). It was observed that the load support of coated materials depends on the loading conditions. The coated aluminium alloys showed poor load support under all loading test conditions but produced a higher surface hardness than uncoated steel. Coated Ti-6Al-4V showed very good load support properties, similar to coated steel. All coated light-metal substrates demonstrated significant improvement in load support behaviour with an increase in coating thickness. The results of the scratch test, which is commonly used to asses adhesion properties of thin coatings, showed an immediate indenter-breakthrough on the aluminium alloy substrates, but causing no coating delamination. Due to this behaviour, the scratch test is not suitable to evaluate adhesion properties on coated soft light-metals. Yet the impact test allowed assessment of coating delamination on the aluminium alloys, proving its usefulness for adhesion measurement even on soft substrates. The study indicates that substitution of steel with coated lightmetal alloys is a viable proposition for certain applications.     

温度稳定型Ph(Ni_(1/3)Nb_(2/3))O_3基复相陶瓷的制备及介电性能

选取居里温度不同的两组元，对其中一组元包覆ＰＴ，再与另一组元混合烧结，制备出满足Ｘ７Ｒ 温度稳定特性的复相陶瓷．用ＴＥＭ观察了ＰＴ包覆前后粉末的颗粒形态，结果表明，ＰＴ较好地附着 在颗粒表面ＰＴ包覆层的存在抑制了两相的固溶反应，使材料保持复相结构，改善了材料的介电温度特 性分析了 ＰＴ包覆层的作用     

Fretting fatigue behaviour of hard anodizing coated 2014‐T6 aluminium alloy with dissimilar mating materials under plane bending loading

The effect of hard anodizing coated 2014‐T6 aluminium alloy test samples with dissimilar mating materials on fretting fatigue was investigated. Fretting fatigue configuration involved bridge‐type pads on the flat specimen. Bridge‐type pads were made of AISI 4140 steel. All the fretting fatigue tests were conducted under plane bending loading with a stress ratio of R=?1. Coated and uncoated specimens were compared for microhardness, surface roughness, tangential force. The specimens were tested under both plain fatigue and fretting fatigue loading at ambient temperature. Micrographs obtained from scanning electron microscope showed that hard anodizing coating had tiny cracks through the thickness of the anodized layer. The hardness of hard anodized coating was higher than that of uncoated specimens and they also exhibited lower tangential force. However, the fretted region of the hard anodizing coated specimens was rougher than that of uncoated samples and despite lower tangential forces, fatigue lives of hard anodizing coated samples were inferior to those of uncoated samples. As the hard anodizing coating had pre‐existing tiny cracks and tension residual stress, cracks propagated from the hard anodizing coating through the interface into the substrate. We conclude that these may be the main reasons for inferior fretting fatigue lives compared with uncoated samples.     

Fatigue Properties of Steel Coated with TiN by a PVD Process

Specimens of the steels S 6-5-2 (AISIM2) and 100 Cr 6 (AISI 52100) were coated with TiN by a reactive DC-magnetron-sputtering process. The fatigue behaviour of coated and uncoated specimens was investigated under cyclic bending. The fatigue limit of the uncoated steel S 6-5-2 is mainly governed by internal defects like carbide clusters and micropipes. Therefore, a coating has no influence on the fatigue limit. At high stress amplitudes the failure of the uncoated material is initiated at the specimen surface. Thus, coating of the surface causes higher mean lifetimes. The fatigue behaviour of the uncoated steel 100 Cr 6 is mainly governed by crack initiation at the surface of the specimens. At low stress amplitudes, a coating may shift the crack initiation place to the interior of the specimens. Hence, a slight improvement of the fatigue limit by coating is observed. At high stress amplitudes the coating has no influence on crack initiation and no improvement of the lifetime can be achieved by coating.     

二水磷酸氢钙包覆镁粉的组织及其在NaCl溶液中的腐蚀行为

运用液相化学沉积技术制备了二水磷酸氢钙包覆镁粉粉末。利用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)及傅里叶变换红外光谱仪(FT-IR)分析包覆层特征,用比表面积和孔隙度分析仪测定包覆前后粉末的比表面积,并通过浸泡实验研究包覆粉末的腐蚀行为。结果表明,包覆处理后的镁粉颗粒仍保持球形,表面形成了一层厚度2~4μm细片状的二水磷酸氢钙(DCPD),与未包覆粉末相比,其比表面积增加约60倍,在3.5%(质量分数)NaCl溶液中的耐腐蚀性能提高四个数量级。     

Determination of the thickness of metal coatings on granular diamond materials by spatially resolved optical methods

The embedding of surface-modified granulates into metallic matrices is a promising way to optimize the interface matrix/granulate in respect to mechanical and thermal properties. In the case of surface modification by coating, a reliable determination of the coating thickness on granulates is desirable, since the interface properties may depend on it to a critical extent. This paper proposes a simple method to determine the thickness of transparent metal coatings on diamond substrates. Diamond granulates with grain sizes between 100 and 120 μm were coated with molybdenum in an intermixing device which allows reasonable film uniformity on granulates. The deposition method was single source DC magnetron sputtering with argon as working gas. By comparing the transmission of the uncoated and coated diamonds with an optical scanner, the coating thickness could be determined from the known extinction coefficient. A good correlation between the measured film thicknesses and the deposition time was achieved. It can be concluded therefore, that the presented method is a viable and cost-efficient way for the determination of the average thickness of transparent metallic coatings on a sample of transparent granular substrates, with an estimated minimum and maximum measurable thickness of 2.5 nm and 15 nm respectively for molybdenum.