Use of polarization contrast for determination of dimensions of the contour of a sessile melt drop

We can improve the measurement accuracy of dimensions of the contour of a sessile melt drop by using polarization contrast of the thermal radiation from different points of the surface of the drop. The improvement of accuracy is achieved by elimination of blurring of the contour of the image edge in the course of detection. The widespread method for measurements of shadow image with illumination, which uses the maximum of the derivative of the transition function (the Laplace function), is physically groundless. By using the maximum of the degree of polarization, we can eliminate some measurement errors. On the basis of the experimental results, we can estimate the efficiency of the method including dependences of the results on the melt temperature. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 5, pp. 88–92, September–October, 1997.     

Operating experience of optical-digital systems for measuring the capillary characteristics of materials

We analyzed the well-known optical-digital systems of optical nondestructive testing and measurement of the capillary characteristics of materials by the method of sessile drop. We show that the parameters and operating modes of such systems should be optimized. We consider a model and created a breadboard on its basis. By using the breadboard, we investigated optical and electronic noises of the system and the other sources of measurement errors of the geometric parameters of a drop image. The results allow one to optimize the parameters of the system in such a way that the measurement errors of the capillary characteristics should be minimum. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 5, pp. 81–87, September–October, 1997.     

Factors limiting the accuracy of measurements of surface tension by the sessile drop method

Different sources of error in determining surface tension by the sessile drop technique are discussed. The influence of uncertainties in measuring drop co-ordinates are quantitatively evaluated, and the results tested on Ag and Pb drops at different temperatures. Shifts in surface tension values, due to errors in determining the exact scale factor and to errors in reading temperature or density, are calculated, and a nomographic chart, to find the optimum drop weight, is also presented.     

Surface tension measurements of refractory liquids using the modified drop weight method

Liquid surface tension measurements using the sessile drop, pendant drop and drop weight methods are discussed. These measurements refer to high temperature materials which melt at temperatures greater than 2000° C. The liquid surface tension of copper was determined to be 1212 dyn/cm at its melting point, and that of Al₂O₃ to be 600 dyn/cm at its melting point. Discussion is presented giving preference to the drop weight method.employed at the Corning Glass Works during the summer of 1966.     

活性钎料Cu_(50)Ti_(50)在Sialon陶瓷表面的润湿动力学观察

采用躺滴技术观察了在1248K 活性钎料 Cu_(50)Ti_(50)在 Sialon 陶瓷表面的铺展动力学过程,并用 X射线衍射技术鉴定了在金属/陶瓷界面上产生的界面反应产物。结果发现,在试验条件下(1248K,0—5min),这种活性钎料在陶瓷表面流动时,润湿半径与铺展时间的平方根之间存在很好的线性关系。就作者所知,这一规律是第一次在金属—陶瓷系统中被发现和报道,其机理有待于进一步研究。     

Solidification of metallic aerosol droplets from floating rafts: a test of the spiral growth mechanism for Cd and Zn

The strain energy developed by surface stresses in a crystalline raft of basal orientation floating on a droplet of melt is calculated and compared to the strain energy of a screw dislocation situated on the raft axis. The suggestion that a dislocation is generated at a characteristic value of the raft/drop radius ratio is tested by making the comparison for arbitrary values of raft aspect ratio and Burgers vector. When b = c, the lattice parameter of the hexagonal crystal, the energies are equal at a combination of aspect ratio and radius ratio that fits experiment. The apparent height of the helical growth step greatly exceeds this value of b and remains to be explained, but the results confirm that a high growth rate anisotropy is required initially to produce the dislocation.     

Generation of isothermal spreading data and interfacial energy data for liquid reactive metals on ceramic substrates: The copper-titanium/alumina system

The sessile drop technique is frequently used to evaluate the wettability and spreadability of liquid metals on ceramic substrates. In this study, the spreading kinetics of copper-20 wt% titanium alloys on polycrystalline alumina were evaluated based on measurements of spreading radius versus time. The process of spreading was monitored by anin situ video recording system. The tests were performed using three different initial metal configurations. It was found that conventional sessile drop testing configurations cannot be used to generate isothermal spreading kinetics data because of significant spreading during the heat-up cycle from the solidus temperature to the test temperature. An improved sessile drop technique was developed which eliminated the non-isothermal experience by introducing the liquid copper to the solid titanium/alumina at the desired testing temperature. Using this technique, only a few seconds of data were lost (while the liquid copper dissolved the solid titanium). Because very limited interfacial energy data exist for the copper-titanium/alumina system, especially at higher titanium concentrations, the equilibrium contact angle, the solid-liquid interfacial energy, and the work of adhesion from 1000 to 1300 °C are also presented.     

Errors of the shadow image of a lying drop of melt caused by the divergence of illuminating rays

With the use of optical digital systems, we analyze the errors in determining the size of a lying liquid drop of melt by its shadow image that are caused by the divergence of illumination rays. Complete elimination or compensation of such errors is impossible. We determine conditions under which one can neglect these errors in comparison with the errors of discretization of the image by the array photodetectors of video cameras. On the optimal use of the array of 2048 x 2048 pixels, the divergence angle of illuminating rays should not exceed 1‡ and, for the array of 512x512 pixels, it should not exceed 2‡. To satisfy these conditions, one should use an optical system with resolving power at the edges of the image two times higher than that of the array photodetector. namely, at least 143 lpmm for the 14 x 14 Μm pixel size, or 250 lpmm for the 8x 8 Μm pixel size. Translated from Fizyko-Khimichna Mekhanika Materialiv. Vol. 36, No. 3, pp. 74–77, May-June, 2000.     

The Surface Tension of Melts of Aluminum–Indium Binary System

The temperature and concentration dependences of the surface tension (ST) of alloys of the Al–In system are investigated by the sessile drop method. It is shown that small (up to 0.6 at. %) additions of indium significantly lower the ST of aluminum, and the temperature coefficients of ST of the investigated alloys have positive values in this range of compositions. The obtained data are used to calculate the adsorption of indium (according to Guggenheim–Adam, N option) and the number of its monolayers (according to Rusanov) in the surface layer of Al–In solutions. It follows from these data that the adsorption of indium on the melt surface reaches the maximal value with a bulk content of indium of about 0.1 at. %, and the excess of indium in the surface layer corresponds to three monolayers of indium.     

Application of push-off shear test for evaluation of wetting-interface structure-bonding relationship of solder joints

The relationship between wetting behavior, interface structure and mechanical properties of solder/substrate couples has been studied on example of Sn-alloys and Cu substrates. The sessile drop method was used to investigate the solder wetting and spreading on polished Cu substrates in vacuum at a temperature of 503 K. The sessile drop samples after solidification were bisected perpendicularly to the substrate at the mid-plane of the contact circle. The first half of each sample was used for structural characterization of interfaces and evaluation of their mechanical properties by improved push-off shear test. The second half was used for investigation of the effect of thermocycling on structural stability and corresponding mechanical behavior of model solder/Cu joints. A comparison with the results obtained on standard solder joints has shown the usefulness of the improved push-off shear test performed directly on solidified sessile drop samples as an express test for evaluation of technological and mechanical compatibility of solder/substrate couples, particularly at the first stage of solder candidate selection.     

Surface tension and contact angles of molten cadmium telluride

The surface tension and contact angle of molten cadmium telluride (CdTe) were measured as a function of temperature by the sessile drop technique. A FORTRAN code was developed to calculate the surface tension of sessile drops, with the contact angle ranging from O to 180°. The wetting of cadmium telluride melt was studied on different surfaces. The surface tension of cadmium telluride was about 160 ±5 dynes · cm^–1[1.6 m^–1] at the melting point of 1093°C. The contact angle of CdTe melt was about 65° on a quartz optical flat, 75° on commercial fused quartz, and 125° on boron nitride coated quartz.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

应用轮廓吻合法测量Li_2B_4O_7·KNbO_3溶液的表面张力系数

讨论了一种表面张力测量方法一轮廓曲线吻合法．它是一种应用计算机技术,用数 字图像信息处理液滴轮廓的方法．应用数字图像测量和信息处理技术,将置于氮化硼水平平板 上的Ｌｉ２Ｂ４Ｏ７＋ＫＮｂＯ３液滴的轮廓图像记录在录像带上,然后转换成数字图像数据,并与理论 方程的数值解吻合,求得表面张力系数．用这种方法侧得的Ｌｉ２Ｂ４Ｏ７＋ＫＮｂＯ３溶液的表面张力 温度系数和表面张力溶质系数分别为 γΤ（ｍＮ／ｍ）＝２１０＋０．１５（Ｔ－９００℃）, ９００℃≤ Ｔ≤１０００℃; γｃ（ｍＮ／ｍ）＝２２９０．４５（ＣＫＮ－１０ｗｔ％）, １０ｗｔ％≤ ＣＫＮ ≤３０ｗｔ％     

An improved method of sessile drop for determining the surface tension of liquids

An improved procedure is developed for the processing of images of meridional section of a liquid drop, obtained as a result of realization of the sessile drop method for determining the surface tension of liquid. The procedure provides for the scanning of digital image of droplet, for numerical solution of the Young-Laplace equation, and for the calculation of surface tension, wetting angle, and volume of the drop.     

The determination of surface tension at elevated temperatures by drop image analysis

The advantages of image analysis as applied to surface tension measurements by the sessile drop technique are discussed. It is demonstrated that valuable effective improvements of dimensional resolution are obtained. Errors in surface tension arising from various unavoidable sources such as chemical reactions or optical distortions are shown to be the main difficulties in applying the sessile drop technique at high temperature. This suggests a limiting spatial resolution of the digitizer beyond which no further improvements to the accuracy of the surface tension results are possible.

The technique has been applied to determine the surface tension of liquid Cu, Bi and Ag as well as a series of sodium borosilicate glasses.     

Density and surface tension polytherms of gallium-lead melts

The density and surface tension of gallium-lead melts have been determined using the sessile drop technique in the temperature range of 600–1000°C. According to the form of polytherms of surface tension of a system with Ga-Pb exfoliation, a conclusion was made about the primary distribution of lead ions on the melt-vapor boundary. The excess entropies of melt formation were calculated. The comparison of experimental and calculated values of excess entropies showed that primary interaction between similar ions highlights the linear character of density polytherms.     

Effect of ZrO2 on the alkali feldspar-aluminosilicate interface

The contact angles of the alkali feldspars containing 0, 4, 8 and 12 vol % ZrO₂ on the aluminosilicate substrate were measured by sessile drop method. During the heating from 1350 to 1520° C and the holding at 1350° C, the contact angles were generally increased with increasing ZrO₂ content. 8 vol % ZrO₂ in the melt drop was very effective to raise the contact angles and 12 vol % ZrO₂ was barely sufficient to maintain the contact angles at around 90° or larger at elevated temperatures. The SEM micrographs indicated that ZrO₂ particles were scattered throughout the drop and also located in the interface between the drop and substrate. The dissolution of the substrate by liquid feldspar and the diffusion of ZrO₂ in the substrate were also observed. The cause of the increase in contact angle with increasing ZrO₂ content are discussed.     

镀铜石墨与铝熔体的润湿性

为了改善石墨与铝的润湿性,通过化学镀使石墨颗粒表面形成完整致密的铜镀层,然后将8%(质量分数)的镀铜石墨粉通过熔体搅拌法加入到铝合金基体中制得金属基复合材料.采用改进的座滴法分别测定了铝熔体与石墨、镀铜石墨的接触角.同时,利用扫描电镜(SEM)对石墨颗粒增强铝基复合材料的微观形貌进行了检测.结果显示,铝熔体与镀铜石墨的接触角为27°,其界面具有良好的润湿性,镀铜石墨粉在铝合金基体中分布均匀.     

The Measurement of the Surface Energy of Solids by Sessile Drop Accelerometry

A new physical method, the sessile drop accelerometry (SDACC) for the study and measurement of the interfacial energies of solid-liquid-gas systems, is tested and discussed in this study. The laboratory instrument and technique—a combination of a drop shape analyzer with high-speed camera and a laboratory drop tower- and the evaluation algorithms, were designed to calculate the interfacial energies as a function of the geometrical changes of a sessile droplet shape due to the effect of “switching off” gravity during the experiment. The method bases on Thermodynamics of Interfaces and differs from the conventional approach of the two hundred-years-old Young’s equation in that it assumes a thermodynamic equilibrium between interfaces, rather than a balance of tensions on a point of the solid-liquid-gas contour line. A comparison of the mathematical model that supports the method with the widely accepted Young‘s equation is discussed in detail in this study. The method opens new possibilities to develop surface characterization procedures by submitting the solid-liquid-system to artificial generated and uniform force fields.     

Wetting of polycrystalline MgO by molten Mg under evaporation

The concomitant wetting and evaporation behaviors of molten Mg on polycrystalline MgO surfaces were studied at temperatures 973–1173 K in a controlled Ar atmosphere using an improved sessile drop method. Representative wetting modes were identified by correlating contact angle with contact diameter and drop height. The intrinsic wettability in this nonreactive system can be characterized by the initial contact angles obtained in better precision from solution to a diffusion model. In addition, the excess free energy stored in the system and the potential energy barrier opposing the movement of the triple line were evaluated to account for the distinct “stick-slip” behavior.     

A high-temperature Auger electron spectrometer setup and its application to reactive wetting experiments at 1700 K

A high-temperature Auger electron spectroscopy setup and its in situ application to sessile drop experiments of molten silicon on oxide substrates are presented. The experimental setup allows for measurements of previously inaccessible surface reactions at temperatures up to 1700 K. Auger electron spectra of SiO₂, MgO, and liquid Si are presented. Furthermore, the areas of the substrates that have been transiently wetted by the silicon melt are investigated. The results are discussed with respect to questions concerning reactive wetting of oxides by metal melts, which are important for the material science of joining processes.