Development Of High Temperature Melt's Surface Tension Measurement System With Pendant Drop Method

Surface tension,as one of the important interface properties of matter,plays an important role in related disciplines such as surface chemistry,material metallurgy,and colloidal interface science.It is very important and necessary to measure the surface tension of melt in the field of high temperature.There are many methods for measuring the surface tension of high temperature materials,including the drop weight method and the maximum bubble method.Compared with other measurement methods,the pendant drop method has relatively high measurement accuracy and less sample volume,and has a good application prospect.Based on the theory of pendant drop method,the fitting algorithm for solving the surface tension of pendant drop is programmed by MATLAB software,including the collection of hanging drop image,edge detection of hanging drop contour,extraction of contour boundary,scale transformation of coordinates and contour correction processing.The Young-Laplace ordinary differential equation is solved by the4-5-order Runge-Kutta algorithm.The objective function between the fitted contour and the actual contour is constructed,and the objective function is optimized by the coordinate contour method.The initial values of the fitting arc length,R₀ and?that need to be provided in the algorithm are explored.It is found that the fitting arc length is smaller than the actual contour arc length,which will bring measurement error.If it is too large,the calculation amount will be too large.The length of the arc should be slightly larger than the actual arc length.The closer the initial values of R₀ and?are to the actual values,the less the calculation time is,and the initial values of R₀ and?can be estimated in advance using the plane selection method.An experimental system for measuring the surface tension of the melt by high-temperature hanging drop method was developed.The experimental device body,temperature control system and image acquisition system were designed and constructed.The surface tension of high temperature materials can be accurately measured in a protective atmosphere or under vacuum at room temperature to1000°C.The factors affecting the surface tension measurement results in the experiment were analyzed,including the pixel,the background wavelength,the size of the image interception,the integrity of the hanging drop,the influence of the standard size,and proposed a reasonable solution.The experimental system was tested with pure water.The uncertainty of measuring the surface tension of the hanging drop experimental system is less than 0.95%,which indicates that the experimental system has high accuracy and reliability.The thermogravimetric and heat flux of mixed bromide salt in the temperature range from room temperature to 800°C was measured.The temperature change process of mixed bromide salt in the temperature range from 800°C to 800°C was analyzed.The mixed bromide salt was measured by the experimental system developed.In the temperature range of 400-600°C,the surface tension of the mixed bromide salt decreases with increasing temperature,and the fitting equation of the mixed bromide salt with respect to temperature in the temperature range of 400-600°C is obtained.Compared with the surface tension values measured by previous scholars,it is shown that the measurement results of the pendant drop method have good accuracy.By properly modifying the experimental system,it is possible to measure the surface tension of the liquid by the sessile drop method.Four different materials,such as glass,alumina,paraffin and hydrophobic membrane,were used as the substrate to obtain different contact angles.The influence of contact angle and droplet volume on the measurement accuracy was analyzed.The measurement error of the seat drop method will decrease with the increase of contact angle and droplet volume.And the surface tension of molten tin in 300-800°C was measured in high purity argon atmosphere.The temperature coefficient of surface tension of molten tin under different experimental conditions has different trends in different temperature range,provide reference for the research of other scholars.