Instantaneous Contact Angle Research Articles

Effect of carbonaceous particles on slag foaming

Use of carbonaceous particles such as coke or coal char in controlling slag foaming is of great practical significance for bath-smelting and other steelmaking processes. The foamability of the liquid slag in terms of the foam index has been determined with the presence of different amounts of coke and coal char particles. Different sized and shaped particles were used in the experiments. It was found that the foam index decreased significantly as the ratio of the total cross-sectional area of the particles to the liquid slag surface area increased. When the foam was generated by argon gas injection through an alumina nozzle (i.d. = 1.5 mm), a liquid slag, CaO-SiO2-CaF2-(Al2O3), depending on the alumina content, could have an initial foam index of about 2 to 4 seconds at 1500 °C without any carbonaceous particles. When the slag surface was covered only 15 ~20 pct with either coke or coal char particles, the foam was totally suppressed regardless of the initial foam index. In order to understand the mechanism of the antifoam effect of the carbonaceous particles, interactions of a coke sphere, an iron ore pellet, an alumina tube, and a coal char particle with the liquid slag foam were examined by X-ray observation. It was concluded that the antifoam effect of coke or coal char particles is primarily contributed by the nonwetting nature of the carbonaceous materials with the liquid slag. Possible mechanisms of carbonaceous particles rupturing a slag film could be (1) the rapid thinning of the liquid slag film driven by a difference between the instantaneous contact angle and the equilibrium contact angle or (2) the “dewetting” of the liquid slag from the interface when the film is “bridged” by the particle.

Influence of n-alkylammonium chlorides on the adhesion of air bubbles to the fluorite surface

The detachment force of air bubbles from the surface of fluorite immersed in aqueous solutions of decyl-, dodecyl- and tetradecyl ammonium chloride at different concentrations was measured. Simultaneously, the instantaneous contact angle and the height of the air bubble at the moment of detachment were determined. From the results obtained, the work of adhesion of an air bubble to the surface of a fluorite grain was evaluated and compared with that determined on the basis of Young's equation. Based on the measurements and calculations carried out, the detachment force was found to depend on the concentration and length of the alkyl chain of the surfactants. A linear relationship between the recovery of fluorite by flotation in the presence of the n-alkylammonium chloride salts and the detachment force was also found, as well as good agreement between the work of adhesion of an air bubble to the fluorite determined from the detachment force and from Young's equation.

The influence of oxidation degree of galena surface and of ethyl xanthate on the stability of galena-air aggregates

Measurements of the detachment force of air bubble from galena surface in water and in potassium ethyl xanthate solution at natural pH and pH 9.5 were made. Also, the influence of the degree of oxidation of galena surface on the detachment force was studied. Instantaneous contact angles were measured at the moment of air bubble disruption in the galena grain-air-bubble-water system and galena grain-air bubble-potassium ethyl xanthate solution. Using the Young's equation and the instantaneous contact angles, the nondispersion component of galena surface free energy was calculated and compared with that obtained from the detachment force values. From the comparison, it is concluded that the changes of detachment force occur particularly under the influence of nondispersion component changes.

Adhesion of air bubbles to Teflon surfaces in water

Measurements of the detachment force of air bubbles from polytetrafluoroethylene (Teflon) surfaces in water were carried out. At the moment of the detachment the Teflon-air bubble-water system was photographed to determine the instantaneous contact angle value. The contact angle and the contact plane diameter of small bubbles left on the Teflon surface after disruption of large bubbles at the moment of their detachment were also measured. A theoretical analysis was made of an earlier derived relationship between the detachment force and the radius of the contact plane, liquid surface tension, contact angle, and the radius of air bubble. On the basis of the performed measurements and theoretical considerations it was found that this relationship holds for the Teflon-air bubble-water system; however, differences between the measured and calculated values of the detachment force are higher than for solid-air bubble-water systems in which the contact angle is less than 90°. It was also found that the theoretically calculated values of a given air bubble contact plane radius corresponding to maximal detachment force is almost equal to that measured for a small bubble left on a Teflon surface after disruption of a large bubble nearby on the Teflon surface.

Dynamics of stick-slip jumps

The dynamics of stick-slip jumps on heterogeneous surfaces is analysed with a simple experimental model system. The heterogeneity of the surface is controlled by the application of thin low-energy ink lines on a high-energy glass surface. The liquid spreads completely on the bare glass surface but has a finite contact angle on the ink. The ink lines serve to pin the contact line in a controllable way. The stick-slip jumps from one pinning position to another manifest themselves as “waves” propagating along the contact line with well-defined shapes and constant velocity. The important findings are: (1) the propagation velocity of a stick-slip wave is to first order independent of the wave amplitude, (2) the velocity depends on the instantaneous contact angle, reminiscent of “Tanner's Law”, and (3) above a certain critical width of the pinning line, the waves halt completely.

Adhesion of an Air Bubble to Quartz Surface in Aqueous Solution of Aliphatic Amine Hydrochloride

Abstract Measurements of the force of air bubble detachment from a quartz surface in aqueous solutions of decylamine hydrochloride (DAC1), dodecylamine hydrochloride (DDAC1) and tetradecylamine hydrochloride (TDAC1) were made in the concentration range from 0 to 200mg/dm3. At the same time, the instantaneous contact angle for the system quartz-air bubble-aqueous solution of aliphatic amine hydrochloride was photographed at the moment of detachment. Wetting contact angles for the system quartz-air bubble-aqueous solution of DDAC1 were also measured. On the basis of the measured values of the instantaneous angle and surface tension of the solutions studied, the changes of polar components of surface free energy of quartz/monolayer water film under the influence of adsorption of molecules of aliphatic amine hydrochloride (RAC1) from aqueous solution were calculated and compared with the literature data. Using these data, the force of air bubble detachment from the quartz surface in the presence of RAC1 was also calculated and compared with the measured force, obtaining a good agreement. From the studies and calculations it appears that a little addition of RAC1 to water considerably changes the stability of the system quartz-air bubble-solution, and that this change is first of all caused by reduction of a polar component of the surface free energy of quartz/monolayer water film as a result of adsorption of RAC1 molecules in the negative places of such a surface. As a result of RAC1 adsorption this surface becomes similar to that of paraffin.

The spreading of liquid droplets on solid surfaces

A model of the spreading of droplets on solids is synthesized from fluid dynamics and surface physics. It predicts that the contact line diameter d of the droplet varies with time t as d = K[( σV 0 2/ μ) t + ( d i/ K) 7] 1/7, where V 0 is the droplet volume and μ and σ are the liquid viscosity and surface tension; the equilibrium contact angle is zero degrees. The 1 7 exponent is a consequence of the fact that the contact line velocity varies as the square of the instantaneous contact angle. A single empirical, nondimensional parameter K is required to quantify the model. Over 100 separate spreading tests, as well as spreading data reported in the literature, are used to show (1) the predicted variation of d with σ, μ, V 0, and t is in good agreement with observation, and (2) K is of order unity and differs by less than 100% from one liquid-solid system to another.

Detachment force of air bubble from the solid surface (sulfur or graphite) in water

Measurements of the force of air bubble detachment from sulfur and graphite surfaces in water were made. Simultaneously, the grain-air bubble system was photographed at the moment of detachment to measure the instantaneous contact angle. The results obtained are discussed as the relationship between detachment force and contact angle for various contact plane radii and air bubble volumes. The measured detachment force values were compared with those calculated from the contact angles. The relationship between the detachment force and the interfacial free energies of the phases in contact was derived for the systems tested.