Wettability and Interfacial Reaction between Molten lron and Zirconia Substrates
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The surface tension of, and the contact angle formed by, molten iron on three types of commercial zirconia substrates containing 8 mol% Y 2 O 3 , 9 mol% MgO, or 11 mol% CaO were measured over a wide range of oxygen concentration in the molten iron by the sessile drop method. The solidified metal–substrate interface was examined in an SEM equipped with an EPMA. The surface tension of molten iron decreased with increasing oxygen concentration. The contact angle of molten iron increased rapidly with increasing oxygen concentration and reached a local maximum value at an oxgyen concentration of ∼100 ppm, and then decreased with increasing oxygen concentration. At lower oxygen concentration, dissociation of ZrO 2 was observed. For the ZrO 2 –9 mol% MgO substrate, segregation of MgO to the interface was observed. For the ZrO 2 –11 mol% CaO substrate, segregation of CaO and the precipitation of small ZrO 2 particles in the segregation layer of CaO were observed at the interface. Conversely, at higher oxygen concentration, penetration of molten iron into the grain boundaries was observed in all types of zirconia substrates.Keywords:
Penetration (warfare)
Many problems related to the quality of protective coatings for more sophisticated applications can be solved on the basis of the wettability of their surfaces measurements. The equilibrium (static) or dynamic contact angle (CA) of solids can be measured and the sessile drop method or Wilhelmy method are usually applied. In the sessile drop method CA is measured optically. The measured values of static CA are influenced by evaporation of the liquid, absorption of the liquid by porous substrate (e.g. paper, building material) and other chemical or physical interactions occurring on the solid surface. The Wilhelmy method is based on the measurements of the force which is needed to overcome the resistance of the liquid as the solid plate with known wetted length is immersed in or withdrawn from the liquid of known surface tension. The precision of the contact angle measurements by Wilhelmy method is higher as compared with the sessile drop method. Very important factor highly influencing the quality of CA measurements is the proper selection of applied liquids which should be selected according to the applied measuring method. The careful selection of the method of CA measurements is a crucial factor influencing the possibility of practical application of the results of wettability measurements.
Wilhelmy plate
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Combining digital photography with AutoCAD and Proe,the parameters in surface tension measured by sessile drop method was determined.The results show that the method for calculating the surface tension has high accuracy,which can provide computer aid for adopting sessile drop method measuring high temperature metal surface tension.
Spinning drop method
Tension (geology)
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This paper investigates the contact angle obtained from wettability tests for smooth spherical glass particles with water by four techniques; (i) visual qualitative assessment at bulk level; (ii) modified sessile drop at bulk level; (iii) gel trapping technique at single particle level; and (iv) environmental scanning electron microscope (ESEM) at different locations on an individual particle. A deeper understanding of wettability is developed from bulk powder to surface heterogeneity over a single particle. Differences were observed between the contact angles (θ) for bulk and individual hydrophobic (silanised) and surfactant treated hydrophobic particles using the sessile drop and gel trapping techniques (GTT). The contact angle value (θ) is reported as 157degrees 2.25degrees for hydrophobic (silanised) particles and θ=118degrees 2.57degrees for surfactant treated silanised particles, as measured by the sessile drop technique. In contrast contact angle measurements made using the GTT were determined as 102degrees 1.6degrees for silanised particles and 95.2degrees 3.09degrees for surfactant treated silanised particles. For ESEM measurements on individual particles, contact angle was seen to vary across the surface of particles (θ=104degrees-130degrees for silanised particles; θ=60degrees-100degrees for surfactant treated silanised particles), suggesting inhomogeneity of the surfactant treatment. Measured contact angle results were consistent with qualitative visual assessment of powders dropped on to water; silanised powders remained clumped on the water surface and surfactant treated silanised particles dispersed over the water surface quickly and then sank.
Particle (ecology)
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Gravity-induced sagging can amplify variations in goniometric measurements of the contact angles of sessile drops on super-liquid-repellent surfaces. The very large value of the effective contact angle leads to increased optical noise in the drop profile near the solid-liquid free surface and the progressive failure of simple geometric approximations. We demonstrate a systematic approach to determining the effective contact angle of drops on super-repellent surfaces. We use a perturbation solution of the Bashforth-Adams equation to estimate the contact angles of sessile drops of water, ethylene glycol, and diiodomethane on an omniphobic surface using direct measurements of the maximum drop width and height. The results and analysis can be represented in terms of a dimensionless Bond number that depends on the maximum drop width and the capillary length of the liquid to quantify the extent of gravity-induced sagging. Finally, we illustrate the inherent sensitivity of goniometric contact angle measurement techniques to drop dimensions as the apparent contact angle approaches 180°.
Goniometer
Dimensionless quantity
Diiodomethane
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Goniometer
Spinning drop method
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The wetting behavior of solid Al2O3 with molten CaO-Al2O3-SiO2 was investigated at 1 873 K using the sessile drop method. A new model was developed to represent the time dependence of the contact angle, i.e., the spreading behavior of a liquid drop on a solid substrate. The model takes into consideration chemical interactions which continually take place at the interface between the solid Al2O3 and molten CaO-Al2O3-SiO2. By applying the model to the experimental results of the present study the equilibrium contact angle between the liquid slag and solid alumina was determined for a number of different slag compositions, and an iso-contact angle diagram was constructed. The equilibrium contact angle was greatly affected by the slag composition, and it was found that the interfacial tension was the major factor governing the equilibrium contact angle. In the region of low SiO2 content, the slag with higher CaO content exhibits a smaller contact angle, i.e., better wettability with alumina. For slag with a given CaO/SiO2 ratio, an increase in Al2O3 results in a corresponding increase in the contact angle, i.e., decrease in wettability. For a given CaO/Al2O3 ratio, the variation of the contact angle with SiO2 content shows a minimum. The contact angle decreases by increasing the surface roughness of the alumina substrate.
Slag (welding)
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The purpose of this study is to measure contact angle and surface tension of liquid Fe-Si-B alloys at high temperature using sessile drop method. The surface tension and contact angle result is based on sessile drop method by use of a digital camera to take the drop profile and fit the profile by Youngs-Laplace equation. The surface tension of liquid Fe-Si-B alloy and its dependence on temperature has been studied. Contact angles of this liquid alloy on various refractories substrate have been determined using this instrument. The result showed that the contact angles and surface tension of Fe-4Si-3B alloy liquid drop on Al 2 O 3 substrate have value of 134 to 127and 1575-1350 mN/m respectively. The result indicated also that increasing temperature can decrease contact angle and surface tension in Fe-Si-B alloy.
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Using the sessile drop technique, the contact angle between a liquid Fe–19%Cr–10%Ni drop and a dense alumina substrate was measured under H2 as well as CO2–H2 atmospheres in the temperature range of 1753 to 1823 K. The measurements were carried out both in the static mode and the dynamic mode. The static measurements in hydrogen showed that the contact angle decreased from 135 to 107° by increasing temperature from 1753 to 1823 K. In the dynamic mode, gas mixtures of different oxygen partial pressures were imposed on the system. At 1753 K, the contact angle was decreased under the condition of oxide formation, whereas the contact angle was not changed under the condition of no oxide formation. At 1823 K, the contact angle did not change regardless of the oxide formation. The time required for the surface oxide layer to fully cover the liquid metal drop was decreased by increasing the temperature.
Atmospheric temperature range
Wetting transition
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To assess the wettability of heterogeneous coal surface, a new modified sessile drop technique named volume–length method is proposed to calculate the contact angle according to the spreading ability of droplet on the coal surface. The tested contact angles were compared with the predicted contact angles using Cassie–Baxter model. Low ash coal and kaoline powders are mixed with different mass ratios and mixing degrees. The mixtures were pressed to plates for sessile drop contact angle tests. The surface chemical component and nonuniform degree determine the droplet spreading on the coal surface, thereby affecting the contact angle.
Solid surface
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