Improved Sessile Drop Method Research Articles

Effect of oxygen and sulfur on alumina particle behavior in front of solid–liquid interface of steel liquid

In this work, the interface characteristics between alumina and the steel liquid with different sulfur and oxygen concentrations were measured by an improved sessile drop method. And the behavior of alumina inclusions in front of the solid–liquid interface of steel liquid with different oxygen and sulfur concentrations was investigated by in-situ observation. Furthermore, the behavior of alumina particles in front of the solid–liquid interface on the surface of the steel liquid was discussed from the interface characteristics between alumina and the steel liquid with different sulfur and oxygen concentrations based on the interface gradient force, coulombic force, and Marangoni effect viewpoints. The results show that the large and small inclusion particles were engulfed and pushed, respectively, at the interface of solid–liquid, while the critical average radius for engulfed inclusion particles decreased from 7.73 μm to 6.21 μm and 4.84 μm, respectively, with sulfur and oxygen concentrations increasing. And the behavior can be described by a function formula concerning the interface characteristics between alumina and the steel liquid with the different sulfur and oxygen concentrations based on the interface gradient force, coulombic force, and Marangoni effect viewpoints. Further, it is found that the aggregation ability due to capillary force is weakened and even dispersed at the solid–liquid interface, which leads to the inclusion being easily pushed away from the front of the solid–liquid interface with the increase in sulfur and oxygen concentrations.

Effect of Al–Ti Concentration on Alumina Inclusions Aggregation Floating Behavior in Molten IF Steel

Understanding the aggregation‐floating behavior of alumina inclusions, which is influenced by the interface properties between inclusions and molten steel, is crucial to control the purity of interstitial‐free (IF) steel in the refining process. In this work, it is attempted to investigate the effect of aluminum and titanium concentrations on the aggregation‐floating behavior of alumina inclusions in the interior of IF molten steel based on the interface properties between molten steel and alumina inclusions. The interface properties between the molten steel and alumina inclusions are measured using an improved sessile drop method. And, the aggregation‐floating behavior of inclusions in the interior of molten steel is quantitatively discussed by an aggregation model based on the attractive force between alumina inclusions, which was combined with the interface properties. In the results, it is shown that the attractive forces between alumina inclusions, ranging from 6.96 × 10−6 to 5.41 × 10−5 N, increase and decrease, respectively, with increasing aluminum and titanium concentrations. Furthermore, the terminal floating speeds of alumina inclusions, ranging from 0.0510 to 0.0873 m s−1, increase and decrease, respectively, with increasing aluminum and titanium concentrations.

Insight into the wetting behavior of AgCu‐xTi on ZrO2: Spreading and microstructural evolution

AbstractUnderstanding the wetting behavior is significant to the fabrication of ceramic/ceramic (or metal) components. Here, the typical AgCu‐xTi/ZrO2 system is selected and its wetting behavior is studied by improved sessile drop method for various Ti content (x = 1, 2, 3, 4, wt%) at temperature range of 800°C to 950°C. The spreading of AgCu‐xTi melt on ZrO2 substrate consists of two stages: (I) rapid‐spreading stage and (II) sluggish‐spreading stage. The spreading is determined by the interfacial interactions. Two kinds of products, TiO and Cu3Ti3O, nucleate and grow at the interface. Because of their metallic property, the wettability of AgCu‐xTi/ZrO2 is significantly improved. Before continuous layer forms, the transportation of reactive mass is fast. Therefore, plenty of interfacial products precipitate at the interface resulting in the rapid spreading of AgCu‐xTi melt on ZrO2. After that, the formed continuous acts as barrier suppressing interfacial reactions, thereby a sluggish‐spreading stage is followed. This work provides insights into the interfacial microstructure inducing spreading of the AgCu‐xTi/ZrO2 system.

Effect of crystal orientation on droplet wetting behavior on single-crystal Al2O3 substrates: An experimental study

The wetting property of liquids on a solid surface is of key relevance to many areas ranging from biological systems to industrial applications. The wetting behavior of water, glycerin, and castor oil (featuring varying viscosities and surface energies) on single-crystal α-Al2O3 substrates with various crystal orientations of (0001), (112¯0), (101¯0), and (011¯2) was studied using the improved sessile drop method at room temperature and a closed environment. The effects of substrate crystal orientation on the liquid wetting behavior and its dependence on the liquid type were investigated. The contact angle of all three liquids on the (0001)-orientated substrates was obviously smaller than those of the other substrate orientations. The effects of α-Al2O3 substrate crystal orientation on the liquid wetting behavior on the substrates can be attributed to the liquid and substrate surface energies, the liquid viscosity, and the substrate atomic arrangement. The wetting process of water on α-Al2O3 could be divided into two stages. The contact angle was basically unchanged in stage I, and evaporation of droplets causes stepwise decreases of the contact angle in stage II. The height and contact angle of glycerin and castor oil on the substrates change very slowly in 1800 s. The findings of this study help provide a better understanding of the wetting behavior of liquids on solids and its mechanism.

Wetting Behavior of TiO2 by Calcium Ferrite Slag at 1523 K

The wetting behaviors of a TiO2 substrate by calcium ferrite (CF) series slags were investigated using an improved sessile drop method at 1523 K (1250 °C). The initial contact angles were in the range 35 to 50 deg, the final equilibrium apparent contact angles were < 20 deg, and the spreading durations were in the range 75 to 180 seconds. The CF-TiO2 system showed reactive wetting, which was categorized into four dynamic stages. Stage I: physical spreading, stage II: slow linear spreading, stage III: fast linear spreading, and stage IV: equilibrium. Interfacial reactions yielded CaTiO3 during reactive spreading, thereby transitioning TiO2 wetting into CaTiO3 wetting and then forming Fe2TiO5 and FeTiO3 owing to the excess Fe2O3 and FeO that had accumulated in the interfacial zone. Although stage III spreading was faster than stage II spreading, adding MgO to the slag slowed stage III spreading. The interfacial microstructure of the residual slag was roughly divided into three layers owing to the different densities of the slag and solid products. The top layer was composed of CaTiO3 and Fe2O3, the middle one was composed of CaTiO3 and Fe2TiO5, and the bottom one was composed of Fe2TiO5 and FeTiO3. Adding TiO2 to the slag produced a dense CaTiO3-containing interfacial layer, resulting in CF being detected in the residual slag.

An improved sessile drop method for assessing the wettability of heterogeneous coal surface

ABSTRACTTo 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.

Synthesizing InxGa1−xAs using molten In and GaAs by the sessile drop method at 400–600 °C

We studied the surface reaction between metallic In and a single-crystal GaAs substrate at 400–600 °C induced by the improved sessile drop method. Studying the surface morphology and microstructure using scanning electron microscopy, we found that many large particles had formed on the GaAs substrate, indicating a violent reaction between the In and GaAs. This reaction became more violent with increasing temperature. Characterizing the generated phases by X-ray diffraction and transmission electron microscopy, we identified the particles as InxGa1−xAs compounds. Our results show that indium (In) reacted with single-crystal GaAs through this method to form InxGa1−xAs compounds. Moreover, during the synthesis of InxGa1−xAs by the sessile drop method, the molten In and GaAs exhibited wettability at 400–600 °C. This experiment lays the foundation for synthesizing InxGa1−xAs compounds only using the metal In and GaAs substrate by a simple method.

Surface Tension of Liquid Ti-Al Alloys

The surface tension of liquid Ti-Al alloys at 1758 K was determined by an improved sessile drop method. The surface tension of liquid Ti-Al alloys was calculated using the Butler's model and several modified ideal solution models. Results show that the surface tension of liquid Ti-Al alloy decreases with increased Al concentration. Experimental results agree well with both the Butler's model and the modified ideal solution model. The segregation of Al atoms to the surface occurs at all bulk concentrations of Ti-Al alloys. Al with lower surface tension prefers to segregate on the surface of liquid Ti-Al alloy, whereas Ti with higher surface tension prefers to segregate inside the molten alloy. The effect of surface active solute on the surface tension of liquid Ti-Al alloy was also discussed. Sulfur is found to have a larger effect on the surface tension of alloy. The surface tension of liquid Ti-Al alloy decreases with increased sulfur concentration. Sulfur concentration on the surface is higher than that in the bulk. Thus, the adsorption of sulfur for Ti-Al alloys is a positive adsorption.

Wetting of carbide ceramics (B4C, SiC, TiC and ZrC) by molten Ni at 1753 K

Wetting of carbide ceramics (B4C, SiC, TiC and ZrC) by molten Ni was investigated by using an improved sessile drop method at 1753 K. Due to the partial metallic bonds in metallic ceramics (TiC and ZrC), the intrinsic wettability of them is better than the predominantly covalent ceramics (B4C and SiC). The smaller density of solid causes that the dissolution is more incline to the vertical direction, which also causes limited improvement of wettability. The final wettability for specific systems (Ni/carbide ceramic systems) is related to the dissolved solute from substrate, the recrystallized phases and the characteristics of interfacial structures. The spreading dynamics for the dissolutive wetting can be described by molecular dynamic model, and then the main energy barrier for the triple line motion may come from the dissolution.

Wettability of 2519Al on B4C at 1000–1250°C and mechanical properties of infiltrated B4C–2519Al composites

Abstract The wettability of 2519Al on boron carbide (B 4 C) was investigated in detail by an improved sessile-drop method at temperature ranging from 1000 to 1250 °C. The interface reactions of B 4 C–2519Al systems were analyzed by means of scanning electron microscopy (SEM), electron probe X-Ray microanalysis (EPMA) and X-ray diffraction (XRD). Typical flexural strength and hardness of infiltrated B 4 C–2519Al composites were studied by three-point-bending tests and Rockwell hardness tester. It is found that the wettability and interaction between molten 2519Al alloy and B 4 C are sensitive to the temperature and contact time. The contact angles significantly decreased and the solid–liquid interaction was more intense as the temperature increased. On the other hand, the formation of various compounds such as Al 3 BC, Al 3 B 48 C 2 and AlB 2 was identified. Some Al 2 Cu and Al 3 Zr phases appeared in the 2519Al drop during cooling, while AlB 2 precipitated far away from the 2519Al/B 4 C interface. Ternary compounds of Al 3 BC and Al 3 B 48 C 2 , formed along the interface, play a key role in the improvement of wettability of B 4 C/2519Al. For infiltrated 2519Al–B 4 C composites, the typical bending strength and HRA are 300.71 MPa and 80.3, respectively. The main fracture way of infiltrated B 4 C/2519Al is transgranular rupture, which has smooth fracture surface and intrinsic brittle fracture mode.

Wetting and adhesion at Mg/MgO interfaces

The wetting of (100), (110), and (111) MgO single crystals by molten Mg was studied in a flowing Ar atmosphere at 1073 K using an improved sessile drop method. The results show that the contact angle and work of adhesion are mildly dependent on MgO substrate orientation. However, the work of separation calculated by density functional theory shows a sequence of (100) < (110) < (111). This discrepancy was explained by a model considering the possible effects of evaporation and deposition of Mg at the substrate surface on the interfacial adhesion. For Mg on the clean MgO surfaces, the adhesion consists primarily of Mg–O ionic bonds with some Mg–Mg metallic bonds. In addition, a small amount of covalent bonds are present in the metal slab adjacent to the Mg/MgO (110) and Mg/MgO (111) interfaces. The different work of separation at three interfaces depends on the strength and amounts of Mg–O and Mg–Mg bonds as well as on the surface free energy of respective planes. For the MgO surfaces pre-deposited by a monolayer of Mg atoms, the interfaces are dominated by the Mg–Mg bonds, thus mitigating the effect of substrate orientation on the wettability and adhesion.

Reactive wetting in liquid magnesium/silica and magnesium/silicon systems

The reactive wetting of SiO2 and Si by molten Mg in a flowing Ar atmosphere was studied using an improved sessile drop method. The initial contact angles in the Mg/SiO2 system decreased from 56° to 35° as temperature increased from 973K to 1073K, and they decreased very rapidly with time during isothermal holding. The interfacial reaction led to the formation of a distinct reaction zone, consisting mainly of a thin Mg2Si layer, an MgO layer, a periodic alternatively arranged MgO and Mg2Si layer, and an aggregated Mg2Si–MgO mixture layer. The formation mechanism of these complex structures was discussed based on thermodynamic and kinetic considerations. Moreover, the effect of the interfacial reaction on the wetting improvement was examined and the primary contribution was ascribed to the formation of Mg2Si at the interface, which was further demonstrated by the result in the Mg/Si system.

Wetting of (0001) α-alumina single crystals by molten Mg–Al alloys in the presence of evaporation

The wetting of (0001) α-alumina single crystals by Mg–Al alloys over a wide composition range at 1073 K was investigated using an improved sessile drop method in a flowing argon atmosphere. The initial contact angles are between 103° and 84°, almost linearly decreasing with increasing nominal Mg concentration, suggesting that the addition of Mg to Al improves the initial wettability. According to the evolution of contact angle and contact diameter, representative stages were identified to characterize the complex wetting behavior in the presence of evaporation. The wetting kinetics was dependent on the nominal Mg concentration in the alloy. Two patterns of “stick–slip” behavior were observed in the wetting process and interpreted by combining the effects of interfacial reaction and evaporation of magnesium. In addition, the dependence of the interfacial reaction on the Mg–Al alloy concentration was thermodynamically analyzed. The dominant reaction product at 1073 K should be MgO when x Mg > 9 mol%, while MgAl2O4 when x Mg < 9 mol%. However, because of the continuous consumption of Mg due to the evaporation and reaction, its concentration in the alloy progressively decreased with time. As a result, MgO formed usually earlier while MgAl2O4 later even for the alloys with higher than 9 mol% Mg.

Measurement of surface tension of molten matte phases by an improved sessile drop method

Surface tensions of Ni3S2, Cu2S and FeS molten phases were measured using an improved sessile drop method in an inert atmosphere of purified argon. The traditional sessile drop method was modified before measurements were obtained. The surface tension values were obtained over a wide range of temperature from their respective melting temperatures to 1300°C. In the temperature range 1000–1300°C, surface tension of molten Ni3S2 decreased linearly with increasing temperature. However, the surface tensions of molten FeS and Cu2S phases were approximately constant over this range of temperature.

Wetting of MgO and α-Al2O3 by molten Mg: a model of droplet with high vapor pressure

The wetting of MgO and α-Al2O3 polycrystalline plates by molten Mg in purified argon was studied between 973 and 1273 K using an improved sessile drop method. The MgO/Mg system is basically non-reactive while Al2O3/Mg is reactive. The common features in the non-reactive and reactive systems are the high tendency for oxidation and the high evaporation rate of Mg. It is shown that wetting kinetics in both systems is governed by the evaporation and pinning phenomenon leading to contact angle versus time curves passing through a minimum: the apparent contact angle first decreases and then increases. The intrinsic contact angle should be estimated using the initial value (advancing contact angle) and the maximum value just before the disappearance of the droplet caused by Mg evaporation (receding contact angle).

High temperature wettability of multicomponent CrAlSiN and TiAlSiN coatings by molten glass

The phenomenon of glass-to-mold sticking is a major problem for industrial glass forming processes. Ternary TiAlN coatings attracted considerable industrial interest because of their excellent tribological performance and high oxidation resistance at high temperatures. Recently, multicomponent CrAlSiN and TiAlSiN coatings have been developed in order to gain high hardness and good thermal stability at temperatures exceeding 800°C. In this study, CrAlSiN, TiAlSiN and AlTiN coatings were deposited on tungsten carbide substrates by using a cathodic-arc deposition system with lateral rotating arc cathodes. Titanium, chromium and AlSi (12at.% of Si) cathodes were used for the deposition of CrAlSiN and TiAlSiN coatings. All the deposited CrAlSiN, TiAlSiN and AlTiN coatings showed a B1-NaCl crystal structure. The deposited CrAlSiN and TiAlSiN coatings exhibited nanocrystalline structure and possessed hardness as high as 35–37GPa after annealing at 700°C in air. The wettability of the CrAlSiN, TiAlSiN and AlTiN coated tungsten carbides by molten glass at temperatures between 300°C and 700°C in controlled air under 1.6Pa was measured by using an improved sessile drop method. The CrAlSiN showed a low oxidation rate and a non-wetting characteristic superior to TiAlSiN and AlTiN coatings.

Wetting and evaporation behaviors of molten Mg–Al alloy drops on partially oxidized α-SiC substrates

The wetting and evaporation behaviors of Mg–Al alloys over a full composition range on partially oxidized polycrystalline α-SiC substrates were studied in a flowing Ar atmosphere using an improved sessile drop method. The time dependence of the changes in contact angle and drop geometry was monitored and representative wetting stages were identified. The initial contact angles at 1173 K were 100° for pure Al and 76° for pure Mg, with the maximum value of 106° for the 7.6 mol.% Mg–Al alloy. The interfacial reaction and the evaporation of Mg led to the decrease in the apparent contact angle in the spreading stage and their respective contribution was evaluated. After the pinning of the triple line, the decrease in the contact angle resulted from the diminishing drop volume as a consequence of the Mg evaporation. The effects of Mg concentration on the wetting and evaporation behaviors were discussed. A mechanism for the time-dependent diminishing drop volume was proposed in light of the competition between the Mg evaporation and its diffusion from the drop bulk to the surface. Finally, the interfacial reaction was analyzed based on thermodynamic considerations.

Wetting of B 4C, TiC and graphite substrates by molten Mg

The isotherm wetting of B 4C, TiC and graphite substrates by molten Mg was studied in a flowing Ar atmosphere at 973–1173 K using an improved sessile drop method. The initial contact angles are in the ranges of 95–87°, 74–60° and 142–124°, respectively, moderately depending on the temperature. All the systems are non-reactive in nature; however, the presence of impurity of free boron at the B 4C surface gave rise to the chemical reaction with molten Mg and thus promoted the wettability to a certain degree. A new method was proposed to evaluate the wetting behavior coupled with evaporation and chemical reaction. Furthermore, based on the comparison of the work of adhesion and cohesion, the bonding in the Mg/B 4C and Mg/TiC systems is presumably mainly chemical while that in the Mg/graphite system is physical.

Pinning–depinning behavior in the wetting of (0 0 0 1) α-Al 2O 3 single crystal by molten Mg

Wetting of (0 0 0 1) α-Al 2O 3 single crystal by molten Mg was studied by an improved sessile drop method in a purified flowing Ar atmosphere. A distinct pinning–depinning behavior was observed during the evaporation-coupled wetting process. The underlying mechanism for this behavior was expatiated from the viewpoints of energetics and geometries at the triple junction.

Wettability of amorphous and nanocrystalline Fe78B13Si9 substrates by molten Sn and Bi

The wettability of amorphous and annealing-induced nanocrystalline Fe78B13Si9 ribbons by molten Sn and Bi at 600 K was measured using an improved sessile drop method. The results demonstrate that the structural relaxation and crystallization in the amorphous substrates do not substantially change the wettability with molten Bi because of their invariable physical interaction, but remarkably deteriorate the wettability and interfacial bonding with molten Sn as a result of changing a chemical interaction to a physical one for the atoms at the interface.