Sessile Drop Experiments Research Articles

Effects of surface-active elements on wettability and interfacial reaction between DD5 superalloy and Al2O3-based ceramic shell

The study investigates the effects of oxygen-sulfur content, holding temperature, and time on the wettability and interfacial reactions between DD5 superalloy and Al2O3-based ceramic shells through non-in-situ sessile drop experiments. Lowering the oxygen-sulfur content in the DD5 master alloy, as well as reducing the holding temperature and time, leads to an increase in the wetting angle and a mitigation of interfacial reactions. Improved wettability promotes interfacial reactions, while intensified interfacial reactions further spread the alloy melt, enhancing its wettability. The main products of the interfacial reaction between the DD5 alloy and Al2O3-based ceramic shells are Al2O3 and Si, with the process being influenced by the presence of Al. When the oxygen-sulfur content is controlled within 6 ppmw, the wettability will undergo a characteristic transformation, resulting in a sharp increase in the wetting angle. It demonstrates that the ultra-pure DD5 master alloy plays a crucial role in reducing wettability and interfacial reaction, as well as slowing down the tendency of the hetero-crystal formation. Therefore, it is of great engineering significance to further reduce the content of oxygen-sulfur impurity elements in DD5 superalloy.

Influence of Tramp Elements on Surface Properties of Liquid Medium‐Carbon Steels

The transformation of the steel industry is inevitably linked to increased recycling rates of steel. However, end‐of‐life scrap is often contaminated with tramp elements like copper, molybdenum, and tin and while their influence on mechanical properties of steels is well described, their effect on nonmetallic inclusions remains largely unknown. Therefore, herein, two medium‐carbon steels are alloyed with up to 1 wt% of the listed tramp elements. The influence these elements have on the inclusion behavior in liquid steel is investigated using the sessile drop method in contact with alumina and zirconia as well as in steel/slag melting experiments to evaluate the formation and separation of new inclusions. Additionally, a semiempirical approach using CALPHAD to model the surface tension of steels with tramp elements is done. Copper and tin decrease the surface tension, while molybdenum increases the surface tension. It is demonstrated that most investigated alloys lead to a decrease of wetting angle as compared to the nonalloyed steels. The shown trends in the sessile drop experiments are lower contact angles with increased surface tension while a higher number of inclusions occurs with a decrease in surface tension. Thus, this study demonstrates that tramp elements affect the oxidic cleanness of steels.

Thermodynamics, Adhesion, and Wetting at Li/Cu(-Oxide) Interfaces: Relevance for Anode-Free Lithium-Metal Batteries.

A rechargeable battery that employs a Li metal anode requires that Li be plated in a uniform fashion during charging. In "anode-free" configurations, this plating will occur on the surface of the Cu current collector (CC) during the initial cycle and in any subsequent cycle where the capacity of the cell is fully accessed. Experimental measurements have shown that the plating of Li on Cu can be inhomogeneous, which can lower the efficiency of plating and foster the formation of Li dendrites. The present study employs a combination of first-principles calculations and sessile drop experiments to characterize the thermodynamics and adhesive (i.e., wetting) properties of interfaces involving Li and other phases present on or near the CC. Interfaces between Li and Cu, Cu2O, and Li2O are considered. The calculations predict that both Cu and Cu2O surfaces are lithiophilic. However, sessile drop measurements reveal that Li wetting occurs readily only on pristine Cu. This apparent discrepancy is explained by the occurrence of a spontaneous conversion reaction, 2 Li + Cu2O → Li2O + 2 Cu, that generates Li2O as one of its products. Calculations and sessile drop measurements show that Li does not wet (newly formed) Li2O. Hence, Li that is deposited on a Cu CC where surface oxide species are present will encounter a compositionally heterogeneous substrate comprising lithiophillic (Cu) and lithiophobic (Li2O) regions. These initial heterogeneities have the potential to influence the longer-term behavior of the anode under cycling. In sum, the present study provides insights into the early stage processes associated with Li plating in anode-free batteries and describes mechanisms that contribute to inefficiencies in their operation.

High-Temperature Reactive Wetting of Natural Quartz by Liquid Magnesium.

High-temperature wetting of natural, high-purity quartz (SiO2) and liquid magnesium (Mg) was investigated at temperatures between 973 and 1273 K. Sessile drop experiments using the capillary purification (CP) procedure were carried out under an Ar gas atmosphere (N6.0), eliminating the native oxide layer on the surface of Mg melt. The results showed that the wetting behavior was strongly dependent on temperature. At 973 and 1073 K, the wetting system displayed relatively large contact angles of 90° and 65°, respectively, demonstrating modest wetting. The wetting increased to some extent by increasing the temperature to 1123 K with a wetting angle of 22°. However, the SiO2/Mg system demonstrated complete wetting at temperatures of 1173 K and above. Furthermore, interface microstructure examination showed different reaction product phases/microstructures, depending on the wetting experiment temperature.

Effect of Camera Parallax Angle on the Accuracy of Static Contact Angle Measurements.

Measuring the contact angle at the solid/liquid/vapor triple point in sessile drop experiments is one of the most popular and simple ways to quantify the wettability of surfaces and determine the surface free energy. Despite decades of technical advancements in contact angle measurements, which allowed for improving the precision of sessile drop measurements below ±1°, an often overlooked source of experimental error in these measurements originates from the camera's parallax angle (PA) - the angle between the camera optical axis and the sample stage surface. Here, we quantified the systematic errors in the measurement of contact angles due to the acquisition of drop images at finite PA values by simulating sessile drop experiments in which synthetic drops were created using the Young-Laplace equation. The absolute contact angle error induced by imaging drops at nonzero PAs was found to increase as the true contact angle (TCA) deviates from 90° and resulted in an overestimation (underestimation) of the contact angle for drops having TCAs lower (higher) than 90°. The computed absolute contact angle error reaches values as high as -20° (+12.2°) for drops having a TCA of 175° (5°) when imaged with a PA of 10°, thus indicating the importance of considering the PA when accurately quantifying contact angles in sessile drop experiments. The shape and, by extension, volume of the sessile drop was also found to affect the magnitude of the absolute contact angle error as sessile drops with higher apex curvatures exhibited lower absolute error than those with lower curvatures at any given PA. The outcomes of this work provide guidelines for minimizing systematic errors in sessile drop measurements due to the collection of drop images at nonzero PAs.

Application of the Lattice-Boltzmann method to wetting on anisotropic textured surfaces: Characterization of the liquid-solid interface

HypothesisTo understand the relationship between topography and wetting, it is not enough to study the contact angle. Indeed, the liquid-solid interface plays an important role in wetting. However, data such as the total triple line length, the wetting area and the anchoring depth are inaccessible or difficult to obtain experimentally. This work proposes to overcome the experimental limitations by using a numerical approach to characterize the wetting behavior on textured surfaces. MethodsThe wetting behavior of an anisotropic textured surface was compared for both experimental and numerical approaches. The experimental wetting is characterized by sessile drop experiments. The simulations were performed by applying the pseudo-potential Lattice-Boltzmann method. The numerical approach was then used to predict the wetting behavior of different materials. FindingsThe simulations capture both the wetting state and the contact angle, in accordance with the experimental observation. Without making any assumptions about the interfacial shape and anchoring, the simulation allows to characterize the liquid-solid interface by quantifying the total length of the triple line and the wetting area. Simultaneously, the simulations enable the characterization of impregnation within textures for complex mixed regimes.

Wettability Prediction for 3D-Printed Surfaces Using Reverse Engineering and Computational Fluid Dynamics Simulations

Additive manufacturing (3D printing) is a promising approach to creating packings for laboratory-scale distillation columns. Current research focuses on experiments and simulations to tailor packing geometry regarding performance (e.g., pressure drop, fluid distribution). These performance benchmarks are, in large part, dependent on the wettability of the manufactured surface. Research shows that the 3D-printing process settings affect wetting significantly. This effect must be quantified to accurately assess the effectiveness of printed packing geometry. Due to the interdependence of wetting, surface roughness, and involved substances, the required experimental effort is not feasible. Sessile drop experiments show that analytical models underpredict the resulting wettability. In this study, a novel method to address this issue is introduced. The rough surface of a printed sample is reverse-engineered, and CFD simulations are performed to predict the static contact angle. The results show agreement between the computational model and experimental investigations.

Enhancement of wettability in AZ91/B4C system by a mechanical purification of liquid alloy

Mg-based alloys are potential candidate materials for a fabrication of lightweight boron carbide based composites through a reactive melt infiltration approach. In this paper, the effect of a mechanical purification of molten AZ91 alloy's surface on its wettability with polycrystalline B 4 C is experimentally evaluated for the first time. For this purpose, sessile drop experiments were performed under the same operating conditions (700 °C/5 min; Ar atmosphere), by using both the classical contact heating (CH) and the improved capillary purification (CP) procedure. It was found that the evolution of contact angle values was strongly influenced by the applied procedure. In particular, by using the classical CH procedure, the presence of a native oxide layer on the metal surface hinders the observations of melting process, resulting in a misleading conclusion that the system is non-wettable. Contrarily, during the wetting test performed by applying the CP procedure, the surface oxide layer was mechanically removed by squeezing the molten AZ91 alloy through a capillary. Accordingly, the oxide-free AZ91 drop with a regular and spherical shape was successfully obtained and dispensed on the B 4 C substrate. A reliable contact angle value of θ =83° was measured at the AZ91/B 4 C triple line at 700 °C, which in turn proves that B 4 C is wetted by the liquid AZ91 alloy. In contradiction to the literature, these good wetting conditions were assisted by a non-reactive wetting mechanism occurring at the AZ91/B 4 C interface. To succeed in the fabrication of AZ91/B 4 C composites by liquid metal infiltration, such experimental observations make it reasonable to expect a spontaneous infiltration process exclusively driven by capillarity, which in turn increases the efficiency of the process by the absence of reaction products that could be a potentially detrimental factor.

Effects of gravity on the capillary flow of a molten metal

Repair and construction in space by means of brazing requires understanding of the effect of gravity on the capillary flow of a molten metal. We perform two sets of experiments: (1) spreading of a sessile drop of liquid aluminum-silicon-flux (Al-Si-KxAlyFz) composite braze on a horizontal alumina (Al2O3) substrate (a non-wetting surface), and (2) capillary flow of the same braze alloy on an inclined aluminum-manganese (AA3003) substrate (a wetting surface). We vary the mass of the brazing liquid and the inclination of the substrate (i.e., the relative direction of gravity).In the composite metal/flux sessile drop experiments, we observe a secondary liquid flux meniscus forming at the contact line between the liquid Al-Si and the alumina substrate. We demonstrate that the equilibrium contact angle appears to be close to 180°, while the apparent contact angle depends on the mass of the braze. In the second set of experiments, we study the molten braze alloy on different inclinations of AA3003 in a wedge-T wetting/non-wetting assembly. As the inclination angle decreases, the wetting distance increases and the surface profile changes from a non-symmetric bag-like shape to a more symmetric pancake shape. With the mass decreasing, the surface profile on the vertical substrate approaches a symmetric shape when the wetting distance is equal or smaller than the capillary length. While the non-homogeneous melting and hence, the non-homogeneous microstructure of the melt, may prevent a full symmetry. Computational predictions of equilibrium shapes are in good agreement with experimental results.

Mo–Si–B alloys for ultra-high-temperature space and ground applications: liquid-assisted fabrication under various temperature and time conditions

Boron-doped molybdenum silicides have been already recognized as attractive candidates for space and ground ultra-high-temperature applications far beyond limits of state-of-the-art nickel-based superalloys. In this work, we are exploring a new method for fabricating Mo–Si–B alloys (as coatings or small bulk components) by utilizing a pressure-less reactive melt infiltration approach. The basic assumption of this approach is a synthesis of binary and/or ternary and complex intermetallic phases (silicides, borides, borosilicides), through a direct interaction of Si–B melt with molybdenum. The main purpose of this work was to examine the effect of temperature and time of Si–B melt interaction on the structure and morphology of the formed reaction products. For this purpose, sessile drop experiments were carried out on the eutectic Si–3.2B (wt%) alloy/Mo couples at temperature varying between 1385 and 1550 °C and holding time between 10 and 30 min. The solidified sessile drop couples were subjected to microstructural characterization by means of light microscopy and scanning electron microscopy analyses performed both at “top-view” and cross-sectioned interfaces. The phases formed within the interaction zone were identified by using TEM/SAED and XRD techniques. It was documented that a thickness of both main product layer (MoSi2 + Mo5Si3) and boron-rich interlayer increases with raising temperature and time of the Si–B melt interaction with Mo substrates.

Surface Tension, Interfacial Segregation, and Graphite Shape in Cast Irons

Using literature data on iron melts, an expression of the surface tension of cast iron melts as a function of temperature and composition was obtained. Its predictions were satisfactorily compared with reported experimental results. Then, an analysis of experimental information of sessile drop experiments with cast iron melts onto graphite substrates showed a strong adhesion between these two phases when sulfur is present and its dramatic decrease when the sulfur activity is reduced by the addition of spheroidizers such as Mg and Ce. Finally, analysis and discussion of results on the segregation of impurities and trace elements at the graphite matrix interface in cast irons led to the proposal of a scheme for their effect on graphite shape.

Influence of surface roughness frequencies and roughness parameters on lubricant wettability transitions in micro-nano scale hierarchical surfaces

In this work, the influence of surface roughness frequencies and roughness parameters on mixed wetting and its transitions are discussed. Sessile drop experiments were conducted on hierarchical engineering surfaces having multiple roughness frequencies. Results show that the net roughness Ra or Rq (RMS roughness) solely cannot dictate the wettability behavior. Fourier Band Pass Filtering (FBPF) and Power Spectral Density (PSD) analysis revealed that all roughness frequencies in a hierarchical rough surface contribute to the net Ra and Rq; however, all need not contribute to wettability transitions. Rz and LSm were found to be the roughness parameters that could predict the range of spatial roughness frequencies that dictate wettability transitions to near Wenzel and Cassie-Baxter states.

Superinsulating composite aerogels from polymethylsilsesquioxane and kapok fibers

A facile method to synthesize light weight thermally superinsulating composite aerogel is being presented here. A polymethylsilsesquioxane (PMSQ) – cellulose composite aerogel starting from a trifunctional precursor viz. methyltrimethoxysilane (MTMS) and kapok fibers have been synthesized. Kapok fibers have been employed as they have a homogeneous hollow structure and also possess intrinsic low density. A PMSQ-Kapok composite aerogel with a density as low as 0.053 gcm−3 with a thermal conductivity of 0.018 W m−1 K−1 in room conditions has been synthesized. Besides, a flexural strength (at maximum stress) of 108 kPa ± 21 has been obtained through three points bending test. All the composite aerogels are mesoporous as characterized by N2 sorption isotherms and hydrophobic as shown by sessile drop experiments. On comparison with the earlier reported works and with some of the commercially available aerogel composites, the current results seem promising. For demonstrating the real application purpose, thin composite aerogel sheets have also been synthesized which could be easily rolled/bended.

Wear-Resistant TiCN-Based Ceramic Materials for High-Load Friction Units

The tribological properties of matrix and skeletal titanium carbonitride composites were studied in dry friction conditions in air. Experiments on wetting of the TiCN–Cr3C2 composite by nickel–chromium alloys and copper using the sessile drop method were performed to choose matrix composition and ascertain whether the samples could be produced by impregnation of the porous skeleton. The sessile drop experiments showed that nickel and its alloys formed a low contact angle on the TiCN–Cr3C2 composite (θ ≈ 8°). In particular, Ni3Al intermetallic had θ < 5°, allowing it to be used as a metal matrix. The same situation was observed for copper. A technique was developed for producing TiN–Cr3C2 composites by impregnation of the porous skeleton with Ni3Al and copper melts, and the tribological behavior of the cermets was tested in dry friction conditions. When the starting composite was impregnated with Ni3Al intermetallic, the friction coefficient decreased (μ = = 0.25). Structural studies were conducted with a MIM-10 metallographic microscope and X-ray diffraction with a DRON-2 diffractometer. The hardness and contact area thickness were measured employing a Falcon 9 hardness tester (manufactured in the Netherlands). Thin cross sections were made to examine the structure and phase composition of the contact area. The structure was analyzed using X-ray diffraction and scanning electron microscopy. The effect exerted by hardness of the counterface (steel 45, 40Kh, ShKh15) on the tribological properties of the TiCN–Cr3C2 composite was established. When steel hardness was 60 HRC, the friction coefficient increased with friction distance. These results were, however, obtained at low speeds and loads. Friction losses decreased with loading increasing from 2 to 6 MPa at 12 m/sec: friction coefficient reduced to 0.23. The TiCN–20% Cr3C2 cermets impregnated with Ni3Al may be recommended as antifriction materials for use in high-speed and high-load friction units.

Electrodeposited TiB2 on graphite as wettable cathode for Al production

AbstractTitanium diboride (TiB2) is considered as a promising cathode material for Al production. However, the manufacture of TiB2 cathodes is facing numerous challenges. In this study, electrodeposition of TiB2 on graphite was performed in molten fluoride (FLiNaK) electrolyte at 600°C by using a periodically interrupted current technique for various electrodeposition times (from 10 to 75 minutes) and at two different current densities (−0.12 and −0.5 A/cm2). It is shown that the TiB2 coating morphology/microstructure strongly depends on the applied current density. Denser coatings were obtained at jon = −0.12 A/cm2 with a growth rate of ca. 0.7 µm/min. The thicker films display a preferential crystallographic orientation along the [110] plan. At jon = −0.5 A/cm2, TiB2 coatings are deposited at a growth rate of ca. 6 µm/min with no crystallographic texture. They present a porous and stratified morphology with numerous transversal macrocracks. All TiB2 coatings show excellent wettability for molten Al as confirmed by sessile drop experiments. However, significant molten Al infiltration occurs in the TiB2 coatings, which accumulates at the coating/graphite interface, inducing the coating delamination.

Mechanisms of yttrium on the wettability, surface tension and interactions between Ni-20Co-20Cr-10Al-ξY alloys and MgO ceramics

The mechanisms of Y on the wettability, surface tension, and interactions between the Ni-20Co-20Cr-10Al-ξY alloys and MgO ceramics at 1873 K were investigated by sessile drop experiments. The results of nonlinear fitting showed that the equilibrium contact angles and Y concentrations were approximately in accord with the log-normal distribution law. The equilibrium contact angles changed from 101.5° to 140.5° with Y increasing from 0 wt.% to 1.23 wt.%. Cross-sectional microstructure observations revealed that the thermal dissociation of ceramics occurred and the released [O] atoms can react with Y to produce Y2O3 reaction layer along three-phase interphase area. Wetting kinetics analyses indicated that surface tension of the melt droplets had been positively correlated with the Y concentrations, and it increased from 737.8–1045.1 mN/m. Meanwhile, the pinning effect of the rough substrate surface on the three-phase line hindered the spreading of the liquid on ceramics. The change in total free energy of the alloys/ceramics system was considered as the key factor affecting the wettability. Moreover, the surface morphology and thermodynamic stability of ceramics also had some influence on the wettability.

LIPSS combined with ALD MoS2 nano-coatings for enhancing surface friction and hydrophobic performances

To enhance the friction and hydrophobic performances of contact interfaces, the laser-induced periodic surface structures (LIPSS) by picosecond pulses and atomic layer deposition (ALD) MoS2 nano-coatings are fabricated on the cement carbide surface. The friction and wettability tests are carried out by the unidirectional sliding friction and sessile drop experiments. Results show that the friction and wetting properties can be regulated by the LIPSS and ALD MoS2 nano-coatings, and the anisotropic friction and hydrophobic properties are observed with respect to the groove orientations. A combination of ALD MoS2 nano-coatings with LIPSS in parallel orientation (MS-HT) exhibits the best potential for improving the friction and wear performance, and the ALD nano-MoS2 coated surface combined with LIPSS in perpendicular to the observation direction (MS-VT) is the most effective way for enhancing the hydrophobic property.

Silicon-Boron Alloys as New Ultra-High Temperature Phase-Change Materials: Solid/Liquid State Interaction with the h-BN Composite

Silicon-boron alloys have been recently pointed out as novel ultra-high temperature phase change materials for applications in Latent Heat Thermal Energy Storage (LHTES) and conversion systems. One of the emerging challenges related to the development of such devices is a selection of refractories applicable to build a vessel for storing molten Si-B alloys at high temperatures and under consecutive melting/solidification conditions. Previously, it has been documented that hexagonal boron nitride (h-BN) is the only one ceramic showing a non-wettability and limited reactivity with Si-B alloys at temperatures up to 1750 °C, what makes it a good candidate of the first selection for the predicted application. Nevertheless, pure h-BN shows a rather low mechanical strength that could affect a durability of the LHTES vessel. Therefore, the main purpose of this work was to examine high temperature behavior of commercial high strength h-BN composite having a nominal composition of h-BN-24ZrO2-6SiC (vol.%) in contact with a solid/liquid eutectic Si-3.2B alloy. Two types of sessile drop experiments were carried out: a step-contact heating up to 1750 °C, and a thermocycling at 1300 − 1450 °C composed of 15 cycles of the alloy melting/solidification. The obtained results showed a lack of wettability in the examined system at temperatures up to 1750 °C. The Si-3.2B alloy presented good repeatability of melting/solidification temperatures in consecutive thermal cycles, which was not affected by the interaction with the h-BN composite. However, due to reactions taking place between the composite’s components leading to structural degradation, it is not recommended to increase operational temperature of this material above 1450 °C.

Evaluation of DC-MS and HiPIMS TiB2 and TaN coatings as diffusion barriers against molten aluminum: An insight into the wetting mechanism

TaN and TiB2 ceramic coatings on steel were tested as barriers to protect steel against molten aluminum by sessile drop experiments. Coatings tested were deposited by PVD using conventional DC-MS (Direct Current Magnetron Sputtering) and HiPIMS (High-Power Impulse Magnetron Sputtering) techniques. The evolution of contact angle and contact radius of the molten aluminum drop was recorded at 800 °C for H13 tool steel bare and coated samples. The influence of the thickness and microstructure of the coatings was investigated by XRD, SEM/EDS to elucidate the mechanism of the wetting process. Spreading rate of aluminum on coated samples was between 10 and 50 times slower than on bare steel samples. Coated samples showed reactive wettability with a reaction-controlled spreading stage observed as a constant spreading rate after an initial transient stage. The spreading mechanism of the molten metal on coated samples is a two-step mechanism: (i) molten metal infiltration through the coatings and (ii) fracture of the coating after the formation of Fe-Al intermetallic compounds that leads to an increased volume of the metallic substrate. The quantification of both steps proves that the coating's thickness plays a key role in the reactive wettability kinetics. Results show that HiPIMS deposited TaN coatings could be a promising candidate to protect steels against molten aluminum attack.

Studying the wettability of Si and eutectic Si-Zr alloy on carbon and silicon carbide by sessile drop experiments

The contact angles of two different systems, molten silicon and a eutectic Si-8 at. pct Zr alloy and their evolution over timeon vitreous carbon and polycrystalline silicon carbide (SiC) substrates were investigated at 1500°C under vacuum, as well as in argon using the sessile drop technique. The contact angle and microstructure of the liquid droplet/solid substrate interface were studied to understand fundamental features of reactive wetting as it pertains to the infiltration process of silicon and silicon alloys into carbon or C/SiC preforms. Both pure Si and theeutectic alloy showed good wettability onvitreous carbon and SiC characterized by equilibrium contact angles between 29° and 39°. Theeutectic alloy showed a higher initial contact angle and slower spreading as compared to that of pure Si. On vitreous carbon bothsilicon and the eutecticalloy formed SiC at the interface, while no reaction was observed on the SiC substrates.