Papers by Keyword: Wetting

Abstract: The wetting phenomenon between solids and liquids has an outstanding role in several technological processes [1, 2]. The knowledge of physical and chemical factors acting on the surface tension is needed to ensure the successful processing in casting, brazing and sintering. The surface oxide layer influences the wetting conditions and makes difficult the exact measurement of contact angle [3]. In this paper the effect of oxide layer disruption and recovery was observed using a high speed camera.

Abstract: The glass molding process is considered to have a great potential for the mass production of aspherical glass lenses with high precision and low cost. However, glass molding has a serious problem of mold sticking with glass which needs to be resolved. This research investigates the interface reaction between glass and mold by high temperature wetting experiment, which provides the reference for the designing anti-stick coatings. The SUMITA K-PSK200 optical glass gobs with low Tg were used in this study. The influence of operation temperature, ambient gas, substrate materials, and thin film composition on wettability of glass at high temperature were studied. The results show that the higher the temperature, the smaller the wetting angle between glass gob and substrate could be observed. This indicates that severe interface chemical reaction occured and resulted in the loss of transparency in glass appearance. The wetting experiment in nitrogen ambient improved the sticking situation. The combination of chemically stable substrates and coatings, such as Sapphire (substrate) / GaN (film) and Glass (substrate) / Al2O3 (film) can achieve the best antistick propose. The precious metal films, such as Pt, Ir, coated on the ceramic substrates can effectively reduce the interface reaction between the glass and substrates.

Abstract: The contact angles of pure Ni, Ni/7wt%Ni3Al, Ni/5wt%Ni3Al/ 5wt%Cr and Ni/10wt%Cr anodes for the MCFC were measured by means of the capillary rise method in 62mol%Li2CO3+ 38mol%K2CO3 and 52mol%Li2CO3+ 48mol% Na2CO3 electrolyte and at different atmosphere. Also surface fractal dimension (Ds), which could characterize pore structure of the anodes, was calculated from experimental data obtained by mercury porosimetry and nitrogen adsorption method. The surface fractal dimensions of the anode were in range from 2.75 to 2.81, because porosities of the anodes for MCFC were controlled regularly to about 62% during sintering. It was investigated from wetting-in experiment by capillary-rise method that the contact angles between the anodes and the carbonate electrolytes were relatively decreased at CO2 atmosphere rather than air atmosphere and the angles were also decreased in the 62mol%Li2CO3+38mol%K2CO3 electrolyte rather than that measured and in the 52mol%Li2CO3+48mol% Na2CO3 electrolyte.

Abstract: Orientational patterns of wetted grain boundaries (GB's) in stressed NaCl polycrystals have been used for describing the GB penetration process on the basis of combined interfacial and mechanical energy balance considerations. The response of the internally wetted polycrystals to static loading has been shown to obey “pressure solution” constitutive laws involving dissolution at stressed surfaces, diffusive transport of dissolved matter and precipitation at less stressed surfaces. Direct experimental evidence for pressure solution mechanism is presented.

Abstract: The wettability of calcium fluoride by liquid Ga and Ge was studied. The initial contact angles indicate that pure liquid Ge and Ga do not wet CaF2. Different spreading kinetics during the experiments was observed. The contact angle in CaF2/Ge system increases with time, while the contact angle in CaF2/Ga system decreases. The same differences were also observed for temperature dependences of the contact angle. It was suggested that these wetting/dewetting tendencies are related to the ratio of the vapor pressure values for the melt and for the substrate. The experimental observations were confirmed by a thermodynamic analysis.

Abstract: The wetting as a multi scale phenomenon, including micro- and nano-scale aspects, is considered to be the essential step in the evaluation of the transport phenomena during metal/ceramics joining with active filer metal. Micro-scale aspect deals with diffusivity at the interface and into the bulk, as well as mass transfer around the grain boundary grooves (GBG) of the ceramic surface. In that sense, the explanation of mass transport mechanism around the GBG’s is presented. Mathematical analysis is based on experimental values taken from literature. Nanoscale wetting aspect is an atomistic approach, which includes the investigation of phase boundary structure. The mathematical model, which enables the contact angle calculation depending on the features of crystal lattice and interactions between atoms and molecules of the liquid and solid phases, is proposed.

Abstract: Al-cBN cermets have been hot pressed at temperature between 800oC and 1100oC and pressure of 50MPa in vacuum. The effect of particle size of the starting powders as well as the effect of starting compositions and temperature was investigated. The materials could only densify up to 84-92% of theoretical density. After hot pressing at 800oC only Al and cBN could be observed by XRD, whereas higher hot pressing temperature result in the formation of AlN and AlB2 which retard the densification. The microstructure of the hot pressed material was studied using scanning electron microscopy. It was observed that oxide layers exist at the interface between Al and cBN phases. The presence of these oxide layers resulted in blocking the Al from spreading and therefore preventing full densification.

Abstract: We have tried to develop the following new material processing for the production of value-added materials from by-products such as kish-graphite, Fe & Cu mixed scraps etc. in steelmaking processes : 1) Production of PdCl2 graphite intercalation compound (PdCl2-GIC) in hydrothermal conditions to create nano-particles encapsulated in kish-graphite. 2) Application of “unusual wetting” of liquid Cu on surface-oxidized Fe to produce composite materials between Cu and ceramics.

Abstract: The wetting phenomena and adhesion between Ag-Cu-Zr molten alloys (where Zr is an active brazing element) and ZrB2-ceramic substrate have been investigated from theoretical and experimental point of view. The wetting phenomena of molten alloy/ceramic substrate depend on the bonding characteristics of liquid alloys and ceramics as well as the magnitude of interactive forces at the interface. Accordingly, the first step of this investigation is to determine the surface properties of Ag-Cu, Ag-Zr and Cu-Zr liquid alloys. The energetics of the bulk and the surface of liquid alloys have been analysed in the framework of statistical mechanical theory in conjunction with Quasi-Lattice Theory (QLT), through the study of the concentration dependence of various properties such as surface tension, surface composition, concentration fluctuations in the long wavelength limit and Warren-Cowley chemical short-range order parameter. Combining the Young and the Dupré equations, the obtained values of surface tension together with contact angle data have been used to calculate the work of adhesion.

Abstract: Wetting can be regarded as a kind of effective nanostructure-forming process. To control the structure, a study on the relationship between atomic interactions and the resultant wetting behaviors is required. To model the wetting system, two sets of interatomic potentials for Metal/MgO(100) systems are derived from first principles calculation results for the simple configurations. A molecular dynamics method is applied to simulate the system and shows that Al atoms wet better than Sn atoms on the MgO substrate. The tendency is consistent with the experimental contact angles. The interfacial structures are different between these two systems.