Papers by Keyword: Wetting

Abstract: In this paper, the physico-mechanical properties of alkali-activated mortars (CF/S) containing calcareous fly ash (CF) from the combustion of lignite and ladle furnace slag (S) from the steelmaking process as binders as well as sand and glass cullet as inert material have been studied. The constituents were mixed with the alkaline activator (NaOH:Na2SiO3 was 1:1). The binders and aggregates were used in a ratio 1:3 while a part of sand was replaced by glass aggregates (60%). The specimens (dimensions 40x40x160 mm) of alkali-activated mixtures CF/S: 100/0, 80/20 and 50/50 were cured at 25 °C for 2 days and then were placed in humid environment (95±5 % RH, 25 °C). Then the mechanical strength and porosity at 7-d, 28-d and 90-d age were measured. All of the CF/S specimens exhibited compressive strength around 15 MPa at 28 days. After the 28-d age the specimens of CF/S mortars were exposed to wetting/drying and freeze/thaw cycles to have an estimation of durability of alkali-activated CF/S mortars and compared to the Portland I42.5 cement mortars (PC) of high strength 43 MPa. Mass loss of specimens was measured by weighing them. The results showed that alkali-activated CF/S mortars appear to have similar or slight lower behavior to wetting/drying and freeze/thaw cycles compared to net cement mortars.

Abstract: The microstructure of Nd–Fe–B-based liquid-phase sintered alloy has been studied. The Nd₂Fe₁₄B/Nd₂Fe₁₄B GBs can be pseudo-incompletely (or pseudo-partially) wetted by the Nd-rich melt. Such GBs form the non-zero contact angle with the melt in the triple junctions and contain the uniformly thin (7-10 nm) Nd-rich layer. Such GBs are different from the completely wetted as well as from partially wetted GBs. Most probably, such thin Nd-rich GB layers are responsible for the excellent magnetic properties of the NdFeB-base permanent magnets because these GB layers ensure the magnetic isolation between the Nd₂Fe₁₄B grains needed for the high coercivity.

Abstract: The types of defects occurring during the formation of local zones on the surface of silicon wafers have been established. The dependences of defect formation on the surface from the surface microrelief, thickness of the protective coating of silicon oxide, process temperature, flow rate of the melt, the height of the melt, and the concentration of gallium additives in the aluminum have been determined. The optimum conditions of the process of zones formation have been revealed, and the total relative number of all types of defects has been significantly reduced.

Abstract: To investigate the wetting behavior of unsized carbon fibers with a sizing dispersion and the wettability of sized fibers with the liquid polymeric resin, contact angle measurements by capillary rise experiments are performed by tensiometry. First, the sizing behavior of fibers with different degrees of surface activation is analyzed. Increasing activation levels result in increasing oxygen surface concentrations and accordingly increasing polar components of the surface energies. These conditions result in a better wettability of the higher activated fibers. Secondly, the influence of the type of sizing dispersion is addressed by using two water-based epoxy sizing dispersions, i.e. a standard epoxy sizing and an advanced functional epoxy sizing with high reactivity. Using the functional sizing the wettability is further improved. Finally, the influence of the sizing on the wettability of the carbon fibers by the matrix polymer during resin infiltration is investigated using the differently sized fibers and a liquid epoxy resin. Carbon fibers with functional sizing show improved wettability by the resin compared to fibers with standard sizing. The results show that the wetting behavior of carbon fibers with respect to sizing and polymer matrix can be controlled by a suitable choice of surface activation of the fibers and reactivity of the polymeric sizing dispersion.

Abstract: Metal matrix composites (MMC) are often applied to tool surfaces to increase resistance to wear and tear. However, some matrix and particle materials such as Ni, Co, WC or TiC are expensive and partly classified as critical elements. With respect to tribo-mechanical properties, Fe-alloys reinforced with oxide particles are promising compound materials to produce wear-resistant MMC with low-cost and readily available materials. However, thus far the technical application of such MMCs is limited due to poor wettability of the oxides by Fe-base melts and an associated weak bonding between the oxide particles and the metal matrix phases. In this work two novel production techniques (namely pre-metallization and active sintering) are introduced, which improve the wettability and interfacial reactions between both materials and therefore enable supersolidus liquid-phase sintering (SLPS) of the MMC. For the first technique the oxide particles are pre-metallized by depositing a thin film of TiN on the surfaces. The second technique is called active sintering. For this technique the alloy design is adapted from active brazing, so that wettability of the oxide particles by the alloy-melt is increased. The resulting effects of these techniques are investigated using wetting and sintering experiments, and are analyzed with respect to the developed microstructures and interfacial reactions between the oxide particles and the metallic phases.

Abstract: Solid-liquid interactions in metal-ceramic systems are extremely important in high temperature brazing processes. These interfacial phenomena are reviewed here, from both the thermodynamic and microstructural viewpoints. At high temperature, the wetting characteristics and the adhesion properties of the joints are strongly related to the high atomic mobility of the different phases, giving rise to different phenomena, ranging from the dissolution of the ceramic in the liquid phase, reactions, formation of new phases and reprecipitation at the solid-liquid interface. The role phase diagrams in guiding the choice of the filler alloys composition and to optimize the brazing procedures is emphasized. In particular, it is shown that the computation of new diagrams and the critical use of the existing ones is essential to understand how to suppress the substrate dissolution and to interpret the evolution of the system. Experimental data are presented and discussed concerning the interactions between liquid metals with early-transition-metal diborides (TiB₂, ZrB₂, HfB₂) as a typical example involving the joining of Ultra-High Temperature Ceramics (UHTCs). Overall, these studies represent the basic step linking the chemical and structural information to the design of industrial processes involving a liquid phase at high temperature, such as the production of metal-ceramic joints or composite materials to be used in highly demanding applications.

Abstract: This work focuses on capillary-induced collapse of high-aspect-ratio silicon nanopillars. Modification of the surface chemistry is demonstrated to be an efficient approach for reducing capillary forces and consequently reduce pattern collapse. Special effort is spent on determination of the wetting state of chemically modified surfaces as complete structure wetting is of utmost importance in wet processing. In light of this, an ATR-FTIR based method has been developed to unambiguously distinguish between wetting and non-wetting states.

Abstract: The introduction of 3-D nanostructures in semiconductor manufacturing may create wetting issues in aqueous processing. In this work we evaluated the use of a CO₂ gas atmosphere to promote the wetting of superhydrophobic nanopillars, relying on the high solubility of CO₂ in aqueous solutions. The patterned surface was first flushed with CO₂ gas, before dispensing the aqueous solution that was saturated with N₂ and switching the gas flow from CO₂ to N₂. The liquid penetration was characterized by monitoring the disappearance of CO₂ gas using ATR-FTIR. Results showed only a modest improvement in wetting, presumably due to a fast N₂-CO₂ gas exchange at the wetting front.

Abstract: The current paper concerns the angle of silicon carbide wetting with high-carbon molten iron under vacuum. Our research was conducted with a wetting examination complex at the Institute of Energy and Interfacial Interactions (Genoa, Italy). It has been revealed that reaction of the substrate with a high-carbon molten metal results in the gaseous phase formation. We have also ascertained the temperature rate at which the substrate/metal reaction with gas formation starts.

Abstract: The work deals with the research of wettability of lead-free solders for higher application temperatures. For the research of wettability, SnSb5, ZnAl4, ZnAl6Ag6 and BiAg11 solders were used on Ag, Cu and Ni substrates. The measurement was carried out in a controlled atmosphere by trigonometric method. Zn based solders wets none of the examined substrates. SnSb5 solder wets only Cu substrate with wetting angle of 54o. Soldering alloy BiAg11 wets all substrates, wherein the best results (23 o) was achieved on Ag substrate.