Ice Adhesion to Hydrophilic and Hydrophobic Surfaces

The adhesional shear strength has been determined for ice formed against polished steel, monolayers adsorbed on steel and thin plastic coatings painted on metal surfaces. The adsorbed monolayers reduced the shear strength to about one-third of that for ice on clean steel. The monolayers also had the effect of changing the character of the breaks from clearly cohesional to apparently adhesional failure. The shear strength from the plastic coatings ranged from values equal to that of ice against clean steel to values 70 to 80% lower. The reduction in shear strength did not correlate with the water contact angle on the coatings but was usually found to be due either to air entrapment at the ice/coating interface or to cohesive failure of the coating itself.

The ice separated from the various substrates was examined microscopically by forming plastic replicas of the ice surface. These studies helped determine the mechanism of failure and, since one of the replicating solutions was also an ice etchant, much was learned about the crystal structure and the crystal defects of ice near surfaces. The ice lattice was found to be highly defective near the substrates and this is discussed in connection with the “liquid-like,” behavior of interfacial ice.     

Effect of Adsorbed Water on the Spreading of Organic Liquids on Soda-Lime Glass

The spreading behavior and equilibrium contact angle, θ, of organic liquids on soda-lime glass surfaces were observed at relative humidities (rh) varying from 1 to 95%. Increasing rh increased θ for many nonhydrophilic liquids on glass; no comparable effects occurred with nonadsorptive solid surfaces. The decrease in wettability of the glass with increasing rh resulted from the physical adsorption of a surface layer of water molecules sufficient to convert the normally high-energy glass surface into one that behaves as a low-energy surface, i.e. a surface with a low critical surface tension for spreading, γ_c, toward nonhydrophilic liquids. As the thickness of the adsorbed water layer increased, glass behaved like a surface with progressively decreasing γ_c, approaching that of bulk water. These results are discussed in relation to the effect of moisture on the spreading or adhesion of resins to glass and other hydrophilic solids.     

The NRL Cyclotron Beam Control and Handling System

The beam handling apparatus and its associated remote control arrangements are described for the NRL Cyclotron Beam Transport System. The need for reducing duplication of controls and power supplies for such a multi-beam-path facility resulted in the development of a rapid master selector system which can be programmed to accommodate the different beam path requirements. All ion optics and beam sensing components along any particular beam path can be activated from a single selector panel, and then individually controlled. The beam transport display, vacuum control display, and control console, are laid out in graphic form wherever feasible in an effort to present readout and control information concisely and continuously. Precision, versatility, modular construction, and ease of maintenance guided the mechanical and electrical design criteria. Design details and prototypes of beam stops, scanners, viewers, collimators, probes, and pumping stations, are discussed.     

Hot-Pressing of MgO with NaF

The results of using NaF additives in hot-pressing MgO are described and compared with the results when LiF is used. To obtain nearly theoretical density, the temperatures required for hot-pressing with NaF are ∼100°C higher than those required with LiF. Specimens made with NaF were generally translucent after hot-pressing or subsequent annealing. Sodium fluoride inhibits grain growth and can produce a duplex grain structure, whereas LiF enhances grain growth during annealing. Both NaF and LiF wet MgO and lubricate it well. The present study and other investigations of fluoride densification aids indicate that the formation of a liquid phase, with resultant wetting and lubrication, is important, especially in the early stages of densification. Possible solution of anions and cations is discussed.     

The effect of yttrium and erbium dispersoids on the deformation behaviour of titanium

The deformation characteristics at 295 K and 575 K of polycrystalline Ti-Y and Ti-Er alloys containing 20 to 90 nm diameter dispersions were investigated by stress-strain measurements and by transmission electron microscopic observations of deformation substructures. The presence of the dispersoids increases the yield stress at both 295 K and 575 K, with the dispersion strengthening being more pronounced for the larger grain size and at the higher temperature. In dispersoid-free titanium the yield stress varies with grain size at both 295 K and 575 K in accordance with the Hall-Petch relation, but the yield stress of the Ti-Er alloys does not show a well-defined linear dependence on the inverse square root of grain size. The work hardening is less sensitive to grain size in the Ti-Er alloys than in pure titanium. The extent of twinning is significantly higher in the Ti-Er and Ti-Y alloys than in titanium at both temperatures. The influence of the dispersoids on deformation substructure and grain size related deformation behaviour is discussed.     

Characterization of platinum electrodes in H2-saturated sulphuric acid solution under steady-state potentiostatic conditions

The character of platinum-bead and -(111) electrodes at anodic steady-state potentials was determined by analysing with cathodic galvanostatic pulses for reducible, Pt-associated species. There was a considerable amount of potential overlap in the reduction of adsorbed and dermasorbed O. The θ_so^2?4- dependence on potential and the effects of adsorbed SO^2?₄ on H and O sorption were shown. SO^?₄ adsorption passivated the surface for H₂ oxidation below 1·0 V and stabilized the associated oxygen species at higher potentials. Pre-saturation of Pt with dermasorbed oxygen caused a hysteresis effect requiring potentiostating at or below 0·85 V for its removal. H₂ has a strong effect on the steady-state character below 1·0 V, but has essentially no effect for the transient formation of Pt—O, Pt-bead and -(111) electrodes showed important differences.     

Preferred orientation of NiAl2O4 spinel grown on sapphire

The orientation relationships between the spinel nickel aluminate (NiAl₂O₄) and the aluminum oxide single crystal from which it is grown have been investigated. A variety of sapphire surface orientations were used. The nickel source was primarily nickel vapor, but nickel metal was also used. The large grained spinel layer growing in contact with the sapphire is highly textured, and a thinner fine grained layer on its outer surface is only lightly textured. Two principal textures were observed: for sapphire surfaces oriented near the basal plane, the {111} spinel is parallel to the (0001) sapphire; for surfaces oriented away from the basal plane the {111} spinel is parallel to the {1120} sapphire. In both cases the directions 〈110〉 spinel and 〈1010〉 sapphire are aligned. Considerable twinning and several secondary textures have also been seen.     

Influence of substrate on the in-plane ferromagnetic spectrum of epitaxial YIG films

We find a direct correspondence between the lattice mismatch and the in-plane angular dependence of the FMR field for epitaxial YIG films on non-magnetic garnet substrates.