To wet or not to wet: that is the question

Wetting transitions have been predicted and observed to occur for various combinations of fluids and surfaces. This paper describes the origin of such transitions, for liquid films on solid surfaces, in terms of the gas-surface interaction potentials V(r), which depend on the specific adsorption system. The transitions of light inert gases and H2 molecules on alkali metal surfaces have been explored extensively and are relatively well understood in terms of the least attractive adsorption interactions in nature. Much less thoroughly investigated are wetting transitions of Hg, water, heavy inert gases and other molecular films. The basic idea is that nonwetting occurs, for energetic reasons, if the adsorption potential's well-depth D is smaller than, or comparable to, the well-depth of the adsorbate-adsorbate mutual interaction. At the wetting temperature, Tw, the transition to wetting occurs, for entropic reasons, when the liquid's surface tension is sufficiently small that the free energy cost in forming a thick film is sufficiently compensated by the fluid- surface interaction energy. Guidelines useful for exploring wetting transitions of other systems are analyzed, in terms of generic criteria involving the "simple model", which yields results in terms of gas-surface interaction parameters and thermodynamic properties of the bulk adsorbate.Comment: Article accepted for publication in J. Low Temp. Phy

Kjemisk behandling mot Gyrodactylus salaris i Steinkjervassdragene 2006

Årsliste 2007Kjemisk behandling mot Gyrodactylus salaris i Steinkjervassdraget er gjennomført på oppdrag fra Direktoratet for naturforvalting (DN). Tiltakshaver har vært Fylkesmannen (FM) i Sogn og Fjordane. Behandlingen av Steinkjervassdraget høsten 2006 er en del av en totalbehandling som har som hovedmål å utrydde lakseparasitten G. salaris i regionen. Hensikten med behandlingen i august 2006 var å redusere smitten av G. salaris internt i Steinkjervassdragene og eksternt til nærliggende vassdrag i regionen. Dette ble gjort ved å tilsette surt aluminiumsulfat (AlS) i elvevannet og CFT-L (rotenon) i dammer og sig. Behandlingen foregikk i tidsrommet 21.august-2.september 2006. AlS ble dosert ut i hovedelvene og i de største sidevassdragene. I andre små vannkilder i periferien, som for eksempel små sig og mindre avsnørte dammer ble det brukt CFT-Legumin (rotenon). Under behandlingen ble det dosert ut totalt 2 tonn med aluminium og 11 liter CFT-Legumin (0,3 kg rotenon). Lakseunger infisert med G. salaris ble plassert i kar langs elva og eksponert for behandlet elvevann. Ved behandlingens slutt ble alle lakseungene i karene sjekket for G. salaris. Ingen dødelighet ble registrert og det ble heller ikke funnet G. salaris på noen av fiskene i karene.Direktoratet for naturforvaltning

Creep processes in magnesium alloys and their composites

A comparison is made between the creep characteristics of two squeeze-cast magnesium alloys (AZ 91 and QE 22) reinforced with 20 vol pct Al2O3 short fibers and the unreinforced AZ 91 and QE 22 matrix alloys. The results show the creep resistance of the reinforced materials is considerably improved by comparison with the unreinforced matrix alloys. It is suggested that creep strengthening in these short-fiber composites arises primarily from the existence of a threshold stress and the effect of load transfer. By testing samples to failure, it is demonstrated that the unreinforced and reinforced materials exhibit similar times to failure at the higher stress levels. A detailed microstructural investigation by transmission electron microscopy (TEM) reveals no substantial changes in matrix microstructure due to the presence of the reinforcement. This suggests that direct composite strengthening dominates over indirect effects

Microstructure and Strengthening Mechanisms in an Ultrafine Grained Al-Mg-Sc Alloy Produced by Powder Metallurgy

Additions of Sc to an Al-Mg matrix were investigated, paying particular attention to the influence of Al3Sc precipitates and other dispersoids, as well as grain size, on mechanical behavior. Prior studies have shown that Sc significantly increases the strength of coarse-grained Al-Mg alloys. Prompted by these findings, we hypothesized that it would be of fundamental and technological interest to study the behavior of Sc additions to an ultrafine-grained (UFG) microstructure (e.g., 100\u27s nm). Accordingly, we investigated the microstructural evolution and mechanical behavior of a cryomilled ultrafine grained Al-5Mg-0.4Sc (wt pct) and compared the results to those of an equivalent fine-grained material (FG) produced by powder metallurgy. Experimental materials were consolidated by hot isostatic pressing (HIP\u27ing) followed by extrusion or dual mode dynamic forging. Under identical processing conditions, UFG materials generate large Al3Sc precipitates with an average diameter of 154 nm and spaced approximately 1 to 3 μm apart, while precipitates in the FG materials have a diameter of 24 nm and are spaced 50 to 200 nm apart. The strengthening mechanisms are calculated for all materials and it is determined that the greatest strengthening contributions for the UFG and FG materials are Mg-O/N dispersion strengthening and precipitate strengthening, respectively