Surface iron needle

Another well-known example is the floating of a metal needle (heavier than water) on the surface of water (Figure 1.4.) The surface of a liquid can thus be regarded as the plane of potential energy. It may be assumed that the surface of a liquid behaves as a membrane (at a molecular scale) that stretches across and needs to be broken in order to be penetrated. One observes this tension when considering that a heavy iron needle (heavier than water) can be made to float on the water surface when carefully placed (Figure 1.4). 

FIGURE 1.4 An iron needle floats on the surface of water (only if carefully placed otherwise, it should sink due to gravity forces). 

Surface tension and floating of iron needle on water ... 

Silvery, shiny, and hard. Unique metal, gives off an odor as it forms volatile 0s04 on the surface (oxidation states 81). Osmium is the densest element (22.6 g cm3 record ). Was replaced in filaments (Osram) by the cheaper tungsten. Used in platinum alloys and as a catalyst. Haber s first catalyst in ammonia synthesis was osmium, which fortunately could be replaced by doped iron. The addition of as little as 1 to 2 % of this expensive metal increases the strength of steel (e.g. fountain-pen tips, early gramophone needles, syringe needles). 

The catalytic properties of a surface are determined by its composition and structure on the atomic scale. Thus, it is not sufficient to know that a surface consists of a metal and a promoter, say iron and potassium, but it is essential to know the exact structure of the iron surface, including defects, steps, etc., as well as the exact location of the promotor atoms. Thus, from a fundamental point of view, the ultimate goal of catalyst characterization should be to look at the surface atom by atom, and under reaction conditions. At present, this is only occasionally possible in highly simplified model systems such as the well defined surfaces of single crystals, or the needle shaped tips used in field emission studies [8]. 

Coke formed on solid surfaces during the pyrolyses of acetylene, ethylene, ethane, propylene, and butadiene were examined by using a scanning electron microscope. Seven types of coke have been identified braided filament, uniform diameter filament, needle or spike, ribbon, fluffy or cottonlike fibers, knobby, and amphorous. The first four types contained metal (especially iron) and were magnetic. Magnetic cokes formed sometimes on Incoloy 800, stainless steel 304, stainless steel 410, and Hastelloy X surfaces, but never on Vycor glass or aluminized Incoloy 800 surfaces. Conditions at which each type of coke was formed are discussed. 

Figure 3 shows an example of needle or arrowhead coke. This coke is produced from ethylene, propylene, and butadiene on Incoloy 800 surfaces in the temperature range from about 365°C up to at least 600° C. The size of needles as shown in Figure 3 was smaller than that observed in most other photographs this coke was magnetic because of the iron present in it. The coke produced on alonized Incoloy 800 at comparable conditions was amorphous, however, as shown in Figure 3. 

Construction.—Runners of reaction turbines are of cast iron, bronze, cast steel and composite of plate steel in cast hubs. The material used is determined chiefly by manufacturing considerations. Thrust bearings for horizontal units are of the plain collar type. For vertical turbines, ball, roller or oil-pressure (step) bearings are commonly used. Impulse turbine buckets are of bronze, cast iron or cast steel cast iron being used only for the lower heads. Nozzles are cast iron or cast steel, usually with removable bronze tips and steel needles. Interior surfaces should be polished smooth. The housing is usually cast iron, sometimes with steel-plate covers. 

Particles may be nearly spherical, cubic, nodular (a rounded irregular shape), acicular (needle- or rod-like) or lamellar (plate-like). Since particle shape affects pigment packing, it therefore affects hiding power. Rod-shaped particles can reinforce paint films, like iron bars in concrete, or they may tend to poke through the surface reducing gloss. 

The sandwich technique has the advantage that it enables the analytical sample to react in a bath which is probably not yet saturated with carbon, and from which the escape of carbon monoxide is thus not yet impeded by needles of graphite or carbide deposited on the surface of the bath, as frequently occurs in the bath procedure. In addition, a further considerable effect on the release of gas, is obtained by the fact that titanium and zirconium form alloys with platinum or palladium, which results in a large evolution of heat. This causes a sudden and considerable increase in temperature (a flash of light ). The sandwich method is however limited to bath metals with very low oxygen contents, which is e.g. not the case with nickel, cobalt or iron. Therefore, the metal foil required is preferably a piece of platinum or palladium foil of about 50 Mm thick. The oxygen blank values of platinum and palladium in compact form are between 1 and 5 Mg/g. They amount to 5 to 15 Mg/g for the corresponding foils. 

---