Iron surface clean

Some basic BW treatment objectives include keeping boiler surfaces clean and corrosion-free to minimize fuel bills and managing variable quality FW smoothly and efficiently to limit upsets and other downstream problems. But the nature of potential boiler deposition problems changes with increases in pressure and, simply put, is primarily concerned with a reduction in simple, hardness-related deposits and an increase in complex, iron oxide deposits. The effect of dirty boilers on fuel costs can be seen in Figure 10.4. 

Very cold. Immersing a clean iron surface into liquid nitrogen at 77 K (—196 °C) yields a weak physisorptive bond. The N=N molecule is probably aligned parallel to the metal surface, with electron density donating from the centroid of the triple bond directly to iron atoms on the surface of the metal via a van der Waals type of interaction. The experimental value of A //fadsj is small at about 1.5 kJ mol-1. 

Iron films behave in every way similar to nickel films except that upon admitting oxygen, about seven oxygen atoms are sorbed instantaneously for every crystallographic site, forming an iron oxide film seven atom layers deep, and except that the heat of adsorption of hydrogen on such an oxide covered film is almost identical with that on the clean iron surface even immediately after the oxidation has taken place. 

On a freshly cleaned iron surface, oxidation is initially fast, but as the oxide layer grows, it acts as a barrier between the interacting species and the reaction rate soon falls. The higher the temperature, the thicker the film before the fall in oxidation rate becomes significant. 

FLUX (Solder). A material which by its chemical action facilitates the soldering and brazing of metals. Such a flux applied to a metallic surface cleans it and renders it receptive to amaigamalion with the solder or brazing metal. Some fluxes are rosin, for soldering tin muriatic acid, fnr galvanized iron and other zinc surface and borax for brazing,... 

O-PO4 is often used in combined preoperational cleaning and passivation programs and acts, in the presence of oxygen, to promote passivity on iron surfaces, changing it from an active state to a passive state by forming a barrier to corrosive ions (although the starting material may actually be P-PO4). 

Morecroft, D.W., Reaction of n-Octadecane and Decoic Acid with Clean Iron Surfaces, Proc. Conf. on Chemical Effects at Bearing Surfaces, Swansea, Jan. 1971, p. 225. 

Auger spectroscopy was used by Buckley to study the interaction of the following chlorine compounds with sputter-cleaned iron surfaces methyl chloride, ethyl chloride, vinyl chloride and benzyl chloride [7, 13]. With the exception of benzyl chloride, these halogen compounds left... 

Figure 7.23. Ammonia TPD from clean Fe(lll) and K/Fe(lll) surfaces. The desorption temperature of ammonia from Fe(111) is lowered in the presence of potassium. Thus potassium lowers the adsorption energy of ammonia on the iron surface [59].

Starting with initially clean rhodium and iron surfaces, the surface rapidly becomes covered with a monolayer of active carbon. This active carbon layer appears to hydrogenate directly to produce methane by a mechanism which is very similar for both rhodium and iron. While rhodium-carbon monolayer systems remain stable indefinitely under our... 

The electron energy spectra of a clean Fe/W(l 10) film with a thickness of about 20 A and of O on such FeAV(l 10) films with an oxygen exposure of 3 L are shown in Fig. 5.22. The structure at high kinetic energies is caused by Fe kI electrons near the Fermi level. After dosing oxygen to the iron surface, the emission of these electrons is drastically reduced. 

D.H. Buckley, "Adhesion of Metals to a Clean Iron Surface Studied with DEED and Auger Emission Spectroscopy," Wear, 2, 89 (1972). 

Iron in air is covered with a thick and dense oxide layer, which is further blocked with contaminants such as water, CO, or hydrocarbons. Clean oxide-free iron surfaces can be prepared by Ar ion sputtering in UHV or by electrochemical reduction. 

An attempt was made to study the catalytic activity of a heavily oxidized iron surface, but the oxide was found to be so short-lived under the reducing conditions of the reactant mixture that its activity could not be distinguished from that of clean iron. Addition of 5 Torr of water to the reaction mixture, however, completely suppressed catalytic activity, possibly suggesting that if it is continually replenished, the oxidized surface is inactive as a catalyst. 

The iron surface is wetted by promoter oxides. The potassium atoms can migrate to the iron surface under ammonia synthesis conditions to adsorb on the free iron atoms or cover the layer of the other promoter oxides present there earlier. A recent paper demonstrates that under ammonia s3mthesis conditions a clean iron surface which is in direct contact with the multiply promoted iron catalyst is covered with a potassium oxygen layer. This result indicates that despite the presence of other promoters (Al, Ca) in the catalyst it is potassium that covers the iron surface. Even prolonged maintenance of such a sample under ammonia synthesis conditions (700 K, 10 MPa) does not change the composition of its surface. 

The clean iron surface exhibits a tendency to minimize an excess of the surface energy by reduction of the surface area. It is assumed in the model that the surface is covered by an oxygen layer (there are promoters on top). In this case the surface energy is compensated by Fe-O bonds. The greater the oxygen... 

Low energy electron diffraction (LEED)-surface crystallography studies clearly indicate that the surfaces of most clean metals relax inward. The rougher the surface (the more open the surface structure), the greater is the relaxation. The (Iff) and (211) iron surface structures as determined by LEED-surface crystallography are shown in Fig. 3.84. d90... 

The delamination rate was determined with a scanning Kelvin probe. A small amount of fine sodium chloride was introduced into a circular deepening in the middle of the polished and ethanol-cleaned iron sample. After the sample was introduced into the plasma reactor, it was cleaned and activated in one step by an oxygen plasma, leading to a carbon-free and highly oxidized iron surface. In the next step an ultrathin plasma polymer of hexamethyldisilane was deposited on the cleaned substrate, leading to a well-defined metal-polymer interface. The thickness of the deposited polymer was controlled by the in situ measurement of the resonance frequency of the quartz crystal and was about 5 nm, so that the film thickness is in the range of the escape depth of the photoelectrons. 

The reaction mechanism could follow one of two routes according to the nature of the transition state formed in conjunction with the clean Iron surface (See Fig. 2). 

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