Rough surface preparation

The inspection possibility of welds and rough surfaces also under the coating of various foulings, oils, scale, rust etc. without the preliminary preparation. 

Quantifying the effect of surface roughness or morphology is difficult, however. Surface preparations that provide different degrees of surface roughness also usually produce surfaces that have different oxide thicknesses and mechanical properties, different compositions, or different contaminant levels. The problem of separation of these variables was circumvented in a recent study [52] by using a modified microtome as a micro milling machine to produce repeatable, well-characterized micron-sized patterns on clad 2024-T3 aluminum adherends. Fig. 2 shows the sawtooth profile created by this process. 

One of the biggest challenges in this industry is the wide variety of substrates that can be encountered for any given application. Not only can the materials be substantially different in their chemical make up, but they may also be quite different in surface roughness, surface curvature and thermal expansion behavior. To help adhesion to these substrates, preparation of the surface to be bonded may be critical. This preparation may be as simple as a cleaning step, but may also include chemical priming and sanding of the surface. 

Direct bonding. In many high-volume production applications (i.e., the automotive and appliance industries), elaborate surface preparation of steel ad-herends is undesirable or impossible. Thus, there has been widespread interest in bonding directly to steel coil surfaces that contain various protective oils [55,56,113-116], Debski et al. proposed that epoxy adhesives, particularly those curing at high temperatures, could form suitable bonds to oily steel surfaces by two mechanisms (1) thermodynamic displacement of the oil from the steel surface, and (2) absorption of the oil into the bulk adhesives [55,56]. The relative importance of these two mechanisms depends on the polarity of the oil and the surface area/volume ratio of the adhesive (which can be affected by adherend surface roughness). 

It is difficult to give precise costs of floor treatments as size of total area, areas to be coated at one time, degree of surface preparation required and other factors all influence costs. Table 9.2 is a rough guide to comparative applied costs. 

Deposition by metal spraying can also be used for the reclamation of worn parts in this case, surface preparation is often accomplished by machining, i.e. by cutting a rough thread on the surface or by increasing the surface area of the part by grooving. Such methods. are not, however, normally used in corrosion prevention, except in the case of pump rods, which can be built up with nickel or stainless steel. 

Nature of the metal surface Clean, smooth, metal surfaces usually require a lower concentration of inhibitor for protection than do rough or dirty surfaces. Relative figures for minimum concentrations of benzoate, chromate and nitrite necessary to inhibit the corrosion of mild steel with various types of surface finish have been given in a recent laboratory studyThese results show that benzoate effectiveness is particularly susceptible to surface preparation. It is unwise, therefore, to apply results obtained in laboratory studies with one type of metal surface preparation to other surfaces in practical conditions. The presence of oil, grease or corrosion products on metal surfaces will also affect the concentration of inhibitor required with the... 

Nature of the metal surface The critical concentration of an anion required to inhibit the corrosion of iron may increase with increasing surface roughness. Thus, Brasher and Mercer" showed that the minimum concentration of benzoate required to protect a grit-blasted steel surface was about 100 times greater than that required to protect an abraded surface. However, surface preparation had little effect on the critical inhibitive concentrations for chromate" or nitrite " The time of exposure of the iron surface to air after preparation and before immersion may also affect the ease of inhibition by anions. There is evidence """ that the inhibition by anions occurs more readily as the time of pre-exposure to air increases. Similarly, if an iron specimen is immersed for some time in a protective solution of an inhibitive anion, it may then be transferred without loss of inhibition to a solution of the anion containing much less than the critical inhibitive concentration . ... 

The dependence of the C,E curves for a solid metal on the method of electrode surface preparation was reported long ago.10 20 67 70 219-225 in addition to the influence of impurities and faradaic processes, variation in the surface roughness was pointed out as a possible reason for the effect.10 67,70 74 219 For the determination of R it was first proposed to compare the values of C of the solid metal (M) with that of Hg, i.e., R = C-M/c-Hg 10,74.219-221 data at ff=0 for the most dilute solution (usually... 

Figure 7. Au particles deposited on different supports (a) a-FeOOH, (b) p-FeOOH, (c) Z1O2 (A) (rough surface), (d) ZrOi (B) (smooth surface), and (e) Xi02 particles. Support particles were also prepared by the authors.

The diazoalkanes are toxic substances and aay explode on contact with rough surfaces. Consequently, aany workers prefer not to sake large quantities of these aaterials when only snail quantities are needed for derivatization reactions. Sinple aicro-diazoalkane generators capable of rapidly preparing snail quantities of the reagents, as required, are coaaercially available [499-501]. 

The relative importance of the two mechanisms - the non-local electromagnetic (EM) theory and the local charge transfer (CT) theory - remains a source of considerable discussion. It is generally considered that large-scale rough surfaces, e.g. gratings, islands, metallic spheres etc., favour the EM theory. In contrast, the CT mechanism requires chemisorption of the adsorbate at special atomic scale (e.g. adatom) sites on the metal surface, resulting in a metal/adsorbate CT complex. In addition, considerably enhanced Raman spectra have been obtained from surfaces prepared in such a way as to deliberately exclude one or the other mechanism. 

Finely divided metal samples can also be prepared in the form of evaporated films in high vacuum, usually deposited on IR-transparent alkali halide plates (76-78). Such spectra are of interest in themselves, but tend to be much weaker than those obtained from the metal-particles-in-depth, oxide-supported catalysts. The rough surfaces of films of Cu, Ag, and Au, prepared by deposition on cold surfaces, can lead to very high-quality surface-enhanced Raman spectra (27, 28, 79, 80). The results from such experiments will be discussed in the later sections devoted to particular adsorbed hydrocarbons and metals, alongside the majority of spectra that are obtained on oxide-supported samples. 

If correlations do exist for simple metals, predictions are much more difficult for composite materials. On the other hand, cathode activation has two aims (i) to replace active but expensive materials with cheaper ones, and (ii) to enhance the activity of cheaper materials so as to approach or even surpass that of the more expensive catalysts. In the case of pure metals there is little hope to find a new material satisfying the above requirements since in the volcano curve each metal has a fixed position which cannot be changed. Therefore, activation of pure metals can only be achieved by modifying its structure so as to enhance the surface area (which has nothing to do with electrocatalysis in a strict sense), and possibly to influence the mechanism and the energetic state of the intermediate in the wanted direction. This includes the preparation of rough surfaces but also of dispersed catalysts. Examples will be discussed later. 

The Li surface preparation is very important. Immersion of Li electrodes covered by native films leads to complicated surface film replacement processes that may form a highly nonhomogeneous metal-solution interphase. In situ electrochemical surface preparation by dissolution or deposition may form very rough surfaces whose impedance spectra may be difficult to interpret properly. Hence, it seems that the most preferred way of studying the electrochemical behavior of a Li electrode in a specific solution is by using Li surfaces freshly and smoothly prepared in solutions. 

The analyst should be aware of certain less common preparations which may be encountered. Homoeopathic Preparations. These are usually round, flat/flat tablets witii rough surfaces, 5 to 6 mm in diameter, and contain mainly lactose. Injection Tablets. Small, totally soluble tablets used for making solutions for injection. The most commonly encountered until recently were diamor-phine tablets. These were round, flat/flat tablets, 4 mm in diameter and 2 mm tiiick, weighing 30 mg. They have been discontinued but they may still be seen, having been burgled from pharmacies. These tablets should not be confused with LSD microdots which are usually highly coloured. 

---