Pre-treatment of steel

Phosphate pre-treatments may be either zinc phosphate (from zinc dihydrogen phosphate solutions) or an iron phosphate (fi om alkali phosphate solutions) (see Conversion coating and Pre-treatment of steel). The conversion reactions are promoted by accelerators (depolarizers), for example, bromates or molybdates in alkali phosphate baths or chlorates in zinc phosphate baths (with Ca or Ni grain-refining additions). Iron phosphate pre-treatment coatings are often described as amorphous . In practice, however, they are usually crystalline deposits of iron oxides and iron phosphate. Zinc phosphate pre-treatment coatings are always crystalline. A fine, dense crystal pattern of zinc phosphate on the metal surface is the ideal, as it improves both paint adhesion and corrosion resistance most effectively. 

Pre-treatment of steel J F WATTS Abrasion, pickling and conversion coatings... 

Phosphating n. Pre-treatment of steel or certain other metal surfaces by chemical solutions containing metal phosphates and phosphoric acid as the main ingredients, to form a thin, inert, adherent, corrosion-inhibiting phosphate layer which serves as a good base for subsequent paint coats. 

Coating life in moist atmospheres is also influenced by the effects of moisture on the substrate-coating interface, and marked improvements in life have been claimed by the use of moisture-protective pre-treatments of the substrate. Niederhauser et al ° studied a wide range of metals and titanium nitride, titanium carbide and chromium carbide as pre-treatments. The material was sputter-deposited on a steel substrate, and then sulphided by introducing hydrogen sulphide into the sputtering chamber in order to improve molybdenum disulphide adhesion. They found a marked improvement in life, particularly with a rhodium or palladium interlayer, but the actual degree of improvement is confused because they also used co-sputtered PTFE, and this is discussed further in Section 10.6. 

A number of other strategies have been investigated in order to improve the quality (selectivity and fluxes) or the synthesis efficiency of zeolite membranes by pre-treatment of the support. Most of these treatments are listed in [49], and include laser ablation, utilisation of diffusion barriers to limit sol infiltration, oxidation of stainless-steel supports, deposition of iron oxide to favour heterogeneous nucleation on the support and the use of acid attacks to activate the surface. 

Two different pre-treatments of the foil and of the reactor surface have been used either prereduction or preoxidation (with oxygen). During prereduction each foil was reduced for 18 h in flowing hydrogen at 770°C and 1 h at the actual experimental temperature prior to the run. With steel foils it was impossible to oxidize the foil to constant weight and preoxidation involved heating in oxygen (850°C) for various times as detailed in the text. 

A. Li, J. Grace and C. J. Lim, Preparation of thin Pd-based composite membrane on planar metallic substrate Part I Pre-treatment of porous stainless steel substrate, J. Membr. Sci., 2007, 298, 175-181. 

Anodic treatment may also be considered when bonding other metals. Examples inclnde the anodizing of magnesium in ammonium bifluoride solution, the anodic etching of stainless steel in nitric acid and anodizing of titanium in sodium hydroxide or chromic acid (see Pre-treatment of titanium). Alternative anodizing of copper can prodnce a Microflbrous surface (see Pre-treatment of copper). 

Fig. 2. Influence of a sacrificial pre-treatment for steel on the strength of tensile butt joints made under water with an epoxy-amine adhesive...

Pre-treatment of cultured hamster tracheal goblet cells with 100 piM atropine 1 h before addition of 100 fiM carbachol significantly inhibited the carbachol-induced mucin secretion (Steel and Hanrahan 1997). 

There are various suggested systems for the pre-treatment of stainless steels which consist of treating the metal surface with strong acids to attack crystal grain boundaries in the... 

Trabelsi W., Cecilio R, Ferreira M.G.S., Montemor M.F. (2005), Electrochemical assessment of the self-healing properties of Ce-doped silane solutions for the pre-treatment of galvanised steel substrates . Prog. Org. Coat., 54,276-284. 

According to Allsopp et al [5] the rather large spread in the wear coefficients of POM with concentration should he explained by the use of an untreated steel ball, as they found that slight surface pitting of the metal ball lead to better reproducibility of the wear results. As was already mentioned in the experimental section, we used the same ball for our complete series of experiments described here without any pre-treatment of the ball surface. We assumed that our measurements are not influenced by the surface condition of the ball. This is confirmed by the following observations the random order of the measurements of the foiu polymers under specific experimental conditions, still lead to clear trends of wear with normal load or slurry concentration as displayed in the figures 1 till 7. 

Precipitation Hardening. With the exception of ferritic steels, which can be hardened either by the martensitic transformation or by eutectoid decomposition, most heat-treatable alloys are of the precipitation-hardening type. During heat treatment of these alloys, a controlled dispersion of submicroscopic particles is formed in the microstmeture. The final properties depend on the manner in which particles are dispersed, and on particle size and stabiUty. Because precipitation-hardening alloys can retain strength at temperatures above those at which martensitic steels become unstable, these alloys become an important, in fact pre-eminent, class of high temperature materials. 

Various pre-treatment protocols have been developed including pickling and anodic/cathodic pulses to remove the oxide films. It was apparent that different types of steel require different pre-treatments, i.e. cast pieces behave differently to rolled pieces. Significant success was achieved in electropolishing cast pieces and the finish obtained with the ionic liquid was superior to that with phosphoric add, however, the converse was true for rolled pieces because the oxide film is thicker in the latter samples and hence slower to dissolve in the ionic liquid. 

Figure 12.2 presents the optical view of the polished cross-section of A1 layers made at —20 mAcm-2 on a mild steel substrate without performing in situ etching prior to the electroplating. An interstice between the substrate and the electroplated layer is seen due to a thin oxide layer which forms after the last pre-treatment step. 

---