Stainless steel acid etch

Stainless steel Acid etch Vinyl-phenolic 49.7... 

Plating T anks. An electroless plating line consists of a series of lead-lined (for plastics etching) or plastic-lined tanks equipped with filters and heaters, separated by rinse tanks (24). Most metal tanks, except for passivated stainless steel used for electroless nickel, cannot be used to hold electroless plating baths because the metal initiates electroless plating onto itself. Tank linings must be stripped of metal deposits using acid at periodic intervals. 

Good bonding was obtained to several substrates under aqueous conditions. Values obtained were 41 to 10-3 MPa to composite resins, and 9-8 to 15-6 MPa to stainless steel (Table 9.6). They were also reported as adhering to porcelain. No adhesion was obtained to untreated dentine or enamel. The cements could be bonded to enamel etched with add (3-5 MPa) and to dentine conditioned with poly(acrylic acid) (10 MPa). 

Figure 5. Typical Microstructures of Forged Type 21-6-9 Stainless Steel (Oxalic Acid Etch, 90 s) (a) Conventionally Forged and, (b) High-Energy-Rate Forged.

This contamination, as in aluminum, is called smut. The usual method for desmutting is to wipe the work piece after rinsing, while it is still wet or to brush mechanically with a stiff wire bristle brush. However, it has been found that only a portion of the smut is removed by these methods and chemical etches are required to remove all of the material. An example of smut on stainless steel is shown in Figure 5 (12), where a surface which had been treated in hot sulfuric acid is shown. 

The general sequence of surface preparation for ferrous surfaces such as iron, steel, and stainless steel consists of the following methods degreasing, acid etch or alkaline clean, rinse, dry, chemical surface treatment, and priming. The chemical surface treatment step is not considered a standard procedure, but it is sometimes used when optimum quality joints are required. It consists of the formation of a corrosion-preventing film of controlled chemical composition and thickness. These films are a complex mixture of phosphates, fluorides, chromates, sulfates, nitrates, etc. The composition of the film may be the important factor that controls the strength of the bonded joint. 

Acid etching can be used to treat types 301 and 302 of stainless. These processes result in a heavy black smut formation on the surface. This material must be removed if maximum adhesion is to be obtained. The acid etch process produces bonds with high peel and shear strengths. The 400 series of straight chromium stainless steels should be handled in the same manner as the plain carbon steels. The various types of precipitation hardening (PH) stainless steels each present an individual problem. Processes must be adopted or developed for each type. 

Figure 38 Comparison of data from SL-EPR, acid ferric sulfate, and oxalic acid etch test for seven separate heats of Type 304 and 304L stainless steel. Note that for low levels of sensitization, the SL-EPR can quantitatively distinguish among degrees of sensitization. At higher levels, the coupon exposure tests are more discriminating. (From Ref. 32.)...

Hydrofluoric acid — (HF) A solution of hydrogen fluoride in water. The pure hydrogen fluoride is characterized by Mw of 20.0063 gmol-1 m.p. -83.55 °C (1 atm) b.p. 19.5 °C (latm). When concentrated, this colorless fuming liquid is extremely corrosive and can dissolve almost all inorganic oxides such as silicate compounds or oxides of metals like stainless steel, aluminum, and uranium however, it can be stored in casted iron bottles because a corrosion-resistant iron fluoride layer protects the metal. It is used for several purposes such as the preparation of titanium oxide nano tube arrays [i], silicon nanoparticles [ii] and electrochemical etching of silicon [iii], electrochemical deposition of lithium [iv], etc. 

Etching of stainless steel represents the most typical case of the application of electrolytic etching. This technique has been used on die 18/8 stainless steels in order to obtain a reliable and rapid measure of their sensitization to intergranular corrosion after a thermal treatment at 600 to 900°C. Several organic electrolytes such as oxalic acid (1) and tartaric acid (2) as well as inorganic electrolytes such as chromic acid (3) and sodium cyanide (4) have been employed. All these electrolytes attack preferentially the grain boundaries in which a second phase has precipitated. The composition of this phase responsible for the etching is not always known. 

Solutions used for electrolytic etching of stainless steels may be divided into two classes (a) Electrolytes which readily etch grain boundaries in the form of grooves regardless of the presence or absence of intergranular precipitates. Nitric acid is of this type [ J. Electrochem. Soc., 106, 161 (1959)]. ... 

Fig. 1. Annealed steel. 18 Cr-8 Ni stainless steel etched electrolytically in 10% oxalic acid for 1.5 min. at 1 amp/sq. cm X500.

The electrolytic etches in oxalic acid, as described above, are carried out under standardized conditions of current density and length of etching time. Measurement of the electrode potential of the stainless steel during this etching procedure shows that this potential is also constant throughout the etching period, and, that therefore, such etches are equivalent to etching under conditions of controlled potential. 

Hard troweled floor surfaces are usually broom finished to provide a surface profile and to eliminate costly abrasive blasting. Some abrasive blasting will be required on the typical job however. The use of muriatic acid etching is prohibited on nuclear sites due to the adverse effect of chlorides on stainless steel. 

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