Chromic-sulfuric acid Etch

Processing details for the optimized FPL etching procedure, other chromic-sulfuric acid etches and the P2 etch are summarized in Table 1 [2,62J. 

Chromic-sulfuric acid etch Coupling agent 30.27 21.29 0.708 0.105 0.091 0.108... 

Fig. 5. Effect of outdoor weathering on the strength of aluminum alloy/epoxy-polyamide joints (chromic-sulfuric acid-etch metal surface pretreat-ment)61 (Reprinted from Ref. 61, p. 194, by courtesy of Gordon and Breach...

The outdoor durability of epoxy bonded joints is very dependent on the type of epoxy adhesive, specific formulation, nature of the surface preparation, and specific environmental conditions encountered in service. The data shown in Fig. 15.19, for a two-part room temperature cured polyamide epoxy adhesive with a variety of fillers, illustrates the differences in performance that can occur due to formulation changes. Excellent outdoor durability is provided on aluminum adherends when chromic-sulfuric acid etch or other chemical pretreatments are used. 

A chromic-sulfuric acid etch gives the best resistance to weathering and saltwater environments. 

For each alloy studied, the chromic-sulfuric acid etching, Alodining, and anodizing surface pretreatment produced the most durable joints, although the relative order of effectiveness could vary with different alloys. 

The Forest Products Laboratory (FPL) and other chromic-sulfuric acid etching procedures are the oldest surface pretreatments for aluminum adherends,(3) other than simple degreasing or mechanical abrasion. In addition to being used as a complete adherend pretreatment, it is also frequently used as the first step in other pretreatments, such as PA A and CAA. 

The ability to probe surfaces using in situ SERS can be exploited in polymer chemistry to characterise the surface of polymers for comparison with the bulk properties and to study polymer-metal composites such as adhesives and coatings. Interactions between adhesives and metal polymeric surfaces have been investigated [437]. The applicability of SERS to polymer surfaces has also been reported in a study on poly-/ -nitrostyrene [438], and in another study on the effects of chromic/sulfuric acid etching on PE films [439]. The desired surface sensitivity... 

The oldest treatment is an etching process in highly concentrated chromic-sulfuric acid with a temperature near 80°C. Highest adhesional strength between PP and, for example, a two-component epoxy (EP) adhesive is reached after etching times between 120 and 240 s. The recipe of the etching solution is 5078 parts of sulfuric add (density 1.82g/ml), 120 parts demineralized water and 75 parts potassium dichromate. 

Surface treatment etched in chromic sulfuric acid... 

This section is a survey of the technology and chemistry of the copper etching systems in common use. Selection of practically available etchants has been hmited by economic, operational, and (environmental) regulatory concerns. Fabricators have been forced into practical trade-off decisions to suit situations. Two etchants in particular, chromic-sulfuric acid and ammonium persulfate, are no longer practical considerations due to environmental pressures. Other formulations and choices have been modified to suit these pressures. 

These etchants for solder- and tin-plated boards were preferred for many years. More recently, their use has been completely eliminated due to Cr(VI) listing as a critical environmental hazard. Other problems with chromic-sulfuric etchants are difficulty in regeneration, inconsistent etch rate, the low limit of dissolved copper (4 to 6 oz/gal), and dangerous degradation of PVC and polypropylene equipment. Chromic add etchant is suitable for use with solder, tin/nickel, gold, screened vinyl lacquer, and dry or liquid film photoresists. Chromic-sulfuric mixtures etch copper slowly, and additives are needed to increase the etch rate. For example, sodium sulfate and iodine have been used for rate increase. Alkaline etchants have become so well controlled that there is no justification for the risks and costs of chromic acid formulations. 

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