title = "Chemical Etching and Acid Pickling of Metals"

content = """
Chemical etching and acid pickling are controlled chemical dissolution processes used at Ridgecrest Metalworks to remove oxide scale, heat tint, weld discoloration, and surface contamination from metal components. The processes prepare surfaces for subsequent coating, plating, or inspection.

Acid pickling of steel typically uses hydrochloric acid (HCl, 10–20 % concentration) or sulfuric acid (H₂SO₄, 10–25 % at elevated temperature). HCl works at ambient temperature and dissolves mill scale and rust rapidly; however, it carries risk of hydrogen embrittlement in high-strength steels (above 1000 MPa tensile) and must be used with inhibitors to limit excessive base metal attack. H₂SO₄ is slower at ambient temperature but more economical for high-volume continuous operations. Pickling inhibitors (organic compounds added to the bath) reduce base metal dissolution while maintaining oxide attack.

Stainless steel pickling uses a mixed acid bath of nitric acid (HNO₃) and hydrofluoric acid (HF), typically 10–15 % HNO₃ and 1–3 % HF. This combination dissolves chromium oxide and iron-rich scale from welds and heat-affected zones, restoring the corrosion-resistant passive film. HF is an acute systemic hazard and requires stringent engineering controls: enclosed systems, emergency calcium gluconate gel on hand, and dedicated PPE including chemical gloves rated for HF service.

Aluminum is etched using sodium hydroxide (NaOH, caustic soda) solution, which dissolves aluminum and its oxide uniformly. Etching time is controlled to achieve the specified material removal (bright or matte etch finish). Following caustic etch, a desmutting step using dilute HNO₃ removes the dark smut (metallic residue) left on the surface.

Chemical etching for marking or decorative patterns uses photoresist masking: a UV-sensitive resist is applied, exposed through a film artwork, developed to remove unwanted areas, and then etched with ferric chloride (FeCl₃) for stainless or copper alloys. This technique produces identification marks, scales, and decorative textures.

Post-pickling rinsing is critical. Multiple cascading rinse tanks ensure acid carryover is removed completely. Parts are dried promptly and proceed immediately to the next process step or are coated with temporary corrosion inhibitor. All spent pickle liquor is neutralized and treated as chemical waste per environmental regulations.
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