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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Chemical milling | 2/2 | https://en.wikipedia.org/wiki/Chemical_milling | reference | science, encyclopedia | 2026-05-05T10:46:37.502171+00:00 | kb-cron |
=== Scribing === Scribing is the removal of maskant on the areas to be etched. For decorative applications, this is often done by hand through the use of a scribing knife, etching needle or similar tool; modern industrial applications may involve an operator scribing with the aid of a template or use computer numerical control to automate the process. For parts involving multiple stages of etching, complex templates using colour codes and similar devices may be used.
=== Etching === Etching is the immersion of the part into the chemical bath, and the action of the chemical on the part to be milled. The time spent immersed in the chemical bath determines the depth of the resulting etch; this time is calculated via the formula:
E
=
s
t
{\displaystyle E={\frac {s}{t}}}
where E is the rate of etching (usually abbreviated to etch rate), s is the depth of the cut required, and t is the total immersion time. Etch rate varies based on factors such as the concentration and composition of the etchant, the material to be etched, and temperature conditions. Due to its inconstant nature, etch rate is often determined experimentally immediately prior to the etching process. A small sample of the material to be cut, of the same material specification, heat-treatment condition, and approximately the same thickness is etched for a certain time; after this time, the depth of the etch is measured and used with the time to calculate the etch rate. Aluminium is commonly etched at rates around 0.178 cm/h, and magnesium about 0.46 cm/h.
=== Demasking === Demasking is the process of clearing the part of etchant and maskant. Etchant is generally removed with a wash of clear, cold water. A de-oxidizing bath may also be required in the common case that the etching process left a film of oxide on the surface of the material. Various methods may be used to remove the maskant, the most common being hand removal using scraping tools. This is frequently time-consuming and laborious, and for large-scale processes may be automated.
== Common etchants == Etchants are chemical solutions used to selectively corrode or dissolve specific metals, alloys, or materials, thereby revealing their microstructures or facilitating further processing. Different materials require different etching agents depending on their chemical composition and physical properties.
Aluminium Common etchants used for aluminium and its alloys include:
Sodium hydroxide (NaOH) Keller's reagent Phosphoric acid and nitric acid mixtures (H3PO4/HNO3) Hydrocloric acid (HCI) Ferric chloride (FeCI3) These reagents are employed for cleaning, surface preparation, or microstructural examination of aluminium specimens.
Steels For steels, the following etchants are commonly used:
Hydrochloric and nitric acid mixtures Ferric chloride, particularly for stainless steels Nital, a mixture of nitric acid and ethanol, methanol, or methylated spirits, used primarily for mild steels. A 2% solution of Nital is a standard etchant for plain carbon steels and is frequently used in metallographic analysis to reveal grain boundaries and phases.
Copper Typical etchants used for copper and copper alloys include:
Cupric chloride (CuCl2) Ferric chloride (FeCl3) Ammonium persulfate ((NH4)2S2O8) Aqueous ammonia (NH3) 25-50% nitric acid (HNO3) Hydrochloric acid and hydrogen peroxide (HCl/H2O2) mixtures These reagents are applied in both electronic fabrication and metallographic preparation to remove oxides or delineate microstructural features.
Silica For silica and silicon dioxide–based materials, hydrofluoric acid (HF) is the standard etchant. It reacts with the silicon–oxygen bonds, effectively dissolving the silica surface.
== See also == Photochemical machining Etching (microfabrication) Electroetching Plasma Etching Microelectromechanical systems (MEMS)
== Notes ==
== References == Harris, William T. (1976). Chemical Milling: The Technology of Cutting Materials by Etching. Oxford: Clarendon Press. ISBN 0-19-859115-2.