ASTM E407-07(2015)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E407 − 07(Reapproved 2015)
Standard Practice for
Microetching Metals and Alloys
This standard is issued under the fixed designation E407; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope constituents, usually in color, by thin films formed by vacuum
deposition of a dielectric compound (such as ZnTe, ZnSe,
1.1 This practice covers chemical solutions and procedures
TiO ,ZnSorZnO)withaknownindexofrefraction,generally
to be used in etching metals and alloys for microscopic
duetolightinterferenceeffects(alsoknownasthe“Pepperhoff
examination. Safety precautions and miscellaneous informa-
method”).
tion are also included.
1.2 This standard does not purport to address all of the
4. Summary of Practice
safety concerns, if any, associated with its use. It is the
4.1 Table1 is an alphabetical listing of the metals (includ-
responsibility of the user of this standard to establish appro-
ing rare earths) and their alloys for which etching information
priate safety and health practices and determine the applica-
is available. For each metal and alloy, one or more etchant
bility of regulatory limitations prior to use. For specific
numbers and their corresponding use is indicated. Alloys are
cautionary statements, see 6.1 and Table2.
listed as a group or series when one or more etchants are
common to the group or series. Specific alloys are listed only
2. Referenced Documents
when necessary. When more than one etchant number is given
2.1 ASTM Standards:
for a particular use, they are usually given in order of
D1193Specification for Reagent Water
preference. The numbers of electrolytic etchants are italicized
E7Terminology Relating to Metallography
to differentiate them from nonelectrolytic etchants.
E2014Guide on Metallographic Laboratory Safety
4.2 Table2 is a numerical listing of all the etchants refer-
3. Terminology enced in Table1and includes the composition and general
procedure to be followed for each etchant.
3.1 Definitions:
3.1.1 For definition of terms used in this standard, see
4.3 To use the tables, look up the metal or alloy of interest
Terminology E7.
in Table1 and note the etchant numbers corresponding to the
3.2 Definitions of Terms Specific to This Standard:
results desired. The etchant composition and procedure is then
3.2.1 tint etch—an immersion etchant that produces color
located in Table2corresponding to the etchant number.
contrast, often selective to a particular constituent in the
4.4 If the common name of an etchant is known (Marble’s,
microstructure, due to a thin oxide, sulfide, molybdate, chro-
Vilella’s, etc.), and it is desired to know the composition,
mate or elemental selenium film on the polished surface that
Table3contains an alphabetical listing of etchant names, each
reveals the structure due to variations in light interference
codedwithanumbercorrespondingtotheetchantcomposition
effects as a function of the film thickness (also called a ''stain
given in Table2.
etch”).
3.2.2 vapor-deposition interference layer method— a tech-
5. Significance and Use
niqueforproducingenhancedcontrastbetweenmicrostructural
5.1 This practice lists recommended methods and solutions
for the etching of specimens for metallographic examination.
Solutions are listed to highlight phases present in most major
This practice is under the jurisdiction of ASTM Committee E04 on Metallog-
raphy and is the direct responsibility of Subcommittee E04.01 on Specimen alloy systems.
Preparation.
Current edition approved June 1, 2015. Published September 2015. Originally
6. Safety Precautions
ɛ1
approved in 1999. Last previous edition approved in 2007 as E407–07 . DOI:
10.1520/E0407-07R15.
6.1 Beforeusingormixinganychemicals,allproductlabels
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and pertinent Material Safety Data Sheets (MSDS) should be
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
read and understood concerning all of the hazards and safety
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. precautions to be observed. Users should be aware of the type
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E407 − 07 (2015)
of hazards involved in the use of all chemicals used, including lowest useable concentration will significantly reduce risk.
those hazards that are immediate, long-term, visible, invisible, Additionally, it is recommended that a calcium gluconate
andwithorwithoutodors.SeeGuideE2014onMetallographic cream or other appropriate HF neutralizing agent be available
Laboratory Safety for additional information on; Chemical for use if direct skin contact of the etchant occurs.
Safety, Electrolytic Polishing/Etching and Laboratory 6.2.8 The EPA states that human studies have clearly
Ventilation/Fume Hoods. establishedthatinhaledchromium(VI)isahumancarcinogen,
resulting in an increased risk of lung cancer. Animal studies
6.1.1 ConsulttheproductlabelsandMSDSsforrecommen-
dations concerning proper protective clothing. haveshownchromium(VI)tocauselungtumorsviainhalation
exposure. Therefore, when working with Cr(VI) compounds
6.1.2 All chemicals are potentially dangerous. All persons
such as K Cr O and CrO always use a certified and tested
usinganyetchantsshouldbethoroughlyfamiliarwithallofthe
2 2 7 3
fume hood.Additional information can be obtained at the EPA
chemicals involved and the proper procedure for handling,
website .
mixing, and disposing of each chemical, as well as any
6.2.9 For safety in transportation, picric acid is distributed
combinations of those chemicals. This includes being familiar
by the manufacturer wet with greater than 30% water. Care
with the federal, state, and local regulations governing the
must be taken to keep it moist because dry picric acid is shock
handling, storage, and disposal of these chemical etchants.
sensitive and highly explosive especially when it is combined
6.2 Some basic suggestions for the handling and disposing
with metals such as copper, lead, zinc, and iron. It will also
of etchants and their ingredients are as follows:
react with alkaline materials including plaster and concrete to
6.2.1 When pouring, mixing, or etching, always use the
form explosive compounds. It should be purchased in small
proper protective equipment, (glasses, gloves, apron, etc.) and
quantities suitable for use in six to twelve months and checked
it is strongly recommended to always work under a certified
periodically for lack of hydration. Distilled water may be
and tested fume hood. This is imperative with etchants that
addedtomaintainhydration,Itmustonlybestoredinplasticor
give off noxious odors or toxic vapors that may accumulate or
glass bottles with nonmetallic lids. If dried particles are noted
become explosive. In particular, note that solutions containing
on or near the lid, submerge the bottle in water to re-hydrate
perchloric acid must be used in an exclusive hood equipped
them before opening. It is recommended that any bottle of
with a wash down feature to avoid accumulation of explosive
picric acid that appears dry or is of unknown vintage not be
perchlorates. See Guide E2014 on Metallographic Laboratory
opened and that proper emergency personnel be notified.
Safety for additional information on safety precautions for
6.2.10 Wipe up or flush any and all spills, no matter how
electrolytes containing perchloric acid.
minute in nature.
6.2.2 No single type of glove will protect against all
6.2.11 Properly dispose of all solutions that are not identi-
possible hazards.Therefore, a glove must be carefully selected
fied by composition and concentration.
andusedtoensurethatitwillprovidetheneededprotectionfor
6.2.12 Store, handle and dispose of chemicals according to
the specific etchant being used. In some instances it may be
the manufacturer’s recommendations. Observe printed cau-
necessary to wear more than one pair of gloves to provide
tions on reagent bottles.
properprotection.Informationdescribingtheappropriateglove
6.2.13 Information pertaining to the toxicity, hazards, and
may be obtained by consulting the MSDS for the chemical
working precautions of the chemicals, solvents, acids, bases,
being used. If that does not provide enough detailed
etc. being used (such as material safety data sheets, MSDS)
information, contact the chemical manufacturer directly.
shouldbeavailableforrapidconsultation.Aselectionofuseful
Additionally, one can contact the glove manufacturer or, if 4
books on this subject is given in Refs. (1-11) .
available, consult the manufacturers glove chart. If the chemi-
6.2.14 Facilities which routinely use chemical etchants
cal is not listed or if chemical mixtures are being used, contact
should have an employee safety training program to insure the
the glove manufacturer for a recommendation.
employees have the knowledge to properly handle chemical
6.2.3 Use proper devices (glass or plastic) for weighing,
etchants.
mixing, containing, and storage of solutions. A number of
6.2.15 Whenworkingwithetchantsalwaysknowwherethe
etchantsgeneratefumesorvaporsandshouldonlybestoredin
nearest safety shower, eye-wash station, and emergency tele-
properly vented containers. Storage of fuming etchants in
phone are located.
sealed or non-vented containers may create an explosion
hazard.
7. Miscellaneous Information
6.2.4 When mixing etchants, always add reagents to the
7.1 If you know the trade name of an alloy and need to
solvent unless specific instructions indicate otherwise.
know the composition to facilitate the use of Table1, refer to
6.2.5 When etching, always avoid direct physical contact
a compilation such as Ref (12).
with the etchant and specimen; use devices such as tongs to
7.2 Reagent grade chemicals shall be used for all etchants.
hold the specimen (and tufts of cotton, if used).
Unless otherwise indicated, it is intended that all reagents
6.2.6 Methanol is a cumulative poison hazard. Where etha-
conform to specifications of the Committee on Analytical
nol or methanol, or both are listed as alternates, ethanol is the
preferred solvent. Methanol should be used in a properly
designed chemical fume hood.
http://www.epa.gov/ttn/atw/hlthef/chromium.html
6.2.7 When working with HF always be sure to wear the
The boldface numbers in parentheses refer to the list of references at the end
appropriategloves,eyeprotectionandapron.BuyingHFatthe of this standard.
E407 − 07 (2015)
Reagents of the American Chemical Society where such 7.13 Tint etchants (13, 14-16) are always used by
specificationsareavailable.Othergrades,suchasUnitedStates immersion, never by swabbing, as this would inhibit film
Pharmacopeia (USP), may be used, provided it is first ascer- formation.An extremely high quality polish is required as tint
tainedthatthereagentisofsufficientlyhighpuritytopermitits etchants will reveal remaining polishing damage even if it is
use without detrimental effect. not visible with bright field illumination. After polishing, the
7.2.1 Unless otherwise indicated, references to water shall surface must be carefully cleaned. Use a polyethylene beaker
be understood to mean reagent water as defined by Type IV of to contain the etchant if it contains fluorine ions (for example,
specification D1193. Experience has shown that the quality of etchants containing ammonium bifluoride, NH FHF). The
tap water varies significantly and can adversely affect some specimen is placed in the solution using tongs, polished face
etchants. up. Gently agitate the solution while observing the polished
surface.Aftercolorationbegins,allowthesolutiontosettleand
7.3 Methanolisusuallyavailableonlyasabsolutemethanol.
remain motionless. Remove the specimen from the etchant
When using this alcohol it is imperative that approximately 5
when the surface is colored violet, rinse and dry. A light
volume % of water is added whenever an etchant composition
pre-etch with a general-purpose chemical etchant may lead to
calls for 95% methanol. Some of these etchants will not work
sharper delineation of the structure after tint etching.
at all if water is not present.
7.14 Specimens should be carefully cleaned before use of a
7.4 For conversion of small liquid measurements, there are
vapor-deposition interference film (“Pepperhoff”) method (13,
approximately 20 drops/mL.
14-17).Alight pre-etch, or a slight amount of polishing relief,
7.5 Etching should be carried out on a freshly polished
may lead to sharper delination of the constituents after vapor
specimen.
deposition. The deposition is conducted inside a vacuum
evaporator of the type used to prepare replicas for electron
7.6 Gentle agitation of the specimen or solution during
microscopy.Oneorseveralsmalllumpsofasuitabledielectric
immersion etching will result in a more uniform etch.
compound with the desired index of refraction is heated under
7.7 The etching times given are only suggested starting
avacuumuntilitevaporates.Avacuumlevelof1.3to0.013Pa
ranges and not absolute limits. −3 −5
(10 to 10 mm Hg) is adequate and the polished surface
7.8 In electrolytic etching, d-c current is implied unless
should be about 10–15 cm beneath the device that holds the
indicated otherwise.
dielectric compound. Slowly evaporate the lumps and observe
the surface of the specimen. It may be helpful to place the
7.9 Agoodeconomicalsourceofd-ccurrentforsmallscale
specimenonasmallpieceofwhitepaper.Asthefilmthickness
electrolytic etching is the standard 6-V lantern battery.
increases,thesurface(andthepaper)willbecomecoloredwith
7.10 In electrolytic etching, the specimen is the anode
the color sequence changing in the order yellow, green, red,
unless indicated otherwise.
purple,violet,blue,silveryblue.Stoptheevaporationwhenthe
7.11 Do not overlook the possibility of multiple etching color is purple to violet, although in some cases, thinner films
with green or red colors have produced good results.
with more than one solution in order to fully develop the
structure of the specimen.
7.15 Metals Handbook (18) provides additional advice on
etching solutions and techniques for various alloys.
7.12 Microscope objectives can be ruined by exposure to
hydrofluoricacidfumesfrometchantresidueinadvertentlyleft
8. Precision and Bias
on the specimen. This problem is very common when the
specimen or mounting media contain porosity and w
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