ASTM E1558-09(2021)

Standard Guide for Electrolytic Polishing of Metallographic Specimens

SIGNIFICANCE AND USE
4.1 Advantages of Electrolytic Polishing:  
4.1.1 For some metals, a high quality surface finish can be produced that is equivalent to, or better than, that which can be obtained by mechanical methods.  
4.1.2 Once procedures have been established, satisfactory results can be obtained rapidly with reproducibility.  
4.1.3 There can be a marked saving of time if many specimens of the same material are polished sequentially.  
4.1.4 Electropolishing a selected area on the surface of a relatively large metal part can be accomplished nondestructively, that is, without the need for sectioning to remove a piece.  
4.1.5 Soft, single-phase metals, which may be difficult to polish by mechanical methods, may be successfully electropolished.  
4.1.6 The true microstructure of a specimen can be obtained because artifacts (such as disturbed metal, scratches, and mechanical twins) produced on the surface, even by careful grinding and mechanical polishing operations, can be removed. These features are important in low-load hardness testing, X-ray diffraction studies, and in electron microscopy, where higher resolution puts a premium on undistorted metal surfaces.  
4.1.7 After electropolishing is completed, etching can often be accomplished by reducing the voltage (generally to about one-tenth that required for polishing) for a short time before it is turned off.
Note 2: Not all electropolishing solutions produce good etching results.  
4.2 Disadvantages of Electrolytic Polishing:  
4.2.1 Many of the chemical mixtures used in electropolishing are poisonous or dangerous if not properly handled (see Section 5). These hazards are similar to those involved in the mixing and handling of etchants, see Test Methods E407.  
4.2.2 In multi-phase alloys, the polishing rate of each phase may be different. The result may be a non-planar surface.  
4.2.3 Electropolished surfaces may be slightly undulated rather than perfectly planar and, therefore, may not be suitable for exami...
SCOPE
1.1 This guide deals with electrolytic polishing as a means of preparation of specimens for metallographic purposes. Procedures are described for polishing a variety of metals.  
Note 1: References (1-133)2 on electrolytic polishing will provide the reader with specific information beyond the scope of this guide.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific safety precautions are described in Section 5 and 6.3.1.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Aug-2021
• ICS: 49.025.05 - Ferrous alloys in general
• ICS: 49.025.15 - Non-ferrous alloys in general
• Technical Committee: E04 - Metallography
• Drafting Committee: E04.01 - Specimen Preparation

Relations

• Refers: ASTM E407-23 - Standard Practice for Microetching Metals and Alloys
• Effective Date: 01-Nov-2023
• Refers: ASTM E7-15 - Standard Terminology Relating to Metallography
• Effective Date: 01-Jun-2015
• Refers: ASTM E407-07(2015)e1 - Standard Practice for Microetching Metals and Alloys
• Effective Date: 01-Jun-2015
• Refers: ASTM E7-14 - Standard Terminology Relating to Metallography
• Effective Date: 01-Nov-2014
• Refers: ASTM E7-03(2009) - Standard Terminology Relating to Metallography
• Effective Date: 01-Oct-2009
• Refers: ASTM E407-07 - Standard Practice for Microetching Metals and Alloys
• Effective Date: 01-May-2007
• Refers: ASTM E7-03 - Standard Terminology Relating to Metallography
• Effective Date: 10-May-2003
• Refers: ASTM E7-01 - Standard Terminology Relating to Metallography
• Effective Date: 10-Dec-2001
• Refers: ASTM E7-00 - Standard Terminology Relating to Metallography
• Effective Date: 10-Dec-2001
• Refers: ASTM E407-99 - Standard Practice for Microetching Metals and Alloys
• Effective Date: 10-Oct-1999

Overview

ASTM E1558-09(2021), Standard Guide for Electrolytic Polishing of Metallographic Specimens, provides a comprehensive framework for preparing metal specimens using electrolytic polishing for metallographic analysis. Developed by ASTM International, this guide outlines procedures for achieving high-quality, reproducible surfaces suitable for microstructural examination while emphasizing safety and best handling practices. Electrolytic polishing, or electropolishing, involves removing material from the specimen surface by making it the anode in an electrolytic cell, resulting in minimal mechanical damage and artifact-free preparation ideal for advanced analytical techniques.

Key Topics

• Advantages of Electrolytic Polishing

  • Delivers a surface finish equal to or better than mechanical polishing, particularly for soft or single-phase metals.
  • Offers rapid, repeatable specimen preparation once parameters are established.
  • Enables efficient sequential polishing for multiple specimens of the same material.
  • Capable of nondestructive polishing on selected areas of large parts, eliminating the need for sectioning.
  • Effective at removing surface artifacts (disturbed metal, scratches, mechanical twins) introduced by mechanical preparation.
  • Maintains the true microstructure, which is essential for high-resolution electron microscopy, X-ray diffraction, and low-load hardness testing.
  • Some electrolytic polishing solutions can perform both polishing and etching, streamlining specimen preparation.

• Disadvantages and Limitations

  • Many electrolytic solutions require careful handling due to toxicity and potential hazards.
  • Variable polishing rates in multi-phase alloys can lead to non-planar surfaces.
  • Slight surface undulations and artifacts may remain, affecting examination at very high magnifications.
  • Edge rounding and preferential attack near inclusions or voids are possible.
  • Developing effective procedures for new alloys and managing a variety of electrolyte chemistries can be time-consuming.

• Safety Precautions

  • Detailed safety measures are critical, especially when handling perchloric acid, chromic acid, cyanides, strong alkalis, and other hazardous chemicals.
  • Use of fume hoods, protective equipment, and proper disposal procedures is mandatory.
  • Familiarization with Material Safety Data Sheets (MSDS) and adherence to local regulations are required practices.

Applications

Electrolytic polishing is a key step in the preparation of metallographic specimens in materials science, metallurgy, and quality control laboratories. The standard is widely used for:

• Failure Analysis: Revealing true microstructure for accurate characterization of fracture surfaces and material defects.
• Research and Development: Preparing samples for advanced imaging (SEM, TEM) without introducing artifacts from mechanical abrasion.
• Quality Assurance: Ensuring consistent surface finishes for comparative analysis in industrial metallurgy.
• Teaching and Training: Reference for best-practice procedures in metallography courses and laboratory settings.
• Support for Analytical Techniques: Prepares specimens suited for low-load hardness testing, X-ray diffraction, and electron microscopy where an undistorted surface is vital.

Related Standards

• ASTM E7: Terminology Relating to Metallography
• ASTM E407: Practice for Microetching Metals and Alloys
• Additional referenced guides and procedures related to specimen preparation, etching, and metallographic analysis.

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Keywords: ASTM E1558, electrolytic polishing, electropolishing, metallographic specimen preparation, metal surface finishing, metallography, microstructure preparation, laboratory safety, material analysis, surface quality, polishing electrolytes.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1558 − 09 (Reapproved 2021)
Standard Guide for
Electrolytic Polishing of Metallographic Specimens
This standard is issued under the fixed designation E1558; 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.
1. Scope 3.2.1 electrolytic polish (electropolish)—A method of pol-
ishingmetalsandalloysinwhichmaterialisremovedfromthe
1.1 This guide deals with electrolytic polishing as a means
surface by making the metal the anode in an electrolytic bath.
of preparation of specimens for metallographic purposes.
Procedures are described for polishing a variety of metals.
4. Significance and Use
NOTE 1—References (1-133) on electrolytic polishing will provide the
4.1 Advantages of Electrolytic Polishing:
reader with specific information beyond the scope of this guide.
4.1.1 For some metals, a high quality surface finish can be
1.2 The values stated in SI units are to be regarded as producedthatisequivalentto,orbetterthan,thatwhichcanbe
standard. No other units of measurement are included in this obtained by mechanical methods.
standard. 4.1.2 Once procedures have been established, satisfactory
results can be obtained rapidly with reproducibility.
1.3 This standard does not purport to address all of the
4.1.3 There can be a marked saving of time if many
safety concerns, if any, associated with its use. It is the
specimens of the same material are polished sequentially.
responsibility of the user of this standard to establish appro-
4.1.4 Electropolishing a selected area on the surface of a
priate safety, health, and environmental practices and deter-
relatively large metal part can be accomplished
mine the applicability of regulatory limitations prior to use.
nondestructively, that is, without the need for sectioning to
Specific safety precautions are described in Section 5 and
remove a piece.
6.3.1.
4.1.5 Soft, single-phase metals, which may be difficult to
1.4 This international standard was developed in accor-
polish by mechanical methods, may be successfully electrop-
dance with internationally recognized principles on standard-
olished.
ization established in the Decision on Principles for the
4.1.6 Thetruemicrostructureofaspecimencanbeobtained
Development of International Standards, Guides and Recom-
because artifacts (such as disturbed metal, scratches, and
mendations issued by the World Trade Organization Technical
mechanical twins) produced on the surface, even by careful
Barriers to Trade (TBT) Committee.
grindingandmechanicalpolishingoperations,canberemoved.
These features are important in low-load hardness testing,
2. Referenced Documents
X-ray diffraction studies, and in electron microscopy, where
2.1 ASTM Standards:
higher resolution puts a premium on undistorted metal sur-
E7Terminology Relating to Metallography
faces.
E407Practice for Microetching Metals and Alloys
4.1.7 After electropolishing is completed, etching can often
be accomplished by reducing the voltage (generally to about
3. Terminology
one-tenth that required for polishing) for a short time before it
3.1 Definitions—All terms used in this guide are either
is turned off.
defined in Terminology E7 or are discussed in 3.2.
NOTE 2—Not all electropolishing solutions produce good etching
3.2 Definitions of Terms Specific to This Standard:
results.
4.2 Disadvantages of Electrolytic Polishing:
1 4.2.1 Many of the chemical mixtures used in electropolish-
ThisguideisunderthejurisdictionofASTMCommitteeE04onMetallography
and is the direct responsibility of Subcommittee E04.01 on Specimen Preparation.
ing are poisonous or dangerous if not properly handled (see
Current edition approved Sept. 1, 2021. Published November 2021. Originally
Section 5). These hazards are similar to those involved in the
approved in 1993. Last previous edition approved in 2014 as E1558–09(2014).
mixing and handling of etchants, see Test Methods E407.
DOI: 10.1520/E1558-09R21.
4.2.2 In multi-phase alloys, the polishing rate of each phase
The boldface numbers in parentheses refer to the references at the end of this
standard.
may be different. The result may be a non-planar surface.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
4.2.3 Electropolished surfaces may be slightly undulated
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
rather than perfectly planar and, therefore, may not be suitable
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. for examination at all magnifications.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1558 − 09 (2021)
4.2.4 The rate of polishing in areas adjacent to various must only be used in an exclusive hood equipped with a wash
inhomogeneities, such as nonmetallic inclusions and voids, is down feature. To avoid the accumulation of explosive, dry
usuallygreaterthanthatinthesurroundingmatrixandtendsto perchlorates, the hood should undergo a wash down cycle
exaggerate the size of the inclusions and voids. following each use.
4.2.5 Dimples, pits, and waviness limit applications involv-
5.2.2 When pouring, mixing, or using electrolytes, always
ingsurfacephenomena,coatings,interfaces,andcracks.Edges
use the proper protective equipment (eyewear, gloves, apron,
tend to be attacked preferentially, resulting in edge rounding.
and so forth).
4.2.6 Artifacts may be produced by electropolishing.
5.2.3 Use proper devices (glass or plastic) for weighing,
4.2.7 Specimen mounting materials may react with the
measuring, mixing, containing, and storage of solutions.
electrolyte.
5.2.4 When mixing electrolytes, always add reagents to the
4.2.8 The electropolished surfaces of certain materials may
solvent unless specific instructions indicate otherwise.
be passive and difficult to etch.
5.2.5 When using an electrolyte, always avoid direct physi-
4.2.9 Metal removal rates by electropolishing are usually
cal contact with the electrolyte and the specimen. Use tongs or
quite low, typically about 1 µm/min, and all of the prior
some other indirect method of handling specimens.
induced damage from cutting and grinding may not be re-
5.2.6 Methanol is a cumulative poison hazard. Where etha-
moved if preparation is stopped after a 600-grit SiC grind and
nolormethanolarelistedasalternates,ethanolisthepreferred
electropolishing times are short.
solvent. Methanol should be used in a properly designed
4.2.10 A large number of electrolytes may be needed to
chemical fume hood.
polish the variety of metals encountered by a given laboratory.
5.2.7 All spills should be cleaned up and disposed of
Considerable time may be required to develop a procedure for
properly, no matter how small the spill.
a new alloy.
5.2.8 Properly dispose of all solutions that are not identified
by composition and concentration.
5. General Safety Precautions
5.2.9 Store, handle, and dispose of chemicals according to
5.1 Beforeusingormixinganychemicals,allproductlabels
the manufacturer’s recommendations. Observe printed cau-
and pertinent Material Safety Data Sheets (MSDS) should be
tions on reagent containers.
read and understood concerning all of the hazards and safety
5.2.10 Information pertaining to the toxicity hazards and
precautions to be observed. Users should be aware of the type
working precautions of chemicals, solvents, acids, bases, and
of hazards involved in the use of all chemicals used, including
so forth, being used (such as MSDS) should be available for
those hazards that are immediate, long-term, visible, invisible,
rapid consultation.
and with or without odors.
5.1.1 Consult the product labels and MSDS for recommen- 5.3 Many of the electrolytes in the following listing can be
dations concerning proper protective clothing. exceedingly dangerous if carelessly handled. The pertinent
5.1.2 All chemicals are potentially dangerous. All persons safety precautions for each class of electrolyte should be read
using any electrolyte should be thoroughly familiar with all of before any electrolyte is mixed or used.
the chemicals involved and the proper procedure for handling,
5.4 Electrolytes containing perchloric acid and acetic anhy-
mixing, and disposing of each chemical, as well as any
dride are very dangerous to mix and may be unpredictable in
combinations of those chemicals.
use. Many industrial firms and research laboratories forbid the
5.1.3 When pouring, mixing, or etching, always use the
use of such mixtures. Certain cities also have ordinances
properprotectiveequipment(glasses,gloves,apron,etc.)andit
prohibiting the use of such potentially explosive mixtures.
is strongly recommended to always work under a certified and
These facts are considered sufficient reason for recommending
testedfumehood.Thisisimperativewithetchantsthatgiveoff
against their use.
noxious odors or toxic vapors. In particular, note that solutions
5.5 Mixtures of oxidizable organic compounds and power-
containing perchloric acid must be mixed and used in an
ful oxidizing agents are always potentially dangerous. After
exclusive hood equipped with a wash down feature to avoid
some use, any electrolyte will become heavily laden with ions
accumulation of explosive perchlorates.
of the metals polished. These ions may interfere with further
5.1.4 Table 1 includes specific safety precautions for the
polishing or catalyze the decomposition of the electrolyte.The
mixing or use of some electrolytes. The user should take care
electrolyte then must be discarded in accordance with appro-
to observe each of these specific precautions.
priate regulations.
5.2 Somebasicsuggestionsforthehandlinganddisposalof
electrolytes and their ingredients are as follows: 5.6 Most electrolytes (with few exceptions) should be
5.2.1 As previously stated, it is good practice to always mixed and stored in clean glass containers and never be in
work under a certified fume hood when mixing and utilizing contact with foreign materials or organic compounds. The
any electrolyte and it is imperative with those electrolytes that exceptions are those electrolytes containing fluorides and
give off noxious odors or toxic vapor. Additionally, the strong alkaline solutions that should be mixed and stored in
electrolytes in Groups I and II must be treated with extra polyethylene or other appropriate material containers. Electro-
caution because dried perchlorates can accumulate in hood lytes must never be allowed to become concentrated by
ductwork and on work surfaces creating the potential for a evaporation.All electrolytes should be discarded appropriately
powerful accidental explosion. Therefore, these electrolytes as soon as they have exceeded their immediate usefulness.
E1558 − 09 (2021)
TABLE 1 Electrolytes for Electropolishing
Class Use Formula Cell Voltage Time Remarks
Group I (Electrolytes Composed of Perchloric Acid and Alcohol With or Without Organic Additions) Use in a washdown/perchloric rated fume hood.
I-1 Al and Al alloys with less than ethanol (95 %) 800 mL 30 to 80 15 s to 60 s
2 percent Si distilled water 140 mL
perchloric acid (60 %) 60 mL
steels—carbon, alloy, stainless 35 to 65 15 s to 60 s
Pb, Pb-Sn, Pb-Sn-Cd, Pb-Sn-Sb 12 to 35 15 s to 60 s
Zn, Zn-Sn-Fe, Zn-Al-Cu 20 to 60 .
Mg and high Mg alloys . . nickel cathode
I-2 stainless steel and aluminum ethanol (95 %) 800 mL 35 to 80 15 s to 60 s
perchloric acid (60 %) 200 mL
I-3 stainless steel ethanol (95 %) 940 mL 30 to 45 15 s to 60 s
perchloric acid (65 %) 60 mL
I-4 steel, cast iron, Al, Al alloys, Ni, ethanol (95 %) 700 mL 30 to 65 15 s to 60 s one of the best formulas for
Sn, Ag, Be, Ti, Zr, U, 2-butoxy ethanol 100 mL universal use
heat-resisting alloys perchloric acid (30 %) 200 mL
I-5 steels—stainless, alloy, ethanol (95 %) 700 mL 15 to 50 15 s to 60 s universal electrolyte comparable to
high-speed; Fe, Al, Zr, Pb glycerin 100 mL I-4
perchloric acid (30 %) 200 mL
I-6 Al, Al-Si alloys ethanol (95 %) 760 mL 35 to 60 15 s to 60 s particularly good with Al-Si alloys
diethyl ether 190 mL
perchloric acid (30 %) 50 mL
I-7 Mo, Ti, Zr, U-Zr alloy methanol (absolute) 600 mL 60 to 150 5 s to 30 s
2-butoxy ethanol 370 mL
perchloric acid (60 %) 30 mL
I-8 Al-Si alloys methanol (absolute) 840 mL 50 to 100 5 s to 60 s
glycerin 125 mL
perchloric acid (65 %) 35 mL
I-9 vanadium methanol (absolute) 590 mL 30 3 s three-second cycles repeated at
2-butoxy ethanol 350 mL least seven times to prevent heating
perchloric acid (65 %) 60 mL
germanium 25 to 35 30sto60s
titanium 58 to 66 45 s polish only
zirconium 70 to 75 15 s polish and etch simultaneously
I-10 aluminum methanol (absolute) 950 mL 30 to 60 15 s to 60 s
nitric acid 15 mL
perchloric acid (60 %) 50 mL
I-11 steels—carbon, alloy, stainless methanol (absolute) 600 mL 30–40 5 s–60 s good all purpose electropolish
Ti, high-temperature alloys, Pb, butylcellosolve 360 mL
Mo perchloric acid 60 mL
I-12 Al and Al alloys ethanol (95 %) 1000 mL 10 2 min not good for Al-Cu and Al-Si alloys.
perchloric acid 200 mL Black film forms. Peel off after 1–1.5
min and polish 1 min more.
I-13 steel, Al, Ni, Sn, Ti, Be ethanol (95 %) 700 mL 20 20 s Mix ethanol and water, add
stainless steel butylcellosolve 100 mL perchloric acid carefully. Then, add
Al Ni water 137 mL butylcellosolve before use.
perchloric acid 62 mL
I-14 Ni, Ag, or Cu alloys ethanol (95 %) 700 mL 70–80 15 s
Cd butylcellosolve 100 mL
perchloric acid 200 mL
I-15 Mo and Mo alloys methanol (absolute) 600 mL 20 s Mix methanol and water, add
water 13 mL perchloric acid carefully. Add
butylcellosolve 360 mL butylcellosolve before use.
perchloric acid 47 mL
Group II (Electrolytes Composed of Perchloric Acid and Glacial Acetic Acid in Varying Proportions) Use in a washdown/perchloric rated fume hood.
II-1 Cr, Ti, Zr, U, acetic acid (glacial) 940 mL 20 to 60 1 min to good general-purpose electrolyte
Fe, steel—carbon, alloy, stainless perchloric acid (60 %) 60 mL 5min
II-2 Zr, Ti, U, steel—carbon and alloy acetic acid (glacial) 900 mL 12 to 70 0.5 min to
perchloric acid (60 %) 100 mL 2min
II-3 U, Zr, Ti, Al, steel—carbon and acetic acid (glacial) 800 mL 40 to 100 1 min to
alloy perchloric acid (60 %) 200 mL 15 min
II-4 Ni, Pb, Pb-Sb alloys acetic acid (glacial) 700 mL 40 to 100 1 min to
perchloric acid (60 %) 300 mL 5min
II-5 3 percent Si-Fe acetic acid (glacial) 650 mL . 5 min 0.06 A/cm
perchloric acid (60 %) 350 mL
II-6 Cr acetic acid (glacial) 1000 mL 30–50 2 min–3 min can lower voltage to 25 V by adding
perchloric acid 5mL 5 %–15 % water.
II-7 Hf, steel—carbon and alloy acetic acid (glacial) 1000 mL . . Used to polish Hf wires.
perchloric acid 50 mL
Group III (Electrolytes Composed of Phosphoric Acid in Water or Organic Solvent)
III-1 cobalt phosphoric acid (85 %) 1000 mL 1.2 3 min to
5min
III-2 pure copper distilled water 175 mL 1.0 to 1.6 10 min to copper cathode
phosphoric acid (85 %) 825 mL 40 min
III-3 stainless, brass, Cu and Cu water 300 mL 1.5to1.8 5min to copper cathode
alloys except Sn bronze phosphoric acid (85 %) 700 mL 15 min
E1558 − 09 (2021)
TABLE 1 Continued
Class Use Formula Cell Voltage Time Remarks
III-4 alpha or alpha plus beta brass, water 600 mL 1to2 1min to copper or stainless steel cathode
Cu-Fe, Cu-Co, Co, Cd phosphoric acid (85 %) 400 mL 15 min
III-5 Cu, Cu-Zn water 1000 mL 1 to 2 10 min copper cathode
pyrophosphoric acid 580 g
III-6 steel diethylene glycol monoethyl 500 mL 5to20 5 minto 49 °C
ether 15 min
phosphoric acid (85 %) 500 mL
III-7 Al, Ag, Mg water 200 mL 25 to 30 4 min to aluminum cathode, 38 °C to 43 °C
ethanol (95 %) 380 mL 6min
phosphoric acid (85 %) 400 mL
III-8 uranium ethanol (absolute) 300 mL . .
glycerin (cp) 300 mL
phosphoric acid (85 %) 300 mL
III-9 Mn, Mn-Cu alloys ethanol (95 %) 500 mL 18 .
glycerin 250 mL
phosphoric acid (85 %) 250 mL
III-10 Cu and Cu-base alloys distilled water 500 mL . 1 min to
ethanol (95 %) 250 mL 5min
phosphoric acid (85 %) 250 mL
III-11 stainless steel ethanol (absolute), to 1L . 10 min good for all austenitic heat resistant
pyrophosphoric acid 400 g alloys, 38 °C plus
III-12 Mg-Zn ethanol (95 %) 625 mL 1.5to2.5 3min to
phosphoric acid (85 %) 375 mL 30 min
III-13 uranium ethanol (95 %) 445 mL 18 to 20 5 min to 0.03 A/cm
ethylene glycol 275 mL 15 min
phosphoric acid (85 %) 275 mL
III-14 Al-Mg alloys water 250 mL 50–60 2 min
ethanol (95 %) 380 mL
phosphoric acid (85 %) 400 mL
III-15 Cu-Pb alloys ethanol (95 %) 620 mL good up to 30 % Pb
phosphoric acid (85 %) 380 mL
III-16 Neptunium ethanol (95 %) 400 mL after P1200–grit SiC, use 6-µm
glycerol 400 mL diamond on nylon before
phosphoric acid (85 %) 800 mL electropolishing.
Group IV (Electrolytes Composed of Sulfuric Acid in Water or Organic Solvent)
IV-1 stainless steel water 250 mL 1.5to6 1min to
sulfuric acid 750 mL 2min
IV-2 stainless steel, Fe, Ni water 400 mL 1.5to6 2min to
sulfuric acid 600 mL 6min
IV-3 stainless steel, Fe, Ni, Mo water 750 mL 1.5to6 2min to particularly good for sintered Mo—
sulfuric acid 250 mL 10 min 0°Cto27°C
Mo—
0.3to1min
IV-4 molybdenum water 900 mL 1.5to6 0.3min to particularly good for sintered Mo—
sulfuric acid 100 mL 2min 0°Cto27°C
IV-5 stainless steel water 70 mL 1.5to6 0.5min to
glycerin 200 mL 5min
sulfuric acid 720 mL
IV-6 stainless steel, aluminum water 220 mL 1.5to12 1 minto
glycerin 200 mL 20 min
sulfuric acid 580 mL
IV-7 molybdenum methanol (absolute) 875 mL 6to18 0.5 minto1.5 0°Cto27°C
sulfuric acid 125 mL min
IV-8 Ni-base superalloys methanol (absolute) 800 mL 30 20 s for alloy 625
sulfuric acid 200 mL
Group V (Electrolytes Composed of Chromic Acid in Water)
V-1 stainless steel water 830 mL 1.5to9 2min to
chromic acid 620 g 10 min
V-2 Zn, brass water 830 mL 1.5to12 10s to
chromic acid 170 g 60 s
Group VI (Mixed Acids or Salts in Water or Organic Solvent)
VI-1 stainless steel phosphoric acid (85 %) 600 mL . .
sulfuric acid 400 mL
VI-2 stainless steel water 150 mL . 2 min 0.3 A/cm
phosphoric acid (85 %) 300 mL
sulfuric acid 550 mL
2 2
VI-3 stainless and alloy steel water 240 mL . 2 min to 0.1 A/cm to 0.2 A/cm
phosphoric acid (85 %) 420 mL 10 min
sulfuric acid 340 mL
VI-4 stainless steel water 330 mL . 1 min 0.05 A/cm
phosphoric acid (85 %) 550 mL
sulfuric acid 120 mL
VI-5 bronze (to 9 % Sn) water 450 mL . 1 min to 0.1 A/cm
phosphoric acid (85 %) 390 mL 5min
sulfuric acid 160 mL
E1558 − 09 (2021)
TABLE 1 Continued
Class Use Formula Cell Voltage Time Remarks
VI-6 bronze (to 6 % Sn) water 330 mL . 1 min to 0.1 A/cm
phosphoric acid (85 %) 580 mL 5min
sulfuric acid 90 mL
2 2
VI-7 steel water 140 mL . 1 min to 1 A/cm to 5 A/cm , 38 °C plus
glycerin 100 mL 5min
phosphoric acid (85 %) 430 mL
sulfuric acid 330 mL
VI-8 stainless steel water 200 mL . 5 min 1 A/cm ,27°Cto49°C
glycerin 590 mL
phosphoric acid (85 %) 100 mL
sulfuric acid 110 mL
VI-9 stainless steel water 260 mL . 30 min 0.6 A/cm ,27°Cto49°C
chromic acid 175 g
phosphoric acid (85 %) 175 mL
sulfuric acid 580 mL
VI-10 stainless steel water 175 mL . 60 min 0.5 A/cm ,27°Cto49°C
chromic acid 105 g
phosphoric acid (85 %) 460 mL
sulfuric acid 390 mL
VI-11 stainless and alloy steel water 240 mL . 5 min to 0.5 to A/cm ,38°Cto54°C
chromic acid 80 g 60 min
phosphoric acid (85 %) 650 mL
sulfuric acid 130 mL
VI-12 tantalum hydrofluoric acid 100 mL . 9 min graphite cathode, 0.1 A/cm ,32°C
sulfuric acid 900 mL to 38 °C
VI-13 stainless steel water 210 mL . 5 min 0.5 A/cm ,21°Cto49°C
hydrofluoric acid 180 mL
sulfuric acid 610 mL
VI-14 zinc water 800 mL . . 0.002 A/cm ,21°Cto49°C
chromic acid 100 g
sulfuric acid 46 mL
sodium dichromate 310 g
acetic acid (glacial) 96 mL
VI-15 stainless steel hydrogen peroxide (30 %) 260 mL . 5 min 0.5 A/cm (Caution) Dangerous
(Caution)
hydrofluoric acid 240 mL
sulfuric acid 500 mL
VI-16 stainless steel water 520 mL . ⁄2 to 0.08 A/cm
hydrofluoric acid 80 mL 4min to 0.3 A/cm
sulfuric acid 400 mL
VI-17 stainless steel water 600 mL . .
chromic acid 180 g
nitric acid 60 mL
hydrochloric acid 3mL
sulfuric acid 240 mL
VI-18 bismuth glycerin 750 mL 12 1 min to 0.5 ± A/cm (Caution) This mixture
acetic acid (glacial) 125 mL 5min will decompose vigorously after a
nitric acid 125 mL short time. Do not try to keep.
VI-19 magnesium ethylene-glycol-monoethyl ether 900 mL 50 to 60 10 s to Bath should be stirred. Cool with
hydrochloric acid 100 mL 30 s cracked ice below 2 °C
VI-20 molybdenum, sintered and cast methanol (absolute) 685 mL 19 to 35 20 s to Mix slowly. Heat is developed. Avoid
hydrochloric acid 225 mL 35 s contamination with water. Use below
sulfuric acid 90 mL 2°C.
Group VI (Mixed Acids or Salts in Water or Organic Solvent)— Continued
VI-21 titanium ethanol (95 %) 900 mL 30 to 60 1 min to (Caution) Anhydrous aluminum
n-butyl alcohol 100 mL 6min chloride is extremely dangerous to
aluminum chloride (anhydrous) 60 g handle.
(add very slowly) (Caution)
zinc chloride (anhydrous) 250 g
VI-22 uranium acetic acid (glacial) 750 mL 80 5 min to The chromic acid is dissolved in the
distilled water 210 mL 30 min water before adding to the acetic
chromic acid 180 g acid. Use below 2 °C.
VI-23 pure zinc ethanol (95 %) 720 mL 25 to 40 0.5 min to (Caution) Anhydrous aluminum
aluminum chloride (anhydrous) 50 g 3min chloride is extremely dangerous to
(Caution) handle. Use below 16 °C.
zinc chloride (anhydrous) 225 g
distilled water 160 mL
n-butyl alcohol 80 mL
VI-24 zirconium. Polish and etch glycerin (Caution) 870 mL 9to12 1minto (Caution) will decompose on
simultaneously hydrofluoric acid 43 mL 10 min standing, dangerous if kept too long
nitric acid 87 mL
VI-25 bismuth saturated solution KI in distilled 980 mL 7 30 s polish 30 s but allow to remain in
water electrolyte until brown film is
hydrochloric acid 20 mL dissolved
E1558 − 09 (2021)
TABLE 1 Continued
Class Use Formula Cell Voltage Time Remarks
VI-26 Sb methanol (absolute) 300 mL 6–10 2 min– pure Sb. Use Pt cathode and anode
sulfuric acid 50 mL 4min lead wires. Agitate bath. Do not
hydrochloric acid 30 mL touch polished surface with cotton.
VI-27 Sb ethanol (95 %) 30 mL good for polarized light work
glycerol 30 mL
phosphoric acid 100 mL
sulfuric acid 30 mL
VI-28 Bi water 200 mL good for polarized light work
phosphoric acid 100 mL
sulfuric acid 200 mL
VI-29 Cr water 210 mL 18 stir bath or specimen
phosphoric acid 640 mL
sulfuric acid 150 mL
VI-30 Ge methanol (absolute) 1000 mL
hydrochloric acid 10 mL
VI-31 Nb water 300 mL 40 polish to α-alumina before
sulfuric acid 100 mL electropolishing
hydrofluoric acid 100 mL
VI-32 Nb methanol (absolute) 940 mL 50–60 10 s
sulfuric acid 50 mL
hydrofluoric acid 15 mL
VI-33 Ni-base superalloy methanol (absolute) 170 mL 30 20 s for Waspaloy and IN-100 mod. Etch
hydrochloric acid 30 mL at 5Vfor 4s.
Group VII (Alkaline Electrolytes)
VII-1 gold water to 1000 mL 7.5 2 min to graphite cathode
potassium cyanide 80 g 4min
potassium carbonate 40 g
gold chloride 50 g
VII-2 silver water to 1000 mL 2.5 To 1 min graphite cathode
sodium cyanide 100 g
potassium ferrocyanide 100 g
VII-3 silver water to 1000 mL . To 9 min graphite cathode, 0.003 A ⁄cm to
potassium cyanide 400 g 0.009 A/cm
silver cyanide 280 g
potassium dichromate 280 g
VII-4 tungsten water to 1000 mL . 10 min graphite cathode, 0.09 A/cm ,38°C
trisodium phosphate 160 g to 49 °C
VII-5 tungsten, lead water to 1000 mL . 8 min to graphite cathode, 0.03 A ⁄cm to
sodium hydroxide 100 g 10 min 0.06 A/cm
VII-6 zinc, tin water to 1000 mL 2 to 6 15 min copper cathode, 0.1 A ⁄cm to 0.2
potassium hydroxide 200 g A/cm
VII-7 W water 1000 mL 5min
sodium hydroxide 20 g
Group VIII (Mixture of Methyl Alcohol and Nitric Acid)
VIII-1 Ni, Cu, Zn, Monel, brass, methanol (absolute) 660 mL 40 to 70 10 s to very useful but dangerous
Ni-chrome, stainless steel nitric acid 330 mL 60 s
5.7 Specimens mounted in bismuth or bismuth-containing 5.8.2.1 Theseelectrolytesarebelievedtobesafetomixand
metals must not be electropolished in perchloric acid solutions use provided the following safety precautions are followed.
because this mounting medium may react explosively with the
Use these electrolytes in an exclusive hood equipped with a
electrolyte. Likewise, bismuth or bismuth-containing alloys
wash down feature. The hood should undergo a wash down
must not be electropolished in solutions containing perchloric
cycle following each use to avoid accumulation of explosive,
acid. Specimens mounted in organic mounting compounds,
dry perchlorates. Only small quantities should be mixed and
such as Bakelite, must not be electropolished in electrolytes
stored in glass-stoppered bottles filled to capacity.Any evapo-
containing perchloric acid as they may also react explosively.
rated solvents should be replaced to keep the bottle filled.
Spent or exhausted polishing baths are to be promptly dis-
5.8 Specific Safety Precautions for Each Group of Electro-
carded in a manner consistent with prevailing regulations. The
lytes:
electrolytes are always to be protected from heat or fire.
5.8.1 The electrolytes recommended for use are classified
into eight groups. Their chemical components are listed in the
NOTE 3—In this, and all the following formulations, the term 95%
order of mixing. This ordering has been done to prevent
ethanolreferstoaspecificallydenaturedalcoholwhichiscomposedof95
possibly dangerous reactions. Unless other instructions are
parts by volume absolute ethanol and 5 parts by volume absolute
specifically given, the electrolytes are intended to be used in methanol. In case this formulation is not available, the use of 100%
absolute ethanol is advised. Alcohol formulations containing benzene,
the temperature range from about 18°C to 27°C. Cooling may
gasoline,orotherdenaturingsubstancesarelikelytocausedifficultiesand
be necessary to maintain this range during use.
their use is not recommended.
5.8.2 Group I—(Electrolytes Composed of Perchloric Acid
5.8.3 Group II—(Electrolytes Composed of Perchloric Acid
and Alcohol (Methanol or Ethanol) With or Without Organic
Additions): and Glacial Acetic Acid):
E1558 − 09 (2021)
5.8.3.1 Usetheseelectrolytesinanexclusivehoodequipped to avoid skin contact with acid fluorides since exposure to
with a wash down feature. The hood should undergo a wash them, which may pass unnoticed at the time, may result in
down cycle following each use to avoid accumulation of serious burns later. In those electrolytes containing anhydrous
explosive, dry perchlorates. Very little heat is developed when aluminum chloride, extreme care must be exercised. The
perchloricacidismixedwithglacialaceticacid.Inmixing,the reactionbetweenthiscompoundandwaterisalmostexplosive.
perchloric acid should be added to the acetic with stirring. Chromates and dichromates cannot be safely mixed with most
These mixtures are normally perfectly safe to mix and use but, organic liquids but can be mixed with saturated organic acids.
nonetheless, great care should be exercised with them. Tem- Care should be taken to prevent contact with the skin.
peratures must never be allowed to exceed 29°C. They are 5.8.8 Group VII—(Alkaline Electrolytes):
flammable and must be guarded against fire or the evaporation 5.8.8.1 These mixtures can be grouped into two general
oftheaceticacid.Plasticpartsarelikelytobequicklydamaged categories, those containing cyanide, and those not containing
by exposure to such mixtures. cyanide.
(1) Theuseofcyanidebyanyonenotproperlytrainedand
5.8.4 Group III—(Electrolytes Composed of Phosphoric
familiar with it is extremely dangerous. Cyanides are among
Acid in Water or Organic Solvents):
the quickest acting and most potent poisons likely to be
5.8.4.1 These mixtures are generally quite easy to prepare.
encountered in the laboratory. Cyanide is so quick-acting and
In mixing, they are handled exactly as a mineral acid; namely,
deadly that the administration of an antidote is usually inef-
the acid must be slowly poured into the water or solvent with
fectual. Extreme care must be taken that no droplet of the
constant stirring to prevent the formation of a heavy layer of
solutionorcrystalofthesaltiseverleftaroundwhereitcanbe
acid at the bottom of the vessel. Some solid phosphoric acids
accidentally picked up and carried to the mouth.
are quite energetic in their combination with water, requiring
(2) Solutions of the alkali hydroxides are very useful for
extra care in their mixing.
the polishing of certain amphoteric metals. Their attack on the
5.8.5 Group IV—(Electrolytes Composed of Sulfuric Acid in
skin is drastic, so great care should be exercised in their use.
Water or Organic Solvents):
The dissolution of alkali hydroxides, such as NaOH, in water
5.8.5.1 The addition of sulfuric acid to water produces an
produces substantial heat. Add the pellets to the water a little
extremely exothermic reaction. The acid must always be
bit at a time with constant stirring until the required concen-
poured into the water slowly and with constant stirring.
trationisobtained.Ifthetemperaturebecomesexcessive,allow
Cooling is necessary. Great care should be taken to prevent
the solution to cool back to ambient before adding more
spattering.Evendilutesolutionsofsulfuricacidstronglyattack
hydroxide.
the skin or clothing. Such solutions are also very hygroscopic.
5.8.9 Group VIII—(Mixtures of Methyl Alcohol and Nitric
They vigorously attack most plastics. The mixtures of sulfuric
Acid):
acid with other inorganic acids are generally more useful as
5.8.9.1 Nitric acid can be mixed with methanol with appar-
electrolytes.
ent safety (mixtures with up to about 33% nitric acid can be
5.8.6 Group V—(Electrolytes Composed of Chromium Tri-
safely stored). This is done by adding the acid to the alcohol
oxide in Water):
with careful stirring. HNO cannot be safely mixed and stored
5.8.6.1 The addition of crystalline chromium trioxide
with any higher alcohol except in very dilute solutions (for
(CrO ) to water is simple, since very little heat is developed.
example, do not store solutions of more than 3% HNO in
Theresultingchromicacidisapowerfuloxidant.Undercertain
ethanol). Under certain conditions, extremely unstable or
conditions it will liberate considerable quantities of free
explosivenitrocompounds,azidesorfulminatescanbeformed
oxygen. It is generally dangerous, and possibly incendiary, in
in alcoholic HNO solutions. The spontaneous decomposition
the presence of oxidizable materials. It cannot be safely mixed
of the mixture can also be catalyzed by impurities or heat. It
with most organic liquids, such as alcohols or glycerol. It can
should always be discarded as soon as it has served its
besafelymixedwithcertainsaturatedorganicacids,butshould
immediate purpose. Due to its dangerous nature, it should not
not be mixed with acetic acid. Chromic acid solutions cannot
be employed if its use can be avoided.
be used in contact with plastic parts without their eventual
destruction.Careshouldbetakentopreventitscontactwiththe
6. Apparatus
skin since repeated exposure to even dilute solutions of
6.1 For the electropolishing of metal specimens in an
chromicacidorthechromateswillcausepersistentandpainful
appropriate electrolyte, a suitable electrolysis cell and a con-
ulcers that are slow to heal. Chromium trioxide is a human
trollable power supply are needed. Simple laboratory
poison and is a carcinogen.
apparatus, such as shown in Fig. 1, can be assembled to
5.8.7 Group VI—(Mixed Acids or Salts in Water or Organic
perform this function. Many such arrangements are described
Solutions):
in the literature. There are also several commercially available
5.8.7.1 Thesemixturesaresafetomixanduseprovidingthe
models of electropolishing apparatus for either laboratory or
mixing is done properly. It must be remembered that in all
field use.
cases,theacidisaddedtothesolventslowlyandwithconstant
stirring. If sulfuric acid is in the formula, it is added last and 6.2 Whenever an attempt is made to polish large surface
withparticularcare.Ifhydrofluoricacidorfluoridesarepartof areas, the problems of obtaining sufficient current density and
a formula, polyethylene or other similar hydrofluoric acid- cooling of the specimen and electrolyte become troublesome.
resista
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