ASTM C912-93(1997)
(Practice)Standard Practice for Designing a Process for Cleaning Technical Glasses
Standard Practice for Designing a Process for Cleaning Technical Glasses
SCOPE
1.1 This practice is intended to provide information that will permit design of a rational cleaning procedure that can be used with a glass that is somewhat soluble in many aqueous chemical solutions. Typically, this type of glass is used in applications such as optical ware, glass-to-metal seals, low dielectric loss products, glass fibers, infrared transmitting products, and products resistant to metallic vapors.
1.2 In most cases, this type of glass contains high concentrations of oxides that tend to react with a number of aqueous chemicals. Such oxides include B2 O3 , Al2 O3 , R2 , RO, La2 O3 , ZnO, PbO, P2 O5 , and Fe2 O3 . The more conventional high-silica glasses are usually more chemically resistant, but the cleaning principles outlined here also apply to them.
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 and health practices and determine the applicability of regulatory limitations prior to use. Specific hazard statements are given in Section 4 and Table 1.
General Information
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Standards Content (Sample)
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Designation: C 912 – 93 (Reapproved 1997)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Practice for
Designing a Process for Cleaning Technical Glasses
This standard is issued under the fixed designation C 912; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope assist in step (3). General references on glass cleaning and on
various methods of evaluating cleanliness and associated
1.1 This practice is intended to provide information that will
information has been published.
permit design of a rational cleaning procedure that can be used
with a glass that is somewhat soluble in many aqueous
4. Hazards
chemical solutions. Typically, this type of glass is used in
4.1 Many of the chemicals that can be used in cleaning glass
applications such as optical ware, glass-to-metal seals, low
are hazardous. This is true of most of the aqueous chemicals
dielectric loss products, glass fibers, infrared transmitting
discussed in Section 5 and shown in Table 1 as well as the
products, and products resistant to metallic vapors.
organic chemicals discussed in Section 6.
1.2 In most cases, this type of glass contains high concen-
4.2 Special care should be used with hydrofluoric acid (HF),
trations of oxides that tend to react with a number of aqueous
which will react with glass generating heat. The vapors as well
chemicals. Such oxides include B O ,Al O ,R O, RO, La O ,
2 3 2 3 2 2 3
as the liquid destroy dermal tissue and can be fatal if inhaled.
ZnO, PbO, P O , and Fe O . The more conventional high-
2 5 2 3
4.3 Concentrated acids can react violently if water is added
silica glasses are usually more chemically resistant, but the
into them. When it is necessary to dilute acid, add the acid to
cleaning principles outlined here also apply to them.
the water slowly and with constant stirring so that heat is never
1.3 This standard does not purport to address all of the
allowed to concentrate locally in the solution.
safety concerns, if any, associated with its use. It is the
4.4 Organic solvents may be flammable or toxic, or both.
responsibility of the user of this standard to establish appro-
Threshold limit values for some common solvents are shown in
priate safety and health practices and determine the applica-
Table 2. Note that the fluorocarbons are most likely to exhibit
bility of regulatory limitations prior to use. Specific hazard
toxic effects as a result of inhalation or skin absorption.
statements are given in Section 4 and Table 1.
Benzene is not recommended as a solvent since it is a known
2. Terminology carcinogen.
2.1 Definitions of Terms Specific to This Standard:
5. Aqueous Solvents
2.1.1 technical glass—glasses designed with some specific
5.1 Selection—In using aqueous solvents for cleaning, gen-
property essential for a mechanical, industrial, or scientific
erally two extreme choices are available. One is to select an
device.
aqueous system that dissolves the soil to be removed, but has
3. Significance and Use little effect on the glass. The other is to select a system that
dissolves the glass uniformly, thus undercutting the soil and
3.1 Many of the low-silica technical glasses which contain
leaving a chemically polished glass surface. It is best to avoid
soluble or reactive oxides require processing or involve appli-
a solvent that selectively attacks the glass, dissolving only
cations that require cleaning. Very often these cleaning proce-
some components, or a solvent that produces a precipitate that
dures have evolved over several decades and are considered an
adheres to the surface to be cleaned.
art. They usually contain numerous steps, some of questionable
5.2 Minimum Glass Dissolution:
validity. It is the premise of this practice that cleaning glass can
5.2.1 Water is the most frequently used aqueous solvent.
be more scientific. Design of a cleaning procedure should
Even this can attack some glasses appreciably.
involve (1) a definition of the soil to be removed, (2)an
5.2.2 Try to choose an aqueous system that completely
awareness of the constraints imposed by the glass composition,
removes the soil with minimal effect on the underlying glass.
and (3) a rational selection of alternative methods that will
Obviously, to achieve this the glass composition must be
remove the soil and leave the glass in a condition suitable for
known. However, one cannot simply calculate glass solubility
its intended application. This practice provides information to
in a specific reagent. Reference to Table 1 will then help
This practice is under the jurisdiction of ASTM Committee C-14 on Glass and
Glass Products and is the direct responsibility of Subcommittee C14.02 on Chemical Campbell, D. E., and Adams, P. B., “Bibliography on Clean Glass: Supplement
Properties and Analysis. 1,” Journal of Testing and Evaluation, Vol 14, No. 5, September 1986, pp. 260–265.
Current edition approved Nov. 15, 1993. Published January 1994. Originally A useful reference is the Handbook of Laboratory Safety, ed., CRC Press, Inc.,
e1
published as C 912 – 79. Last previous edition C 912 – 79 (1988) . 2255 Palm Beach Lakes Blvd, West Palm Beach, FL 33409.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 912
TABLE 1 Relative Solubility of Various Glass Component Oxides in HF, Other Inorganic Acids, and NaOH, in Concentrated Solutions at
Room Temperature
NOTE 1—Macro or minor/trace levels will determine degree of precipitation, especially in acids, for example, HNO (Sn, Sb, Mo).
NOTE 2—W is soluble in acid but heat may precipitate it, for example, H WO .
2 4
+4 +2
NOTE 3—Sn is soluble in hot H SO ;Sn is soluble in other reagents as well.
2 4
NOTE 4—Most alkali solutions must be hot to effect solution.
NOTE 5—PbSO is soluble in hot concentrated H SO .
4 2 4
NOTE 6—Sb and Bi form insoluble oxychlorides in dilute HCl.
NOTE 7—Ba is insoluble in concentrated HNO .
HF H SO HNO HCl H PO NaOH
2 4 3 3 4
Oxides of HBr HI
49 % 96 % 70 % 37 % 85 % 50 %
A
Al s s s s iii s
A
Sb i i i sss i s
As s s s sssss
Ba i i s sssss
Be s s s ssss i
Bi s s s ssss i
B s s s sssss
Cd s s s sssss
Ca i s s sssss
Ce i s i iiiii
Cr i i i iiiii
Co s s s ssss i
Cu s s s ssss i
Er i s s ssss i
Eu i s s ssss i
Gd i s s ssss i
Ga s s s ssss i
Ge s s s sssss
Au i i i iiiii
Hf s i i iiiii
Fe s s s ssss i
La i s s ssss i
Pb i i s iii s s
Li s s s sssss
Mg i s s ssss i
Mn s s s ssss i
B
Mo s s i sssss
Nd i s s ssss i
Ni s s s ssss i
Nb s i i iiiii
Pd s s i iiiii
P s s s sssss
Pt i i i iiiii
K s s s sssss
Pr i s s ssss i
Pm i s s ssss i
Rh i s s ssss i
Rb i s s ssss i
Ru i s s ssss i
Sm i s s ssss i
Se s s s sssss
Si s i i iiii s
Ag s s s iii s i
Na s s s sssss
Sr i i i iiiii
Ta s i i iiiii
Te s s s sssss
Tl s s s s i i s i
B
Th s s i iiiii
Sn s s s sssss
B
Ti s s i s iiii
W s i i iiii s
U s s s iiiii
V s s s sssss
Yb i s s ssss i
Y i s s ssss i
Zn s s s sssss
B
Zr s s i iiiii
A
s 5 relatively soluble, i 5 relatively insoluble.
B
hot
determine if an aqueous solvent exists that will not attack the trial and error will usually be necessary also. Individual glass
glass. The table provides guidance in selecting a solvent, but components do not act independently with specific solvents, in
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 912
TABLE 2 Threshold Limit Values for Some Common Solvents
5.4.2 Sometimes it is necessary to use a multicomponent
A
TLV, ppm aqueous system to achieve the desired results. Obviously,
concentrations of various reagents and temperatures at which
1,1,2-trichloro-1,2-trifluorethane 1000
Acetone 750
the process can be carried out are important. It is not the intent
Ethyl alcohol 1000
of this practice to explore all these possibilities, but, by
n-Hexane 50
knowing the glass composition, the correct solvent-
Isopropyl alcohol 400
Methyl chloroform 350
concentration-temperature-time conditions to effect the desired
Perchloroethylene 50
result can be devised.
Trichloroethylene 50
5.5 Residues and Defects:
Methylene chloride 100
Carbon tetrachloride 5
5.5.1 Any reaction between a solvent and a complex mix-
A
The TLV values establish parts per million by volume of solvent vapors allowed ture of oxides affects the possibility of formation of some
in air for a normal work week of8haday,5 days a week. These are standards set
insoluble reaction products. Agitation may help prevent their
by the American Conference of Governmental Industrial Hygienists, and the values
adherence to the glass. Additionally, the reagent itself is
shown in this table were effective in 1984–1985. The most recent recommended
R
values should be consulted in“ TLV’s Threshold Limit Values for Chemical
potentially a “residue.”
Substances and Physical Agents in the Work Environment and Biological Expo-
5.5.2 Reaction with the glass may also leave a roughened
sure Indices with Intended Changes for 1984–1985,” published by ACGIH, 6500
surface (selective reaction with certain glass components),
Glenway Ave., Bldg D-5, Cincinnati, OH 45211.
streaks (selective reaction with nonhomogeneous “cords”), or
most cases, as described in 5.2.3.
with latent grinding marks hidden by a previous polishing step.
5.2.3 It is not necessary that the glass contain absolutely
6. Detergents
none of the components that are soluble in the chosen reagent.
For instance, a glass containing 80 % SiO and 5 % Na O 6.1 Surface Active Agents:
2 2
could be cleaned in H SO without appreciable glass attack 6.1.1 Surface active agents accelerate the cleaning action of
2 4
even though Na O is very soluble in H SO ; however a glass aqueous solutions and provide mechanisms of cleaning that
2 2 4
containing 50 % SiO and 25 % Na O would probably show water does not have by itself. Many compounds are available,
2 2
considerable attack by H SO . Often this can only be deter- usually under trade names that give no hint of their chemical
2 4
mined by trial. nature. Selection of the best compound for a particular use is
5.3 Uniform Glass Dissolution: usually a matter of experimentation, since the available litera-
5.3.1 It may be necessary to select a system that uniformly ture gives few clues to aid in prediction.
attacks the glass either because there is no other solvent for the 6.1.2 Generally, however, such “agents” consist of long-
soil or there is no solvent available that does not attack the chain organic molecules, one end of which is attracted to the
glass. For glasses containing substantial concentrations of soil or the substrate, or both, the other end of which is “water
silica, HF or HF plus some other reagent may be a good choice. soluble.” They “wet” the glass surface by lowering the surface
HF can often be used for cleaning provided there are no glass tension of water; thus decreasing the contact angle between
components that form insoluble fluorides. For non-silicate solvent and glass and between solvent and soil. The net effect
glasses, some other reagent would probably be appropriate. is that the particle or oily film is dislodged. They “surround”
Table 1 is a general guide to selection of such reagents. the particle or droplet to suspend or emulsify and prevent its
5.3.2 There are two further modifications that can allow the redeposition.
successful use of HF even if insoluble products form. One is to 6.1.3 The activity of surface active agents is usually en-
combine chemical cleaning with a mechanical cleaning process hanced by the blending of two or more and by the addition of
either simultaneously or sequentially. The other is to mix the non-surface active agents (called “builders”). A compound
HF with another acid to achieve complete solution of all with good emulsification will be blended with a good wetter,
products. and built with a polyphosphate for water softening, dispersion,
5.3.3 Alkali solutions can be used as a glass solvent for and micelle formation. EDTA and similar compounds are used
cleaning, but, in most cases, it will be necessary to use them for water softening and solubilization of inorganic compounds,
hot to achieve a sufficiently rapid reaction. soda ash, and ammonia for pH regulation and sodium silicates
5.3.4 Many glasses can be cleaned by the uniform dissolu- for achieving high alkalinity while inhibiting attack on the
tion process without the use of HF or alkali. Reference to Table glass.
1 will suggest the types of glasses to which this approach is 6.1.4 The builders can either promote or inhibit solution of
applicable. For instance, a glass containing 60 % PbO and less glasses, depending on whether the reaction products or the
than 15 % SiO could probably be cleaned in this way with builder and the glass components are soluble or insoluble.
HNO , particularly if mechanical action by polishing or Polyphosphates and EDTA, in particular, will chelate with and
rubbing is used. solubilize metallic ions, promoting a preferential leaching and
5.4 Other Possibilities: leaving a porous or etched surface on the glass.
5.4.1 When all else fails, organic complexing agents, either 6.1.5 Water-soluble surface active agents are usually long-
alone or in combination with other chemicals, may succeed in chain organic molecules with a hydrophobic end and a hydro-
removing soil without damaging the glass. For instance, philic end. The ionic nature of the hydrophilic end determines
alkaline EDTA is a powerful complexing agent for a number of the broad basic classification of the material—if negative, it is
elements, such as calcium, magnesium, silicon, aluminum, anionic, if positive, cationic, and if the material is not ionized,
lead, zinc, and barium. it is nonionic. There are a few amphoteric materials available,
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 912
TABLE 3 Relative Solvent Power of Some Organics (Removal of
and these hybrids can be either cationic or anionic, depending
Stearic Acid from Glass by a 30-s Soak at the Boiling Point)
on the pH of the solution.
Stearic Acid
6.2 Anionic Agents—The oldest, and one of the most
Solvent
Remaining,
...
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