ASTM C912-93(2008)e1
(Practice)Standard Practice for Designing a Process for Cleaning Technical Glasses
Standard Practice for Designing a Process for Cleaning Technical Glasses
SIGNIFICANCE AND USE
Many of the low-silica technical glasses which contain soluble or reactive oxides require processing or involve applications that require cleaning. Very often these cleaning procedures have evolved over several decades and are considered an art. They usually contain numerous steps, some of questionable validity. It is the premise of this practice that cleaning glass can be more scientific. Design of a cleaning procedure should involve (1) a definition of the soil to be removed, (2) an awareness of the constraints imposed by the glass composition, and (3) a rational selection of alternative methods that will remove the soil and leave the glass in a condition suitable for its intended application. This practice provides information to assist in step (3). General references on glass cleaning and on various methods of evaluating cleanliness and associated information has been published.
SCOPE
1.1 This practice covers 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 B2O3, Al2O3, R2O, RO, La2O3, ZnO, PbO, P2O5, and Fe2O3. 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.
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, HNO3 (Sn, Sb, Mo).
Note 2—W is soluble in acid but heat may precipitate it, for example, H2WO4.
Note 3—Sn+4 is soluble in hot H2SO4; Sn+2 is soluble in other reagents as well.
Note 4—Most alkali solutions must be hot to effect solution.
Note 5—PbSO4 is soluble in hot concentrated H2SO4.
Note 6—Sb and Bi form insoluble oxychlorides in dilute HCl.
Note 7—Ba is insoluble in concentrated HNO3. Oxides ofHF
49 %H2SO4
96 %HNO3
70 %HCl
37 %HBrHIH3PO4
85 %NaOH
50 % Al sAsssiiis Sb iAiisssis Asssssssss Baiissssss Besssssssi Bisssssssi Bssssssss Cdssssssss Caisssssss Ceisiiiiii Criiiiiiii Cosssssssi Cusssssssi Erissssssi Euissssssi Gdissssssi Gasssssssi Gessssssss Auiiiiiiii Hfsiiiiiii Fesssssssi Laissssssi Pbiisiiiss Lissssssss Mgissssssi Mnsssssssi Moss iBsssss Ndissssssi Nisssssssi Nbsiiiiiii Pdssiiiiii Pssssssss Ptiiiiiiii Kssssssss Prissssssi Pmissssssi Rhissssssi Rbissssssi Ruissssssi Smissssssi Sessssssss Sisiiiiiis Agsssiiisi Nassssssss Sriiiiiiii Tasiiiiiii Tessssssss Tlssssiisi Ths sBiiiiii Snssssssss Tis sBisiiii Wsiiiiiis Usssiiiii Vssssssss Ybissssssi Yissssssi Znssssssss Zrs sBiiiiii
A s = relatively soluble, i = relatively insoluble.
B hot
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Designation: C912 − 93(Reapproved 2008)
Standard Practice for
Designing a Process for Cleaning Technical Glasses
This standard is issued under the fixed designation C912; 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 (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—This standard was revised editorially in December 2012.
1. Scope involve (1) a definition of the soil to be removed, (2)an
awareness of the constraints imposed by the glass composition,
1.1 This practice covers information that will permit design
and (3) a rational selection of alternative methods that will
of a rational cleaning procedure that can be used with a glass
remove the soil and leave the glass in a condition suitable for
that is somewhat soluble in many aqueous chemical solutions.
its intended application. This practice provides information to
Typically, this type of glass is used in applications such as
assist in step (3). General references on glass cleaning and on
optical ware, glass-to-metal seals, low dielectric loss products,
various methods of evaluating cleanliness and associated
glass fibers, infrared transmitting products, and products resis-
information has been published.
tant to metallic vapors.
1.2 In most cases, this type of glass contains high concen- 4. Hazards
trations of oxides that tend to react with a number of aqueous
4.1 Manyofthechemicalsthatcanbeusedincleaningglass
chemicals. Such oxides include B O ,Al O ,R O, RO, La O ,
2 3 2 3 2 2 3
are hazardous. This is true of most of the aqueous chemicals
ZnO, PbO, P O , and Fe O . The more conventional high-
2 5 2 3
discussed in Section 5 and shown in Table 1 as well as the
silica glasses are usually more chemically resistant, but the
organic chemicals discussed in Section 6.
cleaning principles outlined here also apply to them.
4.2 Specialcareshouldbeusedwithhydrofluoricacid(HF),
1.3 This standard does not purport to address all of the
which will react with glass generating heat. The vapors as well
safety concerns, if any, associated with its use. It is the
as the liquid destroy dermal tissue and can be fatal if inhaled.
responsibility of the user of this standard to establish appro-
4.3 Concentrated acids can react violently if water is added
priate safety and health practices and determine the applica-
into them. When it is necessary to dilute acid, add the acid to
bility of regulatory limitations prior to use. Specific hazard
the water slowly and with constant stirring so that heat is never
statements are given in Section 4 and Table 1.
allowed to concentrate locally in the solution.
2. Terminology
4.4 Organic solvents may be flammable or toxic, or both.
2.1 Definitions of Terms Specific to This Standard:
Thresholdlimitvaluesforsomecommonsolventsareshownin
2.1.1 technical glass—glasses designed with some specific
Table 2. Note that the fluorocarbons are most likely to exhibit
property essential for a mechanical, industrial, or scientific
toxic effects as a result of inhalation or skin absorption.
device.
Benzene is not recommended as a solvent since it is a known
carcinogen.
3. Significance and Use
5. Aqueous Solvents
3.1 Many of the low-silica technical glasses which contain
soluble or reactive oxides require processing or involve appli-
5.1 Selection—In using aqueous solvents for cleaning, gen-
cations that require cleaning. Very often these cleaning proce-
erally two extreme choices are available. One is to select an
dures have evolved over several decades and are considered an
aqueous system that dissolves the soil to be removed, but has
art.Theyusuallycontainnumeroussteps,someofquestionable
little effect on the glass. The other is to select a system that
validity.Itisthepremiseofthispracticethatcleaningglasscan
dissolves the glass uniformly, thus undercutting the soil and
be more scientific. Design of a cleaning procedure should
leaving a chemically polished glass surface. It is best to avoid
a solvent that selectively attacks the glass, dissolving only
some components, or a solvent that produces a precipitate that
This practice is under the jurisdiction of ASTM Committee C14 on Glass and
adheres to the surface to be cleaned.
GlassProductsandisthedirectresponsibilityofSubcommitteeC14.02onChemical
Properties and Analysis.
Current edition approved Sept. 1, 2008. Published October 2008. Originally
approved in 1979. Last previous edition approved in 2003 as C912–93(2003). DOI: Campbell, D. E., andAdams, P. B., “Bibliography on Clean Glass: Supplement
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10.1520/C912–93R08 . 1,” Journal of Testing and Evaluation,Vol 14, No. 5, September 1986, pp. 260–265.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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C912 − 93 (2008)
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
i iiiii
Th s s
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 = relatively soluble, i = relatively insoluble.
B
hot
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C912 − 93 (2008)
TABLE 2 Threshold Limit Values for Some Common Solvents
5.3.4 Many glasses can be cleaned by the uniform dissolu-
A
TLV, ppm tionprocesswithouttheuseofHForalkali.ReferencetoTable
1,1,2-trichloro-1,2-trifluorethane 1000 1 will suggest the types of glasses to which this approach is
Acetone 750
applicable. For instance, a glass containing 60 % PbO and less
Ethyl alcohol 1000
than 15 % SiO could probably be cleaned in this way with
n-Hexane 50
Isopropyl alcohol 400 HNO , particularly if mechanical action by polishing or
Methyl chloroform 350
rubbing is used.
Perchloroethylene 50
Trichloroethylene 50
5.4 Other Possibilities:
Methylene chloride 100
5.4.1 When all else fails, organic complexing agents, either
Carbon tetrachloride 5
alone or in combination with other chemicals, may succeed in
A
The TLV values establish parts per million by volume of solvent vapors allowed
removing soil without damaging the glass. For instance,
in air for a normal work week of8haday,5 days a week.These are standards set
bytheAmericanConferenceofGovernmentalIndustrialHygienists,andthevalues
alkaline EDTAis a powerful complexing agent for a number of
shown in this table were effective in 1984–1985. The most recent recommended
elements, such as calcium, magnesium, silicon, aluminum,
R
values should be consulted in “TLV’s Threshold Limit Values for Chemical
lead, zinc, and barium.
Substances and Physical Agents in the Work Environment and Biological Expo-
sure Indices with Intended Changes for 1984–1985,” published by ACGIH, 6500
5.4.2 Sometimes it is necessary to use a multicomponent
Glenway Ave., Bldg D-5, Cincinnati, OH 45211.
aqueous system to achieve the desired results. Obviously,
concentrations of various reagents and temperatures at which
the process can be carried out are important. It is not the intent
of this practice to explore all these possibilities, but, by
5.2 Minimum Glass Dissolution:
knowing the glass composition, the correct solvent-
5.2.1 Water is the most frequently used aqueous solvent.
concentration-temperature-time conditions to effect the desired
Even this can attack some glasses appreciably.
result can be devised.
5.2.2 Try to choose an aqueous system that completely
removes the soil with minimal effect on the underlying glass.
5.5 Residues and Defects:
Obviously, to achieve this the glass composition must be
5.5.1 Any reaction between a solvent and a complex mix-
known. However, one cannot simply calculate glass solubility
ture of oxides affects the possibility of formation of some
in a specific reagent. Reference to Table 1 will then help
insoluble reaction products. Agitation may help prevent their
determine if an aqueous solvent exists that will not attack the
adherence to the glass. Additionally, the reagent itself is
glass. The table provides guidance in selecting a solvent, but
potentially a “residue.”
trial and error will usually be necessary also. Individual glass
5.5.2 Reaction with the glass may also leave a roughened
components do not act independently with specific solvents, in
surface (selective reaction with certain glass components),
most cases, as described in 5.2.3.
streaks (selective reaction with nonhomogeneous “cords”), or
5.2.3 It is not necessary that the glass contain absolutely
with latent grinding marks hidden by a previous polishing step.
none of the components that are soluble in the chosen reagent.
For instance, a glass containing 80 % SiO and 5 % Na O 6. Detergents
2 2
could be cleaned in H SO without appreciable glass attack
2 4
6.1 Surface Active Agents:
even though Na O is very soluble in H SO ; however a glass
2 2 4
6.1.1 Surface active agents accelerate the cleaning action of
containing 50 % SiO and 25 % Na O would probably show
2 2
aqueous solutions and provide mechanisms of cleaning that
considerable attack by H SO . Often this can only be deter-
2 4
water does not have by itself. Many compounds are available,
mined by trial.
usually under trade names that give no hint of their chemical
5.3 Uniform Glass Dissolution:
nature. Selection of the best compound for a particular use is
5.3.1 It may be necessary to select a system that uniformly usually a matter of experimentation, since the available litera-
attacks the glass either because there is no other solvent for the ture gives few clues to aid in prediction.
soil or there is no solvent available that does not attack the 6.1.2 Generally, however, such “agents” consist of long-
glass. For glasses containing substantial concentrations of chain organic molecules, one end of which is attracted to the
silica,HForHFplussomeotherreagentmaybeagoodchoice. soil or the substrate, or both, the other end of which is “water
HF can often be used for cleaning provided there are no glass soluble.” They “wet” the glass surface by lowering the surface
components that form insoluble fluorides. For non-silicate tension of water; thus decreasing the contact angle between
glasses, some other reagent would probably be appropriate. solvent and glass and between solvent and soil. The net effect
Table 1 is a general guide to selection of such reagents. is that the particle or oily film is dislodged. They “surround”
5.3.2 There are two further modifications that can allow the the particle or droplet to suspend or emulsify and prevent its
successful use of HF even if insoluble products form. One is to redeposition.
combinechemicalcleaningwithamechanicalcleaningprocess 6.1.3 The activity of surface active agents is usually en-
either simultaneously or sequentially. The other is to mix the hanced by the blending of two or more and by the addition of
HF with another acid to achieve complete solution of all non-surface active agents (called “builders”). A compound
products. with good emulsification will be blended with a good wetter,
5.3.3 Alkali solutions can be used as a glass solvent for and built with a polyphosphate for water softening, dispersion,
cleaning, but, in most cases, it will be necessary to use them and micelle formation. EDTAand similar compounds are used
hot to achieve a sufficiently rapid reaction. for water softening and solubilization of inorganic compounds,
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C912 − 93 (2008)
TABLE 3 Relative Solvent Power of Some Organics (Removal of
soda ash, and ammonia for pH regulation and sodium silicates
Stearic Acid from Glass by a 30-s Soak at the Boiling Point)
for achieving high alkalinity while inhibiting attack on the
Stearic Acid
glass.
Solvent
Remaining, %
6.1.4 The builders can either promote or inhibit solution of
A
Combination No. 1 35.0
glasses, depending on whether the reaction products or the A
Combination No. 2 2.4
A
builder and the glass components are soluble or insoluble. Combination No. 3 1.4
Trichlorotrifluoroethane 74.0
Polyphosphates and EDTA, in particular, will chelate with and
Acetone 1.3
solubilize metallic ions, promoting a preferential leaching and
Methanol 0.30
leaving a porous or etched surface on the glass. Hexane 44.0
Methyl chloroform 1.6
6.1.5 Water-soluble surface active agents are usually long-
Benzene 6.7
chain organic molecules with a hydrophobic end and a hydro-
Isopropanol 0.60
philic end. The ionic nature of the hydrophilic end determines Trichloroethylene 0.80
Perchloroethylene 1.0
the broad basic classification of the material—if negative, it is
A
See Table 4 for description.
anionic, if positive, cationic, and if the material is not ionized,
it is nonionic. There are a few amphoteric materials available,
and these hybrids can be either cationic or anionic, depending
7.1.1 Hydrocarbons such as hexane can be used to remove
on the pH of the solution.
oils and other nonpolar contaminants from glass. However, for
6.2 Anionic Agents—The oldest, and one of the most effec-
the removal of adsorbed polar compounds or intermediate size
tive anionic detergents if used in “soft” water, is soap. The
particulate matter (0.1 to 1000 µm), more active solvent
largest class of synthetic anionic detergents is the sulfonated
systems such as those shown
...
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