ASTM C912-93(2003)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:C912–93(Reapproved 2003)
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 its intended application. This practice provides information to
assist in step (3). General references on glass cleaning and on
1.1 This practice covers information that will permit design
various methods of evaluating cleanliness and associated
of a rational cleaning procedure that can be used with a glass
information has been published.
that is somewhat soluble in many aqueous chemical solutions.
Typically, this type of glass is used in applications such as
4. Hazards
optical ware, glass-to-metal seals, low dielectric loss products,
4.1 Manyofthechemicalsthatcanbeusedincleaningglass
glass fibers, infrared transmitting products, and products resis-
are hazardous. This is true of most of the aqueous chemicals
tant to metallic vapors.
discussed in Section 5 and shown in Table 1 as well as the
1.2 In most cases, this type of glass contains high concen-
organic chemicals discussed in Section 6.
trations of oxides that tend to react with a number of aqueous
4.2 Specialcareshouldbeusedwithhydrofluoricacid(HF),
chemicals. Such oxides include B O ,Al O ,R O, RO, La O ,
2 3 2 3 2 2 3
which will react with glass generating heat. The vapors as well
ZnO, PbO, P O , and Fe O . The more conventional high-
2 5 2 3
as the liquid destroy dermal tissue and can be fatal if inhaled.
silica glasses are usually more chemically resistant, but the
4.3 Concentrated acids can react violently if water is added
cleaning principles outlined here also apply to them.
into them. When it is necessary to dilute acid, add the acid to
1.3 This standard does not purport to address all of the
the water slowly and with constant stirring so that heat is never
safety concerns, if any, associated with its use. It is the
allowed to concentrate locally in the solution.
responsibility of the user of this standard to establish appro-
4.4 Organic solvents may be flammable or toxic, or both.
priate safety and health practices and determine the applica-
Thresholdlimitvaluesforsomecommonsolventsareshownin
bility of regulatory limitations prior to use. Specific hazard
Table 2. Note that the fluorocarbons are most likely to exhibit
statements are given in Section 4 and Table 1.
toxic effects as a result of inhalation or skin absorption.
2. Terminology Benzene is not recommended as a solvent since it is a known
carcinogen.
2.1 Definitions of Terms Specific to This Standard:
2.1.1 technical glass—glasses designed with some specific
5. Aqueous Solvents
property essential for a mechanical, industrial, or scientific
5.1 Selection—In using aqueous solvents for cleaning, gen-
device.
erally two extreme choices are available. One is to select an
3. Significance and Use aqueous system that dissolves the soil to be removed, but has
little effect on the glass. The other is to select a system that
3.1 Many of the low-silica technical glasses which contain
dissolves the glass uniformly, thus undercutting the soil and
soluble or reactive oxides require processing or involve appli-
leaving a chemically polished glass surface. It is best to avoid
cations that require cleaning. Very often these cleaning proce-
a solvent that selectively attacks the glass, dissolving only
dures have evolved over several decades and are considered an
some components, or a solvent that produces a precipitate that
art.Theyusuallycontainnumeroussteps,someofquestionable
adheres to the surface to be cleaned.
validity.Itisthepremiseofthispracticethatcleaningglasscan
5.2 Minimum Glass Dissolution:
be more scientific. Design of a cleaning procedure should
5.2.1 Water is the most frequently used aqueous solvent.
involve (1) a definition of the soil to be removed, (2)an
Even this can attack some glasses appreciably.
awareness of the constraints imposed by the glass composition,
5.2.2 Try to choose an aqueous system that completely
and (3) a rational selection of alternative methods that will
removes the soil with minimal effect on the underlying glass.
remove the soil and leave the glass in a condition suitable for
This practice is under the jurisdiction of ASTM Committee C14 on Glass and
GlassProductsandisthedirectresponsibilityofSubcommitteeC14.02onChemical Campbell, D. E., andAdams, 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 Oct. 1, 2003. Published October 2003. Originally Auseful reference is the Handbook of Laboratory Safety, ed., CRC Press, Inc.,
approved in 1979. Last previous edition approved in 1997 as C 912 – 93 (1997). 2255 Palm Beach Lakes Blvd, West Palm Beach, FL 33409.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C912–93 (2003)
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 = relatively soluble, i = relatively insoluble.
B
hot
C912–93 (2003)
TABLE 2 Threshold Limit Values for Some Common Solvents
than 15 % SiO could probably be cleaned in this way with
A
TLV, ppm HNO , particularly if mechanical action by polishing or
rubbing is used.
1,1,2-trichloro-1,2-trifluorethane 1000
Acetone 750
5.4 Other Possibilities:
Ethyl alcohol 1000
5.4.1 When all else fails, organic complexing agents, either
n-Hexane 50
alone or in combination with other chemicals, may succeed in
Isopropyl alcohol 400
Methyl chloroform 350
removing soil without damaging the glass. For instance,
Perchloroethylene 50
alkaline EDTAis a powerful complexing agent for a number of
Trichloroethylene 50
elements, such as calcium, magnesium, silicon, aluminum,
Methylene chloride 100
Carbon tetrachloride 5
lead, zinc, and barium.
A
TheTLVvaluesestablishpartspermillionbyvolumeofsolventvaporsallowed 5.4.2 Sometimes it is necessary to use a multicomponent
in air for a normal work week of8haday,5 days a week.These are standards set
aqueous system to achieve the desired results. Obviously,
bytheAmericanConferenceofGovernmentalIndustrialHygienists,andthevalues
concentrations of various reagents and temperatures at which
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
the process can be carried out are important. It is not the intent
Substances and Physical Agents in the Work Environment and Biological Expo-
of this practice to explore all these possibilities, but, by
sure Indices with Intended Changes for 1984–1985,” published by ACGIH, 6500
knowing the glass composition, the correct solvent-
Glenway Ave., Bldg D-5, Cincinnati, OH 45211.
concentration-temperature-time conditions to effect the desired
result can be devised.
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
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,HForHFplussomeotherreagentmaybeagoodchoice.
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-
combinechemicalcleaningwithamechanicalcleaningprocess
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. EDTAand 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
tionprocesswithouttheuseofHForalkali.ReferencetoTable 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
C912–93 (2003)
TABLE 3 Relative Solvent Power of Some Organics (Removal of
builder and the glass components are soluble or insoluble.
Stearic Acid from Glass by a 30-s Soak at the Boiling Point)
Polyphosphates and EDTA, in particular, will chelate with and
Stearic Acid
solubilize metallic ions, promoting a preferential leaching and
Solvent
Remaining, %
leaving a porous or etched surface on the glass.
A
Combination No. 1 35.0
6.1.5 Water-soluble surface active agents are usually long-
A
Combination No. 2 2.4
A
chain organic molecules with a hydrophobic end and a hydro-
Combination No. 3 1.4
Trichlorotrifluoroethane 74.0
philic end. The ionic nature of the hydrophilic end determines
Acetone 1.3
the broad basic classification of the material—if negative, it is
Methanol 0.30
anionic, if positive, cationic, and if the material is not ionized,
Hexane 44.0
Methyl chloroform 1.6
it is nonionic. There are a few amphoteric materials available,
Benzene 6.7
and these hybrids can be either cationic or anionic, depending
Isopropanol 0.60
on the pH of the solution.
Trichloroethylene 0.80
Perchloroethylene 1.0
6.2 Anionic Agents—The oldest, and one of the most
A
effective anionic detergents if used in “soft” water, is soap.The See Table 4 for description.
largest class of synthetic anionic detergents is the sulfonated
hydrocarbons such as sodium dodecyl benzene sulfonate. 7. Nonaqueous Solvents
Sulfatedalcoholsandpolyethers,suchassodiumlaurylsulfate,
7.1 Types of Solvents:
are also used extensively.
7.1.1 Hydrocarbons such as hexane can be used to remove
6.3 Cation
...