1、Designation: C912 93 (Reapproved 2013)Standard Practice forDesigning a Process for Cleaning Technical Glasses1This standard is issued under the fixed designation C912; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers information that will permit designof a rational cleaning procedure that can be used with a glasstha
3、t is somewhat soluble in many aqueous chemical solutions.Typically, this type of glass is used in applications such asoptical ware, glass-to-metal seals, low dielectric loss products,glass fibers, infrared transmitting products, and products resis-tant to metallic vapors.1.2 In most cases, this type
4、 of glass contains high concen-trations of oxides that tend to react with a number of aqueouschemicals. 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 thecleaning principles outlined here a
5、lso apply to them.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to u
6、se. Specific hazardstatements are given in Section 4 and Table 1.2. Terminology2.1 Definitions of Terms Specific to This Standard:2.1.1 technical glassglasses designed with some specificproperty essential for a mechanical, industrial, or scientificdevice.3. Significance and Use3.1 Many of the low-si
7、lica technical glasses which containsoluble or reactive oxides require processing or involve appli-cations that require cleaning. Very often these cleaning proce-dures have evolved over several decades and are considered anart. They usually contain numerous steps, some of questionablevalidity. It is
8、 the premise of this practice that cleaning glass canbe more scientific. Design of a cleaning procedure shouldinvolve (1) a definition of the soil to be removed, (2)anawareness of the constraints imposed by the glass composition,and (3) a rational selection of alternative methods that willremove the
9、 soil and leave the glass in a condition suitable forits intended application. This practice provides information toassist in step (3). General references on glass cleaning and onvarious methods of evaluating cleanliness and associatedinformation has been published.24. Hazards4.1 Many of the chemica
10、ls that can be used in cleaning glassare hazardous. This is true of most of the aqueous chemicalsdiscussed in Section 5 and shown in Table 1 as well as theorganic chemicals discussed in Section 6.4.2 Special care should be used with hydrofluoric acid (HF),which will react with glass generating heat.
11、 The vapors as wellas the liquid destroy dermal tissue and can be fatal if inhaled.4.3 Concentrated acids can react violently if water is addedinto them. When it is necessary to dilute acid, add the acid tothe water slowly and with constant stirring so that heat is neverallowed to concentrate locall
12、y in the solution.4.4 Organic solvents may be flammable or toxic, or both.Threshold limit values for some common solvents are shown inTable 2. Note that the fluorocarbons are most likely to exhibittoxic effects as a result of inhalation or skin absorption.Benzene is not recommended as a solvent sinc
13、e it is a knowncarcinogen.5. Aqueous Solvents5.1 SelectionIn using aqueous solvents for cleaning, gen-erally two extreme choices are available. One is to select anaqueous system that dissolves the soil to be removed, but haslittle effect on the glass. The other is to select a system thatdissolves th
14、e glass uniformly, thus undercutting the soil andleaving a chemically polished glass surface. It is best to avoida solvent that selectively attacks the glass, dissolving onlysome components, or a solvent that produces a precipitate thatadheres to the surface to be cleaned.5.2 Minimum Glass Dissoluti
15、on:5.2.1 Water is the most frequently used aqueous solvent.Even this can attack some glasses appreciably.1This practice is under the jurisdiction of ASTM Committee C14 on Glass andGlass Products and is the direct responsibility of Subcommittee C14.02 on ChemicalProperties and Analysis.Current editio
16、n approved Oct. 1, 2013. Published October 2013. Originallyapproved in 1979. Last previous edition approved in 2008 as C91293(2008)1.DOI: 10.1520/C91293R13.2Campbell, D. E., and Adams, P. B., “Bibliography on Clean Glass: Supplement1,” Journal of Testing and Evaluation, Vol 14, No. 5, September 1986
17、, pp. 260265.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1TABLE 1 Relative Solubility of Various Glass Component Oxides in HF, Other Inorganic Acids, and NaOH, in Concentrated Solutions atRoom TemperatureNOTE 1Macro or minor/trace
18、levels will determine degree of precipitation, especially in acids, for example, HNO3(Sn, Sb, Mo).NOTE 2W is soluble in acid but heat may precipitate it, for example, H2WO4.NOTE 3Sn+4is soluble in hot H2SO4;Sn+2is soluble in other reagents as well.NOTE 4Most alkali solutions must be hot to effect so
19、lution.NOTE 5PbSO4is soluble in hot concentrated H2SO4.NOTE 6Sb and Bi form insoluble oxychlorides in dilute HCl.NOTE 7Ba is insoluble in concentrated HNO3.Oxides ofHF49 %H2SO496 %HNO370 %HCl37 %HBr HIH3PO485 %NaOH50 %Al sAs ssiiisSb iAi i sssiAs sssssBa se s s ssssiiB s sssssCd s sa ie i iiiiiCr io
20、 s s s ssssiuEr is s ssssiGda se s s sssssAu i i i iiiiiHf sFe s s ssssiLa iPb i iiissi s s s sssssMg i ssssinMo s s iBsssssNd i s ssssiib s i i iiiiiPd ss ssssst i i i iiiiiK s sPr s ssssim iRh sb s ssssiu iSm se s s sssssi i i iiiisAg s iiisiNa s s sssssSr i i i iiiiiTe s s s sssssTl s s s s i i s
21、 iTh s sBi iiiiiSn sssssTi s sBsiiiiW i i iiiisU siiiiiV s s sssssYb i ssssisZn s s sssssZr s sBi iiiiiAs = relatively soluble, i = relatively insoluble.BhotC912 93 (2013)25.2.2 Try to choose an aqueous system that completelyremoves the soil with minimal effect on the underlying glass.Obviously, to
22、achieve this the glass composition must beknown. However, one cannot simply calculate glass solubilityin a specific reagent. Reference to Table 1 will then helpdetermine if an aqueous solvent exists that will not attack theglass. The table provides guidance in selecting a solvent, buttrial and error
23、 will usually be necessary also. Individual glasscomponents do not act independently with specific solvents, inmost cases, as described in 5.2.3.5.2.3 It is not necessary that the glass contain absolutelynone of the components that are soluble in the chosen reagent.For instance, a glass containing 8
24、0 % SiO2and 5 % Na2Ocould be cleaned in H2SO4without appreciable glass attackeven though Na2O is very soluble in H2SO4; however a glasscontaining 50 % SiO2and 25 % Na2O would probably showconsiderable attack by H2SO4. Often this can only be deter-mined by trial.5.3 Uniform Glass Dissolution:5.3.1 It
25、 may be necessary to select a system that uniformlyattacks the glass either because there is no other solvent for thesoil or there is no solvent available that does not attack theglass. For glasses containing substantial concentrations ofsilica, HF or HF plus some other reagent may be a good choice.
26、HF can often be used for cleaning provided there are no glasscomponents that form insoluble fluorides. For non-silicateglasses, some other reagent would probably be appropriate.Table 1 is a general guide to selection of such reagents.5.3.2 There are two further modifications that can allow thesucces
27、sful use of HF even if insoluble products form. One is tocombine chemical cleaning with a mechanical cleaning processeither simultaneously or sequentially. The other is to mix theHF with another acid to achieve complete solution of allproducts.5.3.3 Alkali solutions can be used as a glass solvent fo
28、rcleaning, but, in most cases, it will be necessary to use themhot to achieve a sufficiently rapid reaction.5.3.4 Many glasses can be cleaned by the uniform dissolu-tion process without the use of HF or alkali. Reference to Table1 will suggest the types of glasses to which this approach isapplicable
29、. For instance, a glass containing 60 % PbO and lessthan 15 % SiO2could probably be cleaned in this way withHNO3, particularly if mechanical action by polishing orrubbing is used.5.4 Other Possibilities:5.4.1 When all else fails, organic complexing agents, eitheralone or in combination with other ch
30、emicals, may succeed inremoving soil without damaging the glass. For instance,alkaline EDTAis a powerful complexing agent for a number ofelements, such as calcium, magnesium, silicon, aluminum,lead, zinc, and barium.5.4.2 Sometimes it is necessary to use a multicomponentaqueous system to achieve the
31、 desired results. Obviously,concentrations of various reagents and temperatures at whichthe process can be carried out are important. It is not the intentof this practice to explore all these possibilities, but, byknowing the glass composition, the correct solvent-concentration-temperature-time cond
32、itions to effect the desiredresult can be devised.5.5 Residues and Defects:5.5.1 Any reaction between a solvent and a complex mix-ture of oxides affects the possibility of formation of someinsoluble reaction products. Agitation may help prevent theiradherence to the glass. Additionally, the reagent
33、itself ispotentially a “residue.”5.5.2 Reaction with the glass may also leave a roughenedsurface (selective reaction with certain glass components),streaks (selective reaction with nonhomogeneous “cords”), orwith latent grinding marks hidden by a previous polishing step.6. Detergents6.1 Surface Acti
34、ve Agents:6.1.1 Surface active agents accelerate the cleaning action ofaqueous solutions and provide mechanisms of cleaning thatwater does not have by itself. Many compounds are available,usually under trade names that give no hint of their chemicalnature. Selection of the best compound for a partic
35、ular use isusually a matter of experimentation, since the available litera-ture gives few clues to aid in prediction.6.1.2 Generally, however, such “agents” consist of long-chain organic molecules, one end of which is attracted to thesoil or the substrate, or both, the other end of which is “waterso
36、luble.” They “wet” the glass surface by lowering the surfacetension of water; thus decreasing the contact angle betweensolvent and glass and between solvent and soil. The net effectis that the particle or oily film is dislodged. They “surround”the particle or droplet to suspend or emulsify and preve
37、nt itsredeposition.6.1.3 The activity of surface active agents is usually en-hanced by the blending of two or more and by the addition ofnon-surface active agents (called “builders”). A compoundwith good emulsification will be blended with a good wetter,and built with a polyphosphate for water softe
38、ning, dispersion,and micelle formation. EDTA and similar compounds are usedfor water softening and solubilization of inorganic compounds,soda ash, and ammonia for pH regulation and sodium silicatesfor achieving high alkalinity while inhibiting attack on theglass.TABLE 2 Threshold Limit Values for So
39、me Common SolventsTLV, ppmA1,1,2-trichloro-1,2-trifluorethane 1000Acetone 750Ethyl alcohol 1000n-Hexane 50Isopropyl alcohol 400Methyl chloroform 350Perchloroethylene 50Trichloroethylene 50Methylene chloride 100Carbon tetrachloride 5AThe TLV values establish parts per million by volume of solvent vap
40、ors allowedin air for a normal work week of8haday,5days a week. These are standards setby theAmerican Conference of Governmental Industrial Hygienists, and the valuesshown in this table were effective in 19841985. The most recent recommendedvalues should be consulted in “TLVsRThreshold Limit Values
41、for ChemicalSubstances and Physical Agents in the Work Environment and Biological Expo-sure Indices with Intended Changes for 19841985,” published by ACGIH, 6500Glenway Ave., Bldg D-5, Cincinnati, OH 45211.C912 93 (2013)36.1.4 The builders can either promote or inhibit solution ofglasses, depending
42、on whether the reaction products or thebuilder and the glass components are soluble or insoluble.Polyphosphates and EDTA, in particular, will chelate with andsolubilize metallic ions, promoting a preferential leaching andleaving a porous or etched surface on the glass.6.1.5 Water-soluble surface act
43、ive agents are usually long-chain organic molecules with a hydrophobic end and a hydro-philic end. The ionic nature of the hydrophilic end determinesthe broad basic classification of the materialif negative, it isanionic, if positive, cationic, and if the material is not ionized,it is nonionic. Ther
44、e are a few amphoteric materials available,and these hybrids can be either cationic or anionic, dependingon the pH of the solution.6.2 Anionic AgentsThe oldest, and one of the most effec-tive anionic detergents if used in “soft” water, is soap. Thelargest class of synthetic anionic detergents is the
45、 sulfonatedhydrocarbons such as sodium dodecyl benzene sulfonate.Sulfated alcohols and polyethers, such as sodium lauryl sulfate,are also used extensively.6.3 Cationic AgentsThe cationic detergents are usuallyquaternary ammonium salts. The classic cation active surfaceactive agent has an aryl group,
46、 a long-chain alkyl group, andtwo methyl groups bonded to the nitrogen atom. The cationicsare not usually found in glass-cleaning detergents, probablybecause they might be adsorbed, causing difficulty in rinsing.6.4 Nonionic AgentsThe nonionics are usually producedby ethoxylating various base molecu
47、les with ethylene oxide.The ethylene oxide adduct of nonyl or isooctyl phenol is themost popular of these. Water solubility, oil solubility,detergency, surface tension reduction, and other characteristicscan be adjusted by the length of the ethoxy chain, which is atthe hydrophilic end of the molecul
48、e.6.5 Amphoteric CompoundsThe amphoterics are usuallyamine sulfonates, and have not had as broad use as the anionicsand nonionics, probably because of the greater cost of produc-ing them.6.6 Other AdditivesAdditives that enhance the cleaningaction of organic solvents have not received as much attent
49、ionas water-soluble additives. The dry cleaning industry usescoupling agents and water-in-oil emulsifiers to incorporatewater in solvents for the purpose of removing water-solublesolids from fabrics; detergents have been developed for lubri-cating oils; and amines are used to accelerate the action of paintstrippers; but otherwise there are few such materials commer-cially available.6.7 ResiduesAll detergent compounds could potentiallyleave residues. Cationic detergents are the most likely to be aproblem since they can readily bond to the surface. An acidrinse wi
