1、Designation: C282 10Standard Test Method forAcid Resistance of Porcelain Enamels(Citric Acid Spot Test)1This standard is issued under the fixed designation C282; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.INTRODUCTIONThe described method furnishes a means of test
3、ing and grading glossy porcelain enamels withrespect to their resistance to citric acid at room temperature. Citric acid has been selected because itis the most common and one of the more severe of the food acids in its action on conventionalporcelain enamels. The degree of etching by a citric acid
4、solution provides a good indication of thesusceptibility of attack of a porcelain enamel coating to common food-based acids.1. Scope1.1 This test method covers a procedure for evaluatingporcelain enamels in their resistance to citric acid exposure atroom temperature. No attempt is made to categorize
5、 porcelainenamels as to their acid-resistance or non acid-resistanceproperties, since the requirements in the several branches of theindustry differ.1.2 The test method is applicable for ware of various shapesproviding they contain a substantially flat area approximately50 mm in diameter.1.3 The tes
6、t method is not applicable to finishes on chemicaland hospital ware, which may come in contact with strongmineral acids, nor to cooking utensils, which may come inprolonged contact with hot acid solutions.1.4 This standard does not purport to address all of thesafety concerns, if any, associated wit
7、h 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 use.2. Summary of Test Method2.1 The test method consists of a 15 min exposure of the testsurface to a small pool
8、of 10 % citric acid, and an evaluation ofthe effect in terms of the change in appearance and the “relativecleanability” of the surface resulting from the treatment.3. Significance and Use3.1 This test method is intended specifically for testing theporcelain enamel finish on stoves, refrigerators, ta
9、ble tops,sinks and other sanitary ware, laundry appliances, architecturalunits, etc., where the surface may come in contact with foodacids at room temperature.3.2 Citric acid has been chosen as the test medium becauseit is one of the most common of the food acids and willgenerally provide a measurab
10、le result in its action on porcelainenamel.4. Apparatus4.1 Dropper Bottle, or medicine dropper,4.2 Watch Glass, 25 mm in diameter with fire polished edge,4.3 Towel, soft cotton, and4.4 Drafting Pencil, conventional graphite, degree 3B.5. Reagents and Materials5.1 Citric Acid SolutionDissolve 10 g of
11、 anhydrous citricacid crystals (H3C6H5O7) in 100 mL of water. Solution shall beprepared not more than 48 h prior to use.5.2 Cleaner SolutionDissolve 10 g of trisodium phos-phate (Na3PO4) in 1 L of tap water.6. Sampling6.1 The test specimens may be articles of commerce, piecescut from articles of com
12、merce, or laboratory specimens pre-pared especially for this test.NOTE 1Processing variables in the application and drying and firingoperations materially affect the degree of attack by the acid on the surfaceof porcelain enamels. Sample specimens used for classification of acidresistance must be pr
13、ocessed under identical conditions to the commercialware they represent.1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.12 onMaterials for Porcelain Enamel and Ceramic-Metal Systems.Current editio
14、n approved April 1, 2010. Published May 2010. Originallyapproved in 1951. Last previous edition approved in 2005 as C282 99(2005). DOI:10.1520/C0282-10.This test method is based on the Test for Acid Resistance of Porcelain Enamels(Citric Acid Spot Test) Bulletin T-21, of the Porcelain Enamel Institu
15、te.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7. Procedure7.1 Thoroughly wash area to be tested using a soft cottontowel moistened with a warm, 1 % solution of trisodiumphosphate. Rinse in warm, running tap water, and dry with a
16、soft towel by blotting. Store the specimen at a temperature of26 6 1C (79 6 2F) for a time sufficient to bring it within thisrange prior to and during the test.NOTE 2If, when rinsing, the water gathers in drops on the surface,repeat washing treatment until water spreads evenly.7.2 On articles of com
17、merce, select areas that are horizontalor nearly horizontal in service. Place the specimen in a positionsuch that a flat area at least 38.1 mm in diameter is horizontal.With the specimen and the citric acid solution at 26 6 1C (796 2F), place several drops of the solution on the test area toform a p
18、ool, and immediately cover with a clean watch glass inthe inverted position. Use a quantity of solution that is justsufficient to fill the inverted watch glass except for a small airbubble (three to six drops are usually required, depending uponthe dropper and the curvature of the watch glass). Afte
19、r 15 minof treatment, remove the watch glass and immediately rinse thespot of solution from the surface. Dry the specimen with a dry,clean, soft cotton towel by blotting (not rubbing).NOTE 3The test surface must be thoroughly dry before grading. Thepresence of a slight film of water on the surface m
20、ay change the rating ofspecimens near the borderline between classes.8. Grading8.1 Grade the test specimen within 2 h after exposure to thetest solution using the procedure outlined in the diagram, Fig.1. Rate each specimen with the appropriate classification grade,AA, A, B, C or D, as explained in
21、Table 1. The criteria referredto in Fig. 1 and Table 1 are described as follows:8.1.1 Visual ExaminationView the specimen at variousangles with respect to the light source and eye, in order todetect whether the “treated area” differs in any respect from the“protected area.” Use partially diffused da
22、ylight, supplementedif necessary by artificial light, the total intensity being approxi-mately that available within a few feet of an outside window,but do not examine in direct sunlight. During observation, holdthe specimen no nearer the light source (such as a window)than the minimum diameter of t
23、he source.NOTE 4The term “treated area” refers to that portion of the specimenwhich has been subjected to acid solution confined by the watch glassduring treatment. The term “protected (untreated) area” refers to the areaadjacent to the treated area.NOTE 5Some colored porcelain enamels exhibit a cha
24、nge in color asa result of the acid treatment. Since the test is designed primarily toevaluate durability, color changes as revealed by this test should beignored except where otherwise specified.8.1.2 Dry-Rubbing TestUsing the flat point of a degree3B, conventional graphite drafting pencil held in
25、a normalwriting position and applied with firm pressure, draw two ormore approximately parallel lines extending across the treatedarea. Starting with gentle pressure and then applying graduallyincreasing pressure, rub repeatedly across the lines with a dry,clean, soft cotton towel as illustrated in
26、Fig. 2. If marks arecompletely removed from the treated area, the specimen shallbe rated as Class AA. Otherwise, continue as directed.NOTE 6The pencil point should be prepared by holding a sharpenedpencil in a normal writing position and rubbing on abrasive paper (1/0Emery polishing or 400-grit sili
27、con carbide or aluminum oxide abrasivepaper) until the minimum diameter of the flat, circular cross section is halfthat of the full graphite core.8.1.3 Blurring-Highlight TestIn a well-lighted location,hold the specimen so that the image of a small light source,such as a frosted lamp bulb, is observ
28、ed as a highlight in theprotected area, the line of vision being within 45 perpendicu-lar to the surface (a desk lamp with an incandescent bulb isrecommended for this purpose). Focus the eyes on the image ofthe light source, then slowly shift the specimen just sufficientlyto bring this image into th
29、e treated area observing it as it passesFIG. 1 Flow Sheet of Test Procedure for Classification of Treated SpecimensTABLE 1 Requirements for Respective Classes of AcidResistanceClassification RequirementsClass AA No visible stain, andPass dry-rubbing testClass A Pass blurring-highlight test, andPass
30、wet-rubbing testClass B Pass blurring-highlight test, andFail wet-rubbing testClass C Fail blurring-highlight test, andPass disappearing-highlight testClass D Fail disappearing-highlight testC282 102across the boundary line between the two areas. Ignore anycolor difference in the enamel due to stain
31、ing. If a definiteblurring of the image is observed as it passes from theprotected to the treated area, the specimen shall be rated asClass C or Class D. Proceed to 8.1.5 to determine finalclassification. If a blurring image is not observed, the specimenshall be rated as Class A or Class B. Proceed
32、to 8.1.4 todetermine final classification.8.1.4 Wet-Rubbing TestUsing the procedure specified in8.1.2 mark the treated area and rub the marks with a clean, softcotton towel which has been dipped in water and twisted toremove any excess. For this test, make new marks in a locationother than that used
33、 for the dry-rubbing test. Do not use soap,abrasive, or similar cleaning material. If the marks are com-pletely removed from treated area, the specimen shall be ratedas Class A. Otherwise it shall be rated as Class B.8.1.5 Disappearing-Highlight TestThis test is similar inall respects to the blurrin
34、g-highlight test specified in 8.1.3,except that the criterion in this case is the complete disappear-ance of the highlight in the treated area. If the highlight isvisible in the treated area, the specimen shall be rated as ClassC. If the highlight disappears in the treated area, the specimenshall be
35、 rated as Class D.9. Report9.1 Report the assigned grade for each specimen. If thecitric acid treatment is performed at temperatures outside thestated tolerances, this variation should be reported.10. Reproducibility10.1 Since variations may occur during enameling whichaffect the acid resistance, se
36、veral specimens should be treatedto determine the class of commercial ware.10.2 Ratings of individual specimens shall be considered asdue to actual differences in the acid resistance of the speci-mens, not to differences in the test procedure.11. Precision and Bias11.1 The precision and bias of this
37、 test method is beingestablished.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof
38、 infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this s
39、tandard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake you
40、r views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by con
41、tacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).FIG. 2 Method of Applying and Rubbing Pencil Marks on theTreated AreaC282 103
