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1、INTERNATIONAL STANDARD IS0 7529 First edition 1989-10-15 Nickel alloys - Determination of chromium content - Potentiometric titration method with ammonium iron sulfate Alliages de nickel - Dosage du chrome - M V, is the volume, in millilitres, of ammonium iron sulfate solution used for the titration
2、. 5 Apparatus Ordinary laboratory apparatus and 5.1 Potentiometric titration apparatus 5.1.1 indicator electrode, of bright platinum, which shall be kept in a clean, highly polished condition. It shall be cleaned by dipping in the nitric acid (4.3) or aqua regia and rinsed with water prior to use. 5
3、.1.2 Reference electrode, of silver/silver chloride, calomel or mercury(l) sulfate. The manufacturer s instructions on the care and maintenance of these electrodes shall be followed. 5.1.3 Titration assembly, consisting of a 400 ml beaker, two 50 ml burettes complying with the requirements of IS0 38
4、5-1, class A, and a magnetic stirrer. 5.1.4 High-impedance electronic voltmeter : Normally a pH meter can be used as a voltmeter. Commercial automatic titrators or potentiographs have an advantage over manual systems in that the titration curve is plotted and the end-point can be evaluated by interp
5、olation of the curve rather than by calculation from the first or second derivative. See 10.1. 5.2 Volumetric glassware 5.2.1 Burette, of capacity 50 ml, graduated in 0,l ml div- isions, complying with the requirements of IS0 385-1, class A. 5.2.2 One-mark pipettes, complying with the requirements o
6、f IS0 648, class A. 5.2.3 One-mark volumetric flasks, complying with the re- quirements of IS0 1042, class A. 6 Sampling and sample preparation 6.1 Sampling and preparation of the laboratory sample shall be carried out by normal agreed procedures or, in case of dispute, by the relevant International
7、 Standard. 6.2 The laboratory sample is normally in the form of millings or drillings and no further preparation of the sample is necessary. 6.3 If it is suspected that the laboratory sample is con- taminated with oil or grease from the milling or drilling process, it shall be cleaned by washing wit
8、h high-purity acetone and dried in air. 6.4 If the laboratory sample contains particles or pieces of widely varying sizes, the test sample should be obtained by riffling. 7 Procedure 7.1 Preparation of the test solution 7.1.1 Weigh a test portion containing between 20 mg and 80 mg of chromium accord
9、ing to table 1 and transfer to a 400 ml or 600 ml tall-form beaker. Table 1 - Mass of sample to be taken Expected chromium Mass of sample Weighing content % (m/m! accuracy a a 7.1.2 Add 20 ml of the nitric/hydrochloric acid mixture (4.7) and heat until the sample is dissolved. If the alloy resists d
10、issolution, add the hydrochloric acid (4.1) in 1 ml increments and continue heating to dissolve the sample. For some alloys, an acid mixture containing 30 ml of hydrochloric acid and 2 ml of nitric acid is more effective. 2 Copyright International Organization for Standardization Provided by IHS und
11、er license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 19:44:47 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7529 : 1989 (El NOTE - If the laboratory sample consists of large pieces, a 1 g test portion may be taken for chromium
12、levels higher than 10 %(mlm). The solution should be transferred to a 100 ml one-mark volumetric flask and a test portion of 50 ml for IO % (m/m) to I5 % (m/m) chromium or 25 ml for 15 % (m/m) to 30 % (m/m) chromium taken, using a pipette, and processed as in 7.1.3. 7.1.3 Add 20 ml of the sulfuric a
13、cid diluted 1 + 1 (4.4) and evaporate to fumes. Cool slightly, add 100 ml of hot water and boil until the residue is dissolved. 7.1.4 Dilute the solution to 200 ml, add a piece of porous porcelain or boiling chip and heat to boiling. Add 5 ml of the silver nitrate solution (4.5) and 5 g of ammonium
14、peroxy- disulfate (4.6). Boil gently for 15 min to oxidize the chromium completely to chromium(W). This is indicated by a pink colour which persists for about IO min if the manganese content of the sample is significant. For a sample with a very high chromium content associated with a low manganese
15、content, add a few drops of potassium permanganate solution (IO g/l) to supply this indication of complete oxidation. 7.15 Add 5 ml of the hydrochloric acid diluted 1 + 3 (4.2) and continue boiling for a further 5 min, when all the pink per- manganate colour should disappear. If the permanganate col
16、- our persists after boiling for the further 5 min, add 5 ml more of the hydrochloric acid and boil again for 5 min. Repeat, if necessary, until the permanganate colour is completely re- moved. 7.1.6 Cool the solution to room temperature and titrate potentiometrically with the ammonium iron(h) sulfa
17、te solution (4.9) as specified in 7.2. 7.2 Determination Place the beaker containing the test portion on the stirrer of the titration apparatus (5.1). Insert the indicator electrode (5.1. I) and reference electrode (5.1.2) and connect to the electronic voltmeter (5.1.4). Switch on the stirrer and ti
18、trate with the am- monium iron solution (4.9). Add the titrant fairly rapidly until the end-point is approached. Continue the titration in 0,l ml or one drop increments and record the burette and potential readings when equilibrium is reached after each incremental ad- dition. Continue the titration
19、 through the end-point. Determine the end-point by interpolation or from the titration curve (see 10.1). 7.3 Blank test Carry out a blank test in parallel with the determination, by the same procedure, using the same reagents as in the determi- nation. 7.4 Number of determinations Carry out the dete
20、rmination at least in duplicate. 8 Expression of results 8.1 Method of calculation The chromium content, expressed as a percentage by mass, is given by the formula IV3 - vo, x c x 0,01733 x 100 m where Vc is the volume, in millilitres, of the ammonium iron sulfate solution (4.9) used in the blank te
21、st; Vs is the volume, in millilitres, of the ammonium iron sulfate solution used in the determination; c is the actual concentration, expressed in moles of (NH 0,017 33 is the mass, in grams, of chromium correspond- ing to I,00 ml of ammonium iron sulfate solution, c (NH4)2Fe(S04)21 = 1,000 mol/l; m
22、 is the mass, in grams, of the test portion. 8.2 Precision 8.2.1 Laboratory tests Fourteen laboratories in six countries participated in the inter- laboratory testing of methods for the analysis of nickel alloys. Of these, ten reported a complete set of results for this Inter- national Standard. Six
23、 samples of nominal composition given in table 2 were analysed in duplicate on different days, Table 2 - Nominal composition of test samples % (m/m)1 Sample reference 825 902 3 920 3 927 7 013 7049 Al co Cr 02 0,07 21 0,4 0,05 5 0,15 2 19 0.1 I 20 I,5 17 20 1 0,Ol 15 cu Fe 1.6 30 0,04 48 O,l 3 0,05
24、44 02 02 0,15 7 Mn Ni Si Ti 0,7 Remainder 0,4 I,1 0,4 Remainder 0.35 25 0,3 Remainder 6 3 2,s 0.4 Remainder 0.8 3.6 0.05 Remainder 0,7 24 3.8 Remainder 0,3 2,3 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/997254
25、5001 Not for Resale, 04/26/2007 19:44:47 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7529 : 1989 (E) 8.2.2 Statistical analysis 8.2.2.1 Results from the inter-laboratory test programme were evaluated according to IS0 5725, using the means of the duplicate results. T
26、he data were tested for statistical outliers by the Cochran and Dixon tests given in IS0 5725. 8.2.2.2 The principle of the Cochran test is that a set of results is an outlier if the within-laboratory variance is too large in relation to others. Dixon s test is to determine if the mean from a labora
27、tory is too far from the other laboratory means. Both tests were applied at the 95 % confidence level. 8.2.2.3 Repeatability and reproducibility were calculated ac- cording to IS0 5725 at the 95 % confidence level. Results of the statistical analysis are given in table 3. 8.2.2.4 For sample 825, one
28、 laboratory was rejected as both a Cochran and a Dixon outlier and two laboratories were rejected as Cochran outliers. For samples 3920 and 7049, one laboratory in each was rejected as a Cochran outlier. However, all of these results could be classified as statistical stragglers and would not have b
29、een rejected at the less critical test level given in IS0 5725. 9 Special cases : Alloys containing vanadium Vanadium, if present in the alloy, causes a positive bias in the results for chromium. The ratio of the milliequivalent weights of chromium to vanadium is 0,340. Therefore, if the vanadium co
30、ntent is known, a correction may be applied by subtracting the vanadium content multiplied by 0,340 from the chromium content. At a vanadium level of 0,2 % (m/m), this correction is 0,088 % (m/m), which is about half the reproducibility of the method and is not considered to be significant. The vana
31、dium content of nickel alloys can be determined by flame atomic absorption spectrometry. 10 Notes on procedure 10.1 Determination of the end-point 10.1.1 The accurate and reproducible evaluation of the poten- tiometric end-point differs from the normal visual end-point detection in that the titratio
32、n is normally carried out well past the equivalence point. The classical S-shaped titration curve shows a steep rise of the potential in the vicinity of the equivalence point. The mid-point of the steep portion of the curve is usually the inflection point and as such coincides with the equivalence p
33、oint for a symmetrical titration curve. For an asymmetrical titration curve where the true equivalence point does not coincide with the mid-point, the change in potential is usually large enough to make the titration error negligible. 10.1.2 Manual potentiometric titrations are slow as the equilibri
34、um potential must be established and recorded after each addition of titrant. In the vicinity of the equivalence point, the titrant must be added in small increments and at least three measurements must be taken after a large change in potential has been observed. From the data recorded, the end-poi
35、nt can be determined by plotting the titration curve and interpolating the end-point from the steep part of the curve. However, it is more desirable to calculate the first derivative (dE/d VI, which has a maximum at the equivalence point. The exact value of the end-point volume can be determined by
36、calculation of the second derivative of the potential, with respect to volume, which must be numerically equal to zero. If equal increments of titrant are added just before and after the large potential change, it is easy to see that the second derivative function changes sign between two additions.
37、 Thus, it must have pass- ed through zero at some point which is determined by inter- polation. 10.1.3 There is a great advantage in using automatic titrators which record the titration curve directly or process the data in a digital form. Such instrumentation is recommended for this International S
38、tandard. 11 Test report The test report shall include the following particulars : a) the reference of the method used; b) the results of the analysis; c) the number of independent replications; d) any unusual features noted during the analysis; e) any operation not included in this International Sta
39、n- dard or regarded as optional. Table 3 - Results of statistical analysis I% (m/m)1 Sample reference Mean 825 21.37 Within-laboratory Between-laboratory standard deviation standard deviation Repeatability Reproducibility 0,042 0,oo 0,12 0,12 902 5,17 0,051 0,oo 0.14 0,14 3 920 19,19 0,046 0,032 0.1
40、3 0,16 3 927 20,31 0,057 0,055 0.16 02 7 013 19,52 0,071 0,oo 0.20 0,20 7049 15,04 0,046 0,022 0.14 0.20 4 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 19:44:47 MDTNo reproduc
41、tion or networking permitted without license from IHS -,-,- ISO7529:1989 (E) Annex A (informative) Examples of composition of some nickel alloys The examples of composition given in table A.1 are not to be interpreted as specifications for chemical compositions. Table A.1 - Examples of composition o
42、f some nickel alloys % (mlm)ll Alloy*) Al B C Co31 Cr Cu Fe Mn MO Ni P s Si Ti Others A - - 0,30 - - 28,0 2.5 2.0 - 63,041 - 0,025 0,5 - - 34,0 B 0,15 - 14,0 0,5 60 I,0 - 72,04) - 0,015 0,5 - - 17,0 10,o C 0,4 - 0,08 - 14,0 0,5 5,O I,0 - 70,04) - 0,015 0,5 2,2 Nb plus Ta I,0 17,0 98 23 0,7 to I,2 D
43、02 0,006 0,08 - 17,0 0.3 Remainder 0,4 2,8 50,o 0,015 0,015 0,4 0,6 Nb plus Ta 03 21.0 3,3 55,0 12 4,7 to 5,5 E 0,15 - 0,lO - 19,0 0,7 Remainder I,5 - 30,o - 0,015 I,0 0,15 - 0,60 23.0 35,0 0,60 F 0,08 5,0 18,0 0,5 5,O I,0 - Remainder41 - 0,020 I,0 0,2 Pb 0,15 21 ,o 05 0,005 G 18 0,020 0,13 15.0 18,
44、0 0,2 I,5 1,o - Remainder - 0,015 I,0 2,0 Zr 28 21,0 21,0 3,O 0.15 - H 4,5 0,003 0.12 18,0 14,0 0.2 I,0 I,0 4,5 Remainder - 0,015 l,o 0,9 Zr 43 0,010 0.17 22,0 15,7 5.5 I,5 0,15 I 0,3 0,005 0,04 19,0 19,0 0,2 0,7 0,6 5,6 Remainder - 0,007 0,4 I,9 Ti plus Al 66 0,08 21,0 21,0 61 2,4 2,4 to 2,8 J 0.02
45、 I,0 l,o - zo I,0 26,0 Remainder4) 0,040 0,035 0,l - - 30.0 K 12 0,003 0,02 12.0 18,0 0,l w I,0 3,5 Remainder 0,015 0,015 0,l 2,8 Zr 18 0,010 0,lO 15,0 21,0 5.0 3.3 0,02 to 0.08 L - - 0,02 2,5 14,5 - 4,O 1,o 15.0 Remainder 0,040 0,035 0,08 - v 0.35 16,5 7,O 17.0 w 3,0 to 4,5 I) Single values are max
46、imum limits, except for nickel, where single values are minimum. 2) Alloy letters are used instead of commercial names until a neutral IS0 designation is developed. 3) Where no limits are given, cobalt is up to a maximum of 1,5 % (m/m). 4) Cobalt counts as nickel in some alloys. 5 Copyright Internat
47、ional Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 19:44:47 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7529 : 1989 (E) UDC 543.257.1 : 669.245 : 546.76 Descriptors
48、: nickel, nickel alloys, chemical analysis, determination of content, chromium, potentiometric methods. Price based on 5 pages Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 19:44:47 MDTNo reproduction or networking permitted without license from IHS -,-,-