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发表于 2006-7-12 13:55:51
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IEC62321+ W( G! z8 Z/ [- S+ d7 x' S
9.7.2 Boiling-water-extraction procedure7 _% \. ^; I% K3 o6 Y# {8 G$ P% e
a) The sample to be tested shall have a surface area of (50±5) cm2. For small parts, such asfasteners, or samples with irregular surface shapes, use a suitable number of samples to
! t' J K$ T# i. z+ g. P8 ^get the total required surface area of (50±5) cm2.
/ P4 s8 p: |$ k8 s. Z9 cb) Heat in a suitable beaker (with volume graduation) 50ml of DI water to boiling and totally4 w& \1 x5 Y- \! ^" E: i
immerse the sample(s) inside the beaker. Leach for exactly 5 minutes while the water
/ ?; h2 g! ^6 @. `8 |9 T9 @continues to boil. Remove the sample(s), and cool the beaker and its content to room, d( A% h( s$ @4 H
temperature. Fill up with DI water to 50ml if some water evaporated. If the solution is milky! ~* M# B% P3 V" o
or has a precipitate, filter it through a paper filter (0.45μm pore size) into a dry beaker. F2 l9 l7 s% y4 v; q
Add 1ml of orthophosphoric acid solution (9.5 e) and mix well. Pour half the solution into. }, e4 e9 K& s8 }/ h0 b
another dry beaker. Add 1ml test solution (9.7.1. a) to one of the two beakers, mix and
: F9 s" x o1 [% R2 o4 z5 j6 @observe the color against the other beaker which serves as the blank. A red color
% _# }+ w0 w9 g0 _! Nindicates the presence of Cr (VI
$ @. ^6 C( E, N- Y# d. W. U' l! jc) If the color developed during the test is difficult for the analyst to judge, transfer a portion
+ A! V! l4 ^( W& \of the solution to an absorption cell. After a reaction time of 2 minutes, measure thebbs
3 V9 K5 v# P( \7 Dabsorbance in a colorimetric equipment against the blank.- y; t( t% K; F; H
d) Dilute 1ml of 1mg/kg K2Cr2O7 standard solution (9.5 b) to 50ml with DI water. Add 1ml of0 p- ^; V3 c$ z0 C; x2 c. ^
orthophosphoric acid solution (9.5 e) and mix well. Add 2ml test solution (9.7.1 a), mix and0 @ b! q; F9 k4 q1 b4 x S
measure the absorbance as above.9 g& z+ w2 N4 ~2 x! A0 p+ o
e) If the absorbance value obtained in 9.7.2 c) is equal to, or greater than that obtained in2 `+ }7 g' X: b, g
9.7.2 d), the sample is considered to have a hexavalent chromium coating. If not, the testbbs
0 [; s: i# ?/ o/ x. ]% X, s1 Oresult is negative. The detection limit for the boiling-water-extraction test is 0.02mg/kg
# l: R t9 V4 |, l# ?with 50cm2 sample surface area used. |
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发表于 2006-7-11 09:49:34
