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发表于 2006-7-12 13:55:51
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来自： 中国
IEC62321& A6 [# S, [( J: m
9.7.2 Boiling-water-extraction procedure$ k6 q# M' Y" C9 T7 |0 y" l
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" q/ ~: O5 Q& m. _- m! c
get the total required surface area of (50±5) cm2." q: p% ]* j2 d- S7 u. S$ I9 J
b) Heat in a suitable beaker (with volume graduation) 50ml of DI water to boiling and totally
9 N6 S/ v2 H+ y# G4 Z3 v5 \5 }1 ^immerse the sample(s) inside the beaker. Leach for exactly 5 minutes while the water
6 v( h4 r( R$ M- d$ ccontinues to boil. Remove the sample(s), and cool the beaker and its content to room7 g; {; X) Q; \( m X* ~
temperature. Fill up with DI water to 50ml if some water evaporated. If the solution is milky; \. _& K7 X+ _' T7 k( [$ Q
or has a precipitate, filter it through a paper filter (0.45μm pore size) into a dry beaker
+ [- K1 E; _& c* P2 HAdd 1ml of orthophosphoric acid solution (9.5 e) and mix well. Pour half the solution into6 p! v! H) [0 M& L& b
another dry beaker. Add 1ml test solution (9.7.1. a) to one of the two beakers, mix and+ @ h& D# M1 M) |
observe the color against the other beaker which serves as the blank. A red color
7 U6 k# g7 M* o( ?/ Windicates the presence of Cr (VI
4 a6 k7 h8 W, Jc) If the color developed during the test is difficult for the analyst to judge, transfer a portion
" |4 h2 w D/ G) Tof the solution to an absorption cell. After a reaction time of 2 minutes, measure thebbs( S% X3 V0 W! t6 S( n
absorbance in a colorimetric equipment against the blank.5 T6 ]: p: I6 [! s2 m3 O3 } k; x, x6 G
d) Dilute 1ml of 1mg/kg K2Cr2O7 standard solution (9.5 b) to 50ml with DI water. Add 1ml of$ ^* w% D9 R0 `% P* U; P0 [) R1 d
orthophosphoric acid solution (9.5 e) and mix well. Add 2ml test solution (9.7.1 a), mix and
& v# j% V) w7 d6 P8 `$ |- ~6 Omeasure the absorbance as above.# y# [/ n7 ]; K
e) If the absorbance value obtained in 9.7.2 c) is equal to, or greater than that obtained in
, D' p# ]3 i: r! Q, r2 f9.7.2 d), the sample is considered to have a hexavalent chromium coating. If not, the testbbs
5 j! M1 M7 _- [7 s- m }" bresult is negative. The detection limit for the boiling-water-extraction test is 0.02mg/kg
' R& \6 N$ t3 F! qwith 50cm2 sample surface area used. |
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发表于 2006-7-11 09:49:34
