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发表于 2006-7-12 13:55:51
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来自： 中国
IEC62321' P) }0 ]7 C& E0 h# I8 i9 }# O
9.7.2 Boiling-water-extraction procedure5 u, e& z1 }2 }+ V. @- 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/ s" \$ L0 Z1 t1 L/ y5 C
get the total required surface area of (50±5) cm2.
# D0 d6 d# Z; Lb) Heat in a suitable beaker (with volume graduation) 50ml of DI water to boiling and totally
0 ?) r, [6 d3 U5 {3 z' _immerse the sample(s) inside the beaker. Leach for exactly 5 minutes while the water
4 }' u8 ~- Z/ ~ _' \continues to boil. Remove the sample(s), and cool the beaker and its content to room* g9 ~! B: Z7 Y/ f
temperature. Fill up with DI water to 50ml if some water evaporated. If the solution is milky
, y6 P9 \# x9 h$ {7 g0 c" _' y( Bor has a precipitate, filter it through a paper filter (0.45μm pore size) into a dry beaker; x6 R- j5 r) u2 G/ P! @! N
Add 1ml of orthophosphoric acid solution (9.5 e) and mix well. Pour half the solution into# [- a0 |7 t/ ^* k6 ^8 a1 z, M
another dry beaker. Add 1ml test solution (9.7.1. a) to one of the two beakers, mix and& u" y/ i, S- m
observe the color against the other beaker which serves as the blank. A red color
% J [2 m! D- @! Vindicates the presence of Cr (VI
+ z9 N" o' P+ d7 B- @2 N7 c7 Hc) If the color developed during the test is difficult for the analyst to judge, transfer a portion
& F: H6 ^ j' D! U M" Jof the solution to an absorption cell. After a reaction time of 2 minutes, measure thebbs' u3 K% I- a$ y) G" s% m1 [
absorbance in a colorimetric equipment against the blank.& X( v5 l% G- V( u' ]& Z% h8 n
d) Dilute 1ml of 1mg/kg K2Cr2O7 standard solution (9.5 b) to 50ml with DI water. Add 1ml of' i/ p3 d9 m1 T1 o- Y: G+ u
orthophosphoric acid solution (9.5 e) and mix well. Add 2ml test solution (9.7.1 a), mix and
) u, K9 X2 ]! Z5 Tmeasure the absorbance as above.
6 x2 H/ l6 Y& ?* r. h$ ~: v7 b6 ve) If the absorbance value obtained in 9.7.2 c) is equal to, or greater than that obtained in1 b0 a- l2 M$ e! z+ b" s% X
9.7.2 d), the sample is considered to have a hexavalent chromium coating. If not, the testbbs* b. @1 t0 e# P% d
result is negative. The detection limit for the boiling-water-extraction test is 0.02mg/kg
% Z; x2 ~# ?. P% D- W$ ^with 50cm2 sample surface area used. |
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发表于 2006-7-11 09:49:34
