GB/T 20975.29-2019 PDF English
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Methods for chemical analysis of aluminium and aluminium alloys -- Part 29: Determination of molybdenum content -- Thiocyanate spectrophotometry
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GB/T 20975.29-2019: PDF in English (GBT 20975.29-2019) GB/T 20975.29-2019
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.120.10
H 12
Methods for chemical analysis of aluminium and
aluminium alloys - Part 29: Determination of
molybdenum content - Thiocyanate spectrophotometry
ISSUED ON: JUNE 04, 2019
IMPLEMENTED ON: MAY 01, 2020
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 6
2 Normative references ... 6
3 Method summary ... 6
4 Reagents ... 7
5 Instruments ... 8
6 Sample ... 8
7 Analysis steps ... 8
8 Calculation of analysis result ... 10
9 Precision ... 10
10 Quality assurance and control ... 11
11 Test report ... 11
Foreword
GB/T 20975, Methods for chemical analysis of aluminium and aluminium alloys,
is divided into 31 parts:
-- Part 1: Determination of mercury content;
-- Part 2: Determination of arsenic content;
-- Part 3: Determination of copper content;
-- Part 4: Determination of iron content - Orthopenanthroline photometric
method;
-- Part 5: Determination of silicon content;
-- Part 6: Determination of cadmium content - Flame atomic absorption
spectrometric method;
-- Part 7: Potassium periodate spectrophotometric method;
-- Part 8: Determination of zinc content;
-- Part 9: Determination of lithium content - Flame atomic absorption
spectrometric method;
-- Part 10: Determination of tin content;
-- Part 11: Determination of tin content;
-- Part 12: Determination of titanium content;
-- Part 13: Determination of vanadium content - N-bezoyl-
Nphenylhydroxylamine spectrophotometric method;
-- Part 14: Determination of nickel content;
-- Part 15: Determination of boron content;
-- Part 16: Determination of magnesium;
-- Part 17: Determination of strontium content - Flame atomic absorption
spectrometric method;
-- Part 18: Determination of chromium content;
-- Part 19: Determination of zirconium content;
Methods for chemical analysis of aluminium and
aluminium alloys - Part 29: Determination of
molybdenum content - Thiocyanate spectrophotometry
Caution -- The personnel who uses this Part shall have hands-on
experience in formal laboratory work. This Part does not address all
possible security issues. It is the responsibility of the user to take
appropriate safety and health measures and to ensure compliance with
the conditions which are set by the relevant national regulations.
1 Scope
This Part of GB/T 20975 specifies the method for the determination of
molybdenum content in aluminum and aluminum alloys by thiocyanate
spectrophotometry.
This Part applies to the determination of molybdenum content in aluminum and
aluminum alloys. Determination range: 0.005% ~ 12.0%.
2 Normative references
The following documents are indispensable for the application of this document.
For dated references, only the dated version applies to this document. For
undated references, the latest edition (including all amendments) applies to this
document.
GB/T 6682, Water for analytical laboratory use. Specification and test
methods
GB/T 8170-2008, Rules of rounding off for numerical values & expression
and judgement of limiting values
3 Method summary
Dissolve the sample in acid; use sodium hydroxide sediment to separate most
of the elements such as iron, copper, cobalt, nickel, and rhodium; use citric acid
to cover tungsten. In the sulfuric acid medium, use iron sulfate as a catalyst;
use ascorbic acid and thiourea to reduce molybdenum (VI) to molybdenum (V);
make molybdenum and thiocyanate form a colored complex; measure the
absorbance at a wavelength of 460 nm of a spectrophotometer, so as to
calculate the molybdenum content.
4 Reagents
Unless otherwise stated, in the analysis, only use analytical reagent and grade-
2 water in accordance with GB/T 6682.
4.1 Hydrochloric acid (ρ = 1.19 g/mL).
4.2 Nitric acid (ρ = 1.42 g/mL).
4.3 Hydrofluoric acid (ρ = 1.15g/mL).
4.4 Sodium hydroxide solution (400 g/L).
4.5 Sodium hydroxide solution (40 g/L).
4.6 Sulfuric acid (1+1).
4.7 Citric acid solution (500 g/L).
4.8 Potassium thiocyanate solution (500 g/L).
4.9 Ascorbic acid solution (100 g/L), prepare when necessary.
4.10 Thiourea solution (80 g/L).
4.11 Ferric sulfate solution: weigh 0.100 0 g of metallic iron; place it in a beaker;
add 15 mL of sulfuric acid (4.6); heat to completely dissolve; cool; transfer to a
1 000 mL volumetric flask; use water to dilute to the mark; mix well. 1 mL of this
solution contains 100 μg of iron.
4.12 Molybdenum standard stock solution: weigh 1.839 8 g of ammonium
molybdate in a beaker; place it in a 100 mL beaker; use a small amount of water
to dissolve; transfer it to a 1 000 mL volumetric flask; use water to dilute to the
mark; mix well. 1 mL of this solution contains 1 000 μg of molybdenum.
4.13 Molybdenum standard solution A: pipette 10.00 mL of molybdenum
standard stock solution (4.12) into a 200 mL volumetric flask; use water to dilute
to the mark; mix well. 1 mL of this solution contains 50 μg of molybdenum.
4.14 Molybdenum standard solution B: pipette 20.00 mL of molybdenum
standard solution (4.13) into a 100 mL volumetric flask; use water to dilute to
the mark; mix well. 1 mL of this solution contains 10 μg of molybdenum.
immediately use water for cooling; then, add 0.5 mL of ferric sulfate solution
(4.11), 2 mL of potassium thiocyanate solution (4.8), 2 mL of ascorbic acid
solution (4.9), 1 mL of thiourea solution (4.10); immediately shake well when
each reagent is added. Use water to fix volume; mix well; place for 30 min.
7.4.3 When the molybdenum content is >1.0% ~ 12.0%, dry-filter the test
solution; transfer 10.00 mL of the filtrate and place in a 100 mL volumetric flask;
use sodium hydroxide solution (4.5) to fix volume; mix well. Transfer 10.00 mL
(V) of the diluted filtrate into a 25 mL volumetric flask; add 1 mL of citric acid
solution (4.7); shake well; add 6 mL of sulfuric acid (4.6); immediately use water
for cooling; then, add 0.5 mL of ferric sulfate solution (4.11), 2 mL of potassium
thiocyanate solution (4.8), 2 mL of ascorbic acid solution (4.9), 1 mL of thiourea
solution (4.10); immediately shake well when each reagent is added. Use water
to fix volume; mix well; place for 30 min.
7.4.4 Transfer some of the solution into the corresponding absorption dish
(consistent with the working curve); use water as the reference; measure the
absorbance at 460 nm of the spectrophotometer; subtract the blank absorbance
of accompanied sample; find the corresponding molybdenum mass (m1) from
the working curve.
7.5 Drawing of the working curve
7.5.1 Working curve 1: applicable to molybdenum content of 0.005% ~ 0.10%
Pipette 0 mL, 0.20 mL, 0.50 mL, 1.00 mL, 2.00 mL, 3.00 mL, 5.00 mL of
molybdenum standard solution (4.14); respectively place in the 25 mL
volumetric flasks; add sodium hydroxide solution (4.5) to 10 mL; perform the
following according to 7.4.2; pipette some of the solution in a 2 cm absorption
dish; use water as the reference; measure the absorbance at 460 nm of the
spectrophotometer. Take the molybdenum mass as the abscissa and the
absorbance as the ordinate to draw the working curve.
7.5.2 Working curve 2: applicable to molybdenum content of >0.10% ~ 12.0%
Pipette 0 mL, 0.40 mL, 1.00 mL, 1.50 mL, 2.00 mL, 3.00 mL, 5.00 mL of
molybdenum standard solution (4.13); respectively place in the 25 mL
volumetric flasks; add sodium hydroxide solution (4.5) to 10 mL; perform the
following according to 7.4.2; pipette some of the solution in a 0.5 cm absorption
dish; use water as the reference; measure the absorbance at 460 nm of the
spectrophotometer. Take the molybdenum mass as the abscissa and the
absorbance as the ordinate to draw the working curve.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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