GB/T 223.26-2008 English PDF (GB/T223.26-2008)

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GB/T 223.26-2008: Iron, steel and alloy -- Determination of molybdenum content -- The thiocyanate spectrophotometric method
GB/T 223.26-2008
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.080.01
H 11
Replacing GB/T 223.26-1989, GB/T 223.27-1994
Iron, steel and alloy - Determination of molybdenum
content - The thiocyanate spectrophotometric method
ISSUED ON: MAY 13, 2008
IMPLEMENTED ON: NOVEMBER 01, 2008
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine of PRC;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Normative references ... 4 
3 Method-1: Thiocyanate direct spectrophotometry ... 5 
4 Method-2: Thiocyanate-butyl acetate extraction spectrophotometry ... 8 
5 Test report ... 13 
Appendix A (Informative) Raw data of common precision test ... 14 
Iron, steel and alloy - Determination of molybdenum
content - The thiocyanate spectrophotometric method
Warning: Personnel who use this part shall have hands-on experience
with formal laboratory work. This part does not address all possible safety
issues. It is the responsibility of the user to take appropriate safety and
health measures and to ensure compliance with the conditions set by the
relevant national regulations.
1 Scope
This part of GB/T 223 specifies the determination of molybdenum by
thiocyanate direct spectrophotometry and thiocyanate-butyl acetate extraction
spectrophotometry.
The method-1 of this part is applicable to the determination of molybdenum
content of 0.10%~2.00% (mass fraction) in medium-and-low alloy steel, high-
temperature alloy steel, precision alloy. The method-2 of this part is applicable
to the determination of molybdenum content of 0.0025% ~ 0.20% (mass fraction)
in pig iron, carbon steel, alloy steel.
2 Normative references
The provisions in following documents become the provisions of this standard
through reference in this part of GB/T 223. For the dated references, the
subsequent amendments (excluding corrections) or revisions do not apply to
this part; however, parties who reach an agreement based on this standard are
encouraged to study if the latest versions of these documents are applicable.
For undated references, the latest edition of the referenced document applies.
GB/T 6379.1 Accuracy (trueness and precision) of measurement methods
and results - Part 1: General principles and definitions
GB/T 6379.2 Measurement methods and results - Accuracy (trueness and
precision) - Part 2: Determine the standard methods of measurement
repeatability and reproducibility of the basic method
GB/T 20066 Steel and iron - Sampling and preparation of samples for the
determination of chemical composition
3 Method-1: Thiocyanate direct spectrophotometry
3.1 Principle
In the sulfuric acid-perchloric acid medium, use stannous chloride to reduce
iron and molybdenum. Molybdenum reacts with sodium thiocyanate to produce
an orange-red complex. Measure the absorbance. In the color-developing
solution, there is no impact if the amount of copper is less than 0.2 mg, the
amount of vanadium is less than 0.05 mg, the amount of cobalt is less than 0.8
mg, the amount of antimony is less than 0.8 mg, the amount of chromium is
less than 2.4 mg.
3.2 Reagents and materials
Unless otherwise stated, only analytically pure reagents and distilled water or
water of comparable purity are used in the analysis.
3.2.1 Hydrochloric acid, ρ is about 1.19 g/mL.
3.2.2 Nitric acid, ρ is about 1.42 g/mL.
3.2.3 Sulfuric acid, ρ is about 1.84 g/mL, which is diluted to 1 + 1.
3.2.4 Sulfuric acid, ρ is about 1.84 g/mL, which is diluted to 5 + 95.
3.2.5 Mixed acid of sulfuric acid-phosphoric acid, in 700 mL of water, slowly add
150 mL of sulfuric acid (ρ is about 1.84 g/mL). After cooling it slightly, add 150
mL of phosphoric acid (ρ is about 1.70 g/mL). Mix it uniformly.
3.2.6 Perchloric acid, ρ is about 1.67 g/mL, which is diluted to 1 + 5.
3.2.7 Stannous chloride solution, 100 g/L. Weigh 10 g of stannous chloride
(SnCl2 • 2H2O). Place it in a 250 mL beaker. Add 10 mL of hydrochloric acid
(3.2.1). Heat to dissolve it and boil it. Cool it. Use water to dilute it to 100 mL.
Mix it uniformly. Prepare it before use.
3.2.8 Sodium thiocyanate solution, 100 g/L.
3.2.9 Iron solution, 20 g/L. Weigh 2.0 g of pure iron (the molybdenum content,
in mass fraction, must be less than 0.001%). Place it in a 250 mL beaker. Add
40 mL of mixed acid of sulfuric acid-phosphoric acid (3.2.5). Heat to dissolve it.
Add nitric acid (3.2.2) dropwise to oxidize it. Heat it until sulfuric acid smoke is
produced. Take it off and cool it slightly. Add 40 mL of water. Heat to dissolve
the salt. Cool it to room temperature. Transfer it to a 100 mL volumetric flask.
Use water to dilute it to the mark. Mix it uniformly. 1 mL of this solution contains
20 mg of iron.
min ~ 3 min. Remove to slightly cool it. Add 20 mL of water. Heat to dissolve
the salt. Cool it down. Transfer it into a 100 mL volumetric flask. Use water to
dilute it to the mark. Mix it uniformly.
3.5.3.3 Pipette two sets of 10.00 mL of test solution into two 50 mL volumetric
flasks, respectively [where the iron content is less than 30 mg, add iron solution
(3.2.9) to make up].
3.5.3.4 Add 4 mL of sulfuric acid (3.2.3) and 10 mL of perchloric acid (3.2.6) to
one set of solution. Mix it uniformly. Add 10 mL of sodium thiocyanate solution
(3.2.8). Mix it uniformly. Add 10 mL of stannous chloride solution (3.2.7) whilst
shaking it. Use sulfuric acid (3.2.4) to dilute it to the mark. Mix it uniformly. This
is the color-developing solution.
In the other test solution, except for adding the sodium thiocyanate solution
(3.2.8), the rest operations are same as that of the color-developing solution.
This is the reference solution.
3.5.3.5 Place it at room temperature for 10 min ~ 15 min. Transfer part of the
solution into a 1 cm ~ 2 cm absorption dish. Use the reference solution as a
reference. At the wavelength of 470 nm of the spectrophotometer, measure the
absorbance. Subtract the absorbance of the blank solution as made along with
the sample. From the calibration curve, check the corresponding mass of
molybdenum (μg) in the color-developing solution.
3.5.4 Drawing of calibration curve
Weigh 9 parts of 0.30 g of pure iron (molybdenum’s mass fraction is less than
0.001%). Place them in a 250 mL conical flask. Respectively pipette 0, 0.50 mL,
1.00 mL, 1.50 mL, 2.00 mL, 2.50 mL, 3.00 mL, 3.50 mL, 4.00 mL of
molybdenum standard solution (3.2.10). Add 40 mL of the mixed acid of sulfuric
acid-phosphoric acid (3.2.5). Heat to dissolve it. Follow the procedures of
3.5.3.2 ~ 3.5.3.5, until measuring the absorbance. Subtract the absorbance of
the compensation solution. Use the mass of molybdenum (μg) as the abscissa
and the absorbance as the ordinate, to draw the calibration curve.
3.6 Calculation of results
The molybdenum content is expressed in mass fraction wMo, the value is
expressed in % and calculated according to formula (1):
Where:
V1 - The volume of the divided test solution, in milliliters (mL);
When the tungsten in the specimen is less than 5 mg, use phosphoric acid to
mask it. When the tungsten in the specimen is more than 5 mg ~ 20 mg, add 2
~ 3 g of tartaric acid to mask it. When the molybdenum is less than 0.010%, the
ratio of molybdenum to tungsten is not more than 1:80. In the pipetted solution,
when copper is more than 5 mg, add thiourea to mask it. When antimony is
more than 0.15 mg, it interferes with this method. ...