GB/T 5124.3-1985 Chemical analysis method for cemented carbide - Determination of cobalt content by potentiometric titration GB/T5124.3-1985 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Chemical Analysis Methods of Hard Alloys
Determination of Cobalt Content by Potentiometric Titration
Methodsfor Chemical Bnalysis of Hard MetalsThe potentiometric method for the determinatlonof cobalt content
UDC 669.018.25
: 543.257.1
GB5124.S--85
This standard is applicable to the determination of cobalt content in mixed powder of carbide and bonding metal (without lubricant and binder) and pre-sintered or sintered hard alloys of various grades. Determination range: above 1.00%. This standard complies with GB1467-~78 "General Principles and General Provisions for Chemical Analysis Methods of Metallurgical Products". This standard is equivalent to the international standard IS03909-1976 "Cemented Carbide-Determination of Cobalt-Potentiometric Titration". 1 Method Summary
The sample is dissolved in sulfuric acid and ammonium sulfate. Cobalt is oxidized to a monovalent state with an excess of potassium ferrocyanide in a strong ammonia medium. Excess potassium ferrocyanide is titrated back with a cobalt sulfate solution by potentiometric titration. Vanadium and manganese are also oxidized by potassium ferrocyanide. Vanadium participates in the reaction quantitatively, and correction can be made if its content is less than 0.5n% (m/m). If the total amount of molybdenum in the sample is less than 0.02% (m/m), the reaction can still be almost quantitative when the amount of manganese is as high as 0.20% (m/m). If the total amount of sawdust exceeds 0.02% (m/m), this method can only be used when the amount of manganese is less than 0.03% (m/m). 2 Reagents
Ammonium sulfate.
2.2 Hydrochloric acid (specific gravity 1.19).
Hydrofluoric acid (specific gravity 1.12).
Nitric acid (specific gravity 1.42).
Sulfuric acid (specific gravity 1.84).
2.6Ammonium hydroxide (specific gravity 0.90).
2.7Ammonium citrate solution: Dissolve 100g of citric acid in 900ml of water, then add 100ml of ammonium hydroxide (2.6) and mix. 2.8Cobalt sulfate standard solution: Weigh 3.0000g of metal cobalt, place it in a 500ml beaker, add 100ml of sulfuric acid (1+5), cover with blood, and slowly dissolve it on a low-temperature electric furnace. After it is completely dissolved, cool it to room temperature, transfer it to a 1000ml volumetric flask, dilute it to the scale with water, and mix it. This solution contains 3g of cobalt.
This standard solution can also be prepared with diammonium cobalt sulfate or cobalt sulfate. If necessary, its concentration can be calibrated by 1-nitroso-2-naphthol weight method or electrolysis method.
2.9Potassium ferrocyanide standard solution (1 L is approximately equivalent to 3g of cobalt). 2.9.1 Preparation
Dissolve 17g potassium ferrocyanide in 1000ml water, mix well and place in a brown bottle. Store in a dark place. 2.9.2 Calibration
Add 5g ammonium sulfate (2.1), 40l ammonium citrate solution (2.7), 100ml water and 80ml cold ammonium hydroxide to a 40mm beaker. Instructions; international standard is lubricant-free. National Bureau of Standards 1985-04-24
1986-02-01 implementation
GB 5124. 3-86
(2.6), add 9.00ml potassium ferrocyanide standard solution (2.9) with a burette, the volume used is V. ml. Immediately titrate with cobalt sulfate standard solution (2.8), the volume used is V ml. Calculate the volume ratio of potassium ferrochlore standard solution to sulfuric acid standard solution according to formula (1): K-
2.10His red indicator solution (1g/L) or pH 3~5 precision test paper. Instruments
3.1 Potentiometric titrator: with stirring device.
3.2 Pin electrode.
3.3 Calomel intermediate electrode or chromium electrode
3.4 ​​10ml burette.
In a grinder that will not change the sample composition, grind the laboratory sample into powder and pass it through a 0.18-2 sieve. 5
Analysis steps
Quantity of determination
One or three samples should be weighed for determination during analysis. 5.2 Sample quantity
Weigh 0.100~0.5000g of sample according to the amount. 5.3 Determination
5.a1 Sample dissolution
Put the sample (5.2) in a 400 ml flask, add 5.g ammonium sulfate (2.1), 10-15 ml sulfuric acid (2.5) and 3 ml hydrochloric acid (2.2), cover with blood, heat and allow the sample to completely dissolve, and cool. Slowly add 40-50 ml of ammonium citrate solution (2.7) in batches. Rinse the gauge and cup with 20-50 ml of water: heat until all salts are dissolved, and cool thoroughly. The sample can also be dissolved by the following method. Place the sample (5.2) in a 400 ml polypropylene beaker (or platinum dish), add 10 ml of water and 1.5 ml of hydrochloric acid (2.3), and cover the beaker with a polypropylene beaker. Heat to nearly 60°C, add nitric acid (2.4) dropwise until the mixture is completely dissolved, cool, and slowly add 10 ml of ceric acid (2.5) and 40-50 ml of ammonium citrate solution (2.7) in batches. (If vanadium is present, heat the solution and cool it again). Rinse the gauge and cup with 26-59 ml of water. Cool thoroughly. 3.2 Add a small precision test paper or 1 drop of methyl red indicator solution (2.10) and carefully neutralize a large amount of acid with ammonium hydroxide (2.6) to pl3-5. Prevent excessive cooling. 6.3.3 Add 80ml of ammonium hydroxide (2.6) pre-cooled to 10 (mm) and then use a burette to add an excess of potassium ferrocyanide standard solution (2.9) with a volume of . Immediately back titrate with cobalt sulfate standard solution (2.8) with a volume of V2 ml. Calculation of analytical results
6.1 Calculate the cobalt content according to formula (2): Co (%) = (KV/-V,)-×100
2.9.2 has been specified!
Adoption Note: The international standard is tungsten wire or other reference electrode. (2) Www.bzxZ.net
GB 5124. 3B5
, the volume of potassium ferric chloride standard solution added; - the volume of cobalt sulfate standard solution consumed in the back titration: T
- the amount of cobalt contained in the cobalt sulfate standard solution after calibration, g/nl, - the amount of sample, g.
6.2 Verification
The following correction values ​​may be experimentally specified:
: 0.100% (m/m) vanadium is equivalent to 0.116% (m/m) cobalt manganese: 0.100% (m/m) manganese is equivalent to 0.107% (m/m) cobalt. Allowable Difference
The extreme difference between the results of two independent determinations should not be greater than the allowable difference listed in the following table:
1.00~5.00
5.00~8.00
2-8.00 ~20.00
Permissible difference of three independent determination results
The arithmetic mean of qualified determination values ​​shall be the final result. Additional remarks:
This standard is proposed by China Nonferrous Metals Industry Corporation. This standard is drafted by Zhuzhou Hard Metal Factory. The main drafters of this standard are Zhang Jing and Wang Jishen. 178
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Permissible difference of three independent determination results
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