This standard specifies the method for determining the amount of silver in silver tungsten carbide electrical contact materials. This standard is applicable to the determination of the amount of silver in silver tungsten carbide electrical contact materials. Determination range: 0.50% to 2.00%. JB/T 7778.1-1995 Chemical analysis method for silver tungsten carbide electrical contact materials JB/T7778.1-1995 Standard download decompression password: www.bzxz.net

Mechanical Industry Standard of the People's Republic of China
Chemical analysis method of silver tungsten carbide electric contact material Determination of silver content by thiocyanate volumetric method
Subject content and scope of application
This standard specifies the determination method of silver content in silver tungsten carbide electric contact material. JB/T 7778.1—1995
This standard is applicable to the determination of silver content in silver tungsten carbide electric contact material. Determination range: 80.00%~90.00%. Reference standard
JB4107.1-85 General principles and general provisions for chemical analysis methods of electric contact materials 3 Principle of method
After the sample is decomposed with nitric acid, it is titrated with potassium thiocyanate standard titration solution with ammonium ferric sulfate as the indicator. The thiocyanate first reacts with the silver ions in the solution to form an insoluble silver-white precipitate of thiocyanate. When the silver ions are completely precipitated, an excess drop of thiocyanate reacts with trivalent iron ions to form a red iron thiocyanate complex, which is the end point. 4 Reagents
4.1 Nitric acid (1+1).
4.2 Potassium thiocyanate standard titration solution [C(KCNS)=0.04mol/L]. 4.2.1 Preparation
Weigh about 9.7g potassium thiocyanate and dissolve it in water, dilute to 2500mL, mix thoroughly, and let it stand for 3 days. 4.2.2 Calibration
Weigh 0.1000g pure silver (99.99%) and place it in a 250mL conical flask, add 10mL nitric acid (4.1), heat and melt it at low temperature on an electric furnace, boil it to remove all yellow smoke, cool it to room temperature, add water to 100mL, add 5mL ammonium ferric sulfate (4.3), and titrate with potassium thiocyanate standard titration solution (4.2) until it turns light red.
The amount of silver equivalent to each milliliter of potassium thiocyanate standard titration solution is calculated according to formula (1): Ca
Wherein:
m-mass of pure silver, g:
V-volume of potassium thiocyanate standard titration solution consumed in titrating pure silver, mL. (1)
4.3 Ammonium ferric sulfate solution (20 g/L): Weigh 2 g of ammonium ferric sulfate and dissolve it in 100 mL of water, and add freshly boiled nitric acid (4.1) until the brown color disappears.
5 Analysis steps
5.1 The measurement environment is free of hydrochloric acid mist. www.bzxz.net
5.2 Sample
Weigh 0.1 g of sample, accurate to 0.0001 g. 5.3 Determination
Approved by the Ministry of Machinery Industry on October 9, 1995
Implemented on January 1, 1996
JB/T 7778.1-1995
5.3.1 Place the sample (5.2) in a 250mL conical flask, add 10mL nitric acid (4.1), place it on an electric stove and heat it at low temperature until the sample is completely dissolved, then boil it to remove all yellow smoke, and cool it to room temperature. 5.3.2 Add water to 100mL, add 5mL ammonium ferric sulfate (4.3), and shake well. 5.3.3 Titrate with potassium thiocyanate standard titration solution (4.2) until the solution turns a stable light red, which is the end point. Record the volume of potassium thiocyanate standard titration solution consumed.
Calculation of analysis results
The percentage of silver is calculated according to formula (2): cv
Ag(%)=
-the amount of silver equivalent to each milliliter of potassium thiocyanate standard titration solution, g; where: C-
V——the volume of potassium thiocyanate standard titration solution consumed by the titration sample, mL; the mass of the sample, g.
7 Allowable difference
The difference in analysis results between laboratories should not be greater than the allowable difference listed in Table 1: Table 1
80.0090.00
Additional instructions:
This standard was proposed and managed by the Guilin Electrical Science Research Institute of the Ministry of Machinery Industry. Allowable difference
This standard was drafted by the Guilin Electrical Science Research Institute of the Ministry of Machinery Industry, and Tianshui Great Wall Electrical Alloy Material Factory participated in the drafting. The main drafters of this standard are Li Peitian
Zhao Guangying Li Yuren
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