GB/T 15072.7-1994 Chemical analysis methods for precious metals and their alloys - Determination of chromium content in gold alloys

GB/T 15072.7-1994 Methods for chemical analysis of precious metals and their alloys Determination of chromium content in gold alloys GB/T15072.7-1994 standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Chemical analysis methods for precious metals and their alloysbZxz.net
Determination of chromium content in gold alloys
Gold alloys .- Determination of chromium content1 Subject content and scope of application
This standard specifies the method for determining the chromium content in gold alloys. GB/T 15072.7..--94
This standard is applicable to the determination of chromium content in AuNiCr5-1 and AuNiCr5-2 alloys. Determination range: 0.5%~3%. 2 Reference standards
GB1.4 Guidelines for standardization work Provisions for the preparation of chemical analysis method standards GB1467 General principles and general provisions for chemical analysis method standards for metallurgical products 3 Summary of the method
The sample is dissolved in mixed acid and the gold is separated by sulfurous acid reduction. Using silver (I) as a catalyst, chromium (I) is oxidized to chromium (I) with ammonium persulfate solution. In a dilute sulfuric acid solution containing ammonium ferric sulfate, chromium (V) is titrated with electrogenerated ferrous iron as a titrant, and the end point is indicated by the potentiometric method. The chromium content is calculated with the help of physical quantities such as mass, time, current, and Faraday constant. 4 Reagents
4.1 Sulfurous acid (pl.03g/ml.).
4.2 Mixed acid: Three unit volumes of hydrochloric acid (pl.19g/ml) and one unit volume of nitric acid (pl.42g/ml.) are mixed. Prepare immediately.
4.3 Silver nitrate solution (50g/1).
4.4 Ammonium persulfate solution (250g/L.). Prepare immediately when used. 4.5 Potassium dichromate solution (0.5g/L).
4.6 Anode electrolyte solution: c(H,S0.)=2mol/L. 4.7 Catholyte solution: Add 800ml of water to a 1000ml beaker, slowly add 111ml of sulfuric acid (1.84g/mL) under stirring, cool to room temperature, add 96.4g of ammonium ferric sulfate [FeNH, (SO)·12H.O to dissolve, and dilute to 1L with water. 5 Instruments and devices
5.1 Precision coulometric titrator: constant current accuracy should be better than or equal to 1/10000; potential detection accuracy should be 1mV; six-digit display timing can read 0.1s.
5.2 Electrolytic cell, as shown in the figure.
5.3 Electromagnetic stirrer,
Approved by the State Administration of Technical Supervision on May 11, 1994 and implemented on December 1, 1994
6 Sample
GB/T15072.7-94
Schematic diagram of electrolytic cell
1-titration cell beaker (lid with electrode jack); 2-saturated calomel electrode; 3-platinum indicator electrode: $×L, mm, 0.5×20; 4-counter electrode chamber with sand center; 5---platinum sheet anode; 6-platinum sheet working electrode: its area is not less than 10cm; 7-stirring rotor The sample is processed into debris, and finally degreased with acetone, washed, dried and mixed. 7 Analysis steps
7.1 Sample
Weigh about 0.2g of sample, accurate to 0.0001g. Perform two independent measurements and take the average value. 7.2 Determination
7.2.1 Place the sample in a 150mL beaker, add 4mL of mixed acid and heat to dissolve completely, rinse the surface III and the wall of the cup with water, and evaporate to nearly dryness on a water bath. Add 4mL of water and evaporate to nearly dryness, repeat twice. 7.2.2 Dissolve the residue with water to make the volume about 25mL. Add 10mL of sulfurous acid, cover with a watch glass, boil for 20min, remove and cool, and rinse the surface III. Pour the clear liquid into a 50mL volumetric flask, and wash the precipitate and the wall of the cup several times. Combine the washing liquid into the volumetric flask, dilute to the scale with water, and mix well.
7.2.3 Take 10.00mL of the test solution into the titration cell beaker. Add 3mL of silver nitrate solution and 1mL of ammonium persulfate solution, add water to make the volume about 15mL, and boil at low temperature until there are no small bubbles (about 5min). Remove, cool, and rinse the watch glass and the wall of the cup with water. 7.2.4 Take about 40mL of cathode electrolyte solution and add it to another titration cell beaker, add 2 drops of potassium dichromate solution. Put in a stirring rotor. Then install the electrodes according to Figure (5.2). Add the anode electrolyte solution to the electrode chamber, and its liquid level is slightly higher than the cathode electrolyte solution level in the titration cell beaker. Stir, and titrate the electrolyte solution with a current of 1mA to the endpoint potential of chromium (698±2mV, the determination method is shown in Appendix A). Ignore time. 7.2.5 Add the above blank electrolyte solution to the test solution titration cell beaker (7.2.3), titrate with a current of 10mA to the endpoint potential, and record the titration time.
8 Expression of analysis results
Calculate the percentage of chromium according to the following formula:
Wherein: 1 Constant current.mA;
GR/T 15072.7- 94
Cr(%)
t-Time consumed for titrating chromium in the test solution, s;M-Atomic weight of chromium.51.996;
n-Number of transferred electrons, 3;
F--Faraday constant, 96484.56;
V,-Total volume of sample solution, mL;
Volume of test solution taken, mL;
Mass of sample, mg.
The result should be expressed to two decimal places
Allowable difference
I×t×MXV.
nxFxVxm
The difference between the analysis results of laboratories should not exceed 0.05%. X100
GB/T 15072.7--94
Appendix A
Method for determining the endpoint potential of chromium
(reference)
Pipette 2ml. chromium standard solution (0.3mg/mL) into the titration cell beaker, add about 40mL. empty cathode electrolyte solution, add 5-6ml. anolyte solution to the electrode chamber, connect the electrodes and the instrument, and titrate with a current of 10mA. With potential (E) as the ordinate and time (1) as the abscissa, automatically record the chromium potential titration curve and calculate its endpoint potential. Alternatively, use the second derivative method to determine its endpoint potential. Additional Notes:
This standard was proposed by China Nonferrous Metals Industry Corporation and drafted by Kunming Precious Metals Research Institute. This standard was drafted by Kunming Precious Metals Research Institute. The main drafters of this standard are Dong Shouan and Wu Jiangchun.
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