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Method for determination of chromium in silicon chromium alloy

from: | update:2019-10-19 | font:small-middle-big | views236

First, drugs

1, vanadium reagent: N-phenyl anthranilic acid, weigh 2g of vanadium reagent, 2g of anhydrous Na2CO3, formulated into 1000ml, (heat dissolved).
2, potassium dichromate standard solution (0.2500mol / L): Weighed (140-150 ° C) dried potassium dichromate 12.2588g dissolved in water, and diluted to 1000ml constant volume.
3. Ammonium ferrous sulfate standard: 0.17mol/L: Weigh 68g of ammonium ferrous sulfate in a 1000ml beaker, add 500ml of water, carefully add 100ml of concentrated H2SO4, dissolve it completely, cool, dilute with water, shake well Constant volume in a 1000ml volumetric flask.
Calibration of ammonium ferrous sulfate standard solution: Pipette potassium dichromate standard solution (0.2500mol / L) 25ml in a 250ml flask, add 20ml sulfur and phosphorus mixed acid, dilute with water to 100ml, titrate with ammonium ferrous sulfate standard solution, Add 3 drops of vanadium reagent to the end point, and drop to bright green to reach the end point.
Concentration calculation: C2=C1×(V1/V2)
4, concentrated nitric acid;
5. Hydrofluoric acid;
6, perchloric acid;
7. Sulfuric acid (1+3);
8. Potassium permanganate (4%);
9. Ammonium chloride (25%);
Second, the determination of chromium

Weigh 0.2000g sample in F4 beaker (platinum dish), add 10ml of HNO3, add HF 3~4ml dropwise, dissolve and transfer to hot plate for heating for about 1min, add HClO4 1ml, smoke to near dry (brown) Red), remove the cooling, add H2SO4 (1+3) 20ml, heat to dissolve the salt, remove the heat into the 500ml beaker, add KMnO4 (4%) 10ml, heat to boil, chrome to hexavalent, add 25 % NH4Cl 70ml, take off slightly cold, add sulfur and phosphorus mixed acid (2:1:7) 20ml, heat to boil until the solution turns yellow, remove, cool in a water bath, add water to 280~300ml, put into the glass rod, Titrate with ammonium ferrous sulfate standard solution, add 3 drops of vanadium reagent (0.2%) to the end point, the solution is dark red, and the solution turns into bright green as the end point.

Calculation:

1, then titration, the sample solution should be reduced to room temperature;

2. The standard solution of ammonium ferrous sulfate should be protected from light and heat.

3. The ammonium chloride should be added during the analysis, such as 70ml in this method.

4. The slag in the sample will cause a large error in carbon content.






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