GB/T 223.61-1988Methods for chemical analysis of iron, steel and alloy--The ammonium phosphomolybdate volumetric method for the determination of phosphorus content (English PDF)

2.5 Nitric acid (rho=

2.6 Nitric acid (1+3).

2.7 Nitric acid (2+100).

2.10 Ammonium hydroxide (rho=

0.90 g/ml).

2.11 Ammonium hydroxide (5+95).

2.12 Sodium nitrite solution (10%).

2.13 Beryllium sulfate solution (2%). prepare with sulfuric acid (1+100).

2.14 Hydroxylamine hydrochloride solution (10%). prepare just before use.

2.15 Ammonium molybdate solution. weigh 135 g of ammonium molybdate [(NH4)6·Mo7O24·4H2O], dissolve it in warm water and cool it; dilute to 1000 ml with water, stir, and slowly pour into 1000 ml of nitric acid (2+3, mix; add 5 mg of diammonium hydrogen phosphate, standing 24h; and filter it with slow filter paper before use.

2.16 Neutral water. boil the distilled water to remove carbon dioxide, and then cool it by following water. Prepare just before use.

2.17 Phenolphthalein solution. weigh

0.25 g of phenolphthalein, dissolve it in 30ml of alcohol, and dilute to 50 ml with water.

2.18 Standard sodium hydrate solution, C(NaOH) =

0.1 mol/L or C(NaOH) =

0.05 mol/L.

2.18.1 Preparation Weigh 4 g or 2 g of sodium hydrate, dissolve it in 1000 ml of neutral water (2.16), and store the solution in a sealed plastic bottle.

2.18.2 Calibration Weigh 0.3000 g of reference potassium hydrogen phthalate (stove at 105°C in advance, place it in a dryer and cool it to the ambient temperature) (three portion), dissolve them with 80 ml of neutral water respectively, and add 2~3 drops of phenolphthalein solution (2.17) respectively; titrate them with standard sodium hydrate solution (2.18) to light red; the maximum difference of the amount consumption (mL) of standard sodium hydrate solution for the three solutions shall not exceed 0.05ml, the mean shall be taken, and the concentration of standard sodium hydrate solution is taken according to the formula below. Where, C - The mass concentration of the standard sodium hydrate solution, mol/l; m - The mass of potassium hydrogen phthalate weighed, g; V - The mean volume of the standard sodium hydrate solution consumed for calibration, ml; 204.22 - The mole mass of potassium hydrogen phthalate, g/mol.

2.19 Standard nitric acid solution, C(HNO3)=

0.1 mol/l or C(HNO3)=

0.05 mol/l.

2.19.1 Preparation Pipette

3.3 ml of nitric acid (2.5) that has been remove nitric oxide and cooled up, and dilute it to 1000 ml with water, mix.

2.19.2 Calibration Pipette

25.00 ml of standard sodium hydrate solution (2.18) (three portions), add 50 ml of neutral water (2.16) and 3 drops of phenolphthalein (2.17) respectively, titrate them with standard nitric acid solution (2.19.1) respectively till the red disappears; the maximum difference of the consumptions of standard nitric acid solutions (2.19.1) for three portions of the solution shall not exceed

0.05 mL, and the mean (V1) shall be taken according to the formula below. Where, K - The coefficient for reduction of standard nitric acid solution to standard sodium hydrate solution; V - The mean volume of standard nitric acid solution used for titrating, ml; 25.00 - The volume of the standard sodium hydrate solution (2.18) pipetted, ml.

3.3.1 Sample dissolution

3.3.1.1 Common sample Place the sample (3.1) into a 300 ml conical beaker, and add nitric acid as required by Table 1, and heat for dissolving [for indissoluble sample, add appropriate amount of hydrochloric acid (2.8) dropwise to promote dissolution]. Add perchloric acid as required by Table 1, heat it till the fume appears, slightly cool, add

0.5 ml of hydrofluoric acid (2.4) dropwise, and heat again and make it fume till the conical beaker becomes transparent inside and refluxes 3~ 4 min (it the sample contains over 10 mg of manganese, add more 7~8 ml of perchloric acid (2.3), heat and make it fume till the conical beaker becomes transparent inside and refluxes 20~25 min, so as to oxidize phosphorus completely); and continue to evaporate it to nearly dry, and cool it up.

3.3.1.2 Sample containing over 50 mg of chromium Proceed the procedure as

3.3.1.1 till adding

0.5 ml of oxygen-fluorine acid (2.4); after this, re-evaporate and make it fume till chromium is oxidized to hexavalent one; add hydrochloric acid (2.8) dropwise by several times, and repeat 2~3 times; and re-evaporate till the conical beaker becomes transparent inside and refluxes 3~4 min; and re-evaporate again to nearly dry, and cool it up.

3.3.1.3 Sample containing over limit of arsenic Proceed the procedure as

3.3.1.1 till adding

0.5 ml of hydrofluoric acid (2.4); after this, re-evaporate till fume appears; take it down and cool it slightly; add 10 ml of hydrochloric acid (2.8) and 5 ml of hydrobromic acid (2.9); heat and evaporate till white fume appears and remove arsenic. Continue to evaporate till the conical beaker becomes transparent inside and refluxes 3~4 min; and re-evaporate it to nearly dry, and cool it up.

3.3.2 Salt dissolution Add 5ml of nitric acid (2.5) and 40 ml of water to dissolve the salt, add sodium nitrite solution (2.12) dropwise to reduce chromium to low-valency one, and add 2 excessive drops, and boil for 1~2 min; remove nitric oxide.