1 Sample weight
If the boron content in ferroboron is high, the sample weight is too small, the weighing error will increase; if the sample weight is too much, the reagent addition amount will increase correspondingly, and the sample is not easy to dissolve completely, and the overflow may occur in the determination of ICP-AES, which will affect the determination results. The weight of sample determined by the method is 0.100 G.
2 Alkali melting method
If the sample is melted by sodium peroxide alone, the reaction will be violent when heated at low temperature, and the conditions are difficult to control, which will lead to the analysis failure. Therefore, the use of anhydrous sodium carbonate for melting can slow down the intensity of the reaction. Sodium peroxide is added at 700 ℃ and the sample is completely melted at 800 ℃. It should be noted that the melting sample should not be placed directly at high temperature, but should be low temperature first and then high temperature.
2 g anhydrous sodium carbonate + 4 g sodium peroxide, 20 ml nitric acid or 1.5 g anhydrous sodium carbonate + 3 G sodium peroxide and 20 ml nitric acid were used for ferroboron samples. It can be seen from the test that the latter can completely dissolve the sample, and ICP ICP-AES has certain requirements for the salt content of the solution. Too much flux will affect the extraction amount of the solution and the accuracy of the instrument measurement.
3 Microwave digestion
3.1 selection of sample dissolving acid
Hydrochloric acid, nitric acid, hydrofluoric acid, sulfuric acid, phosphoric acid and their mixed acids are commonly used in microwave digestion. Because boron is soluble in nitric acid and sulfuric acid, the combination of sample dissolving acid is nitric acid + sulfuric acid + hydrofluoric acid. Under the same other conditions, different amount of sample dissolving acid was used to microwave digestion of ferroboron samples. After repeated tests, the best mixed acid that can completely dissolve ferroboron is sulfuric acid 4 ml + nitric acid 4 ml + hydrofluoric acid 2 ml.
3.2 selection of digestion temperature and digestion time
It is found that the sample can be completely dissolved by step heating. The specific steps of digestion of ferroboron are as follows: 50-160 ℃, heating for 10 min, holding for 10 min; 160-230 ℃, heating for 10 min, holding for 30 min.
3.3 selection of digestion pressure
In microwave digestion, the boiling point of acid increases with the increase of pressure in the container, which can greatly speed up the digestion speed of the sample. However, if the pressure is too high, the reaction of the sample will be too intense and the result will be low. After many tests, the digestion pressure of ferroboron is set at 4 MPa (40 bar).