Synthesis method:

1. Drop sodium hydroxide solution without carbon dioxide into bismuth nitrate solution (8090 ℃) and mix. The solution remains alkaline during the precipitation process, forming white and bulky bismuth oxide hydrate Bi (OH) 3 precipitation. After short stirring, the solution is heated and dehydrated to yellow bismuth trioxide. After decanting and washing with water, filtering and drying, the finished bismuth oxide is prepared.

2. Under nitrogen atmosphere, add 1.5 mol/L CO2 free sodium hydroxide aqueous solution to 0.1 mol/L bismuth nitrate solution (80-90 ℃) dissolved in 1 mol/L nitric acid to mix it. The solution remains alkaline during precipitation. Although white bulky bismuth oxide hydrate Bi (OH) 3 is precipitated, it will dehydrate into light yellow bismuth trioxide after stirring in hot solution for a while. Pour water and wash with water, air and carbon dioxide for 15 times, then filter and dry.

3. After the bismuth metal is melted into the graphite crucible and melted, an arc is formed between the graphite electrode and the surface of the metal liquid to be heated and oxidized under the flow of oxygen. To ensure sufficient oxygen supply, the crucible should be placed in a large container and oxygen should be continuously supplied. The reaction temperature is 750800 ℃, and the purity of 99.8% or higher can be rapidly produced β- Bismuth trioxide. After quenching the product in water or on a cold metal plate, the high-temperature phase can be obtained β Type product.

4. Slowly add Bi (NO3) 3 · 5H2O acid solution (20g dissolved in 2mol/L HNO3) into excessive sodium carbonate solution and stir vigorously. Obtain Bi 2O 3 CO 3 precipitation, filter, wash and dry. Put it in an aluminum boat and heat it in air of 650K for about 1.5 hours to obtain β- Bi2O3 5. Burn basic bismuth nitrate at 400500 ° C for about 34h to remove NO 3 - ions. After combustion, it will turn into lemon yellow after cooling, which is the finished product.

6. Use a small amount of dilute nitric acid to clean the surface of 16kg 99.9% industrial bismuth, and then use conductive water to clean the nitric acid on the surface. Then add 1:1 high-purity nitric acid (35kg nitric acid with relative density of 1.42+20L conductive water), and add 1 μ 50. And continue to react for 10 minutes after adding. Slightly cool, after filtration, heat the filtrate to 6570 ℃, evaporate and concentrate to the relative density of 1.9, cool and crystallize, and spin dry to obtain bismuth nitrate. The bismuth nitrate obtained is dissolved in a dilute solution with conductive water and hydrolyzed under stirring. Allow it to settle completely to precipitate basic bismuth nitrate. The precipitate is rotated and dried or filtered with a centrifuge, and then washed with heat conduction water for several times. Crush, burn at 500 ℃ for 7 to 8 hours, crush after slightly cooling, and burn for 4 to 5 hours. After cooling, 99.99% high-purity bismuth oxide is obtained.