The Synthesis Method Of Boron Nitride Powder

Boron nitride powder as a refractory raw material, there are more than 10 synthetic methods, but can achieve industrial production of only a few.

(1) Borax - ammonium chloride method. First of all, borax is dehydrated in vacuum at 200~400℃, and ammonium chloride is dissolved into a saturated solution, and impurities are removed by filtration and recrystallization, which can be repeated. Then the above raw materials were crushed, dried, mixed with borax and ammonium chloride at 7:3 (weight ratio), pressed into billets and synthesized in the reactor. The reaction temperature was 9001000℃ and held for 6h. NH3 is introduced in the reaction to compensate for the lack of ammonia atmosphere formed by the reactants. The reaction products were washed with water to remove the remaining impurities such as boric acid and sodium chloride, and then dried and crushed to get boron nitride powder (containing about 97% OF BN).

(2) Borax - urea method. The borax dehydration and drying, grinding, urea purification and drying, grinding. Mix borax and urea evenly in a ratio of 1:1.52 and place in a container of quartz glass, corundum, graphite or stainless steel in the reactor. Heating to 100℃, heat preservation 0.5h, 140℃, heat preservation 2h, 180℃, heat preservation 2h, 800℃, heat preservation 2h, the final temperature 8001000℃, heat preservation 24h. Below 300℃, nitrogen gas first, above 300℃ change into ammonia gas. The reaction product was pickled with hydrochloric acid to remove Na2O, then washed with water to remove chloride ions, and then washed with alcohol to remove H3BO3. After repeated treatment with water and alcohol, the boron nitride powder (containing BN96%) was obtained.

(3) Boron anhydride method. Boron anhydride (B2O3) as the main raw material, tricalcium phosphate as the filler, the ratio of the two is 5:3, dry mixing, adding water into a paste, granulation, drying at 80℃. The mixture is nitrided in a quartz tube or corundum tube electric furnace. The furnace body should be slightly inclined to facilitate drainage. Reaction temperature 9001000℃, holding for 6h, through NH3 gas. The reaction products were pickled with 3% hydrochloric acid for 16h to remove Ca3 (PO4) 2 and H3BO3, and then with 25% hydrochloric acid for 3h, and then with water to remove HCl. Dried at 180s, washed with alcohol to remove H3BO3, and finally dried to obtain BN.