Indirect heating sintering is the sintering of tantalum and tantalum alloy bar material by heat radiation and heat convection to increase the furnace temperature of the sintering furnace. Heat is generated by electric energy through the tungsten mesh heating body or graphite heating body. The sintered billet is in a uniform temperature field with a small temperature gradient, so that the consistency of the sintered bar material is better. The way of generating heat from the heating body is generally resistive, and the corresponding sintering furnace has a resistance furnace.
The invention uses a high temperature vacuum sintering furnace to indirectly heat and sinter tantalum and tantalum alloy bar used for capacitor tantalum wire, especially for pure tantalum bar, doped tantalum bar and tantalum alloy, which can realize the refining of tantalum and tantalum alloy bar and achieve the performance index of vertical melting and sintering, and the heating of the whole blank is uniform along its height and cross section. At the same time, the furnace loading capacity of each furnace can reach about 300kg, and the performance of tantalum strips after sintering tends to be consistent, reducing the difference caused by different furnace times. The application of vacuum induction sintering technology will greatly reduce the sintering electricity cost. ① Increase yield; ② Increase the amount of furnace loading, improve the sintering efficiency ③ reduce the single consumption of electric energy, to achieve clean production.
34 tantalum strips weighing 6kg were prepared. Put 6kg of tantalum powder with purity greater than 99.9% into a rubber sheath with an inner diameter of 32mm. Insert a rubber plug into the opening of the sheath. When the air in the sheath is discharged, the latex sheath at the rubber plug part is bound tightly with a wire. Knead the covered strip evenly with two splints, and then use a rubber band to fix the splints and strips together. Prepare 34 billets as above, and then place them in a cold isostatic press with a maximum holding pressure of 250MPa and a holding time of 15min. Complete the cold isostatic pressing forming, and finally unload the mold, and obtain 34 compact pieces.
Put 34 compact pieces into the vacuum heating furnace, and gradually heat up and hold heat according to the sintering process in the table below. After reaching the final sintering temperature of 2400℃, hold heat for 8 hours. Then it is removed by cooling to obtain rod sintered tantalum rod.
Then it is rolled into a 3mm round tantalum bar with H2S04: HN03: HF= 5:3: 3(volume ratio, molar concentration of the three are 18.4mol/L, 16mol/L, 22.8mol/L) Acid washing with mixed acid, then washing, drying and annealing in vacuum annealing furnace, annealing temperature is higher than the recrystallization temperature of 200℃, heat preservation for 120 minutes.
After annealing, the round tantalum wire is continuously drawn into 0.11mm tantalum wire, and then the finished product is directly annealed after cleaning and natural drying. The annealing temperature is 500℃ higher than the recrystallization temperature, and the wire collection speed is 15m/min. Finally, the product is rewound, and then the physical property, chemical impurity and electrical properties of the product are tested.
