Preparation method for silicon nitride heating body

[0021] (Example 1)

[0022] The silicon nitride heating element of this embodiment is composed of silicon nitride heating element and a high temperature metal heating wire arranged in the silicon nitride heating element. The metal heating wire is tungsten wire, molybdenum wire or tungsten-molybdenum alloy wire.

[0023] The manufacturing method of the above-mentioned silicon nitride heating element includes:

[0024] Step 1. Put the silicon nitride powder and the high temperature liquid phase sintering aid at a weight ratio of 0.96:0.04 to 0.80:0.20 into absolute ethanol and mix (specifically, a ball mill mixer can be used for mixing), and the mixture is mixed for 10-72 hours Then, it is sprayed and granulated to make formula;

[0025] Step 2. Embed the metal heating wire in the formula for dry pressing, and then further press it into a shape by 180-220MPa cold isostatic pressing, and keep the pressure for 3-10 minutes to make a green body;

[0026] Step 3. Coating a layer of boron nitride isolation layer uniformly on the surface of the green body and then drying;

[0027] Step 4. Then perform hot pressing sintering, sintering pressure 20-30MPa, sintering temperature 1600-1900°C, holding time 0.5-4 hours, to make a blank;

[0028] Step 5. Put the blank in a vacuum atmosphere furnace, keep it at a constant temperature of 1300-1600°C for 10-24 hours, then cool it naturally to room temperature, and finally weld electrodes on both ends of the metal heating wire.

[0029] The boron nitride isolation layer is a thick slurry formed by mixing boron nitride powder and silicon nitride powder with absolute ethanol; wherein the weight ratio of the silicon nitride powder to the boron nitride powder It is: 0.10:0.90 to 0:1.00.

[0030] In the step 4, during the hot pressing and sintering, a layer of the boron nitride isolation layer is coated on the contact surface of the hot pressed graphite mold used with the blank.

[0031] (Example 2)

[0032] On the basis of Embodiment 1, the manufacturing method of the silicon nitride heating element of this embodiment includes:

[0033] Combine 92wt% silicon nitride powder and 3wt% Al 2 O 3 , 3wt% Y 2 O 3 , 1wt% of MgO and 1wt% of AlN are mixed with 99.9% absolute ethanol for 72 hours, and then placed in an explosion-proof spray granulation tower to spray granulation to make a formula.

[0034] Pour the formula into the mold, and then embed the metal heating wire into the powder and dry press to form, the size is 120*20*10. Then encapsulate the dry-pressed and formed blank, and put it into a cold isostatic pressing equipment for isostatic pressing. The isostatic pressure is 200MPa and the pressure holding time is 3-10 minutes. Use high-purity absolute ethanol and boron nitride fine powder to blend into a thick slurry, and use the knife coating method to coat a uniform boron nitride isolation layer on the surface of the blank, and then dry it. A layer of boron nitride isolation layer is also coated on the contact surface between the hot-pressed graphite mold and the blank, and the processed blank is placed in the mold. Put the mold into a hot pressing furnace, press at 1800 degrees Celsius, 25MPa for 2 hours, and naturally cool down to within 50 degrees Celsius, and get out of the furnace. Put the sintered blank into a heat treatment furnace, protected by flowing nitrogen, keep it at 1300-1500 degrees Celsius for a total of 15 hours, then slowly lower the temperature to room temperature and leave the furnace. The finished heating sheet blank is processed into a high-performance and high-reliability silicon nitride heating sheet through subsequent processes such as surface grinding and welding.

[0035] About cold isostatic pressing: At room temperature, the powder is placed in a closed liquid environment, and the liquid transmits ultra-high pressure to make the powder shape. Because the pressure in the liquid is equal everywhere, it is called isostatic pressure. Because it is at room temperature, it is cold isostatic pressing. When the working temperature is 100-200℃, it is thermostatic pressure. Higher working temperature is hot isostatic pressing. Some can reach 2000℃

[0036] The traditional spray granulation technology is to inject hot air into the drying tower, rely on large area contact with the material liquid to evaporate the water, and obtain the shaped particles.

[0037] Hot pressing sintering is a sintering method in which dry powder is filled into the model, and then heated from the uniaxial direction while pressing, so that the molding and sintering are completed at the same time. Hot pressing equipment: The commonly used hot pressing machine is mainly composed of a heating furnace, a pressurizing device, a mold, and a temperature and pressure measuring device.