The main purpose of silicon carbide vacuum sintering furnace

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Silicon carbide has extremely strong covalent bonds and still has high-strength bonding at high temperatures. Silicon carbide ceramics have relatively low density, high hardness, wear resistance, corrosion resistance, high thermal conductivity, and good thermal shock resistance. They are cost-effective structural ceramics.

Compared with alumina and boron carbide ceramics, silicon carbide ceramics are between the two in terms of low cost, high performance, and density. The conventional preparation processes of silicon carbide ceramics include: hot pressing sintering, pressureless sintering, vacuum sintering, etc.

Vacuum sintering process	Method	Advantage	Shortcoming
Hot Press Sintering	Silicon carbide powder is placed in a mold and an axial pressure of 20 to 50 MPa is applied while heating.	The process is simple, the product density is high, the temperature is low, and the sintered grains are small and firm.	The equipment is complex, the mold material requirements are high, the production process is strict, the energy consumption is large, the efficiency is low, the cost is high, and it is only suitable for preparing parts with simple shapes.
Pressureless sintering	Solid phase sintering, liquid phase sintering (based on a certain amount of multi-eutectic oxide sintering additives, SiC and its composite materials are liquid phase sintered to achieve densification at a lower temperature.)	The grain boundaries are clean, the high temperature performance is good, and the performance remains basically unchanged at 1600℃.	The vacuum sintering temperature is high (>2000℃), the raw material purity is high, the fracture toughness of the sintered body is low, and the crack strength sensitivity is strong.

The pressureless sintering process of silicon carbide can be divided into solid phase sintering and liquid phase sintering. In recent years, the research on silicon carbide ceramics has mainly focused on liquid phase sintering.

Silicon carbide vacuum sintering process

The preparation process of silicon carbide ceramics is: mixed ball milling–> spray granulation–> dry pressing–> green body solidification–> vacuum sintering.

Add 96-99 parts of silicon carbide ultrafine powder (50-500nm), 1-2 parts of boron carbide ultrafine powder (50-500nm), 0.2-1 parts of nano-sized titanium boride (30-80nm), 10-20 parts of water-soluble phenolic resin, and 0.1-0.5 parts of high-efficiency dispersant to the ball mill for ball milling and mixing for 24 hours, and put the mixed slurry into a mixing barrel for stirring for 2 hours to remove bubbles in the slurry. The above mixture is sprayed into the granulation tower, and the granulation powder with good particle morphology, good fluidity, narrow particle distribution range and moderate moisture is obtained by controlling the spray pressure, air inlet temperature, air outlet temperature and spray piece particle size. The centrifugal frequency conversion is 26-32, the air inlet temperature is 250-280℃, the air outlet temperature is 100-120℃, and the slurry inlet pressure is 40-60. The above granulation powder is placed in a cemented carbide mold for pressing to obtain a green body. The pressing method is bidirectional pressurization, and the machine tool pressure tonnage is 150-200 tons. The pressed green body is placed in a drying oven for drying and curing to obtain a green body with good green body strength. The above cured green body is placed in a graphite crucible and arranged closely and neatly, and then the graphite crucible with the green body is placed in a high-temperature vacuum sintering furnace for firing. The firing temperature is 2200-2250℃, and the insulation time is 1-2 hours, and finally a high-performance vacuum sintered silicon carbide ceramic is obtained.

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