Silicified graphite are obtained by saturating the initial graphite with liquid silicon at a temperature above 2000 0C, while a reaction occurs with the formation of silicon carbide [1-4].
To improve the properties of materials, it is necessary to consider the process of their manufacture and the causes of defects, as well as to maximize the physical and mechanical properties of the product.
The simplest and most common method of forming products from powders is pressing in metal molds [2-4]. One of the ways to improve pressing in molds is the use of vacuumed powder mass, which creates conditions for increasing the uniformity of density distribution and reducing the risk of formation of layered cracks at high pressing pressures.
The purpose of this work is to study the influence of compressed air on the properties and operational characteristics of silicon carbide based materials.
Electrode graphite fractions of 5-8 μm and 50-100 μm were used to form pressed products. A 15% solution of Bakelite in ethyl alcohol was used as a binder. It was not possible to obtain crack-free samples during air pressing of powder with a fine fraction. Whole samples were obtained by air pressing only when the content of the fine fraction was reduced to 15-20 wt. %. When pressing in a vacuum, the formation of samples without cracks is possible in the entire range of ratios of small and large fractions.
During vacuum sintering of compressed products with a powder content of fine fractions of 20-100%, the formation of cracks was observed in 80-90% of the samples. Whole samples after sintering were obtained with the content of the fine fraction in the pressed products at the level of 10-15%.
The physical and mechanical properties of silicified graphite pressed and sintered in a vacuum are 10-15% higher than pressed and sintered in air: density – 2.57-2.59 g/cm3, bending strength – 110-135 MPa, hardness HV10 – 11,5-12 GPa, K1Ñ10 – 3.2-3.8 MPa•m1/2 and friction pairs of end seals made of this material demonstrate 15-20% higher wear resistance.
As a result of the work, the negative impact of compressed air, namely the delamination of the compressed product after removing the load, was substantiated and practically investigated.
It has been established that the production of silicified graphite without breaking the integrity is possible when the content of graphite powder of a fine fraction of 5-8 μm is no more than 10-15% (the remaining fraction is 50-100 μm).
On the basis of experimental results and available literature data, a conclusion was made about the expediency of implementing the vacuum process when forming products based on silicon carbide.
References
1. Rosario Gerhardt Properties and Applications of Silicon Carbide 536 p. ISBN 978-953-307-201-2
2. Hidehiko TANAKA Silicon carbide powder and sintered materials Review Journal of the Ceramic Society of Japan 119 [3] 218-233 2011
3. Alexander S. Mukasyan Combustion Synthesis of Silicon Carbide Rosario Gerhardt Properties and Applications of Silicon Carbide, p.390-409
4. Mohd Aizat Hafiz, Mohd Sohor, Mazli Mustapha, Jundika Chandra Kurnia Silicon carbide - from synthesis to application: a review MATEC Web of Conferences 131, 04003 (2017) DOI: 10.1051/matecconf/201713104003 UTP-UMP SES 2017
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