Infiltration of Molten Silicon in a Porous Body of B ₄ C Under Microwave Heating

Abstract

Boron Carbide is an attractive material for various applications that require high hardness and neutron absorption. Fully dense boron carbide bodies are usually fabricated using hot pressing at temperatures above 2000 °C. Therefore, the production cost is very high, that constitutes the major drawback for widespread applications in the fields of defense and nuclear energy. An alternative route to decrease the production costs is the reactionbonded technique (RBBC). In this latter, a preform of porous B 4 C is obtained by compaction and partial densification. Then the material is infiltrated by molten metal or alloy. The metal can react with residual carbon and boron carbide to form carbide. This technique was extensively studied using conventional furnace but the use of microwave as a source of heating, as not used for this purpose so far, or only in a very few attempts. In the present study, the microstructure and mechanical properties of reaction bonding B 4 C infiltrated by silicon using microwave (2.45GHz) heating will be presented. The results will be discussed in the light of conventional RBBC.

The effect of microwave heating on the microstructure and the mechanical properties of reaction‐bonded boron carbide

“…Note: These observations explain the almost complete transformation of the initial B 4 C in the composites, fabricated from fine (less than 5 μm) B 4 C powders, into the ternary carbide phase …”

Investigation of Microstructural Features and Mechanical Characteristics of the Pressureless Sintered B4C/C(Graphite) Composites and the B4C-SiC-Si Composites Fabricated by the Silicon Infiltration Process

“…The EDS spectroscopic analysis depicted that the silicon infiltrated composites were composed primarily of boron, silicon, and carbon, thereby demonstrating that the composites obtained following silicon infiltration comprised boron carbide and silicon carbide along with some content of silicon. It can therefore be assumed that the liquid silicon infiltrated into the interior of the composite and produce silicon carbide upon reaction with boron carbide, according to the following reaction equations [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ]: 5 Si + 3 B 4 C = 3 SiC + 2 SiB 6 2 Si + B 4 C = SiC + SiB 4 …”

“…The liquid silicon underwent a chemical reaction with graphite producing silicon carbide as shown by the following chemical reactions [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ]: Si + C = SiC …”

“…While the boron carbide reacted only partially [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ], the graphite reacted completely with silicon producing silicon carbide [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ]. The residual boron carbide and silicon existed within the matrix of the composite [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ] and together with silicon carbide gave rise to the B 4 C-SiC-Si composites [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ]. The pressureless sintered B 4 C/C(graphite) composites are thus transformed into the B 4 C-SiC-Si composites via the silicon infiltration process [ 40 ,…”

“…The residual boron carbide and silicon existed within the matrix of the composite [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ] and together with silicon carbide gave rise to the B 4 C-SiC-Si composites [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ]. The pressureless sintered B 4 C/C(graphite) composites are thus transformed into the B 4 C-SiC-Si composites via the silicon infiltration process [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ]. The microstructural details, phase composition, and mechanical characteristics of the B 4 C/C(graphite) composites as well as B 4 C-SiC-Si composites fabricated by the silicon infiltration process were then investigated and compared.…”