The effect of carbon nanotubes introduction on the mechanical properties of reaction bonded boron carbide ceramics

Advances, Challenges, and Applications of Graphene and Carbon Nanotube-Reinforced Engineering Ceramics

Engineering ceramics and their composites are widely used owing to their excellent properties, including high wear, corrosion and heat resistance, low friction coefficient, and low thermal conductivity; thus, the current paper presents a comprehensive review of the most common types of engineering ceramics, demonstrating their key properties, advantages, potential applications, and challenges. This paper also provides prevailing methods for tackling the engineering ceramic challenges and maximizing their applicability. This review paper focuses on alumina (Al2O3), silicon carbide (SiC), zirconia (ZrO2), aluminum nitride (AlN), and silicon nitride (Si3N4), and explores their usability in automotive, aerospace, and tribological applications. Additionally, the incorporation of reinforcing nanomaterials, i.e., graphene and carbon nanotubes or their combination with second-phase reinforcing nanomaterials in these types of ceramics to improve their physico-mechanical properties is also discussed. By strategically adding these reinforcing materials, the brittleness of ceramics can be mitigated, leading to materials that are more suitable for demanding applications in various high-performance industries.

Continuous SiC Skeleton-Reinforced Reaction-Bonded Boron Carbide Composites with High Flexural Strength

Reaction-bonded boron carbide (RBBC) composites have broad application prospects due to their low cost and net size sintering. The microstructure, reaction mechanism of boron carbide with molten silicon (Si), and mechanical properties have been substantially studied. However, the mechanical properties strengthening mechanism of reaction-bonded boron carbide composites are still pending question. In this study, dense boron carbide ceramics were fabricated by liquid Si infiltration of B₄C-C preforms with dispersed carbon black (CB) as the carbon source. Polyethyleneimine (PEI) with a molecular weight of 1800 was used as the dispersant. CB powders uniformly distributed around boron carbide particles and efficiently protected them from reacting with molten Si. The uniformly distributed CB powders in situ reacted with molten Si and formed uniformly distributed SiC grains, thus forming a continuous boron carbide-SiC ceramic skeleton. Meanwhile, the Si content of the composites was reduced. Using PEI-dispersed CB powders as additional carbon source, the composites' flexural strength, fracture toughness, and Vickers hardness reach up to 470 MPa, 4.6 MPa·m^1/2, and 22 GPa, which were increased by 44%, 15%, and 10%, respectively. The mechanisms of mechanical properties strengthening were also discussed.

Effect of C3-Alcohol Impurities on Alumina-Catalyzed Bioethanol Dehydration to Ethylene: Experimental Study and Reactor Modeling

The impact of feedstock impurities on catalytic process is among the crucial issues for processing real raw materials. A real and model 92%-bioethanol contaminated with 0.03–0.3% mol 1-propanol or 2-propanol were used to make ethylene on a proprietary alumina catalyst in isothermal flow reactor. We proposed a formal kinetic model to describe the impure bioethanol conversion to ethylene and byproducts and used it to evaluate the multi-tubular reactor (MTR) for 60 KTPA ethylene production. The simulated data agree well with experimental results. Under reaction-controlled conditions, C3-alcohols strongly suppress the formation of by-products and ethylene-from-ethanol, and slightly inhibit the formation of ethylene-via-ether. It is the suppression of the ethylene-via-ether route that causes a decrease in ethanol conversion. The predominant formation of ethylene-via-ether results in an increased ethylene yield but doubling the catalyst load is required to achieve conversion as for pure feedstock. 2-Propanol has a stronger effect on dehydration than 1-propanol. Diffusion inside the grain’s levels out the effect of C3-alcohols on the process in MTR, giving an ethylene yield as high as ~98% while dehydrating a contaminated 92% ethanol. However, impurities dilute ethanol and generate propylene (which contaminates target product), and these worsen feedstock consumption and ethylene productivity in MTR.