Using Mechanical Alloying to Create Bimetallic Catalysts for Vapor-Phase Carbon Nanofiber Synthesis

Abstract

Carbon nanofibers were generated over bimetallic catalysts in an atmospheric pressure chemical vapor deposition (APCVD) reactor. Catalyst compositions of Fe 30 at%, Cu and Ni 30 at% and Cu were mechanically alloyed using high-energy ball milling over durations of 4,8,12,16, and 20 h. The catalyst powders were then used to produce carbon nanofibers in ethylene and hydrogen (4:1) at temperatures of 500, 550, and 600 °C. The microstructures of the catalysts were characterized as a function of milling time as well as at deposition temperature. The corresponding carbon deposition rates were assessed and are correlated to the microstructural features of each catalyst. The milling process directly determines the performance of each catalyst toward carbon deposition, and both catalysts performed comparably to those made by traditional co-precipitation methods. Considerations in miscible and immiscible nanostructured alloy systems are discussed.

Direct Synthesis of Nanofibrous Nonwoven Carbon Components: Initial Observations, Capabilities, and Challenges

“…% Cu catalyst was chosen for its ease of processing, low cost, and high selectivity toward nanofiber growth. In kinetic studies [31], it resulted in a deposition rate of $5000% mass gain per hour of reaction and yields a fiber mass dominated by nanofibers approximately 100 nm in diameter with a high degree of integration, even during unconstrained growth. The growth rate observed in this work was $ 2100% mass gain per hour of reaction (e.g., 20 mg of catalyst yields 2 g of carbon over about 5 h).…”

“…Each alloy was milled with 1 wt.% stearic acid (reagent grade, 95%) to prevent cold welding during the 4 h milling duration (see Ref. [31], for more information on this preparation method). All starting materials were obtained from Sigma-Aldrich and used without modification.…”

Parametric Effects of Mechanical Alloying on Carbon Nanofiber Catalyst Production in the Ni-Cu System

“…Each alloy was milled with 1 wt % stearic acid to prevent cold welding. Separate powder charges were milled under argon for 5,10,15,20,30,45,60,75,90,120,180 and 240 min, in that order, without cleaning the vial in between runs to reduce contamination from the vial and milling media (stainless steel). Pure nickel was milled under the same conditions as a control.…”

“…Pure nickel was milled under the same conditions as a control. Previous studies [20,21] demonstrated pure copper to have negligible catalytic properties for CNF synthesis and was not used as a control. Ni and Ni 30 at % Cu were also used in "unmilled" form as an experimental control.…”

“…MA is a powder processing method that produces alloys from elemental powder mixtures using repeated impacts from milling media to plastically deform and intimately mix the materials [19]. Previous work [20] determined that mechanical alloying is a viable method for creating bimetallic catalysts used in CNF synthesis. Nickel-copper and iron-copper alloys were prepared by MA and their performance in the deposition of CNFs was found comparable to literature values for alloys formed using the co-precipitation method.…”