Process-Structure Map for Diamond-Like Carbon Fibers from Ethene at Hyperbaric Pressures

Abstract

High‐pressure laser chemical vapor deposition (HP‐LCVD) is a powerful tool for growing complex microstructures at rapid rates. Not only is it possible to deposit functionally graded materials, but new metastable phases, alloys, and composite materials may be realized. In this paper, the diversity of microstructures that may be obtained through HP‐LCVD is demonstrated, including the growth of metastable materials, e.g., diamond‐like carbon (DLC). For the first time, a pressure–temperature (P–T) phase diagram has been created for HP‐LCVD, identifying nine distinct material phases of carbon from ethene. Regions of high sp3 content are identified via Raman spectroscopy. The kinetics, rate limitations, and thermodynamics of the process are also characterized at hyperbaric pressures, creating a first‐ever process‐rate map—covering the entire useful pressure range for ethene. Thermodynamically enhanced growth is also documented for the first time, where the contribution of the heat of reaction is much greater than the incident laser power—demonstrating a quasi‐self‐sustaining reaction. Finally, sufficient information is provided to reconstruct specific fiber geometries, structures, and growth rates for potential industrial production of carbon fibers from the gas phase.

On “how to start a fire”, or transverse forced-convection, hyperbaric laser chemical vapor deposition of fibers and textiles

“…where again, A s is the surface area of the hemispherical tip 2r 2 s , h is the heat transfer coefficient, and T is the gas temperature. Note that during steady-state fiber growth, at sufficiently large pressures, the mode of heat transfer can be assumed to be primarily convective, 10 so then, the convective heat loss, Q conv , equals the absorbed laser power, Q L , that is, Q conv ¼ Q L . As a result, (16) can be rewritten:…”

“…HP-LCVD is an emerging process that can be used to deposit three-dimensional microstructures from gasphase precursors using a focused laser beam. [4][5][6][7][8][9][10] At sufficiently high deposition rates, if the laser focus is stationary, the deposit may grow away from the substrate and along the laser beam axis, forming a freestanding fiber. [11][12][13][14][15][16][17][18][19][20][21][22][23] If the orientation and position of the beam is changed slowly relative to the sample during growth, complex three-dimensional structures may be grown in a freeform manner.…”

“…Forced convection, for example through the use of a micronozzle directing gas across the reaction zone, has been studied by several authors with varying results (see Maxwell,9 pp.152-165, Bauerle, 45 Maxwell and Pegna, 46 Goduguchinta and Pegna, 47 Lackey et al, 48 Duty et al, 49 and Yu 50 ). As fiber growth can be mass-transport-limited (MTL), 9 kinetically limited (KL), 10 or both, 10 during HP-LCVD, the addition of forced convection can simultaneously increase the transport rate while lowering the reaction temperature at the fiber. The purpose of this paper is to show which of these growth limitations dominates, as the velocity of a flow is increased-for the geometry of a transverse flow, as illustrated in Figure 3.…”

Demonstrating a Target Supply for Inertial Fusion Energy

“…14 The challenge of the HIF target that is unique for fabrication is its distributed radiators. To fabricate these materials, a new process, high-pressure laser chemical vapor deposition (LCVD), is being experimentally demonstrated 27 LCVD utilizes a laser to catalyze a chemical vapor deposition in a controlled manner. A precursor molecule containing the high Z element of interest is laser-decomposed to form lattices of high Z low density material.…”

A novel synthetic strategy for bioinspired functionally graded nanocomposites employing magnetic field gradients

“…Besides exhibiting locally varying mechanical properties, [8][9][10] FGMs may combine different and apparently incompatible features within the same structure, giving rise to a variety of unusual, high-impact properties, such as spatially varying electronic performances, 11 super hardness, 12 graded refractive indexes, 13 improved wear resistance and efficient residual stress distribution. [14][15][16] Depending on the desired gradient morphology and on the nature of the materials employed, techniques such as chemical vapor deposition (CVD), 17 powder densification, 18 thermal spraying, 19 solvent-welding, 20 centrifugal casting, electrodeposition (EPD) or self-driven transport-based processes [21][22][23] may be used. However, these may either be multi-step processes, often requiring the use of computer-aided automated systems and making use of expensive apparatuses and/or complex synthetic strategies, or have strong limitations when parts with complex geometries are required.…”