Preparation and Evaluation of Hybrid Composites of Chemical Fuel and Multi-walled Carbon Nanotubes in the Study of Thermopower Waves

Summary

A protocol for conducting thermopower wave experiments is presented. The synthesis of hybrid composites of a chemical fuel and micro/nanostructured material, manufacturing of a thermopower wave generator, and methods for measuring the corresponding physical phenomena are described.

Abstract

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs along the interface between the fuel and core materials. Simultaneously, dynamic changes in thermal and chemical potentials across the micro/nanostructured materials result in concomitant electrical energy generation induced by charge transfer in the form of a high-output voltage pulse. We demonstrate the entire procedure of a thermopower wave experiment, from synthesis to evaluation. Thermal chemical vapor deposition and the wet impregnation process are respectively employed for the synthesis of a multi-walled carbon nanotube array and a hybrid composite of picric acid/sodium azide/multi-walled carbon nanotubes. The prepared hybrid composites are used to fabricate a thermopower wave generator with connecting electrodes. The combustion of the hybrid composite is initiated by laser heating or Joule-heating, and the corresponding combustion propagation, direct electrical energy generation, and real-time temperature changes are measured using a high-speed microscopy system, an oscilloscope, and an optical pyrometer, respectively. Furthermore, the crucial strategies to be adopted in the synthesis of hybrid composite and initiation of their combustion that enhance the overall thermopower wave energy transfer are proposed.

Introduction

Chemical fuels have very high energy density and have been widely used as useful energy sources in a broad range of applications from microsystems to macrosystems.¹ In particular, many researchers have endeavored to use chemical fuels as the energy source for next-generation micro/nanosystems-based technologies.² However, owing to the difficulty in integrating energy conversion components in extremely small spaces in micro/nanodevices, there are fundamental limitations to the conversion of chemical fuels into electrical energy. Therefore, the combustion of chemical fuels has mainly been employed for the production of chemical or mechanical energy....

Protocol

1. Synthesis of Vertically Aligned Multi-walled Carbon Nanotubes (VAMWCNTs)

1. Preparation of wafer and deposition of catalyst layers
   1. Prepare a n-type (100) Si wafer.
   2. Deposit a 250-nm-thick SiO₂ layer on the Si wafer by thermal oxidation or alternative methods such as sputtering. Inject 200 sccm of O₂ for 3 hr 20 min at 1,000 °C in a horizontal furnace.
   3. Use bulk Al₂O₃ (99.9%) as a multi-sputter (RF power: 1,000 W) source and deposit a 10 nm-thick Al₂O₃ (99.9%) layer on the SiO₂ layer. Use a slow deposition rate of 10 nm/min with a deposition pressure....

Results

The aligned MWCNT array, as a core nanostructured material for thermopower waves, was synthesized by TCVD,^11-13 as shown in Figure 4A. The diameter of as-grown MWCNTs is 20–30 nm (Figure 4B). The aligned hybrid composite of the picric acid/sodium azide/MWCNTs is shown in Figure 5A. This composite was synthesized by the wet impregnation process,¹⁴ as described in the protocol section. In order to form an interface between the chemical fuel and MWCNTs.......

Discussion

The protocols of thermopower wave experiments involve critical steps that enable ideal thermal wave propagation as well as electrical energy generation. First, the specific position of ignition and the corresponding reaction transfer are considerable factors in controlling energy conversion from thermopower waves. Ignition at one end of the hybrid composite launched guided combustion along the interfaces between the core materials and chemical fuels in one direction. However, ignition at any other position generated bi-d.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
4” n-type silicon wafer	Unisill	4” Si-wafer
Al2O3	TAEWON	A-1008	99.9999% Purity
Fe	Sigma Aldrich	267945	99.9999% Purity
Ar	Seoul specialty gas	Ar(N60)	99.9999% Purity
C2H4	Seoul specialty gas	C2H4	99.5% Purity
H2	Seoul specialty gas	H2(N60)	99.9999% Purity
Silver paste	Fujikura Kasei	D-550
Picric acid	Sigma Aldrich	197378	>98% Purity Highly toxic
Sodium azide	Sigma Aldrich	S2002	>99.5% Purity
Acetonitrile	Sigma Aldrich	271004	99.8% Purity
Power supply	Mastech	HY3010
TCVD	Scientech	TCVD
Oscilloscope	Tektronix	DPO2004B
High-speed microscopy system	Phantom	V7.3