Alireza Badakhshan

Photothermal deoxygenation of graphene oxide for patterning and distributed ignition applications.

A xenon discharge tube, such as is used to produce a photographic flash, has been reported to cause the ignition of carbon nanotubes, silicon nanowires, and welding of nanofibers of the conducting polymer polyaniline. In these reactions, the high surface-to-volume ratio of the nanomaterials being irradiated, coupled with the inability of the small structures to efficiently dissipate the absorbed energy, leads to a rapid increase in temperature and subsequent ignition or welding of the materials. Although heating materials through the use of light energy is not a new phenomenon, achieving such a rapid and dramatic temperature change using only millisecond pulses of light demonstrates a tangible and technologically significant capability that is unique to nanoscale materials. Graphene oxide (GO) is a deeply colored, water dispersible, oxidized form of graphene obtained through the treatment of graphite powder with powerful oxidizing agents. Although GO has been known for over 150 years, only recently have scientists had access to the tools necessary to properly analyze its atomically thin sheet structure. This has rekindled interest in graphite oxide and has led to a number of recent discoveries, including: the stacking of GO platelets to form paper-like materials of high modulus and strength. Many studies have suggested that GO can be reduced to graphene-like carbon sheets by applying chemical reducing agents or by using thermal treatments. This has led to speculation that GO could find use as a precursor in a bulk route to dispersible graphene sheets. Already, several groups have succeeded in creating conducting polymer composites, transparent conducting films, and simple electronic devices based on reduced GO. In addition to the chemical reduction of GO, Aksay, et al. have reported the thermal deoxygenation of GO to create functionalized graphene sheets upon rapid heating to 1100 8C under an inert atmosphere. These organic solvent dispersible sheets have enabled the direct creation of polymer composites, without the need for surfactants. Thermal deoxygenation of GO to form graphitic carbon dates back to the 1960s when Boehm and Scholz first reported on the ignition and deflagration of graphite oxides prepared by different methods. Upon rapid heating to temperatures of 200 8C, GO decomposes to the most thermodynamically stable oxide of carbon, CO2. Along with the exothermic release of CO2, H2O, and CO also form as minor products. [31]

Raman Scattering Measurement in the Initial Region of Sub- and Supercritical Jets

Abstract : A high-pressure chamber is used to investigate and further enhance our knowledge and physical understanding on effects of thermodynamical subcritical-to-supercritical transition of ambient condition on cryogenic liquid injection using two-dimensional scattering. Pure liquid N2 is injected into N2. The injector is a 508-micron diameter straight hole having a long length-to-diameter ratio of 100. The optical setup uses a pulsed Nd:Yag laser frequency-doubled to 532 nm. Difficulties arise with optical breakdown of the N2 molecules in drops and ligaments by local focusing of the laser beam dominating the Raman signal particularly at sub- and near-critical regions. The severity of this problem is reduced by stretching the laser pulse width using a double-loop design with mirrors and beam splitters. Careful and painstaking alignment is needed to take advantage of this pulse-stretcher design. Two-dimensional images are taken near the injector and results interpreted in terms of density plots. At subcritical ambient conditions a small number of images are needed for averaging and strong Raman signal is obtained.

Nano-Ignition Torch Applied to Cryogenic H2/O2 Coaxial Jet

Abstract : A high-pressure photoignition torch has been developed which takes advantage of the photoignition properties of single wall carbon nanotubes (SWNTs). The goal was to initiate combustion in a cryogenic O2-H2 coaxial injector at about 35 atm (520 psi) at O2 temperature of about 130 K with SWNT-based solid fuel mixtures. Our investigation includes the effects of chamber pressure, the presence of different solid oxidizers such as BKNO3 and KMnO4, as well as solid fuels and solid propellants, on the functionality of the photoignition torch. We have shown that the ignition parameters such as burn temperature, burn duration and the ignition byproducts can be tailored to meet different ignition requirements. It is anticipated that photoignition provides a suitable method for ignition of systems that require the start of combustion at a high pressure up to about 135 atm (2000 psi) as well as ignition of certain thrusters and liquid rocket engines that require an extremely small and light weight torch igniter. This ignition method can be applied to large combustion chambers such as gas turbines, gas generators, liquid rocket engines and possibly multi grain solid rocket motors.