Obtaining iron and graphite nanoparticles in argon plasma

The experimental equipment designed for obtaining iron and graphite nanoparticles in argón plasma, the building mechanisms of pgirticles as well as the experimental results on Fe(CO)5 and ,2-ethylhexyl-iron maleat dissociation by plasma jet are presented. The dimensions of the metal partióles obtained range from 30 to 200 A, while the graphite partióles vary from 30 to 100 A.

An experimental capacitive plasma equipment for the thermal dissociation of a solution of toluene with Fe(C0)5 was proposed in (17).The nanoparticles obtained with this equipment were succesfully used for the preparation of magnetic fluid samples.
Iron and graphite nanoparticles could be obtained using argón plasma jets.The corresponding equipment and the experimental results are presented below.1900, Timisoara (Romania).

EXPERIMENTAL EQUIPMENT
The equipment designed for obtaining nanoparticles in argón plasma is shown in figure 1.The operation mode of the equipment is as follows.
The electric are in the argón médium is started between the cathode K and the anode A of the plasma generator, employing a high frequency generator.The source S supplies the electric are at a preset, constant-in-time current.Under argón pressure, a jet of ionized gas streams out through the nozzle A of the plasma generator, with the flow rate controlled by the R2 flow controller.
A solution of Fe(C0)5 or 2-ethyl-hexyl-iron maleat is introduced through the tube TI in the plasma jet.The carrier gas flow is adjusted by the flow controller Rl, while the gas/solution ratio is adjusted by the sprayer/doser 5.The thermal dissociation reaction of Fe(C0)5 takes place in the plasma jet.The reaction elements condénsate so that, for a given temperature, pressure and concentration phase, solid particles are formed.
The particles are drawn by the gas in the collecting liquid MLl, which is thermostated and strongly stirred by the agitator M. The particles which remain in the carrier gas are driven through the water/gas heat exchanger 4, and then into the collecting chamber 3. The fine particle fraction is collected by the liquid ML2.
The liquids MLI and ML2 containing the nanoparticles are recovered through the taps R3 and R4.The residual gases are drawn out by the pipe T2.

THERMAL DISSOCIATION OF Fe(CO)5. EXPERIMENTAL RESULTS
The speed, v^ of the plasma jet, obtained with the plasma generator shown in figure 1, has a linear dependence of the intensity, /, of the discharge current (Fig. 2).At speeds between 130 and 230 m/s, the flow is turbulent {R^ » 1) (18 and 19).The Fe(CO)5 solution drops introduced under argón pressure into the plasma jet have a speed of (18 and 19): Vd t +t [1] and covers in t time the distance: The time f ( 19) is obtained from the expression: The Fe(C0)5 solution drop diameter, d^, is estimated to be in the range 0.1-1 (xm.For (20), v^ = 3.4-10-3 m/s, pp = 6.5-103 kg-m-3, ^ = 6.66 and, respectively, for v^ = 132 m/s (Fig. 2) (3) yields /' = 86-10-12 s.
Considering that í' » t, eq.[1] yields v^ ^ Vy From [2], it can be seen that L is approximately equal to the length of the plasma jet.
Mossbauer spectroscopic analysis of the achieved material, performed at the IFTM Bucharest showed the existence of 26.5 % of paramagnetic iron partióles, 18 % of supermagnetic partióles (which are not ordered at 70 K) and 55.5 % of iron carbide, repsectively.
Cooling speeds of 4,050 K/(ms) only for about 25 % of the metal partióles created at plasma level,  FiG.6.-Distribución dimensional de las nanopartículas metálicas.
were found to produce an amorphous material.Due to the existence of a notable amount of CO, there is no iron particle carburation during the thermal dissociation of Fe(CO)5.
It is possible to reduce the iron carbide quantity by creating a connection between the 3d free orbitals of iron and nitrogen atoms.This is possible by using mixed plasmagenous gas (Ar + NH3).

OBTAINING GRAPHITE NANOPARTICLES. EXPERIMENTAL RESULTS
The temperatures obtained in argón plasma jets (Fig. 3) (13) initiate the thermal dissociation of 2ethyl-hexyl-iron maleat jet sprayed in argón: Fe[OOC-CH=CH-COO-(CH2)4-CH-CH3] ^ C2H5 Fe + C + H20< [15] .O2 Nanoparticles were obtained at a flow rate of 2 ml/min of 2-ethyl-hexyl-iron maleat at plasma jet parameters corresponding to data shown in figure 7. The granulation of the obtained particles is between 30 and 100 Á, with an average of 63 Á (Fig. 8).Dimensional control of nanoparticles using the 2ethyl-hexyl-iron maleat is done by means of the quantity introduced in argón plasma (22).So, at a 2-ethyl-hexyl-iron maleat flow rate of 6 ml/min, particle granulation increased by about 80 %, comparing to that presented in figure 7.
The obtained powder is coUected in 2-ethylhexyl-sodium-sulphosuccinate.The temperature of the coUecting liquid is maintained at 353 K ± 20 %.
The iron in 2-ethyl-hexyl-iron maleat in a mass ratio of 1/5 is transformed into ultrafine particles.
At pressures of 3-10^ N/m^, a part of the ultrafine iron particles is deposited on the walls of the powder collecting chamber while another part is drawn by residual passes toward the exterior.The cooling speed of 160,000 K/s obtained in the plasma jet makes it possible to obtain not only   crystal graphite (G.C.) but amorphous graphite (G.A.) (Fig. 9).

CONCLUSIONS
Through monitoring pressure, temperature and concentration of Fe(CO)5 or 2-ethyl-hexyl-iron maleat both the nucleation and the partióle growing conditions are estabilised.The dimensional control of the partióles is performed from material flow rate introduced to plasma jet.Besides orystalline graphite, also amorphous graphite was obtained at a oooling rate of ló-lO^ K/s.

TABLE L -
Optimal technological conditions found experimentally