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Obtaining of SiO2 micro-tubes in plasma jet
Materials Science and Engineering B56 (2001) 265– 268
www.elsevier.com/locate/mseb
Letter
Obtaining of SiO2 micro-tubes in plasma jet Ioan Bica West Uni6ersity of Timisoara, Faculty of Physics, Bd. V. Paˆr6an no. 4, 1900 Timis¸oara, Romania Received 21 February 2001; received in revised form 9 May 2001; accepted 14 May 2001
Abstract An experimental method for producing SiO2 micro-tubes in the argon plasma jet is presented. SiO2 micro-tubes, having the exterior diameter between 10 and 11.2 mm, and respectively the interior diameter between 3.44 and 6.49 mm were obtained. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Micro-tubes; Plasma jet; Micro-particles; SiO2; Fibers
1. Introduction Micro-tubes are materials with cylindrical shape, and the values of their diameters varies between 0.1 and 100 mm. These materials are used to produce micro-systems: dielectric micro-systems with pre-established dielectric permitivity [1], reflecting layers [2], magneto-rheological fluids [3] used for ultra-fine polishing of solid surfaces [4] and to produce dampers [5], valves [6] and mechanical vibration transducers [7], etc. SiO2 micro-tubes are also used in biological and medical researches and to transport well dosed active substances, respectively. Since there is interest in this type of materials, we will present in this paper the experimental device designed to produce SiO2 micro-tubes in plasma jet and the experimental results.
2. Experimental device The experimental device mentioned above is shown schematically in Fig. 1. The device consists of the de plasma generator with: (1) cathode; (2) anode; (3) current source; (4) advance system for the rod 5, which is introduced in plasma jet 6. The dc generator is water cooled (water discharge: 0.25×10 − 3 m3 s − 1;
water pressure: 2 bar). It runs at a maximum discharge current intensity of 600 Adc, in argon medium. The current source has an idle voltage Uo =160 Vdc 9 10% and it supplies a continuously adjustable electric current in the range of 40 and 300 Adc 910% on a pure ohmic charge. The advance system for the rod allows: a modification of the incidence angle, h, between, p/6 and p/2 radian; a uniform motion of the rod with the velocity between 1× 10 − 3 m s − 1 9 10% and 3× 10 − 3 m s − 1 9 5%; a pulsatory motion of the rod, with a continuously adjustable repetition period in the range of 1 s910% and 10 s95%. A thermally ionized medium is formed at an electric current I, pre-establish by the electric arc primed between the electrodes of the plasma generator in argon medium. Under the pressure of argon (1.5 bar), the ionized gas is pushed out through the nozzle of the generator anode, and it forms the plasma jet 6. The diameter of the generator nozzle is d. For the vaporization of a pre-established quantity of the rod substance a power Q= 2× 108 W m − 2 is necessary in the plasma jet. The vapours and the ionized argon form a system, which has the same velocity as the plasma jet.
0921-5107/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 1 0 7 ( 0 1 ) 0 0 6 8 1 - X
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I. Bica / Materials Science and Engineering B56 (2001) 265–268
Fig. 1. Experimental device for production of SiO2 micro-tubes in plasma jet: (1) tungsten electrode; (2) nozzle; (3) current source; (4) leading system for the rod; (5) rod; (6) plasma jet. U, arc voltage; I, electric current intensity; h, advance angle of the rod in plasma jet; 6, advance velocity.
In under-cooling conditions, in the marginal zones of the vapour–gas system, the formation of a membrane in liquid phase takes place. The membrane has cylindrical shape because of the surface tension and because of the stable fluid flow [8]. This membrane separate the vapour– gas system by the rest of the fluid [9]. A non-stationary condensation diffusion process, followed by the vapours condensation, takes place in the closed space, until the quantity of vapours is condensed on the membrane. The membrane is thickening, and it forms a space full of gas inside. This space has a tube space and its dimensions are pre-established by controlling the technological parameters.
Fig. 2. SiO2 fibers (with and without hollow) and particles shown at optical microscope.
Fig. 3. SiO2 micro-particles stroke: fiber diameter is 0.2 mm and micro-particle diameters are between 4 and l6 mm.
I. Bica / Materials Science and Engineering B56 (2001) 265–268
267
Fig. 4. SiO2 micro-particles, with diameters between 12 and 36 mm.
3. Experimental results Using the experimental setup presented in Fig. 1 there were obtained SiO2 micro-tubes in plasma jet. The electrical characteristics of the discharge are: the arc voltage: U = 80 Vdc; the arc current intensity: I =240 Adc; the distance between the plasma generator electrodes: 5×10 − 3 m; the argon discharge: 0.5×10 − 3 m − 3 s − 1, at pressure 1.5 bar; the nozzle diameter: d =3 × 10 − 3 m.
A plasma jet with approximately 8× 10 − 2 m length is formed at a 1.85 bar relative pressure of argon. The chamotte rod, with 10× 10 − 3 m diameter, is introduced in plasma jet, at an incidence angle h=p/2 radian. Particles, with different shapes and dimensions are obtained (Fig. 2) in a pulsatory motion regime of the rod (3 s— repetition period), with 6= 5×10 − 3 m s − 1 — the rod velocity. The chemical analysis indicates the composition of the resulting produce, as follows: 93% SiO2; 0.1% Na2O; 6.2% Al2O3; 0.2% CaO and 0.5% Fe2O3.
Fig. 5. Cross section through SiO2 tubes (unfinished surfaces).
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I. Bica / Materials Science and Engineering B56 (2001) 265–268
The transition fluid flow [8] corresponds to a continuous regime at a rod motion velocity in plasma, 6= 2.5 ×10 − 3 m s − 1. Consequently, micro-particles connected with fibers are obtained (Fig. 3). On the other side, for velocity values 6 =1.7 ×10 − 3 m s − 1, the fluid flow is unstable, and the experimental device produce individual micro-particles (Fig. 4). When the incidence angle decreases from p/2 to p/4 radian and the rod has a uniform motion in plasma (6 =2 × 10 − 3 m s − 1), the fluid flow becomes stable. By solidification, fibers appear. Using an optical microscope, it can be observed that the SiO2 fibers have tubular shape. Their exterior diameter varies between 10 and 11.2 mm, and the interior one varies between 3.44 and 6.49 mm (Fig. 5).
4. Conclusions 1. The experimental device presented (Fig. 1) allows generation of plasma jet at technological parameters necessary for producing SiO2 micro-particles and -tubes. 2. SiO2 micro-particles are obtained in continuous mo-
.
tion regime of the chamotte rod (6= 2.5×10 − 3 m s − 1), at the value h= p/2 radian for the incidence angle. 3. For the incidence angle h= p/2 radian and the velocity 6 =1.7×10 − 3 m s − 1, the exterior diameter of SiO2 micro-tubes varies between 10 and 11.2 mm, and the interior one varies between 3.42 and 6.49 mm.
References [1] J. Paletto, The´ se, L’Universite´ Claude-Bernard, Lyon, 1972. [2] G.J. Liu, L. David, S.r. Wilcox, J. Mater. Res. 10 (1995) 84. [3] A.J. Margida, K.D. Weiss, J.D. Carlson, J. Mod. Phys. B10 (1996) 3335. [4] W.I. Korodonski, S.D. Jacobs, J. Mod. Phys. B10 (1996) 2837. [5] H. Janocha, B. Rech, R. Bo¨ lter, J. Mod. Phys. B10 (1996) 3243. [6] J.D. Carlson, D.M. Catanzarite, K.A. St. Clair, J. Mod. Phys. B10 (1996) 2857. [7] S.H. Choi, Z.T. Choi, S.B. Choi, C.C. Chong, J. Mod. Phys. B10 (1996) 3143. [8] I. Bica, In: Mirton (Ed.), Mesoscopic Particles, Timis¸oara, 1997, p. 135, (in Romanian). [9] I. Bica, Mat. Sci. Eng. B77 (2000) 210 – 212.
www.elsevier.com/locate/mseb
Letter
Obtaining of SiO2 micro-tubes in plasma jet Ioan Bica West Uni6ersity of Timisoara, Faculty of Physics, Bd. V. Paˆr6an no. 4, 1900 Timis¸oara, Romania Received 21 February 2001; received in revised form 9 May 2001; accepted 14 May 2001
Abstract An experimental method for producing SiO2 micro-tubes in the argon plasma jet is presented. SiO2 micro-tubes, having the exterior diameter between 10 and 11.2 mm, and respectively the interior diameter between 3.44 and 6.49 mm were obtained. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Micro-tubes; Plasma jet; Micro-particles; SiO2; Fibers
1. Introduction Micro-tubes are materials with cylindrical shape, and the values of their diameters varies between 0.1 and 100 mm. These materials are used to produce micro-systems: dielectric micro-systems with pre-established dielectric permitivity [1], reflecting layers [2], magneto-rheological fluids [3] used for ultra-fine polishing of solid surfaces [4] and to produce dampers [5], valves [6] and mechanical vibration transducers [7], etc. SiO2 micro-tubes are also used in biological and medical researches and to transport well dosed active substances, respectively. Since there is interest in this type of materials, we will present in this paper the experimental device designed to produce SiO2 micro-tubes in plasma jet and the experimental results.
2. Experimental device The experimental device mentioned above is shown schematically in Fig. 1. The device consists of the de plasma generator with: (1) cathode; (2) anode; (3) current source; (4) advance system for the rod 5, which is introduced in plasma jet 6. The dc generator is water cooled (water discharge: 0.25×10 − 3 m3 s − 1;
water pressure: 2 bar). It runs at a maximum discharge current intensity of 600 Adc, in argon medium. The current source has an idle voltage Uo =160 Vdc 9 10% and it supplies a continuously adjustable electric current in the range of 40 and 300 Adc 910% on a pure ohmic charge. The advance system for the rod allows: a modification of the incidence angle, h, between, p/6 and p/2 radian; a uniform motion of the rod with the velocity between 1× 10 − 3 m s − 1 9 10% and 3× 10 − 3 m s − 1 9 5%; a pulsatory motion of the rod, with a continuously adjustable repetition period in the range of 1 s910% and 10 s95%. A thermally ionized medium is formed at an electric current I, pre-establish by the electric arc primed between the electrodes of the plasma generator in argon medium. Under the pressure of argon (1.5 bar), the ionized gas is pushed out through the nozzle of the generator anode, and it forms the plasma jet 6. The diameter of the generator nozzle is d. For the vaporization of a pre-established quantity of the rod substance a power Q= 2× 108 W m − 2 is necessary in the plasma jet. The vapours and the ionized argon form a system, which has the same velocity as the plasma jet.
0921-5107/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 1 0 7 ( 0 1 ) 0 0 6 8 1 - X
266
I. Bica / Materials Science and Engineering B56 (2001) 265–268
Fig. 1. Experimental device for production of SiO2 micro-tubes in plasma jet: (1) tungsten electrode; (2) nozzle; (3) current source; (4) leading system for the rod; (5) rod; (6) plasma jet. U, arc voltage; I, electric current intensity; h, advance angle of the rod in plasma jet; 6, advance velocity.
In under-cooling conditions, in the marginal zones of the vapour–gas system, the formation of a membrane in liquid phase takes place. The membrane has cylindrical shape because of the surface tension and because of the stable fluid flow [8]. This membrane separate the vapour– gas system by the rest of the fluid [9]. A non-stationary condensation diffusion process, followed by the vapours condensation, takes place in the closed space, until the quantity of vapours is condensed on the membrane. The membrane is thickening, and it forms a space full of gas inside. This space has a tube space and its dimensions are pre-established by controlling the technological parameters.
Fig. 2. SiO2 fibers (with and without hollow) and particles shown at optical microscope.
Fig. 3. SiO2 micro-particles stroke: fiber diameter is 0.2 mm and micro-particle diameters are between 4 and l6 mm.
I. Bica / Materials Science and Engineering B56 (2001) 265–268
267
Fig. 4. SiO2 micro-particles, with diameters between 12 and 36 mm.
3. Experimental results Using the experimental setup presented in Fig. 1 there were obtained SiO2 micro-tubes in plasma jet. The electrical characteristics of the discharge are: the arc voltage: U = 80 Vdc; the arc current intensity: I =240 Adc; the distance between the plasma generator electrodes: 5×10 − 3 m; the argon discharge: 0.5×10 − 3 m − 3 s − 1, at pressure 1.5 bar; the nozzle diameter: d =3 × 10 − 3 m.
A plasma jet with approximately 8× 10 − 2 m length is formed at a 1.85 bar relative pressure of argon. The chamotte rod, with 10× 10 − 3 m diameter, is introduced in plasma jet, at an incidence angle h=p/2 radian. Particles, with different shapes and dimensions are obtained (Fig. 2) in a pulsatory motion regime of the rod (3 s— repetition period), with 6= 5×10 − 3 m s − 1 — the rod velocity. The chemical analysis indicates the composition of the resulting produce, as follows: 93% SiO2; 0.1% Na2O; 6.2% Al2O3; 0.2% CaO and 0.5% Fe2O3.
Fig. 5. Cross section through SiO2 tubes (unfinished surfaces).
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I. Bica / Materials Science and Engineering B56 (2001) 265–268
The transition fluid flow [8] corresponds to a continuous regime at a rod motion velocity in plasma, 6= 2.5 ×10 − 3 m s − 1. Consequently, micro-particles connected with fibers are obtained (Fig. 3). On the other side, for velocity values 6 =1.7 ×10 − 3 m s − 1, the fluid flow is unstable, and the experimental device produce individual micro-particles (Fig. 4). When the incidence angle decreases from p/2 to p/4 radian and the rod has a uniform motion in plasma (6 =2 × 10 − 3 m s − 1), the fluid flow becomes stable. By solidification, fibers appear. Using an optical microscope, it can be observed that the SiO2 fibers have tubular shape. Their exterior diameter varies between 10 and 11.2 mm, and the interior one varies between 3.44 and 6.49 mm (Fig. 5).
4. Conclusions 1. The experimental device presented (Fig. 1) allows generation of plasma jet at technological parameters necessary for producing SiO2 micro-particles and -tubes. 2. SiO2 micro-particles are obtained in continuous mo-
.
tion regime of the chamotte rod (6= 2.5×10 − 3 m s − 1), at the value h= p/2 radian for the incidence angle. 3. For the incidence angle h= p/2 radian and the velocity 6 =1.7×10 − 3 m s − 1, the exterior diameter of SiO2 micro-tubes varies between 10 and 11.2 mm, and the interior one varies between 3.42 and 6.49 mm.
References [1] J. Paletto, The´ se, L’Universite´ Claude-Bernard, Lyon, 1972. [2] G.J. Liu, L. David, S.r. Wilcox, J. Mater. Res. 10 (1995) 84. [3] A.J. Margida, K.D. Weiss, J.D. Carlson, J. Mod. Phys. B10 (1996) 3335. [4] W.I. Korodonski, S.D. Jacobs, J. Mod. Phys. B10 (1996) 2837. [5] H. Janocha, B. Rech, R. Bo¨ lter, J. Mod. Phys. B10 (1996) 3243. [6] J.D. Carlson, D.M. Catanzarite, K.A. St. Clair, J. Mod. Phys. B10 (1996) 2857. [7] S.H. Choi, Z.T. Choi, S.B. Choi, C.C. Chong, J. Mod. Phys. B10 (1996) 3143. [8] I. Bica, In: Mirton (Ed.), Mesoscopic Particles, Timis¸oara, 1997, p. 135, (in Romanian). [9] I. Bica, Mat. Sci. Eng. B77 (2000) 210 – 212.