# The Rotating Plasma Source as an innovative tool to synthesize fine powder for industrial applications

Ahmed Hala

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## To cite this version:

Ahmed Hala. The Rotating Plasma Source as an innovative tool to synthesize fine powder for industrial applications. Doctoral. France. 2021. hal-05210972

HAL Id: hal-05210972

https://hal.science/hal-05210972v1

Submitted on 14 Nov 2025

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VIRTUAL
ICOPS
2021

SEPT 12 - 14, 2021

THE 48TH IEEE INTERNATIONAL CONFERENCE ON PLASMA SCIENCE

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# The Rotating Plasma Source (RPS) as an innovative tool to synthesize fine powder for industrial applications

Dr. Ahmed M. Hala

Gaseous Electronics, LLC
Riyadh, Saudi Arabia

www.gaselco.com

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Gaseous Electronics
Content

SCIENCE

TECHNOLOGY

DISCUSSION

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# Science

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# Nanoparticles synthesis

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- Many applications exist in catalysis, energy storage and conversion, and sensing and imaging due to their unique properties of metal and metal oxide nanostructures.

- The new chemical, optical, and thermal properties of metallic nanoparticles are observed when their size is confined to the nanometer length scale.

- Numerous production techniques were developed to control particle size, morphology, aggregation state, crystal structure, surface charge and composition of nanoparticles.

- Metal nanoparticles are prepared by:

- Chemical processes: material synthesis from atomic or molecular species via a suitable chemical reaction, allowing the particles to grow from smaller units.

- Physical processes: targeting bulk materials to produce smaller nanoparticles.
Nanopowders
synthesis methods

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- Physical processes: are "top down" that include lithography, milling, ultrasound treatment, laser ablation & plasma etching.

- Chemical processes: are "bottom up" that rely on material synthesis from atomic or molecular species via a suitable chemical reaction, allowing the particles to grow from smaller units.

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Physical Methods

Chemical Methods

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Aggregation

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Metal Atom

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Precursor Molecule
Copper nanoparticles

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- Copper is a precious but not a noble metal such as gold or silver. In a nanopowder form, it exhibits distinct properties that make it a useful and economical alternative to these metals in many applications.

- Copper nanopowder is prepared by chemical methods that involve toxic materials & physical methods that are clean but still costly.

- Copper nanoparticles have high thermal & electrical conductivity, excellent physiochemical properties, good biocompatibility and high surface activity.

- This talk presents a method to produce fine powder (nanoscale in size) and its application to produce Copper nanoparticles via the Rotating Plasma Source.
# Thermionic emission phen

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## Richardson's equation

At fixed positive potential $V$, the current from a hot cathode to an anode increased with cathode temperature $T$ as:

$$i = a\sqrt{T} e^{\frac{-b}{T}}$$

## Child-Langmuir Law

For an infinitely long, thin hot wire placed concentrically within a cylindrical anode, of radius $r$, the maximum current per unit length is:

$$i = \frac{2\sqrt{2}}{9} \sqrt{\frac{e}{m}} \frac{V^{3/2}}{r}$$
Ion current vs. temperature
of cathode in thermionic
emission plasma sources

- 1st part of the curve is governed by the Richardson's equation.

- 2nd part of the curve is a transition region.

- 3rd part of the curve is a current saturation region whose value is independent of the cathode temperature.

- The anode conditions generally affect the process of extracting high current.

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Inert gases-on
Copper sputter
yields as a function
of ion energy

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- Plasma sputtering allows for the plasma to interact with solids to do some or all of the following effects:

- Target atoms to be ejected.

- Incident ion to be implanted
  on target surface.

- Cascades of impact ions that
  cause surface reordering.

- Ejecting secondary electrons.

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Biased
thermionic
sputter process

* The process initially was designed as a 3-electrodes sputter deposition process.

* By turning the film substrate into a nanoparticles collector, the powder will be accumulated there and can be dispensed under vacuum by a load-lock.

* This ensures that nanoparticles do not get oxidized if this is not desirable.

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## Sheaths & electrodes electric field connection

- Perturbing biased plate sheaths can extend the equipotential contours deep in the opposite side of the biased plate.

- If the cathode is placed appropriately, this will facilitate an electron flow towards the biased plate for better etch selectivity & control.

- Electrons are provided from:

- Primary emission from the cathode &,

- Gas ionization to produce plasma.

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Technology
The Rotating
Plasma Source
(RPS)

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- This configuration uses an RF power supply because this preserves the electrodes longer.

- However, when sputtering one of the electrodes (anode) is desired, a DC power generator can be used.

- Biased thermionic emission technology is versatile and provides selectivity & control.

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The Rotating
Plasma Source
demo

- The capacitively coupled RF powered RPS is demonstrated except for that Copper electrodes are on the outside.

- Based on Child-Langmuir's law, it is feasible to use a DC power source and string a very thin hot metal wire horizontally in the discharge chamber.

- The hot wire acts as a cathode while the Copper foil is engulfed by the cylindrical thick glass chamber.

- Rotation is provided as needed for homogenous treatment of species.

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Working principals of a
fixed fluorescent lamp
discharge

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- Current choke (ballast) is an artificial component limiting the current flow.

- Geometrical design considerations (aspect ratios, thicker walls etc.) are important particularly for the overall distribution of current that interacts with wall materials.

- No-Arc initiation is theoretically possible if a thin hot metal wire is strung concentrically along the tube as a cathode.

- The wall is to be jacketed from the inside with a metal anode of thin foil that is sputtered to produce nanoparticles.

Preheat Fluorescent Lamp

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Discussion
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- Health physics issues.

- Thermionic emission technology has more physics to be worked out.

- Modeling & mapping electric field lines inside plasma discharges is important.

- Qualitative arguments should be pursued. However, creative mathematical tools must be employed e.g. elements of chaos theory.

- Modern load-luck powder handling systems are to be developed as they are important for example in the issues of particle oxidation degree.

- Concept fixed cylindrical discharges can be developed by adopting some changes to the fluorescent light technology configuration.
# Summary

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- **Science**

- Fine powders (1-100 nanometers) have applications that differ from the properties of their original bulk materials.

- They find many applications in biosciences, catalysis, electronics and other applications.

- Copper nanopowder was found to behave similar to precious noble metals such as gold & silver where its chemical characteristics are altered but its physical properties are the same.

- Thermionic emission plasma generation technology did not receive proper attention as a reliable plasma processing method even though it was among the first methods to be studied expensively by pioneers in the plasma sciences early on.

- **Technology**

- The cylindrical rotating plasma source is an innovative tools to produce nanoparticles under vacuum and using different plasma generating power sources (RF - Thermionic emission).

- **Discussion**

- Health physics hazards must be addressed no matter what nanoparticle process is used.

- Handling & packaging nanoparticles after production is important particularly to control the degree of oxidation.

- It is possible now to reinterpret electric field measurements and models based on different re-emerging mathematical approached.
References

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[1] Gehr, Peter, and Reinhard Zellner, eds., "Biological Responses to Nanoscale Cellular Aspects and Methodological Approaches," Springer, (2019).

[2] Suits, C. G. "The Collected Works of Irving Langmuir: With Contributions in Memoriam Inc. A. Complete Bibliography, of His Works," Langmuir, the Man and the Scientist: Including a Biography, Pergamon Press, 1962. Volume (3).

[3] Chapman B., "Glow discharge processes: sputtering & plasma etching." John Wiley & Sons, Inc. (1980).

[4] A. M. Hala, "A plasma system that transforms cheap metals into materials with precious metals like properties" - SAIP Patent pending (2020).

[5] Hershkowitz, Noah. "Sheaths: More complicated than you think," Physics of plasmas 12, no. 5 (2005): 055502.

[6] Sun, Jian, Jiafeng Yu, Qingxiang Ma, Fanqiong Meng, Xiaoxuan Wei, Yannan Sun, and Noritatsu Tsubaki. "Freezing copper as a noble metal-like catalyst for preliminary hydrogenation." Science advances 4, no. 12 (2018): eaau3275.

[7] Oksuz, Aysegul Uygun, Sorin Manolache, Lutfi Oksuz, and Noah Hershkowitz. "Plasma nanocoating of thiophene onto TiO2 nanoparticles." Industrial & Engineering Chemistry Research 52, no. 19 (2013): 6610-6616.

[8] Kiristi, Melek, Ferhat Bozduman, Aysegul Uygun Oksuz, Lutfi Oksuz, and Ahmed Hala. "Solid state electrochromic devices of plasma modified WO3 hybrids." Industrial & Engineering Chemistry Research 53, no. 41 (2014): 15917-15922.

[9] https://edisontechcenter.org/Fluorescent.html.
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Thank you

amhala@gaselco.com