Kinetics Modeling of Ar Plasma with O2 and H2O

Natalie Parker Author

07/29/2020 Added

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This is the REU 2020 Presentation for Natalie Parker. I studied the behavior of Plasma using computer simulation.

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[00:00:00.610]Hello everyone, My name is Natalie Parker.
[00:00:02.740]Today I'll be discussing the research
[00:00:04.400]I conducted over the summer with Dr. Barry Cheung.
[00:00:07.440]My research uses a computer simulation called ZDPlasKin
[00:00:10.310]to observe plasma.
[00:00:11.560]Plasma is an ionized gas used within chemistry
[00:00:14.190]for surface modification
[00:00:15.380]and supplying large amounts of energy.
[00:00:17.560]This project rigs with a specific kind of plasma
[00:00:20.130]known as weakly ionized plasma.
[00:00:22.100]It is non-thermal, selectively reactive,
[00:00:24.160]and it works as a multi-component system
[00:00:25.940]with varying temperatures and molecule sizes.
[00:00:28.620]The plasma pipette is a handheld device
[00:00:30.670]that uses weakly ionized argon plasma.
[00:00:33.430]The project goal was to model a mixture of argon, water
[00:00:36.310]and oxygen plasma by modifying the ratio
[00:00:38.980]of water to oxygen density.
[00:00:41.880]ZDPlasKin is a Fortran-based software
[00:00:44.030]that incorporates a differential equation solver
[00:00:46.320]to quickly simulate the plasma and set environments.
[00:00:49.360]The software uses kinetics to predict the behavior
[00:00:51.670]of multiple reactions at once
[00:00:53.410]based on predetermined rate constants
[00:00:55.320]and cross sections pulled from the IST Lisbon database.
[00:00:58.590]In figure one located in the bottom right
[00:01:00.510]of my methods section,
[00:01:02.050]it provides a guide on how the software uses
[00:01:04.260]the Maxwell Boltzmann reactions
[00:01:06.440]to predict the collisions between reactions.
[00:01:09.390]It uses classical kinetic equation methods
[00:01:12.190]for elementary reactions while applying
[00:01:14.240]the law of conservation of mass.
[00:01:16.070]For more detail on the process of coding itself,
[00:01:19.100]I have included an additional figure, figure two,
[00:01:21.360]located in the top right of my reaction section.
[00:01:24.290]Moving forward onto my own experiment,
[00:01:26.450]in order to get a good idea
[00:01:27.540]of what reactions were necessary to test,
[00:01:30.040]I referenced an article titled
[00:01:31.447]"He+O2+H2O Plasmas as a source of reactive oxygen species".
[00:01:36.050]This species observes the behavior of the ratio
[00:01:38.220]between water and oxygen density.
[00:01:40.210]I tested five ratios,
[00:01:41.660]0.01 0.1, one, 10 and a hundred
[00:01:45.290]with a set hydrogen density of 50 PPM.
[00:01:48.350]I wrote my own test with 35 species and 214 reactions.
[00:01:52.590]I've included a few of those notable reactions
[00:01:54.610]located in the top right of my reaction section.
[00:01:57.260]Additionally, in table one,
[00:01:58.990]I've provided a list of all of my species,
[00:02:01.370]and in table two,
[00:02:02.280]I have provided all of the list of oxygen densities
[00:02:04.870]for each trial.
[00:02:07.120]As I was examining my results,
[00:02:08.640]it became apparent that each reaction
[00:02:10.510]would run for different periods of time,
[00:02:12.200]despite being specified in my user code.
[00:02:14.760]This was caused by a lack of oxygen at the reaction.
[00:02:17.720]Off my list, I had far more reactions
[00:02:19.820]that would use O2 as a reactant,
[00:02:21.500]rather than as a product.
[00:02:23.740]This caused the trial to appear to be completed
[00:02:25.970]as there were no more oxygen species being produced.
[00:02:29.300]Looking at graphs one and two,
[00:02:31.210]this is density versus the relation
[00:02:34.840]of water and oxygen ratios.
[00:02:38.320]Graph one is the hydroxide species,
[00:02:41.330]which appears to be increasing, while the ratio increases.
[00:02:44.550]Graph two shows all of my oxygen species,
[00:02:47.410]showing how most of them remain constant during each trial.
[00:02:50.850]Graphs three and four are density as a function of time.
[00:02:54.100]Graph three shows oxygen.
[00:02:56.160]It shows that at the beginning,
[00:02:57.380]there is a significant large amount per trial,
[00:03:01.430]but is immediately being used up to form different species
[00:03:04.580]seen in previous trials.
[00:03:07.420]Graph four shows all the hydroxide species
[00:03:09.510]as a function of time.
[00:03:10.660]And it's showing a similar pattern to my graph one.
[00:03:13.990]From this, I can conclude that
[00:03:15.780]with the reactions that I have now,
[00:03:17.630]the oxygen density is highly significant.
[00:03:20.540]It is currently all being used as an intermediate,
[00:03:23.110]as it is being used up faster than it is being produced.
[00:03:26.340]If I were to add more reactions,
[00:03:27.830]such as the ones listed my conclusion section,
[00:03:30.470]I would see a more realistic trend.
[00:03:32.540]It would be useful to add more species
[00:03:34.270]and it would be useful to include more reactions
[00:03:37.990]that would produce oxygen
[00:03:39.280]as well as expanding my database to help with the reactions.
[00:03:42.690]In addition, I am currently working on a series
[00:03:44.670]of ZDPlasKin video tutorials
[00:03:46.320]to teach others how to become familiar with the software.
[00:03:49.440]I would like to thank you for taking the time to join me
[00:03:51.950]for my presentation,
[00:03:52.880]as well as thank the NSF-REU program for providing me
[00:03:57.090]with such an exciting experience. Thank you.

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Kinetics Modeling of Ar Plasma with O2 and H2O

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