Particulate Formation, Evolution, and Fate -Michelson Day 2 Part 2

Summary

The speaker delves into the relationship between specific heat and density, proposing a model based on molecular weight and molar volume. They explore the concept through the lens of soot formation, utilizing data from X-ray crystallography and historical literature. The talk progresses to discuss thermodynamic properties, surface growth mechanisms, and oxidation of soot particles. Advanced diagnostics, such as laser-induced incandescence and small angle X-ray scattering, are highlighted for analyzing particle maturity and composition in flames. The presentation concludes with an exploration of oxidation mechanisms and the challenges of sampling and diagnostics in studying soot particles.

Takeaways

• 🔍 The speaker is exploring the relationship between specific heat and density, observing an anti-correlation in the data and attempting to model it.
• 🧪 A simple model for density is proposed, based on molecular weight divided by mean molar volume, which is further explained through the concept of average volume per atom in a solid.
• 📊 The mean molar volume is calculated using data from x-ray crystallography, which provides insights into the unit cell structure and the number of atoms per molecule.
• 🌟 The speaker discovered a wealth of old scientific literature (from the 1945-1955 period) that provided valuable x-ray crystallography data, which was instrumental for their research.
• 🔬 The research involves analyzing the evolution of soot particles, their thermodynamic properties, and how these properties can be estimated without direct measurement in a flame.
• 🔥 The study discusses the use of laser-induced incandescence (LII) for measuring the volume fraction and maturity of soot particles in a flame.
• 🌡️ The concept of thermal expansion coefficient is introduced, showing its relevance to density and specific heat, and how it can be used to estimate these properties at different temperatures.
• 📉 The speaker presents data suggesting different oxidation behaviors of soot particles depending on their maturity and size, with implications for environmental and climate effects.
• 🔬 Various diagnostics techniques are mentioned for studying soot particles, including transmission electron microscopy (TEM), small angle x-ray scattering (SAXS), and aerosol mass spectrometry.
• 🤔 The script raises questions about the accuracy and consistency of measurements related to soot particle composition and maturity, highlighting the need for better experimental methods.

Q & A

What is the main focus of the discussion in the script?

The script focuses on the study of the properties of soot particles, specifically the relationship between specific heat and density, and how these properties can be analyzed and measured in various conditions such as in flames and through different diagnostic techniques.

What is the correlation the speaker mentions between specific heat and density?

The speaker mentions an anti-correlation between specific heat and density, suggesting that as one property increases, the other decreases, which they observed through analyzing data.

What model does the speaker use to represent density?

The speaker uses a simple model for density which is the molecular weight divided by the mean molar volume. The mean molar volume is calculated based on the volume occupied by atoms in a solid, considering the average volume per atom.

How does the speaker determine the mean molar volume?

The speaker determines the mean molar volume by using x-ray crystallography data, which provides information on the unit cell and the number of atoms per molecule. This data helps in calculating the molar volume per atom and understanding the structure of the material.

What is the significance of the thermal expansion coefficient in this context?

The thermal expansion coefficient is significant as it indicates how much a material expands when heated. It is tied to density and can be used to calculate changes in density as a function of temperature, which is essential for understanding material properties at different temperatures.

How does the speaker relate specific heat to density and molar heat capacity?

The speaker relates specific heat to density by considering that specific heat is relative to weight (grams per gram of material), and molar heat capacity is relative to the number of atoms in the material. The density serves as a bridge between these two properties, allowing the calculation of specific heat based on density and volumetric heat capacity.

What is the purpose of using the dispersion exponent in the study?

The dispersion exponent is used to infer the carbon to hydrogen ratio in particles. By measuring the dispersion exponent, researchers can estimate the maturity of the particles and understand the composition of the flame at different heights.

What is the Haka mechanism mentioned in the script?

The Haka mechanism is one of the basic mechanisms for surface growth mentioned in the script. It involves the growth of graphene-type sheets on the surface of a particle through a process of hydrogen abstraction and acetylene addition, leading to the formation of larger conjugation lengths on the surface.

How does the speaker use laser-induced incandescence (LII) in their research?

The speaker uses LII to measure the volume fraction of soot in a flame and to determine the dispersion exponent, which indicates the maturity of the soot particles. LII is a technique that is sensitive to absorption and allows for the measurement without worrying about scattering.

What is the core-shell model mentioned in the script?

The core-shell model is developed for analyzing small angle x-ray scattering (SAXS) data. It helps in understanding the structure of particles in the flame, indicating whether they have a core-shell structure or are homogeneous, which provides insights into the maturity and composition of the particles.

Outlines

00:00

🔬 Investigating the Correlation Between Specific Heat and Density

The speaker begins by discussing their curiosity about a potential connection between specific heat and density. They describe creating a simple model based on molecular weight and mean molar volume to explore this relationship. The process involves calculating the mean molar mass and using x-ray crystallography data to determine the unit cell and the number of atoms per molecule. The speaker highlights the importance of understanding the shape of the crystal lattice and how it can provide valuable information about the material's properties. They also reflect on the wealth of data available from historical research papers, particularly from the 1940s and 1950s, which were instrumental in understanding the toxicity of various molecular species.

05:00

📚 Density and Specific Heat Analysis in Thermal Processes

This paragraph delves into the relationship between specific heat, density, and molar heat capacity. The speaker uses a simple equation to determine density and suggests an association between specific heat and density. They explain how specific heat is measured per gram and molar heat capacity per mole of atoms, and how these are related through density. The speaker then discusses the application of these concepts in modeling, such as predicting soot formation and evolution in flames. They also touch on the importance of comparing these models to real-world materials like polycrystalline and single crystal graphite, and how temperature affects these properties through thermal expansion coefficients.

10:01

🔍 Analyzing Carbon to Hydrogen Ratios and Their Impact on Material Properties

The speaker discusses their research into the impact of carbon to hydrogen ratios on material properties, specifically focusing on density and specific heat. They describe a method to calculate these properties as a function of the carbon to hydrogen ratio and temperature, using graphite as a reference material. The speaker also explores how these calculations can be applied to measure and compare different carbon and hydrogen compositions in materials like soot and graphite. They express excitement about the potential applications of this research in understanding and modeling the behavior of materials at high temperatures.

15:02

🔬 Studying Soot Formation and Growth Mechanisms

In this section, the speaker focuses on the mechanisms of soot formation and growth, particularly the surface growth of particles. They differentiate between two primary growth mechanisms: sequential growth through reactions on the surface and the adsorption of gas-phase species onto the particle surface. The speaker also discusses various measurement techniques, such as laser-induced incandescence (LII), photoacoustic spectroscopy, and multi-wavelength LII, which are used to determine the maturity of particles in a flame. They highlight the importance of understanding these mechanisms to accurately model and predict soot formation in different conditions.

20:04

🔬 Advanced Techniques for Measuring Soot Maturity and Growth

The speaker describes advanced experimental techniques used to study soot maturity and particle growth. They discuss the use of a linear Henken burner for creating a linear flame, which allows for precise measurements at different heights. The speaker also explains the use of laser-induced incandescence (LII) for measuring the volume fraction of soot and the dispersion exponent, which indicates particle maturity. Additionally, they mention small angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) for analyzing particle size and structure. The speaker presents data from these techniques, illustrating the changes in particle maturity and size as they move through the flame.

25:06

🧪 Analyzing the Composition and Maturity of Soot Particles

This paragraph explores the composition and maturity of soot particles, focusing on the changes in aliphatic and aromatic character as particles move through a flame. The speaker presents conflicting results from different studies, which show varying trends in the aromatic to aliphatic ratio. They discuss the implications of these findings for understanding the chemical processes occurring within the flame and the need for accurate measurement techniques to resolve these discrepancies.

30:07

🔬 Visualizing the Oxidation of Soot Particles

The speaker discusses the importance of understanding the oxidation process of soot particles, as it plays a crucial role in their overall impact. They present studies that visualize the oxidation of soot, showing how particles can oxidize from both the inside and the outside. The speaker highlights the differences in oxidation pathways for mature and immature particles, as well as the effects of temperature on these processes. They also mention the potential for oxidation to break apart particle aggregates, further complicating the understanding of soot behavior.

35:08

🧐 Investigating the Fragmentation and Oxidation of Soot Particles

This section delves into the fragmentation and oxidation of soot particles, particularly in the context of environmental chambers and flame studies. The speaker describes experiments that allow for the observation of particles as they oxidize and break apart, leading to the formation of smaller particles. They discuss the use of scanning mobility particle sizing and transmission electron microscopy to analyze these processes, emphasizing the importance of understanding oxidation mechanisms to predict the behavior and impact of soot particles.

40:09

🔎 Exploring the Composition and Growth of Soot Particles

The speaker examines the composition and growth of soot particles, discussing how the average size of species changes as particles mature. They present data from aerosol mass spectrometry, which shows a decrease and subsequent increase in the average mass of species as particles grow. The speaker also addresses conflicting results from different studies and the potential explanations for these discrepancies, such as the role of oxidation in altering particle composition.

45:11

🤔 Considering Oxidation Mechanisms and Their Impact on Soot Particles

In this section, the speaker considers various oxidation mechanisms and their effects on soot particles. They discuss how oxidation can occur through different pathways, such as the involvement of O2, OH, or other radicals, and how these processes can lead to the fragmentation or surface oxidation of particles. The speaker also addresses questions about the preferential oxidation of certain areas on particles and the potential for temperature variations within particles themselves.

50:13

🧐 Discussing Diagnostic Techniques for Soot Particle Analysis

The speaker discusses the challenges and techniques associated with diagnosing and analyzing soot particles. They mention the need for sampling methods that minimize perturbation of the reactive environment and highlight the importance of in-situ diagnostics that can probe the flame or reactive environment without the need for sampling. The speaker also touches on the potential for using laser or x-ray based diagnostics for this purpose.

55:15

🌐 Exploring the Atmospheric Effects of Soot Particles

The speaker briefly mentions the upcoming discussion on the atmospheric effects of soot particles. They indicate that understanding these effects is crucial for assessing the impact of soot on climate and other environmental factors. The speaker suggests that there are many unknowns in this area and emphasizes the importance of further research to better understand the complex interactions between soot particles and the atmosphere.

Keywords

💡Specific Heat

Specific heat is the amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius. In the context of the video, it is used to understand the thermodynamic properties of different materials, particularly as it relates to the carbon to hydrogen ratio in molecular species. The script mentions an anti-correlation between specific heat and density, indicating a relationship that the speaker is trying to model and understand.

💡Density

Density is defined as mass per unit volume, and it is a key property in understanding the behavior of materials under various conditions. The video discusses a model for density based on molecular weight and mean molar volume, suggesting a connection between density and specific heat. The script also explores how density can be used to infer the maturity of soot particles in a flame.

💡Molar Volume

Molar volume refers to the volume occupied by one mole of a substance. It is used in the script to calculate the average volume per atom in a solid, which is essential for determining the density of different molecular species. The mean molar volume is a critical component in the simple model the speaker describes for understanding density.

💡Unit Cell

A unit cell in crystallography is the smallest repeating unit in a crystal lattice that can be used to describe the entire structure. The script mentions the unit cell in the context of calculating molar volume and understanding the shape and arrangement of atoms in a crystal, which is vital for determining the thermodynamic properties of the material.

💡X-ray Crystallography

X-ray crystallography is a technique used to determine the atomic and molecular structure of a crystal. In the script, the speaker refers to x-ray crystallography data to find information about the unit cell and the shapes of molecular species, which is crucial for understanding their thermodynamic properties.

💡Thermal Expansion Coefficient

The thermal expansion coefficient measures how much a material expands per degree of temperature increase. The video discusses how this coefficient is related to density and how it can be used to understand changes in density with temperature, which is important for modeling the behavior of materials like soot in a flame.

💡Soot

Soot is a black carbonaceous material produced by the incomplete combustion or pyrolysis of organic matter. The script explores the formation and properties of soot particles, including their density, specific heat, and how these properties change with the carbon to hydrogen ratio and temperature.

💡Laser-Induced Incandescence (LII)

Laser-Induced Incandescence is a technique used to measure the volume fraction and properties of soot particles in a flame. The script mentions LII as a method to determine the maturity of soot particles, as more mature soot absorbs light more strongly and thus provides a stronger LII signal.

💡Dispersion Exponent

The dispersion exponent is a parameter related to the wavelength dependence of the extinction or absorption of light by particles in a flame. The script discusses how the dispersion exponent can be measured and used to infer the carbon to hydrogen ratio in soot particles, indicating their maturity.

💡Oxidation

Oxidation refers to the chemical process where oxygen reacts with a substance, often resulting in the substance breaking down or changing its structure. In the context of the video, oxidation is discussed in relation to soot particles, where it can cause changes in the particle's structure and thermodynamic properties, and is important for understanding the environmental impact of soot.

Highlights

Exploration of the correlation between specific heat and density, suggesting an anti-correlation based on data analysis.

Development of a simple model for density using molecular weight and mean molar volume.

Calculation of mean molar mass and volume per atom to understand material properties.

Utilization of x-ray crystallography data to determine the unit cell and shape of molecular species.

Historical data from the 1940s and 1950s provided valuable insights into material toxicity and properties.

Innovative use of old literature to understand the relationship between specific heat, density, and carbon to hydrogen ratio.

Derivation of equations to predict thermodynamic properties of different molecular species.

Application of the model to understand soot formation and evolution in combustion processes.

Comparison of model predictions with actual measurements of soot density.

Investigation of thermal expansion coefficients to relate density and temperature.

Discussion on the use of dispersion exponent and angstrom exponent in measuring flame properties.

Techniques like laser-induced incandescence and photoacoustic spectroscopy for measuring particle maturity.

Combining various measurements to analyze particle growth mechanisms in flames.

Study of surface growth mechanisms through sequential growth on graphene sheets or gas-phase adsorption.

Use of synchrotron techniques for small angle x-ray scattering to observe incipient particles.

Development of a core-shell model for analyzing particle structure from SAX data.

Findings from transmission electron microscopy showing changes in particle maturity and structure.

XPS analysis indicating surface oxidation and its effects on particle maturity.

Observations of oxidation mechanisms and their impact on particle fragmentation.

Aerosol mass spectrometry revealing the average size and composition of species in the flame.

Controversial findings on soot nucleation and the role of large species in flame chemistry.

Discussion on the challenges and methods of sampling in reactive environments.

Introduction to in-situ diagnostics for probing reactive environments without sampling.

Upcoming discussion on atmospheric effects of particles and their impact on climate.

Transcripts

okay I think we're all back

um so

to enter to finish our story

um

uh so I I saw this and I was like okay

um

let's see if we can figure this out and

um

and I was like you know

I there should be a connection between

specific heat and density

I don't know what it is but it seems

like just looking at the data there's an

anti-correlation

so um

so what I did

um so we have our measured values

are the points

and I made a little model

um for the density

um and and it was really really simple

it was just

um the molecular weight

divided by the mean molar volume

so the mean molar volume is and it it

was kind of like you take

um all the atoms in your your solid and

and what is the volume of of per

basically what's the average volume per

atom

um and you would think it would depend

on whether it's hydrogen or carbon but I

was like let's just start simple and and

figure out if we can uh assume that we

have some kind of average

um volume so how did I get the mean

molar volume

um

uh okay so that's that's how I calculate

the mean molar mass

um knowing how many carbon and hydrogen

atoms were in each molecule and then I

had to figure out how many molecules

were in each like unit cell for the

solid right

um so

um

I need to factor in the time of delay

here

um so and then I was like okay what's

the molar volume per atom and I just

um plotted it as a function of the

carbon to hydrogen ratio so how did I

get that number right so so this is

where I was like okay I gotta I gotta

figure I gotta figure something out

um

so turned out that

all of these all the ones that I

included here in the study where I had

like that a lot of the ones that I found

specific heat and density for

um I actually also found

um x-ray crystallography data for

um so here's uh the um

the mean molar volume is a function of

the unit cell times avocado number just

to convert from moles to number of atoms

to moles

time divided by the number of atoms per

molecule times divided by the number of

molecules per unit cell

and a unit cell is if you've ever taken

a class where you've looked at

crystallography

you'll notice that you know you'll

remember that

um a crystal can have different shapes

depending on how the molecules or atoms

align with each other and these are the

basic types of shapes the monoclinic the

orthorhombic and the triclinic so it

turns out all of these um molecular

species I found had one of these three

types of shapes

um and and if you look in the crystal

x-ray crystallography data in the papers

they actually tell you what the shape is

in fact they tell you basically

everything you need to know you just

have to figure out what the language is

like what they're actually saying so um

I so here are what the different shapes

look like for these different molecular

species

um so uh so these are all images from

these different papers that people have

published and most of the data I found

was from 1950 like in that eight range

1945 1950 to 1955 these are all really

like old papers and I was like wow

there's tons of data here there's tons

of information it must have been the

time when people figured out how to do

x-ray crystallography of these types of

of uh materials and then they just did a

whole bunch and if you look in the old

literature is all when they're trying to

figure out how toxic they were so it was

tied to the funding was all coming from

like

um places that were like paying them to

figure out the toxicity of these

different molecular species so

I just happened to stumble on a like a

gold mine and um and just started

plunging into like figuring out

um how to use all the data

and it's just it was kind of a it was a

it was a really

um cool like I was you know I had papers

all over the place I was like trying to

figure all this stuff out writing

writing all the numbers all over the

place

um so back to this guy

um

so

um so then so I figured out the density

like with that simple equation so I was

like okay well there has to be an

association

um between the specific heat and the

density and this if you you know what

remember from your thermal classes

um this is the specific heat is relative

to remember

um weight so uh grams like per gram

right avoided the

um or mass of your material and the um

the heat capacity the molar heat

capacity is relative to the molar in the

number of you know atoms you have in

your material right so there's a

correspondence between obviously between

the specific heat and grams and the

molar heat capacity so that is just the

density

so now we can go back we know what the

density is

um so we have so I substituted here in

this equation the density times that

volumetric heat capacity well it turns

out

five minutes from now when this comes up

that that volumetric heat capacity is

constant

so we can just use a constant and and

put that into the equation and now we

have the specific heat for these species

as a function of carbon to hydrogen

ratio okay so now you can start thinking

oh my gosh well how would I use that

say you're doing a model and you're

trying to um calculate you want to

calculate like how the your soot is

evolving your your modeling soot

formation and you start to get Inception

you start to get these

um these molecules are starting to form

then you can go okay my once I get to a

carbon hydrogen ratio of X I'm going to

say that has a density of this and then

you can evolve the density of your

particles as they grow right so as you

like get rid of the hydrogens in your

mole you're you have that mechanism down

you're going you can get rid of your

hydrogens right

um so now you can calculate for your

model the different

um thermodynamic properties

um you can also use this uh okay so here

so then I took that equation those

equations and I propagated them out and

I said okay let's go out to see what it

looks like when we actually have a sit

particle so that's how you know and we

start to have mature soot what happens

when we have mature set can we compare

this to polycrystalline graphite can we

compare it to single Crystal graphite

okay so here's the graph you know it

actually notice the bottom is a log

scale it actually works all the way out

to graphite so I was like oh my gosh

this is just amazing so

um I was just so excited

um I was bouncing into my radiation

treatment like oh this is like great day

um and so so here are the equations they

actually work

um

a

come on come on come on come on

okay there's our graph our polychrystone

graphite our single Crystal graphite

this I put soot on there there are a

couple measurements for the density of

soot right

um so that's on there see where it

actually goes on the line it's like

awesome like I actually got it to work

so okay so okay I gotta calm down here

um now it can use this we can use the

data okay we get our success

um we can use the data to compare to

measurements and this is oh oh so so so

that was a as a function of of

um our our composition rate so carbon to

hydrogen we're in a flame we actually

want to know what's happening inside the

flame at high temperature can we and

that's so all the data we're taking at

low temperature can we actually now

um get the the um these relationships as

a function of temperature so how do we

do that so we can use so here's density

as a function of temperature

um for graphite right for polychristian

graphite and for single Crystal graphite

and you notice that we actually have a

relationship so this is all tied to the

thermal expansion coefficient

right it's thermal expansion coefficient

will tell you how much a material

changes how much it expands when you

heat it up

that is tied to density right it's just

one over density so we have these um

I shouldn't have put so many animations

in here

um okay so this is the relationship we

have for

um for that we get from graphite for the

um thermal expansion coefficient

um and we can actually use that thermal

expansion coefficient

um and calculate what we get for

different carbon to hydrogen ratios

um based on you know starting point and

just expanding it as a function of

temperature right so that's for so then

we calculate for different carbon

hydrogen ratios starting from an

incipient soot moving out to like mature

graphite we have we have it all there

um so so that's how we can

um calculate now we have density

specific heat as a function of carbon

hydrogen ratio and temperature okay so

there we are yes

where we so and then let's see can we

use this

um for um one and connect this to

measurements like so if I make a

measurement can I connect this

okay

um

oh this is we

okay so

um I can okay so that was for density we

can do this for specific heat I'm not

going to spend a lot of time on this

except the computer wants to uh

okay okay yeah we got it

okay so we can do this for specific heat

using graphite as a proxy the the

functional form for graphite and then do

the same thing for the specific key

laughs

[Laughter]

no problem

[Laughter]

excellent thank you

yeah no problem

um okay so here here's here's our

specific heat as a function of

temperature

laughs

thank you

um okay so we got this down

ah

okay

oh if I turn the laser pointer off

oh that would thank you Dalton

um oh I think I can do that here

they turn it off okay so let's connect

this too I turned the laser pointer off

so that's good

um so now so let's connect this to

measurements right

okay remember yesterday I said

um we can measure the um uh dispersion

exponent right or the angstrom exponent

whatever you want to call it that that

exponent up there that um tells you that

yeah see I think I don't know how to say

yes yes good

oops oh

okay wait let me go back I'm trying to

go back

okay yes

does it does single Crystal graphite

what

oh does it the morphology change when

you change temperature for graphite

itself

um so graphite will so it's interesting

because um the morphology

um so the fine structure of single

Crystal graphite what happens when you

they're D okay this is a really

interesting

um point in materials

um graphite has these sheets of graphene

so you'll have a thermal expansion

coefficient that goes like this

um that's um perpendicular to the basal

plane and then you'll have a different

expansion coefficient that goes like

this

um and uh there's a if you look at

polycrystalline graphite that

um there are two uh expansion

coefficients that will have an impact on

on the specific heat

um so you can plot this you could plot

this you know

um perpendicular or parallel

that one I can't remember is

perpendicular or parallel but or it's

just an average of the two I can't

remember which one it is it might be an

average of the two but polycrystalline

graphite will be right in the middle

right between the two

so polycrystalline graphite is just

crystallites that are kind of randomly

oriented

does that make sense

so soot is like a polycrystalline

graphite much more like polycrystalline

graphite

yeah but that one's for single Crystal

graphite and I think I probably took an

average if if I found two or it might

just be that as as I can't remember but

it might just be in the literature as

that one curve yeah

okay

now let's see if we go

okay

so we have this dispersion exponent we

can measure the Distortion exponent

and we have this correlation so if we

know this person exponent we can infer

the carbon to hydrogen ratio if you can

measure the dispersion exponent right

remember I showed you the the multiple

times now like maybe three times I

showed you the dispersion exponent for

that one study as a function of height

in the flame

um

we can actually measure the dispersion

exponent there are different ways of

measuring it and we'll talk about that a

little bit you can either measure it

with Extinction that's harder to do

because you have absorption and

scattering

um

or you can measure it with a technique

that's explicitly dependent on

absorption so

um like laser induced incandescence or

photoacoustic spectroscopy

um uh so uh or a multi-wavelength um so

the dispersion exponent can you can get

it from multi-wavelength lii or

photoacoustic spectroscopy

um

and then temperature and then you also

want temperature right because you want

to know in the flame what as a function

of temperature you can do that with a

whole bunch of different spectroscopy so

we'll we'll talk about that in a little

bit

um so so now you can make a measurement

of flame you don't have to put a probe

in there and you can get these

thermodynamic properties at least

estimate them until someone figures out

that's wrong too but let's assume that

it's right let's hope that is right okay

uh okay

yes okay right let's go let's go

um

I don't know it's still darn slow okay

so there's our whole equation for

density

here's our whole equation for specific

heat

and then here's our volumetric heat

capacity

okay so let's talk about surface growth

there are two um basic mechanisms for

surface growth that people talk about

one is that you have sequential growth

on the surface of

um like of like through the Haka type

mechanism right so you you uh you have

this um

like a graphene type sheet on your

surface and you uh you get hydrogen

abstraction from one of those carbon

atoms an acetylene addition

um and then you get hydrogen abstraction

another

um acetylene addition then you close the

ring so you basically grow the rings on

on these sheets on the surface so you

basically grow these sheets out so you

get these bigger and bigger

conjugation lengths of the stuff on the

surface that's one way to add carbon to

your particle another way

um is to so this is the Haka mechanism

another way is to actually add

um uh so there's the Haka mechanism

what's going to happen is you're going

to grow the the graphene sheets another

way is to actually just add whatever is

in the gas phase is just adsorbing to

the surface and then whatever it's doing

once it hits the surface it's doing use

reacting or whatever but so so you have

these gas-based species flying around in

around your particle they they attach

the surface somehow maybe through a

radical mechanism we don't know and then

they stick to the surface and they add

to your particle so that's another way

so what we want to do is figure out can

we can we get some information to

um figure out what kind of mechanism and

then different mechanisms could be

happening in different under different

conditions

okay so what we did is combine a number

of different types of measurements to

see if we can sort out what's going on

so we have this you know we have our our

we can make these measurements of of

particle maturity using our dispersion

exponent right we use laser-induced

incandescence which is a technique where

it's you don't have to worry about

scattering because you're only sensitive

to absorption so you take a high powered

laser you send it into your flame it

absorbs the light

um use 1064 nanometers which isn't

absorbed by easily by the other species

running around the flame so the um the

laser the particle absorbs the light

heats up and then we look at the

emission okay so that and then we change

the laser wavelength that allows us to

get a wavelength dependence and then

that gives us the dispersion exponent

okay

um uh that's how we get so here's our

flame so I'm going to show you some

results here's our flame it's it's what

we call linear henken burner so it's a

Hank and burner which is a whole bunch

of like hypodermic needles sitting in a

honeycomb

um so they're really tiny little micro

Jets

um of fuel and then and the honeycomb is

where your co-flow of air is going so

you basically have little tiny diffusion

Flames

um uh we were doing this experiment we

designed this burner for some

experiments we're doing at a synchrotron

where we had very little space so we

made a little teeny tiny burner and it

was we did it in a line so we had these

um little hypodermic like 15 or 25 or

something a little hypodermic needles

sitting in a a small honeycomb section

okay so made along a linear

um Flame

so so we're looking down the side and

then down the end and then along the

side and this is the laser-induced in

condenser incandescence as a function of

height in the burner so on the bottom is

volume fraction so as you go up in the

burner

um I made it exactly the same height as

that picture so you can see that as you

go up in the burner laser induced

incandescents

um actually measures the main reason

people use it is to measure volume

fraction of soot in a flame it's just

linearly dependent on the amount of

incandescent signal okay so so we

measured how much you have in the flame

okay the one thing to remember about Lai

is it's usually you know is sensitive to

matures so the soot has to absorb

strongly in order for you to get enough

signal for it to and it can't vaporize

it has to go up to pretty high

temperature

um because it's dependent on temperature

of the fifth power so has to go to

pretty high temperature to get adequate

signal okay so there's our

um Extinction and we used lii to get the

dispersion exponent so so that blue

curve is the dispersion exponent

um the pink curve you can also get from

Lai is that beta parameter and the cross

section and calculation I won't go into

that right now we'll talk about that

later but they're anti-correlated and

they both tell you about this that

maturity

but remember dispersion exponent goes

down as maturity goes up yes a question

oh so I think that your question is

um uh what is the error associated with

the measurements and and I didn't put

error bars on the measurements right

um that's a really good question and I'm

not exactly sure how to assess the error

um the full error because there's a lot

that goes into evaluating that

dispersion exponent I would say it's

probably on the order of 10 to 20

percent yeah yeah so if you do Lai two

different temperatures you can get the

dispersion exponent yeah definitely

so um and then the I we calibrated the

um the Lai signal for volume fraction

with Extinction

and we used the the dispersion exponent

in the extinction measurements to get

the absorption cross section so we knew

what the extinction was so we so we

basically used both to get the volume

fraction

okay that was a good question

um Okay so

um so so we kind of have a measure of

the

um maturity

and it's stuck in my computer

okay here we go so the next thing we did

is we um did a study where we took that

little burner to a synchrotron and we

did small angle x-ray scattering so

small angle x-ray scanning or sacs

should be

um sensitive to the incipient particles

as short wavelength we should be able to

see the insubian particles though I

don't think we really can see this

incipient particles based on some of uh

some of this analysis I've done recently

I think we need a better technique but

we do have some sensitivity to the less

mature particles than what we have

sensitivity for with Lai

so we did that

and we did we extracted from the flame

and did tem transmission electron

microscopy and got the size of the

primary particles both the size of the

primary particles and the aggregate size

from sacs and the sax measurements and

we'll talk a little bit more about that

later

um okay

okay so here are the T some of the tem

measurements

um so you see that

um in the middle we have what looks like

mature soot and that so at five and

seven millimeters above the burner we

have those big stringy Aggregates that

we're talking about that looks that's

what matures it looks like

um and that's where we see the strongest

Lei signal and it's pretty flat right at

lower Heights um our Lei signal goes

away and now we get this globby like big

globby thing I think those are when we

extract we get

um coalescence or like coagulation of

the particles they kind of stick

together in our sampling

I'll talk about how we did the sampling

a little bit later and then at the top

what store we get oxidation the

particles go away

okay so the particles are small Lis

signal goes away and the tem images get

tiny

okay this is what the sac signal looks

like and you see we see sax

um particles lower in the flame where

the particles are less mature where we

don't see Lai where the Lai goes away we

see Sac signals still not I think that's

because of the difference in sensitivity

to the less mature particles

foreign

so the next thing we did

um okay so I ran I we developed a a core

shell model for analyzing the sax data

and this is what the core shell model

gave us is we actually have

um it's it's inversed a little bit like

we actually have core shell structure in

the middle of the flame and then we have

homogeneous particles so that that one

means that we have homogeneous particles

at the top and bottom where we have

oxidation we oxidize away the surface

and on the bottom we just have you know

homogeneous incipient particles I think

that's what that is but I still am

thinking about this so kind of a new

result

um okay come on come on come on

and then growth of the particles so this

is our where we see all these um

species in our aerosol Mass Spec is down

low in the flame where we see growth of

the particles okay

okay we also did XPS and that's that

blue curve right below the um

a pink curve so you have Lai which gives

you an indication of maturity and then

the XPS

um is so XPS is a Surface sensitive it's

just surface sensitive so Lai is bulk

sensitive so sensitive to the material

the entire material of the particle it

tells you the maturity of the entire

particle XPS is only sensitive to the

surface so it you know like the top

nanometer or so

um and what we see is defects that are

higher on the surface of the particle so

basically did you know what is the

maturity of the particle if it has high

defects then the maturity is lower then

it has fewer defects so we plotted that

our basically our defect ratio and the

maturity of the particles from XPS

um it goes up kind of like Lai does but

it takes a couple extra millimeters to

go to get to our highest maturity on the

surface and I think this is because

um as you're adding if you're your

um ions are drifting around in space we

see the same types same distribution of

types of species you'll see that on the

right hand side as a function of height

the types of species don't change as a

function of height it's the same type of

like four to seven

um ring type species they're adding to

the surface continuously so as the bulk

is maturing the surface is not maturing

because it's just growing with these

non-mature

um species these non these kind of

constant sized species so the maturity

would be how big is that

sheet so what it looks like is that

we're not getting

um

in this flame in this region where we

did all these measurements we're not

getting

um the the growth of the big sheet on

the top because that would make our

surface maturity grow faster than our

our bulk maturity but our bulk maturity

is actually getting fat growing faster

than our surface maturity so what I

think is happening is oops is that we're

getting this this mechanism absorption

of pH is on the surface is is what's

causing surface growth okay so um

yeah so here's kind of a a summary of

what we think all these things that are

happening inside the flame

um

I'm going too slowly so I need to move

on but um

okay so let's talk about composition and

maturity so remember we talked about

this result yesterday this one where we

saw where High Wong's group saw

um High uh aliphatic character in these

particles and this this um the aliphatic

so here's another figure that shows us

and as they go up in the flame they

actually see more aliphatic to aromatic

character so it's higher aromatic

aliphatic to aromatic totally not what

we expect totally not what other people

seem to see so that's one result see so

um if we so we talked about that

yesterday

um

this is actually really annoying this

doing this

um

okay come on come on

okay and here's a different result

um so in this case listen they looked at

the H to C they did um infrared

spectroscopy and they looked at

um the which which high Wongs group did

right they did at infrared spectroscopy

the same type of experiment and this is

also a pre-mixed flame right and what

they saw is the aromatic to aliphatic

ratio so if you look at the um

the uh

so H to C ratio on the bottom so that I

usually think of C to H but H to C goes

down that means C to H goes up that

means there's more aromatic content in

these particles as they go up in the

flame that's opposite of what I just

showed you from high Wong's group okay

so this is and and the middle figure

shows H's that are in aromatic Rings

versus H's and aliphatic rings from the

um from the IR spectroscopy and notice

how the aromatic stays high in the alpha

it goes down as you go up in the flame

so that's opposite of what high Wong's

group was showing so this is this is all

like you know we need to have better

ways of doing this so I challenge you if

you're an experimentalist come up with

good ways to make this measurement

okay so

um we go back to this flame and try to

understand the composition oh

I think I I skipped over something but I

I don't know what it is

um I I think I get the orders but anyway

okay whatever

um so let's talk about uh

so are there any questions so far on

composition and maturity before we move

on to oxidation

okay

so here's a question

how would you define if you have a

particle that's oxidizing so we're going

to talk about oxidation if you have a

particle that's oxidizing

um you've gotten rid of all your

hydrogens or a lot of your hydrogen

right and you become mostly carbonaceous

and now you have an oxidation mechanism

that's like grabbing carbons from your

particle so your order like your you

know you're getting defects in these you

know if you're some of you have told me

about some of your materials work that

you're doing if you're grabbing carbons

from these graphene sheets would you

call that less mature

that's just a question I'm going to

throw out there because I don't know the

answer to it just that we could we could

just ponder that one

um okay so let's talk about oxidation

um oxidation is really important because

um

uh

if you think about it if you have a

process that's generating soot right

if you oxidize it away if you you can

generate a ton of soot if you oxidize

away it doesn't matter right so we

really want to understand oxidation how

that happens this is a beautiful like

experiment

um from Murray Thompson's group uh this

is the group that Mani sarathi was was

in as a grad student

um this is a really really nice paper

where they looked at oxidation of

particles kind of

um in an environmental chamber so they

could watch oxidation and their their

um

different Studies have shown that

sometimes particles are oxidized from

the inside so oxygen percolates into the

particle and oxygen oxidizes the inside

and sometimes particles are oxidized

from the outside right on the surface

um so this was kind of a curiosity and

this is actually important if you're

trying to understand how oxidation is

happening so they put these um

particles in and where they could watch

through tem they could actually watch

the particles as they were oxidizing so

they start so if you start out on the

left hand side and you move over to the

right hand side you'll see that the you

know the particles are kind of

disintegrating right they're going away

as they oxidize and you'll notice that

you know they're oxidizing in different

different Pathways so it turns out that

particles that are not very mature tend

to oxidize from the inside

so they did so they did a whole bunch of

studies with different types of

particles

here's one that shows that particles

that are mature so I just showed you one

that the particles are not very mature

like it looked kind of amorphous like

there weren't you didn't see that clear

ring structure here's one that shows

that clear range structure so they they

put a circle around it right they

started out on the left and on the

inside you see the inside is a little

bit disordered there are a couple of

little spots where it doesn't look like

you have a strict green structure

um and they put a couple arrows kind of

pointing to those different regions

right as you oxidize

um you see that this is uh the little

um ring structures or the

um the uh the disorder part seems to be

going away

so

um

so at so you can get oxidation of of

particles at uh

so particles that are really small can

actually oxidize from the inside but

particles that are larger

um that are mature can actually uh let

me go see that so here's another one

that's where your have a bigger particle

and a temperature you have the like the

graphene sheets right the

polycrystalline graphite on the outside

um and those are now oxidizing from the

outside so these are large mature

particles small mature particles can can

oxidase from the inside and also from

the outside and not mature particles

oxidized tend to oxidize from the inside

so I think that's actually really cool

and it's probably a matter of the

auction being able to filter into the

center of the particle and get to the

more reactive part of the particle

um and if the part if the particle is

Big it's probably harder for the oxygen

to get in but it takes a higher

temperature to oxidize these a more

mature like sheets of graphene so I

think that's actually really cool and so

you see in the upper right hand side

what they they see is like you are like

probably pull off individual oxygens and

you start to flake off parts of your

graphene sheets your polycrystalline

graphite sheets

um so it's I I just I don't know I I

love I guess I love these studies where

you can actually see like you think you

know what's going on and they actually

can see it in an image it's really makes

me excited

okay

uh

oops Yeah and this is another this is an

old study

um from 1984

um and this is a study that indicated

that you can also have oxidation that

breaks your Aggregates apart so if you

think about it

um remember how you're holding your

aggregate into primary particles by

these graphing sheets just they're going

over the outside if you start to oxidize

the outside of the particle that the the

those primary particles may not be so

connected once you like break away those

bridges those necks right in the in the

particle

um so people um this is from seraphim's

group from uh you know 1984 showing this

kind of like fuzzy at the bottom is your

Aggregate and at the top is after you've

oxidized it

um so uh so let me show you actually a

newer one that that has a similar type

of technique

um where you can see a little bit more

clearly so this is from Joanne

lighting's ladies crew

and you see

um that how they did this experiment is

they had two burners so they had a lower

burner that was burning rich and

generating particles okay and then they

had and and they're generating mature

particles and then they had an upper

burner that was burning lean

um uh and they sent the particles from

the first burner into the upper burner

to see if they could watch the oxidation

of the particles so they they looked at

this with scanning Mobility particle

sizing and you see that on the right

hand on the very furthest one where it

says case one

you have a large size distribution so

the x-axis on here is the mobility size

the y-axis gives you the size

distribution so the number of particles

in in a particular size bin so um and

that as you go up in that second burner

so this is height above the second

oxidizing burner you see that you start

to get a small a small fraction right a

second Peak starts to grow in at smaller

sizes and they interpret this as the

particle starts to break apart and

generates small particles this is a

really nice a very nice study showing as

the particle like the big particles go

away and they generate small particles

then those particles oxidize away

um

and I think they can get rates from this

um this study to figure out how fast

you're getting those particles to go

away

okay

um so we can see when we do sax

measurements without sampling from the

flame we can actually look at oxidation

rates and we see something similar just

by doing so we have our you know x-ray

probe sending it into the the chamber

into our Flame

and we detect the angle at which we

scatter so that allows us to get the

size distribution of our particles so

low in the flame so this is um at going

from five millimeters up to

um nine millimeters the height scale is

actually on the left hand side of the of

the graph over here

um

remember at five millimeters is when

where we have we're starting to see

mature soot and kind of the highest

volume fraction in our Lai measurements

right and we see a nice size

distribution the um the sax measurements

are the purple curve and then the uh the

bins are are that um

distribution is from a transmission

electron microscopy when we extract it

remember we looked at tem that's from

the tem and you notice and as we get up

to eight eight millimeters that's where

the Lei signal is going away right

that's where the sac signal is going

away on the volume fraction

um and what we see is when we run this

model we have to put in a second mode

this small once we get to that height we

I I didn't expect it actually I was

having a really hard time fitting the

data and the only way I could get it to

fit is if I put a smaller distribution

size like I and then I was like oh yeah

that's of course it should be there

um so you see as you go up in height

this you have this this small size

distribution and that's without

extracting so that so that's like hey

yay success

um but we can't see that with with tem

we can't see those particles they're too

small for us to catch we just can't

catch them okay so I think probably if

we did smps we could see them

yeah

okay so that's uh

so here's another study um showing in

one of these machines from the same

um group like from the same paper

actually I'm showing fragmentation of

the particles in the tem in the

environmental TM machine right so you

start out you know of that

that a is is one section of that

Aggregate and you can see where the

necks are getting eaten away and the

Aggregates are breaking apart

um so you can actually see why this

fragmentation is happening

um and you start to fragment into just

these smaller pieces

okay

yeah here's another one showing the neck

actually going away

um so if you go from left to right you

can see where the ox your oxidation is

occurring and they say when they do

these studies that it seems to

preferentially go for these necking

regions

um I'm not sure why but they seem to be

like more reactive than the actual

um

regular primary particle coding like

polycrysten graphite coating

okay

um

I'm going to skip this guy

yeah we we looked at our XPS

measurements also seem to indicate that

oxidation occurs on the surface

um

uh oh yeah okay so what's the

composition now of the particles as they

grow so we can do

um aerosol Mass Spec but we get to so

what starts to happen is our signal

starts to go away right as you get more

mature you're not going to get those

things vaporizing off your surface and

what we see for the average size the

species is as we're growing the

particles the average size of the

species of the mass Spectra we see goes

down and then it goes back up again so

the average size decreases and then

increases

um so you can kind of see this in the

Mass Spectrum see at um the at three

millimeters

um is kind of like almost at the minimum

and then as you go up to 5.5 millimeters

you you see it increases so let me just

show you what other people see

because this is kind of a fascinating

area

um okay so what we see is

um the total ion signal increases and

then decreases like this is the same

burner right

um oh no this is a pre-mix burner the

last one was the hankenburn this is a

premix burner very similar to some of

the other results that I'll be showing

you

um and then on the average mass goes

down instead of going up so it's

opposite in the pre-mixed burner than it

is in the diffusion burner okay so this

is kind of interesting so this is starts

to be starting to get your like thinking

going it's like okay what's what's going

on what's Happening Here

okay

um and and this is actually really

common this this distribution uh that we

see as we go up in the flame the size

um we get these like big Peaks

um that like just seem to grow in this

like um 202 and 226 I don't know they're

they just always grow in haven't figured

it out so if you're thinking about like

what's happening this is a good thing to

think about

um and it's not just us we a lot of

people see this when they do aerosome

aspect must be okay so that's pre-mixed

ethylene the same thing happens in um a

methane flame right very similar type of

results

um the average

a mass goes down

okay

but remember the average mass went up in

the diffusion Flame

okay this is this is a controversial

um result okay uh in that

um this paper came out recently and

notice that these species are huge right

they're much larger than I was showing

you in our aerosol Mass Spectrum right

so this paper was written and you know

says and it says Okay

um soot is forming by nucleation the

species are large enough

um maybe no one else sees them but

they're there and we see them and the

species are large enough to nucleate no

question boom is over we figured it out

so it is nucleating by large species

just

um you know coming together by

dispersion forces in the flame

none of this chemistry stuff none of

this radical stuff matters it's only you

have big species so I'm here to explain

why they see this okay so what they see

is

um this this result but notice where

they take the res notice where they take

the result and you actually if you read

this paper right now you'd be able to

spot this too because I've given you all

the information and you've you've been

thinking about it I can see your faces

like you know concentrating and figuring

this out okay this is a diffusion Flame

they made the measurements on the edge

of the flame where you have what do you

think you have on the edge of the flame

where you have laser induced

incandescents they see very strong

laser-induced incandescents

who said that who said mature soot right

exactly Hannah said matures it you have

mature said so does if you're making a

measurement looking at matures are you

looking at Inception

no you're not looking at Inception and

what happens when in a diffusion flame

to the average mass of the species

increases right it increases yes so I

think what they're seeing is they're

actually seeing mature soot that's um

one it could be mature but two think

about this we just talked about

oxidation what's happening when you

oxidize mature particle and a high

temperature

you're fragmenting stuff right you're

getting flakes of stuff coming off the

surface I think that explains these

results it's not that you have big

species that are going to nucleate okay

so I may be completely wrong

um but that's that's what I think is

happening so if you see this result like

think about it and maybe you can come up

with another story

okay

um good job good job like you're paying

attention hey okay oxidation mechanisms

here's a couple of oxidation mechanisms

people talk about right there are

different types of of oxidation

mechanisms how do you you can oxidize

with 802 you can oxidize with oh you're

grabbing these carbon atoms you know on

this on the

um edges of these

things like you know these sheets maybe

in the center you're fragmenting they're

falling apart they're flaking

um

I gotta make sure I don't go over okay

okay so that's our oxidation

um

I think

okay

Let's uh

quickly start the okay so does anyone

have any questions

yes

so the question is I'm going to repeat

it

um is is it so we we preferentially

oxidize on the bridges

and maybe that's because it the surface

area to volume is higher so we're

oxidizing those surfaces

that could be or or another explanation

is this the um the necks may be more

curved and may actually have more strain

like you know maybe they're you know

have when you have um like so oxidizing

some of these curved species actually is

easier than oxidizing a flat

um all six member rings so maybe your

explanation is right I don't really know

actually why they're but that's a really

good question yeah

a temperature distribution

of agglomerations and

that's a whole because surely hot spots

you know inside there which may give

yeah so the question is

um are there um is there a temperature

distribution of the soot particles

themselves

um within other homogeneous temperature

right yeah could you have a an

inhomogeneous temperature distribution

of the particle itself usually

um so I'm going to say that um even when

you're heating particles up with laser

induced incandescence when we calculate

this when I calculate how fast the um

and I use con you know heat conduction

equations for along the basal plane and

then perpendicular to the basal plane I

calculate that it should take about six

picoseconds to heat through a particle

uh primary particle so I doubt it

um but you never know because you have

you'd have like conduction

preferentially on the outer

um things particles and and who knows

there may be something going on that

we're not accounting for yeah

yeah thanks for the questions and so I

saw another hand up yeah Saturday

yeah at that stage cut those off still

coming

oh where are you getting the oxygen yeah

so the question is if you're trying to

mature oxidized mature soot where is

oxygen coming from if you're in in

so so okay so so that um if there are

going to be conditions so you're asking

if you have a condition where you don't

have oxygen what's happening

you're not you're not oxidizing right so

uh so the in these cases where we see

oxidation is because we have

um we're in a diffusion flame and you

have air flowing and at the surface

where you have the most mature soot

that's where you're having oxygen um

diffusing into the flame

that's where the oxygen is coming

and in the environmental tem they add

oxygen

yeah yeah those are great questions

thank you oh so okay and so are there

any more questions

okay okay so we have like five minutes

and then we'll take a break and I'll

just get start getting going on um uh

our next

topic

hey

so we'll be talking about

um let me so we'll have in so

um in this uh section

um we have a lot of Diagnostics that are

available to us some of them are X2 so

we have to extract the particles from

the flame and then maybe process them

um maybe put them under vacuum

um do like there are a whole bunch of

things we can do with these particles

there are a lot of Material Science

Diagnostics that are available to us

um so we'll start out by talking about

oh

anyway I'll get this going during break

um so there are a lot of Diagnostics we

can talk about

um for exit you uh and then I'll talk

about sampling like what like so an

origin of these exit 2 diagnostics we

have to do some kind of sampling and

sampling it alone is a real problem

because you have a really reactive

environment

um once you put a say like a quartz tube

or a metal tube close to your flame

you're going to start to perturb the

flame itself you're going to perturb the

the radicals are going to start to react

with a surface so you're going to have a

change in the radical distribution the

temperature you're going to have like

you know temperature changes because of

the probe

um so there are a lot of different

things will happen we'll talk about

sampling and then maybe there are ways

of getting around sampling and that's

another challenge we have is hike how do

we get around the sampling issues

because there are a lot of Diagnostics

we really want to use for sampling

um with sampling and then and then I'll

talk about

um Institute Diagnostics where we can

usually it's either laser or x-ray that

we can actually probe the The Flame or

the reactive environment not just flame

I mean there are other cases when you're

trying to synthesize particles you have

a very reactive environment you don't

want to be able to set you want don't

have to sample so are there ways that we

can do some of these Diagnostics so I

spent a good part of my career actually

trying to figure out ways that we can do

this so I'll talk a little bit about

that and what all the problems are

associated with them

um and how we can get around those

um and then and so that will be kind of

like our our Diagnostics section and

then and then after that we'll move into

not today but tomorrow we'll move into

atmospheric effects of particles and and

how we you know like what what are the

issues and

um how do we like what are the things

that we need to understand in order to

understand say impact on climate

um and and then that brings up a whole

host of things we don't we also don't

understand so um so how about if we take

a break oh let's let's just take a break

now like it's two minutes anyway

um and then I'll see you uh in 15

minutes or at 4 30.