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.