22. Engineering Glass Properties; Introduction to Kinetics

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Session Overview

Prerequisites

Before starting this session, you should be familiar with:

• Properties, composition, and manufacturing of glass (Session 21)
• The shapes of molecules and factors affecting their mobility (Session 8 through Session 12)
• How to write chemical equations (Session 2)
• The distribution of energies per the Maxwell-Boltzmann curve (Session 14)

Looking Ahead

The solution hardening processes (chemically toughened glass, carburized steel) described in this session involve diffusion along concentration gradients, as quantified in Session 23 and Session 24.

Learning Objectives

After completing this session, you should be able to:

• Describe how to design glasses with the following properties: thermal shock resistance; low working temperature; high yield stress; high index of refraction; high optical clarity.
• Explain how intermediates act as network formers in some mixes and modifiers in others.
• Contrast thermal strengthening of glass with chemical strengthening.
• Write the rate law for a given chemical reaction, and determine the values of the rate constant k, rate order n, and activation energy E_a from the available data.
• Explain the effect of temperature on chemical reactions using the Maxwell-Boltzmann distribution.
• For a multi-step reaction, determine which step is rate-limiting and write the overall rate law.
• Describe how radioisotope dating works, and calculate the age of artifacts using their ¹⁴C content.

Reading

Archived Lecture Notes #7 (PDF)

Archived Lecture Notes #8 (PDF)

Book Chapters	Topics
[Saylor] 14.5, "Half-Lives and Radioactive Decay Kinetics."	Half-lives, radioactive decay rates, radioisotope dating techniques
[Saylor] 14.6, "Reaction Rates – A Microscopic View."	Molecularity and the rate-determining step, chain reactions
[Saylor] 14.7, "The Collision Model of Chemical Kinetics."	Activation energy, graphing the energy changes during a reaction, the Arrhenius equation
[JS] 12.2, "Glasses – Noncrystalline Materials."	Network formers, modifiers, and intermediates; commercial silicate glasses; nonsilicate glasses; applications of amorphous solids
[JS] 12.3, "Glass-Ceramics."	Heat treatment and crystallization, mechanical and thermal shock resistance, nucleating agents, glass processing techniques

Lecture Video

Resources

Lecture Slides (PDF)

Lecture Summary

Glasses can be engineered for specific applications by altering their proportions of network formers, network modifiers, and intermediates (e.g. Al₂O₃), and through careful processing. For example, glass can be strengthened by introducing compressive stress near the surface, by thermal (e.g. tempering) or chemical treatment (e.g. solution hardening).

The next unit covers chemical kinetics, the study of reaction rates and mechanisms. For a generalized reaction system, the rate of change of c_i (concentration of species i) is proportional to the instantaneous concentration of c_i; the exact values of the rate constant k and the rate order n are typically determined by experiment. The rate constant can be increased by raising the temperature and/or lowering the activation energy. Radiocarbon dating, although not a chemical reaction, has a first-order rate law, resulting in a constant decay rate over time.

Homework

Problems (PDF)

Solutions (PDF)

MATDL VirtualDL Lessons 1-4

Textbook Problems

For Further Study

Supplemental Readings

Libby, Willard F. Radiocarbon Dating. Chicago, IL: University of Chicago Press, 1969.

People

Svante Arrhenius – 1903 Nobel Prize in Chemistry

Willard Libby – 1960 Nobel Prize in Chemistry

Culture

Chambers, Joe, and Willie Chambers. "Time Has Come Today." The Time Has Come. Performed by The Chambers Brothers. Columbia Records, 1967.

Other OCW and OER Content

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