Materials science in the chemistry curriculum.
Ed note: In ACCN's annual look at education, the following six articles study various facets of the subject. ACCN is indebted to the Contributing Editor from the Chemical Education Division, Susan Boyd, MCIC, for all her work in organizing the theme and soliciting texts.
Do you know how a photocopy machine works? Why heat sensitive T-shirts change color? Why rubies are red and emeralds are green? Should a chemistry student graduate without learning the answers to these questions?
In the 1990-91 academic year, Dalhousie University's chemistry department introduced a new class, Materials Science. The class grew out of interest in the subject on my part, and a guess that students also would be interested in the subject. In my view, the class fills a vast void in the curriculum; the purpose of this class is to provide students with the background needed to understand materials applications on a molecular level.
The class is offered at the third-year level, with a prerequisite of an introductory class in thermodynamics, or permission of the instructor. The class is taken by honors chemistry students (it is not mandatory but can be used as one of the chemistry classes counted towards the degree), chemistry majors, and also students in physics, engineering, earth sciences and education programs. The class is officially categorized as physical chemistry as the perspective is physical.
The approach to the class is through the study of properties of materials. In this way, categories of materials are introduced as needed, circumventing the problem of having much of the lecture material purely descriptive in nature. The overall theme is understanding of the basis of physical properties.
The course begins with investigations of color and other optical properties of matter. This includes categorization of sources of color, and leads naturally to introductory spectroscopic matters.
It allows introduction of concepts such as atomic transitions, black body radiation, the Boltzmann distribution, molecular orbitals, the Fermi distribution, band theory, interference, soaps and soap films. It also allows the student to learn about such (apparently), diverse topics as why the sky is blue, why colors swirl in soap films, and how the photographic process works.
Heat at the heart
The second part concerns thermal and thermodynamic properties. This is the "heart" of the class, partly because of my interests in thermodynamics and partly because the predecessor to this class was an advanced chemical thermodynamics class. (One measure of the success of the materials science class is that its enrolment is 30 to 40, whereas its predecessor typically had eight or 10 students per year.)
This section begins with an introduction to heat capacity and heat storage, including the fundamentals of equipartition theory for all states of matter. Phase transitions and glasses are also introduced. The basics of other important thermal properties such as heat conduction and thermal expansion are introduced and exemplified for a variety of materials.
Thermodynamic stability in multicomponent systems (including congruent and incongruent melting) is introduced with use of the phase rule. The thermodynamic section ends with discussion of surface and interfacial phenomena, including surface energetics and tension, capillarity, Langmuir-Blodgett films, colloids, micelles and emulsions. Throughout this section, and the entire class, real examples of uses of these properties of materials are of paramount importance to the approach.
The third section concerns electrical properties of materials. By this point, the students are already familiar with the concepts of the free electron gas model for metals, and band theory. (These were introduced in the context of optical properties and reinforced in thermodynamic properties.) The electrical aspects of materials science are presented in the context of unified theories that encompass electrical, optical and thermal aspects. Superconductivity is also introduced.
The final section of the class describes the mechanical properties of materials. This includes the basis of elasticity, and concepts such as piezoelectricity and crack propagation (from a molecular energetic viewpoint).
The format of the class is two lecture hours per week, and one tutorial per week, for one term. The lectures are used to introduce the basic theory of the properties under consideration, and tutorials focus on applications.
In the tutorials, the students work in groups of four or five, using an instructor-provided "prompt sheet" to focus on questions concerning a materials science application. For example, in a tutorial How Does a Photocopy Machine Work? the students are led, through "prompt questions", to discover that the basis of the photocopier is the photoelectric response of the semiconductor, selenium. They work out the band gap for Se, and its relation to visible light, and then, by a series of prompts and information, determine how an electrical image is produced on the selenium drum and then transferred to paper as an optical image.
The tutorial is set up to "solve" the process by the end of the hour, taking up bits at intermediate points, while learning some applications of materials science along the way. The group interaction in the tutorial is important to the "discovery" of these processes. Other tutorial topics include: the photographic process; heat storage materials; thermal analysis; phase diagrams of important materials such as superconductors; designing new materials with special properties.
Both the tutorials and the lectures benefit greatly from the use of demonstration materials. These range from "pass arounds" such as mood rings and geologic specimens with special properties, to formal demonstrations such as supersaturated solutions used as heat storage materials, sheets of thermochromic liquid crystals, and piezoelectric devices.
There is, at present, no formal textbook suitable for this class. Since most of the students have purchased a book entitled Physical Chemistry for second-year classes, this is used as a general reference. In addition, The Cambridge Guide to the Material World by Rodney Cotterill was recommended for purchase until this past year when it went out of print. This beautifully illustrated book has excellent non-mathematical descriptions of properties of materials, and a copy of both it and the second year textbook are on reserve in the library.
The sources for lecture materials are eclectic, including chemistry, physics, geology and engineering books, Physics Today and Scientific American, research journal articles, trade papers and technical support sheets. Hand-outs, especially diagrams and data tables, are provided to the students.
The students are evaluated through midterm tests, a final three-hour examination, assigned problems and an essay. The essay is one of the most important parts of the class; each student chooses a topic that can be posed as a question in materials science, and which can be answered by exposing the underlying principles. In keeping with the physical approach of the class, the essay must contain mathematical equations quantifying the relations among pertinent physical properties.
The essays have been fascinating. Some topics include: Why Are Spider Webs So Strong?; How Do 3-Dimensional Movies Work?; What Are Quantum Wells, Wires and Dots?; Aqueous Foams: Why Are They Metastable?; How Do Light-Sensitive Glasses Work?
The essay is limited to 1,500 words of text, but up to eight pages are permitted to allow for equations and figures. I feel the essays provide students with an opportunity to find the answer to an interesting question, while learning some underlying fundamental physical principles.
Many topics arise in the class, and nowhere else in the curriculum of a chemistry student. Examples are: Buckminsterfullernenes, superconductors, liquid crystal devices, the chemical basis for photographic processes, properties of surfaces and films, ceramics, scanning tunneling microscopy, heat-sensitive T-shirts. Through study of the applications of fundamental processes, this class allows the student many opportunities to see connections with the "real world". In fact, I consider this class to have been a success if those who complete it are then able to understand the molecular principles of new products, based on scant information in the business pages of a newspaper.
Mary Ann White, MCIC, department of chemistry, Dalhousie University, Halifax, NS. This paper was delivered at the 1992 Canadian Chemical Conference, Edmonton.
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|Title Annotation:||introduction of materials science subject at Dalhousie University's chemistry department|
|Author:||White, Mary Anne|
|Publication:||Canadian Chemical News|
|Date:||Apr 1, 1993|
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