Thermal Analysis of Materials

298 Pages·1994·12.949 MB·English

by  Robert Speyer

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THERMAL
ANALY S I S
OF
UATERlALS
ROBERT F. SPEYER
School of Materials Science and Engineering
Georgia Institute of Technology
Atlanta, Georgia
Marcel Dekker, Inc. New York*Basel*Hong Kong
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Library of Congress Cataloging-in-PublicationD ata
Speyer, Robert F.
Thermal analysis of materials / Robert F. Speyer.
--
p. cm. (Materials engineering ; 5)
Includes bibliographical references and index.
ISBN 0-8247-8963-6 (alk. paper)
1. Materials--Thermal properties--Testing. 2. Thermal analysis-
-Equipment and supplies. I. Title. 11. Series: Materials
engineering (Marcel Dekker, Inc.) ; 5.
TA4 18 .24.S66 1993
620.1* 1 '0287-&20 93-25572
CIP
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Dedicated to my mother, June
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PREFACE
Technology changes so fast now, it must be frustrating for de-
sign engineers to see their products become out of date shortly
after they hit the market. With the advent of inexpensive
personal computers and microprocessors over the past decade,
there has been a virtual explosion of new thermal analysis com-
panies and products. The level of instrument sophistication
has practically left the scientist/technician out of the loop; af-
ter popping the specimen in the machine, an elegant multi-
colored printout completely describes a series of characteristics
and properties of the material under investigation.
There is an inherent danger in trusting black boxes of this
sort, and it is the intent of this monograph to elucidate their
inner workings and provide some intuition into their operation.
I have avoided being encyclopedic in enumerating pertinent
journal and product literature. Rather, the narrative attempts
to develop important underlying principles. The design and
optimal use of thermal analysis instrumentation for materials’
property measurements is emphasized, as necessary, based on
atomistic models depicting the thermal behavior of materials.
This monograph, I believe, is unique in that it covers the
broader topic of pyrometry; the latter chapters on infrared and
optical temperature measurement, thermal conductivity, and
glass viscosity are generally not treated in books on thermal
analysis but are commercially and academically important. I
have resisted the urge to elaborate on some topics by using ex-
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vi PRE FA CE
tensive footnoting, in an attempt to maintain the larger picture
in the flow of the main body of the text.
This should be a useful text for a junior or senior collegiate
materials engineering student, endeavoring to learn about this
topic for the first time, or corporate R & D personnel, attempt-
ing to decipher what all the bells and whistles of their new,
quite expensive, instrument will do for them. By basing this
treatment on the elementary physical chemistry, heat transfer,
materials properties, and device engineering used in thermal
analysis, it is my hope that what follows will be a useful text-
book and handbook, and that the information presented will
remain “current” well into the future.
I would like to acknowledge those who have assisted in the
preparation of this work: Rita M. Slilaty and Kathleen C.
Bade for copyediting of earlier versions of the manuscript, as
well as Wendy Schechter and Andrew Berin for later versions.
Dr. Jen Yan Hsu for figure preparation, and my colleagues
at Georgia Tech: Drs. Joe K. Cochran, D. Norman Hill, and
James F. Benzel for technical editing and helpful discussions. I
am grateful to Professor Tracy A. Willmore for introducing me
to the subject of pyrometry during my undergraduate years at
the University of Illinois at Urbana-Champaign.
Robert F. Speyer
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CONTENTS
PREFACE V
1 INTRODUCTION 1
1.1 Heat. Energy. and Temperature . . . . . . . . . 2
1.2 Instrumentation and Properties of Materials . . 5
2 FURNACES AND TEMPERATURE
MEASUREMENT 9
2.1 Resistance Temperature Transducers . . . . . . 9
2.2 Thermocouples . . . . . . . . . . . . . . . . . . 12
2.3 Commercial Components . . . . . . . . . . . . 18
2.3.1 Thermocouples . . . . . . . . . . . . . . 18
2.3.2 Furnaces . . . . . . . . . . . . . . . . . . 19
2.4 Furnace Control . . . . . . . . . . . . . . . . . 23
2.4.1 Semiconductor-Controlled Rectifiers . . 24
2.4.2 Power Transformers . . . . . . . . . . . 26
2.4.3 Automatic Control Systems . . . . . . . 28
3 DIFFERENTIAL THERMAL ANALYSIS 35
3.1 Instrument Design . . . . . . . . . . . . . . . . 35
3.2 An Introduction to DTA/DSC Applications . . 40
3.3 Thermodynamic Data from DTA . . . . . . . . 46
3.4 Calibration . . . . . . . . . . . . . . . . . . . . 49
3.5 Transformation Categories . . . . . . . . . . . . 49
3.5.1 Reversible Transformations . . . . . . . 49
3.5.2 Irreversible Transformations . . . . . . . 60
3.5.3 First and Higher Order Transitions . . . 63
3.6 An Example of Kinetic Modeling . . . . . . . . 66
3.7 Heat Capacity Effects . . . . . . . . . . . . . . 70
vii
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Vlll CONTENTS
3.7.1 Minimization of Baseline Float . . . . . 71
3.7.2 Heat Capacity Changes During
Transformations . . . . . . . . . . . . . 75
3.7.3 Experimental Determination of Specific
Heat . . . . . . . . . . . . . . . . . . . . 79
3.8 Experimental Concerns . . . . . . . . . . . . . 80
3.8.1 Reactions With Gases . . . . . . . . . . 80
3.8.2 Particle Packing, Mass, and Size Distri-
bution . . . . . . . . . . . . . . . . . . . 81
3.8.3 Effect of Heating Rate . . . . . . . . . . 85
4 MANIPULATION OF DATA 91
4.1 Methods of Numerical Integration . . . . . . . 91
4.2 Taking Derivatives of Experimental Data . . . 95
4.3 Temperature Calibration . . . . . . . . . . . . . 99
4.4 Data Subtraction . . . . . . . . . . . . . . . . . 102
4.5 Data Acquisition . . . . . . . . . . . . . . . . . 105
5 THERMOGRAVIMETRIC ANALYSIS 111
5.1 TG Design and Experimental Concerns . . . . 111
5.2 Simultaneous Thermal Analysis . . . . . . . . . 120
5.3 A Case Study: Glass Batch Fusion . . . . . . . 125
5.3.1 Background . . . . . . . . . . . . . . . . 126
5.3.2 Experimental Procedure . . . . . . . . . 126
5.3.3 Results . . . . . . . . . . . . . . . . . . 128
5.3.4 Discussion . . . . . . . . . . . . . . . . . 133
6 ADVANCED APPLICATIONS OF DTA
AND TG 143
6.1 Deconvolution of Superimposed Endotherms . . 143
6.1.1 Background . . . . . . . . . . . . . . . . 143
6.1.2 Computer Algorithm . . . . . . . . . . . 144
6.1.3 Models and Results . . . . . . . . . . . 146
6.1.4 Remarks . . . . . . . . . . . . . . . . . . 151
6.1.5 Sample Program . . . . . . . . . . . . . 152
6.2 Decomposition Kinetics Using TG . . . . . . . 159
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CONTENTS ix
7 DILATOMETRY AND INTERFEROMETRY 165
7.1 Linear vs . Volume Expansion Coefficient . . . . 166
7.2 Theoretical Origins of Thermal Expansion . . . 168
7.3 Dilatometry: Instrument Design . . . . . . . . 169
7.4 Dilatometry: Calibration . . . . . . . . . . . . . 173
7.5 Dilatometry: Experimental Concerns . . . . . . 175
7.6 Model Solid State Transformations . . . . . . . 179
7.7 Interferometry . . . . . . . . . . . . . . . . . . 186
7.7.1 Principles . . . . . . . . . . . . . . . . . 187
7.7.2 Instrument Design . . . . . . . . . . . . 191
8 HEAT TRANSFER AND PYROMETRY I99
8.1 Introduction to Heat Transfer . . . . . . . . . . 199
8.1.1 Background . . . . . . . . . . . . . . . . 199
8.1.2 Conduction . . . . . . . . . . . . . . . . 199
8.1.3 Convection . . . . . . . . . . . . . . . . 203
8.1.4 Radiation . . . . . . . . . . . . . . . . . 205
8.2 Pyrometry . . . . . . . . . . . . . . . . . . . . . 210
8.2.1 Disappearing Filament Pyrometry . . . 211
8.2.2 Two Color Pyrometry . . . . . . . . . . 216
8.2.3 Total Radiation Pyrometry . . . . . . . 218
8.2.4 Infrared Pyrometry . . . . . . . . . . . . 220
9 THERMAL CONDUCTIVITY 227
9.1 Radial Heat Flow Method . . . . . . . . . . . . 227
9.2 Calorimeter Method . . . . . . . . . . . . . . . 231
9.3 Hot-Wire Method . . . . . . . . . . . . . . . . . 234
9.4 Guarded Hot-Plate Method . . . . . . . . . . . 240
9.5 Flash Method . . . . . . . . . . . . . . . . . . . 242
10 VISCOSITY OF LIQUIDS AND GLASSES 251
10.1 Background . . . . . . . . . . . . . . . . . . . . 251
10.2 Margules Viscometer . . . . . . . . . . . . . . . 255
10.3 Equation for the Rotational Viscometer . . . . 257
10.4 High Viscosity Measurement . . . . . . . . . . . 262
10.4.1 Parallel Plate Viscometer . . . . . . . . 262
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