Differential Scanning Calorimetry

Transcription

1 Differential Scanning Calorimetry

2 Springer-Verlag Berlin Heidelberg GmbH

3 G. W. H. H6hne. W. F. Hemminger H.-J. Flammersheim Differential Scanning Ca lori metry 2nd revised and enlarged edition With 130 Figures and 19 Tables " Springer

4 Dr. G.W.H. H6hne (Retired from Universitat Ulm) Morikeweg Laupheim, Germany Dr. W. F. Hemminger Physikalisch-Technische Bundesanstalt Bundesallee Braunschweig, Germany Dr. H.-J. Flammersheim Universitat Jena Institut fur Physikalische Chemie Lessingstraf5e Jena, Germany ISBN Library of Congress Cataloging-in-Publication Data Hohne, G. (Glinther) Differential scanning calorimetry: an introduction for practitioners / G. W. H. Hohne, W. Hemminger, H.-J. Flammersheim. -- 2nd rev. and en!. ed. p. cm. Includes bibliographical references and index. ISBN ISBN (ebook) DOI / Calorimetry. 1. Hemminger, W., 1941-II. Flammersheim. H.-J., 1942-II1. Title. QC29I.H '.6--dc This work is subject to copyright. AII rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilrns or in any other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the German Copyright 1.aw of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag Berlin Heidelberg GmbH. Violations are liable for prosecution under the German Copyright Law. Springer-Veriag Berlin Heidelberg 2003 Originally published by Springer-Verlag Berlin Heidelberg New York in 2003 Softcover reprint of the hardcover 2nd edition 2003 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Product liability: The publisher cannot guarantee the accuracy of any information about dosage and application contained in this book. In every individual case the user must check such information by consulting the relevant literature. The instructions given for the practical carrying-out of HPLC steps and preparatory investigations do not absolve the reader from being responsible for safety precautions. Liability is not accepted by the author. Cover Design: Klinkel & Lopka, Heidelberg Typesetting: Data-conversion by Fotosatz-Service Kohler GmbH, Wlirzburg Production Editor: Christiane Messerschmidt, Rheinau Printed on acid-free paper 52/

5 Preface Differential Scanning Calorimetry (DSC) is a well established measuring method which is used on a large scale in different areas of research, development, and quality inspection and testing. Over a large temperature range, thermal effects can be quickly identified and the relevant temperature and the characteristic caloric values determined using substance quantities in the mg range. Measurement values obtained by DSC allow heat capacity, heat of transition, kinetic data, purity and glass transition to be determined. DSC curves serve to identify substances, to set up phase diagrams and to determine degrees of crystallinity. This book provides, for the first time, an overall description of the most important DSC measuring systems and measuring programs, including the modulated temperature DSC. Furthermore many examples of typical and widely used applications of Differential Scanning Calorimetry are presented. Prerequisites for reliable measurement results, optimum evaluation of the measurement curves and estimation of the uncertainties of measurement are, however, the knowledge of the theoretical bases of DSC, a precise calibration of the calorimeter and the correct analysis of the measurement curve. The largest part of this book deals with these basic aspects: The theory of DSC is discussed for both heat flux and power compensated instruments, and for the recently introduced modulated temperature mode of operation (TMDSC) as well. Temperature calibration and caloric calibration are described on the basis of thermodynamic principles. Desmearing of the measurement curve in different ways is presented as a method for evaluating the curves of fast transitions. The instrumental data which are most important for the characterization of Differential Scanning Calorimeters are defined, and it is explained how they are determined experimentally. This enables every potential instrument buyer to ask the manufacturer for measured characteristic data which will allow him to compare the different instruments available. To make measurement results comparable, in addition to their traceability (via reference materials) a standardized evaluation of measurement uncertainty is indispensable. How this may be done is explained in some detail. We are indebted to S.M. Sarge for a critical examination of the manuscript and valuable suggestions for improvement, to S. Rudtsch for contributions to the chapter on calibration and to the expression concerning uncertainties and in particular to M. J. Richardson for helping us with the translation. Braunschweig, Jena and Ulm March 2003 G. W. H. Hahne w. F. Hemminger H.-f. Flammersheim

6 Contents 1 Introduction Types of Differential Scanning Calorimeters and Modes of Operation.... Heat Flux DSC.... Heat Flux DSC with Disk-Type Measuring System. Heat Flux DSC with Turret-Type Measuring System Heat Flux DSC with Cylinder-Type Measuring System Power Compensation DSC..... Function Principle Special Power Compensating DSC.... DSC with Combined Heat Flux and Power Compensation Measuring System.. Modes of Operation.... Constant Heating Rate Variable Heating Rate (Modulated Temperature). Theoretical Fundamentals of Differential Scanning Calorimeters. Heat Flux DSC.... Power Compensation DSC Temperature-Modulated DSC (TMDSC) The Temperature-Modulated Method Influences of the Sample... Influences of Heat Transport Conclusions Calibration of Differential Scanning Calorimeters Aspects of Quality Assurance Basic Aspects of Calibration..... Temperature Calibration Temperature Calibration on Heating Temperature Calibration on Cooling Caloric Calibration Heat Flow Rate Calibration... Heat (Peak Area) Calibration.. Examples of Caloric Calibration Caloric Calibration in Cooling Mode

7 VIII Conclusions Regarding the Calibration of DSCs Reference Materials for DSC Calibration..... Reference Materials for Temperature Calibration Reference Materials for Heat Flow Rate Calibration Reference Materials for Heat (Peak Area) Calibration Additional Calibration in Temperature-Modulated Mode of Operation.... Calibration of Magnitude Calibration of Phase... DSC Curves and Further Evaluation. Characteristic Terms of DSC Curves. Parameters Influencing the DSC Curve Further Evaluation of DSC Curves... Determination of the Real Sample Heat Flow Rate The Baseline and the Determination of Peak Areas (Enthalpy Differences).... Desmearing of the DSC Curve.... Correction of the Temperature and Heat Flow Rate Indicated Subtraction of the Zeroline.... Calculation of the True Heat Flow Rate into the Sample Advanced Desmearing Further Calculations TMDSC Curves Reversing and Non-Reversing Heat Capacity Complex Heat Capacity..... Curves from Step-Scan Evaluation.... Interpretation and Presentation of Results. Applications of Differential Scanning Calorimetry Measurement of the Heat Capacity "Classical" Three-Step Procedure The ''Absolute'' Dual Step Method.... General Precautions for the Minimization of Errors and their Estimation Procedure of Small Temperature Steps The Temperature-Modulated Method.... Typical Applications of Heat Capacity Measurements Determination of Heats of Reaction Kinetic Investigations.... Introduction and Definitions.... Experimental Prerequisites for a Reliable Kinetic Analysis Selection of the Measuring Conditions - Isothermal or Non-Isothermal Reaction Mode Activation of the Sample by UV Irradiation Different Strategies of Kinetic Evaluation. Selected Examples and Possible Predictions Contents

8 Contents The Glass Transition Process.... The Phenomenology of the Glass Transition.... The Nature of the Glass Transition and Consequences for DSC Measurements.... Definition and Determination of the Glass Transition Temperature T g Applications of Glass Transition Measurements... The Dynamic Glass Process, an Example.... Characterization of Substances, the Phase Behavior Applications in Biology and Food Science Applications in Pharmacy Other Applications Porosity Measurements.... Determination of Phase Diagrams Safety Aspects and Characterization of High-Energetic Materials Characterization of Polymers Effects of Origin and Thermal History Determination of the Degree of Crystallinity... Advanced Characterization with the TMDSC Method Purity Determination of Chemicals.... Evaluation of the Performance of a Differential Scanning Calorimeter Characterization of the Complete Instrument Characterization of the Measuring System Characterization of the Results of a Measurement: Uncertainty Determination Black Box Method. GUM Method... Check List for DSCs Appendix 1 Appendix 2 References. Subject Index IX

9 List of Symbols A area, pre-exponential factor C heat capacity, electric capacity D diffusivity E energy H enthalpy K factor (calibration), coefficient L thermal conductance P electric power, transfer function Q heat R resistance (thermal, electric), gas constant S entropy T temperature U internal energy, voltage V volume W work, electric energy a coefficient, apparatus function c specific heat capacity d distance i electric current k proportionality factor, calibration factor, rate constant, conductivity 1 length, distance m mass n reaction order p pressure r rate of reaction, radius t time w weight fraction x mole fraction a degree of reaction f3 heating rate 6 phase angle y expansivity coefficient E emissivity A thermal conductivity v stoichiometric number tp heat flow rate p density a standard deviation

10 XII List of Symbols r time constant w angular frequency X compressibility ~ extent of reaction, composition, conversion Subscripts A activation, amplitude a amorphous bl baseline c extrapolated offset, crystalline cal calorimeter e extropolated onset el electric eq equilibrium exp experimental F furnace f final fix fixpoint fus fusion g glass h, i, k, n running numbers initial iso isothermal I liquid lin linear lit literature M measurement point m measured mix mixing o onset p peak, constant pressure prop proportional 4> related to heat flow rate Q related to heat R reference sample r reaction Ref reference material used for calibration (e. g. Certified Reference Material) S sample s solid st steady state th thermal tot total tr true trs transition u underlying V constant volume o zero, zero line