DTA and Heat-flux DSC Measurements of Alloy Melting and Freezing
File : pdf, 7.1 MB, 96 pages
TOC
Part 1: Introduction
1.1 Focus of the guide
1.2 Information sought from DTA/heat-flux DSC measurements
1.3 Relevant standards
1.3.1 Terms and definitions
1.3.2 Calibration and sensitivity
1.3.3 Analysis of data
1.4 Major points
Part 2: Instruments and Operation
2.1 Variations among instruments
2.1.1 Heat transfer between system components
2.1.2 DTA/ heat flux DSC vs. power compensating (true) DSC
2.1.3 How does instrument control heating rate?
2.1.4 What is the signal, millivolts or Kelvin?
2.1.5 Plotting signal vs. temperature or time
2.2 Samples
2.2.1 Mass
2.2.2 Shape
2.2.3 Powder samples
2.2.4 Inert powder cover
2.2.5 Lid
2.2.6 Atmosphere
2.2.7 Crucible selection/reaction
2.2.8 Evaporation
2.2.9 Initial metallurgical state of alloy samples
2.3 Reference materials
2.4 Calibration and DTAsignal from pure metals
2.4.1 Fixed point (pure metal) enthalpy vs. temperature and DTAresponse function
2.4.2 Temperature calibration: effect of instrument therma lags on onset determination
2.4.3 Temperature calibration: choice of onset temperature
2.4.4 Quantitative enthalpy and heat capactiy calibration
2.5 Major points
Part 3: Analysis of DTAdata for binary alloys
3.1 General behavior for a binary eutectic system; example Ag-Cu alloy melting
3.1.1 Enthalpy vs. temperature curves
3.1.2 Derivative of enthalpy vs. temperature curves and their relation to DTAcurves
3.1.3 Comparison to experiment
3.2 Problems with solidus determination on heating
3.2.1 Incipient melting point vs. solidus
3.2.2 Effect of hold time prior to melting
3.2.3 Errors caused by using extrapolated melting onset (tangent construction)
3.3 Problems with liquidus determination on heating
3.3.1 General DTAcurve analysis
3.3.2 Details of computed behavior of an alloy on melting
3.3.3 Small liquidus solidus separation
3.3.4 Resolution of difficulties using temperature cycling near the liquidus
3.3.5 Alloys with k<1 and k>1; peak temperature
3.3.6 Failure to completely melt
3.4 Supercooling problem with liquidus determination on cooling
3.4.1 Onset of freezing
3.4.2 Slope of DTAcurve on initial freezing
3.4.3 Simulation of DTAresponse for alloys with supercooling
3.5 Eutectics reactions vs. peritectic reactions
3.5.1 Diffusion
3.5.2 DTAresponse
3.6 Major points
Part 4: Analysis of DTAdata for ternary alloys
4.1 Al – rich corner of Al-Cu-Fe phase diagram
4.2 Al – 20% Cu – 0.5% Fe
4.3 Al – 6% Cu – 0.5% Fe
4.4 Major points
Part 5: Concluding Remarks
Appendices
A. Glossary
B. Recommended Reading
C. Model for simulating DTAresponse for melting and solidification of materials with known or assumed enthalpy
vs. temperature relations. Also method for computing thermal lags of DTA/DSC instruments
D.Expressions for the rate dependence of melting onset temperatures for a pure metal
E.Enthalpy vs. temperature relations for dilute binary solid solution alloy
F.Binary phase diagrams and DTAresponse
G.Tutorial on melting and freezing of multicomponent alloys
G.1 Aluminum alloy 2219
G.2 Udimet 700
