Transcript Thermal Analysis
BMFB 3263 Materials Characterization
Thermal Analysis
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Thermal Analysis
A group of methods by which the physical & chemical properties of a substance, mixture &/or reaction mixtures are determined as a function of temperature and/or time , while sample is subjected to a controlled temperature program.
Include heating or cooling (dynamic) or holding temperature constant (isothermal), or combination.
Thermogravimetry Analysis (TGA) – against temperature or time.
mass Differential Scanning Calorimetry (DSC) – function of temperature or time.
of substance heat flow as a Thermal Mechanical Analysis (TMA) – static load vs T or time.
deformation under Dynamic Mechanical Analysis (DMA) – substance under oscillating load .
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Thermogravimetric Analysis (TGA)
Used to measure changes in weight (mass),
m, of sample as a function of T and/or time .
Commonly used to
Determine polymer degradation temperature, Residual solvent level, Absorbed moisture content, and amount of inorganic (noncombustible) filler in polymer or composite material compositions.
Decomposition temperature of materials-impurities in ceramic etc 3
Response ;
Weight gain (chemical).
– adsorption (physical), oxidation Weight loss – vaporization (physical), desorption (physical), oxidation (physical), decomposition (chemical), dehydration & desolvation (chemical).
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Applications of TGA
Determines temperature and weight change of decomposition reactions, which often allows quantitative composition analysis. May be used to determine water content. Allows analysis of reactions with air, oxygen, or other reactive gases (see illustration below). Can be used to measure evaporation rates, such as to measure the volatile emissions of liquid mixtures. Allows determination of Curie temperatures of magnetic transitions by measuring the temperature at which the force exerted by a nearby magnet disappears on heating or reappears on cooling. Helps to identify plastics and organic materials by measuring the temperature of bond scissions in inert atmospheres or of oxidation in air or oxygen. Used to measure the weight of fiberglass and inorganic fill materials in plastics, laminates, paints, primers, and composite materials by burning off the polymer resin. The fill material can then be identified by XPS and/or microscopy. The fill material may be carbon black, TiO2, CaCO3, MgCO3, Al2O3, Al(OH)3, Mg(OH)2, talc, Kaolin clay, or silica, for instance. 5
Applications of TGA
Can measure the fill materials and titanium dioxide. added to some foods, such as silica gels Can determine the purity of a mineral, inorganic compound, or organic material. Distinguishes different mineral compositions from broad mineral types, such as borax, boric acid, and silica gels.
Identify filler content , ash content by weight %.
Characterize decomposition patterns , study degradation mechanisms & kinetics.
Prediction of lifetime (stability) at desirable time & temperature conditions in desirable environment.
Screening of additives Impurities analysis (stabilizers, flame retardant, plasticizers, etc).
in materials.
Compositional analysis Examine flame retardant of polymeric formulations & combustion properties.
Magnetic transitions in metallic materials.
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Schematic thermobalance – sample heated at certain rate in a controlled atm. Solid samples 1 mg to 100 mg but sometimes up to 100 g.
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TGA
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Thermogravimetric Analysis
Sample is placed into a tared TGA sample pan attached to a sensitive microbalance assembly.
which is Sample holder is then placed into high temperature furnace.
Balance assembly weigh the initial sample at room T & then continuously monitors changes in sample weight (losses or gains) as heat is applied to sample.
Heat applied at certain rate , in various environment. Typical environment: ambient air, vacuum, inert gas, oxidizing/reducing gases, corrosive gases, carburizing gases, vapors of liquids or "self-generating atmosphere". The pressure can range from high vacuum or controlled vacuum, through ambient, to elevated and high pressure; the latter is hardly practical due to strong disturbances. 10
Typical weight loss profiles are analyzed for the amount or % of weight loss at any given temperature, amount or % of noncombusted residue at final temperature, & temperature of various sample degradation processes.
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(i) No decomposition with loss of volatile products.
(ii) Rapid initial mass loss characteristic of desorption or drying.
(iii) decomposition in single stage .
(iv) multi-stage decomposition. (v) multi-stage decomposition but no stable intermediates .
(vi) Gain in mass as a result of sample reaction.
(vii) reaction product decompose again .
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Depending on polymer composition, reaction upon heating will give their own characteristic TG curve. Result can give thermal stability of material – desorption, decomposition & oxidation information.
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Calcium oxalate monohydrate – 3 distinct weight losses. CaC 2 O 4 .H
2 O CaC 2 O 4 CaCO 3 CaO 14
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Molded underfill material (flip chip application) – 3 degradation stages ; moisture & volatiles in resin, weakly bonded monomers, then breakage of cross-linked monomers. 16
Multiple-stage reaction : dehydration reaction of hydroxide from LiOH.H
2 O (exo).
4LiOH.H
2 O (solid) + O 2 2Li 2 O + 4H 2 O Then formation reaction of Li 2 SnO 3 due to reaction between Li 2 O with SnO 2 in mixture (exo).
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• Thermogravimetric analysis was used as one of several complementary techniques in the identification of an unknown polymer composite.
• TGA was then performed on the material to find the weight percent of each material. • The sample was heated from room temperature to 900°C at a rate of 5°C/min in air. •Polyester (71% of the polymer), •Polystyrene (29% of the polymer), • Fiberglass (22.9% of the whole) and CaCO3 (49.3% of the whole) were easily identified by their different temperatures of combustion or evaporation. •The combustion of the styrene polymer component produced enough energy that the temperature momentarily increased more than the programmed rate. 18
Thermogravimetric Analysis
Factors affecting TG curve heating rate sample size particle size of sample the way it is packed crucible shape gas flow rate DTG – detail .
derivative of TG curve , often useful in revealing extra TG also often used with DTA (differential thermal analysis). DTA – record difference in T (∆T) between sample and reference material . Each DTA curve should be marked with either endothermic or exothermic direction. Curve – peak represent exothermic or endothermic reaction.
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What is endothermic and exorthermic?
Endothermic-
"within-heating" describes a process or reaction that absorbs energy in the form of heat. Comes from Greek prefix
endo-,
meaning “inside” and the Greek suffix
–thermic
, meaning “to heat”.
E.g. melting of ice
Exothermic
- one that releases energy in the form of heat. 20
Differential Thermal Analysis (DTA)
Record temperature difference material.
between sample & reference If endo event (e.g melting) temperature sample will lower than reference material.
If exo event (e.g oxidation) response will be in opposite direction.
Reference material: thermally stable at a certain temperature range Not react with sample holder or thermocouple both thermal conductivity heat capacity should be similar to those of sample Both solid sample & reference material usually powdered form.
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Butter & margarine – how different they are!
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TG/DTA scan of montmorillonite clay. • Large endotherm at 114 °C is assigned to loss of interlayer absorbed water. • 2 nd endotherm at 704 °C is dehydroxylation reaction of the mineral. • Last 2 peaks are attributed to structural changes, since no weight loss are evident in TG.
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Differential Scanning Calorimetry (DSC)
A thermal analysis technique in which the amount of energy absorbed (endothermic) or released (exothermic ) by a material is measured.
Both events are the result of physical and/or chemical in a material.
changes Normally the weight of sample is 5 – 10 mg , Sample can be in solid or liquid form .
Many of the physical (e.g evaporation) or chemical (e.g decomposition) transformation are associated with heat absorption (endothermic) or heat liberation (exothermic).
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DSC provides a direct calorimetric measurement of the transition energy at T of transition. Often used to characterize thermal transition in polymers – glass transition T (T g ) and melting point (T m ). Organic liquids or solids, and inorganic can be analysed.
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Features of DSC curves
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DSC – Applications :
Identify melting point, glass transition, Curie temperature, energy required to melt material. Evaluation of phase transformation.
Decomposition, polymerization, gelation, curing.
Evaluation of processing, thermal & mechanical histories.
Process modeling, material’s min process temperature (processing condition).
Determine crystallization temperature upon cooling.
Perform oxidative stability testing (OIT).
Compare additive effects on material.
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Differential Scanning Calorimetry (DSC)
2 pans sit on a pair of identically positioned platforms connected to a furnace by common controlled heat.
Record any energy difference – endothermic or exothermic depending on whether more or less energy has to be supplied to the sample relative to the reference material.
Endothermic response usually represented positive , opposite of usual DTA convention (endothermic as negative side) Correlate endothermic or exothermic peaks with thermal events in sample.
One way – test if readily reversible on cooling & reheating. Exothermic process usually not, unlike melting & many solid solid transitions.
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Computer makes sure that the 2 separate pans heat at the same rate (usually 10 °C/min or lower) as each other. So if endothermic or exothermic events, results in more or less energy has to be supplied to the sample.
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2 modes – depending on method of measurement used.
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Heat is being absorbed by sample (increase in its heat capacity). Polymers gone thru T g , but transition occur over a temperature range. So T g is taken as middle of the incline.
Heat absorbed by polymer, heat flow given by q/t, q heat supplied per unit time. Heat capacity, C p amount of heat it takes to increase T. displacement, h = BØC p . Ø is heating rate & B calibration factor.
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Heat absorbed in order to melt – additional heat to increase temperature. Area of dip = heat of melting. Crystallization point – Tc where at this temperature polymer have enough energy to arrange into ordered arrangements , crystal. Polymers give off heat at this point. Area of peak = latent energy of crystallization.
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•Typical DSC curve for polymer (especially thermoplastic), for polymers that don’t crystallize (amorphous), T c & T m will not present. •Comparing T g capacity .
with T c & T m , T g only involve changes in heat 33
DSC Responses
Physical changes : Exothermic – adsorption, crystallization .
Endothermic – vaporization .
desorption, melting , Chemical changes : Exothermic – curing.
oxidation, decomposition, Endothermic – dehydration.
reduction, decomposition, 34
DSC directly measures ∆H of transitions. Also degree of crystallinity, degree of curing.
DSC curve for typical organic polymer.
Tg – change in heat capacity but no change in enthalpy, ∆H = 0.
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During curing, polymer chains cross-link, this process release heat, which is reflected DSC curve; When polymer going through curing process, its DSC curve will show a broad peak at the curing temperature at first scan; When cross-linking is complete, the curing peak disappear and its replaced by a feature of glass transition as shown in the curve of the second scan 36
Differential Scanning Calorimetry (DSC)
DSC have many applications in field of polymer science & engineering.
Tg, Tc & Tm transitions are characteristic of each polymer identification.
Curing conditions for thermoset – heat for curing which allows calculation of degree of curing.
But, DSC technology is not sensitive to detect Tg in cross-linked or highly crystalline resins . Also for polymer with high filler content .
Handling liquid also difficult. Interpretation of phase transition requires further info – XRD, etc.
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Polymer blend – immiscible blend . If fully soluble, Tm peak will be in between Tm each elements.
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% of crystallinity calculated relative to 100% crystal material’s Tm peak.
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Higher crystallinity Higher crystallinity gives larger & higher Tm peak .
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Different grades gives different Tg , and thus, different processing temperature .
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THERMO-MECHANICAL ANALYSIS (TMA)
Dimensional properties of a sample are measured as sample is heated, cooled or held under isothermal conditions. Loading or force applied can be varied.
Change of dimensions as a function of temperature is recorded.
TMA measurements record changes caused by changes in free volume of polymer .
Changes in free volume – by absorption or release of heat associated with that change, loss of stiffness, increase flow, change in relaxation time.
Free volume related to viscoelasticity, aging, penetration by solvents, & impact properties.
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As the space between the chains increases, the chain can move.
Physical aging T g Increase in free volume caused by increased energy absorbed in chains and this increased free volume permits various types of chain movement to occur. Below Tg various paths with different free volume exist depending on heat history & processing of polymer, where the path with the least free volume is most relaxed. 44
T g in polymer corresponds to the expansion of free volume allowing greater chain mobility above this transition.
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Thermo-Mechanical Analysis (TMA)
Application : Determine coefficient of thermal expansion (CTE ) of material.
Identify T g & T m of material.
Measure material’s heat deflection temperature (HDT).
Composite delamination temperature.
All types of solid – powders, films, fibers, molded pieces, etc.
Use of probe resting on sample under a positive load. As sample is probe.
heated, cooled or held isothermally, dimensional changes in sample is translated into linear displacement of 46
Thermo-Mechanical Analysis (TMA)
Probe configuration – expansion, penetration, compression, flexure, extension & dilatometry.
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TMA : (a) penetration & (b) extension.
LVDT – linear variable differential transformer. Also use other types of transducer – laser, optoelectronic.
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TMA : (c) flexure & (d) torsional measurement.
Dimensional changes are monitored and transducer transform responses into electrical signal (output).
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Measurement of Tg of epoxy PCB – probe rest on surface under low load. As sample expands during heating, probe is pushed up & resulting expansion of sample is measured. At Tg, epoxy matrix exhibits significant change in slope due to an increase in its rate of expansion. Onset T of this expansion = Tg.
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CTE measurement – quantitative assessment of expansion over a T interval. CTE before Tg = 50.5 µm/m°C, while above Tg, CTE increases to 270.7 µm/m°C. Also shows residual thermal stress – 1 st heat result show undulation in region near Tg reflects release of stresses.
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TMA penetration probe – during measurement, loading is added so probe moves down thru sample as it softens. Useful for measuring Tg of coatings on substrate. TMA of wire sample with 2 coatings – inner coating prevents electrical contact between adjacent wires and outer coating used to bond the coil.
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TMA penetration results on crosslinked and non crosslinked polyethylenes. Crosslinked sample exhibits smaller degree of penetration due to higher viscosity in liquid region above Tm.
High sensitivity of TMA tech allows it to detect weak transitions otherwise may not be observed by DSC.
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Extensive crystalline transition, & softening point, Tg.
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Another sample shows significantly smaller crystalline to amorphous transition dimension increase compared to 1 st sample.
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Thermo-Mechanical Analysis (TMA)
Since many materials are used in contact with dissimilar material, rate & amount of expansion needs to be known to help design around mismatches that can cause failure of final product.
Limitation – only for solid samples. Also material creep occurring concurrently with normal dimensional changes.
Thermodilatometry – dimensional changes over wider T range, up to 2000°C in variety of atm (inert, vacuum, air, etc) TD – sintering behavior of ceramic, clays.
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Sintering behavior of kaolin & kaolinitic clays – on heating loses water & form metakaolin structure. Then converts to spinel structure (above 960°C) & then above 1100°C to mullite.
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DSC scan of amorphous metal alloy.
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TMA of LDPE sample – compression mode 59
TMA of polyester partially oriented fibers – extension mode 60
Dynamic Mechanical Analysis (DMA)
Characterize Visco-Elastic properties Storage Modulus E’ (elastic response) and Loss Modulus E’’ (viscous response) of polymers are measured as a function of T or time as the polymer is deformed under an oscillatory load (stress) at a controlled (programmed) T in specified atmosphere.
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Dynamic Mechanical Analysis (DMA)
In viscous system, all work done by system dissipated as heat.
Elastic system – work stored as potential energy.
Polymer dual manner, i.e viscous-elastic.
DMTA – info on dynamic properties relating to these 2 behaviour. Gives 2 properties as a function of T : elastic modulus, E’ – energy stored (dynamic storage modulus).
viscous modulus, E’’ – ability to dissipate energy as heat (dynamic loss modulus).
Thus, stiffness & its dampening capacity.
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Dynamic Mechanical Analysis (DMA)
Measures dynamic modulus and/or damping of material under oscillatory load as a function of T or time at various frequencies.
Samples – fibers, films, molded sheets, powder.
DMA measures amplitude & phase of displacement of sample in response to an applied oscillating force.
Data then used to calculate stiffness & convert to modulus. Damping factor is also calculated.
A T scan at constant frequency can generate a fingerprint of material’s relaxation processes & its Tg.
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Dynamic Mechanical Analysis (DMA)
DMTA vs DSC – advantage of measuring side-chain and main-chain motion in specific regions of polymer, as well as relaxation.
Also, DTMA is more sensitive in detecting Tg especially Tg of minor component.
The elastic modulus plotted as a function of T give characteristic profile for polymer system.
Limitation – cannot measure mechanical properties over full T range, because sample excessively dampens the applied oscillation as it approaches its softening point.
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Dynamic Mechanical Analysis (DMA)
Sample is fixed between 2 parallel arms that are set into oscillation by an electromagnetic driver at an amplitude selected by operator.
DMA module measure changes in viscoelastic properties of materials resulting from changes in T, atm and time.
It then detects changes in the system’s resonant frequency and supplies the electrical energy needed to maintain the preset amplitude.
Frequency of oscillation is a measure of modulus of the material. The amount of electrical energy needed to maintain constant amp damping properties.
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An oscillatory strain is applied to sample in bending or tensile deformation modes as a function of T or time. Frequency & strain pre-selected & maintain constant. 66
DMA – sample subjected to sinusoidally varying stress of angular frequency. For viscoelastic material, resulting strain will also be sinusoidal, but will be out of phase with the applied stress owing to energy dissipation as heat, or damping. is the phase angle between stress & strain. Damping calculate from h = (v2 – v1)/vr, or measure driving force to maintain constant amplitude.
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Dynamic Mechanical Analysis (DMA)
Young’s modulus, E is related to square of resonance frequency, r .
E = c L 4 r 2 / B 2 c – constant, L – sample length between clamps, B – sample thickness & - sample density.
Damping usu expressed as logarithmic decrement per cycle, i.e amplitude decay by half, log (A measure of how much damping is.
1 /A 2 ) = log 2 = 0.3. Damping is then 3.0 dB. Rate of decay is a DMA output is plots of resonance frequency and of damping as functions of T.
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Dynamic Mechanical Analysis (DMA)
3 parameters are calculated : dynamic storage modulus, E’, dynamic loss modulus, E’’, & dissipation or damping factor, tan = E’’/E’.
Application : examine viscoelastic behavior as a function of stress, strain, frequency, time & T.
measure modulus vs T.
examine additive (filler, plasticizer) & cure time effects on viscoelastic properties & Tg.
examine mechanical behavior.
quantify impact properties / toughness.
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A – linear amorphous polymers.
B – crosslinked polymers.
C semicrystalline polymers.
D & E – poly(ester urethane)s.
# elastic modulus plotted as a function of T.
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DMA result of FRP sample – resonant frequency vs T. storage modulus is proportional to resonant frequency. As T increased, resonant frequency decreased. On-set T taken as Tg.
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Transition phenomena / mechanical relaxation in HDPE. Low T relaxation, γ in polymers is normally associated with improved toughness & impact behavior. α -relaxation is assigned as Tg of polyethylene. accelerated softening. α -relaxation requires mobility within crystalline phase & coincides with 72
DMA of 2 diff samples of PE. (a) 2 peaks : lower T peak attributed to long chain (-CH 2 -) n relaxation in amorphous region, & higher T peak to similar motion in crystalline phase. T & elative size can be related to degree of crystallinity.
(b) Branched PE show 3 peaks, 1 st and 3 rd as above, and 2 nd to –CH 3 peak is attributed relaxation in amorphous phase.
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Behavior of styrene-butadiene rubber (SBR). Various formulations of SBR – different styrene-butadiene ratios, diff butadiene isomers, diff additives, i.e carbon black affected Tg, modulus of elasticity.
# Changes in Young’s modulus indicate changes in rigidity and hence strength. Damping measurements give practical info on Tg, change in crystallinity, occurrence of cross-linking, & show up features of polymer chains. 74
Study of thermoset curing process (cure T & time fixed) – amount of cross-linker (hexamethylene tetramine) is shown to effect not only the Tg, but also modulus-T behavior..
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