Thermal Analysis : Thermal Analysis Dr. Rina H.Gokani
S.J. Thakkar Pharmacy College
Rajkot 3 October 2010 1 Copyright@RGH Different Techniques : Different Techniques Thermometric Titration (TT)
Heat of mixing
Thermal Mechanical Analysis (TMA)
Thermal Expansion Coefficient
Dynamic Mechanical Analysis (DMA)
Differential Scanning Calorimetric (DSC)
Heat flow during Transitions
Thermal Gravimetric Analysis (TGA)
Weight Loss due to decomposition
Derivative Thermogravimetric Analysis (DTG)
Differential Thermal Analysis (DTA)
Heat of Transitions
Temperature Programmed Desorption (TPD)
Temperature at which gas is desorbed from (catalyst) surface
Emission gas Thermoanalysis (EGT) 3 October 2010 2 Copyright@RGH Basic Principle : Basic Principle Sample is heated at a constant heating rate
Sample’s Property Measured
Heat Flow DSC
Temp DTA 3 October 2010 3 Copyright@RGH Thermal Analysis … : Thermal Analysis … A group of analytical techniques
Each technique defines a material property TA Use DSC
Differential Scanning Calorimetry
Mass & Heat Flow
Dimension TA Techniques Research / Analytical 70%
Routine / QC 20% 3 October 2010 Copyright@RGH Thermal Analysis is widely used … : Thermal Analysis is widely used … 3 October 2010 5 Copyright@RGH For a wide variety of applications … : For a wide variety of applications … 3 October 2010 6 Copyright@RGH Slide 7: A Thermogravimetric Analyzer (TGA) measures the change in mass of a sample as the sample is heated, cooled or held at a constant (isothermal) temperature. Thermogravimetric Analysis (TGA) 3 October 2010 7 Copyright@RGH TGA Technology … : TGA Technology … Top loading – Balance below sample area
Horizontal – balance behind sample area
Bottom loading – balance above sample area 3 October 2010 Copyright@RGH PerkinElmer High Sensitivity TGA & TG/DTA family ... : PerkinElmer High Sensitivity TGA & TG/DTA family ... Research …. for fast, accurate, reproducible results Pyris 1 TGA
Highest scan rates and throughput
Autosampler with AccuPik Diamond TG/DTA
Simultaneous TGA & DSC
30 position Autosampler
User-friendly beam change
Convenient connection to MS and FT-IR 3 October 2010 Copyright@RGH Thermogravimetric curve : Thermogravimetric curve A A’ B B’ ti tf Temperature WEIGHT 3 October 2010 10 Copyright@RGH Factors affecting TG curve : Factors affecting TG curve Instrumental
Effect of furnace atmosphere
Characteristic s of the sample
Weight of sample
Sample particle size
Heat of reaction
Compactness of sample
Previous history of the sample 3 October 2010 11 Copyright@RGH Instrumentation: : Instrumentation: Principle: In this technique the change in sample weight is measured while the sample is heated at a constant rate (or at constant temperature), under air (oxidative) or nitrogen (inert) atmosphere.
This technique is effective for quantitative analysis of thermal reactions that are accompanied by mass changes, such as evaporation, decomposition, gas absorption, desorption and dehydration. 3 October 2010 12 Copyright@RGH Working principle of balance : Working principle of balance 3 October 2010 13 Copyright@RGH Slide 14: 3 October 2010 14 Copyright@RGH Working Principle of balance : Working Principle of balance Change in the sample mass causes a deflection of the beam.
The resulting imbalance in the photodiode current is amplified and fed into coil E, which is situated between the poles of permanent magnet F.
The magnetic field generated by the current in the coil restores the beam to its original position.
The amplified photodiode current is monitored and transformed into mass or mass loss information by the data acquitting system.
In most cases mass vs temperature data can be either plotted in real time or stored for further manipulation or display at a later time. 3 October 2010 15 Copyright@RGH The various components of modern thermo balance are : The various components of modern thermo balance are Recording balance
Furnace temperature programmer or controller
Recorder 3 October 2010 16 Copyright@RGH Recording Balance : Recording Balance It is the most important component of the thermobalance.
Commercially available balance can provide quantitative information about 1 mg-100 gm mass.
Most common type of balance has a range of 5 to 20 mg. 3 October 2010 17 Copyright@RGH Slide 18: A good quality balance must fulfill the following requirements.
1 Its accuracy, sensitivity, reproducibility and capacity should be similar to those it should of analytical balance.
2 It should have an adequate range of automatic weight adjustment.
3 It should have a high degree of mechanical and electronic
4 It should have a rapid response to weight changes
5 It should be unaffected by vibration
6 The balance should be simple to operate and versatile. 3 October 2010 18 Copyright@RGH Slide 19: There are two types of balance.
null type 3 October 2010 19 Copyright@RGH Slide 20: 1) Deflection type 3 October 2010 20 Copyright@RGH Beam type : Beam type In these balances, there occurs a conversion of beam deflection about the fulcrum into a suitably identifiably weight change curves by either of the following.
By photographic recorded trace
By recorded signals generated by suitable displacement measuring transducer or electromechanically drawn curves. 3 October 2010 21 Copyright@RGH Helical type : Helical type In this balances, elongation or contraction of the spring take place as a result of weight change.
Transducers are used for recording these changes in length of the spring.
Quartz fibers are most widely used to avoid fatigue problems as well as anomalous results with change of temperature. 3 October 2010 22 Copyright@RGH Cantilevered beam type : Cantilevered beam type One end of the beam is fixed and the other end on which the sample is placed is free to under go deflections.
The technique of deflection measurement is same as in beam type balance. 3 October 2010 23 Copyright@RGH Torsion wire type : Torsion wire type The beam is attached to a taut wire which acts as a fulcrum.
The wire is fixed at one or both ends so that the deflections of the beam are proportional to weight changes and the torsional characteristics of the wire.
A metallic ribbon is also used instead of the taut wire. Detection devices are similar to the beam type. 3 October 2010 24 Copyright@RGH Slide 25: 3 October 2010 25 Copyright@RGH 2) Null-point Balance : 2) Null-point Balance It is more commonly used. In this balance, a sensor is employed to detect the deviation of the beam from its null position.
A restoring force of either electrical or mechanical weight loading is applied to the beam to restore its null position from the horizontal or vertical norm.
The restoring force is proportional to the weight change and this force is recorded directly or by transducer. 3 October 2010 26 Copyright@RGH 2) Sample holder: : 2) Sample holder: It is constructed from glass, quartz, alumina, stainless steel, platinum, graphite etc.
In practice 4 types of sample holders have been used. 3 October 2010 27 Copyright@RGH Slide 28: Shallow pans.
Suitable where it is necessary to eliminate diffusion as the rate controlling step.
e.g. in case of polymers side reactions may occurs.
So in that case sample is arranged in a thin layer so that as soon as a volatile fragment is formed, it is free to escape. 3 October 2010 28 Copyright@RGH Slide 29: 2. Deep Crucibles.
It is used in such cases where side reactions or partial equilibrium is to be desired.
Used in study of industrial scale calcinations. 3 October 2010 29 Copyright@RGH Slide 30: Loosely covered crucibles.
Suitable when rate of weight loss and not the exact temperature is taken into consideration, as in case of self generated atmosphere studies. 3 October 2010 30 Copyright@RGH Slide 31: Retort cups:
These are useful in boiling point studies.
The retort provides the single plate of reflux essential for a simple boiling point determination. 3 October 2010 31 Copyright@RGH 3) The furnace: : 3) The furnace: The choice of furnace heating element and type of furnace depends upon the temperature range being studied.
1100 0C Nichrome
1100-1500 0C Platinum or alloy of pt-rhodium
1100-1750 0C Pt-Rh in which (Rh-40)
>1750 0C tungsten or molybdenum 3 October 2010 32 Copyright@RGH Slide 33: The size of a furnace is an important factor.
High mass furnace is much better than low mass furnace because it becomes easier to obtain a larger uniform hot zone in the high mass furnace. 3 October 2010 33 Copyright@RGH Slide 34: A purge system:
Nitrogen or argon: for purging the furnace to prevent oxidation of sample.
In some analysis purging gas supply is continued during analysis process. 3 October 2010 34 Copyright@RGH Slide 35: Example: sample bituminous coal.
Nitrogen was employed during first 18 min (moisture content and the percent volatiles was recorded.)
The gas was switched to oxygen for 4-5 min (oxidation of carbon to dioxide)
Further application of nitrogen gas (measurement of ash content) 3 October 2010 35 Copyright@RGH 4) Temperature measurement : 4) Temperature measurement The most common method is thermocouple.
For 1100 0C: chromel or alumel thermocouples made up of alloys of Pt and rhodium.
For higher temperature: tungsten or rhenium thermocouple.
The position of temperature measuring device relative to the sample is very important. 3 October 2010 36 Copyright@RGH Slide 37: 3 October 2010 37 Copyright@RGH Slide 38: There are mainly three ways.
Not suitable where low pressures are employed. The thermocouple is placed near the sample container and it has no contact with sample container.
The thermocouple is kept inside the sample holder but not in contact with it. It is much better than because it responds to small temperature changes.
Iii The thermocouple is placed either in contact with sample or with the sample container.
This is best arrangement of sample temperature detection. 3 October 2010 38 Copyright@RGH Slide 39: 5) Recorder
1. Time-base potentiometric strip chart
2. X-Y recorders.
In some instruments, light-beam-galvanometer photographic paper recorders or one recorder with two or more pens are used.
One can check the heating rate of the furnace for linearity.
In x-y recorders we get curves having plot of weights against temperature.
In most cases normal mode of recording data for Thermogravimetry is the weight change vs temperature or time.
But % mass change vs time or temperature is more suitable. 3 October 2010 39 Copyright@RGH Application of TG : Application of TG 1) In the study of polymer
It provides information about the decomposition mechanism in the polymer. Decomposition pattern is characteristic for each kind of polymers so useful for identification purpose. 3 October 2010 40 Copyright@RGH Slide 41: 2) For quantitative analysis
The analysis of polyethylene formulated with fine carbon-black particle inhibit degradation from exposure to sunlight is difficult by most other analytical methods.
The thermogravimetric method is most suitable for this polyethylene. 100 75 50 25 0 75% polyethylene 25 % carbon black 250 500 750 3 October 2010 41 Copyright@RGH Slide 42: In case of thermogram obtained by increasing the temperature of pure CaC2O4.H2O at a rate of 5 0C/min.
The horizontal region obtained in thermogram correspond to temperature ranges in which the indicated calcium compounds are stable.
This is important application of Thermogravimetry in defining the thermal condition necessary to produce a pure form for the gravimetric determination of a species. 3 October 2010 42 Copyright@RGH Slide 43: It is useful in the quantities analysis of calcium, strontium and barium ions.
The three are first precipitated as the monohydrated oxalates.
The mass in the temperature range between 320 0C and 400 0C is that of the three anhydrous compounds, CaC2O4, SrC2O4 and BaC2O4 while the mass between about 580 0C and 620 0C corresponds to the weight of the three carbonates.
The weight change in the next two steps results from the loss of carbon dioxide, as first CaO and then SrO are formed.
Sufficient data are available in the thermogram to calculate the weight of each of the three elements present in the sample. 3 October 2010 43 Copyright@RGH Slide 44: Derivative of the thermogram reveal information that is not detectable in the ordinary thermogram.
The three peaks at 140 0C, 180 0C and 205 0C suggest that the three hydrates lose moisture at different temperature.
All appear to lose carbon monoxide simultaneously and thus yield a single sharp peak at 450 0C. 3 October 2010 44 Copyright@RGH Slide 45: 3) Evaluation of suitable standards:
Combined TG studies with infrared absorption spectrophotometric studies shows that substance such as
Magnesium ammonium chloride, ammonium bicarbonate and
ammonium fluoride cannot be used for preparing standard solution
While compounds like sodium dichromate, sodium cobaltinitrite, hydrazinium chloride, ascorbic acid and methylglucamine are most suitable for preparing standard solution.
The maximum temperature of heating of some compounds like
EDTA 109 0C
Urea 165 0C
NaF 850 0C etc. 3 October 2010 45 Copyright@RGH Slide 46: 4) Testing of sample purity:
Useful for testing of purity of sample
E.g. an unusual weight loss below 100 0C in TG curve of calcium oxalate is due to impurity in the sample. 3 October 2010 46 Copyright@RGH Slide 47: 5) Study of organic compound:
By making use of DTA, TG and using derivatography a large no of the compound have been studied.
E.g. in the study of decomposition of malonic acid the phase transition occurred in the region of 70 0C with melting at about 140 0C followed by decomposition above 150 0C.
In case of decomposition of L-glutamic acid by TG has three clear stages of decomposition in air. 3 October 2010 47 Copyright@RGH Other applications. : Other applications. It is used for the determination of correct drying temperature for precipitates used in gravimetric analysis by using this one can get accurate and reproducible results in gravimetric analysis.
Also useful for the identification of the gases given off while a samples temperature increases. 3 October 2010 48 Copyright@RGH Slide 49: The composition of the residue is also determined in addition and also useful in identifications of the formulas of the residue.
Ca-ox is heated → Ca(COO)2 (upto 400 0C) >400 0C→ CaCO3 + CO↑→>800 0C→CaO + CO2↑ 3 October 2010 49 Copyright@RGH Slide 50: Identification of compound present in the mixture.
In case of mixture thermogram obtained for each component is superimposed on each other to provide a single composite thermogram for the sample.
By using this method not only can the components of the mixture be identified but a quantitative determination of each is possible. 3 October 2010 50 Copyright@RGH Questions: : Questions: a) Give the significance of ‘Thermal Analysis’ in pharmaceuticals.
b) Explain the term ‘Thermal Analysis’. Write a note on thermogravimetric analysis.
c) Explain the thermogravimatric curve and the various factors affecting it.
d) With the help of a suitable example, explain the thermogravimetric curve and discuss any 2 factors that affect the curve. 3 October 2010 51 Copyright@RGH Differential Thermal Analysis : Differential Thermal Analysis Definition: : Definition: It is a technique in which the difference in temperature between a substance and a reference material is measured as a function of temperature while the substance and refrence material are subjected to a controlled temperature program.
It is more versatile and yields data of a considerably more fundamental nature. 3 October 2010 53 Copyright@RGH Thermogram : Thermogram In most of the cases, physical changes give rise to endothermic curves
whereas chemical reactions give rise to exothermic peaks. A differential thermogram consists of a record of the difference in sample and reference themperature(∆T) plotted as a function of time t, sample temperature(Ts), reference temperature(Tr) or furnace temperature(Tf). 3 October 2010 Copyright@RGH Factors affecting the DTA curve : Factors affecting the DTA curve A] Environmental factors
B] Instrumental factors
i. Sample holder
ii. Differential temperature sensing devices
iii. Furnace characteristics:
iv. Temperature- programmer controller:
v. Thermal Regime:
C] Sample factors
2] Chemical: 3 October 2010 55 Copyright@RGH Slide 56: 3 October 2010 56 Copyright@RGH Instrumentation : Instrumentation A typical DTA apparatus consists of the following components.
2} Sample holder
3} temperature controller and recorder
5} Cooling device 3 October 2010 57 Copyright@RGH Slide 58: Differential Thermal Analysis sample
pan inert gas
coil sample holder
sample and reference cells (Al)
Pt/Rh or chromel/alumel thermocouples
one for the sample and one for the reference
joined to differential temperature controller
alumina block containing sample and reference cells
controls for temperature program and furnace atmosphere alumina block Pt/Rh or chromel/alumel
thermocouples 3 October 2010 58 Copyright@RGH Slide 59: Differential Thermal Analysis advantages:
instruments can be used at very high temperatures
instruments are highly sensitive
flexibility in crucible volume/form
characteristic transition or reaction temperatures can be accurately determined
uncertainty of heats of fusion, transition, or reaction estimations is 20-50% DTA 3 October 2010 59 Copyright@RGH 1} Furnace : 1} Furnace Tubular furnace is most commonly used because it possess the desired characteristic for good temperature regulation and programming.
Dimension of the furnace is depends upon the length of the uniform temperature zone desired.
The choice of resistance material and refreector material is depends on the maximum temperature of the operation and gaseous environment.
e.g. Nichrome V and chromel C maximum elemental temperature is 1200 0C fitted in porcelain support, thermal insulator is fire bricks and gaseous environment is air. 3 October 2010 60 Copyright@RGH 2} Sample holder : 2} Sample holder While selecting the material for preparation of sample holder one should take care into mind the cost, ease of fabrication and inertness towards the sample.
Metallic material: nickel, stainless steel, platinum
Non-metallic material: glass, vitreous silica or sintered alumina.
Most commonly the shape of holder is cylindrical.
The nature of physical constant between the sample, thermocouple junction and the specimen holder affect the DTA signals.
So to maintain a good physical constant between the metallic sheath or sample holder and the thermocouple junction, a sample holder with dimples in which thermocouple junctions are inserted (thermocouple wells) are used. 3 October 2010 61 Copyright@RGH 3} Temperature controller and recorder : 3} Temperature controller and recorder a. Temperature Controller
In order to control temperature, the three basic elements are required.
These are sensor, control element and heater.
The control element governs the rate of heat-input required to match the heat loss from the system.
The location of sensor with respect to the heater and mode of heat transfer measure the time elapsed between sensing and variation in heat input. 3 October 2010 62 Copyright@RGH Slide 63: b. Temperature programming
It transmits a certain time-based instruction to the control unit.
The simplest device is to use a variable speed motor-driven autotransformer which gives a power input to the furnace i.e. proportional to the rate of movement of the drive mechanism.
By this device one can achieve linearity in the rate of heating or cooling it it is driven in a non-linear fashion using a special cam-drive.
The signals obtained from the sensors can be recorded in which the signal trace is produced on paper or film, by ink, heating stylus, electric writing or optical beam. 3 October 2010 63 Copyright@RGH 4} Thermocouple : 4} Thermocouple Thermocouples are the temperature sensors.
It is made up from chromel p and alumel wires (both nickel-chromium alloys) are used to measure and control temperature up to 1100 0C in air.
For above 1100 0C one should use thermocouple made from pure platinum & platinum-rhodium alloy wires. 3 October 2010 64 Copyright@RGH 5} Cooling device : 5} Cooling device It is separate from the temperature programmer because it is independent from heating. 3 October 2010 65 Copyright@RGH Typical results from DTA : Typical results from DTA Analysis of a polymer shows several features due to physical and chemical changes, including:
glass transition: glassy, amorphous polymer becomes flexible, H = 0, but change in Cp. Often Tg ~ 2/3 Tm.
crystallization of amorphous polymer into microcrystals is exothermic.
oxidation peak would be absent in N2 atmosphere 3 October 2010 66 Copyright@RGH Slide 67: 3 October 2010 67 Copyright@RGH Slide 68: 3 October 2010 68 Copyright@RGH Slide 69: 3 October 2010 69 Copyright@RGH Slide 70: Application of DTA
To construct phase diagrams and study phase transitions.
shows DTA curve for sulfur, in this 113°C solid phasechange from the rhombic to the monoclinic form; 124 °C indicated- melting poing of the element, liquid form in 3 forms exists at 179°C and 446°C indicate boiling of sulfur. 3 October 2010 70 Copyright@RGH Slide 71: 2. To find H
Peak areas depend upon sample mass, m, enthalpy change H of the process, and geometric and conductivity factors such as heating rate and particle size (included in a constant k for a certain substance).. peak area H m
(cm2) (Jg-1) ( g) 3 October 2010 71 Copyright@RGH Slide 72:
T 3. To fingerprint substances DTA of (a) butter and (b) margarine endo temp a b 4. To determine M.Pt., B.Pt., decomposition temperatures of organic compounds DTA of benzoic acid
A ambient pressure;
B 200 lb in-2 pressure
what are the two peaks? 3 October 2010 72 Copyright@RGH Application of DTA : Application of DTA 1) Physical chemistry
DTA is useful in studying heat of reaction, specific heat and thermal diffusivity.
2) Analytical chemistry
a. identification of substance: It serves as finger prints for various substances. It is generally used for identification of clays.
identification of products: When a substance react with another substance the products are identified by their specific DTA curves which known as reaction DTA.
c. melting points: with DTA one can easily determine the melting point so it is used as a direct check of the purity of the compound. It also provides information about the temperature range over which melting take place and this information is used to know the size of crystals. 3 October 2010 73 Copyright@RGH Slide 74: d. Quantitative analysis
The area of DTA peak is proportional to the total heat of reaction and hense to the weight of sample.So the quantitative analysis is possible with the help of standard curves of peak area vs. weight. peak area H m
(cm2) (Jg-1) ( g) 3 October 2010 74 Copyright@RGH Slide 75: (vi)Studing and charachterisation of polymers
It is most suitable for polymer. In case of polymer transition take place until the sample decomposed. But the softening of polymer absorbs some heat and so the curve is not linear and this non-linearity indicates the amorphous nature of the polymer.
Information about the amount of crystalline material in polymer get from the transition peak.
Information about the percentage of crystallinity of a polymer of unknown crystalline content is obtained by DTA.
For identification of polymers HIPPE- high pressure polyethylene
LPPE: low pressure polyethylene
POM- polyoxymethylene 3 October 2010 75 Copyright@RGH Slide 76: Quantitative DTA can be carried out comparing a sample’s DTA curve with those of known compound.
Mixtures of compounds can be analyzed quantitatively by DTA by measuring the amount of heat involved in the various transitions.
DTA is useful for industrial controls, to determine the structural and chemical changes occurring during sintering, fusing and other heat treatments like identification of the components of alloys, determination of structural changes in the production of metal sheets and wire. 3 October 2010 76 Copyright@RGH Slide 77: e. inorganic chemistry
it is used to study the thermal stability of a large no of inorganic compound.
It is also helpful in distinguishing between reversible phase changes and irreversible decomposition.
It is used to study oxalates, metal amine complexes, carbonates and oxides. 3 October 2010 77 Copyright@RGH Slide 78: f. organic chemistry
it is used for identification, purity determination and quantitative analysis.
For evaluation of kinetic parameters of polymers, explosives, pharmaceuticals, oils, fats and other organic chemical. 3 October 2010 78 Copyright@RGH Differential Scanning Calorimetry (DSC) : Differential Scanning Calorimetry (DSC) Definition: DSC : Definition: DSC it is a thermal method in which the energy required to establish a zero temperature difference between a substance and a reference material is recorded as a function of temperature or time when both are heated or cooled at a predetermined rate.
It is a thermal technique in which the difference in the amount of heat required to increases or decreased the temperature of a sample and reference are measured as a function of temperature. 3 October 2010 80 Copyright@RGH Principle: : Principle: When the sample undergoes a physical transformation such as phase transitions, more or less heat will need to flow to it than the reference to maintain both at the same temperature.
Whether more or less heat must flow to the sample depends on whether the process is exothermic or endothermic.
e.g. as a solid sample melts to a liquid it will required more heat flowing to the sample to increases its temperature at the same rate as the reference.
This is due to the absorption of heat by the sample as it undergoes the endothermic phase transition from solid to liquid.
Likewise, as the sample undergoes exothermic processes (such as crystalization) less heat is required to raise the sample temperature.
By observing the difference in heat flow between the sample and reference, differential scanning calorimeters are able to measure the amount of heat absorbed or released during such transitions. 3 October 2010 81 Copyright@RGH Schematic of DSC Instrument : Schematic of DSC Instrument N2 flow Pt thermopile Sample Reference Pt thermopile T1 T2 heater heater Low mass
1 gram DW 3 October 2010 82 Copyright@RGH Slide 83: DSC differs fundamentally from DTA in that the sample and reference are both maintained at the temperature predetermined by the program.
during a thermal event in the sample, the system will transfer heat to or from the sample pan to maintain the same temperature in reference and sample pans
two basic types of DSC instruments: power compensation and heat-flux Differential Scanning Calorimetry power compensation DSC heat flux DSC 3 October 2010 83 Copyright@RGH Variants of DSC : Variants of DSC Heat flux
1 large (30 – 100 g) furnace
Separate small (1 g) microheaters for sample and reference
Very fast scan rates 500°C/min
Mimic processing conditions
Short dynamic and isothermal scan steps
Separate reversible and irreversible effects 3 October 2010 84 Copyright@RGH Instrumentation: : Instrumentation: There are two types
1. Power compensated DSC
2. Heat flux DSC 3 October 2010 85 Copyright@RGH Slide 86: Power Compensation DSC sample holder
Al or Pt pans
Pt resistance thermocouples
separate sensors and heaters for the sample and reference
separate blocks for sample and reference cells
differential thermal power is supplied to the heaters to maintain the temperature of the sample and reference at the program value 3 October 2010 86 Copyright@RGH 1. Power compensated DSC : 1. Power compensated DSC a) Furnace:
b) Temperature controlled heat sink:
c) Sample and reference holders:
d) Platinum resistance thermometers:
e) Two controlled circuits:
1. Average temperature control
2. differential temperature 3 October 2010 87 Copyright@RGH Slide 88: sample holder
sample and reference are connected by
a low-resistance heat flow path
Al or Pt pans placed on constantan disc
chromel®-constantan area thermocouples (differential heat flow)
chromel®-alumel thermocouples (sample temperature)
one block for both sample and reference cells
the temperature difference between the sample and reference is converted to differential thermal power, dDq/dt, which is supplied to the heaters to maintain the temperature of the sample and reference at the program value Heat Flux DSC 3 October 2010 88 Copyright@RGH 2. Heat flux DSC : 2. Heat flux DSC Components:
sample and reference pan
dynamic sample chamber
gas purge inlet 3 October 2010 89 Copyright@RGH Output of DSC : Output of DSC Temperature, K Thermogram dH/dt, mJ/s Glass transition crystallization melting exo endo 3 October 2010 90 Copyright@RGH Glass Transition : Glass Transition Step in thermogram
Transition from disordered solid to liquid
Observed in glassy solids, e.g., polymers
Tg, glass transition temperature Temperature, K Thermogram dH/dt, mJ/s Glass transition Tg 3 October 2010 91 Copyright@RGH Crystallization : Crystallization Sharp positive peak
Disordered to ordered transition
Material can crystallize!
Observed in glassy solids, e.g., polymers
Tc, crystallization temperature Temperature, K Thermogram dH/dt, mJ/s Crystallization Tc 3 October 2010 92 Copyright@RGH Melting : Melting Negative peak on thermogram
Ordered to disordered transition
Tm, melting temperature
NB: melting happens to crystalline polymers; glassing happens to amorphous polymers Temperature, K Thermogram dH/dt, mJ/s Melting Tm 3 October 2010 93 Copyright@RGH Analysis : Analysis Sharp positive peak
Disordered to ordered transition
Observed in glassy solids, e.g., polymers
Tc, crystallization temperature Temperature, K dH/dt, mJ/s Crystallization Tc 3 October 2010 94 Copyright@RGH Slide 95: Technical Group Talk Other DSC Techniques Hyper-DSC
Based on principle that high heating rates give large broad transitions.
Heating rates typically 400-500oC/min
Need very small sample sizes (~nanograms)
A quick overview of new sample
Picking out minute transition
Accuracy: transitions can be shifted by as much as 40oC
Repeatabiliy: Very sensitive to thermal lag. 3 October 2010 95 Copyright@RGH Slide 96: Technical Group Talk Other DSC Techniques Modulated DSC
Composite heating profile:
Determines heat capacity and separates heat flow into that due to reversible and non-reversible events. Typicaly:
Heating rates: 0 - 50C
Period: 60 second
Amplitude: +/-10C 3 October 2010 96 Copyright@RGH Slide 97: Benefits
Increased Sensitivity for Detecting Weak (Glass) Transitions
Eliminates baseline curvature and drift
Increased Resolution Without Loss of Sensitivity
Two heating rates (average and instantaneous)
Ability to Separate Complex Thermal Events and Transitions Into Their Heat Capacity and Kinetic Components
Ability to Measure Heat Capacity (Structure) Changes During Reactions and Under Isothermal Conditions
Slow data collection Technical Group Talk Modulated DSC 3 October 2010 97 Copyright@RGH Slide 98: Technical Group Talk Example MDSC 3 October 2010 98 Copyright@RGH Slide 99: Technical Group Talk Modulated DSC Reversible Transitions
Evaporation 3 October 2010 99 Copyright@RGH What Can You Measure with DSC? : What Can You Measure with DSC? Qualitative analysis
Fingerprinting of minerals, clays, polymers
Heat capacity, cp
Glass transition temperature, Tg
Crystallization temperature, Tc
Phase diagrams 3 October 2010 100 Copyright@RGH Where Used? : Where Used? Pharmaceutical industry
Characterization of fats and oils
Synthetic blends 3 October 2010 101 Copyright@RGH Application: : Application: To estimate degree of crystallization that has occurred at particular temperature at 124 0C min are required to develop max. crystallinity.
To characterize the crystallization behavior at a series of temperature.
To test the purity of drug samples.
Pure data with relative uncertainties of 10 %. 3 October 2010 102 Copyright@RGH