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Tharmal analysis 4

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differential thermal analysis, differential scanning calorimetry, thermogravimetric analysis

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Tharmal analysis 4

  1. 1. THERMAL ANALYTICAL TECHNIQUE BINDU KSHTRIYA
  2. 2. CONTENTS THERMAL ANALYSIS TECHNIQUES. DIFERENTIAL SCANNING CALORIMETRY . THERMOGRAVIMETRIC ANALYSIS DIFFERENTIAL THERMAL ANALYSIS APPLICATIONS
  3. 3. Thermal Analysis … A group of analytical techniques Each technique defines a material property DSC Differential Scanning Calorimetry Heat Flow TGA Thermogravimetric Analysis Mass TG/DTA Differential Thermal Analysis Temperature difference TMA Thermomechanical Analysis Dimension
  4. 4. Calorimetric principle Ti is the initial temperature(before reaction ) Tf is the final temperature(after reaction) If; Ti <Tf, rxn is exothermic Ti> Tf, rxn is endothermic Heat flow is calculated as Q=M.Cp.T
  5. 5. 5 DIFFERENTIAL SCANNING CALORIMETRY 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. DIFFERENTIAL-measure difference in heat flow from sample & reference. SCANNING –scan over a range of temperature. CALORIMETER-used to measure heat or heat flow.
  6. 6. PRINCIPLE Metal 1 Metal 2 Metal 1 Metal 2 Sample Empty Sample Temperatur e Reference Temperatur e Temperature Difference = Heat Flow ISOTHERMAL PROCESS
  7. 7. 7 Principle of the thermal analysis : Heating of the sample and the inert reference material at a constant heating rate Record of the furnace, sample and inert reference material temperatures Difference between sample and inert reference material temperatures
  8. 8. BASIC DSC APPARATUS A DSC apparatus is built around : - a differential detector - a signal amplifier - a furnace - a temperature controller - a gas control device - a data acquisition device 8
  9. 9. COMPONENTS PURGE GAS TYPICAL PURGE GASES ARE AIR/NITROGEN HELIUM MAY BE USEFUL FOR VOLATILE COMPONENTS CAN BE CARRIED OUT UNDER HIGH PRESSURE
  10. 10. CRUCIBLE ALUMINUM - INEXPENSIVE,LOW TEMP. COPPER-FOR POLYMERS ALUMINA-FOR HIGHER TEMP
  11. 11. Mathematical expression of the calorimetric signal Expression of the heat flux from the reference side Expression of the heat flux from the sample side 12
  12. 12. HEAT FLUX FROM REFERENCE ( dq /dt )r = Cr dT/dt (1) HEAT FLUX FROM SAMPLE (dq/dt)s = CsdT/dt+dh/dt (2) Differential heat flux (1-2) dq/dt=Cs dT/dt+dh/dt-Cr dT/dt Also ,dq/dt=Ts-Tr/R(thermal equivalent of ohm law) on derivatising the above equation Rd2q/dt2=-dTs/dt+dTr/dt Final calorimetric equation= dq/dt=(Cs-Cr)b+dh/dt-CsRd2q/dt2 Where b =scanning rate(dT/dt) CsRd2q/dt2 = thermal lag
  13. 13. 14 Heat Flux Plate DSC Power compensated DSC
  14. 14. Power Compensated DSC sample holder • Al or Pt pans sensors • Pt resistance thermocouples • separate sensors and heaters for the sample and reference furnace • separate blocks for sample and reference cells temperature controller • differential thermal power is supplied to the heaters to maintain the temperature of the sample and reference at the program value 15
  15. 15. 16 HEAT COMPENSATED DSC sample holder • sample and reference are connected by a low-resistance heat flow path • Al or Pt pans placed on constantan disc sensors • chromel®-constantan area thermocouples (differential heat flow)
  16. 16. furnace one block for both sample and reference cells temperature controller the temperature difference between the sample and reference is converted to heat flow in & out of the sample and is recorded against time or temperature.
  17. 17. REFERENCE MATERIALS MATERIALS MELTING POINT(oC) INDIUM 156.6 TIN 231.9 LEAD 327.5 ZINC 419.5 K2SO4 585.2 K2Cr2O7 670.03
  18. 18. DSC: Main Sources of Errors •Calibration •Contamination •Sample preparation – how sample is loaded into a pan •Residual solvents and moisture. •Thermal lag •Heating/Cooling rates •Sample mass •Processing errors
  19. 19. MINIMISING ERRORS PROPER CALIBERATION OF INSTRUMENT PROPER PLACING INSTRUMENT IN THE LAB AVOID EXCESSIVE HEATING RATE PROPER GAS FLOW RATE CONSTANT POWER SUPPLY
  20. 20. MAJOR APPLICATIONS 1) ENTHALPY OF TRANSITION:-Hd=KA 2) GLASS TRANSITIONS(Tg) 3) POLYMER DEGRADATION STUDIES 4) LIQUID CRYSTALS 5) OXIDATIVE STABILITY 6) DRUG PURITY ANALYSIS
  21. 21. THERMOGRAVIMETRIC ANALYSIS
  22. 22. 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. INTRODUCTION
  23. 23. TYPES OF THERMOGRAVIMETRIC ANALYSIS Isothermal or static Quasistatic thermo gravimetry Dynamic thermogravimetry
  24. 24. 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. INSTRUMENTATION
  25. 25. WORKING PRINCIPLE OF BALANCE 27
  26. 26. Copyright@RGH 10 May 2014 28
  27. 27. 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. 29
  28. 28. The various components of modern thermo balance are Recording balance Sample holders Furnace Furnace temperature programmer or controller Recorder 30
  29. 29. RECORDING BALANCE It is the most important component of the thermobalance. Commercially available balance can provide quantitative information about 1 mg-100 gm mass. 31
  30. 30. There are two types of balance. deflection type null type 32
  31. 31. 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. 33
  32. 32. 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. Shallow pans Deep crucibles Loosely covered crucibles Retort cups 34
  33. 33. 3) THE FURNACE The choice of furnace heating element and type of furnace depends upon the temperature range being studied. Temperature Material 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 35
  34. 34. 4) TEMPERATURE MEASURMENT 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. 36
  35. 35. 5)RECORDER Two types: 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. 37
  36. 36. FACTORS AFFECTING TG CURVE Instrumental Heating rate Effect of furnace atmosphere Sample holder Characteristic s of the sample Weight of sample Sample particle size Compactness of sample Previous history of the sample 38
  37. 37. DIFFERENTIAL THERMAL ANALYSIS
  38. 38. What is DTA ? A technique in which the temperature difference between a substance and a reference(Al2o3) material is measured as a function of temperature while the substance and reference are subjected to a controlled temperature program
  39. 39. Thermogram A differential thermogram consists of a record of the difference in sample and reference temperature(∆T) plotted as a function of time t, sample temperature(Ts), reference temperature(Tr) or furnace temperature(Tf).
  40. 40. Instrumentation A differential thermal analyzer is composed of five basic components, namely : 1}Furnace 2}Sample holder 3}temperature controller and recorder 4}thermocouple 5}Cooling device
  41. 41. 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 is depends on the maximum temperature of the operation and gaseous environment. Grooved muffled cores preferred.
  42. 42. 2} Sample holder Should having low 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 it, a sample holder with dimples in which thermocouple junctions are inserted (thermocouple wells) are used.
  43. 43. 3} Temperature controller and recorder A] Temperature Controller In order to control temperature, the three basic elements are required. 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.
  44. 44. B] Temperature programming It transmits a certain time-based instruction to the control unit. By this device one can achieve linearity in the rate of heating or cooling it is driven in a non-linear fashion using a special cam- drive. Heating rates of 10-20 o C / mints are employed. C] Recorder 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.
  45. 45. 4} Thermocouple Thermocouples are the temperature sensors. It is made up from chromel and alumel wires 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.
  46. 46. Applications: Thermal Stability Material characterization Compositional analysis Used to analyze filler content in polymers; carbon black in oils; ash and carbon in coals. Kinetic Studies Corrosion studies Automatic Thermogravimetric Analysis Evaluation of gravimetric precipitates Evaluation of suitable standards Testing of purity of samples Curie point determination
  47. 47. THANK YOU BINDU KSHTRIYA

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