Thermal AnalyticalTechniques Thermal Analytical Techniques Thermal analysis is a group of Technique in Which a physical property Is Measured as a function of temperature. It is subdivided in five different techniques •Differential Thermal Analysis (DTA) •Thermal Gravimetric Analysis (TGA) •Thermo Mechanical Analysis (TMA) •Dynamic Mechanical Analysis (DMA) •Differential Scanning Calorimetry (DSC) Differential Thermal Analysis (DTA) DTA: The temperature difference between a sample and reference material is measured as both are subjected to identical heat treatment. APPLICATION To Study the thermal behavior of Compounds. EXAMPLE: •Heating Calcium Oxalate monohydrate in flow of air. •Two minima and one maximum observed in graph. . Determination decomposition in various atmospheres.Differential Thermal Analysis (DTA) •APPLICATIONS : For identification purpose . Determination of heat change. APPLICATION: Thermal Stability Determination of bonded Silicas for use in Packing Columns by Thermogravimetric Analysis. ANALYSIS: Comparative TGA results .Thermal Gravimetric Analysis (TGA) TGA is used to measure weight changes in material with temperature . PROBLEM: Silica materials used as chromatography support material gave inconsistent performance when packed in Columns. . Thermal Gravimetric Analysis (TGA) Silica A(Superior material) Silica B (Inferior material) OBSERVATION: •Silica A(Superior material) exhibit a smaller total weight loss. •Silica B (Inferior material) exhibit a larger total weight loss. . CONCLUSION : •Either improve the Quality of silica B or by replacement with good quality silica. APPLICATION: Effect of Residual Solvent Levels in Wire Coatings. PROBLEM: Blistering and delaminating can occur due to residual solvent in the adhesive coating. Thermo mechanical analysis (TMA) TMA: Measurement of a change of a mechanical property of the sample while it is subjected to a temperature. . 7°C CONCLUSION : Decrease in Softening temperature due to residual Solvent. Softening temperature 49. Softening temperature 92. Thermo mechanical analysis (TMA) Suspect sample. .5°C Control sample. It is most useful for studying the viscoelastic behavior of polymers. PROBLEM: A good quality of thermo set composite materials such as brake linings in vehicle are dependent on the degree of cure achieved.Dynamic Mechanical Analysis (DMA) DMA: Is a technique used to study and characterized materials . APPLICATION Determination of Composite Cure. . . Dynamic Mechanical Analysis (DMA) OBSERVATION: Reheating Material 1(Superior quality) does not show much increase in the Tg. CONCLUSION : Material 1(Superior quality) initially fully cured. Dynamic Mechanical Analysis (DMA) OBSERVATION: Reheating Material 2(Inferior quality)show much increase much increase in Tg. CONCLUSION :Material 2(Inferior quality) initially not fully cured . • An enclosure to control parameters. • A computer to control data collection and processing. Basic Principles of Thermal Analysis Modern DSC instrumentation consists of four parts: • Sample holder. • Sensors to measure a heat flow and temperature of the sample. Diagram of Differential scanning calorimetry . DSC Modern instrument used for thermal analysis Cost :Range from 12 lakh to 75 lakh rupees . DSC sample cell . DSC sample pans . DSC Cross section . inert gas Temperature controller vacuum • Controls for temperature program and furnace atmosphere Thermocouples . Heat Flux DSC Furnace Alumina block • Common alumina block containing sample heating and reference cells. coil sample reference Sensors pan pan • One for the sample and one for the reference. Sensors • Separate sensors and heaters for the sample and reference. Power Compensation DSC Individual Controller DP heaters Sample Reference pan pan Inert gas Inert gas vacuum vacuum Thermocouple DT = 0 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 . Pt. •Small sample masses and low heating rates increase resolution. Al Pt alumina Ni Cu quartz .) •The same material and configuration should be used for the sample and the reference. etc.Sample Preparation •Accurately-weigh samples (~3-20 mg) •Small sample pans of inert metals (Al. •Avoid overfilling the pan to minimize thermal lag from the bulk of the material to the sensor. •Ensure good thermal contact. Ni. in pan lid Burst of pan lid . Recognizing Artifacts Mechanical Sample pan Cool air entry Sample topples shock of distortion Shifting of over in pan measuring cell into cell Al pan Sensor contamination RT changes Intermittant Electrical effects. closing of hole power spikes. etc. .Best Practices of Thermal Analysis •Small sample size. •Proper sample encapsulation. •Starting temperature well below expected transition temperature. •Use purge gas (N2 or He) to remove corrosive off-gases. •Proper instrument calibration. •Good thermal contact between the sample and the temperature-sensing device. •Avoid decomposition in the DSC. •Slow scanning speeds. When Exo Down . glass like state to a rubber like state.The Glass Transition Temperature •The glass transition is the temperature where the polymer goes from a hard. . •DSC the transition appears as a step transition and not a peak such as seen with a melting transition. •DSC defines the glass transition as a change in the heat capacity. t. •Heat absorbed by the polymer against temperature. Heat Capacity •The computer will plot the difference in heat output of the two heaters against temperature. . t. q supplied per unit time. •The heating rate is temperature increase T per unit time. •The heat flow is heat. divided by the temperature increase.Heat Capacity •We divide the heat flow q/t by the heating rate T/t. or Cp . •The amount of heat it takes to get a certain temperature increase is called the heat capacity. We end up with heat supplied. they give off heat.don't have to put much heat to keep the temperature of the sample pan rising. •When polymers fall into these crystalline arrangements. That is a latent heat of crystallization. arrangements. . which we call crystals. •Heater under the sample pan. Crystallization Temperature(Tc) •Polymer will have gained enough energy to move into very ordered. Melting Temperature (Tm) •When polymer reach melting temperature. . •Polymer absorb heat There is a latent heat of melting. those polymer crystals begin to fall apart. •Heater under the sample pan is going to have to extra heat into the polymer . The chains come out of their ordered arrangements. When Exo up Tc Tg Tm . •Specific heat capacity. •Rate and degree of cure. •Crystallization time and temperature. •Percent crystallinity. What can DSC measure? •Transitions. •Heats of fusion and reactions. •Purity. . .Differential Scanning Calorimetry (DSC) DSC: The energy required to maintain zero temperature differential between the sample and the reference is measured. APPLICATION Long term Stability Testing of Printing Inks By Differential Scanning Calorimetric. PROBLEM: Degradation (loss in finish quality) occurring in the ink during Storage. Differential Scanning Calorimetry (DSC) Fig 1. Exothermic behavior observed is the result of degradation in ink. Superior Quality ink Aging is an exothermic process detectable by DSC. Inferior Quality ink Fig 2. . Thermal stability of sample . Melting point Analysis of Phthalic Anhydride MP of Standard Phthalic Anhydride is= 131°C MP 130.8°C . 59°C -25 -4 20 40 60 80 100 120 140 160 180 200 Exo Up Temperature (°C) Universal V4.001 119.62°C 151.0J/g 0 0 -5 120.5J/g Heat Flow (mW) Heat Flow (W/g) -1 -10 -2 -15 127.51°C 156.001 a10609a1.5A TA Instruments % crystallinity = Enthalpy of fusion of sample X 100 Enthalpy of fusion of 100% crystalline polymer ( Enthalpy of fusion of 100% crystalline polymer value is taken from literature) .53°C -3 -20 127.% crystallinity determination Sample a1 = HDPE Imported Sample b2 = HDPE Local 5 1 a10609b2. 83J/g 424.001 420.16% ––––––– 02608a.5A TA Instruments % Metallic Zinc = Heat of Fusion of sample X 100 Heat of Fusion of std zinc (this value is taken from literature) (heat of fusion Zn std literature.001 –––– 02608b1.06°C -2 Heat Flow (W/g) -4 -6 -8 420.19°C 102.4J/g 423.9 J/g) . value =103.63°C -10 380 390 400 410 420 430 440 450 Exo Up Temperature (°C) Universal V4.38°C 97. % Purity determination sample a = Zinc Dust A = 98.56% sample 0 b = Zinc Dust B = 94. 8°C .Melting point Analysis of Phthalic Anhydride MP of Standard Phthalic Anhydride is= 131°C MP 130. 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