Dnyanasadhana College, Thane. hhh Department of Chemistry T.Y.B.Sc. Analytical Chemistry Paper-IV Sem-VI DIFFERENTIAL THERMAL analysis Dr.Bhagure G.R.

Contents 4.1.3 Differential Thermal Analysis (DTA): Principle, Instrumentation –balance, Thermocouple Reference material used in TA (MgO,Al2O3,SiC), DTA curve Applications : DTA of CaC2O4.H2O and CuSO4.5H2O, Difference between TGA and DTA.

A graph of ∆T Vs. temperature is plotted DTA is a technique in which the temperature difference between the sample and the reference material (thermally inert ) is continuously recorded as a function of temperature or time. The sample and reference material are subjected to a controlled temperature programme A graph of ∆T Vs. temperature is plotted

Principle of DTA When a graph of ∆T Vs. temperature is plotted, the maxima and / or minima due to exothermic and/ or endothermic processes. Maxima and minima are called as peaks. Maxima = exothermic process in which heat is evolved from the sample causing temperature to increase. Minima = endothermic process in which heat is absorbed by the sample causing temperature to decrease.

Peak area (A) is corrected to the mass of the analyte (m) as A = K G m ∆ H = K’ m ∆ H G = calibration factor related to sample geometry K = constant related to thermal conductivity of sample K’ = constant related to heating rate, particle size, placement of sample etc. The mass of a particular analyte can be determined if K’ and ∆ H can be known by calibration.

Solid–solid phase transitions Endothermic MELTING Vaporization Boiling Desolvation Solid–solid phase transitions Chemical degradation

Oxidative decomposition EXOTHERMIC REACTIONS Crystallization Oxidative decomposition Solid state reactions Chemisorption

DIFFERENTIAL THERMAL ANALYSER Instrumentation 1.Sample holder 2.Furnace. 3.Temperature programmer 4.Recording system

SCHEMATIC DIAGRAM OF DTA INSTRUMENT ---------------------------------------------------------------

2.Furnace or heating device The sample holder assembly consists of a thermocouple each for the sample and reference, surrounded by a block to ensure an even heat distribution. sample containers made from ceramic or metallic block. 1.Sample holder Furnace consist of electrical heating systems. Electrical heating coils are made from Nichrome wire windings & platinum wire windings. Furnace should provide uniform hot & linear heating rate one Should have cooling facility for rapid return to ambient temperature 2.Furnace or heating device

Thermocouple are used as temperature sensors. Thermocouples are made from Chromel P Alumel wires (both made of Nickel-chromium alloys) are used to measure temperature upto 11000C. Thermocouples are made of pure Platinum and Platinum-Rhodium are used to measure temperature above 11000C. While selecting thermocouples as temperature sensors, the following points should be consider, Temperature interval Thermoelectric coefficient Chemical compatibility with the sample Chemical gaseous environment Reproducibility Availability Cost 3. THERMOCOUPLES

4.Differntial Temperature Detector The thermocouples served as the temperature sensor .The voltage signal produced dependence on the temperature different, ∆T between two junctions of the thermocouples 4.Differntial Temperature Detector It Consist of an amplifier to magnify signals coming from temperature sensor (T) & differential temperature sensor (∆T) of the thermocouples 5.Recorder

6.Atmpospheric Control & Cooling Controls: A Facility for flushing the sample & reference assembly with selected gas is provided. There is also cooling facility to cool the assembly to ambient temperature . Liquid Nitrogen is used in a special low temperature assembly. 6.Atmpospheric Control & Cooling Controls:

Reference material used in DTA (MgO,Al2O3,SiC

Characteristic of the Reference material used in DTA Should not under go thermal events over the operating temperature It should be inert towards sample holder or thermocouple Thermal conductivity & het capacity should be similar to that of sample

Factors affecting DTA curve Sample characteristics 2. Instrumental characteristics 3.Environmentl factors

Sample characteristics Amount of Sample: Small size sample give best peak which can be easy for resolution. Particle size: Finely powdered sample size sample give best peak. Particles having bigger size increases the peak area. Sample packing: It is regular practice to mix Sample with inert material like glass like alumina. The degree of crystallinity of sample and compactness also affect on DTA curve.

Instrumental characteristics Sample holder Sample holders made up from high thermal conducting material gives sharp exothermic peak but relatively flat endothermic peak. Generally very small sample holders made from glass or ceramic re used. Sometimes shallow metallic pans are used. Thermocouples: Position of Thermocouples affect on DTA curve. If Position of Thermocouples is not varies reproducible results can be obtained Furnace characteristics: The type of winding on furnace shows direct effect on DTA curve. The grooved muffled core furnace are preferred because it gives uniformity in windings. Heating rate: Heating rate has great influence on DTA curve. Generally ,heating rate of 100c to 200c is preferred for sharper peak . Recorder: DTA curve also effect by type, chart speed, and pen response of recorder.

3.Environmentl factors Static gaseous atmosphere: Studies in Static gaseous atmosphere are not precise. Dynamic gaseous atmosphere: The results obtained in Dynamic gaseous atmosphere re more precise & accurate

Qualitative analysis Clay Reaction products

Quantitative analysis DTA peaks re proportional to total het of reaction which is equivalent to wt. of the sample Analysis of Polymers Ceramic & metal Industry Phase transitions Ex.Sulphur

DTA Curves

DTA curve of CaC2O4.H2O in the presence of O2. Heating rate = 80C/min

Calcium oxalate monohydrates gives two endotherms CaC2O4.H20CaC2O4 +H20 1. Around 200 Oc CaCO3.CaO +C02 2. 800 Oc

Calcium oxalate monohydrates gives one exotherms 2CaC2O4O+O2CaCO3+CO2 (In Air) 1. Intermediate Exotherm In Nitrogen atmosphere the above process is endothermic

DTA curve of CuSO4.5H2O in the presence of O2. Heating rate = 80C/min 100 200 250 300 

DTA curve of CuSO4.5H2O gives three endotherms CuSO4.5H2O CuSO4.3H2O 1. 81-96 Oc CuSO4.3H2OCuSO4.2H2O 2. 111- 120 Oc CuSO4.2H2OCuSO4.H2O 3. 220-250 Oc

DIFFERENCE BETWEEN TGA & DTA Change in mass of sample with increase in temperature Plots a graph of change in mass Vs. T Change in mass gives information about Change in sample composition Change in thermal stability Change in kinetic parameter Measure the temperature difference between sample and reference with increase in temperature. Plots a graph of ∆T Vs. T maxima and minima gives information about exothermic and endothermic processes associated with sample

Instruments can be used at very high temperatures Advantages Instruments can be used at very high temperatures Instruments are highly sensitive Characteristic transition or reaction temperatures can be accurately determined.