dta

DIFFERENTIAL THERMAL ANALYSIS (DTA) : 

By, Charmi kotecha department of (q.a) 1st m.pharm s.c.p -Mangalore DIFFERENTIAL THERMAL ANALYSIS (DTA)

Content… : 

Content… Thermal methods of Analysis Types – Introduction Special emphasis on Differential Thermal Analysis Theory, Instrumentation, Methodology, Applications.

Thermal methods of Analysis : 

Thermal methods of Analysis This is based on the concept of heating a sample – followed by well-defined modified procedures, such as : gravimetric analysis, differential analysis and titrimetric analysis. Some property of a system is measured as a function of temperature. Thermal spectra or Thermograms

Conti…. : 

Conti…. Thermo grams characterize a single or multi component system in terms of : Thermodynamic properties, and physicochemical reaction kinetics.

Thermal Analysis is widely used … : 

Thermal Analysis is widely used …

Different Techniques : 

Different Techniques Thermometric Titration (TT) Thermal Mechanical Analysis (TMA) Dynamic Mechanical Analysis (DMA) Differential Scanning Calorimetric (DSC) Thermal Gravimetric Analysis (TGA) Differential Thermal Analysis (DTA) Temperature Programmed Desorption (TPD)

Principle : 

Principle Sample is heated at a constant heating rate Sample’s Property Measured Wt TGA Size TMA Heat Flow DSC Temp. DTA Heat of mixing TT Tem. at which TPD gas is desorbed at the surface.

What is DTA ? : 

What is DTA ? Involves the technique of recording the difference in temperature between the Test and Reference material time being constant for both. Hence the Differential Thermogram consists record of difference in Temperatures.

Slide 9: 

Thermogram 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). In most of the cases, physical changes give rise to endothermic curves, whereas chemical reactions give rise to exothermic peaks.

Factors affecting DTA curve : 

Factors affecting DTA curve A] Environmental factors B] Instrumental factors i] Sample holder ii] Differential temperature sensing device iii] Furnace characteristics iv] Temperature- programmer controller v] Thermal Regime vi] Recorder C] Sample factors 1] Physical 2] Chemical

Instrumentation : 

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

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 is depends on the maximum temperature of the operation and gaseous environment.

2} Sample holder : 

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.

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.

Conti… : 

Conti… 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. 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.

4} Thermocouple : 

4} Thermocouple Thermocouples are the temperature sensors. It is made up from chromel p and alumel wires are used to measure and control temperature upto 1100 0C in air. For above 1100 0C one should use thermocouple made from pure platinum & platinum-rhodium alloy wires.

5} Cooling device : 

5} Cooling device It is separate from the temperature programmer because it is independent from heating.

DTA Analyzer : 

DTA Analyzer

Slide 20: 

Methodology Insert a very thin thermocouple into a disposable sample tube 2 mm in diameter and containing 0.1- 10 mg of sample, Another identical tube is either kept empty or filled with a reference substance, such as quartz, sand, alumina. The two tubes are simultaneously inserted into the sample block and subsequently heated (or cooled) at a uniform predetermined programmed rate

Requirements : 

Requirements DTA—A few of the vital aspects are : Pre-treatment of the specimen, Particle size and packing of the specimen, Dilution of the specimen, Nature of the inert diluent, Crystalline substances must be powdered, and sieved through 100-mesh sieve

Cont… : 

Cont… Either to suppress an unwanted reaction (e.g., oxidation), or to explore the study of a reaction(e.g., gaseous reaction product)—the atmosphere should be controlled adequately.

DTA Curve : 

DTA Curve

Slide 24: 

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. Disadvantage: uncertainty of heats of fusion, transition, or reaction estimations is 20-50%.

Applications of DTA : 

Applications of DTA Physical Chemistry Heat of a Reaction Specific Heat of substance like Naphthalene. Thermal Diffusivity of samples Analytical Chemistry Identification of Products since no two products have identical curves. Determination of Melting point.

Cont… : 

Cont… Quantitative analysis of Compounds Determination of Structural and Chemical changes occurring during heat treatments. Quality Control of Cement, glass, textiles, soils, explosives and resins.

References : 

References Instrumental Methods of Chemical Analysis- By, G.R. Chatwal & S.K. Anand. Instrumental methods of analysis; seventh edition by Willard. Merritt, Dean Seffle. www. wekipedia.com

Slide 28: 

THANK U