sushil dta

DIFFERENTIAL THERMAL

ANALYSIS (DTA)

Presented

By;Sushil kumar

1205068

Thermal Analysis Techniques

It is a group of techniques in which a physical property is measured as a function of temperature, while the sample is subjected to a controlled temperature programme (heating, cooling or isothermal).

Thermal Analysis Techniques

& Types of thermal analysis :

Differential Thermal Analysis (DTA) –temperature difference

Differential Scanning Calorimetry (DSC) –heat difference

Thermogravimetric analysis(TGA)-change in weight

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.

DTA Principle:DTA is a technique in which the difference between the sample and reference material is measured as a sample of furnace temp(t) while sample and ref. materials are subjected to a controlled programme.Usually a tempr programme involves heating the sample and ref. material in such a way that tempr of sample (ts) increases linerally with time.

• In Differential Thermal Analysis, the temperature difference that develops

between a sample and an inert reference material is measured, when both are subjected

to identical heat - treatments.

• The related technique of Differential Scanning Calorimetry relies on differences in energy required to maintain the sample and reference at an identical temperature.

INTRODUCTION(DTA)

• This is a comparison method

• Analytical method for recording the difference in temperature (∆T) b/w a substance and an inert reference material as a function of temperature or time

• Any transformation – change in specific heat or an enthaply of transition can be detected by DTA

• In DTA both test sample & an inert reference material (alumina) – controlled heating or cooling programming

• If zero temperature difference b/w sample & reference material – sample does not undergo any chemical or physical change.

• If any reaction takes place temperature difference (∆T) will occur b/w sample & reference material

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.

DTA CURVE

• A DTA curve can be used as a finger print

for identification purposes, for example,

• in the study of clays where the structural

similarity of different forms renders

diffraction experiments difficult to interpret.

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

∆T VS Temp.

Sharp Endothermic – changes in crystallanity or fusion

Broad endotherms - dehydration reaction

Physical changes usually result in endothermic curves

Chemical reactions are exothermic

Instrumentation

• A differential thermal analysis is composed of five

basic components, namely :

1} Furnace

2} Sample holder

3} temperature programmer/sensors

4} Recorders

5}Atmosphere control and Amplifiers

• .

1} Furnace Assembly

The furnace is of high temperature electric tube,max

temperature upto 1000 ºc can be provided.

It is a tube containing sample ,a similar tubecontaining reference material such as alumina orsilicon carbide which are inert substances .This tubeare inserted into a metallic heaterblock.Thermocouple are inserted in sample &reference tube.

In low temp range termocouple are used & otherdetector such as prt and thermistor can also beused.

It provides smooth heating or cooling at a linearrate by changing the voltage through heatingcomponent.

Modern DTA instruments incorporate electronictemp controller in which the signal fromthermocouple in furnace is comparedelectically against ref.potential which can beprogrammed to corresponds to a variety ofheating modes & heating rates.

It is a dual pen strip chart recorder usually ∆tchange in temperature is recorded at y-axis & Tzfurnace temp is x-axis.

5} Atmosphere control and Amplifiers

For some type of samples the

atmosphere must be controlled to

suppress and undesirable reaction such

as oxidation by flowing an inert gas. • AMPLIFIERS;It is used for amplification of signals

obtained from (T) c.It is gain and low noise circuit.

Differential Thermal Analysisadvantages:

• instruments can be used at very hightemperatures

• instruments are highly sensitive

• characteristic transition or reactiontemperatures can be accuratelydetermined

disadvantages:

• uncertainty of heats of fusion, transition,or reaction estimations is 20-50%

DTA

Physical Chemistry

1. Heat of a Reaction

2. Specific Heat of substance like Naphthalene.

3. Thermal Diffusivity of samples

Analytical Chemistry

1. Identification of Products since no two products have identical curves.

2. Determination of Melting point.

Applications Of DTA;

1.A DTA curve can be used only as a finger print for identification purpose but usually the applications of this method are the determination of phase diagrams,heat change measurements & decomposition in various atmospheres.

Applications of DTA……….2.DTA is widely used in medical(pharmaceutical)and food industries.3.DTA may be used in cement chemistry,mineralogical research and enviromental studies.4.DTA curves may also be used to date bone remains or to study archaeological materials.