TGA & TMA

Theory, instrumentation & applications of TGA & tma.: 

Theory, instrumentation & applications of TGA & tma . A seminar on Presented By Mr. gunjan amin 1 st semester (2010-2011) M.Pharm. [Q.A.] Roll No. 17 Guided By Dr.N.J.SHAH M.Pharm.Ph.D Principal Department of Pharmaceutical chemistry 1

CONTENTS:- : 

INTRODUCTION PRINCIPLE INSTRUMENTATION FACTORS APPLICATIONS CONTENTS:- 2 Gunjan Amin

THERMAL METHODS OF ANALYSIS:-: 

There are mainly four types: TGA-Thermo gravimetric analysis TMA-Thermo mechanical analysis DTA-Differential thermal analysis DSC-Differential scanning analysis THERMAL METHODS OF ANALYSIS:- 3 Gunjan Amin

INTRODUCTION OF TGA:- : 

Definition : The basic defined as those techniques in which change in physical or chemical properties of a substance are measured as a function of temperature . Method that involves changes in weight or changes in energy comes within this definition. INTRODUCTION OF TGA:- 4 Gunjan Amin

TGA (THERMO GRAVIMETRIC ANALYSIS):- : 

Is a technique in which a change in a weight of a substance is recorded as a function of temperature or time. ∆ weight (Vs) temperature/time. The basic instrumental requirement for thermo gravimetry is a precision balance with a furnace program for a linear rise of temperature with time. The result may be presented as, thermo gravimetry curve in which the weight changes is recorded as a function of temperature or time or derivative thermo gravimetric curve ( DTC) where the first derivative of the TG curve is plotted with respect to either temperature or time. TGA (THERMO GRAVIMETRIC ANALYSIS):- 5 Gunjan Amin

Slide 6: 

A B C D DTG E F TG T i T m T f Weight (W) TG Curve DTG Curve (Rate of Wt. Change) dW / dt 6 Gunjan Amin

Slide 7: 

AB , CD, EF = ranges of stability of compound Ti = inception temperature Tm = maximum reaction rate Tf = completion of reaction 7 Gunjan Amin

PRINCIPLE:- : 

A typical TGC, for copper sulphate pentahydrate CuSO 4 *5 H 2 O, as reaction shows: The horizontal portion indicates the regions where there is no weight change The curved portions are indicative of weight loses Since the TG curve is quantitative, calculation on compound stoichiometry can be made at any given temperature. As reaction shows, copper sulphate pentahydrate has four distinct regions of decomposition. Temperature region CuSO 4* 5H 2 O ⤍ CuSO 4* H 2 O 90 to 150 ˚C CuSO 4* H 2 O ⤍ CuSO 4 200 to 275˚C CuSO 4 ⤍ CuO + SO 2 +1/2 O 2 700 to 900˚C 2CuO ⤍ Cu 2 O +1/2 O 2 1000 to 1100˚C PRINCIPLE :- 8 Gunjan Amin

Slide 9: 

An additional features of TG curve should now be examined, namely the two regions B & C where there are changes in the slope of weight of loss curve . If the rate of the change of weight with time dw / dt is plotted against temperature . In the DTG curve when there is no weight loss then dw / dt =0. Inflection B & C on figure may imply the formation of intermediate compounds in fact the inflection at B arises from the formation of the tri hydrate CuSO 4 *3H 2 O, & that C point is reported by dual to be due to formation of golden yellow basic sulphate of composition 2CuO*SO 3 . 9 Gunjan Amin

INSTRUMENTATION:- : 

Principle:- The principle of thermo gravimetry is based on the simple fact that the sample is weighed continuously as it is being heated to elevated temperature. Following criteria should be for good thermo balance:- The thermo balance should be capable of continuously resisting the weight changes of sample studied as a function of temperature and time. The furnace should reach the maximum desired temperature 1500˚C. The rate of heating is linear and reproducible. The sample holder should be in the hot zone of furnace and this zone should be of uniform temperature. The thermo balance should have facility or the provision of variable heating rates, to permit heating in a variety of controlled atoms. INSTRUMENTATION:- 10 Gunjan Amin

Slide 11: 

The balance mechanism should be protected from the furnace and from the effect of corrosive gases. The temperature of the sample must be measured as accurately as possible. Sensitivity of balance to be high. An additional requirement is a facility for rapid heating and cooling of the furnace to permit the several TG analysis to be carried out in a relative short period of time. A modern thermo balance is shown in figure. The various component are, (a) recording balance (b) furnace (c) furnace temperature, programmer and controller (d) recorder. 11 Gunjan Amin

Slide 12: 

Furnace Temp. Sensor Atmospheric Control Recorder Balance Control Recording Balance Furnace Sample Holder Temperature Sensor 12 Gunjan Amin

Slide 13: 

Basic units of thermo balance. THE BALANCE:- Its accuracy, sensitivity, reproducibility, and capacity should be similar to those of analytical balance. It should have an adequate range of automatic weight adjustment. It should have a high degree of mechanical and electrical stability. It should have rapid response to weight changes. The balance should be simple to operate and versatile. Recorded balance is mainly of two types: (a) deflection type instruments (b) null type instrument. 13 Gunjan Amin

Slide 14: 

Deflection balance : Beam type: In these type of balance, there occurs a conversion of beam deflection which is recorded as a signal on photographic recorder or measuring device. Helical type: In these balances there occurs a contraction of the spring with weight change. This change in the length of spring may be suitably recorded by use of transducer. Beam 14 Gunjan Amin

Slide 15: 

The cantilevered beam: In these types of balances, one end of the beam is fixed and other end, on which sample is placed, is free to undergo deflections. Spring 15 Gunjan Amin

Slide 16: 

Torsion wire: In these types of balances, the beam is attached to a taut wire which acts as the fulcrum. The wire is firmly fixed at either or both ends so that the deflections of the beam are proportional to weight changes and the torsional characteristic of the wire . Cantilever Torsion 16 Gunjan Amin

Slide 17: 

Null-point balance: In these balances, there should be a sensor to detect the deviation of the balance beam from its null position. Then, 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 form. Null Detector Restoring Force Weight Change 17 Gunjan Amin

Slide 18: 

SAMPLE HOLDERS:- The size and shape of sample holders depend upon the nature, weight of the sample and maximum temperature range to be employed. The materials for the construction of sample holders are glass quartz, alumina, stainlessteel, platinum, graphite. Shallow pans: These are generally used for such samples where it becomes necessary to eliminate diffusion as the rate controlling step. Deep crucible : These are employed in such cases where side reaction and/or partial equilibrium are to be desired. Retort cups: These are useful in boiling point studies. 18 Gunjan Amin

Slide 19: 

THE FURNACE:- FOR 1100˚C the material of furnace is “NICHROME” wire or ribbon. If a wire is being used, it should be wound “coiled-coil” fashion to accommodate differential thermal expansion of various components. For temperature between 1400 & 1500˚C one should use platinum or alloy of platinum and rhodium. For temperature above 1750˚C, tungsten or molybdenum may be employed. The size of furnace is an important factor advantage of low mass furnace is that it cools very quickly but its linear temperature rise is very difficult to control. On other hand, a high mass furnace may hold an isothermal temperature but it requires comparatively more time to achieve the require temperature. 19 Gunjan Amin

Slide 20: 

TEMPERATURE MEASUREMENT:- Is done by thermo couple for measuring 1100˚C, chromel or alumel thermo couple are used. For 1750˚C, thermo couple made up of alloys of platinum and rhodium are employed. For higher temperature tungsten are used. The position of temperature measuring device relative to the sample is very important. 20 Gunjan Amin

Slide 21: 

The thermo couple is placed near the sample container and it has no contact with the sample container. The thermo couple is kept inside the sample holder but not in contact with it, these arrange respond to small temperature changes. The thermo couple is placed either in contact with sample or with the sample container this is the best arrangement. RECORDER:- Time- based potentiometric strip chart recorders. X-Y recorders. In this we get curves having plot of weight directly against temperature. 21 Gunjan Amin

Slide 22: 

Strantum Red croft TG-750 Balance:- 22 Gunjan Amin B N Flow meter Water in Water out S Gas out G Flow meter A F C

Slide 23: 

B is an electronic micro balance. It is housed in a glass bottle. Its capacity is one gram with a switched range of sensitivity from 1 to 250mg full scale deflection. S is a platinum crucible to contain the sample. It is suspended by means suspension attached to the beam of balance. The suspension is of platinum-rhodium alloy and passes through a narrow glass tube A with a glass flange F at one end and also through an aluminium tube N. The furnace assembly C can be raised or lowered mechanically, and seats against F with on O-ring making a complete seal. The gas and the water flow paths are also shown in the figure. 23 Gunjan Amin

Slide 24: 

The system may be evaluated and then flushed with an inert gas. Access to the reference pan is obtained by removing the glass cap G. The furnace F is approximately 12 mm in diameter and 20 mm long. T is a thermo couple of platinum vs. platinum rhodium. This is used to measure the sample temperature. The balance is fitted with X-Y recorder. This records a plot of the sample weight against the temperature. The TG 750 operates from the ambient room temperature to 1000˚C. By this one can maintain heating rate of 1 to 100˚C per min. It only requires 4 min. to cool from 1000 to 50˚C. 24 Gunjan Amin

ADVANTAGES OF TG 750 OVER OTHER BALANCES:-: 

It requires only small sample weights (1 to 10mg). Fast heating rates with good resolution. In this cooling time is very short. Therefore more thermo grams can be recorded. No need to draw a correction curve. Used for isothermal studies. One can hold the furnace at 1000˚C without any balance drift. ADVANTAGES OF TG 750 OVER OTHER BALANCES:- 25 Gunjan Amin

FACTORS:-: 

The factors which may affect the results can be classified in to the two main groups: Instrumental factors Sample characteristics Instrumental factors: Heating rate:- When a substance is heated at a fast heating rate temperature of decomposition will be higher than that obtained at slower rate of heating. The single step reaction shown in figure. The curve AB represents the decomposition curve at slow heating rate, whereas the curve CD is that due to the faster heating rate. FACTORS:- 26 Gunjan Amin

Slide 27: 

The heating rate has only a small effect when a fast reversible reaction is considered. The point of inflection B & C obtained on thermo gravimetric curve for CuSO 4 pentahydrate. Weight Temperature A C B D 27 Gunjan Amin

Slide 28: 

Furnace atmosphere:- The nature of the surrounding atmosphere can have a profound effect upon the temperature of decomposition stage. For e.g. the decomposition of calcium carbonate occurs at a much higher temperature if carbon dioxide rather than nitrogen is employed as the surrounding atmosphere is to remove the gaseous product evolved during thermo gravimetry, in order to ensure that the nature of the surrounding gas remains as constant as possible throughout the experiments. 28 Gunjan Amin

Slide 29: 

This condition is achieved in much modern thermo balance by heating the test sample. The most common atmosphere employed in thermo gravimetry are: “static air” (air from the surrounding flow through the furnace). “Dynamic air” where compressed air from a cylinder is passes through the furnace at a measured flow rate. Since TG is dynamic technique convection current arising in a furnace will cause a continuous change in gas atmosphere. 29 Gunjan Amin

Slide 30: 

Sample Characteristics: Weight of the sample: This will effect the shape of a TG curve if a large sample is used there occurs a deviation from linearity as the temperature rises. This is particularly found to be true in case of exothermic reaction. In order to detect the presence of intermediate compounds a small sample is preferred to a large one. 30 Gunjan Amin

Slide 31: 

Sample particle size: Various particle size of samples alter the reaction rate and hence the curve shape. With a particle size of smaller dimension the decomposition takes place earlier while with greater particle size the decomposition process at higher temperature. Heat of reaction: The heat of reaction will alter the difference between the sample temperature and the furnace temperature. If the heat effect is exothermic or endothermic this will cause the sample temperature to lead behind the furnace temperature. 31 Gunjan Amin

Slide 32: 

Compactness of the sample: A compressed sample will decompose at higher temperature than a loose sample. Previous history of the sample: Previous history of the sample can also affect the shape of TG curve for e.g. TG studies showed that magnesium hydroxide prepared by precipitation method has a different temperature of decomposition from that for the naturally occurring material. 32 Gunjan Amin

APPLICATIONS OF THERMOGRAVIMETRY:- : 

Automatic thermo gravimetric analysis: This is modern technique in analytical chemistry. APPLICATIONS OF THERMOGRAVIMETRY:- Weight Temperature C D E F G B B’ WDE WFG 33 Gunjan Amin

Slide 34: 

The crucible is removed from the thermo balance than it is cleaned and dried again put in position in the thermo balance. Then thermo balance is operated to get a base line which is indicated by dashed line BB’. The substance to be determined is precipitated by a suitable precipitant and the weight loss curve is recorded as usual to get a thermo gram of type. There are two horizontal levels DE and FG corresponding to weights WDE and WFG. The horizontal weights level indicates the definite stoichiometry of the precipitate. The WDE and WFG by the gravimetric factors give the mass of metal ion present. 34 Gunjan Amin

Slide 35: 

This method is quite rapid in certain precipates for the entire operation filtration, drying and recording only 12 mins. Are required. For a binary mixer, the same procedure is to be carried out. Evaluation of the suitable standards: “Duval” combined his TG studies with IR absorption spectrophotometric studies in order to arise at this conclusion. He confirmed that the following substance can not be used for preparing standard solution: Magnesium ammonium chloride, ammonium bicarbonate and ammonium fluoride. 35 Gunjan Amin

Slide 36: 

Compounds those are most suitable for preparing standard solutions. Lithium sulphate monohydrate, sodium dichromates dehydrate sodium cobaltnitrile and methylglucamine. Duval also confirmed that it is advisable not to heat the compounds above the temperature indicated. Substance Temperature ˚C EDTA 100 UREA 165 NaF 850 KHCO 3 125 NiSO 4* 7H 2 O 100 36 Gunjan Amin

Slide 37: 

Testing of purity of sample: Impure sample of calcium oxalate showed an unusual weight loss below 100˚C. When calculations were carried out, it was observed that the weight loss was not due to absorbed water but due to same impurity. Organic compounds: When the decomposition of malonic acid was studied by DTA and TG techniques, it was found that a phase transition occurred in the region of 70˚C with melting at about 140˚C followed by decomposition above 150˚C. COOH I CH 2  CO 2 + CH 3 COOH I COOH 37 Gunjan Amin

Slide 38: 

Study of polymorphism: Melting, sublimation, kinetics, stability, solubility, dissolution rate etc. (For sorbitol, mannitol, glyceride, TiO 2 , organic acid) Study of pseudo polymorphism: Hydrates, solvents (for lactose α-anhydrous, monohydrate, calcium phosphate etc.) Entrapped solvents: affects LOD results by conventional techniques. To checkout Purity and thermal stability of compound: 38 Gunjan Amin

TMA (THERMO MECHANICAL ANALYSIS):- : 

The determination of the change In length or volume of the sample as a function of the temperature constitutes techniques called dilatometry or TMA. This technique is used for polymeric materials. One of the several thermo mechanical analyzers are commercially used is shown in figure. In the penetration and expansion modes, the sample is placed on the platform of a quartz sample tube. The appropriate quartz probe is connected to armature of a LVDT(linear variable differential transformer). TMA (THERMO MECHANICAL ANALYSIS):- 39 Gunjan Amin

Slide 40: 

40 Gunjan Amin

Slide 41: 

Any change in the position of armature results in a output voltage from the transformer which is than recorded. The probe assembly contains a weight tray, which permits a choice of loading on the sample surface. The assembly are supported by a plastic float rigidly fix to the shaft and totally immersed in a high density fluid. The advantage of the method is that true loading on the sample is essentially independent of the probe position over the range where the float remains totally immersed. 41 Gunjan Amin

APPLICATIONS:- : 

The technique is valuable for detecting phase transition, glass transition in polymeric materials and firing characteristics of ceramics. Softening temperature of suppositories. Heat distortion temperature of soft gelatin capsule. Glass transition of containers etc… APPLICATIONS:- 42 Gunjan Amin

REFERENCES:-: 

Principle of instrumental analysis ,Douglas A Skoog , Thomson Asia pvt ltd,5 th edition 789-809. Instrumental methods of chemical analysis, Sharma B.K, Goel Publishing House, Meerut, 6 th ed,M-308-36. Gunjan Amin 43 REFERENCES:-

Slide 44: 

THANK YOU ... Gunjan Amin 44