Chemistry (Hons.) B.U. SEM-V Course Code: DSE-2H)_Ther… · Chemistry (Hons.) B.U. SEM-V; DSE-2:...

Chemistry (Hons.) B.U. SEM-V

Course Code: DSE-2

Course Title: Analytical methods in chemistry (Theo)

Chapter-3: Thermal methods of analysis

Structure

3.1 Introduction

Objectives

3.2 Instrumentation

3.3 Sources of Error in TGA

3.4 Interpretation of TG Curve

3.5 Factors Affecting TG Curve

3.6 Applications of Thermogravimetric Analysis

3.7 Composition determination from the TG curve ob binary compounds mixture

3.8 Glossary

3.9 References and Further Readings

3.10 Questions and Problems

Chemistry (Hons.) B.U. SEM-V; DSE-2: Analytical methods in chemistry


Dr. Goutam Hazra, Assistant Professor in Chemistry, Kalna College, E-mail ID: [email protected]

Introduction:

The study of the effect of heat on materials obviously has a long history, from man's earliest attempts at

producing pottery, extracting metals (about 8000 BC) and making glass (about 3400 BC) through the

philosophical discussions of the alchemists on the elements of fire, air, earth and water, to early work on the

assaying of minerals (about 1500 AD), followed by the development of thermometry and calorimetry. Only in

the late 19th

century did experiments on the effect of heat on materials become more controlled and more

quantitative. Much of this work depended upon the development of the analytical balance which has its own

interesting history.

In very brief summary, heat is one of the forms in which energy can be transferred. Such transfer

requires a temperature difference and three mechanisms of transfer have been identified: conduction,

convection and radiation. The laws of thermodynamics deal with thermal equilibrium (zeroth), conservation of

energy (first), direction of spontaneous processes including heat transfer (second), and the reference point for

entropy measurements (third).

To provide useful qualitative and quantitative information on the effect of heat on materials, experiments have

to be carefully planned, and use is often made of sophisticated equipment. The following formal definition of

thermal analysis was originally provided by the International Confederation for Thermal Analysis and

Calorimetry (ICTAC).

Previous

Thermal analysis (TA) refers to a group of techniques in which a property of a sample is monitored

against time or temperature while the temperature of the sample, in a specified atmosphere, is

programmed.

A recent discussion of the above ICTAC definition by Hemminger and Sarge points out some of the difficulties

and suggests some modification to:

New




Thermal analysis (TA) means the analysis of a change in a property of a sample, which is related to an

imposed temperature alteration.

The current field of thermal analysis is both diverse and dynamic. Although not a new field, more

advanced instrumentation, techniques and applications are constantly appearing on the market and in the

literature. Theoretically, almost any substance whether solid, semi-solid or liquid can be analyzed and

characterized with thermal analytical techniques. The schematic diagram of a generalized thermal analysis

instrument is shown in the Figure 3.2. Common materials include foods, pharmaceuticals, electronic materials,

polymers, ceramics, organic and inorganic compounds, even biological organisms. In theory, all thermal

analytical techniques simply measure the change of a specific property of a material as a function of

temperature. This in turn allows researchers access to information regarding macroscopic theories of matter

including, equilibrium and irreversible thermodynamics and kinetics. While numerous techniques are available,

the primary differences in the techniques are the properties of the material being studied as listed in the bellow

(Figure 3.1).

• Dielectric thermal analysis (DEA): dielectric permittivity and loss factor

• Differential thermal analysis (DTA): temperature difference

• Differential scanning calorimetry (DSC): heat difference

• Dilatometry (DIL): volume

• Dynamic mechanical analysis (DMA): mechanical stiffness and damping

• Evolved gas analysis (EGA) : gaseous decomposition products

• Laser flash analysis (LFA): thermal diffusivity and thermal conductivity

• Thermogravimetric analysis (TGA): mass

• Thermomechanical analysis (TMA): dimension

• Thermo-optical analysis (TOA): optical properties




Figure 3.1 Flow chart of the different types of thermal analysis.




Figure 3.2 A generalized thermal analysis instrument and resulting thermal analysis curve.

Objectives

After studying this unit, you should be able to:

• explain the principle of TGA,

• describe the experimental setup of TGA,

• interpret the analytical information from TGA curves, and

• describe the applications of TGA in qualitative and quantitative analysis of inorganic, organic and

polymer materials.




Thermogravimetric Analysis

Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in

which the mass of a sample is measured over time as the temperature changes. This measurement provides

information about physical phenomena, such as phase transitions, absorption and desorption; as well as

chemical phenomena including chemisorptions, thermal decomposition, and solid-gas reactions (e.g., oxidation

or reduction). TGA measurements are used primarily to determine the composition of materials and to predict

their thermal stability. The technique can characterize materials that exhibit weight loss or gain due to

sorption/desorption of volatiles, decomposition, oxidation and reduction.

Thermogravimetric analysis (TGA) is the most widely used thermal method. It is based on the

measurement of mass loss of material as a function of temperature. In thermogravimetry a continuous graph of

mass change against temperature is obtained when a substance is heated at a uniform rate or kept at constant

temperature. A plot of mass change versus temperature (T) is referred to as the thermogravimetric curve (TG

curve). For the TG curve, we generally plot mass (m) decreasing downwards on the y axis (ordinate), and

temperature (T) increasing to the right on the x axis (abscissa) as illustrated in Figure 3.3. Sometime we may

plot time (t) in place of T. TG curve helps in revealing the extent of purity of analytical samples and in

determining the mode of their transformations within specified range of temperature. In thermogravimetry, the

term ‘decomposition temperature’ is a complete misnomer. In a TG curve of a single stage decomposition, there

are two characteristic temperatures; the initial Ti and the final temperature Tf (see Figure 3.3). Ti is defined as

the lowest temperature at which the onset of a mass change can be detected by thermo balance operating under

particular conditions and Tf as the final temperature at which the particular decomposition appear to be

complete. Although Ti has no fundamental significance, it can still be a useful characteristic of a TG curve and

the term procedural decomposition temperature has been suggested. The difference Tf – Ti is termed as reaction

interval.




Figure 3.3 A Typical TG Curve.

In a dynamic thermogravimetry a sample is subjected to continuous increase in temperature usually linear with

time whereas in isothermal or static thermogravimetry the sample is maintained at a constant temperature for a

period of time during which any change in mass is noted. Now we will take up the instrumentation commonly

used to obtain TG Curve. The first derivative of the TGA curve (the DTG curve) may plotted to determine

inflection points useful for in-depth interpretations as well as differential thermal analysis. From a TGA curve

we can predict the following informations i.e.

• Thermal Stability of Materials

• Oxidative Stability of Materials

• Composition of Multi-component Systems

• Estimated Lifetime of a Product

• Decomposition Kinetics of Materials

• The Effect of Reactive or Corrosive Atmospheres on Materials

• Moisture and Volatiles Content of Materials

In most of the TGA curves there occurs either weight loss or weight gain (or both) due to

sorption/desorption of volatiles, decomposition, oxidation and reduction of the samples.




•The Weight Loss occurs for:

Decomposition: The breaking apart of chemical bonds.

Evaporation: The loss of volatiles with elevated temperature.

Reduction: Interaction of sample to a reducing atmosphere (hydrogen, ammonia, etc.).

Desorption: Desorption of gasses from the surface of the sample.

•Weight Gain occurs for:

Oxidation: Interaction of the sample with an oxidizing atmosphere.

Absorption: Absorption of the gasses on the surface of the sample.

3.2 Instrumentation

A typical thermogravimetric analyzer consists of a precision balance with a sample pan located inside a

furnace with a programmable control temperature. The temperature is generally increased at constant rate (or

for some applications the temperature is controlled for a constant mass loss) to incur a thermal reaction. The

thermal reaction may occur under a variety of atmospheres including: ambient air, vacuum, inert gas,

oxidizing/reducing gases, corrosive gases, carburizing gases, vapors of liquids or "self-generated atmosphere";

as well as a variety of pressures including: a high vacuum, high pressure, constant pressure, or a controlled

pressure. The basic components of a typical thermobalance are listed below:

i) Balance

ii) Furnace: heating device

iii) Unit for temperature measurement and control (Programmer)

iv) Recorder: automatic recording unit for the mass and temperature changes

These components may be represented by simple block diagram as in Figure 3.4 and different parts of the TGA

instrument are shown in the Figure 3.5.




Figure 3.4 Block diagram of a Thermobalance.

Figure3.5 Different parts of the TGA instrument

Balance




The basic requirement of an automatic recording balance are includes accuracy, sensitivity, reproducibility, and

capacity. Recording balances are of two types, null point and deflection type. The null type balance, which is

more widely used, incorporates a sensing element which detects a deviation of the balance beam from its null

position; a sensor detects the deviation and triggers the restoring force to bring the balance beam to back to the

null position. The restoring force is directly proportional to the mass change. Deflection balance of the beam

type involve the conversion of the balance beam deflection about the fulcrum into a suitable mass – change

trace by (a) photographic recoding i.e change in path of a reflected beam of light available of photographic

recording, (b) recording electrical signals generated by an appropriate displacement measurement transducer,

and (c) using an electrochemical device. The different balances used in TG instruments are having measuring

range from 0.0001 mg to 1 g depending on sample containers used.

Furnace

The furnace and control system must be designed to produce linear heating at over the whole working

temperature range of the furnace and provision must be made to maintain any fixed temperature. A wide

temperature range generally -150 °C to 2000 °C of furnaces is used in different instruments manufacturers

depending on the models. The range of furnace basically depends on the types of heating elements are used.

Temperature Measurement and Control

Temperature measurement are commonly done using thermocouples , chromal – alumel thermocouple are often

used for temperature up to 1100 °C whereas Pt/(Pt–10% Rh) is employed for temperature up to 1750 °C.

Temperature may be controlled or varied using a program controller with two thermocouple arrangement; the

signal from one actuates the control system whilst the second thermocouple is used to record the temperature.

Recorder

Graphic recorders are preferred to meter type recorders. X-Y recorders are commonly used as they plot weight

directly against temperature. The present instrument facilitate microprocessor controlled operation and digital

data acquisition and processing using personal computer with different types recorder and plotter for better

presentation of data. In Figure 3.4 we have shown a schematic diagram of the specific balance and furnace




assembly as a whole to better understand the working of a thermobalance. In this diagram you can clearly see

that the whole of the balance system is housed in a glass to protect it from dust and provide inert atmosphere.

There is a control mechanism to regulate the flow of inert gas to provide inert atmosphere and water to cool the

furnace. The temperature sensor of furnace is linked to the programme to control heating rates, etc. The balance

output and thermocouple signal may be fed to recorder to record the TG Curve.

3.3 Sources of Error in TGA

There are a number of sources of error in TGA, and they can lead to inaccuracies in the recorded temperature

and mass data. Some of the errors may be corrected by placing the thermobalance at proper place and handling

it with great care. For understanding we are discussing some common source of errors during operation of a

thermobalance.

i. Buoyance effect: If a thermally inert crucible is heated when empty there is usually an apparent weight

change as temperature increases. This is due to effect of change in buoyancy of the gas in the sample

environment with the temperature, the increase convection and possible effect of heat from the furnace

in the balance itself. Now, in most modern thermobalances, this effect is negligible. However, if

necessary, a blank run with empty crucible can be performed over the appropriate temperature range.

The resultant record can be used as a correction curve for subsequent experiment performed in the same

condition.

ii. Condensation on balance suspension: Condensation of the sample will also affect the mass of the

sample and consequently the shape of TG curve .This can be avoided by maintaining a dynamic

atmosphere around the sample in the furnace so that the entire condensable product may be driven by

the flowing gases.

iii. Random fluctuation of balance mechanism

iv. Reaction between sample and container

v. Convection effect from furnace




vi. Turbulence effect from gas flow

vii. Induction effect from furnace

Errors of type (iii) can be avoided by proper placing of balance in the laboratory and error (v) can be avoided

by sensible choice of sample container. Last three errors (v-vii) have to be considered in the design of the

furnace, the balance and its suspension system. By avoiding excessive heating rate and proper gas flow rate

some of above mentioned errors may be avoided. In the light of above discussion it is necessary to calibrate

thermobalance before to use.

Calibration of thermobalance for the measurement of mass. It can be done by adding known mass of the sample

container and noting the reading of the chart. Temperature calibration: ferromagnetic standards are used for this

purpose. In a magnetic field there substances have shown detectable mass changes. The ferromagnetic

standards are quite suitable for the temperature range from 242 to 771° C.

3.4 Interpretation of TG Curve

Three factors should be noted when you get a TG curve:

1. General shape.

2. The particular Temperature at which changes in mass occur.

3. The magnitudes of the mass changes.

From the different shapes of the TG curves we can get the different information. Some shapes of the TG curves

(Figure 3.6) with their interpretations are given bellow:




Figure3.6 Different shapes of the TG curves.

i. The sample undergoes no decomposition with loss of volatile products over the temperature range

shown but solid phase transformation, melting, etc cannot be detected by TG.

ii. The rapid initial mass loss is characteristic of desorption or drying. If it is true, then re-run the sample

should result in type (i) curves,

iii. Single stage decomposition,

iv. Multi-stage decomposition with relatively stable intermediates: provide information on the temperature

limit of stability of reactants and intermediate products and also stoichiometry,




v. Multi-stage decomposition with no stable intermediate product. However heating-rate effect must be

considered. At low heating rate, type (v) resembles type (iv). At high heating rate, type (iv) and (v)

resemble type (iii) and lose all the details,

vi. Gain in mass due to reaction with atmosphere, e.g. oxidation of metals,

vii. Oxidation product decomposes again at higher temperature; this is not often encountered.

3.5 Factors Affecting TG Curve

. There have the following main factors which affect the shape, precision and accuracy of the experimental

results in thermogravimetry.

1. Instrumental factors: The Instrumental factors are classified into the following parts

i) Furnace heating rate.

ii) Recording or chart speed

iii) Furnace atmosphere

iv) Geometry of Sample holder/ location of sensors

v) Sensitivity of recording mechanism.

vi) Composition of sample container.

2. Sample Characteristics: The Sample Characteristics are classified into the following parts

a) Amount of sample

b) Solubility of evolved gases in sample.

c) Particle size

d) Heat of reaction

e) Sample packing

f) Nature of sample

g) Thermal conductivity.




3.6 Applications of Thermogravimetric Analysis

Followings are the different applications of Thermogravimetric Analysis.

Thermal Stability: related materials can be compared at elevated temperatures under the required atmosphere.

The TG curve can help to elucidate decomposition mechanisms.

Material characterization: TG curves can be used to "fingerprint" materials for identification or quality

control.

Compositional analysis: by careful choice of temperature programming and gaseous environment, many

complex materials or mixtures may be analyzed by decomposing or removing their components. The weight

loss at a temperature is helpful to determine the composition of a compound and follow reactions in its

decomposition. It also enables to identify crystals of unknown composition. It is used to analyze e.g. filler

content in polymers; carbon black in oils; ash and carbon in coals, and the moisture content of many substances.

Simulation of industrial processes: the thermo balance furnace is thought as mini-reactor and has ability to

perform operations like some types of industrial reactors.

Kinetic Studies: by understanding the controlling chemistry or predictive studies, a variety of methods can be

used to analyze the kinetic features of weight loss or gain.

Corrosion studies: TG provides a means of studying oxidation or some reactions with other reactive gases or

vapours.




Example of some TGA curves with their explanation:

Figure3.6 TGA thermal curve for CuSO4.5H2O

Figure3.7 Comparison of TG and DTG curves.




Figure3.8 TGA thermal curve for pure anhydrous calcium carbonate, CaCO3. The loss in mass is due to the

loss of CO2 (g) and the compound remaining is CaO.

Figure 3.9 TGA thermal curve of hydrated calcium oxalate, Ca(COO)2.nH2O, with both absorbed water from

precipitation process and water of crystallisation. There is a loss of absorbed water starting at about 90oC, and

loss of bound water at about 150oC. The stable compound above 225

oC is anhydrous calcium oxalate,

Ca(COO)2. This loses CO at about 450oC to form CaCO3. The calcium carbonate is stable until approximately

600oC, when it loses CO2to form CaO.




Composition determination from the TG curve ob binary compounds mixture

Figure 3.10 TGA thermal curves for (top) pure A compound, (middle) pure B compound and (bottom dotted

line) a mixture of A and B compounds. Because A and B compounds have unique temperatures at which mass

is lost, the composition of the mixture may be determined.




The decomposition of pure compound A and B occur at T1, and labelled as β1β2 and temperature T2, and

labelled as β3β4 respectively, as illustrated in Figure 3.10. The TG curve of mixture of A and B together is also

shown in Figure 3.10. You can see in this figure, the plateaus (corresponding to the regions of constant mass)

commence at about the same temperature as they do in the TG Curves for the pure compounds A and B. You

can also notice that the mass loss overall up to T1 is x mg and from T1 to T2 it is an additional y mg. By

measuring these two quantities x and y from the TG curves of Figure 3.10, we can determine the relative

quantities of A and B in the original binary mixture. To understand further consider the mixtures of calcium and

magnesium carbonates.

Estimation of Magnesium Oxide in a mixture of Magnesium Oxide [MgO] and Magnesium Oxalate

[Mg(COO)2.2H2O]

The following data were obtained from our TGA curve:

Original weight of sample = 25.00 mg

Weight of the sample after heating to 500oC = 10.40 mg

Loss in weight = 14.60 mg

Figure 3.11 TGA thermal curve of Magnesium oxalate.




But we have already calculated that Mg(COO)2.2H2O losses 73% of its mass upon heating to 500oC; therefore

the weight of the Mg(COO)2.2H2O in the original sample was:

mg Mg(COO)2.2H2O = �14.60�� .��

��= 20�

Then the concentration of Mg(COO)2.2H2O in the original sample was:

% Mg(COO)2.2H2O =��.��

!��"��"�#�$%$&�'�&(��)100

% Mg(COO)2.2H2O =��

�*.��)100 = 80%

Thus the other 20% of the starting mixture is MgO.

Analysis of a mixture of calcium and magnesium carbonates from TGA curve

A typical TG curve of a mixture of calcium and magnesium carbonates is shown in Figure 3.12 You can notice

that a significant mass loss occurs before 210° C. This is due to the moisture present in the mixture. Another

mass loss at about 480° C is due to the following reaction:

Earlier we mentioned that CaCO3 decomposes at about 800 °C. In Figure 3.9 mass loss between about 600 °C

and 900 °C can be interpreted due to decomposition of CaCO3.




Portion of the curve ab represents a mixture of MgO and CaCO3 and cd represents a residue of the mixture of

MgO and CaO. Both these plateaus ab and cd represent weight m1 and m2, respectively. In fact mass m1 is due

to CaCO3 + MgO.

Figure 3.12 TG curve of mixture of calcium and magnesium carbonates.

Thus, m1 – m2 is the loss of CO2 between 500° C and 900° C due to the decomposition of CaCO3. Using TGA

curve we can relate the mass of different components formed during TGA experiment.

The mass of CaO (m3) formed can be calculated using following

m3 = 1.27 (m1 – m2)

This equation can be obtained as follows:

The CaO is formed by the evolution of CO2 on the decomposition of CaCO3,




From the above equation 1mole of CaCO3 gives 1 mole of CO2 and 1mole of CaO. Thus, moles of CO2 in the

given examples =��-–�/�

�0��/� and this is equal to moles of CaO formed.

Thus the amount of CaO must be, �� =��-–�/�

112M4�CaO�

Where, Mr(CaO) is the relative molar mass of CaO

�� =��-–�/�

11256g

�� = 1.27��–��g

We know the mass of residue left, i.e. m2, the mass of MgO (m4) can be calculated.

m4= m2-m3

Here m3 is the mass of CaO formed, which is equal to 1.27(m1-m2). Thus m4=m2-1.27(m1-m2)

Mass of the Ca (mCa) in the original sample can also be related to m1 and m2 by the following formula.

mCa = 0.91(m1-m2)

This can be obtained as follows:

We know amount of Ca in CaCO3 and CaO will be equal in moles, therefore amount of Ca is

�;" = ��2<0��=�

�0��=��= 1.27�� −��2

<0��=�

�0��=��

Where, Ar(Ca) and Mr(CaO) are the relative atomic mass and relative molar mass of Ca and CaO, respectively.

Thus,

= 1.27�� −��240

56= 0.91�� −��

Similarly, mass of magnesium in the original sample can be related to m1 and m2:




= �massofresidue − massofCaO�2IJ�K�

KJ�KL�

�M� = �� −��2IJ�K�

KJ�KL�= �� −��

24.3

40.3

�M� = 0.60�� −��

Analysis of a mixture of calcium oxalate and magnesium oxalate from TGA curve

Calcium oxalate monohydrate is unsatisfactory weighing form for determining calcium as oxalate because its

tendency to retain excess moisture even at 110°C, co-precipitated ammonium oxalate remains un-decomposed.

The anhydrous calcium oxalate is hygroscopic but CaCO3 is excellent weighing form if heated to 500 ± 25°C as

can be seen in TG curve of CaC2O4.H2O. Above 635oC the decomposition of CaCO3 commences to become

significant under usual laboratory conditions and completely converted to CaO at 900°C. Thus, calcium oxalate

monohydrate decomposes in three steps, first dehydration, second removal of CO and formation of CaCO3 then

third step CaCO3 decomposes to CaO (Figure 3.13).

CaC2O4.H2O → CaC2O4 + H2O at about 135-220 °C

CaC2O4 → CaCO3+CO at about 400-480 °C

CaCO3 → CaO+ CO2 at about 635-900 °C

But magnesium oxalate dihydrate decomposes in two steps instead of three steps. First, dehydration then

removal of CO and CO2 simultaneously and forming MgO, there is no horizontal corresponding to MgCO3 as it

is thermally unstable at this temperature.

MgC2O4.2H2O → MgC2O4+2H2O at about 135-220 °C

MgC2O4 → MgCO3 + CO → MgO+CO2 at about 500 °C

The TG curve for the mixture of CaC2O4.H2O and MgC2O4.2H2O shows two mass losses up to 500 °C, first at

about 200 °C due to loss of water and the second mass loss occurs in the 390-500 °C range which is due to




decomposition of both calcium and magnesium oxalates. Thus, at 500°C, the composition of the mixture will be

CaCO3 and MgO. Third mass loss after 500 °C is due to only the decomposition of CaCO3. If m1 and m2 are the

mass of the mixture at 500°C and 900°C then similar to the previous example we can calculate the amount of

calcium and magnesium in the original sample.

Figure 3.13 TG curve of mixture of calcium and magnesium oxalates.

3.8 Glossary

Decomposition is the process by which substances are broken down into more simple ingredients.

Oxidation and combustion a combustion reaction occurred at a high-temperature between sample and an

oxidant (usually oxygen) into a thermogravimetric analyzer at normal conditions.t is a high-temperature

exothermic redox chemical reaction. The thermogravimetric analyzer would ion combustion the sample by

heating it beyond the ignition temperature of a sample.

TGA the weight loss of a sample as a function of temperature is determined. In most cases, the sample is

heated with a constant heat rate under air or nitrogen. Sometimes, the differential weight-loss curve is also

obtained (DTG).




TGA curve a plot of weight% vs. temperature, usually consisting of a series of steps, obtained by measuring

the mass of a sample during heating.

Thermal stability In a desired temperature range, if a species is thermally stable, there will be no observed

mass change. TGA can be used to evaluate the thermal stability of a material.

3.9 References and Further Readings

1. G. Lombardi, For Better Thermal Analysis, 2nd ed., ICTA, Rome (1980).

2. J. O. Hill, For Better Thermal Analysis and Calorimetry, 3rd ed., ICTAC (1991).

3. P.J. Haines, Thermal Methods of Analysis: Principles, Applications and Problems, Springer (1995),

ISBN 978-94-011-1324-3.

4. T. Hatakeyama, Liu Zhenhai. Handbook of Thermal Analysis Hardcover, Wiley-Blackwell

(1998)ISBN-13: 978-0471983637.

5. Paul Gabbott, Principles and Applications of Thermal Analysis, Blackwell Publishing Ltd (2008),

ISBN: 9781405131711.

6. Robert F. Speyer, Thermal Analysis of Uaterlals. Marcel Dekker, Inc. New York (1993), ISBN 0-8247-

8963-6.

7. 3.10 Questions and Problems

Q1. Calculate the percentage mass change (m %) for the following reactions.

Q2. What are common source of errors in thermogravimetric analysis?

Q3. What are the common instrumental factors affecting TG curves.




Q4. A thermogram of a magnesium compound shows a loss of 94.0 mg from a total of 180.0 mg

used for analyte. Identify the compound either as MgO, MgCO3, or MgC2O4.

Q5. A mixture of CaO and CaCO3 is analysed by TGA. The result indicates that mass of the

sample decreases from 250.6 mg to 190.8 mg only between 600°C and 900°C calculate the percentage

of calcium carbonate in the mixture.

Q6. What types of standard are required to calibrate the mass variation obtained with TGA

equipment?

Q7. What types of standards are required for temperature calibration of any TGA.

Q8. A mixture of CaCO3 and CaO is analysed using TGA technique. TG curve of the sample

indicates that there is a mass change from 175.3 mg to 125.4 mg between 500–900°C. Calculate the

percentage of CaCO3 in the sample.

Q9. A 250 mg hydrated sample of Na2HPO4 decreases to a mass of 165.7 mg after heating to 15

°C. What is the number of water hydration in Na2HPO4.

Q10. Draw a labeled diagram of the TG curve obtained by heating a mixture of 90 mg of

CaC2O4.H2O and 80 mg of MgC2O4.H2O to 1200 °C. Calculate the amount of all mass losses.

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