Thermal Analysis of Inorganic Materials
On Demand Webinar

Thermal Analysis of Inorganic Materials

On Demand Webinar

"Thermal Analysis of Inorganic Materials" details various applications for characterizing inorganics

Thermal Analysis of Inorganic Materials
Thermal Analysis of Inorganic Materials

In the webinar titled "Thermal Analysis Inorganic Materials", we describe a number of techniques and methods that can be used to characterize the physical properties of inorganic materials and compounds.

Inorganic materials and industrial applications

Inorganic materials encompass everything else, that is, compounds such as metals, salts, minerals, and so on. Chemical bonding is largely ionic.
Oxides and sulfides of carbon, and metal carbides are regarded as inorganic compounds. Coal is classed as an inorganic substance and is of great importance as a source of energy.

Thermal analysis is mainly used to measure moisture content, thermal and oxidative stability, and solid-solid transitions. In addition, it can be employed to determine the composition of raw materials such as gypsum and to characterize energetic materials with regard to storage conditions and safety.
Other important applications have to do with the compatibility of construction materials.

Thermal analysis of inorganic materials

The most important effects that can be analyzed by DSC are the glass transition and melting behavior.

TOA is the method of choice for the visual observation of samples, for example during crystallization, and to detect different polymorphs.
The main applications of TGA are content analysis, thermal stability and evaporation behavior.

TMA can be used to characterize expansion, shrinkage or melting behavior.

DMA is an excellent method for characterizing the viscoelastic behavior of materials.

English

Thermal Analysis Inorganic Materials

Slide 0: Thermal Analysis of Inorganic Materials

 

Ladies and Gentlemen,

Welcome to the METTLER TOLEDO webinar on the Thermal Analysis of Inorganic Materials.

 

Inorganic chemistry is the study of the structure and properties of materials such as minerals, inorganic salts, metals and the chemical elements. We encounter inorganic materials almost everywhere in our daily life. They are used for a vast multitude of applications and often exhibit high temperature resistance.

 

Methods based on the thermal analysis techniques DSC, TGA, TMA and DMA are important for characterizing inorganic materials. In this webinar, I want to describe a number of application examples that demonstrate this.

The applications have to do with the measurement of the physical properties and behavior of materials as a function of temperature. The properties include melting, the glass transition, thermal stability and dimensional changes.

 

Slide 1: Contents

The slide lists the topics I plan to cover.

First, I would like to make some general remarks about inorganic materials.

I then want to discuss the most important thermal properties of inorganic materials and describe the thermal analysis techniques that can be used to measure them.

The techniques include:

Differential Scanning Calorimetry, or DSC;

Thermo-optical Analysis, or TOA;

Thermogravimetric Analysis, or TGA;

Thermomechanical Analysis or TMA; and finally

Dynamic Mechanical Analysis, or DMA.

 

After this, I will present a number of examples that illustrate how thermal analysis can be used to investigate the physical behavior of inorganic materials and compounds.

 

Finally, I want to summarize the different thermal analysis techniques and their application areas and list a number of useful references for further information and reading.

 

Slide 2: Introduction

Traditionally, chemistry is divided into organic and inorganic chemistry:

 

Organic chemistry is the study of compounds such as hydrocarbons, alcohols, esters, amines, etc. These compounds contain carbon atoms covalently linked to other carbon atoms, hydrogen, oxygen, and nitrogen.

 

Inorganic chemistry is effectively the study of more or less everything else, that is, compounds such as metals, salts, minerals, and so on. Chemical bonding is largely ionic.

Oxides and sulfides of carbon, and metal carbides are regarded as inorganic compounds. Coal is classed as an inorganic substance and is of great importance as a source of energy.

 

Inorganic chemistry is closely related to disciplines such as materials science, physical chemistry, thermodynamics, geosciences, mineralogy, crystallography, etc.

 

Slide 3: Introduction

Typical questions that might arise in connection with inorganic materials are:

 

- Are you interested in the decomposition of minerals such as bauxite, or the composition of gypsum?

- Is the analysis of inorganic polymorphic transitions important for your work?

- Do you want to know more about the dehydration of your product?

- Is the thermal expansion of materials a property you want to measure?

- Are you interested in corrosion and the oxidation of metals?

 

 

For example, the corrosion of metals like iron in contact with air and water can lead to problems and damaged products. We can study oxidation easily by TGA.

The diagram on the right of the slide displays the TGA heating curve of iron powder in an oxidative atmosphere. From about 300 degrees Celsius onward, the curve shows an increase in weight of about 39% due to the oxidation of the iron to iron oxide.

 

Slide 4: Thermal Analysis

But let’s start at the beginning. What exactly is Thermal Analysis?

 

The ICTAC definition is:

 

“A group of techniques in which a physical property of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature program”.

The schematic diagram on the right shows a simple linear temperature program in which the temperature of a sample is increased at a constant heating rate.

 

The lower half of the slide illustrates typical events and processes that occur when a sample is heated. For example, the melting process in which the sample changes from the solid to the liquid state; or oxidation - if the sample is exposed to air or oxygen it will start to oxidize and finally decompose.

We use thermal analysis techniques to investigate effects like this.

 

Slide 5: Thermal Analysis                                                                                                Techniques

The slide shows five important thermal analysis techniques that are employed to characterize inorganic materials, namely:

 

Differential Scanning Calorimetry, or DSC. This is the most widely used thermal analysis technique. The picture shows a DSC sensor with a crucible containing a sample colored red, and a reference crucible.

Thermo-optical Analysis, or TOA. In the picture, we see a video camera installed above a DSC instrument.

Thermogravimetric Analysis, or TGA. The picture shows part of the TGA ultra-micro balance with its automatic internal ring weights.

Thermomechanical Analysis, or TMA. Here we see the sample area with a sample colored red and the quartz probe and sensor.

And finally, Dynamic Mechanical Analysis, or DMA. The picture shows one of the different sample-clamping assemblies.

 

I will explain the measurement principles of these instruments and the properties that they can measure in more detail during the webinar and describe some typical application examples.

 

Slide 6: Industries and Applications

The table summarizes the most important industries and the different applications of thermal analysis for inorganic materials.

It shows that thermal analysis is mainly used to measure moisture content, thermal and oxidative stability, and solid-solid transitions.

In addition, it can be employed to determine the composition of raw materials such as gypsum and to characterize energetic materials with regard to storage conditions and safety.

Other important applications have to do with the compatibility of construction materials.

 

Slide 7: Differential Scanning Calorimetry (DSC)

The first technique I want to discuss is DSC.

DSC allows us to determine the energy absorbed or released by a sample as it is heated, cooled or held at constant temperature.

 

DSC instruments exist in different versions depending on their temperature range, the type of sensor, and the available heating and cooling rates.

 

The standard METTLER TOLEDO DSC instruments measure from minus one hundred and fifty degrees Celsius to plus seven hundred degrees at heating rates of up to three hundred kelvin per minute. Samples are normally measured in small crucibles made of aluminum, alumina or other materials, using sample amounts of two to twenty milligrams.

 

Another useful DSC technique is high-pressure DSC, or HPDSC for short. The METTLER TOLEDO HP DSC instrument can analyze samples under inert or reactive gases at pressures of up to ten megapascals, or 100 bar. This suppresses any undesired vaporization of samples or enables the stability of samples to be studied under increased oxygen pressures.

 

The schematic diagram on the left shows a DSC measurement curve of sulfur.

According to convention, exothermic effects point in the upward direction and endothermic effects downward. The effects are numbered next to the curve and explained in the table, namely:

One, the initial deflection proportional to the heat capacity of the sample;

Two, a glass transition;

Three, cold crystallization;

Four, a polymorphic transition;

Five, melting of the crystalline fraction; and finally

Six, polymerization.

 

Slide 8: Differential Scanning Calorimetry (DSC)

DSC is used to study thermal behavior and events such as melting, crystallization, solid-solid transitions, and chemical reactions.

The table summarizes the analytical applications of DSC for inorganic materials. The main applications have to do with melting behavior, crystallization and the glass transition.

DSC measurements also provide information about the composition and the thermal history of materials as well as the enthalpy of transitions, the specific heat capacity, and the influence of impurities, additives or fillers on melting behavior.

 

The picture on the right shows a view of an open DSC furnace with sample and reference crucibles. The standard crucibles are made of aluminum.

 

Slide 9: Application 1: DSC                                           Glass transition of a glass

In glass making, a number of reference temperatures are important for the processing and use of different types of glass. These include the transformation point or softening point, the processing temperature, and the short-term maximum permissible temperature of use, the glass transition temperature, Tg.

The glass transition can easily be measured by DSC as shown in the slide.

The diagram displays the DSC heating and cooling curves of a glass powder measured at 10 kelvin per minute. The location of the glass transition on cooling depends on the cooling rate. The steps on the curves clearly show the glass transition occurs in the temperature range 500 to 550 degrees Celsius

 

Slide 10: Application 2: DSC                                          Phase diagram of an alloy

Metals and metal alloys very often have complex phase diagrams with different transformation temperatures between the individual crystalline structures and the liquid state. The melting points and the melting behavior depend on the composition of the alloy. The phase transitions can easily be determined by DSC. This allows us to describe the thermal behavior of mixtures of two or more metals for different concentrations.

The slide shows a typical example, namely mixtures of high purity lead and tin. As expected, the two pure metals exhibit sharp endothermic melting peaks. The same applies to the eutectic mixture and the sixty-forty tin-lead solder sample. The melting points were determined as the onsets because there is effectively no melting range.

If we add tin to the pure lead, for example 20 weight percent as shown by the thick black curve labeled Sn 20, melting begins at the eutectic point as a sharp peak. At this temperature, the entire amount of added tin melts together with part of the lead in the eutectic ratio of 62 to 38. On further heating, the remainder of the lead melts continuously up to the liquidus point, at which only liquid metal is present. The curve exhibits a broad peak.

In DSC measurements, the liquidus point is usually determined as the peak temperature. The peak temperatures in the diagram show that the liquidus temperatures decrease with decreasing lead content. After reaching the eutectic composition, the peak temperature increases again with increasing tin content until the melting point of pure tin is reached.

 

Slide 11: Application 3: DSC                                                          Decomposition reaction

Chemical substances like ammonium nitrate are potentially highly explosive and are used as a propellants and explosives, but also as fertilizers.

The following application example shows differences in the DSC curves due to different measurement conditions - in one experiment, the sample was measured in a standard aluminum crucible, and in the other experiment in a high-pressure crucible.

Both measurement curves show the same behavior up to 200 degrees Celsius namely a solid-solid transition at 130 degrees and melting at 170 degrees. The shape of the peak measured with the high-pressure crucible is somewhat broader compared with that using the aluminum crucible because the time constant of the high-pressure crucible is longer.

In an open crucible, ammonium nitrate decomposes almost completely from 200 degrees onward in an endothermic process with the loss of ammonia and nitric acid. This was confirmed by TGA measurements. In contrast, in the hermetically sealed, pressure-tight crucible, an exothermic decomposition reaction occurs without weight loss in a first large step at 335 degrees followed by a smaller reaction step at 360 degrees.

The curve shows that the reaction begins slowly but accelerates and ends in a large, relatively sharp exotherm. At this point, the heat produced cannot be dissipated fast enough. This causes the sample to momentarily overheat, that is, the sample heats up faster than programmed by the heating rate. The temperatures and heat flows measured show whether or not a substance is a potential thermal risk.

The results also provide important information for assessing chemical and thermal stability as well as the duration of the reaction. This is important for process design and risk assessment.

 

Slide 12: Thermooptical Analysis (TOA)

The next technique I want to describe is thermo-optical analysis or TOA for short.

 

TOA comprises a group of techniques that are used to measure optical properties of a sample as it is heated or cooled. The properties can be monitored by a DSC, an HPDSC, or a hot-stage system in combination with a microscope or a camera. The HPDSC instrument can also be connected to a chemiluminescence system. Some TOA instrumentation allows us to simultaneously measure calorimetric effects while visually observing the sample.

The table lists the most important applications of TOA for inorganic materials. These include the measurement of changes in morphology, melting and crystallization behavior, thermochromism, and oxidation stability.

The picture shows a hot-stage cell that is set up for visual sample monitoring. When combined with a microscope and video camera, video images can be captured and overlaid with the temperature in real time.

The next slide shows an example of such an experiment.

 

Slide 13: Application 1: TOA             Polymorphic transitions of rubidium nitrate

The diagram displays the DSC curve of rubidium nitrate measured at a heating rate of 1 kelvin per minute. The measurements were performed using the HS 84 hot-stage system equipped with a camera. The sample was prepared in a glass crucible. This allowed the transitions to be observed visually during the DSC measurement.

The DSC heating curve in fact exhibits six peaks due to different phase transitions. The crystal structures of the phases can be easily recorded by capturing images at specific temperatures – for illustration, in this experiment at 150, 248.5 and 284.5 degrees Celsius.

 

Slide 14: Thermogravimetric Analysis (TGA)

Now let’s turn our attention to thermogravimetric analysis, or TGA.

In this technique, the mass of a sample is continuously measured as it is heated or cooled in a defined atmosphere. We simply put a few milligrams of the material into a crucible, weigh the sample, heat it and record the weight change. From this, we can obtain information about the composition of the sample.

 

The schematic curve shows a typical TGA measurement curve of an inorganic material. Initially, before the heating ramp begins, the TGA measures the mass of the sample. At the end of the measurement, inorganic fillers like glass fibers remain behind as a residue after heating to temperatures of one thousand degrees Celsius or more. The steps due to loss of mass provide information about the composition of materials.

 

The steps are numbered next to the curve and explained in the table, namely:

One, heating begins and volatile components vaporize;

Two, pyrolysis in inert atmosphere;

Three, at six hundred degrees Celsius the atmosphere is switched from nitrogen to air to obtain oxidative conditions;

Four, carbon black or carbon fibers burn;

Five, inorganic fillers such as glass fibers remain behind as a residue.

 

Slide 15: Thermogravimetric Analysis (TGA)

TGA is used to investigate processes such as vaporization or decomposition. Evolved gases can be analyzed online using hyphenated techniques such as TGA-MS, TGA-FTIR or TGA-GC/MS.

 

The table summarizes the main analytical applications of TGA for inorganic materials. The technique provides information about the composition of samples including their filler content. Furthermore, it allows us to check the thermal stability of products, or to analyze the content of moisture or volatiles in formulated products.

 

The picture on the right is a view of the open furnace showing a sample holder with two positions for the sample and reference crucibles in a TGA instrument designed for simultaneous DSC measurements. The standard crucibles are made of alumina in order to withstand high temperatures.

 

Slide 16: Application 1: TGA/DSC                                 Analysis of gypsum

The first application example has to do with the measurement of gypsum, that is, calcium sulfate dihydrate, by simultaneous TGA and DSC. The analysis of this mineral substance is important in order to estimate its quality. The content of certain impurities such as calcium carbonate can depend on the depth of the deposit in the mine.

The upper diagram displays the TGA weight loss curve and the lower diagram the simultaneously recorded DSC curve.

The TGA curve exhibits three distinct steps.

The first step is due to dehydration of the sample and provides information about its moisture content.

The second step at about 700 degrees Celsius results from the decomposition of the calcium carbonate present as an impurity to calcium oxide. From this, we can estimate the content of calcium carbonate in the sample.

Finally, the third step from about 1200 degrees onward arises from the decomposition of calcium sulfate to calcium oxide. Inorganic oxides remain behind as a residue.

The simultaneously recorded DSC curve gives us information about phase transitions such as that of anhydrous calcium sulfate, known as anhydrite, to beta calcium sulfate at 362 degrees, or beta calcium sulfate to alpha calcium sulfate at 1218 degrees.

 

Slide 17: Application 2: TGA/DSC-MS                                          Analysis of coal

Standard analytical methods have long been available to determine the quality and the economic value of different types of coal. Methods such as the ASTM E1131 standard test procedure are often used for this purpose.

The methods are however somewhat time-consuming and laborious. Analysis time can be greatly reduced by using an automated TGA instrument.

The slide displays TGA, SDTA and DTG curves obtained from the measurement of a coal sample. The TGA curve shows three weight-loss steps. The first is due to the loss of moisture, the second to the loss of volatile constituents in the coal, and the third to the combustion of the coal in an oxidative atmosphere to CO2. Ash remains as a residue.

 

Slide 18: Application 3: TGA/DSC                                 TGA-FTIR analysis

The diagrams in the next slide describe decomposition of ammonium heptamolybdate tetrahydrate using a TGA-FTIR combination.

The TGA curve colored blue in the upper part of the diagram displays the mass-loss as a function of temperature. The curve shows that the material decomposes in three main steps. A total of six molecules of ammonia and seven molecules of water are eliminated.

The black and red curves in the lower diagram present the chemigrams of water and ammonia calculated from the simultaneously recorded FTIR spectra.

The results indicate that water and ammonia are formed simultaneously but not in a fixed ratio to one another. This means that the decomposition reaction does not proceed stoichiometrically. This conclusion could only be reached with the aid of the TGA-FTIR analysis.

 

Slide 19: Thermomechanical Analysis (TMA)

I now want to move on to thermomechanical analysis, or TMA. This technique measures the dimensional changes of a sample as it is heated or cooled.

The schematic curve on the left shows a typical TMA curve of a sample measured in the compression mode using a small sample load. The different effects are numbered next to the curve and explained in the table, namely:

One, expansion below the glass transition;

Two, the glass transition point at which the rate of expansion changes;

Three, expansion above the glass transition; the steeper slope indicates a greater rate of expansion;

Four, softening with plastic deformation.

 

Slide 20: Thermomechanical Analysis (TMA)

The table summarizes the analytical applications of TMA for inorganic materials.

The main application is the determination of the expansion behavior and the coefficient of thermal expansion, or CTE.

TMA is also an excellent technique for determining glass transition temperatures, and for studying softening behavior, creep, or polymorphism. The picture on the right shows the typical experimental setup with a ball-point sample in contact with a sample specimen.

 

Slide 21: Application 1: TMA                                           CTE of inorganic materials

This slide presents the result obtained for the determination of the coefficient of thermal expansion of three inorganic materials.

The main diagram displays the TMA curves of quartz, invar and a borosilicate glass. The CTE results are shown as curves in the inset diagram and as tables.

Borosilicate glass has a CTE of 3.3 ppm in the glassy state; the glass transition occurs at about 550 degrees Celsius.

Invar is an iron-nickel alloy that shows practically no thermal expansion up to 150 degrees.

Crystalline alpha-quartz expands continuously with a steadily increasing CTE. A phase transition occurs at about 575 degrees after which the material contracts.

 

Slide 22: Application 2: TMA                                                           Solid-solid transitions

This application shows how solid-solid transitions can be investigated using TMA and DSC.

In this case, the sample investigated was ammonium nitrate. Solid-solid transitions of this type are always accompanied by a change in volume. This can influence the flow properties and handling of materials.

In a TMA curve, solid-solid transitions appear as a step. The red and blue curves in the upper diagram display the first and second heating runs of a single grain of ammonium nitrate. The curves show that the transitions occur quite rapidly. The transition temperatures are influenced by internal stresses in the sample and therefore by the thermal history of the sample. This explains why the first and second heating runs are different.

The green curve in the lower diagram is the second DSC heating run of a sample. The curve shows that the solid-solid transitions appear as peaks at the same temperatures as in the second TMA measurement.

 

Slide 23: Application 3: TMA                                           High-performance ceramics

Modern high-performance ceramics exhibit high temperature stability. This is demonstrated in the following example using two materials that were investigated using high-temperature TMA. Both samples were silicon dioxide that had been sintered in different ways. Silicon dioxide occurs as crystalline quartz or as cristobalite in various modifications.

The diagram displays the two TMA curves colored red and black. The curve of Sample 1 colored red shows the transition from the alpha to the beta form of cristobalite at 245 °C. This occurs relatively quickly and can result in the formation of cracks or fissures in the material.

The quartz transition observed in the second silicon dioxide sample labeled Sample 2 is slower and occurs at a higher temperature. This minimizes the risk of fractures. In addition, the sample contains crystallization nuclei. This leads to crystallization from about 1200 degrees onward. These properties make Sample 2 a better high performance ceramic material at high temperatures.

 

Slide 24: Dynamic Mechanical Analysis (DMA)

Dynamic mechanical analysis is used to measure the mechanical properties of a viscoelastic material as a function of time, temperature and frequency when the material is deformed under a periodic oscillating stress.

 

The schematic diagram on the left shows the results of a DMA measurement of silicone oil measured in the shear mode. The curves display the storage modulus, gee prime; the loss modulus, gee double prime;and tan delta as a function of temperature.

The different effects are numbered next to the curve and explained in the table, namely:

One, glassy state of the quench-cooled liquid;

Two, the glass transition, seen as a decrease in the storage modulus;

Three, viscous liquid state;

Four, crystallization of the oil;

Five, melting of the oil;

Six, liquid state of the oil.

 

Slide 25: Dynamic Mechanical Analysis (DMA)

The table lists the main analytical applications of DMA for materials used in the field of inorganic materials.

In general, DMA provides information about the mechanical modulus, compliances, damping and viscoelastic behavior. The glass transition temperature, softening temperatures, or beta-relaxation processes are detected as peaks in tan-delta or by changes in the modulus.

The picture on the right shows a sample installed in the DMA clamping assembly ready for measurement in the bending mode.

 

Slide 26: Application 1: DMA          Analysis of a shape memory alloy

So-called shape memory alloys are materials that can be converted back to their original shape by heating after they have been deformed. In addition, the materials are also superelastic, that is, they can be deformed and return to their initial shape when the deformation stress is removed.

Alloys like this are for example used to manufacture stents for medical applications. The materials can be characterized by DSC or by DMA.

This example shows how the elasticity of nitinol can be investigated by DMA. The sample was a nitinol wire 9 mm long with a diameter of 0.8 mm. It was measured in the tension mode using a displacement amplitude of 2 microns and an Auto Offset of 120%.

The slide shows the results of the initial heating measurement and the cooling measurement afterward. The upper diagram displays the storage modulus curves and the lower diagram the loss factor or tan delta curves. In the thermally induced phase transformation from austenite to martensite, or the other way around, the modulus changes and a peak is observed each time in the tan delta curve. Besides this, a hysteresis effect occurs between heating and cooling. Above the austenite temperature, products made from shape memory alloys can be reversibly deformed by up to about 10% in a limited temperature range under stress. Further information on this subject can be found in UserComs 40 and 41.

 

Slide 27: Summary

The table summarizes the most important events and properties that characterize inorganic materials as well as the techniques recommended for investigating the various effects. A box marked red means that the technique is strongly recommended; a box marked blue indicates that the technique can also be used.

 

The most important effects that can be analyzed by DSC are the glass transition and melting behavior.

TOA is the method of choice for the visual observation of samples, for example during crystallization, and to detect different polymorphs.

The main applications of TGA are content analysis, thermal stability and evaporation behavior.

TMA can be used to characterize expansion, shrinkage or melting behavior.

DMA is an excellent method for characterizing the viscoelastic behavior of materials.

 

Slide 28: Summary

This slide presents an overview of the temperature ranges of the METTLER TOLEDO DSC, TOA, TGA, TMA, and DMA instruments.

 

In general, DSC experiments are performed at temperatures between minus one hundred and fifty degrees Celsius and plus seven hundred degrees. The temperature range may be different if special equipment or accessories are used.

TOA experiments can carried out between minus sixty degrees and plus three hundred and seventy five degrees. Several modes of operation are possible depending on the information required.

TGA measurements normally begin at room temperature. The maximum possible temperature is about sixteen hundred degrees.

TMA experiments can be carried out between minus one hundred and fifty degrees Celsius and plus sixteen hundred degrees.

DMA measurements are performed in the range minus one hundred and fifty degrees to plus five hundred degrees.                

 

Slide 29: For More Information

Finally, I would like to draw your attention to information about the use of thermal analysis in the field of inorganic materials that you can download from the Internet.

METTLER TOLEDO publishes articles on thermal analysis applications twice a year in UserCom, the well-known METTLER TOLEDO technical customer magazine. Back issues can be downloaded as PDFs from the Internet as shown lower down on the slide. A compilation of applications can be found in the “Thermal Analysis in Practice” handbook.

 

Slide 30: For More Information on Thermal Analysis

In addition, you can download details about webinars, application handbooks or information of a more general nature from the Internet addresses given on this slide.

 

Slide 31: Thank You

This concludes my presentation on the thermal analysis of inorganic materials. Thank you for your interest and attention.

 
 
 
 
 
 
 
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