Application Of Thermal Analysis: Complete Technical Guide

Thermal analysis is the family of laboratory methods that measures the behavior of a material while it is heated: the weight loss of the sample, the heat effects of its reactions and its dimensional changes are recorded against the temperature, and the resulting curves are the fingerprints of the material’s chemistry: for the cement industry, the methods reveal the calcination behavior of the raw meal, the clinkering reactions in miniature, the dehydration of the gypsum and the hydration of the cement: the laboratory instrument of a few hundred thousand dollars answers questions that the plant asks every week.

The Complete Cement Technical Package (931 files including the books, the courses, the Excel tools and the presentations: $249.99 one-time: instant download via the PayPal payment) includes this thermal analysis guide with the method descriptions, the reference curves, the interpretation tables and the report templates: the article walks the file: the methods, the instruments, the raw meal calcination, the clinkering reactions, the clinker and the hydration analysis, the gypsum studies, the quantitative kinetics and the quality control applications: the laboratory engineer finishes the page with the complete working knowledge of the thermal analysis in the cement context.

This page is organized as a laboratory course: the method fundamentals come first, the cement-specific applications second, the quantitative techniques third, and the quality control practice last: the two tables of the article summarize the methods and the characteristic thermal events of the cement materials, and the FAQ answers the questions of the laboratory staff: the reader can follow the article with the file in hand, because the file follows the same order.

1. What is Thermal Analysis and Why the Cement Industry Uses It

Thermal analysis is not one method but a family: the common thread is the controlled heating of a sample and the measurement of a physical property as a function of the temperature: the thermogravimetric analysis (TGA) measures the mass, the differential thermal analysis (DTA) measures the temperature difference against an inert reference, and the differential scanning calorimetry (DSC) measures the heat flow directly: the three methods read the same reactions from different angles.

• The weight events: the drying, the dehydration, the decarbonation and the oxidation change the mass of the sample, and the TGA curve quantifies each change: the cement materials are rich in the weight events;
• The thermal events: the crystallization, the polymorphic transitions, the melting and the decomposition absorb or release the heat, and the DTA and the DSC curves record the peaks;
• The reaction studies: the cement process is a chain of the thermal reactions, and the laboratory reproduces the chain in the instrument at the controlled heating rates;
• The quantitative power: the modern instruments couple the thermal signal with the evolved gas analysis, the mass spectrometry or the infrared, identifying the gases of each reaction;
• The economic value: the thermal analysis of the raw meal predicts the burnability of the kiln feed and the moisture of the fuels, the data that protect the fuel and the quality budgets of the plant;

The cement industry was one of the first industrial adopters of the methods, because its entire process is a sequence of the thermal reactions: the clay dehydration at 450 to 650°C, the limestone calcination at 700 to 950°C, the clinker melt at 1250 to 1450°C and the cement hydration at the ambient temperature: each reaction leaves its signature on the heating curve, and the file teaches the reading of the signatures: the thermal analysis is, in the deepest sense, the laboratory mirror of the kiln, and the plants that keep the mirror polished see their process in a resolution that the routine chemistry cannot offer.

2. The Methods: TGA, DTA, DSC and the Extensions

The four methods of the classical thermal analysis cover the needs of the cement laboratory, and their selection follows the question that the laboratory asks:

Table 1: The thermal analysis methods and their cement applications

Method	Signal measured	Typical cement application
TGA (thermogravimetric)	Sample mass vs temperature	Moisture, LOI, calcination degree, gypsum dehydration
DTA (differential thermal)	Temperature difference vs reference	Clay dehydration peaks, carbonate decomposition, clinker melt formation
DSC (differential scanning calorimetry)	Heat flow vs temperature	Hydration heat of the cement, gypsum transitions, reaction enthalpies
TMA / dilatometry	Dimension vs temperature	Expansion of the concrete and the refractory test pieces
TGA-EGA (evolved gas analysis)	Mass + gas identity	Decomposition gas identification, carbon and sulphur speciation

The table is the selection guide of the laboratory: the TGA answers the questions of the quantity, the DTA the questions of the temperature and the sequence, the DSC the questions of the heat and the energy, and the hyphenated systems the questions of the chemistry of the gases: the file explains each method with its measurement principle, its calibration and its typical curve shapes, and it gives the method selection matrix that routes the laboratory requests to the correct instrument: the plants that own the thermal analysis laboratory run the methods as the daily instruments, and the file is written so that the selection takes minutes, not days.

The scientific discipline of the methods rests on the standards that the file references and explains: the ISO 11357 series covers the DSC, the ISO 11358 the TGA, and the ASTM E1131 and the related documents define the procedures of the cement and the fuel applications: the standards fix the heating rates, the atmospheres, the sample masses and the reporting formats, and the laboratories that follow them produce the results that the customers, the certifiers and the auditors accept: the file includes the standards summary tables and the mapping of the cement applications to the standard numbers, so the laboratory can establish its procedures from the recognized documents instead of the folklore: the methods of the thermal analysis are a century old in their fundamentals and the standards keep them honest, and the file positions the standards as the common language between the laboratory and the world.

3. The Instruments: The Furnace, the Balance and the Sample

The thermal analysis instrument is a laboratory machine of three parts: the furnace that heats the sample at the programmed rates, the balance or the sensor system that measures the property, and the sample holder that carries the material: the quality of the measurement lives in the details of the three.

• The furnace: the modern furnaces reach 1000 to 1600°C, and their heating rates run from 0.1 to 100°C per minute: the cement applications favor the 10 to 20°C per minute rates with the inert or the air atmospheres;
• The balance: the TGA balance measures the mass with the sensitivities of 0.1 to 1 microgram, and the buoyancy and the gas flow effects are the systematic errors that the calibration corrects;
• The sample holders: the alumina and the platinum crucibles serve the different materials: the sample masses of 10 to 100 milligrams are the typical working range, and the sample uniformity is the law;
• The atmosphere: the nitrogen, the air and the CO2 atmospheres change the reaction temperatures dramatically, and the atmosphere of the measurement must match the question: the calcination in the nitrogen decomposes at a lower temperature than in the CO2;
• The calibration: the temperature and the mass calibrations run with the reference materials, the indium, the zinc, the gold and the calcium oxalate, on the fixed schedules of the laboratory;

The instrument practice of the file follows the manufacturers’ procedures and the laboratory standards, and it adds the cement-specific lessons of the field: the raw meal samples must be ground and homogenized before the small aliquot is taken, the sample mass must be matched to the reaction intensity, and the atmosphere must be chosen with the question of the measurement: the file includes the instrument checklists, the calibration schedules and the preventive maintenance plans of the three instrument families, because the thermal analysis data are only as good as the instrument that produced them: the well-maintained instrument of the file’s discipline returns the curves that the plant trusts.

4. The TGA of the Raw Meal: Calcination and Weight Loss

The thermogravimetric analysis of the raw meal is the most used thermal application of the cement laboratory: the heating curve of the raw meal shows the drying, the clay dehydration, the carbonate decomposition and the residual weight, and the curve quantifies the four fractions that the quality control of the raw mix needs.

• The drying step: the free moisture leaves below 105°C, and the small weight loss reads the moisture of the meal: the hygroscopic samples demand the careful handling before the measurement;
• The clay dehydration: the bound water of the clay minerals leaves at 450 to 650°C, and the weight step of 3 to 8% identifies the clay type and the clay content of the mix;
• The carbonate decomposition: the calcination of the limestone releases the CO2 at 650 to 950°C, and the weight step of 30 to 38% of the raw meal is the dominant feature of the curve;
• The loss on ignition: the total weight loss to 1000°C, the LOI of 34 to 38% for the typical raw meals, is the standard number that the raw mix proportioning uses;
• The residue: the final weight at 1000°C is the ignited material, the basis of the oxide calculations of the raw mix chemistry;

The TGA replaces the classical muffle furnace LOI determination with the continuous record: the plant laboratory gains the moisture, the clay water and the carbonate fractions in one measurement instead of the single LOI number, and the carbonate fraction becomes the direct instrument of the kiln feed control: the file includes the TGA-LOI correlation tables, the sample preparation rules and the worked examples that convert the TGA curve into the raw mix numbers: the plants that run the TGA daily report the tighter kiln feed chemistry, because the carbonate reading of the instrument reaches the raw mix control hours before the classical analysis: the TGA of the raw meal is the first module of the thermal analysis course of the file.

The calcination degree measurement deserves its own paragraph because it is the most valuable TGA application of the kiln feed control: the sample of the kiln feed or the hot meal is heated in the TGA, and the residual carbonate step above 600°C measures directly how much of the calcination the kiln system has already achieved: the calcination degree of the kiln feed at 90 to 95% is the number that the precalciner control needs, and the TGA delivers it in under an hour against the classical methods that take the same day: the plants that monitor the calcination degree weekly catch the precalciner performance drift before the kiln free lime reacts: the file includes the calcination degree method, the sampling points of the preheater and the correlation with the kiln operation, the module that the kiln engineers of the package value most.

5. The DTA of the Raw Meal: The Clinkering Reactions in Miniature

The differential thermal analysis of the raw meal reproduces the kiln chemistry in the laboratory crucible: the DTA curve of the raw meal shows the endothermic sequence of the drying, the clay water and the calcination, and the high-temperature portion shows the melt formation and the clinker phase reactions that the routine chemistry never sees.

• The endothermic drying: the broad low-temperature peak of the free water, the first event of the curve, overlapped with the equipment drift at the low temperatures;
• The clay dehydration peak: the endothermic doublet at 450 to 650°C, whose shape identifies the kaolinite, the montmorillonite and the illite of the clay component;
• The calcination peak: the strong endothermic peak at 700 to 900°C, whose area is proportional to the carbonate content: the peak temperature and the width carry the information about the limestone particle sizes;
• The melt formation: the endothermic shoulder at 1250 to 1350°C marks the appearance of the first liquid of the clinker system: the shoulder temperature is the direct measurement of the flux effect;
• The alite formation: the high-temperature exothermic events above 1300°C accompany the alite crystallization, the events that the burnability interpretation of the file quantifies;

The DTA of the raw meal is the laboratory mirror of the burnability: the raw meal that shows the melt shoulder at 1350°C will burn harder in the kiln than the meal that melts at 1280°C, and the comparison of the two curves is the fastest burnability screening of the plant: the file includes the reference DTA curves of the typical raw meals, the interpretation tables of the peak temperatures and the correlation of the DTA melt temperature with the kiln free lime: the plants that run the DTA alongside the burnability tests build the two-layer knowledge of their feed: the chemistry of the oxides on one layer and the thermal behavior on the other, and the file teaches the reading of both layers from the single experiment.

6. The Thermal Analysis of the Clinker and the Cement Hydration

The thermal analysis extends beyond the raw meal to the finished products: the clinker and the cement carry their own thermal signatures, and the hydration of the cement in the calorimeter is one of the most informative measurements of the cement quality laboratory.

• The clinker LOI and the moisture: the TGA of the clinker measures the free moisture and the re-carbonation, the numbers that the storage and the dispatch control watch;
• The free lime of the clinker: the classic chemical method measures the free lime, but the TGA-based methods and the derivative peaks give the complementary confirmation for the modern laboratories;
• The gypsum dehydration: the cement sample shows the two gypsum dehydration steps at 120 to 180°C, and the shape of the steps distinguishes the gypsum, the hemihydrate and the anhydrite of the grinding additions;
• The hydration heat by DSC: the isothermal calorimetry of the cement paste records the heat release of the hydration, the early peak of the aluminate and the main peak of the alite: the curve is the fingerprint of the cement’s reactivity;
• The phase quantification: the modern laboratories combine the thermal analysis with the X-ray diffraction to quantify the phases of the clinker and the hydration products at the different ages;

The hydration analysis deserves the special attention of the file, because it connects the cement laboratory to the concrete: the isothermal calorimeter at 20 or 25°C records the heat flow of the paste for the first 24 to 72 hours, and the curve reveals the sulfate balance of the cement, the effect of the grinding aids and the compatibility with the admixtures: the file includes the reference hydration curves of the standard cements, the interpretation rules of the induction period and the peak timing, and the case studies of the cement-admixture incompatibilities that the calorimetry caught while the concrete test still slept: the thermal analysis closes the loop from the raw meal to the concrete, and the file documents the whole loop.

The thermal analysis and the X-ray diffraction form the modern phase-analysis pair of the cement laboratory, and the file explains the partnership: the XRD quantifies the crystalline phases of the clinker and the hydrated cement, while the thermal analysis quantifies the carbonate, the sulfate and the water fractions that the XRD sees poorly, and the combination of the two closes the mass balance of the sample: the modern software merges the datasets into the single phase report, and the laboratories that run the pair report the phase numbers that the classical microscopy confirms within its own uncertainties: the file includes the phase quantification procedures, the correlation exercises between the thermal and the XRD numbers, and the inter-method reconciliation rules: the cement science of the modern laboratory is the science of the complementary instruments, and the thermal analysis is the senior partner of the pair: the file documents the partnership honestly, with the strengths and the boundaries of each method.

7. The Gypsum and the Dehydration Analysis

The gypsum of the finish mill is the regulator of the cement setting, and its dehydration chemistry is a classic subject of the thermal analysis: the calcium sulfate dihydrate loses its water in the two steps, and the TGA-DSC combination records the dehydration with the precision that the setting behavior demands.

• The dihydrate step: the gypsum (CaSO4·2H2O) loses 1.5 molecules of the water at 120 to 150°C, forming the hemihydrate, and the weight step of about 15.7% of the gypsum mass is the first marker;
• The hemihydrate step: the remaining half molecule leaves at 160 to 200°C, and the anhydrite forms: the two steps of the TGA curve identify the sulfate form of the cement;
• The mill temperature effects: the finish mill at 100 to 120°C partially dehydrates the gypsum, and the thermal analysis measures the hemihydrate content that the mill produced: the number explains the false setting complaints;
• The anhydrite control: the natural and the synthetic anhydrites of the additions show no dehydration step, and the TGA quantifies the anhydrite share of the total SO3;
• The setting correlation: the laboratory correlates the sulfate speciation with the setting time and the mortar strength, building the control chart that links the mill temperature to the cement quality;

The gypsum analysis of the file is the practical answer to the classic quality puzzle: the cement that sets too fast or too slow, the false setting incidents and the sulfate balance complaints are all resolved by the thermal analysis of the finish mill product: the file includes the calibration curves of the sulfate forms, the sample preparation rules that protect the dihydrate from the moisture of the grinding, and the interpretation tables that convert the TGA steps into the SO3 speciation report: the plants that run the gypsum thermal analysis weekly report the dramatic reduction of the setting complaints, because the speciation, not the total SO3, is what the concrete actually feels: the file documents the correlation with the field data.

8. The Mineralized and the Alternative Raw Materials

The thermal analysis is the ideal instrument for the study of the non-standard raw materials and the alternative fuels, because it reveals the thermal behavior that the oxide chemistry alone cannot describe: the mineralized mixes, the waste-derived meals and the alternative fuels all carry their thermal surprises, and the laboratory curve catches them before the kiln does.

• The mineralized mixes: the DTA of the fluorine-mineralized raw meal shows the melt shoulder shifted down by 30 to 100°C, the direct laboratory proof of the mineralizer effect that the plant wants to verify;
• The alternative raw materials: the sludge, the ashes and the residues enter the raw mix with their own weight loss curves, and the TGA quantifies their organic and the carbonate fractions for the mix design;
• The alternative fuels: the TGA of the RDF and the biomass measures the moisture, the volatiles and the fixed carbon fractions, the numbers that the firing system design and the combustion control need;
• The combustion studies: the DSC of the fuel samples in the air atmosphere shows the ignition and the burnout temperatures, the indicators of the combustion behavior in the calciner;
• The hazardous residues: the thermal analysis screens the wastes for the mercury and the organic loads before they enter the kiln system, protecting the emission limits of the plant;

The alternative material studies are the growth area of the cement thermal analysis, and the file covers them with the methods and the examples: the lab that characterizes every new waste stream with the TGA-DSC before the plant accepts it protects the process from the surprises that the oxide chemistry misses: the file includes the characterization protocols of the fuels and the raw material substitutes, the acceptance criteria tables and the worked examples of the RDF and the sludge blends: the thermal analysis is the honest broker between the waste supplier and the kiln operator, and the file positions it as such: the material that the kiln has never seen must be seen by the laboratory first, and the thermal curve is the seeing.

9. The Quantitative Methods: Kinetics and the Reaction Enthalpies

Beyond the qualitative curves, the thermal analysis delivers the quantitative kinetics: the activation energies of the calcination and the clinker reactions, the reaction enthalpies and the reaction models that the process simulation needs: the file teaches the methods without the mathematics overload, but with the honest depth of the science.

• The reaction extent: the TGA conversion curves express the calcination degree as a function of the temperature at the fixed heating rate, the laboratory reproduction of the kiln calcination curve;
• The Kissinger method: the shift of the peak temperature with the heating rate yields the activation energy of the reaction, the classic single-peak kinetic analysis;
• The model fitting: the isoconversional and the model-based analyses fit the conversion curves to the reaction models, the Avrami and the diffusion models, and extract the kinetic triplets;
• The enthalpies: the DSC measures the enthalpies of the gypsum dehydration and the carbonate decomposition, the numbers that the heat balance calculations of the plant use;
• The process prediction: the kinetic parameters feed the kiln simulation models that predict the calcination behavior at the real kiln conditions, the bridge between the laboratory and the process;

The quantitative chapter of the file is written for the engineer who needs the numbers without the statistical theater: the activation energy of the limestone calcination runs from 150 to 200 kJ/mol in the reported studies, the enthalpy of the calcination about 1780 kJ per kg of the calcium carbonate, and the kinetic parameters of the plant’s own materials are measured, not borrowed: the file includes the kinetic analysis worksheets, the software procedures of the common packages and the worked examples of the calcination kinetics: the numbers of the chapter turn the thermal analysis from the descriptive tool into the predictive instrument, and the engineer who holds the kinetics of his own raw meal holds the kiln model of his own plant: the file delivers that hold.

The evolved gas analysis completes the quantitative picture with the identity of the released gases: the TGA coupled to the mass spectrometer or the infrared cell follows the CO2 of the calcination, the H2O of the dehydration and the SO2 and the CO of the combustion samples, and the gas traces separate the overlapping weight steps that the mass curve alone cannot resolve: the carbon speciation of the alternative fuels, the organic and the inorganic carbon of the raw materials, and the sulphur release curves of the clinker feeds are the applications that the hyphenated systems serve: the file includes the coupling configurations, the interpretation of the gas profiles and the worked examples of the fuel and the raw material characterizations: the evolved gas analysis is the witness of the reactions, and the file gives the laboratory the procedures to run the witness reliably: the quantitative power of the thermal analysis, the gas identity included, is the full evidence of the material behavior.

10. The Quality Control Applications in the Plant Laboratory

The daily quality control of the plant is the home of the thermal analysis, and the file organizes the applications into the routine of the laboratory:

Table 2: The characteristic thermal events of the cement materials

Material	Thermal event	Temperature range	Typical use
Raw meal	Free moisture loss	Below 105 °C	Moisture control of the feed
Clay minerals	Dehydration	450 – 650 °C	Clay type and content check
Limestone / raw meal	Carbonate decomposition	650 – 950 °C	LOI and carbonate fraction, calcination degree
Raw meal	Clinker melt formation	1250 – 1350 °C	Burnability screening, flux effects
Gypsum in cement	Dihydrate and hemihydrate dehydration	120 – 200 °C	Sulfate speciation, mill temperature control
Hydrating cement paste	Hydration heat peaks	20 – 25 °C (isothermal)	Reactivity, sulfate balance, admixture compatibility

The quality control routines of the file follow the rhythm of the plant: the daily raw meal TGA replacing the LOI muffle analysis, the weekly gypsum speciation of the finish mill product, the monthly clinker re-carbonation check and the calorimetry of the cement dispatch samples: the file includes the standard operating procedures, the control chart templates and the inter-laboratory comparison exercises, because the quality control data are only comparable when the methods are identical: the laboratory manager of the file’s plants runs the thermal analysis as the third pillar of the quality system, next to the chemistry and the physical testing, and the reports of the two pillars confirm each other: the thermal analysis catches the chemistry that the oxides hide, and the file documents the cases where the curves found what the XRF missed.

The accreditation and the proficiency testing close the quality chapter: the modern laboratories run the thermal analysis methods under the ISO 17025 accreditation, and the quarterly proficiency rounds with the reference laboratories verify the comparability of the numbers: the file includes the method validation procedures, the measurement uncertainty budgets and the proficiency round instructions, because the accreditation is not a certificate on the wall but the discipline of the evidence: the round-robin results of the industry show the thermal analysis of the raw meal LOI and the gypsum water comparable within the 0.1 to 0.5% ranges between the accredited laboratories, and the file uses these numbers as the acceptance criteria of its own procedures: the laboratory that participates in the rounds knows its standing against the world, and the file positions the participation as the routine of the professional laboratory: the quality of the thermal analysis is demonstrated, not claimed, and the file demonstrates it.

11. The Sample Preparation and the Sources of Error

The thermal analysis is unforgiving to the sloppy sampling: the sample masses of the milligrams must represent the tons of the plant, and the preparation steps are the largest source of the measurement errors: the file dedicates its error chapter to the discipline of the sample.

• The representative sampling: the plant stream is sampled, crushed, split and ground to below 0.5 mm, and the final aliquot of 10 to 100 milligrams is taken from the homogenized powder: the sampling chain is the error chain;
• The moisture protection: the hygroscopic samples, the raw meals and the gypsum-bearing cements, absorb the ambient water during the handling: the closed containers and the fast measurement are the rules;
• The atmosphere effects: the same raw meal shows the different calcination temperatures in the nitrogen and the CO2 atmospheres, and the atmosphere must be stated with every result;
• The heating rate effects: the peak temperatures shift with the heating rate by tens of degrees, and the comparison of the curves is only valid at the same rate;
• The instrument drift: the balance buoyancy, the furnace gradients and the sensor aging drift the baselines: the baseline subtraction and the calibration runs are the monthly discipline;

The error chapter of the file converts the sources of the error into the checklist of the measurement: the file includes the sampling and the preparation procedures, the baseline correction methods, the validation runs with the reference materials and the audit trail of the results: the laboratory that follows the checklist produces the curves that the plants exchange with the confidence, and the laboratory that does not, produces the artifacts that confuse the decisions: the file is explicit on this point because the thermal analysis industry records show that the majority of the disputed results traced back to the preparation, not to the instrument: the sample is the message, and the file teaches the sending of the clean message.

12. The Interpretation and the Reporting of the Results

The final skill of the thermal analysis is the interpretation and the reporting: the curves of the modern instruments are clean and labeled, but the engineering judgment still decides what the peaks mean for the plant, and the report carries the judgment to the decision makers.

• The curve reading: the baseline, the peak shape and the peak temperature are read together: the sharp symmetric peaks mark the pure single reactions, the broad asymmetric peaks mark the overlapped or the diffusion-limited processes;
• The derivative curves: the first derivative of the TGA (DTG) separates the overlapping weight steps and pinpoints the maximum rate temperatures, the instrument of the fine analysis;
• The quantification: the peak areas and the weight steps are converted to the mass fractions and the enthalpies with the calibration factors, and the uncertainty of each number is stated;
• The correlation with the plant: the laboratory results are correlated with the kiln free lime, the setting times and the strength, building the plant-specific interpretation tables;
• The report: the report states the sample identity, the method, the atmosphere, the heating rate, the curves and the interpretation, in the format that the plant engineers and the auditors both accept;

The reporting discipline of the file follows the laboratory standards and adds the cement-specific templates: the raw meal report, the gypsum speciation report, the fuel characterization report and the hydration study report, each with its fixed sections and its interpretation tables: the file includes the report templates and the worked examples, so the laboratory produces the documents that the plant can act on: the interpretation is the value of the whole method, and the report is the vehicle of the value: the thermal analysis laboratory of the file delivers the curves, the numbers and the judgments in one package, and the plant receives the answers to its questions instead of the data it must question: the file closes the course with this final skill, the communication of the science to the plant.

The interpretation pitfalls close the chapter with the honest warnings: the baseline drift of the aged furnace creates the false peaks that the young analyst interprets as the reactions, the sample that reacts with the crucible material produces the events that belong to the container, and the overlapped dehydration and decomposition steps mislead the eye without the derivative curves: the file teaches the recognition of the artifacts, the duplication of the critical runs and the second-opinion review of the difficult curves: the case studies of the chapter show the false interpretations that cost the plants the wrong conclusions, and the correction paths that the file’s discipline would have caught: the thermal analysis is a powerful instrument and an honest one, but the interpretation is a human skill, and the file builds the skill with the warnings, the exercises and the review procedures: the laboratory that reads the curves with the skepticism of the science earns the trust of the plant, and the file closes its course on that trust.

13. The Frequently Asked Questions

What is the difference between the TGA and the DTA?

The TGA measures the mass of the sample as it is heated, capturing the weight losses of the drying, the dehydration and the decomposition, while the DTA measures the temperature difference between the sample and the inert reference, capturing the heat effects of the reactions: the two methods are complementary, and the modern instruments often record both from the same run.

Can the thermal analysis replace the LOI and the free lime tests?

The TGA complements and in many plants replaces the classical muffle furnace LOI test, because it delivers the moisture, the clay water and the carbonate fractions in one curve: the free lime of the clinker is still measured by the classical chemical method or the titration, with the thermal methods as the confirmation: the replacement decisions follow the validation studies of the specific plant.

Why does the calcination temperature depend on the atmosphere?

The carbonate decomposition is an equilibrium reaction with the CO2: in the nitrogen atmosphere the CO2 is swept away and the decomposition proceeds at the lower temperatures of 650 to 800°C, while in the CO2 atmosphere the equilibrium shifts and the decomposition needs 900 to 950°C: the atmosphere of the measurement must therefore match the question that the laboratory asks.

What sample mass is used for the thermal analysis of the raw meal?

The working range is 10 to 100 milligrams, taken from the homogenized and ground sample: the small mass demands the meticulous sampling chain from the plant stream, and the file prescribes the crushing, splitting and grinding procedures that keep the milligrams representative of the tons.

How does the calorimetry detect the cement-admixture incompatibility?

The isothermal calorimetry records the hydration heat flow of the paste with the admixture: the incompatible combinations show the shortened induction period, the abnormal second peak and the reduced total heat, the signatures that the file correlates with the field problems: the calorimetry catches the incompatibility within hours, while the concrete tests would take days.

14. Conclusion

The thermal analysis is the laboratory mirror of the cement process: the raw meal calcination, the clinkering reactions, the gypsum chemistry and the cement hydration all carry their thermal signatures, and the TGA, the DTA and the DSC read the signatures with the precision that the plant decisions need: the method is old, the instruments are modern, and the value is permanent.

The Complete Cement Technical Package includes this thermal analysis guide with the method descriptions, the reference curves, the interpretation tables and the report templates: the one-time price of $249.99: the instant download: the library of the cement engineer: the curves of the package, the knowledge of the plant: the thermal analysis of your laboratory, mastered from the sample to the report.

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