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THERMAL ANALYSIS IN METTLER TOLEDO'S TGA/DSC1 UNIT
Thermal analyses (TGA, DTG, DTA, and DSC) of construction materials are useful for detection of various hydrous, carbonate, and sulfate phases from their characteristic decomposition temperatures and associated weight changes (as detected in TGA and DTG) or differential temperature change (in DTA) or change in heat flow (detected in DSC), such as:
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120-150°C = Ettringite decomposition from cement paste (thaumasite at 150ºC) and water release (endotherm)
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120, 180-200°C = Gypsum decomposition and water release (endotherm)
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100-200ºC = Hydrate water from decomposition of calcium silicate hydrate (CSH)
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300-400°C = Brucite decomposition from dolomitic lime mortar (or from soluble magnesium salts in the paste from the use of natural cement) and water release (endotherm)
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400-600°C = Portlandite decomposition from Portland cement paste and water release (endotherm)
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500-680°C = Magnesite decomposition for dolomitic lime mortar (endotherm)
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573°C = Alpha-to-beta polymorphic transformation of quartz the main component of silica sand in mortar
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620-690°C = Calcite decomposition for cryptocrystalline calcite formed during carbonation of lime in mortar
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680-800°C= Calcite decomposition for coarsely crystalline calcite in limestone or marine shells (endotherm)
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740-800ºC = Dolomite decomposition (endotherm)
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>950°C = Slight exotherm from initial surface reaction of lime and silica, followed by larger endotherm from melting.
CMC has a Mettler-Toledo TGA/DSC1 thermal analysis unit that can analyze up to 34 samples simultaneously to determine various hydrous, sulfate, and carbonate phases in construction materials.
METTLER TOLEDO'S ONLINE TUTORIALS ON THERMAL ANALYSIS AND SOFTWARE
This tutorial from Mettler Toledo explains standard calibrations for our TGA/DSC1 unit
This video provides information about the benefits of differential scanning calorimeters from METTLER TOLEDO
This video provides information about the benefits of the STARe thermal analysis software
This tutorial from Mettler Toledo explains DSC calibration and adjustment
This tutorial from Mettler Toledo explains TGA sample robot, the efficient and robust automation solution in thermal analysis that greatly increases sample output in CMC's thermal analysis lab
This video demonstrates the basic operation of the STARe Thermal Analysis Evaluation software
In this TGA tutorial, Mettler Toledo provides information on how Thermogravimetric Analysis (TGA) can be applied to help solve analytical problems
This tutorial from Mettler Toledo explains interpretation of DSC curves
This tutorial from Mettler Toledo explains interpretation of TGA curves
METTLER TOLEDO'S BROCHURES ON TGA/DSC1 AND STAR SOFTWARE
SAMPLE PREPARATION FOR
THERMAL ANALYSIS
Simultaneous TGA and DSC analyses are done in Mettler Toledo TGA/DSC 1 unit on 30-70 mg of finely ground (<0.6 mm) mortar in alumina crucible (70 µl, no lid) from 30°C to 1000°C at a heating rate of 10°C/min with high purity nitrogen as purge gas at a flow rate of 75.0 ml/min. Additional DSC analyses were done in TGA/DSC 1 on finely ground (<0.6 mm) mortar (30-70 mg) in sealed aluminum crucible (100 µl, sealed with a pierced lid) from 30°C to 600°C at a heating rate of 10°C/min with nitrogen purge gas at a flow rate of 75.0 ml/min.
HOW WE DO THERMAL ANALYSIS
DEHYDRATION & DECARBONATION OF CALCIUM OXALATE MONOHYDRATE
Calcium oxalate monohydrate is used as a tutorial sample to demonstrate the decomposition reaction and stoichiometry in Mettler Toledo's TGA/DSC1 unit. Calcium oxalate monohydrate decomposes in three reaction steps shown in the above figure. The TGA curve shows three weight loss steps in agreement with the three-step reaction scheme given above. The loss of water of crystallization and the two decomposition steps yielded weight losses of 12.3%, 19.2% and 30.1% respectively. This is in good agreement with the theoretical stoichiometric values based on the fact that one mole of CaC2O4⋅H2O gives rise to one mole each of H2O, CO and CO2.
THERMAL ANALYSIS OF A STANDARD MIX OF SILICA SAND, PORTLAND CEMENT, CALCITE, AND BRUCITE
In order to determine quantitative proportions of various phases in a masonry mortar, a standard mix having known proportions of 70% silica sand, 20% Portland cement, 5% calcite, and 5% brucite is mixed at a water-cement ratio of 0.50 and cured for 7 days to be hardened and used for recovering mineral proportions by thermal analysis in TGA/DSC1. Results show a good recovery of 69% quartz, 4.6% brucite, and 4.8% calcite from TGA, DSC, and DTG curves. This standard mix represents a good candidate for many conventional cement-lime mortars made using Portland cement, dolomitic lime, and silica sand.
THERMAL ANALYSIS OF A HISTORIC NATURAL CEMENT LIME MORTAR
TGA (bold black), DSC (dotted red), and DTG (dashed blue) curves of a historic natural cement-lime mortar from Fort Zachary Taylor, Key West Florida showing losses in weight due to various decompositions (loss of water and cardon dioxide) during controlled heating in a Mettler-Toledo’s simultaneous TGA/DSC 1 unit from 30ºC to 1000ºC in a ceramic crucible (alumina 70µl, no lid) at a heating rate of 10ºC/min in a nitrogen purge at a rate of 75 ml/min. In the TGA curve, successive losses in weights at (i) 50-250ºC, (ii) 300-450ºC, (iii) 400-600ºC, (iv) 600-750ºC, and (v) 700-850ºC are due to water release from (i) capillary pores and CSH, (ii) brucite, (iii) portlandite, and CO2 release from (iv) finely crystalline calcite in cabronated paste, and (v) coarsely crystalline calcite in seashells, respectively. Dehydration and decarbonation reactions are marked as endothermic peaks in the superposed DSC and DTG curves. DSC curve does not show any polymoprhic transition from alpha to beta form of quartz at 573ºC that is common in many masonry mortars made using silica (quartz) sand (due to the use of carbonate beach sand). A small hump in the DSC-DTG curves at 800ºC is due to dissociation of halite. Portlandite component of cement hydration is mostly carbonated, hence did not show noticeable decomposition peak in the DTG or DSC curves.
THERMAL ANALYSIS OF A
POINTING MORTAR
TGA (bold black), DSC (dotted red), and DTG (dashed blue) curves of stone-pointing mortar showing losses in weight due to various decompositions (loss of water and cardon dioxide) during controlled heating in a Mettler-Toledo’s simultaneous TGA/DSC 1 unit from 30ºC to 1000ºC in a ceramic crucible (alumina 70µl, no lid) at a heating rate of 10ºC/min in a nitrogen purge at a rate of 75 mL/min. In the TGA curve, successive losses in weights at (i) 50-250ºC, (ii) 300-450ºC, (iii) 400-600ºC, (iv) 600-750ºC, and (v) 700-850ºC are due to water release from (i) capillary pores and CSH, (ii) brucite, (iii) portlandite, and CO2 release from (iv) finely crystalline calcite in cabronated paste, and (v) coarsely crystalline calcite, respectively. Dehydration and decarbonation reactions are marked as endothermic peaks in the superposed DSC and DTG curves. DSC curve shows polymorphic transition from alpha to beta form of quartz at 573ºC from silica (quartz) sand. Portlandite component of cement hydration is less carbonated, hence shows noticeable decomposition peak in the DTG or DSC curves.
THERMAL ANALYSIS OF A
GYPSUM DECK
Thermogravimetric analysis (TGA, black solid line), first derivative of TGA (DTG, blue dashed line), and differential scanning calorimetry (DSC, red dotted line) of gypsum roof deck. Semi-quantitative analyses showed about 70% gypsum and 16% calcite from thermal decompositions.
SOME RELEVANT PUBLICATIONS ON APPLICATIONS OF THERMAL ANALYSIS IN CONSTRUCTION MATERIALS
Copyright materials, not to be downloaded
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