On the quantitative thermogravimetric analysis of calcite content in hydrated cementitious systems

Calcite is a compound that is present in hydrated cementitious materials when carbonation of portlandite occurs or when limestone constituents are used. The quantification of its content in cementitious systems is then frequently necessary. Thermogravimetry (TG) measures the change in mass of a material (as a function of time) over a temperature range using a predetermined heating rate. It can be applied to estimate calcite content in the hydrated cement system, considering the temperature range at which it decomposes and releases carbon dioxide. However, the quantification is not easy because the onset of this decomposition is a function of many variables. The tangential method over the TG signal or the integration method over the derivative TG curve (DTG) are usually used to discount the background over the temperature range at which calcite decomposes. However, consistent underestimation of compounds is frequently described. The reasons for this are unclear and some hypothesis are discussed in this paper. Additionally, experimental quantitative TG of cement paste and aggregate containing calcite and diluted with low contents of analytical calcite are compared with the expected contents, as a calibration method regarding calcite content in the samples is given to improve the reliability of the results

Cyclic thermogravimetry of TBC systems

The previously developed cyclic thermogravimetry analysis (CTGA) method is applied to the cyclic oxidation at 1100 °C of ZrO2–Y2O3/NiPtAl or NiCoCrAlYTa/single crystal nickel-base AM3 superalloy TBC systems. Cyclic thermogravimetry with fast heating and cooling and high accuracy in mass measurement allows to measure oxidation kinetics of the bond coating and also to detect and quantify the occurrence of the top coating cracking and spalling. The resulting data could be used later on, for time of life modelling of TBC systems

Characterization and biodegradation of poly (vinyl alcohol)/cassava starch

A series of poly (vinyl alcohol)/cassava starch (PVA/CS) blends at 50, 60, 70 and 80 wt.% cassava starch contents were prepared in one-step compounding process. One step compounding means, all blends were compound together without solely plasticized PVA or cassava starch at beginning. All blends were characterized and testing accordingly. In this research, comparison between one-step compounding and two-step compounding (plasticized PVA/CS at the beginning) were tested by tensile strength. It shows that their tensile strengths were comparatively higher than the two-step compounding process of PVA/CS blends. In term of impact test, it indicates that CS acts as non-reinforcing filler. The compatibility of PVA/CS represents the similarity functional group and possess same polar group. Studies on thermal stability and crystallinity shows, increasing the cassava starch loading in PVA matrix, has reduced the enthalpy of melting point as well as degree of crystallinity. The onset degradation had shifted to a higher temperature when a higher percentage of cassava starch was used in PVA matrix. This is due to cyclic hemiacetal had been introduced into PVA blend by cassava starch. It resist to thermal attack. In biodegradability test, several factors have been determined to evaluate the rate of biodegradation. Increase the humidity as well as increasing the cassava starch loading in PVA matrix will improve the susceptibility contact of microorganism onto the surface of PVA/CS blend. Aspergillus Oryzae had been selected as a good reagent used to degrade the sample of PVA/CS blend compared to Bacillus Amyloliquefaciens and effective microorganism. The biodegradation process of PVA/CS blends in anaerobic condition is much more faster compared to aerobic conditions

Thermal Decomposition and Combustion of γ-irradiated Polyamide 6 Containing Phosphorus Oxynitride or Phospham

Polyamide 6 (PA-6) containing the fire retardants phosphorus oxynitride ((PON)m) or phospham ((PN2H)n) was exposed to 60Co-γ-rays (absorbed dose: 1.0–4.0 MGy). The irradiation led to crosslinking of the polymer which caused an increase in the char yield and a decrease in the flammability of the polymer. The combustion behavior was strongly affected by irradiation: dripping was totally prevented in the case of system PA-6/(PN2H)n and strongly retarded in the case of system PA-6/(PON)m. The thermal stability of the system PA-6/(PN2H)n decreased with increasing absorbed dose whereas the thermal stability of the system PA-6/(PON)m did not change

Influence of hydrogen bonds on glass transition and dielectric relaxations of cellulose

The molecular dynamics in hydrated cellulose has been investigated by a combination of thermal analyses and dielectric spectroscopy. Differential scanning calorimetry shows the dependence upon hydration of the glass transition temperature Tg. A physical ageing phenomenon has been observed. At the molecular scale, bound water is hydrogen bonded to polar sites of cellulose macromolecules. At the macroscopic scale, water molecules play the role of a plasticizer for cellulose lowering its Tg. Dynamic dielectric spectroscopy combined with thermostimulated currents have allowed us to follow more localized molecular mobility. The β relaxation mode is characterized by activation entropies that vanish for higher water contents indicating molecular mobility localization. It is plasticized by water like the glass transition. This analogy is explained by a common origin of both mechanisms: the mobility of the cellulose backbone. The evolution of the γ mode upon hydration follows an anti-compensation law. Water acts as an anti-plasticizer in a hydrogen bonded network

Constant rate thermal analysis for thermal stability studies of polymers

This paper explores the relationship between the shapes of temperature-time curves obtained from experimental data recorded by means of constant rate thermal analysis (CRTA) and the kinetic model followed by the thermal degradation reaction. A detailed shape analysis of CRTA curves has been performed as a function of the most common kinetic models. The analysis has been validated with simulated data, and with experimental data recorded from the thermal degradation of polytetrafluoroethylene (PTFE), poly(1,4-butylene terephthalate) (PBT), polyethylene (PE) and poly(vinyl chloride) (PVC). The resulting temperature-time profiles indicate that the studied polymers decompose through phase boundary, random scission, diffusion and nucleation mechanisms respectively. The results here presented demonstrate that the strong dependence of the temperature-time profile on the reaction mechanism would allow the real kinetic model obeyed by a reaction to be discerned from a single CRTA curve.Junta de Andalucía TEP-03002Ministerio de Ciencia e Innovación MAT 2008-06619/MA

Investigation of the Oven Process in Indirect Metal Laser Sintering

This paper deals with the optimization of Indirect Metal Laser Sintering. Different experimental analyses have proven that the oven process is highly responsible for the part distortion. By means of polished micrograph sections and thermogravimetric and dilatometric investigations, the oven process has been divided into four main steps: polymer removal, solid-state sintering, infiltration and liquid-phase sintering. Further experiments were carried out at higher temperature phases of the oven process, using modified process parameters. The aim of this research is to improve the knowledge about the oven process. In another step, this process will be simulated by means of finite element analysis in order to minimize the part distortion.Mechanical Engineerin

Thermooxidative stability of PMMA composites

Tato práce se zabývá studiem termooxidační stability kompozitů polymethylmethakrylátu (PMMA) plněného mikro a nanočásticemi siliky. V připravených vzorcích byly použity různé objemové zlomky a různé velikosti částic siliky. Studium stability bylo prováděno pomocí termogravimetrie, která umožňuje simulovat podmínky termooxidační degradace. Indukční perioda byla stanovena za použití různých rychlostí ohřevu a aplikací izokonverzních metod. Závislosti teplot degradací na rychlostech ohřevu sloužily pro určení parametrů odvozených ze čtyř různých teplotních funkcí, které dovolují předpověď stability materiálu (indukční periody) při zvoleném rozsahu teplot. Zjištěné výsledky ukazují, že větší částice siliky snižuji stabilitu PMMA, zatímco nanočástice v nízkých koncentracích ji nijak neovlivňují.In this work the thermooxidative stability of poly(methyl metacrylate) (PMMA) composites reinforced with silica micro and nanoparticles was studied. Different volume fractions and particles sizes of silica particles were used. PMMA/silica composites were analysed by thermogravimetry which simulated the conditions of thermooxidative degradation. The induction periods were determined using different heating rates and applying the isoconversional methods. The dependence of degradation temperatures on heating rates were used for the determination of adjustable parameters derived for four different temperature functions allowing the prediction of material stability (induction periods) at chosen temperatures. Results showed that the larger silica particles destabilized the PMMA structure while smallest nanoparticles at low concentration had no effect on the stability.

New frontiers in thermal analysis: A TG/Chemometrics approach for postmortem interval estimation in vitreous humor

The coupling of thermogravimetric analysis (TG) associated with chemometrics is proposed as an innovative approach in thanatochemistry in order to develop a new analytical tool using thermal analysis for the characterization of vitreous humor. Vitreous samples were selected from the medicolegal deaths which occurred in casualty and where the death interval is known. Only hospital deaths with no metabolic disorders were taken, and the precise time of death was certified by the treating physician. Samples were analyzed by TG7 thermobalance, and principal component analysis was used to evaluate the results. The TG/Chemometrics outcomes show a clearly distinct behavior according to the postmortem interval, concluding that TG and Chemometrics are capable of predicting the time since death using only a few microliters of vitreous, without any pretreatment and with an hour of analysis tim

Thermogravimetric kinetics of crude glycerol.

The pyrolysis of the crude glycerol from a biodiesel production plant was investigated by thermogravimetry coupled with Fourier transform infrared spectroscopy. The main gaseous products are discussed, and the thermogravimetric kinetics derived. There were four distinct phases in the pyrolysis process of the crude glycerol. The presence of water and methanol in the crude glycerol and responsible for the first decomposition phase, were shown to catalyse glycerol decomposition (second phase). Unlike the pure compound, crude glycerol decomposition below 500 K leaves behind a large mass fraction of pyrolysis residues (ca. 15%), which eventually partially eliminate in two phases upon reaching significantly higher temperatures (700 and 970 K, respectively). An improved iterative Coats-Redfern method was used to evaluate non-isothermal kinetic parameters in each phase. The latter were then utilised to model the decomposition behaviour in non-isothermal conditions. The power law model (first order) predicted accurately the main (second) and third phases in the pyrolysis of the crude glycerol. Differences of 10-30 kJ/mol in activation energies between crude and pure glycerol in their main decomposition phase corroborated the catalytic effect of water and methanol in the crude pyrolysis. The 3-D diffusion model more accurately reproduced the fourth (last) phase, whereas the short initial decomposition phase was poorly simulated despite correlation coefficients ca. 0.95-0.96. The kinetics of the 3rd and 4th decomposition phases, attributed to fatty acid methyl esters cracking and pyrolysis tarry residues, were sensitive to the heating rate