Kinetic model of the ammonium chloride sublimation process

Thermal analysis is widely used for the measurement of the relationship between temperature and physical properties of the materials. Many studies have reported different thermal analysis methods, including thermogravimetry (TG), derivative thermogravimetry (DTG), differential heat analysis (DTA), and differential scanning calorimetry (DSC), but few comprehensively studied the factors influencing TG-DTA by the combined thermogravimetry–differential thermal methods. In this study, taking chalcanthite as the research object, the thermogravimetric–differential thermal analyses were systematically conducted by using synchronous thermal analyzer technology. The results demonstrate that 1) DTA curves of low- and medium-weight chalcanthite show five dehydration endothermic peaks, while TG curves do not display obvious weight-loss steps; DTA and TG curves of high-weight chalcanthite samples, on the other hand, illustrate three endothermic peaks, indicating three-step loss of crystalline water; 2) higher weight of samples may cause longer time of internal heat transfer and larger temperature gradient, consequently resulting in the expansion of DTA peak shape and the decline of resolution as well as the increase of the peak temperature; 3) the weight-loss deviation between the measured and theoretical data is relatively higher in the low-weight samples than that in the medium- and high-weight samples; 4) the heating rate can increase the DTA curve peak and thermal inertia and the temperature at the thermodynamic equilibrium, causing the temperature lagging behind and the overall peak moving toward high temperature; 5) sample grinding may destroy the structure of the crystal, thereby breaking the relatively weak chemical bond, and thus affects the structure of thermogravimetric–differential thermal analyses. These suggest that the sample weight, heating rate, and sample grinding probably have significant effects on the thermogravimetric–differential thermal analyses. Therefore, proper experimental conditions are needed to obtain the accurate results during the thermogravimetric–differential thermal analyses. This study can provide a basis and reference for future synchronous thermal analyses.

ABSTRACTDifferential scanning calorimetry (DSC) analysis is a standard thermal analysis technique used to determine the phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy of phase change materials (PCMs). To determine the appropriate heating rate and sample mass, various DSC measurements were carried out using two kinds of PCMs, namely N-octadecane paraffin and calcium chloride hexahydrate. The variations in phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy were observed within applicable heating rates and sample masses. It was found that the phase transition temperature range increased with increasing heating rate and sample mass; while the heat of fusion varied without any established pattern. The specific heat decreased with the increase of heating rate and sample mass. For accuracy purpose, it is recommended that for PCMs with high thermal conductivity (e.g. hydrated salt) the focus will be on heating rate rather than sample mass.

Thermal analysis has been proven to be an efficiently technique to analyse thermal decomposition reactions of different type of materials. This technique is widely used in different fields. Among them, fire science, where polymeric materials are very common, has a particular issue, being the combustion reactions recurrent on these analyses. Thermal analysis has different particularities depending on the studied material. For instance, polymeric materials could undergo different decomposition reactions that are highly dependent on definition of the thermal analysis boundary conditions. The International Confederation for Thermal Analysis and Calorimetry (ICTAC) (Vyazovkin et al. in Thermochim Acta 590:1–23, 2014) and standards (ISO 11358-1. Plastics—Thermogravimetry (TG) of polymers—Part 1: General principles. ISO. 2014; https://www.iso.org/standard/59710.html. Accessed 31 Jan 2022), (ISO 11357-1. Plastics — Differential scanning calorimetry (DSC) — Part 1: General principles. ISO. 2016; https://www.iso.org/standard/70024.html. Accessed 31 Jan 2022) stablish how to set-up these boundary conditions in the thermogravimetric (TG) and differential scanning calorimetry (DSC) standards. As far as initial amount of sample mass is concern, some discrepancies can be found between the standards. For instance, the standards suggest a sample mass between 10 and 100 mg for TG and between 2 and 40 mg for DSC, whereas the ICTAC recommendations suggests that the sample mass times the heating rate should not exceed 100 mg K·min−1 in thermo-oxidative decomposition analysis, which is equivalent to samples masses lower than 10 mg for heating rates of 10 K·min−1, or lower than 5 mg for heating rates of 20 K·min−1. This discrepancy may lead to obtain different results from the tests. Additionally, according to the thermal and thermo-oxidative decomposition of polymers, the ICTAC remarks the influence on the results of the sample thicknesses, carrier gas and heating rates, but it does not analyse the influence of self-heating as it does for the hazardous materials. This work presents a study of the self-heating influence in the thermal decomposition processes of two widely used polymers as poly methyl methacrylate (PMMA) and linear low-density polyethylene (LLDPE). TG/DSC tests are used to evaluate the thermal decomposition processes. Boundary conditions of the tests definition as sample mass, atmospheres, and heating rate are considered to evaluate its influence on the polymers self-heating effect on the thermal decomposition. It also includes how to check if TG/DSC tests follows the theoretical principles of the thermal analysis, or if the results are affected by the self-heating. In the present study, a series of 32 experimental tests has been performed, analysing 16 boundary conditions. These experimental tests allow evaluating the influence of selected boundary conditions on the mass loss, the heat flux, and the materials decomposition reactions. Additionally, we analyse the effect of the boundary conditions on the temperature of the sample. Results show the impact of each different boundary conditions of the self-heating effect, and its influence in the final thermal decomposition measured and they represent an aid to define the suitable conditions to perform TG/DSC test on PMMA and LLDPE, or similar polymer materials. This is done by the evaluation of the influence of the self-heating in parameters as the sample temperature lags defined in [1], the reactions heat fluxes, and the difference between the sample and the programmed temperature. It is also analysed the influence of the auto-ignition temperature in the thermal analysis. It is remarkable the PMMA auto-ignition temperature effect on the TG/DSC results. Finally, some useful recommendations have been defined.

Despite the large use of differential scanning calorimetry (DSC) technique in advanced polymer materials characterization, the new methodology called DSC in high heating rates was developed. The heating rate during conventional DSC experiments varying from 10 to 20oC.min -1 , sample mass from 10 to 15mg and standard aluminum sample pan weighting, approximately, 27mg. In order to contribute to a better comprehension of DSC behavior in different heating rates, this work correlates as high heating rate infl uences to the thermal events in DSC experiments. Samples of metallic standard (In, Pb, Sn and Zn) with masses varying from 0.570mg to 20.9mg were analyzed in multiples sample heating rate from 4 to 324°C. min -1 . In order to make properly all those experiments, a precise and careful temperature and enthalpy calibrations were performed and deeply discussed. Thus, this work shows a DSC methodology able to generate good and reliable results on experiments under any researcher choice heating rates to characterize the advanced materials used, for example, for aerospace industry. Also it helps the DSC users to fi nd in their available instruments, already installed, a better and more accurate DSC test results, improving in just one shot the analysis sensitivity and resolution. Polypropylene melting and enthalpy thermal events are also studied using both the conventional DSC method and high heating rate method.

Thermogravimetry (TG) is the study of the relationship between a sample's mass and its temperature. It can be used to study any physical (such as evaporation) or chemical process (such as thermal degradation) that causes a material to lose volatile gases. Polymers have different thermal stabilities and thus the qualitative “fingerprint” afforded by TG in terms of temperature range, extent and kinetics of decomposition provides a rapid means to distinguish one polymer from another using only milligram quantities of material. Experiments are most commonly carried out under conditions where the temperature is increased in a linear fashion with time or the sample is held isothermally at an elevated temperature, although more sophisticated temperature profiles are occasionally used for compositional and kinetic analysis. Processes which do not result in a change in sample mass are not detected by TG. Therefore simultaneous measurements by differential scanning calorimetry (DSC) are useful. Volatile decomposition products may be detected and identified (e.g. by infrared (IR) spectrometry or mass spectrometry (MS)) in order to elucidate the mechanism of mass changes. TG is used for quantitative compositional analysis of polymers, lifetime prediction and kinetic studies, making the technique invaluable in all stages of polymer development, fabrication and component testing.

Thermogravimetry is the study of the relationship between a sample's mass and its temperature. Thus it is possible to study physical or chemical processes that cause a material to lose volatile gases. These include sublimation, evaporation, and thermal degradation. Experiments are most commonly carried out under conditions where the temperature is increased in a linear fashion with time or the sample is held isothermally at an elevated temperature. More sophisticated temperature profiles are occasionally employed for compositional and kinetic analysis. Processes that do not result in a change in sample mass are not detected by this technique. Therefore, simultaneous measurements by differential scanning calorimetry are useful. Volatile decomposition products may be detected and identified (e.g. by infrared spectrometry or mass spectrometry) in order to elucidate the mechanism of mass changes. Thermogravimetry is used for quantitative compositional analysis of many substances, lifetime prediction and kinetic studies making the technique invaluable in many areas of materials characterisation.

A calorimetric method for determining isothermal partial and integral heats of hydration reactions (ΔH¯R,T,P${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ and ΔH∼R,T,P${\rm{\Delta }}{\tilde H_{{\rm{R,}}T,\,P}}$, respectively) in zeolites and other mineral hydrates is presented. The method involves immersing a dehydrated sample in a humid gas stream under isothermal conditions within a thermal analysis device that records simultaneous differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA) signals. Monitoring changes in sample mass (corresponding to extent of reaction progress) coincident with a quantitative measurement of heat flow allows for direct detection of ΔH¯R,T,P${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ as a function of the extent of hydration, which can be integrated to determine ΔH∼R,T,P${\rm{\Delta }}{\tilde H_{{\rm{R,}}T,\,P}}$. In addition, it eliminates uncertainties associated with imprecise knowledge of the starting and final states of a sample during hydration. Measurement under isothermal conditions removes uncertainties associated with heat capacity effects that complicate interpretations of DSC measurements of dehydration heats conducted under traditional scanning temperature conditions. Example experiments on the zeolites natrolite, analcime and chabazite are used to illustrate strategies for quantifying ΔH¯R,T,P${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ and ΔH∼R,T,P${\rm{\Delta }}{\tilde H_{{\rm{R,}}T,\,P}}$ and minimizing errors associated with baseline uncertainties. Results from this method agree well with previously published values determined by other calorimetric techniques and regression of phase equilibrium data. In the case of chabazite, the results allowed detailed measurements of the variation in ΔH¯R,T,P${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ for energetically different water types encountered progressively as the sample absorbed water. This technique complements and in many cases improves the quality of thermodynamic data obtained through phase equilibrium observations and other calorimetric techniques.

We studied the effects of two common chemical extraction techniques on bottlenose dolphin (Tursiops truncatus) skin tissues with the intent to develop a mathematical lipid correction for dolphin skin δ13C. One method employs a hot solvent mixture (chloroform and methanol) while the other method requires washing the samples with cold solvent followed by water. The water wash method resulted in significant alteration of tissue δ15N. We found no correlation between change in sample mass and C/N or between change in sample mass and the change in δ13C (Δδ13C) following lipid extraction. Although Δδ13C was positive following lipid extraction (mean = 1.6‰ and 1.2‰, for the two methods), there was no correlation between C/N and Δδ13C for either method. Cumulatively, these results prevented us from applying a mathematical lipid normalization. Based on our findings and consideration of previously reported results, we suggest that applying these extraction techniques to dolphin skin with C/N < 4.5 introduces greater uncertainty than is warranted. We recommend against lipid correction for dolphin skins with C/N < 4.5, but stress that the resulting uncertainty in δ13C needs to be accounted for when implementing isotope mixing models to assess diet or organic matter sources.

The results of experimental studies of the behavior of fireproof materials of Russian production – OGNEZA-LTU, OGNEZA-M-KOR, OG-NEZA-M-KOR (NG), «OGNEBAZALT» PMBOR, OGNEZA-GT under thermal action are presented. Research method – synchronous thermal analysis TG/DCS/dDSC, including differential scanning calorimetry (DSC) and thermogravimetry (TG). Experimental conditions on the NETZSCH thermal analyzer: measurement mode – TG/DCS/dDSC; heating rate: 20 °C /min; heating – up to 1000 °С; atmosphere – N2. The rates of weight loss of the investigated fire-retardant materials have been studied. A high rate of weight loss was established for the OGNEZA-LTU samples (20.5 %/ min at 335 °C) and OGNEZA-GT (11.9 %/min at 369 °C); low – OGNEZA-M-KOR (NG) – 1.7 %/min at 349 °C, OGNEZA-M-KOR – 6.1%/min at 341 °C, «OGNEBASALT» PMBOR - 3.5 %/min at 388 °С. Time intervals of weight loss were determined: all test samples had maximum weight loss in the range of 15-20 minutes. The temperature ranges of the maximum rate of weight loss were determined: 349 - 388 °C. The best heat-resistant properties were shown by OGNEZA-M-KOR (NG), «OGNEBASALT» PMBOR, OGNEZA-M-KOR. It is proposed to consider the revealed properties when using fire retardant materials for the constructive fire hazard of civil and industrial facilities.

Despite the large use of differential scanning calorimetry (DSC) technique in advanced polymer materials characterization, the new methodology called DSC in high heating rates was developed. The heating rate during conventional DSC experiments varying from 10 to 20oC.min-¹, sample mass from 10 to 15mg and standard aluminum sample pan weighting, approximately, 27mg. In order to contribute to a better comprehension of DSC behavior in different heating rates, this work correlates as high heating rate influences to the thermal events in DSC experiments. Samples of metallic standard (In, Pb, Sn and Zn) with masses varying from 0.570mg to 20.9mg were analyzed in multiples sample heating rate from 4 to 324°C. min-¹. In order to make properly all those experiments, a precise and careful temperature and enthalpy calibrations were performed and deeply discussed. Thus, this work shows a DSC methodology able to generate good and reliable results on experiments under any researcher choice heating rates to characterize the advanced materials used, for example, for aerospace industry. Also it helps the DSC users to find in their available instruments, already installed, a better and more accurate DSC test results, improving in just one shot the analysis sensitivity and resolution. Polypropylene melting and enthalpy thermal events are also studied using both the conventional DSC method and high heating rate method.

The energy value of fossil fuels may be improved by changing their excess moisture content. In studying the development of heat and mass transfer in the heating of coal samples at a rate of 5°C/min in air, with the plotting of a complete differential scanning calorimetry (DSC) curve, it is found that initial heating of the coal sample is accompanied by the removal of physical moisture up to 180°C and increase in its heat content (period 1). At ~340°C, oxidation of carbon develops, with the release of excess heat (period 2). The intensity of heat emission may be judged from the change in sample mass at 460–676°C. Heating period 3 (up to 740°C) is associated with endothermal decomposition of the coal components and culminates in combustion of the combustible mass. On the basis of the kinetics of moisture removal from a weighed sample on isothermal heating at 250°C in a 2-m/s air flux, the total drying time is found to be 229 min, with increase in the rate of moisture removal for 12 min and steady drying for 20 min. According to the laws governing the motion of friable materials in a drum-type dryer, the drying time for coal with a mean moisture content of 9% is 20–28 min, with 20–25% mean filling of the working space. To prevent restoration of the moisture content of a dried coal sample in air, the total drying time cannot exceed 64–88 min, while drying must end with a residual moisture content of at least 7%.

Despite many studies of heavy oil oxidation characteristics, kinetic mechanisms with the comparison of different kinetics models are not well understood, because of the complexities of oil components and nonisothermal oxidation processes. Moreover, it is urgent to further evaluate the feasibility and accuracy variations of different kinetic models to optimize the kinetic model for specific situations and purposes. Therefore, thermogravimetry (TG-DTG)/differential scanning calorimeter (DSC-DDSC) thermograms under different heating rates were comprehensively studied in this work to elucidate the nonisothermal oxidation behavior with the heating rate influence. Then, based on the comparison analysis of model-fitting and model-free methods, the comparisons of kinetic parameters, reaction order, and activation energy distribution were evaluated. In addition, the results indicated the nonisothermal oxidation kinetics parameters varied with the reaction orders and kinetic models. Besides, an obvious increase of low-temperature oxidation (LTO) activation energy resulted from the negative temperature coefficient (NTC) effect. Moreover, the preferable kinetic model is ascribed to the specific analysis purposes, as well as the acceptable accuracy of the calculated result and the model practicability.

The aim of this study was to determine the impact of the heating rate of steel balls made of AISI 52100 alloy steel on the kinetics and efficiency of the gas nitriding process when carried out using a chemical reactor with precise thermo-gravimetric measurements, which allowed for changes in sample mass during heating and nitriding to be monitored with an accuracy of 50 µg. In the chemical reactor, the examined alloy steel was subjected to a heating process at the selected nitriding temperature of 590 °C. Two heating variants were used: the first variant relied on heating to the nitriding temperature with different rates-1 °C per minute, 2 °C per minute, 5 °C per minute and 10 °C per minute, respectively-whereas the second variant relied on the fast-25 °C per minute-heating of treated specimens to a temperature of 475 °C, at which, the nitrogenous potential of the atmosphere promotes faster nitrogen diffusion deep into the nitrided substrate, followed by reheating up to the nitriding temperature at different rates: 1 °C per minute, 2 °C per minute, 5 °C per minute, and 10 °C per minute, respectively. To evaluate the impact of heating rate kinetics and effectiveness during nitriding on the obtained surface layer quality, we investigated the phase composition, microhardness distribution, and thickness of the obtained diffusion layers. It was found that heating to a temperature of 475 °C in the nitriding process does not significantly affect the average mass gain of a sample. Above this temperature, within the range of nitriding temperatures, the extension of time increases the sample's mass gain. Simultaneously, it was found that the use of a constant heating rate allows for thicker nitrided layers and a greater sample hardness to be obtained. Dual-stage heating, in turn, is more effective in the context of sample mass gain per time unit.

To track changes in organic matter (OM) in peat soils, analytical techniques are needed that effectively characterize their chemical components. Pyrolysis-gas chromatography/mass spectrometry is a useful method for obtaining a chemical “fingerprint” of OM. To obtain representative fingerprints, the pyrolysis process should be highly reproducible and representative of the original sample; however, these key indicators for successful volatilization are underreported in the literature. We investigated the influence of instrumental parameters (temperatures, heating rates, sample mass), original organic C and nitrogen (N) content, and instrument type (“slow” vs “flash”), on volatilization of different peat samples by monitoring sample mass loss and changes in organic C and N content before and after pyrolysis. Average percent C by mass volatilized (“C pyrolysis efficiency”) across all pyrolysis experiments conducted (mass, instrument types, and settings) was 47.8 ± 1.8%. Sample mass was not a major driver; however, instrument temperatures, heating rate, and original N content had a significant influence on pyrolysis efficiency. N pyrolysis efficiency occurred at significantly higher rates (56.7–75.8%) than C pyrolysis efficiency (45.1–51.6%). N pyrolysis efficiency was also negatively influenced by decreasing concentrations of original sample N, suggesting that N-containing compounds may undergo preferential volatilization in high pyrolysis temperatures. Our data suggest that C pyrolysis efficiency is relatively insensitive to instrumental parameters; whereas when seeking to identify N-containing compounds, appropriate temperatures and heating rates must be chosen. These results provide an expected range for pyrolysis efficiency as a reference for peat samples analyzed with this technique.

Thermal behaviour kinetic study of dihydroglyoxime and dichloroglyoxime