High-temperature Thermogravimetric Analysis Research Articles

Experimental study on the kinetics of magnesiohornblende dehydration and its implications

Abstract Magnesiohornblende dehydration was studied using both high-temperature thermogravimetric analysis and high-pressure differential thermal analysis (HP-DTA). The high-temperature thermogravi-metric analysis results revealed that magnesiohornblende dehydration at high temperatures could be divided into three steps: 848–1058, 1058–1243, and 1243–1473 K, and each step followed an n-order reaction (Fn). The dehydration process is characterized by an oxidation-dehydrogenation mechanism, and the dehydration of the last step can be explained as the direct decomposition of the hydroxyl groups connected to the magnesium ions. The HP-DTA of magnesiohornblende dehydration under pressures of 0.5, 1.0, 2.0, and 3.0 GPa revealed the occurrence of two endothermic peaks, indicating that the dehydration occurs in two steps at high temperature and pressure. Our experimental results reveal that during subduction, the fluid released during the dehydration of magnesiohornblende may trigger earthquakes and cause high electrical conductivity anomalies in the subduction zones.

Nanostructured SiC/BN/C ceramics derived from mixtures of B3N3H6and [HSi(Me)C≡C]n

AbstractThree borazine-modified polycarbosilanes were synthesized by reaction of poly[1,2-ethynediyl-(methylsilylene)], [HSi(Me)C≡C]n, and borazine, B3N3H6using different stoichiometries. The polymeric precursors were transformed into inorganic Si–B–C–N materials by solid state thermolysis at 1400 °C each in 88% yield. High temperature thermogravimetric analysis in an argon atmosphere showed no substantial decomposition reactions below 1800 °C. Crystallization behavior up to 2000 °C in a nitrogen atmosphere was studied by post-thermolysis heat treatment of as-obtained ceramics at various temperatures and subsequent examination of samples at room temperature using powder X-ray diffraction. Ceramics annealed at 1800 °C were additionally characterized by transmission electron microscopy.

Interaction of O2, H2O and H2 with proton-conducting oxides based on lanthanum scandates

An interaction of components from the gas phase, containing gaseous oxygen, hydrogen and water, with the La1–xSrxScO3–α oxides in the temperature range of 300–950 °С and partial pressure of 6.1–24.3 kPa 8.1–50.7 kPa has been studied using a high temperature thermogravimetric analysis. The effects of partial pressure of the gaseous oxygen, water and hydrogen on the apparent uptake level of protons with oxides has been found. The studies of incorporation processes of hydrogen from molecular hydrogen atmosphere into the structure of proton-conducting oxides based on strontium-doped lanthanum scandates were performed in the temperature range of 300–800 °C and hydrogen pressure of 0.2 kPa by means of the isotope exchange method with the equilibration of isotope composition in the gas phase. The protons and deuterons concentrations were determined for the La0.91Sr0.09ScO3–α oxide. The existence of proton defects in the structure of studied oxides after the exposure in H2O and H2-containing atmospheres was revealed using the 1Н NMR. The role of oxygen vacancies in the proton incorporation processes is considered in the present work.

Interaction of H2O, O2 and H2 with Proton Conducting Oxides Based on Lanthanum Scandates

The research uses the method of high-temperature thermogravimetric analysis to study the processes of interaction of the gas phase in the temperature range 300–950 °C in the partial pressure ranges of oxygen 8.1–50.7 kPa, water 6.1–24.3 kPa and hydrogen 4.1 kPa with La1–xSrxScO3–α oxides (x = 0; 0.04; 0.09). In the case of an increase in the partial pressure of water vapor at a constant partial pressure of oxygen (or hydrogen) in the gas phase, the apparent level of saturation of protons is shown to increase. An increase in the apparent level of saturation of protons of the sample also occurs with an increase in the partial pressure of oxygen at a constant partial pressure of water vapor in the gas phase. The paper discusses the causes of the observed processes. The research uses the hydrogen isotope exchange method with the equilibration of the isotope composition of the gas phase to study the incorporation of hydrogen into the structure of proton-conducting oxides based on strontium-doped lanthanum scandates. The concentrations of protons and deuterons were determined in the temperature range of 300–800 °C and a hydrogen pressure of 0.2 kPa for La0.91Sr0.09ScO3–α oxide. The paper discusses the role of oxygen vacancies in the process of incorporation of protons and deuterons from the atmosphere of molecular hydrogen into the structure of the proton conducting oxides La1–xSrxScO3–α (x = 0; 0.04; 0.09). The proton magnetic resonance method was used to study the local structure in the temperature range 23–110 °C at a rotation speed of 10 kHz (MAS) for La0.96Sr0.04ScO3–α oxide after thermogravimetric measurements in an atmosphere containing water vapor, and after exposures in molecular hydrogen atmosphere. The existence of proton defects incorporated into the volume of the investigated proton oxide from both the atmosphere containing water and the atmosphere containing molecular hydrogen is unambiguously shown. The paper considers the effect of the contributions of the volume and surface of La0.96Sr0.04ScO3–α oxide on the shape of the proton magnetic resonance spectra.

Sulfur removal from petroleum coke during high-temperature pyrolysis. Analysis from TG-MS data and ReaxFF simulations

Petroleum coke (petcoke) contains high carbon and low ash qualities, but often with an undesirably high sulfur content. High-temperature (>1000 K) calcination produces a coke, suitable for many industrial uses, with an acceptable S content. Here the sulfur removal behavior during high-temperature pyrolysis was evaluated by combining high-temperature thermogravimetric analysis with product gas mass spectrometry (TG-MS), and reactive molecular dynamics (ReaxFF) simulations. From the TG-MS data the pyrolysis temperature of >1000 K significantly affected the S rejection. Three petcokes under 1273–1773 K in six different particle sizes (≤6 mm) were pyrolyzed to determine the desulfurization initiation temperature and desulfurization extent. A non-uniform behavior across the particle size ranges was obtained. Six Qingdao petcoke samples with cut sizes of <0.038, 0.07–0.05, 0.11–0.09, 0.25–0.15, 1.18–0.88, and 5.00–6.00 mm all achieved a similar desulfurization extent (∼80%) at >1673 K. However, considerable variability was shown in larger particles (1.18–0.88 and 5.00–6.00 mm) for Qingdao, Zhenhai, and Qilu petcoke between 1473 and 1773 K. The products included water (presumably from coke quench, 350–410 K), volatiles (430–550 K), CO2 and H2 (>800 K, mainly), CO and SO2 (>1200 K, mainly), and trace quantities of CS2 (>1400 K). The stable sulfur-containing products of this petcoke during high-temperature pyrolysis were SO2 and trace amounts of CS2. However, COS and H2S pyrolysis products were absent or below the detection limits. The pyrolysis behavior was explored using ReaxFF on a macromolecular petcoke structure with the S atoms in thiophene-like functional groups. The mechanism of S loss, under the simulation conditions, involved molecular rearrangement and thermolysis into intermediate states (C2S and CNS) and COS. These were explored for 250 ps for 3000, 3500, and 4000 K with the constant volume/temperature (NVT) ensemble. The sulfur removal transformation during pyrolysis is generally followed: thiophene sulfur → COS, C2S, or CNS → HS → SO2 or CS2.

Silicon carbide-based membranes with high soot particle filtration efficiency, durability and catalytic activity for CO/HC oxidation and soot combustion

We report here the solution coatings of Diesel Particulate Filter (DPF) with allylhydridopolycarbosilane (AHPCS)-based polymers leading to supported silicon carbide (SiC)-based membranes with high temperature soot particle filtration efficiency, durability and catalytic activity. In a first part of the present study, our objective was to reduce the pore size of DPF to filtrate finer particles without altering filtration efficiency by coating DPF with an additional fine porous AHPCS-derived SiC membrane. The latter is produced by dip-coating AHPCS on DPF following by a pyrolysis of the AHPCS membrane-modified DPF at 1000°C under argon. We investigated the influence of dip-coating parameters and viscosity of different AHPCS solutions on the SiC membrane-coated DPF by SEM, mercury porosimetry, XRD and high-temperature thermogravimetric analysis. The evolution of the filtration capacity has been determined with a synthetic gas bench. An additional fine SiC membrane (∼150nm in thickness) prepared from a 10vol% of AHPCS in THF deposited on DPF allowed maintaining filtration efficiency as high as the virgin DPF while the pore size of the SiC membrane coated-DPF decreased to filter finer particles. Results are confirmed using a commercially-available polysiloxane (Si–C–O precursor). Furthermore, the SiC membrane acted as a thermal barrier coating and provided a better durability to the DPF by preventing apparition of cracks after heat-treatment to 1500°C under argon. The use of mixed oxide and metallic phases formed in-situ in SiC constitutes one of the solutions to generate new and effective catalytic performances to membranes. Within this context, in a second part of the study, we applied a reverse AHPCS-based microemulsion to combine SiC and oxide phases in the same additional porous membrane. As a proof of concept, we have prepared catalytically active Ce–O–Fe–Pt/SiC membrane coated DPF after dip-coating and pyrolysis under argon. These materials have been characterized and tested with regard to CO/HC oxidation and soot combustion. Ce–O–Fe–Pt/SiC membrane coated DPF showed an activity for CO conversion reaching a light-off temperature T50=270°C and the presence of the catalytic phase allowed burning soot at 486°C.

Preparation of N-Methylpolyborosilazane -Derived Bulk Si-B-N-C Ceramics by Warm-Pressing and Pressureless Pyrolysis

Additive-free bulk Si-B-N-C ceramics were prepared by pyrolysis of preceramic precursor (PBS-Me), which mainly involves cross linking, warm-pressing and pyrolysis. The density of crack-free bulk ceramic attains 1.94 g/cm3 when Calcined at 1300 °C. The shaped workpieces exhibit amorphous structure even be pyrolysised at 1400°C in N2, and there are some pores existing in the green body derived from warm-pressing and the resulting Si-B-N-C ceramic body, and these pores allow the gaseous byproducts be expeled from bodies. The pyrolyzed samples were studied by high temperature thermo gravimetric analysis, it shows that the Si-B-N-C body had an excellent high temperature resistance.

Synthesis and characterization of a new liquid polymer precursor for Si–B–C–N ceramics

A new liquid polyborosilazane precursor for Si–B–C–N ceramic was synthesized by co-condensation reaction of boron trichloride, organodichlorosilanes, and hexamethyldisilazane. The structure and properties of polyborosilazane were studied by means of Fourier transform-infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), rheology, and thermogravimetric analysis (TGA). The conversion of polymer to ceramic and the high-temperature behavior of the new polymer-derived ceramic were investigated by TG–MS, FT-IR, X-ray diffraction (XRD) and high-temperature TGA (HTGA). The ceramics showed good oxidative resistance and thermal stability with weight gain of 1.8 wt% at 1350 °C under air atmosphere and weight loss of 2.6% at 1900 °C under Ar atmosphere.

Cl2MeSi–NH–BCl2 and ClMe2Si–NH–BCl2: novel processable single source precursors of amorphous Si/C/B/N ceramics

The synthesis and polymerization of Cl2MeSi–NH–BCl2 (MADB) and ClMe2Si–NH–BCl2 (DADB) is reported. MADB and DADB are obtained in two-step reaction sequences from MeSiCl3, Me3Si–NH–SiMe3 (HMDS), and BCl3 (→ MADB) or Me2SiCl2, HMDS and BCl3 (→ DADB). The monomeric single source precursors are structurally characterized by means of NMR and IR spectroscopy and mass spectrometry. The molecular structure of DADB is additionally investigated by single crystal X-ray diffraction. It crystallizes orthorhombically in space groupPbca with a = 1334.4 pm, b = 1375.4 pm, c = 1607.8 pm, and Z = 8. In the solid state two molecules are associated via intermolecular B–N coordination, forming planar B2N2 rings with almost identical B–N bond lengths. Polymerization of MADB and DADB is performed by ammonolysis and aminolysis (MeNH2) releasing MADB–NH, DADB–NH, MADB–NMe, and DADB–NMe as colorless solids (MADB–NH) or colorless viscous liquids. The viscosity increases with increasing cross-linking density from DADB–NMe to MADB–NMe to DADB–NH. Accordingly, ceramic yields decrease from 77% (MADB–NH) to 45% (DADB–NH) to below 30% DADB–NMe). As-obtained ceramics are fully amorphous. Their near-range order is investigated using solid state 11B, 13C, and 29Si NMR spectroscopy. All materials display BN3 coordination at boron whereas the bonding situation at silicon is different. Silicon atoms in DADB–NH have ‘mixed’ SiNxCy (x + y = 4) environments, whereas the 29Si NMR spectra of MADB–NMe and DADB–NMe suggest SiN4 coordination. High temperature TGA performed in a He atmosphere up to 2000 °C indicates that DADB–NH ceramics are most stable; the onset of decomposition is above 1900 °C. SiC and Si3N4 reflections in the XRD patterns of the heated samples indicate that partial crystallization occurs during the heat treatment at elevated temperature.

The oxygen nonstoichiometry, defect structure, and thermodynamic characteristics of disordering of nickel-and iron-substituted lanthanum cobaltites

The oxygen nonstoichiometry of nickel-and iron-substituted lanthanum cobaltites of the compositions LaCo1−x Ni x O3−δ (x = 0.1, 0.3) and LaCo0.9Fe0.1O3−δ was studied by high-temperature thermogravimetric analysis over the temperature and oxygen partial pressure ranges 1223–1473 K and 10−3–0.21 atm. The partial replacement of cobalt with nickel (an acceptor impurity) in lanthanum cobaltite was found to increase the number of defects in the oxygen sublattice, whereas the replacement with iron (a donor impurity) decreased this number. Correlations between the experimental $$\log p_{O_2 } = f(\delta )$$ dependences and the suggested models of formation of point defects were analyzed taking into account the formation of Schottky defects. Interrelation between the defect structure, partial molar thermodynamic characteristics of oxygen release from the crystal lattices of the oxides studied, and the nature of substituting impurities (Ni and Fe) in lanthanum cobaltite was demonstrated.

Characterization of Au and Pd nanoparticles by high-temperature TGA–MS

Noble metal nanoparticles (NPs) prepared by a surfactant-free single-phase solution method have been proposed to contain fewer ionic contaminants than similar NPs prepared by a two-phase method. Reported herein is the possible contamination of Au and Pd NPs, prepared by a surfactant-free single-phase method, with Li2CO3 and other Li salts. High-temperature thermal gravimetric analysis measurements coupled with mass spectrometry (TGA–MS) up to 1100 °C were employed to determine the relative amounts of ionic contaminants since protecting thiolate groups and inorganic contaminants were removed in separate weight loss events. Assignment of the different weight loss events was supported by MS analysis of the evolved gases. TGA–MS also revealed the presence of larger amounts of oxidized sulfur species in the Pd NPs. High-resolution transmission electron microscopy (HRTEM), UV–vis, IR, elemental analysis (EA), and X-ray photoelectron spectroscopy (XPS) measurements complemented the characterization of the NPs. The amount of ionic contaminants crucially depended on the workup conditions, and quenching of the reaction mixture with ethanol was found to be essential for the formation of Li2CO3. Workup procedures that avoid the formation of TGA–MS detectable ionic contaminants are proposed along with purification steps for contaminated NPs.Key words: gold, palladium, nanoparticles, TGA, mass spectrometry, ionic contamination.

Nanostructured SiC/BN/C ceramics derived from mixtures of B3N3H6 and [HSi(Me)C≡C]n

Abstract Three borazine-modified polycarbosilanes were synthesized by reaction of poly[1,2-ethynediyl-(methylsilylene)], [HSi(Me)C≡C]n, and borazine, B3N3H6 using different stoichiometries. The polymeric precursors were transformed into inorganic Si–B–C–N materials by solid state thermolysis at 1400°C each in 88% yield. High temperature thermogravimetric analysis in an argon atmosphere showed no substantial decomposition reactions below 1800°C. Crystallization behavior up to 2000°C in a nitrogen atmosphere was studied by post-thermolysis heat treatment of as-obtained ceramics at various temperatures and subsequent examination of samples at room temperature using powder X-ray diffraction. Ceramics annealed at 1800°C were additionally characterized by transmission electron microscopy.

Novel polysilazanes as precursors for silicon nitride/silicon carbide composites without “free” carbon

Polysilazanes with chemical composition Si 4N 4CH x ( x = 12–14) were obtained on two different reaction pathways. In the first route three equivalents of dichlorosilane, H 2SiCl 2, were mixed with one equivalent of methyldichlorosilane, H 3CSiHCl 2, and reacted with ammonia to yield [(SiH 2–NH) 3(H 3CSiH–NH)] n ( 1) after appropriate work-up. In the second route, dichlorosilane was reacted with methylamine and ammonia in a 3:1 ratio to deliver [(SiH 2–NH) 3(SiH 2–NCH 3)] n ( 2). The raw products were further cross-linked by base-catalyzed dehydrocoupling reactions involving Si H and N H units to yield products 1a and 2a, respectively. The molecular structure of 1 and 2 was investigated by means of high resolution 1H, 13C{ 1H}, and 29Si{ 1H} NMR spectroscopy in C 6D 6 solution as well as by IR spectroscopy. Because of the insolubility of the cross-linked products 1a and 2a solid state 1H, 13C, and 29Si CP-MAS NMR in combination with IR spectroscopy were applied for their spectroscopic characterization. Chemical compositions were determined using elemental analysis. Thermolysis in an argon atmosphere up to 1400 °C of the cross-linked products delivered Si 3N 4/SiC ceramics in ∼94% yield. The absence of “free” carbon was revealed by mass spectra-coupled thermogravimetric analysis (TGA). These investigations indicated a one-step decomposition in the 250–700 °C range with predominant evaporation of hydrogen. In contrast, elimination of methane and ammonia ( 1) or methane and methylamine ( 2) was below 0.5 mass%. Additionally, neutron wide angle scattering proved the absence of a “free” carbon phase. High-temperature properties were investigated using high temperature TGA as well as XRD, EDX and TEM of annealed ceramic samples. The onset of crystallization in both materials was around 1500 and 1300 °C (1 atm N 2), respectively, and α- as well as β-Si 3N 4 formed besides α/β-SiC. Above 1900 °C ceramics derived from both 1a and 2a decomposed to α/β-SiC/β-Si 3N 4/α-Si composites.

Correlation of boron content and high temperature stability in Si–B–C–N ceramics

The preparation and characterization of precursor derived Si–B–C–N ceramics with similar Si/C/N ratios but variable boron content are reported. The polymeric precursors were prepared via hydroboration of poly(methylvinylsilazane) using different BH 3·SMe 2/polymer stoichiometries. High temperature thermogravimetric analysis of as-pyrolysed ceramics as well as XRD studies of post-annealed samples display a retarding effect of boron on both crystallization of SiC and Si 3N 4 and stabilization of crystalline β-Si 3N 4.

Design of Polymeric Si−B−C−N Ceramic Precursors for Application in Fiber-Reinforced Composite Materials

The synthesis, detailed spectroscopic characterization, polymer-to-ceramic conversion, and high-temperature behavior of a new class of polymeric precursors for Si−B−C−N composites are discussed. The title compounds [B(C2H4−SiR1R2−C2H4−SiHNH)3]n (C2H4 = CHCH3, CH2CH2; 5a: R1, R2 = H; 5b: R1 = H, R2 = CH3; 5c: R1, R2 = CH3) were designed especially for the preparation of ceramic films and fiber-reinforced ceramic composite matrixes. They are obtained in quantitative yields by the reaction of oligovinylsilazane [(H2CCH)SiH−NH]n (4) with tris(hydridosilylethyl)boranes of general type B(C2H4SiHR1R2)3 (C2H4 = CHCH3, CH2CH2; 3a: R1, R2 = H; 3b: R1 = H, R2 = CH3; 3c: R1, R2 = CH3) in a thermally induced hydrosilylation reaction without catalyst and/or solvent and without the formation of byproducts. Ceramic yields are 83% for 5a, 82% for 5b, and 63% for 5c as shown by thermogravimetric analysis (TGA). High-temperature TGA of the as-obtained amorphous ceramic materials, carried out in an argon atmosphere, re...

Synthesis and Thermal Behavior of Novel Si−B−C−N Ceramic Precursors

Several boron-modified polysilazanes of general type {B[C2H4Si(R)NH]3}n (C2H4 = CHCH3 or CH2CH2) were synthesized and their thermal behavior studied. In contrast to the known derivatives with R = alkyl or aryl, we describe ceramic precursors in which the bulky moieties R are substituted with lower weight groups and/or reactive entities. Reactive units enable further cross-linking of the polymeric framework and therefore minimize depolymerization during ceramization. The polymer-to-ceramic conversion of all synthesized polymers was monitored by thermogravimetric analysis. Both low molecular weight substituents and/or cross-linking units increase the ceramic yield from 50% (R = CH3) to 83−88%. High-temperature thermogravimetric analysis in an inert gas atmosphere indicates the ceramics obtained are stable up to ∼2000 °C. XRD studies of the fully amorphous materials point out that, with increasing temperature, formation of α-SiC or α-SiC/β-Si3N4 crystalline phases occurs at 1550−1750 °C, depending on the material's composition. The resistance of these novel materials toward oxidative attack was investigated by TGA in air up to 1700 °C and SEM/EDX, indicating that the materials efficiently self-protect toward oxidation.

High-temperature thermogravimetric analysis. Influence of gas pressure on kinetics of reactions in the solid state

A magnetic balance apparatus has been set up to follow reactions in the solid state under controlled conditions of pressure and temperature (25–1000°). Magnetic properties are characteristic of solid structures, and thermomagnetic analysis (T. M. A.) can give the variations of the sample susceptibility during the course of a reaction (susceptibilities of the new phases and of initial compounds not yet transformed). By continuous measurement of this susceptibility with the Faraday method, the conversion degree of the synthesis can be obtained.T. M. A. has been used to study the influence of a gas on a solid-solid reaction in which no gas can be evolved or consumed. An example is given for iron tungstate synthesis: Fe2O3(s)+WO3(s) → Fe2WO6(s). At 800° the reaction kinetics depends on the nature and the pressure of the gas.

The nature of water in sound human enamel: A preliminary study

The water protons in ground enamel as measured by wide line nuclear magnetic resonance spectrometry and as indicated by chemical analysis, in conjunction with high temperature thermogravimetric analysis, are of three types. The water lost by 100 °C and exchangeable with D 2O, is from 0.6 to 1 per cent. It was freely tumbling (i.e. unbound). That water formerly called “bound” water ( Little, Cueto and Rowley, 1962) and associated with the Ca:P ratio, is removable by 900 °C; it is a “caged” but a freely tumbling fraction equal to 0.8 moles of water. Of the same type is water, equivalent to 2 moles, removable only between 900 and 1300 °C. Since the NMR line widths indicated only H 2O and no H 3O + or OH −, it is speculated that enamel apatite and synthetic apatites may not be a hydroxy- but a hydro-apatite.