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The formation mechanisms of Pd-Os and Pt-Os alloys in the course of thermal decomposition of iso-formular and isostructural complex salts [Pd(NH3)4][OsCl6] and [Pt(NH3)4][OsCl6] in an inert atmosphere have been studied by in-situ QXAFS, XPS and PXRD. The mechanisms of thermal decomposition of the precursors are found to differ from each other, but the detected intermediate products show no significant effect on the local atomic structure around Os, Pt/Pd in their final products. A crystalline beta-trans-[Pd(NH3)2Cl2] intermediate of the first step of thermal decomposition of [Pd(NH3)4][OsCl6] makes the anion [OsCl6]2− transform differently than that of [Pt(NH3)4][OsCl6]. It transforms into a short-lived [Os(NH3)xCl6-x] (2≤x≤4), and then to a distorted octahedron [OsCl6]2−, similar to the high-temperature modification of OsCl4. In case of [Pt(NH3)4][OsCl6], the intermediate [Os(NH3)2Cl4] modifies into four chlorine coordinated Os,{OsCl4}0/1−. Consecutive reduction of Pd(II)/Pt(II) and Os(IV) to the metals defines the homophilic atomic order with the fcc-Pd covered by a random Pd-Os alloy layer and Os on the surface, that is supported by High-Resolution Transmission Electron Mictroscopy (HRTEM) and Scanning TEM (STEM) energy dispersive X-ray (EDX) data, and the diffusion direction going from the surface (hcp-Os) to bulk (fcc-Pd/Pt). As a result, the heterogeneous alloys are formed with a very similar electronic and local atomic structure of Os and Pd/Pt. Upon alloying, the Os 5d5/2,3/2 and Pt 5d5/2,3/2 levels are depleted in the Pt-Os alloys compared to dispersed hcp-Os, fcc-Pt, and Pt foil. This is an unusual behaviour for Os and Pt, calling into question the versatility of d-band theory in bimetallic Os-alloys. The spin-orbit effect at the Os site has been found for both the Pd-Os and Pt-Os alloys, but it is about 4 times less compared to the complex salts. The obtained values for the complex compounds are comparable with those for the iridates, proposed as materials with spin-orbit-induced properties.
Self-reactive substances are unstable chemical substances which can easily decompose and may lead to explosion. For this reason, their thermal stability properties are required within regulatory frameworks related to chemicals in order to assess their hazardous properties. Due to the fast development and availability of computers, predictive approaches like QSPR models are increasingly used in the evaluation process of hazardous substances complementary to experiments.
In that context, the HAZPRED project (2015-2018) aimed to develop QSPR models to predict physical hazards of substances to fill the lack of knowledge on these hazardous substances quickly.
An experimental campaign, based on 50 samples provided by Industrial producers, was carried out on potential self-reactive substances, for which no QSPR model already existed. Their heats of decomposition were characterized using differential scanning calorimetry in homogeneous experimental conditions.
QSPR models were derived using the GA-MLR method (using a genetic algorithm and multi-linear regressions) using molecular descriptors calculated by Dragon software based on both 3D molecular structures from density functional theory (DFT) optimizations, to access three-dimensional descriptors, and SMILES codes, favoring the access to simpler models, requiring no preliminary quantum chemical calculations. All models respected the OECD validation guidelines for regulatory acceptability of QSPR models. They were tested by internal and external validation tests and their applicability domains were defined and analyzed.
If improved models should be expected with larger database (and a better ratio between size and chemical diversity), these first models already represent a screening tool capable to access early reactive hazards.
Insight of the thermal decomposition of ammonium hexahalogenoiridates(IV) and hexachloroiridate(III)
(2020)
Thermal decomposition of (NH4)3[IrCl6]·H2O, (NH4)2[IrCl6] and (NH4)2[IrBr6] in reductive and inert atmospheres has been investigated in situ using quick-EXAFS and temperature-resolved powder X-ray diffraction. For the first time, (NH4)2[Ir(NH3)Cl5] and (NH4)2[Ir(NH3)Br5] have been proven as intermediates of thermal decomposition of (NH4)3[IrCl6]·H2O, (NH4)2[IrCl6] and (NH4)2[IrBr6]. Thermal degradation of (NH4)2[IrCl6] and (NH4)2[IrBr6] is a more complex process as suggested previously and includes simultaneous formation of (NH4)2[Ir(NH3)Cl5] and (NH4)2[Ir(NH3)Br5] intermediates mixed with metallic iridium. In the inert atmosphere, complexes (NH4)[Ir(NH3)2Cl4] and (NH4)[Ir(NH3)2Br4] as well as [Ir(NH3)3Br3] were proposed as possible intermediates before formation of metallic iridium particles
The products of thermal decomposition in an argon atmosphere of [Ni(NH3)6]3[Fe(CN)6]2 as a precursor has been studied. Decomposition products were studied up to 800◦C. Above 600◦C, all coordination bonds in the residues are broken with a formation of Ni3Fe, Fe, and free carbon with a small admixture of nitrogen. Elementary carbon can be easily separated from metals by treatment with a water solution of hydrochloric acid. Only carbon is responsible for the specific surface of the composite products. The released carbon has a high degree of graphitization and begins to oxidize in air above 500°C and is completely oxidized above 700°C.
In this study, the thermal decomposition of 1,3,5-tris-(2,3-dibromopropyl)-1,3,5-triazine-2,4,6-trione (TDBPTAZTO) and 2,4,6-tris-(2,4,6-tribromo-phenoxy)-1,3,5-triazine (TTBP-TAZ) were investigated for the first time by thermogravimetric analysis. Both compounds were thermal degraded between 225 and 350 °C (TDBP-TAZTO) as well as 300 and 400 °C (TTBP-TAZ).
As a result, mass loss (%) of 98.5% for TTBP-TAZ and 95.4% for TDBP-TAZTO at 600 °C under N2 were observed. The major pyrolytic degradation products of TTBP-TAZ were formed in a single step and identified by FTIR analysis as 2,4,6-tribromophenol and further bromine-substituted aromatic compounds. In comparison, TDBP-TAZTO was pyrolytic degraded in two steps, whereby on the first step the release of hydrogen Bromide and 1,3,5-triallyl-1,3,5-triazine-2,4,6-trione could be detected. In the second minor step, isocyanic acid could be additionally identified.
Subsequently, the obtained products of the TGA-FTIR measurements were used for a targeted search for mass fragments in mass spectrometry measurements. For TTBP-TAZ, only the degradation product 1,3,5-tribromobenzene could be detected by MS/MS analyzes. No comparable thermal degradation products, except hydrogen bromide, were observed in the MS/MS spectra of TDBP-TAZTO. Therefore, the search of further mass fragments was not possible compared to the findings of the TGA-FTIR measurements.
Basic paths towards fully green flame retarded kenaf fiber reinforced polylactic acid (K-PLA) biocomposites are compared. Multicomponent flame retardant Systems are investigated using an amount of 20 wt% such as Mg(OH)2 (MH), ammonium polyphosphate (APP) and expandable graphite (EG), and combinations with Silicon dioxide or layered silicate (LS) nanofillers. Adding Kenaf fibers and flame retardants increases the E modulus up to a factor 2, although no compatibilizer was used at all. Thus, in particular adding EG and MH decreases the strength at maximum elongation, and kenaf fibers, MH, and EG are crucial for reducing the elongation to break. The Oxygen index is improved by up to 33 vol% compared to 17 vol% for K-PLA. The HB classification of K-PLA in the UL 94 test is outperformed. All flame retarded biocomposites show somewhat lower thermal stability and increased amounts of residue. MH decreases the fire load significantly, and the greatest reduction in peak heat release rate is obtained for K-PLA/15MH/5LS. Synergistic effects are observed between EG and APP (ratio 2:1) in flammability and fire properties. Synergistic multicomponent systems containing EG and APP, or MH with adjuvants offer a promising route to green flame retarded natural fiber reinforced PLA biocomposites.
The thermal decomposition of dicumyl peroxide dissolved in ethylbenzene has been studied in our laboratories using differential scanning calorimetry (DSC), calvet calorimetry (C80), adiabatic calorimetry, reaction calorimetry and micro calorimetry.
Based on the DSC and C80 experiments a formal kinetics model has been derived, which was compared to the other applied techniques. Finally we used our model to predict the thermal response of 216.5 L steel drums to exposure to constant elevated temperatures, both using the stationary Semenov approach as well as time-resolved CFD simulations. The prediction was compared to one-to-one testing using the UN-Test H.1. The observed level of consistency between model and experiments is remarkably good. The comparison with the 216.5 L testing clearly demonstrates that reliable and conservative predictions for technically relevant scales are possible as long as a validated model is used.
A large number of azodicarboxylates and their derivatives are produced and used in the chemical industries. The versatile applications of these azodicarboxylates in research institutes and in the chemical industries for chemical synthesis arouse additional hazards. The intent of this paper is to obtain first knowledge about the structure–response relationship regarding the explosive properties and the thermal hazards of different versatile used azodicarboxylates. The substances are examined with the differential scanning calorimetry (DSC). Furthermore, different laboratory test methods, based on the UN Recommendations on the Transport of Dangerous Goods, are applied to determine the explosive properties of the mentioned substances. On the basis of the obtained results, the known influence of the nitrogen content within the molecule regarding their thermal behaviour could be confirmed. The measured heat of decomposition appeared to be proportional to the nitrogen content within the group of the aliphatic and the aromatic azodicarboxylates. To emphasize this dependency, further investigations should be done. The long term objective of this research is to develop structure–response relationships of the explosive properties and the thermal hazards originating from azodicarboxylates.
A large number of Azodicarboxylates and their derivatives are produced and used in the chemical industries. The versatile applications of these Azodicarboxylates in research institutes and in the chemical industries for chemical synthesis arouse additional hazards. The aim of this paper is to obtain a predication about the structure-response relationship regarding the explosive properties and the thermal hazards of different versatile used Azodicarboxylates. The substances were examined with the Differential Scanning Calorimetry (DSC). Furthermore, different laboratory test methods, based on the UN Recommendations on the Transport of Dangerous Goods, were applied to determine the explosive properties of the mentioned substances.
Conventional simultaneous thermal analysis, capillary-coupled TGMS, in situ and ex situ Raman and Mössbauer spectroscopy, as well as chemical analysis have been used for the investigation of the first decomposition step of the mixed valence chloroferrate (dmpipzH2)6[Fe(II)Cl4]2[Fe(III)Cl4]2[Fe(II)Cl5][Fe(III)Cl6]. Under argon at ca. 200°C, an almost complete reduction proceeds in a solid state reaction forming Fe(II). It is accompanied by the release of HCl and, to a minor degree, carbon containing species. A multi-phase product with at least two chloroferrate species, coke, and C,H,N-containing polymers is formed. Binuclear iron complexes, such as (dmpipzH)2[Fe(II)2Cl6], and small amounts of (dmpipzH)[Fe(III)Cl4] have been proposed to be the major and minor component of the product mixture, respectively.