solid state reactions
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2021 ◽  
Author(s):  
Waqas Muhammad Khan ◽  
Wiqar Hussain Shah

In future, the most common batteries will be the thallium. As there is many types of batteries but the thallium batteries are better from them. In here, we have made the compound which is more positive work than the other batteries. The different elements are doping in the tellurium telluride to determine the different properties like electrical and thermal properties of nanoparticles. The chalcogenide nanoparticles can be characteristics by the doping of the different metals which are like the holes. We present the effects of Pb and Sn doping on the electrical and thermoelectric properties of Tellurium Telluride Tl10-xPbxTe6 and Tl10-xSnxTe6 (x = 1.00, 1.25, 1.50, 1.75, 2.00) respectively, which were prepared by solid state reactions in an evacuated sealed silica tubes. Structurally, all these compounds were found to be phase pure as confirmed by the x-rays diffractometery (XRD) and energy dispersive X-ray spectroscopy (EDS) analysis. The thermo-power or Seebeck co-efficient (S) was measured for all these compounds which show that S increases with increasing temperature from 295 to 550 K. The Seebeck coefficient is positive for the whole temperature range, showing p-type semiconductor characteristics. Similarly the electrical conductivity (σ) and the power factors have also complex behavior with Pb and Sn concentrations. The power factor (PF = S2σ) observed for Tl10-xPbxTe6 and Tl10-xSnxTe6 compounds are increases with increase in the whole temperature range (290 K–550 K) studied here. Telluride’s are narrow band-gap semiconductors, with all elements in common oxidation states, according to (Tl+)9(Pb3+)(Te2−)6 and (Tl+)9(Sn3+)(Te2−)6. Phases range were investigated and determined with different concentration of Pb and Sn with consequents effects on electrical and thermal properties.


2021 ◽  
Author(s):  
◽  
Susan Margaret Maciver

<p>This thesis describes a kinetic study of the high temperature solid state reactions of a well characterized halloysite mineral and five of its cation-saturated forms, the cations used being sodium, calcium, manganese, copper and iron (Ill). The reaction sequence may be represented by the idealised equations: The formation of mullite from metakaolinite has been studied in the temperature range 1020° - 1200°C, by X-ray analysis. Comparison of the experimental data with several theoretical models suggests that up to 90% conversion the reaction takes place by exponential nucleation followed by crystal growth. There is, however, some evidence for diffusion occurring as a rate controlling process, especially at high degrees of conversion to mullite. The rate constants and experimental thermodynamic functions have been evaluated for all halloysite samples. The free energies of activation (111-128 k cal.mole-1) and the rate constants are independent of the starting materials, but the enthalpies of activation (51-118 k cal.mole-1) and the entropies of activation (0 to -50 cal.deg.-1 mole-1) are not.</p>


2021 ◽  
Author(s):  
◽  
Susan Margaret Maciver

<p>This thesis describes a kinetic study of the high temperature solid state reactions of a well characterized halloysite mineral and five of its cation-saturated forms, the cations used being sodium, calcium, manganese, copper and iron (Ill). The reaction sequence may be represented by the idealised equations: The formation of mullite from metakaolinite has been studied in the temperature range 1020° - 1200°C, by X-ray analysis. Comparison of the experimental data with several theoretical models suggests that up to 90% conversion the reaction takes place by exponential nucleation followed by crystal growth. There is, however, some evidence for diffusion occurring as a rate controlling process, especially at high degrees of conversion to mullite. The rate constants and experimental thermodynamic functions have been evaluated for all halloysite samples. The free energies of activation (111-128 k cal.mole-1) and the rate constants are independent of the starting materials, but the enthalpies of activation (51-118 k cal.mole-1) and the entropies of activation (0 to -50 cal.deg.-1 mole-1) are not.</p>


Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6590
Author(s):  
Tengteng Xu ◽  
Yibiao Xu ◽  
Ning Liao ◽  
Yawei Li ◽  
Mithun Nath

Al2O3-CaO-Cr2O3 castables are used in various furnaces due to excellent corrosion resistance and sufficient early strength, but toxic Cr(VI) generation during service remains a concern. Here, we investigated the relative reactivity of analogous Cr(III) phases such as Cr2O3, (Al1-xCrx)2O3 and in situ Cr(III) solid solution with the calcium aluminate cement under an oxidizing atmosphere at various temperatures. The aim is to comprehend the relative Cr(VI) generation in the low-cement castables (Al2O3-CaO-Cr2O3-O2 system) and achieve an environment-friendly application. The solid-state reactions and Cr(VI) formation were investigated using powder XRD, SEM, and leaching tests. Compared to Cr2O3, the stability of (Al1-xCrx)2O3 against CAC was much higher, which improved gradually with the concentration of Al2O3 in (Al1-xCrx)2O3. The substitution of Cr2O3 with (Al1-xCrx)2O3 in the Al2O3-CaO-Cr2O3 castables could completely inhibit the formation of Cr(VI) compound CaCrO4 at 500–1100 °C and could drastically suppress Ca4Al6CrO16 generation at 900 to 1300 °C. The Cr(VI) reduction amounting up to 98.1% could be achieved by replacing Cr2O3 with (Al1-xCrx)2O3 solid solution. However, in situ stabilized Cr(III) phases as a mixture of (Al1-xCrx)2O3 and Ca(Al12-xCrx)O19 solid solution hardly reveal any reoxidation. Moreover, the CA6 was much more stable than CA and CA2, and it did not participate in any chemical reaction with (Al1-xCrx)2O3 solid solution.


2021 ◽  
Vol 922 (1) ◽  
pp. 62
Author(s):  
Alessandra Canta ◽  
Richard Teague ◽  
Romane Le Gal ◽  
Karin I. Öberg

Abstract We report the first detection of the molecule cyanomethyl, CH2CN, in a protoplanetary disk. Until now, CH2CN had only been observed at earlier evolutionary stages, in the molecular clouds TMC-1, Sgr2, and L483, in the prestellar core L1544, and toward the protostar L1527. We detect six transitions of ortho-CH2CN toward the disk around nearby T Tauri star TW Hya. An excitation analysis reveals that the disk-averaged column density, N , for ortho-CH2CN is (6.3 ± 0.5) × 1012 cm−2, which is rescaled to reflect a 3:1 ortho-para ratio, resulting in a total column density, N tot, of (8.4 ± 0.7) × 1012 cm−2. We calculate a disk-average rotational temperature, T rot = 40 ± 5 K, while a radially resolved analysis shows that T rot remains relatively constant across the radius of the disk. This high rotation temperature suggests that in a static disk and if vertical mixing can be neglected, CH2CN is largely formed through gas-phase reactions in the upper layers of the disk, rather than solid-state reactions on the surface of grains in the disk midplane. The integrated intensity radial profiles show a ring structure consistent with molecules such as CN and DCN. We note that this is also consistent with previous lower-resolution observations of centrally peaked CH3CN emission toward the TW Hya disks, since the observed emission gap disappears when convolving our observations with a larger beam size. We obtain a CH2CN/CH3CN ratio ranging between 4 and 10. This high CH2CN/CH3CN is reproduced in a representative chemical model of the TW Hya disk that employs standard static disk chemistry model assumptions, i.e., without any additional tuning.


Author(s):  
Istvan Hargittai

AbstractJack D. Dunitz (1923–2021) was Professor of Chemical Crystallography at the Swiss Federal Institute of Technology, Zurich. He received his degrees from Glasgow University, was at the ETH Zurich since 1957, and retired in 1990. His research interests included crystal structure analysis as a tool for solving chemical problems, polymorphism, solid state reactions, and a broad area of structural variations during chemical events under the umbrella term of structure correlation.


Processes ◽  
2021 ◽  
Vol 9 (10) ◽  
pp. 1852
Author(s):  
Juan Arcenegui-Troya ◽  
Pedro E. Sánchez-Jiménez ◽  
Antonio Perejón ◽  
Luis A. Pérez-Maqueda

Kinetic models used for the kinetic analysis of solid-state reactions assume ideal conditions that are very rarely fulfilled by real processes. One of the assumptions of these ideal models is that all sample particles have an identical size, while most real samples have an inherent particle size distribution (PSD). In this study, the influence of particle size distribution, including bimodal PSD, in kinetic analysis is investigated. Thus, it is observed that PSD can mislead the identification of the kinetic model followed by the reaction and even induce complex thermoanalytical curves that could be misinterpreted in terms of complex kinetics or intermediate species. For instance, in the case of a bimodal PSD, kinetics is affected up to the point that the process resembles a reaction driven by a multi-step mechanism. A procedure for considering the PSD in the kinetic analysis is presented and evaluated experimentally by studying the thermal dehydroxylation of kaolinite. This process, which does not fit any of the common ideal kinetic models proposed in the literature, was analyzed considering PSD influence. However, when PSD is taken into account, the process can be successfully described by a 3-D diffusion model (Jander’s equation). Therefore, it is concluded that the deviations from ideal models for this dehydroxylation process could be explained in terms of PSD.


2021 ◽  
Vol 118 (35) ◽  
pp. e2109945118
Author(s):  
M. B. Sreedhara ◽  
Simon Hettler ◽  
Ifat Kaplan-Ashiri ◽  
Katya Rechav ◽  
Yishay Feldman ◽  
...  

Asymmetric two-dimensional (2D) structures (often named Janus), like SeMoS and their nanotubes, have tremendous scope in material chemistry, nanophotonics, and nanoelectronics due to a lack of inversion symmetry and time-reversal symmetry. The synthesis of these structures is fundamentally difficult owing to the entropy-driven randomized distribution of chalcogens. Indeed, no Janus nanotubes were experimentally prepared, so far. Serendipitously, a family of asymmetric misfit layer superstructures (tubes and flakes), including LaX-TaX2 (where X = S/Se), were synthesized by high-temperature chemical vapor transport reaction in which the Se binds exclusively to the Ta atoms and La binds to S atoms rather than the anticipated random distribution. With increasing Se concentration, the LaS-TaX2 misfit structure gradually transformed into a new LaS-TaSe2-TaSe2 superstructure. No misfit structures were found for xSe = 1. These counterintuitive results shed light on the chemical selectivity and stability of misfit compounds and 2D alloys, in general. The lack of inversion symmetry in these asymmetric compounds induces very large local electrical dipoles. The loss of inversion and time-reversal symmetries in the chiral nanotubes offers intriguing physical observations and applications.


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