Download or read book Synthesis and Characterization of Solid Solutions AA Mo3O12 written by La'Nese Lovings and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Expansion of solid-state materials is an important physical property that can affect the performance of many devices. When the thermal expansion coefficients of two materials that are in intimate contact in a device are mismatched, the outcome can be detrimental and lead to device failure. Negative thermal expansion (NTE) materials can be utilized to counteract the undesirable positive thermal expansion (PTE) of a material by forming a controlled expansion composite that can retain other important properties of the matrix material. Here, we study NTE materials in the A2M3O12 family (A= trivalent cation, M= Mo, W). Within this family, some materials undergo a phase transition from an orthorhombic NTE phase at high temperatures to a monoclinic PTE phase at low temperatures. Lowering of this phase transition temperature could be beneficial to achieve the largest possible temperature range with NTE. Such a suppression has been observed in AlScMo3O12, which shows a much lower transition temperature than either Al2Mo3O12 or Sc2Mo3O12. It was suggested that the large size difference between Al3+ and Sc3+ played an important role in the observed behavior. The goal of this research was to synthesize mixed A-site occupancy materials and probe their phase transition behavior as a function of composition to understand the design rules for materials in which the orthorhombic phase is stabilized. To investigate the behavior observed for AlScMo3O12 more deeply, various AlxSc2-xMo3O12 compounds were synthesized using solid-state and non-hydrolytic sol-gel (NHSG) methods (Chapter 3). Solid-state methods did not produce single-phase samples; however, NHSG methods led to single-phase samples for a wide range of compositions. Optimization was necessary for the NHSG synthesis, with solvent system, reaction temperature and synthesis duration as main variables. It was found that the stabilizing agent in the chloroform used played a key role in the production of single-phase samples. Compositions close to the parent compounds could be obtained as single-phase samples with a synthesis duration of 7 days, while a longer reaction time of 12 to 15 days was necessary near the middle of the solid solution series. To investigate a system with an even larger size difference between the A-site cations, the AlxIn2-xMo3O12 solid solution series was synthesized via solid-state and NHSG chemistry (Chapter 4). Solid-state synthesis led to high weight losses attributed to MoO3 evaporation during heating and never produced phase pure materials. Similar to the previously mentioned solid solution series, the compositions near the end members produced phase pure samples with relative ease while significant optimization was required near the middle of the solid solution, and single-phase samples could not be produced for many compositions. Increasing the temperature of synthesis in chloroform lead to improved homogeneity, while no positive effect was noted for acetonitrile samples. An increase in reaction duration improved the purity of some samples as well. It was also found that the exact heat treatment chosen could affect whether single- or multi-phase samples were obtained. A single heat treatment near the end members could produce single-phase samples, while compositions near the middle of the solid solution benefited from a lower temperature heat treatment followed by a second higher temperature heat treatment. The samples in the AlxSc2-xMo3O12 and AlxIn2-xMo3O12 solid solution series were subjected to variable temperature (VT) in-house and synchrotron PXRD studies to determine the temperatures of the phase transition (Chapter 5). Both systems showed a phase transition temperature suppression near the middle of the solid solution, with AlxSc2-xMo3O12 samples showing the largest suppression when x = 0.9 and 1. These samples showed no phase transition down to -193 °C, which was the lowest temperature measured. AlxIn2-xMo3O12 showed a phase transition suppression even for substitution levels of only 5 to 10%. During the variable temperature study, it was found that compositions that resulted in a lowering of the phase transition temperature also had a tendency to display PTE instead of NTE. A possible explanation for both effects is that the difference in A-site cation size can lead to localized strain of the system. This strain is more readily accommodated in the less dense orthorhombic phase, but also interferes with the phonon modes that cause NTE. Stress analysis of the synchrotron data showed that the compounds near the end members possessed low strain, but as the cation composition changed across the solid solution series an increase in strain was observed. A serendipitous discovery showed that raw AlxSc2-xMo3O12 samples could crystallize over an extended period of time under ambient conditions. To investigate this behavior, the effect of storage in different environments was investigated (Chapter 6). It was found that absorption of water from the atmosphere was crucial for the crystallization of the samples. To our knowledge, moisture-induced crystallization at room temperature has never been observed for any NTE materials. Typically, amorphous samples require heat treatments to 450 to 700 °C to form a crystalline product. An in-situ crystallization study was carried out using synchrotron diffraction experiments to observe the phase evolution of amorphous AlxSc2-xMo3O12 precursors during different heat treatments (Chapter 7). This study was designed to determine optimum heat treatment protocols to favor formation of single-phase samples. Surprisingly, conditions mimicking those used during ex-situ heat treatments resulted in crystallization of an MoO3 impurity at relatively low temperatures for all samples, many of which formed single-phase materials during ex situ studies. This revealed that all samples were inhomogeneous during heating. In a significant number of samples, formation of two distinct A2M3O12 phases was observed at intermediate temperatures. However, most samples were determined to be phase pure after heating to 700 °C, suggesting that these intermediate phases react during continued heating.

Download or read book Bibliography written by Pierre Villars and published by Walter de Gruyter. This book was released on 2012-12-21 with total page 1827 pages. Available in PDF, EPUB and Kindle. Book excerpt: By browsing about 10 000 000 scientific articles of over 200 major journals mainly in a 'cover to cover approach' some 200 000 publications were selected. The extracted data is part of the following fundamental material research fields: crystal structures (S), phase diagrams (also called constitution) (C) and the comprehensive field of intrinsic physical properties (P). This work has been done systematically starting with the literature going back to 1900. The above mentioned research field codes (S, C, P) as well as the chemical systems investigated in each publication were included in the present work. The aim of the Inorganic Substances Bibliography is to provide researchers with a comprehensive compilation of all up to now published scientific publications on inorganic systems in only three handy volumes.

Download or read book Removal of Refractory Pollutants from Wastewater Treatment Plants written by Maulin P. Shah and published by CRC Press. This book was released on 2021-10-08 with total page 561 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book discusses new and innovative trends and techniques in the removal of toxic and or refractory pollutants through various environmental biotechnological processes from wastewater, both at the laboratory and industrial scale. It focuses primarily on environmentally-friendly technologies which respect the principles of sustainable development, including the advanced trends in remediation through an approach of environmental biotechnological processes from either industrial or sewage wastewater. Features: Examines the fate and occurrence of refractory pollutants in wastewater treatment plants (WWTPs) and the potential approaches for their removal. Highlights advanced remediation procedures involving various microbiological and biochemical processes. Assesses and compares the potential application of numerous existing treatment techniques and introduces new, emerging technologies. Removal of Refractory Pollutants from Wastewater Treatment Plants is suitable for practicing engineers, researchers, water utility managers, and students who seek an excellent introduction and basic knowledge in the principles of environmental bioremediation technologies.