scholarly journals Formation of ZrC–SiC Composites from the Molecular Scale through the Synthesis of Multielement Polymers

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3901
Author(s):  
Fabien Bouzat ◽  
Romain Lucas ◽  
Yann Leconte ◽  
Sylvie Foucaud ◽  
Yves Champavier ◽  
...  
Keyword(s):  
Ceramic Composites ◽  
Inorganic Materials ◽  
Oxide Ceramic ◽  
X Ray Diffraction ◽  
Preceramic Polymers ◽  
Fragmentation Mechanisms ◽  
Sic Composites ◽  
The Stability ◽  
The Impact ◽  
Polymeric Structures

In the field of non-oxide ceramic composites, and by using the polymer-derived ceramic route, understanding the relationship between the thermal behaviour of the preceramic polymers and their structure, leading to the mechanisms involved, is crucial. To investigate the role of Zr on the fabrication of ZrC–SiC composites, linear or hyperbranched polycarbosilanes and polyzirconocarbosilanes were synthesised through either “click-chemistry” or hydrosilylation reactions. Then, the thermal behaviours of these polymeric structures were considered, notably to understand the impact of Zr on the thermal path going to the composites. The inorganic materials were characterised by thermogravimetry-mass spectrometry (TG-MS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). To link the macromolecular structure to the organisation involved during the ceramisation process, eight temperature domains were highlighted on the TG analyses, and a four-step mechanism was proposed for the polymers synthesised by a hydrosilylation reaction, as they displayed better ceramic yields. Globally, the introduction of Zr in the polymer had several effects on the temperature fragmentation mechanisms of the organometallic polymeric structures: (i) instead of stepwise mass losses, continuous fragment release prevailed; (ii) the stability of preceramic polymers was impacted, with relatively good ceramic yields; (iii) it modulated the chemical composition of the generated composites as it led, inter alia, to the consumption of free carbon.

Thermal and Chemical Stability of Micron Aluminum Powders Subjected to Gaseous Water

2016 ◽  
Vol 712 ◽  
pp. 241-245
Author(s):  
Sergey V. Zmanovskiy ◽  
Alexander M. Gromov ◽  
Valentina V. Smirnova ◽  
Vadim F. Petrunin ◽  
Jin Chun Kim
Keyword(s):  
Room Temperature ◽  
Gravimetric Analysis ◽  
X Ray Diffraction ◽  
Aluminum Powders ◽  
X Ray ◽  
The Stability ◽  
Heating Up ◽  
The Impact ◽  
Thermal And Chemical Stability ◽  
Composition Of Products

The paper studies the impact of gaseous water on the stability of micron aluminum powders in time at room temperature using the method of gravimetric analysis. The stability was studied using methods of thermal analysis during heating up to 1200 °С in air. The composition of products was analyzed using X-ray diffraction analysis. It was found out that the stability of micron aluminum powders depends on partial pressure of water vapor: the increase of pressure results in decreased stability of powders. The work gives recommendations for storing micron aluminum powders.

Development and Characterization of the Al2O3-YAG Ceramic Composites

2014 ◽  
Vol 798-799 ◽  
pp. 383-388 ◽  
Author(s):  
Eduardo Sousa Lima ◽  
A.P.O. Santos ◽  
L.M. Itaboray ◽  
C. Santos ◽  
R.F. Cabral
Keyword(s):  
Relative Density ◽  
Microstructural Characterization ◽  
Ceramic Composites ◽  
Oxide Ceramic ◽  
X Ray Diffraction ◽  
Powder Mixtures ◽  
X Ray ◽  
Resistance To Oxidation ◽  
Oxidation And Corrosion

YAG (Y3Al5O12) and Al2O3 ceramics have high resistance to oxidation and corrosion in harsh environments and high temperatures, which turns into a quite attractive material as compared to other ceramics. Thus, lately oxide ceramic YAG has been extensively used as reinforcement phase to Al2O3 in order to obtain a composite with improved mechanical properties. This research focused on the development of sintered Al2O3-Y2O3 powder mixtures for the production of Al2O3-YAG composite. Powder mixtures composed of 63.65:36.35wt.% and 80.00:20.00wt.% of Al2O3 and Y2O3, respectively, were milled by planetary milling for 2h. The compositions were compacted by cold uniaxial pressing, at 70 MPa, for 30s. The two mixtures were sintered at 1500 and 1600°C for 3h. The samples were evaluated for relative density, shrinkage, weight loss, and X-Ray Diffraction (XRD). Scanning Electron Microscopy (SEM) was used for microstructural characterization. The X-Ray Diffraction showed the presence of Al2O3 and Y3Al5O12 as crystalline phases in both compositions. Samples composed by 80:20wt.% of Al2O3/Y2O3 powder sintered at 16000C-3h presented the higher relative density ranging around 86% of theoretical density.

scholarly journals Boosting the Stability of Boron Peroxides through Subphthalocyanine Coordination

2021 ◽  
Vol 03 (02) ◽  
pp. 141-145
Author(s):  
Jorge Labella ◽  
Elisa López-Serrano ◽  
Tomás Torres
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Lewis Base ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray ◽  
The Stability ◽  
The Impact ◽  
Structural And Optoelectronic Properties

The great potential of subphthalocyanines (SubPcs) to stabilize boron peroxides has been demonstrated. In particular, a subphthalocyanato boron (III) peroxide has been prepared in good yield via boron triflate. This derivative is remarkably stable under ambient conditions and can be fully characterized. The impact of the peroxide group on the structural and optoelectronic properties of SubPc was examined by NMR and UV/Vis spectroscopies, as well as single-crystal X-ray diffraction analysis. Moreover, density functional theory calculations were performed to explain the experimental results. The reactivity of this peculiar boron peroxide as an oxidant and a Lewis base was also studied.

scholarly journals On the Impact of the Degree of Fluorination on the ORR Limiting Processes within Iron Based Catalysts: A Model Study on Symmetrical Films of Barium Ferrate

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2532
Author(s):  
Stephan Wollstadt ◽  
Oliver Clemens
Keyword(s):  
Variable Temperature ◽  
Fluorine Content ◽  
Bulk Diffusion ◽  
Decomposition Temperature ◽  
X Ray Diffraction ◽  
Impedance Model ◽  
Degradation Temperature ◽  
Model Study ◽  
The Stability ◽  
The Impact

In this study, symmetrical films of BaFeO2.67, BaFeO2.33F0.33 and BaFeO2F were synthesized and the oxygen uptake and conduction was investigated by high temperature impedance spectroscopy under an oxygen atmosphere. The data were analyzed on the basis of an impedance model designed for highly porous mixed ionic electronic conducting (MIEC) electrodes. Variable temperature X-ray diffraction experiments were utilized to estimate the stability window of the oxyfluoride compounds, which yielded a degradation temperature for BaFeO2.33F0.33 of 590 °C and a decomposition temperature for BaFeO2F of 710 °C. The impedance study revealed a significant change of the catalytic behavior in dependency of the fluorine content. BaFeO2.67 revealed a bulk-diffusion limited process, while BaFeO2.33F0.33 appeared to exhibit a fast bulk diffusion and a utilization region δ larger than the electrode thickness L (8 μm). In contrast, BaFeO2F showed very area specific resistances due to the lack of oxygen vacancies. The activation energy for the uptake and conduction process of oxygen was found to be 0.07/0.29 eV (temperature range-dependent), 0.33 eV and 0.67 eV for BaFeO2.67, BaFeO2.33F0.33 and BaFeO2F, respectively.

Phase Stability - Structural and Microstructural Characterization of Al2O3-TiO2 Ceramic Composites Reinforced with La2O3 Addition

2015 ◽  
Vol 820 ◽  
pp. 256-261
Author(s):  
Andrea G. de Sousa ◽  
Sheila A.B.C. Rego ◽  
Ricardo A.S. Ferreira ◽  
Armando H. Shinohara ◽  
Yogendra Prasad Yadava
Keyword(s):  
Phase Stability ◽  
Microstructural Characterization ◽  
Rare Earth Oxide ◽  
Ceramic Composites ◽  
Phase Changes ◽  
X Ray Diffraction ◽  
Good Surface ◽  
The Stability ◽  
New Phase

In this work, we have s produced Al2O3-TiO2 ceramic composites reinforced with rare earth oxide, lantânia (La2O3) ranging from 0 to 2 wt%, for the study of their phase stability, structureand microstructural chacteristics. The ceramic composites were produced by thermo-mechanical process. It was observed from the results of XRD after sintering no new phase is formed in addition to the characteristics of the precursor oxides. DTA shows the stability of the composites studied from 460oC temperature, meaning it does not present more phase changes. It was observed through the analysis of the results of X-ray diffraction after sintering the samples that no new phase is formed in addition to the characteristics of the precursor oxides indicating formation of the composite. However, there was variation in the peak concentration and intensities due to variations in the Al2O3 and La2O3 contents. The results obtained by scanning electron microscopy proved satisfactory with regard to good surface morphology, homogeneity and particle size distribution of the composite sintered at 1390oC for 40 hours. The samples with 1.0% and 1.5% La2O3 addition presented best results regarding these aspects

Processing and Properties of (Zr,Hf)B2-SiC Ceramic Composites

2018 ◽  
Vol 281 ◽  
pp. 438-443 ◽  
Author(s):  
Xiao Tong Zhao ◽  
Hai Long Wang ◽  
Gang Shao ◽  
Bing Bing Fan ◽  
Hong Xia Lu ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Flexural Strength ◽  
Solid Solutions ◽  
Hot Pressing ◽  
Ceramic Composites ◽  
Molar Ratio ◽  
X Ray Diffraction ◽  
X Ray ◽  
Sic Ceramic ◽  
Sic Composites

Different molar ratio of HfB2and ZrB2had been mixed, and 30 vol.% SiC was selected as sintering additives. The mixing powders were sintered by hot pressing at 1900 °C for 1 h under a pressure of 20 MPa in Ar atmosphere. X-ray diffraction, scanning microscopy and Archimedes’s method were used to characterize the phase, microstructure and density of the sintered composites. Meanwhile, the hardness, the fracture toughness and flexural strength of the obtained composites were considered too. It can be found that the (Zr,Hf)B2solid solutions were formed by HfB2and ZrB2during the sintering. The flexural strength of (Zr,Hf)B2-SiC composites increased with the amount of HfB2increasing, which reached (332±40) MPa for the composites content of 70% HfB2. Which fracture toughness was (2.22±0.25) MPa·m1/2. The highest Vickers’ harness of was (24.8±3.4) GPa for the composites content of 50% HfB2.

Fractionation of polymethylene chains: An electron crystallographic investigation

1986 ◽  
Vol 44 ◽  
pp. 794-795
Author(s):  
Douglas L. Dorset
Keyword(s):  
Cross Section ◽  
Binary Systems ◽  
Linear Chain ◽  
Pure Component ◽  
Organic Substrates ◽  
Crystallographic Investigation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Molecular Sizes ◽  
The Stability

A variety of linear chain materials exist as polydisperse systems which are difficultly purified. The stability of continuous binary solid solutions assume that the Gibbs free energy of the solution is lower than that of either crystal component, a condition which includes such factors as relative molecular sizes and shapes and perhaps the symmetry of the pure component crystal structures.Although extensive studies of n-alkane miscibility have been carried out via powder X-ray diffraction of bulk samples we have begun to examine binary systems as single crystals, taking advantage of the well-known enhanced scattering cross section of matter for electrons and also the favorable projection of a paraffin crystal structure posited by epitaxial crystallization of such samples on organic substrates such as benzoic acid.

Dietary Vitamin and Stability of Oral Anticoagulation: Proposal of a Diet with Constant Vitamin K1 Content

1997 ◽  
Vol 77 (03) ◽  
pp. 504-509 ◽  
Author(s):  
Sarah L Booth ◽  
Jacqueline M Charnley ◽  
James A Sadowski ◽  
Edward Saltzman ◽  
Edwin G Bovill ◽  
...  
Keyword(s):  
Dietary Intake ◽  
Vitamin K ◽  
High Performance ◽  
Case Reports ◽  
Food Composition ◽  
Dietary Guidelines ◽  
Dietary Vitamin ◽  
Vitamin K1 ◽  
The Stability ◽  
The Impact

SummaryCase reports cited in Medline or Biological Abstracts (1966-1996) were reviewed to evaluate the impact of vitamin K1 dietary intake on the stability of anticoagulant control in patients using coumarin derivatives. Reported nutrient-drug interactions cannot always be explained by the vitamin K1 content of the food items. However, metabolic data indicate that a consistent dietary intake of vitamin K is important to attain a daily equilibrium in vitamin K status. We report a diet that provides a stable intake of vitamin K1, equivalent to the current U.S. Recommended Dietary Allowance, using food composition data derived from high-performance liquid chromatography. Inconsistencies in the published literature indicate that prospective clinical studies should be undertaken to clarify the putative dietary vitamin K1-coumarin interaction. The dietary guidelines reported here may be used in such studies.

HUMO-LUMO Studies on Methyl Orange Doped ZTS Crystals for Laser Applications

2018 ◽  
Vol 6 (6) ◽  
pp. 362
Author(s):  
G. Suresh ◽  
K. Sambath Kumar ◽  
P. Ambalavanan ◽  
P. Kumaresan
Keyword(s):  
Molecular Electrostatic Potential ◽  
Nbo Analysis ◽  
Inorganic Materials ◽  
Thermo Gravimetric ◽  
Laser Applications ◽  
Charge Delocalization ◽  
Device Applications ◽  
Warming Rate ◽  
The Stability ◽  
Homo Lumo

Zinc Thiourea Sulphate (ZTS), crystal is a magnificent metal natural compound, which consolidates the upsides of both natural and inorganic materials when contrasted and other customary non-linear optical materials and in this way can be utilized as a part of a more extensive scope of uses. Late endeavors at delivering new recurrence transformation materials have concentrated essentially on expanding the extent of the NLO properties that can recurrence twofold low pinnacle control sources, for example, diode lasers.  The thermo gravimetric examination (TGA) and differential warm investigation (DTA) were completed utilizing Seiko warm analyzer at warming rate 20°C/min in air to decide the warm dependability of the compound. ZTS crystals were developed by moderate cooling procedure. This empowers the development of mass gems along all the three bearings at an ideal pH. FTIR examines demonstrate that in the spectra of ZTS there is a move in the recurrence band in the low-recurrence district which uncovers that thiourea shapes sulfur-to-zinc securities in the ZTS crystals. The stability and charge delocalization of the molecule were also studied by natural bond orbital (NBO) analysis. The HOMO-LUMO energies describe the charge transfer takes place within the molecule. Molecular electrostatic potential has been analyzed.  The developments try in extensive scale with this enhanced pH qualities is required to yield mass crystal appropriate for laser combination tests and SHG device applications.

IMPACT OF GOVERNMENT DEBT ON FINANCIAL SECURITY OF UKRAINE

2017 ◽  
Author(s):  
Olena Pikaliuk ◽  
◽  
Dmitry Kovalenko ◽  
Keyword(s):  
Economic Development ◽  
Public Debt ◽  
Positive Impact ◽  
The State ◽  
Financial Security ◽  
State Budget ◽  
The Public ◽  
Debt Security ◽  
The Stability ◽  
The Impact

One of the main criteria for economic development is the size of the public debt and its dynamics. The article considers the impact of public debt on the financial security of Ukraine. The views of scientists on the essence of public debt and financial security of the state are substantiated. An analysis of the dynamics and structure of public debt of Ukraine for 2014-2019. It is proved that one of the main criteria for economic development is the size of public debt and its dynamics. State budget deficit, attracting and using loans to cover it have led to the formation and significant growth of public debt in Ukraine. The volume of public debt indicates an increase in the debt security of the state, which is a component of financial security. Therefore, the issue of the impact of public debt on the financial security of Ukraine is becoming increasingly relevant. The constant growth and large amounts of debt make it necessary to study it, which will have a positive impact on economic processes that will ensure the stability of the financial system and enhance its security.

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