Structural features in fluorite compounds relevant for nuclear applications

2012 ◽  
Vol 1383 ◽  
Author(s):  
Gianguido Baldinozzi ◽  
Lionel Desgranges ◽  
David Simeone ◽  
Dominique Gosset ◽  
Laurence Luneville
Keyword(s):  
Phase Transition ◽  
Homogeneity Range ◽  
Structural Features ◽  
Radiation Tolerance ◽  
High Radiation ◽  
Structural Modifications ◽  
Ideal Composition ◽  
Nuclear Applications ◽  
Nonstoichiometric Compounds ◽  
The Ideal

ABSTRACTOxides with fluorite (or fluorite related) structures form a large class of compounds with a high radiation tolerance, somewhat related to their peculiar ability to accommodate a variety of defects and to form nonstoichiometric compounds with a large homogeneity range. Structural modifications are generally observed when the departure from the ideal composition is large. We discuss these structural features using an approach based on the crystal symmetry analysis based on the phase transition mechanisms in compounds relevant for nuclear applications.

Critical temperatures of superconductivity and neutron diffraction studies at 293 and at 10 K of molybdenum–iridium single crystals of A15 structure

1989 ◽  
Vol 22 (1) ◽  
pp. 23-25 ◽  
Author(s):  
R. Koksbang ◽  
S. E. Rasmussen ◽  
R. G. Hazell
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Structural Phase ◽  
Cylindrical Sample ◽  
Inductive Method ◽  
Critical Temperatures ◽  
Lattice Constants ◽  
Main Transition ◽  
Ideal Composition ◽  
The Ideal

A crystal of dimensions 2.5 × 2.5 × 1.8 mm and of composition Mo3.25Ir was examined by neutron diffraction at 293 and 10 K. It has the A15 structure for which the space group is Pm3n and the ideal composition would be Mo3Ir. Least-squares refinements gave R(F) values of 0.013 and 0.017 for the 293 and the 10 K data, respectively. No structural phase transition was observed at 10 K. The lattice constants found were a = 4.967 (2) Å at 293 K and 4.958 (2) Å at 10 K. The transition temperature to superconductivity of the crystal was measured by an inductive method. An onset of superconductivity was found at 9.25 (5) K and a main transition at 9.10 (5) K. Another, approximately cylindrical, sample of volume 117 mm3 showed an onset at 8.6 (1) K and a main transition at 8.0 (1) K. About two thirds of this sample was a single-crystal.

[NiEn3]WO4. Crystal Structural Features Of The Phase Transition At 269 K

2018 ◽  
Vol 59 (8) ◽  
pp. 1897-1902 ◽  
Author(s):  
S. P. Khranenko ◽  
A. S. Sukhikh ◽  
D. P. Pishchur ◽  
P. S. Buneeva ◽  
V. Yu. Komarov ◽  
...  
Keyword(s):  
Phase Transition ◽  
Structural Features ◽  
Crystal Structural

From Structure Topology to Chemical Composition. XXIX. Revision of the Crystal Structure of Perraultite, NaBaMn4Ti2(Si2O7)2O2(OH)2F, a Seidozerite-Supergroup TS-Block Mineral from the Oktyabr'skii Massif, Ukraine, and Discreditation of Surkhobite

2021 ◽  
Author(s):  
Elena Sokolova ◽  
Maxwell C. Day ◽  
Frank C. Hawthorne ◽  
Atali A. Agakhanov ◽  
Fernando Cámara ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Chemical Composition ◽  
Structure Type ◽  
Titanium Silicate ◽  
Space Group ◽  
Structure Topology ◽  
Ideal Composition ◽  
Using Data ◽  
Cation Sites ◽  
The Ideal

ABSTRACT The crystal structure of perraultite from the Oktyabr'skii massif, Donetsk region, Ukraine (bafertisite group, seidozerite supergroup), ideally NaBaMn4Ti2(Si2O7)2O2(OH)2F, Z = 4, was refined in space group C to R1 = 2.08% on the basis of 4839 unique reflections [Fo > 4σFo]; a = 10.741(6), b = 13.841(8), c = 11.079(6) Å, α = 108.174(6), β = 99.186(6), γ = 89.99(1)°, V = 1542.7(2.7) Å3. Refinement was done using data from a crystal with three twin domains which was part of a grain used for electron probe microanalysis. In the perraultite structure [structure type B1(BG), B – basic, BG – bafertisite group], there is one type of TS (Titanium-Silicate) block and one type of I (Intermediate) block; they alternate along c. The TS block consists of HOH sheets (H – heteropolyhedral, O – octahedral). In the O sheet, the ideal composition of the five [6]MO sites is Mn4 apfu. There is no order of Mn and Fe2+ in the O sheet. The MH octahedra and Si2O7 groups constitute the H sheet. The ideal composition of the two [6]MH sites is Ti2 apfu. The TS blocks link via common vertices of MH octahedra. The I block contains AP(1,2) and BP(1,2) cation sites. The AP(1) site is occupied by Ba and the AP(2) site by K > Ba; the ideal composition of the AP(1,2) sites is Ba apfu. The BP(1) and BP(2) sites are each occupied by Na > Ca; the ideal composition of the BP(1,2) sites is Na apfu. We compare perraultite and surkhobite based on the work of Sokolova et al. (2020) on the holotype sample of surkhobite: space group C , R1 = 2.85 %, a = 10.728(6), b = 13.845(8), c = 11.072(6) Å, α = 108.185(6), β = 99.219(5), γ = 90.001(8)°, V = 1540.0(2.5) Å3; new EPMA data. We show that (1) perraultite and surkhobite have identical chemical composition and ideal formula NaBaMn4Ti2(Si2O7)2O2(OH)2F; (2) perraultite and surkhobite are isostructural, with no order of Na and Ca at the BP(1,2) sites. Perraultite was described in 1991 and has precedence over surkhobite, which was redefined as “a Ca-ordered analogue of perraultite” in 2008. Surkhobite is not a valid mineral species and its discreditation was approved by CNMNC IMA (IMA 20-A).

Tanshinone IIA: Pharmacology, total synthesis, and progress in structure-modifications

2021 ◽  
Vol 28 ◽  
Author(s):  
Xing Huang ◽  
Hao Deng ◽  
Qing-kun Shen ◽  
Zhe-Shan Quan
Keyword(s):  
Herbal Medicine ◽  
Total Synthesis ◽  
Chinese Herbal Medicine ◽  
Biological Activities ◽  
Structural Features ◽  
Tanshinone Iia ◽  
Structural Modifications ◽  
Chinese Herbal ◽  
Bioactive Constituent

: Tanshinone IIA, a major bioactive constituent of Danshen, a Chinese herbal medicine, has gained extensive exploration owing to its unique structural features and multiple promising biological activities. This review focuses on the pharmacology, total synthesis, and structural modifications of tanshinone IIA. We hope this review will contribute to a better understanding of the progress in the field and provide constructive suggestions for further study of tanshinone IIA.

scholarly journals Pathological transitions in myelin membranes driven by environmental and multiple sclerosis conditions

2018 ◽  
Vol 115 (44) ◽  
pp. 11156-11161 ◽  
Author(s):  
Rona Shaharabani ◽  
Maor Ram-On ◽  
Yeshayahu Talmon ◽  
Roy Beck
Keyword(s):  
Multiple Sclerosis ◽  
Phase Transition ◽  
Lipid Composition ◽  
Environmental Conditions ◽  
Structural Changes ◽  
Environmental Changes ◽  
Hexagonal Phase ◽  
Structural Phase ◽  
Structural Modifications ◽  
Transition Points

Multiple sclerosis (MS) is an autoimmune disease, leading to the destruction of the myelin sheaths, the protective layers surrounding the axons. The etiology of the disease is unknown, although there are several postulated environmental factors that may contribute to it. Recently, myelin damage was correlated to structural phase transition from a healthy stack of lamellas to a diseased inverted hexagonal phase as a result of the altered lipid stoichiometry and low myelin basic protein (MBP) content. In this work, we show that environmental conditions, such as buffer salinity and temperature, induce the same pathological phase transition as in the case of the lipid composition in the absence of MBP. These phase transitions have different transition points, which depend on the lipid’s compositions, and are ion specific. In extreme environmental conditions, we find an additional dense lamellar phase and that the native lipid composition results in similar pathology as the diseased composition. These findings demonstrate that several local environmental changes can trigger pathological structural changes. We postulate that these structural modifications result in myelin membrane vulnerability to the immune system attacks and thus can help explain MS etiology.

scholarly journals OPTIMIZATION OF THE USE OF FLY ASH AS AN ADDITIVE PORTLAND COMPOSITE CEMENT (PCC)

2019 ◽  
Vol 4 (2) ◽  
pp. 61-72 ◽  
Author(s):  
Leni Rumiyanti ◽  
Listiani Listiani ◽  
Tika Damayanti
Keyword(s):  
Fly Ash ◽  
Setting Time ◽  
Quality Analysis ◽  
Insoluble Residue ◽  
Optimum Conditions ◽  
Free Lime ◽  
Composite Cement ◽  
Ideal Composition ◽  
Physical And Chemical ◽  
The Ideal

Research has been carried out on the optimization of the use of Lahat Fly Ash as an Additive Portland Composite Cement (PCC) which aims to determine the optimum conditions for adding Lahat fly ash to produce cement with physical and chemical requirements in accordance with SNI 7064:2014 and discover the ideal composition of cement with fly additions Lahat ash from various cement compositions. The quality analysis in making PCC cement is chemically in the form of Insoluble Residue (IR), Loss of Ignition (LOI), and free lime (FCaO) as well as the quality of physics in the form of Blaine, setting time, and cement mortar compressive strength. The results obtained after the process of making PCC cement with the addition of 14% Lahat fly ash, namely PCC cement in optimum conditions with physical and chemical requirements in accordance with SNI 7064: 2014 where the ideal composition of PCC cement manufacture is 14% Lahat fly ash, clinker 62%, 3% gypsum, 18% limestone, and 3% pozzolans in making PCC cement. Therefore, Lahat fly ash can be used as an alternative mixture in making PCC cement.

Compatibility of Ionic Liquid With Glycerol Monooleate and Molybdenum Dithiocarbamate as Additives in Bio-Based Lubricant

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
A. Z. Syahir ◽  
M. H. Harith ◽  
N. W. M. Zulkifli ◽  
H. H. Masjuki ◽  
M. A. Kalam ◽  
...  
Keyword(s):  
Ionic Liquid ◽  
Antiwear Additives ◽  
Box Behnken Design ◽  
Base Oil ◽  
Order Polynomial ◽  
Ideal Composition ◽  
Worn Surface ◽  
Glycerol Monooleate ◽  
Rsm Technique ◽  
The Ideal

Abstract This study reports the tribological characteristics of trimethylolpropane trioleate (TMPTO) additivated with antifriction and antiwear additives, which are ionic liquid (IL), glycerol monooleate (GMO), and molybdenum dithiocarbamate (MoDTC). In addition, to obtain the ideal composition that results in the minimal coefficient of friction (COF), optimization tool was employed using response surface methodology (RSM) technique with the Box–Behnken design. The IL used in this study was a phosphorus-type IL, namely trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl) phosphinate, [P14,6,6,6][TMPP]. The resulting COF and worn surface morphology were investigated using high-frequency reciprocating rig (HFRR) tribotester and scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. From the experimental results, a second-order polynomial mathematical model was constructed and able to statistically predict the resulting COF. The optimized values that resulted in the lowest average COF of 0.0458 were as follows: 0.93 wt% IL, 1.49 wt% GMO, and 0.52 wt% MoDTC. The addition of IL into neat base oil managed to reduce the COF, while the combination of IL, GMO, and MoDTC at optimum concentration further reduced the average COF and wear as observed through SEM micrographs when compared with those of additive-free TMPTO, suggesting that GMO and MoDTC were compatible to be used with IL.

scholarly journals Lipid vesicles: applications, principal components and methods used in their formulations: A review

2020 ◽  
Vol 25 (2) ◽  
pp. 339-352
Author(s):  
Cicera Janaine Janaine Camilo ◽  
Débora Odilia Duarte Leite ◽  
Angelo Roncalli Alves Silva ◽  
Irwin Rose Alencar Menezes ◽  
Henrique Douglas Melo Coutinho ◽  
...  
Keyword(s):  
Lipid Vesicles ◽  
Phospholipid Bilayer ◽  
Future Research ◽  
Ionic Surfactants ◽  
Medical Field ◽  
Lipophilic Compounds ◽  
Ideal Composition ◽  
Low Toxicity ◽  
Main Components ◽  
The Ideal

Liposomes and niosomes are currently the most studied lipid vesicles in the nanomedicine field. The system formed by a phospholipid bilayer in aqueous medium allows these vesicles to carry both hydrophilic and lipophilic compounds, providing an increase in solubility of drugs lready used in conventional therapy. The focus on the development of these vesicles should be directed to determining the ideal composition, with low toxicity, biocompatibility and which remains stable for long periods. These characteristics are related to the components used for formulation and the substances that will be encapsulated. Another important point relates to the methods used during formulation, which are important in determining the type of vesicle formed, whether these be large or small, unilamellar or multilamellar. Because of the deliberate actions applied in the development of these vesicles, this review sought to gather updated information regarding the different methods used, including their main components while considering the behavior of each of them when used in different formulations. Also, data showing the importance of formulations in the medical field evidencing studies performed with liposome and niosome vesicles as promising in this area, and others, were included. The approach allows a better understanding of the participation of components in formulations such as cholesterol and non-ionic surfactants, as well as the basis for choosing the ideal components and methods for future research in the development of these vesicles.

Phase stability of Ni–Al nanoparticles

1999 ◽  
Vol 14 (7) ◽  
pp. 2849-2854 ◽  
Author(s):  
S. Ramos de Debiaggi ◽  
J. M. Campillo ◽  
A. Caro
Keyword(s):  
Phase Stability ◽  
Intermediate Phase ◽  
Surface Effect ◽  
Embedded Atom ◽  
Al Nanoparticles ◽  
Simulation Techniques ◽  
Ideal Composition ◽  
Nanoparticle System ◽  
Equilibrium Structures ◽  
The Ideal

The phase stability of Ni–Al clusters of nanometer size was studied by using the embedded atom model and Monte Carlo simulation techniques. For temperatures of 500 and 1000 K and for a range of compositions below 70 at.% Al, the equilibrium structures of the system were determined and compared with the bulk results. We found that the bulk NiAl (B2) and Ni3Al (L12) phases were stable phases in the nanoparticle system; however, for deviations from ideal composition, the analysis revealed that, because of the surface effect, the composition of the clusters was not uniform. There was a core region in which the structure was ordered, B2 or L12, with a composition very close to the ideal, and a chemically disordered mantle region that allocated the deviations from ideal stoichiometries; in this way, a larger phase field appeared, indicating trends similar to those found in experiments on nanocrystalline Ni–Al powder [S.K. Pabi and B.S. Murty, Mater. Sci. Eng. A214, 146 (1996)]. For concentrations between 37 and 51 at.% Al, an intermediate phase, similar to the tetragonal L10 martensite, appeared.

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