scholarly journals Low-temperature Mossbauer studies of the phase composition and structural stability of iron (III) oxide/hydroxide nanocomposite

2021 ◽  
Vol 22 (2) ◽  
pp. 307-312
Author(s):  
B.K. Ostafiychuk ◽  
V.V. Moklyak ◽  
V.D. Fedoriv ◽  
A.B. Hrubiak ◽  
Yu.V. Yavorskyi ◽  
...  
Keyword(s):  
Low Temperature ◽  
Structural Stability ◽  
Integral Intensity ◽  
Amorphous State ◽  
Mössbauer Studies ◽  
X Ray ◽  
Annealing Temperatures ◽  
Oxide Hydroxide ◽  
Mechanism Of Growth ◽  
Magnetically Ordered

In article present the results of low-temperature Mossbauer studies of iron (III) oxide/hydroxide nanocomposite synthesized by the method of deposition. Based on these studies, the composition of the synthesized composite was revealed. The nanodispersed composite with a specific surface 280 m2/g is a hematite in the weakly disordered crystalline state (CSR 10 nm), and a lepidocrocite in the X-ray amorphous state (particles size 3-4 nm). The relative integral intensity of the Zeeman sextet, which corresponds to the magnetically ordered phase of hematite, is practically unchanged and is about 17%. The tendency to divide the magnetically ordered component into two sextets, which differ in quadrupole splitting QS= –0.21 mm/s and QS= 0.21 mm/s, respectively, is observed starting from a temperature of 190 K. As a result of annealing of the synthesized material at a temperature of 200°C, a slight redistribution (≈ 5%) of the content of paramagnetic and magnetically ordered components was recorded, which indicates the structural stability of the nanoparticles of the lepidocrocite γ-FeOOH phase at this temperature. Increase of  annealing temperatures to 500oC leads to the predicted course of the phase transition γ-FеООH ® α-Fе2О3. The mechanism of growth of hematite crystallites during sintering due to fixation side faces of larger α-Fe2O3 phase of nanoparticles of the γ-FeOOH phase with simultaneous transformation of their crystal structure to side faces of larger α-Fe2O3 phase particles is presented.

Crystallized Rubber

1932 ◽  
Vol 5 (3) ◽  
pp. 245-248
Author(s):  
R. Pummerer ◽  
G. von Susich
Keyword(s):  
Low Temperature ◽  
Specific Gravity ◽  
Amorphous State ◽  
Heat Content ◽  
X Rays ◽  
Discontinuous Change ◽  
Spontaneous Crystallization ◽  
X Ray ◽  
Degree Of Orientation ◽  
Crystallization From Solution

Abstract In recent years various attempts have been made to crystallize natural rubber by some means other than by stretching. In the present paper the results of these experiments are described, together with some new observations, in order to settle the present status of the problem. The processes of crystallization are divided into three groups and discussed individually. 1. Spontaneous crystallization under conditions which vary but little from the normal conditions. 2. Crystallization from solution after purification. 3. Crystallization of a solution of purified rubber by cooling to a low temperature. It is a generally known fact that after storage for a year, plantation rubber becomes stiff, inelastic, and opaque. A rubber altered in this way is known as “frozen” rubber, because this change has been observed most frequently after storage in a cold place. The x-ray investigations of Katz and Bing have rendered it certain that during “freezing” there is crystallization of the rubber, because when subjected to x-rays frozen rubber shows crystalline interferences from which the same crystal lattice is calculated as that which is formed on stretching, except that the degree of orientation in frozen rubber differs from that of stretched rubber. This is seen in x-ray diagrams, where the nearly point interferences of the stretched samples lie on the same Debye-Scherrer circles as those of frozen rubber. There have been rather exhaustive investigations on those changes in frozen rubber which appear on warming, viz., during transformation of the crystalline to the amorphous state (the “fusion process”), and which are characterized by disappearance of the crystal interferences and by a discontinuous change in the heat content, specific gravity, hardness, and light absorption.

scholarly journals Особенности фазообразования TbBO-=SUB=-3-=/SUB=- при изотермических отжигах

2019 ◽  
Vol 61 (2) ◽  
pp. 340
Author(s):  
И.М. Шмытько
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Annealing Temperature ◽  
Initial Mixture ◽  
Amorphous Precursor ◽  
Two Phase ◽  
X Ray ◽  
Annealing Temperatures ◽  
Low Temperature Annealing ◽  
Hypothetical Explanation

AbstractDetailed X-ray studies of changes in the structure of terbium orthoborate TbBO_3 in the course of successive high-temperature isothermal annealing of the initial mixture in the form of an amorphous precursor and in the form of a homogenized mixture of microcrystalline Tb_7O_12 and B_2O_3 powders have been carried out. It is shown that the formation of TbBO_3 crystals in both cases occurs through the formation of intermediate two-phase states. Particularly, the triclinic high-temperature ν-TbBO_3 phase is formed already at the first crystallization stages (about 600°C) almost simultaneously with the equilibrium vaterite modification of TbBO_3 (sp. gr. P 63/ mmc ) during low-temperature annealing of an amorphous precursor, which transforms into the vaterite modification at an annealing temperature of 850°C. The phase of monoclinic terbium trioxoborate TbB_3O_6 is formed at the first stages of phase formation (about 800°C) almost simultaneously with the vaterite phase when the feedstock is annealed in the form of a homogenized mixture of microcrystalline Tb_7O_12 and B_2O_3 powders. It also transforms into the vaterite modification at an annealing temperature of 950°, which is preserved up to the highest annealing temperatures in the experiment (1200°C). A hypothetical explanation of the formation of such two-phase states during low-temperature annealing of the feedstock and their disappearance at higher annealing temperatures is proposed.

scholarly journals Role of the electronically-active amorphous state in low-temperature processed In2O3 thin-film transistors

2020 ◽  
Vol 1 (2) ◽  
pp. 167-176 ◽  
Author(s):  
Ahmad R. Kirmani ◽  
Emily F. Roe ◽  
Christopher M. Stafford ◽  
Lee J. Richter
Keyword(s):  
Thin Film ◽  
Low Temperature ◽  
Electron Mobility ◽  
Thin Film Transistors ◽  
Sol Gel ◽  
Amorphous State ◽  
X Ray ◽  
X Ray Scattering ◽  
Process Structure

Process-structure-transport relationships in low-temperature-processed, blade-coated In2O3 transistors using sol–gel and combustion chemistries are explored with X-ray scattering techniques. Electron mobility of ≈4.5 cm2 V−1 s−1 is achieved at ≈220 °C.

Low temperature x-ray microanalysis of frozen-hydrated tobacco leaves

1984 ◽  
Vol 42 ◽  
pp. 284-285
Author(s):  
S. Edith Taylor ◽  
Patrick Echlin ◽  
May McKoon ◽  
Thomas L. Hayes
Keyword(s):  
Low Temperature ◽  
Lemna Minor ◽  
Root Tips ◽  
Tobacco Leaves ◽  
X Ray ◽  
Whole Cells ◽  
Carbon Coated ◽  
The Right ◽  
Beam Currents ◽  
The University

Low temperature x-ray microanalysis (LTXM) of solid biological materials has been documented for Lemna minor L. root tips. This discussion will be limited to a demonstration of LTXM for measuring relative elemental distributions of P,S,Cl and K species within whole cells of tobacco leaves.Mature Wisconsin-38 tobacco was grown in the greenhouse at the University of California, Berkeley and picked daily from the mid-stalk position (leaf #9). The tissue was excised from the right of the mid rib and rapidly frozen in liquid nitrogen slush. It was then placed into an Amray biochamber and maintained at 103K. Fracture faces of the tissue were prepared and carbon-coated in the biochamber. The prepared sample was transferred from the biochamber to the Amray 1000A SEM equipped with a cold stage to maintain low temperatures at 103K. Analyses were performed using a tungsten source with accelerating voltages of 17.5 to 20 KV and beam currents from 1-2nA.

Bulk standards for low-temperature biological x-ray microanalysis

1984 ◽  
Vol 42 ◽  
pp. 282-283
Author(s):  
P. Echlin ◽  
M. McKoon ◽  
E.S. Taylor ◽  
C.E. Thomas ◽  
K.L. Maloney ◽  
...  
Keyword(s):  
Phase Separation ◽  
Low Temperature ◽  
Analytical Method ◽  
Salt Solutions ◽  
Absolute Concentration ◽  
Cooling Process ◽  
X Ray ◽  
The Absolute ◽  
Analytical Procedures ◽  
Electrical Conductors

Although sections of frozen salt solutions have been used as standards for x-ray microanalysis, such solutions are less useful when analysed in the bulk form. They are poor thermal and electrical conductors and severe phase separation occurs during the cooling process. Following a suggestion by Whitecross et al we have made up a series of salt solutions containing a small amount of graphite to improve the sample conductivity. In addition, we have incorporated a polymer to ensure the formation of microcrystalline ice and a consequent homogenity of salt dispersion within the frozen matrix. The mixtures have been used to standardize the analytical procedures applied to frozen hydrated bulk specimens based on the peak/background analytical method and to measure the absolute concentration of elements in developing roots.

Role of boundaries in the crystallization of amorphous films

1988 ◽  
Vol 46 ◽  
pp. 626-627
Author(s):  
D. A. Smith
Keyword(s):  
Low Temperature ◽  
Amorphous State ◽  
Nucleation And Growth ◽  
Amorphous Films ◽  
Island Nucleation ◽  
Surface Steps ◽  
Transmission Electron ◽  
Component Systems ◽  
Temperature Deposition

The nucleation and growth processes which lead to the formation of a thin film are particularly amenable to investigation by transmission electron microscopy either in situ or subsequent to deposition. In situ studies have enabled the observation of island nucleation and growth, together with addition of atoms to surface steps. This paper is concerned with post-deposition crystallization of amorphous alloys. It will be argued that the processes occurring during low temperature deposition of one component systems are related but the evidence is mainly indirect. Amorphous films result when the deposition conditions such as low temperature or the presence of impurities (intentional or unintentional) preclude the atomic mobility necessary for crystallization. Representative examples of this behavior are CVD silicon grown below about 670°C, metalloids, such as antimony deposited at room temperature, binary alloys or compounds such as Cu-Ag or Cr O2, respectively. Elemental metals are not stable in the amorphous state.

Micro X-Ray Diffraction Study of Polycrystalline MgB 2 Wire and Evaluation of Carbon Doping Effect Via Low-Temperature Sintering

2019 ◽  
Author(s):  
Minoru Maeda ◽  
Dipak Patel, Dr. ◽  
Hiroaki Kumakura, Dr. ◽  
Gen Nishijima, Dr. ◽  
Akiyoshi Matsumoto, Dr. ◽  
...  
Keyword(s):  
Low Temperature ◽  
Diffraction Study ◽  
Carbon Doping ◽  
Doping Effect ◽  
Low Temperature Sintering ◽  
X Ray Diffraction ◽  
X Ray

The Application of X-Ray Diffraction at Elevated Temperatures to Study the Mechanism of Formation of Sodium Tripolyphosphate

1961 ◽  
Vol 5 ◽  
pp. 276-284
Author(s):  
E. L. Moore ◽  
J. S. Metcalf
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Amorphous Phase ◽  
Elevated Temperatures ◽  
Sodium Tripolyphosphate ◽  
X Ray Diffraction ◽  
Mechanism Of Formation ◽  
X Ray ◽  
Temperature Form ◽  
High Temperature Form

AbstractHigh-temperature X-ray diffraction techniques were employed to study the condensation reactions which occur when sodium orthophosphates are heated to 380°C. Crystalline Na4P2O7 and an amorphous phase were formed first from an equimolar mixture of Na2HPO4·NaH2PO4 and Na2HPO4 at temperatures above 150°C. Further heating resulted in the formation of Na5P3O10-I (high-temperature form) at the expense of the crystalline Na4P4O7 and amorphous phase. Crystalline Na5P3O10-II (low-temperature form) appears after Na5P3O10-I.Conditions which affect the yield of crystalline Na4P2O7 and amorphous phase as intermediates and their effect on the yield of Na5P3O10 are also presented.

scholarly journals Low Temperature Water-Gas Shift: Enhancing Stability through Optimizing Rb Loading on Pt/ZrO2

Catalysts ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 210
Author(s):  
Caleb Daniel Watson ◽  
Michela Martinelli ◽  
Donald Charles Cronauer ◽  
A. Jeremy Kropf ◽  
Gary Jacobs
Keyword(s):  
Low Temperature ◽  
Hydrogen Transfer ◽  
Water Gas Shift ◽  
Significant Shift ◽  
Catalyst Activation ◽  
X Ray ◽  
Temperature Programmed ◽  
Water Gas ◽  
X Ray Absorption ◽  
Temperature Water

Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. At sufficient loadings, the alkali metal can weaken the formate C–H bond and promote formate dehydrogenation, which is the proposed rate determining step in the formate associative mechanism. In a continuation of these studies, the effect of Rb promotion on Pt/ZrO2 is examined herein. Pt/ZrO2 catalysts were prepared with several different Rb loadings and characterized using temperature programmed reduction mass spectrometry (TPR-MS), temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), an X-ray absorption near edge spectroscopy (XANES) difference procedure, extended X-ray absorption fine structure spectroscopy (EXAFS) fitting, TPR-EXAFS/XANES, and reactor testing. At loadings of 2.79% Rb or higher, a significant shift was seen in the formate ν(CH) band. The results showed that a Rb loading of 4.65%, significantly improves the rate of formate decomposition in the presence of steam via weakening the formate C–H bond. However, excessive rubidium loading led to the increase in stability of a second intermediate, carbonate and inhibited hydrogen transfer reactions on Pt through surface blocking and accelerated agglomeration during catalyst activation. Optimal catalytic performance was achieved with loadings in the range of 0.55–0.93% Rb, where the catalyst maintained high activity and exhibited higher stability in comparison with the unpromoted catalyst.

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