Doping effects on coarsening of Y2BaCuO5 phase in liquid

1993 ◽  
Vol 8 (6) ◽  
pp. 1240-1246 ◽  
Author(s):  
Teruo Izumi ◽  
Yuichi Nakamura ◽  
Yuh Shiohara
Keyword(s):  
Ostwald Ripening ◽  
Average Diameter ◽  
Holding Time ◽  
Doping Effects ◽  
Thomson Coefficient

The coarsening rate of Y2BaCuO5 (211) phase in liquid was investigated by observations of samples which were held at 1070 °C for different holding times. The 211 phase formed rod-like shapes, and the diameters increased with the increase in the holding time. The average diameter increased in proportion to t1/3 (t, holding time). This means that coarsening can be explained by the modified Ostwald ripening theory. Platinum-doping suppressed the coarsening rate and alumina-doping promoted it. However, both coarsening rates were also proportional to t1/3. The changes in the rate can be represented by the changes of the DLΓ value (DL, diffusivity in liquid and Γ, Gibbs—Thomson coefficient) using the Ostwald ripening theory; i.e., the value is made lower by platinum-doping and higher by alumina-doping.

Growth Mechanism and Electrochemical Properties of Porous Hollow Tin Dioxide Nanospheres

NANO ◽  
2015 ◽  
Vol 10 (06) ◽  
pp. 1550087 ◽  
Author(s):  
Youwen Yang ◽  
Dongming Ma ◽  
Ting Cheng ◽  
Yuanhao Gao ◽  
Guanghai Li
Keyword(s):  
Growth Mechanism ◽  
Tin Dioxide ◽  
Ostwald Ripening ◽  
Lithium Ion ◽  
Average Diameter ◽  
Reversible Capacity ◽  
Cycling Performance ◽  
Experimental Conditions ◽  
Electrochemical Tests ◽  
Hydrolysis Method

Porous hollow SnO 2 nanospheres were prepared by means of enforced Sn 2+ hydrolysis method under hydrochloric acid medium. These hollow nanospheres with an average diameter of 220nm had a very thin shell thickness of about 40nm and were surrounded by elongated octahedral-like nanoparticles with the apex oriented outside. The experimental conditions, such as HCl content, reaction temperature and time directly dominated the morphology, structure and crystallinity of the obtained samples. A pre-oxidation-nucleation-growth mechanism and inside-out Ostwald-ripening method was proposed on the basis of the previous research and time-dependent experiments. Electrochemical tests showed that the porous hollow SnO 2 nanospheres exhibited improved cycling performance for anode materials of lithium-ion batteries, which retained a high reversible capacity of 540.0mAhg-1, and stable cyclic retention at 120th cycle.

Millimetre-scale growth of single-wall carbon nanotube forests using an aluminium nitride catalyst underlayer

MRS Advances ◽  
2019 ◽  
Vol 4 (3-4) ◽  
pp. 177-183
Author(s):  
Takashi Tsuji ◽  
Naoyuki Matsumoto ◽  
Hirokazu Takai ◽  
Shunsuke Sakurai ◽  
Don N. Futaba
Keyword(s):  
Carbon Nanotube ◽  
Photoelectron Spectroscopy ◽  
High Efficiency ◽  
Ostwald Ripening ◽  
Average Diameter ◽  
Aluminium Nitride ◽  
High Yield ◽  
Force Microscopy ◽  
Transmission Electron ◽  
Carbon Nanotube Forests

ABSTRACTWe have demonstrated the high yield (∼900 μm) and highly single-wall selective (>95%) growth of carbon nanotube (CNT) forest using aluminium nitride (AlN) as a catalyst underlayer. Such high efficiency and single-wall selectivity have not been previously reported using this underlayer system. Evaluation with transmission electron microscopy showed that the average diameter of the grown carbon nanotubes was ∼3.0 nm, which is similar to those grown on alumina underlayers. In addition, characterization of the catalyst/underlayer system using atomic force microscopy and X-ray photoelectron spectroscopy suggests that neither Ostwald ripening along the surface nor catalyst subsurface diffusion into the AlN underlayer are severely occurring at the growth temperature, leading to the creation of the stable and dense small nanoparticle array to achieve an efficient growth of single-wall CNTs.

Effect of isothermal process parameters on semi-solid microstructure of chip-based Al–Cu–Mn–Ti alloy prepared by SIMA method

2020 ◽  
Vol 34 (33) ◽  
pp. 2050385
Author(s):  
Ye Wang ◽  
Maoliang Hu ◽  
Hongyu Xu ◽  
Zesheng Ji ◽  
Xuefeng Wen ◽  
...  
Keyword(s):  
Process Parameters ◽  
Ostwald Ripening ◽  
Isothermal Holding ◽  
Treatment Temperature ◽  
Holding Time ◽  
Isothermal Treatment ◽  
Isothermal Process ◽  
Semi Solid ◽  
Average Size ◽  
Relationship Of

A typical Al–Cu–Mn–Ti aluminum alloy chip was adopted to prepare semi-solid billets by a Strain-Induced Melt Activation (SIMA) method, and the effects of isothermal process parameters on the semi-solid microstructure evolution of the alloy were investigated in this work. The result showed that semi-solid billets with highly spheroidal and homogeneous fine grains could be prepared from chips by the SIMA method. With the increase of isothermal temperature, the finer and near-spherical grains are obtained, the grains coarsen and became ellipse at 903 K because of the coarsening mechanisms of coalescence and Ostwald ripening. The relationship of isothermal holding time and grains size followed the LSW theory well, and more spherical microstructure can be brought by prolonging the holding time until 3000 s. Thus, the optimal isothermal treatment temperature is 893 K and holding time is 3000 s, the corresponding average size and roundness of grains are 137 [Formula: see text]m and 1.108, respectively.

scholarly journals The Influence of Holding Time on the Microstructure Evolution of Mg–10Zn–6.8Gd–4Y Alloy during Semi-Solid Isothermal Heat Treatment

Metals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 420 ◽  
Author(s):  
Shuang Nie ◽  
Bingyang Gao ◽  
Xuejian Wang ◽  
Zhiqiang Cao ◽  
Enyu Guo ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Grain Boundaries ◽  
Microstructure Evolution ◽  
Treatment Process ◽  
Ostwald Ripening ◽  
Eutectic Structure ◽  
Holding Time ◽  
Isothermal Heat Treatment ◽  
Heat Treatment Process ◽  
Semi Solid

A semi-solid microstructure of Mg–10Zn–6.8Gd–4Y alloys is acquired via an isothermal heat treatment process, and the effects of the holding time on the microstructure evolution of Mg–10Zn–6.8Gd–4Y alloys are investigated. The results show that the microstructure of the cast alloy is composed of primary α-Mg dendritic grains with a eutectic structure (W-phase and eutectic Mg) distributed at the grain boundaries. The primary α-Mg dendritic grains grow in size with increasing holding time, and they tend to grow into more globular structures in the initial stage; they then become a bit more dendritic, as small branches grow from the grain boundaries after holding the sample at 580 °C for 10 min. Meanwhile, the interdiffusion of magnesium atoms within the eutectic region, and between the primary α-Mg and eutectic structure, leads to the formation of fine and relatively globular eutectic Mg grains in the eutectic structure after holding for 10 min. The eutectic Mg grains begin to grow, coarsen, coalesce, or be swallowed by the surrounding primary grains, causing fluctuations of the general grain size. Over the whole isothermal heat treatment process, two mechanisms—coalescence and Ostwald ripening—dominate the grain coarsening.

Microstructure Evolution of TiB2/7075 Composites in Semi-Solid State near Liquids within Holding Time

2019 ◽  
Vol 285 ◽  
pp. 127-132
Author(s):  
Gui Sheng Gan ◽  
Da Quan Xia ◽  
Xin Liu ◽  
Cong Liu ◽  
Han Lin Cheng ◽  
...  
Keyword(s):  
Solid State ◽  
Microstructure Evolution ◽  
Ostwald Ripening ◽  
Holding Time ◽  
Al Alloy ◽  
Matrix Composites ◽  
Semi Solid ◽  
Al Matrix Composites ◽  
Settling Process ◽  
Al Matrix

Novel reactive technique has been employed in synthesis of 7075 Al matrix composites, and effect of TiB2 particles on sedimentation and microstructure of 7075 Al Alloy in near liquidus was investigated. Researchers have shown that 4.5%TiB2/7075 composites had the smallest grains and the minimum liquidus and solidus temperatures in 7075 Al matrix composites. 4.5%TiB2/7075 composites holding for 21 hours appeared stratification phenomenon, the globular grains were 61μm and 214μm, 250μm and 283μm with the increase of holding time respectively. The microstructures evolution of TiB2 /7075 composites holding for different time at 635°C was a two-stage mechanism that the globular grains was formed firstly and secondly sedimentation and layering were began after a period of time of Ostwald ripening. The globular grain continued to increase during the settling process.

scholarly journals Effect of Holding Time on Populations of Microparticles in Spheroidal Graphite Irons

2022 ◽  
Author(s):  
L. Michels ◽  
A. J. F. Pires ◽  
C. A. S. Ribeiro ◽  
B. Kroka ◽  
E. G. Hoel ◽  
...  
Keyword(s):  
Ostwald Ripening ◽  
Holding Time ◽  
Spheroidal Graphite ◽  
Size Distributions ◽  
Statistical Parameters ◽  
Silicon Alloys ◽  
Graphite Phase ◽  
Central Hypothesis ◽  
2D To 3D ◽  
Number Of Particles

AbstractNon-metallic microparticles in spheroidal graphite irons are a product of the inoculation and the Mg-treatment of the liquid melt. Besides the influence on the mechanical properties of these iron–carbon–silicon alloys, they are also responsible for the nucleation and the morphology of the graphite phase. The present investigation is undertaken to study holding time effects of a (Ba, Ca, Al)–ferrosilicon (called Ba-inoculant) and (Ca, Al)–ferrosilicon (called Ca-inoculant) inoculants on the overall distribution of microparticles. Using the 2D to 3D conversions method, which is typically used for graphite nodules, the non-metallic microparticles’ statistical parameters, such as size distributions and number densities, are quantified. The total number of particles is similar after Mg-treatment and inoculation for Ca-inoculant but not for Ba-inoculated samples, which lose approximately 25 pct of microparticles after 1 minute of holding time. Iron treated with the Ca-inoculant loses about 37 pct of its nodules after 5 minutes, while the Ba-inoculated melts maintain their performance even after 10 minutes. Based on extrapolating the trend of the undercooling, Ba-inoculated samples would reach the uninoculated undercooling values in 48 minutes, while Ca-inoculated samples in only 11 minutes. By evaluating the size distributions of the non-metallic microparticles, the Ostwald ripening hypothesis or particle aggregation can be verified. The results suggest that sulfides are more critical for graphite nucleation since they can be correlated with the graphite number densities. However, due to the small difference in the microparticle population of the uninoculated sample with Ca-inoculated samples, other aspects of the fading mechanism need to be considered, such as transient metastable states, since the central hypothesis of loss of inclusions cannot alone explain the decrease in the nucleation frequency of graphite.

Effects of cooling rate and isothermal holding on the characteristics of MnS particles in high-carbon heavy rail steels

2020 ◽  
Vol 117 (1) ◽  
pp. 110 ◽  
Author(s):  
Xuewei Zhang ◽  
Caifu Yang ◽  
Lifeng Zhang
Keyword(s):  
Cooling Rate ◽  
Isothermal Holding ◽  
Average Diameter ◽  
Holding Time ◽  
Area Fraction ◽  
Air Cooling ◽  
Steel Matrix ◽  
Number Density ◽  
3D Morphology ◽  
Holding Temperature

The characteristics of MnS particles were intensively investigated at three different cooling rate of 80.4 K · s−1 (water cooling), 3.8 K · s−1 (air cooling) and 1.8 K · s−1 (furnace cooling) as well as the different isothermal holding temperature and time in laboratory experiments. The three-dimensional (3D) morphology of MnS particles was extracted from steel samples using non-aqueous solution electrolysis. The results showed that the 3D morphology of MnS changed from a nearly spherical into rod-like and the area fraction and average diameter of MnS increased with decreasing cooling rate. During isothermal holding process, the morphology of MnS changed little at 1473 K (1200 °C), but their shape profiles varied from a nearly spherical and spindle-like to irregular at higher holding temperature 1673 K (1400 °C) when the holding time exceeded 60 min. Moreover, the number density and area fraction of MnS decreased with increasing holding time at 1573 K (1300 °C) and 1673 K (1400 °C), respectively. Especially at 1573 K (1300 °C), the 1 ∼ 3 µm MnS inclusions were dissolved and lead to decreasing of number density, but that > 3 µm one occurs growth and resulted in increasing of average diameter. The calculation results show that the starting temperature of precipitation of MnS was about 1627 K (1354 °C) and effect of cooling rate on the segregation of Mn and S is insignificant. Considering the segregation of solutes, MnS formation and growth takes place in the solid/liquid interface of steel when the solid fraction is close to 0.9567 during solidification. It has been found that the increase of cooling rate gives rise to the decreased of MnS diameter because the growth time of MnS is short. Furthermore, thermodynamic calculations of MnS solid solubility product were carried out to reveal the high holding temperature and long holding time favors the dissolution of MnS particles. It is necessary to decrease the sulfur content by less than 16 ppm in order to assure that the larger MnS which formed during solidification redissolves in the steel matrix, rather than relying on increasing the heating temperature which is above 1649 K (1376 °C). Subsequent, the MnS will precipitate again in a finely dispersive state during rolling process, and it can hinder annealing grain growth and finally make for the improvement of the toughness property of the steel.

Hexadecylpyridinium Chloride Mediated Hydrothermal Synthesis of NaYF4:Yb, Er Nanocrystal and Their Luminescent Properties

2020 ◽  
Vol 20 (3) ◽  
pp. 1866-1872 ◽  
Author(s):  
Na Li ◽  
Haihu Tan ◽  
Shaowen Xie ◽  
Simin Liu ◽  
Chao Tong ◽  
...  
Keyword(s):  
Ostwald Ripening ◽  
Hydrothermal Process ◽  
Medical Engineering ◽  
Luminescent Properties ◽  
Average Diameter ◽  
Fluorescent Properties ◽  
Experimental Conditions ◽  
Uniform Size ◽  
Characterization Methods ◽  
Upconversion Nanocrystals

Upconversion nanocrystals with uniform size and hydrophilic surface have potential applications in biological medical engineering. In this study, hydrophilic NaYF4:Yb, Er nanospheres were synthesized via hexadecylpyridinium chloride (CPC) mediated hydrothermal process. The synthesized NaYF4:Yb, Er upconversion nanospheres (UCNSs) were characterized by various characterization methods. Results showed that the synthesized UCNSs exhibited a uniform sphere-like structure with average diameter of ~250 nm. The surface of UCNSs was captured by CPC molecule indicating hydrophilic properties of UCNSs. The spherical UCNSs composed of mixed phase (α+β) NaYF4 nanocrystals. This is the novel study for synthesis of NaYF4:Ln3+ crystal employing CPC as ligand. Moreover, the effect of CPC concentration on synthesis of UCNSs was investigated by comparatively studying morphology, crystal phase and luminescent properties of desired sample prepared under different experimental conditions. It was found that high concentrations of CPC ligands were more favorable for forming NaYF4 crystal nanospheres with morphology that is more regular, have smoother surface, with higher crystallinity and better upconversion fluorescent properties. The possible growing mechanism was proposed and growing of NaYF4:Yb, Er nanospheres followed the classical Ostwald ripening process.

scholarly journals The influence of the starch coating on magnetic properties of nanosized cobalt ferrites obtained by different synthetic methods

2020 ◽  
Author(s):  
Marija Šuljagić ◽  
Predrag Vulić ◽  
Dejan Jeremić ◽  
Vladimir Pavlović ◽  
Suzana Filipović ◽  
...  
Keyword(s):  
Ostwald Ripening ◽  
Average Diameter ◽  
Magnetic Behaviour ◽  
Synthetic Methods ◽  
Microwave Assisted ◽  
Functionalized Nanomaterials ◽  
Cobalt Ferrites ◽  
Phase Spinel ◽  
Co Precipitation ◽  
Spinel Structures

Abstract To investigate the magnetic behaviour of starch coated cobalt ferrites, five well established synthetic methods, i.e. co-precipitation, mechanochemical, ultrasonically assisted co-precipitation, microemulsion, and microwave-assisted hydrothermal syntheses were chosen for the materials’ preparation. Obtained cobalt ferrites had pure single-phase spinel structures. Scanning and transmission electron microscopy analyses revealed that the morphology of samples is not uniform, and aggregation of individual particles is a dominant process in all cases. Fourier-transform infrared spectra confirmed the presence of starch in all coated samples. The unusually higher magnetization of starch-coated samples than the magnetization of their as-prepared analogs obtained by co-precipitation, ultrasonically assisted co-precipitation and microwave-assisted hydrothermal methods might be explained by the Ostwald ripening mechanism induced by coating process. On the other hand, the decrease of saturation magnetization value was noticed for starch-functionalized nanomaterials synthesized in mechanochemical and microemulsion manner, in comparison to their as-prepared analogs, showing that the size distribution of such nanoparticles is narrow and the average diameter of the grains is near critical for the Ostwald ripening process.

scholarly journals Characterization of (Mg1.0Zn0.0)TiO3+4 wt%Bi2O3 Ceramics for Application as Resonator in Dielectric Resonator Oscillator Circuit

2021 ◽  
Vol 13 (2) ◽  
pp. 62-69
Author(s):  
Lailatul Izza ◽  
Frida Ulfah Ermawati
Keyword(s):  
Bulk Density ◽  
Dielectric Resonator ◽  
Milled Powder ◽  
Average Diameter ◽  
Holding Time ◽  
Crystalline Powder ◽  
Ceramic Structure ◽  
Microwave Frequencies ◽  
Potential Applications

MgTiO3-based ceramics have potential applications in telecommunications systems at microwave frequencies, such as resonators in dielectric resonator oscillator (DRO) circuits. This paper reports the results of (Mg1.0Zn0.0)TiO3+4wt% Bi2O3 (abbreviated MZT0+4wt%Bi2O3) ceramic fabrication to assess its potential to be used as a resonator in the DRO circuit. We characterized its structure, microstructure, and bulk density. The addition of 4wt%Bi2O3 to MZT0 crystalline powder was carried out via ball-mill. The milled powder was compacted using a die press to obtain pellets. All pellets were sintered at 1100ºC for 4, 6, and 8 h. Ceramic structures of the 4 and 6 h holding time consists of MgTiO3 phase (94.33±2.68) and (95.34±1.95)% molar respectively, while the rest phase was TiO2. The 8-h ceramic structure comprises (96.11±2.94) % molar MgTiO3 accompanied by Mg2TiO5 and TiO2. The ceramics' microstructure consists of a cluster of grains with an average diameter of 1.32-2.24 μm and pores. Bulk density decreases with the increase of sintering holding time. The DRO characterization records a resonance signal each at 5.207, 5.005, and 5.121GHz with power approaching 0 dBm, suggesting that the MZT0+4wt%Bi2O3 ceramics can be used as a resonator in the DRO circuit working in microwave frequencies, especially at 5.0-5.2GHz.

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