scholarly journals The Formation and Application of Submicron Spherical BaTiO3 Particles for the Diffusion Layer of Medical Dry Films

Crystals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 594
Author(s):  
Baodan Zhang ◽  
Haibo Jin ◽  
Xu Liu ◽  
Xiaoyan Guo ◽  
Guangxiang He ◽  
...  
Keyword(s):  
Particle Size ◽  
Barium Titanate ◽  
Formation Mechanism ◽  
Alkaline Solution ◽  
Ostwald Ripening ◽  
Reaction System ◽  
Chemical Reagent ◽  
Crystal Nucleus ◽  
Hydroxyl Ion ◽  
Batio3 Crystal

Submicron spherical barium titanate (BaTiO3) was prepared by batch precipitation in an alkaline solution of a BaCl2–TiCl4–NaOH reaction system. The influence of various parameters on the morphology of BaTiO3 powders was investigated in this study. Spherical BaTiO3 particles can be obtained by reacting for 20 min, which was used to prepare the dry sheet of a medical dry chemical reagent. The morphology of the particles was affected by the stirring speed and the alkaline concentration; the particle size decreased as the stirring speed increased. The hydroxyl ion in the solution acts as a catalyst that can promote the formation of spherical BaTiO3. The formation mechanism of the BaTiO3 sphere is proposed to have three steps: the formation of a Ba–Ti gel and nucleation, self-combination/growth of the BaTiO3 crystal nucleus, and Ostwald ripening. In addition, it is feasible to apply the prepared BaTiO3 sphere to medical dry chemical detection reagents.

Tracking the Catalyst Layer Depth-Dependent Electrochemical Degradation of a Bimodal Pt/C Fuel Cell Catalyst: A Combined Operando Small- and Wide-Angle X-Ray Scattering Study

2021 ◽  
Author(s):  
Johanna Schröder ◽  
Rebecca K. Pittkowski ◽  
Isaac Martens ◽  
Raphaël Chattot ◽  
Jakub Drnec ◽  
...  
Keyword(s):  
Particle Size ◽  
Fuel Cell ◽  
Ostwald Ripening ◽  
Catalyst Layer ◽  
Wide Angle ◽  
Layer Depth ◽  
X Ray ◽  
Fuel Cell Catalyst ◽  
X Ray Scattering ◽  
Size Population

The combination of operando small- and wide-angle X-ray scattering (SAXS, WAXS) is here presented to provide insights into the changes in mean particle sizes and phase fractions in fuel cell catalyst layers during accelerated stress tests (ASTs). As fuel cell catalyst, a bimodal Pt/C catalyst was chosen that consists of two distinguishable particle size populations. The presence of the two different sizes should favor and uncover electrochemical Ostwald ripening as degradation mechanism, i.e., the growth of larger particles in the Pt/C catalyst at the expense of the smaller particles via the formation of ionic metal species. However, instead of electrochemical Ostwald ripening, the results point toward classical Ostwald ripening via the local diffusion of metal atoms on the support. Furthermore, the grazing incidence mode provides insights into the catalyst layer depth-dependent degradation. While the larger particles show the same particle size changes close to the electrolyte-catalyst interface and within the catalyst layer, the smaller Pt nanoparticles exhibit a slightly decreased size at the electrolyte-catalyst interface. During the AST, both size populations increase in size, independent of the depth. Their phase fraction, i.e., the ratio of smaller to larger size population, however, exhibits a depth-dependent behavior. While at the electrolyte-catalyst interface the phase fraction of the smaller size population decreases, it increases in the inner catalyst layer. The results of a depth-dependent degradation suggest that employing a depth-dependent catalyst design can be used for future improvement of catalyst stability.

Experimental assessment of the inhibition of reduction of Ca2+-doped barium titanate in a reducing atmosphere

1999 ◽  
Vol 14 (5) ◽  
pp. 1910-1915 ◽  
Author(s):  
Tsang-Tse Fang ◽  
Jyh-Tzong Shuei
Keyword(s):  
Barium Titanate ◽  
Formation Mechanism ◽  
Driving Force ◽  
Experimental Assessment ◽  
Reducing Atmosphere ◽  
Doped Barium Titanate

Several experiments have been conducted to assess the possible mechanisms for the inhibition of reduction of Ca2+-doped barium titanate in a reducing atmosphere. Three methods, i.e., conventional, semiwet, and citrate processes, have been used to prepare the powders. It was found that the formation mechanism would influence the occupation of Ca2+ in the B site. Moreover, it was concluded that Ca2+ occupation of the B site is the major cause for the inhibition of reduction of Ca2+-doped barium titanate. Ti deficiency would be the driving force for Ca2+ to occupy the B site.

Effect of Seedings on the Microstructure of Hydrated Alumina

2012 ◽  
Vol 554-556 ◽  
pp. 709-713
Author(s):  
Yan Hong Liu ◽  
Hong Wen Ma ◽  
Mei Tang Liu
Keyword(s):  
Electron Microscopy ◽  
Particle Size ◽  
Decisive Role ◽  
Mechanism Study ◽  
Hydrated Alumina ◽  
Crystal Nucleus ◽  
X Ray ◽  
Intrinsic Mechanism ◽  
Scanning Electron

The morphology and particle size of boehmite play a decisive role on the application of alumina that derived from it. In this paper, we employed pseudoboehmite that produced from Al2 (SO4)3•18H2O and NH3•H2O at 70 °C, pH 7.5 as precursor to synthesize boehmite, and utilized different seeding when preparing pseudoboehmite and boehmite. To identify the influence of seeding on the microstructure of pseudoboehmite and boehmite, the products were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and BET. The results indicate that the pseudoboehmite seeding has a significant influence on the morphology and particle size of pseudoboehmite to which we should pay high attention. However, the boehmite seeding does not play the role of crystal nucleus as expected. The further intrinsic mechanism study is ongoing.

scholarly journals Theoretical analysis of particle size re-distribution due to Ostwald ripening in the fuel cell catalyst layer

Open Physics ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 779-789 ◽  
Author(s):  
Ambrož Kregar ◽  
Tomaž Katrašnik
Keyword(s):  
Particle Size ◽  
Fuel Cells ◽  
Fuel Cell ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Electric Potential ◽  
Ostwald Ripening ◽  
Particle Growth ◽  
Mean Particle Size ◽  
Fuel Cell Catalyst

Abstract The limited durability of hydrogen fuel cells is one of the main obstacles in their wider adoption as a clean alternative technology for small scale electricity production. The Ostwald ripening of catalyst material is recognized as one of the main unavoidable degradation processes deteriorating the fuel cell performance and shortening its lifetime. The paper systematically studies how the modeling approach towards the electrochemically driven Ostwald ripening in the fuel cell catalyst differs from the classical diffusion driven models and highlights how these differences affect the resulting evolution of particle size distribution. At moderately low electric potential, root-law growth of mean particle size is observed with linear relation between mean particle size and standard deviation of particle size distribution, similar to Lifshitz-Slyozov-Wagner theory, but with broader and less skewed distribution. In case of high electric potential, rapid particle growth regime is observed and qualitatively described by redeposition of platinum from a highly oversaturated solution, revealing the deficiencies of the existing platinum degradation models at describing the Ostwald ripening in the fuel cells at high electric potentials. Several improvements to the established models of platinum degradation in fuel cell catalysts are proposed, aimed at better description of the diffusion processes involved in particle growth due to Ostwald ripening.

scholarly journals An Alternative Process for Leaching Chalcopyrite Concentrate in Nitrate-Acid-Seawater Media with Oxidant Recovery

Metals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 518 ◽  
Author(s):  
César I. Castellón ◽  
Pía C. Hernández ◽  
Lilian Velásquez-Yévenes ◽  
María E. Taboada
Keyword(s):  
Particle Size ◽  
Sulfuric Acid ◽  
Alkaline Solution ◽  
Sodium Nitrite ◽  
Sodium Nitrate ◽  
Room Temperature ◽  
Leaching Test ◽  
Copper Concentrate ◽  
Leaching Process ◽  
Chalcopyrite Concentrate

An alternative copper concentrate leaching process using sodium nitrate and sulfuric acid diluted in seawater followed by gas scrubbing to recover the sodium nitrate has been evaluated. The work involved leaching test carried out under various condition by varying temperature, leaching time, particle size, and concentrations of NaNO3 and H2SO4. The amount of copper extracted from the chalcopyrite concentrate leached with seawater, 0.5 M of H2SO4 and 0.5 M of NaNO3 increased from 78% at room temperature to 91% at 45 °C in 96 h and 46 h of leaching, respectively. Gas scrubbing with the alkaline solution of NaOH was explored to recover part of the sodium nitrate. The dissolved salts were recovered by evaporation as sodium nitrate and sodium nitrite crystals.

Formation mechanism of barium titanate nanocrystals under hydrothermal conditions

1997 ◽  
Vol 40 (5) ◽  
pp. 479-488 ◽  
Author(s):  
Weizhuo Zhong ◽  
Changtai Xia ◽  
Erwei Shi ◽  
Buguo Wang ◽  
Wenjun Li ◽  
...  
Keyword(s):  
Barium Titanate ◽  
Formation Mechanism ◽  
Hydrothermal Conditions
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