Search results for "amorphou"

Low-temperature Zr mobility: An in-situ synchrotron-radiation XRF study of the effect of radiation damage in zircon on the element release in $H_{2}O…

2006

The release of Zr, U, and Pb from nearly metamict zircon and its recrystallized analog and of Zr from fully crystalline and slightly radiation-damaged zircon in H 2 O + HCl ± SiO 2 fluids was investigated in situ at temperatures between 200 and 500 °C using a hydrothermal diamond-anvil cell and time-resolved synchrotron-radiation XRF analyses. Dissolution of nearly metamict zircon proceeded much faster than that of zircon with little or no radiation damage and resulted in a 1.5 to 2 log units higher Zr molality in 6 to 7 m HCl fluids. Extensive recrystallization of the almost fully amorphous material started at 260 to 300 °C in H 2 O + HCl, and at about 360 °C if quartz was added, and was c…

Role of Water During Crystallization of Amorphous Cobalt Phosphate Nanoparticles

2016

The transformation of amorphous precursors into crystalline solids and the associated mechanisms are still poorly understood. We illuminate the formation and reactivity of an amorphous cobalt phosphate hydrate precursor and the role of water for its crystallization process. Amorphous cobalt phosphate hydrate nanoparticles (ACP) with diameters of ∼20 nm were prepared in the absence of additives from aqueous solutions at low concentrations and with short reaction times. To avoid the kinetically controlled transformation of metastable ACP into crystalline Co3(PO4)2 × 8 H2O (CPO) its separation must be fast. The crystallinity of ACP could be controlled through the temperature during precipitati…

Anhydrous Amorphous Calcium Oxalate Nanoparticles from Ionic Liquids: Stable Crystallization Intermediates in the Formation of Whewellite

2015

The mechanisms by which amorphous intermediates transform into crystalline materials are not well understood. To test the viability and the limits of the classical crystallization, new model systems for crystallization are needed. With a view to elucidating the formation of an amorphous precursor and its subsequent crystallization, the crystallization of calcium oxalate, a biomineral widely occurring in plants, is investigated. Amorphous calcium oxalate (ACO) precipitated from an aqueous solution is described as a hydrated metastable phase, as often observed during low-temperature inorganic synthesis and biomineralization. In the presence of water, ACO rapidly transforms into hydrated whewe…

Primary Cell Culture of Fresh Water Hyriopsis cumingii Mantle/Pearl Sac Tissues and Its Effect on Calcium Carbonate Mineralization

2014

Primary cell cultures of the fresh water Hyriopsis cumingii mantle and pearl sac tissues were produced in this study, and the influence of the tissue, cells, and secreted protein on calcium carbonate crystal nucleation and growth was studied. The study contributes to a further understanding of the influence of organic matrices on CaCO3 crystal formation. This research started from the protein level to the tissue/cell level, which is crucial for understanding the inorganic deposition process. The new data also add relevant theoretical approaches to an overall understanding of biomineralization processes. In the experimental groups with mantle or pearl sac tissue, the growth patterns of arago…

O2 Diffusion in Amorphous SiO2 Nanoparticles Probed by Outgassing

2012

An experimental study of the O2 diffusion process in nanoparticles of amorphous SiO2 in the temperature range from 98 to 157 °C was carried out by Raman and photoluminescence techniques. We studied O2 diffusion in high purity silica nanoparticles with a mean diameter of 14, 20, and 40 nm detecting the outgassing of molecules trapped during the manufacturing. The kinetics of diffusion is well described for all the investigated nanoparticles by the Fick’s equation proving its applicability to nanoscale systems. The diffusion coefficient features an Arrhenius law temperature dependence in the explored temperature range, and the diffusion coefficient values are in good agreement with extrapolat…

A laboratory study of the effects of a kerosene-burner exhaust on ice nucleation and the evaporation rate of ice crystals

1998

Abstract Laboratory experiments are described during which the influence of gases and particles from the exhaust of a kerosene burner on microphysical processes were studied. In one experimental investigation the evaporation rates of ice crystals polluted with the kerosene-burner exhaust were compared with the evaporation rates of pure ice crystals. During another experimental investigation the ice nucleating ability of the exhaust particles was studied in terms of the efficiency of the exhaust particles to act as deposition and condensation freezing nuclei, as immersion freezing nuclei, and as contact nuclei. The results of our experiments showed that the evaporation rate of ice crystals p…

2017

Abstract. Eleven particle samples collected in the polar stratosphere during SOLVE (SAGE III Ozone loss and validation experiment) from January until March 2000 were characterized in detail by high-resolution transmission and scanning electron microscopy (TEM/SEM) combined with energy-dispersive X-ray microanalysis. A total of 4202 particles (TEM  =  3872; SEM  =  330) were analyzed from these samples, which were collected mostly inside the polar vortex in the altitude range between 17.3 and 19.9 km. Particles that were volatile in the microscope beams contained ammonium sulfates and hydrogen sulfates and dominated the samples. Some particles with diameters ranging from 20 to 830 nm were re…

A laboratory study of the uptake of HNO3 and HCl vapor by snow crystals and ice spheres at temperatures between 0 and −40°C

1995

Abstract A laboratory experiment is described during which the uptake of HNO3 and HCl vapor by dendritic snow crystals and by single crystalline and polycrystalline small ice spheres was studied at ppbv and ppmv gas levels and at temperatures between 0 and −40°C. In one experimental investigation the vapor was allowed to be adsorbed onto the surface of the ice particles. During another experimental investigation the ice particles were allowed to grow from water vapor on fine fibers in the presence of the HNO3 and HCl vapor. The results of our experiments show that under both conditions significant amounts of HNO3 and HCl became scavenged by the ice particles. Scavenging by adsorption was ma…

Reactivity of H2S and H2S/H2 Mixture With Molybdenum Oxide Thin Films Epitaxied on CoO (100) : Characterization by Rheed and Auger Spectroscopy

2010

Molybdenum-Cobalt composite oxide films were prepared by the evaporation of molybdenum trioxide on a fresh cleaved CoO (100) surface (Thickness = 10 A). The MoO3-CoO interface has been characterized simultaneously by reflexion high electron diffraction (RHEED) and Auger Electron Spectroscopy (AES). The thin film structure and composition depend on the annealing temperature. After a 300°C treatment, metallic cobalt islands nucleate at the interface thin film - CoO (100) and crystallize with the cubic FCC symmetry. After a 700°C treatment cobalt molybdate (a CoMoO4) islands grow. The metastable crystallites are epitaxied on CoO (100). After a 900°C treatment, the thin film consists of flat tw…

Microstructural evolution of wear-resistant FeCrB and FeCrNiCoB coating alloys during high-energy mechanical attrition

2008

Mechanical milling/attrition provides a convenient scope of simulating the microstructural changes encountered by wear-resistant coating alloys subjected to deformation under high frequency and high-intensity impact loading or accelerated wear condition. In the present study, the microstructural evolution of two commercial coating materials, FeCrB (Armacor M) and FeCrNiCoB (Armacor C), in the course of low- and high-intensity mechanical attrition, was monitored by X-ray diffraction and high-resolution transmission electron microscopy. While low-intensity milling leads to marginal grain refinement but no change in phase-aggregate in FeCrB, similar mechanical attrition causes boride precipita…