Search results for "nucleation"

Thermal analysis applied to the characterization of degradation in soil of polylactide: II. On the thermal stability and thermal decompositon kinetics

2010

[EN] The disposal stage of polylactide (PLA) was assessed by burying it in active soil following an international standard. Degradation in soil promotes physical and chemical changes in the polylactide properties. The characterization of the extent of degradation underwent by PLA was carried out by using Thermal Analysis techniques. In this paper, studies on the thermal stability and the thermal decomposition kinetics were performed in order to assess the degradation process of a commercial PLA submitted to an accelerated soil burial test by means of multi-linear-non-isothermal thermogravimetric analyses. Results have been correlated to changes in molecular weight, showing the same evolutio…

Thermal and thermo-oxidative stability of reprocessed poly(ethylene terephthalate)

2013

An exhaustive assessment of the behaviour of virgin and mechanically reprocessed poly(ethylene terephthalate) (PET) facing thermal and thermo-oxidative decomposition processes is presented in this work, as an approach for the energetic valorisation of post-consumer PET goods. Multi-rate linear-non-isothermal thermogravimetric (TGA) experiments under inert (Ar) and reactive (O2) conditions were performed to virgin PET and its recyclates in order to simulate the thermal behaviour of the materials facing pyrolysis and combustion processes. The release of gases was monitored by evolved gas analysis of the fumes of the TGA experiment, by in-line Fourier-transform infrared (IR) analysis, with the…

Synthesis and Characterization of Monodisperse Manganese Oxide Nanoparticles−Evaluation of the Nucleation and Growth Mechanism

2009

Magnetic nanoparticles of the 3d transition metal oxides have gained enormous interest for applications in various fields such as data storage devices, catalysis, drug-delivery, and biomedical imaging. One major requirement for these applications is a narrow size distribution of the particles. We have studied the nucleation and growth mechanism for the formation of MnO nanoparticles synthesized by decomposition of a manganese oleate complex in high boiling nonpolar solvents using TEM, FT-IR, and AAS analysis. The exceptionally narrow size distribution indicates that nucleation and growth are clearly separated. This leads to a uniform growth with a very narrow size distribution on the existi…

2021

Abstract. Homogeneous freezing of aqueous solution aerosol particles is an important process for cloud ice formation in the upper troposphere. There the air temperature is low, the ice supersaturation can be high and the concentration of ice-nucleating particles is too low to initiate and dominate cirrus cloud formation by heterogeneous ice nucleation processes. The most common description to quantify homogeneous freezing processes is based on the water activity criterion (WAC) as proposed by Koop et al. (2000). The WAC describes the homogeneous nucleation rate coefficients only as a function of the water activity, which makes this approach well applicable in numerical models. In this study…

Effect of TiO2 on the mullite formation and mechanical properties of alumina porcelain

2010

Abstract The effect of adding TiO 2 to standard alumina porcelain on its microstructure and flexural strength was investigated. A series of alumina porcelain bodies containing increasing amounts of TiO 2 were prepared by extruding mixtures of raw materials and TiO 2 . Porcelain rods were fired under industrial scheduling in a manufacturing kiln. The overall degree of crystalline and amorphous phase content within the porcelain bodies was quantitatively determined using a Rietveld analysis. Results indicated a higher amount of mullite formation in porcelain bodies containing TiO 2 . Examination of the product materials using field emission scanning electron microscopy showed a high density o…

Crystallization of hard spheres revisited. II. Thermodynamic modeling, nucleation work, and the surface of tension

2018

Combining three numerical methods (forward flux sampling, seeding of droplets, and finite-size droplets), we probe the crystallization of hard spheres over the full range from close to coexistence to the spinodal regime. We show that all three methods allow us to sample different regimes and agree perfectly in the ranges where they overlap. By combining the nucleation work calculated from forward flux sampling of small droplets and the nucleation theorem, we show how to compute the nucleation work spanning three orders of magnitude. Using a variation of the nucleation theorem, we show how to extract the pressure difference between the solid droplet and ambient liquid. Moreover, combining th…

Synthesis and characterization of V2O5SiO2ZrO2 pigments by sol-gel method

1992

Abstract Polymeric gels in the V2O5 SiO2 ZrO2 system were prepared from tetraethylorthosilicate (TEOS), zirconium(IV)-n-propoxide and vanadium(IV) oxyacetylacetonate, precursors. The effects of prehydrolysis time of TEOS and drying gel method on the stabilization of tetragonal zirconia in the silica amorphous matrix, nucleation and growth of the zircon (ZrSiO4) phase, and stabilization of the blue and green stains of vanadium zircon were studied. Results provide evidence that long time of prehydrolysis and fast drying do not favour zircon crystallization but stabilize the tetragonal zirconia in the amorphous matrix.

Impact of small organic molecules on the nucleation of calcium silicate hydrate

2021

Superplasticizers are nowadays commonly employed in concrete to improve its workability and mechanical performance. They generally have the side effect of retarding the hydration of Portland cement which results from two simultaneous reactions: the dissolution of cement grains and the precipitation of cement hydrates. The mechanisms responsible for this retardation and thus delay the setting time of cement remain however largely unexplained. The present work intended to tackle this puzzle from the perspective of cement hydrate formation and employing four small organic molecules as model for superplasticizers. In particular, the impact of these organics on the homogeneous nucleation of calc…

Growth of zinc-blende GaN on muscovite mica by molecular beam epitaxy

2021

Abstract The mechanisms of plasma-assisted molecular beam epitaxial growth of GaN on muscovite mica were investigated. Using a battery of techniques, including scanning and transmission electron microscopy, atomic force microscopy, cathodoluminescence, Raman spectroscopy and x-ray diffraction, it was possible to establish that, in spite of the lattice symmetry mismatch, GaN grows in epitaxial relationship with mica, with the [11–20] GaN direction parallel to [010] direction of mica. GaN layers could be easily detached from the substrate via the delamination of the upper layers of the mica itself, discarding the hypothesis of a van der Waals growth mode. Mixture of wurtzite (hexagonal) and z…

Phase partitioning of aerosol particles in clouds at Kleiner Feldberg

1994

The partitioning of aerosol particles between cloud droplets and interstitial air by number and volume was determined both in terms of an integral value and as a function of size for clouds on Mt. Kleiner Feldberg (825 m asl), in the Taunus Mountains north-west of Frankfurt am Main, Germany. Differences in the integral values and the size dependent partitioning between two periods during the campaign were observed. Higher number and volume concentrations of aerosol particles in the accumulation mode were observed during Period II compared to Period I. In Period I on average 87 ± 11% (±one standard deviation) and 73 ± 7% of the accumulation mode volume and number were incorporated into cloud…