Simón Bolívar University

About: Simón Bolívar University is a education organization based out in Caracas, Venezuela. It is known for research contribution in the topics: Population & Crystallization. The organization has 5912 authors who have published 8294 publications receiving 126152 citations.

Thick aluminosilicate coatings on carbon steel via sol-gel

Abstract: Sol-gel aluminosilicate coatings were deposited on a carbon steel substrate Three application methods were compared: wet deposition techniques as dipping and spraying of the sol and xerogel thermal spraying with flame torch Characterization by X-ray diffraction and scanning electron microscopy shows that amorphous thick coatings (> 5 μm) were obtained Coatings present an acceptable oxidation resistance in air atmosphere at 600°C

Grafting of polyethylenes by reactive extrusion. I. Influence on the molecular structure

Abstract: Grafting of polyethylenes is an important method used in the modification of polyolefins with functional groups. Lately, the use of extruders as polymerization reactors has increased considerably. However, knowledge of the details of the reaction in the extruder is still limited. In this investigation, the grafting of various commercial polyethylenes, high-density polyethylenes (HDPEs), and linear low-density polyethylenes (LLDPEs) with diethyl maleate (DEM) was carried out in two corotating twin-screw extruders with different screw configurations and extrusion conditions. Two initiators at different concentrations were used. It was found that when the initiator level was raised in the LLDPEs the grafting degree increased and the molecular weight distribution of the grafted LLDPE2 did not show appreciable differences when they were compared to the virgin resin. On the other hand, the terminal vinyl group concentrations decreased at the expense of increasing the trans unsaturation concentrations. This last result is consistent with the formation of long-chain branching. Additionally, the weight-average molecular weight of grafted high-density polyethylene (HDPE1-g-DEM) decreased. The grafting efficiencies were consistent with the attained residence times and also with the kinetics of the decomposition of the peroxides. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 161–176, 1998

Influence of external salinity on the osmolality of xylem sap, leaf tissue and leaf gland secretion of the mangrove Laguncularia racemosa (L.) Gaertn

Abstract: This study assessed if mature leaves of Laguncularia racemosa were able to demonstrate salt secretion, and if the magnitude of secretion was a function of soil salinity. Thus, salinity influence on the osmolality of leaf tissue, xylem sap and leaf secretion was assessed in field and glasshouse experiments. As salinity increased, solutes were accumulated in sufficient quantity to decrease osmotic potential over the whole range of water potential. In the field, xylem osmolality (mol m−3) increased with salinity from 32.4±2.9 at 17‰ to 38.2±0.6 at 28‰. Similarly, in the glasshouse, xylem sap osmolality (mol m−3) increased from 33.4±1.8 (15‰) to 40.6±1.5 (30‰). Changes in Na+ concentration explained about 51–58% of increase in xylem osmolality. Rates of secretion (mmol m−2 day−1) in the field increased from 0.80±0.12 (17‰) to 1.16±0.14 (28‰), and in the glasshouse the secretion increased from 0.73±0.07 (15‰) to 1.25±0.07 (30‰). The Na+ accounted for 40–53% of total secretion. This study presented evidence of the capability of mature leaves of L. racemosa to secrete salt for the first time, and that the rates of secretion were enhanced as soil salinity increased.