Presence Of Blacks Research Articles

The free radical polymerization of vinyl monomers in the presence of carbon black

The polymerization of vinyl monomers has been carried out in the presence of furnace blacks using initiators such as 2,2′-azobisisobutyronitrile (AIBN) and benzoyl peroxide (Bz 2O 2) in nitrogen or oxygen atmosphere. The results indicate that free radicals form by the decomposition of initiators reacting with carbon blacks to give active sites on their surface which then capture either the free radicals or the growing polymer radicals. Using the monomers with negative e values, such as styrene and vinyl acetate, a marked retardation was observed in Bz 2O 2-initiated polymerization in the presence of furnace blacks, while a moderate inhibition was found in the polymerization initiated by AIBN. The polymerization reaction using Bz 2O 2 was found to be very sensitive to oxygen in the presence of furnace blacks and the involvement of oxygen was found to promote grafting onto the surface of carbon black by the growing polymer radicals, consequently giving polymer-grafted particles while hindering the formation of homopolymers. Furthermore, the reaction of Bz 2O 2 with the surface of furnace blacks in oxygen atmosphere has been studied in carbon tetrachloride at 45°C. The resulting carbon blacks show an increase in the number of surface quinone groups with an increase in reaction time.

Blacks as Communicators and Interpreters of Mass Communication

Data on black media use patterns are mixed. Content studies document increased presence of blacks in ads in all media.

Blacks in the Early Southwest

Beginning with Esteban de Dorantes in 1539, there was a growing number of Blacks - both male and female - who entered the American Southwest during the 16th and 17th centuries. Who these Blacks were and their largely unheralded roles in the history of the Spanish Colonial Southwest are discussed on the basis of a survey of the ethnohistorical literature. Their contributions long went unrecognized, but in the sixteenth and early seventeenth centuries, Blacks were present and active in what became the southwestern United States of America and adjacent northern Mexico. They reached this area in various ways, though invariably in some relationship to Spanish exploration, conquest and settlement of the area. Some came involuntarily as slaves; others as free adventurers; and at least one as a leader and dazzling entrepreneur. The presence of Blacks is easier to establish and evaluate than are their cultural contributions. We may be certain that they made an impact on southwestern Indian culture, but as we see the Blacks in the early Southwest through Spanish eyes, these kinds of data are virtually never noted. Someday, archaeology, ethnohistory, and detailed ethnological work, especially in comparative mythology, may help determine the Black component in the early contact culture of the Greater Southwest. In this paper, however, we shall document Blacks in the Southwest and comment rather generally on what may have been their contributions. The first Black to reach the present southwestern United States of America was a man named Esteban de Dorantes, a slave who was one of four survivors of the mishandled and tragic Narvaez expedition to Florida. In 1528 the conquistador Panfilo de Narvaez landed an expedition of some 260 men in the Tampa Bay area. Narvaez already had a considerable record of failure.

The decomposition of hydrogen peroxide in the presence of carbon blacks

The catalytic activity of carbon blacks for the decomposition of aqueous hydrogen peroxide under given conditions of time, temperature and concentration depends on surface alkalinity and surface area of the blacks. A small fraction only of the total oxygen evolved in the process gets chemisorbed by the black provided the latter is not presaturated with oxygen. Chemisorption of oxygen does not appear to be an essential step in the progress of the reaction.

Hydrogenation of cyclopropylbenzene in presence of palladium and platinum blacks

Substantial differences were found in the course of reaction in the hydrogenation of cyclopropylbenzene in the presence of platinum and palladium blacks.

Hydrogenation of cyclopentadiene in binary mixtures with unsaturated hydrocarbons over palladium and platinum blacks

1. A study was made of the selectivity of the hydrogenation of cyclopentadiene into cyclopentene in binary mixtures with unsaturated hydrocarbons in presence of palladium and platinum blacks. 2. It was found that, like Raney nickel. palladium black brings about selective hydrogenation of cyclopentadiene in its binary mixture with cyclohexene, but nonselective hydrogenation in mixtures with styrene. Palladium black differs from Raney nickel in that it does not bring about selective hydrogenation of cyclopentadiene in its mixtures with diphenylacetylene. In presence of platinum black, cyclopentadiene is not hydrogenated selectively in binary mixtures with cyclopentene and 1-octene.