Magnetorheological polymeric gels (MRPG) have been developed for use in semi-active magnetorheological fluid (MRF) dampers and other magnetorheological (MR) devices. The novel MRPGs are prepared by suspending iron particles in polymeric gels. Off-state (i.e, no applied magnetic field) viscosity and settling behavior can be controlled through the selection of polymeric gels. In this study, tunable rheological properties were investigated with a piston-driven flow type rheometer with a shear rate varying from 20 s Ϫ1 to 6,000 s
Ϫ1. Silicone MRPG (with 84.5 wt % iron particles) has controllable viscosity and a high shear yield stress over a wide range of shear rates. Silicone MRPG (79.5 wt % iron particles) has the lowest viscosity of those studied. Polyurethane MRPG has the lowest settling rate. The order of addition of magnetic particles and polymer during the polymerization process affects the MRPG final off-state apparent viscosity (80% increase in apparent viscosity for silicone MRPG polymerized after adding iron particles). This indicates that polymer gels modify the surface properties of the magnetic particles, causing interaction among particles. The dynamic shear yield stress is higher for fluids with better dispersion stability. Polyurethane MRPG, which has the lowest settling rate, has a high dynamic yield stress (23 kPa at 350 mT). Both dynamic and static shear stress values of the MRPGs were found to be similar in magnitude (5-8 kPa at 120 mT for silicone MRPG with 84.5 wt % iron particles and polyurethane MRPG), indicating that MRPGs can provide consistent performance in devices.
This paper presents data from controlled laboratory experiments focused on investigating the effect of moisture and visible and ultraviolet light on the emission and re-emission of mercury (Hg) from two soils, one with low or background Hg concentrations (14 ng g(-1)) and a soil naturally enriched in Hg (4800 ng g(-1)). Water addition was found to increase emissions from dry soils by an amount greater than that occurring during exposure to PAR or UV-A radiation, whereas UV-B and UV-C exposures facilitated the greatest release. Over all exposures, only a small percentage of Hg(ll) added in a wet spike simulating a precipitation input was released immediately after addition (< 3%). The majority of the Hg being released during all exposures was indigenous and either an original component of the soil or derived from past wet and dry deposition. Under dark and light conditions, elemental Hg was deposited to the dry low Hg-containing soil. On the basis of experimental results, it is hypothesized that dry deposition of gaseous elemental Hg is an important input to low Hg soils and that light, water, and UV-A exposure promote desorption and re-emission of elemental Hg. UV-B exposure is hypothesized to promote indirect photoreduction of Hg(II) existing in the soil. The available pool and the form of Hg in the soil, as well as the chemistry of the soil, will determine the overall flux response to environmental stimulation of emissions.
The reduction of nitric oxide by propene in the presence of
excessive oxygen over Pt/ZSM-5 has been
investigated by in situ diffuse reflectance infrared Fourier transform
spectrometry (DRIFTS) over a wide
range of temperatures. It has been found that the main surface
species formed during the reaction at low
temperature (≤473 K) are nitro and nitrito organic compounds on both
Pt/ZSM-5 and NaZSM-5, while at
higher temperature (≥473 K) carbonyl−carbonate−carboxylates are
formed. Surface species formed under
exposure to various mixtures of gases have also been studied. It
has been further found that the reaction
between nitric oxide and propene over Pt/ZSM-5 can produce carbon
monoxide at 473 K. On the basis of
these results, the direct-decomposition mechanism is proposed. It
is concluded that neither the nitro and
nitrito organic compounds nor isocyanate species are the most abundant
species in this reaction on Pt/ZSM-5.
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