Mercury(II) exchange by highly charged swelling micas, sodium Engelhard titanosilicate-4, and sodium titanosilicate

Selective Hg(2+)-exchange properties of highly charged sodium swelling micas (Na-2-, Na-3-, and Na-4-micas), sodium Engelhard titanosilicate-4 (Na-ETS-4), and sodium titanosilicate were determined by use of distribution coefficients (K(d)), ion-exchange isotherms, and Kielland plots for their potential use of Hg decontamination from groundwater and soils. X-ray diffraction (XRD) patterns after 2Na(+) → Hg(2+) exchange were collected to check for change in (001) spacings of differently charged sodium micas. The isotherms and Kielland plots suggested that Na-ETS-4 was highly selective for Hg(2+). Also, the K(d) value of Na-ETS-4 was the highest among the tested exchangers, supporting its high selectivity. Hg releases from Hg-exchanged Na-4-mica and Na-ETS-4 were found to be lower compared to other samples tested with simulated groundwater. The (001) spacings of sodium micas after Hg(2+) exchange changed from ～ 12 to ～ 14 ? or/and 12 ? depending on their layer charge density and the uptake amount of Hg. Our results suggest that Na-ETS-4 is a good candidate for mercury(II) decontamination from groundwater and soils.     

Passive range estimation for rotorcraft low-altitude flight

The automation of rotorcraft low-altitude flight presents challenging problems in control, computer vision, and image understanding. A critical element in this problem is the ability to detect and locate obstacles, using on-board sensors, and to modify the nominal trajectory. This requirement is also necessary for the safe landing of an autonomous lander on Mars. This paper examines some of the issues in the location of objects, using a sequence of images from a passive sensor, and describes a Kalman filter approach to estimate range to obstacles. The Kalman filter is also used to track features in the images leading to a significant reduction of search effort in the feature-extraction step of the algorithm. The method can compute range for both straightline and curvilinear motion of the sensor. An experiment is designed in the laboratory to acquire a sequence of images along with the sensor motion parameters under conditions similar to helicopter flight. The paper presents range estimation results using this imagery.     

Assessment of Soil Moisture Dynamics of the Nebraska Sandhills Using Long-Term Measurements and a Hydrology Model

Soil moisture, evapotranspiration, and other major water balance components were investigated for six Nebraska Sandhills locations during a 6 year period (1998–2004) using a hydrological model. Annual precipitation in the study period ranged from 330 to 580?mm. Soil moisture was measured continuously at 10, 25, 50, and 100?cm depth at each site. Model estimates of surface (0–30?cm), subsurface (30–91?cm), and root zone (0–122?cm) soil moisture were generally well correlated with observed soil moisture. The correlations were poorest for the surface layer, where soil moisture values fluctuated sharply, and best for the root zone as a whole. Modeled annual estimates of evapotranspiration and drainage beneath the rooting zone showed large differences between sites and between years. Despite the Sandhills’ relatively homogeneous vegetation and soils, the high spatiotemporal variability of major water balance components suggest an active interaction among various hydrological processes in response to precipitation in this semiarid region.     

Laser power coupling efficiency in conduction and keyhole welding of austenitic stainless steel

Laser welding of thin sheets of AISI 304 stainless steel was carried out with high power CW CO₂ laser. The laser power utilized in the welding process was estimated using the experimental results and the dimensionless parameter model for laser welding; and also the energy balance equation model. Variation of laser welding efficiency with welding speed and mode of welding was studied. Welding efficiency was high for high-speed conduction welding of thin sheets and also in keyhole welding process at high laser powers. Effect of pre-oxidization of the surface and powder as filler material on laser power coupling is also reported. The paper also discusses effect of microstructure on the cracking susceptibility of laser welds.     

Computer simulation and comparative study on the pervaporation separation characteristics of sodium alginate and its blend membranes with poly(vinyl alcohol) to separate aqueous mixtures of 1,4‐dioxane or tetrahydrofuran

A comparative study on the pervaporation separation has been attempted for water + 1,4‐dioxane and water + tetrahydrofuran mixtures using sodium alginate and blend membranes of sodium alginate with 5, 10, and 20 mass % of poly(vinyl alcohol). Pure sodium alginate membrane has a selectivity of 111 to water at 0.35‐mol fraction of water in the feed mixture containing 1,4‐dioxane while for water + tetrahydrofuran mixture, the membrane selectivity to water was 291 at 0.31‐mol fraction of water in the feed mixture. Pervaporation results have been discussed using the solution–diffusion principles. Arrhenius activation parameters for diffusion and permeation have been computed from the temperature‐dependent pervaporation results. Furthermore, experimental results have been analyzed using the complete mixing and plug flow models to compute membrane area as well as design parameters that are useful in scale‐up operations. The plug flow model is more appropriate than the complete mixing model to analyze the pervaporation results. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1827–1840, 2004     

Epitaxial Crystallization of Seeded Albite Glass

Glasses that are extremely difficult to crystallize are generally avoided in making glass-ceramics. It is now possible to crystallize such glasses epitaxially using isostructural seeds. The role of solid-state epitaxy in the crystallization of such albite (NaAlSi₃O₈) glass to glass-ceramic was investigated. The glass was seeded with extremely fine ZrO₂ (nonisostructural) and albite (isostructural) seed crystals. X-ray diffraction results indicated that the albite-seeded glass, heat-treated at 1000°C for 100 h, epitaxially crystallized to albite, while the ZrO₂ and unseeded glasses did not crystallize in identical heat-treatment conditions. In addition, the albite-seeded glass, heat-treated at 905°C for 10 d, crystallized mostly to albite, whereas the ZrO₂ and unseeded glasses at the same conditions contained only a small amount (<5 wt%) of nepheline (NaAlSiO₄). The microstructure of the epitaxially grown glass-ceramics showed that extremely fine crystals (∼0.2 μm thickness) were formed around the seed.     

Chloridization beneficiation of ilmenite

Chloridization is a potential method of beneficiating ilmenite. Studies on beneficiation of ilmenite were carried out by using titanium chloride as the chloridizing agent in a laboratory scale fluidized bed reactor. Experiments were conducted on 1, 10, and 36 grams per batch scale, and the effect of the various rate determining steps on conversion was studied. Treated particles of ilmenite were examined for chemical composition, surface properties, and structural changes. The paper presents the experimental results on the chloridization treatment of natural and oxidized ilmenite.     

Diphasic ceramic composites via a sol-gel method

A sol-gel process is described for the preparation of diphasic composite materials. The method involves the growth of extremely fine crystalline or non-crystalline materials inside a pre-made gel structure (of SiO₂) by soaking the gel in metal nitrate solution and subsequent precipitation of the metal with the selected anions (using mineral acids) followed by a densification step.     

Structure and properties of a near-α titanium alloy after β solution treatment and aging at 625 °

The microstructure, tensile properties, and fractographic features of a near alpha titanium alloy, IMI 829 (Ti-6.lAl-3.2Zr-3.3Sn-lNb-0.5Mo-0.32Si) have been studied after aging at 625 ° for 24 hours following solution treatment in the beta phase field at 1050 ° and cooling at various rates (furnace, air, oil, or water). Transmission electron microscopy studies revealed that aging at 625 ° for 24 hours of this alloy had led to the precipitation of only one kind of silcide with a hexagonal structure (c = 0.36 nm andα = 0.70 nm). The precipitates are ellipsoidal in shape and their size depends on the cooling rate given to the alloy after beta solution treatment. Extremely fine precipitation of Ti₃Al phase has also been observed in the furnace cooled and aged condition. There is a significant improvement in both yield and ultimate tensile strengths after aging of both the oilquenched and water-quenched specimens whereas it is minimal in the case of furnace-cooled and air-cooled specimens. Aging the alloy has also resulted in a drastic reduction in both percentage elongation and percentage reduction in area for all the conditions investigated. While the fracture surfaces of the unaged specimens showed characteristic dimples, a large number of facets appeared in the fractographs of the aged specimens. formerly with Banaras Hindu University, is with the National Metallurgical Laboratory, Jamshedpur, India.     

The liquidus surface and tie-lines in the iron-nickel-sulfur system between 1473 and 1673 K

The liquidus compositions and the tie-lines for the solid alloy plus liquid sulfide two-phase region were determined for the iron-nickel-sulfur system in the temperature range 1473 to 1673 K. Experiments were conducted by sampling the liquid sulfide in equilibrium with the alloy phase and chemically analyzing the sulfide. The alloy was quenched and analyzed by electron microprobe. The results represent a significant revision to existing data.