POLYCYCLIC AROMATIC HYDROCARBON CONCENTRATIONS OF AIRBORNE PARTICLES IN URBAN AIR OVER THE PAST TWENTY YEARS

To estimate human exposure to hazardous chemicals, it is important to measure the annual trends regarding the concentrations of these compounds in the environment. Airborne particulate samples were collected over the past 20 years (1980–2001) from ambient air using a quartz fiber filter with the help of a high-volume air sampler placed on the top of the National Institute of the Public Health building, Minato-ku, Tokyo, Japan. In the present study, portions of these filter samples were analyzed to investigate the trends regarding the concentration of PAHs in urban air over the sampling period. The concentrations of various PAHs per unit air volume were determined. The concentrations of seven PAHs decreased within the sampling periods, especially in the late 1980s, and slowly decreased from the middle 1990s. The concentrations of seven PAHs were higher in autumn and winter than in the spring and summer.     

A POSSIBLE USE OF PHOTO-REACTION IN LIQUID-LIQUID EXTRACTION OF SUBSTITUTION-INERT METAL COMPLEXES. EXTRACTION OF CHROMIUM(III) AND COBALT(III) COMPLEXES.

A liquid-liquid extraction of chromium(III) ion was achieved by a cooperative action of light (photoreduction) and conventional extractants on chromium(VI) species. The extraction of chromium spcies was studied by both molecular and atomic absorption spectrophotometry measurements. Trioctylphosphine oxide (TOPO) was the most effective among the extractants studied (TOPO, dibutylsulfoxide, tributyl phosphate, 2-ethyhexyl hydrogen 2-ethylhexylphosphonate, di (2,4,4-trimethylpentyl)-phosphinic acid). A back-extraction of chromium(III) species to aqueous solution was also promoted by photo-irradiation. The nature of the extraction system was studied under various operational conditions such as wavelength of illuminating light, coordinating ah ionic species in aqueous solution, and coexisting metal ions. A liquid- liquid (back-) extraction of some     

Encapsulation of nitride phosphors into sintered phosphate glass by pressureless firing and hot isostatic pressing

The encapsulation conditions of Eu²⁺-doped calcium silicon nitride ((Ca_0.90Eu_0.10)₂Si₅N₈) and strontium silicon nitride ((Sr_0.98Eu_0.02)₂Si₅N₈) phosphors into phosphate glass ((50-x)Na₂O–xZnO–5B₂O₃–45P₂O₅; x = 10-40) were examined by pressureless sintering (normal or infrared firing) and subsequent oxygen-assisted hot isostatic pressing. The evaluation of water resistivity, as well as glass transition temperature (T_g), indicated that the excellent water resistivity and low T_g (313°C) could be achieved at x = 30. The colorless and clear glass body could be fabricated by infrared firing at 370°C for 20 minutes in air, followed by the hot isostatic pressing at 370°C for 24 hours (80%Ar + 20%O₂, pressure: 130 MPa). The encapsulations of 3.0 mass% (Ca_0.90Eu_0.10)₂Si₅N₈ and (Sr_0.98Eu_0.02)₂Si₅N₈ into the glass body produced reddish orange light emission (peak wavelength: 604 nm under excitation wavelength of 423 nm) and red-light emission (617 nm under 383 nm), respectively, showing higher chemical and thermal stability of nitride phosphors in the glass matrix.     

Effects of yttria and magnesia on densification and thermal conductivity of sintered reaction-bonded silicon nitrides

A variety of combinations of Y₂O₃ and MgO were used as additives in preparing Si₃N₄ ceramics by the sintering of reaction-bonded silicon nitride (SRBSN) method. By varying the amount of Y₂O₃ in the range of 0-5 mol% and that of MgO in the range of 0-8 mol%, the effects of Y₂O₃ and MgO additives on nitridation and sintering behaviors as well as thermal conductivity were studied. It was found that appropriate amount and combination of Y₂O₃ and MgO additives were essential for attaining full densification and achieving high thermal conductivity. The sample doped with 2.5 mol% of Y₂O₃ and 5 mol% of MgO attained a thermal conductivity of 128 Wm⁻¹K⁻¹ when sintered at 1900°C for 6 hours, and the sample doped with 2 mol% of Y₂O₃ and 4 mol% of MgO achieved a thermal conductivity of 156 Wm⁻¹K⁻¹ when sintered for 24 hours.     

Preparation and characterization of lotus ceramics with different pore sizes and their implication for the generation of microbubbles for CO2 sequestration applications

Four kinds of porous mullite ceramics, named lotus ceramics because of the similarity of their microstructure with lotus roots, were prepared by an extrusion method using rayon fibers of four different diameters (8.1, 9.6, 16.8 and 37.6 μm) as the pore formers. The physicochemical properties of these samples were characterized to test their applicability for the generation of microbubbles. The lotus ceramic samples contained pores of 9.4, 10, 15.6 and 30 μm size and porosities of 45–48%. SEM micrographs confirmed that the cylindrical pores were oriented unidirectionally along the extrusion direction and the degree of alignment was greater with larger fiber diameter. The permeability for gaseous CO₂ increased with increasing pore size from 3×10^?13 to 8×10^?13 m². The four lotus ceramic samples, a commercial air stone (72 μm) and two simple tubes (1000 and 3500 μm) were used to generate microbubbles in water under ambient conditions from a gas mixture of CO₂ and air. It was found that the bubble size could be decreased with bubblers of smaller pore size. In the bubble size measurements for pure CO₂ and air, the air bubbles were larger than the CO₂ bubbles due to partial dissolution of CO₂ into the water during bubbling. In order to generate smaller size bubbles using porous ceramic bubblers, the liquid must penetrate through the pores of the lotus ceramics before the gas is introduced into the system.     

Effects of Amorphous and Crystalline SiO2 Additives on γ-Al2O3-to-alpha-Al2O3 Phase Transitions

This paper focused on the effects of various phases of SiO₂ additives on the γ-Al₂O₃-to-α-Al₂O₃ phase transition. In the differential thermal analysis, the exothermic peak temperature that corresponded to the theta-to-α phase transition was elevated by adding amorphous SiO₂, such as fumed silica and silica gel obtained from the hydrolysis of tetraethyl orthosilicate. In contrast, the peak temperature was reduced by adding crystalline SiO₂, such as quartz and cristobalite. Amorphous SiO₂ was considered to retard the γ-to-α phase transition by preventing γ-Al₂O₃ particles from coming into contact and suppressing heterogeneous nucleation on the γ-Al₂O₃ surface. On the other hand, crystalline SiO₂ accelerated the α-Al₂O₃ transition; thus, this SiO₂ may be considered to act as heterogeneous nucleation sites. The structural difference among the various SiO₂ additives, especially amorphous and crystalline phases, largely influenced the temperature of γ-Al₂O₃-to-α-Al₂O₃ phase transition.     

Very Rapid Densification of Nanometer Silicon Carbide Powder by Pulse Electric Current Sintering

Rapid densification of a nanometer SiC powder doped with 2.04 wt% Al₄C₃ and 0.4 wt% B₄C was conducted by using a nonconventional sintering technique called pulse electric current sintering (PECS). In all experiments, the sintering temperature and applied pressure were kept to be 1600^oC and 47 MPa, respectively, while heating rates varied between 100^oC/min and 400^oC/min and the holding time was either 2 or 5 min. All of the specimens which were PECS-sintered under various conditions reached near-theoretical density. The microstructures of the rapidly densified SiC ceramics consisted of large elongated grains, and the grain size increased with the increase of heating rate. Polytype transformation of SiC occurred during the PECS process, where faster heating favored the formation of 6H polytype while slower heating favored 4H polytype.