Mariko Ono-Ogasawara

Approach to the Exposure Assessment of MWCNT by Considering Size Distribution and Oxidation Temperature of Elemental Carbon

Multi-walled carbon nanotubes (MWCNTs) have many beneficial characteristics, but it is concerned that exposure to MWCNTs may pose health risks. As an approach to the quantitative exposure assessment of MWCNTs, we have characterized and determined MWCNTs by elemental carbon (EC) using an aerosol carbon monitor. The EC fractions oxidized at different temperatures correspond sample characteristic such as diameter of MWCNT or origins of particles. As MWCNTs aggregate/agglomerate easily, they are usually observed as micron-size particles. Whereas, EC contained in ambient particulate matter (APM) is mainly observed in fine particles. Therefore, the size of airborne particles is a good parameter to distinguish MWCNT from other carbonaceous particles, especially APM. The size and oxidized temperature of EC suggested the origin of the carbonaceous aerosol samples. Exposure assessment of MWCNT was conducted by utilizing the size distribution of EC in the environment where particulate MWCNT or MWCNT-containing composite was handled. A procedure for exposure assessment of MWCNT-related workplace is proposed.

CNTs in Composites: A Case Study

Abstract To understand the exposure to Carbon nanotubes (CNTs) from CNT composites in work environments, case studies were conducted on machining, weaving, and incineration, in work environments and in simulation studies. The case studies showed that fragments of CNT composites having protruding CNTs were observed in most of the cases, moreover, individual CNTs or agglomerates were also observed in some cases during mechanical processes. In most cases, direct-reading instruments are being used; however, most of the released particles are a mixture of fragments with or without CNTs. Moreover, in real workplaces, direct-reading instruments are not sensitive enough to detect the release of small numbers of particles. To distinguish CNTs or CNTs embedded in polymers from the interference of background particles, scanning electron microscopy and transmission electron microscopy observations should be conducted. The release of particles should be evaluated quantitatively to compare the results and assess the health effects. To quantify these particles, a harmonized method is needed.

Adsorption Sampling of Phosphine and Some Other Semiconductor Material Gases

Abstract The adsorption sampling methods of airborne diborane, phosphine, arsine, and silane for the monitoring of workplaces of advanced industries such as the manufacturers of semiconductor integrated circuits and fine ceramics were studied. As those gases are highly toxic and their threshold limit values recommended by American Conference of Governmental Industrial Hygienists are very low, the sampling methods and the successive analytical methods are required to be sensitive. To satisfy the requirement, suitable adsorbents and effective analytical methods were searched or newly developed. This study includes the experimental results on the basic properties of adsorbents such as the impurity contents and the specific surface areas, the gas adsorption capacities, the improvements of the adsorption capacities with chemical modifications, the desorption efficiencies of the adsorbed gases from the adsorbents with various solvents, and the quantitative determination of boron, phosphorus, arsenic, and silico...

Effective Adsorption and Desorption Systems for Semimetal Hydrides

Publisher Summary Diborane, silane, phosphine, arsine, and hydrogen selenide are the hydrides of semimetals in III to VI groups. The industrial consumption of these gases is increasing as the materials of semiconductor IC and fine ceramics, but they are highly toxic substances. This chapter provides information for the selection of effective adsorption and desorption systems of these gases for the practical purposes, such as waste gas treatments and airborne gas analysis, and the mechanisms included in the processes. These gases have rather small molecular weights but undergo various chemical reactions such as oxidation, metal complexation, acid-base adduct formation, and various replacement reactions. Their basic properties are shown in this chapter. In adsorption and desorption of these gases, chemical reactivities are the potential factors, especially to diborane, silane, and phosphine with small molecular weights. This chapter later examines various adsorbents and desorbing solutions for the above gases, from which the characteristics of these gases in adsorption and desorption are exhibited.