Although atmospheric transport and
deposition could be an important
pathway of terrestrial pollutants to the ocean, little information
concerning the presence and distribution of these suspended atmospheric
microplastics in marine air is available. We investigated, for the
first time, the occurrence and distribution of suspended atmospheric
microplastics (SAMPs) in the west Pacific Ocean. In this study, the
spatial distribution, morphological appearance, and chemical composition
of suspended atmospheric microplastics were studied through continuous
sampling during a cruise. SAMPs abundance ranged from 0 to 1.37 n/m3, the median of 0.01 n/m3. Fiber, fragment, and
granule SAMPs quantitively constituted 60%, 31%, and 8% of all MPs,
respectively. Interestingly, plastic microbeads with numerical proportion
of 5% were also observed. A high suspended atmospheric microplastics
abundance was found in the coastal area (0.13 ± 0.24 n/m3), while there was less amount detected in the pelagic area
(0.01 ± 0.01 n/m3). The amount of suspended atmospheric
microplastics collected during the daytime (0.45 ± 0.46 n/m3) was twice the amount collected at night (0.22 ± 0.19
n/m3), on average. Our observations provide field-based
evidence that suspended atmospheric microplastics are an important
source of microplastics pollution in the ocean, especially the pollution
caused by textile microfibers.
The mineral zircon (ZrSiO 4 : I4 1 /amd) can accommodate natural actinides, such as thorium and uranium. The zircon structure has also been obtained for several of the end member compositions of other actinides, such as plutonium and neptunium. However, the thermodynamic properties of these actinide zircon structure-types are largely unknown due to the difficulties in synthesizing these materials and handling transuranium actinides. Thus, we have completed a thermodynamic study of cerium orthosilicate, stetindite (CeSiO 4), a surrogate of PuSiO 4. For the first time, the standard enthalpy of formation of CeSiO 4 was obtained by high temperature oxide melt solution calorimetry to be-1971.9 ± 3.6 kJ/mol. Stetindite is energetically metastable with respect to CeO 2 and SiO 2 by 27.5 ± 3.1 kJ/mol. The metastability explains the rarity of the natural occurrence of stetindite and the difficulty of its synthesis. Applying the obtained enthalpy of formation of CeSiO 4 from this work, along with those previously reported for USiO 4 and ThSiO 4 , we developed an empirical energetic relation for actinide orthosilicates. The predicted enthalpies of formation of AnSiO 4 are then made with a discussion of future strategies to efficiently immobilize Pu or minor actinides in the zircon structure.
We fabricate transparent MgAl 2 O 4 nano-ceramics, which are composed of 40 nm grains, by sintering under high pressure and low temperatures. Analysis of the grain size, differential strains, yield strength and porosity obtained from transmission electron microscopy and x-ray diffraction indicates that the pores at the grain boundary triple junctions can retard grain boundary migration and thus prevent grain growth. It is found that the relatively high density for MgAl 2 O 4 nano-ceramics produced at low-temperature and high pressure is attributed mainly to the large energy in the grain exteriors. The decrease in the transparency with increasing temperature (>700 • C) is therefore a result of the light scattering at large pores. On the basis of these results, we propose a mechanism of transparency in MgAl 2 O 4 nano-ceramics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.