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Insights Into Emissions and Exposures From Use of Industrial-Scale Additive Manufacturing Machines
A.B. Stefaniak,A.R. Johnson,S. du Preez,D.R. Hammond,J.R. Wells,J.E. Ham,R.F. LeBouf,S.B. Martin Jr.,M.G. Duling,L.N. Bowers,A.K. Knepp,D.J. de Beer,J.L. du Plessis 한국산업안전보건공단 산업안전보건연구원 2019 Safety and health at work Vol.10 No.2
Background: Emerging reports suggest the potential for adverse health effects from exposure to emissions from some additive manufacturing (AM) processes. There is a paucity of real-world data on emissions from AM machines in industrial workplaces and personal exposures among AM operators. Methods: Airborne particle and organic chemical emissions and personal exposures were characterized using real-time and time-integrated sampling techniques in four manufacturing facilities using industrial-scale material extrusion and material jetting AM processes. Results: Using a condensation nuclei counter, number-based particle emission rates (ERs) (number/min) from material extrusion AM machines ranged from 4.1 1010 (Ultem filament) to 2.2 1011 [acrylonitrile butadiene styrene and polycarbonate filaments). For these same machines, total volatile organic compound ERs (mg/min) ranged from 1.9 104 (acrylonitrile butadiene styrene and polycarbonate) to 9.4 104 (Ultem). For the material jetting machines, the number-based particle ER was higher when the lid was open (2.3 1010 number/min) than when the lid was closed (1.5e5.5 109 number/min); total volatile organic compound ERs were similar regardless of the lid position. Low levels of acetone, benzene, toluene, and m,p-xylene were common to both AM processes. Carbonyl compounds were detected; however, none were specifically attributed to the AM processes. Personal exposures to metals (aluminum and iron) and eight volatile organic compounds were all below National Institute for Occupational Safety and Health (NIOSH)-recommended exposure levels. Conclusion: Industrial-scale AM machines using thermoplastics and resins released particles and organic vapors into workplace air. More research is needed to understand factors influencing real-world industrial- scale AM process emissions and exposures.
Insights Into Emissions and Exposures From Use of Industrial-Scale Additive Manufacturing Machines
Stefaniak, A.B.,Johnson, A.R.,du Preez, S.,Hammond, D.R.,Wells, J.R.,Ham, J.E.,LeBouf, R.F.,Martin, S.B. Jr.,Duling, M.G.,Bowers, L.N.,Knepp, A.K.,de Beer, D.J.,du Plessis, J.L. Occupational Safety and Health Research Institute 2019 Safety and health at work Vol.10 No.2
Background: Emerging reports suggest the potential for adverse health effects from exposure to emissions from some additive manufacturing (AM) processes. There is a paucity of real-world data on emissions from AM machines in industrial workplaces and personal exposures among AM operators. Methods: Airborne particle and organic chemical emissions and personal exposures were characterized using real-time and time-integrated sampling techniques in four manufacturing facilities using industrial-scale material extrusion and material jetting AM processes. Results: Using a condensation nuclei counter, number-based particle emission rates (ERs) (number/min) from material extrusion AM machines ranged from $4.1{\times}10^{10}$ (Ultem filament) to $2.2{\times}10^{11}$ [acrylonitrile butadiene styrene and polycarbonate filaments). For these same machines, total volatile organic compound ERs (${\mu}g/min$) ranged from $1.9{\times}10^4$ (acrylonitrile butadiene styrene and polycarbonate) to $9.4{\times}10^4$ (Ultem). For the material jetting machines, the number-based particle ER was higher when the lid was open ($2.3{\times}10^{10}number/min$) than when the lid was closed ($1.5-5.5{\times}10^9number/min$); total volatile organic compound ERs were similar regardless of the lid position. Low levels of acetone, benzene, toluene, and m,p-xylene were common to both AM processes. Carbonyl compounds were detected; however, none were specifically attributed to the AM processes. Personal exposures to metals (aluminum and iron) and eight volatile organic compounds were all below National Institute for Occupational Safety and Health (NIOSH)-recommended exposure levels. Conclusion: Industrial-scale AM machines using thermoplastics and resins released particles and organic vapors into workplace air. More research is needed to understand factors influencing real-world industrial-scale AM process emissions and exposures.
Kang, Junmo,Jariwala, Deep,Ryder, Christopher R.,Wells, Spencer A.,Choi, Yongsuk,Hwang, Euyheon,Cho, Jeong Ho,Marks, Tobin J.,Hersam, Mark C. American Chemical Society 2016 Nano letters Vol.16 No.4
<P>Black phosphorus (BP) has recently emerged as a promising narrow band gap layered semiconductor with optoelectronic properties that bridge the gap between semimetallic graphene and wide band gap transition metal dichalcogenides such as MoS2. To date, BP field-effect transistors have utilized a lateral geometry with in-plane transport dominating device characteristics. In contrast, we present here a vertical field-effect transistor geometry based on a graphene/BP van der Waals heterostructure. The resulting device characteristics include high on-state current densities (>1600 A/cm(2)) and current on/off ratios exceeding 800 at low temperature. Two distinct charge transport mechanisms are identified, which are dominant for different regimes of temperature and gate voltage. In particular, the Schottky barrier between graphene and BP determines charge transport at high temperatures and positive gate voltages, whereas tunneling dominates at low temperatures and negative gate voltages. These results elucidate out-of-plane electronic transport in BP and thus have implications for the design and operation of BP-based van der Waals heterostructures.</P>
Dynamics processes between Sm2+, Sm3+ and color centers in KY3F10 : Sm crystals
Mitsuo Yamaga,Shin-ichiro Tsuda,Jon-Paul R. Wells,Thomas P. J. Han 한양대학교 세라믹연구소 2014 Journal of Ceramic Processing Research Vol.15 No.3
Three distinct Sm2+ impurity centers, a single Sm3+ impurity center, and a color center were identified in KY3F10 with 1 mol.% of Sm ion dopant by their emission and excitation spectra in the vacuum ultraviolet (VUV), ultraviolet (UV), and visible regions. The excited states of the Sm2+ centers consisted of the lower 5 DJ (J = 0,1,2,3) multiplets and the higher lying 4f5 5d excited states. VUV or UV excitation directly into the 4f6 → 4f5 5d transitions of Sm2+ produced cascade emission from the metastable 5 DJ (J = 3,2,1,0) multiplets to the lowest 7 FJ (J = 0,1,2,3,4) multiplets at low temperatures. Energy transfer from Sm2+ to Sm3+ ions was observed in the excitation spectra of the Sm3+ emission. Excitation at 532 nm for a sample temperature of 300 K produced a broad emission band with a peak at 660 nm and sharp emission lines at 680, 692 and 738 nm, being due to Sm2+. 532 nm irradiation for 30 minutes decreased the intensity of the broadband to one-quarter of the initial intensity and increased slightly the intensities of the sharp lines.
Evidence for phonon skew scattering in the spin Hall effect of platinum
Karnad, G. V.,Gorini, C.,Lee, K.,Schulz, T.,Lo Conte, R.,Wells, A. W. J.,Han, D.-S.,Shahbazi, K.,Kim, J.-S.,Moore, T. A.,Swagten, H. J. M.,Eckern, U.,Raimondi, R.,Klä,ui, M. American Physical Society 2018 Physical Review B Vol.97 No.10