The Experts below are selected from a list of 195 Experts worldwide ranked by ideXlab platform

John R Andrews - One of the best experts on this subject based on the ideXlab platform.

  • shape and surface texture of molten droplets deposited on Cold Surfaces
    Surface & Coatings Technology, 2008
    Co-Authors: Ri Li, Nasser Ashgriz, Sanjeev Chandra, John R Andrews
    Abstract:

    When a molten droplet impacts on a Cold surface, the interaction between solidification and fluid dynamics can lead to different shapes and surface textures of deposited droplets. This article presents an experimental study on deposition of small droplets (39 μm diameter) of molten wax ink on solid Surfaces. Our results show that both the final shape and the surface texture of deposited droplets are extremely sensitive to deposition conditions, which include initial temperature of droplets, type of substrate surface and distance between substrate and printhead. Different surface textures are observed and shown to depend on the thermal and flow histories of ink droplets during the process of impact. A test using crystalline wax reveals crystallization as one of the major factors in determining the final texture.

  • Solidification contact angles of molten droplets deposited on solid Surfaces
    Journal of Materials Science, 2007
    Co-Authors: Ri Li, Nasser Ashgriz, Sanjeev Chandra, John R Andrews
    Abstract:

    Droplet impact and equilibrium contact angle have been extensively studied. However, solidification contact angle, which is the final contact angle formed by molten droplets impacting on Cold Surfaces, has never been a study focus. The formation of this type of contact angle was investigated by experimentally studying the deposition of micro-size droplets (∼39 μm in diameter) of molten wax ink on Cold solid Surfaces. Scanning Electron Microscope (SEM) was used to visualize dots formed by droplets impacted under various impact conditions, and parameters varied included droplet initial temperature, substrate temperature, flight distance of droplet, and type of substrate surface. It was found that the solidification contact angle was not single-valued for given droplet and substrate materials and substrate temperature, but was strongly dependent on the impact history of droplet. The angle decreased with increasing substrate and droplet temperatures. Smaller angles were formed on the surface with high wettability, and this wetting effect increased with increasing substrate temperature. Applying oil lubricant to solid Surfaces could change solidification contact angle by affecting the local fluid dynamics near the contact line of spreading droplets. Assuming final shape as hemispheres did not give correct data of contact angles, since the final shape of deposited droplets significantly differs from a hemispherical shape.

Marco Minissale - One of the best experts on this subject based on the ideXlab platform.

  • Reactivity of formic acid (HCOOH) with H atoms on Cold Surfaces of interstellar interest
    Astronomy and Astrophysics, 2020
    Co-Authors: H. Chaabouni, S. Baouche, Stephan Diana, Marco Minissale
    Abstract:

    Context. Formic acid (HCOOH) is the simplest organic carboxylic acid in chemical synthesis and the significant species in interstellar chemistry. HCOOH has been abundantly detected in interstellar ices, dense molecular clouds and star-forming regions. Aims. Laboratory hydrogenation experiments of HCOOH molecules with H atoms were performed with two cryogenic ultra-high vacuum devices on amorphous solid water ices, and highly oriented pyrolytic graphite Surfaces. The aim of this work is to study the reactivity of HCOOH molecules with H atoms at low surface temperature 10 K, low surface coverage of one monolayer to three layers, and low H-atom flux of about 3.0 × 10 12 molecule cm −2 s −1. Methods. HCOOH and H beams were deposited on Cold Surfaces held at 10 K, and the condensed films were analyzed by in-situ Reflection Absorption InfraRed Spectroscopy and temperature programmed desorption mass spectrometry technique by heating the sample from 10 to 200 K. Results. Using the temperature programmed during exposure desorption technique, we highlight the possible dimerization of HCOOH molecules at low surface temperatures between 10 and 100 K. In our HCOOH+H experiments, we evaluated a consumption of 20-30% of formic acid by comparing the TPD curves at m/z 46 of pure and H-exposed HCOOH ice. Conclusions. The hydrogenation HCOOH+H reaction is efficient at low surface temperatures. The main products identified experimentally are carbon dioxide (CO 2) and water (H 2 O) molecules. CO bearing species CH 3 OH, and H 2 CO are also detected mainly on graphite Surfaces. A chemical surface reaction route for the HCOOH+H system is proposed to explain the product formation.

  • quantum tunneling of oxygen atoms on very Cold Surfaces
    Physical Review Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, A Moudens, F Dulieu
    Abstract:

    Any evolving system can change state via thermal mechanisms (hopping a barrier) or via quantum tunneling. Most of the time, efficient classical mechanisms dominate at high temperatures. This is why an increase of the temperature can initiate the chemistry. We present here an experimental investigation of O-atom diffusion and reactivity on water ice. We explore the 6-25 K temperature range at submonolayer surface coverages. We derive the diffusion temperature law and observe the transition from quantum to classical diffusion. Despite the high mass of O, quantum tunneling is efficient even at 6 K. As a consequence, the solid-state astrochemistry of Cold regions should be reconsidered and should include the possibility of forming larger organic molecules than previously expected.

  • formation of nitrogen oxides via no o2 gas solid reaction on Cold Surfaces
    Chemical Physics Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, F Dulieu, Audrey Moudens, G Manico, V Pirronello
    Abstract:

    Abstract The oxidation of nitrogen monoxide has implications for the complex atmospheric chemistry of Antarctica, as well as for planetary atmospheres. In this study we unveil that O 2 adsorbed on a Cold surface reacts with a very high efficiency with NO coming from the gas phase to form NO 2 . Via two molecular beams, O 2 and NO molecules are aimed at a Cold (10 K) sample held in a UHV chamber. NO 2 is formed independently of the surface composition and morphology. We show that the NO + O 2 reaction occurs mainly through the direct Eley Rideal mechanism to form nitrogen oxides (NO 2 , N 2 O 3 , N 2 O 4 ).

  • Formation of nitrogen oxides via NO + O2 gas–solid reaction on Cold Surfaces
    Chemical Physics Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, Audrey Moudens, G Manico, François Dulieu, V Pirronello
    Abstract:

    Abstract The oxidation of nitrogen monoxide has implications for the complex atmospheric chemistry of Antarctica, as well as for planetary atmospheres. In this study we unveil that O 2 adsorbed on a Cold surface reacts with a very high efficiency with NO coming from the gas phase to form NO 2 . Via two molecular beams, O 2 and NO molecules are aimed at a Cold (10 K) sample held in a UHV chamber. NO 2 is formed independently of the surface composition and morphology. We show that the NO + O 2 reaction occurs mainly through the direct Eley Rideal mechanism to form nitrogen oxides (NO 2 , N 2 O 3 , N 2 O 4 ).

V Pirronello - One of the best experts on this subject based on the ideXlab platform.

  • formation of nitrogen oxides via no o2 gas solid reaction on Cold Surfaces
    Chemical Physics Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, F Dulieu, Audrey Moudens, G Manico, V Pirronello
    Abstract:

    Abstract The oxidation of nitrogen monoxide has implications for the complex atmospheric chemistry of Antarctica, as well as for planetary atmospheres. In this study we unveil that O 2 adsorbed on a Cold surface reacts with a very high efficiency with NO coming from the gas phase to form NO 2 . Via two molecular beams, O 2 and NO molecules are aimed at a Cold (10 K) sample held in a UHV chamber. NO 2 is formed independently of the surface composition and morphology. We show that the NO + O 2 reaction occurs mainly through the direct Eley Rideal mechanism to form nitrogen oxides (NO 2 , N 2 O 3 , N 2 O 4 ).

  • Formation of nitrogen oxides via NO + O2 gas–solid reaction on Cold Surfaces
    Chemical Physics Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, Audrey Moudens, G Manico, François Dulieu, V Pirronello
    Abstract:

    Abstract The oxidation of nitrogen monoxide has implications for the complex atmospheric chemistry of Antarctica, as well as for planetary atmospheres. In this study we unveil that O 2 adsorbed on a Cold surface reacts with a very high efficiency with NO coming from the gas phase to form NO 2 . Via two molecular beams, O 2 and NO molecules are aimed at a Cold (10 K) sample held in a UHV chamber. NO 2 is formed independently of the surface composition and morphology. We show that the NO + O 2 reaction occurs mainly through the direct Eley Rideal mechanism to form nitrogen oxides (NO 2 , N 2 O 3 , N 2 O 4 ).

S. Baouche - One of the best experts on this subject based on the ideXlab platform.

  • Reactivity of formic acid (HCOOH) with H atoms on Cold Surfaces of interstellar interest
    Astronomy and Astrophysics, 2020
    Co-Authors: H. Chaabouni, S. Baouche, Stephan Diana, Marco Minissale
    Abstract:

    Context. Formic acid (HCOOH) is the simplest organic carboxylic acid in chemical synthesis and the significant species in interstellar chemistry. HCOOH has been abundantly detected in interstellar ices, dense molecular clouds and star-forming regions. Aims. Laboratory hydrogenation experiments of HCOOH molecules with H atoms were performed with two cryogenic ultra-high vacuum devices on amorphous solid water ices, and highly oriented pyrolytic graphite Surfaces. The aim of this work is to study the reactivity of HCOOH molecules with H atoms at low surface temperature 10 K, low surface coverage of one monolayer to three layers, and low H-atom flux of about 3.0 × 10 12 molecule cm −2 s −1. Methods. HCOOH and H beams were deposited on Cold Surfaces held at 10 K, and the condensed films were analyzed by in-situ Reflection Absorption InfraRed Spectroscopy and temperature programmed desorption mass spectrometry technique by heating the sample from 10 to 200 K. Results. Using the temperature programmed during exposure desorption technique, we highlight the possible dimerization of HCOOH molecules at low surface temperatures between 10 and 100 K. In our HCOOH+H experiments, we evaluated a consumption of 20-30% of formic acid by comparing the TPD curves at m/z 46 of pure and H-exposed HCOOH ice. Conclusions. The hydrogenation HCOOH+H reaction is efficient at low surface temperatures. The main products identified experimentally are carbon dioxide (CO 2) and water (H 2 O) molecules. CO bearing species CH 3 OH, and H 2 CO are also detected mainly on graphite Surfaces. A chemical surface reaction route for the HCOOH+H system is proposed to explain the product formation.

  • quantum tunneling of oxygen atoms on very Cold Surfaces
    Physical Review Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, A Moudens, F Dulieu
    Abstract:

    Any evolving system can change state via thermal mechanisms (hopping a barrier) or via quantum tunneling. Most of the time, efficient classical mechanisms dominate at high temperatures. This is why an increase of the temperature can initiate the chemistry. We present here an experimental investigation of O-atom diffusion and reactivity on water ice. We explore the 6-25 K temperature range at submonolayer surface coverages. We derive the diffusion temperature law and observe the transition from quantum to classical diffusion. Despite the high mass of O, quantum tunneling is efficient even at 6 K. As a consequence, the solid-state astrochemistry of Cold regions should be reconsidered and should include the possibility of forming larger organic molecules than previously expected.

  • formation of nitrogen oxides via no o2 gas solid reaction on Cold Surfaces
    Chemical Physics Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, F Dulieu, Audrey Moudens, G Manico, V Pirronello
    Abstract:

    Abstract The oxidation of nitrogen monoxide has implications for the complex atmospheric chemistry of Antarctica, as well as for planetary atmospheres. In this study we unveil that O 2 adsorbed on a Cold surface reacts with a very high efficiency with NO coming from the gas phase to form NO 2 . Via two molecular beams, O 2 and NO molecules are aimed at a Cold (10 K) sample held in a UHV chamber. NO 2 is formed independently of the surface composition and morphology. We show that the NO + O 2 reaction occurs mainly through the direct Eley Rideal mechanism to form nitrogen oxides (NO 2 , N 2 O 3 , N 2 O 4 ).

  • Formation of nitrogen oxides via NO + O2 gas–solid reaction on Cold Surfaces
    Chemical Physics Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, Audrey Moudens, G Manico, François Dulieu, V Pirronello
    Abstract:

    Abstract The oxidation of nitrogen monoxide has implications for the complex atmospheric chemistry of Antarctica, as well as for planetary atmospheres. In this study we unveil that O 2 adsorbed on a Cold surface reacts with a very high efficiency with NO coming from the gas phase to form NO 2 . Via two molecular beams, O 2 and NO molecules are aimed at a Cold (10 K) sample held in a UHV chamber. NO 2 is formed independently of the surface composition and morphology. We show that the NO + O 2 reaction occurs mainly through the direct Eley Rideal mechanism to form nitrogen oxides (NO 2 , N 2 O 3 , N 2 O 4 ).

E Congiu - One of the best experts on this subject based on the ideXlab platform.

  • quantum tunneling of oxygen atoms on very Cold Surfaces
    Physical Review Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, A Moudens, F Dulieu
    Abstract:

    Any evolving system can change state via thermal mechanisms (hopping a barrier) or via quantum tunneling. Most of the time, efficient classical mechanisms dominate at high temperatures. This is why an increase of the temperature can initiate the chemistry. We present here an experimental investigation of O-atom diffusion and reactivity on water ice. We explore the 6-25 K temperature range at submonolayer surface coverages. We derive the diffusion temperature law and observe the transition from quantum to classical diffusion. Despite the high mass of O, quantum tunneling is efficient even at 6 K. As a consequence, the solid-state astrochemistry of Cold regions should be reconsidered and should include the possibility of forming larger organic molecules than previously expected.

  • formation of nitrogen oxides via no o2 gas solid reaction on Cold Surfaces
    Chemical Physics Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, F Dulieu, Audrey Moudens, G Manico, V Pirronello
    Abstract:

    Abstract The oxidation of nitrogen monoxide has implications for the complex atmospheric chemistry of Antarctica, as well as for planetary atmospheres. In this study we unveil that O 2 adsorbed on a Cold surface reacts with a very high efficiency with NO coming from the gas phase to form NO 2 . Via two molecular beams, O 2 and NO molecules are aimed at a Cold (10 K) sample held in a UHV chamber. NO 2 is formed independently of the surface composition and morphology. We show that the NO + O 2 reaction occurs mainly through the direct Eley Rideal mechanism to form nitrogen oxides (NO 2 , N 2 O 3 , N 2 O 4 ).

  • Formation of nitrogen oxides via NO + O2 gas–solid reaction on Cold Surfaces
    Chemical Physics Letters, 2013
    Co-Authors: Marco Minissale, H. Chaabouni, S. Baouche, E Congiu, Audrey Moudens, G Manico, François Dulieu, V Pirronello
    Abstract:

    Abstract The oxidation of nitrogen monoxide has implications for the complex atmospheric chemistry of Antarctica, as well as for planetary atmospheres. In this study we unveil that O 2 adsorbed on a Cold surface reacts with a very high efficiency with NO coming from the gas phase to form NO 2 . Via two molecular beams, O 2 and NO molecules are aimed at a Cold (10 K) sample held in a UHV chamber. NO 2 is formed independently of the surface composition and morphology. We show that the NO + O 2 reaction occurs mainly through the direct Eley Rideal mechanism to form nitrogen oxides (NO 2 , N 2 O 3 , N 2 O 4 ).