Chemical Science , 8 9 , Cheung , Jack R. Lancaster , Ana Denicola. Solubility and diffusion of oxygen in phospholipid membranes. Journal of Nuclear Materials , , Ngo , Connie P. Ow , Bruce S.
Gardiner , Saptarshi Kar , James T. Pearson , David W. Smith , Roger G. Diffusive shunting of gases and other molecules in the renal vasculature: physiological and evolutionary significance. Journal of Plant Growth Regulation , 35 3 , Ben Amar. Collective chemotaxis and segregation of active bacterial colonies. Dissolved atmospheric gas in xylem sap measured with membrane inlet mass spectrometry. Permeability of dried gases and gases dissolved in water through polyimide membranes modified by immersing in amino compound solutions.
Florence Chow , Geoffrey C. Maitland , J. The Journal of Chemical Thermodynamics , 93 , Biosensors , 5 3 , Aeration and air—water mass transfer on stepped chutes with embankment dam slopes. Environmental Fluid Mechanics , 15 4 , Aeration performances of a gabion stepped weir with and without capping. DeSain , Brian B. Brady , Thomas J. Curtiss , Lawrence T.
Greenberg , Mark B. Smith , Randy M. Journal of Propulsion and Power , 31 4 , B M. Fleige , G. Wiberg , M.
Rotating disk electrode system for elevated pressures and temperatures. Review of Scientific Instruments , 86 6 , Lehmann , Marja Tiirola ,. Dhanaliwala , Adam J. Dixon , Dan Lin , Johnny L. Chen , Alexander L.
Klibanov , John A. In vivo imaging of microfluidic-produced microbubbles. Amann-Hildenbrand , B. Krooss , J. Harrington , R. Cuss , C. Davy , F. Skoczylas , E. Jacops , N. Gas Transfer Through Clay Barriers. Journal of Biotechnology , , McLamore , D. Marshall Porterfield , Maria S. Comparative study of non-invasive methods for assessing Daphnia magna embryo toxicity. Environmental Science and Pollution Research , 21 18 , Nuske , V.
Joekar-Niasar , R. Non-equilibrium in multiphase multicomponent flow in porous media: An evaporation example. International Journal of Heat and Mass Transfer , 74 , Temperature dependence of diffusion coefficient of nitrogen gas in water: A molecular dynamics study. From these results, it was proposed a model of nitrogen diffusion into a two-phase stainless steel to explain the morphology of the interface between the layer and the substrate. Duplex stainless steels DSS are used in applications where they must have good wear resistance properties, having a good resistance to corrosion.
Improvement of the mechanical properties of austenitic stainless steel after plasma nitriding. Surface and Coatings Technology. Characterization of surface microstructure and properties of low-energy high-dose plasma immersion ion-implanted L austenitic stainless steel.
Tribological behaviour and mechanical properties of low temperature gas nitrided austenitic steel in relation to layer morphology. Plasma nitriding of L austenitic stainless steel: Experimental investigation of fatigue life and surface evolution. Nitriding is done at low temperatures to prevent nitrides formation, which reduces corrosion resistance 5 5 Kliauga M and Pohl M. Effect of plasma nitriding on wear and pitting corrosion resistance of X2 CrNiMoN 22 5 3 duplex stainless steel. Hardening is given by the nitrogen diffusion into the crystal lattice.
The nitrogen transport in austenitic stainless steel at moderate temperatures. Applied Physics Letters. Determination of the concentration dependent difusion coefficient of nitrogen in expanded austenite.
Materials Research. Plasma nitriding of stainless steels at low temperatures. Microstructure and properties of layers on chromium steel. This study aims to study the kinetics of nitrided layer formation on DSS and its morphology.
The material used in this study was a duplex stainless steel with 0. Nitrided layers, obtain for each temperature, were measured on the micrographs using a conversion of the rule present on the photographs and the real distance on them. Microstructures of nitride layers, for each temperature, are present on Figures 1 to 4.
Table 1 shows that temperature increase leads to formation of thicker nitrided layers. Diffusion coefficients were calculated as function of layer thickness obtained for each treatment temperature, using the Equation 1. In addition, shown on Table 2. Calculated diffusion coefficients for austenite and for ferrita are apparent for nitrogen diffusion in each phase.
In theory, coefficients of ferrite phase should have around two orders of greatness rather than coefficients for nitrogen in austenitic phase. At room temperature, a gaseous molecule will experience billions of collisions per second.
The mean free path is the average distance a molecule travels between collisions. The mean free path increases with decreasing pressure; in general, the mean free path for a gaseous molecule will be hundreds of times the diameter of the molecule. In general, we know that when a sample of gas is introduced to one part of a closed container, its molecules very quickly disperse throughout the container; this process by which molecules disperse in space in response to differences in concentration is called diffusion shown in Figure 1.
The gaseous atoms or molecules are, of course, unaware of any concentration gradient, they simply move randomly—regions of higher concentration have more particles than regions of lower concentrations, and so a net movement of species from high to low concentration areas takes place.
In a closed environment, diffusion will ultimately result in equal concentrations of gas throughout, as depicted in Figure 1. The gaseous atoms and molecules continue to move, but since their concentrations are the same in both bulbs, the rates of transfer between the bulbs are equal no net transfer of molecules occurs.
We are often interested in the rate of diffusion , the amount of gas passing through some area per unit time:.
The diffusion rate depends on several factors: the concentration gradient the increase or decrease in concentration from one point to another ; the amount of surface area available for diffusion; and the distance the gas particles must travel.
Note also that the time required for diffusion to occur is inversely proportional to the rate of diffusion, as shown in the rate of diffusion equation. A process involving movement of gaseous species similar to diffusion is effusion , the escape of gas molecules through a tiny hole such as a pinhole in a balloon into a vacuum Figure 2. Although diffusion and effusion rates both depend on the molar mass of the gas involved, their rates are not equal; however, the ratios of their rates are the same.
If a mixture of gases is placed in a container with porous walls, the gases effuse through the small openings in the walls. The lighter gases pass through the small openings more rapidly at a higher rate than the heavier ones Figure 3. This means that if two gases A and B are at the same temperature and pressure, the ratio of their effusion rates is inversely proportional to the ratio of the square roots of the masses of their particles:. Using the same apparatus at the same temperature and pressure, at what rate will sulfur dioxide effuse?
Heating a gas increases the kinetic energy of the particles, causing the gas to expand. In order to keep the pressure constant, the volume of the container must be increased when a gas is heated. In the lungs, whilst oxygen is smaller than carbon dioxide, the difference in solubility means that carbon dioxide diffuses roughly 20 times faster than oxygen.
Diffusion in liquids is slower than diffusion in gases because the particles in a liquid move more slowly. It happens faster if the temperature is increased. Gaseous particles tend to undergo diffusion because they have kinetic energy. Diffusion is faster at higher temperatures because the gas molecules have greater kinetic energy. The diffusion of chemicals and gases in and out of cells is an essential activity in human organs.
Diffusion of oxygen and carbon dioxide gas occurs in the lungs. Diffusion of water, salts, and waste products occurs in the kidneys. Diffusion of calcium from food into cells occurs in the intestines.
Diffusion is very important in the body for the movement of substances eg the movement of oxygen from the air into the blood and carbon dioxide out of the blood into the air in the lungs, or the movement of glucose from the blood to the cells. Cell membranes are partially permeable. Begin typing your search term above and press enter to search.
0コメント