Pipe Diffusion Research Articles

Microstructure and Impression Creep Properties of Ca-Containing AS31 Magnesium Alloy

The effect of Ca addition on the microstructure and impression creep properties of AS31 magnesium alloy was investigated in the current study. The results showed that the microstructure of AS31 alloy is composed of α(Mg) phase, massive Mg17Al12 and some Chinese script Mg2Si compounds. Addition of 2 wt% Ca to AS31 alloy resulted in complete elimination of Mg17Al12 phase and formation of Al2Ca compound. Ca improved the alloy’s creep properties especially at higher temperature. Improvement in the creep properties was attributed to the elimination of soft Mg17Al12 and formation of thermally stable Al2Ca compound. According to the obtained stress exponent and creep activation energy, pipe diffusion climb-controlled creep was estimated as the dominant creep mechanism and Ca had no influence on the dominant mechanism.

Pengaruh Aerasi Injeksi Udara terhadap Beberapa Parameter Kualitas Air di Lokasi Budidaya Ikan Waduk Ir. H. Djuanda

Waste of fish farming in floating net are fish feces, urine and undigested feed which is one source of organic matter inputs in Ir. H. Djuanda. Waste organic materials can cause eutrophication of waters. Air injection is one way aeration to increase oxygen to help the process of organic matter decomposition. The purpose of this study was to assess the effect of air injection on some parameters of water quality in fish farming side. This research was conducted at the location of fish farming Ir. H. Djuanda in June-September 2013. Injection of air using a compressor with a pressure of 3 atm as a source of air and perforated pipe at a depth of 3.6 m. Air injection carried out for 8 hours. Observation point vertically at a depth of 3.6 m and horizontally at a distance of -1.5 m (behind the diffuser pipe); 0 (the diffuser pipe); 1.5 m (right and left pipe); +1.5; +3 And +6 m (in front of the pipe diffuser) and a distance of 17 m of pipe which is control. After eight hours of aeration showed that the concentration of organic matter, free carbondioxide, N-NO2 tend to belower in cages aerated but N-NO3 concentration was higher in locations aeration cage than controls cageKeywords: air injection aeration, water quality, fish cage culture, Ir. H. Djuanda Reservoir

Ab initiomodeling of quasielastic neutron scattering of hydrogen pipe diffusion in palladium

A recent quasielastic neutron scattering (QENS) study of hydrogen in heavily deformed fcc palladium provided the first direct measurement of hydrogen pipe diffusion, which has a significantly higher diffusivity and lower activation barrier than in bulk. While ab initio estimates of hydrogen diffusion near a dislocation corroborated the experimental values, open questions remain from the Chudley-Elliott analysis of the QENS spectra, including significant nonmonotonic changes in jump distance with temperature. We calculate the spherically averaged incoherent scattering function at different temperatures using our ab initio data for the network of site energies, jump rates, and jump vectors to directly compare to experiment. Diffusivities and jump distances are sensitive to how a single Lorentzian is fit to the scattering function. Using a logarithmic least squares fit over the range of experimentally measured energies, our diffusivities and jump distances agree well with those measured by experiment. However, these calculated quantities do not reflect barriers or distances in our dislocation geometry. This computational approach allows for validation against experiment, along with a more detailed understanding of the QENS results.

Fast, vacancy-free climb of prismatic dislocation loops in bcc metals.

Vacancy-mediated climb models cannot account for the fast, direct coalescence of dislocation loops seen experimentally. An alternative mechanism, self climb, allows prismatic dislocation loops to move away from their glide surface via pipe diffusion around the loop perimeter, independent of any vacancy atmosphere. Despite the known importance of self climb, theoretical models require a typically unknown activation energy, hindering implementation in materials modeling. Here, extensive molecular statics calculations of pipe diffusion processes around irregular prismatic loops are used to map the energy landscape for self climb in iron and tungsten, finding a simple, material independent energy model after normalizing by the vacancy migration barrier. Kinetic Monte Carlo simulations yield a self climb activation energy of 2 (2.5) times the vacancy migration barrier for 1/2〈111〉 (〈100〉) dislocation loops. Dislocation dynamics simulations allowing self climb and glide show quantitative agreement with transmission electron microscopy observations of climbing prismatic loops in iron and tungsten, confirming that this novel form of vacancy-free climb is many orders of magnitude faster than what is predicted by traditional climb models. Self climb significantly influences the coarsening rate of defect networks, with important implications for post-irradiation annealing.

Pipe and grain boundary diffusion of He in UO2

Molecular dynamics simulations have been conducted to study the effects of dislocations and grain boundaries on He diffusion in . Calculations were carried out for the {1 0 0}, {1 1 0} and {1 1 1} edge dislocations, the screw dislocation and Σ5, Σ13, Σ19 and Σ25 tilt grain boundaries. He diffusivity as a function of distance from the dislocation core and grain boundaries was investigated for the temperature range 2300–3000 K. An enhancement in diffusivity was predicted within 20 Å of the dislocations or grain boundaries. Further investigation showed that He diffusion in the edge dislocations follows anisotropic behaviour along the dislocation core, suggesting that pipe diffusion occurs. An Arrhenius plot of He diffusivity against the inverse of temperature was also presented and the activation energy calculated for each structure, as a function of distance from the dislocation or grain boundary.

Numerical investigation on hydrogen/air non-premixed combustion in a three-dimensional micro combustor

In order to obtain a higher combustion efficiency and a lager heat transfer from outer wall, a new type of micro cylindrical combustor with suction pipe, mixing pipe, diffuser pipe and shrinkage pipe and the combination of cavity and backward-facing step is designed and a numerical investigation on non-premixed hydrogen/air reacting flow inside three micro combustors has been carried out at atmospheric pressure. Moreover, the combustion characteristics and working performance of micro combustors are also investigated. Results show that the cavity and the backward-facing step in micro combustor is useful for the heat recirculation and the flame stability. Moreover, the combustion efficiency and the heat transfer from outer wall can be improved by increasing the length of combustion chamber within limited range. A high and uniform outer wall temperature distribution is desirable for the L2 micro combustor, therefore, the L2 micro combustor is more suitable for the micro thermo photovoltaic (MTPV) system when hydrogen volume flow rate is equal to 150mL/min and equivalence ratio φ is equal to 1.0.

Impression creep behaviour of squeeze-cast Ca and Sb added AZ91 magnesium alloy

Impression creep technique has been employed to investigate creep behaviour of the squeeze-cast AZ91 Mg alloy modified by the addition of Ca and/or Sb. All the modified alloys exhibit superior creep resistance than the base AZ91 alloy. The combined additions of Ca and Sb are more effective in improving creep resistance than the individual additions. Individual Ca added AZX911 results superior creep resistance than the Sb added AZY911 owing to the higher thermal stability of the Al2Ca phase in the former alloy compared to that of the Mg3Sb2 phase in the later one. The AZXY9120 alloy pertaining 2.0Ca and 0.3Sb (wt%) exhibits the best creep resistance due to reduced amount of β-Mg17Al12 phase and presence of higher amount of dense network of thermally stable Al2Ca phase at grain boundaries. Post creep microstructural observation confirms the ability of the Al2Ca phase to withstand applied high stresses at elevated temperature without undergoing significant changes in its structure. The values of stress exponents and activation energies are in the range of 4.3–6.5 and 111.9±1.1 to 114.9±3.0kJ/mol, which concludes dislocation climb controlled by pipe diffusion is the dominant creep mechanism for all the alloys in the temperature and stress level employed.

The microstructure and creep characteristics of cast Mg–3Si and Mg–3Si–1Gd alloys

The effect of 1wt% Gd addition on the creep behavior of a cast Mg–3Si alloy was investigated by impression creep testing in the temperature range of 448–523K under punching stresses in the range of 175–450MPa for dwell times up to 4200s. It was found that the creep strength of the Mg–3Si base alloy was improved by Gd addition. This was attributed to the modification of the primary Mg2Si particles, solid solution strengthening of Gd in the Mg matrix, and the formation of a new intermetallic phase with a composition close to Mg3Si2Gd2. Creep behavior of the binary Mg–3Si alloy can be divided into the low- and high-stress regimes, with the respective stress exponent values in the range of 5.1–6.0 and 8.8–11.5 and average activation energies of about 81kJmol−1 and 124.5kJmol−1. The creep behavior of the ternary Gd-containing alloy, however, was expressed by a single linear relationship over the whole stress and temperature ranges studied, with stress exponents in the range of 8.2–8.5 and an average activation energy of 111.1kJmol−1. The creep activation energies were all stress dependent, and thus in the binary alloy, stress-assisted climb of dislocations, controlled by pipe and lattice diffusion were the dominant creep mechanisms in the low- and high-stress regimes, respectively. In the ternary Gd-containing alloy, power law creep is valid and it can be suggested that the operative creep mechanism is dislocation climb controlled by lattice diffusion.

Oxide particle coarsening at temperature over 1473 K in 9CrODS steel

The oxide particle coarsening was evaluated at temperature over 1473K by means of transmission electron microscopy (TEM). After annealing of the 9CrODS extruded bar, the size of oxide particles increases while the number density decreases, indicating that the oxide particles coarsen through Ostwald ripening. The growth rate of the oxide particles follows the fifth-power law, which is in the region of dislocation ‘pipe’ diffusion. The activation energy for pipe diffusion, however, was remarkably high, derived as 891KJ/mole. The stability of oxide particles and the difference of the diffusion velocity in between bcc-δ phase and fcc-γ phase should be considered as the contributions to the activation energy.

Novel “open-sorption pipe” reactor for solar thermal energy storage

In the last decade sorption heat storage systems are gaining attention due to their high energy storage density and long term heat storage potential. Sorption reactor development is vital for future progress of these systems however little has done on this topic. In this study, a novel sorption pipe reactor for solar thermal energy storage is developed and experimentally investigated to fulfill this gap. The modular heat storage system consists of sorption pipe units with an internal perforated diffuser pipe network and the sorption material filled in between. Vermiculite–calcium chloride composite material was employed as the sorbent in the reactor and its thermal performance was investigated under different inlet air humidity levels. It was found that, a fourfold increase of absolute humidity difference of air led to approximately 2.3 times boost in average power output from 313W to 730W and an 8.8 times boost of average exergy from 4.8W to 42.3W. According to the testing results, each of three sorption pipes can provide an average air temperature lift of 24.1°C over 20h corresponding to a system total energy storage capacity of 25.5kWh and energy storage density of 290kWh/m3.Within the study, vermiculite–calcium chloride performance was also compared with the widely investigated Zeolite 13X. Vermiculite–calcium chloride showed a good cyclic ability at regeneration temperature of 80°C with a steadier thermal performance than Zeolite. Energetic and exergetic cyclic efficiencies varied in the range of 0.69→0.61 and 0.21→0.14 in the cycles performed with vermiculite–calcium chloride whilst energetic and exergetic cyclic efficiencies of Zeolite testing were between 0.72→0.48 and 0.25→0.06.

In-situ TEM Observation of Cementite Coarsening Behavior of 5Mn Steel during Tempering

The cementite formation and coarsening behaviors of 0. 2 mass% C-5 mass% Mn steel during tempering at 500 °C were investigated by in-situ transmission electron microscope (TEM). In-situ TEM observation showed uniform distribution of cementite particles at the early stage of tempering in the rapidly heated (500 °C/s) sample. Elemental analysis confirmed that the cementite growth was dominated by Mn diffusion. During the cementite growth, the coarsening behavior of intragranular cementite was significantly controlled by the matrix diffusion, while that of the intergranular cementite was mainly governed by the boundary diffusion. The in-situ TEM observation revealed that the dislocation pipe diffusion of Mn took place during tempering, which accelerated the Mn diffusion between cementite particles. The coarsening rates of individual cementite particles were calculated based on the in-situ TEM observation.

(Invited) Advanced Control of Two-Phase Flow in Gdl for PEM Fuel Cells

Water management is a central issue in the development of polymer electrolyte fuel cells (PEFCs): liquid water could considerably increase the oxygen transport resistance and hence the transport polarization whereas dryness dehydrates the electrolyte membrane, raising the Ohmic voltage loss. PEFCs produce water during operation and the electro osmosis enlarges the water imbalance between the anode and cathode sides, making water management a complex operation that requires a careful treatment. Issues such as diffusion media dewetting, anode rehydration, and internal humidification have received much attention in recent years. Modeling, numerical simulation, and advanced imaging techniques are capable of revealing details of transport phenomena, and are a powerful tool for elucidating water management. In this talk, I will cover the below subjects which are the major contributions of UC Irvine to water management: 1.) nonisothermal two-phase flow modeling; 2.) transient dewetting of gas diffusion layer (GDL); 3.) theoretical approach of defining control parameters to characterize two-phase flows; and 4.) experimental evaluation of two-phase flow in PEFCs using neutron radiography. In 1.), a nonisothermal two-phase model, accounting for vapor-phase diffusion and heat pipe effect, was developed and implemented to investigate liquid water distribution. The model was validated in detail against liquid water distribution across GDLs. In 2.), a transient model was developed to capture the phase change and interface movement in PEFCs. A case study will be presented to show the timescale of material dewetting at different regions of GDLs. In 3.), A dimensionless parameter Da0 will defined to characterize the in-plane two-phase region. When Da0 is over 1, part of the GDL region is free of water due to waste heat production and evaporation. A liquid-free GDL region is defined and related to Da0. Impacts of operating temperatures, GDL thermal conductivities, and current densities on the region will be discussed. In 4.), I will present an in-situ study to examine the water content in PEFCs using neutron radiography. Various conditions such as different PTFE loadings in the GDL including the micro-porous layer (MPL), different flow fields (single-channel and quad-serpentine channels), and co-/counter-flow configurations are investigated.

Effects of TiB2 particles and Ag on the activation energy of Ω phase in Al alloys

This work analyses the effects of TiB2 reinforcement particles and silver additions on the activation energy of the GP zones and the Ω phase in an aluminium matrix composite (AMC). Several additions of TiB2 and Ag were made to a 2xxx series alloy. Differential scanning calorimetry (DSC) was used to identify the temperature peaks and the Kissinger approach used to calculate activation energies. Results showed that the activation energy for the Ω phase was greatly reduced by the addition of both elements; however, the TiB2 particles were more effective. In addition, experimental results show that the lowest value of the activation energy, 68 kJmol-1, was not affected by the silver content. This value is lower than any value found in literature and suggests that the formation of the Ω phase is related to the pipe diffusion of Cu in Al.

Deformation-induced trace element redistribution in zircon revealed using atom probe tomography.

Trace elements diffuse negligible distances through the pristine crystal lattice in minerals: this is a fundamental assumption when using them to decipher geological processes. For example, the reliable use of the mineral zircon (ZrSiO4) as a U-Th-Pb geochronometer and trace element monitor requires minimal radiogenic isotope and trace element mobility. Here, using atom probe tomography, we document the effects of crystal–plastic deformation on atomic-scale elemental distributions in zircon revealing sub-micrometre-scale mechanisms of trace element mobility. Dislocations that move through the lattice accumulate U and other trace elements. Pipe diffusion along dislocation arrays connected to a chemical or structural sink results in continuous removal of selected elements (for example, Pb), even after deformation has ceased. However, in disconnected dislocations, trace elements remain locked. Our findings have important implications for the use of zircon as a geochronometer, and highlight the importance of deformation on trace element redistribution in minerals and engineering materials.

501 散気管内外の流れに散気孔の周方向角度が及ぼす影響(GS5 流体工学(1),研究討論セッション)

Experiments on aeration from a bubble diffuser pipe having five aeration holes are carried out to investigate effects of azimuthal angle of the holes on flows inside and outside the pipe. The azimuthal angle of the holes was varied by rotating the pipe. When the azimuthal angle becomes larger than a certain angle, the liquid height inside the pipe is limited at just below the holes, which results in suppression of the onset of slugging. Uniform aeration is thus realized just by rotating the pipe.

On nano-oxide coarsening kinetics in the nanostructured ferritic alloy MA957: A mechanism based predictive model

Nanostructured ferritic alloys are dispersion strengthened and imbued with remarkable neutron irradiation damage tolerance by an ultrahigh density of nano-oxide precipitates that must remain stable under prolonged high-temperature service. Here, previously reported long-time and high-temperature thermal aging data is used to derive a simple, but physically based and quantitatively predictive nano-oxide coarsening model using least square fits to equations representing different underlying mechanisms. A dislocation pipe diffusion model adequately fit the data with a dislocation-detachment climb mechanism providing the best fit. This model is consistent with microstructural observations and recently reported thermo-kinetic nano-oxide nucleation, growth and coarsening simulations that rationalize the underlying physics of coarsening. It is predicted that the nano-oxides will remain fully stable up to 900°C. This remarkable coarsening resistance is due to the extremely low matrix solubility and diffusion rate of Y in equilibrium with Y2Ti2O7 that activates lower resistant paths along dislocations.

Unraveling the Effect of Thermomechanical Treatment on the Dissolution of Delta Ferrite in Austenitic Stainless Steels

Considering the detrimental effects of delta ferrite stringers in austenitic stainless steels and the industrial considerations regarding energy consumption, investigating, and optimizing the kinetics of delta ferrite removal is of vital importance. In the current study, a model alloy prone to the formation of austenite/delta ferrite dual phase microstructure was subjected to thermomechanical treatment using the wedge rolling test aiming to dissolve delta ferrite. The effect of introducing lattice defects and occurrence of dynamic recrystallization (DRX) were investigated. It was revealed that pipe diffusion is responsible for delta ferrite removal during thermomechanical process, whereas when the DRX is dominant, the kinetics of delta ferrite dissolution tends toward that of the static homogenization treatment for delta ferrite removal that is based on the lattice diffusion of Cr and Ni in austenite. It was concluded that the optimum condition for dissolution of delta ferrite can be defined by the highest rolling temperature and strain in which DRX is not pronounced.

Effect of Zn and Sb Additions on the Impression Creep Behavior of Lead-Free Sn-3.5Ag Solder Alloy

The effect of separate additions of 1.5 wt.% Zn and 1.5 wt.% Sb on the creep behavior of Sn-3.5 wt.% Ag lead-free solder alloy was investigated by impression testing. The tests were carried out under constant punching stresses in the range of 60–120 MPa and at temperatures in the range of 298–370 K. Both of the ternary alloys showed creep resistances higher than that of the eutectic binary Sn-3.5Ag alloy. The superior creep resistance of the ternary Sn-3.5Ag-1.5Sb alloy is attributed to the strong solid solutioning effect of antimony in the tin matrix, while the formation of AgZn particles and refinement of the Ag3Sn precipitates account for the higher creep resistance of the Sn-3.5Ag-1.5Zn alloy. The average stress exponents of 8.2, 8.5, and 8.6 and activation energies of 47.4 kJ mol−1, 45.3 kJ mol−1, , and 43.3 kJ mol−1 were obtained for Sn-3.5Ag, Sn-3.5Ag-1.5Zn, and Sn-3.5Ag-1.5Sb, respectively. These activation energies are close to 46 kJ mol−1 for dislocation pipe diffusion of tin. This, together with the stress exponents of 8.2–8.6, suggests that dislocation climb controlled by dislocation pipe diffusion is the predominant creep mechanism in these alloys.

Impression creep behavior of Zn–4Al–3Mg–xSn high-temperature lead-free solders

The microstructure and impression creep behavior of the high-temperature Zn–4Al–3Mg–xSn (x=0, 7, and 13wt.%) alloys were studied under constant punch stress in the range of 50–800MPa and at temperatures in the range of 345–473K. The results showed that for all loads and temperatures, addition of Sn to the base alloy results in higher creep rates, and thus lower creep resistances. The inferior creep behavior of the quaternary alloys is ascribed to the presence of the soft Sn that reduces the volume fraction of the fine α–η eutectic and eutectoid structures, and the hard MgZn2 and Mg2Zn11 second phase particles. Despite the deteriorating effects of Sn, the creep resistance of the quaternary alloys was still higher than those of the Zn–Sn and Pb–Sn high-temperature solders. The stress exponents of 4.0–7.9 and activation energy values of 51.6–92.6kJmol−1, are indicative of a dislocation climb controlled creep mechanism. Dislocation climb controlled by pipe diffusion is the rate controlling mechanism at low temperatures, whereas dislocation climb controlled by lattice diffusion is the dominant creep mechanism at high temperatures.

Duckbill elastomer check valve use effects on domestic wastewater discharging marine outfalls initial dilution performance improvement

Most of the domestic wastewater discharging marine outfall diffusers have simply opened circular ports on the diffuser pipe wall. In order to protect the diffuser from seawater intrusion and clogging by sediments during lower flow rate periods, “duckbill” check valve (DBV) can be mounted on circular ports. Because of the DBV use instead circular ports at the same conditions, jet velocity at port could be increased. It was reported in some of the studies that the initial dilution was also increased in changed diffusers with DBVs. In this study, the initial dilution estimations of multiport diffusers were compared before and after DBV mounted conditions of horizontally opened circular sharp edged ports on the thin pipe wall. For Q = 0.5 m3/s design flow rate, t = 30-year lifespan, H = 20–50 m port depths and, ρa = 1,015–1,035 kg/m3 receiving water densities, 12 different diffusers with d = 150 mm diameter sized circular ports were designed. With the same total head, all diffusers were converted to 150-mm DBV nozzles. All hydraulic parameters and initial dilutions of before and after DBV usage were recalculated from the literature data for line source in this study. Dilution comparisons for the end of the project were shown that all DBV used results were lower than circular port results as ΔS (%) from −0.19 to −19.18 ranges. Except for two of the lower density values at the shallowest port depths, ΔS (%) had similar results for project start year.