Wagner Theory Research Articles

From embryos to precipitates: A study of nucleation and growth in a multicomponent ferritic steel

The nucleation and growth of nanoscale precipitates in a new class of high-strength, multicomponent, ferritic steels has been studied with complementary state-of-the-art microstructural characterization techniques of atom probe tomography for individual embryos and precipitates and small-angle neutron scattering for their statistical averages. Both techniques revealed a bimodal size distribution, with subnanometer embryos, and nanoscale precipitates. The embryos, which have a radius of \ensuremath{\sim}0.4 nm, are enriched in Cu and served as preferential sites for nucleation. The critical radius for nucleation was determined to be \ensuremath{\sim}0.7 nm. Subsequent growth of the precipitates is dictated by volumetric diffusion, as predicted by the Lifshitz--Slyozov--Wagner theory.

Hydrodynamic loads during water impact of three-dimensional solids: Modelling and experiments

The problem of three-dimensional liquid–solid impact is considered. A numerical method has been developed to predict the hydrodynamic loads acting on the entering body. The proposed approach is based on the Wagner theory and the boundary element method. In order to validate the numerical simulation, an original experimental study has been performed. It consists of a series of impact tests carried out with a hydraulic machine. Three specimens have been tested: an elliptic paraboloid, a wedge with conical ends and a square pyramid. An excellent agreement between theory and experiments has been observed.

Predicting Internal Oxidation: Building on the Wagner Model

Wagner’s 1959 diffusion model of the internal oxidation process provided a method of predicting the rate at which a binary alloy was penetrated by dissolved oxygen as it precipitated the more reactive (but dilute) alloy component. Parabolic kinetics were predicted to depend on oxygen permeability in the unreacted alloy solvent and also, in cases where the reactive component was sufficiently mobile, the diffusion coefficient of the latter. The model has proven very successful, but is restricted to single oxidant-binary alloy systems, in which the precipitated oxide has extremely low solubility. This paper reviews recent results on a number of internal precipitation processes which cannot be described with the Wagner theory. These include formation of low stability carbides and nitrades; internal precipitation driven by multiple oxidants; the templating effects of prior precipitates on subsequently formed corrosion products; cellular precipitation morphologies; internal interface diffusion effects; volume changes in the reaction zone and the effects upon them of simultaneous external scaling.

Synthesis, magnetic and dielectric properties of Er–Ni doped Sr-hexaferrite nanomaterials for applications in High density recording media and microwave devices

A sol–gel combustion method has been successfully employed for the synthesis of Sr-hexaferrite nanomaterials doped with Er3+ and Ni2+ at strontium and iron sites, respectively. The X-ray diffraction analysis confirmed the single magnetoplumbite phase and the crystallite size was found to be in the range of 14–16nm, suitable for obtaining signal-to-noise ratio in the high density recording media. The magnetic properties such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) were calculated from hysteresis loops. Ms, Mr and Hc are observed to increase with the Er–Ni content. The dielectric constant (ε´) and dielectric loss (tanδ) is found to decrease with the increase in frequency and is explained on the basis of Maxwell–Wagner and Koops theory. The decrease in dielectric constant and dielectric loss but increase in saturation magnetization and remanence with Er–Ni content suggests that the materials are suitable for applications in microwave devices and high density recording media .

Evolution of the semi-solid microstructure of ADC12 alloy in a modified SIMA process

Abstract Semi-solid metal processing is a new developing technology. This processing has a more advanced technology than traditional ones such as forming and casting. The quasi-spherical grain has been formed by recrystallization of the dendrites during reheating in semi-solid state. The strain-induced melt activation is simple and does not need expensive equipment for preparing semi-solid billets. In this paper a modified method was proposed based on the strain-induced melt activation process. The microstructure and mechanical properties of ADC12 aluminum alloys prepared by the modified strain-induced melt activation process were studied. Different levels of heating temperatures and holding times were used in this investigation. The results of heating experiment revealed that the optimum heating temperature, isothermal holding time and average size of particles were 828 K, 1800 s and 70 μm, respectively. The results of isothermal treatment showed that the size of spherical particles increased linearly with extending the holding time at the 828 K. In the meantime the quantity of particles showed the parabola descent. These phenomena are in accordance with the Lifshitz–Slyozov–Wagner theory and Ostwald ripening.

Process optimization and stability of d-limonene-in-water nanoemulsions prepared by ultrasonic emulsification using response surface methodology

d-limonene in water nanoemulsion was prepared by ultrasonic emulsification using mixed surfactants of sorbitane trioleate and polyoxyethylene (20) oleyl ether. Investigation using response surface methodology revealed that 10% d-limonene nanoemulsions formed at S 0 ratio ( d-limonene concentration to mixed surfactant concentration) 0.6–0.7 and applied power 18 W for 120 s had droplet size below 100 nm. The zeta potential of the nanoemulsion was approximately −20 mV at original pH 6.4, closed to zero around pH 4.0, and around −30 mV at pH 12.0. The main destabilization mechanism of the systems is Ostwald ripening. The ripening rate at 25 °C (0.39 m 3 s −1 × 10 29) was lower than that at 4 °C (1.44 m 3 s −1 × 10 29), which was in agreement with the Lifshitz–Slezov–Wagner (LSW) theory. Despite of Ostwald ripening, the droplet size of d-limonene nanoemulsion remained stable after 8 weeks of storage.

Competitive short-term and long-term memory processes in spatial habituation.

Exposure to a spatial location leads to habituation of exploration such that, in a novelty preference test, rodents subsequently prefer exploring a novel location to the familiar location. According to Wagner's (1981) theory of memory, short-term and long-term habituation are caused by separate and sometimes opponent processes. In the present study, this dual-process account of memory was tested. Mice received a series of exposure training trials to a location before receiving a novelty preference test. The novelty preference was greater when tested after a short, rather than a long, interval. In contrast, the novelty preference was weaker when exposure training trials were separated by a short, rather than a long interval. Furthermore, it was found that long-term habituation was determined by the independent effects of the amount of exposure training and the number of exposure training trials when factors such as the intertrial interval and the cumulative intertrial interval were controlled. A final experiment demonstrated that a long-term reduction of exploration could be caused by a negative priming effect due to associations formed during exploration. These results provide evidence against a single-process account of habituation and suggest that spatial habituation is determined by both short-term, recency-based memory and long-term, incrementally strengthened memory.

Local water slamming impact on sandwich composite hulls

The local water slamming refers to the impact of a part of a ship hull on stationary water for a short duration during which high local pressures occur on the hull. We simulate slamming impact of rigid and deformable hull bottom panels by using the coupled Lagrangian and Eulerian formulation included in the commercial software LS-DYNA. We use the Lagrangian formulation to describe plane-strain deformations of the hull panel and consider geometric nonlinearities. The Eulerian formulation is used to analyze deformations of the water. Deformations of the hull panel and of the water are coupled through the hydrodynamic pressure exerted by water on the hull, and the velocity of particles on the hull wetted surface affecting deformations of the water. The continuity of surface tractions and the inter-penetrability of water into the hull are satisfied by using a penalty method. The computer code is verified by showing that the computed pressure distributions for water slamming on rigid panels agree well with those reported in the literature. The pressure distributions computed for deformable panels are found to differ from those obtained by using a plate theory and Wagner's slamming impact theory. We have also delineated jet flows near the edges of the wetted hull, and studied delamination induced in a sandwich composite panel due to the hydroelastic pressure.

Preparation and oxygen permeation of U‐shaped perovskite hollow‐fiber membranes

AbstractThe oxygen permeation of dense U‐shaped perovskite hollow‐fiber membranes based on Ba0.5Sr0.5Co0.8Fe0.2O3−δ prepared by a phase inversion spinning process is reported. The perovskite hollow fibers with totally dense wall were obtained with the outer diameter of 1.147 mm and the inner diameter of 0.691 mm. The dependences of the oxygen permeation on the air flow rate on the shell side, the helium flow rate on the core side, the oxygen partial pressures, and the operating temperatures were experimentally investigated. According to the Wagner theory, it follows that the oxygen transport through the U‐shaped hollow‐fiber membrane is controlled by both surface reaction and bulk diffusion at the temperature ranges of 750–950°C. High oxygen permeation flux of 3.0 ml/(min cm2) was kept for about 250 h at 950°C under the conditions of the air feed flow rate of 150 ml/min and the helium flow rate of 50 ml/min. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Size control of Sb 2Te 3 Widmanstätten precipitates in thermoelectric PbTe

The number density and area per unit volume of Sb 2Te 3 Widmanstätten plates in thermoelectric PbTe were controlled through two types of heat treatments of (PbTe) 1− x –(Sb 2Te 3) x , where x = 0.04 and 0.06: isothermal annealing at various temperatures and cooling from a solid-solution regime to a two-phase region with various rates. The microstructure was quantified by image analysis of scanning electron micrographs and Rietveld refinements of X-ray diffraction profiles. Isothermal annealing of (PbTe) 0.94–(Sb 2Te 3) 0.06, results in increasing number density and area per volume of precipitates with decreasing temperature. In controlled cooling rate experiments, faster cooling rates or smaller x result in higher number density and area per volume. These trends are discussed using phase transformation theories. Overall the number density and area per volume of precipitates were controlled in the ranges from 0.4 to 44 μm −3 and from 0.5 to 1.8 μm −1, respectively. Isothermal annealing was performed for time periods from 10 to 166 h at 723 K to check the stability of the microstructure at the (PbTe) 0.94–(Sb 2Te 3) 0.06 composition. While the Boyd and Nicholson model of the Greenwood–Lifshitz–Slyozov–Wagner theory for the average diameter of plates gives a reasonable value for peripheral interfacial energy, the time dependence was found to decelerate more than the t 1/3 rule. It has also been found that the coarsening mechanism involves the elongation of plates.

Oxidation protection of Ni-base superalloys by halogen treatment

A new concept of oxidation protection is proposed for Ni-base alloys with Al-amounts of 2–5 wt%. Following Wagner's theory of oxidation the formation of a dense protective alumina scale is possible if the Al-activity is sufficiently high. This condition can be fulfilled by using the halogen effect. Thermodynamical calculations reveal the existence of regions for a positive effect of F and Cl for the alloys IN738 and IN939. In the case of fluorine these results are transformed into F concentrations in a screening by using ion implantation. By the F-effect the oxidation mechanism at 1050 °C/air was changed from internal oxidation of Al to an external formation of an Al2O3 – scale. Optimal implantation parameters were defined. The formation and stability of the protective alumina scale was proved within 1000 h/1050 °C.

Ostwald ripening of binary alloy particles

Classical Lifshitz-Slyozov-Wagner theory is generalized for Ostwald ripening of particles composed of random binary alloy. We show that the steady state ripening process is characterized by self-similar particle size and composition distributions. The shape of particle size distribution depends on whether the process is diffusion controlled (Lifshitz-Slyozov) or reaction controlled (Wagner) and is consistent with the predictions of classical theory for one-component materials. The steady state composition distribution, in contrast, has the same functional form in both extreme cases featuring a universal dependence of the composition upon particle size. We also found that transients in particle's composition can be very quick resulting in a steady state distribution well before it is reached by particles sizes. These transients involve significant changes in particle sizes and open an opportunity for producing metastable particle size distributions of required shape.

Physical stability of nanosuspensions: Investigation of the role of stabilizers on Ostwald ripening

The effect of stabilizer type (small molecule vs. polymeric) and the amount of micellar solubilized drug on Ostwald ripening of nanosuspensions was investigated. Indomethacin nanosuspensions were prepared with small molecule stabilizers (sodium lauryl sulfate (SLS) and Dowfax 2A1 (DF)) and a polymeric stabilizer (hydroxypropyl methyl cellulose (HPMC)). Two different drug:stabilizer ratios were used to evaluate the effect of micellar solubilized drug. The Ostwald ripening potential of nanosuspensions was evaluated by subjecting them to various stress conditions (temperature (15, 25, 35 and 45 °C), thermal cycling, and mechanical shaking) for three months. The mean particle size increased in all SLS and DF formulations stored under different stress conditions. No effect of micellar solubilized drug on the Ostwald ripening rate was observed. In the case of HPMC formulations only those stored at higher temperatures (35 or 45 °C) exhibited an increase in mean particle size. The increase in size in the HPMC formulation stored at 45 °C was attributed to dehydration of the HPMC chains and subsequent loss of protection of the nanoparticles. The cube of the mean particle diameter versus time plot was determined to be non-linear for all formulations exhibiting Ostwald ripening. Therefore, according to the Lifshitz, Slyozov and Wagner theory the process was not diffusion controlled. The most probable mechanism for Ostwald ripening was surface nucleation controlled.

Growth kinetics of ZnO nanocrystallites: Structural, optical and photoluminescence properties tuned by thermal annealing

In this paper, we report temperature dependent studies of ZnO nanocrystallites deposited by the sol-gel spin coating process. The films are annealed at different temperature from 500 to 900 °C to grow the size of crystallites in controlled environment. The crystallite size, lattice parameters, and strain in the nanocrystallites are calculated. A coarsening kinetics is understood by Lifshitz, Slyozov and Wagner (LSW) theory and the activation energy of the coarsening process is estimated. Optical absorption and Photoluminescence (PL) measurements were carried out to investigate the effect of coarsening on optical properties of the ZnO thin films. The origin of PL spectra is explained in terms of the stabilization of structural defects and size of the crystallites.

Solution-processed ZnO nanocrystals in thin-film light-emitting diodes for printed electronics

Thin-film light-emitting diodes (LEDs) containing solution-processed ZnO nanocrystals (NCs) were prepared as printed electronics. The electroluminescent (EL) properties of thin-film LEDs were investigated along with the structural and photoluminescence (PL) properties of the ZnO NCs. Scanning electron microscope and x-ray diffraction studies revealed that the crystal sizes D were ranged from 5–11 nm, and can be controlled by varying growth time tG in the Zn2+/OH− solution at 40 °C. The time evolution of D was analyzed using Lifshitz–Slyozov–Wagner theory, showing that growth is limited by diffusion. The results of PL studies indicated that increases in the peak energies in the ultraviolet (UV) region could be attributed to the quantum-size effects on the exciton emission in the NCs with a small D, the ZnO surfaces became sufficiently passivated as D increases. Printed layers containing well-passivated ZnO NCs with different D of 8–11 nm were used as emission layers in thin-film LEDs together with pentacene hole transport layers. The current-voltage characteristics were analyzed using the trapped-charge-limited current mechanism. EL spectral measurements revealed the presence of weak UV emission that increased slightly as D decreased.

Natural law as inspiration to Adolph Wagner's theory of public intervention

Adolph Wagner is best known for his principle regarding the increase of state intervention into the economy. Such a principle is characterised by an ‘ethical economy’ perspective, incorporating some original ideas based on the relationship between the law and political economy. Wagner's theory sought to legitimise state intervention and progressive taxation by referring to both a broad Aristotelianism and a specific philosophy of law derived from Krausian natural law. This paper analyses and compares how this idea of the law affects Wagner's theorisation of state–economy interaction and his insights into public economics.

Comparaison de différentes approches pour la simulation numérique d’impacts hydrodynamiques

The aim of this paper is to compare several simulation methods for hydrodynamic impact problems. For this purpose, three models has been developed: (i) a finite element model based on the Wagner theory, (ii) a finite element model based on a Arbitrary Lagrangian Eulerian (ALE) formulation, (iii) a finite volume model based on a two-phase eulerian formalism and the Volume-of-Fluid technique. The different results are compared with published and experimental data.

Matthew Wilson Smith: The Total Work of Art: From Bayreuth to Cyberspace

Matthew Smith's book testifies to the recent and long overdue resurgence of interest in the idea and history of the total work of art. Despite the centrality of Wagner's theory and practice to any discussion of the Gesamtkunstwerk, it is important to recognize that the idea goes back to the German Romantics and the festivals of the French Revolution, which mobilized the arts to celebrate the People, the Republic, and the Nation, and that the history of the total work of art since Wagner extends from the avant-garde movements of the early years of the twentieth century through to Hollywood and contemporary mass culture. Smith has not set out to tackle the still unwritten history of the total work. His aim, rather, is to illuminate this history through the prism of the relationship between the total work, technology, and mass culture, with reference to Wagner (Chapter 2), Germany between the wars (Chapters 3–5), and postwar America (Chapters 6–8). This history is one of discontinuities as much as of continuities. Between Wagner and the Bauhaus and Brecht lies the First World War. Between the German avant-garde and Disneyland lies the Second World War and the Götterdämmerung of the Third Reich.

Non-Debye dielectric behavior and near-field interactions in biological tissues: When structure meets function

The Maxwell–Wagner theory of interfacial polarization treats dielectric particles suspended in homogeneous media and subjected to alternating fields as systems of independent induced dipoles, and therefore predicts simple Debye-type dispersion in which both permittivity and conductivity vary between low- and high-frequency plateaus. Unfortunately, Maxwell–Wagner theory cannot replicate its own success when applied to more concentrated and structured (i.e., non-random) systems of cells such as tissues. The effective medium theory, devised to incorporate contributions of the induced dipoles to the average far-field, brought about some improvement, but the general shape of the dielectric spectra remained that of a simple Debye – in contrast with experimental data. Supracellular organization of tissues induces non-Debye behavior due to near-field interactions between neighboring cells. Specifically, biological cells may perturb each other’s electrical environment via dipolar (multipolar) fields or conductance bridges (such as pores and gap junctions) between cytoplasms and across cell membranes. We substantiate this hypothesis by presenting comparatively data from yeast and red blood cell suspensions, blood forming reversible supra-cellular structures, called ‘rouleaux’, breast tissues, as well as from brain treated with anesthetics that are known to affect the gap-junctional connectivity between cells.

The Imaginary Significations of Modernity: A Re-Examination

This article deals with the concept of modernity upon which one of the most interesting contemporary theories about modern social change is based—Peter Wagner's theory of successive modernities. Wagner understands modernity as a double imaginary signification which entails a basic tension between liberty and discipline. This conception is almost directly taken from Cornelius Castoriadis. I argue that this tension exists in two versions in Castoriadis' philosophy and that the two versions are incompatible. It is further claimed that the two versions reappear in Wagner's theory, which makes his theory of successive modernities partly inconsistent. A stance is taken for one of these versions and it is argued that the theory of successive modernities should appropriate that version as its point of departure in order to grasp the history of modernity in a consistent way.