Modeling of the ElectriCOIL system

Theoretical studies have indicated that sufficient fractions of O/sub 2/(/sup 1//spl Delta/) may be produced in an electrical discharge that will permit lasing of an electric discharge oxygen-iodine laser (ElectriCOIL) system. Results of those studies along with more recent experimental results show that electric excitation is a very complicated process that must be investigated with advanced diagnostics along with modeling to better understand this highly complex system. A kinetic package appropriate for the ElectriCOIL system is presented and implemented in the detailed electrodynamic GlobalKin model and the Blaze II chemical laser modeling code. A parametric study with the Blaze II model establishes that it may be possible to attain positive gain in the ElectriCOIL system, perhaps even with subsonic flow. The Blaze II model is in reasonable agreement with early gain data. Temperature is a critical issue, especially in the subsonic cases, and thus it appears that supersonic flow will be important for the ElectriCOIL system. Simulations of a supersonic ElectriCOIL system indicate that it may be possible to attain reasonable performance levels, even at low yield levels of 20% or less. In addition, pre-dissociation of the iodine is shown to be very important for the supersonic flow situation.     

Noise sensitivity of sparse signal representations: reconstruction error bounds for the inverse problem

Certain sparse signal reconstruction problems have been shown to have unique solutions when the signal is known to have an exact sparse representation. This result is extended to provide bounds on the reconstruction error when the signal has been corrupted by noise or is not exactly sparse for some other reason. Uniqueness is found to be extremely unstable for a number of common dictionaries.     

Correlations Between Growth Kinetics and Microstructure for Scales Formed by High-Temperature Oxidation of Pure Nickel. II. Growth Kinetics

The oxidation kinetics of high-purity nickel were studied between 500 and 1200°C, in pure oxygen at atmospheric pressure, for average oxide-scale thicknesses of 1, 5, 10, and 30 m. In the overall temperature range studied, a decrease in the parabolic rate constant k_p with increasing scale thickness was observed. Depending on temperature and oxide-scale thickness, growth kinetics can be interpreted as a mixture of parabolic- and cubic-growth kinetics. Possible correlations between growth kinetics and microstructures of the oxide scales were investigated. From this set of experimental data, oxidation-kinetics models were tested. In particular, the effect of grain-boundary diffusion on NiO-growth kinetics was discussed. The correlations between growth kinetics and oxide microstructures appear to be more complex than usually reported.     

Yttrium aluminum garnet powders by nitrate decomposition and nitrate–urea solution combustion reactions—a comparative study

Precursors for yttrium aluminum garnet (Y₃Al₅O₁₂—YAG) were synthesized by simple decomposition of concentrated aqueous solution of nitrates and combustion of concentrated aqueous solution of nitrates with urea on a heater. The precursor formed by the former reaction was granules of agglomerated powder while that from the latter reaction was a voluminous and porous sponge-like mass. Both precursors were ground to powders and subjected to detailed thermogravimetric–differential thermal analysis and X-ray diffraction studies. The precursor from the simple decomposition of nitrates exhibited a total loss in weight of about 18% in stages (25 to 300 °C and 300 to 600 °C) accompanied by endotherms—characterized as processes of dehydration of absorbed moisture and decomposition of residual nitrates, respectively. The as formed precursor and that heated to 820 °C were amorphous. Crystallization to YAG phase occurred from an amorphous oxide characterized by an exotherm above 820 °C with no loss of weight. The precursor from nitrate–urea combustion reaction was found to exhibit a weight loss of 2.5% accompanied by a shallow endotherm in the range of 25 to 300 °C—characterized as the process of dehydration of absorbed moisture. No further weight loss or heat effect was noticed, confirming it to be chemically pure YAG. This as formed precursor was found to be crystalline YAG. The difference in chemical composition of the precursors formed by these two reactions is attributed to the difference in the actual reaction temperatures during their formation—lower reaction temperature for the endothermic decomposition of nitrates and higher reaction temperature for the exothermic combustion associated with the formation of a bright flame. The morphology of the precursor powder formed by the former reaction exhibited only cracks while that of the precursor from the latter reaction exhibited pores and voids. The precursor from the former reaction was calcined at 1100 °C to form into chemically pure YAG. Zeta potential variation with pH for the aqueous suspensions of the crystalline YAG powders from both the reactions exhibited a maximum value in the range of 40 to 50 mV around a pH of 4, indicating stability of these dispersions towards coagulation at this pH. Particle size distribution of wet ground powders (slurries with 20%, v/v, solid at a pH of 4) showed that the powder from combustion reaction could be formed into a finer size than that from simple nitrate decomposition, indicating the agglomerates of combustion reaction were softer.     

Metallurgical characterization and determination of residual stresses of coatings formed by thermal spraying

This work presents an experimental determination of residual stresses in 35CrMo4 (Euronorm) low alloyed steel substrates with thermally sprayed coatings. Two different materials were separately deposited. The first one consisted of a blend of two superalloys: Cr-Ni steel and Cr-Mn steel, designated 55E and 65E, respectively. The second material was molybdenum. In a first part, basic characteristics of the deposited layers (metallographic analysis, hardness, and adhesion) are presented. In a second part, the determination of the residual stresses, in both substrate and thermal sprayed layers is performed using an extensometric method in combination with a simultaneous progressive electrolytic polishing. The influence of a nickel-aluminum (80:20%) bond-coat and/or a post-annealing at 850 °C in air for 1 h is studied.     

Assessment of vitrified CBN wheels for precision grinding

Methods of measuring topographical features of grinding wheels are reviewed. Each technique has advantages and limitations for resolution, measuring depth, ease of application, data analysis and interpretation. Results obtained vary according to the method and instrument employed. Advantages and difficulties experienced with different techniques are discussed. Different replication techniques and materials are compared and suggestions made. A set of parameters that describe the wheel and grain characteristics is defined. Experimental studies with grinding wheels having different structures are carried out in terms of observations and measurements of changes in wheel topography. Experimental results are analysed and discussed in relation to theoretical understanding of abrasive wear and loading.     

Effect of cold deformation on age hardening of alloy VT35

The effect of cold deformation on the variation of hardness during aging of sheets from alloy VT35 with β-structure is studied. Diagrams of isothermal transformations due to aging of alloy VT35 with β-phase are plotted for sheets without work hardening and for sheets with an initial β-structure subjected to cold rolling.     

Production of coatings of powders of self‐fluxing alloys by Shockwaves and heat treatment

The experimental results show that friction stir welding of aluminium alloys may be accompanied by the formation of defects in the form of discontinuities, delamination cavities, ‘sticking’ and also a specific ‘tunnel’ defect. The majority of these defects are associated with the welding conditions and are efficiently detected by X-ray inspection.     

Computational analysis of a three-dimensional high-velocity oxygen fuel (HVOF) thermal spray torch

An analysis of a high-velocity oxygen fuel thermal spray torch is presented using computational fluid dynamics (CFD). Three-dimensional CFD results are presented for a curved aircap used for coating interior surfaces such as engine cylinder bores. The device analyzed is similar to the Metco diamond jet rotating wire torch, but wire feed is not simulated. The feed gases are injected through an axisymmetric nozzle into the curved aircap. Argon is injected through the center of the nozzle. Premixed propylene and oxygen are introduced from an annulus in the nozzle, while cooling air is injected between the nozzle and the interior wall of the aircap. The combustion process is modeled assuming instantaneous chemistry. A standard, two-equation, k-ε turbulence model is employed for the turbulent flow field. An implicit, iterative, finite volume numerical technique is used to solve the coupled conservation of mass, momentum, and energy equations for the gas in a sequential manner. Computed flow fields inside and outside the aircap are presented and discussed.     

A pilot study on the content and the release of Ni and other allergenic metals from cheap earrings available on the Italian market

The capability of alloys used in cheap jewellery to release metal ions on contact with the skin causing allergic contact dermatitis (ACD) is generally acknowledged. To reduce the diffusion of the Ni-induced ACD the Council Directive 94/27/EC [Council Directive 94/27/EC of 30 June 1994. Official Journal L 188, 22/07/1994, 1.] limited the total Ni content in alloys and its release rate in artificial sweat. In this work, three different aspects were explored: i) the frequency of skin sensitization to Ni-containing earrings in patients before and after the introduction of the Directive's limit; ii) metal composition of alloys by X-ray analysis; iii) metal leaching in artificial sweat followed by Sector Field Inductively Coupled Plasma Mass Spectrometry (SF-ICP-MS) quantification. Well-known allergenic metals, as Ni, Cr and Co, and possible emergent allergens, as Al, Ag, Au, Cd, Cu, Fe, Ir, Mn, Pb, Pd, Pt, Rh, Sn, V and Zn, were studied. Results showed that the frequency of allergy due to earrings did not decrease after the introduction of the Ni limit: in 1994 and in 2005 patients positive to Ni patch tests were 54.3% and 53.5%, respectively. The earring components analyzed were Fe-based or alloys of Cu/Zn or Fe/Cr/Ni, plated with a thin film of precious metal (Ag, Au) which, in several cases, was combined with a Ni layer beneath. Five out of 10 items were not in compliance with the Ni Directive 94/27/EC having a total Ni content >0.05%. In three cases the release of Ni concentrations was higher than the safe sensitizing limit given by the above mentioned Regulation (i.e., <0.5 microg/cm(2)/week). The release of Cu and Zn was very variable among the different pieces (Cu: 0.134-30.9 microg/cm(2)/week; Zn: 0.141-160 microg/cm(2)/week); two objects released high amounts of Fe (358 and 586 microg/cm(2)/week) and one released considerable Mn (21 microg/cm(2)/week). Lead was released from 70% of the objects, while Ag, Al, Cd, Co, Cr and Sn from ca. 30% of the items and concentrations of these elements were well below 0.5 microg/cm(2)/week. Vanadium was released by only one item whereas Au, Ir, Pd, Pt and Rh were never leached.