Phase structure of electrodeposited alloys

By electrodeposition it is possible to obtain alloy phases of metastable structure; these phases may be different from those reported for metallurgical equilibrium conditions or may have different compositions for the solubility limits, in some cases with very important enlargement. Typical cases are examined, discussing published results and presenting new findings. To understand the general behaviour, free energy versus composition g/x diagrams were calculated and are presented for the alloys examined in equilibrium conditions and after modification to obtain composition limits for the electrodeposited phases in stable and metastable state.The first reported case is Ni-Sn alloy, where the well known metastable phase NiSn is obtained. The second case is the electrodeposition of IB-Sn alloys from non-cyanide electrolytes. Phase structure of Zn-rich electrodeposited Zn-Ni alloys is also discussed as representative of grain size effect on phase stability.From the different cases examined, the occurrence of electrodeposited intermediate phases can be interpreted according to a local thermodynamic equilibrium, whilst long range order is difficult to observe in as-deposited layers. These phases depend on bath composition and operation conditions (temperature, stirring, direct or pulse current density) giving phases of different grain size which in turn can influence their stability.     

An experimental and kinetic modeling study of cyclopentadiene pyrolysis: First growth of polycyclic aromatic hydrocarbons

The importance of 1,3-cyclopentadiene (CPD) and cyclopentadienyl (CPDyl) moieties in the growth of polycyclic aromatic hydrocarbons (PAHs) was studied using new experimental data and ab initio calculations. The experimental investigation was performed in a tubular continuous flow pyrolysis reactor under both high (24molN₂/molCPD)$(24{\text{mol}}_{{\text{N}}_2}/{\text{mol}}_{\text{CPD}})$ and low (5molN₂/molCPD)$(5{\text{mol}}_{{\text{N}}_2}/{\text{mol}}_{\text{CPD}})$ nitrogen dilutions, covering a temperature range of 873–1123 K, at a fixed pressure of 1.7 bara. At the most severe conditions up to 84% of CPD is converted, and the amount of PAHs is more than 65 wt%. Major products observed during CPD pyrolysis were benzene, indene, methyl-indenes and naphthalene, in line with previous studies. On-line GC × GC-FID/(TOF-MS) also allowed to quantify minor species (methane, toluene, styrene, phenanthrene, anthracene, etc.), never reported before at this level of accuracy. The new experimental data have been used to further analyze the role of the successive interactions of CPD, indene, and naphthalene as well as the recombination and addition reactions of their resonantly stabilized radicals and refine their kinetics. The results of the modeling study are in good agreement with existing and new experimental observations.     

Reactivity of no-clean pastes and fluxes for the surface mount technology process—part II: Corrosion risk measurements for printed circuit boards and solder joints

The introduction of no-clean pastes and fluxes for the surface mount technology process needs testing methods of high sensitivity and reliability to evaluate the activity of the residues after the reflow process. An electrochemical method is proposed, suitable to ascertain the reactivity and the corrosion risk of these residues. Products of normal use are tested, and their behavior described and compared. Surface morphologies and compositions are examined after reflow and after testing. Local surface oxides are investigated with x-ray photoelectron spectroscopy. Surface analytical results are interpreted and related to the electrochemical behavior of solder joints. Tin is shown to have the most important role toward the onset of possible localized corrosion.     

Calculation of multicomponent multiphase equilibria

An algorithm which gives very good first trial values for the computation of chemical equilibrium composition is proposed. It is based on writing the chemical reactions in “canonical form” and changing the independent component set until it is formed by the species present in greatest quantity at equilibrium. The advancement degrees ξ_r of the reactions are calculated considering the reactions to occur independently of any other. By applying a similar procedure to the series reactor method, a new powerful solution algorithm of the Rosenbrook's type is obtained. In the first method we linearize the equilibrium equations written making null the gradient of the free energy of the system with respect to the corresponding ξ_r whilst in the second one we make successive unidimensional searches solving the equations for ξ_r     

Catecholaminergic innervation of the human dura mater involved in headache

The effects of pulsed Nd:YAG laser irradiation with different laser initiators on the permeability and ultrastructure of the root canal wall dentin were investigated in vitro. Forty extracted human single-rooted teeth were randomly assigned to four groups. Group 1 teeth were not lased as a control. Group 2 specimens received four 10-s duration laser exposures for a total exposure of 40 s/canal. In group 3 specimens, the root canals were painted with black ink and then lased by the same method as group 2 teeth. In group 4 specimens, root canals were treated with 38% Ag(NH3)2F and then lased by the same method as group 2 teeth. Laser parameters were set at 2 W, 20 pps. After being placed in 0.6% rhodamine B solution for 48 h, the teeth were sectioned for study by stereoscope and scanning electron microscopy. Statistical analysis showed there were significant differences (p < 0.05) in dentin permeability in the apical areas between groups 3 and 1, 4 and 1, and 4 and 2. Scanning electron microscopic examination showed that laser treatment alone had no obvious effects on the root canal wall. The root canal surfaces prepared for by laser irradiation with black ink or 38% Ag(NH3)2F revealed melting, smear layer evaporation, and open dentinal tubules. Black ink was more effective than 38% Ag(NH3)2F as a Nd:YAG laser initiator.     

Departmental organization of health care institutions

The economic forces that are reshaping the practice of medicine and the funding of medical research will have great impact on clinical education and research in teaching hospitals and their associated medical schools. Changes in the setting of and approach to medical education will need to be made in order to continue to train physicians at the same high level as in the past and to maintain the productivity of our national biomedical research enterprise and its contributions to health. Academic leaders, such as department chiefs who have clinical service responsibilities, are finding it more and more difficult to manage simultaneously the demands of the clinical business, education, and research. In an effort to organize a teaching hospital and a medical school in a manner that would position them to maintain more effectively their common academic mission front and center with the clinical business, Harvard Medical School and the Beth Israel Hospital created a joint venture in 1996. The new nonprofit Institute for Education and Research has education and research as its top (and only) mission. It is designed to provide additional and specific academic leadership and to enable the joint venture to undertake strategic planning for the academic mission. In addition to the challenges it faces from changes in the external environment, the Institute for Education and Research will need to establish a new pattern of interactions internally within the parent institutions. Collaborations with department chairs and faculty are an essential ingredient for its success. It is hoped that this structure will prove to be a useful template for organizing other medical school-hospital collaborations on behalf of the academic mission.     

Crystal growth of chemical Co-P and electrodeposited Co on Ni and Cu single crystals

The crystal growth of Co-P alloys chemically reduced with hypophosphites from aqueous solutions on the (0 0 1) faces of Ni and Cu single crystals has been studied in a wide range of thicknesses: 10 Å to 12μm. Smooth deposits ofβ-Co and martensitically transformedα-Co are first obtained. Upon increasing the thickness, outgrowth is observed and the mechanism of formation is attributed to an anomalous (1 0. 1) twinning mode. At high thickness, outgrowing basal planes become perpendicular to the base, transform towards the growth mode imposed by the bath and form regions of equi-oriented planes. Electrodeposition of Co films at medium thickness yields similar results.     

Electrodeposition and characterization of Au–Cu–Cd alloys

The electrodeposition of Au–Cu–Cd alloys from cyanide baths was investigated under different hydrodynamic conditions. Alloys obtained at different current densities were characterized from the compositional, structural and morphological points of view. Depending on the electrodeposition current density, the deposit structure displays either one or two-phase disordered solid solutions; corresponding changes in mechanical properties were observed. Morphology and roughness show a marked smoothing transition when the current density is increased over the limit for the inception of Cu codeposition. The Cd²⁺ concentration in the bath is a critical factor for control of the electrodeposition process, especially in respect to compositional stability and absence of hydrogen incorporation. Alloy composition was shown to be critically affected by hydrodynamic conditions; strict control of flow conditions is needed in order to obtain alloys of desired and reproducible composition.     

Gas-Carburizing Kinetics of a Low-Alloy Steel

Gas-carburizing kinetics of a low-alloy steel (Pyrowear 53) was investigated by thermogravimetric experiments. Kinetic curves were modeled by adapting the approximate integral method, and the diffusion coefficient of carbon as well as the rate constant of the surface reaction were estimated. These parameters were evaluated after several carburizing procedures, which differ from each other in the surface treatments performed before the carburizing step. It is known that the carbon enrichment is low when this steel is carburized without any pretreatment, and this behavior was found to be related to a low value of carbon diffusivity. The interaction between the selective oxidation of alloying elements by the carburizing atmosphere and carbon diffusion is discussed. The pretreatment procedures investigated in this work consist of different combinations of oxidation, reduction, and grit-blasting processes. The most effective procedures involve oxidation in dry air or oxidation in wet air followed by grit blasting.     

An investigation into the electrodeposition of Au–Cu-matrix particulate composites

The electrodeposition of AuCu/B4C composites from alkaline baths containing free cyanide is described. The electrochemical behaviour of the bath and the metallographic and crystalline structures of the electrodeposited alloys were studied with and without addition of particles. Electrochemical instabilities were observed and their bearing on the structure of both pure matrix and composite electrodeposits is shown and elucidated. The electrochemical and structural conclusions on the AuCu/B4C system are thought to be general for alloy-matrix composite plating with nonconductive particles.