Focused ion beam assisted analysis of the oxidation of a NiAl coating on pure Ni

peer-reviewedDiscs of (pure nickel 15 mm diameter and 4 nun thickness) have been polished to a 1 mu m finish, aluminised using a standard pack CVD process to give a beta-NiAl coating and then the surface of this coating polished to a 1 mu m finish again. Samples have then been isothermally oxidised in a muffle furnace for 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 and 1024 hours at 950 degrees C, and subjected to surface and cross-sectional microscopy and analysis. Scales were also cross-sectioned and imaged using Focused Ion Beam Milling. The oxidation rate was determined to be 2.6 x 10(-13) g(2) cm(-4) s(-1) and for times less than 512 hours the predominant alumina phase was theta alumina. Al depletion effects were observed due to both oxidation and interdiffusion between the Ni substrate and the NiAl coating. Using these effects, it has been shown that tensile strains of up to 9% can arise and these strains readily explain the formation of intrefacial elliptical pores observed by FIB cross sectioning. FIB sectioning also indicated that different coating grains exhibit different oxide-coating interfaces which arise due to different grain orientations. The faceting of the coating-oxide interface and the development of cuboidal faceted coating structures beneath spalled oxide is thought to be due to substructure development (sub-grain development or recrystallisation) arising from the plastic strains generated by Al depletion effects.Acceptedpeer-reviewe

Topology of "white" stars in relativistic fragmentation of light nuclei

In the present paper, experimental observations of the multifragmentation processes of light relativistic nuclei carried out by means of emulsions are reviewed. Events of the type of "white" stars in which the dissociation of relativistic nuclei is not accompanied by the production of mesons and the target-nucleus fragments are considered. A distinctive feature of the charge topology in the dissociation of the Ne, Mg, Si, and S nuclei is an almost total suppression of the binary splitting of nuclei to fragments with charges higher than 2. The growth of the nuclear fragmentation degree is revealed in an increase in the multiplicity of singly and doubly charged fragments with decreasing charge of the non-excited part of the fragmenting nucleus. The processes of dissociation of stable Li, Be, B, C, N, and O isotopes to charged fragments were used to study special features of the formation of systems consisting of the lightest $\alpha$, d, and t nuclei. Clustering in form of the $^3$He nucleus can be detected in "white" stars via the dissociation of neutron-deficient Be, B, C, and N isotopes.Comment: 20 pages, 3 figures, 9 tables, conference: Conference on Physics of Fundamental Interactions, Moscow, Russia, 1-5 Mar 2004.(Author's translation

Investigation of Light Nucleus Clustering in Relativistic Multifragmentation Processes

The use of emulsions for studying nuclear clustering in light nucleus fragmentation processes at energies higher than 1A GeV is discussed. New results on the topologies of relativistic Li-7 and B-10 nucleus fragmentation in peripheral interactions are given. A program of research of the cluster structure in stable and radioactive nuclei is suggested.Comment: 4 pages, 1 figure. Presented at Conference on Fundamental Interactions, 2-6 December 2002, ITEP, Moscow, Russia (misprints are removed

Correlations in STAR: interferometry and event structure

STAR observes a complex picture of RHIC collisions where correlation effects of different origins -- initial state geometry, semi-hard scattering, hadronization, as well as final state interactions such as quantum intensity interference -- coexist. Presenting the measurements of flow, mini-jet deformation, modified hadronization, and the Hanbury Brown and Twiss effect, we trace the history of the system from the initial to the final state. The resulting picture is discussed in the context of identifying the relevant degrees of freedom and the likely equilibration mechanism.Comment: 8 pages, 6 figures, plenary talk at the 5th International Conference on Physics and Astrophysics of Quark Gluon Plasma, to appear in Journal of Physics G (http://www.iop.org

Azimuthal anisotropy and correlations at large transverse momenta in p+p and Au+Au collisions at sqrt[sNN] = 200 GeV

Results on high transverse momentum charged particle emission with respect to the reaction plane are presented for Au+Au collisions at sqrt[sNN]=200 GeV. Two- and four-particle correlations results are presented as well as a comparison of azimuthal correlations in Au+Au collisions to those in p+p at the same energy. The elliptic anisotropy v2 is found to reach its maximum at pt~3 GeV/c, then decrease slowly and remain significant up to pt ~ 7-10 GeV/c. Stronger suppression is found in the back-to-back high-pt particle correlations for particles emitted out of plane compared to those emitted in plane. The centrality dependence of v2 at intermediate pt is compared to simple models based on jet quenching