Michael Friman

ESOMAT 2009 - 8th European Symposium on Martensitic Transformations

The high temperature transformations (e.g. liquidus, ordering temperature) of the alloys Ni47.7Mn31.2Ga21.1, Ni49.7Mn28.7Ga21.6, and Ni49.6Mn24.0Ga26.6, Ni47.3Mn30.3Ga20.3Fe2.1, Ni49.9Mn28.3Ga20.1Fe1.7, Ni51.3Mn14.4Ga26.3Fe8.0, Ni47.3Mn25.5Ga24.5Cu2.7, Ni48.3Mn29.7Ga21.1Cu0.9, and Ni49.4Mn23.3Ga25.6Cu1.7 were studied for the practical melting and annealing purposes. At first the chemical compositions (SEM-EDS) and the martensitic and magnetic transition temperatures (DSC, ac magnetic susceptibility) of the alloys were determined. High temperature DSC measurements were made in argon with 10 K/min. Two first measurements were carried out in the solid state (301 1273 K) and in the third measurement the material was melted (max meas. temp. 1573 K). The ordering temperature was obtained from the measurements in the solid state. As the e/a ratio was above 7.53 the ordering temperature was in the range of 1019-1039 K, otherwise a clear change was observed. The variation in heating and cooling was less than 5 K with small quaternary additions, but alloying of 8% Fe increased this difference to 18 K. Alloys with close Ni/Mn/Ga-ratio showed only minor differences in solidus and liquidus temperatures, but if there was a clear change in the Ni/Mn-ratio even those alloys having close e/a ratios showed a clear difference in melting behavior. When Ni/Mn is 1.5with higher values not clear region could be determined.

Effect of Annealing on Ag-doped Submicron Silica Powder Prepared with Modified Stöber Method

Antibacterial silver can be used against such micro-organisms as bacteria and molds. When Ag nanoparticles are attached to an inorganic carrier, e.g., silica long-term antimicrobial functionality can be gained. Such Ag-SiO2 particles are potential for water purification or bactericidal applications. In this work, submicron sized silica particles doped with Ag were prepared by the modified Stöber method. The as-prepared powder was air-dried and annealed for 75 minutes at 573, 673, 773, 873, 973, 1073, 1173, or 1273 K in air. The powders were studied by DSC/TGA, XRD, SEM, TEM and UV-vis methods. The as-prepared powder consisted of round silica particles having size around several hundred nanometers. XRD and SEM studies confirmed that the powder consisted of metallic silver nanoparticles on the submicron silica surface after annealing at 873 K or higher. According to the SEM study the silver particles had an average particle size between 19-400 nm depending on the annealing temperature. DSC was used to determine the phase transformation temperatures. After annealing the Ag-SiO2 powder at 873 K the TEM study suggested that the silver had crystalline structure. The XRD studies confirmed that silver appeared as a FCC crystal structure. The UV-vis measurements of Ag-SiO2 powder annealed at and below 773 K showed a steady increase in absorption with decreasing wavelength without absorption peaks. Annealing at 873 K and above resulted in a strong peak in between 404 nm and 416 nm. This peak can be attributed to the surface plasmon resonance of silver nanoparticles.

Melting Behavior of Sn–Bi Alloy Powder Compacts Observed Using Optical Dilatometry

Abstract The melting behavior of Sn – Bi alloy powder compacts was observed using optical dilatometry. The change in standard deviation of compact width with temperature obtained by dilatometry was used to evaluate the melting behavior by considering the factors in the shape change of the compact under heating. The effects on melting behavior of alloy composition, particle size and pressing load at compacting are discussed in this study. The difference in composition affected the melting behavior in accordance with the phase diagram. Smaller particle size showed a lower degree of melting. The effects of these two parameters, viz. composition and particle size, however, are highly dependent on surface oxidation of powders. The influence of surface oxidation, on the other hand, was reduced by producing the compacts with a higher pressing load.