Tayfur Öztürk

Effects of additives on mechanical milling and hydrogenation of magnesium powders

Abstract A study is carried out on the role of additives for structural refinement of magnesium powders in mechanical milling. Additives, namely Al2O3, SiC, V and graphite are chosen so as to cover a wide hardness range. Structural refinement after milling is studied both metallographically and in terms of X-ray line broadening. It is found that for efficient structural refinement, the additives should be chosen not on the basis of their hardness but rather whether or not they are preserved with an acceptable size during milling. Thus, of the additives, it is found that graphite and Al2O3 are most effective. The milled structures are modified upon exposure to hydrogenation temperature, leading to similar structural sizes. In terms of hydrogenation, graphite appears to be the most effective additive. A storage capacity of 6.0 wt % is reached with a quite fast sorbing rate.

Strain partitioning and plastic flow in some metal/metal laminates

An investigation is carried out into the plane strain deformation of model laminates incorporating a single hard layer. A total of four laminates based on Al alloy(5053)-steels and CuW are investigated in which the relative hardness of the constituent layers, rh, are in the range between 2 and 13. It is found that the deformation is uniform in the initial stages of plane-strain, the strain being partitioned equally between the constituent layers. The regime of uniform deformation is prolonged in samples with low rh, and nonexistent in CuW (rh = 13). End of uniform deformation is marked first by necking and then the rupture of the hard layers into platelets leading to the so-called boudin structure. The deformation then becomes grossly inhomogeneous. The platelets deform less than the matrix and moreover volumes evolve in the matrix rhombic in shape in the immediate vicinity of the platelets into which deformation penetrates less. With continued deformation the platelets rupture further, whereby releasing parts of the constrained volumes. The relative hardness of the constituents layers are modified and the range initially as wide as 2 < rh < 13 narrows down with increasing strain and seems to move to a common value of around rh = 2.5.

A study of impurity effect on ordering characteristics of Fe3Al intermetallics

Abstract A study is carried out into energetical and structural characteristics of atomic ordering processes in Fe 3 Al. The statistico-thermodynamical theory of ordering by a quasichemical method is combined with the electronic theory of alloys in pseudopotential approximation in order to predict impurity effects on DO 3 ↔ B2 phase transition temperature and the characteristics of atomic short-range order in Fe 3 Al-type intermetallics. Impurity elements in Fe 3 (Al, Me) Me = Cr, Si, Ge, Cu, Mn, Zn, V, Nb, Ta, Mo, W, Zr or Hf are considered (up to 1 at.% concentration). The study shows, in agreement with experimental observations in literature, that all impurity elements raise the DO 3 ↔ B2 transition temperature relative to that of the binary alloy. It is further found that impurities of Nb, Ta, Mo, W, Zr or Hf substitute mainly Fe sites in the Fe 3 Al (DO 3 ) superstructure and are more effective in increasing the transition temperature.

Effects of different parameters on the densities of uranium dioxide and uranium dioxide-gadolinium oxide fuels produced by the sol-gel technique

Uranium dioxide-gadolinium oxide fuel was produced by the sol-gel technique. The effects of different parameters such as calcination and reduction temperature, compaction pressure, particle size of powder, type of binder, sintering temperature, sintering atmosphere, and duration of sintering on pore size distribution were investigated. The experiments were carried out on three different fuels, (a) pure urania, (b) urania-gadolinia (10%), and (c) urania-gadolinia (10%)-titania (0.1%) doped fuel. It was observed that compaction pressure as low as 200 MPa is sufficient to obtain high-density pellets, while the use of binder or grinding the powder below 400 mesh does not affect densities. Reduction of powder at 1,000 K always gives lower density fuels than the powder reduced at 873 K. Sintering at high temperature and the use of a wet atmosphere each independently increases the fuel density.

Design of a high temperature erosion apparatus for testing of boiler tubes

The synthesis and polymerization of a novel diamine monomer, 1,1-(sulfonylbis (4,1-phenylene)) bis (thiourea) (SPT), with various aromatic dianhydrides were carried out. In addition, the fabrication of poly(thiourea-sulfone-imide)s (PTSIs) with noble thermal properties and flame retardancy was conducted. The structures of SPT and polymers were characterized by FT-IR, H NMR, and C NMR spectroscopy along with elemental analysis. Crystallinity, organosolubility, inherent viscosity, and gel permeation chromatographic measurements were taken as well. The amorphous nature was exhibited by PTSIs containing C=S and –SO2 moieties in the backbone that were readily soluble in highly polar organic solvents. The inherent viscosities of PTSIs were 0.89–1.13 dL g−1 and molecular weights were 87,000–96,550 g mol−1 , respectively. Their thermal stability was studied in terms of temperature at 10% weight loss, which ranged between 478 and 526 ◦C under inert atmosphere. Polyimides had a glass transition temperature around 253–268 ◦C depending on the dianhydrides used. The flame retardant properties of PTSIs were studied in terms of limiting oxygen index values and were measured in the range of 50–56.