Enthalpies of formation of selected Pd2YZ Heusler compounds

Standard enthalpies of formation of selected ternary Pd-based Heusler type compositions Pd₂YZ (Y = Cu, Hf, Mn, Ti, Zr; Z = Al, Ga, In, Ge, Sn) were measured using high temperature direct synthesis calorimetry. The measured enthalpies of formation (in kJ/mole of atoms) of the Heusler compounds are, Pd₂HfAl (−81.6 ± 2.4); Pd₂HfGa (−79.9 ± 2.9); Pd₂HfIn (−76.4 ± 1.4); Pd₂HfSn (−77.6 ± 1.6); Pd₂MnSn (−54.6 ± 3.1); Pd₂TiGa (−65.6 ± 3.6); Pd₂TiIn (−69.9 ± 2.1); Pd₂TiSn (−78.6 ± 2.4); Pd₂ZrAl (−85.3 ± 3.0); Pd₂ZrGa (−76.2 ± 1.9); Pd₂ZrIn (−85.1 ± 3.9); Pd₂ZrSn (−92.2 ± 3.1); for the B2 compounds, Pd₂MnAl (−87.1 ± 3.0); Pd₂MnGa (−54.5 ± 1.7); Pd₂MnIn (−41.0 ± 2.5); Pd₂TiAl (−81.4 ± 1.9); for the tetragonal compound Pd₂CuAl (−55.2 ± 3.0) and for the orthorhombic compound Pd₂CuSn (−43.1 ± 2.3). Values were compared with those from published first principles calculation and the Open Quantum Materials Database (OQMD). Lattice parameters of these compounds were determined by X-ray diffraction analysis (XRD). Microstructures were identified using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Selected alloys were annealed at various temperatures to investigate phase transformations and phase relationships.     

Strengthening of AISI 2205 duplex stainless steel by strain ageing

In this study, static strain ageing behavior of commercially available and solution heat treated duplex stainless steel was investigated and the effect of static strain ageing on the mechanical properties was also determined in detail. Some of as-received duplex stainless steel test specimens were pre-strained in tension by 5% and then aged at 100 °C, 200 °C, 300 °C, 400 °C, 500 °C and 600 °C for 30 min in furnace. Some of duplex stainless steel test specimens were solution heat treated at 1050 °C for 30 min, water quenched and then pre-strained for 5% in tension shortly after the solution heat treatment.In order to identify the effect of static strain ageing on the mechanical properties, the tensile strength, the change in the strength due to ageing (ΔY), elongation fracture and hardness were determined. The test results showed that the mechanical properties were affected by static strain ageing mechanism which was applied at different temperatures for same time interval.     

A research on the creep properties of titanium matrix composites rolled with different deformation degrees

(TiB + La₂O₃)/Ti composites were in situ synthesized and deformed with different deformation degrees. The influence of TiB whisker orientation and grain refinement on the creep properties of titanium matrix composites (TMCs) are discussed. The creep test reveals that the steady state creep rate of TMCs first decreases and then increases with the increase of deformation degree, which can be attributed to competing effects: TiB whisker rotating to the rolling direction, α plate grain boundary hindering and pinning dislocations can all decrease the creep rate, however, dislocation movement on the α plate grain boundary and dislocation emitting from the α plate grain boundary can both increase the creep rate.     

In situ infrared reflection spectroscopy studies of the initial atmospheric corrosion of Zn–Al–Mg coated steel

NaCl induced atmospheric corrosion of ZnAl2Mg2 coated, electrogalvanised (EG) and hot dipped galvanised (HDG) steel was studied using in situ infrared reflection absorption spectroscopy, XRD and SEM. Initial corrosion leads to the formation of Mg/Al and Zn/Al layered double hydroxides (LDHs) on ZnAl2Mg2, due to the anodic dissolution of Zn–MgZn2 phases and cathodic oxygen reduction on Zn–Al–MgZn2, Al-phases and on zinc dendrites. In contrast to EG and HDG, were no ZnO and Zn₅(OH)₈Cl₂⋅H₂O detected. This is explained by the buffering effect of Mg and Al which inhibit the ZnO formation, reduce the cathodic reaction and corrosion rate on ZnAl2Mg2.     

The effect of Co doping on the magnetic entropy changes in Ni44−xCoxMn45Sn11 alloys

A series of Ni_44?xCo_xMn₄₅Sn₁₁ (x = 0, 1, and 2) ferromagnetic shape memory alloys (FSMAs) were prepared by arc melting method. The martensitic transition (MT) and Curie temperatures vary obviously with Co addition. With the increasing temperature, the magnetization increases from a weak-magnetic martensite to a ferromagnetic austenite, for x = 0 and 1. But in the case of x = 2, the magnetization increases from a ferromagnetic martensite to another ferromagnetic austenite. Under an applied magnetic field of 10 kOe, the peak values of magnetic entropy changes are 10.1, 14.1, and 6.2 J/(kg K), for x = 0, 1, and 2, respectively. The magnetic phase transition near the martensitic transition temperatures and the field-induced metamagnetism should account for the large magnetic entropy changes.     

Multistep impregnation method for incorporation of high amount of titania into SBA-15

A multistep impregnation method was employed to incorporate high amount of titania into the mesoporous SBA-15 silica. No damage to the SBA-15 silica mesostructures was caused by the loading of titania in every cycle. The existence of titania small nanodomains were confirmed to be present by Raman spectra and UV–vis DRS measurements. High dispersion of them was realized via this method according to the results of low-angle X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and N₂ sorption measurements. Importantly, no blockage of mesostructures was acknowledged with titania content up to 24.4 wt.%. In comparison, normally used one-step impregnation method led to serious blockage of mesopores as the results of formation of bulk titania particles in the mesochannels. Photo-activity test for the removal of oestrogen showed the superiority of the materials synthesized by multistep impregnation method to one-step impregnation method.     

Semiconductor/porous silica glass nanocomposites via the single-source precursor approach

The utilization of single-source molecular precursor approach to obtain II–VI and IV–VI semiconductors encapsulated in porous Vycor glass (PVG) is described. The procedure is based on the impregnation of cadmium and lead(II) diethyl-dithiocarbamate complexes, Cd(S₂CNEt₂)₂ and Pb(S₂CNEt₂)₂, inside the porous environment of PVG followed by a thermal treatment of the glass. The pyrolysis of the impregnated precursor gives rise to binary semiconductors CdS and PbS, respectively. The impregnation step is driven by interactions between the precursors and active sites located at glass pore surfaces. After completing the impregnation–decomposition cycle, it was found that the active glass sites were regenerated, making new cycles possible. The amount of encapsulated semiconductor increases linearly as a function of the number of cycles. Nanocomposites obtained after 1–10 cycles were prepared and characterized by optical spectroscopy, X-ray diffraction powder and transmission electron microscopy.     

Formation of lanthanum beryllate real structure under different crystallization conditions

The aim of this paper is to characterize the major structural defects of lanthanum beryllate single crystals grown by the Czochralski method, including those doped with rare-earth elements, and to reveal their relationship to specific properties of the crystal structure of La₂Be₂O₅ and with their crystallization conditions. As a basic method for research, we used transmission X-ray topography. It was established that the defect state of La₂Be₂O₅ crystals prepared by this method can be caused by different types of dislocations and their ordered assemblies, solid-phase inclusions of crucible metal and eutectically co-crystallizing phases, as well as by face growth sectors with elevated content of dopant. We show a possibility for growing single crystals of doped lanthanum beryllate having a minimum quantity of structural defects that could be suitable for manufacture of high quality laser rods.