Fethi Dagdelen

Effects of thermal treatments on transformation behaviour in shape memory Cu–Al–Ni alloys

Abstract The martensitic transformation behaviour, morphology and transition temperatures in copper-based shape memory alloys are strongly influenced by heat treatments. The effects of various quenching, up-quenching and step-quenching in a water bath 100 °C and in an oil bath at 200 °C have been studied on two shape memory Cu–Al–Ni alloys. The changes at entropy and enthalpy at the martensitic transition have been determined by means of differential scanning calorimeter (DSC) measurements. It was observed that quenching has a marked influence on the transformation temperatures.

Electrical and optical properties of semiconducting metal complexes

Abstract The electrical conductivity, crystal structure, thermoelectric power, thermal conductivity and optical properties of newly synthesized Cu(II), Ni(II) and Co(II) complexes have been investigated. The crystal structure of the complexes was carried out by powder X-ray diffraction (XRD). XRD show that samples are polycrystalline. The conduction mechanism was determined by activation energy process. The electronic parameters of the complexes were calculated, such as, activation energy E for dc conductivity and the density of localized states at the Fermi level N ( E F ). The electrical conductivity measurements exhibit three-dimensional variable hopping conduction. The mechanism of the optical absorption follows the rule of direct transition. As a result, it is interpreted that the samples show semiconducting behavior as their conductivity increases with increasing temperature and they have direct optical band gap.

SYNTHESIS, CHARACTERIZATION, AND ELECTRICAL PROPERTIES OF METAL COMPLEXES OF 2-PYRIDINECARBALDEHYDE THIOSEMICARBAZONE

ABSTRACT The synthesis, characterization, physico-chemical and electrical properties of complexes of pyridine-2-carbaldehyde thiosemicarbazone (PTSC) with transition element cations are reported. The complexes [Fe(PTSC)2Cl2]Cl and [Ni(PTSC)2-(H2O)2]Cl2 were prepared. Molecular structures of these complexes were identified by using elemental analyses, FT-IR, UV-VIS, thermogravimetric and molar conductivity techniques. The structure, along with other physico-chemical studies, established that the complexes of PTSC were low-spin. The spectroscopic study of the compounds showed that the transition metal complexes had octahedral geometry. A spectrophotometric determination of nickel(II) with pyridine-2-carbaldehde thiosemicarbazone in methyl alcohol solution is proposed and the stability constants of the nickel(II) complex were determined by the Job method. The electrical conductivity of the compounds increases with elevated temperature. Their conductivities follows the order Ni>Fe. The calculated values of the activation energy of mobility, Eμ, suggests that conduction in the studied complexes takes place by a hopping mechanism, where one electron hops from one molecule to another.

The change of transformation temperature on NiTi shape memory alloy by pressure and thermal ageing

We have investigated the effect of pressure and thermal ageing on transformation behavior of Ni-%45.16Ti shape memory alloy. 70-320 MPa pressure was applied and annealed at 500 °C for 2 hour to see the effect of applied pressure on transformation temperature. It was observed that the starting and final temperature of austenit increased, the martensite start temperature almost remain constant and final temperature decreased with the increase of pressure. The interval stress value of NiTi alloy was determined as 13.77 MPa/°C during austenite transformation. The transformation temperature of Ni-%45.16Ti alloys after thermal ageing was also investigated. No significant variation in these parameters was obtained. According to XRD measurements, there are two phases namely R (rhombohedral) and B19 (monoclinic) martensite were obtained. We did not see any change on the peaks after ageing.

The effects of thermal procedure on transformation temperature, crystal structure and microstructure of Cu-Al-Co shape memory alloy

The purpose of this study is to investigate the effects of different thermal procedures of the Cu-Al-Co shape memory alloy on its crystal structure, transformation temperature and microstructure. The alloys were subjected to a heat treatment and then cooling was applied at four different conditions. After the thermal process, XRD, DSC, optical microscopy and micro-hardness measurements were carried out. The experimental studies showed that crystal structure, microstructure and transformation temperature of Cu-Al-Co alloy were changed from the cooling conditions.

X-ray diffraction study and electrical properties of the metal complex Fe(II) including sodium oxalate ligand (Na2C2O4)

Abstract The crystal structure, microstructure and electrical properties of the Fe(II) complex including sodium oxalate ligand (Na 2 C 2 O 4 ) have been investigated. X-ray diffraction data shows that the sample is triclinic with the cell parameters a =4.8283 A, b =3.9195 A, c =12.7633 A, β =97.818° and cell volume V =239.30 A 3 . The dc conductivities have been measured as a function of temperature. It is seen that this sample has inorganic semiconductor property.