Papers by Keyword: Defect Structure

Abstract: Corrosion leakage became serious due to cyclic sewage injection and continuous increase in water injection pressure. Corrosion behavior for N80 casing was studied during long-term service, using corrosion reaction kettle and weight loss method. The morphology and composition were characterized with laser confocal microscopy (LCM), scan electron microscopy (SEM) and energy disperse spectroscopy (EDS). These results showed that corrosion rate remained constantly at initial stage, and increased gradually, then sharply reached to 0.327mm/a at later stage, accompanying with inflection point under oxygen condition. Meanwhile, corrosion rate decreased significantly from 0.028mm/a to 0.020mm/a under oxygen-free condition. The corrosion of N80 steel was dominated by dissolved oxygen, and accelerated by chloridion. The micro-mechanism was suggested to be the transition of defect structure from crack with micron range to etch pit with millimeter range.

Abstract: The composition of (1-x) (Ba_0.85Sr_0.15)TiO₃ – x (K_0.5Na_0.5)NbO₃ (BST-KNN) for x=0.1 and x=0.2 were successfully prepared by two separate synthesis namely oxalate co-precipitation (for BST) and solid-state reaction (for KNN). Sintered pellet at 1200 °C for 2h exhibits a single phase except x= 0.2 showing a secondary phase and was identified as Ba₂TiO₄. KNN doped BST system show tetragonal symmetry in which higher dopant expand its tetragonality (c/a). The density of sintered samples deduced by Archimedes method are slightly higher than 90%. Permittivity measurements as function of temperature show almost similar Tc= 90 °C at frequency 1.273 kHz and shift to higher temperature as frequency increases indicating a typical relaxor characteristics. At room temperature the relative permittivity showing Debye relaxation characteristic with ωr=12560 (x=0.1) and ωr =20096 (x-0.2). Furthermore, as function of temperature the activation energy deduced from relaxation time was obtained Ea=0,564 eV for x=0.1 and 0,58 eV for x=0.2.

Abstract: The paper is focused on the effect of homogenous and inhomogeneous magnetic fields on crystallization, and some physical and chemical properties of silver azide (morphology, electric resistance, defect structure, reactivity) as well. The authors put forward an efficient procedure for growing crystals with specified sizes, reactivity and minimized impurities.

Abstract: The effect of different plastic deformation methods on the phase composition, lattice defect structure and hardness in 316L stainless steel was studied. The initial coarse-grained γ-austenite was deformed by cold rolling (CR) or high-pressure torsion (HPT). It was found that the two methods yielded very different phase compositions and microstructures. Martensitic phase transformation was not observed during CR with a thickness reduction of 20%. In γ-austenite phase in addition to the high dislocation density (~10 × 10¹⁴ m^-2) a significant amount of twin-faults was detected due to the low stacking fault energy. On the other hand, γ-austenite was gradually transformed into ε and α’-martensites with transformation sequences γ→ε→α’ during HPT deformation. A large dislocation density (~133 × 10¹⁴ m^-2) was detected in the main phase (α’-martensite) at the periphery of the disk after 10 turns of HPT. The high defect density is accompanied by a very small grain size of ~45 nm in the HPT-processed sample, resulting in an very large hardness of 6130 MPa.

Abstract: Solid-phase chemical reaction speed control is one of the most essential problems of physics and chemistry of solid bodies. Special attention is paid to the studies of sensitivity and stability of explosive substances (ES). Fundamental issues of studies of azides of heavy metals (AHM) are connected with developing ways of controlling new chemical reactions – solid-phase chain reactions in which electron excitations of a crystal lattice serve as active particles. Applied value is determined by safety issues of ES that include such wide range of problems as storage, transfer, destruction, etc.The result of this work is the use of the experimental results for purposeful change of energetic material

Abstract: The effect of ultrasonic treatment (UST) on the defect structure of the Si–SiO₂ system is characterised by means of electron spin resonance (ESR), metallography, MOS capacitance measurements and secondary ion mass spectroscopy (SIMS). A non-monotonous dependence of the defect densities on the ultrasonic wave intensity has been observed. The influence of the UST frequency on the ESR signal intensity of the defect centres depended on the defect’s type and structure and may be caused by vibrational energy dissipation which is a function of the defect centre’s type. The influence of the UST on the Si–SiO₂ interface properties depends on the oxide thickness and crystallographic orientation. The density of point defects and absorbed impurities at the Si–SiO₂ interface can be reduced and its electrical parameters improved by an appropriate choice of UST and oxidation conditions.

Abstract: The paper addresses experimental data that describe a constant noncontact electric field influence on physicotechnical specifications of materials, grown in an electric field, and conditioned in it. Experiments have shown that it is possible to control physical and technical specifications of materials changing intensity of a noncontact electric field during crystallization. It is observed that an electric field influences size, optical purity and conductivity of crystals grown in a field. Crystallization of inorganic salts in an electric field allows obtaining chemically pure crystals with minimum defects. A mechanism of an electric field influence on inorganic salts crystallization is provided.

Abstract: Our message is oxidation process must be minimized as possible. Many carbon-related defect structures are reported in SiC/SiO2 interface. In this paper, we investigated the effect of oxidation to the defect forming by density functional theory (DFT). In the result, we found carbon defect structure that completely different from in the present report. This defect structure has carbon-carbon single bond with no dangling bond. To see the forming process, compressive strain from inserted oxygen atoms induce the rearrangement of structure and cause C-C defect structure. We can know that this structure is formed with energy gain about 3.8eV. And this C-C defect induces trap state under the conduction bottoms.

Abstract: Ferromagnetic shape memory alloys can produce large strains in a magnetic field by twin boundary motion. The mobility of parent-martensite inter-phase interfaces and twin-twin inter-variant boundaries is closely related to their interfacial structures and the mechanism of migration, therefore a thorough understanding of its nature is of importance. A physical model of the structure of parent-martensite interface has been developed recently based on dislocation theories and topological arguments. On the basis of the topological model, the present work performs a theoretical study of the defect structure of the martensitic interface, and the transformation crystallography in Ni₂MnGa alloy. The habit plane, i.e., the parent-martensite interface plane was determined to be (-0.761, -0.054, -0.646)_P for the parent crystal index frame, and (-0.818, 0.067, -0.571)_M for the martensite frame. The habit plane inclination angle is 5.945° and 5.953° with respect to the terrace plane in the parent and martensite crystals, respectively.

Abstract: The local distortion of the impurity Ni+ center in magnesium oxide is theoretically studied by analyzing its electron paramagnetic resonance g factor from the formula of a 3d9 ion under octahedra with tetragonal elongation deformation. The defect center is suggested to exhibit the relative elongation along the four-fold axis by about 0.05 Å of the Jahn-Teller nature. The observed isotropic g factor ( 2.2391) is attributable to the dynamical average of the anisotropic g values under tetragonal elongation due to the dynamical Jahn-Teller effect.