[en] The capacity of passive metal to repassivate after film damage determines the development of local corrosion and the resistance to corrosion failures. In this work, the repassivation kinetics of 316L stainless steel (316L SS) was investigated in borate buffer solution (pH 9.1) using a novel abrading electrode technique. The repassivation kinetics was analyzed in terms of the current density flowing from freshly bare 316L SS surface as measured by a potentiostatic method. During the early phase of decay (t < 2 s), according to the Avrami kinetics-based film growth model, the transient current was separated into anodic dissolution (i_d_i_s_s) and film formation (i_f_i_l_m) components and analyzed individually. The film reformation rate and thickness were compared according to applied potential. Anodic dissolution initially dominated the repassivation for a short time, and the amount of dissolution increased with increasing applied potential in the passive region. Film growth at higher potentials occurred more rapidly compared to at lower potentials. Increasing the applied potential from 0 V_S_C_E to 0.8 V_S_C_E resulted in a thicker passive film (0.12 to 0.52 nm). If the oxide monolayer covered the entire bare surface (θ=1), the electric field strength through the thin passive film reached 1.6 x 10"7 V/cm

[en] Nanocrystalline NdFeB magnets were prepared by spark plasma sintering (SPS) and SPS followed by HD using melt spun ribbons as the starting materials. The microstructure of SPSed and HDed magnets were analyzed. The effects of process including temperature and compression ratio on the microstructure and properties were investigated. High magnetic properties were obtained in anisotropic HDed magnets. The combination of Zn and Dy additions was successfully employed to improve the coercivity and thermal stability of the SPSed magnets. Open recoil loops were found in these magnets with Nd-rich composition and without soft magnetic phase for the first time. The relationship between the recoil loops and microstructure for SPS and HD NdFeB magnets were investigated. The investigations showed that the magnetic properties of SPS+HDed magnets are related to the extent of the aggregation of Nd-rich phase, which was formed during HD due to existence of porosity in SPSed precursor. Large local demagnetization fields induced by the Nd-rich phase aggregation leads to the open loops and significantly reduced the coercivity. By reducing the recoil loop openness, the magnetic properties of HDed NdFeB magnets were successfully improved. (author)

[en] The purpose of the research was to determine the effect of nano-hydroxyapatite concentrations on initial enamel lesions under dynamic pH-cycling conditions. Initial enamel lesions were prepared in bovine enamel with an acidic buffer. NaF (positive control), deionized water (negative control) and four different concentrations of nano-hydroxyapatite (1%, 5%, 10% and 15% wt%) were selected as the treatment agents. Surface microhardness (SMH) measurements were performed before/after demineralization and after 3, 6, 9 and 12 days of application, and the percentage surface microhardness recovery (%SMHR) was calculated. The specimens were then examined by a scanning electron microscope. The %SMHR in nano-hydroxyapatite groups was significantly greater than that of negative control. When the concentration of nano-HA was under 10%, SMH and %SMHR increased with increasing nano-hydroxyapatite concentrations. There were no significant differences between the 10% and 15% groups at different time periods in the pH-cycling. The SEM analysis showed that nano-hydroxyapatite particles were regularly deposited on the cellular structure of the demineralized enamel surface, which appeared to form new surface layers. It was concluded that nano-hydroxyapatite had the potential to remineralize initial enamel lesions. A concentration of 10% nano-hydroxyapatite may be optimal for remineralization of early enamel caries.

[en] The Cu–In binary system is receiving increasing attention due to its application in the low-temperature assembly of heat-sensitive devices. Nevertheless, the fundamental behaviors of this binary system are very difficult to study because of the extreme softness of indium. This difficulty was successfully overcome in this study, and the phase stabilities and chemical reactions were established. Binary Cu–In diffusion couples were prepared by electroplating In onto a Cu substrate. During the plating process, CuIn₂ formed even though this intermetallic is not present in the Cu–In binary phase diagram. It was established in this study that CuIn₂ is indeed a stable phase below 100 °C, but decomposes at a temperature between 100 and 120 °C. In addition, the microstructure evolution during solid-state aging at 100, 120, and 140 °C was investigated. The hardness values and Young’s moduli for CuIn₂ and Cu₁₁In₉ were measured by using nanoindentation.

[en] A method for solving a class of normal frictionless indentation problems in a multilayered piezoelectric half-space is proposed. The half-space is deformed by a rigid axisymmetric indenter that includes flat-ended cylinder, cone and sphere shapes. Three different interfacial models, i.e. perfectly bonded, frictionless contact and spring-like models, are investigated. Both insulating and conducting indenters are considered. The complete solution in the half-space is obtained by integrating the elastic and electric displacements due to a point load and a point charge with unknown distribution functions over the contact area. These distribution functions are to be determined by using the boundary conditions of the contact problems. The numerical results of the indentation responses of a piezoelectric thin film in contact with a piezoelectric half-space are given as an example of the proposed method. (paper)

[en] The purpose of this research was to investigate the wear behavior of early carious enamel remineralized with gallic acid. Forty natural human premolar specimens with early caries lesions were prepared. A remineralization pH-cycling treatment agent of 4000 ppm gallic acid was used for 12 days to treat the early lesions. The changes in microhardness were monitored. Nanoscratch tests were used to evaluate wear resistance. The experimental data were analyzed by using a t-test. The widths of traces were measured by an AMBIOS XP-2 stylus profilometer. After remineralization, all samples re-hardened significantly. The coefficients of friction became higher, and the widths of scratches were larger than they were before remineralization. Gallic acid significantly improved the early carious enamel's hardness. The wear damage of the samples treated with gallic acid was more severe than that of the control group. There were more obvious cracks and delaminations on the traces of the treated group. Compared with the control group, the enamel remineralized with gallic acid had inferior wear resistance. After remineralization, the dominant damage mechanisms of early carious enamel had changed from plastic deformation and adhesive wear to a combination of brittle cracks and delamination of enamel.

[en] (La,Ce)–Al–Cu alloys with different La/Ce ratios were employed as the diffusion sources for grain boundary diffusion of sintered NdFeB magnets. The coercivity changed from 990 kA m⁻¹ to 984, 1021 and 1031 kA m⁻¹ after diffusion by (La_xCe_1−x)–Al–Cu alloys with La/Ce ratio (x) of 0, 0.5 and 1, respectively. Varied magnetic properties resulted from different effects of La and Ce on the microstructure, in particular the formation and amount of the REFe₂ phase. REFe₂ phase formed after diffusion deteriorated the magnetic properties but improved the wettability between grain boundary and main phase. After (La,Ce)–Al–Cu alloys diffusion, the corrosion resistance was reduced but the mechanical properties were improved. The underlying mechanisms have been discussed in this paper. (paper)

[en] Nanocrystalline NdFeB magnets were prepared by spark plasma sintering (SPS) and SPS followed by HD using melt spun ribbons as the starting materials. The microstructure of SPSed and HDed magnets were analyzed. The effects of process including temperature and compression ratio on the microstructure and properties were investigated. High magnetic properties were obtained in anisotropic HDed magnets. The combination of Zn and Dy additions was successfully employed to improve the coercivity and thermal stability of the SPSed magnets. Open recoil loops were found in these magnets with Nd-rich composition and without soft magnetic phase for the first time. The relationship between the recoil loops and microstructure for SPS and HD NdFeB magnets were investigated. The investigations showed that the magnetic properties of SPS+HDed magnets are related to the extent of the aggregation of Nd-rich phase, which was formed during HD due to existence of porosity in SPSed precursor. Large local demagnetization fields induced by the Nd-rich phase aggregation leads to the open loops and significantly reduced the coercivity. By reducing the recoil loop openness, the magnetic properties of HDed NdFeB magnets were successfully improved

[en] Completely inverted hysteresis loops (IHL) are obtained by the superconducting quantum interference device with large cooling fields (>10 kOe) in (La,Sr)MnO₃ films with self-assembled LaSrMnO₄, an antiferromagnetic interface. Although the behaviours of measured loops show many features characteristic to the IHL, its origin, however, is not due to the exchange coupling between (La,Sr)MnO₃/LaSrMnO₄, an often accepted view on IHL. Instead, we demonstrate that the negative remanence arises from the hysteresis of superconducting coils, which drops abruptly when lower cooling fields are utilized. Hence the completely inverted hysteresis loops are experimental artifacts rather than previously proposed inhomogeneity effects in complicated materials

[en] Partially inverse spinel CoFe₂O₄, which may be prepared through various heat treatments, differs remarkably from the ideal inverse spinel in many properties. The structure of partially inverse spinel CoFe₂O₄ as well as its electronic and magnetic properties through a systemic theoretical calculation of (Co_1-xFe_x)_Tet(Co_xFe_2-x)_OctO₄ (x = 0, 0.25, 0.5, 0.75 and 1.0) have been investigated by the generalized gradient approximation (GGA) + U approach. It is found that the Co and Fe ions prefer their high spin configurations with higher spin moments at octahedral sites in all the studied cases, in line with experimental observations. The Co ions at the octahedral sites favour being far away from each other in the partial inverse spinels, which also show half metallicity at certain inversion degrees.