Effects of different CdCl<Subscript>2</Subscript> annealing methods on the performance of CdS/CdTe polycrystalline thin film solar cells

In this paper, the effects of different CdCl₂ annealing methods, including vapor annealing and dip-coating annealing, on the performance of CdS/CdTe polycrystalline thin-film solar cells are studied. After annealing, the samples are lightly etched with 1% bromine in methanol to remove surface oxides. Both annealing methods give CdTe polycrystalline thin films with good crystallinity and complete structure. For solar cells containing the annealed CdTe films, cell efficiency first increases and then decreases as the concentration of CdCl₂ solution used for dip-coating annealing increases, and the optimized CdCl₂ concentration is 12%. The uniformity of the performance of all cells is analyzed by calculating the relative standard deviation for each parameter. The uniformity of cell performance can be improved dramatically by dip-coating annealing instead of vapor annealing. Most notably, an appropriate concentration of CdCl₂ (12%) acts as a protective layer that is conducive to realizing uniform high-performance CdS/CdTe solar cells. According to the location of depletion regions, the CdTe films treated by dip-coating annealing show a relatively low doping concentration, except for the sample treated with a CdCl₂ concentration of 6%, which is consistent with the changes of short-circuit current density of the cells. It is believed that these results can be applied to the large-scale production of CdTe polycrystalline thin-film solar cells.     

Code-to-code comparison study on rotor aeromechanics in descending flight

This paper conducts the aeromechanics study using the two different rotorcraft computational structural dynamics (CSD) codes, CAMRAD II and DYMORE II, for the rotor in low-speed descending flight. The three test cases of the HART (Higher-harmonic control aeroacoustic rotor test) I -baseline, minimum noise, and minimum vibration- are considered in this study of the blade-vortex interaction (BVI) airloads, rotor trim, blade elastic deformations, and blade structural loads. The two prediction results are compared to each other for a code-to-code comparison study as well as to the measured data. Although CAMRAD II and DYMORE II use different theories and models, most of the prediction results are similar to each other and compared fairly well with the wind tunnel test data. For all the three test cases, the two rotorcraft CSD analyses show good prediction on the fluctuations of the section normal force (M²C_n) due to BVI, but both over-predict the trimmed collective pitch angle. The blade elastic deformations, such as flap deflection and elastic torsion deformation at the tip, are reasonably predicted by both rotorcraft CSD analyses. But, the CAMRAD II result using the multiple-trailer wake model with consolidation is slightly better than the DYMORE II prediction with the single wake panel model particularly for the elastic torsion deformation in the baseline case. In addition, CAMRAD II and DYMORE II both correlate reasonably the blade structural loads, such as flap bending, lead-lag bending, and torsion moments, with the measured data; however, the CAMRAD II results are moderately better than the DYMORE II predictions.     

Interfacial reaction in ASZ/A384 Al composite and its influence on mechanical properties

In an ASZ/A384 Al composite, the interfacial reaction was observed to take place between the SiO₂ binder layer and Mg within the matrix to form MgAl₂O₄ at the interface. Formation of MgAl₂O₄ at the interface between ASZ short fibers and the Al matrix alloy is believed to enhance the interfacial bonding strength, resulting in improved composite strength. However, the interfacial reaction in the ASZ/A384 Al proceeds at the expense of Mg in the matrix, resulting in a composite devoid of Mg bearing precipitates such as Al₂CuMg and Mg₂Si.     

Thermochemistry, lattice energetics and stability of hexahalogenohafnates

The enthalpies of thermal dissociation (Δ_dH) and formation (Δ_fH) found in the literature as well as the crystal lattice energies (E_c) of inorganic and organic hexahalogenohafnates (M^I₂(or M^{II)HfX2−₆}; M^I and M^II denote monovalent and divalent cations respectively and X denotes a halogen) are reviewed and discussed. The enthalpies of formation of the salts were evaluated using the above-mentioned Δ_dH values and known enthalpies of formation of products of decomposition. Combination of the enthalpies of formation of hexahalogenohafnates thus obtained or those of the literature with the literature values of the enthalpy of formation of cations and theoretically determined enthalpies of formation of HfX²⁻₆ (or electrostatic lattice energies of the salts) afforded lattice energies of the salts (or enthalpies of formation of gaseous HfX²⁻₆). Values of Δ_fH were also assessed taking theoretically obtained electrostatic lattice energies of the salts and enthalpies of formation of HfX²⁻₆ and literature or theoretically determined values of the enthalpy of formation of gaseous cations. The independent sets of crystal lattice energies and thermochemical radii for HfX²⁻₆ were obtained following the Kapustinskii—Yatsimirskii approach. Combination of the latter method with the thermochemical cycle afforded information on the influence of the dimensions of ions on the thermodynamic stability of hexahalogenohafnates with respect to dissociation and oxidation processes. The thermochemical quantities of experimental and theoretical origin correlate with each other reasonably well, thus increasing their reliability.     

Effect of surface coating on the screw loosening of dental abutment screws

Regardless of the type of performed restoration, in most cases, a screw connection is employed between the abutment and implant. For this reason, implant screw loosening has remained a problem in restorative practices. The purpose of this study was to compare the surface of coated/plated screws with titanium and gold alloy screws and to evaluate the physical properties of coated/plated material after scratch tests via FE-SEM (field emission scanning electron microscopy) investigation. GoldTite, titanium screws provided by 3i (Implant Innovation, USA) and TorqTite, titanium screws by Steri-Oss (Nobel Biocare, USA) and gold screws and titanium screws by AVANA (Osstem Implant, Korea) were selected for this study. The surface, crest, and root of the abutment screws were observed by FE-SEM. A micro-diamond needle was also prepared for the scratch test. Each abutment screw was fixed, and a scratch on the surface of the head region was made at constant load and thereafter the fine trace was observed with FE-SEM. The surface of GoldTite was smoother than that of other screws and it also had abundant ductility and malleability compared with titanium and gold screws. The scratch tests also revealed that teflon particles were exfoliated easily in the screw coated with teflon. The titanium screw had rough surface and low ductility. The clinical use of gold-plated screws is recommended as a means of preventing screw loosening.     

A scanning tunneling microscopy tip with a stable atomic structure

A single stable adatom on a {110}-type plane of a tungsten tip is created via field-evaporation in a field-ion microscope (FIM) operating at room temperature. This single adatom has sufficient surface mobility at room temperature and migrates, in one-dimension, along a <111>-type direction toward an edge of a {110}-type plane, due to the existence of an electric field gradient. The plane edge has a higher local electric field than its center, since it has a higher local geometric curvature. This result implies that the stable position of a single adatom during a scan of a scanning tunneling microscope (STM) tip on a surface is at the edge and not at the center of a {110}-type plane at room temperature. Therefore, the electron wave function of a tip is not symmetric and this fact should be taken into account in a careful analysis of STM images. Also a tip with a dislocation emerging at a {110}-type plane is suggested as an improved STM tip configuration, as the step at the surface, created by the intersection of the dislocation with it, is a perpetual source of single adatoms.     

Reassessment of Ni-Al and Ni-Fe-Al solidus temperatures

Solidus temperatures of the B2 NiAl phase have been determined by high-temperature differential thermal analysis for binary melt compositions Ni_xAl_100−x (45<x<57) and for ternary alloys Fe_yNi_50−yAl₅₀ (0≤y≤50). It was shown that the melting temperature of the stoichiometric Ni₅₀Al₅₀ phase is 1681 °C, which is 43 K higher than some literature data. The solidus line at the Ni-rich side of the Ni-Al phase diagram exhibits a steeper slope than that reported previously. Substituting Fe for Ni, the decrease of solidus temperature along the isoplethal section with 50 at.% Al of the ternary Ni-Fe-Al phase diagram exhibits a steep initial slope of −13 K/at.% Fe for small Fe-fractions, which changes into a nearly linear decrease with an average slope of −8.5 K/at.% Fe.     

Poly(N-methylaniline) coatings on stainless steel by electropolymerization

Poly(N-methylaniline) (PNMA) coatings have been electropolymerized on 304 stainless steel alloy by potentiodynamic, galvanostatic and potentiostatic synthesis techniques from aqueous solutions of 0.1 M N-methylaniline (NMA) and 0.3 M oxalic acid. Characterization of PNMA coatings was carried out by cyclic voltammetry, UV-Vis and FTIR spectroscopy techniques. Corrosion behavior of PNMA coated stainless steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test, chronoamperometry and electrochemical impedance spectroscopy (EIS) techniques in 0.5 M aqueous HCl solutions. Corrosion test results showed that PNMA coatings possessed protection to uncoated stainless steel against corrosion.     

SiCp/AlMMCs填充含Sc、Ce、Be的TiB2原位增强焊丝与4047焊丝的TIG焊研究

使用自制的含Sc、Ce、Be的TiB₂原位增强与4047焊丝为填充材料对T6态SiCp/AlMMCs 进行TIG焊,对接头的力学性能、显微组织以及断口形貌和第二相粒子进行分析。结果表明：两种焊丝焊接该种材料的焊缝成型优良,4047焊丝成型更加美观；TiB₂接头的抗拉强度明显优于ER4047接头,平均强度达到171.88MPa,相对于4047接头强度提高40.03%,TiB₂粒子起到了原位增强的作用；两种接头的硬度值在焊缝中心近似呈对称分布,焊缝区硬度最低,平均值分别为：71.65HV、60.02HV,热影响区硬度的“过时效”现象明显；焊缝中SiC颗粒较少,存在严重贫瘠区 ,未发现明显的Al₄C₃脆性物；显微组织都为枝晶组织,但4047接头焊缝枝晶粗大,TiB₂接头焊缝晶粒细小,稀土元素Sc、Ce、Be起到了细化晶粒的作用,且TiB₂粒子在焊缝中分布均匀；TiB2接头断口中气孔较少,为韧-脆性混合性断裂,韧窝中第二相粒子较多；4047接头断口中气孔较多,为韧性断裂,韧窝中第二相粒子较少。     

Dynamic Young’s modulus and internal friction in polycrystalline copper

An attempt has been made to measure the temperature dependence of dynamic Young’s modulus together with the related variation of internal friction in polycrystalline copper. A mechanical spectroscopy study was employed using a standard servo hydraulic fatigue testing machine equipped with a scanning laser extensometer. Dynamic Young’s modulus and internal friction were measured over a temperature range of 298 to 873 K at very low frequencies of 0.1, 0.05, and 0.01 Hz. One internal friction peak was observed over the ranges 450 to 700 K, together with marked decreases in the dynamic Young’s modulus in the same temperature range. From a quantitative analysis of the experimental data with the relaxation strength, relaxation time, and activation energy, it is concluded that the peak phenomenon is due to grain-boundary sliding relaxation.