Properties of Coatings: Comparisons of Electroplated, Physical Vapor Deposited, Chemical Vapor Deposited, and Plasma Sprayed Coatings

Properties of coatings (structure, porosity, density, stress, corrosion, hydrogen permeation, adhesion, tribology, fatigue and thermal contact conductance) produced by a number of deposition methods including electrodeposition, physical vapor deposition, chemical vapor deposition, and flame spraying art; compared. In most cases, the films did not exhibit similar properties. In addition, process conditions often could be varied for any given coating process and this, in turn, would affect microstructure and hence the properties. No coating system provided best results for all these properties. In some cases, electroplated films provided superior results while in others PVD or CVD were best.     

Stress changes in electrochromic thin film electrodes:: Laser beam deflection method (LBDM) as a tool for the analysis of intercalation processes

The mechanical effects of the intercalation processes in electrochromic WO₃ thin films are reported here and discussed. In particular the electrochemical insertion of H, Li and Na ions in WO₃ was studied by means of laser beam deflection method (LBDM). Linear changes of WO₃ stress were observed for small amounts of the inserted charge and linearity was always associated with a reversible mechanical behavior of thin films. An explanation in terms of homogeneity of the insertion is given. An analogous trend was also verified in the absorbance vs. charge curves. As a consequence the constancy of the electrochromic efficiency values for the three different ions was found. In this way it was possible to determine a full reversible behavior for M_xWO₃ in the composition range 0x0.2. The onset of new phases formation when x exceeded previous upper limit, was observed during Li and Na intercalation. Such transitions brought about the loss of optical and mechanical reversibility. During prolonged hydrogen insertion a reversible slope inversion occurred in stress curve so that it was necessary to take into account different possible mechanisms of the WO₃ electrochromic reaction.     

Synthesis,spectral characterization,properties and structure of dinuclear rhenium complex containing bis[4-(2-pyridylmethyleneamino)phenyl]methane ligand

The synthesis, characterization, properties and crystal structure of {(bis[4-(2-pyridylmethyleneamino)phenyl]methane)[Re(CO)₃Br]₂} complex are reported. The ¹H NMR data for this complex shows downfield shift of the bis-diimine ligand protons upon coordination to the Re center. The molecular structure of the dinuclear rhenium(I) complex exhibits distorted octahedral geometries around the each metal center with one Br and facial arrangement of three CO and a cis-bonded diimine ligands. The bis-diimine ligand, twists via a half-turn around the metal–metal axis. Electrochemical investigation reveals two oxidation waves and two irreversible reduction waves.     

The in-vitro digestibility and chemical composition of plant parts in white clover,red clover and lucerne during primary growth

White clover (cv. Grasslands Huia), red clover (cv. Norseman) and lucerne (cv. Sabilt) were sampled during primary growth at the flower bud, near full flowering and seeds formed stages in each of 2 years. Each sample was separated into 2–11 plant parts, depending on species and stage of growth, and for each part the in-vitro true dry matter digestibility, digestibility of cell wall and percentages of cell content, nitrogen, water-soluble carbohydrate and lignin were determined. Green leaflets of all three species were consistently high in digestibility. The cell wall fraction of green leaflets was less digestible in red clover than in white clover and lucerne. The digestibility of the upper part of the stem of lucerne and red clover was high at the flower bud stage but declined considerably thereafter, whereas the digestibility of the lower part of the stem was much lower at the flower bud stage and declined relatively little. The green leaf stalks and inflorescences were generally rather less digestible than green leaflets and, in lucerne and red clover, more digestible than stems. In white clover the inflorescence stalks were less digestible than the leaf stalks. The digestibility of plant parts was strongly correlated with the proportion of cell content, and less strongly with the digestibility of cell wall. The proportion of cell content was positively correlated with N%, and the digestibility of cell wall was negatively correlated with the proportion of lignin in cell wall.     

Estimating regions of asymptotic stability with sliding for relay-control systems

The object of this article is the estimation of stability boundaries and regions of asymptotic stability with sliding for a class of single-input relay-control systems. The direct method of Lyapunov is used to obtain these estimates. A coordinate transformation that brings the system into a special canonical form is utilized to facilitate the stability analysis. The proposed approach to stability regions estimation is applied to a class of second-order systems, and analytical expressions for stability regions are derived.Recommended by K. Mizukami     

Characterization of High-Fracture Toughness K-Fluorrichterite-Fluorapatite Glass Ceramics

Stoichiometric K-fluorrichterite (Glass A) and the same composition with 2 mol% P₂O₅ added (Glass B) were prepared and then heat-treated isothermally from 550°–1000°C with 50°C intervals. Samples were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The biaxial flexural strength and indentation fracture toughness of heat-treated glass specimens were also determined for both materials. XRD traces and TEM images showed similar phase evolution and fine microstructures for both systems at ≤950°C, with mica and diopside reacting with residual glass to form K-fluorrichterite as the temperature was increased from 650°C. However, in Glass B, fluorapatite was also present at >800°C. In contrast, coarser microstructures were observed at 1000°C, with larger K-fluorrichterite (20 μm) and enstatite (10 μm) crystals in Glasses A and B, respectively. The highest fracture toughness (2.69 ± 0.01 MPa·m^1/2) and biaxial strength (242.6 ± 3.6 MPa) were recorded for Glass B heat-treated at 1000°C. This was attributed to the presence of enstatite coupled with an interlocked lath-like crystalline microstructure.     

Determination of seasonal and interannual variation in New Zealand pasture growth from NOAA-7 data

The normalized vegetation index (NVI) has been calculated from afternoon overpasses of NOAA-7 for two important farming regions of New Zealand, approximately 1000 k² in area, for the period from October 1981 through June 1984. The uniform nature of the terrain and farming practices in these areas make them ideal targets for remote sensing from satellites with limited spatial resolution. The frequency of useful data coverage has been increased by sampling within cloud-free parts of a partly cloudy target area and also by deriving an empirical correction for off-nadir view angles. Daily area-mean rainfall and soil moisture were estimated for both regions and monthly area-mean pasture growth for one of them. The NVI was found to reflect the varying rainfall and soil moisture on time scales of one week or more during the growing season and between years. A correlation of 0.81 was found between NVI and pasture growth on a monthly mean basis. These results suggest that operational satellite monitoring of these and other areas would provide valuable assistance in agricultural management and forward planning.     

Effect of CaF2 and CaO Substituted for MgO on the Phase Evolution and Mechanical Properties of K-Fluorrichterite Glass Ceramics

Chain silicate glass ceramics based on K-fluorrichterite (KNaCaMg₅Si₈O₂₂F₂, KFR) have potential for use in restorative dentistry and biomedical applications because they may be cast to shape and, when cerammed, have high biaxial flexural strength and fracture toughness. Excess CaO in canasite-based chain silicate compositions is known to enhance their bioactivity. Therefore, two new glass ceramic compositions have been fabricated with 5 mol% CaF₂ (Glass A) and 5 mol% CaO (Glass B) substituted for MgO in the KFR formula unit. The phase evolution of Glasses A and B was studied in detail using X-ray diffraction and transmission electron microscopy. In addition, their mechanical properties were assessed. For Glass A, the fracture toughness (FT=2.66±0.02 MPa·m^1/2) and biaxial flexural strength (BFS=227.3±24.5 MPa) were optimized for samples heat treated at 900°C for 4 h. In Glass B, however, the best FT (2.08±0.02 MPa·m^1/2) and BFS (217.4±4.4 MPa) were obtained at 950°C. In view of their excellent mechanical properties and castability, Glasses A and B are considered potential candidates for fabrication of custom medical devices in restorative dentistry and moderate load-bearing reconstructive bone surgery.     

An Innovative Approach to the Automated Stacking and Grasping of Leather Plies

In this paper, a complete study of automatizing the manipulation process of tanned natural leather plies is presented. The considered leather plies are partially refined and their surface is suitable for grasping by suction grippers. The particular features (non-rigid structure, irregular shape and size, etc.) of such a material make the handling and loading on the workstations very critical and difficult to be approached. To increase the reliability of grasping, the development of customized vacuum cups seems to be advisable. In the paper, an innovative vacuum cup model is proposed. Its performances are quantitatively compared with a other models by means of appropriate measuring methods. Another problem concerning the automatic manipulation of leather plies is to avoid the grasping of more than one ply at a time, due to the irregularity of the ply profile. A device able to solve this problem, using an innovative equipment for moving the entire stack from the store to the workstation and for separating the plies, is also shown and discussed.     

Temperature-dependent nonlinearities in GaN/AlGaN HEMTs

Temperature-dependent nonlinearities of GaN/AlGaN HEMTs are reported. The large-signal device model of the transistor is obtained by using a physics-based analysis. The model parameters are obtained as functions of bias voltages and temperature. The analysis of the device has been carried out using a time-domain technique. f_max for a 0.23 μm×100 μm Al_0.13Ga_0.87N/GaN FET is calculated as 69 GHz at 300 K, while at 500 K, f_max decreases to 30 GHz, which are in agreement with the experimental data within 7% error. f_max as obtained from calculated unilateral gain, decreases monotonically with increasing temperature. For shorter gate lengths irrespective of the operating temperature f_max is less sensitive to bias voltage scaling. For longer gate length devices, f_max becomes less sensitive to the bias voltage scaling at elevated temperatures. 1-dB compression point (P_1-dB ) at 4 GHz for a 1 μm×500 μm Al_0.15Ga_0.85N/GaN FET is 13 dBm at 300 K. At 500 K, P_1-dB decreases to 2.5 dBm for the same operating frequency. Similar results for output referred third intercept point (OIP3) are reported for different gate length devices