Oxidation Behavior and Flexural Strength of Aluminum Nitride Exposed to Air at Elevated Temperatures

The oxidation behavior of a sintered aluminum nitride containing 3 wt% Y₂O₃ as a sintering aid was investigated. Samples were exposed to air at elevated temperatures for times up to 100 h. The weights of the samples were continuously monitored during exposure at various temperatures and humidity levels. The effects of oxidation on room-temperature flexural strength were also determined, and correlated to the observed weight changes of the samples. At temperatures 1200°C, linear weight gains were observed. However, at temperatures above 1200°C, the weight gains became parabolic with respect to exposure time. The oxidation rates were significantly increased by water vapor in the air. The oxidation products were found by X-ray analysis to be a mixture of Al₂O₃ and 5A1₂O₃·3Y₂O₃. The oxide layer formed on the surface was severely cracked because of the thermal expansion mismatch between the oxide layer and the substrate. The cracks initiated in the oxide layer and propagated into the substrate, resulting in severe reduction in the room-temperature flexural strength of the material. When exposed to ambient air for more than 50 h at temperatures greater than 1100°C, the strengths of the samples decreased to less than half that of the as-received material.     

Interfacial adhesion reaction of polyethylene and starch blends using maleated polyethylene reactive compatibilizer

The interfacial reaction of the polyethylene (PE)/starch blend system containing the reactive compatibilizer maleated polyethylene (m‐PE) was directly characterized by Fourier transform infrared (FTIR) spectroscopy. A significant amount of anhydride groups on m‐PE existed as hydrolyzed forms, resulting in a large amount of carboxyl groups. Using a vacuum‐heating‐cell designed in the laboratory, the carboxyl groups were successfully transformed into the dehydrolyzed state (i.e., anhydride group). This result enabled the direct spectroscopic observation of chemical reaction occurring at the interface. For the PE/starch blend system containing m‐PE, the chemical reaction at the interface was verified by the evolution of ester and carboxyl groups in the FTIR spectra. The effect of the reactive compatibilizer on the interfacial morphology was also examined by scanning electron micrography (SEM). Enhanced interfacial adhesion was clearly observed for the blend system containing reactive compatibilizer. Tensile strengths of blend systems containing m‐PE also increased noticeably compared with the corresponding system without compatibilizer. A similar observation was made for the breaking elongation data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 767–776, 2002     

Theoretical assessment of the catalytic (Pt/TiO2) oxidation of formaldehyde at ambient temperature

A recent article [C. Zhang, H. He, K. Tanaka, Catal. Commun. 6 (2005) 211] investigates the use of a Pt/TiO₂ catalyst for the oxidation of formaldehyde. The findings demonstrate nearly complete oxidation at ambient temperature (25 °C) for values of the surface velocity in the range 5–10 × 10⁴ h⁻¹ and a 45% destruction when using a surface velocity of 20 × 10⁴ h⁻¹.In the present communication, this oxidation was assessed by theoretical considerations of the reaction kinetics. The destruction efficiency was predicted using a first-order reaction rate expression, combined with different theoretical or semi-empirical equations for the intrinsic reaction rate constant. Predicted and experimental data are in fair agreement, thus validating the theoretical approach and confirming the experimental results.     

Preparation of porous thin films of a partially aliphatic polyimide

A thermally labile polymer, poly(propylene glycol), was modified to obtain PPG having an amino end group. PPG was incorporated into a partially aliphatic polyimide based on an alicyclic dianhydride, and this afforded triblock copolymers containing various amounts of PPG blocks. The thermal properties of the copolymers were investigated by thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the PPG block in the copolymers was carried out at 240°C under various pressures to obtain porous polyimide films. The pores remained during the thermolysis under a reduced pressure of 710 mmHg, whereas they collapsed under (near) atmospheric pressure. The pore size increased as the amount of the PPG block in the copolymers increased. The dielectric constants of the porous polyimides varied from 2.60 to 2.42 with the original copolymer composition. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 532–538, 2006     

Investigation of electrically conductive acrylonitrile‐butadiene rubber

Electrically conductive acrylonitrile‐butadiene rubbers (NBRs) containing carbon black (CB) as conductive filler were prepared in order to investigate their electrical and mechanical properties. The effects of conductive CB loading, temperature, acrylonitrile content, crosslinking density of vulcanizates, and plasticizer on conductivity were studied. The change in electrical conductivity of NBRs with different amounts of CB showed that there is a certain critical point (percolation threshold) where a significant decrease in electrical resistivity (increase in conductivity) is observed. Mechanical properties such as tensile strength, elongation to break, and surface hardness of vulcanized NBRs were measured. It was found that the percolation threshold was 5 phr of CB for the NBR/CB composites. J. VINYL ADDIT. TECHNOL., 13:71–75, 2007. © 2007 Society of Plastics Engineers.     

The Torque Transmission Capabilities of the Adhesively-Bonded Tubular Single Lap Joint and the Double Lap Joint

With the wide application of fiber-reinforced composite materials in aircraft, space structures and robot arms, the design and manufacture of composite joints have become a very important research area because they are often the weakest areas in composite structures.

In this paper, the stress and torque transmission capabilities of the adhesively-bonded tubular single lap joint and the double lap joint were experimentally tested. In order to compare the experimental results with the calculated results, the stress and torque transmission capabilities were analyzed by the 3-dimensional finite element method taking into consideration the nonlinear properties of the adhesive.

From the experiments it was found that the torque transmission capabilities of the adhesively-bonded double lap joint was 2.7 times as large as that of the single lap joint. Also, it was found that the fatigue limit of the double lap joint was 16 times as large as that of the single lap joint.     

Spinning viscose technical yarn into a bicomponent precipitation bath

Conclusions -- The possibility has been demonstrated of preparing viscose yarn by the centrifugal method from a viscose containing additions of urea by spinning into a bicomponent precipitation bath containing sulfuric acid and sodium sulfate.-- Optimum conditions for spinning viscose yarn have been established: a sulfuric acid content of 115 g/l in the precipitation bath, a urea content of 2.5% based on weight of -cellulose in the viscose, and an orientation stretch of 22%.-- Specimens of viscose yarn having a linear density of 13.3 tex have been prepared with a relative breaking load of up to 19 cN/tex, an elongation at break of 17–19%, and a mean squared deviation in dyeing nonuniformity of 0.8–1.0.Translated from Khimicheskie Volokna, No. 4, pp. 33–34, July–August, 1990.     

Oxidation behaviour of titanium-containing brazing filler metals

Brazements on alumina or partially stabilized zirconia (PSZ) of four silver- or copper-based brazing filler metals that contain titanium to promote wetting of and adherence to structural ceramics, were exposed in a thermogravimetric analyser at temperatures up to 700°C to atmospheres of 100% O₂, Ar-20% O₂ and Ar-3 p.p.m. O₂. The alloys included Cu-41.1Ag-3.6Sn-7.2Ti, Ag-44.4Cu-8.4Sn-0.9Ti, Ag-41.6Cu-9.7Sn-5.0Ti and Ag-37.4Cu-10.8In-1,4Ti, at%. All formed external oxides that were more or less protective under all of the test conditions studied. The growth of the oxides followed a parabolic time law. The gains in weight due to oxidation observed were small, ranging (for 45 h exposure at 400 °C to Ar-20% O₂) from 0.20 mgcm⁻² for the Ag-37.4Cu-10.8In-1.4Ti alloy to 0.46 mgcm⁻² for Cu-41.1Ag-3.6Sn-7.2Ti. As expected, weight gain increased with increasing temperature or . Unexpectedly, the titanium played a minor role in the scale formed on any of the filler metals with a titanium oxide, TiO₂, being found on only one alloy — Ag-41.6Cu-9.7Sn-5.0Ti. The brazements on PSZ gained weight at a higher rate than comparative brazements on alumina. We attribute this behaviour to oxygen transport through the zirconia resulting in the growth of an interfacial layer of titanium oxide.     

Fabrication of fine-grain piezoelectric ceramics using reactive calcination

Fine-grain piezoelectric ceramics with the formula Pb(Zr_0.53Ti_0.47)O₃(PZT) were prepared by a reactive calcination process. Using conventional materials and processing techniques, highly reactive powders of PZT were achieved by calcining to or near the point of maximum volume expansion, whereby associated morphological changes resulted in highly reactive powder. Upon milling, powders <0.3 m were readily obtained allowing densification at temperatures <1000°C. The B-site precursor method, whereby the ZrO₂ and TiO₂ oxides were pre-reacted prior to reaction with PbO, further enhanced reactivity by eliminating intermediate reactions and subsequent phase(s) which can hinder densification and overall homogeneity. Highly dense piezoceramics with grain sizes 1 to 2 m exhibiting dielectric and piezoelectric characteristics comparable to conventionally prepared large grain size materials were obtained.     

Robust person re-identification via graph convolution networks

Person re-identification (re-id) aims to identity the same person over multiple cameras; it has been successfully applied to various computer vision applications as a fundamental method. Owing to the development of deep learning, person re-id methods, which typically use triplet networks based on triplet loss, have demonstrated great success. However, the appearances of people are similar and hence difficult to distinguish in many cases. Therefore, we present a novel graph convolution network and enhances traditional triplet loss functions. Our method defines reference, positive, and negative features for triplet loss as three vertices of a graph, respectively, and adjusts their mutual distance through learning. The method adopts graph convolutions efficiently, thereby affording low computational costs. Experimental results demonstrate that our method is superior to the baseline on the Market-1501 dataset. The proposed GCN-based triplet loss considerably contributes to improve re-identification methods quantitatively and qualitatively.