Study of local oxidative degradation in polypropylene impact copolymer by energy dispersive X-ray system

Summary In this study, the thermal oxidative degradation of a polypropylene (PP) impact copolymer was examined using a transmission electron microscope equipped with an energy dispersive X-ray system (TEM/EDX). The oxidative behavior was visually captured by oxygen line analysis. The oxidation resistance of the ethylene-propylene rubber (EPR) phase was considerably higher than that of the PP matrix, indicating that the degradation behavior of the PP impact copolymer was heterogeneous. It was found that the higher resistance of the EPR phase originated from its primary structure by ¹³C-NMR measurement.     

Polymerization of 4-n-alkylstyrenes with typical Ziegler-Natta and metallocene catalysts

Polymerization of 4-n-alkylstyrenes (alkyl side group; methyl, ethyl, propyl and buthyl) was carried out with the η-C₅(CH₃)₅TiCl₃-methylaluminoxane (MAO) and TiCl₃-triethylaluminum (TEA) catalyst systems. When the η-C₅(CH₃)₅TiCl₃-MAO catalyst was used, the stereoregularity of resulting polymers markedly depended on the length of substituted alkyl groups, i.e., the catalyst gave highly syndiotactic poly(4-methylstyrene), but produced atactic polymers for the monomers with ethyl, propyl and buthyl substituents. On the other hand, all the poly(4-n-alkylstyrene)s obtained with the TiCl₃-TEA catalyst were highly isotactic. As a result, a large difference was observed in the thermal properties of polymers obtained between the two catalyst systems. Received: 6 September 1996/Accepted: 16 October 1996     

Nanosize Powders of Aluminum Nitride Synthesized by Pulsed Wire Discharge

Nanosize particles of aluminum nitride have been successfully synthesized by a pulsed wire discharge (PWD). Intense pulsed current through an aluminum wire evaporated the wire to produce a high-density plasma. The plasma was then cooled by an ambient gas mixture of NH₃/N₂, resulting in nitridation. As a result, nanosize particles of aluminum nitride were formed. The average particle diameter was found to be ∼28 nm with a geometric standard deviation of 1.29. The maximum AlN content of 97% in the powders was achieved by optimizing various parameters: the gas pressure, the ratio of NH₃ and N₂, the wire diameter, the pulse width, and the input electrical energy. The ratio of the AlN powder production to the electrical energy consumption was evaluated as ∼40 g/(kW·h). Thus, PWD is a very efficient and promising method to synthesize nanosize powders of AlN.     

Nanoparticle synthesis of transition-metal borides by pulsed discharge of compacted powder

In this study, boride nanoparticles were synthesized via a low-cost and simple pulsed discharge of compacted crystalline and amorphous B micron-sized powders for the first time. Borides of Ti, Mo, W, and Zr were chosen for synthesis experiments. The as-synthesized powders were spherically shaped and smaller than 100 nm. X-ray diffraction patterns indicated the presence of several minor phases in each boride powder in addition to a single main-phase boride. Specifically, the main phases were TiB₂, MoB₂, WB₄, and ZrB₂ for borides of Ti, Mo, W, and Zr, respectively. Energy-dispersive spectroscopy (EDS) indicated the presence of B and metal in almost all particles of every sample. The observed particles usually exhibited a two-part structure: a boride phase and B. Small amounts of C, Fe, Cr, and Ni were detected by EDS; however, the contents of Fe, Cr, and Ni were substantially reduced after improvements to the experimental setup.     

用X射线晶片分析器同时测定硅片上薄膜的厚度及组成

晶片专用X射线荧光分析装置在半导体工业中被用于多种工程的评价。在半导体分析中XRF法的显著特征是能分析各种薄膜(氧化膜、硅化物膜、金属膜等);能同时分析晶片上同一部位的膜厚及组成;XRF法是非破坏分析,因受化学键的影响不大,同一个试样可以反复使用。 厚度在400nm以上的掺硼磷硅玻璃(BPSG)膜的分析结果已做报道。近年,随着对半导体器件的高度集成化、高性能化(64 Mbit以上)要求的提高,希望能更准确地分析。作为有代表性的氧化膜——BPSG膜,为改善其在工程中的热处理特性,B_2O_3、P_2O_5的浓度控制是不可缺少的。为了满足这些要求,必须分析更薄的薄膜(300nm以下),在薄膜分析中的关键问题是B Kα背底的变动。 B分析的新光学系统改善了声噪比(S/N),使250nm以上的BPSG膜的分析成为可能。为了提高晶片分析器的性能,在装置上做了一些改良:真空度的稳定化;减轻污染的特制真空泵;分光室部分的恒温化。新的晶体分析器无论在短期或长期的测定,对10％B_2O_3的测定能做到1％的相对精度。 对在硅晶片上的钨硅化物的分析,不能使用W Lα及Si Kα两种谱线,而应使用W的两种谱线(浓度分析用W-N线,膜厚分析对用W-Lα线)。 膜厚测定的相对精度在0.2％以下,对于Si/W=2.5,摩尔比精度约0.015％(相对精度约为0.56％)。     

Development of a new continuous Si-Ti-C-O fibre using an organometallic polymer precursor

A polytitanocarbosilane, which is useful as the precursor polymer for ceramic fibre, was synthesized using polydimethylsilane, polyborodiphenylsiloxane and titanium tetraisopropoxide. The polytitanocarbosilane was melt-spun and using the continuous heat-treatment process from the polymer fibre to ceramic fibre, flexible Si-Ti-C-O fibre was produced. The density, tensile strength and Young's modulus of this amorphous ceramic fibre were found to be 2.35 g cm^–3, 3.0±0.2 and 220±10 GPa, respectively. The Si-Ti-C-O fibre retained its high tensile strength to higher temperatures (about 1200° C). The specific resistance of this ceramic fibre covered a wide range of 10⁷ to 10^–1cm. This ceramic fibre is considered to be useful as reinforcement fibre for composites.     

Semiconductor Lasers in Photonics

Research activities on semiconductor lasers related to optical communications and information technologies are reviewed.     

Self-healing behavior and strength recovery of ytterbium disilicate ceramic reinforced with silicon carbide nanofillers

Environmental barrier coatings (EBCs) are necessary to protect SiC/SiC ceramic components against oxidation and hot corrosion in high-temperature applications. The volatilization of SiO₂ in SiC-reinforced materials is a major obstacle for the implementation of these self-crack-healing ceramics. The Yb₂Si₂O₇-Yb₂SiO₅-SiC composite is known as a self-healing material that can help to avoid this SiC recession. In this research, the crack-healing behavior of this composite is investigated by using pre-cracking followed by annealing in an oxidizing environment. The crack-healing mechanism is explored and elucidated as a function of the filler morphology, crack size, annealing time, and annealing temperature. The two main crack-healing mechanisms are the filling of cracks with SiO₂ glass and the volume expansion of Yb₂Si₂O₇ induced by the reaction between SiO₂ and Yb₂SiO₅. Full crack recovery is achieved with only 10 vol% SiC, with evidence from XRD and EDS analyses. SiC nanoparticulates are more efficient fillers than nanofibers and nanowhiskers.     

Preparation of modified polybutene‐1 by oxidation and limonene radical grafting using an Nd2O3‐assisted radical initiator system and its characterization

Free radical graft polymerization has been used as a modification method to incorporate functional groups into polyolefins using a melt‐mixing process. In this work, modification of polybutene‐1 (PB) was performed by limonene radical graft polymerization using the Nd₂O₃/dicumyl peroxide (DCP) radical initiator system with various mixing ratios in air. The effects of the modification on the crystallization and tensile behavior were studied in detail. The modified PB samples had ketone and limonene groups. The contents of both the ketone and the limonene groups were highest in the modified PB prepared using Nd₂O₃/DCP (2/0.2 wt%/PB), and a conjugated diene group was found to be produced by a side‐reaction. Excess Nd₂O₃ lowered the limonene graft content in the modified PB. The rate of crystal phase transition (II → I) decreased with an increase of limonene content. The presence of a small amount of the ketone group increased the rate, and the modified PB having a small ketone content exhibited more ductility due to its higher crystal phase transition rate. It was found that there was an optimum mixing ratio of the Nd₂O₃/DCP initiator system for the modification. The ketone and the limonene groups affected the rate of the crystal phase transition and the tensile properties of the modified PB. Copyright © 2010 Society of Chemical Industry