Search results for "Isothermal"
showing 10 items of 212 documents
High Temperature Oxidation of TiAl and TiAl8Nb Alloys in Air
2011
Isothermal oxidation of two g-TiAl-based intermetallic alloys: Ti48Al and Ti46Al8Nb alloys was studied in synthetic air at 1073-1223 K for up to 240 hrs. Mass change per unit area for the oxidized samples followed approximately the parabolic rate law. The kp values for the studied temperature interval were in the range from 7.2×10-13 to 1.8×10-11 g2cm-4s-1. The activation energy for oxidation of Ti48Al alloy in air at 1073-1223 K was Ea = 165±12 kJ/mol. Niobium addition to Ti48Al alloy in the amount of 8% increased its oxidation resistance. Structure and chemical composition of the oxidation products, and morphology of the oxidized samples were investigated using XRD, SEM-EDS, and TEM. The …
Influence of the mode of introduction of a reactive element on the high temperature oxidation behavior of an alumina-forming alloy. Part I: Isotherma…
2004
Several routes of yttrium introduction were applied to test the high temperature oxidation performance of a FeCrAl alloy. Isothermal oxidation tests were described in a previous paper (Part I of this paper in this journal, 2004, 55, 352). Cyclic oxidation tests were performed in air under atmospheric pressure on blank specimens, Y 2 O 3 sol-gel coated-, Y 2 O 3 metal-organic chemical vapor deposited (MOCVD)-, yttrium ion implanted-alloys, as well as on a steel containing 0.1 wt.% of yttrium as an alloying element. For the 20 hours cycles, all the samples, except FeCrAl-0.1Y, exhibit weight losses after a few cycles, indicating drastic spallation of the oxide scales. The MOCVD coated specime…
Oxidation behavior of γ-TiAl coated with zirconia thermal barriers
2002
Abstract The applicability of the thermal barrier coating concept, which is an established concept for Ni-base alloys, was investigated for the first time for γ-TiAl. As potential bond coats, the following surface treatments were applied: Al-diffusion coating, Al-diffusion coating combined with short term pre-oxidation in air, short term pre-oxidation in oxygen of a rough surface finish γ-TiAl sample without aluminide coating. For the purpose of lowering the temperature of the γ-TiAl substrate surface, and thus, to prolong the life time, a zirconia thermal barrier coating (TBC) was applied on top of the above-mentioned modified TiAl surfaces. Oxidation resistance of the modified γ-TiAl allo…
XRD Line Broadening Studies on Mullite
1996
An X-ray diffraction microstructural study on 110, 220, 001 and 111 peaks has been performed on mullite in the temperature range of primary mullite formation in order to monitor nucleation and growth process. Considering the crystallinity of the starting kaolinites, a greater disorder of the kaolinite has been found to enhance the mullite formation. Isothermal growth is related to a decrease in the Al 2 O 3 content of mullite.
Crystallization and melting of fractions of branched polyethylene
1983
Effects of the molecular weight on the crystallization behaviour of branched polyethylene become observable if isothermal crystallization is studied at temperatures near to the melting end. Crystallinities decrease with decreasing molecular weight. Thicknesses of lamellae grown during isothermal crystallization are independent of the molecular weight. They depend only on temperature. Compared to the effect of the branches polydispersity gives only a minor contribution to the broadening of the crystallization and melting range of low density polyethylene.
Crystallization kinetics of poly(ethylene oxide) from its melt and from mixtures with tetrahydronaphthalene and oligo(ethylene oxide-block-dimethylsi…
2004
The crystallization of poly(ethylene oxide) (PEO) from the pure state and from its mixtures with oligo(dimethyl siloxane-b-ethylene oxide) (COP) and tetrahy- dronaphthalene (THN) was investigated. The crystallization kinetics was studied iso- thermally and nonisothermally with an automated device that monitored the light passing through the corresponding liquids as functions of time and/or temperature. The rate was strongly influenced by the concentration of COP in the mixture. A substantial decrease in the induction time (the time required for the onset of crystallization) and a considerable shift in the crystallization temperature (the transition from a liquid state to a solid state) to h…
Elongational behavior of low density/linear low density polyethylenes
1988
Rheological data have been collected in isothermal elongational flow for three different types of blends, made from one low density polyethylene and three linear low density samples. In addition to the transient curves, elongation at break data are also reported. The influence of the composition and of the molecular weight of the linear low density polyethylene is discussed.
Effect of CTBN rubber inclusions on the curing kinetic of DGEBA–DGEBF epoxy resin
2003
Abstract The curing kinetics of an epoxy resin matrix, based on diglycil ether of bisphenol A and F (DGEBA–DGEBF), associated with an anhydride hardener, at different carboxyl-terminated copolymer of butadiene and acrylonitrile liquid rubber (CTBN) concentration (0–10 phr) are studied using a differential scanning calorimetry (DSC) and a stress-controlled rheometer in isothermal and dynamic conditions. The aim of this work is to correlate the presence of the rubber phase with the transition phenomena that occur during the curing process. The CTBN rubber induces a catalytic effect on the polymerization of the pure resin clearly observed by a significant enhancement of the curing rate. Calori…
Role of thermal history on quiescent cold crystallization of PET
2002
8 pags., 9 figs.
Influence of a Crosslinker Containing an Azo Group on the Actuation Properties of a Photoactuating LCE System
2016
Photoactuating liquid crystalline elastomers (LCE) are promising candidates for an application as artificial muscles in microdevices. In this work, we demonstrate that by optimizing (1) the illumination conditions and (2) the mixture of azo monomer and azo crosslinker, thick films of an all-azo LCE can be prepared, which show a strong length change without bending during photoactuation. This becomes possible by working with white light (about 440 nm), whose absorption is low, leading to a large penetration depth. By adding an azo crosslinker to a previously prepared system, several improvements of the actuation properties—like a stronger photoactuation at lower operational temperatures—coul…