Phase Diagram Mapping of the Fe<Subscript>3</Subscript>Al-Cr-Mo-C Pseudo-Quaternary System at 800 °C Using a New Diffusion-Multiple Technique

A new diffusion-multiple technique was used for mapping the phase diagram in the pseudo-quaternary Fe₃Al-Cr-Mo-C system at 800 °C. The following five carbide phases were formed in an Fe₃Al matrix phase (B2) with composition gradients of Cr, Mo, and C in the diffusion-multiple samples: κ-Fe₃AlC, M₅C, M₆C, Cr₇C₃, and M₂C (M: Mo, Cr, Al, and Fe). It was assumed that B2 phase is in equilibrium with κ, M₅C, M₆C, and Cr₇C₃ but not with M₂C phase at 800 °C. Complex phase equilibria among those phases were efficiently mapped by the diffusion-multiple technique. The results from the technique were consistent with those obtained from the conventional bulk alloy method.     

Studies on chains of bubbles rising through quiescent liquid

The liquid velocity profile induced by a chain of bubbles is studied theoretically and a comparison with measurements is made. The wake velocity and the bubble shape involved in the theoretical development are considered based on the wake theory and the previous empirical relation for single bubbles, respectively. The shape and wake volume of chain bubbles can be treated in the same manner as those of single bubbles by using relative velocity. As a result, using the previous results of the drag coefficient and shape of single bubbles enables the prediction of the rising velocity of chain bubbles.     

Alternating finite automata on ω-words

Alternating finite automata on ω-words are introduced as an extension of nondeterministic finite automata which process infinite sequences of symbols. The classes of ω-languages defined by alternating finite automata are investigated and characterized under four types of acceptance conditions. It is shown that for one type of acceptance condition alternation increases the power in comparison with nondeterminism and for other three acceptance conditions nondeterministic finite automata on ω-words have the same power as alternating ones.     

Synergistic action of Sb2O3 with bromine-containing flame retardant in polyolefins. 1—the variance in their performance versus Sb/Br ratio

The synergistic action of antimony (Sb) with bromine (Br) was studied for polypropylene-2,3-dibromopropylpentabromophenyl ether–Sb₂O₃ systems at various Sb/Br molar ratios. Oxygen index, weight loss rate and heating value were used to evaluate the retardant effect. Bromine and antimony emission and their material balances were measured by gravimetric and X-ray fluorometric analysis of heated samples at each reaction time. Retarded HBr formation in the gaseous phase through SbBr₃, SbOBr and Sb₄O₅Br₂ was proved by X-ray diffraction analysis of heated residues and model products. SbBr₃ and HBr formation were greatest at Sb/Br ratios of 1/3 and 1/4, respectively, while the highest oxygen index and the lowest weight loss rate and heating value were obtained at 1/4. Consequently, HBr will most probably produce the retardant effect rather than SbBr₃. Effective synergistic action at the Sb/Br ratio of 1/4 is explained by presuming the formation of an acidic HBr.SbBr₃ complex in the molten phase for the particular reaction pattern of bromine in 2,3-dibromopropylpentabromophenyl either.     

Atomic Layer Epitaxy of Silicon

Two methods are proposed and demonstrated successfully for low temperature atomic layer epitaxy (ALE) of Si, where H atoms play essential roles. The first method is the use of H as a self-limiting factor. Trisilane (Si₃H₈) was used as source gas and the substrate temperature was modulated in order to alternate steps in an ALE cycle. When the temperature was less than 380°C in the adsorption step and more than 520°C in the desorption step, respectively, the grown layer thickness per cycle was 0.8 ML/cycle. The second method is the use of atomic H as an active reducer of a self-limiting factor. A clean surface was exposed to dichlorosilane (SiH₂Cl₂) as source gas to grow an Si monolayer covered with CI. Next, atomic H was injected to reduce CI from the surface. An ideal monolayer growth was obtained with the substrate temperature over 540°C.     

Development of three-dimensional electric field analysis by segment arrangement based on a charge simulation method

This paper describes the development of three-dimensional electric field analysis by using the so-called segment method which enables the electric field to be calculated with high accuracy and with enhanced efficiency, for high-voltage apparatus. In the segment method, electrode configuration of high-voltage apparatus is simulated by small components which are called segments and by the arrangement of several kinds of such segments. In this calculation, the charge simulation method is used which is suitable for segment application. As basic segments, spherical, cylindrical and ring segments are used and in addition to these, as subsegments, disc and elbow segments are adopted for good simulation of the total electrode configuration. In this paper, the fundamental construction and arrangement parameter of segments were discussed. Moreover, the segment method was applied to an actual high-voltage apparatus and the calculation accuracy was discussed. It was clarified that the segment method has sufficient calculation accuracy and is a very efficient means for three-dimensional electric field analysis.     

Electron-microscopic imaging of single-walled carbon nanotubes grown on silicon and silicon oxide substrates

Direct imaging of single-walled carbon nanotubes (SWNTs) suspended on pillar-patterned Si or SiO2 substrates is investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The suspended nanotubes are successfully observed by direct TEM imaging and it is seen that they have either individual or bundles of SWNTs. Low energy (< or =2 keV) SEM produces high contrast images of suspended SWNTs. On the contrary, when SWNTs contact a SiO2 substrate, they are imaged using electron-beam induced current. The image brightness depends on the length of SWNTs.