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Abstract  

A thermal analysis study on the reduction of iron oxide rich slags under different conditions is presented in this paper. The effects of important process variables such as time, temperature, lime-silica ratio, FeO level in slag etc. are discussed. It is shown that the mechanism of reduction by externally added graphite is different from that by a carbon saturated bath although the activation energy values are similar.

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Abstact  

The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the catalyst proceeds in two steps:

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$Co_3 O_4 + H_2 \to 3CoO + H_2 O, 3CoO + 3H_2 \to 3Co + 3H_2 O$$ \end{document}
which was validated by the TPR and in-situ XRD experiments. The kinetic parameters of the reduction process were obtained with a comparative method. For the first step, the activation energy, E a, and the pre-exponential factor, A, were found to be 104.35 kJ mol−1 and 1.18�106∼2.45�109 s−1 respectively. The kinetic model was random nucleation and growth and the most probable mechanism function was found to be f(α)=3/2(1−α)[−ln(1−α)]1/3 or in the integral form: g(α)=[−ln(1−α)]2/3. For the second step, the activation energy, E a, and the pre-exponential factor, A, were found to be 118.20 kJ mol−1 and 1.75�107∼2.45 � 109s−1 respectively. The kinetic model was a second order reaction and the probable mechanism function was f(α)=(1−α)2 or in the integral form: g(α)=[1−α]−1−1.

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Abstract  

The method of a stepwise differential isothermal analysis (SDIA) has been designed for studies of reduction processes in metallurgical systems. The basis of the method is in multi-parameter control of reaction rate and its use for monitoring temperature, heating rate, and gas-phase composition. In this study hydrogen reduction of MoO3 and its mix with 30% Fe have been carried out using the SDIA technique. During the measurements, TG, DTG, DTA, EGA, and temperature control are carried out. Kinetics parameters were determined and possible reduction mechanism was suggested. The SDIA technique is well suited for these studies.

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Abstract  

Thermodynamic calculations predict the formation of hydrochloric acid gas and alkali tungstates during hydrogen reduction of WO3 doped with alkali chlorides MCl (M=Li, Na, K). The formation of HCl was proved experimentally by simultaneously coupled TG-MS measurements from RT to 1200C. The formation of HCl is the result of the reaction between MCl, WO3 and water. Ubiquitous traces of moisture in the gas are sufficient for reaction according to WO3+(2+2n)MCl +(1+n)H2O→M2+2nWO4+n+(2+2n)HCl (n=0, 1, 2). Laboratory reduction tests showed that the formed tungstates differ. NaCl and KCl form monotungstates (n=0), while LiCl produces more lithium-rich compounds (n=1, 2). Temperature and humidity, among other process factors, control subsequent reduction of the tungstates to metals.

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Speech technology has made it possible to use speech recognition for the simultaneous subtitling of live television broadcasts using the technique of respeaking. Analyses show that live subtitles, like pre-recorded subtitles, are nearly always a reduced form of the spoken comments. However, the live-subtitling process in itself may have an effect on the reduction strategies used by live subtitlers. The aim of this study is to gain a better understanding of the causes and consequences of quantitative text reduction in live subtitling. Three excerpts of an infotainment talk show were subtitled by twelve respeakers of the Flemish public television channel, VRT. They were instructed to complete the task using three different reduction conditions. Various subtitle features, such as reduction percentages and delay, as well as measures of the respeakers’ working memory were collected. In a hierarchical multilevel analysis we defined which external factors affect the degree of reduction. The results show that reduction is not a random process. In contrast, its occurrence and form are largely determined by a number of external factors, viz. delay, amount of source text and the proportion of ‘full’ deletions. A large volume of evidence suggests that respeakers opt to omit certain comments rather than reducing them. It also appears that the decision to delete a comment seems not to be primarily based on the amount of input, while the decision to reduce partially is.

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Abstract  

The reduction of cinnabar (HgS) and stibnite (Sb2S3) by hydrogen was investigated. These investigations were performed in the temperature region 636–765 K for cinnabar and in the region 825–954 K for stibnite. It has appeared that the mechanical activation positively affects the thermal reduction of the sulphides. The thermal decomposition of HgS is accompanied by a change in mechanism taking place at 744 K. As to Sb2S3, the change in mechanism inthe investigated temperature region was not observed.

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Journal of Thermal Analysis and Calorimetry
Authors:
I. Szilágyi
,
J. Madarász
,
G. Pokol
,
F. Hange
,
G. Szalontai
,
Katalin Varga-Josepovits
, and
A. Tóth

Abstract  

This paper discusses the changes in the structure and thermal reduction of nanosize hexagonal ammonium tungsten bronze (HATB), (NH4)0.33−xWO3−y, which were caused by K+ ion exchange (doping) and studied by XRD, XPS, 1H-MAS NMR, FTIR, SEM and TG/DTA-MS. Comparison of the cell parameters of undoped and doped HATB revealed that both a and c cell parameters decreased after the ion exchange reaction, which showed that smaller K+ ions partly replaced the larger NH4 + ions in the hexagonal channels of HATB. After the reaction, from the hexagonal channels less NH3 evolved, which also supported the incorporation of K+ ions into the hexagonal channels.

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Abstract  

A mode is an idempotent and entropic algebra. We show that each variety Rm of m-step left reductive Ω-modes is the Mal'cev product (relative to modes) of Rkand Rm-k. The dual result holds for varieties R n 1 of n-step right reductive Ω-modes. The main result says that the join Rm V R n 1 is independent and coincides with the Mal'cev product Rm ∘ R n 1 . We also give an equational characterization of this variety, and discuss the structure of such modes.

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Introduction Many studies of the reductions of metal oxides by gases have characterized the chemical properties and kinetic behavior of these (often) simple reactions. Among the numerous investigations reported, the reduction

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