No description available.

No description available.

Constant activity nitriding experiments were performed in Fe-V and Fe-Mo alloys. The nitriding was accomplished aging the alloys in a NH(,3)/H(,2) atmosphere at temperature between 400(DEGREES)C and 600(DEGREES)C, during which fine substitional-interstitial clusters are formed. These coherent clusters are small platelets lying on 100 ferrite matrix planes. During the nitriding process, these clusters form first near the surface of the sample. For the Fe-V alloys, nitriding proceeds by the advance of a interface bounding region with and without clusters. This results in a hardness profile which is discontinuous at the interface. The rate of the hardness front movement in Fe-V can be predicted by internal oxidation equation. For the Fe-Mo alloys, a distinct interface is not observed, and the hardness varies in a continuous fashion through the cross section of the sample. No particular model has been developed for those alloys. The resistivity rises during the nitriding for both Fe-V and Fe-Mo alloys. In Fe-V alloys, the nitrided region and unnitrided region are separated by a sharp boundary. Thus, the resistivity can be calculated by analogize this system to a pair of resistor connected in parallel. The resistivity at full saturation of nitrogen were explained mainly by formation of the coherent clusters in the alloys. It is a function of density, size distribution and average size of the clusters. From the resistivity maxima upon full saturation at different nitriding temperatures, we can understand the size distribution and average size of the clusters are function of nitriding temperature, while density of the clusters and total volume of the strain field are function of concentration of alloy elements and nitriding temperature. The static displacement around clusters has been estimated, from resistivity data, and equal 0.68(ANGSTROM) for a full nitrided Fe-3.0at.%Mo.

A critical study of the Jiles and Atherton Mean Field Model was done to determine the validity of the model, a tool in describing and understanding the magnetization process in textured silicon steels. / Hysteresis loops were generated using an Epstein apparatus in various directions with respect to the rolling direction and for various external magnetic fields. Techniques were then used to obtain the model parameters, namely a$ sp prime,$ $ alpha sp prime,$ and k$ sp prime.$ After creating a new version of the model, M$ sb{ rm s}$ was also obtained from the data hysteresis loops. / The model gives a close description of the influence of texture on hysteresis behaviour and predicts the variation of the parameter k$ sp prime,$ which agrees with our understanding of the role of texture in changing the parameter. We have observed that the highest value of this parameter coincides with the angles at which it is most difficult to magnetize the specimen. / The proposal of the model's creators that the main drawback of the model that the pinning parameter $k sp prime$ is not constant, is not justified by them and not supported by our analysis of experimental data.

The manufacture of ceramic composites has traditionally been a complex and often expensive process. A new processing method, the DIMOX$ sp{ rm TM}$ process, takes advantage of the high temperature oxidation behaviour of aluminum alloys to produce a ceramic-metal composite. Although this process is fairly simple to implement, there has not been any attempt to link the starting materials and manufacturing conditions to the properties of the final composite. This work attempts to identify some critical parameters in the manufacturing process and how they affect the end product. The reaction temperature, alloy composition, and powder bed condition were optimized with respect to the growth process, final composition, and resulting microstructure. These characteristics were then related to the elasticity, strength, fracture toughness, and fracture mode of the final composite. / Aluminum-magnesium-silicon alloys were oxidized into an alumina bed of either Alcan C-70 UNG power or Struers' 400 grit. The process conditions were optimized in air at 1120$ sp circ$C with a 10% silicon, 2% magnesium alloy. The growth rate was dependent on the powder bed. The material was composed of alumina, silicon, aluminum, and trace amounts of magnesium aluminate spinel. The fracture mode was dependent on the composition of the material and the alumina bed.

In this work, the carbothermal reduction of Al$ sb2$O$ sb3$ to AlN was studied. Several kinds of aluminum oxides including $ alpha$-Al$ sb2$O$ sb3$, $ gamma$-Al$ sb2$O$ sb3$, $ theta$-Al$ sb2$O$ sb3$ and boehmite (AlOOH) were examined in order to observe the differences in reaction behaviour and powder characteristics obtained from each type of precursor. Cane sugar (sucrose) and carbon black were used as carbon sources. Reaction conditions studied were carbon to alumina ratio, temperature and reaction time. Sucrose resulted in a close-to-stoichiometric ratio of Al$ sb2$O$ sb3$:C (1:3.2) achieving full conversion to AlN and produced a regular powder morphology, whilst carbon black required higher ratio ($>$1:4) to reach full conversion with agglomeration of the AlN powder. The optimal reaction temperature was 1600$ sp circ$C with the reaction time being dependent on the Al$ sb2$O$ sb3$ source. The results of the thermodynamic study for the Al-N-O-C system suggest a solid-state reaction process which is consistent with the experimental observations. Moreover, flowing N$ sb2$ gas flushes out the product CO gas and thus forces the equilibrium in favour of AlN formation. Reaction mechanisms are proposed for the two forms of carbon precursor.

Vacuum levitation experiments have been conducted to study the decarburization kinetics of levitated steel droplets in order to determine the factors and relationships which control the rate of decarburization especially at C levels below 30 ppm. It was found from the experiments that (1) vacuum chamber pressure had a significant effect on the rate of decarburization when the carbon content was below 35 ppm; (2) sulfur did not show any significant effect on the rate of decarburization due to the strong stirring inside the droplet caused by magnetic levitation field; (3) the rate of decarburization of levitated droplets was 3 ppm/sec at (C) = 30 ppm which was 40 times higher than the overall rate of decarburization in the RH process at (C) 30 ppm; (4) high initial oxygen contents improved the rate of decarburization at high carbon contents. / The following suggestions are made: (1) increase the amount of liquid steel droplets without increasing the size of the droplets; (2) increase the fraction of the amount of decarburization reaction inside the molten steel by gas and powder injection; (3) further reduce the partial pressure of CO and CO$ sb2$ gas in the gas phase. (Abstract shortened by UMI.)

The addition of frother in flotation has two main functions, to help reduce bubble size and help produce a stable froth. A role of frother on bubble behavior in pulp zone is usually not considered. A previous study showed that as frother type was changed the same gas holdup was given by different size bubbles. This implies that bubble rise velocity depends on the nature of the surfactant (frother type). A study using bubble swarms appears to support the frother type effect but bubble interactions are a possible confounding factor. This study resolved the question by measuring terminal rise velocity profile of single bubbles (ca. 1 to 2 mm) as a function of frother type. It is shown that at the concentrations of interest in flotation, 1-pentanol hardly alters the velocity compared to water alone while F150 (a polyglycol) reduces the velocity by up to 50%. The results become in 1-pentanol bubble did not reach terminal velocity. For high concentration of 1-pentanol (>130ppm) the rise velocity is reduced comparable to F150. To investigate, experiments were performed using aliphatic alcohols from 1- butanol (C4) to 1-octanol (C8). It was found there is a minimum concentration for the frother to give terminal velocity close to the Clift et al. contaminated eater result. The concentration decreases as molecular weight (chain length) of alcohol increases. Larger bubbles (1.8 vs. 1.5mm) require higher minimum concentration. To study the influence of molecular structure, three 6-C alcohols, 1-hexanol, MIBC and 2-hexanol, were used. The results show that molecular structure influences rise velocity through the position of OH group, and whether the alcohol is straight chained or branched. The observation can make a useful link frother to chemistry for understanding frother influence on bubble rise and possibly its function in flotation. The influence of three industrial frother, MIBC, F150 and DF250, was studied and / Deux raisons principales commandent à l´ajout de la mousse dans le processusde flottation, à savoir, la réduction de la bulle et la production d´une moussestable. Léffet de la mousse sur le comportement de la bulle en zone pulpairenést pas pris en compte. Un travail antérieur a démontré que pour la mêmefraction d´air transporté par les bulles, le type de mousse a de l´influence sur lataille des bulles. Cela implique que la vélocité de la bulle dépend de la nature dusurfactant (type de mousse). Une étude basée sur l´usage de plusieurs bullessemble s´accorder avec l´hypothèse relative au type de mousse, néanmoins lesinteractions des bulles rendent le problème complexe.La présente étude a résolu cette question en mesurant la vélocité d´une bulledont les dimensions sont presque égales à 1 ou 2 mm, suivant le type demousse. Il en est résulté que dans l´intervalle des concentrations d´importanceen flottation, le pentanol peine à influencer la vélocité, alors que léau toute seuleen serait capable. En revanche, le F150 (un polyglycol) réduit la vélocité de 50%.Pour les concentrations élevées de pentanol (>100 ppm), la vélocité décroit etdevient comparable à celle engendrée par la présence du F150. Il va de soi quel´observation antérieure est confirmée dans l´intervalle pratique desconcentrations.En guise d´investigations, des expériences au cours desquelles les alcoolsaliphatiques allant du butanol (C4) à l´octanol (C8), ont été réalisées. Il a étédémontré que léffet du type de mousse sur la vélocité dépend de laconcentration. Il existe une concentration minimale de la mousse en dessous delaquelle, la bulle monte comme dans le modèle de léau contaminée de Clift etal. La concentration minimale critique dépend de la dimension de la bulle et dudéplacement mesuré à partir du point terminal du tube capillaire. L´on rapporteque les bulles les

The addition of Nb significantly retards recovery and recrystallization through solute drag and precipitation pinning effects. It is important to describe the precipitation behaviour precisely because finely distributed precipitates retard the restoration process abruptly. The isothermal precipitation behaviour has been studied frequently. However, during industrial hot deformation processing, the temperature decreases continuously, so that isothermal data cannot be applied directly to predict the precipitation under these conditions. The focus of this study is therefore on the CCP (Continuous-Cooling-Precipitation) behaviour of Nb carbonitride in austenite. / To calculate the CCP behaviour, isothermal PTT (Precipitation-Time-Temperature) data in terms of the P$ sb{ rm s}$ (precipitation start) and P$ sb{ rm f}$ (precipitation finish) times are first required. In 1987, Dutta and Sellars developed a thermodynamic model to predict P$ sb{ rm s}$ times for the precipitation of niobium carbonitride, and in 1989, Liu and Jonas developed a model for titanium carbonitride. In the present work, the L-J (Liu-Jonas) model is used to calculate the P$ sb{ rm s}$ time at a given temperature from experimental data. Since the prediction models are only limited to the P$ sb{ rm s}$ times, a new calculation method for the P$ sb{ rm f}$ time, based on reaction kinetics and classical nucleation and growth theory, is proposed in this study. Two models are developed to follow the precipitation process, and the time exponent and rate constant for the kinetics are formulated for each model. The additivity rule, which was developed by Scheil in 1935, is then used to calculate the extent of precipitation during continuous cooling. / Isothermal precipitation rates for 0.040% Nb steels are measured experimentally by the stress relaxation method. The CCP behaviour is then calculated and is then examined by continuous cooling testing, using a hot deformation dilatometer. Precipitates are observed by transmission electron microscopy of specimens quenched after a period of cooling at various cooling rates. The P$ sb{ rm s}$ and P$ sb{ rm f}$ times estimated from the particle size data show good agreement with the calculated CCP behaviour.

The subject of this work is gallium extraction from sulphate solutions--an additional source of this metal from hydrometallurgical zinc production--with organophosphorus acid reagents: di-2-ethyl hexyl phosphoric acid (D2EHPA) and OPAP, a mixed extractant consisting of mono- and di-octyl phenyl phosphoric acids. Extraction proceeds via cation-exchange and Ga$ sp{3+}$ is the reacting species. Gallium is extracted with D2EHPA mostly as GaR$ sb3$ - HR. The results for OPAP suggest existence of four reactions, which form GaM$ sb3,$ GaM$ sb2$D, GaMD$ sb2,$ and GaD$ sb3;$ this explains and allows prediction of behaviour over a wide range of OPAP compositions. Sulphate complexation causes decrease in concentration of the reacting species, and thus lower $D sb{ rm Ga}$ values and extraction rates. Prior knowledge on gallium aqueous complexes is used, and an algorithm developed, to allow quantitative prediction of complexation effects on extraction. The model of mass-transfer with chemical reaction, verified with several known criteria for reaction site determination, describes well the kinetic data for the Ga-D2EHPA system. The model is further developed to account for the stronger acidity and the monomer/dimer equilibria typical for the kind of extractants used. A detailed reaction mechanism is proposed and the first organic ligand addition is found as rate-limiting. The model parameters, estimated from extraction kinetic data, are reasonable, when compared with those obtained for other metals elsewhere. The model's predictions agree with the results from stripping kinetics; the equilibrium conditions (zero rate) can also be satisfactorily predicted, as found by comparisons with the equilibrium data. Ga-D2EHPA and Ga-OPAP systems are compared with an emphasis given to the potential for metal separation; the importance of the ligand exchange rate constant is illustrated with the example of Ga and Al extraction/stripping and their separation based on different rates with