Application of Response Surface Methodology to the Selection of Machining Variables

This paper presents the use of Response Surface Methodology for analysis of material removal processes. Mathematical models of tool life, surface finish and cutting force are developed in terms of cutting speed, feed, and depth of cut. The models were then used to select the levels of the machining variables such that certain criteria could be achieved. Specific examples include increasing the rate of metal removal without sacrificing surface finish and with a minimum loss in tool life.     

Lithium ore in Brazil

Brazil, one of the largest countries in the world both in territory and in population, has a vast range of mineral resources, as well as a large industrial plant in full development. The country is both a lithium producer and a consumer at a moderate level now, and there is potential for medium-range growth. Forecasting the future of the lithium industry in Brazil is difficult because of uncertainties in both the producing and consuming industries. The pressure of demand will be the main incentive factor in the exploration and production of lithium ores in Brazil.Presently, Brazil uses lithium ores in the manufacture of ceramics, enamels and special glasses, and annually consumes about 1600 tons of petalite, 1200 tons of lepidolite, and 800 tons of spodumene. Brazil also uses lithium-based chemical products, and consumes about 1000 tons per year of amblygonite for their manufacture. All these minerals are produced in Brazilian territory, and fair quantities of the excess petalite are exported to the United States and Japan at about 2500 tons per year.Brazilian production entirely from pegmatite deposits located in the Eastern part of the Brazilian shield and mainly in the district of Araçuai-Itinga (northern Minas Gerais State). The known reserves of lithium pegmatites are not well measured, but available data indicate that the small sizes of these bodies compared with the bigger ones of Kings Mountain, Bikita and elsewhere, are largely compensated by their large numbers and their geographic occurrence. These features present the possibility of considerable reserves, particularly of spodumene and petalite. These reserves are not less than 25,000 tons of lithium, based on studies already performed in some deposits. Additionally, there is evidence that in the district of Araçuai-Itinga there are occurrences of lithium brines in basins of accumulation. This may also be true of some areas of Brazilian Northeast. In order to prove this hypothesis, Arqueana de Minerios e Metais is preparing a program of systematical sampling.Brazilian consumption for conventional purposes, either of ores or of lithium-based chemical products, will increase with the development of the Brazilian economy. Brazil still has a long way to go to reach the level of consumption of America, Europe of Japan. As an example of this perspective, it is worth mentioning that Brazil does not yet use lithium carbonate for the reduction of aluminum, nor is lithium ore used in the manufacture of heat-resistant glass and ceramics. Besides these potential factors for increasing consumption, consideration must be given to the possibility of new uses of lithium as in thermonuclear power generation, the development of which is already underway in Brazil. Another new use is in lithium batteries for electric cars and, if this application becomes a reality, Brazil will be a big consumer, ranking at the same level as the most developed countries in the world, with the advantage of being one of the few countries capable of producing its own raw material.     

Electrochemical Studies on the passive behaviour of tin in different buffer solutions

The effect of pH on the passivity of Sn has been investigated in buffered (phthalate-borate, and citrate phosphate buffer series), and in unbuffered phosphate solutions, using the cyclic voltammetric technique. Two anodic peaks; the first being more pronounced than the second, and on cathodic peak have been observed in the two buffer series at different scan rates and pH values. The anodic and cathodic peak current densities (I_p) and potentials (E_p) are functions of the scan rate (v) and the pH value. Plots of I_p against v^1/2 yield straight lines at each pH value. The effect of pH on I_p for the first anodic peak shows a shallow minimum in the near neutral and slightly alkaline range at all scan rates. Straight lines are also observed between E_p and v^1/2, the extrapolation of which to v = 0 gives the spontaneous (no polarization) oxidation or reduction potentials (E′ and E″). The absence of polarization effects in E′ and E″ make them the most suitable values for comparison with thermodynamic data. Therefore, the two straight lines obtained between E′ and E″ on one hand and the pH on the other hand to give an estimate of (i) the slope (dE°/dpH), and (ii) the value of E° at pH - 0 (from intercept). Comparison of the two experimental values with all available thermodynamic data for Sn(II) and Sn(IV) oxides and hydroxides shows that: (i) the first anodic peak represents the formation of Sn(OH)₂ from Sn and OH^?, (ii) the second anodic peak represents the formation of Sn(OH)₄ directly from Sn and OH^?, and (iii) the cathodic reduction peak correponds to the reduction of Sn(IV) oxidized species to Sn. The results in citratephosphate buffer have been treated in the same manner. However, the result of (dE°/dpH) and E° at pH = 0 deviate from thermodynamic data, because of the possible participation of other anodic reactions such as the formation of soluble Sn compounds, Sn complexes, and incorporation of anions in the anodic film.     

Dissolution Rates of Commercial Phenylbutazone Tablets: Inter-And Intra-Brand Effects

A study has been carried out to investigate the dissolution rate profiles of twelve batches of sugar-coated phenylbutazone tablets belonging to four commercial brands. Using the rotating basket method, significant inter-brand and inter-batch variations in dissolution rates were found. Only two batches of one brand passed the B.P. dissolution limit whilst other batches had percentages dissolution between 0.3 and 58 after 45 min. Batches with poor dissolution characteristics exhibited significant tablet-to-tablet variations in dissolution rates; a finding which was not observed in the relatively fast-dissolving batches. When the paddle method was substituted for the B.P. basket method, the dissolution rates were relatively faster but similar dissolution failure was found. However, the tablet-to-tablet dissolution variability was decreased in some of the batches. The observed differences in dissolution rates of the batches examined were unrelated to their disintegration times. Inspite of the poor dissolution characteristics of most of the batches studied, no apparent chemical degradation was found. It is recommended that when evaluating the dissolution rates of brands of phenylbutazone tablets, a number of batches from each brand should be tested.     

Corrosion Behaviour of Manganese-Containing. Stainless steels. I. Galvanostatic measurements in H2SO4 solutions

The results of galvanostatic polarization experiments on four 17.3% Cr / 5.3% Ni stainless steels containing increasing amounts of Mn (upto 13.9%) are compared with those of an 18/8 stainless steel. All alloyes exhibit an initial step for the dissolution of Fe. A second arrest is recorded in dilute acid solutions and/or when applying high currents, and is related to the oxidation of the Cr. With an alloy containing traces of N₂, a third arrest is observed in dilute acid solutions; it is attributed to the oxidation of Cr₂N. The incorporation of Mn in CrNi steels is detrimental to their anti-corrosion characteristics. The content of this metal should be kept as low as feasible.     

Design of strip-loaded weak-guiding multimode interferencestructure for an optical router

We introduce a new multimode interference structure that can be used as an integrated optical router. This structure is based on the existence of a first cross state in weakly guiding multimode waveguides. Such a cross image, not expected by the self-imaging technique, is tested by rigorous modal analysis as well as the nonmodal beam propagation method. We show that the quality of this image could be enhanced by strip loading the multimode section of the structure. Making use of this image, we propose a new optical router based on the large nonlinearity associated with the blockaded reservoir and quantum-well electron transfer structure