This paper presents the results of a study on carbothermal reduction of iron ore made under the microwave field in equipment specially developed for this purpose. The equipment allows the control of radiated and reflected microwave power, and therefore measures the microwave energy actually applied to the load in the reduction process. It also allows performing energy balances and determining the reaction rate with high levels of confidence by simultaneously measuring temperature and mass of the material upon reduction with high reproducibility. We used a microwave generator of 2.45 GHz with variable power up to 3000 W. Self‐reducing pellets under argon atmosphere, containing iron ore and petroleum coke, with 3.5 g of mass and 15 mm of diameter were declined. We obtained the kinetic curves of reduction of iron ore and of energy consumption to the process in the maximum electric field, in the maximum magnetic field and at different values of power/mass. The data allow analyzing how the microwave energy was actually consumed in the reduction of ore. 相似文献
The main goal of the present research effort was to evaluate the physical-chemical properties of blends of lard and soybean oil following enzymatic interesterification catalyzed by an immobilized lipase from Thermomyces lanuginosa (Lipozyme™ TL IM). Lipase-catalyzed interesterification produced new triacylglycerols that changed the physical-chemical properties of the fat blends under study. Solid fat content (31.3 vs 31.5 g/100 g), consistency (104.7 vs 167.6 kPa), crystallized area (0.6 vs 11.8) and softening point (31.8 vs 32.2 °C) of lard increased after interesterification, and this was mostly due to the increase of SSS (saturated) + SSU (disaturated-monounsaturated) triacylglycerols. These contents (SSU + SSS) increased in lard after interesterification from 42.9 to 46.7 g/100 g. The interesterified blends exhibited lower values for the physical properties when compared with their counterparts before enzymatic interesterification. The interesterification of blends of lard with soybean oil increased the amounts of UUU (triunsaturated) and SSS triacylglycerols and reduced the amounts of UUS (diunsaturated-monosaturated) triacylglycerols. The interesterified blends of lard and soybean oil demonstrated physical properties and chemical composition similar to human milk fat and they could be used for the production of a human milk fat substitute. 相似文献
Catechin and epicatechin are important phenolic compounds found mainly in tea leaves, cocoa beans, and in the peels and seeds of fruits. The reliable detection of these compounds by spectrophotometry is limited by the interference with substances that absorb light at similar wavelengths; thus, an effective alternative is to detect the oxidation products of these compounds at more specific wavelengths. This study aimed to develop an analytical method to quantify total catechin and epicatechin in some food samples (cocoa beans, guarana powder, apples, and tea leaves) by enzymatic oxidation with tyrosinase. The samples were extracted in an ultrasonic bath and the purified extracts were oxidized with tyrosinase solution. The quinones formed in the reaction were detected by spectrophotometry. The method was selective and presented linearity between 1.21 and 7.26 mg g?1, limit of detection of 0.48 mg g?1, and limit of quantification of 1.61 mg g?1. The accuracy of the proposed method was reasonable, with recoveries between 84.3 and 90.7% in the fortified matrices. High precision was observed, with low coefficients of variation for repeatability (3.17 to 3.68%) and intermediate precision (3.27%). In cocoa beans, the total catechin and epicatechin level was 1.65 mg g?1 (3.58 mg g?1). The successful application of the method was also demonstrated in guarana powder. Therefore, the method can be applicable for spectrophotometric analysis of catechin and epicatechin in samples containing above 1.61 mg g?1 of these compounds. 相似文献
In the present study, Nb-stabilized ferritic stainless steel was prepared with annealing (430-A) and without annealing (430-NA) annealing, and the microstructure of the resulting samples was examined. The steel was then subjected to cold rolling and isothermal annealing in order to analyze its recrystallization kinetics and texture evolution. Microstructural characterization was performed by scanning and transmission electron microscopies. Recrystallization kinetics were evaluated by measuring the microhardness of the samples, and analyzing their kernel average misorientation and grain orientation spread via electron backscatter diffraction. The Avrami exponent data revealed that one-dimensional grain growth occurred owing to the migration of high-angle grain boundaries. The mean activation energies for recrystallization for 430-NA and 430-A was found to be 365 and 419 kJ mol−1, respectively. The recrystallization texture was influenced by oriented nucleation and selected growth mechanisms, as well as by the Nb carbonitride distribution and grain boundary energy. The recrystallized and growing grains with the {554}〈225〉 orientation showed a dimensional advantage over the other recrystallized components. The coincident site lattice boundaries were attributed to the progression of recrystallization since the CSL numeric fraction increased as the temperature increased. The {554}〈225〉 component was associated with the ∑19a boundary, which exerted a significant control on the selective growth during the recrystallization.
This paper discusses the massive colonization plan and settlement scheme implemented in the early 1970s by the Brazilian government as part of the development of the Amazonian territory, and accounts for some of the reasons for its failure. Building on the notion that the Amazonian settlement scheme had taken a mid-twentieth-century private-colonization enterprise in northern-Paraná state as a planning model, this paper reveals that they were both grounded in garden-city repertoire; particularly the ideas of decentralization, satellite towns, and the marriage of town and country. However, unlike its model, the Amazonian settlement scheme failed badly. The adaptations made to the model and the innovations of the new scheme will also be identified. 相似文献
The in vitro fermentability of two resistant starch preparations type 2 (RS2) and type 3 (RS3) was investigated using human colonic microbiota. Prior to the fermentation experiments, samples were digested using two in vitro models, a batch (ba) and a dynamic (dy), as well as an in vivo method (il) for RS3. Digestion residues were fermented in vitro using a simple batch model lasting 24 h and a more sophisticated dynamic model enduring 72 h. During batch fermentation, metabolite productions and starch degradation rates were similar for RS2 and RS3 but higher for dy- compared to ba-digested samples. RS3il led to the lowest fermentability. Furthermore, increased butyrate ratios were observed for all preparations. The varying RS preparations behaved similarly in the dynamic fermentation but showed high SDs. Moreover, the fermentability was slow during the first 24 h, indicating that the microbiota needed an adaptation period to ferment RS. Propionate ratios increased at the expense of butyrate with exception for RS2dy showing an increase in acetate only. Differences in fermentability observed between the dynamic model, allowing a closer simulation of the in vivo behavior, and the batch model, recommended for screening purposes, could be due to the varying microbiota used. 相似文献
In order to reduce the total number of experiments for achieving the best conditions for Cr(VI) uptake using Araucaria angustifolia (named pinh?o) wastes as a biosorbent, three statistical design of experiments were carried out. A full 2(4) factorial design with two blocks and two central points (20 experiments) was experimented (pH, initial metallic ion concentration-C(o), biosorbent concentration-X and time of contact-t), showing that all the factors were significant; besides, several interactions among the factors were also significant. These results led to the performance of a Box-Behnken surface analysis design with three factors (X, C(o) and t) and three central points and just one block (15 experiments). The performance of these two statistical designs of experiments led to the best conditions for Cr(VI) biosorption on the pinh?o wastes using a batch system, where: pH 2.0; C(o) = 1200 mg l(-1) Cr(VI); X = 1.5 g l(-1) of biosorbent; t = 8 h. The maximum Cr(VI) uptake in these conditions was 125 mg g(-1). After evaluating the best Cr(VI) biosorption conditions on pinh?o wastes, a new Box-Behnken surface analysis design was employed in order to verify the effects of three concomitant ions (Cl(-), NO(3)(-) and PO(4)(3-)) on the biosorption of Cr(VI) as a dichromate on the biosorbent (15 experiments). These results showed that the tested anions did not show any significant effect on the Cr(VI) uptake by pinh?o wastes. In order to evaluate the pinh?o wastes as a biosorbent in dynamic system, a glass column was fulfilled with pinh?o wastes (4.00 g) as biosorbent, and it was fed with 25.0 mg l(-1) Cr(VI) at pH 2.0 and 2.5 ml min(-1). The breakpoint was attained when concentrations of effluent of the column attained the value of 0.05 mg l(-1) Cr(VI) using 5550 ml of the metallic ion solution. In these conditions, the biosorbent was able to remove completely Cr(VI) from aqueous solution with a ratio of Cr(VI) effluent volume/biosorbent volume of 252.3. 相似文献