A mixture of orange vesicle flour, commercial nixtamalized corn flour and potato starch was extruded using a Brabender Laboratory single screw extruder (2:1 L/D). The resulting pellets were expanded by microwaves. Expansion index, bulk density, penetration force, carotenoid content, and dietary fiber were measured for this third-generation snack and optimum production conditions were estimated. Response surface methodology was applied using a central composite rotatable experimental design to evaluate the effect of moisture content and extrusion temperature. Temperature mainly affected the expansion index, bulk density and penetration force, while carotenoids content was affected by moisture content. Surface overlap was used to identify optimum processing conditions: temperature: 128-130°C; moisture content: 22-24 %. Insoluble dietary fiber decreased and soluble dietary fiber increased after extrusion.
A diffusion model was suggested to analyse the growth kinetics of Fe 2 B layers formed on AISI D2 steel by the pack-boriding process. It was used to estimate the boron diffusion coefficients of Fe 2 B in the temperature range of 1123-1273 K by applying the mass balance equation at the (Fe 2 B/ substrate) interface. The proposed model was validated experimentally at 1253 K for a treatment time of 5 h by comparing the experimental Fe 2 B layer thickness with the predicted value. Furthermore, the pack-borided AISI D2 steel was characterised by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis. A contour diagram describing the evolution of Fe 2 B layer thickness as a function of the process variables was also proposed. In addition, the boron activation energy for AISI D2 steel was found to be equal to 201?50 kJ mol 21 , on the basis of our experimental results.
This work shows the physicochemical behavior of two different diatoms from the country of Mexico (State of Jalisco and Hidalgo) with similar compositions. These were used to eliminate toxic cations from a synthetic solution containing 5.270 mg As 3+ /L; 4.280 mg Ag + /L; 3.950 mgNi 2+ /L; 4.090 mg Cr 6+ /L; and 4.081 mg Pb 2+ /L. These diatoms were used as filters, and the quantity of cations remaining in the solution after filtering was measured. According to the most important results found, for the recovery of metals, both minerals achieved arsenic, silver, lead, and nickel recoveries up to 95%, and lower than 10% for chromium. This could be due to the absence of an environment to reduce Cr 6+ to Cr 3+ . On the other hand, it was observed that there was no selectivity during the recovery of the other cations present in the solution. According to efficiency of interchange, the mineral from Hidalgo is slightly better than the mineral from Jalisco for the removal of arsenic, lead, and silver. For nickel, and particularly Cr 6+ , the efficiency is higher for the sample from Jalisco.
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