Thermodynamic Evaluation of the Phase Stability and Microstructural Characterization of a Cast B1914 Superalloy

The boron-carbon superalloys (BC alloys) were developed to reduce the carbon content of the alloys to less than 0.02 wt.% and increase the boron content to 0.1 wt.% in some Ni-based superalloys. In this study, we have used characterization techniques, such as DTA, XRD, SEM coupling, and thermodynamic calculation using Thermo-Calc software, to obtain information about the phase transformation reaction temperatures and the elemental compositions of the microstructural constituents encountered in the B1914 superalloy. The microstructure of the B1914 superalloy was composed of a gamma (γ) phase with a dendritic structure and gamma prime (γ′) phase with a cuboidal shape. Precipitates of γ′ and a lamellar eutectic, composed of γ/(Mo,Cr,Ni)₃B₂, were identified in the interdendritic region. The thermodynamic calculation results have shown to be a valuable tool for predicting the transformation temperature, such as liquidus, γ’ solvus, and incipient melting point. These transformations are important parameters used in casting simulation software for determining the heat treatment and welding repair conditions for parts made from this alloy.     

Electrochemical Evaluation of Corrosion on Borided and Non-borided Steels Immersed in 1 M HCl Solution

In this study the corrosion resistances of AISI 1018 and AISI 304 borided and non-borided steels were estimated using polarization resistance and electrochemical impedance spectroscopy (EIS) techniques. Boriding of the steel samples was conducted using the powder-pack method at 1223 K with 6 h of exposure. Structural examinations of the surfaces of the borided steels showed the presence of a Fe₂B layer with isolated FeB teeth on the AISI 1018 steel, whereas a compact layer of FeB/Fe₂B was formed on the AISI 304 steel. Polarization resistance and EIS of the borided and non-borided steels surfaces were performed in a corrosive solution of 1 M HCl. The EIS data were analyzed during 43 days of exposure to the acid solution. Impedance curves obtained during this period for the borided and non-borided steels were modeled using equivalent electrical circuits. The results of both electrochemical techniques indicated that boride layers formed at the steel surfaces effectively protect the samples from the corrosive effects of HCl. The main corrosion processes observed on the boride layers were pitting and crevice corrosion.     

Sizing methodology for hybrid systems based on multiple renewable power sources integrated to the energy management strategy

This work presents a design methodology for a hybrid energy system based on multiple renewable power sources and bioethanol. The new concept of generation consists on having multiple power sources such as a PEM fuel cell system fed by the hydrogen produced by a bioethanol reformer and wind-solar sources working all together supervised by the energy management system. The necessary heating for the bioethanol reforming reaction can be provided by the renewable sources to enhance the efficiency of the hydrogen production. It is worth noting that, from the power balance as well as backup point of views, the hybrid system is equipped with energy storage devices. An optimal sizing methodology integrated with the energy management strategy is proposed here for designing the overall hybrid system. The suggested approach is based on genetic algorithms, using historical climate data and load demands over a period of one year. Several simulation results are given to show the methodology performance in terms of loss of power supply probability (LPSP), costs and bioethanol consumption.     

Antioxidant protection of high-pressure processed minced chicken meat by industrial tomato products

Pressure-treatment at 300 MPa of minced chicken breast meat did not induce significant lipid oxidation during chill storage for up to 15 days, while pressure-treatment at 600 and 800 MPa enhanced formation of secondary lipid oxidation products measured as thiobarbituric acid reactive substances. However, a waste product from industrial tomato paste production was found to yield efficient protection against lipid oxidation in pressurized chicken meat. Addition of 0.30% tomato waste or of 0.10% final tomato paste to minced meat led to a lag phase of 6 days for formation of secondary oxidation products in meat pressure treated at 600 MPa. The waste product seemed special efficient in protecting chicken meat pressurized at 800 MPa, as a notably lower rate of formation of secondary oxidation products was found. Flavonoids washed out with the waste fraction may be more efficient as antioxidant than the other phenolics or carotenoids present in the other paste processing fractions. Addition of tomato paste fractions did not influence radical formation measured by electron spin resonance spectroscopy and the tomato waste is considered to be effective as antioxidant at subsequent reactions leading to secondary lipid oxidation products.     

Juice from king palm (Archontophoenix alexandrae) leaf sheathes: chemical characterisation and use in soft drink formulation

The heart of palm is a food extracted from several species of palm trees. Only 10–20% of the raw material is transformed into canned hearts of palm, therefore this agro‐industry generates a large quantity of solid residue. The aim of this work was to extract and characterise a juice produced from this solid residue. This extract is compared with the traditional fruit juices (orange and pineapple juices), obtaining higher contents of minerals, such as magnesium (22.80 mg/100 g) and potassium (276.90 mg/100 g), phenolic compounds (gallic, 3,4‐dihydroxybenzoic, chlorogenic, syringic and caffeic acids) and high free radical scavenging capacity (expressed as 2,2‐diphenyl‐1‐picrylhydrazyl), which suggest high antioxidant activity. Additionally, a new soft drink was formulated using this king palm juice as its main ingredient. The soft drink samples formulated with this juice had high sensory acceptability and high intention of consumption, which suggests an important and low‐cost application for this industrial residue.     

The mineral phase quantification of vermiculite and interstratified clay minerals-containing ores by X-ray diffraction and Rietveld method after K cation exchange

Hydrothermal transformations and weathering are important mineralizing processes in carbonatite-related ores. But the transformation products of mafic minerals, such as the clay minerals, vermiculite and interstratified phases, preclude the use of X-ray diffraction, particularly the Rietveld method, for mineral phase quantification. After treatment with KCl, vermiculite and interstratified phases (all peaks roughly at 1.2, 1.4-1.5 and 2.4 nm) are converted to a phlogopite-like structure with d(0 0 1) = 1.0 nm, which can successfully be refined. The method was tested using three carbonatite-derived ores, with a total phlogopite-like phase content ranging from 1.2 to 32.3 wt.%. Comparison of the chemical analyses with the calculated chemical composition, based on the phase quantification and the mineral composition is in good agreement for major elements, such as Si, Fe and Al. For P results were also very good, but Ti and Nb are generally underestimated, and Ba is overestimated. Minerals with lower contents, as pyrochlore, approach the diffraction detection limit. Problems to accurately determine mineral composition for some of the phases also impacts on the reconciliation. The chemical composition of the pyrochlore group minerals changed, but not to an extent to constrain the usefulness of the technique. Cation exchange successfully extended the amenability of the Rietveld method for phase quantification.     

Statistical treatment of misalignments in particle accelerators

To know how much misalignment is tolerable for a particle accelerator is an important input for the design of these machines. In particle accelerators the beam must be guided and focused using bending magnets and magnetic lenses, respectively. The alignment of the lenses along a transport line aims to ensure that the beam passes through their optical axes and represents a critical point in the assembly of the machine. There are more and more accelerators in the world, many of which are very small machines. Because the existing literature and programs are mostly targeted for large machines, in this work we describe a method suitable for small machines. This method consists in determining statistically the alignment tolerance in a set of lenses. Differently from the methods used in standard simulation codes for particle accelerators, the statistical method we propose makes it possible to evaluate particle losses as a function of the alignment accuracy of the optical elements in a transport line. Results for 100 keV electrons, on the 3.5-m long conforming beam stage of the IFUSP Microtron are presented as an example of use.     

Solid state NMR study of poly(methyl methacrylate)/polyvinylpyrrolidone blends

The behaviour of poly(methyl methacrylate)/polyvinylpyrrolidone (PNMA/PVP) blends was investigated by solid state nuclear magnetic resonance (NMR) using proton spin-lattice relaxation time in the rotating frame (T1^Hρ), which was measured from the variable contact time experiment. From T1^Hρ relaxation measurements scale, it was possible to obtain a response of the degree of intimacy mixture of polymer blend components. Good compatibility was observed for all proportions studied, as a consequence of the interaction process of blends components. Received: 18 February 1998/Revised version: 25 May 1998/Accepted: 10 June 1998     

Assessment of production efficiency,physicochemical properties and storage stability of spray-dried propolis,a natural food additive,using gum Arabic and OSA starch-based carrier systems

The aim of this work was to obtain propolis in a powder, alcohol-free, water-dispersed and shelf-stable form. Propolis extract was spray-dried using gum Arabic and octenyl succinic anhydride (OSA) starch as carriers in two different weight ratios (1:4 and 1:6). Spray-dried propolis samples were evaluated for morphology, moisture, water activity, water dispersibility, hygroscopicity, particle size, particle distribution, entrapping efficiency, stability, isotherms and antioxidant properties. The spray-drying process produced round particles with sizes ranging from 15 to 24 μm. This process preserved the antioxidant activity of propolis and also allowed propolis to be obtained in a powder form, which was stable during storage at room temperature, had low hygroscopicity and was highly dispersible in cold water. The application of this technology could increase the use of propolis in various industrial applications, such as an antimicrobial and as an antioxidant in food.     

Nucleation with Simultaneous Chemical Reaction in the Vapor-Phase Synthesis of AlN Ultrafine Powders

Using the classical (one-component) homogeneous nucleation theory approach of a constrained equilibrium distribution of sub- critical particles, a nucleation equation that considers the effect of heterogeneous reaction is derived for the AlN system. In the absence of more detailed information about the aluminum nitride (AlN) reaction kinetics, a simplified surface reaction model is formulated. Clusters, which can be formed by AlN and pure Al, are assumed to grow from the condensation of Al vapor followed by surface reaction between condensed Al and absorbed NH₃. The composition of any subcritical particle is assumed to be determined by the rates at which Al and AlN species are added to their surface and thus made entirely dependent upon local gas concentrations. This assumption resulted in important simplifications that allowed this development to be cast in a form resembling the one used by the classical theory for one-species nucleation. An analysis intended to evaluate the dependence of this nucleation equation on temperature, concentration of reacting species, and degree of aluminum supersaturation is presented. Considerable changes of the nucleation rate were observed between low and high concentration ratio of reacting species. These changes are directly related to the changes of the surface energy and bulk free energy terms determined as a function of the free-Al content in a nucleus.