Procedia Materials Science最新文献

In the production process for producing recycled pulp cellulose, there are waste generated by the raw material entering the system. This residue is separated from the pulp by physical methods, and is mainly composed of plastics, paper, laminated papers and other materials in smaller proportions.

In order to recycle this waste, in this paper we analyze the viability of use in the production of insulated panels.

With the untreated residue extracted from the plant, panels of 30 cm side and thickness of approximately 6 cm were made. On these panels, parameters such as density and compression strength were evaluated for the study of the homogeneity of the material obtained.

The corrosion protection offered by coatings of hexagonal Sr ferrites on steel samples in the presence of chloride was evaluated by electrochemical techniques. Different samples were prepared using Nd-Co doped and un-doped strontium hexaferrite coatings, and tested in sodium chloride (NaCl) solutions during 45 days. Time variation of the corrosion potential and polarization resistance measurements were carried out for each of the tested steel samples at different immersion times. All the samples were characterized by scanning electronic microscopy and energy dispersive X-ray analysis (SEM/EDX).

All the tested ferrite coatings offered good protection and corrosion resistance, which increased as the samples remained immersed in the chloride solution. When a concentrated NaCl solution was employed as corrosive agent, the coatings continued offering protection and the currents increased one order of magnitude, while remaining constant with the variation of the immersion time. The samples coated with doped ferrite showed the highest resistance to the aggressive environment, with low corrosion rates even after 48 hours of immersion in NaCl 0.5 M.

This paper presents results corresponding to the densification of WC-Fe composites. Commercial WC (4NPO H.C. Starck) was mixed with iron (Fe) added from a precursor obtained via sol-gel route. Results of the kinetics of phase formation in materials obtained via this sol-gel route, which involves several precursors of W, Fe and C, plus the addition of colloidal alumina (Al₂O₃) are also reported. Samples with different concentrations of Fe were studied using a vertical dilatometer up to 1230 °C with 10% H₂-Ar gas flow up to 800 °C, and then in vacuum of 30mTorr until the final temperature. Densification is discussed in terms of kinetics analysis of selected experimental data to identify the different mechanisms involved. These samples were subjected to X-ray diffraction to identify the resulting phases, where WC and W were the main phases. On the other hand, samples prepared from a sol-gel route containing Fe and alumina were treated under an atmosphere of 10% H₂-Ar, in order to analyze the transformations produced in the temperature range 500 to 800 °C. XRD studies indicated the formation of different phases, such as WC (of primary interest), and the subcarbide M₆C type: W₃Fe₃C, among others. The analysis of all diffractograms indicates the evolution of the system as a function of temperature, leading first to oxidation (formation of FeWO₄) and reductions (formation of Fe) in the system. Simultaneous mass losses of this system are shown in the same range of 500-800 °C.

Shank adapters or start bars are slim parts of hardened steel used in rock drilling hammers for the mining industry. This extreme type of work occasionally generates premature failures to the bar because of the heavy-duty working conditions.

In the present case, we will analyze the study of a bar, which has fractured suddenly and prematurely near the center of the piece. We are looking for an accurate method to detect the causes responsible for the problem applying the Scientific Method as a strategic tool to perform each of the steps in an orderly manner, without risking possible solutions prematurely or discarding hypotheses that seem unlikely at first sight.

It has been performed a detailed study including part design, material, and working conditions, considering all possible combinations of cause and effect that may influence the final result, and considering the same using a Pareto analysis.

Methodical

analysis is supported by actual experience through performance of mechanical tests, computer simulation of stress and fracture analysis through macroscopy and optical microscopy. From the results obtained, it was found that to suit the type of material used by the manufacturer, the adjustment of the variables in the heat treatment and certain geometric details in the construction of parts are essential to achieve the desired results, optimizing perforation work.

Eddy currents non destructive testing is a well known method for material characterization, which is sensitive to different properties of conductive materials, such as: electrical conductivity, magnetic permeability, phase proportions, hardness, size, discontinuities, etc. These properties alter the flow of the currents induced in the sample under test by an AC magnetic field. One of the most common applications of the method is the evaluation of electrical conductivity, by a procedure that requires at least two reference standards, and is not valid for very thin samples (less than 1 mm, roughly). In this paper a variation of that procedure is proposed, in which only one reference standard is needed. The procedure allows for the evaluation of conductivities in the range 0.9 - 59 MS/m on planar samples with thickness greater than 30 μm.

The crevice corrosion repassivation potential was determined by the Potentiodynamic–Galvanostatic-Potentiodynamic (PD–GS–PD) method. Alloys 625, C–22, C–22HS and HYBRID–BC1 were used. Specimens contained 24 artificially creviced spots formed by a ceramic washer (crevice former) wrapped with a PTFE tape. Crevice corrosion tests were performed in 0.1 mol/L and 1 mol/L NaCl solutions at temperatures between 20 and 90 °C, and CaCl₂ 5 mol/L solution at temperatures between 20 and 117 °C. The crevice corrosion resistance of the alloys increased in the following order: 625 < C–22 < C–22HS < HYBRID–BC1. The repassivation potential (E_CO) showed the following relationship with temperature (T) and chloride concentration ([Cl⁻]) E_CO = (a + b T) log [Cl⁻] + c T + d; where a, b, c and d are constants. At temperatures above 90 °C, E_CO for alloy 625 stabilized at a minimum value of –0.26 V_SCE.

In order to improve adsorptive properties and provide a viable alternative to humidity control techniques, the desiccants can be modified with chemical aggregates such as calcium chloride (CaCl₂), the latter often used as dehydrating due to its hygroscopicity and low cost. Its use as a drying agent has disadvantages because of its particles form a liquid film. However, the CaCl₂ may be mixed with other materials for preparing desiccant products. In this work we studied, at 298 K and different relative humidities (RH), the adsorption processes of desiccants mixtures composed of a bentonite clay Argentinian and CaCl₂. The results showed a better performance of the desiccant mixture with respect to natural clay in the whole HR working range. It was also observed that addition of CaCl₂ favors adsorptive properties with respect to a purification treatment.

A new photoluminescence material cadmium [(1,10-phenanthroline)(8-hydroxyquinoline)] Cd(Phen)q has been synthesized and characterized. The prepared material Cd(Phen)q was characterized by Fourier-infrared spectroscopy(FTIR),Nuclear magnetic resonance spectroscopy (NMR),Thermo gravimetric analysis (TGA), UV-visible spectroscopy and photoluminescence (PL). Solution of this material Cd(Phen)q in toluene showed absorption maxima at 256 nm and 295 nm which may be attributed to the moderate energy (π – π*) transitions of the aromatic rings while absorption maxima at 335 nm and 387 nm observed were due to the coordination of cadmium and organic ligands (Phen and q). The photoluminescence spectrum of Cd(Phen)q in toluene solution showed peak at 510 nm. This material is thermally stable up to 400⁰C. The time resolved photoluminescence spectra of this material Cd(Phen)q showed two life time components, 3.8 ns and 15 ns respectively.

It is the need of time to ensure the safe operation of compressed natural gas (CNG) cylinders under adverse conditions; the extremities should be predicted under which these cylinders continue to operate without failing. A comprehensive modelling approach in order to predict the behavior and failure of CNG cylinders under various loading conditions has been proposed using Finite Element (FE) Software-ANSYS. In the present investigation two different materials viz. glass/epoxy and carbon/epoxy are used separately and in combination with different patterns of helical and hoop windings, for outer reinforced layers of all composite gas cylinder. Cloud diagram of stress and strain under operating pressure, test pressure and burst pressure are obtained and discussed in detail. The material of the innermost layer of the cylinder i.e. liner should be selected reasonably as it serves as the gas permeation barrier.

Composite materials obtained by adding particles to the metallic matrix (MMCs) have made remarkable progress in its development and applications in automotive and aerospace industries in recent decades. Among them the most current application is MMCs with zinc and aluminum matrix. The present work is focused on the study of the effect of the directional heat extraction on the alumina distribution inside the zinc-aluminum matrix and on the columnar – to – equiaxed (CET) phenomenon in samples directionally solidified. The ZA-27 alloy was reinforced with ceramic-particulates of alumina (Al₂O₃) and then vertically directionally solidified. The following parameters were measured: cooling rates, temperature gradients, interphase velocities. And the influence of heat transfer on the solidification microstructure of the MMCs was analyzed. Experimental results include transient metal/mould heat transfer coefficients, secondary dendrite arm spacings and particle distribution as a function of solidification conditions imposed by the metal/mould system. The results about the conditions for the CET in MMCs are compared with those obtained in directional solidification of Zn-Al alloys.