Surface Nanostructuring of a CuAlBe Shape Memory Alloy Produces a 10.3 ± 0.6 GPa Nanohardness Martensite Microstructure

Severe plastic deformation (SPD) has led to the discovery of ever stronger materials, either by bulk modification or by surface deformation under sliding contact. These processes increase the strength of an alloy through the transformation of the deformation substructure into submicrometric grains or twins. Here, surface SPD was induced by plastic deformation under frictional contact with a spherical tool in a hot rolled CuAlBe-shape memory alloy. This created a microstructure consisting of a few course martensite variants and ultrafine intersecting bands of secondary martensite and/or austenite, increasing the nanohardness of hot-rolled material from 2.6 to 10.3 GPa. In as-cast material the increase was from 2.4 to 5 GPa. The friction coefficient and surface damage were significantly higher in the hot rolled condition. Metallographic evidence showed that hot rolling was not followed by recrystallisation. This means that a remaining dislocation substructure can lock the martensite and impedes back-transformation to austenite. In the as-cast material, a very fine but softer austenite microstructure was found. The observed difference in properties provides an opportunity to fine-tune the process either for optimal wear resistance or for maximum surface hardness. The modified hot-rolled material possesses the highest hardness obtained to date in nanostructured non-ferrous alloys.

Removal of arsenic III and V from laboratory solutions and contaminated groundwater by metallurgical slag through anion-induced precipitation

Metallurgical slag was used for the simultaneous removal of high concentrations of arsenite and arsenate from laboratory solutions and severely contaminated groundwater. Apart from demonstrating the high efficiency of arsenic removal in presence of competing species, the work aims to explore the physicochemical mechanisms of the process by means of microscopy observation and a detailed statistical analysis of existing kinetic and isotherm equations. Fitting was performed by non-linear least squares using weighted residuals; ANOVA and bootstrap methods were used to compare the models. Literature suggests that the metal oxides in the slag are efficient adsorbents of As(III) and (V). However, the low surface area of the slag precludes adsorption; SEM observation provide evidence of a mechanism of co-precipitation of lixiviated cations with contaminant anions. The reaction kinetics provide essential information on the interaction between the contaminants, particularly on the common ion effect in groundwater. The Fritz-Schlünder isotherm allows modelling the saturation effect at low slag doses. The efficiency of the process is demonstrated by an arsenic removal of 99% in groundwater using 4-g slag/L, resulting in an effluent with 0.01 mg As/L, which is below Mexican and international standards for drinking water.

Optimization of the synthesis process of an iron oxide nanocatalyst supported on activated carbon for the inactivation of Ascaris eggs in water using the heterogeneous Fenton-like reaction

An experimental design methodology was used to optimize the synthesis of an iron-supported nanocatalyst as well as the inactivation process of Ascaris eggs (Ae) using this material. A factor screening design was used for identifying the significant experimental factors for nanocatalyst support (supported %Fe, (w/w), temperature and time of calcination) and for the inactivation process called the heterogeneous Fenton-like reaction (H2O2 dose, mass ratio Fe/H2O2, pH and reaction time). The optimization of the significant factors was carried out using a face-centered central composite design. The optimal operating conditions for both processes were estimated with a statistical model and implemented experimentally with five replicates. The predicted value of the Ae inactivation rate was close to the laboratory results. At the optimal operating conditions of the nanocatalyst production and Ae inactivation process, the Ascaris ova showed genomic damage to the point that no cell reparation was possible showing that this advanced oxidation process was highly efficient for inactivating this pathogen.

Inactivation of Ascaris eggs in water using hydrogen peroxide and a Fenton type nanocatalyst (FeOx/C) synthesized by a novel hybrid production process

Inactivation tests of Ascaris eggs (Ae) were performed using hydrogen peroxide and a Fenton type nanocatalyst supported on activated carbon (AC) (FeOx/C). Blank inactivation tests were also carried out using H2O2 and H2O2/AC as oxidation systems. The FeOx/C nanocatalyst was synthesized through a novel hybrid method developed in this work. The method is based on the incipient impregnation technique, using isopropyl alcohol as dissolvent and chelating agent of the iron salt and the ultrasonic method. The supported nanocatalyst contained 2.61% w/w of total iron and the support 0.2% w/w. Transmission electron microscopy (TEM)-energy dispersive spectrometer (EDS) images permitted verification of the presence of finely dispersed FeOx nanoparticles, with sizes ranging from 19 to 63 nm. SEM-EDS analysis and TEM images also showed good dispersion of iron oxide nanoparticles, most probably maghemite; γ-Fe2O3, able to produce hydroperoxyl radical as reported in the literature. The FeOx/C nanocatalyst-H2O2 system showed an average Ae inactivation efficiency of 4.46% Ae/mg H2O2. This value is significantly higher than the result obtained using the support-H2O2 system and H2O2 alone and it is also better than data reported for the classical Fenton process (homogeneous phase) with or without UV light.

Multi-analytical assessment of iron and steel slag characteristics to estimate the removal of metalloids from contaminated water

A multi-analytical approach was used to develop a mathematical regression model to calculate the residual concentration of borate ions in water present at high initial content, as a function of the main physicochemical, mineralogical and electrokinetic characteristics after adsorption on five different types of iron and steel slag. The analytical techniques applied and slag properties obtained in this work were: X-ray Fluorescence for the identification of the main chemical compounds, X-ray Diffraction to determine crystalline phases, physical adsorption of nitrogen for the quantification of textural properties and zeta-potential for electrokinetic measurements of slag particles. Adsorption tests were carried out using the bottle-point technique and a highly concentrated borate solution (700 mg B/L) at pH 10, with a slag dose of 10 g/L. An excellent correlation between the residual concentration of boron and three independent variables (content of magnesium oxide, zeta potential and specific surface area) was established for the five types of slag tested in this work. This shows that the methodology based on a multi-analytical approach is a very strong and useful tool to estimate the performance of iron and steel slag as adsorbent of metalloids.

Optimization of the preparation conditions of ceramic products using drinking water treatment sludges

The aim of this work is to optimize, via Response Surface Methodology, the values of the main process parameters for the production of ceramic products using sludges obtained from drinking water treatment in order to valorise them. In the first experimental stage, sludges were collected from a drinking water treatment plant for characterization. In the second stage, trials were carried out to elaborate thin cross-section specimens and fired bricks following an orthogonal central composite design of experiments with three factors (sludge composition, grain size and firing temperature) and five levels. The optimization parameters (Y(1)=shrinking by firing (%), Y(2)=water absorption (%), Y(3)=density (g/cm(3)) and Y(4)=compressive strength (kg/cm(2))) were determined according to standardized analytical methods. Two distinct physicochemical processes were active during firing at different conditions in the experimental design, preventing the determination of a full response surface, which would allow direct optimization of production parameters. Nevertheless, the temperature range for the production of classical red brick was closely delimitated by the results; above this temperature, a lightweight ceramic with surprisingly high strength was produced, opening possibilities for the valorisation of a product with considerably higher added value than what was originally envisioned.

Primary silver extraction with a high sulphur activated petroleum coke

An extended study was performed to determine the mechanisms that are responsible for the significant silver extraction capacity of activated carbons prepared from a high-sulphur petroleum coke that is available as a waste material from Mexican petroleum refineries. Earlier studies had shown the feasibility of the production of these adsorbents but indicated that the mechanisms of metal adsorption in the present carbons are significantly different from what is classically accepted for commercial carbons. Therefore, selective titration, IR-spectroscopy and scanning electron microscopy of carbons were combined with adsorption experiments and the determination of electrochemical parameters of mixtures of carbon-AgNO3 solution to explain the fundamental reasons for the performance of the obtained carbons. This allowed us to determine the identity of the surface functional groups and to distinguish the effect of different activation processes. The experiments permitted us to explain why these activated carbons, which have a low specific area and lack classical surface functional groups, show such a high silver adsorption capacity.

Scanning electron microscopy observation of the substructural evolution of aluminium alloys during cold rolling and partial annealing

Classical etching techniques for revealing cold deformation and partial recrystallisation in metals have been optimised for optical microscopy, which is limited by its resolution. Detailed studies of the mechanisms involved in recovery and recrystallisation during heat treatment are generally made by transmission electron microscopy. The limitation of this technique, with a few exceptions, is its small field of view and the small fraction of the sample available for inspection. The present article departs from the statement that etching, which is a surface alteration technique, must have effects that are detectable by scanning electron microscope (SEM). It was found that carefully adapted polishing and etching procedures allow for substructural investigations by SEM, resulting in various advantages compared with both optical microscopy and TEM.