Nb-doped BaTiO₃ solid solutions of general formula, BaTi_1−5xNb_4xO₃ prepared by two methods, solid state reaction at 1500 °C and sol–gel synthesis from high purity alkoxide precursors with final heat treatment at 900 °C, form over the range 0 ≤ x ≤ 0.055(5). Permittivity measurements demonstrated the difficulty in obtaining high quality, electrically-homogeneous samples by solid state reaction, even though samples were nominally phase-pure by X-ray powder diffraction. A partial phase diagram has been constructed showing the transitions between tetragonal, cubic and hexagonal polymorphs as a function of composition. Pellets derived from sol–gel samples and sintered at 900 °C were highly insulating, with an activation energy of ∼1.5 eV. Under these firing conditions, there was no evidence of electronic compensation, and semiconductivity, on doping BaTiO₃ with Nb.

In this study, four samples of recycled aggregates from the construction and demolition waste of Mexico City were characterized in order to find innovative uses for these types of materials. Gravel and sand from a recycling plant were analyzed, as well as aggregates produced in the laboratory from demolished concrete collected from landfills. The characterization was carried out by means of XRD (X-ray Diffraction), chemical microanalysis (EDS), X-ray fluorescence (XRF), pH measurement, and sieve analysis. The minerals present in the analyzed materials were feldspars, cristobalite and pyroxene, which corresponded to the natural aggregates, as well as variable amounts of calcite, a product of the carbonation of the cement paste adhered to these aggregates, and in a smaller proportion, calcium hemicarboaluminate, rosenhanite, and tobermorite. The quality (amount of cement) of the original concrete has a great influence on the granulometry and the chemical–mineralogical composition of the aggregates, since there will be different quantities and qualities of the cement paste adhered to the aggregates depending on their size. Finally, the pH values measured in all samples fluctuated between 10.15 and 12.08, suggesting that these materials can be used in soil stabilization or in agricultural applications.

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 As³⁺/L; 4.280 mg Ag⁺/L; 3.950 mgNi²⁺/L; 4.090 mg Cr⁶⁺/L; and 4.081 mg Pb²⁺/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 Cr⁶⁺ to Cr³⁺. 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 Cr⁶⁺, the efficiency is higher for the sample from Jalisco.

A diffusion model was suggested to analyse the growth kinetics of Fe₂B layers formed on AISI D2 steel by the pack-boriding process. It was used to estimate the boron diffusion coefficients of Fe₂B in the temperature range of 1123–1273 K by applying the mass balance equation at the (Fe₂B/substrate) interface. The proposed model was validated experimentally at 1253 K for a treatment time of 5 h by comparing the experimental Fe₂B 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 Fe₂B 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⁻¹, on the basis of our experimental results.

In this work, American Iron and Steel Institute (AISI) O1 steel was pack borided in the temperature range of 1123–1273 K for treatment times between 2 and 8 hours. A kinetic model was proposed for estimating the boron diffusion coefficients through the Fe₂B layers. As a result, the boron activation energy for the AISI O1 steel was estimated as 197·2 kJ mol^− 1. This value of energy was compared to the literature data. In addtion, to extend the validity of the present model, two additional boriding conditions were done. The Fe₂B layers grown on AISI O1 steel were characterised by use of the following experimental techniques: scanning electron microscopy, X-ray diffraction analysis and Daimler-Benz Rockwell-C indentation technique. Finally, the scratch and pin on disc tests for wear resistance were respectively performed using an LG Motion Ltd and a CSM tribometer under dry sliding conditions.