Joaquín Lira-Olivares

Phase relations, microstructure and mechanical properties of VC substituted WC-10Co cemented carbide alloys

Abstract As an effort to investigate a possible extent of substitution of W, the metal from strategic mineral, by a less strategic V, phase relations, microstructure, and hardness and fracture strength, of powder metallurgically processed 90 mass% [(1 − y )WC− y VC]−10 mass% Co alloys are studied. Throughout the composition eight phases, α-Co, β-Co, WC, V 4 C 3 , V 8 C 7 , η 3 (Co 3 W 3 C ), η 6 (Co 6 W 6 C) and graphite C(g), were encountered and a distinct microstructural difference existed across midcomposition. On the basis of combined mechanical properties of hardness and fracture strength the alloys between y = 0.2 and 0.4, which correspond to 18–36 mass % VC, were most promising. Contrary to the antagonistic relations between hardness and toughness commonly encountered in cemented carbides and hard materials, the hardness and fracture strength of the present WC-VC-10Co alloys were nearly parallel.

Influencia de la piezoelectricidad del colágeno tipo I en la adhesión celular

Bone healing and growth are controlled by the rate of deposition of hydroxyapatite (HA). This process have been so far accredited to the work of osteoblasts, which are attracted by the electrical dipoles produced either by piezoelectricity, due to deformation of the bone, specially the collagen in it, or due to outside electrical stimuli. The main purpose of this work was to study the influence of the cortical bone collagen piezoelectricity effect, on the osteoblastic cells orientation. To evaluate the cellular adhesion on the cortical bone collagen subject to deformation, bone cells of newborn calvaria’s rats were extracted. The bone collagen was prepared and deformed following the specifications described in earlier studies. The results of this study shown that the piezoelectric phenomena of bone collagen promotes the cell’s adhesion on the compression side more than tension side compared with undeformed surface. Further studies ascertaining the osteoblastic activity due to the electric field are being advanced.

Influence of the Ball Diameter, Material and Taper Design on Transferred Stresses of Ceramic THR

The brittleness of ceramics has been their weak spot when considering them for total hip replacements. There are several situations from which concentrated stresses can develop and induce failure of the components. It is not a problem of the material’s properties in particular but also its design. This means that even proof tested-third generation-ISO obeying ceramics may fail if the incidence of the design parameters on them is not carefully evaluated. In this paper, the finite element analysis technique is used to show how the change of ball diameter can affect the Vonmises stress on the ball head component when it is subjected to a high (trauma-like) load. The analysis is nonlinear and was carefully tested for convergence. 3D models of four different ball head diameters where constructed, two designs of the bore/cone interface with two sets of material properties (Alumina and Zirconia) were considered. The results from these analyses are given in the form of stress maps on the ball heads; such data may be useful for surgeons, patients, and designers because it shows a direct relationship between two important parameters on ball head design (diameter and bore) and material properties, on the stresses that can cause failure of the component when they are concentrated in small elements of volume.

Electrochemical Influence of Collagen Piezoelectric Effect in Bone Healing

Bone healing and growth are controlled by the rate of deposition of hidroxiapatite (HA). This process have been so far accredited to the work of osteoblasts, which are attracted by the electrical dipoles produced either by piezoelectricity, due to deformation of the bone, specially the collagen in it, or due to outside electrical stimuli. The present work shows that even without osteoblasts present, the piezoelectric dipoles produced by deformed collagen, can produce the precipitation of HA by electrochemical means, without catalyzer as in biomimetic deposition. These findings could clarify the contribution of osteoblasts in bone growth as compared to the electrochemical action by itself. Further studies ascertaining the osteoblastic activity due to the electric field are being advanced.

Synthesis and Characterization of a Porous Silicon Filter with Si3N4 Whiskers

Removal of fine particles from some gas-product effluents from motors and industries, using filters, is an important subject in the field of public health and environment. In the present work, a porous silicon filter was produced, which is able to capture most of the particles undesirable for the environment (transported by gases), larger than the pore diameter (micrometer) of the filter and even smaller size particles. The development of whiskers inside of the pores of the silicon filter, improve its ability to catch smaller particles than the filter’s size pores. Those whiskers are made of Silicon Nitride, produced by a Nitridation process. A different time-temperature schedule for the formation of -silicon nitride (-Si3N4) whiskers by direct Nitridation of the porous silicon filter was studied, in order to optimize the amount of whiskers and improve the filter quality. Four different temperatures (1000, 1100, 1200 and 1300 °C) were selected, each with two different holding times (15 min and 1 hour) for complete Nitridation with N2 and N2+H2 gases. The as-formed whiskers were characterized by SEM, XRD techniques and the process conditions were studied. The filter with the Si3N4 whiskers was characterized evaluating mechanical properties of the porous silicon filter (Micro Hardness and Young Modulus). The permeability measurements were made before and after the Nitridation process. Analysis indicates that the higher Si3N4 whiskers formation temperature was 1300 °C for the gas (N2+H2) phase reaction results from the lower PSiO2/Psio ratio in the Si-N system. Titanium (99% pure) was used with the purpose of reduction of the oxygen partial pressure and the increase of the amount of -silicon nitride whiskers. The porous silicon filter improved its conditions with the silicon nitride whiskers, even though decreases also the fluid permeability measurement. However, it has a smaller flow decrement than filters with smaller porosity. The mechanical properties did not have variation at all, the porosity size increased because of the diffusion of Si to form whiskers in the Nitridation process.

Tribological analysis of Al2O3/TiO2/ZrO2 nanocomposites as an alternative for THR materials

This work studied the microstructure and tribological behavior of Al2O3/TiO2/ZrO2 nanocomposites to be used in hip joint replacements. To increase the fracture toughness of alumina and enhance the tribological properties, nanometer sized particles of TiO2 and ZrO2 were added. The specimens contained 10 mol% of TiO2, different percentages of ZrO2 (0, 2.5, 5, 7.5, 15 and 20 mol %), and alumina as a remainder. Disks were hot pressed at 1500 °C and 25 MPa, in an Argon atmosphere for 1 hour. Given the fact that the sample containing 7.5 mol% of ZrO2 showed the lowest wear volume, it was hot pressed again at 1500, 1400, 1300 and 1200 °C to assess the best temperature condition for sintering. For a composition of 7.5 mol% of ZrO2 the lowest coefficient of friction (0.1-0.3) and the lowest wear volume (0.0046 mm3) were achieved. A direct relation between mechanical and tribological properties was not found. However, these nanocomposites may be considered as a candidate for a new generation of hip joint replacement material.

Mechanical Properties of Al2O3-TiO2-SiC Nanocomposites for the Femoral Head of Hip Joint Replacement

Microstructure and mechanical properties of Al2O3-TiO2-SiC nanocomposites were studied. To improve the mechanical and tribological properties of alumina, nano-sized TiO2 and SiC powders were dispersed. Spark Plasma Sintering (SPS) technique, at 1400°C, 50 MPa for 5 minutes, was applied for the densification of Al2O3-TiO2-SiC nanocomposites. Characterization of Al2O3- TiO2-SiC nanocomposites was carried out using Scanning Electron Microscopy (SEM), Transmission Electron Microscope (TEM), X-ray diffractometer and EDX. Fracture toughness and Vickers hardness were estimated by indentation technique. These experimental results on mechanical properties of Al2O3-TiO2-SiC nanocomposites indicated that they can be a potential material with high hardness and high fracture toughness to be used as femoral head in total hip joint replacement.

Optimization of Sheet Metal Process Parameters of a Shield Case Piece Using Computer Simulation

Numerical simulations based on Finite Element Analysis (FEA) are widely used to predict and evaluate the forming parameters before performing the physical processes. In the sheet metal industry, there are basically two types of FE programs: the inverse (one-step) programs and the incremental programs. In the present paper, the forming process of the shield case piece (LTA260W1-L05) was optimized by performing simulations with both types of software. The main analyzed parameter was the blankholding force while the rest of the parameters were kept constant. The criteria used to determine the optimum value was based on the Forming Limit Diagram (FLD), fracture and wrinkling of the material, thickness distribution, and the principal strains obtained. It was found that the holding force during the forming process deeply affects the results, and a range of values was established in which the process is assumed to give a good quality piece.

Influence of the Cup's Edge Geometry on the Transferred Stresses to the Ball/Cup Interface in all Ceramic THR

Alumina ceramics as well as zirconia ceramics have been used to manufacture hip replacement components since the 1990’s. These materials have been used for the ceramic balls and cups in the replacements for the following reasons: in the case of alumina for its excellent wear behavior; and in the case of zirconia, for its good wear behavior but with greater fracture toughness than alumina. Nevertheless, since ceramics are brittle, the design of the components must consider ways to avoid detrimental stress concentrations. In this study the stress concentration on the rim of the ceramic cup is inspected by means of a two-dimensional axis symmetric finite element model. This model simulates contact between the components to obtain the stresses that are transferred from the ball to the cup. Different geometries of the cup’s edge are simulated to evaluate the incidence of the geometry over the stress pattern. Although this model concentrates on the contact between the ball and the cup, the loading is made from the stem to the ball, which means that the load is transferred from the stem to the ball and then to the cup. This approach may offer a more realistic output. The data from this study may be useful for hip replacement designers as well as for surgeons because it shows a direct relationship between the stress patterns and the geometrical parameters of the design.

An Approach to Legal and Technical Norms to Manage Hazardous Materials and Wastes in Latin America

The Basel Convention (1989) and Rio Summit (1992) were two major instances to tackle with the main issues on Hazardous Waste. The first one is the mechanism to control the illegal traffic of hazardous waste, and to promote an Environmental Sound Management for the overall waste cycle. On the other hand, Rio Summit launched a renewed interest on regulatory environmental instruments for pollution prevention, control and mitigation of environmental damages generated by industrial activities. Among them, one of the major challenges is related to the hazardous waste management. In Latin America, as well as in the rest of the world, the theme has been considered mainly through the environmental regulations, pushing the enterprises to look for different solutions to face the high costs involved in the production processes. In this paper, a comparative assessment was made of the hazardous waste management in four Latin American oil-producing countries. The specific environmental regulations adopted are reviewed, to show the status of present environmental policies and legal measures to promote reuse, recycle, recovering and reduction of hazardous materials and wastes. Coincidential provisions are reported, as well as the differences in the legal approach, which is a clear signal of the efforts made in environmental regulations, trying to control and prevent the pollution generated by industries.