Search

Crystalline CuCexFe2-xO4 nanoparticles with different rare earth metal content (x = 0.00, 0.03, 0.05, 0.08 and 0.10) were synthesized using a co-precipitation technique that involves a 600 °C calcination treatment. The newly obtained powders were pressed into pellets and heated up to 950 °C in order to form a compact and less porous material, ideal for dielectric measurements. X-ray investigations revealed a structural modification from typical cubic system to a tetrahedral spinel form, accompanied by Ce3+ cations exclusion and formation of secondary phases. The amount of phases and cations distribution were determined by Rietveld refinement method. A degradation process of cerium doped copper ferrite was proposed based on X-ray analysis and Rietveld refinement. Furthermore, the magnetic behavior of both 600 °C and 950 °C samples was investigated from the hysteresis loops recorded from a vibrating sample magnetometer (VSM) in a ±10 kOe range. Room temperature dielectric values for the 950 °C samples were determined using the parallel-plate capacitor configuration in a frequency range of 10 Hz – 1 MHz.

Beside metallic biomaterials there is increasing interest in using degradable materials in a high number of applications. Zinc-based materials are a solution for biodegradable applications based on their mechanical and chemical properties. The experimental alloy ZnMg-Ca was obtained in an air-controlled atmosphere furnace after five re-melting operations. The material was in vitro analyzed from a corrosion resistance point of view. The experiments were realized by linear polarization (LP) and cyclic polarization (CP). Material surfaces before and after corrosion tests were analyzed through scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX).

A commercial Fe-C material (P265GH) used for natural gas delivery and transportation systems was analyzed in H2S atmosphere in order to establish the corrosion resistance. In most of the industrial processes for gas purification the corrosion rate is speed up by the presence of sulphur (S) especially as ions (HS-, SO32−) or different species like H2S. The H2S (hydrogen sulphide) is, beside a very toxic compound, a very active element in the acceleration of metallic materials deterioration. For experiments we used a three electrodes cell with Na2SO4 + Na2S solution at pH 3 for two different temperatures, room temperature ∼ 25 °C (sample 1) and at 60 (sample 2) ±1 °C in order to realize EIS (electrochemical impedance spectroscopy) and potentiodynamic polarization. After electro-chemical tests and corrosion resistance characterisation the material surface was analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS).

High damping capacity materials present an increased interest in many applications were vibration and noise reduction is absolutely necessary. Metallic materials with a high internal friction (IF) are becoming valuable because of them usual mechanical properties that fulfill the damping capacity in applications. Some of the shape memory alloys present a huge damping capacity during the solid state transformation (M↔A) based on the re-orientation and accommodation of the material structure. Iron based shape memory alloy present the best advantages for industrial application as dumpers in different areas. Beside civil construction domain these materials can cover also applications in automotive industry as shock impact absorbers for low velocities as protection for engine parts and also for noise reduction. By these means in this article we analyze FeMnSi+Al alloy with a new chemical composition obtained through classical melting method in Ar controlled atmosphere.

New requests from the automotive industry suppose to apply new materials with mechanical resistance to heat and vibrations and also with low weight. In order to replace plastic materials with high damping capacity a viable solution can be the metallic materials with sufficient internal friction to transform the external mechanical energy in thermal energy without affecting the microstructure or the mechanical properties of the metallic materials. In automotive applications an important role, especially in low velocity impacts, are the bumper elements. In this article possibility of copper-based shape memory alloys to fulfill the damping necessity of metallic materials is analyzed. Dynamic - mechanical analyze of few copper based shape memory alloys is realized and the results compared to proposed a better solution of Cu-based shape memory alloy for damping materials applications. The damping capacity difference between martensite and austenite like phases is also analyzed.

In vitro electrochemical characterization and in vivo implantation in an animal model were employed to evaluate the degradation behavior and the biological activity of FeMnSi and FeMnSiCa alloys obtained using UltraCast (Ar atmosphere) melting. Electrochemical characterization was based on open circuit potential measurement, electrochemical impedance spectroscopy and potentiodynamic polarization techniques while the alloys were immersed in Ringer’s solution at 37 ºC for 7 days. Higher corrosion rates were measured for the Ca-containing material, resulting from inefficient passivation of the metal surface by oxy-hydroxide products. In vivo osseointegration was investigated on a tibia implant model in rabbits by referring to a standard control (AISI 316L) stainless steel using standard biochemical, histological and radiological methods of investigation. Changes in the biochemical parameters were related to the main stages of the bone fracture repair, whereas implantation of the alloys in rabbit’s tibia provided the necessary mechanical support to the injured bone area and facilitated the growth of the newly connective tissue, as well as osteoid formation and mineralization, as revealed by computed tomography reconstructed images and validated by the bone morphometric indices. The present study highlighted that the FeMnSiCa alloy promotes better osteoinduction and osseointegration processes when compared to the base FeMnSi alloy or with AISI 316L, and in vivo degradation rates correlate well with corrosion resistance measurements in Ringer’s solution.

A biodegradable iron based alloy was obtained through classical melting method using a furnace with controlled atmosphere. The metallic material was obtained from high purity materials using a proper obtaining method. The material is proposed as an alternative to magnesium alloys that have a very fast degradation period for applications with longer healing periods (more than 3 and between 12 to 18 months). The material was analyzed using scanning electron microscopy (SEM) and X-ray dispersive energy analyze EDAX, before and after implantation to observe the influence of the human medium on the metallic implant. Both implantation areas (subcutaneous and in bone) indicate reactions with the biological environment as compounds form on the surface or with loss of metallic material. Bio-chemistry of Ca, P and Mg of the implanted subjects was realized for subcutaneous and in bone implantation comparing with the results of a Zr implant behavior. In vivo experiment on Wistar rats highlight a very good bio-compatibility of the subcutaneous implant by the absence of any kind of local reaction or toxic systemic fact, which is explained by slow degradation of FeMnSi alloy and the metabolism of resulted products in conditions of maintaining organism homeostasis.

The class of biomaterials (metallic, polymer or ceramics) has applications as implants with a temporary function. Among magnezium (high corrosion rate) and iron (slow corrosion rate) based biodegradable alloys a new class based on zinc try to fullfill the gap between the first two alloy systems concerning the degradation rate. The role of these alloys is to provide some specific characteristics for a limited period of time. In this article preliminary results based on microstructural and chemical characteristics of a Zn-Mg alloy are presented. The results were obtained using optical and electronic microscopy (MO and SEM) and dispersive energy spectroscpy (EDS) and X-ray difraction (XRD).

Biodegradable alloys are very attractive biomaterials. Electrochemical impedance spectroscopy (EIS) and linear potentiodynamic polarization (LPP) techniques were used for the study of the electrochemical behavior of uncoated FeMnSi and coated FeMnSi with hydroxyapatite + zirconia (HA-ZrO2) through pulsed laser deposition (PLD) technique. Experiments were carried out using Hank’s balanced salt solution (HBSS). It has been shown that in HBSS the impedance for uncoated FeMnSi was mainly characterized by one capacitive effect, which related to the alloy charge transfer control. The charge transfer resistance increases for HA-ZrO2-coated FeMnSi alloy. The equivalent circuits simulating the electrochemical behavior of both uncoated and HA-ZrO2-coated FeMnSi alloys in HBSS were proposed. From LPP the corrosion resistance was evaluated by means of the zero current potential (ZCP) and corrosion current density (jcorr). The surface morphology of both uncoated and HA-coated FeMnSi alloys in HBSS obtained after LPP was studied using scanning electron microscopy (SEM).

Some metallic materials exhibit good damping capacity of mechanical energy into thermal energy. This property along with the others metallic characteristics make this materials interesting for a big number of applications. These materials can be used as bumpers in different applications including automotive field. Beside grey cast iron and shape memory alloys few new metallic materials are presented for the supposition of high damping capacity. We analyze the causes that increase the internal friction of some metallic materials and possibilities to enhance this property through different mechanical, physical or chemical methods. Shape memory alloys, especially those based on copper, present a different damping capacity on martensite, austenite or transition state. In the transformation range M ↔A, which in case of copper base shape memory alloys is quite large, the metallic intelligent materials present a high internal friction, almost comparable with natural rubber behavior that can transform mechanical energy into thermal energy till a certain value of the external solicitation. These materials can be used as noise or small vibrations bumpers or even as shock absorbers in automotive industry.