Abstract: Powder metallurgy products may be started from powders with widely varying oxygen affinity. Thus the natural oxygen content of the powder compacts also varies in reducibility in the early stages of sintering. Here it is shown that prealloyed powders containing Cr require higher temperatures for oxygen removal than e.g. unalloyed or Ni-Cu alloyed grades. In case of powder mixes of base iron powder with Cr, Mn or Si, oxygen transfer from Fe to the additive powders may occur during heating up to sintering temperature, the “internal getter effect”. A similar effect can be observed in Cr prealloyed powders in which iron oxides initially present on the powder surfaces are transformed to more stable oxides in a fairly early stage of heating. Finally, also the formation of CH4 observed when sintering alloy steels containing Si, Mn or Cr in H2 can be attributed to an oxygen transfer effect.
Abstract: Multilayered forged steel plates, which combine the properties of diverse steel qualities, are referred to as Damascus steels. Since the 3rd century AD blades and weapons have been produced by the Damascus technique in Europe. In this work four different steel combinations were investigated. Combining Fe with carbon steel C60 resulted in a ferritic-pearlitic microstructure. By forging two heat-treatable steels C40 and C60 martensite with an inhomogeneous carbon distribution was formed. Combining Fe with an austenitic stainless steel showed ferrite and austenite with grain boundary carbides and segregation bands. The last combination of two cold working steels K110 and K600 led to a complex microstructure with martensite, retained austenite and two special types of carbides. After metallographic preparation and using of different etchants the various microstructures were characterized by light optical microscopy and confirmed by Vicker ́s microhardness measurements. Of high interest are the interfaces and the quality of the weld between the individual steel layers. In some regions oxidation and carbon diffusion were observed.
Abstract: The current research represents one section of our studies concerning the improvement of the biocompatibility related to the biocomposite materials for bone grafts application. The submicronic/nanometric hydroxyapatite stands for the progress in biocompatibility. This study highlights the wet mechanical milling process and its effects on the morphological and thermophysical properties of the hydroxyapatite powder particles (30-50µm as raw material) obtained by this method (500 nm average). The scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) facility point out the morphological and chemical compositional features of the processed powders during 10 hours in dry argon atmosphere. The thermal analysis (TA) in argon atmosphere, too, reveals the influence of the milling parameters on the thermal effects generated by the processed hydroxyapatite powders. The experimental results of our research validate some milling mechanisms reported by the literature for wet/dry mechanochemical process conditions.
Abstract: Porous hydroxyapatite (HAp) based biocomposites used in biomedical applications were developed in this paper as artificial bone substitute for vertebrae grafts. The trabecular or spongy bone tissue is an open-cell porous network having 40-90% porosity. In order to obtain a porous structure calcium carbonate and ammonium bicarbonate were added as foaming agents to the biocomposite matrix. The biocomposite matrix was prepared using submicronic powder particles of HAp and titanium hydride powder, which was added as reinforcement’s precursor as well as foaming agent. The aim of this study is to emphasize the effect of the foaming agent additions on the pores morphology by performing analyses at both macro and micro scale. These analyses consist of linear measurements, surface auto-detection and statistics of the pores and optical images as well. The powders mixture was homogenized in a planetary ball mill, uniaxial cold compacted and then heated in argon atmosphere using the two step sintering technique.
Abstract: Designing and processing of the alloplastic bone grafts represent one of the newest trends in bone tissue engineering, solving a lot of trauma problems of the patients simultaneously with technological and economical achievements. Recent developments in the field provide advantageous aspects concerning the internal architecture, mechanical properties and biocompatibility of the alloplastic bone grafts processed by the powder metallurgy (PM) technology. In this respect, the PM biocomposite materials based on hydroxyapatite powder particles reinforced by metallic or ceramic powders afford great benefits combining classic PM processes with different foaming techniques. The obtained biocomposites present special morphological and structural features matching the genuine bone tissue to be grafted, cortical respectively trabecular. This study focuses on the mechanical testing of the hydroxyapatite-based biocomposites reinforced by different foaming agents, specifically TiH2, CaCO3 and NH4HCO3 up to 25% mass. The overlapping of the obtained experimental results with those reported by the literature leads to the conclusion that the mechanical response of the PM biocomposites studied in this paper may play as a selection criteria to depict their application in hard tissue engineering.
Abstract: The very important strategy in parts processing by powder injection molding (PIM) technology is the use of organic polymeric materials made from raw and auxiliary materials and from renewable natural sources. Using natural polymers to obtain binders for PIM use is of particular interest. The inulin extraction from the onion bulbs has a major alternative in this area.
Abstract: The aim of the paper is to study the possibility of welding some sintered steels, which were obtained from mixtures of iron with different concentrations of graphite powders (between 0.2 and 0,8% weight). The sintered steels were resistance spot welded using different parameters and were investigated by optical microscopy in order to study the evolution of microstructures of the welded areas and base materials. There were perform studies regarding the evolution of microhardness respectively the evolution of tensile strength too.
Abstract: In this paper, calcium doped cobalt layered perovskite type 114 electrode electrocatalytic activity for methanol oxidation reaction (MOR) in aqueous alkaline solution (1 M KOH) has been investigated in order to find the relationship between methanol concentration in the solution and oxidation potential, current density, and oxidation efficiency. For a complete characterization of MOR on this electrode, several electrochemical methods were used: chronoamperometry, chronopotentiometry, chronocoulometry. Also, in order to understand the oxidation mechanism, kinetic parameters were determined using Tafel method and electrochemical impedance spectroscopy (EIS) was performed. MOR on layered cobalt perovskite electrodes becomes a serious issue, especially due to their use as anode in alkaline fuel cells.
Abstract: In this paper, the possibility of using ceftriaxone (CEFTR) active substance from expired cefort drug as corrosion inhibitor for nickel in acid solutions has been investigated. 0.5 M sulfuric acid and 1 M hydrochloric acid were used as corrosive media in experimental studies. The electrochemical behavior of ceftriaxone and its stability in test solutions have been examined by cyclic voltammetry. Further, the inhibitory effect has been studied by several methods: weight loss measurements, linear polarization and electrochemical impedance spectroscopy. As well, Tafel plots method was used in order to determine the kinetic parameters. Surface morphology of corroded samples has been characterized by scanning electron microscopy.