Papers by Author: Codruta Pavel

Abstract: Although titanium is considered to be the most successful metal for uncemented endosseous implants, its biocompatibility may be unsatisfactory in certain clinical cases. As an early osseointegration is essential in order to reduce the implant failure risk, the bioactive fixation becomes the appropriate solution for bone applications. The method requires bioactive materials such as hydroxyapatite (HA) to facilitate the chemical bonding to tissue. The present work refers to Ti-HA composites designed for endosseous implants and obtained through the classic PM route. Grade 1 c.p. Ti powder obtained through the hydriding – milling – dehydriding process, 63 - 100 μm grain size, was used. Sol-gel HA powder, grain size of less than 100 μm, was obtained through the sol-gel method. Blends of Ti and 5 to 50% HA were compacted in a rigid die (0.5 cm2), without the use of any lubricant, with 400, 500 and 600 MPa, then vacuum sintered (10-6 torr) at 1160°C for 60 minutes. Samples are well sintered with a compactness that increases with the applied compaction pressure. A transition layer can be seen in the EDX at the interface between the Ti matrix and the HA particles and is expected to increase the overall mechanical stability of compacts. The pores, essential for osseointegration, are interconnected, with irregular shapes and sizes that reach 100 μm, the critical size needed for the formation of a vital new bone. The HA content has to be limited to 30%, not to lead to an excessive brittleness. The biologic viability of compacts was assessed by immersion for 7 days into a simulated body fluid (SBF). The subsequent XRD analyses have proven that a new HA layer is formed on the surface of samples. This layer is essential for accelerating the cellular response of osteoblasts in the body.

Abstract: The goal of present work was to study the possibility to produce bars from heavy alloys based tungsten through rotary forging. For the experiment there were selected two compositions from the system W-Ni-Fe (90, respectively 93 %W/wt., Ni/Fe ratio = 7/3). From the two compositions there were prepared samples by conventional route of liquid phase sintering, followed by thermal treatment in a neutral atmosphere (N2, Ar) and by rotary forging with different reduction degree.

Abstract: The main objective of this study is to find out a simple method to ensure a good dispersion of Al2O3 in the Cu matrix. The method should avoid the segregation effect due to the high difference of the densities of Cu (8.93 g/cm3) and Al2O3 (3.96 g/cm3). In the process of obtaining of the Cu-Al2O3 composite we have considered starting with a material whose density is closer to the density of Al2O3. We have chosen CuO whose density is about 6 g/cm3 so the composite material was obtained starting with copper oxide and alumina powder. We have studied the influence of Al2O3 content and of the compacting pressure upon material’s compactness and hardness. The dispersion finer is highlighted by the microstructure of the surfaces.