Andreas Rosin

Synthesis and Properties of Graded Porous Ti-TiO2 Multifunctional Composites Obtained by Different Processing Methods

Functionally graded materials for load bearing implants have a long history of academic development and an already high degree of maturity. Efforts are now undertaken to improve the biocompatibility and even induce bioactivity within the implant-bone interface by optimised surface nanostructure of porous ceramic and metalic layers grown or sintered on a metallic implant, in order to arrive at cementless implants capable of fast osteointegration and high interface strength. Several new methods for surface structure and composition modification are presented for Ti-alloy based implants: a nano-structuring of the surface by re-deposition of TiO2 using an ECR-Microwave Plasma treatment combined with ion bombardment on a sintered TiO2 ceramic surface, a multiscale modification of porous Ti-coatings by means of Micro-Arc-Oxidation, MAO, and a meso-structuring of the surface by means of a laser treatment. The goal is to establish a multi-functionality in such materials by formation of a morphological and compositional gradient spanning many dimensions. The applicability of these methods to real implants is discussed for a dental implant.

Additive manufacturing of ceramic composites by laser assisted microwave plasma processing, LAMPP

Additive manufacturing of ceramic materials is difficult because of high temperature required to sinter or melt refractory oxides. Available energy sources, like e.g., laser or electron beam exert high photonic pressure to the surface and promote evaporation and ablation of ceramic materials rather than densification. A new high energy process with low photonic pressure is presented, based on combination of laser and microwave plasma heating, which enables sintering and melting of the ceramic without drilling and ablation of the surface. This new process is abbreviated as LAMPP, Laser Assisted Microwave Plasma Processing. The paper presents details of the equipment developed for LAMPP and analyses the energy efficiency of LAMPP as compared to laser sintering. The mechanism of plasma ignition and sustainment is discussed.

Laser-assisted microwave plasma processing of ceramic coatings

The aim of Laser-Assisted Microwave Plasma Processing of materials, abbreviated as LAMPP, is to utilize a spatially well-confined laser beam to ignite and localize a microwave plasma plume as an energy source for the sintering, melting or recrystallization of ceramic coatings. The energy required for the high-temperature treatment is supplied to a significant extent from the microwave source that feeds the plasma while the laser beam is used to scan the microwave plasma over the surface area to be treated. The phenomena underlying ignition and sustainment of the plasma are described in respect of the two possible ignition mechanisms: Laser-Induced Breakdown, LIB, or Microwave-Induced Breakdown, MIB. The influence of the material to be processed on prevalence of one of these ignition mechanisms is discussed. Examples of equipment built in our laboratory to enable LAMPP in different atmospheres for different substrates and coatings are shown. As potential applications of LAMPP, re-melting of ceramic plasma-sprayed thermal barrier coatings and melting of non-stabilized ZrO2 ceramic for coating purposes are presented.

Analysis of microwave heating in a fluidized bed reactor

Analysis of microwave heating in a fluidized bed reactor, FBR, is presented. Simulation yields a detailed picture of selective heating by energy conversion from electromagnetic to thermal. However, particle movement and gas convection which distribute thermal radiation generated locally by microwave absorption into the volume of the FBR are not included. In order to analyze the superposition of microwave heating with convection and conduction in the FBR a unique 3D-temperature recording device has been applied. The simulated and the dynamic heating profiles are compared for an FBR filled with a microwave-absorbing material, like e.g., SiC.

High-temperature oxidation behavior of ZrO2-ZrSiO4/NiCr composites and its applicability for functionally graded materials

In the present study, high-temperature oxidation behavior of pressurelessly sintered ZrO2-ZrSiO4/NiCr8020 samples with different volume fractions of ceramic is investigated with the aim to develop oxidation resistant ZrO2-ZrSiO4/NiCr functionally graded materials out of them. Sintered samples with 0, 25, 50 and 75 vol% ceramic were oxidized at 1000 °C for 36 h in synthetic air. The oxidation kinetics depends strongly upon the phase connectivity of NiCr in the ceramic matrix, which also governs the crack pattern formed due to the volume expansion of NiCr particles. While nearly full oxidation of the NiCr particles occurs in the 75 vol% ceramic composite with a relatively low phase connectivity of NiCr, the 25 vol% ceramic composite with a highly percolative NiCr phase exhibits a metal-like oxidation behavior and its overall oxidation was limited to the surface near area.

Microwave antenna array for high temperature materials processing

Industrial scale high temperature microwave processing of materials, like e.g., dielectric heating for sintering or heat treatment of powder metals and ceramics has not been successful yet, mainly because of lack of suitable equipment. The paper presents results of antenna development aiming at 2.45 GHz microwave transmission into hot processing chambers, with minimum heat loss because only minor cooling of windows or transmission lines is required. High power microwave coupling is enabled by an array of high temperature resistant rod antennas. The design is performed in two steps: first simulation (FDTD) and experimental validation is done for a single antenna, than the results are transferred into the design of a 6 antenna array. This antenna array is capable of transmitting up to 36 kW 2.45 GHz radiation into a 1m3 volume process chamber at temperatures up to 1500°C. The homogeneity of E-H-field distribution in the chamber and the limitations of material selection for the antenna array are discussed.

High pressure microwave flow reactor for raw oil treatment

A high pressure short time heat treatment is required for improvement of fluid properties of viscous raw oil and reduction of energy consumption for pumping. Microwave heating is investigated to achieve significant process improvements as compared to conventional heating technology. The engineering of a lab-scale flow reactor is presented that allows continuous microwave treatment for a maximum flow rate of 11 kg/h at 300 to 400 °C and up to 30 bar pressure. A unique microwave cavity design has been developed to enable homogeneous temperature distribution, high energy efficiency, and safe operation at high pressure.

New method for temperature dependent dielectric property investigation in polymer composite materials

Industrial processing of products made from light weight fiber reinforced composites could benefit from microwave heating providing the temperature dependent dielectric properties of the composite materials are known. Three methods of permittivity measurement at ambient temperature are compared: cavity perturbation, coaxial probe and SPDR, Split-Post Dielectric Resonator. The measured values differ significantly for each setup. Therefore a reverse simulation is performed. It is based on a new approach which utilizes the slope, ΔT/Δt of microwave heating curves recorded in a cavity perturbation type setup as indicative for changes in the imaginary part of the permittivity. Two simulation tools are compared: COMSOL® and Quickwave®.

Microwave antenna for selective heating of glass melts

Glass processing is energy intensive, therefore the possibility to reduce energy consumption by selective energy intake into portions of glass using microwave heating is investigated. The paper describes how microwave radiation is guided into a limited volume of glass melt subjected to extrusion into a mold for forming. A parametric study is performed to establish the best geometry for the microwave antenna inside a plunger structure which is used industrially to feed glass melt into molds. Experimental proof and material issues are discussed.