György Thalmaier

Characterization of Gradual Porous Ceramic Structures Obtained by Powder Sedimentation

Asymmetric membranes present better separation and service characteristics than the symmetric ones. In our preliminary studies the possibility of obtaining sintered porous materials with gradual structure by sedimentation of metallic and ceramic powders was demonstrated. Zirconium silicate (ZrSiC 4 ) particles were used for the manufacturing of the porous supports, and mullite powder was deposited by sedimentation in order to achieve the active layer with pores size gradient. The used powders and the obtained structures were characterized by laser scattering particle size analyzer, scanning electron microscopy and mercury porosimetry. The permeability and the filtration fineness of the structures were also determined. By using a thin active layer made of small particles deposited onto a macro-porous support, one can achieve membranes with high flow rates and filtration fineness in the microfiltration area.

Metallic Foams Obtained from Nickel Based Superalloy Hollow Spheres

In this work, hollow spherical nickel based superalloy powders obtained by liquid phase atomization were used. The obtained powder was divided into six size particle ranges between 200 µm and 630 µm using a shatter box. Samples from all six ranges were obtained by spreading the powder into the sintering die and consolidating them by sintering at 900°C and 1000°C for 30 minutes in vacuum (10-4 Torr). The metallic foams obtained by sintering hollow particles presents high porosity, and can be used as thermal barriers, catalyst support, shock absorbers or lightweight structural elements.

Corrosion Resistance Measurements of Amorphous Ni40Ti40Nb20 Bipolar Plate Material for Polymer Electrolyte Membrane Fuel Cells

Metallic bipolar plates have the advantages of better manufacturability, higher strength over graphite bipolar plates. The higher strength and toughness of the metallic materials permits the reduction of the width of the bipolar plate so, the volume and mass of the fuel cell can also be reduced. In this paper we are investigating the use of Ni-based amorphous material as a bipolar plate for polymer electrolyte membrane fuel cell (PEMFC). The major requirements of the metallic bipolar plate material are low weight, high corrosion and low contact resistance. The corrosion property of the present alloy has been investigated under conditions that simulate the fuel cell environment. Hydrogen gas and air were bubbled into a 1 N H2SO4 solution at 70 °C, throughout the experiment to simulate the respective anodic and cathodic PEMFC environment. The Ni-base amorphous alloys displayed higher corrosion resistance than stainless steel.

Preliminary Studies and Researches on the Elaboration of Gradual Porous Sintered Structures by Powder Sedimentation

Spherical bronze powders were used for studies the obtaining of gradual porous structures by sedimentation and sintering methods. The powder size classes above 100 μm were used for the manufacturing of the macroporous support by spreading the powder into the sintering die. Sintering was conducted in vacuum (10-4 Torr) at a temperature of 750 °C for 40 minutes. On the macroporous support a layer of fine powder fraction was deposited by gravitational sedimentation. The deposited layers were consolidated by sintering at 750 °C for 30 minutes. The analysis of the gradual porous layers was done using scanning electron microscopy and mercury porosimetry. The fluids viscosity influences the sedimentation velocity of particles. The height of the column directly affects the quality of porous structure. If the sedimentary column is short, the turbulences created by adding the suspension of the dispersed powder in the sedimentary tube are more harmful.

Ti-Al Membranes for Microfiltration

Porous membranes made of Ti – 48 at. % Al intermetallic compound was obtained by elemental powder synthesis. These disks can be used as microfiltration membranes due to their low pores size and interconnected porosity. During this study titanium (purity 99.5%) and aluminum (purity 99 %) with low particle size range were mixed in corresponding ratios. The powder mixture was pressed at 500 MPa and the samples were heat treated in two stages. In the first step is the forming of Al3Ti compound by a solid state reaction at a temperature of 640 °C, slightly below the melting point of aluminum. In the second step the Ti-Al compound was formed at the temperature of 1300 °C and the sintering the porous structure was accomplished too. The obtained membranes were characterized by X-ray diffraction and scanning electron microscopy (SEM).

Open Cell Al-Si Foams by a Sintering and Dissolution Process

Open cell foams from AlSi12 alloy were successfully fabricated by the Sintering and Dissolution Process, using NaCl as space holder (60 %). The size of the aluminum alloy powder is less than 45 μm, while the space holder powder size is 315-500 μm, 630-800 μm and 800-1250 μm respectively. The appropriate quantities of alloy powder and salt were mixed and cold pressed at 250 MPa. The sintering process was done at 500 °C and 545 °C, in vacuum (10-5 torr) for 10, 20 and 30 minutes respectively. The space holder was eliminated by holding the sintered samples in running hot water (70 °C). After the salt was dissolved, the samples were dried and the mass loss was analyzed. Keywords: Aluminum foam, Powder metallurgy, Sintering and dissolution process

Studies and Researches on the Obtaining of Sintered Gradual Porous Structures by Irregular Nickel Powders Sedimentation

The aim of this work is to obtain sintered porous membranes with graded structure for microfiltration by sedimentation and sintering of metallic powders. Our previous studies have demonstrated the possibility of obtaining sintered porous materials with graded structure by sedimentation. In this paper, irregular nickel particles were used having a grain size in the 2-90 µm range evaluated using scanning electron microscopy and laser scattering particle size analyzer. The powders were sedimented into a sintering die in a sedimentation medium consisting of water and dispersant agent. After drying, the samples were sintered at 1000°C for 10 minutes in vacuum (~1•10-3 Pa). The structures obtained were characterized by scanning electron microscopy and mercury porosimetry. The pore size distribution was between 5-72 µm. The flow rate - pressure drop curves were experimentally determined and the viscous permeability coefficient was calculated using Darcy’s law (Ψv=0.14•10-12 m2). The absolute filtration fineness measured was 20 µm and the relative filtration fineness (95%) obtained for our membranes was 11 µm respectively. The possible applications for the studied membrane are: water microfiltration, environmental technologies, filtering lubricants and cleaning agents

Thermal Stability of Ni40Ti40Nb20 and Ni32Ti48Nb20 Tapes Obtained by Rapid Solidification Technique

Nickel–titanium- group 5A metal (V, Nb, Ta, Zr) alloys are known as promising hydrogen-selective membrane materials. They can potentially be used in membrane reactors, which can produce high-purity H2 and CO2 streams from coal-derived syngas at elevated temperatures. The master alloys were prepared by arc melting using high purity metals in a Ti-gettered argon atmosphere. The alloys were melted several times in order to improve homogeneity. The ingots were induction-melted under a high-purity argon atmosphere in a quartz tube and graphite crucible injected through a nozzle onto a Cu wheel to produce rapidly solidified amorphous ribbons. Thermal stability of the Ni40Ti40Nb20 and Ni32Ti48Nb20 thin tapes has been examined using DTA analysis.

FeNi-TiC Composite Powders Obtained by Electrolytic Co-Deposition

The paper presents a preliminary study on the obtaining of a composite powder by an electrolytic method. The composite powder particles are composed of iron nickel alloy that represents the matrix of the composite, and titanium carbide as the reinforcement. The matrix was obtained by electrolytic co-deposition from pure iron and nickel, in form of consumable electrodes. The titanium carbide powder is in suspension in the electrolyte. By the migration of metallic ions towards the cathode, the iron- nickel alloy is formed and, by simultaneously driving the carbide particles found in the electrolyte onto the cathode, the composite powder is obtained. The resulted composite powders were characterized by optical and electron microscopy. The influence of obtaining conditions over the morphology and structure of composite powders is emphased.