Aleksandra Miazga

Characterization of composites containing NiAl2O4 spinel phase from Al2O3/NiO and Al2O3/Ni systems

This paper focused on the characterization of the composites containing nickel aluminate spinel from Al2O3/NiO and Al2O3/Ni systems. The composites were prepared by die pressing of powders and subsequent sintering of green bodies in air atmosphere. Composites were characterized by XRD, SEM, EDS and DTA/TG/MS analyses. The physical properties of the composites were measured by Archimedes method. Quantitative description of the composites microstructure was made on the basis of SEM images using computer image analysis. The XRD studies and SEM observations of composites confirmed the presence of two phases Al2O3 and NiAl2O4 in the whole volume of samples from both systems. Spinel phase was evenly distributed throughout the volume of the material. Morphology of NiAl2O4 obtained from both systems was characterized by the presence of voids. The DTA/TG/MS measurements showed the characteristics of organic binder decomposition and type of gases released to the atmosphere during thermal treatment. Moreover, the DTA/TG analysis showed the temperature of spinel-phase formation for both systems. It was found that the spinel-phase NiAl2O4 formation retards the process of densification. Therefore, it can be concluded that densification of samples with spinel phase depends mainly on the volume of spinel phase in composite material and does not depend on the substrates used to prepare spinel phase. The values of the selected properties of Al2O3–Ni- and Al2O3–NiO-based materials confirmed that the physical properties depend on the type of substrates used in the fabrication of composites. The type of powder influences the open porosity of samples. For composites produced using NiO powder, open porosity is lower than for samples formed with nickel powder.

Thermoanalytical studies of the ceramic-metal composites obtained by gel-centrifugal casting

Composite material with a gradient concentration of the metallic phase was prepared by the novel gel-centrifugal casting method. This method combines the consolidation of powders by the centrifugal force with the reaction of radical polymerization of an organic monomer which simultaneously proceeds within the composite slurry. The combination of the centrifugal casting with gel-casting permits production of ceramic–metal composites, including materials with a gradient distribution of metallic particles in a ceramic matrix. Special attention was paid to the thermal analysis of the composite Al2O3–Ni green bodies and the binder used in the fabrication of the material. The experiments were performed on the simultaneous thermal analyzer coupled with the mass spectrometer. The measurements were carried out in air and the inert atmosphere (argon) what allowed to determine the effects characteristic for organic binder decomposition and type of gases released to the atmosphere during thermal treatment. The measurements allowed also to establish the sintering program of the green composite samples and evaluate whether harmful gases are released to the atmosphere. The thermal experiments were complemented with physical and structural measurements, including X-ray diffraction and scanning electron microscopy.

The Formation of ZrO2–Ti Composites by Spark Plasma Sintering

The preliminary analysis of the ZrO2–Ti composite is conducted. The samples are prepared from the nanosized ZrO2 powder stabilized with 3 mol.% Y2O3 and 10 vol.% Ti powder with particles ~15 μm in size. The samples are formed by spark plasma sintering. The spark plasma sintering parameters are: temperature 1350°C, pressure 20 MPa, and duration 10 min. All process is carried out in argon. The density of the sintered ZrO2–Ti composites is determined by the Archimedes method. The microstructural characterization is carried out using X-ray diffraction and a scanning electron microscope. Additionally, the hardness and fracture toughness are measured. The obtained composite samples have a density of ~98–99% of the theoretical value. The homogenous distribution of titanium in zirconia matrix is SEM-confirmed. Moreover, the existence of a new phase in the Ti–Zr–O system is revealed by the X-ray diffraction analysis.

Al2O3/Ni functionally graded materials (FGM) obtained by centrifugal-slip casting method

The fabrication and the characterization of Al2O3/Ni composites with a gradient distribution of the Ni particles are reported. The composites have been obtained by centrifugal-slip casting and subsequent sintering and had the shape of a hollow cylinder. TG/DTA analysis was done for the nickel powder with the addition of the dispersant used in centrifugal-slip casting as well as for the composite green body. The measurements were performed in two atmospheres: argon and the mixture of argon and hydrogen (1:1). Additionally, coupling the thermobalance with the mass spectrometer allowed to determine type of gases released from the samples during thermal treatment. The morphology and chemical composition of the produced composites were analyzed using a scanning electron microscope equipped with an EDS detector. Interface between alumina and nickel was described. Moreover, the X-ray diffraction was made. The stereological analysis confirmed that the nickel particles are distributed in the composite in a gradient way.

Fabrication and characterization of ZrO2/Ni composites

This paper focuses on a research on the influence of nickel content in zirconia matrix and its impact on the mechanical properties of obtained composites. ZrO2/Ni mixed powders were uniaxially pressed and sintered in a nitrogen atmosphere to obtain ZrO2/Ni composites that were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDS). The stereological analysis allows obtaining information about the size distribution of zirconia grains in the sintered composites. Relative density, hardness, fracture toughness, and bending strength were also analyzed. The results revealed that the presence of Ni particles in the composites affects the mechanical properties of the materials. An increased Ni concentration caused a decrease in Vickers hardness and increased the fracture toughness of the ZrO2/Ni composites compared to the ZrO2 samples. This kind of composite is of interest for temperature and flow sensors, thermal barrier coatings for gas turbines and supersonic propulsion systems of spacecrafts, as well as as a material for anode in solid oxide fuel cell.

SEM and TEM analysis of composite of ZrO2-Ti system

Abstract 3Y-ZrO2-Ti composites obtained by slip casting method were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, the Vickers hardness was measured. The experiments show the complex microstructure of composites. The tetragonal zirconium dioxide (t-ZrO2) and monoclinic zirconium dioxide (m-ZrO2) as a composite matrix were detected at XRD analysis. SEM observations revealed that Ti -rich phase are uniform distributed in composites. Moreover, the large and very fine precipitations were found. The very fine Ti rich precipitations were located at ZrO2 grain boundaries as well as in the triple-points. TEM experiments confirmed that in the sintered composites 3Y-ZrO2 – 10%Ti the uniaxial ZrO2 grains (100–600 nm), fine monoclinic martensitic plates and fine round monoclinic particles (20–40 nm) of ZrTiO2 phase were exist. The complex microstructures of 3Y-ZrO2-Ti composites have a high hardness as a result of existing fine ZrTiO2 and other Ti oxides precipitations.

The Size and Shape Analysis of Titanium Particles in Composites from ZrO2 – Ti System

The morphology ZrO2-Ti composites depends on used powders substrates, methods of forming and sintering conditions. In this study a composite from the nanosize ZrO2 powder stabilized by 3 mol% Y2O3 and 3 vol. % Ti powder with particle size about 15 μm was prepared. A composite material was formed by uniaxial pressing. Sintering process was conducted in an argon atmosphere at 1300°C with retention time 2h. The selected physical properties of the green body and sintered ZrO2-Ti composites were determined by Archimedes method. The microstructural characterization was carried out using the x-ray diffraction and the scanning electron microscope (SEM) with EDS analysis. Stereological analysis by using computer programs was supported. The SEM observation and EDS analysis of the cross-section of the samples confirmed that the Ti particles are distributed homogenously in analysed areas. The EDS analysis revealed partial solution of titanium in ZrO2 matrix. Moreover, the x-ray diffraction exposed the existence of tetragonal zirconium oxide and titanium or a new phase from Ti-Zr-O system. The stereological analysis showed similarity between the starting particles of Ti powder and particles of titanium in the composite matrix.

Synthesis and Characterization of Nickel Aluminate Spinel (NiAl2O4) Prepared from the Equilibrium Mixture of Al2O3 and NiO

The aim of this study was to synthesis and characterization of nickel aluminate spinel (NiAl2O4) prepared of the equilibrium mixture of Al2O3 and NiO. The materials were produced by the solid phase synthesis. In the experiments the following powders were used: α-Al2O3 TM-DAR from Taimei Chemicals (Japan) of an average particle size 133 nm and density 3.96g/cm3 and NiO powder from Sigma-Aldrich of an average particle size 200 nm and density 6.67 g/cm3. The preliminary calcination was carried out at two temperatures: 1000°C and 1200°C. The final sintering of the samples were performed at 1600°C. The characteristics of the powder after calcination and sintered samples were performed using X-ray diffraction studies (XRD), energy dispersive X-ray analysis (EDS) and scanning electron microscopy (SEM). The study of composites confirmed the presence of nickel aluminate (NiAl2O4) in whole volume of the material.