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This paper focused on the characterization of the composites containing nickel aluminate spinel from Al 2 O 3 /NiO and Al 2 O 3 /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 Al 2 O 3 and NiAl 2 O 4 in the whole volume of samples from both systems. Spinel phase was evenly distributed throughout the volume of the material. Morphology of NiAl 2 O 4 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 NiAl 2 O 4 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 Al 2 O 3 -Ni-and Al 2 O 3 -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.

The fabrication and the characterization of Al 2 O 3 /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.

The paper is focused on the possibility of fabricating the alumina matrix ceramic-nickel composites with gradient concentration of metal particles. Centrifugal slip casting method was chosen for the composite fabrication. This method allows fabrication of the graded distribution of nickel particles in the hollow cylinder composites. The horizontal rotation axis was applied. The samples were characterized by XRD, SEM and quantitative description of the microstructure. The macroscopic as well as SEM observations of the prepared composites confirmed the gradient concentration of Ni particles in the composite materials. The application of the centrifugal slip casting method allows for the graded distribution of metal particles in the samples.

The aim of this study was to investigate the effect of the nickel particle size on the changes in metallic phase content in the graded structure in the Al2O3-Ni composites. Centrifugal slip casting was chosen as the method of composite fabrication. This method allows the creation of a graded distribution of Ni particles in the hollow cylinder composite sample. Functional graded materials were prepared in the vertical rotation axis. In the experiments the following powders were used: a-Al2O3 TM-DAR from Taimei Chemicals (Japan) of an average particle size 0.133 μm and density 3.96 g/cm 3 and Ni powders from Sigma-Aldrich of average particle sizes 3 μm and 8.5 μm. Aqueous slurries containing alumina (50 % of volume fractions of solid phase volume content) and nickel powders (10 % of volume fractions) were tested. Deflocculates diammonium citrate (p.a., Aldrich) and citric acid (p.a., POCH Gliwice) were also added. Final sintering was conducted on all the specimens at 1400°C in a reducing atmosphere (N2/H2). The obtained samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, quantitative analyses of the Ni particles distribution were made. In the fabricated samples the graded structure were characterized by zones with different Ni particles concentration. The size of the Ni particles influences the width of these zones. Vickers indentation was used to determine the hardness of the materials. Keywords: functionally graded material (FGM), centrifugal slip casting (CSC), Al 2 O 3 -Ni system Namen {tudije je bil preiskati vpliv velikosti delcev niklja na spreminjanje vsebnosti kovinske faze v gradientni strukturi kompozita Al2O3-Ni. Centrifugalno oblikovalno ulivanje je bilo izbrano kot metoda za izdelavo kompozita. Ta metoda omogo~a stopenjsko razporeditev delcev Ni v votlem cilindri~nem kompozitnem vzorcu. Funkcionalno razporejen material je bil izdelan na vertikalni rotacijski osi. Za preizkuse so bili uporabljeni naslednji prahovi: a-Al2O3 TM-DAR iz Taimei Chemicals (Japan) s povpre~no velikostjo delcev 0.133 μm in gostoto 3.96 g/cm 3 ter prah Ni iz Sigma-Aldrich, s povpre~no velikostjo delcev 3 μm in 8.5 μm. Preizku{ena je bila na vodi osnovana me{anica (z vsebnostjo 50 % volumenskega dele`a trdne faze), ki je vsebovala prah glinice in niklja (10 % volumenskega dele`a). Uporabljeni deflokulant je bil sestavljen iz diamonium citrata (p.a., Aldrich) in citronske kisline (p.a., POCH Gliwice). Kon~no sintranje je bilo pri vseh vzorcih na 1400°C, v reduktivni atmosferi (N2/H2). Dobljeni vzorci so bili pregledani z rentgensko difrakcijo (XRD) in vrsti~no elektronsko mikroskopijo (SEM). Poleg tega je bila izvedena tudi kvantitativna analiza razporeditve Ni delcev. V vzorcih je bila analizirana gradientna struktura po podro~jih z razli~no koncentracijo Ni delcev. Velikost Ni delcev vpliva na {irino teh podro~ij. Dolo~ena je bila trdota materiala po Vickersu. Klju~ne besede: funkcionalno gradientni material (FGM), centrifugalno oblikovalno ulivanje (CSC), Al2O3-Ni sistem