Malgorzata Sopicka-Lizer

Analysis of load-penetration depth data using Oliver–Pharr and Cheng–Cheng methods of SiAlON–ZrO2 ceramics

Depth sensing indentation tests were carried out to obtain load–penetration depth curves of SiAlON–ZrO2 ceramics under different peak loads ranging from 200 to 1800 mN. The values of indentation hardness (HOP, HCC) and reduced elastic modulus (EOP, ECC) were calculated by using Oliver–Pharr (OP) and Cheng–Cheng (CC) methods. The experimental results revealed that the indentation hardness and reduced elastic modulus exhibit peak-load dependence, i.e. indentation size effect. Both indentation hardness and reduced elastic modulus values were obtained by considering indenter tip roundness and machine compliance. These values obtained from the OP method are higher than from the CC method. On the other hand, hf/hm ratios were used to clarify the indentation deformation behaviour of the SiAlON–ZrO2 ceramic. The experimental hf/hm values were lower than the reported critical value (0.7) for all applied test loads, which is attributed to work-hardening behaviour of SiAlON–ZrO2 composites.

Effect of Carbon in Fabrication Al-SiC Nanocomposites for Tribological Application

Aluminium-based hybrid composites are a new class of advanced materials with the potential of satisfying the demands in engineering applications. This paper describes the effects of carbon addition on the formation and properties of AMC with SiC nanoparticles reinforcement. The composites were produced via mechanical alloying followed by hot pressing. Three forms of carbon, graphite (GR), multiwalled carbon nanotubes (CNTs), and, for the first time, glassy carbon (GC), were used for the hybrid composites manufacturing and compared with tribological properties of Al-SiC composite without carbon addition. GC and CNTs enhanced formation of Al-SiC composite particles and resulted in a homogeneous distribution of reinforcing particles. On the other hand, GR addition altered mechanochemical alloying and did not lead to a proper distribution of nanoparticulate SiC reinforcement. Hot pressing technique led to the reaction between Al and carbon as well as SiC particles and caused the formation of Al4C3 and γ-Al2O3. The subsistence of carbon particles in the composites altered the predominant wear mechanisms since the wear reduction and the stabilization of the friction coefficient were observed. GC with simultaneous γ-Al2O3 formation in the hybrid Al-SiC(n)-C composites turned out to be the most effective additive in terms of their tribological behaviour.

The New Top-To-Bottom Method of SiAlON Precursor Preparation by Activation in a Planetary Mill with a High Acceleration

Nano-structured β-sialon precursor powders were obtained as a result of milling in a planetary mill with a high acceleration. Various mixtures of initial nitrides/oxides have been prepared as β-sialon precursor with low (0.4-1.0z) substitution and were milled in a planetary mill of acceleration 28g (TTD, Russia) with zirconia or silicon nitride balls for a various times (30-45 min). The resultant powder showed various extents of crystalline lattice deformation: smaller crystallites, dislocations, bumpy surface. The degree of lattice destruction was influenced by the milling time and grinding media, however various mixture components showed diverse susceptibility to deformation.

The Effect of SiAlON Precursor Nanostructurization in a Planetary Mill on the Properties of Sintered Ceramics

The results on the effect of nanostructured β-sialon precursor on the sintering and properties of the resultant ceramics are presented. The standard mixture of β-sialon precursor with 0.4z substitution degree was activated for 30 min in a planetary mill with an acceleration of 28g. Activation in the planetary mill resulted in diminution of the crystallite size and significant imperfection of the crystal lattice of the powder particles. The sintering experiments were performed at 1450-1600 °C in a powder bed. The relative density of the sintered bodies achieved the value of 97 %. The nanostructured material was produced after pressureless sintering at 1500 °C. It is concluded that high activation degree of the powders is necessary to obtain fully dense ceramics.

Influence of Process Parameters on the Phase Composition of SiAlON Ceramics from Polish Fly Ash

The fly ash with high calcia content (Lagisza power station) has been chosen for the present study. Possible nitrogen for oxygen substitution was estimated on the base of the Si:Al ratio or Ca:Si:Al ratio in fly ash and necessary carbon amount was calculated from the stoichiometric reaction. Fly ash with addition of clay and carbon was reacted at 1520 °C. After sintering at 1350-1450 °C XRD, EDS and SEM examinations were applied to the specimens sintered with yttria addition. It has been found that phase composition of the carbothermal reduction product depended on the amount of carbon and resulted in βor α/β-sialons besides 15R and 12H phases. Subsequent sintering involved changes of the phase composition, dissolution of Ca-α-sialon and crystallization of YAG or secondary β-sialon, depending on temperature of sintering.

THE APPLICABILITY OF DTA TO THE STUDY OF THE CRYSTALLISATION PROCESS OF CERAMIC FIBRES

Abstract Sestaks method for the determination of the activation energy of the crystallisation of mullite in ceramic fibres has been applied. The investigations performed proved that the mechanism of the crystallisation of mullite is far from the classical theories describing the devitrification process of glass. The determination of the kinetic parameters by Sestaks method requires the verification of the introduced simplification every single time.

Influence of planetary milling parameters on the properties of the activated silicon and aluminium nitride powders

Mechanochemical processing of the silicon nitride based powders by high energy milling in a planetary mill is reported. The particle size distribution, specific surface area and their morphology after milling were studied after a period of a short (30 min) or long (up to 360 min) grinding. It has been shown that mechanochemical processing with the high energy led to the considerable destruction of the component crystal lattice apart from particles diminution, and moreover, to decomposition of the applied surfactant. As a result, significant agglomeration of powder particles occurred after the given milling time.

Influence of m and n Parameters of Ca-α-Sialon: Eu Solid Solution on Phosphor’s Optical Properties

Ca-α-sialon doped by Eu2+ is a promising material for white LED phosphors due to the strong UV absorption and a yellow broad band emission of activator. The general formula of α sialon enables changing matrix composition by altering m (Al-N) and n (Al-O) parameters of cross-substitution. Changes of the neighboring Eu ligands in the host crystal lattice would trigger important modification of the photoluminescence properties because of different crystal field splitting and the energy of the d orbital. The aim of this study was to correlate the matrix solid solution parameters with photoluminescence spectra features. The specimens of Ca-α-sialon:Eu2+ with m, n parameters in the range of 0.5-2.5 and 0.25-1.25 respectively, were prepared by the solid state reaction method in the reducing atmosphere of a graphite furnace. The phase composition of the obtained specimens was characterized by XRD, microstructure and morphology by the SEM/EDS techniques. The photoluminescence spectra (excitation, emission) were also recorded. Results show that m/n parameters have a significant influence on the final optical properties.

Preparation of translucent YAG:Ce ceramics by reaction sintering

The paper presents preparation of YAG precursor powders mixture with ability for the reaction sintering at lower temperature. The powder mixture was mechanochemically processed and characterized for the specific surface area and crystallinity (XRD). Sintering experiments were performed on the batched powders, mechanochemically processed powders and as-synthesised YAG powders. XRD measurements and SEM/TEM studies were applied for characterization of the phase composition and development of YAG ceramics. Transmittance of the resultant ceramics was measured. It has been shown that YAG structure formed at 200 ?C lower temperature in comparison to the reference specimen and contamination by the side phases (YAM, YAP) was limited. The best translucency was achieved for the reaction sintering of the mechanochemically processed powders.

Corrosion Resistance of Alumina-Sialon Refractories for Application in Aluminium Industry

This paper describes the manufacturing and corrosion resistance of sialon based ceramics for application in the modern aluminium industry. Sialon based ceramics are characterized by excellent mechanical properties at high temperatures, good corrosion and thermal shock resistance and low wettability, thus this material is suitable for the long term liquid aluminium contact. To obtain reaction bonded materials in this work, relatively cheap and commonly available components were used: fine Si and Al2O3 powders. The specimens were examined after heating in flowing nitrogen for the phase composition and dimension stability. Sintered materials were tested for corrosion resistance and wettability in liquid aluminium. The microstructure of the contact surface was examined by SEM/EDS methods.