Servet Turan

Effects of cobalt, copper, manganese and titanium oxide additions on the microstructures of zinc containing soft porcelain glazes

Abstract Different types of glazes, which are nearly all based upon silicate compositions, are used to meet a wide range of requirements in service. Many artistic effects are achieved by departing from a clear, smooth, transparent system. Coloured glazes are produced by several means such as the inclusion of colouring oxides, addition of stains, dispersing finely divided particles and the use of precious metals, applied in the form of lines or bands, or even screen-printed patterns. Colouring oxides commonly used include iron, copper, cobalt, chromium, manganese, nickel, vanadium, cadmium and selenium. Zinc oxide has a beneficial effect in many coloured glazes amongst which crystalline ones are more noteworthy. With this paper the effects of CoO, CuO, MnO 2 and TiO 2 additions into zinc oxide containing crystal glazes differentially heat-treated are described on micro-scale appearances. Experimental techniques used were X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDX).

The development and characterisation of zinc crystal glazes used for Amakusa-like soft porcelains

In porcelain production, as well as bodies expected to have white colour, compaction and translucency, suitable glaze compositions have great importance from both a technological and decoration point of view. Supplying the desired firing conditions is generally quite difficult for the porcelains having white colour after being fired in reducing atmospheres. In the present study, firstly it has been tried to make porcelain bodies similar to the Amakusa porcelain, which has been traditionally prepared in the Nagasaki Prefecture of Japan and widely used, by applying domestic raw materials and firing them in an oxidation atmosphere. Secondly, several zinc-containing glazes coloured with different colorants have been developed and applied to those bodies. After biscuit and gloss firing procedures, products have been characterised using dilatometry, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy.

The dependence of equilibrium film thickness on grain orientation at interphase boundaries in ceramic-ceramic composites

High-resolution transmission electron microscope observations of hexagonal boron nitride - 3C silicon carbide interphase boundaries suggest that where one or more phases is highly anisotropic, an orientation dependence on equilibrium film thickness can arise. Theoretical considerations of this phenomenon in terms of the equilibrium thickness of an amorphous film between two crystalline media are consistent with the trend seen experimentally.

Production of brown and black pigments by using flotation waste from copper slag

One of the major problems in copper-producing countries is the treatment of the large amount of copper slag or copper flotation waste generated from copper slag which contains significant amounts of heavy metals such as Cu, Zn, Pb and Co. Dumping or disposal of such large quantities of flotation waste from copper slag causes environmental and space problems. In this study, the treatment of flotation waste from copper slag by a thermal method and its use as an iron source in the production of inorganic brown and black pigments that are used in the ceramic industry were investigated. The pigments were produced by calcining different amounts of flotation waste and chromite, Cr2O3, ZnO and CoO mixtures. The pigments obtained were added to transparent ceramic glazes and porcelainized tile bodies. Their colours were defined by L*a*b* measurements with a spectrophotometer. The results showed that flotation waste from copper slag could be used as an iron source to produce brown and black pigments in both ceramic body and glazes.

Novel SiAlON Ceramics for Cutting Tool Applications

New α-β SiAlON ceramics were produced in aqueous medium using multiple oxides as densifying additives. The sintered materials were c hara terised using a combination of techniques such as XRD, SEM and TEM. The samples machined to cutt ing tool geometries were tested in turning and milling operations of cast iron and superal loy. The results were compared with some commercially available ceramic inserts. Introduction Ceramics have always had a potential as cutting tool material s due to their high hot hardness and chemical stability. Ceramic inserts based on Al 2O3 and Si 3N4 are applied in machining of cast iron, hardened steel and heat resistant alloys. Metal remova l rates of such inserts are significantly higher than those of conventional coated or uncoated ceme nt d carbide tools. The reason to use Al 2O3 as a cutting tool material is its high chemical stability and wear resistance. Al 2O3-ZrO2 cutting tools were developed for machining cast iron and steel a nd have higher strength, toughness and thermal shock resistance than pure Al2O3. Another type of Al2O3 based cutting tool is that of Al 2O3-TiC composites with better hot hardness and thermal conductivity compared to pure Al 2O3. These properties make this material suitable for machining chilled cast iron and hardened steel and also for fine mac hining of cast iron. SiC whisker reinforced Al 2O3 (SiCw-Al2O3) composites are used commercially in superalloy machining due to their high strength, toughness and thermal shock re sistance. Si 3N4 based ceramic inserts have an advantage of high strength and high toughness as a result of elongated β-Si3N4 grains in the microstructure. Therefore, Si 3N4 cutting tools are the most extensively used materials in cast iron machining [1]. SiAlON ceramics have been known for a few decades for their outstanding high temperature mechanical and thermal properties. In single phase form, β-SiAlON has higher toughness and strength and possesses good oxidation and creep resistance up to 1300°C sim ilar to Si3N4. On the other hand, α-SiAlON has excellent hardness, but slightly worse strength, toug hness and oxidation resistance compared to β-SiAlON. α and β-SiAlONs are in thermodynamic equilibrium and by combining two phases it is clearly possible to de fine quite precisely an optimum combination of mechanical properties [2]. Due to the favourable properties of α-β SiAlONs mentioned above, they are attractive materials for cutting tool applications. Such applications require mat rials with high hardness, high fracture toughness and high strength. Si 3N4 ceramics have favourable fracture toughness and strength to meet these requirements, but their hardness is lowe r than α-β SiAlON composites. Although α-β SiAlON composites possess better mechanical properties than Si3N4 ceramics, they have not been commercialised as cutting tool insert s. This was mainly due to two reasons. The first reason is the difficulty in obtaining de sign d microstructure and/or phases. For example; when 75% α and 25% β-SiAlON microstructure with elongated Key Engineering Materials Online: 2003-04-15 ISSN: 1662-9795, Vol. 237, pp 193-202 doi:10.4028/www.scientific.net/KEM.237.193

Reaction Model for the Boron Carbide/Aluminium System

An attempt has been made to shed light on the reaction mechanism during the production of B4C/Al composites by making use of the measured phase contents of the phases B4C, Al, Al3BC and AlB2. It was found that the agreement between the measured and calculated Al3BC contents is good for all the processing conditions investigated. The measured and predicted Al contents, on the other hand, were oberved to be reasonably close to each other for short holding periods at the infiltration temperature but deviated at higher holding periods.

Interphase boundaries between hexagonal boron nitride and beta silicon nitride in silicon nitride-silicon carbide particulate composites

Abstract Interphase boundaries between hexagonal boron nitride and β-Si 3 N 4 in hot isostatically pressed Si 3 N 4 -SiC particulate composites, in which boron nitride appears as a trace contaminant, have been examined using high resolution transmission electron microscopy. A number of characteristic orientation relationships were observed between these two phases. Significantly, high resolution transmission electron microscopy showed that the interphase boundaries tended not to contain any intergranular films.

Influence of Type of Cations on Intergranular Phase Crystallisation of SiAlON Ceramics

25α:75β SiAlON composition was designed with different cations and at different molar ratios. Effect of the type of cations both on the composition and the type of intergranular phase investigated after gas pressure sintering and further post sintering heat treatment.

Boron nitride–silicon carbide interphase boundaries in silicon nitride–silicon carbide particulate composites

Abstract Interphase boundaries between SiC and h-BN grains in hot isostatically pressed Si3N4–SiC particulate composites made from both as-received powders and deoxidised powders, in which sub-micron size h-BN particles occur as a contaminant, have been characterised using transmission electron microscopy techniques. Most of the h-BN grains observed were aligned with respect to SiC grains so that (111) 3C SiC and (0001) α-SiC planes were parallel to (0001) h-BN planes. The h-BN–SiC interphase boundaries in the composites made from as-received powders were covered with thin silica-rich intergranular films, in contrast to the interphase boundaries in the composites made from deoxidised powders. These observations are discussed in the light of models for the formation of intergranular amorphous films in ceramic materials, geometric considerations for low interfacial energies and the possible bonding at h-BN–SiC interphase boundaries free of intergranular films.

The Crystallography of Interphase Boundaries Between Silicon Carbide and Silicon Nitride in Silicon Nitride—Silicon Carbide Particulate Composites

AbstractInterphase boundaries between 3C SiC grains and two different β-Si3N4 morphologies in Si3N4–SiC composites have been studied by transmission electron microscopy. In general, boundaries between small β-Si3N4 intragranular precipitates and surrounding SiC grains were relatively free of intergranular films, whereas boundaries between large β-Si3N4 grains and adjacent SiC grains were invariably covered with thin intergranular films. Orientation relationships approximating to [110] 3C SiC ‖ [0001] β-Si3N4 and (001) 3C SiC ‖ (10