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The nature as well as composition of the Egyptian clay deposits exposed all over the country are summarized. The influence of composition on their ceramic properties in terms of plasticity as well as drying and firing behaviour is discussed. According to their clay mineral composition, they are classified into kaolinite-, smectite- and illite- rich clays. The kaolinite rich clays are used in the production of shaped and unshaped refractories as well as vitreous china and white Portland cement. However, they are not suitable for the production of white wares due to their high colouring iron and titanium oxides content. Smectiterich clays are applied for the production of ordinary Portland cement and building bricks. Also, they are recommended for the manufacture of light-weight clay aggregate due to their bloating on firing up to 1250 °C. Illite-rich clays are recommended for manufacturing building bricks and other heavy-clay products, after blending their varieties.
In the present study, three Egyptian clays from different localities with different Al/Si ratio were investigated to recognize their chemical and mineralogical compositions, thermal decomposition and particle size distribution in order to investigate the effect of up to 4 wt.% MgO addition on the phase formation, morphology of the developed mullite as well as physical and mechanical properties of these clays sintered in the range 1200-1400oC. XRD results revealed that mullite, quartz, and cristobalite were the main phases of the sintered clays; however, cordierite was formed on the expense of the other phases in compositions containing 4 wt.% MgO. SEM revealed the role of MgO in mullite grain growth and the formation of pseudohexagonal cordierite phase. The physical and the mechanical properties of the sintered clays were discussed in terms of their phase constitutions and microstructures.
From a wall mosaic, dating back to the end of the 16th century, of the S.Pietro basilica in Rome samples of glassy tesserae have been taken and analysed to characterize their composition and trace their production technology. For the most part they are made of lead-silicatic glass and are of various colours, opacified with tin, obtained with batches of a material known as ‘lead-tin yellow’, and a silicatic glass or frit, with a complex composition, in variable proportions, plus colouring agents. For the production of some colours extra lead oxide had been most probably added to the basic mix. Some analysed glasses show particular compositions that can identify them as contemporary materials from different productions or glasses used in restoration works. The Roman glass production, particularly that of mosaic glass, had been given a substantial boost in the 16th century due to the project of decorating the basilica with mosaics, copying and replacing the previous fresco paintings. The glass for the tesserae initially imported from Venice has been gradually substituted by that produced in Rome; thus, at the starting stage of the project, to which the studied materials go back, it is likely their importation from Venice, as it is attested by historical archive information and the analyses carried out.
The scratch resistance of the working surface of ceramic tiles represents a fundamental characteristic to defining their performances during service. The lack, in the EN ISO standards, of a specific standard regarding the determination of the scratch resistance, suggested to use a commercial available instrument, suitably designed and able to strictly control all the parameters involved in performing the test. For the present work, several ceramic tiles were selected and their working surface was subjected, under well established experimental conditions, to the scratch test. The possibility to quantify a parameter, in order to distinguish the different products, was also verified. The results pointed out a satisfactory repeatability, revealing moreover a dependence on the working surface conditions and the microstructure of the materials. As well known, in the quality control of these products, this latter aspect is particularly important.
Materials like natural stones and terracotta have high water absorption levels, values and behaviour depend on porosity/compactness of each individual material. Water absorption could cause different problems, i.e. a slow surface deterioration, dirt transfer, efflorescences, or growth of micro-organisms (moss, lichen, ...). In the field of buildings, the materials with high water absorption can be protected by the application of water-repellent products. The most utilised are silicon-based water-repellent products, which penetrate into the materials reducing significantly the water absorption and allowing at the same time their transpiration. Such methods avoid water spread into the material and the consequent above mentioned problems. The aim of this investigation is to determine water absorption of different materials, and study the effects associated to the application of silicon water-repellent water- or solvent-based products .
The ceramic cutting tool requirements for metal machining are reviewed, taking into account the trends in industry towards dry high-speed cutting and the need for tools with complex geometry. The emphasis will be on bulk materials rather than on coatings and most attention will be devoted to machining of iron-based alloys (steels). In the development of new tool materials, special attention should be given to the chemical matching of tool and workpiece material at elevated temperatures. The chemical compatibility of the toolworkpiece combination can be investigated by means of static interaction couples at elevated temperatures, which have been exposed for times long enough to be able to characterise the interaction layer. Complementary to the experimental investigation, the chemical compatibility of tool and workpiece materials can be predicted from thermodynamic equilibrium solubility calculations of tool materials in a selected workpiece material. Taking into account the mechanical properties needed, new ZrO2-based composites were defined based on the thermodynamically estimated chemical stability. The selection, development and proof testing of the new ZrO2-based composites is highlighted and their wear behaviour and performance in high speed dry turning of construction steel is compared with that of stateof-the-art cutting tool materials.
Rice husk is an agricultural waste, generated by the rice producing countries, mainly being utilized as cattle feed and cheap source of fuel for the boilers of rice mills. Ash generated after burning is regarded as a waste which contains > 80% silica and some free carbon. Acid resistance characteristics of silica enable the possibility of the use of rice husk ash for the development of acid resistant ceramic products. Acid resistant porous ceramic pots are useful for electroplating industries. The present study was planned to develop slip cast acid resistant porous ceramic pots using a mix of rice husk ash as the main raw material and clay. Three different compositions were tried with rice husk ash content in the range of 50 - 70 wt%. Sintering was carried out in the temperature range of 1150 - 1200 oC. Final products were characterized by various physical, mechanical, phase content and acid resistant properties.
A rapid manufacturing method for fabrication of 3D ceramic parts will be presented. The structural information is printed by ink jet in powder layers of 80 μm thickness. Different granulated powders can be used, such as zirconia and alumina if they show a good flow ability. After printing the structures a heating process takes place. After these the parts can picked out from the powder bed. The manufactured parts can be impregnated with epoxy. Another option is the infiltration with ceramic slurries and glass with sintering to higher density. The sintering process has been studied and the shrinkage and material properties evaluated. The interrelationship between the raw material qualities, infiltration media and the sinter parameters as well as the material-specific properties such as density and stability will be presented. The manufacturing method is used for fabrication of moulds and cores for casting processes. Otherwise the process can be used for fast fabrication of models and prototypes. The possibilities to use these methods for implant manufacturing will be shown. A cost analysis has been performed comparing direct manufacturing of small batches of components to mould injection processes.
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