Issue No. 3, December

Abstract

Pyrophyllite is largely an overlooked raw material available in huge quantities in nature. This is mainly due to the fact that other comparable aluminosilicate raw materials like china clay are available in much purer form. However, fast depleting reserves of standard raw materials necessitated renewed attention on so far sparingly used raw materials like pyrophyllite. Investigative work on pyrophyllite is also insignificant in comparison to other ceramic raw materials. Available information are scattered and it is felt that a comprehensive review is needed for effective dissemination of the information already generated and available in the public domain. In the present article salient points on the material including structure, chemistry of heating and possibility of future applications particularly in triaxial ceramic system is discussed. In a case study one Indian pyrophyllite was incorporated (15%) in a triaxial body composition replacing both china clay and quartz. The changes in fired properties was tried to correlate with phase development and microstructure.

Abstract

Mineralogical, microstructural, and firing characteristics of dead burned magnesia produced from hydrothermal magnesite deposits of eastern Iran have been evaluated. The ore bodies are highly pure crystalline magnesite with only trace amounts of impurities such as quartz, calcite, and dolomite. Ratio of CaO/SiO₂ in the bulk ore is variable. It was shown that the composition of dead burned magnesite from these deposits, calcined at different temperatures and durations, is predictable from phase equilibria. Textures of the calcined magnesite were studied by SEM; results show that the principal impurities produced during calcination are forsterite (F₂S), monticellite (CMS), merwinite (C₃MS₂), dicalcium and tricalcium silicates (C₂S, C₃S) and that these are located primarily at triple junctions of the periclase crystals. The size of periclase crystals increased with temperature and duration of calcination and the amount of periclase-periclase grain contacts was reduced by increasing the concentration of impurities in the starting ore EPMA analyses revealed that CaO and FeO contents in periclase increase steadly with an increase in the CaO/SiO₂ ratio and FeO content of the bulk ore, respectively. Moreover, it was found that limited solid solution exists between impurities. This study demonstrates that high quality dead-burned magnesia refractories with low CaO, SiO₂ and FeO contents can be produced from the studiedmagneiste deposits.

Abstract

Agacli-Kemerburgaz area, NW of Istanbul, is one of the most important underclay deposits of Turkey. This area is composed of Paleozoic sedimentary sequence, Upper Cretaceous volcanic rocks, Neogene sediments and Quaternary alluvium deposits. The calc-alkaline volcanic rocks are the parent rocks of the underclays in this area. In this work, mineralogical and chemical analyses and relevant technological tests were conducted in order to assess the potential of selected underclays of this region. The technological properties were characterized by firing shrinkage, water absorption and breaking strength after firing. The chemical analyses generally showed the characteristics of typical kaolinized materials. Underclays containing (up to 33 wt. %) porcelain stoneware formulations were prepared and standard tests were applied to the porcelain tiles after single fast firing under industrial conditions. The densification behaviour and phase evolution of the bodies upon firing were evaluated. Physical, thermal and optical properties and chromatic coordinates were also measured. The results revealed that it was possible to employ the underclays to replace more expensive clay in porcelain tile production without deterioration of the required properties.

Abstract

The successful design of mixers is known to depend primarily on the mixed fluids properties as well as the geometry of both impeller and vessel. A classical approach commonly used to predict the power requirements in the mixing process is to make use of the relation between the Power number (N_p) and the Reynolds number (Re). Here, Re = ρ.n.D² /μ, where ρ is the density of the liquid mixture, μ its viscosity, n the rotational speed of the impeller (rps), and D its diameter. On the other hand, N_p = P / ρ.n³.D⁵, where P is the power required for mixing. This approach has been conventionally applied to Newtonian fluids and suspensions but not to pastes. In the present paper, relationships were developed for mixing of ceramic pastes used in the manufacture of sewer pipes. A standard mix was chosen and the effect of the following variables on the power number - Reynolds number relation was investigated: water content, grog content and particle size of clay. All paste mixes investigated followed a relation of the type: N_p = a / Re^b, where a and b are constants that depend essentially on the fraction of grog used and to lesser extent on the water fraction and clay particle size. The values of the constant b were close to unity in all cases, emphasizing the fact that the laminar regime mixing relation N_p = a / Re, applicable for Newtonian fluids is also valid for pastes.

Abstract

Suitability of using limited additions of three solid waste by-products; homra (H), granulated slag (GS) and fly ash (FA), with Egyptian clay, belonging to Dakhla formation in south western desert, in the conventional red brick batches fired at different temperatures was assessed in comparison with a blank batch. The results showed that as the firing temperature increases, the densification parameters as well as the mechanical properties are improved. Fired brick bodies, containing 10% (FA), exhibit higher densification and mechanical properties at all firing temperatures than those of the other batches. The firing shrinkage was also increased slightly between 750 to 800 °C and sharply from 850 to 950 °C. The XRD and EDAX analyses illustrate that during firing, the main clay constituents of the brick batch react with those of the FA, GS and H additions, forming calcium-rich silicate phases.

Abstract

The aim of this work was to evaluate the use of the Bornova shale (BS) from Bornova-Izmir, west Turkey, as a raw material in the production of red fired ceramics. The Bornova-Izmir area is a convenient region for establishing a ceramics factory in terms of climate and proximity to Izmir harbour. The BS consists of phyllosilicates (illite, chlorite, and smectite), quartz, feldspar, and calcite. The dominant clay minerals are either illite or chlorite with smectite making up 0-7%. Differential thermal analysis (DTA) reveals that an amorphous phase occurs above 918°C. For the production of red fired ceramics, we used illiteand chlorite-rich BS in the following proportions: addition of 40% Fe-rich Eymir (Havran) kaolin (EK) to the BS, addition of EK (40%) and 2% Bigadiç Borate Concentrator Waste (BBCW), addition of EK (40%) and 3% BBCW, and addition of only 2% BBCW. Representative samples were prepared by pressing clay bodies at 15 MPa, which were then fired at temperatures between 850 and 1200 °C. The physical properties of the representative samples (e.g., water absorption and bending strength) were obtained from specific tests. Based on the desired colour and physical characteristics, the optimum batch was that with 98% BS +2% BBCW fired at 1100 °C. Addition of BBCW to the BS imparts binding and fluxing properties during the production process. These properties, in turn, improve mechanical strength and reduce energy usage.

Abstract

Three different mullite precursors were prepared from Al(OH)3 and silica sol with variation in the calcination temperature of Al(OH)3. These precursors were added to high alumina low cement castable composition to an extent of 6 wt%. The castables were conventionally processed and fired at 1000, 1200 and 1500 °C. Dried and fired castables were characterized for various properties for the comparative study of the effect of different mullite precursors on the castables. No strength degradation was observed at the intermediate temperature due to the formation of mullite phase in the castable matrix.

Abstract

Basic bricks containing chromium based complex spinel are used in the nonferrous industry due to their corrosion resistance against fayalite-type slags. Objective of this work is to replace Cr³⁺ with Me⁴⁺ ions that form complex spinel. The incorporation of iron oxide in the MgO-Al₂O₃-Me₄+O₂ systems contributes to reactive sintering. The mixes contain 60 wt.% MgO similar to most basic refractories used in non-ferrous converters and thus called “magnesia-rich” compositions. The investigation shows that incorporation of nano-oxides reduces the temperature of spinel formation and activates both synthesis and sintering. Magnesia-rich compositions with Al₂O₃, Fe₂O₃, SnO₂ and TiO₂ containing less than 3 wt.% nano-oxides fired at 1450 °C for 3 hours have resulted in formation of complete spinel solid solution and less than 5% open porosity.

Abstract

In this report, the trends in refractories technologies for iron and steel production at Nippon Steel Corporation in the last few decades are outlined. Amid dramatic changes in crude steel production accompanying increased ratios in higher quality of steel and sophisticated refining methods, in our refractory ceramics R&D Div., actual machines have been realized by practicing developed outcomes with technologies for every production process relating to: refractory material quality, furnace building or execution, reparation, diagnosis, demolition, and recycling. Thus, continuing reduction in the unit consumption of refractories has been steadily performed. Additionally, technical issues are reduced to further enhance and maintain our international competitiveness in refractories technologies.