Taner Kavas

Physical, Mechanical and Micro-Structural Properties of F Type Fly-Ash Based Geopolymeric Bricks Produced by Pressure Forming Process

Geopolymer is a new class of three-dimensionally networked amorphous to semi-crystalline alumino-silicate materials, and first developed by Professor Joseph Davidovits in 1978. Geopolymers can be synthesized by mixing alumino–silicate reactive materials such as kaolin, metakaolin or pozzolans in strong alkaline solutions such as NaOH and KOH and then cured at room temperature. Heat treatment applied at higher temperatures may give better results. Depending on the mixture, the optimum temperature and duration vary 40-100 °C and 2-72 hours, respectively. The properties of geopolymeric paste depend on type of source material (fly ash, metakaolin, kaolin), type of activator (sodium silicate-sodium hydroxide, sodium silicate-potassium hydroxide), amount of activator, heat treatment temperature, and heat treatment duration. In this experimental investigation, geopolymeric bricks were produced by using F-type fly ash, sodium silicate, and sodium hydroxide solution. The bricks were treated at various temperatures for different hours. The compressive strength and density of F-type fly ash based geopolymeric bricks were determined at the ages of 7, 28 and 90 days. Test results have revealed that the compressive strength values of F-type fly ash based geobricks ranged between 5 and 60 MPa. It has been found that the effect of heat treatment temperature and heat treatment duration on the density of F-type fly ash based geobricks was not significant. It should be noted that the spherical particle size increased as the heat treatment temperature increased in the microstructure of F-type fly ash based geobricks treated in oven at the temperature of 60 °C for 24 hours.

Corrosion behavior of MgO-MgAl2O4-FeAl2O4 composite refractory materials

This paper investigated the corrosion behavior of refractory materials that were produced by incorporating hercynite (FeAl2O4, H) at different ratios into MgO-MgAl2O4 (spinel, S). Meanwhile, the values of density and open porosity of those samples were also measured. The corrosion resistance of those composite refractory materials was determined by measuring the penetration distances and spreading areas. The influence of corrosion resistance based on the microstructural changes occurred as a result of solubility of constituents in the interface of clinker-refractory for different regions was examined by using SEM. The incorporation of FeAl2O4 into MgO-MgAl2O4 decreased the porosity of composite refractory materials and also reduced the penetration distances and spreading area values of the corroded regions of refractories, leading to improvement on the corrosion resistance. The optimum amounts of constituents incorporated into new composite refractory materials used for obtaining longer service life in industrial applications were determined.

Effect of ZrSiO4 on the corrosion behavior of MgO-FeAl2O4 composite refractory materials

Abstract In this study, the corrosion behavior of refractory materials that were produced by incorporating ZrSiO4 (zircon) at different ratios into MgO-FeAl2O4 (hercynite) were investigated. The values of density and open porosity of those samples were also measured, and the corrosion behaviors of those materials produced were examined. After performing corrosion tests, the corrosion resistance of composite refractory materials were determined by measuring the penetration distances and spreading areas. The incorporation of ZrSiO4 into MgO-FeAl2O4 generally decreased the porosity of composite refractory materials, and consequently reduced the penetration distances and spreading area values of the corroded regions of refractories as well. In addition, the formation of new phases and the microstructural changes which occurred were determined by XRD measurements and SEM analyses. On the basis of microstructural characterization carried out in the interface of clinker-refractory, the following observations had been determined: i) Ca2+ and Zr4+ elements forming CaZrO3 were located together in the same regions, ii) forsterite phase was formed due to the reaction between SiO2, which is released after dissociation of zircon as ZrO2 and SiO2 during sintering, and MgO, iii) the formation of new CaZrO3 and forsterite (Mg2SiO4) phases made a barrier effect against clinker, and iv) the amount of CaO decreased based on the EDX analysis made from clinker to refractory in a corroded region. The penetration of clinker to refractory showed a minimum level for the composition of MgO-5 wt.-% FeAl2O4-5 wt.-% ZrSiO4 and an improvement by about 38 % as compared to MgO-5 wt.-% FeAl2O4. This improvement is associated with a long service life of MgO-FeAl2O4-ZrSiO4 refractories for industrial applications.

Effect of Afyon Region Volcanic Tuffs on Floor Tile Masse Body Properties

In this study, the production of floor tile with addition of tuff into the standard masse was aimed. Chemical, mineralogical, particle size distribution and thermal analysis were performed on Afyon region tuffs. Samples were produced by adding 11, 18, 20, 24 % volcanic tuff by weight into the standard floor tile masse which were composed of clay, pegmatite, feldspar, and kaolin. In the 5 various mixing series test specimen were produced by dry pressing method. Samples were fired at 1213 °C and were kept for 40 minutes which is standard sample fire temperature. Water absorption, viscosity, apparent density, firing shrinkage and compressive strength tests were performed on the fired specimen and compared with specifications and evaluated. As a result, addition of volcanic tuff into the standard masse by adding 10-20 % can be used for the production of tile floor. Alkaline properties were observed on the volcanic tuff. Water absorption and viscosity values of tuff were affected in very little amount. It is determined that usage of volcanic tuff is possible with decreasing amount of clay, kaolin and pegmatite.

Effects of Inorganic Salts on Rheological Properties of Slips

Abstract . Rheological properties of casting slips are of great importance in ceramic manufacturing techniques such as extruding, pressing, slip casting and glazing. In casting, the success of the forming process depends on the control of rheological properties [1]. In this study, casting clay prepared by using local raw materials and Na 2 SiO 3 were added at the optimum point to the casting clay. Then viscosities of the salt solutions at various concentrations were examined. Shrinkage, resistance, casting rate, water absorption and apparent porosity tests have been applied to these samples. According to 0.5 wt % -2.5 wt % and 5 wt % concentrations of salt solutions, results were evaluated. The viscosity was observed to increase with an increasing amount of salt added. Introduction Rheology is the science of deformation and flow. Ceramic slurries and pastes are relatively complex in structure and often poorly characterized. Particles may range from granular sizes to colloids. The interparticle spacing depends directly on solid loading, the state of dispersion and the particle packing [2]. The rheological properties of slip casting are of importance because they are one of the significant parameters which control of production. The rheological properties depend on physical and chemical properties of the raw material and on the conditions under which the slip casting is prepared. Since the properties of the raw material are variable, depending on the area where the raw material is produced. Therefore, the rheological properties must be determined for each new raw material in casting process [3]. Rheological properties of a slip effect rheological behaviour and characteristics of casting slips. The most important factors are chemical and mineralogical composition of raw materials, viscosity, particle size and shape, temperature, time, type of mixing, pH value and quality of water. During the preparation of slip, modification of some of the parameters may be required to achieve desired properties [4]. Slip viscosity is used widely in controlling ceramic casting slips. Viscosity affects density, thickness and quality of cake. Adjusting viscosity can, therefore, control the casting rate and thickness [4]. The water used for preparation of slip must not contain some ions that effect colloidal properties of particles which in the suspension. Because some ions effect colloidal properties of clays negatively. Some ions cause precipitation of the slip and spoil its stability [3]. When suspensions are highly flocculated, the particles’ electrostatic surface charges will be near zero. This usually occurs when multivalent cations such as Ca