Yüksel Sarıkaya

BASELINE STUDIES OF THE CLAY MINERALS SOCIETY SOURCE CLAYS: SPECIFIC SURFACE AREA BY THE BRUNAUER EMMETT TELLER (BET) METHOD

Specific surface area measurements of The Clay Minerals Society source clays were made by the Brunauer, Emmett and Teller (BET) method of adsorption of nitrogen gas. Two replicate measurements of specific surface area were performed for each source clay. All pair values were within 3%, which is very good agreement for this type of measurement.

THE EFFECT OF THERMAL TREATMENT ON SOME OF THE PHYSICOCHEMICAL PROPERTIES OF A BENTONITE

A white calcium bentonite (CaB) from the Kütahya region, Turkey, contains 35 wt. % opal-CT and 65 wt. 9c Ca-rich montmorillonite (CaM). Samples were heated at various temperatures between 100–1300°C for 2 h. Thermal gravimetric (TG), derivative thermal gravimetric (DTG), and differential thermal analysis (DTA) curves were determined. Adsorption and desorption of N2 at liquid N2 temperature for each heat-treated sample was determined. X-ray diffraction (XRD) and cation-exchange capacity (CEC) data were obtained. The change in the <i(001) value and the deformation of the crystal structure of CaM depend on temperature. Deformation is defined here as changes of the clay by dehydration, dehydroxylation, recrystallization, shrinkage, fracture, etc. The activation energies related to the dehydration and dehydroxylation of CaB calculated from the thermogravimetric data are 33 and 59 kJ mol−1, respectively. The average deformation enthalpies, in the respective temperature intervals between 200–700°C and 700–900°C, were estimated to be 25 and 205 kJ mol−1 using CEC data and an approach developed in this study. The specific surface area (S) and the specific micropore-mesopore volume (V) calculated from the adsorption and desorption data, respectively, show a “zig zag” variation with increasing temperature to 700°C, but decrease rapidly above this temperature. The S and V values were 43 m2 g−1 and 0.107 cm3 g−1, respectively, for untreated bentonite. They reach a maximum at 500°C and are 89 m2 g−1 and 0.149 cm3 g−1 respectively. The XRD data clearly show that, at 500°C, where the irreversible dehydration is completed without any change in the crystal structure, the porosity of CaM reaches its maximum.

Workability test method for metals applied to examine a workability measure (plastic limit) for clays

Abstract The Kure clay (KC) and the Deresakari clay (DC), taken from the Soǧut region (Bilecik, Turkey), were examined by chemical analysis, X-ray diffraction (XRD) and thermal analysis techniques. It was determined that the KC and DC, whose basic clay mineral was kaolinite, contained 37% and 66% free quartz as mass percentage, respectively. The compression and upset tests applied to metals were applied to KC and DC. The KC and DC green bodies were passed through an extruder, and cylindrical clay green bodies having different moisture contents were obtained and used in the experiments. The yield stresses ( σ 0.2 ) were determined from the compression tests. Plastic tensile strain limit values ( e θ *) were determined from the upset tests. The product of the two characteristic values, σ 0.2 e θ *, was defined as the workability. The variation of the σ 0.2 , e θ * and σ 0.2 e θ * values as a function of the moisture content of the green bodies was discussed for KC and DC. From the maxima of the σ 0.2 curves, the optimum moisture percentages were determined as 22.0 and 26.5 for the KC and DC, respectively. These results and the results obtained from the Atterberg and Pfefferkorn tests were discussed comparatively.

The effect of the electrolyte concentration and pH on the rheological properties of the original and the Na2CO3-activated Kütahya bentonite

The effect of the Na2CO3 activation on the rheological properties of a bentonite from Kutahya (Turkey) was investigated. The bentonite was activated with Na2CO3 at different dosages (1–15 g Na2CO3/100 g bentonite). The activated samples were examined by chemical and X-ray diffraction analysis. The calcium bentonite was completely converted to sodium bentonite when the Na2CO3/bentonite ratio was 2.5%. The rheological values showed a maximum after addition of 2.5% Na2CO3 (bentonite concentrations 2–6% w/w). At 2.5 g Na2CO3/100 g bentonite, the shear stress was also measured at several NaCl and Na-hexametaphosphate concentrations. NaCl addition decreased the rheological properties up to NaCl concentrations of 0.005 mol l−1. Further addition of NaCl increased the rheological properties again. The addition of Na-hexametaphosphate caused a decrease in the rheological properties to a constant value higher phosphate concentrations. The lowest yield stress was obtained around pH 7.

The effect of calcination temperature on some of the adsorptive properties of fine alumina powders obtained by emulsion evaporation technique

Abstract The thermal decomposition of an alumina precursor, obtained by the emulsion evaporation technique, was investigated by thermogravimetry (TG) and differential thermal analysis (DTA). The thermal decomposition was completed in four steps between 100°C and 550°C. For each step, the activation energy was determined from the TG data by the Coats–Redfern procedure and the decomposition was discussed. The X-ray diffraction (XRD) data revealed that diaspore (β-AlOOH) was formed during the emulsion evaporation. The resulting pure but porous α-Al 2 O 3 powders were then calcined for 2 h at various temperatures between 600°C and 1600°C. The adsorption and desorption of N 2 on the calcined specimens at approximately 77 K was investigated. The variation of the total micro and mesopore volumes, the micropore volumes, the surface area and heat of adsorption as calculated from experimental data were discussed as a function of the calcination temperature. It was observed that the above mentioned properties reached a maximum at 800°C, and then decreased rapidly by increasing temperature. It was concluded that it was possible to prepare fine α-Al 2 O 3 powders whose specific surface areas varied between 20 and 90 m 2 g −1 by changing the calcination temperature between 600°C and 1600°C.

The effect of heating on the surface area, porosity and surface acidity of a bentonite

The Hançılı bentonite from Turkey shows significant changes in surface area, micro- and mesoporosity, surface acidity and acid strength with heating from 100 to 900°C for 2 h. The specific surface area (S) and specific micro-mesopore volume (V) of the original and heated samples were evaluated from N2 adsorption and desorption data, respectively, by standard methods. The adsorption of n-butylamine from the solution in cyclohexane on the samples was used to determine the total surface acidity (nm) and the adsorption equilibrium constant (K) was taken as a measure of the acid strength. S, V and nm having initial values of 98 m2g−1, 0.080 cm3g−1 and 4.8 × 10−4 mol g−1, respectively, stayed approximately constant as the temperature increased to 450°C and then decreased almost in parallel with each other, reaching their minimum or zero at 900°C. The total surface acidity, in general, declines with increasing temperature. The most acidic sites, however, increase with heating, and especially at dehydration and dehydroxylation. Acid strength reaches its maximum during the dehydroxylation phase at ∼600°C. It was concluded that the total surface acidity does not necessarily parallel the strength of the most acid sites.

Preparation of alumina microshells by the emulsion evaporation technique

Spherical hollow alumina powders (alumina microshells) were prepared from evaporation of water-in-oil (w/o) type emulsions by employing an aqueous Al(NO3)3 solution as water, mineral oil as the organic phase and a non-ionic surfactant, Arlacel 83, as the emulsifier. It was found that 65% mineral oil, 30% aqueous Al(NO3)3 and 5% Arlacel 83 composition produced stable, w/o type emulsions by mechanical stirring at 20°C. The aluminum ion concentration was varied between 0·25 and 2·0m to investigate its effect on the emulsion droplet size. Alumina microshells obtained from the evaporation of w/o emulsions were characterized with respect to size and distribution. The influence of aluminum ion concentration on these properties was also studied.

Modification of rheology and permeability of Turkish ceramic clays using sodium silicate

Abstract Rheological properties of two ceramic clays (Sindirgi and Kure) having different chemical and mineral compositions were determined. The variation in viscosity for suspensions having 50%, 55% and 60% (w/w) clay was measured as a function of initial loading of sodium silicate. The relationship between shear rate (0–120 s −1 ) and shear stress (0–350 Pa) was determined for these suspensions in the presence of various amounts of sodium silicate. The effect of the amount of clay on the suspension thixotropy properties was investigated for original and treated suspensions. Slip viscosities of 1500, 500 and 100 cP were evaluated and the suspensions were filtered to obtain cakes. From rheological measurements, thixotropy properties changes were correlated with increased solid and electrolyte in the suspension and the clay mineral type. In addition, results showed that the permeability, the porosity and the casting rate increase with the viscosity in the clay suspensions and the permeability decreases with decreasing porosity. When the clay ratio in the suspensions is 50% (w/w) and the viscosity 1500 cP, the porosity and the permeability values obtained in each sample are higher than the others.

Adsorption characteristics of alumina powders produced by emulsion evaporation

Alumina powders were produced by emulsion evaporation technique. Powders exhibiting various characteristics were produced by varying the concentration of aluminum ion in the aqueous solution, ratio of aqueous solution-to-mineral oil, and evaporation temperature. Calcined powders were found to be spherical in shape and with an average particle size of 1·5–8·5 μm. Electron microscope observations indicated that most of these spheres were broken porous microshells. Adsorptive properties of these powders were determined from nitrogen adsorption measurements. Specific surface area was determined by BET method, specific microporosity by Dubinin-Radushkevitch and total pore volume from desorption isotherms. Specific surface area was found to range between 60 and 95 m2/g, and total pore volume ranged between 0·15 and 0·25 cm3/g for various samples.

SOME PHYSICOCHEMICAL PROPERTIES OF THE WHITE SEPIOLITE KNOWN AS PIPESTONE FROM ESKIŞEHİR, TURKEY

Various physicochemical characteristics of a sepiolite sample from the Eskişehir area, Turkey, were investigated to help in making predictions about possible uses of the material. The sample was examined by chemical analysis (CA), thermal analysis (DTA/TGA), X-ray diffraction (XRD) analysis, particle-size analysis (PSA), linear dilatometry (LD), scanning electron microscopy (SEM), mercury porosimetry (Hg-Por.), and low-temperature nitrogen adsorption/desorption (N2-AD) techniques. The CA and XRD data indicated that the sepiolite contains only 6% dolomite by mass. The XRD patterns showed that sepiolite anhydride, enstatite, diopside, and opal-CT form upon heating the sepiolite above 600, 800, 900, and 1200°C, respectively. The maximum rate of endothermic changes in the DTA and TGA curves were observed at 82, 287, and 491°C, corresponding to the loss of external, zeolitic, and bound water from the sepiolite, respectively. Dehydroxylation and recrystallization of the sepiolite were fastest at 845°C and 862°C, respectively. The LD curve indicated that the shrinkage began at 800°C and reached 4.0% at 1000°C. The proportion of particles with diameters of <2 µm, and the external surface area of the long-term (24 h) water-treated sepiolite were determined by PSA as 79% by volume, and 8 m2g−1, respectively. The SEM view revealed discrete bundles of sepiolite fibers of various lengths. The specific surface area found from adsorption data was 316 m2g−1. The specific micro-, meso-, macro-, and total-pore volumes obtained from the combination of Hg-Por. and N2-AD results were 0.16, 0.21, 0.45, and 0.82 cm3g−1, respectively. The average macropore and micro-mesopore radii in the sepiolite were estimated (using the Hg-Por. and N2-AD data) tobe 35 and 2.4 nm, respectively.