Search Results

You are looking at 1 - 9 of 9 items for

  • Author or Editor: Y. Sarıkaya x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

A sodium smectite (NaS) with a cation exchange capacity (CEC) of 1.08 mol kg−1 was intercalated with methyltributylammonium cation (MTBA+) with proportions equivalent to 0.2, 0.4, 0.6, 0.8 and 1.0 times the CEC. The contents of adsorbed water and intercalated MTBA+ in the prepared organosmectites (OSs) were determined by using the differential thermal analysis (DTA) and thermogravimetry (TG) curves. The adsorbed water of 8% in the NaS decreases greatly in OSs with the increase of the MTBA+ content and reduces to 2.0% for the 1.0 CEC sample. This explains the gradual change of the NaS from hydrophilic to hydrophobic character. Thermal degradation of the intercalated MTBA+ in OSs occurs approximately between 250–450°C. The oxidation of the formed charcoal to CO2 occurs between 450–850°C. The intercalated MTBA+ content for each OS is obtained from both the TG and carbon analysis. The results do not agree exactly, but both the results tend to increase by increasing initial content of the MTBA+ in solution.

Restricted access

Abstract  

Thermogravimetric (TG) and differential thermal analysis (DTA) curves of methyltributylammonium smectite (MTBAS), methyltrioctylammonium smectite (MTOAS), and di(hydrogenatedtallow)dimethylammonium smectite (DHTDMAS), and also corresponding sodium smectite (NaS) and tetraalkylammonium chlorides (TAAC) were determined. The TAACs was decomposed exactly by heating up to 500°C. The adsorbed water content of 8.0% in the pure NaS was decreased down to 0.2% depending on the size of the non-polar alkyl groups in the tetraalkylammonium cations (TAA+). The thermal degradation of the organic partition nanophase formed between 2:1 layers of smectite occurs between 250–500°C. Activation energies (E) of the thermal degradations in the MTBAS, MTOAS and DHTDMAS are 13.4, 21.9, and 43.5 kJ mol−1, respectively. The E value increases by increasing of the interlayer spacing along a curve depending on the size of the alkyl groups in the TAA+.

Restricted access

Abstract  

The monthly variation of selenium concentration in atmospheric particulate material of Ankara was investigated. The selenium concentrations in possible pollution source materials like coal, fuel oil and their bottom and fly ashes were determined to obtain the percent transference of selenium into the atmosphere. Instrumental thermal neutron activation analysis and atomic absorption spectroscopy were applied for the analysis of selenium in the samples. Selenium enrichment factors with respect to the fuels, soil of Ankara and crustal material were also calculated. Atmospheric selenium concentration is found to increase during winter months and the main cause of this increase is the emission of selenium into the atmosphere due to fuel combustion.

Restricted access

Abstract  

The mineralogical composition of the Kütahya calcium bentonite (CaB) from Turkey was obtained as mass% of 60% calcium rich smectite (CaS), 30% opal-CT (OCT), trace amount illite (I), and some non-clay impurities by using chemical analysis (CA), X-ray diffraction (XRD), and thermal analysis (TG-DTA) data. The crystallinity, porosity, and surface area of the samples heated between 25–1300°C for 2 h were examined by using XRD, TG, DTA and N2-adsorption-desorption data. The position of the 001 reflection which is the most characteristic for CaS does not affect from heating between 25–600°C and then disappeared. The decrease in relative intensity (I/I 0) from 1.0 to zero and the increase in full width at half-maximum peak height (FWHM) from 0.25 to 1.0° of the 001 reflection show that the crystallinity of the CaS decreased continuously by rising the heating temperature from 25 to 900°C and then collapsed. The most characteristic 101 reflection for opals intensifies greatly between 900 and 1100°C with the opal becoming more crystalline. The total water content of the natural bentonite after dried at 25, 105 and 150°C for 48 h were determined as 8.8, 5.0 and 2.5%, respectively. The mass loss occurs between 25 and 400°C over two steps with the maximum rate at 80 and 150°C, respectively. The exact distinction of the dehydration temperatures for the adsorbed water and interlayer water is seen almost impossible. The temperature interval, maximum rate temperature, and mass loss during dehydroxylation are 400–800°C, 670°C and 4.6–5.0%, respectively. The maximum rate temperatures for decrystallization and recrystallization are 980 and 1030°C, respectively. The changes in specific micropore volume (V mi), specific mesopore volume (V me), specific surface area (S) were discussed according to the dehydration and dehydroxylation of the CaS. The V mi, V me and S reach to their maxima at around 400°C with the values of 0.045, 0.115 cm3 g−1 and 90 m2 g−1, respectively. The radii of mesopores for the bentonite heated at 400°C are distributed between 1–10 nm and intensified approximately at 1.5 nm.

Restricted access

Abstract  

A method has been purposed to calculate some of the thermodynamic quantities for the thermal deformation of a smectite without using any basic thermodynamic data. The Hançılı (Keskin, Ankara, Turkey) bentonite containing a smectite of 88% by volume was taken as material. Thermogravimetric (TG) and differential thermal analysis (DTA) curves of the sample were obtained. Bentonite samples were heated at various temperatures between 25–900°C for the sufficient time (2 h) until to establish the thermal deformation equilibrium. Cation-exchange capacity (CEC) of heated samples was determined by using the methylene blue standard method. The CEC was used as a variable of the equilibrium. An arbitrary equilibrium constant (K a) was defined similar to chemical equilibrium constant and calculated for each temperature by using the corresponding CEC-value. The arbitrary changes in Gibbs energy (ΔG a 0) were calculated from K a-values. The real change in enthalpy (ΔH 0) and entropy (ΔS 0) was calculated from the slopes of the lnK vs. 1/T and ΔG vs. T plots, respectively. The real changes in Gibbs energy (ΔG 0) and real equilibrium constant (K) were calculated by using the ΔH 0 and ΔS 0 values. The results at the two different temperature intervals are summarized as below: ΔG 1 0H 1 0−ΔS 1 0 T=−RTlnK 1=47000−53t, (200–450°C), and ΔG 2 0H 2 0S 2 0T=−RTlnK 2=132000−164T, (500–800°C).

Restricted access

Abstract  

A model was proposed to calculate some thermodynamic parameters for the acid dissolution process of a bentonite containing a calcium-rich smectite as clay mineral along with quartz, opal and feldspar as impurities. The bentonite sample was treated with H2SO4 by applying dry method in the temperature range 50–150°C for 24 h. The acid content in the dry bentonite-sulphuric acid mixture was 45 mass%. The total content (x) of Al2O3, Fe2O3 and MgO remained in the undissolved sample after treatment was taken as an equilibrium parameter. An apparent equilibrium constant, K a, was calculated for each temperature by assuming K a=(x mx)/x where x m is the total oxide content of the natural bentonite. Also, an apparent change in Gibbs free energy, ΔG a o, was calculated for each temperature by using the K a value. The graphs of lnK a vs. 1/T and ΔG a o vs. T were drawn and then the real change in both the enthalpy, ΔH o and the entropy, ΔS o, values were calculated from the slopes of the straight lines, respectively. Inversely, real ΔG o and K values were calculated from the real ΔH o and ΔS o values through ΔG o = −RT ln K = ΔH oTΔS o equation. The best ΔH o and ΔS o fittings to this relation were found to be 65687 J mol−1 and 164 J mol−1K−1, respectively.

Restricted access

Abstract

The specific micro- and mesopore volumes (V) of alumina compacts fired between 900 and 1250 °C for 2 h were determined from nitrogen adsorption/desorption data. The V value was taken as a sintering equilibrium parameter. An arbitrary sintering equilibrium constant (K a) was estimated for each firing temperature by assuming K a = (V iV)/V, where V i is the largest value at 900 °C before sintering. Also, an arbitrary Gibbs energy (ΔG a °) of sintering was calculated for each temperature using the K a value. The graph of ln K a versus 1/T and ΔG a ° versus T were plotted, and the real enthalpy (Δ) and the real entropy (Δ) of sintering were calculated from the slopes of the obtained straight lines, respectively. On the contrary, real Δ and K values were calculated using the real Δ and Δ values in the Δ = −RT lnK = 165814 − 124.7T relation in SI units.

Restricted access

Abstract  

An industrial raw material taken from Sivrihisar (Eskişehir, Turkey) region was heat-treated at different temperatures in the range of 100–1000�C for 2 h. The volumetric percentage of the particles having a diameter below 2 μm after staying in an aqueous suspension of the material was determined as 67% by the particle size distribution analysis. The mineralogical composition of the material was obtained as mass% of 32% palygorskite, 10% metahalloysite, 35% magnesite, 20% dolomite and 3% interparticle water by using the acid treatment, X-ray diffraction and thermal analysis (TG, DTA) data. The temperature ranges were determined for the endothermic dehydrations for the interparticle water as 25–140�C, for the zeolitic water as 140–320�C, and for the bound water as 320–480�C, in the palygorskite. The temperature range for the endothermic dehydroxylation and exothermic recrystalization of the palygorskite is 780–840�C. The temperature range for the endothermic dehydroxylation of the metahalloysite and calcinations of magnesite are coincided at 480–600�C. Dolomite calcined in the temperature range of 600–1000�C by two steps. The zig-zag changes in the specific surface area (S/m2 g−1) and specific micro and mesopore volume (V/cm3 g−1) as the temperature increases were discussed according to the dehydrations in the palygorkskite, dehydroxylation of palygorskite and metahalloysite, and calcinations in magnesite and dolomite.

Restricted access

Abstract  

An industrial raw material taken from Beypazarı (Ankara, Turkey) region was heated at different temperatures in the 100–1100�C interval for 2 h. The volumetric percentage of particles having diameter below 2 μm in an aqueous suspension of the material held 24 h were determined as 85% by the particle size distribution analysis. The mineralogical composition of the material was obtained as mass% of 81% sepiolite, 15% dolomite, and 4% interparticle water by using the X-ray diffraction (XRD) and thermal analysis (TG, DTA) data. The temperature ranges were determined for the dehydrations of the interparticle water and the zeolitic water as 25–340�C, for the dehydration of the bound water as 340–580�C, and for the dehydroxylation of the hydroxyls as 800–833�C in the sepiolite. The zig-zag changes in the specific surface area (S/m2 g−1) and specific micro-and mesopore volume (V/cm3 g−1) with the temperature increases were discussed according to the dehydrations and dehydroxylation of the sepiolite.

Restricted access