Ömer Şahin

Transition metal complexes with tridentate salicylaldimine derived from 3,5-di-t-butylsalicylaldehyde

Several new binuclear CuII, NiII, OVIV and MnII complexes of tridentate salicylaldimine (H2L), obtained from 3,5-di-t-butylsalicylaldehyde and o-aminophenol, have been prepared and characterized by analytical, spectroscopic (i.r., u.v.–vis., e.s.r.) techniques, magnetic and thermal measurements. The adduct formation or dissociation of these complexes in the presence of strongly coordinating solvents like pyridine and DMSO did not take place. The complexation of CoII with H2L is accompanied by intramolecular electron transfer from the metal to the coordinated ligand yielding the radical ligand CoIII complex (g = 2.003, ACo = 10 G). The e.s.r. spectra of the CuII, OVIV and MnII complexes in the solid state and in solution are very broad due to intramolecular dipolar antiferromagnetic interactions.

Application of genetic algorithm for determination of mass transfer coefficients

Abstract The mass transfer coefficient, k d , surface reaction constant, k r , and reaction rate order, r , have been calculated by applying the genetic algorithm analysis. This analysis provides the parameter estimations as new data are recorded and consequently yields the time variability of the parameters. In this study, the application of the genetic algorithm procedure is presented for determining the coefficients and their relative standard deviation. The relative standard deviation does not exceed 0.9% taking into account the crystal growth rate, R g calculated from the equation R g =k r (Δ C−R g /k d ) r and the one experimentally obtained and represented by the equation R g =k g (Δ C) g , where k r is the rate constant for the surface reaction, k d is the mass transfer coefficient, r is the reaction order, k g is the overall crystal growth rate constant, Δ C is the supersaturation and g is the overall crystal growth rate order. This new proposed method is compared with the previous methods for the cases of growth of NiSO 4 and CuSO 4 ·5H 2 O crystals in a fluidized bed crystallizer.

Determination of growth and dissolution mass rate of boric acid crystals by a simple computer program

Growth and dissolution rates of boric acid were measured in a laboratory-scale fluidized-bed crystallizer under well-established conditions of supersaturation, undersaturation, temperature and fluidization. It was found that the overall growth rate of boric acid is controlled by both diffusion and reaction steps. But reaction step is the main controller of the crystal growth of boric acid. It was also determined that the dissolution region of boric acid, apart from other known materials is controlled by diffusion and reaction steps. An improved computer program procedure was used to determine the effect of diffusion and reaction steps on the growth and dissolution rates of boric acid crystals. This simple program gives a high accuracy of determination of the mass transfer coefficient, kd, the surface reaction constant, kr and the surface reaction order r. The relative standard deviation between the equation RG=kr(ΔC−RG/kd)r and those experimentally obtained and represented by the equation RG=KG(ΔC)g do not exceed 0.08% for both growth and dissolution region.

Surface potential dominating crystal growth rates of K2SO4

Abstract This study is based on the hypothesis claiming that solubility and crystal growth and dissolution kinetics of K 2 SO 4 are dominated by the surface potential distribution. Specific anion adsorption is the main reason for the occurrence of negatively charged surface and this adsorption is a function of the surface quality. Anion adsorption results in the formation of the electrical double layer, which leads to extra resistance to crystal growth. K 2 SO 4 seed crystals having different surface potentials were classified by an electrostatic separator and used in the measurement of crystal growth rates in a single crystal cell. It has been shown that growth rates of crystals with lower charges are higher than those having higher charges. Dispersions in growth and dissolution rates were explained by surface potential distribution.

Microwave treatment and fluorine addition on Co-B catalyst to improve the hydrogen production rate

ABSTRACT In this paper, microwave heating treatment process and fluorine addition over Co-B-F catalyst was applied to produce hydrogen via the hydrolysis of NaBH4. The effects of microwave heating treatment time, microwave heating treatment power, microwave inert gases and temperature on the catalyst were studied. X-ray absorption spectrometer, scanning electron microscopy coupled to energy-dispersive spectroscopy, nitrogen adsorption analyzer and infrared spectrometer were performed for the chemical characterization of the catalysts. It was found that Co-B-F and microwave-treated Co-B-F catalysts exhibited excellent catalytic activity to produce hydrogen. The rates of the maximum hydrogen production for untreated and microwave-treated Co-B-F catalysts are 1868 and 3400 mL/g/min, respectively.

The role of transport processes in crystallization kinetics of ammonium pentaborate

Abstract The growth rate of ammonium pentaborate octahydrate has been measured as a function of supersaturation for various particle sizes, at different temperature range of 20–50°C in a laboratory-scale fluidized bed crystallizer. The values of mass transfer coefficient K, reaction rate constant, kr, and reaction order, r, were determined from the general mass transfer equation without assumption using an improved computer program which gives a high accuracy. The relative standard deviation between the overall growth rate data obtained from the general mass transfer equation by using kinetic parameters (kr, K and r) found in an improved program and those experimentally obtained do not exceed 0.8%. It was found that increasing the temperature and particle size cause an increase in the values of the kinetic parameters (Kg, kr, K). Overall growth rate of ammonium pentaborate octahydrate is controlled by both diffusion and reaction steps at temperatures lower than 40°C, whereas it is completely controlled by diffusion at temperatures higher than 40°C.

Baryum klorür ve sodyum metaborat reaksiyonu ile baryum metaborat sentez parametrelerinin incelenmesi

Bu çalışmada baryum metaborat üretimi için gerekli optimum şartlar belirlenmeye çalışılmıştır. Üretim, baryum klorür dihidrat (BaCl2.2H2O) ve sodyum metaborat tetrahidrat (NaBO2.4H2O)’ın sulu ortamdaki reaksiyonu ile gerçekleştirilmiştir. Üretim için en uygun sıcaklık, NaBO2/BaCl2 oranı, karıştırma hızı, karıştırma zamanı, dinlendirme zamanı, çözücü tipi ve derişimi, etil alkol etkisi gibi parametreler incelenmiştir. Elde edilen kristallerinin karakterizasyonu, X-ışını kırınımı (XRD), taramalı elektron mikroskobu (SEM) ve partikül boyut ölçüm cihazları yardımıyla yapılmıştır. Kristallerin yapı suyu içerikleri ise TG-DTA analizleri ile belirlenmiştir. Baryum metaborat sentezi için en yüksek verim değeri %88 olarak bulunmuştur. Sentez açısından en uygun şartlar ise; reaksiyon sıcaklığı 80 oC, 400 rpm karıştırma hızı, 60 dk karıştırma ve 60 dk dinlendirme zamanı olarak tespit edilmiştir. BOR ISSN: 2149-9020

Preparation and TG/DTG, FT-IR, SEM, BET Surface Area, Iodine Number and Methylene Blue Number Analysis of Activated Carbon from Pistachio Shells by Chemical Activation

Abstract In this study, low cost activated carbon was prepared from the pistachio shell by chemical activation with zinc chloride (ZnCl2). The prepared activated carbon was characterized by thermogravimetry (TG) and differential thermal gravimetry (DTG), infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and Brunauer, Emmett and Teller (BET) surface area analyses. Results showed that the activation temperature and impregnation ratio have significant effect on the iodine number of the prepared activated carbon. The optimum conditions for preparing the activated carbon having the highest surface area were found to be an activation temperature of 700 °C, soaking time of 24 h and ZnCl2/ pistachio shell ratio of 50 %. The results showed that the BET surface area, total pore volume, iodine number and methylene blue (MB) number of activated carbon prepared under the optimum conditions were 1108 m2/g, 0.39 cm3/g, 1051 mg/g, 98.48 mg/g, respectively.

NaCl+NaH2PO2+H2O Üçlü Sisteminin 333 K’de Çözünürlük ve Fizikokimyasal Özellik Değişimlerinin İncelenmesi

NaCl+NaH 2 PO 2 +H 2 O uclu sisteminin 333 K’de kati-sivi denge verileri ve fizikokimyasal ozellikleri izotermal yontem kullanilarak arastirilmistir. Kati faz bilesimleri Schreinemaker yontemi ile belirlenmistir. NaCl+NaH 2 PO 2 +H 2 O uclu sisteminin basit otonik yapiya sahip oldugu tespit edilmistir. Faz egrisinde, bir otonik nokta, iki invariant egrisi ve iki kristallenme bolgesi gorulmustur. Kristallenme bolgelerinde NaCl ve NaH 2 PO 2 .H2O yapilari tespit edilmistir. NaCl+NaH 2 PO 2 +H 2 O uclu sisteminde NaH 2 PO 2 ’in NaCl uzerine salting-out (cozeltiden tuz uzaklastirma) etkisi gozlenmistir.

Effect Of NaoH In Hydrogen Production From NaBH4 By Using Co-B-F And Co-B-P Catalysts

In this study, Co-B-F and Co-B-P catalysts were synthesized in order to produce hydrogen from sodium boron hydride hydrolysis. Sodium hydroxide concentration in hydrogen production from sodium boron hydride is immensely important to stabilize the reaction. In the case of over use of sodium hydroxide, catalytic activity of the catalyst will decrease, On the other hand, In the case of under-use or without any usage of the catalyst, sodium boron hydride degradation will occur. For these reasons, optimum sodium hydroxide concentrations were determined in the case of synthesized Co-B-F and Co-B-P catalysts usage in sodium boron hydride hydrolysis. In the presence of different sodium hydroxide concentrations, reaction rates and reaction rate constants were examined separately which hydrolysis of sodium borohydride with sodium hydroxide concentration was determined to be effective and how important the hydrogen production. Co-BF in the presence of catalyst for hydrogen production rate of 2.5% concentrations of NaOH in 2400 ml / dk.catalyst, Co-BP for the catalysts was 1605 ml / dk.catalyst was determined.