Browsing by Author "Erdem, Sezer"
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Item 2D finite-element analysis of interlaminar flux density distribution at joints of zip-type unicore(Elsevier, 2006-09) Moses, Anthony; Erdem, Sezer; Derebaşı, Naim; Uludağ Üniversitesi.; 0000-0003-2546-0022; AAI-2254-2021; AAI-1248-2021; 13805689400; 11540936300Normal flux distribution along the rolling directions at joints of overlapped stacked electrical laminations is investigated to set up a flux distribution similar to that in the zip-type unicore. A 2D model of a C-core and three layers of overlapped laminations with joints with similar characterisitics to a zip-type unicore were formed and an FE analysis was carried out to solve the problem using a static magnetic analysis and unidirectional vector potential formulation. The results show that when the reluctance changes in the closed magnetic paths causes the flux deviates towards shorter magnetic paths moving to adjacent layers increasing the magnetic flux density. This redistribution causes the flux to transfer easier at joints in the unicore compared to other jointed cores.Publication Adsorption of light green and brilliant yellow anionic dyes using amino functionalized magnetic silica (Fe 3 O 4 @SiO 2 @NH 2) nanocomposite(Taylor, 2019-01-01) Erdem, Beyhan; Avşar, Saliha Buşra; Erdem, Sezer; Tekin, Nalan; ERDEM, BEYHAN; Avşar, Saliha Buşra; ERDEM, SEZER; Bursa Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Bölümü; Bursa Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü; AAI-1238-2021; AAI-1248-2021; CDX-3142-2022Fe3O4@SiO2@NH2 nanocomposite was prepared for highly effective adsorption of two anionic dyes one of which is triarylmethane dye (light green, LG) and the other is azo dye (brilliant yellow, BY). The characterization results demonstrated that superparamagnetic Fe3O4 nanoparticles were covered with silica and functionalized with amino groups successfully without losing magnetic character. The effects of adsorbent dosage, contact time, pH, temperature, and dye molecular structure on the adsorption were investigated. Acidic pH was better for both LG and BY, on the other hand, alkaline pH was favorable to some extent for LG in comparison with BY due to the contribution of stacking effect in addition to electrostatic attraction. Kinetic data demonstrated that the driving force for adsorption process could be explained by pseudo-second order mechanism in both systems. The equilibrium data were more compatible with Langmuir isotherm than those of Freundlich isotherm and the maximum adsorption capacities of Fe3O4@SiO2@NH2 calculated from Langmuir isotherm model for LG and BY at 30 degrees C and natural pH of the solution were 40.2 and 35.5 mg g(-1). Thermodynamic calculations related to temperature dependence demonstrated that the adsorption process was spontaneous and exothermic.Item Bazı moleküllerde moleküler orbital hesaplamaları(Uludağ Üniversitesi, 1997-08-22) Erdem, Sezer; Cebe, Emine; Uludağ Üniversitesi/Fen Bilimleri Enstitüsü/Fizik Anabilim Dalı.STO-3G, 3-21G, 4-31G, 6-31G(d), 6-31+G(d) ve 6-311G(d) taban kümeleri ile ab initio RHF ve yan deneysel MNDO, AMI, PM3 ve CNDO/2 yöntemleri kullanarak akrîdîn geometrisi optimize edilmiştir. Hesaplamalar, akridin yapısının hemen hemen düzlemsel alınabileceğini göstermektedir. Geometri parametreleri, mevcut kristal yapısı ile karşılaştırılmıştır. CNDO/2 ve RMP2/STO-3G dışındaki bütün kuramsal modeller kıyaslanabilir kalitede sonuçlar vermektedir. KBr disk tekniği ile akridinin İR spektrumu alınmıştır. Optimize geometride titreşim frekansları ve kırmızıaltı şiddetleri hesaplanmıştır. Hesaplanan sonuçların, gerek bu çalışmadaki deneysel verilerle ve gerekse mevcut deneysel ve kuramsal sonuçlarla kıyaslanması, PM3 yönteminin frekans ve şiddetleri yeterince iyi tahminlediğini ve ölçekleme yapılırsa ab initio RHF/6- 31G ve RHF/3-21G modellerinin daha iyi frekanslar oluşturduğunu belirtmektedir. Yan-deneysel SCF-MO yöntemleri, gerilme frekanslarını olduğundan yüksek tahminlemektedir. Oysa bu çalışmada kullanılan ab initio metodlar, elektron korrelasyonu etkilerinin ihmali sonucu tüm frekansları sistemli biçimde yüksek vermektedir. Bu nedenle RMP2/STO-3G sonuçları, RHF/STO-3G değerlerinden önemli ölçüde daha iyi bir duruma gelmektedir. On farklı çözgende muhtelif akridin çözeltilerinin UV/VİS spektrumlan kaydedilmiştir. Akridinin elektronik uyarılmış durumları, CIS/3-21G ve CIS/4- 31G düzeylerinde tekli uyarmalı konfigürasyon etkileşmesi (CIS) yöntemi ile incelenmiştir. Singlet ve triplet durumlar için elektronik geçiş enerjileri ve titreşken güçleri hesaplanmıştır. UV/VİS spektrumları ile uyum gözlenmektedir.Item Bifunctional Fe-SBA-15-SO3H mesoporous catalysts with different Si/Fe molar ratios: Synthesis, characterization and catalytic activity(Wiley-V C H Verlag, 2013-05) Öksüzoglu, Ramis Mustafa; Çıtak, Alime; Erdem, Sezer; Erdem, Beyhan; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Anabilim Dalı.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Anabilim Dalı.; AAI-1238-2021; AAI-1248-2021; 13805689400; 14023997200Bifunctional Fe-SBA-15-SO3H mesoporous materials with different Si/Fe molar ratios (3, 5, and 7) have been synthesized via a simple direct hydrothermal method and characterized by XRD, N-2-adsorption/desorption, TG/DTG and FT-IR techniques, and used as solid acid catalysts in the esterification of lactic acid with methanol. XRD and N-2 sorption characterizations show successful iron doping within the mesoporous channels of SBA-15-SO3H. The FT-IR and TG/DTG characterizations also reveal the presence of iron. With the incorporation of Fe ions into the SBA-15-SO3H, the acid sites substantially increased because of the self-separated acidity of the hydrolysis of Fe3+ solutions. However, in the Si/Fe = 3 molar ratio, the catalytic conversion decreased which is caused by the reduced cooperation effect between the acid pairs due to the weakened hydrogen bonds and collapse of the pore structure. This further suggests that the mesoporous structure decreases with the decrease in Si/Fe ratio.Item Catalytic applications of large pore sulfonic acid-functionalized SBA-15 mesoporous silica for esterification(De Gruyter Poland, 2018-01) Öksüzoğlu, Ramis Mustafa; Erdem, Beyhan; Erdem, Sezer; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Bölümü.; 0000-0002-1803-9400; 0000-0003-1119-9863; AAI-1238-2021; AAI-1248-2021; 14023997200; 13805689400We report the preparation of pore expanded and sulfonic acid functionalized mesoporous silica catalysts by using different kinds of swelling agents such as 1,3,5-trimethyl benzene (TMB), n-decane (D), n-tridecane (TD), and n-hexadecane (HD) at two different ratios of swelling agent/surfactant. Non-swelled mesoporous silica catalyst, SBA-15-SO3H, was also prepared for comparison. The performance of the sulfonic acid functionalized solid acid catalysts by using one-pot synthesis procedure was evaluated in terms of their catalytic activity in the esterification of propionic acid with methanol. The catalysts have been characterized by X-ray diffraction to investigate the phase transition between the hexagonally packed arrangement of cylindrical pores and mesocellular silica foams (MCF), and N-2 adsorption/desorption technique in terms of pore size and distributions. It was concluded from the XRD and N-2 adsorption/desorption analyses that hexagonally packed and cylindrical pore structure is maintained only for low ratio of swelling agent/surfactant and the increase of the dimension of a template micelle is accompanied by an increase in structural disruption, which was attributed to the phase transition from highly ordered hexagonal arrangement to mesocellular foam (MCF) phase with large nodded pore structures rather than cylindrical pores. Among the different swelling agents, TMB and D were found to be effective for the increase in pore diameter (up to 8 and 7.8 nm), whereas, TD and HD (6.6 nm) are effective to maintain the ordered X-ray diffraction patterns resulting mesoporous materials without giving enlargement of pore diameter in comparison with TMB and D. Pore expanded catalysts, SBA-15-SO3H-TMB-0.1 and SBA-15-SO3H-D-0.1, exhibit 68 and 43% enhancement in turnover frequency toward propionic acid methanol esterification, respectively, over non :swelled SBA-15-SO3H, despite possessing similar acid strengths. The increased activity especially for SBA-15-SO3H-TM B-0.1 and SBA-15-SO3H-D-0.1 likely reflects the accessibility to the active sulfonic acid sites as well as acidity.Publication Cationic surfactant templated synthesis of magnetic mesoporous nanocomposites for efficient removal of Light Green(Korean Institute Chemical Engineers, 2021-06-22) Erdem, Beyhan; Erdem, Sezer; Tekin, Nalan; ERDEM, BEYHAN; ERDEM, SEZER; Bursa Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Bölümü; AAI-1238-2021; AAI-1248-2021Fe3O4-SiO2-NH2, Fe3O4-CTABSiO(2)-NH2 and Fe3O4-SiO2-CTABSiO(2)-NH2 magnetic adsorbents were successfully prepared and could be used effectively for the adsorption of Light Green from aqueous solutions. Unlike the first sample, mesoporous silica coatings were created using cetyltrimethylammoniumbromide micelles as molecular templates on superparamagnetic iron oxide in one sample, and on silica-coated iron oxide in the other sample to improve the adsorptive properties of the nanocomposites. The characterization by FT-IR, SEM/EDX, Zeta-potential, XRD, VSM, and N-2-adsorption/desorption confirmed the production of mesoporous silica layer. Although coating processes with both silica and mesoporous silica layers led to a vaguely decrease in saturation magnetization of the Fe3O4-SiO2-CTABSiO(2)-NH2, the nanoparticles were protected with silica coatings for environment conditions and made more suitable for subsequent amino functionalization. The results determined from Batch adsorption experiments fitted to Langmuir isotherm model with maximum adsorption capacity (q(max)) equal to 56.18, 196.08 and 227.27 mg g(-1), for Fe3O4-SiO2-NH2, Fe3O4-CTABSiO(2)-NH2 and Fe3O4-SiO2-CTABSiO(2)-NH2, respectively, and it was seen from the kinetic results, the LG adsorption was identified by pseudo-second-order kinetics, revealing that LG adsorption process is homogeneous, monolayer and based on chemical interactions. According to the results, both silica and mesoporous silica coating strategy can play crucial role in improving the adsorptive properties of nanocomposites.Item Changing of geometry related magnetic flux distribution in electrical steels used in transformer cores(Amer Scientific Publishers, 2013-01) Erdem, Sezer; Derebaşı, Naim; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Anabilim Dalı.; 0000-0003-2546-0022; AAI-2254-2021; AAI-1248-2021; 13805689400; 11540936300The efficiency of a transformer core is affected by the design of the joints used at the junctions. Air gaps cause some variations on the flux distribution at the joints of the transformer laminations depending on the geometry. For this purpose, two samples were formed by electrical steels, so different geometries were prepared. A varied flux distribution was determined from an array of search coils for each sample. 2D model of the samples formed by three layers of overlapped laminations was used to compute the magnetic flux distributions. It was observed that flux density in sample-1 starts to approach saturation at low flux density level compared to sample-2. In addition that the geometry of sample-2 design causes the flux distribution to be more uniform than that of sample-1. At high frequencies, the sample-2 is more efficient than the sample-1 because of increasing flux density.Item Direct and postsynthetic functionalization of mesoporous B-SBA-15-SO3H acid catalyst and application to methyl propionate esterification(Polish Acad Sciences Inst Physics, 2017) Öksüzoğlu, R. M.; Erdem, Beyhan; Azko, Q.; Erdem, Sezer; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Bölümü.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; AAI-1238-2021; AAI-1248-2021; 14023997200; 57196450981; 13805689400Organic functionality can be added to mesoporous silicates in two ways: either by covalent grafting (postsynthetic) of various functional groups onto the channel walls or by incorporating functionalities directly during the synthesis (one-pot). If the grafted catalytically active groups experience similar environments and are isolated from each other, catalysis process is greatly facilitated. For this purpose, boric acid, as boron source, was added into the initial reaction mixture and then acid functionalization was performed by post and direct method. The obtained acid catalysts were tested in the esterification of propionic acid with methanol and the activity of these new materials was compared to that of SBA-15-SO3H. Boron addition has facilitated the methyl propionate esterification for both postsynthetic and direct functionalized acid catalyst. Boron incorporated and postsynthetic functionalized mesoporous acid catalyst has highly enhanced the esterification reaction, compared to direct functionalized acid catalyst. The post functionalization method seems to be superior to one-pot functionalization method for preparation of mesoporous acid catalysts.Publication Effect of calcination temperature on the structural and magnetic properties of Ni/SBA-15 nanocomposite(Springer, 2015-06-01) Erdem, Sezer; Erdem, Beyhan; Öksüzoğlu, Ramis Mustafa; Çitak, Alime; ERDEM, SEZER; ERDEM, BEYHAN; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Bölümü; AAI-1238-2021; AAI-1248-2021The effect of calcination temperature on the structural and magnetic properties of Ni/SBA-15 nanocomposite prepared by reductant-impregnation method was studied using SBA-15 mesoporous silica as support. The structure, morphology and magnetic properties of the samples were characterized using X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectrometry, N-2 adsorption/desorption (BET and BJH), vibrating sample magnetometer, and FT-IR. Characterization results showed the presence of crystalline phases characteristics of the Ni and/or NiO, and that the structural characteristics of the support were maintained after the impregnation of nickel ions followed by calcinations. Calcination process helps in crystallization and formation of the desired phase such as well crystalline NiO and Ni nano-particles. Moreover, this heat resulted in significant effects on different properties of the products such as the crystallite size, homogeneity, particle distribution, porosity, surface area and the sintering process. Magnetic measurements suggested that the magnetic properties in nanocomposites is probably the sum of two contributions: superparamagnetic and ferromagnetic one depending on the calcination temperature. Calcination at high temperatures affects both of the structural and magnetic properties of Ni/SBA-15. Because the location of the Ni particles depends on the pore size of the support, the uniformity of particle size was related to the interaction between the Ni particles and support.Item High-surface-area SBA-15-SO3H with enhanced catalytic activity by the addition of poly(ethylene glycol)(Springer, 2013-10) Öksüzoğlu, Ramis Mustafa; Çıtak, Alime; Erdem, Beyhan; Erdem, Sezer; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Anabilim Dalı.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Anabilim Dalı.; AAI-1248-2021; AAI-1238-2021; 14023997200; 13805689400The influence of poly(ethylene glycol) (PEG) and synthesis temperature in the synthesis of SBA-15-SO3H was investigated to evaluate the catalytic activity in the esterification of propionic acid with methanol. The catalysts were characterized by means of surface and structure analyses; X-ray diffraction, FT-IR, scanning electron microscopy, Thermo-gravimetric and N-2 adsorption/desorption techniques. It was found that, by the addition of PEG, the surface area and porosity of SBA-15-SO3H increased, while the structure and size of mesopores remained unchanged. Nitrogen sorption measurements indicate that PEG introduces additional pores into the pore walls of SBA-15-SO3H. Thus, a simple way of improving the porosity of mesoporous SBA-15-SO3H was presented that could enhance transport of substrates through the porous system and allow the generation of stable mesoporous replicas, important for catalytic applications and also beneficial for replication and nanocasting purposes.Item Interlaminar flux density distribution at joints of overlapping stacked electrical steel and amorphous ribbons(Korean Magnetics, 2010-12) Erdem, Sezer; Derebaşı, Naim; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; AAI-2254-2021; AAI-1248-2021; 13805689400; 11540936300The design of joints in a transformer core significantly affects the transformer's efficiency. Air gaps cause variations in the flux distribution at the joints of the laminations, which depend on the geometry. Two similar samples consisting of electrical steel strips and amorphous ribbons were made. The spatial flux distributions were determined using an array of search coils for each sample. 2D models of these samples were created and examined by finite element analysis. The magnetic flux distribution for each lamination in the samples was computed. The results show that the flux density in amorphous ribbons above and below the air gap starts to approach saturation at lower flux density levels than for electrical steel. The flux density measured using the search coil under the air gap is increased in amorphous ribbons and decreased in the electrical steel with increasing frequency.Item Magnetic mesoporous silica nanocomposite for biodiesel production(Polish Acad Sciences Inst Physics, 2017-09) Öksüzoğlu, R. M.; Erdem, Sezer; Avşar, Saliha Büşra; Erdem, Beyhan; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Bölümü.; AAI-1248-2021; AAI-1238-2021; 13805689400; 57196458837; 14023997200Ordered mesoporous silicas can be utilized as support because of having large surface area, tunable porosity, uniform pore size distribution, high thermal stability and modifiable properties. However, these materials introduce separation problems in liquid-phase processes. We have prepared Fe3O4-SBA-15-SO3H solid acid catalyst by combining the properties of a magnetic material and the mesoporous character of silica. The sulfonic acid functionalized solid acid catalyst, containing both magnetic nanoparticles and mesoporous silica, is not only separable but also stable under hydrothermal conditions, which are usually employed for biodiesel production. Esterification of oleic acid with methanol for biodiesel production was carried out effectively and 75% conversion of ester was approximately reached within six hours in the presence of Fe3O4-SBA-15-SO3H magnetic solid acid catalyst. In addition, the catalyst could be separated from the reaction system by applying external magnetic field and reused without deactivation.Item Magnetic nano-sized solid acid catalyst bearing sulfonic acid groups for biodiesel synthesis(De Gruyter Poland Sp Z. O. O., 2018-05-04) Öksüzoǧlu, Ramis Mustafa; Erdem, Sezer; Erdem, Beyhan; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Bölümü.; AAI-1238-2021; AAI-1248-2021; 13805689400; 14023997200In our approach for magnetic iron oxide nanoparticles surface modification, the fabrication of an inorganic shell, consisting of silica by the deposition of preformed colloids onto the nanoparticle surface and functionalization of these particles, was realized. The magnetic nanoparticles, non-coated and coated with silica layer by Stober method, are functionalized with chlorosulfonic acid. The magnetic nanoparticles (MNPs), in size of 10-13 nm, could be used as acid catalyst in biodiesel production and show superparamagnetic character. The prepared nanoparticles were characterized by different methods including XRD, EDX, FT-IR and VSM. The catalytic activity of the coated and non-coated solid acids was examined in palmitic acid-methanol esterification as an industrial reaction for biodiesel synthesis. Although thin silica layer results in only a minor obstacle with respect to magnetism, it can accelerate the mass transportation due to its relatively porous structure and magnetic core may be more stable in the acidic reaction medium by means of covering process. Accordingly, coating strategy can be efficient way for allowing applications of MNPs in acid catalyzed esterification.Item Mathematical model for cutting effect on magnetic flux distribution near the cut edge of non-oriented electrical steels(Elsevier, 2008-10) Peksöz, Ahmet; Erdem, Sezer; Derebaşı, Naim; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; 0000-0003-2546-0022; AAI-2254-2021; AAG-9772-2021; AAI-1248-2021; 23100976500; 13805689400; 11540936300Basic magnetic properties of non-oriented electrical steel sheets with different grain size and silicon content have different behaviour before and after cutting into strips. Cutting process causes a significant drop in flux density and deterioration of magnetic properties occurs over a region up to 10 mm from close to the cut edge. Therefore some degraded regions are formed at each side of the cut. A new mathematical model was formed for the degree of deterioration on flux distribution near the cut edge. The variation of magnetic induction in the cutting region was given as a function of four different parameters depending on the material. The model also included the variation of these parameters with the grain size and silicon content. It is observed that the change in the parameters until 2.5% Si content is not significant, while it has a remarkable variation for them after 2.5% Si content and similar effect was found to be for grain size. The mathematical model gives the degree to which the magnetic properties of the region around the edge degrade after the cutting process. The calculated results of the model showed good agreements with the experimental results.Item Normal flux density distribution at joints of overlap stacked electrical steel laminations(Amer Inst Physics, 2007) Erdem, Sezer; Derebaşı, Naim; Uludağ Üniversitesi/Fen Edebiyat Fakültesi/Fizik Bölümü.; AAI-1248-2021; AAI-2254-2021; 13805689400; 11540936300Three layer of M4 laminations with search coil wound around them were used to measure the magnetic flux density. When the samples were magnetised under controlled sinusoidal conditions, the magnetic flux density increased in the top and bottom laminations while it decreased in the middle due to less permeability of air gap. The results confirm that the normal flux density leaving from the middle lamination when approaching to the air gap is almost equal to the total extra flux joining to the top and bottom laminations.Item Preparation, characterization and catalytic properties of SBA-15-SO3H supported tungstophosphoric acid for esterification reaction(Polish Acad Sciences, 2017) Çıtak, Alime; Yavru, Celal Alp; Öküzoğlu, R. M.; Erdem, Beyhan; Erdem, Sezer; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Bölümü.; AAI-1248-2021; AAI-1238-2021; 14023997200; 13805689400SBA-15-SO3H supported tungstophosphoric acid (TPA, H3PW12O40) mesoporous materials were synthesized by impregnation of TPA into the hydrothermally synthesized SBA-15-SO3H and the catalytic performances were compared for the esterification reaction. The physical and chemical properties of the catalysts were characterized by XRD, SEM/EDX, FT-IR and N-2 adsorption/desorption techniques. The characterization results show that TPA/SBA-15-SO3H retained the typical mesoporous structure of SBA-15-SO3H. The experimental results indicated that TPA/SBA-15-SO3H is a more efficient catalyst than SBA-15-O3H for the esterification reaction. The higher activity of TPA/SBA-15-SO3H compared with that of SBA-15-SO3H was consistent with the material having the low pKa value, confirming that the esterification rate was mostly dependent on the acid strength of the additional functional groups of solid acid catalyst. Accordingly, the reason for the catalytic activity difference was simply explicated by the effect of TPA, having low pKa value, affecting the pore structure and the total acidity.Item Synthesis, characterization and catalytic behavior of functionalized mesoporous SBA-15 with various organo-silanes(Academic Press Inc Elsevier Science, 2012-03-01) Çıtak, Alime; Öksüzoğlu, Ramis Mustafa; Erdem, Beyhan; Erdem, Sezer; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Kimya Bölümü.; Uludağ Üniversitesi/Fen-Edebiyat Fakültesi/Fizik Bölümü.; AAI-1238-2021; AAI-1248-2021; 14023997200; 13805689400Mesoporous silica SBA-15 has been synthesized and functionalized by one-step synthesis method to widen their various application possibilities. In this study, phenyltrimethoxysilane (PTMS), 3-mercapto-propyltrimethoxysilane (MPTMS) and trimethoxypropylsilane (TMPS) were used as silane precursors for the functionalization, and after treated with HCl solution, their catalytic activities were evaluated in the lactic acid-methanol esterification. The presence of anchoring of functional groups on SBA-15 was proved by XRD, FT-IR, BET surface area and pore size distributions. Good catalytic activity was observed especially for SBA-15-SO3H-MPTMS, and the catalytic activity order was determined as follows: SBA-15SO(3)H-MPTMS > SBA-15-TMPS > SBA-15-PTMS, which is directly associated with the surface area, pore size and pore volume. As compared with homogeneous catalyst, SBA-15-SO3H-MPTMS heterogeneous catalyst shows remarkable performance, such as separation, recovery and reusability.Item Transformatör çekirdeklerinde kullanılan elektrik çelikleri ve amorf şeritlerin uç uca gelen birleşim yerlerindeki manyetik akı dağılımının deneysel ve kuramsal incelenmesi(Uludağ Üniversitesi, 2006-06-30) Erdem, Sezer; Derebaşı, Naim; Uludağ Üniversitesi/Fen Bilimleri Enstitüsü/Fizik Anabilim Dalı.Transformatör çekirdekleri oluşturulurken kullanılan manyetik maddeler (elektrik çelikleri, amorf şeritler vb.) dışında çekirdeklerin geometrisi de çok önemlidir. Bir transformatör çekirdeği yapılırken geometriye bağlı olarak levhaların köşe ve orta yerlerinde hava aralıkları oluşmaktadır. Bu hava aralıkları akı dağılımında değişmelere yol açmaktadır. Bu çalışmada, hava aralıklarının manyetik akı yoğunluğu dağılımları üzerindeki etkisi üç katlı elektrik çeliklerinden (M4) ve amorf şeritlerden (Metglas-2605SC) yapılmış örneklerde incelenmiş ve karşılaştırılmıştır. Levhalar arasındaki akı geçişleri aynı örnekte (M4) farklı yerlere yerleştirilen algılama bobinlerinin yardımıyla ayrıntılı olarak incelenmiş ve manyetik akı yoğunluğu değişimi yüzde olarak hesaplanmıştır. z- tipi (Unicore) transformatör çekirdeğinde oluşan hava aralıklarının da akı dağılımına etkisi incelenmiştir. Akının, Unicore’ daki hava aralıklarının oluşumu nedeniyle levhalar arasından kolayca geçtiği teorik ve deneysel olarak saptanmıştır. Bazı örneklerdeki manyetik akı yoğunluğu değişimlerinin sonlu elemanlar yöntemi kullanılarak benzeşimleri yapılmıştır. Ayrıca, deneysel sonuçlar 2-boyutlu statik manyetik analiz (manyetik vektör potansiyel formülasyonu) kullanılarak da teyid edilmiştir.