Browsing by Author "Akyol, Mustafa"

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Çözücü ve Isıl İşlem Sürecinin Mos2 İnce Filmlerinin Yapısal Özelliklerine Etkisinin İncelenmesi
(2022) Akyol, Mustafa; Kıvrak, Burak
Son yıllarda, geçiş metali kalkojenleri (GMK) kendilerine özgü fiziksel ve kimyasal özelliklerinden dolayı çokça çalışılan malzeme gruplarından biri olmuştur. GMK’ler, optoelektronik uygulamalarda, hidrojen evrim reaksiyonları, enerji depolama sistemleri, güneş pili uygulamalarında ve radar emici sistemlerde sıkça kullanılmaktadır. Bu çalışmada, farklı çözücüler ve ısıl işlem süreçleri kullanılarak üretilen GMK grubundan olan MoS2 ince filmlerinin yapısal özellikleri araştırılmıştır. İnce filmler sol-gel spin kaplama yöntemi ile üretilmiştir. Filmlerin kristalizasyonu farklı sıcaklık değerlerinde vakum altında tutulan ve azot gazı (N2) akışı sağlanan fırın sisteminde sağlanmıştır. Isıl işlem sıcaklığı ve çözücü kimyasalın etkisi yapısal analiz metotları ile değerlendirilmiştir. Bu kapsamda, X-ışını kırınım metodu (XRD) ve Raman saçınım ve taramalı elektron mikroskop (SEM) metodu filmlerin yapısal analizlerinin yapılmasında kullanılmıştır.
Effect of Ho Substitution on Structural, Magnetic and Magnetocaloric Properties of Co(crfe)o-4
(SPRINGER, 2021) Kıvrak, Burak; Gülkesen, Semiramis; Ayaş, Ali Osman; Akyol, Mustafa; Ekicibil, Ahmet
In this study, structural, magnetic and magnetocaloric properties of Ho-substituted Co(CrFe)O-4 spinel compounds produced by the sol-gel method were investigated. The Ho concentration in Co(CrFe)O-4 spinel structure was changed from 0 to 20% by 5% steps. It is observed that the Ho3+ ions create a new phase HoCrO3/HoFeO3 in the host spinel lattice. SEM images of samples indicate that the average particle size increases with Ho content. The paramagnetic to ferro-/ferrimagnetic phase transition temperature increases from 312 to 344 K with Ho content. While the fluctuation in saturation magnetization of samples was detected at low temperature, it almost becomes a linear change with the Ho content. The maximum magnetic entropy change under 7 T magnetic field was found as - 1.39, - 1.50, - 1.20, - 0.98 and - 0.91 J/kgK for Ho-free, 5, 10, 15 and 20 wt% Ho content in CoCrFeO4 spinel structure, respectively.
Effect of Synthesis Conditions on the Size and Morphology of Magnetic Nickel Particles
(Wiley-v C H verlag Gmbh, 2025) Kivrak, Burak; Akyildiz, Hasan; Aka, Cemal; Akyol, Mustafa
This study compares the properties of nickel (Ni) particles synthesized through the chemical-reduction-reactions (CRRs) under open-atmosphere and pressurized (solvothermal) conditions. The primary objective was to produce Ni particles with sizes below 100 nm with smooth surfaces, single-phase composition, highly crystalline, mono-disperse, and magnetic which are essential for constructing nanostructured Ni suitable for diverse applications. CRRs were conducted in a glass beaker for ambient pressure synthesis and a solvothermal reactor for pressurized conditions. The structural, morphological, and magnetic characteristics of the samples were investigated in detail. The findings demonstrated that the manipulation of the synthesis conditions in both methods allowed the formation of Ni particles with a wide range of morphologies, crystallinity, and purity. Besides, particle sizes varied from nanometer to micrometer scale, depending on the synthesis approach and processing conditions. Moreover, the relation between magnetic characteristics and morphological features was discussed in detail. Therefore, this research provides a comparative evaluation of two different synthesis methods, offering insight into the optimization of conditions for producing phase-pure, magnetic, and equiaxed Ni nanoparticles (NPs). By addressing the challenge of achieving mono-disperse Ni NPs, this study contributes to the understanding of synthesis techniques and elucidating the mechanisms underlying the formation of magnetic Ni NPs.
Citation - WoS: 3
Citation - Scopus: 3
Investigation of Structural and Magnetic Characteristic of Pure and M-Doped (m: Fe and Cu) Mos2 Thin Films
(Springer, 2022) Kıvrak, Burak; Akyol, Mustafa; Ekicibil, Ahmet
In this study, structural and magnetic properties of pure and M-doped MoS2 (M: Fe and Cu) thin film were investigated. Two-step film growing process were used to create a thin film which are (i) spin coating and (ii) thermal decomposition. Raman spectroscopy results indicate that two characteristic vibration modes of E-2(g)1 (in-plane) and A(18) (out-of-plane) 2H MoS2 were observed in all samples. The surface morphology of samples studied by scanning electron microscopy (SEM) images shows that MoS2 crystals formed a back-to-back triangle shape. However, the triangle-shaped grains transform to nanorods when M is doped into the MoS2. Pure and Fe-doped samples show magnetic transition temperatures at similar to 247 and 95.5 K, respectively. In constrast, the Cu-doped sample shows strong diamagnetic characteristics in measurements. In addition, the magnetization values increase with the introduction of the Fe atoms into the main structure. According to the magnetic hysteresis curves of samples, pure and Fe-doped samples show ferromagnetic characteristics, while the Cu-doped sample shows weak magnetic characteristics in both 5 and 300 K.
Citation - WoS: 1
Citation - Scopus: 2
Investigation of Structural, Magnetic and Microwave Absorption Properties of Nixco1-xfe2o4/Ni:zno (x:0.0, 0.5, and 1.0) Embedded Epoxy Composites
(Springer Heidelberg, 2022) Kıvrak, Burak; Tümen, Kutluhan Utku; Karaaslan, Muharrem; Akyol, Mustafa
In this study, NixCo1-xFe2O4/Ni:ZnO (x:0.0, 0.5, and 1.0) epoxy-based composite structures were manufactured by sol-gel method. The structural, morphological and magnetic characteristics were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). Electromagnetic wave (EMW) absorption measurements were carried out using a vector network analyzer (VNA) between 8 and 12 GHz (X band). Ni substitution with Co decreases the crystallite size, average particle size, magnetic saturation (M-s) and the coercive field (H-c) values of cobalt-ferrite spinel structure. EMW characterization results showed that minimum reflection loss (RL) - 30.91 dB (99.9% absorption) at 10.76 GHz, and the maximum bandwidth of 1.81 GHz were observed for the RAM1 composite. In addition, the substitution of Ni2+ into the cobalt-ferrite structure resulted in the shifting absorption peaks to the higher frequency region (towards K-u band).
Citation - WoS: 9
Citation - Scopus: 11
Pani-Coated Yig/Cfo Hybrid Composites as Advanced Electromagnetic Wave Absorber Through X-Band
(Elsevier Science Sa, 2023) Kıvrak, Burak; Sergun, Atalay; Karaaslan, Muharrem; Akyol, Mustafa
Polyaniline (PANI)-coated Y3Fe5O12(YIG)/CoFe2O4(CFO) hybrid composites were synthesized via sol-gel and oxidative polymerization methods to achieve advanced microwave absorption properties. The structural, morphological, magnetic, and microwave absorption characteristics of the resulting samples were analyzed by performing X-ray diffraction (XRD), scanning electron microscopy (SEM), vibration sample magnet-ometer (VSM), and vector network analyzer (VNA). XRD results revealed that CFO and YIG have cubic crystal structures with Fd3m and Ia3d space symmetry, respectively, with an average crystallite size of 35.3 nm and 42.9 nm. The Ferro/ferrimagnetic signals were detected from the ferrite samples' room temperature magnetic hysteresis loops. The incorporation of PANI and YIG into the composites resulted in a decrease in their magnetic saturation (Ms) and coercive field (Hc) values. VNA measurements demonstrated that nearly all samples achieved 90% absorption (& LE;-10 dB) of incident electromagnetic waves throughout the X-band frequency range. The minimum reflection loss (RLmin) value reaches - 47.34 dB at 8.14 GHz, with an effective bandwidth of 4.00 GHz, covering the entire X-band and beyond. These impressive absorption characteristics suggest that the manufactured composites possess potential as viable candidates for defense applications conducted at X-band frequency.& COPY; 2023 Elsevier B.V. All rights reserved.
Citation - WoS: 10
Citation - Scopus: 11
Phase (1t/2h) Dependent Electromagnetic Wave Absorbing Performance of Flower-Like Mos2 Nanosheets
(Elsevier, 2023) Aka, Cemal; Kıvrak, Burak; Teksen, Fikret Alpay; Akyıldız, Hasan; Akgöl, Oğuzhan; Karaaslan, Muharrem; Akyol, Mustafa
A study was carried out to determine the phase-dependent electromagnetic wave (EMW) absorption performance of MoS2 particles via systematically diversified hydrothermal synthesis conditions such as time, temperature, precursor molarity, and oxalic acid concentration. The formation of mixed-phase structure was verified depending on the presence of the characteristic diffraction peaks belong to 1T (trigonal, P3?m1 space group) and 2H (hexagonal, P63/mmc space group) phases in the X-ray diffraction (XRD) patterns. Phase-pure 2H-MoS2 was obtained at 200 degrees C after 12 h of reaction and using 5 mmol oxalic acid. Microscopic examinations indicate that MoS2 particles formed by assembling several nanosheets to create a flower-like morphology. The size, shape, and the distance between the nanosheets were observed to change with increasing temperature, time, and acid concentration. The band gap was found to be modified depending on the phase distribution and decreased from 1.54 eV (2H) to a minimum of 0.64 eV (1T/2H) with the formation of the 1T (metallic) phase. Finally, the minimum reflection loss was measured as -67.73 dB (99.9999 % of absorption at 9.05 GHz) with an effective absorption bandwidth (EAB) of 3.52 GHz for the sample composed of 1T/2H mixed-phased structure.
Polianilin (pani)-kaplanmış MoS2@MNP (Manyetik Nanoparçacık) Kompozitlerin Sentezi ve Elektromanyetik Dalga Soğurma Kapasitelerinin Araştırılması
(2025) Kıvrak, Burak; Akyıldız, Hasan; Akyol, Mustafa
Bu tez çalışmasında, farklı oranlarda MoS2 partikülleri, Co/Ni manyetik nanoparçacıkları (MNP) ve PANI kaplamadan oluşan kompozitler sentezlenmiş ve mikrodalga frekans aralığında elektromanyetik dalga soğurma performansları incelenmiştir. Çalışmanın temel amacı, dielektrik ve manyetik kayıpların sinerjik etkisini kullanarak düşük kalınlıkta, geniş frekans aralığında etkili ve yüksek performanslı elektromanyetik soğurucu malzemeler geliştirmektir. Bu doğrultuda MoS2 konak yapısı hidrotermal yöntemle sentezlenmiş, Co ve Ni nanoparçacıkları sırasıyla kimyasal reaktantların indirgenmesi yöntemi ve solvotermal yöntemle üretilmiştir. Sonrasında MNP'ler sonikasyon yöntemiyle ağırlıkça %5, 10, 15 ve 20 olacak şekilde MoS2 ile birleştirilmiştir. Ardından anilin monomerinin yerinde polimerizasyonu ile bu birleşimlerin yüzeyi ağırlıkça %25, 50 ve 75 oranlarında PANI ile kaplanmıştır. Son olarak ağırlıkça %70 epoksi matris ve %30 sentezlenen numuneler olacak şekilde nihai kompozitler hazırlanmış ve VNA cihazı ile koaksiyel ve Ku dalga bant kılavuzları kullanılarak soğurma performansları değerlendirilmiştir. Elde edilen veriler hem Co hem de Ni içeren MoS2@MNP birleşimlerinin, tekli bileşenlere kıyasla daha iyi soğurma performansı gösterdiğini kanıtlamıştır. MoS2@Co birleşimlerinde, %15 Co içeren numune, 3 mm kalınlıkta 13,84 GHz frekansta -17,17 dB yansıma kaybı (RLmin) ve 7,51 GHz efektif bant aralığı (EBA) ile en yüksek performansı göstermiştir. MoS2@Ni birleşimlerinde ise en iyi performans, %5 Ni içeren numuneden elde edilmiştir ve bu numune 3 mm kalınlıkta 13,92 GHz frekansta -20,24 dB RLmin ve 4,38 GHz EBA sergilemiştir. PANI kaplaması, iletkenlik kayıplarını artırarak RLmin ve EBA değerlerini belirgin şekilde iyileştirmiştir. En iyi sonuçları sunan ağ. %25 PANI kaplı, ağ. %10 Co + ağ. %90 MoS2 ve ağ. %50 PANI kaplı, ağ. %15 Ni + ağ. %85 MoS2 numuneleri, düşük kalınlıklarda bile geniş frekans aralıklarında -20 dB'nin (%99 soğurma) altında yansıma kayıpları göstermiştir. Co-esaslı numune 3 mm kalınlıkta: 12,21 GHz'de -20,09 dB RLmin ve 9,23 GHz'den başlayarak 18 GHz'e kadar 8,27 GHz EBA'lık bir soğurma performansı ile X (8-12 GHz) bandının yaklaşık %70'ini ve Ku (12-18 GHz) bandının tamamını soğurmuştur. Öte yandan Ni-esaslı numune 3 mm kalınlıkta 10,44 GHz frekansta -24,03 dB RLmin ve ~7,5 GHz'den ~12,6 GHz'e kadar 5,04 GHz EBA'lık soğurma ile C bandının ~%12'sini ve X bandının tamamını kapsayacak şekilde soğurma gerçekleştirmiştir. Çalışmada ayrıca, numunelerin soğurma performansından sorumlu kayıp mekanizmaları sonuçlarla desteklenerek kapsamlı bir biçimde açıklanmıştır. Bu bulgular, tez çalışmasında amaçlanan düşük kalınlıklı, geniş bant aralığında soğurma yapan PANI kaplı MoS2@MNP malzemelerin başarıyla geliştirildiğini ve bu malzemelerin, askeri görünmezlik teknolojileri ve elektromanyetik parazit koruması gibi savunma uygulamaları için yüksek potansiyel sunduğunu ortaya koymaktadır.
Citation - WoS: 2
Citation - Scopus: 4
Polyaniline-Functionalized Nanosized Cobalt Ferrite-Decorated Mos2 Composites for Broadband Electromagnetic Wave Absorption
(Amer Chemical Soc, 2024) Kivrak, Burak; Akyildiz, Hasan; Akgol, Oguzhan; Karaaslan, Muharrem; Akyol, Mustafa
This study presents the synthesis of polyaniline (PANI)-coated cobalt ferrite-decorated molybdenum disulfide (MoS2@CoFe2O4); a composite architecture engineered to combine unique morphological, magnetic, and dielectric properties for the electromagnetic wave/radar absorption applications. MoS2 and CoFe2O4 were produced separately using a one-step hydrothermal process. Then, the CoFe2O4 nanoparticles were integrated into the flower-like MoS2 nanosheets using the sonication method. Finally, PANI was synthesized through in situ polymerization of aniline on the surface of MoS2@CoFe2O4 to create the final design as well as to boost the dielectric performance. Structural analysis confirmed the existence of the 2H phase and a minor trace of the 1T phase in MoS2, while CoFe2O4 displayed a cubic structure without any detectable impurities. Scanning electron microscopy verified the successful distribution of CoFe2O4 particles within the MoS2 nanosheets, aligning with the design's intended configuration. The electromagnetic wave (EMW) characteristics of the composites were analyzed by using a vector network analyzer. The MoS2@CoFe2O4 demonstrated a broad effective absorption bandwidth, spanning from the X-band to the Ku-band with a minimum matching thickness of just 2 mm. The reflection loss minimum value (RLmin) reached -22.82 dB at 8.96 GHz, corresponding to a 99.47% absorption of the incident EMWs. The addition of PANI at 50% by weight further increased the RLmin value to approximately 99.999% absorption (-50 dB), indicating enhanced impedance matching and absorption efficiency.
Citation - WoS: 13
Citation - Scopus: 15
Synthesis and Characterization of Nanoparticles Reinforced Epoxy Based Advanced Radar Absorbing Composites
(SPRINGER, 2021) Tümen, Kutluhan Utku; Kıvrak, Burak; Alkurt, Fatih Ozkan; Akyol, Mustafa; Karaaslan, Muharrem; Ekicibil, Ahmet
In this study, the structural and magnetic properties of NixCo1-xFe2O4 (0.0 <= x <= 1.0) and ZnO nanoparticles synthesized by the sol-gel method were investigated. The microwave property of the composite structures produced from the combination of ZnO and NixCo1-xFe2O4 nanoparticles dispersed in the epoxy matrix property was studied in the X-band frequency range. The crystal structures of NixCo1-xFe2O4 have not been disrupted by Ni substitution, however, the lattice parameters of samples decrease due to the smaller ionic radii of Ni+2 compared to Co+2 ions. The magnetic saturation (M-s) and remanence magnetization (M-r) decreased with an increasing amount of Ni in NixCo1-xFe2O4 structure. According to the microwave absorption properties of samples, the maximum reflection loss (RL) value was found as -28.10 dB at 10.23 GHz frequency in RAC(4) sample. On the other hand, maximum bandwidth was found at 2.95 GHz around -10 dB for RAC5 sample. All composites exhibit efficient RL in the X-band indicating that they can be used in potential applications in aviation, radar, and defense vehicles.