1. UKM Learning and Research Repository
2. PHD Thesis / Tesis PHD
3. Faculty of Science and Technology / Fakulti Sains dan Teknologi

Title:	Sifat magnet dan elektromagnet gelombang mikro bagi nanokomposit getah asli termoplastik-ferit barium
Authors:	Nurhidayaty Mokhtar (P28208)
Supervisor:	Mustaffa bin Haji Abdullah, Prof. Dr.
Keywords:	Getah asli Termoplastik-ferit Thermoplastics
Issue Date:	8-Nov-2014
Description:	Kesan peningkatan kandungan nanozarah BaFe12O19 (2% – 14%) dan nisbah getah asli:polietilena ketumpatan tinggi (NR:HDPE) (20:80 – 60:40) dalam matriks getah asli termoplastik (TPNR) ke atas sifat struktur, magnet dan elektromagnet pada frekuensi gelombang mikro telah dikaji bagi nanokomposit TPNR–BaFe12O19. Sampel TPNR dan komposit disediakan dengan kaedah pengadunan leburan dalaman pada suhu 140 °C dan kadar 70 putaran per minit selama 13 minit. Mikrostruktur dan morfologi sampel dianalisis menggunakan kaedah-kaedah pembelauan sinar-X (XRD), mikroskopi elektron imbasan (SEM) dan mikroskopi elektron penghantaran (TEM). Pencirian sifat magnet dan elektromagnet masing-masingnya dilaksanakan dengan alat magnetometer sampel bergetar (VSM) dan penganalisis rangkaian vektor gelombang mikro (MVNA, julat frekuensi 2 – 20 GHz). Difraktogram sinar-X mengesahkan struktur hablur ferit barium yang dikaji adalah ferit heksagon jenis-M, manakala matriks TPNR pula bersifat separa hablur. Mikrograf-mikrograf TEM dan SEM menunjukkan darjah kelarutcampuran NR dan HDPE meningkat dengan bertambahnya nisbah NR:HDPE dalam matriks TPNR; keadaan ini disusuli dengan taburan pengisi yang semakin seragam dalam komposit. Di bawah tindakan medan luaran maksimum 10 kOe, gelung histeresis sampel BaFe12O19 tulen menunjukkan pemagnetan maksimum (Mm), pemagnetan baki (Mr) dan daya paksa (Hc) masingmasing adalah 31.22 emu/g, 17.48 emu/g dan 3821 Oe. Gelung histeresis sampel komposit didapati teranjak ke kiri iaitu ke arah medan negatif sebanyak Hs; pemerhatian sebegini adalah mirip kepada fenomenon pincang salingtukar. Mm, Mr dan Hc didapati meningkat dengan bertambahnya peratus pengisi dan nisbah NR:HDPE dalam komposit. Hs juga meningkat dengan bertambahnya kandungan pengisi tetapi menyusut dengan bertambahnya nisbah NR:HDPE. Perubahan pada sifat magnet yang ditunjukkan oleh sampel boleh dijelaskan berdasarkan model yang menganggap nanozarah ferit terdiri daripada spin-spin teras yang tersusun mengikut tertib ferimagnet dan spin-spin permukaan yang tidak kolinear. Keadaan tidak kolinear tersebut berubah mengikut nisbah NR:HDPE. Komponen nyata dan khayalan bagi ketelusan dielektrik (ε′ dan ε′′) didapati meningkat dengan bertambahnya kandungan pengisi BaFe12O19 dan juga nisbah NR:HDPE dalam komposit. Keputusan ini menunjukkan bahawa zarah-zarah ferit barium dan molekul-molekul getah asli mempunyai sumbangan yang positif ke atas mekanisme pengutuban dalam komposit. Sebaliknya, keputusan yang diperolehi bagi komponen nyata dan khayalan bagi ketelapan magnet (μ′ dan μ′′) adalah bertentangan; kedua-duanya menyusut dengan meningkatnya peratus pengisi BaFe12O19 dan juga nisbah NR:HDPE. Perubahan sebegini dipercayai berpunca daripada fenomenon resonans yang mungkin berlaku pada frekuensi di bawah 2 GHz, yang menyebabkan penyusutan ketelapan magnet dalam julat GHz. Dengan menggunakan data-data ε′, ε′′, μ′ dan μ′′, sifat penyerapan gelombang mikro sampel telah dianalisis dengan kaedah simulasi. Keputusan menunjukkan kehilangan pantulan (RL) sebanyak -20 dB (serapan kuasa 99%) berlaku pada ketebalan penyerap yang semakin nipis dan frekuensi padanan yang semakin tinggi apabila peratus pengisi dan nisbah NR:HDPE bertambah.,Studies were conducted on the effect of increasing BaFe12O19 nanoparticles percentage (2% – 14%) and natural rubber:high density polyethylene (NR:HDPE) ratio (20:80 – 60:40) in thermoplastic natural rubber (TPNR) matrices on the structure, magnetic and microwave electromagnetic properties of TPNR–BaFe12O19 nanocomposites. TPNR and composite samples were prepared using internal mixer melt-blending technique at 140 °C and mixing rate of 70 rotations per minute for 13 minutes. Microstructure and morphology were analysed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Magnetic and electromagnetic characterizations were made using a vibrating sample magnetometer (VSM) and a microwave vector network analyzer (MVNA, frequency range 2 – 20 GHz), respectively. X-ray diffractogram confirmed the studied barium ferrite crystal structure is M-type hexagonal ferrite, while the TPNR matrix is semicrystalline. TEM and SEM micrographs showed that the degree of miscibility between NR and HDPE increases with the increase in NR:HDPE ratio in TPNR matrix; this is followed by better homogeneity of filler dispersion in the composites. Under the maximum applied magnetic field of 10 kOe, hysteresis loop of the pure BaFe12O19 sample revealed maximum magnetisation (Mm), remanence (Mr) and coercive force (Hc) of 31.22 emu/g, 17.48 emu/g and 3821 Oe respectively. Hysteresis loops of the composites were shifted by an amount of Hs to the left i.e. towards the negative field; this observation is similar to exchange bias phenomenon. Mm, Mr and Hc increase with the increase in filler content and NR:HDPE ratio in composites. Hs also increases with the increase in filler content but decreases with the increase in NR:HDPE ratio. Variations in the magnetic properties as revealed by the samples can be explained based on the model which assumes that ferrite nanoparticles are consisted of ferrimagnetically ordered core spins and non-collinear surface spins. The non-collinearity state changes according to the NR:HDPE ratio. The real and imaginary components of dielectric permittivity (ε′ and ε′′) were found to increase with BaFe12O19 filler content and NR:HDPE ratio in the composites. These results indicate that the barium ferrite particles and natural rubber molecules contribute positively towards the polarisation mechanisms in the composites. On the other hand, results shown by the real and imaginary components of magnetic permeability (μ′ and μ′′) were on the contrary, where both components decrease with the increase in BaFe12O19 filler content and NR:HDPE ratio. Such changes are believed to be caused by resonance phenomenon that occurred at frequencies below 2 GHz, resulting in the reduction of magnetic permeability in the GHz range. With the ε′, ε′′, μ′ dan μ′′ data, microwave absorbing properties of the samples were analyzed by using the simulation method. Results revealed that reflection loss (RL) of -20 dB (absorbed power of 99%) is achievable with thinner absorbers and at higher matching frequency when the filler content and NR:HDPE ratio are increased.,PhD
Pages:	175
Call Number:	TP1180.T5N846 2014 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Science and Technology / Fakulti Sains dan Teknologi

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.