Dissertations/Theses - Department of Materials & Metallurgical Engineering
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Item Synthesis of hydroxyapatite biomedical ceramic by spark plasma sintering and it's characterization(Department of Materials and Metallurgical Engineering, 2020-03-02) Ahmed, Shabbir; Gulshan, Dr.FahmidaThis work describes the unique features and controlled sintering ability of modern spark plasma sintering machine for the preparation of transparent hydroxyapatite biomedical ceramic. It also investigated the effect of contact electrical poling to measure and justifies its piezoelectric behaviors. In this research work, highly specialized electric current assisted Spark Plasma Sintering (SPS) technique was used for hydroxyapatite (HA) powder sintering. All the sintering parameters were controlled with high precision by its computerized mechanism that suppressed several limitations of conventional sintering techniques. HA biomedical ceramic pellets were prepared at prolonged temperature ranges around 850oC to 1000oC with calcined and un-calcined HA powder. Transmittances of prepared samples were measured by using UV Vis spectrometer. Phase changes in sintered pellets were analyzed by X- ray diffraction pattern and optical micrograph. XRD analysis confirmed phase purity and crystal orientation of produced samples. Relevant orientation indexes of HA materials were measured from X ray diffraction patterns of planes perpendicular and parallel to the applied pressure direction to identify c-axis elongation so as to evaluate the possibility of introducing piezoelectric property in the HA sample. HA samples prepared at sintering temperature 900oC using calcined powder shows maximum transmittance nearly 75%. On the other hand, HA samples that were prepared from un-calcined powder showed maximum transmittance around 70%. Comparatively, lower sintering pressure 3.9kN was found more favorable for producing transparent HA pellets at temperature 900oC but after crossing 975oC, opposite phenomenon was also observed that is higher pressure was better for producing more transparent HA pellets. Textured transparent HA samples were then applied in high voltage contact electrical poling devices to create a net polarization and therefore to induce piezoelectricity. Here, sufficiently strong electric fields were applied across these ceramics to cause reorientation of spontaneously elongated unit cell into more isotropic alignment along the field lines. Finally, applied field was removed and samples were cooled rapidly to induce a net overall piezoelectric property. Here, the effect of applied voltages and poling temperatures were investigated and found to induce longitudinal piezoelectric coefficient (D33) around 0.8pC and 0.5pC for those sample sintered at temperature 875oC and 975oC when they were polled parallel and perpendicular direction of SPS pressure surface respectively. Keywords: Hydroxyapatite, Spark Plasma Sintering, Transparent HA ceramic, high voltage contact electrical poling, Piezoelectricity.Item Study of multi-doping effect on the structure and multiferroic properties of Bismuth ferrite (BiFeO3)(Department of Materials and Metallurgical Engineering, 2020-08-29) Sen, Aungkan; Gulshan, Dr. FahmidaIn this study an attempt was taken to experiment and compare conventional co-doping and novel compositionally-complex ceramics (CCCs) concept in multiferroic bismuth ferrite (BiFeO3). Both co-doped BiFeO3(BBFMO; 〖Bi〗_0.8 〖Ba〗_0.2 〖Fe〗_(1-x) 〖Mo〗_x O_3;where,x=0,0.5,0.10 and 0.15) and compositionally complex BiFeO3 (CCBFO; BiFe1-5xMoxTixZrxNixCexO3; where, x=0.01, 0.02, 0.03) samples were prepared by conventional solid-state synthesis method. Reitveld refinement revealed notable distortion in all structures, but Fe-O-Fe bond angle reduced to more extent in CCBFO samples, as low as 100.2° from the ideal value of 180°. Despite structure remained unchanged in the complex samples, while a transition from tetragonal P4mm to rhombohedral R3c phase was observed with doping in BBFMO ones. Presence of Mo-based impurities i.e. BaMoO4and Bi12Mo4O30were found and the influence of those impurities were evaluated in details. SEM images evidenced a gyroid like mesoporous morphology in CCBFO, whereas more compact, round shaped but irregular type morphology in the other type. A very slight increase in particle size from 0.52 µm to 0.58 µm with doping was observed for CCBFO. In contrast, a lofty upraise from 0.361µm to 0.61 µm was found for BBFMO samples. Substantial reduction in bandgap was observed for both types of samples, but a steeper fall from 2.88 eV to 2.14 eV was recorded with the increase of doping from 5% to 15% for the CCBFO ceramics. Although, ferromagnetism was found in both types of samples, it is more prominent in co-doped ones, as high as 2.35 emu/gm of saturation magnetization for BBFMO-10compared to only 0.45 emu/gm for CCBFO-15.Paramagnetic secondary phases found to have a negative influence in the magnetic properties of the later ones. Dielectric constant showed an increasing trend with co-doping, the highest of 1200 at 0.1 kHz for BBFMO-15.These changes in functionalities are in good agreement with the measured structural and morphological parameters. The obtained results suggest that along with the conventional co-doping strategy, CCCs concept can be effectively used to tune the properties of multifunctional ceramic oxides and careful selection of cations might improve the functionalities even to a new extent. Keywords: Bismuth ferrite, Co-doping, Compositionally-complex ceramics, Structural distortion, Bandgap, Ferromagnetism.Item Development and characterization of spark plasma sintered bismuth ferrite (BiFeO3) multiferroic ceramics(Department of Materials and Metallurgical Engineering, 2019-07-03) Islam, Md. Shofiqul; Sharif, Dr. AhmedBiFeO3 (BFO) Ferrite ceramics were synthesized by an improved solid-state technique in conjunction with high-energy ball milling. Calcination was carried out at 800°C for 2 hours at a heating rate 5 °C/min and cooling rate was same as heating rate. High density BiFeO3 ceramics were further sintered using by Spark Plasma Sintering (SPS) at different temperatures. Comparatively minimal amount of secondary phases was achieved than conventional sintering because of the higher heating rate with less holding time. They were contrived by different characterization techniques such as X-Ray Diffraction (XRD), Energy Dispersive X-Ray Spectroscopy (EDS), Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Ferromagnetic, Ferroelectric and Piezoelectric Measurements, Raman Spectroscopy, Fourier-Transform Infrared Spectroscopy (FTIR) as well as shaped up Linear Optical Properties. The sintering conditions were optimized in order to attain high density, minimal amount of secondary phases and improved magnetic, piezoelectric and optical properties. The optimal structure and properties were achieved after Spark Plasma Sintering at 750°C for 5 minutes, under uniaxial pressure of 50 MPa. It was found that with decreasing grain size there occurs an enhancement in magnetization. This enriched magnetization is attributed to the improved grain boundaries. BFO-750 showed copious % transmittance about 27 with a long-range wavenumber. Piezoelectric measurements using a quasi-static method based on the Berlincourt method confirmed that conspicuous d33 coefficient measured maximum 7.2 ± 0.5 pCN-1 without poling. Ferroelectric hysteresis loop measurement revealed that the samples have good ferroelectricity except BFO-800 and BFO-825 samples. Raman spectroscopy confirmed that there were maximum 13 modes formed in BFO-750. SPS + high density ball milling was supposed to be responsible for the outstanding obtained properties. Keywords: Multiferroic, Perovskite, SPS, BFO, Piezoelectric, Optical properties.Item Study of the effects of composition and sintering parameters on dielectric properties of zirconia and niobium oxide doped barium titanate ceramics(Department of Materials and Metallurgical Engineering (MME), 2011-06) Sazzad Hossain, Md.; Fakhrul Islam, Dr. Md.In this research, the effects of ZrO2and Nb2O5addition to BaTiO3 and sintering parameters on the dielectric properties were observed. When BaTiO3 ceramics are doped with ZrO2 or Nb2O5, the substitution of Ti4+ ions by Zr4+or Nb5+ions is expected, which isa temperature dependent process and can significantly alter the dielectric properties. However, it is also proved that a very small addition of ZrO2 or Nb2O5 e.g. 0.1 to 2wt% has the potential to yield very good dielectric characteristics. In this thesis the optimum sintering temperature yielding the smallest grain size along with 95-97% of theoretical density was found to be 1290°C for both 1 and 2 wt% ZrO2 added samples and 1275°C for 0.1 to 0.3 wt% Nb2O5 added samples. The experiments revealed that low soaking time e.g. 0 minute, can yield the best combination of sintering outputs. Double stage sintering was found to give better control over the grain size and thus more effective for the dielectric properties. The smallest grain size achieved was 500 nm for ZrO2 added samples and 600 nm for Nb2O5 added samples. Images from SEM suggested that the inhibition to grain growth in BaTiO3is a function of the amount of dopants and sintering parameters. Above 1300°C, significant grain growth was observed for ZrO2 added samples and the grains reduced in size with increasing ZrO2 content from 1 to 2 wt% BaTiO3.Microstructures showed the grain size to be finer in 2 wt% samples than in 1 wt% samples. These observations suggested ZrO2 diffusion inside BaTiO3 lattice above 1300°C and therefore the need for higher amount of ZrO2 to inhibit grain growth. For Nb2O5 modified samples 1320°C was the maximum sintering temperature and yet no significant grain growth occurred. Nb2O5 was found to yield the same microstructural effects brought by ZrO2 with addition of much lower amount than that of ZrO2. 1275°C sintering was found to yield the best dielectric characteristics for Nb2O5 added samples.XRD analysis showed reduction in tetragonality in both pure anddoped BaTiO3samples after sintering followed by decrease in cubic to tetragonal transition temperature and suppression of curie peak to some extent. The shift of tetragonal to orthorhombic transition point to higher temperatures was also understandable from the experiments.Such shifting of cubic-tetragonal peak and tetragonal-orthorhombic peak towards each other is a plausible cause of the rise in dielectric constant at intermediate temperatures.Nb2O5 added samples showed similar characteristics. At low temperatures where ZrO2 is known to linger at grain boundaries, long sintering time by means of double stage sinteringhas shown to improve permittivity on many occasions.Nb2O5 added samples were found to yield increasing dielectric constant with the percent increase in Nb2O5content even with lower percent theoretical density achievement.The permittivity (k) was found to yield consistent and flat response with temperature.ZrO2doped samples have shown permittivity (k) values as much as 3500 and that for Nb2O5 samples were found to be as high as 6500.Item Preparation and characterization of BaTiO3 based dielectric ceramics(Department of Materials and Metallurgical Engineering, BUET, 2008-03) Tareque Chowdhury, Mohammed; Fakhrul Islam, Dr. Md.TIle microstructure-propcrty relationship of BaTiO), Bai.,Sr,TiO)(x=O.lO, 0.15, 0.20) and SrTiOJ has been studied in this thcsis. BaTiO) and SrTiO) powders of 100nm ,,'ere used to prepJ.!'epellet shaped samples using 130-150 MPa pn:ssure. The green samples were dricd and then sintered in the tcmperature range of 1100"C to 1275°C, varying the holding time from 2 hours to 6 hours. The density, dielectric constant and loss tangent were measured using available equipment> at BUET and the Atomic Fnagy Center, Dhaka (AECD). Optical Minoscopc, Scanning Electron Microscope (SEt'..'I), Differential Scanning Calorimeter (DSC) and X-ray Diffractometer (XRD) were used to observc the microslruclmc, identify the Curie temperature and different phases to find the correlatiotl betw,eenmicrostlUcture and property ofthc sintered samples. Ninet}' five pcreent of the theoretical density has been fOlllldfor BaTiO) samples sintcrcd in the temperature range of J::!25°C-1250°C. It has been ohserycd from the microstructllTethat grain gro,vth occur, at higher temperature but porosity still remains inside the grain and in the grain boundItem Role of Ca doping and process variables in the dielectric properties of Barium Titanate Ceramics(Department of Materials and Metallurgical Engineering, BUET, 2005-08) Abu Mohammed Rashed Chowdhury; Fakhrul Islam, Dr. Md.Effects of Ca doping, ~alc;nation and sintet'ing teml'cTJlme on the dielectric propertlcs of BaTiO) b",ed eemmi~ weI e stmhcd in this th~,,,s Convcntional mi"ed oxide melhod was u,ed to prepare disc shape ,anlp!c. The three dOplllg levels "ere 0.05, 0 08 "nd 0.12 mole fraction of Ca substituting lla. Regardless tll~ stoichiomelry or sllltering pammeters, lhe fi[';t set of ,amples cxhihited the Curie kmperatlll'G (T,) at 55°C, much lower th~n 120"C - th~ usual Ic"nsition tempcraturc oj" Ba riO" Inslcad of ,h"rp pcol, tiley CXhlbited bell :shaped hump at 55"(. Thcse allC>nULlie, W~n; due to 11"Onpickup during milling: with sled ball, in water media. ror verification, anothcr tWObatche, of ,ample, were prepared following identic"1 powde, proce,<>ing tcchl1lqne, One boteh "al prepared using BUET precursor powder and another li'om I\IILC >ource, Thc later One was 1l00mai BaT,OJ but the other on~ did llot even simeT lo 75'((, of theorGtical den,ily. ']'i02 and B~COJ u,ed at BUET S~ern 10 COl1lamimpunlies and d~trimel\l,,1 phases, In general the die1cclric comlant (k') was bellcr for denser samples and so "a, tangent loss, Density S~elm to be a conjugcate t'C,ult of CJ1clllalion and sintcring Incomplete calcination, Or lllcomplctc reaCllOl1, leads to the formatl()n 01 ga, or blowhole during ,intering and most importantly de,ircd properrLC" not l'eah.oed owing; to nOnformation (01' pamal fOfmatlOn) of required phas,,{ '1, Due to sluggi,h nature of ,olid-Slate leaetion, calcinallon at 11OO"Cfot 7 hOllis seem, to bc o~li,factor), Sinlcring temperature and timing; ShOllld be tuned to achie\'c abO\lt 95% of theorelical density. Properly c~lcilled un-doped IhTiOJ can be sintered at 1325°C for 4 ilour, to achieve that go,,1. It was oh,erved th"t Ca did un as ~ sintering aId for doping level of O,O~ mole fraction and" bove. Dcnsitic, of doped .,an'pte did folio" a non-lineal' rciation,hip "ilh doplllg; concetllmlion and the change Ove, wu, ob,ervcd al 0.07 mole fraction. Th;s effect "a, obseTved ill'csp~~live of&inkring thcmml profile. Iron inc1u,ion in s~mples turned the eXJl~cted normal ferl'Ociectric ceramic into relaxor type, with peak k' nearly 4000. In conjunellon with Ca dopmg the Tc was shilled 10 55°C winch: with the increase ofCa dopmg level above 0,08 mole ti~~tlOn ,hined the T~ to 90'C. The k' also changcd non-tine~rly ,,,ith the Ca concentralion kvel From the XRD eMmlnatlOn, it wa, seen thntlhe extonl oftellagOllnt distQrtion "ns lh" govctnmg faclor fixing lho r,. Also observed" prefert"lxl or;elltatlon of i0021 planc at lh~ ~llIfacc of dllring: ,i ntcring. contl'ibuting to increase k' nCar CtColld beYOl]d,