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Experimental & Theoretical Investigations of Fe and A1 Based Spinels

Thesis Info

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Author

Muhammad Azam

Program

PhD

Institute

University of the Punjab

City

Lahore

Province

Punjab

Country

Pakistan

Thesis Completing Year

2018

Thesis Completion Status

Completed

Subject

Solid State Physics

Language

English

Link

http://prr.hec.gov.pk/jspui/bitstream/123456789/11396/1/Muhammad_Azam_Solid_State_Physics_2018_UoP_Punjab_23.10.2019.pdf

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676726153822

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Spinel oxides are an important class of versatile materials, which exhibit complex and tunable structures and offer exceptional properties for their potential applications in wide range of modern fields. In this dissertation, two important classes of spinel materials based on iron and aluminum are reported to have been synthesized and characterized experimentally. These are also checked theoretically for their possible applications in electronic and spintronic devices.Firstly, iron based spinel i.e., MgFe2O4, NiFe2O4, and CrFe2O4 were synthesized by sol-gel method whilst thin films were deposited on copper substrates by spin coating technique. In case of MgFe2O4, Mg/Fe ratio was varied as 0.4, 0.45, 0.5, 0.55 and 0.6 during sol synthesis. Variation of Mg/Fe ratio strongly affected magnetic and electronic properties along with phase purity of magnesium iron oxide thin films. Peaks corresponding to (220), (222), (400), (331), and (620) planes confirmed formation of MgFe2O4 at a very low annealing temperature of 300 oC with Mg/Fe ratio of 0.55. A single magnetic phase has been achieved with high dielectric constant and low tangent loss at Mg/Fe ratio of 0.55. Semiconducting behavior, revealed by Arrhenius plot, is due to electron hoping between Fe2+ and Fe3+ cations. High saturation magnetization of 163emu/cm3 is achieved which decreased at Mg/Fe values of 0.4, 0.45, 0.5 and 0.6. For NiFe2O4, nickel oxide (NiO) was added to hematite (Fe2O3) and NiFe2O4 phase formation was achieved at 6% Ni dopant concentration. Variation of Ni dopant was observed to strongly affect structural, magnetic and dielectric properties. Particle size of around 10 nm was observed through SEM. High saturation magnetization of 25 emu/g, and dielectric constant of 94 was observed with 6% of Ni dopant concentration. High dielectric constant and low dielectric loss of NiFe2O4 was observed at high frequency that is very interesting for high speed electronic and spintronic devices. Furthermore, antiferromagnetic Cr3+ was added in NiFe2O4 by co-precipitation method. This enhances the utility in magnetic storage, computer memory chips and microwave devices. Single-phase cubic spinel structure was achieved with particle size in the range of 38-49 nm. Structural study revealed phase purity of CrFe2O4 spinel at dopant concentration of 6wt% and again at 9-10wt% with crystal size of 15.45 nm and 14.98 nm respectively. Mixed phases of Fe2O3, Cr5O12, CrFe2O4 or amorphous nature was observed for rest of the dopant concentration ranges. vii Secondly, aluminum based spinel, i.e., FeAl2O4 and ZnAl2O4 were synthesized by sol-gel technique and then the sol was spun on copper substrates with variation in Fe/Al ratio as 0.4, 0.45, 0.5, 0.55 and 0.6. XRD patterns revealed that phase pure FelAl2O4 was observed only for the sample with Fe/Al ratio of 0.4. Whereas, Fe2O3 peaks appeared along with iron aluminum oxide peaks for rest of the ratios. M-H curves showed enhanced magnetic properties of films having 42.325 emu/cm3 saturation magnetization, 10 emu/cm3 remnant magnetization, and 430.19 Oe coercivity. Conductivity measurements showed transition in electrical properties at a temperature of 127 K. Room temperature magnetoresistance ̴ 10% was observed for iron aluminum oxide thin films with Fe/Al of 0.4. For ZnAl2O4, glass substrate was used for preparation of thin films by spin coating. Dopant concentration (1-10%) was carried out beyond the solid solubility limit to allow further reaction of ZnO and dopant oxide for the formation of phase-pure ZnAl2O4. XRD results confirmed formation of phase pure ZnO in undoped films with preferred orientation along (101) plane. ZnO phase persisted with aluminum doping till 3% along with change in preferred orientation from (101) to (001) plane. Mixed ZnO, Al2O3, ZnAl2O4 phases were observed at dopant concentrations of 4-6% and 9-10%. Phase pure ZnAl2O4 was obtained at dopant concentrations of 7-8%. Films showed high transmission in the visible and infrared regions. Highest transmission ~ 91% with band gap of 3.756 eV was observed for ZnAl2O4 films with dopant concentration of 8%. Refractive index of 2.16 at 500nm was observed at this dopant concentration whereas dielectric constant of 64.86 (log f=5.0) was observed due to high grain boundary resistance of 3.218 MΩ as determined by ZView software. Temperature dependent dielectric analysis indicated negative temperature coefficient for ZnAl2O4 thin films with activation energy of 1.86 eV.Thirdly, ab-initio calculations were performed to calculate structural, electrical and magnetic properties for MgFe2O4, CrFe2O4, NiFe2O4, FeAl2O4 and ZnAl2O4 by using Density Functional Theory. Generalized Gradient Approximation (GGA) without and with U (PBE, PAW and modified Becke Johnson (mBJ) potentials) was implemented to accomplish theoretical investigations. Experimental results obtained so far are in good agreement with the theoretical observations.
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یار میرا منہ زور

یار میرا منہ زور
دتا مینوں کھور
زلف سیاہ جئی ناگن
موراں ورگی ٹور
گئی جوانی لُٹی
لے گئے کئی چور
جھوریاں ماریا آ
دکھ نہیں کوئی ہور
سولی عاشق لئی
نین سیاہ بلور
کھورے ہڈی ِمکھ
نکی جئی ہِک جھور
ڈنگے ہِک محبت
گل نہیں کوئی ہور

Journey to Khalafah and Tamkeen fil ‘Ard Milestones on the Way

Establishment of khilafah and tamkeen fil ‘ard means supremacy of the dictates of shari‘ah and socio-political justice on earth. This is one of the basic objectives and prominent messages of the Holy Quran and Seerah of Prophet Muhammad (s.a.w). About khilafah and tamkeen fil ‘ard the Holy Quran expresses as:   -وَعَدَ اللَّهُ الَّذِينَ آمَنُوا مِنكُمْ وَعَمِلُوا الصَّالِحَاتِ لَيَسْتَخْلِفَنَّهُم فِي الأَرْضِ …  -الَّذِينَ إِن مَّكَّنَّاهُمْ فِي الأَرْضِ أَقَامُوا الصَّلاَةَ وَآتَوُا الزَّكَاةَ وَأَمَرُوا بِالمَعْرُوفِ وَنَهَوْا عَنِ المُنكَرِ وَلِلَّهِ عَاقِبَةُ الأُمُورِ.  -هُوَ الَّذِي أَرْسَلَ رَسُولَهُ بِالْهُدَى وَدِينِ الْحَقِّ لِيُظْهِرَهُ عَلَى الدِّينِ كُلِّهِ وَكَفَى بِاللَّهِ شَهِيداً.  Prophet Muhammad (s.a.w) proclaims:   - وَاَللَّهِ لَوْ وَضَعُوا الشَّمْسَ فِي يَمِينِي وَالْقَمَرَ فِي يَسَارِي عَلَى أَنْ أَتْرُكَ هَذَا الْأَمْرَ حَتَّى يُظْهِرَهُ اللَّهُ أَوْ أَهْلِكَ فِيهِ مَا تَرَكْتُهُ. The Holy Quran and the Seerah refer to some underlying milestones on the way of religious nations to status of khalafah and tamkeen fin ‘ard. These milestones may be expressed in an order as: da‘wah [preaching], deen [practices of prophetic teachings], hijrah [migration], ma‘iyyat-ul-Allah [companionship of Allah], qital [wars], nusrat-ul-Allah [divine aid], izhar-ud-deen [domination of deen] and khilafah [inheritance of authority]. This is noteworthy that journey of khalafah and tamkeen fin ‘ard begins with da‘wah [preaching towards deen] and passing through various milestones ends up again at da‘wah, as obvious from ayat-ul-istakhlaf quoted above. Therefore, the seekers of khilafah and tamkeen fil ‘ard should strive hard and keep struggling with the work of da‘wah with dedication in all circumstances and all means as per time and place requirements in lined with the modus operandi of Prophets, particularly Prophet Muhammad (s.a.w), instead of awaiting the status of khilafah and tamkeen fil ‘ard as prerequisite to start with the work of da‘wah and establishment of deen. This paper primarily aims to elaborate the milestones of Muslim Ummah to reach to the status of khilafah and tamkeen fil ‘ard. It also cast light on the objectives of khilafah and tamkeen fil ‘ard. This work provides useful guidance to Muslim Ummah in general and Ahlud da‘wah in particular about milestones and objectives of khilafah and tamkeen fil ‘ard.

Optimization of Engineering Parameters for Continuous Mode Biosorption

The discharge of heavy metals into aquatic ecosystems has become a matter of concern over the last few decades. They are extremely toxic elements, which can seriously affect plants and animals and have been involved in causing a large number of afflictions. Due to the high costs of commercial adsorbents, biosorption is an economically feasible way to perform the treatment of potentially toxic species-containing effluents. It is the sequestration of metals by the dead natural material called biosorbent. This research presents experimental optimization of different engineering parameters such as Biosorbent type, Immobilization method, initial solution pH, flow rate, Initial metal concentration and Desorbing agent for the removal of Cu(II). Three types of wastes namely Crop wastes (CW) including Bagasse, Rice Husk, Rice Straw, Wheat Straw, Waste leaves (WL) including Peeple Leaves, Semal Leaves and Dry fruit Waste (DW) including Almond Shell and Walnut shell were selected as they are abundantly available in local areas. First of all, each biosorbent was prepared through washing, crushing and grinding followed by size analysis through seven ASTM screens. Detailed size analysis was performed and presented for the first time in literature to link it with biosorption. This data was used to calculate different mean diameters namely volume surface mean, mass mean and length mean diameters. Size frequency curve was also plotted. For almond shell the volume surface mean diameter showed close resemblance to the median obtained from the size frequency curve while for all the remaining biosorbents, mass mean diameter came out to be representative diameter. Scanning Electron Microscopy was performed to establish different aspects (Physical and chemical) of biosorbent structure. CW showed needle like particles with complex flaky or porous structure. LW showed cylindrical particles with holes while DW showed aggregatesof small particles. FTIR analysis showed typical lignocellulosic profile for each biomass showing the presence of multiple functional groups including –OH, -COOH. XRD showed amorphous nature of the biosorbents. These characterizations showed that selected biosorbent possess structure suitable for biosorption. Selection of the optimum biosorbent was performed through typical kinetic and equilibrium experiments. In these experiments WL showed highest uptake of Cu(II) while CW and DW showed intermediate to low uptakes. Biosorption generally takes place in acidic environment. Therefore, stability of the selected biosorbents (Wheat Straw, Peeple leaves, Seemal Leaves, Almond Shell and Rice Husk) in 0.1M HNO 3 was tested. Almond Shell showed best and WL showed worst results. Thus, Almond Shell (AS) was selected as optimum Biosorbent. This approach has been applied for the first time to select an optimum biosorbent. Among different options of continuous contactors, fixed bed column is preferred due to its effective utilization of biomass bed and subsequent separation from the adsorbate solution. The most important parameter in the fixed bed operation is the nature of immobilization of the biomass. Generally, entrapment of the biosorbent is being performed to apply it in the fixed bed column. However, this process results in addition of a resistive layer of immobilizing media which hinders the mass transfer. Therefore, a novel surface immobilization mm and have complex structure. Braummer-Emmett-Teller (BET) area of beads showed a suitable adsorption area 0.8094 m 2 /g. For fixed bed experiments, optimum pH was estimated to be 4.6. It was an intermediate pH between two extremes i.e., point of zero charge (pH = 3.8) and point of precipitation (pH =5.1). Up flow arrangement was selected due to its inherent capability to avoid channelling. Bed height was selected to 20 cm to avoid axial dispersion of the Cu(II). Column experiments were performed at 19.7mL/min and 36 mL/min to determine optimum flow rate at 10 ppm Cu(II) concentration. Time required to achieve 50 % break through was greater in case of 19.7 mL/min than 36 mL/min. 19.7 mL/min flow rate corresponded to about 3 min residence time in the column and taken as optimum flow rate. In order to determine the optimum influent concentration three column experiments were performed at different initial concentration namely 10 ppm, 50 ppm and 100 ppm. As, expected very quick breakthrough took place at 50 ppm and 100 ppm. Hence, 10 ppm was selected an optimum initial concentration. HNO 3 and NaOH were selected to determine the optimum desorbent. These chemicals were selected due to the fact that H + and Na + ’ metals. Experiments showed that HNO 3 recovered much more Cu(II) ions than NaOH. Also, in case of NaOH, a notable deterioration of immobilized beads was found. Almond shell was identified as an optimum biosorbent as it showed moderate uptake and highest acid resistance amongst selected biosorbent. Kinetic modelling showed that, pseudo 2 nd order kinetic best described biosorption of Cu(II) by AS. Freundlich model enumerated the equilibrium behaviour of Cu(II) removal by AS. Application of Dubinin-Radushkevic (D- R) model suggested the physio-sorption while Boyd''s model showed liquid film diffusion as the rate controlling step in the biosorption of Cu(II) by AS. Powdered AS was immobilized on the surface of beads which showed moderate BET area. Beads showed best performance (50% break through) at lower flow rate (19.7 mL/min) and low Cu(II) concentration (10 ppm). It was possible to regenerate beads saturated with Cu(II) ions using 0.1M HNO 3 without any damage. Thomas model was applied to describe the break through curves. It isrecommended to further explore the surface immobilization of different biosorbents to test their effect on the breakthrough of different pollutants (binary and tertiary) in fixed bed column.