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Synthesis of Metal and Alloy Nanoparticles by Alcogel Electrolysis

Thesis Info

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Author

Rana, Muhammad Zahid

Program

PhD

Institute

Pakistan Institute of Engineering and Applied Sciences

City

Islamabad

Province

Pakistan

Country

Pakistan

Thesis Completing Year

2012

Thesis Completion Status

Completed

Subject

Applied Sciences

Language

English

Link

http://prr.hec.gov.pk/jspui/handle/123456789/1745

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676727486184

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Nanomaterials may be defined as the materials with, at least, one structural dimension in the range of 1 - 100 nm. Nanocomposites are a special class of nanomaterials and are of interest because they exhibit interesting mechanical, electrical, optical and magnetic properties in addition to high catalytic activity. Although nanomaterials can be synthesized by many methods but wet synthesis methods, often offers better control over shape, composition and structure. Wet synthesis include thermal decomposition, pyrolysis, polyol process, hydrothermal/solvothermal, sol-gel, electrochemical, chemical / borohydride reduction and, co-precipitation, etc. However, sol-gel is one of the methods, which offers better control over chemistry and composition. Consequently, sol-gel is a technique most widely used for the manufacturing and synthesis of metal/inert ceramic nanocomposites. Generally, it is difficult to prepare metallic nanoparticles in ceramic matrix, directly through sol-gel method employed for the preparation of nanocomposites, and a subsequent pyrolysis and / or hydrogen reduction treatment becomes almost essential. The metallic ions may also be reduced chemically, but is usually often accompanied by difficulty in controlling reaction conditions and composition and further demonstrated suitable for surface deposition only. Metallic species in the sol-gel ceramic could be reduced by radiations also, but this method is accompanied by inherited safety issues, and found more effective in thin films or solid sections only. Electrolysis is another very simple and often room temperature technique, that can be efficiently applied to reduce the metallic ionic species present in solution phase to their corresponding metallic state. However to get electrodepositable gel, researchers in the past opted for either long duration for gelation and /or high temperature treatments to get aged gels. In some cases gelation time was in weeks, in other case temperatures employed were high such as; >500 o C. Often the technique has been limited to thin gel films for ease in soaking and shorter electrolytic conducting paths. If these limitations are overcome, this combination may possibly the simplest, most versatile, fast enough and cost-effective for the formation of metallic nanoparticles in the oxide matrices. Presently emphasis has been laid on the development of a synthesis technique based on sol-gel and electrodeposition by overcoming all the above observed problems. A new technique based on electrolysis of alcogels has been employed for the synthesis of various metals (Ni, Co & Fe) and alloys (Ni-Fe, Ni-Co, Fe-Co, Fe-Zn and Ni-Zn) nanoparticles in the pores of silica gel. Chloride(s) of respective metal(s) were used as metal precursor and introduced into the alcogel during sol formation step. The as–synthesized alcogels without subsequent heat treatments were immediately subjected to electrochemical reduction, consequently forming metal and alloy nanoparticles into the pores of silica alcogel. Electrolysis of as generated alcogels (i.e., without any subsequent treatment) resulted in the formation of nickel and alloy nanoparticles within reasonable depth of the gel. The method employed, does not require high temperatures or long durations to form electrodepositable gel. This technique is simple and cost effective. Further it can produce nanomaterials in bulk and in a single go. The nanoparticles were characterized by XRD, TEM, surface area, Resistance measurements, BET, AC-Susceptibility, SQUID, VSM, Mössbauer and M-TGA measurements etc.From XRD analysis size of FCC Ni, Ni(Fe), Ni(Co), Ni(Zn) nanoparticles ware around 17-20 nm, 8-15 nm, 11-16 nm and 9-14 nm respectively. The FCC phase in most case was also accompanied by surface oxide; tetragonal nickel. The sample with only iron chloride in alcogel does not revealed presence of any significant amount of BCC phase, this may probably due to oxidation of iron; as a consequent of small particle size. The spinel iron oxide phase had size around 8 nm. Addition of even small quantity of cobalt or zinc along with iron, resulted in the formation of BCC phase. The BCC Fe(Co) particles were around 9-12 nm, while BCC Fe(Zn) nanoparticles were around 6-11 nm. The particle size appeared to decrease with the increase in the concentration of alloying elements. However in case of Fe(Co) alloys size seems independent of alloying element concentration. In gels containing only cobalt chloride, about18 nm cobalt nanoparticles were formed. The formation of small size of nanoparticles was further confirmed from TEM studies. Resistance measurement was carried to further understand the structure of samples. Composites having more metal-oxide content such as; in samples with high iron, cobalt or zinc as alloying element, resulted in increased resistance such as; up to order of MΩ at a load of 100 kg. This is due to the formation of higher quantity of oxides between the interconnected necks of nanoparticles. However, complete metallic contact at low load was observed in FCC Ni and FCC nickel alloys, having low alloying concentrations of iron or cobalt. Besides XRD, the formation of spinel iron oxide in iron containing samples was confirmed from the presence of superparamagnetic doublet appearing in Mössbauer spectra. This corresponds to iron in high spin Fe 3+ state. The formation of Ni(Fe) and Fe(Co) was also confirmed by Mössbauer analysis, showing presence of ferromagnetic sextets, having hyperfine field of the order of 260kOe and 340kOe respectively. The VSM of composites indicated formation of soft magnetic metal and alloy nanoparticles. The coercivity measured for nickel samples comes out around 100 Oe. While for Ni(Fe) it lies between 50 to 100Oe, with low being associated to more iron alloying. Coercivity of Ni(Co) samples lied in the range of 150 to 250Oe with higher being associated to higher concentration of cobalt in the gel. However coercivity of Fe(Co) samples decreased slightly with the cobalt addition from around 160Oe to 120Oe but resulted in increased magnetization. M-TGA studies were also performed to magnetically characterize samples. Presence of exchange coupling was observed in the samples due to ferromagnetic–antiferromagnetic interaction at the surface of nanoparticles. Consequently ferromagnetic nanoparticles remained blocked up to Curie temperature of FCC nickel in case of nickel containing samples and up to Curie temperature of spinel ferrite in case of Fe(Co) samples. The formation of alloy was further confirmed by the change in Curie transition of various samples. The Curie temperature of nickel increased from 620 K to 630 K by iron addition, and it increased to ~ 900 K in case of cobalt addition. In Fe(Co) samples, Curie transition associated with metallic phase was only observed but in samples with higher concentration of cobalt. This probably is due to oxidation of nanoparticles during M-TGA studies. From XRD and M-TGA quantity of alloying can be estimated, such as; up to 20 % Fe in Ni(Fe), up to 30% Co in Ni(Co) and up to ~30-50% Co in case of Fe(Co) samples was estimated. The present technique has proven its versatility by depositing variety of nanoparticles, and having soft magnetic properties, with high resistance. Therefore, if further characterized, these materials could stand potential candidates for high frequency applications. Since surface area of most of the samples was ~100m 2 /gm, besides high well dispersed metallic load (e.g.; 55% Ni in Ni/Silica samples), therefore this technique can produce potential catalytic composites too.
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مُلّا جان محمد

مُلاّ جان محمد
افسوس ہے گذشتہ مہینہ ہمارے دومخلص قومی کارکن ملاجان محمدکلکتہ اورمولانا محمد عاقل الٰہ آباد انتقال کرگئے۔ملا صاحب کااصل وطن پشاور تھالیکن عرصہ دراز سے کلکتہ میں آبسے تھے اوراب سچ مچ وہی ان کاوطن تھا۔نہایت پُرجوش،جری اوربیباک انسان تھے۔گذشتہ نصف صدی میں کوئی قومی اور ملی تحریک ایسی نہیں ہے جس میں انہوں نے بڑھ چڑھ کراورولولہ و عزم کے ساتھ حصہ نہ لیا ہو۔ ان کی علمی زندگی کاآغاز تحریک خلافت سے ہوا اوراختتام مجلس مشاورت پر۔کلکتہ میں شاید ہی کوئی مسلم ادارہ(یہاں تک کہ محمڈن اسپورٹنگ کلب بھی) ایسا ہوجس میں ملاصاحب نے نمایاں حصہ نہ لیاہو۔اسی وجہ سے وہ کلکتہ کے لوگوں میں بے حد مقبول تھے۔ بڑے بے غرض،بے لوث اورنہایت سادہ اورمخلص مسلمان تھے۔۱۹۵۰ء میں کلکتہ کے فساد میں لوگوں نے ان کو بچوں کی طرح چیختے اور روتے دیکھا ہے۔ عمر۸۵ سال کے قریب تھی۔ [نومبر ۱۹۷۲]

 

فتوی اور فتاوی الکاملیہ کا تعارف و اہمیت

From the very beginning Islam has given great importance to discipline. In every facet of life discipline has a role to play. Today when we delve deep in to our lives, we are amazed as to how it has always proved its worth. It has brought the tide of revolution in everyone's mind. Similarly, the element of discipline saves a society from disruption and instability. It infuses in life satisfaction and contentment. Contrarily, indiscipline and mismanagement give birth to dejection and dissatisfaction. Time management plays a vital role in the establishment of discipline in a society. Considering the vast importance of time management in the light of discipline, the following article throws a great deal of light on it in the Islamic perspective.

Evaluation of Dosimetric Properties in External Beam Radiation Therapy

A great level of accuracy and efficiency is required to execute the various paradigms of the radiotherapy processes. The work described in the dissertation was aimed to verify the quality of treatment plans for different techniques in order to enhance the accuracy of planning processes involved. Also dose profile uniformity was verified to improve the Quality Assurance (QA) of radiotherapy process.This project was organized into three major components comprising of ‘comparison of treatment plan quality of RapidArc and Intensity Modulated Radiotherapy (IMRT) using various dosimetric indices’, ‘investigation oftolerance dose to Organs at Risk (OARs) and assessing degree of homogeneity and conformity for Head and Neck (H&N) cancer patients by using Simultaneous Integrated Boost Intensity Modulated Radiotherapy (SIB IMRT) technique’, and ‘determination of quality of 6 MV and 15 MV wedge-shaped radiation beams by analyzing the effect of symmetry parameter on depth, field size, beam energy, and wedge angle.’ First, analysis and comparison of the plan quality of IMRT and RapidArc techniques using various dosimetric indices was carried out to find out the better treatment modality for treating patients with cervix cancer. Thirteen cervical cancer patients treated with IMRT were selected for analysis and original plans were subsequently re-optimized based on the RapidArc technique. Inverse treatment planning was done by Eclipse (Varian Medical Systems, Palo Alto, CA) Treatment Planning System (TPS) for 15 MV photon beams from computed tomographic data. Double arcs were used for RapidArc plans. Quality of treatment plans were evaluated by calculating Conformity Index (CI), Homogeneity Index (HI), Gradient Index (GI), coverage, and Unified Dosimetry Index (UDI) for each plan. RapidArc plans resulted in better Planning Target Volume (PTV) coverage as evident by its superior Conformation Number (CN), coverage, CI, HI, GI, and UDI. Regarding Organs at Risk, RapidArc plans exhibit superior organ sparing as found from integral dose comparison. Difference between both techniques was determined by statistical analysis. For all cases under study, modest differences between IMRT and RapidArc treatment were observed. In conclusion, RapidArc-based treatment planning is safer with similar planning goals compared to the standard fixed IMRT technique. Furthermore, degree of conformity, homogeneity and tolerance dose to organs at risk for head and neck cancer patients were investigated. Fifteen patients receiving treatment based on inverse planned SIB IMRT technique were analyzed in this study. Using a beam energy of 6 MV, two dose levels of 70 Gy and 55·4 Gy were used to treat the tumor. Doses of 2 Gy in 35 fractions and 1·68 Gy in 33 fractions were simultaneously delivered for Effective Planning Target Volume (PTV1) and Boost Planning Target Volume (PTV2) respectively. Dose distribution in PTV and critical organs lie within tolerance dose guidelines protecting spinal cord, brain stem, optic chiasm, and optic nerve. Minor deviation from tolerance limit was observed for parotid glands. This technique provided highly conformal and homogenous dose distribution as well as offered best solution for preserving organ function by keeping dose below tolerance level. Finally, symmetry parameter of wedge-shaped photon beam profile was investigated to determine quality of radiation beams produced by linear accelerator. Analysis of beam profile parameter symmetry was performed for 6 MV and 15 MV photon beam energies by varying different factors such as depth, field size and wedge angle. Photon beam profile was measured from Varian’s Clinac DHX using PTW array detector. Data management, analysis, and processing of isodose curves was carried out by PTW MP3-M water tank and PTW MEPHYSTO version 7.33 software. Variation in symmetry was analyzed to match acceptance criteria as recommended by the American Association of Physicists in Medicine (AAPM) protocols. Results implied that symmetry parameter can be treated as being independent of depth and linearly increase with field size and wedge angle. For wedged beam profiles, measured values of symmetry were generally good and exceeded only slightly from the AAPM’s standard criteria for symmetry for open fields. The difference between open field beam profiles and wedge-shaped profiles were considered so that possible errors involved in radiotherapy process can be rectified.