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The Effect of Grain Size and Phase constitution on the Magnetic Properties of Higher Content Cr substituted Fe73.S.XCrXNb3CUISiI3 5B9 Nanocrystalline Alloys
No full textThis thesis is submitted to the Department of Physics, Khulna University of Engineering & Technology in partial fulfillment of the requirements for the degree of Master of Philosophy in Physics,July 2015.Cataloged from PDF Version of Thesis.Includes bibliographical references (pages 132-142).This thesis is based on the experimental investigation of the effect of grain
size and phase constitution on the magnetic behavior of Fe73.5-xCrxNb3Cu1Si13.5 B9 [x = 7, 9, 10 & 12.5] alloys in the amorphous and annealed states. The samples are initially
prepared in the amorphous state in the form of thin ribbons by rapid quenching
technique at wheel speed of 25m/s in an Ar atmosphere. The alloy has been annealed
in a controlled way in the temperature range of 450-800°C for 30 minutes. The
kinetics of glass formation and crystallization in composition is studied as affected
differential thermal analysis (DTA). Higher content Cr substituted Fe73.5-x
CrxNb3Cu1S13.5B9 amorphous alloys upon annealed undergoes phase transformation
due to primary crystallization of α -Fe(Si) and secondary crystallization of Fe2B
phase re4spectively revealed by DTA and confirmed by XRD. Thermal analysis
experiment and from the obtained data activation energy of primary crystallization
products α -Fe(Si) phase are varies 2.35 to 4.88 eV and secondary crystallization
products Fe2B3.28 to 3.76 eV.
Amorphosity of the ribbon and nanocryatalline state was evaluated by XRD.
In the optimized annealing condition the grain size has been obtained in the range of
11 - 30 nm. The primary crystallization phase shifts to higher annealed temperature
with Cr content implying the enhancement of thermal stability of the amorphous
alloys against crystallization due to increasing amount of Cr. The average grain size
of the a-Fe(Si) phase, almost same under the identical annealing condition as the
higher content Cr is increased. The peak shifts indicate the change of the values of Si-content of nanograins and therefore, the change of the values of lattice parameter of
nanograins. The saturation magnetization (Ms) and Curie temperature (Tc) of these
alloys decrease linearly with the increase of Cr content for the entire composition
range due to dilution of Fe magnetic moment and weakening of exchange interaction
between of magnetic atoms. The critical composition for disappearance of
ferromagnetism fall of curve Ms with the replacement Fe by Cr, where the nearest
neighbor coupling is longer dominant and intermediate range occur, giving rise to a
significant portion of antiferromagnetic interaction. This causes a weaker exchange
interaction among the Fe magnetic moment resulting in a decrease of Tc. This increase
of magnetization (M) up to annealed temperature 600°C is connected to the structural
relaxation and varying degrees of chemical disorder with reference to enhancement of
M of annealed samples. Crystallization seems to take place and accordingly M Vs H
curve sharply rises and look ferromagnetic for x = 12.5 which is paramagnetic in the
amorphous condition with Tc = 246K. This increase of M for the four samples are
due to the evolution of ferromagnetic α-Fe(Si) nanograin crystallites.Mohammad Zashed IqbalMaster of Philosophy in Physic
Evaluation of Flexible Pavement Design Methods for Developing Countries: A Case Study in Bangladesh
No full textThis thesis is submitted to the Department of Civil Engineering, Khulna University of Engineering & Technology in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering, December 2015.Cataloged from PDF Version of Thesis.Includes bibliographical references (pages 77-79).The analysis of data and design of flexible pavement in Bangladesh by conventional
flexible design procedures is mostly based on the basis of test and field condition
prevailing in western countries. These procedures do not comply with the environmental
and material conditions of the region. These conditions generally do not match the
parameters for design used in Bangladesh and south Asia. The result is often overdesigned
being uneconomical or under-design resulting in heavy maintenance and
rehabilitation costs. In this study climatic condition of the region is considered during the
design. Coarse grained river sand shall be used as subgrade material. In this design mostly
accepted conventional methods for flexible pavement design are compared to check their
adaptability for design input condition prevailing in countries of Southeast Asia. For
evaluation of flexible pavement design methods for Bangladesh, two currently used
methods are selected, i.e., AASHTO 1993 Guide for Design of Pavements structures
developed in the U.S.A. and Overseas Road Note 31 from Britain. Indian Road Congress
(IRC 37) is also considered for this study for comparison. Pavement structures are
designed by all the methods using same input parameters obtained from Bangladesh. The
results indicate that both methods recommend nearly equal total thickness. However,
AASHTO 1993 procedure suggests thicker concrete layer. whereas Road Note 31 and
IRC 37 suggest thicker base and sub-base layers. Mechanistic responses in terms of
stresses, strains and deflections at critical points in the pavement structure are calculated
by computer program CIRCLY. The damaging factors are calculated using CIRCLY
software. Mechanistic responses are usually related to failure modes in pavement. These
failure modes generally are rutting, permanent deformation, fatigue and thermal cracking.
The results of both methods show that structures designed by AASHTO 1993 procedure
are safer against rutting, permanent deformation. fatigue and thermal crack failures. The
thicker base and subbase layers suggested by Road Note 31 and IRC 37 to compensate for
thinner asphalt concrete layer do not significantly contribute to lowering of stresses. The
structures recommended by Road Note 31 and IRC 37 may cost less in the beginning due
to lesser asphalt concrete layer thickness, but may fail permanently requiring higher
maintenance and rehabilitation costs.Md. Imrul HassanMaster of Science in Civil Engineerin
Extraction of Liquid Fuel from Pyrolysis of Waste Tyres with Catalyst
No full textThis thesis is submitted to the Department of Electrical and Electronic Engineering, Khulna University of Engineering & Technology in partial fulfillment of the requirements for the degree of Master of Science in Electrical and Electronic Engineering, October, 2015.Cataloged from PDF Version of Thesis.Includes bibliographical references (pages 71-76).Bangladesh is a developing and most densely populated country in the world with a total
population of about 156.6 million. Her per capita energy consumption is much below the
world average. Energy consumption mix is estimated as: indigenous biomass 60%, natural
gas 27.45%, oil 11.89%, coal 0.440/0 and hydro 0.23%. More than 770,'o of the countrvs
population lives in rural areas and meeting most of their energy needs from traditional
biomass fuels. Around 32% have access to electricity, while in rural areas the availability
of electricity is only 22%. Only 3-4% of the households have connection of natural gas for
cooking. About 2-3% households use kerosene for the same and the rest (over 90%)
depend on biomass for their energy needs. Thus, it is crucial to find out alternative and
sustainable resources to mitigate the energy crisis.
Recent environmental issues and energy security have been emerged as public and
political concern which led to alternative way of thinking and renewable energy sources
may be an indigenous source of that kind of thinking. As energy demand is becoming
acute day by day, scientists are giving efforts on the potentials of utilizing appropriate
technologies to recover energy and useful by-products from domestic and industrial solid
wastes. Researchers have been conducted for biodegradable and non-biodegradable waste
materials. Rubber and plastic containing waste is non-biodegradable. About 20.50 million
bicycle/rickshaw tyres become scrap every year and wait for disposal which is about 37%
(wt) of total tyre waste production in Bangladesh. It is estimated that 30,750 tons
bicycle/rickshaw tyres, 5160 tons motorcycle tyres, and 28,900 tons bus/truck tyres
become scrap and are disposed of every year.
Disposal of waste tyres causes typical problems for environment. Dumped scrap tyre. in
massive stockpiles is one of the possible causes of ideal breeding grounds for disease
carrying mosquitoes and other vermin with the aid of rain water deposited in the free space
of tyre wall. On the other hand, tyres left in open air may result in significant disturbances
and dangerous situations like risk of fire. Different means are available for disposal of
waste tyres and one relatively effective way is pyrolysis of there.
In the present work, waste bus-tyres were pyrolysed in a fixed bed reactor with catalyst
and without catalyst. The objectives were to investigate the composition of derived oil
from waste tyre and the effect on oil extraction in presence of catalyst. The influences of
VI
pyrolysis temperature, catalyst/tyre ratio (CT ratio), heating rate, operating time, sample
size etc. oil yield were investigated. The pyrolysis of tyre was carried out within the
temperature range of 300°C to 600°C. The optimum pyrolytic oil of 42.0
obtained for tyres pyrolysis and 36.67% (wt) for catalytic pyrolysis at 450°C. A higher
temperature and smaller particle size increases the heating rate that resulting a decreased
char yield. The cracking of hydrocarbons, resulting increased lI2 content in the gaseous
product, is favored by a higher temperature and smaller particle size. The physical
properties of the pyrolytic oil were examined. It showed that increase in catalytic
temperature and CT ratio resulted in high yield of gas at the expense of oil yield. When CT
ratio is increased from 0.13 to 0.30, the yield of gas increased from 13.33% to 15.33 %
(wt), and oil yield decreased from 36.67% to 28.0% (wt) at temperature 450°C. High CT
ratio favored to increase the concentration of light naphtha in the pyrolytic oil. Fractional
distillation of 97% (wt) of the pyrolytic oil from catalytic pyrolysis below 350CC with CT
ratio of 0.3 and pyrolysis temperature of 450°C shows that after proper treatment these oil
can be used as substitute of alternative fuel or chemical feedstock to Naphtha.Md. Shameem HossainMaster of Science in Energy Technolog
