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Optical modeling of amorphous and metal induced crystallized silicon with an effective medium approximationMuller, Theophillus Frederic George January 2009 (has links)
Philosophiae Doctor - PhD / In this thesis we report on the metal-mediated-thermally induced changes of the structural and optical properties of hydrogenated amorphous silicon deposited by hot-wire CVD, where aluminium and nickel were used to induce crystallization. The metal-coated amorphous silicon was subjected to a thermal annealing regime of between 150 and 520°C. The structural measurements, obtained by Raman spectroscopy, show partial crystallization occurring at 350 °C. At the higher annealing temperatures of 450°C and 520°C complete crystallization occurs. Reflection and transmission measurements in the UV-visible range were then used to extract the optical properties. By adopting the effective medium approximation a single optical model could be constructed that could successfully model material that was in different structural phases, irrespective of metal contamination. Changes in the absorption of the material in various stages of transition were confirmed with a directly measured absorption technique, and the modelled absorption closely followed the same trends This study forms part of the larger overall solar cell research project, of which the primary aim is to eventually develop a silicon solar panel that optimises the characteristics for best performance. / South Africa
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Studies Of Thermal, Nanomechanical And Tribological Characteristics Of Perfluoroalkyl Silanes Self Assembled On Aluminum SurfacesDevaprakasam, D 04 1900 (has links) (PDF)
No description available.
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Ultrarychlá laserová spektroskopie hybridních nanosystémů / Ultrafast spectroscopy of hybrid nanosystemsGalář, Pavel January 2016 (has links)
Title: Ultrafast spectroscopy of hybrid nanosystems Author: RNDr. Pavel Galář Department: Department of Chemical Physics and Optics Supervisor: prof. RNDr. Petr Malý, DrSc. Abstract: This Ph. D. thesis is focused on physical phenomena located at the interface of hybrid nanostructure composed of polycrystalline diamond and polymer polypyrrole. The main method used in our experimental study was ultrafast laser spectroscopy that allowed us to gain new findings about electron recombination processes in polycrystalline diamond layers, polypyrrole and in their hybrid structures. The research was focused on mutual influence of both components, especially through energy and charge transfer. In the first step of our research we carried out optical characterisation of different kinds of polypyrrole and complex study of recombination processes dynamics of photoexcited charge carriers in polycrystalline diamond. The measurements were realized by the methods of time-resolved photoluminescence and transmission spectroscopy in the time scale from picoseconds to milliseconds. On the basis of the obtained results the model explaining the origin of luminescence signal related to the different kinds of electron recombination processes in non- diamond phase and on surface defects of diamond grains in polycrystalline layers was...
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Tenké vrstvy polykrystalického křemíku / Thin Films of Polycrystalline SiliconLysáček, David January 2010 (has links)
The doctoral thesis deals with the structure and properties of the polycrystalline silicon layers deposited on the silicon wafers backside. The wafers are further used for production of semiconductor devices. This work is focused on detailed description of the layers structure and study of the gettering properties and residual stress of the layers. The main goal of this work is to develop two novel technologies. The first one leads to improvement of the temperature stability of the gettering properties of the layers, and the second one solves the deposition of the layers with pre-determined residual stress. This doctoral thesis was created with the support of the company ON Semiconductor Czech Republic, Rožnov pod Radhoštěm.
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Tribopairs in Wellbore Drilling: A Study of PCD Tilting Pad Bearings in an Electric Submersible PumpEllis, Cameron B 01 December 2017 (has links)
A polycrystalline diamond was tested as a bearing material for a tilting pad thrust bearing to be used in an electric submersible pump, which elevates process fluids from the bottom of well bores. The goal of this study was to compare the PCD to a current best of technology, which is stainless steel with an engineering polymer.This study found that PCD can handle larger loads than current technology but is limited in size due to diamond sintering and manufacturing constraints. The maximum size is Ø75mm.
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Tribopairs in Wellbore Drilling: A Study of PCD Tilting Pad Bearings in an Electric Submersible PumpEllis, Cameron B 01 December 2017 (has links)
A polycrystalline diamond was tested as a bearing material for a tilting pad thrust bearing to be used in an electric submersible pump, which elevates process fluids from the bottom of well bores. The goal of this study was to compare the PCD to a current best of technology, which is stainless steel with an engineering polymer.This study found that PCD can handle larger loads than current technology but is limited in size due to diamond sintering and manufacturing constraints. The maximum size is Ø75mm.
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Assessment and Modelling of Wear prediction and Bit Performance for Roller Cone and PDC Bits in Deep Well DrillingMazen, Ahmed Z.M. January 2020 (has links)
Drilling is one of the important aspects in the oil and gas industry due to the high
demand for energy worldwide. Drilling time is considered as the major part of the
operations time where the penetration rate (ROP) remains as the main factor for
reducing the time. Maximizing ROP to lower the drilling cost is the main aim of
operators. However, high ROP if not controlled may impact on the well geometry
in terms of wellbore instability, cavities, and hole diameter restrictions.
Accordingly, more time is needed for the other operations that follow such as:
pool out of hole (POOH), casing running, and cementing. Bit wear is considered
as the essential issue that influences in direct way on the bit performance and
reduce ROP. Predicting the abrasive bit wear is required to estimate the right time
when to POOH to prevent any costly job to fish any junk out to the surface. The
two-common types of bits are considered in the research, rock bits (roller cone
bits) and Polycrystalline Diamond Compact bits (PDC). This study focuses more
on PDC bits because about 60% of the total footage drilled in wells worldwide
were drilled by PDC bits and this is expected to reach 80% in 2020.
The contribution of this research is to help reducing the drilling cost by
developing new tools not to estimating the time when to POOH to surface but
also to measure the wear and enhance the accuracy of prediction the bit
efficiency. The work is broken down into four main stages or models to achieve
the objective: The first stage; estimating of the rock abrasiveness and calculate
the dynamic dulling rate of the rock bit while drilling. The second stage; estimating
the PDC abrasive cutters wear by driving a new model to determine the
mechanical specific energy (MSE), torque, and depth of cut (DOC) as a function
of effective blades (EB). The accuracy of the predicted wear achieves 88%
compared to the actual dull grading as an average for bits used in five wells. The
third stage; modifying the previous MSE tool to develop a more accurate
approach; effective mechanical specific energy (EMSE), to predict the PDC bit
efficiency in both the inner and outer cone to match the standard bit dulling. The
fourth stage; predicting ROP while PDC drilling in hole by accounting three parts
of the process: rock drillability, hole cleaning, and cutters wear. The results
achieve an enhancement of about 40% as compared to the available previous
models.
Consequently, the developed models in this study provide a novelty on
understanding in more details the bit rock interface process and gain an idea of
the relationship between the drilling parameters to enhance the bit performance
and avoid damaging the bit. This is basically about optimisation the controllable
factors such as: weight on bit (WOB), rotary speed (RPM), and flow rate. The
result is the reduction in time losses and the operations cost.
To ensure reliability and consistency of the proposed models, they were
validated with several vertical oil wells drilled in Libya. The results from the
validation of the models are consistent with the real field data. The research
concludes that the developed models are reliable and applicable tool for both: to
assist decision-makers to know when to pull the bit out to surface, and also to
estimate the bit performance and wear.
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Mathematical Modeling of Ammonia Electro-Oxidation on Polycrystalline Pt DepositedElectrodesDiaz Aldana, Luis A. 10 June 2014 (has links)
No description available.
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Pt and Au as electrocatalysts for various electrochemical reactions / Marthinus Hendrik SteynSteyn, Marthinus Hendrik January 2015 (has links)
In this study the focus was on the electrochemical techniques and aspects behind the
establishment of the better catalyst (platinum or gold) for the sulphur dioxide oxidation
reaction (SDOR). One of the primary issues regarding the SDOR is the catalyst material,
thus the comparative investigation of the performance of platinum and gold in the SDOR, as
found in this study. Ultimately, the SDOR could lead to an effective way of producing
hydrogen gas, which is an excellent energy carrier.
The electrochemical application of the oxygen reduction reaction (ORR) and ethanol
oxidation reaction (EOR) is an integral part of the catalytic process of water electrolysis, and
by using fuel cell technology, it becomes even more relevant to this study and can therefore
be used as a control, guide and introduction to the techniques required for electrochemical
investigation of catalyst effectiveness. Subsequently, the EOR as well as the ORR was used
as introduction into the different electrochemical quantification and qualification techniques
used in the electrochemical analyses of the SDOR.
Considering the ORR, gold showed no viable activity in acidic medium, contrarily in alkaline
medium, it showed good competition to platinum. Gold also lacked activity towards the EOR
in acidic medium compared to platinum, with platinum the best catalyst in both acidic and
alkaline media. Ultimately, platinum was established to be the material with better activity for
the ORR with gold a good competitor in alkaline medium, and platinum the better catalyst for
the EOR in both acidic and alkaline media.
With the main focus of this study being the SDOR, gold proved to be the best catalyst in salt
and gaseous forms of SO2 administration compared to platinum when the onset potential,
maximum current density, Tafel slope and number of electrons transferred are taken into
consideration. The onset potential was determined as 0.52 V vs. NHE for both platinum and
gold using SO2 gas and 0.54 V and 0.5 V for gold and platinum respectively, using Na2SO3
salt. The maximum current density using gaseous SO2 for platinum at 0 RPM was 400
mA/cm2 with a Tafel slope of 891 mV/decade whereas gold had a maximum current density
of 300 mA/cm2 and a Tafel slope of 378 mV/decade. Using Na2SO3 salt, the maximum
current density of gold was 25 mA/cm2 with a Tafel slope of 59 mV/decade whereas
platinum only achieved 18 mA/cm2 with a Tafel slope of 172 mV/decade. Concerning the
number of electrons transferred, gold achieves a transfer of 2 while platinum only 1 for both
SO2 gas and Na2SO3 salt. Taking all these summarised determinations into account, gold
was established to be a very competitive catalyst material for the SDOR, compared to
platinum. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015
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Pt and Au as electrocatalysts for various electrochemical reactions / Marthinus Hendrik SteynSteyn, Marthinus Hendrik January 2015 (has links)
In this study the focus was on the electrochemical techniques and aspects behind the
establishment of the better catalyst (platinum or gold) for the sulphur dioxide oxidation
reaction (SDOR). One of the primary issues regarding the SDOR is the catalyst material,
thus the comparative investigation of the performance of platinum and gold in the SDOR, as
found in this study. Ultimately, the SDOR could lead to an effective way of producing
hydrogen gas, which is an excellent energy carrier.
The electrochemical application of the oxygen reduction reaction (ORR) and ethanol
oxidation reaction (EOR) is an integral part of the catalytic process of water electrolysis, and
by using fuel cell technology, it becomes even more relevant to this study and can therefore
be used as a control, guide and introduction to the techniques required for electrochemical
investigation of catalyst effectiveness. Subsequently, the EOR as well as the ORR was used
as introduction into the different electrochemical quantification and qualification techniques
used in the electrochemical analyses of the SDOR.
Considering the ORR, gold showed no viable activity in acidic medium, contrarily in alkaline
medium, it showed good competition to platinum. Gold also lacked activity towards the EOR
in acidic medium compared to platinum, with platinum the best catalyst in both acidic and
alkaline media. Ultimately, platinum was established to be the material with better activity for
the ORR with gold a good competitor in alkaline medium, and platinum the better catalyst for
the EOR in both acidic and alkaline media.
With the main focus of this study being the SDOR, gold proved to be the best catalyst in salt
and gaseous forms of SO2 administration compared to platinum when the onset potential,
maximum current density, Tafel slope and number of electrons transferred are taken into
consideration. The onset potential was determined as 0.52 V vs. NHE for both platinum and
gold using SO2 gas and 0.54 V and 0.5 V for gold and platinum respectively, using Na2SO3
salt. The maximum current density using gaseous SO2 for platinum at 0 RPM was 400
mA/cm2 with a Tafel slope of 891 mV/decade whereas gold had a maximum current density
of 300 mA/cm2 and a Tafel slope of 378 mV/decade. Using Na2SO3 salt, the maximum
current density of gold was 25 mA/cm2 with a Tafel slope of 59 mV/decade whereas
platinum only achieved 18 mA/cm2 with a Tafel slope of 172 mV/decade. Concerning the
number of electrons transferred, gold achieves a transfer of 2 while platinum only 1 for both
SO2 gas and Na2SO3 salt. Taking all these summarised determinations into account, gold
was established to be a very competitive catalyst material for the SDOR, compared to
platinum. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015
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