College of Biological and Physical Sciences

In this study, Electrophoretic Deposition (EPD) technique was used to fabricate TiO2/Nb2O5 composite
thin films on FTO coated glass for application as photoelectrodes in Dye Sensitized Solar Cells (DSSC). A
TiO2/Nb2O5 ratio of 1:1 was used in a 2-propanol suspension solution with a solid loading of 0.25g/L. Optical
investigations showed that the film with thickness of 5.5 µm deposited at 35.0 V for 90.0 s had the highest
transmittance of 55.0 % at a wavelength (λ) of 1,300 nm. The optical band gap energy (Eg) was 3.884 eV and was
found to be dependent on the annealing time. The solar cell fabricated from this film had an open circuit voltage
(VOC) of 0.66 V, fill factor (FF) of 57.0%, short current density (JSC) of 5.25 mA/cm2 and photo conversion
efficiency (PCE) of 2.0%. Electrochemical Impedance Spectroscopy (EIS) analysis indicate that the DSSC device
with thinner photoelectrodes have more efficient electron transport in the photoanode compared to thicker
photoelectrodes to achieve higher conversion efficiencies.
Keywords: electrophoretic deposition, dye-sensitized solar cell, TiO2/Nb2O5 composite thin films

In this study, electrophoretic deposition (EPD) technique was used to deposit titanium dioxide (TiO2) thin films on
conducting glass substrates for application in water purification from organic contaminants. Phenol was used as a model
pollutant. The EPD suspension related parameters and deposition conditions were first optimized for good quality film
deposits. The suspension stability and deposition conditions that result in good adherence of TiO2 particles to the substrate with
homogeneous film coatings, is ethanol with a pH of 3.0, a TiO2 solid loading of 4.0 wt%, a 0.2 wt% iodine concentration in the
solvent and a deposition voltage of 20.0V in a time of 210.0s. The photocatalytic activity of TiO2 thin films decreases
exponentially with the ultraviolet light (UV) illumination time and it is also dependent on film thickness, sintering temperature
and the intensity of the UV light. Highest rate of photocatalytic activity is observed at an optimal film thickness of 95.0 ±
2.0µm sintered at 300.0°C. The implications of these results are discussed for design of inexpensive waste water purification
systems for light industries before discharge into the ecosystem.
Keywords: Electrophoretic Deposition, Titanium Dioxide, Photocatalysis

The installation of Photovoltaic (PV) solar systems in institutions as well as homesteads in the rural areas in
Kenya is increasing at a high rate; and so is the need for the stake holders to make sure the PV solar systems are professionally designed, sized, installed and maintained. In PV solar system installation, the designing, sizing and the installation are very critical steps. A wrongly designed, sized and installed system will not perform optimally and will underperform (for undersized systems) and waste energy and resources (for oversized systems). Furthermore, undersized systems do not perform to the user’s expectation discouraging the user and eventually a negative customer attitude creeps in which may affect the uptake of solar PV systems. On the other hand, an oversized PV system is extra expense on the side of the client, creating an exaggerated high cost of PV solar systems, again discouraging potential clients from the adoption of the technology. Both scenarios mean loss of business, jobs and the economic and social benefits associated with PV technology. We present a case study of poorly installed PV systemsin Makueni County, Kenya. We observed that the solar modules pecifications at the back of the modules were not clearly done, the batteries were poorly matched and the cables used in the installation were undersized. Due to these issues, even a normal television set was not able to work since the system was installed four years ago (in 2012).The above case emphasizes the need for training in PV solar system design, sizing, installation, and maintenance.
Key words: Photovoltaic (PV), modules, solar system, Installation, training, professional

Aluminium induced crystallization (AIC) was used to crystallize sputtered amorphous silicon
thin films on aluminium-coated glass at annealing temperatures ranging from 250-520° C in
vacuum. Crystalline volume fractions were measured by Raman spectrometry as a function
of annealing temperature. It was shown that the crystallized films had large grains as the
Raman peaks were centred at about 520 cm-1 at and over annealing temperatures of 420°
C. The three-layer sample crystallization resulted in crystallization of the films at lower
temperatures compared to the two-layer sample crystallizations which implied a reduction in
the cost of production of the seedlayer and resulting products. Hall mobilities and hole
densities ranging from 17.0-22.8 cm2V-1s-1and (4.7-9.2)× 1018 cm-3 respectively were
measured. Low hole charge densities for films of the same thickness were achieved at high annealing temperatures which was an indication of less aluminium in seed layers prepared at those temperatures. Having seed layers with sufficiently low hole charge densities is desirable for application of the seed layer in photovoltaic applications.
Key words: microcrystalline, silicon, annealed, raman, crystallinity, hall-effect

The installation of Photovoltaic (PV) solar systems in institutions as well as homesteads in the rural areas in
Kenya is increasing at a high rate; and so is the need for the stake holders to make sure the PV solar systems are
professionally designed, sized, installed and maintained. In PV solar system installation, the designing, sizing and the
installation are very critical steps. A wrongly designed, sized and installed system will not perform optimally and will
underperform (for undersized systems) and waste energy and resources (for oversized systems). Furthermore,
undersized systems do not perform to the user’s expectation discouraging the user and eventually a negative customer
attitude creeps in which may affect the uptake of solar PV systems. On the other hand, an oversized PV system is extra
expense on the side of the client, creating an exaggerated high cost of PV solar systems, again discouraging potential
clients from the adoption of the technology. Both scenarios mean loss of business, jobs and the economic and social
benefits associated with PV technology. We present a case study of poorly installed PV systemsin Makueni County,
Kenya. We observed that the solar modules specifications at the back of the modules were not clearly done, the
batteries were poorly matched and the cables used in the installation were undersized. Due to these issues, even a
normal television set was not able to work since the system was installed four years ago (in 2012).The above case
emphasizes the need for training in PV solar system design, sizing, installation, and maintenance

Ultrathin films (50-150nm thick) cuprous oxide (Cu2O) thin films were deposited by low temperature thermal oxidation technique. The structural, optical and photoelectrochemical properties of the thin films were investigated. X-ray diffraction (XRD) and high resolution scanning electron microscope (SEM) was used to study the phase composition and the thin films’ microstructure respectively. XRD results showed that Cu2O was the dominant phase albeit some trace CuO peaks were also observed indicating surface formation of an extremely layer of CuO probably during the cooling process following either deposition or during the annealing steps. SEM showed a highly nanostructure consisting long narrow nanorods with broadening to the surface but with extremely narrow, sharp cylindrical roots standing on the substrate. Photoelectrochemical properties of the films were studied via a standard three electrode using a saturated calomel cell (SCE).

A composite thin film consisting of TiO2 (binder), uniformly mixed CuFeMnO4 paint (solar absorber)
was coated on textured aluminum sheets by dip coating. The film’s elemental analysis was done using energy
dispersive x-ray (EDX) and the surface of the film characterized using scanning electron microscope (SEM). Optical
properties of the TiO2/CuFeMnO4 composite film were also studied using computerized double beam solid-spec
3700 DUV Shimadzu Spectrophotometer. Reflectance was obtained by spectrophotometric measurements, and
thermal emmittance was determined using heat flux- based technique respectively. Reflectance measurement values
less than 0.03 in the solar wavelength (290 nm < λ < 2500 nm) and low thermal emmittance less than 0.016 for
temperatures between 24°C and 100°C were obtained.
Keywords: CuFeMnO4 paint, TiO2- bound, reflectance, thermal emmittance, solar thermal

Aluminum sheets were polished to reduce ruggedness and then textured in varying acid-ethanol
concentration etchant to form pores. The textured surface was characterized structurally by using
X-ray diffraction (XRD) which revealed aluminum crystallographic planes (1 1 1), (2 0 0), (2 2 0)
and (3 1 1). Its morphology was studied by using energy dispersive X-ray (EDX) and scanning
electron microscope (SEM) that confirmed purity of aluminum sheet to be 99.66% at. Reflectance
of textured and plain aluminum sheet was analyzed by spectrophotometric measurements which
showed that texturing reduced the reflectance of the polished surface by 26% in the UV-VIS-NIR
spectrum of solar radiation. With reduced reflectance of the textured aluminum sheet, it was applicable
for solar radiation absorption.
Keywords
Aluminum, Texturing, Reflectance, Solar Energy, Electro-Polishing

Abstract— This paper reports the results of electrical characterization of TiO2/Nb2O5 composite thin films. Uniform TiO2 and Nb2O5 composites thin films were deposited on FTO coated glass substrate using electrophoretic deposition (EPD) technique. The EPD voltage of 35V (DC) and deposition time of 90s, were used for various volume fractions of Nb2O5 in composites. Uniform and crack free composite films were successfully deposited using the EPD technique as shown by the SEM micrographs. The Hall Effect equipment was used to characterize the films through measurement of current and the Hall voltage. Current against Hall voltage plot for films of various volume fractions of Nb2O5 were used to determine Hall coefficients and majority charge carrier density. The sign of Hall coefficient values revealed that TiO2/Nb2O5 composite thin films had a net n-type polarity indicating electrons were the majority charge carrier in the composite films. The results showed that dye-sensitized solar cells should be fabricated with TiO2/Nb2O5 composites thin films in ratio of 1:1 because such ratio 1:1 for TiO2 and Nb2O5 in composite yielded the highest electron mobility in the films.
Keywords— Electrical characterization, TiO2/Nb2O5 composites, Electrophoretic deposition, thin films, Hall Effect

The effects of niobium doping (for doping concentrations: 0.02 – 0.06 at. % Nb5+) on the crystal structure of
TiO2 prepared by high temperature diffusion method were investigated. The samples were characterized using
energy dispersive X-ray fluorescence (EDXRF) and X- ray diffraction (XRD) spectroscopy to investigate the
chemical compositions, phase compositions and crystallinity of the thin films respectively. Despite the expected
high reutilization at high temperatures (>600oC), XRD results confirmed a significant suppression of anatase to
rutile phase transformation at even a higher synthesis (850oC) temperature. Grain growth retardation was also
observed in niobium doped TiO2, results which were attributed to Nb5+ substitution of lattice Ti4+.
Key words: Anatase, rutile, phase transformation, grain growth

In this study doped SnO2 thin films have been prepared by spray pyrolysis technique using an alcoholic precursor solution consisting of stannic chloride (SnCl4.5H2O), ammonium fluoride (NH4F) and palladium chloride (PdCl2). Optimization on the deposition parameters was done so as to obtain high quality thin films. The effect of varying the Fluorine content on the optoelectronic properties of F: SnO2 thin films was studied. Data for transmittance and reflectance in the wavelength range from 300nm – 2500nm was obtained using the solid spec 3700DUV spectrophotometer. Electrical characterization of the thin films was done using the four point probe method at room temperature. Post deposition treatment of the thin films by annealing in air then passivating in nitrogen gas environment was done in a tube furnace at 4500C. Sheet resistivity for the as prepared F: SnO2 was found to be 0.4599 Ωcm and 0.00075 Ωcm being the highest and lowest sheet resistivity at 22.74 at% F and 16.41 at% F doping in SnO2 respectively. Low sheet resistivity of F: SnO2 thin films is due substitutional incorporation of F ions instead of oxygen ions into the crystal lattice of SnO2 thin films which increases free carrier concentration. The effect of annealing generally was found to improve on the electrical conductivity of the thin films which is due to increase in carrier mobility and density. Passivation on the other hand had a slight opposite effect. Effects of annealing and passivation on doped SnO2 thin films band gap energy and their transparency was insignificant, rendering the doped SnO2 thin films good choice for making a transparent thin film gas sensors.
Keywords: Spray Pyrolysis, Fluorine Doping, Palladium Doping, Annealing and Passivation

The effects of niobium doping (for doping concentrations: 0.02 – 0.06 at. % Nb5+) on the crystal structure of
TiO2 prepared by high temperature diffusion method were investigated. The samples were characterized using
energy dispersive X-ray fluorescence (EDXRF) and X- ray diffraction (XRD) spectroscopy to investigate the
chemical compositions, phase compositions and crystallinity of the thin films respectively. Despite the expected
high reutilization at high temperatures (>600oC), XRD results confirmed a significant suppression of anatase to
rutile phase transformation at even a higher synthesis (850oC) temperature. Grain growth retardation was also
observed in niobium doped TiO2, results which were attributed to Nb5+ substitution of lattice Ti4+.
Key words: Anatase, rutile, phase transformation, grain growth

Nano sized powders of TiO2 (titanium dioxide) and Nb2O5 (Niobium (V) oxide) were used to fabricate TiO2/Nb2O5
composites thin films by EPD (electrophoretic deposition) technique. The metal oxide powders, together with magnesium nitrate hexahydrate pellets, were suspended in propan-2-ol inside an EPD cell. The electrodes, placed 1.2 cm apart, were partially immersed in the suspension and a DC potential applied across them. Key EPD process parameters, which include applied DC electric field, deposition time and solid concentration in suspension, were optimized through visual inspection and from UV-Vis-NIR spectrophotometer spectra. The highest (55%) transmittance was obtained for films with deposition time of 90 s, powder concentration of 0.01 g/40 mL, and 35 V DC (direct current) voltage. XRD micrographs confirmed that TiO2 and Nb2O5 particles were presented in the composite film. SEM (scanning electron microscope) micrographs of the composite electrode thin films showed that porous films
of high quality with well controlled morphology were deposited by using the EPD technique.
Key words: Electrophoretic deposition, TiO2/Nb2O5 composite electrode thin films.

Pd-F:SnO2 thin films have been prepared by spray pyrolysis technique using an alcoholic precursor solution
consisting of stannic chloride (SnCl4.5H20), ammonium fluoride (NH4F) and palladium chloride (PdCl2). Optimization on the deposition parameters has been done in order to obtain high quality thin films. The effect of varying the fluorine content on the optical properties of Pd-F:SnO2 thin films were studied. Data for transmittance and reflectance in the wavelength range from 300nm – 2500nm was measured using the solid spec 3700DUV spectrophotometer. The calculated optical band gap of the as prepared thin films has been found to range from 3.8eV to 4.11eV. Fluorine incorporation for Pd-F:SnO2 has been found to have a narrowing effect on the band gap, but at its higher concentration the band gap has been seen to increase. The
band gap narrowing is due to the incorporation of F- ions in the crystal lattice therefore giving rise to donor levels in the SnO2 band gap which is an essential characteristic for the gas sensor applications. Both annealing and passivation have been found to have very insignificant change in optical band gap of Pd-F:SnO2.

Keywords: Spray Pyrolysis, Fluorine Doping, Palladium Doping, Co-Doping, Palladium and Fluorine Co-Doping, Annealing, Passivation, Pd and F Co-Doped SnO2 (Pd-F:SnO2)

Abstract: Different thin films samples made of SnO2, F:SnO2, Pd: SnO2 and and co-doped Pd-F: SnO2 were deposited at a substrate temperature of 450oC using optimized doping concentrations of F and Pd, thereafter the samples were annealed and passivated in a tube furnace at 450oC. Optical and electrical methods were used in characterizing the thin film samples: The band gap energy for all samples was extracted from optical data using a proprietary software, Scout™ 98. The calculated band gap energy were found to be 4.1135eV for Pd:SnO2 and 3.8014eV for F:SnO2 being the highest and the lowest calculated band gap energies, respectively. The wide band gap energy has been attributed to the incorporation of Pd ions in crystal lattice of SnO2 thin film for Pd:SnO2 while for F:SnO2 has been due to incorporation of F- ions in the crystal lattice of SnO2 which gives rise to donor levels in the SnO2 band gap. This causes the conduction band to lengthen resulting to a reduction in the band gap energy value. The electrical resistivity was done by measuring the sheet resistance of the SnO2, Pd:SnO2, F:SnO2 and Pd-F:SnO2 thin films. The undoped SnO2 thin film had the highest sheet resistivity of 0.5992 Ωcm while F:SnO2 had the lowest sheet resistivity of 0.0075 Ωcm. The low resistivity of F:SnO2 results from substitution incorporation of F- ions in the crystal lattice of SnO2 thin
films, instead of O- ions which lead to an increase in free carrier concentration. The Pd-F:SnO2 gas sensor device was tested for CO2 gas sensing ability using a lab assembled gas sensing unit. The performance of the gas sensor device was observed that: the as prepared device was more sensitive to CO2 gas than those subjected to annealing and passivation. The decrease in the sensitivity of the annealed Pd-F: SnO2 gas sensor is attributed to decrease in grain boundary potential resulting from grain growth. This causes a decrement in adsorption properties of CO- and O- species by the annealed Pd-F: SnO2 thin film. The sensitivity of passivated Pd-F: SnO2 gas sensor was found to be the lowest. The low sensitivity is due to the effects of nitration and decrement in grain boundary potential resulting from grain growth, nevertheless, the sensitivity of the passivated Pd-F: SnO2 thin film was found to be within the range for gas sensing applications.

Keywords: Spray Pyrolysis, Fluorine doping, Palladium doping, co-doping, Palladium and Fluorine co-doping, Annealing, Passivation, F -co- doped Pd:SnO2 (Pd-F: SnO2)

Abstract
Perception of livestock farmers on the generation of cattle waste-based biogas methane was evaluated in this
study. The study was carried out in Embu West district in Kenya. A random sampling technique was used to
gather information related to farmers’ perception and the data collected with the help of self designed
questionnaires and face to face interviews. In the study, 92.9% of the one hundred and fifty six (156) livestock
farmers practiced zero-grazing and only fourteen (9%) of them had installed biogas digesters in their farms. Chi square tests yielded a value of χ = 0.591, p >0.05 which indicated that there was no significant relationship between uptake of cattle waste-based biogas and farmer’s perception. The hypothesis that low uptake of cattle waste-based biogas technology was due to negative perception of the farmers was found not to hold. Further Chi square tests indicated significant relationship (χ=23.56, p< 0.05) between farmers’ perception and knowledge of cattle waste-based biogas methane. Thus livestock farmers in Embu district had a very positive perception and were quite knowledgeable about biogas technology despite the minimal installation of the cattle waste-based biogas digesters. The research findings indicated that other factors like installation cost contribute to the low uptake of biogas technology. These research findings should assist government and industry understand the reason behind public ‘reservations’ in the adoption of biogas technology as well as develop strategies for enhanced promotion of renewable energy technologies.

Keywords: Biogas methane, perception, renewable energy, Embu west

Abstract
Aluminium induced crystallization (AIC) was used to crystallize sputtered amorphous silicon thin films on aluminium-coated glass at annealing temperatures ranging from 250-520°C in vacuum. Crystalline volume fractions were measured by Raman spectrometry as a function of annealing temperature. It was shown that the crystallized films had large grains as the Raman peaks were centred at about 520 cm-1 at and over annealing temperatures of 420°C. The three-layer sample crystallization resulted in crystallization of the films at lower temperatures compared to the two-layer sample crystallizations which implied a reduction in the
cost of production of the seedlayer and resulting products. Hall mobilities and hole densities ranging from 17.0-22.8 cm2V-1s-1and (4.7-9.2) x 1018 cm-3 respectively were measured. Low hole charge densities for films of the same thickness were achieved at high annealing temperatures which was an indication of less aluminium in seed layers prepared at those temperatures. Having seed layers with sufficiently low hole
charge densities is desirable for application of the seed layer in photovoltaic applications.

Key Words: microcrystalline, silicon, annealed, raman, crystallinity, hall-effect

Abstract: Nano sized powders of TiO2 (titanium dioxide) and Nb2O5 (Niobium (V) oxide) were used to fabricate TiO2/Nb2O5 composites thin films by EPD (electrophoretic deposition) technique. The metal oxide powders, together with magnesium nitrate hexahydrate pellets, were suspended in propan-2-ol inside an EPD cell. The electrodes, placed 1.2 cm apart, were partially immersed in the suspension and a DC potential applied across them. Key EPD process parameters, which include applied DC electric field, deposition time and solid concentration in suspension, were optimized through visual inspection and from UV-Vis-NIR
spectrophotometer spectra. The highest (55%) transmittance was obtained for films with deposition time of 90 s, powder concentration of 0.01 g/40 mL, and 35 V DC (direct current) voltage. XRD micrographs confirmed that TiO2 and Nb2O5 particles were presented in the composite film. SEM (scanning electron microscope) micrographs of the composite electrode thin films showed that porous films of high quality with well controlled morphology were deposited by using the EPD technique.

Key words: Electrophoretic deposition, TiO2/Nb2O5 composite electrode thin films.

In this work, Titanium Dioxide (TiO2) thin films were prepared by spray pyrolysis and thermally annealed at 400℃. The films were characterized as deposited (no annealing) as well as after annealing. Optical studies showed that the energy band gap of the films was lowered from 3.25 eV to 2.90 eV on Nitrogen (N2) doping. The reduction in energy band gap was attributed to the introduction of N2 impurity states on the bands (conduction band and or valence band). The effect of N2 doping of Titanium Dioxide window layer on the efficiency of the ETA TiO2/In(OH)iSj/Pb(OH)xSy solar cell was investigated using a conventional current-voltage (I-V) technique. The photovoltaic conversion efficiency (η) increased from 1.06% for the solar cell with undoped films to 1.32% for the solar cell with N2-doped films. The increase in photovoltaic conversion efficiency on doping was attributed to increased light absorption due to the Nitrogen doping.

Light soaking characterization on complete SnO2:F/TiO2/ln(OH)xSy/PEDOT:PSS/Au, Pb(OH)xS)pEDOT:PSS/Au, eta solar cell structure
as well as on devices which do not include one or both TiO2 and/or PEDOT:PSS layers has been conducted. Additionally,
studies of SnO2:F/In(OH)xSy/PEDOT:PSS/Au solar cell have been performed. The power conversion
efficiency and the short circuit current density have been found to increase with light soaking duration by a factor of
about 1.6 - 2.7 and 2.1 - 3, respectively. The increase in these two parameters has been attributed to the filling up of trap
states and/or charge-discharge of deep levels found in In(OH)xSy. These effects take place at almost fill factor and open
circuit voltage being unaffected by the light soaking effects.

Transport mechanism studies in Ti02/In(OH)xSy/Pb(OH)xSy/PEDOT:PSS eta solar cell have been carried out. The characterizations have been performed both in the dark and under Varying illumination intensity for temperature range 200 K - 320 K. Calculations from ideality factor have shown that the recombination process of the eta solar cell in the dark to be tunneling enhanced, while under illumination it is thermally activated and takes place through exponentially distributed energy recombination levels. The temperature has been found to influence series resistance of the solar cell. Series resistance has been found to be high at low temperature and low at higher temperature, thus we can conclude that the recombination is thermally activated.

ABSTRACT
Light soaking characterization on complete SnO2:F/TiO2/In(OH)xSy/Pb(OH)xSy/PEDOT:PSS/Au, eta solar cell structure as well as on devices which do not include one or both TiO2 and/or PEDOT:PSS layers has been conducted. Addition- ally, studies of SnO2:F/In(OH)xSy/Pb(OH)xSy/PEDOT:PSS/Au solar cell have been performed. The power conversion efficiency and the short circuit current density have been found to increase with light soaking duration by a factor of about 1.6 - 2.7 and 2.1 - 3, respectively. The increase in these two parameters has been attributed to the filling up of trap states and/or charge-discharge of deep levels found in In(OH)xSy. These effects take place at almost fill factor and open circuit voltage being unaffected by the light soaking effects.

Keywords: Eta Solar Cell; Light Soaking; Conversion Efficiency; TiO2; In(OH)xSy; Pb(OH)xSy

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The study, manipulation and design of materials and devices at level approaching atomic sizes has given rise to nanoscience and nanotechnology, with the former being concerned more with the new properties whereas the latter - nanotechnology focuses on new devices. The nanoscale science and technology involves and cuts across different disciplines. It is now recognized that science founded on the unified concepts on matter at the nanoscale is the new basis for knowledge creation, innovation, and technology integration, and therefore receiving heightened attention world over.

Arising from the current and potential impacts of nanoscience and nanotechnology in all facets of humanity – way of life, health and the environment, it is imperative that any country takes stock of the status of the two intertwined disciplines. For example, it is known that nanotechnology can improve efficiency in manufacturing, energy resources and utilization, reduce environmental impacts of industry and transportation, enhance healthcare, produce better pharmaceuticals, improve agriculture and food production, and expand the capabilities of information technologies. The level of preparedness of a country to create new knowledge, exploit it or absorb such, it will be seen depends on the synergistic relationships amongst all the stakeholders right from the beginning of the research, product development processes, and policy and legislative frameworks that protect the workers producing and consumers of such products.

A study of the Kenya’s situation reveals that so far there minimal understanding or appreciation of what nanoscience and nanotechnology are amongst the key stakeholders, and what their potential benefits are or would be. The teaching of and research in these areas and the accompanying infrastructure are weak and uncoordinated. The regulatory frameworks and policies governing, particularly the manufacturing processes of or nanoscale products are either nonexistent or very weak/inadequate.

Key words: Nanoscience, Nanotechnology, Research, Policies, Kenya

This study investigated the effectiveness of three physical-chemical methods namely; pH adjustment, precipitation with alum and the use of polyelectrolytes. In the treatment of diary wastewater from Brookeside milk processing plant. It also investigated the drainability of the sludge produced by each of the three methods. Laboratory tests were carried out in three different batches, one for each of the three methods. In the alum method enough alum was added to the wastewater samples to cause precipitation by sweep floc. In the pH adjustment method, the pH of samples were lowered to the iso-electric point of the casein proteins of approximately pH 4.5 leading to their precipitation as a result of solubility changes. The polyelectrolytes method involved the use of two polyelectrolytes, Sudfloc 3820 and Sudfloc 3860 each of which was used to coagulate the dirty wastewater. For each of the three methods, the samples were taken in one-litre beakers and subjected to Jar tests to determine the optimum dosages. After one hour of settling the supernatants were decanted and subjected to standard Chemical Oxygen Demand (COD) tests, turbidity and pH measurements. The settled sludge was subjected to drainability studies. Results showed the treatment of dairy wastewater by the three physical-chemical methods to be effective. There were COD removals of between 60% and 90% and turbidity reduction of over 90%. The use of the sudfloc polyelectrolytes was found to be the least demanding in terms of effluent quality control as no pH adjustments of either the wastewater or the effluent was required. The use of polyelectolytes produced the least volumes of sludge and also the better drainability and solids concentration. Sudfloc 3820 was found to achieve better results than Sudfloc 3860 in terms of COD reduction and the drainability of sludge produced although both achieved the same drainability studies. This study showed that each of the three physical-chemical methods can be used effectively to remove the white colour of dairy wastewater as well as the bulk of the proteins and fats, hence, enabling the discharge of the effluents into natural waters to be of good assimilative capacity.

Abstract This paper presents the results of a combined experimental and theoretical study of microstructure and thermal shock resistance of an aluminosilicate ceramic. Shock-induced crack growth is studied in sintered structures produced from powders with different particle size ranges. The underlying crack/microstructure interactions and toughening mechanisms are elucidated via scanning electron microscopy (SEM). The resulting crack-tip shielding levels (due to viscoelastic crack bridging) are estimated using fracture mechanics concepts. The implications of the work are discussed for the design of high refractory ceramics against thermal shock.

Keywords Viscoelastic crack bridging . Crack-tip shielding . Thermal shock . Refractory ceramics

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This study investigated the effectiveness of three physical-chemical methods namely; pH adjustment, precipitation with alum and the use of polyelectrolytes. In the treatment of diary wastewater from Brookeside milk processing plant. It also investigated the drainability of the sludge produced by each of the three methods. Laboratory tests were carried out in three different batches, one for each of the three methods. In the alum method enough alum was added to the wastewater samples to cause precipitation by sweep floc. In the pH adjustment method, the pH of samples were lowered to the iso-electric point of the casein proteins of approximately pH 4.5 leading to their precipitation as a result of solubility changes. The polyelectrolytes method involved the use of two polyelectrolytes, Sudfloc 3820 and Sudfloc 3860 each of which was used to coagulate the dirty wastewater. For each of the three methods, the samples were taken in one-litre beakers and subjected to Jar tests to determine the optimum dosages. After one hour of settling the supernatants were decanted and subjected to standard Chemical Oxygen Demand (COD) tests, turbidity and pH measurements. The settled sludge was subjected to drainability studies. Results showed the treatment of dairy wastewater by the three physical-chemical methods to be effective. There were COD removals of between 60% and 90% and turbidity reduction of over 90%. The use of the sudfloc polyelectrolytes was found to be the least demanding in terms of effluent quality control as no pH adjustments of either the wastewater or the effluent was required. The use of polyelectolytes produced the least volumes of sludge and also the better drainability and solids concentration. Sudfloc 3820 was found to achieve better results than Sudfloc 3860 in terms of COD reduction and the drainability of sludge produced although both achieved the same drainability studies. This study showed that each of the three physical-chemical methods can be used effectively to remove the white colour of dairy wastewater as well as the bulk of the proteins and fats, hence, enabling the discharge of the effluents into natural waters to be of good assimilative capacity.

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