Use of mirage effect for the detection of phase transitions in solids

The phenomenon of mirage effect suffered by a He-Ne laser beam has been utilized to detect phase transitions in solids. It has been observed that anomalous fluctuations of large amplitude occur in the signal level near the transition temperature. The mean square value of the fluctuation is found to exhibit a well-defined peak at this point. Results of measurements made in the case of crystals of TGS ((NH2CH2COOH)3.H2SO4) and a ceramic sample (BaTiO3) are given to illustrate this technique.

Aqueous Sol-gel Process for Nanocrystalline Photocatalytic Titania, Transparent Functional Coatings and Ceramic Membrane

The present thesis develops from the point of view of titania sol-gel chemistry and an attempt is made to address the modification of the process for better photoactive titania by selective doping and also demonstration of utilization of the process for the preparation of supported membranes and self cleaning films.A general introduction to nanomaterials, nanocrystalline titania and sol-gel chemistry are presented in the first chapter. A brief and updated literature review on sol-gel titania, with special emphasis on catalytic and photocatalytic properties and anatase to rutile transformation are covered. Based on critical assessment of the reported information the present research problem has been defined.The second chapter describes a new aqueous sol-gel method for the preparation of nanocrystalline titania using titanyl sulphate as precursor. This approach is novel since no earlier work has been reported in the same lines proposed here. The sol-gel process has been followed at each step using particle size, zeta potential measurements on the sol and thermal analysis of the resultant gel. The prepared powders were then characterized using X-ray diffraction, FTIR, BET surface area analysis and transmission electron microscopy.The third chapter presents a detailed discussion on the physico-chemical characterization of the aqueous sol-gel derived doped titania. The effect of dopants such as tantalum, gadolinium and ytterbium on the anatase to rutile phase transformation, surface area as well as their influence on photoactivity is also included. The fourth chapter demonstrates application of the aqueous sol-gel method in developing titania coatings on porous alumina substrates for controlling the poresize for use as membrane elements in ultrafiltration. Thin coatings having ~50 nm thickness and transparency of ~90% developed on glass surface were tested successfully for self cleaning applications.

Complex permittivity and conductivity of poly aniline at microwave frequencies

Dielectric properties of polyaniline at different frequencies were studied. Cavity perturbation technique was employed for the study. Poly aniline in the powder and pelletised forms were prepared under different environmental conditions. Different samples of poly aniline exhibit high conductivity. However. the conductivity of samples prepared under different environmental conditions is found to vary. All the samples in the powder form have high conductivity irrespective of the method of preparation. The high conductivity at microwave frequency makes it possible to be used for developing microwave components like filters.

Studies on the structural, electrical and magnetic properties of composites based on spinel ferrites

This thesis mainly deals with the preparation and studies on magnetic composites based on spinel ferrites prepared both chemically and mechanically. Rubber ferrite composites (RFC) are chosen because of their mouldability and flexibility and the ease with which the dielectric and magnetic properties can be manipulated to make them as useful devices. Natural rubber is chosen as the Matrix because of its local availability and possible value addition. Moreover, NR represents a typical unsaturated nonpolar matrix. The work can be thought of as two parts. Part l concentrates on the preparation and characterization of nanocomposites based on y-Fe203. Part 2 deals with the preparation and characterization of RFCs containing Nickel zinc ferrit In the present study magnetic nanocomposites have been prepared by ionexchange method and the preparation conditions have been optimized. The insitu incorporation of the magnetic component is carried out chemically. This method is selected as it is the easiest and simplest method for preparation of nanocomposite. Nanocomposite samples thus prepared were studied using VSM, Mossbauer spectroscopy, Iron content estimation, and ESR spectroscopy. For the preparation of RFCs, the filler material namely nickel zinc ferrite having the general formula Ni)_xZnxFez04, where x varies from 0 to 1 in steps of 0.2 have been prepared by the conventional ceramic techniques. The system of Nil_xZn"Fe204 is chosen because of their excellent high frequency characteristics. After characterization they are incorporated into the polymer matrix of natural rubber by mechanical method. The incorporation is done according to a specific recipe and for various Loadings of magnetic fillers and also for all compositions. The cure characteristics, magnetic properties and dielectric properties of these composites are evaluated. The ac electrical conductivity of both ceramic nickel zinc ferrites and rubber ferrite composites are also calculated using a simple relation. The results are correlated.

Acid-Base. Surface Electron Donatin6 &.Catai.Ytlc Properties Of Some Binary Mixed Oxides Containing Rare Earth Elements

Catalysis research underpins the science of modern chemical processing and fuel technologies. Catalysis is commercially one of the most important technologies in national economies. Solid state heterogeneous catalyst materials such as metal oxides and metal particles on ceramic oxide substrates are most common. They are typically used with commodity gases and liquid reactants. Selective oxidation catalysts of hydrocarbon feedstocks is the dominant process of converting them to key industrial chemicals, polymers and energy sources.[1] In the absence of a unique successfiil theory of heterogeneous catalysis, attempts are being made to correlate catalytic activity with some specific properties of the solid surface. Such correlations help to narrow down the search for a good catalyst for a given reaction. The heterogeneous catalytic performance of material depends on many factors such as [2] Crystal and surface structure of the catalyst. Thermodynamic stability of the catalyst and the reactant. Acid- base properties of the solid surface. Surface defect properties of the catalyst.Electronic and semiconducting properties and the band structure. Co-existence of dilferent types of ions or structures. Adsorption sites and adsorbed species such as oxygen.Preparation method of catalyst , surface area and nature of heat treatment. Molecular structure of the reactants. Many systematic investigations have been performed to correlate catalytic performances with the above mentioned properties. Many of these investigations remain isolated and further research is needed to bridge the gap in the present knowledge of the field.

Synthesis, Characterization and Catalytic Activity of Nanocrystalline Ceria Modified With Zirconia

The use of catalysts in chemical and refining processes has increased rapidly since 1945, when oil began to replace coal as the most important industrial raw material. Catalysis has a major impact on the quality of human life as well as economic development. The demand for catalysts is still increasing since catalysis is looked up as a solution to eliminate or replace polluting processes. Metal oxides represent one of the most important and widely employed classes of solid catalysts. Much effort has been spent in the preparation, characterization and application of metal oxides. Recently, great interest has been devoted to the cerium dioxide (CeO2) containing materials due to their broad range of applications in various fields, ranging from catalysis to ceramics, fuel cell technologies, gas sensors, solid state electrolytes, ceramic biomaterials, etc., in addition to the classical application of CeO2 as an additive in the so-called three way catalysts (TWC) for automotive exhaust treatment. Moreover, it can promote water gas shift and steam reforming reactions, favours catalytic activity at the interfacial metal-support sites. The solid solutions of ceria with Group IV transitional-metals deserve particular attention for their applicability in various technologically important catalytic processes. Mesoporous CeO2−ZrO2 solid solutions have been reported to be employed in various reactions which include CO oxidation, soot oxidation, water-gas shift reaction, and so on. Inspired by the unique and promising characteristics of ceria based mixed oxides and solid solutions for various applications, we have selected ceria-zirconia oxides for our studies. The focus of the work is the synthesis and investigation of the structural and catalytic properties of modified and pure ceria-zirconia mixed oxide.

Effect of Carbon Black on the Mechanical and Dielectric Properties of Rubber Ferrite Composites Containing Barium Ferrite

Fine particles of barium ferrite (BaFe12O19) were synthesized by the conventional ceramic technique. These materials were then characterized by the X-ray diffraction method and incorporated in the natural rubber matrix according to a specific receipe for various loadings of ferrite. The rubber ferrite composites (RFC) thus obtained have several applications, and have the advantage of molding into complex shapes. For applications such as microwave absorbers, these composites should have an appropriate dielectric strength with the required mechanical and magnetic properties. The N330 (HAF) carbon black has been added to these RFCs for various loadings to modify the dielectric and mechanical properties. In this article we report the effect of carbon black on the mechanical and dielectric properties of these RFCs. Both the mechanical and dielectric properties can be enhanced by the addition of an appropriate amount of carbon black

Processability, hardness, andmagnetic properties of rubber ferrite composites containingmanganese zinc ferrites

Rubber ferrite composites have the unique advantage of mouldability, which is not easily obtainable using ceramic magnetic materials. The incorporation of mixed ferrites in appropriate weight ratios into the rubber matrix not only modi es the dielectric properties of the composite but also imparts magnetic properties to it. Mixed ferrites belonging to the series of Mn(1 – x )Znx Fe2O4 have been synthesised with diVerent values of x in steps of 0·2, using conventional ceramic processing techniques. Rubber ferrite composites were prepared by the incorporation of these pre-characterised polycrystallineMn(1 – x )Znx Fe2O4 ceramics into a natural rubber matrix at diVerent loadings according to a speci c recipe. The processability of these elastomers was determined by investigating their cure characteristics. The magnetic properties of the ceramic llers as well as of the rubber ferrite composites were evaluated and the results were correlated. Studies of the magnetic properties of these rubber ferrite composites indicate that the magnetisation increases with loading of the ller without changing the coercive eld. The hardness of these composites shows a steady increase with the loading of the magnetic llers. The evaluation of hardness andmagnetic characteristics indicates that composites with optimummagnetisation and almost minimum stiVness can be achieved with a maximum loading of 120 phr of the ller at x=0·4. From the data on the magnetisation of the composites, a simple relationship connecting the magnetisation of the rubber ferrite composite and the ller was formulated. This can be used to synthesise rubber ferrite composites with predetermined magnetic properties

Dielectric andmechanical properties of rubber ferrite composites

Rubber ferrite composites (RFCs) containing powdered nickel zinc ferrite (Ni1 – xZnxFe2O4 ) in a natural rubber matrix have been prepared and their mechanical and dielectric properties have been evaluated. Variations in the relative permittivity of both the ferrite ceramics and RFCs have been studied over a range of frequencies, ceramic compositions, ceramic ller loadings, and temperatures, and the results have been correlated. Appropriate mixture equations have been formulated to calculate the dielectric permittivity of the composite from the dielectric permittivity of its constituents. Values calculated using these equations have been compared with experimental data on relative permittivity, and the two have been found to be in good agreement. In the present investigationit was also observed that for x=0·4 and for the maximum ferrite loading, the composite sample exhibits maximum magnetisation and optimum exibility

Processability And Magnetic Properties Of Rubber Ferrite Composites Containing Barium Ferrite

Rubber ferrite composites (RFC) are magnetic polymer composites and have a variety of applications as flexible magnets, pressure=photo sensors, and microwave absorbers. The mouldability into complex shapes is one of the advantages of these magnetic elastomers. They have the potential of replacing the conventional ceramic materials, due to theire flexible nature. In the present study, the incorporation of pre-characterized hexagonal ferrites, namely barium ferrite (BaFe12O19), into natural rubber matrix is carried out according to a suitable recipe for various loadings of the filler. The processability of these compounds was determined by evaluating the cure characteristics: scorch time, cure time, and minimum and maximum torque. It has been found that the addition of magnetic fillers does not affect the processability of the composites, whereas the physical properties are modified. The magnetic properties of these composites containing various loadings of the magnetic filler were also investigated. The magnetic properties of RFC can be controlled by the addition of appropriate amount of the ferrite filler.

Magnetic and processability studies of nitrile rubber vulcanisates containing barium ferrite and carbon black

Fine particles of barium ferrite (BaFe12O19) belonging to the M-type hexagonal ferrites were prepared by the conventional ceramic techniques. They were incorporated into a nitrile rubber matrix according to a specific recipe for various loadings to produce rubber ferrite composites (RFC). The percolation threshold is not reached for a maximum loading of 130 phr (parts per hundred rubber). Here in this paper, the magnetic properties and processability of the nitrile rubber based RFCs containing barium ferrite (BaF) and HAF carbon black is reported. The magnetic properties of the ceramic ferrite and these rubber ferrite composites were evaluated and it was found that the coercivity values of RFCs were less than that of the ceramic BaF, but remained constant with the loading of both the ferrite filler and carbon black. However, other properties like saturation magnetization and magnetic remanence increased with the loading of ferrite filler.

Butyl rubber- ceramic composites for flexible electronic applications

The first chapter of the thesis gives a general introduction about flexible electronics, dielectrics and composites. The recent developments in flexible electronics also discussed in this chapter. The preparation and characterization techniques used for the butyl rubber ceramic composites are given in chapter 2. The synthesis and characterization of butyl rubber filled with low permittivity ceramic composites are described in chapter 3. The chapter 4 deals with the synthesis and characterization of butyl rubber-high permittivity ceramic composites. The effect of high permittivity ceramic fillers such as TiO2, Sr2Ce2Ti5O15 and SrTiO3 on dielectric, thermal and mechanical properties was studied. The present investigation deals with synthesis, characterization and properties of butyl rubber composites with low, high and very high ceramic fillers and also the effect of particle size on dielectric, thermal and mechanical properties of selected composites.

Pharmaceutical consumption and residuals potentially relevant to nutrient cycling in Greater Accra, Ghana

Recycling nutrients form sanitary wastes back into agricultural ecosystems offers an option to alleviate soil depletion in regions where the use of mineral fertiliser is limited. Exemplary nutrient and water cycling approaches, including collection, treatment and use of human urine, are established at Valley View University (VVU) in Greater Accra, Ghana. Concerns have been recently raised in regard to fate and impact of pharmaceutical residues in soils and interlinked environment. To evaluate in how far emerging knowledge can be transposed onto VVU, urban and rural environments in Greater Accra, spatial disease occurrence and drug consumption patterns were studied. Malaria has been found to represent the most severe health burden in Ghana, but there is also a high prevalence of infectious diseases. Drugs consumed in great quantities and in respect to their residual loads potentially problematic in the environment belong to therapeutic groups of: antibiotics, analgesics, drugs for diabetes, antimalarials, cardiovascular drugs and anthelmintics. Drug consumption revealed to be highest in urban and lowest in rural areas. At VVU the range of consumed drugs is comparable to urban areas except for the negligible use of diabetes and cardiovascular medication as well as contraceptives.

3D Simultaneous Inversion for Seismic Structure and Local Hypocenters in Germany under Consideration of Seismic Anisotropy in the Upper Mantel

The main task of this work has been to investigate the effects of anisotropy onto the propagation of seismic waves along the Upper Mantle below Germany and adjacent areas. Refraction- and reflexion seismic experiments proved the existence of Upper Mantle anisotropy and its influence onto the propagation of Pn-waves. By the 3D tomographic investigations that have been done here for the crust and the upper mantle, considering the influence of anisotropy, a gap for the investigations in Europe has been closed. These investigations have been done with the SSH-Inversionprogram of Prof. Dr. M. Koch, which is able to compute simultaneously the seismic structure and hypocenters. For the investigation, a dataset has been available with recordings between the years 1975 to 2003 with a total of 60249 P- and 54212 S-phase records of 10028 seismic events. At the beginning, a precise analysis of the residuals (RES, the difference between calculated and observed arrivaltime) has been done which confirmed the existence of anisotropy for Pn-phases. The recognized sinusoidal distribution has been compensated by an extension of the SSH-program by an ellipse with a slow and rectangular fast axis with azimuth to correct the Pn-velocities. The azimuth of the fast axis has been fixed by the application of the simultaneous inversion at 25° - 27° with a variation of the velocities at +- 2.5 about an average value at 8 km/s. This new value differs from the old one at 35°, recognized in the initial residual analysis. This depends on the new computed hypocenters together with the structure. The application of the elliptical correction has resulted in a better fit of the vertical layered 1D-Model, compared to the results of preceding seismological experiments and 1D and 2D investigations. The optimal result of the 1D-inversion has been used as initial starting model for the 3D-inversions to compute the three dimensional picture of the seismic structure of the Crust and Upper Mantle. The simultaneous inversion has showed an optimization of the relocalization of the hypocenters and the reconstruction of the seismic structure in comparison to the geology and tectonic, as described by other investigations. The investigations for the seismic structure and the relocalization have been confirmed by several different tests. First, synthetic traveltime data are computed with an anisotropic variation and inverted with and without anisotropic correction. Further, tests with randomly disturbed hypocenters and traveltime data have been proceeded to verify the influence of the initial values onto the relocalization accuracy and onto the seismic structure and to test for a further improvement by the application of the anisotropic correction. Finally, the results of the work have been applied onto the Waldkirch earthquake in 2004 to compare the isotropic and the anisotropic relocalization with the initial optimal one to verify whether there is some improvement.

Perspectives of auto-correcting lens distortions in mosaic-based underwater navigation

When unmanned underwater vehicles (UUVs) perform missions near the ocean floor, optical sensors can be used to improve local navigation. Video mosaics allow to efficiently process the images acquired by the vehicle, and also to obtain position estimates. We discuss in this paper the role of lens distortions in this context, proving that degenerate mosaics have their origin not only in the selected motion model or in registration errors, but also in the cumulative effect of radial distortion residuals. Additionally, we present results on the accuracy of different feature-based approaches for self-correction of lens distortions that may guide the choice of appropriate techniques for correcting distortions