Characterization of Selected Photonic Materials and Systems Using Photoacoustic Technique

The photoacoustic investigations carried out on different photonic materials are presented in this thesis. Photonic materials selected for the investigation are tape cast ceramics, muItilayer dielectric coatings, organic dye doped PVA films and PMMA matrix doped with dye mixtures. The studies are performed by the measurement of photoacoustic signal generated as a result of modulated cw laser irradiation of samples. The gas-microphone scheme is employed for the detection of photoacoustic signal. The different measurements reported here reveal the adaptability and utility of the PA technique for the characterization of photonic materials.Ceramics find applications in the field of microelectronics industry. Tape cast ceramics are the building blocks of many electronic components and certain ceramic tapes are used as thermal barriers. The thermal parameters of these tapes will not be the same as that of thin films of the same materials. Parameters are influenced by the presence of foreign bodies in the matrix and the sample preparation technique. Measurements are done on ceramic tapes of Zirconia, Zirconia-Alumina combination, barium titanate, barium tin titanate, silicon carbide, lead zirconate titanateil'Z'T) and lead magnesium niobate titanate(PMNPT). Various configurations viz. heat reflection geometry and heat transmission geometry of the photoacoustic technique have been used for the evaluation of different thermal parameters of the sample. Heat reflection geometry of the PA cell has been used for the evaluation of thermal effusivity and heat transmission geometry has been made use of in the evaluation of thermal diffusivity. From the thermal diffusivity and thermal effusivity values, thermal conductivity is also calculated. The calculated values are nearly the same as the values reported for pure materials. This shows the feasibility of photoacoustic technique for the thermal characterization of ceramic tapes.Organic dyes find applications as holographic recording medium and as active media for laser operations. Knowledge of the photochemical stability of the material is essential if it has to be used tor any of these applications. Mixing one dye with another can change the properties of the resulting system. Through careful mixing of the dyes in appropriate proportions and incorporating them in polymer matrices, media of required stability can be prepared. Investigations are carried out on Rhodamine 6GRhodamine B mixture doped PMMA samples. Addition of RhB in small amounts is found to stabilize Rh6G against photodegradation and addition of Rh6G into RhB increases the photosensitivity of the latter. The PA technique has been successfully employed for the monitoring of dye mixture doped PMMA sample. The same technique has been used for the monitoring of photodegradation ofa laser dye, cresyl violet doped polyvinyl alcohol also.Another important application of photoacoustic technique is in nondestructive evaluation of layered samples. Depth profiling capability of PA technique has been used for the non-destructive testing of multilayer dielectric films, which are highly reflecting in the wavelength range selected for investigations. Eventhough calculation of thickness of the film is not possible, number of layers present in the system can be found out using PA technique. The phase plot has clear step like discontinuities, the number of which coincides with the number of layers present in the multilayer stack. This shows the sensitivity of PA signal phase to boundaries in a layered structure. This aspect of PA signal can be utilized in non-destructive depth profiling of reflecting samples and for the identification of defects in layered structures.

Photoacoustic Thermal Characterization of Porous Rare-Earth Phosphate Ceramics

The laser induced non-destructive photoacoustic technique has been employed to measure the thermal diffusivity of lanthanum phosphate ceramics prepared by the sol–gel route. The thermal diffusivity value was evaluated by knowing the transition frequency between the thermally thin to thermally thick region from the log–log plot of photoacoustic amplitude versus chopping frequency. Analysis of the data was carried out on the basis of the one-dimensional model of Rosencwaig and Gersho. The present investigation reveals that the sintering temperature has great influence on the propagation of heat carriers and hence on the thermal diffusivity value. The results were interpreted in terms of variations in porosity with sintering temperature as well as with changes in grain size.

Thermal characterization of nanocrystalline porous CePO4 ceramics

A laser-induced photoacoustic technique was employed to investigate thermal transport through nanocrystalline CePO4 samples prepared via the sol–gel route. Evaluation of thermal diffusivity was carried out using the one-dimensional model of Rosencwaig and Gersho for the reflection configuration of the photoacoustic method. Structural analyses of samples revealed that they are nanoporous in nature, possessing micron-sized grains. Analysis of results shows that thermal diffusivity value varies with sintering temperature. Results are explained in terms of the variation in porosity with sintering temperature and the effects of various scattering mechanisms on the propagation of phonons through the nanoporous ceramic matrix. Further analyses confirm that apart from porosity, grain boundary resistance and interface thermal resistance influence the effective value of thermal diffusivity of the samples under investigation.

Thermal characterisation of dye-intercalated K-10 montmorillonite ceramics using photoacoustic technique

Thermal diffusivity (TD) measurements were performed on some industrially important dyes – auramine O (AO), malachite green and methylene blue (MB) – adsorbed K-10 montmorillonites using photoacoustic method. The TD value for the dye-adsorbed clay mineral was observed to change with a variation in dye concentration. The contribution of the dye towards TD was also determined. The repeatedly adsorbed samples with MB and AO exhibited a lower TD than the single-adsorbed samples. TD values of sintered MB samples were also obtained experimentally. These sintered samples exhibit a higher TD, although they show a trend similar to that of non-sintered pellets. A variation in dye concentration and sintering temperature can be used for tuning the TD value of the clay mineral to the desired level.

Sol-Gel Alumina Nano Composites for Functional Applications

The thesis entitled "Sol-Gel Alumina Nano Composites for Functional Applications" investigate sol-gel methods of synthesis of alumina nanocomposites special reference to alumina-aluminium titanate and alumina-lanthanum phosphate composites. The functional properties such as thermal expansion coefficient and thermal shock resistance, machinability of composites as well as thermal protection are highlighted in addition to novel approach in synthesis of composites.A general introduction of alumina matrix composites materials, followed by brief coverage of alumina-aluminium titanate and alumina-lanthanum phosphate composites is highlight of the first chapter. The second chapter deals with the sol-gel synthesis of aluminium titanate and alumina-aluminium titanate composite. The synthesis of machinable substrate, based on alumina and lanthanum phosphate forms the basis of the third chapter. The fourth chapter describes the sol-gel coating of mullite on SiC substrate for the possible gas filtration application.

Thermal transport properties of selected ferroelectrics, mixed valance perovskites and dielectric ceramics using photopyroelectric technique

Photothermal spectroscopy is a group of high sensitivity methods used to measure optical absorption and thermal characteristics of a sample.The basis of photothermal spectroscopy is a photo-induced change in the thermal state of the sample.Light energy absorbed and not lost by subsequent emission results in sample heating.This heating results in a temperature change as well as changes in thermodynamic parameters of the sample which are related to temperature.Measurements of the temperature,pressure,or density changes that occur due to optical absorption are ultimately the basis for the photothermal spectroscopic methods.This is a more direct measure of optical absorption than optical transmission based spectroscopies.Sample heating is a direct consequence of optical absorption and so photothermal spectroscopy signals are directly dependent on light absorption.Scattering and reflection losses do not produce photothermal signals.Subsequently,photothermal spectroscopy more accurately measures optical absorption in scattering solutions,in solids,and at interfaces.This aspect makes it particularly attractive for application to surface and solid absorption studies,and studies in scattering media.

Investigation of dielectric and elastic properties of selected dielectric ceramics and oxide glasses

The dielectric and elastic properties are of considerable significance to the science and technology of matter in the solid state. The study of these properties give information about the magnitude of the forces and nature of the bonding between the atoms. Our aim has been to investigate systematically the effect of doping of an appropriate element on the elastic and dielectric properties of selected dielectric ceramics and oxide glasses. These materials have got wide technological applications due to their interesting electrical, optical, thermal and elastic behaviour. Ultrasound propagation and capacitance measurement techniques have been employed for the systematic investigation of the elastic and dielectric properties of selected number of these materials. Details of the work done and results obtained are presented in this thesis.

Thermal characterisation of dye-intercalated K-10 montmorillonite ceramics using photoacoustic technique

Thermal diffusivity (TD) measurements were performed on some industrially important dyes – auramine O (AO), malachite green and methylene blue (MB) – adsorbed K-10 montmorillonites using photoacoustic method. The TD value for the dye-adsorbed clay mineral was observed to change with a variation in dye concentration. The contribution of the dye towards TD was also determined. The repeatedly adsorbed samples with MB and AO exhibited a lower TD than the single-adsorbed samples. TD values of sintered MB samples were also obtained experimentally. These sintered samples exhibit a higher TD, although they show a trend similar to that of non-sintered pellets. A variation in dye concentration and sintering temperature can be used for tuning the TD value of the clay mineral to the desired level

Osteoconductivity of modified fluorcanasite glass-ceramics for bone tissue augmentation and repair

Modified fluorcanasite glasses were fabricated by either altering the molar ratios of Na(2)O and CaO or by adding P(2)O(5) to the parent stoichiometric glass compositions. Glasses were converted to glass-ceramics by a controlled two-stage heat treatment process. Rods (2 mm x 4 mm) were produced using the conventional lost-wax casting technique. Osteoconductive 45S5 bioglass was used as a reference material. Biocompatibility and osteoconductivity were investigated by implantation into healing defects (2 mm) in the midshaft of rabbit femora. Tissue response was investigated using conventional histology and scanning electron microscopy. Histological and histomorphometric evaluation of specimens after 12 weeks implantation showed significantly more bone contact with the surface of 45S5 bioglass implants when compared with other test materials. When the bone contact for each material was compared between experimental time points, the Glass-Ceramic 2 (CaO rich) group showed significant difference (p = 0.027) at 4 weeks, but no direct contact at 12 weeks. Histology and backscattered electron photomicrographs showed that modified fluorcanasite glass-ceramic implants had greater osteoconductivity than the parent stoichiometric composition. Of the new materials, fluorcanasite glass-ceramic implants modified by the addition of P(2)O(5) showed the greatest stimulation of new mineralized bone tissue formation adjacent to the implants after 4 and 12 weeks implantation. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 94A: 760-768, 2010

COLOR STABILITY OF DENTAL CERAMICS SUBMITTED TO ARTIFICIAL ACCELERATED AGING AFTER REPEATED FIRINGS

Statement of problem. Color stability is an important factor to ensure the long-term clinical success of ceramic restorations. There is a lack of information on how color is affected by fabrication procedures, such as the number of firings. Purpose. The purpose of this study was to evaluate the effects that the number of firings and type of substrate have on the color stability of dental ceramic submitted to artificial accelerated aging. Material and methods. Sixty specimens were fabricated: 30 metal ceramic (Verabond II + IPS d.SIGN) and 30 all-ceramic (IPS d.SIGN). Specimens were divided into 3 groups (n=10), and submitted to 2, 3, or 4 firings (+/- 900 degrees C), respectively, according to the manufacturer`s instructions. Color readings were obtained with a spectro photometer before and after artificial accelerated aging, and L*, a*, and b* coordinates and total color variation (Delta E) were analyzed (2-way ANOVA, Bonferroni, (alpha=05). Results. For metal ceramic specimens, differences for the L* coordinates were significant (P<.05) only for the group submitted to 3 firings. With respect to the all-ceramic specimens, smaller L* coordinates were obtained for greater a* and b* coordinates, indicating that the greater the number of firings, the darker and more reddish/yellowish the specimen. All Delta E values, for all groups, were below 1.0. All-ceramic specimens submitted to 3 and 4 firings presented Delta E means differing statistically (P<.05) from those of the metal ceramic group. Conclusions. The type of substrate and number of firings affected the color stability of the ceramic material tested. Artificial accelerated aging did not produce perceptible color stability changes (Delta E<1.0). (J Prosthet Dent 2009-101:13-18)

Thermoluminescence dating of Brazilian indigenous ceramics

Two indigenous ceramics fragments, one from Lagoa Queimada (LQ) and another from Barra dos Negros (BN), both sites located on Bahia state (Brazil), were dated by termoluminescence (TL) method. Each fragment was physically prepared and divided into two fractions, one was used for TL measurement and the other for annual dose determination. The TL fraction was chemically treated, divided in sub samples and irradiated with several doses. The plot extrapolation from TL intensities as function of radiation dose enabled the determination of the accumulated dose (D(ac)), 3.99 Gy and 1.88 Gy for LQ and BN, respectively. The annual dose was obtained through the uranium, thorium and potassium determination by ICP-MS. The annual doses (D(an)) obtained were 2.86 and 2.26 mGy/year. The estimated ages were similar to 1375 and 709 y for BN and LQ ceramics, respectively. The ages agreed with the archaeologists` estimation for the Aratu and Tupi tradition periods, respectively.

Dating archeological ceramics from the Valley of Vitor, Arequipa by the TL method

The age of some ancient pottery from the Valley of Vitor in the region of Arequipa, Peru, is determined by the thermoluminescence (TL) method. For dating, a 325 degrees C TL peak was used and irradiation with -dose from 5 to 50Gy was carried out for the additive method, and from 0.4 to 5Gy for the regeneration method. For these dose values, the TL intensity is observed to grow linearly, obtaining an accumulated dose of 1.62 +/- 0.09Gy and 1.36 +/- 0.03Gy for the additive and regeneration methods, respectively. The age (A) of the sample was calculated by the two methods, being A=867 +/- 195 years after Christ (AC) for the additive method and A=1050 +/- 157 years AC for the regeneration method. Both results are within 800-1200 years AC, which is the period of the Wari culture.

Structural Phase Transition Studies on PMN-0.35PT using Infrared Spectroscopy

The purpose of the present work is to report studies on structural phase transition for PMN-xPT ferroelectric, with melt PbTiO3 composition around the MPB (x = 0.35 mol %), using infrared spectroscopy technique. The study was centered on monitoring the behavior of the 1-(NbO), 1-(TiO) and 1-(MgO) stretching modes as a function of temperature. The increasing as a function of temperature for 1-(TiO) and 1-(MgO) modes, observed between 230 and 300 K, can be related to the monoclinic (MC) + tetragonal (T) phase coexistence in the PMN-PT.

Correlations between chemical composition and provenance of Justino site ceramics by INAA

Instrumental neutron activation analysis (INAA), have been used for the definition of compositional groups of potteries from Justino site, Brazil, according to the chemical similarities of ceramic paste. The outliers were identified by means of robust Mahalanobis distance. The temper effect in the ceramic paste was studied by means of modified Mahalanobis filter. The results were interpreted by means of cluster, principal components, and discriminant analyses. This work provides contributions for the reconstruction of the prehistory of baixo Sao Francisco region, and for the reconstitution of the Brazilian Northeast ceramist population of general frame.

Quenching of Photoactivity in Phthalocyanine Copper(II)-Titanate Nanotube Hybrid Systems

Titanate nanotubes (TiNTs) were obtained by hydrothermal treatment of anatase powder in aqueous NaOH solution and then modified with 2,9,16,23-tertracarboxyl phthalocyanine copper(H) (CuPc). This hybrid organic inorganic nanoscopic system was characterized by X-ray diffraction, microscopy, and spectroscopy. Transmission electron microscopy (TEM) images of pure and modified TiNTs revealed multiwall structures with an average outer diameter of 9 nm and a length of several hundred nanometers. The tubular morphology of the TiNTs was covered with CuPc-film. The amount of CuPc adsorbed onto the TiNTs was quantified by electron paramagnetic resonance (EPR). Using the same technique and spin-trapping methodology, the photogeneration of reactive oxygen species (ROS) from the TiNTs was systematically investigated. A drastic quenching of photoactivity was observed in the CuPc/TiNT hybrid system. Electron transfer from excited CuPc states to the TiNT conduction band followed by electron recombination may be the cause of this quenching.