Showing papers in "Transactions of The Indian Ceramic Society in 2005"

Bioceramics - a new era

Abstract: In the last few decades with the introduction of bioceramics, a special class of ceramics to perform tailored functional / biological / chemical activities in living systems, treatment procedure through reconstructive surgery has been revolutionized and this has resulted in marked improvement in quality of life of the rehabilitated persons. The procedure involves an innovative use of specially designed ceramics for reconstruction of diseased / damaged parts of body, e.g. hips, knees, wrists, spines, jaws, diseased long-bones and repair for maxillofacial, periodontal disease, etc. Bioceramics are produced in a variety of compositions, forms and phases and are often used in the form of bulk materials of specific shape to perform a special function, which are called implants, prostheses or prosthetic devices. They are also used in powder / granule forms to fill space of the damaged hard tissues, which through natural repair process get integrated and restore function, and as coatings to provide bio-friendly interface on substrate for cement-less fixation and sometimes also as a second phase in composites. In this review, different classes of bioceramics, their chemical compositions, structures, tailored functions and broad application areas have been outlined and the effects of their usage on treatment of different trauma / degenerative diseases have been discussed. Along with the current research status of the advanced laboratories around the world on this emerging subject, the developments made so far at CGCRI, Kolkata have also been outlined.

Corrosion behaviour of some gamma-irradiated phosphate glasses for radioactive wastes burial applications

Abstract: Corrosion behaviour of some lead phosphate glasses containing varying contents of iron oxide was investigated. The grain method was used to estimate the weight loss of the studied glasses by the action of HCI, NaOH solutions, distilled water and underground water. The experimental results show variations of the corrosion behaviour with glass composition and with the leaching medium. The corrosion of the glass grains was investigated after subjecting the grains to varying doses of gamma irradiation. The infrared spectra were measured for the glass grains after immersion in the specified leaching solution to confirm the suggested corrosion mechanism in such glasses. However, the corrosion figures were generally very low which reveals that these glasses are quite resistant and can be considered as promising candidates for burial of radioactive wastes.

Tape Cast Porous Nano Alumina Multilayer Composites

Abstract: Alumina tapes are extensively utilized as useful components for device applications and fabrication of multilayer composites for structural applications. The tapes are mostly fabricated from a stable dispersion of micron size alumina powder in a non-aqueous medium for industrial purpose. Here we report the novel development of a tailored tape cast light weight, porous nano alumina multilayer composite, suitable for structural applications. A 150 nm particle size alumina powder with 99.97% purity was used. For tape casting, oxidized Menhaden fish oil (MFO) was used as dispersant and an azeotropic mixture of methyl ethyl ketone (MEK) and ethanol (EtOH) as solvent. The viscosity value of the nano alumina/solvent/dispersant slurry system was found out to be the minimum at about 8 wt% dispersant concentration. Sintered porous nano alumina tapes with 55% relative density were prepared at 1400°C in air from the suitably optimized tape casting slurry composition obtained from the aforesaid optimization experiment...

Current and Future Possibilities of Sol-Gel Process

Abstract: The sol-gel method is, first of all, characterized by the low temperature processing. Since this method starts from solutions, the product is essentially nanomaterials. So far, various kinds of microstructures, including dense, porous, hybrid, amorphous, crystalline microstructures have been realized. Accordingly, sol-gel materials cover a wide range of functions, such as optical, electronic, mechanical, chemical and bio-functions. All these features are highlighted in this article. Finally, the future of the sol-gel method is discussed.

Microwave sintering of titania

Abstract: Microwave processing was employed to sinter commercial titania powder to obtain rutile as the major phase in the sintered product. About 96% of theoretical density was achieved by exposing the powder in microwave for 1 h at 1300°C. The maximum density obtained for titania ceramics sintered with identical parameters in a conventional muffle furnace was only about 85% of theoretical density, indicating superiority of the previous technique. The dielectric properties of the microwave sintered titania showed increased dielectric constant and decreased dissipation factor values compared to conventionally sintered one. However, DC electrical resistivity was almost comparable for both the samples. Further, the conventional sintering even up to 1300°C did not yield rutile as the major phase in the densified body. The kinetics of rutile formation in the microwave sintered sample was also studied as a function of temperature (900°-1300°C). Scanning electron microscopy (SEM) on the polished surface of the sintered specimens revealed that the microwave processed ones had finer microstructure than that of the conventionally sintered titania ceramics.

Defluoridation of Bore Well Water Using Combustion Derived Nanocrystalline Magnesium Oxide

Abstract: Nanocrystalline MgO powder has been prepared through combustion route using magnesium nitrate as oxidizer and glycine as fuel; the combustion derived MgO powder has been characterized using XRD, SEM, surface area and porosity measurements. The powder XRD pattern confirms the crystallinity and phase purity of the as-made powder. The scanning electron microscope (SEM) results reveal that the combustion derived powder is an agglomeration of fine particles. The particle size of the powder is found to be in the range of 12-23 nm with a large surface area of 107 m2.g−1. The as-made MgO is used for defluoridation of ground water samples with stirring time (5–60 min), adsorbent quantity (0.05–0.3 g.L−1) and pH (5–9) as experimental parameters. It is found that 92% and 97% of fluoride, respectively, could be removed using 0.15 g of MgO from 10 ppm of synthetic fluoride solution and standard sodium fluoride solution. In this technique 90% minimization of sludge could be achieved. It is also observed that the regene...

A Novel Approach for Synthesis of a Nanocrystalline Yttria Stabilized Zirconia Powder via Polymeric Precursor Routes

Abstract: A nanocrystalline powder of 5 mol% yttria stabilized zirconia (YSZ) is prepared by polymeric precursor routes. Three different routes, viz. (i) amorphous citrate process, (ii) Pechini process and (iii) polyethylene glycol (PEG) assisted process are examined. In these processes, parameters such as metal cations to fuel ratio or components of fuel are varied and the effects analyzed. A novel experimental procedure for controlled combustion based on the thermal analysis has been adopted. All the three processes yield nanocrystalline powders with average crystallite size lying in the range of 9 to 18 nm. Densities as high as 99% of theoretical density (TD) could be achieved by sintering the compacts of powders at a relatively low temperature of 1400°C for 2 h.

Synthesis and Characterization of Nanocrystalline Ce0.9Gd0.1O1.95 by Citrate-Gel Decomposition Technique

Abstract: Nanocrystalline gadolinia doped ceria powder (CGO) of composition Ce0.9Gd0.1O1.95 was synthesized by citrate-gel decomposition technique and subsequently calcined at 700°C. The as-prepared and calcined powders were characterized by XRD and TEM analyses. The particle size (between 20 and 30 nm) was determined by TEM analysis. Uniaxially pressed samples were sintered at 1400° and 1500°C. A sintered density of nearly 99% of theoretical density was observed for samples sintered at 1500°C for 6 h. The electrical conductivity of the order of 0.029 and 0.0485 S.cm−1 at 600° and 700°C, respectively was obtained for the sample sintered at 1500°C for 6 h. The sintered density and microstructure were also studied and reported.

Sintering and Hardness Characterization of Nanozirconia Tapes

Abstract: A stable tape casting suspension of a 3 mol% yttria stabilized tetragonal zirconia (3Y-TZP) powder of 27 nm particle size was developed with about 2.5 wt% of phosphate ester dispersant. Green nanozirconia tape cast by the conventional Doctor’s Blade technique was sintered to 65-80% relative density at 1200°-1400°C. The maximum tetragonal phase (98.16%) and densification (80%) were obtained at 1350°C. Vickers microhardness measured at 1.96-19.6 N loads showed an indentation size effect (ISE) for samples of various relative densities. At 19.6 N load, 80% dense tapes showed 12.51 GPa hardness. The highest value of Meyer’s constant (n) was 1.95. Per cent decrease in hardness with load was reduced with enhancement in relative density. As the load and hence the size of the indent is enhanced, the microplastic deformability may increase, thus leading to the observed indentation size effect.

Microstructure Characterization and Thermal Expansion Behaviour of Interpenetrating Alumina/Aluminium Composites

Abstract: Interpenetrating phase composites (IPCs) are a new class of composite materials in which at least two of the constituent phases are three-dimensionally continuous. Such interconnected microstructures suggest improved combination of properties and increased damage tolerance. However, identifying those microstructures has been a difficult task. Interpenetrating phase Alumina/Aluminium composites were fabricated by a displacement reaction between solid silica glass rods and molten aluminium. The composite microstructures were characterized in terms of grain size and contiguity to evaluate the distribution and connectivity of the Al203 and Al phases. The thermal expansion response of these composites was studied. Coefficients of thermal expansion (CTEs) were observed to vary significantly with temperature and displayed non-linear behaviour. It is thought that this indicates an influence of the interconnectivity of the metal phase mainly. Comparisons are made with well-known methods for predicting CTEs of cera...

A New High Temperature Resistant Glass-Ceramic Coating Developed in CGCRI, Kolkata

Abstract: A new high temperature and abrasion resistant glass-ceramic coating system (based on MgO-Al2O]-TiO2 and ZnO-Al2O3-SiO2 based glass systems) for gas turbine engine components has been developed. Thermal shock resistance, adherence at 90°-bend test, static oxidation resistance at the required working temperature 1000°c for continuous service, and abrasion resistance are evaluated using suitable standard methods. The coating materials and the resultant coatings are characterized using differential thermal analysis, differential thermo-gravimetric analysis, X-ray diffraction analysis, optical microscopy and scanning electron microscopy. The properties evaluated clearly showed the suitability of these coatings for protection of different hot zone components in different types of engines. XRD analysis of the coating materials and the resultant coatings showed presence of a number of microcrystalline phases. SEM photographs indicated strong chemical bonding at the metal-ceramic interface. Optical micrographs sho...

Slow Crack Growth during Static and Dynamic Loading in Silicate Glasses

Abstract: Analytical solutions for stable crack growth in silicate glasses are provided in this paper for two important cases of loading, namely (i) constant stress and (ii) constant stress rate. The former simulates real life glass components subjected to uniform tensile stress while the latter represents strength measurement test for glass specimens. In both cases it is desirable to envision the onset and progression of slow crack growth over time. In this manner the state of initial crack and associated strength can be monitored as a function of applied stress and stress duration. In addition, the progressive crack history provided by analytical solutions helps estimate both the threshold and residual strengths of glass articles which, in turn, are needed to quantify their long term mechanical reliability.The analytical solutions obtained by integration of the power law model involve two system constants which are readily evaluated by imposing certain conditions on crack length at threshold stress. These solutio...

Synthesis, Characterization and TL studies of Porous CaSiO3 Ceramic Powders

Abstract: Nanocrystalline porous CaSiO3 ceramic powders have been synthesized by a novel low temperature initiated self-propagating, gas producing solution combustion process and characterized by XRD, SEM, EDS, porosity, surface area and Thermoluminescence (TL) studies. The effect of temperature on crystalline phase formation, amount of porogens and particle size of porous CaSiO3 has been investigated. Single phase beta-CaSiO3 and alpha-CaSiO3 are formed at 950 and 1200 °C respectively. The phase transformation temperatures of combustion derived CaSiO3 were found to be lower compare to the powders obtained via solid state reaction method. The micro structure and morphology were studied by SEM and it is interesting to note that with increase in calcination temperature, the samples becoming more porous and the pore diameter increases from 2 to 10 \mu m. The samples calcined at 950 °C for 3 hours has 17.5 % porosity, however the porosity increases to 31.6 % on calcination at 1200 °C for 3 hours. The surface area of as formed and calcined at 950 and 1200 °C of CaSiO3 samples were found to be 31.93 m2/g, 0.585m2/g and 3.48 m2/g respectively. The TL intensity in powdered sample is more when compared to the pelletized CaSiO3 and it is further observed that there is a shift in glow peak temperatures in pelletized sample. This is attributed to the inter particle spacing and pressure-induced defects.

Determination of Boron in U3O8 by Spectrophotometry

Abstract: Spectrophotometric estimation of boron with curcumin after extraction employing 10% 2-ethyl hexane 1,3-diol (EHD) in CHC13 has been modified and employed for its determination in U3O8.The method gives a precision and accuracy of 4.0% at 100 ppb of boron when about 200 mg sample is taken for analysis; the detection limit is 32 ng of boron. If the availability of the sample is limited and the boron content is low, lower dilutions are resorted to realize the desired sensitivity in the measurements (diluting to 10 mL instead of 25 mL). Interference of different acid media is also discussed.

Comparison of Two Different Commercially Available Polyacrylate Dispersants for Gelcasting Alumina Slurries

Abstract: Rheological behaviour of gelcast alumina slurries, prepared using different amounts of two commercially available dispersants, Darvan 821A and M-20C having difference in molecular weight, were studied. The optimum dispersant amount for each of the dispersants was determined in terms of attainment of minimum in the viscosity. The optimal amount of dispersant required was different for the two dispersants owing to the difference in molecular weight. The lowest viscosity value was found to be a little higher for M-20C based slurries, which could be attributed to the lesser electrosteric repulsion with M-20C as compared to that of Darvan. The differences in power law index value ‘n’ and also the thixotropy were directly correlated with the molecular weight of the dispersants.

Occluded Gas Content in Fast Breeder Reactor Fuels

Abstract: A comprehensive analytical methodology based on hot vacuum extraction principle was developed for the determination of total/occluded gas content in ceramic fast reactor nuclear fuels such as (U, Pu)C and (U, Pu)O2 of different bulk compositions. In view of the stringent specifications imposed on these fuels with respect to total gas, detailed investigations were carried out to understand and interpret the implications of the definition of the occluded gas content. These investigations include selecting the temperature and duration of heating, method of gas collection (with and without gas refrigeration) as well as measuring the gas composition employing quadrupole mass spectrometer. Hydrogen was found to be the major constituent of the occluded gas (>95%) followed by minor quantities of N2, CO and CO2. These observations showed the necessity of introducing a vacuum degassing step after sintering and also helped in redefining the specification of total gas content. The total gas content is less than 0.1 c...

Comparison of wear properties of alumina-alumina articulating surfaces with conventional material couples used for total hip arthroplasty

Abstract: Periodic introduction of different material combinations such as metal-metal, metal-polymer, ceramic-polymer and ceramic-ceramic as the articulating surfaces in artificial total hip arthroplasty exhibited their own merits and demerits. Since the wear between the mating parts of the prostheses ultimately determines the life of the prostheses, tribological performance of the three materials combination used in total hip replacement (THR) was studied with a pin-on-disc (POD) machine and the results were compared. It was observed that in different material couples, a power law form of relationship existed between wear height and load though it changed with severity of abrasion. Alumina-alumina material combination exhibited very low wear with occasional grain pull-out and the generated data clearly established the superiority of the ceramic based material-couples. In SS 316L-UHMWPE, abrasion dominated wear was observed while in AI2O3-UHMWPE, abrasive ploughing was followed by an adhesive form of junction maki...

An approach towards theoretical prediction of viscosity of glasses over a wide range of temperature

Abstract: A model for estimation of viscosities of glass melts at relatively high temperatures has been previously reported from this laboratory in this journal (see text). This paper describes an approach for extension of the model to relatively low temperatures. In addition, another novel method for estimation of viscosity over a wide temperature range is presented. Viscosity data on several commercially important glasses are reported to discuss the applicability of these models, all of which employ Optical Basicity (OB) of the system as a compositional parameter.

Emission Analysis of Rare Earth (Pr3+, Dy3+, Tm3+) Ions doped ZrF4-BaF2-LaF3-YF3-AIF3-NaF Glasses: A Mini-Review

Abstract: This article reports on the newly developed heavy metal based multicomponent ZrF4-BaF2-LaF3-YF3-AIF3-NaF optical glass systems, which are abbreviated as ZBLYAN glasses for easy reference. These host glass matrices have been doped with rare earth ions such as Pr3+ or Dy3+ or Tm3+ to understand their upconverted emission phenomenon and normal emission as well through a systematic approach. NIR upconversion emissions into visible colours have been reported from these rare earth ions doped optical fibre core based standard glass compositions. The possible mechanisms involved in such upconversion emission processes have been explained more clearly in terms of energy levels schemes.

Preparation of (U0.55Th0.45)O2 Microspheres by Sol-Gel Process

Abstract: An internal gelation process has been developed for preparing high density (U0.55Th0.45)O2 microspheres. Parameters such as concentration of gelation agents, total metal concentration etc were standardized to obtain crack free sintered microspheres of 96% theoretical density (TD). The SEM studies of the sintered spheres indicated uniform microstructure with 10-20 μm grain size. SEM-EDAX study indicated uniform distribution of uranium and thorium within the microspheres.

Ophthalmic Lenses for Vision Correction: Review of Application, Usage and Trends

Abstract: This paper aims at providing an overview of the current status and the trends in the manufacture and use of mineral (inorganic) glass ophthalmic lenses. The focus is on the properties, manufacturing processes, and use patterns for mineral lenses, but we briefly touch upon the trend towards newer organic materials that are substituting inorganic glass. The glass itself is evolving, both through improved composition and value added treatments like photochrome treatment, polarizing filters, and antireflection coatings. We examine these important treatments in detail, and also briefly look at some newer coatings and treatments that are emerging in this field.

Synthesis and characterization of sol-gel derived cu doped zno films

Abstract: Well-crystallized Cu doped (1,3 and 5 mol%) ZnO films were deposited on quartz substrates by sol-gel technique. The optical, microstructural and photoluminescence properties of the films were studied. It was found that the band gaps (3.38 eV) of the films did not vary up to 5% Cu doping in ZnO. The preferred orientation along (002) was observed for all the films and the degree of orientation decreased with increasing the molar percentage of Cu in ZnO. Atomic force microscopy (AFM) measurements were performed to study the surface morphology of 1,3 and 5% Cu doped ZnO thin films; the surface roughness of 1 mol% Cu doped ZnO film was smaller (∼6 nm) than those of 3 and 5 mol% Cu doped ZnO films (∼15-20 nm). The photoluminescence spectra of the films showed six peaks at 3.11, 3.03, 2.75, 2.68, 2.65 and 2.27 eV. One peak (3.11 eV) was due to excitonic transition and the other five peaks were due to defect related transitions. The excitonic peak intensity of Cu doped ZnO increased with increasing copper concent...

Advances in Alloy Design of Hardmetals

Abstract: This study describes the alloy design approaches for processing high-performance hardmetals for metal cutting and mining applications. In fine-grained hardmetals for metal cutting applications combined addition of VC and Cr3C2 in optimal proportion, as grain-growth inhibitors, enhances the hardness as well as indentation fracture toughness. In addition, the synergistic action of these grain-growth inhibitors also results in a more homogeneous microstructure. Consequently, the variation in the mechanical properties of these fine-grained hardmetals is reduced. This research also highlights the influence of carbon on the transverse rupture strength and toughness of the mining and fine-grained hardmetals. A lower carbon in the two-phase WC + Co region of the hardmetal microstructure results in higher fracture toughness and transverse rupture strength without compromising the hardness.

Effect of Heat Removal on Pore Growth in Nickel-Aluminide during SHS: A Small-Angle Neutron Scattering Investigation

Abstract: Effects of heat removal on the pore growth during self-propagating high temperature synthesis (SHS) of Nickel-Aluminide have been investigated using small angle neutron scattering (SANS) technique. It has been revealed that the rate of heat removal vis-a-vis the velocity of the propagating wave front during synthesis controls the growth of the pore size in the final product to some extent. Significant growth in pore size occurs mainly due to thermal migration and molar volume contraction. The structure factors of the specimens can be scaled with respect to the average size and the effective radius of gyration of the pores.