Showing papers in "Transactions of The Indian Ceramic Society in 2007"

Ceramic Nanofibers by Electrospinning Technique—A Review

Abstract: Nanofibers are solid-state linear nanomaterials with diameters 1000 and are characterized by high surface area to volume ratio. Nanofibers, due to their high surface area to volume ratio are potential candidates for a large number of applications such as separation of liquids and gases, as sensors, photovoltaic applications, insulation, ultrapurification of water, drug delivery etc. In recent years, electrospinning technique has been successfully used for the preparation of nanofibers. Initially, polymer nanofibers are prepared using this technique. Recently, this technique has also been successfully extended for the preparation of ceramic nanofibers. This paper reviews the electrospinning process, application of electrospinning process for the preparation of ceramic nanofibers and their possible applications.

Corrosion Behaviour of Bismuth-Silicate Glasses and their Glass-Ceramic Derivatives and the Effect of Ionizing Gamma-Irradiation

Abstract: The corrosion weight losses by aqueous acidic or alkaline solutions have been studied for binary bismuth oxide-silica glasses and their corresponding glass-ceramic derivatives with the Bi2O3: SiO2 molar per cent varying from 90:10 to 50:50. The corrosive action on these glasses and glass-ceramics by acid solutions has been found to depend on the pH and the type of anion present in solution, and the attack by NaOH solution has been seen to be slightly lower than that by the acidic solutions. Generally, the corrosion decreases with the increase in the SiO2 content in the samples as expected due to the strong structural role of silica in the glass network. Also, the corrosion has been found to increase with the microcrystalline compact glass-ceramic derivatives. Gamma-irradiation slightly changes the corrosion behaviour. Morphology of the glass surface changes has been studied by scanning electron microscopic (SEM) measurements. Various features of islands and surface cracks have been observed to be formed a...

Rate Controlled Sintering: A Unique Concept for Microstructural Control

Abstract: There has been a renewed interest in the use of rate controlled sintering (RCS) technique for the densification of ceramic/metallic nanopowders. The objective is to retain the sintered grains to submicron sizes together with densification. The mechanism involves extension of pore closure through the application of extremely low shrinkage rates at the final densification regime where there is logarithmic dependence of densification with shrinkage rate. The feedback established between the shrinkage rate and instantaneous temperature facilitates the derivation of a temperature-time path best suited to achieve the twin objectives of densification and fine grained microstructure. The paper surveys the systems investigated exploring the suitability of RCS methodology and thermokinetic analysis and presents the case studies carried out on sintering and controlled microstructural evolution in ceramic systems of alumina and zirconia.

Methods of Synthesis of Y3AI5O12 (YAG)—A Review

Abstract: Y2O3 and AI2O3 form three distinct phases of which YAG of empirical formula Y3AI5O12 is the most important as an industrial material. There are many different methods of synthesizing the material and extensive literature is available in the form of published documents such as paper and patents related to this. In the present article, an alternative is made to summarize different methods of synthesis of the material YAG as described in such documents. Relevant discussion is also included with respect to crystal structure of different phases and phase diagram in Y2O3- AI2O3 system.

Gallium Nitride: Synthesis and Characterization

Abstract: This review article presents the synthesis and important properties of bulk, thin film and different nanoforms of GaN. The nanoforms include nanocrystalline powder, nanowires and nanorods. The preparation and critical aspects of p-type and n-type GaN has been discussed in detail as the semiconducting proterties of this material have already been utilized in the industries for the fabrication of optoelectronic devices. Discussion in relation to improvement of light emitting diode application and some other probable applications based on typical properties of pure and doped GaN have been made.

Crystallization and Properties of Some Glasses Based on Li-silicates

Abstract: Crystallization in lithium silicate glasses containing progressive additions of cement kiln dust was investigated using XRD and SEM analyses. Different properties were characterized by dilatometer, microhardness, and density measurement techniques. Crystallization of the base glass is shown to give lithium di and metasilicate phases. However, the introduction of cement kiln dust in such glass leads to the development of wollastonite as well. The subsequent incorporation of cement kiln dust in the base glass increases the wollastonite crystallization in addition to dominant Li-metasilicate phases. Crystallization in long period heat-treatment shows the formation of Li2Ca3Si6O16 in the entire sample containing cement kiln dust. Gradual decrease of the coefficient of thermal expansion (CTE) and the Vickers hardness values takes place in the crystallized glasses, from 12.8 to 8.2 × 10−6 °C−1 (20°-500°C) and from 5.89 to 5.04 GPa respectively, with the incorporation of cement kiln dust. At the same time, the i...

Physicochemical characteristics of lanthanum hydroxide in hydroxyhydrogel and conventional gel form

Abstract: Lanthanum hydroxide was prepared by wet interaction through precipitation as well as flash polycondensation, using lanthanum nitrate and ammonium hydroxide. The prepared materials were subjected to various physicochemical characterization. Rate constants and activation energies for dehydration, dehydroxylation and decarboxylation of synthesized materials were determined by dynamic and static thermogravimetry. Rate constants and activation energies were calculated with structural transformations, which were supported by XRD and FTIR analyses. The results showed that the physicochemical properties of the materials differ considerably with respect to the process parameters adopted during synthesis.

Ionic Transport through Heterogeneous Solids

Abstract: The conductivities of an ionic polycrystalline solid lithium iodide (Lil), covalent polycrystalline lithium aluminium titanium phosphate (LATP) glass-ceramic material, and Y(Sc)SZ with Al2O3 and Ba0.6Sr0.4TiO3 (0.6BST) additions were investigated. It was determined that blocking and space charge effects coexist in these heterogeneous solids. However, their magnitudes differ from one system to another. The most pronounced blocking effect was evident in the LATP-Al2O3 system, whereas a dominant space charge effect was observed in the Lil-Al2O3 system. The higher dielectric constant of 0.6BST enhanced the space charge effect and thus conductivity in the LATP-0.6BST system. In the Y(SC)SZ-Al2O3 system the magnitudes of blocking and space charge effects were comparable. The space charge effect was also determined to be strongly temperature dependent.

4D Carbon-Carbon Composite Processing and its Properties in Comparison with Other Carbon-Carbon Preforms

Abstract: The re-entry structure of a long range missile will experience severe aero thermal load during flight. The nose tip of the missile shall be capable of withstanding these severe thermal stresses arising out of thermal shock in all the directions. The material has to be so designed as to exhibit symmetric erosion and should have the lowest erosion rate with respect to all directions. So multidirectional reinforced carbon-carbon composite is an ideal choice for this application. To obtain strength in 2, 3 or 4 directions we weave fibers in different directions. Though carbon-carbon composite shows anisotropic (direction dependent) property, 4D carbon-carbon composite shows the same properties (strength, erosion rate, etc) in all 4 directions. The process involved for making 4D carbon-carbon is very tedious as well as very expensive. The properties like density, tensile strength, specific modulus, etc are studied and are very much comparable with those of the other preforms.

Physico-Chemical Characterization of Ukrainian and Indian Plastic Clays—A Comparative Study

Abstract: The chemistry, mineralogy, plastic and dry properties, thermo-mechanical characteristics and rheological properties of imported Ukrainian clay vis-5-vis three Indian plastic clays have been investigated. The presence of illite, poor crystallinity, high degree of disordered kaolinite, lower colouring oxides content, high plasticity and finer particle size present in the Ukrainian clay are found to be the key contributors to its unique characteristics.

Examination of Industrial Practice of Ceramic Glaze Making with Emphasis on Particle Size Distribution

Abstract: This article examines the existing industrial practice of glaze making with emphasis on particle size and particle size distribution of glazes. The importance of fine grinding affecting reduction in particle size on lowering the maturing temperature has been clearly established taking sanitaryware glaze as an example. Studies on gloss and thermal expansion of glazes having varied particle size distribution have also been carried out. An attempt has also been made to redefine the particle size distribution, which could produce better results. It has been found that the ceramic glazes can safely be ground to d100 of 20 μm from the existing industrial practice of maintaining d100 in the range of 45 to 32 μm. It has also been established that, along with the increase in particle fineness, not only the maturing temperature of glaze reduces by ∼80°C but also the maturing range of sanitaryware glaze significantly increases from 1150° to 1230°C as evident from the consistent gloss values of glazes (92–95 GU) and ...

Preparation of α-AI2O3 and to Study of Its Crack Growth Resistance Behaviour

Abstract: A modified sol-gel process was developed and used to prepare α-AI2O3. Details of this process have been reported previously. In this process, gels are obtained by keeping higher concentration of starting solution. DTA of dried gel shows the presence of aluminium hydroxide and aluminium sulphate but both are amorphous in nature, revealing materials in the colloidal state. After calcination of gels at 1250°C for 1 h, α-alumina powder is formed, which has particle size distribution in the range of 100-200 nm. Sintering behaviour shows that nearly 99% of theoretical density is obtained at 1600°C for 3 h of holding time in the uniaxially pressed samples. Alpha alumina bar samples have hardness values and elastic constants close to the theoretical values, which enable them to possess good fracture strength and fracture toughness. The material also resists crack propagation, and fracture toughness increases with the increase in initial crack size. Densification of powder, morphology and mechanical properties obt...

Use of artificial neural network for modelling the interaction between fly ash and lime under steam curing

Abstract: The chemical interaction between fly ash and lime in steam cured fly ash-lime compacts was modelled by artificial neural network to predict the free lime remaining in the mixes after the curing period. Process parameters, like, the pozzolanicity of the ash samples, their surface areas, unburnt carbon content, curing period and the proportion of lime in the fly ash-lime mixes were taken as the inputs for the model and the free lime remaining in the mix was taken as the output parameter. A generalized feed forward back propagation three layered neural network model was used with tan hyperbolic transfer function at both the input and the output layers with 400 exemplars. For the training data after 3000 iterations the mean square error (MSE) value was found to be the minimum for the prediction mode. The model when tested for the test data the difference between the actual value of the free lime and the predicted value of the free lime content in the mixes after different periods of curing was found to be wit...

Study on Wear Phenomena of Tundish Working Lining by Slags of Billet Caster

Abstract: Total number of heats taken in tundish refractory working linings (MgO-based) varies with three steel grades produced in the Long Product Complex at Tata Steel. The duration of the sequence heats (of 60-70 min) for low-C, med-C and high-C steel grades made at billet caster are 14-16, 16-18 and 22-24 h respectively. These differences are due to different rates in erosion and corrosion of the three types of tundish slags arising in three different steel grades and different liquidus temperatures of three steel grades. The tundish slags have different chemical compositions, liquidus temperatures and viscosity. An attempt has been made in the present work to understand the wear mechanisms of MgO-based refractory linings by different tundish slags in the three steel grades. Chemical analysis, optical and scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) have been used to characterize the slag infiltrated MgO-based tundish lining samples collected from the plant. The present work has ...

Leaching Kinetics of Tungstic Acid and in situ Synthesis of Tungsten Carbide in Silica Gel Matrix

Abstract: Leaching of tungstic acid is carried out in ammonium hydroxide solution at two different pH (8 and 10.5), at three different temperatures of 40°, 50° and 60°C. It Is observed that initially the dissolution rate is very fast followed by decrease in rate with time. It also increases with increase of temperature and pH. The mechanism of isothermal leaching kinetics of tungstic acid in ammonium hydroxide is mainly of contracting geometry type. Ammonium tungstate has been used as a precursor to synthesize nano tungsten carbide in the silica gel matrix by in situ generation of hydrogen and extremely fine carbon. The size of tungsten carbide is found to be in the nm range.

Benefits of Enhanced Mullitization upon Addition of Micronised Andalusite to Low Cement Castables

Abstract: In the formulation of low cement castables, microfine additives are so selected that predominating phase will be mullite in the matrix of the alumina based castable refractories. Andalusite behaves like a reactive mullite as during mullitization the expelled glass from the grains can be easily combined with required amount of micronised alumina, giving rise to a secondary mullite acting as a binder and converting the total castable matrix into a well distributed mullite. Mullitization process in andalusite depends on its grain size; attrition milled micronised andalusite grains undergo Mullitization even at 1200°C with release of glassy phase through a topochemical and topotactic process resulting in volume stability and high thermal shock resistance. The effect of micronised andalusite and coarse grained andalusite on the properties like bulk density, apparent porosity, volume change, strength before and after spalling cycles of the low cement castables have been compared. XRD studies have been made to i...

A Model Template for Environmental Management in Ceramic Industry

Abstract: Environmental Performance Evaluation (EPE) is an useful method to assess the effectiveness of critical environmental management of an organization. In this paper the basic concept of EPE and its applicability in the context of ceramic industries has been discussed.

Suitability of Different Grades of Fused Magnesia for Magnesia-Carbon Refractories for Critical Applications

Abstract: In the process of globalization, China has opened up to the international market with its huge mineral resources. As a result, refractory industries world over are flooded with Chinese “fused magne...

Ionic Conductivity of Scandia Stabilized Zirconia and Alumina Composites

Abstract: This paper analyses the conductivity data of composite electrolytes in the 6ScSZ-AI2O3 system. The system provides a heterogeneous solid electrolyte in which the grain conductivity remains unaffected, whereas the grain boundary conductivity increases up to 20 wt% of AI2O3. The bulk conductivity, which includes contributions from both grain and grain boundary conductivity, therefore shows an enhancement with AI2O3 addition. The enhancement is explained on the basis of space charge formation at the ScSZ-AI2O3 boundaries. The conductivity of these composite specimens decreases when the AI2O3 concentration is increased to 30 wt%.

Pore Size and its Distribution for Ca-Hydroxyapatite based Porous Body

Abstract: Ca-hydroxyapatite [Ca10(PO4)6(OH)2] powder was prepared by wet chemical route. The powder was calcined (900°C) and added with various amounts of pore former to produce 4 different mixes. All were pressed cold isostatically (150 MPa) and debinded to remove pore former from the structure. The fragile structures thus obtained were sintered (1250°C) and the pore size distributions of the porous solids were studied by ‘Hg’-porosimetry method. The results indicated same nature of pore size distribution pattern in all the 4 samples of different porosity. Pore surface area (m2.g−1) and pore statistics were also studied.