Mullite-zirconia composites

Mullite-zirconia composite powders were prepared by the combustion of an aqueous heterogeneous redox mixture consisting of Al(NO3)(3), Zr(NO3)(4)/ZrO(NO3)(2), silica fume and urea/diformyl hydrazine at 500 degrees C. X-ray diffraction data showed that a large amount of tetragonal zirconia existed in the composite powders in spite of high temperature calcination. Milled composite powders showed enhanced densification compared to the unmilled powders and the microstructure of the sintered (1600 degrees C) compacts showed the presence of spherical zirconia grains in intergranular positions along with elongated mullite grains.

Properties of concrete containing ultra-fine fly ash

Fly ash and silica fume are two pozzolans that have been widely used for improved concrete strength and durability. Silica fume displays a greater pozzolanic reactivity than fly ash primarily due to its finer particle size. The reactivity of fly ash can be improved by reducing its particle size distribution. This paper discusses the fresh and hardened properties of concrete made with an ultra-fine fly ash (UFFA) produced by air classification. Durability testing for chloride diffusivity, rapid chloride permeability, alkali-silica reaction (ASR), and sulfate attack was also conducted It was found that at a given workability and water content, concrete containing UFFA could be produced with only 50% of the high-range water-reducer dosage required for comparable silica fume concrete. Similar early strengths and durability measures as silica fume concrete were observed when a slightly higher dosage of UFFA was used with a small reduction (10%) in water content.

Fracture processes of self compacting Concrete using image analysis

The mode I fracture toughness of concrete can be experimentally determined using three point bend beam in conjunction with digital image correlation (DIC). Three different geometrically similar sizes of beams are cast for this study. To study the influence of fly ash and silica fume on fracture toughness of SCC, three SCC mixes are prepared with and without mineral additions. The scanning electron microscope (SEM) images are taken on the fractured surface to add information on fracture process in SCC. From this study, it is concluded that the fracture toughness of SCC with mineral addition is higher when compared to those without mineral addition.

Micromechanical analysis of self compacting concrete

The micro-level properties of different self compacting concrete (SCC) mixes with and without mineral admixures are studied. The study considers SCC as a two phase material consisting of matrix and aggregate. Micro indentation technique is employed to obtain the hardness of individual phases and to compute the micro-property (modulus of elasticity). Using a self consistent homogenization procedure, the micro-property is scaled-up to obtain the macro-property which is shown to agree with the experimentally obtained macro values. It is seen that there exists a smaller interfacial transition zone at different ages of curing across all the mixes due to the presence of more fines in SCC. Also, there is no significant change in the property of the SCC having no fly ash or silica fume beyond 28 days whereas a substantial change in the micro and macro properties are seen in the SCC having fly ash and silica fume.

Preparation of lamellar and hexagonal forms of mesoporous silica and zirconiaby the neutral amine route: lamellar-hexagonal transformation in the solid state

The chain length of the surfactant and the solvent composition are two of the factors that determine whether the lamellar or the hexagonal form of mesoporous SiO2 (or ZrO2) is formed by the neutral amine route; a lamellar-hexagonal transformation occurs on removal of the amine from the former.

A fuzzy multistage evolutionary (FUME) clustering technique

n this paper, a multistage evolutionary scheme is proposed for clustering in a large data base, like speech data. This is achieved by clustering a small subset of the entire sample set in each stage and treating the cluster centroids so obtained as samples, together with another subset of samples not considered previously, as input data to the next stage. This is continued till the whole sample set is exhausted. The clustering is accomplished by constructing a fuzzy similarity matrix and using the fuzzy techniques proposed here. The technique is illustrated by an efficient scheme for voiced-unvoiced-silence classification of speech.

A reply to a discussion by D.J. Cook of the paper a reaction product of lime and silica from rice husk asha star, open

Abstract is not available.

Preparation and catalytic studies of palladium nanoparticles stabilized by dendritic phosphine ligand-functionalized silica

Silica is a prominently utilized heterogeneous metal catalyst support. Functionalization of the silica with poly(ether imine) based dendritic phosphine ligand was conducted, in order to assess the efficacy of the dendritic phosphine in reactions facilitated by a silica supported metal catalyst. The phosphinated poly(ether imine) (PETIM) dendritic ligand was bound covalently to the functionalized silica. For this purpose, the phosphinated dendritic ligand containing an amine at the focal point was synthesized initially. Complexation of the dendritic phosphine functionalized silica with Pd(COD)Cl-2 yielded Pd(II) complex, which was reduced subsequently to Pd(0), by conditioning with EtOH. The Pd metal nanoparticle thus formed was characterized by physical methods, and the spherical nanoparticles were found to have >85% size distribution between 2 nm and 4 nm. The metal nanoparticle was tested as a hydrogenation catalyst of olefins. The catalyst could be recovered and recycled more than 10 times, without a loss in the catalytic efficiency.

Reaction product of lime and silica from rice husk ash

Rice husk ash (about 95% silica) with known physical and chemical characteristics has been reacted with lime and water. The setting process for a lime-excess and a lime-deficient mixture has been investigated. The product of the reaction has been shown to be a calcium silicate hydrate, C-S-H(I)+ by a combination of thermal analysis, XRD and electron microscopy. Formation of C-S-H(I) accounts for the strength of lime-rice husk ash cement.

Silica from rice husk through thermal decomposition

The thermal decomposition characteristics of rice husk have been investigated by dynamic thermoanalytical techniques: DTA, TG, DTG and isothermal heating. The observed thermal behaviour is explained on the basis of a superposition of the decomposition of cellulose and lignin, which are the major organic constituents of rice husk. Morphological features of silica in husk as well as the ash are examined by scanning electron microscopy. Silica in the residual ash has been characterised by X-ray diffraction and infrared spectroscopy. Controlled thermal decomposition of rice husk has been shown to be a convenient method for the liberation of silica.

Nanoindentation study on germania-doped silica glass preforms: evidence for the compaction-densification model of photosensitivity

Nanoindentation technique was employed to measure the changes in mechanical properties of a glass preform subjected to different levels of UV exposure. The results reveal that short-term exposure leads to an appreciable increase in the Young's modulus (E), suggesting the densification of the glass, confirming the compaction-densification model. However, on prolonged exposure, E decreases, which provides what we believe to be the first direct evidence of dilation in the glass leading into the Type IIA regime. The present results rule out the hypothesis that continued exposure leads to an irreversible compaction and prove that index modulation regimes are intrinsic to the glass matrix.

Structure and Function of Hemoglobin Confined Inside Silica Nanotubes

Investigations on the structure and function of hemoglobin (Hb) confined inside sol-gel template synthesized silica nanotubes (SNTs) have been discussed here. Immobilization of hemoglobin inside SNTs resulted in the enhancement of direct electron transfer during an electrochemical reaction. Extent of influence of nanoconfinement on protein activity is further probed via ligand binding and thermal stability studies. Electrochemical investigations show reversible binding of n-donor liquid ligands, such as pyridine and its derivatives, and predictive variation in their redox potentials suggests an absence of any adverse effect on the structure and function of Hb confined inside nanometer-sized channels of SNTs. Immobilization also resulted in enhanced thermal stability of Hb. The melting or denaturation temperature of Hb immobilized inside SNTs increase by approximately 4 degrees C as compared with that of free Hb in solution.

Diffusion and Creep in Silica-Doped Tetragonal Zirconia

Silica segregation at two grain junctions or in amorphous triple junction pockets can influence creep by altering the grain-boundary diffusion coefficient. Although the addition of silica to superplastic yttria-stabilized tetragonal zirconia enhances ductility, differences in reported creep parameters have limited critical identification of rate controlling mechanisms. The present study on a pure 3 mol% yttria-stabilized tetragonal zirconia (3YTZ) and 3YTZ with 0.39 or 3.9 wt% silica involved a detailed characterization of creep over a wide range of experimental conditions and also tracer diffusion measurements. The data broadly show transitions in creep stress exponents from n∼1 to ∼2 to ∼3 with a decrease in the stress. The data at high stresses are consistent with Coble diffusion creep, and creep at lower stresses is attributed to interface-controlled diffusion creep. Measurements indicated that silica does not have any significant influence on grain boundary or lattice diffusion, and this is consistent with the observation that 3YTZ and 3YTZ with 0.39% or 3.9% silica exhibit essentially identical creep behavior in the Coble creep regime. Silica influences the interface control process so that the transitions in stress exponents are pushed to lower stresses with an increase in silica content.

Ultrasound-Triggered Controlled Drug Delivery and Biosensing Using Silica Nanotubes

Silica nanotubes (SNTs) have been demonstrated here as a versatile host for controlled drug delivery and biosensing. The sol-gel template synthesized SNTs have a slow rate of drug release. Application of an external stimulus in the form of ultrasound to or chemical functionalization of synthesized SNT results in higher yield of drug release as well as yield of drug release varying linearly with time. In case of controlled drug delivery triggered by ultrasound, drug yield as function of time is found to be heavily dependent on the ultrasound impulse protocol. Impulses of shorter duration (similar to 0.5 min) and shorter time intervals between successive impulses resulted in higher drug yields. Confinement of hemoglobin (Hb) inside nanometer sized channels of SNT does not have any detrimental effect on the native protein structure and function. Observance of significant enhancement in direct electron transfer of Hb makes the SNTs also promising for application in biosensors.

Free energy of mixing of divalent basic oxides with silica

An expression derived for the free energy of mixing of a divalent basic oxide (MO) with SiO2 based on a model of silicate structure, takes into account the distribution of O2- (from MO) into the silica network, the mixing of silicate ions with O2- and the enthalpy of mixing. The resulting expression is ΔGmix=RT{N11n (2N1-N)2/4N1(1-N)+N21n N 2-N/1-N}, where N={(β+N1)-√(β+N 1)2-8βN1N2}/2β β=characteristic constant for the system N1=mol fraction of silica N2=mol fraction of MO. For the proper choice of β, calculated values of the activity of MO for the system PbO-SiO2, MnO-SiO2, FeO-SiO2 and CaO-SiO2 are in good agreement with experiment. The model predicts that the activity of the basic oxide decreases with increase in temperature.