Elastic Constants And Structural Parameters Of Selected Polycrystalline Ceramics By Ultrasonic Technique

The present work is an attempt to probe the elastic properties in some dielectric ceramics, by using ultrasonic pulse echo overlap technique. The base Ba6-xSm8+2xTi18O54 and Ca5Nb2TiO12 are very important dielectrics ceramics used for microwave communication as well as for substrate materials. Ultrasonic is one of the most widely used and powerful techniques to measure elastic properties of solids. The ultrasonic technique is nondestructive in nature and the measurements are relatively straightforward to perform. One unique advantantage of the ultrasonic technique is that both static and dynamic properties can be measured simultaneously. The velocity and attenuation coefficients of the ultrasonic waves propagating through a medium are related to the microscopic structure of the material and they provide valuable information about the structural changes in the system. Among the various ultrasonic techniques, the pulse echo overlap method is the most accurate and precise one. In the present case the decreased elastic properties of Cas-XMg,Nb2TiO12 and Cas-,ZnNb2TiO12 ceramics can be attributed to their mixture phases beyond x = 1. Moreover, the abrupt change in elastic properties observed for x >1 can also be correlated to the structural transformation of the materials from their phase pure form to mixture phases for higher extent of substitution of the concerned material . Ca4(ANb2Ti)012 (A = Mg, Zn) is the strongest compound with the maximum values for elastic properties . This could be due to the possible substitution of Mg/Zn ions with lesser radius [25] than Ca2+ in perovskite B-site of Ca(Cali4Nb2i4Tili4) O3 material to contribute more ordering and symmetry to the system [20]. All other compositions (x > 1) contain mixed-phases and for such mixed-phase samples, the mechanical properties are difficult to explain.

Studies on the Effect of High Energy Ball Milling On the Structural, Electrical and Magnetic Properties of Some Normal Spinets in the Ultrafine Regime

The present work is an attempt to understand the characteristics of high energy ball milling on the structural, electrical and magnetic properties of some normal spinets in the ultra fine regime, Magnetism and magnetic materials have been a fascinating subject for the mankind ever since the discovery of lodestone. Since then, man has been applying this principle of magnetism to build devices for various applications. Magnetism can be classified broadly into five categories. They are diamagnetic, paramagnetic, ferromagnetic antiferromagnetic and ferrimagnetic. Of these, ferro and ferri magnetic materials assume great commercial importance due to their unique properties like appropriate magnetic characteristics, high resistivity and low eddy current losses. The emergence of nanoscience and nanotechnology during the last decade had its impact in the field of magnetism and magnetic materials too. Now, it is common knowledge that materials synthesized in the nanoregime exhibit novel and superlative properties with respect to their coarser sized counterparts in the micron regime. These studies reveal that dielectric properties can be varied appreciably by high-energy ball milling in nanosized zinc ferrites produced by coprecipitation method. A semi conducting behaviour was observed in these materials with the Oxygen vacancies acting as the main charge carrier for conduction, which was produced at the time of coprecipitation and milling. Thus through this study, it was possible to successfully investigate the finite size effects on the structural, electrical and magnetic properties of normal spinels in the ultra fine regime

Structural and spectral studies of novel Co(III) complexes of N(4)-substituted thiosemicarbazones derived from pyridine-2-carbaldehyde

Seven bis(ligand) Co(III) complexes {[CoL21] NO3 · H2 O (1), [CoL21] Cl · 2 H2 O (2),[CoL21] ClO4 (3), [CoL22] NO3 (4), [CoL22] Cl · 2 H2 O (5), [CoL23] Br · 2 H2 O (6), [CoL23] ClO4 · H2 O (7)} of three thiosemicarbazone ligands {pyridine-2-carbaldehyde-N(4)-p-methoxyphenyl thiosemicarbazone [HL1], pyridine-2-carbaldehyde-N(4)-2-phenylethyl thiosemicarbazone [HL2] and pyridine-2-carbaldehyde-N(4)-(methyl),N(4)-(phenyl) thiosemicarbazone [HL3]} were synthesized and physico-chemically characterized. All complexes are assigned octahedral geometries on the basis of spectral studies. The ligands deprotonate and coordinate by means of pyridine nitrogen, azomethine nitrogen, and thiolate sulfur atoms. The single crystal X-ray structures of HL3 and two nitrate compounds are discussed. The structural studies corroborate the spectral characterization.

Spectral and structural studies of mono- and binuclear copper(II) complexes of salicylaldehyde N(4)-substituted thiosemicarbazones

Three copper(II) complexes of salicylaldehyde N(4)-phenyl thiosemicarbazone (H2L1) and two copper(II) complexes of N(4)-cyclohexyl thiosemicarbazone (H2L2) have been synthesized and characterized by different physicochemical techniques like magnetic studies and electronic, infrared and EPR spectral studies. The complexes View the MathML source and [(CuL2)2] (4) having dimeric structure. The thiosemicarbazones bind to the metal as dianionic ONS donor ligand in all the complexes, except in the complex [Cu(HL1)2] · H2O (2). In complex 2, the ligand moieties are coordinated as monoanionic (HL−) ones. Two of the complexes [CuL1dmbipy] · H2O (3) and [CuL2dmbipy] (5) have been found to possess the stoichiometry [CuLB], where B = 4,4′-dimethyl-2,2′-bipyridine (dmbipy). The coordination geometry around copper(II) in 5 is trigonal bipyramidal distorted square based pyramidal (TBDSBP), as obtained by X-ray diffraction studies.

Field Equilibrium Finite Elements for Structural Analysis

Many finite elements used in structural analysis possess deficiencies like shear locking, incompressibility locking, poor stress predictions within the element domain, violent stress oscillation, poor convergence etc. An approach that can probably overcome many of these problems would be to consider elements in which the assumed displacement functions satisfy the equations of stress field equilibrium. In this method, the finite element will not only have nodal equilibrium of forces, but also have inner stress field equilibrium. The displacement interpolation functions inside each individual element are truncated polynomial solutions of differential equations. Such elements are likely to give better solutions than the existing elements.In this thesis, a new family of finite elements in which the assumed displacement function satisfies the differential equations of stress field equilibrium is proposed. A general procedure for constructing the displacement functions and use of these functions in the generation of elemental stiffness matrices has been developed. The approach to develop field equilibrium elements is quite general and various elements to analyse different types of structures can be formulated from corresponding stress field equilibrium equations. Using this procedure, a nine node quadrilateral element SFCNQ for plane stress analysis, a sixteen node solid element SFCSS for three dimensional stress analysis and a four node quadrilateral element SFCFP for plate bending problems have been formulated.For implementing these elements, computer programs based on modular concepts have been developed. Numerical investigations on the performance of these elements have been carried out through standard test problems for validation purpose. Comparisons involving theoretical closed form solutions as well as results obtained with existing finite elements have also been made. It is found that the new elements perform well in all the situations considered. Solutions in all the cases converge correctly to the exact values. In many cases, convergence is faster when compared with other existing finite elements. The behaviour of field consistent elements would definitely generate a great deal of interest amongst the users of the finite elements.

Structural, EPR and Antimicrobial Studies on Some Transition Metal Complexes of Thiosemicarbazones

Department of Applied chemistry, Cochin University of Science and Technology

Structural and biological investigations of metal complexes of some substituted thiosemicarbazones

Department of Applied Chemistry, Cochin University of Science and Technology

Structural and catalytic investigation of vanadia supported on ceria promoted with high surface area rice husk silica

Rice husk silica was utilized as the promoter of ceria for preparing supported vanadia catalysts. Effect of vanadium content was investigated with 2–10 wt.% V2O5 loading over the support. Structural characterization of the catalysts was done by various techniques like energy dispersive X-ray (EDX), X-ray diffraction (XRD), BET surface area, thermal analysis (TGA/DTA), FT-infrared spectroscopy (FT-IR), UV–vis diffused reflectance spectroscopy (DR UV–vis), electron paramagnetic spectroscopy (EPR) and solid state magnetic resonance spectroscopies (29Si and 51V MASNMR). Catalytic activity was studied towards liquid-phase oxidation of benzene. Surface area of ceria enhanced upon rice husk silica promotion, thus makes dispersion of the active sites of vanadia easier. Highly dispersed vanadia was found for low V2O5 loading and formation of cerium orthovanadate (CeVO4) occurs as the loading increases. Spectroscopic investigation clearly confirms the formation of CeVO4 phase at higher loadings of V2O5. The oxidation activity increases with vanadia loading up to 8 wt.% V2O5, and further increase reduces the conversion rate. Selective formation of phenol can be attributed to the presence of highly dispersed active sites of vanadia over the support.

Thermo-Structural Analysis of 3D Composites

Three dimensional (3D) composites are strong contenders for the structural applications in situations like aerospace,aircraft and automotive industries where multidirectional thermal and mechanical stresses exist. The presence of reinforcement along the thickness direction in 3D composites,increases the through the thickness stiffness and strength properties.The 3D preforms can be manufactured with numerous complex architecture variations to meet the needs of specific applications.For hot structure applications Carbon-Carbon(C-C) composites are generally used,whose property variation with respect to temperature is essential for carrying out the design of hot structures.The thermomechanical behavior of 3D composites is not fully understood and reported.The methodology to find the thermomechanical properties using analytical modelling of 3D woven,3D 4-axes braided and 3D 5-axes braided composites from Representative Unit Cells(RUC's) based on constitutive equations for 3D composites has been dealt in the present study.High Temperature Unidirectional (UD) Carbon-Carbon material properties have been evaluated using analytical methods,viz.,Composite cylinder assemblage Model and Method of Cells based on experiments carried out on Carbon-Carbon fabric composite for a temparature range of 300 degreeK to 2800degreeK.These properties have been used for evaluating the 3D composite properties.From among the existing methods of solution sequences for 3D composites,"3D composite Strength Model" has been identified as the most suitable method.For thegeneration of material properies of RUC's od 3D composites,software has been developed using MATLAB.Correlaton of the analytically determined properties with test results available in literature has been established.Parametric studies on the variation of all the thermomechanical constants for different 3D performs of Carbon-Carbon material have been studied and selection criteria have been formulated for their applications for the hot structures.Procedure for the structural design of hot structures made of 3D Carbon-Carbon composites has been established through the numerical investigations on a Nosecap.Nonlinear transient thermal and nonlinear transient thermo-structural analysis on the Nosecap have been carried out using finite element software NASTRAN.Failure indices have been established for the identified performs,identification of suitable 3D composite based on parametric studies on strength properties and recommendation of this material for Nosecap of RLV based on structural performance have been carried out in this Study.Based on the 3D failure theory the best perform for the Nosecap has been identified as 4-axis 15degree braided composite.

Chelating behavior of acylhydrazones towards transition metals:Spectral and structural aspects

The current work deals with the synthesis and characterization of metal complexes derived from some substituted acylhydrazones. The hydrazones under investigation were characterized by IR, UV, NMR spectral studies and the molecular structure of one of the hydrazones was solved by single crystal XRD studies. In the present work dioxovanadium(V), manganese(II), cobalt(II/III), nickel(II), copper(II), zinc(II) and cadmium(II) complexes were synthesized and characterized by various spectroscopic techniques, molar conductance measurements, magnetic susceptibility measurements and cyclic voltammetry. Single crystals of some of the complexes were isolated and characterized by single crystal X-ray diffraction.The thesis is divided into eight chapters. Chapter 1 gives an introduction on hydrazones, diversity in their chelating behavior and their application in various fields. This chapter also describes different analytical techniques employed for the characterization of hydrazones and their metal complexes. Chapter 2 includes the synthesis and characterization of two substituted acylhydrazones. This chapter also discusses how the coordination behavior of hydrazones under investigation is interesting. Chapters 3-8 discuss the synthesis and characterization of some transition metal complexes derived from the acylhydrazones under study.The hydrazones synthesized were found to exist in the amido form. Various characterization techniques were carried out to explore the structure of the synthesized complexes. The results indicate that both the hydrazones coordinate through the pyridyl and azomethine nitrogens and amide oxygen either in enolate or neutral form. Out of synthesized complexes V(V), Zn/Cd(II) and one of the cobalt complex was found to diamagnetic. We could isolate single crystals of some of the complexes and most of the complexes crystallized were found to have a distorted octahedral geometry. Thus X-ray crystallographic study which was used as major tool in the structure determination revealed that the hydrazones undergo a rotation about the azomethine bond on complexation. We hope the work presented in the thesis would be helpful for those who are working in the field of metal complexes and can further they can be utilized for various applications.

Transition Metal Complexes of Schiff Bases with Azide and Thiocyanate as Coligands:Spectral and Structural Investigations

Metallo-organic chemistry,incorporating the frontiers of both inorganic and organic chemical aspects,is a topic of utility concern.The first exploration of coordinated metal complexes dates back to the ninettenth century,during the days of Alfred Werner.Thereafter,inorganic chemistry witnessed a great outflow of coordination compounds,with unique structural characteristics and diverse applicatons.The diversity in structures exhibited by the coordination complexes of multidentate ligands have led to their usage as sensors,models for enzyme mimetic centers,medicines etc.The liganda chosen are of prime importance in determining the properties of coordination compounds.Schiff bases are compounds obtained by the condensation of an aidehyde or ketone with an amine.The chemical properties of Schiff bases and their complexes are widely explored in recent years owing to their pharmacological activity,their catalytic activities and so on.On the other hand pseudohalides like azide and thiocyanate are versatile candidates for the construction of dimeric or polymeric complexes having excellent properties and diverse applications.So a combination of the Schiff bases and the pseudohalogens for the synthesis of metal complexes can bring about interesting results.An attempt into this area is the besis of this Ph.D theis.

Template assisted fabrication of I-D nanostructures of Nickel,Cobalt, Iron Oxide and Carbon nanotubes and a study on their structural, magnetic and nonlinear optical properties for applications

Department of Physics, Cochin University of Science & Technology

Transition metal complexes of some bis(thiosemicarbazones) derived from 2,6-diacetylpyridine and N4-substituted thiosemicarbazides:Synthesis, spectral and structural studies

Coordination chemistry of pentadentate 2,6-diacetylpyridine bis(thiosemicarbazone) Schiff base ligands has been intensively studied due to the versatility of the molecular chain in order to obtain very different geometries as well as their broad therapeutic activity. Metal complexes of thiosemicarbazone with aldehydes and ketones have been widely reported. But there have been fewer reports on potential pentadentate bis(thiosemicarbazones) formed from 2,6-diacetylpyridine. Keeping these in view, we have synthesized four bis(thiosemicarbazone) systems with 2,6-diacetylpyridine. In the present work, the chelating behavior of bis(thiosemicarbazones) are studied, with the aim of investigating the influence of coordination exerts on their conformation and or configuration, in connection with the nature of the metal and of the counter ion. The selection of the 2,6-diacetylpyridine as the ketonic part was based on its capability to form polynuclear complexes with different coordination number. The doubled armed bis(thiosemicarbazones) can coordinate to a metal centre as dianionic ligand by losing its amide protons or it can coordinate as monoanionic ligand by losing its amide proton from one of the thiosemicarbazone moiety or it can also be coordinate as neutral ligand. Hence it is interesting to explore the coordinating capabilities of these ligands whether in neutral form or anionic form and to study the structural variations occurring in the ligands during complexation such as change in conformation.