Bismuth Phosphate Glasses

Homogeneous glasses are formed in the Bi₂O₃-P₂O₅ system up to 35 mol% (63.8 wt%) Bi₂O₃. In property vs composition plots, the thermal expansion coefficient and tan δ exhibit minima, and hardness and activation energy for conduction show maxima at about 20 mol% Bi₂O₃. The deformation temperature of the glasses also increases abruptly at this composition. This anomalous behavior is interpreted in terms of a change in the function of Bi³⁺ ions from network formers to network modifiers.     

Kinetics of Zircon Synthesis

The synthesis of zircon from ZrO₂ and SiO₂ at fixed temperatures from 1200° to 1400°C was studied as a function of time up to 16 h. Quantitative X-ray diffraction was used to estimate the phases in the product. Quartz transforms to cristobalite through an amorphous transitional phase. Assuming a homogeneous reaction model, analog computer simulation of reactions was used to determine the rate constants at different temperatures. In the temperature range studied, the transitional phase is the most reactive form of silica in zircon synthesis, followed by cristobalite.     

Defect Structure and Electrical Conductivity of ThO2-Y2O3 Solid Solutions

Compositions in the system ThO₂-YO_1.5 were coprecipitated as oxalates and converted to oxides. Disks were pressed and sintered in oxygen at 1400° to 2200°C. Densities of the sintered disks were 96 to 98% of theoretical. Solid solutions with the fluorite-type structure were formed up to 20 to 25 mole % YO_1.5 at 1400°C and up to 45 to 50 mole % YO_1.5 at 2200°C. Density data showed that these solid solutions correspond to Th_{1— x} Y _x O_{2—0.5 x} , having a complete cation sub-lattice filled by Th⁴⁺ and Y³⁺ ions, and vacancies in the anion sublattice. The observed increase in electrical conductivity with increase in YO_1.5content is consistent with charge transport by oxygen ions through a vacancy mechanism. Approximately 7 mole % ThO₂ is soluble in YO_1.5 at 2200°C. Density results indicate an anion interstitial structure for the Y₂O₃ phase. Transference number measurements indicate that the electrical conductivities are only partly due to ions.     

Inverse control for nonlinear excitation and governor control

This paper presents the results of a study of the Inverse Control technique for the design of excitation and governor controllers for a power system. Control laws for rotor angle and field flux are derived. The closed loop system is shown to be asymptotically stable. The system can be transferred to a new operating condition corresponding to any desired terminal voltage Vl and tie-line power P_tie. Although this control law was not experimentally tested on a power system, implementation issues are discussed in robotic and aerospace applications.     

Crystal Chemistry of Mixed Bismuth Oxides with Layer-Type Structure

Several compounds with m = 2, 3, 4, and 5 in the general formula (Me₂'O₂)²⁺ (Me_m–1 R_mO_3m+1)^2– were synthesized, a number of them for the first time. They possess a layer-type crystal structure. Bi³⁺ may be the only suitable ion for the Me' sites; R may be Ga^s+, Ti⁴⁺, Nb⁵⁺, or Ta⁵⁺. The restrictions on the size of Me ions increases with increasing value of m . Lattice parameter data for the compounds and indexed X-ray powder patterns for m = 5 compounds are presented.     

Grain Growth in Ca0.16Zr0.84O1.84

Isothermal grain growth in Ca_0.16Zr_0.84O_1.84, a cubic solid solution of the fluorite type, was studied between 1600° and 2000°C. The grain size increased as the 0.4 power of time. The growth rate was found to be slower than in metals. The activation energy for grain-boundary migration was about 80 kcal per mole. The influence of sintering atmosphere on grain growth is shown.     

PLGA 50:50 nanoparticles of paclitaxel: Development, in vitro anti-tumor activity in BT-549 cells and in vivo evaluation

Clinical administration of paclitaxel is hindered due to its poor solubility, which necessitates the formulation of novel drug delivery systems to deliver such extreme hydrophobic drug. To formulate nanoparticles which makes suitable to deliver hydrophobic drugs effectively (intravenous) with desired pharmacokinetic profile for breast cancer treatment; in this context in vitro cytotoxic activity was evaluated using BT-549 cell line. PLGA nanoparticles were prepared by emulsion solvent evaporation technique and evaluated for physicochemical parameters, in vitro anti-tumor activity and in vivo pharmacokinetic studies in rats. Particle size obtained in optimized formulation was <200?nm. Encapsulation efficiency was higher at polymer-to-drug ratio of 20:1. In vitro drug release exhibited biphasic pattern with initial burst release followed by slow and continuous release (15?days). In vitro anti-tumor activity of optimized formulation inhibited cell growth for a period of 168?h against BT-549 cells. AUC_(0???) and t _1/2 were found to be higher for nanoparticles with low clearance rate.     

Dielectric and Structural Studies in the Systems Ba(Ti, Nb)O3 and Ba(Ti, Ta)O3

The dielectric properties, lattice parameters, and X-ray and neutron diffraction intensities of solid solutions of BaTiO₃ containing Nb or Ta were studied. These solid solutions have a perovskite-type structure with part of the Ti⁴⁺ ions replaced by Nb⁵⁺ or Ta⁶⁺ ions and with some cation vacancies. These solid solutions exhibit a remarkable lowering of the Curie point, but the tetragonal-orthorhombic and the orthorhombic-rhombohedral transition points are raised.     

Studies on Lead Titanate Ceramics Containing Niobium or Tantalum

Dielectric, lattice constant, and thermal-expansion measurements have been made on solid solution ceramics in the systems PbTiO₃Pb_0.5NbO₃ and PbTiO₃-Pb_o.5TaO₃. The ferro-electric Curie temperature is lowered to 465OC. at the solubility limit (2 to 5% Nb or Ta). Replacement of Ti⁴⁺ by Nb⁵⁺ or Ta⁵⁺ in these perovskite-type solid solutions is accompanied by the creation of cation vacancies. These vacancies seem to facilitate material transport and aid sintering. Thus ceramics were obtained with up to 91% of theoretical density. These compositions have peak dielectric constants of the order of 10,000 with tan δ less than 0.1 in the interval 25° to 525°C.     

Kinetics and Burst Phenomenon in ZrO2 Transformation

The monoclinic-tetragonal transformation in ZrO₂ was studied by DTA. The reverse transformation occurs at 850° to 1000°C, depending on the crystallite size, which is a function of the experimental variables. Isothermal kinetics are exhibited by material containing small crystallites; athermal behavior begins to appear as the crystallite size increases. On cooling, strain-free samples undergo a very rapid transformation which is evident as a burst.