Effect of prior treatment on the low cycle fatigue behaviour of aluminium alloy RR58 at 423K

The effect of the quenching medium and of varying the microstructure on low cycle fatigue behaviour of aluminium alloy RR58 has been investigated at 423K. It is observed that fatigue resistance is significantly impaired if, following solutionizing, the alloy is quenched in water instead of in oil. Thermal as well as thermomechanical treatments were employed to produce different microstructures. The overaged microstructure displayed the highest fatigue life. It is shown with the help of fractographic observations that differences in fatigue resistance due to differences in severity in quenching or in microstructure arise mainly due to the influence of these variables on crack initiation and early crack propagation. It has also been demonstrated that as the rate of hardening or softening is increased, cyclic strength coefficient K′ and fatigue hardening exponent n′ increase; the fatigue ductility coefficient ?′_f decreases as a result of varying microstructures, and the fatigue resistance at 423K of the alloy is lowered. When compared with the behaviour at ambient temperature, the test temperature of 423K has been found to have no significant effect on the fatigue life/strain plot.     

Effect of formulation composition on the properties of controlled release tablets prepared by roller compaction

This study discusses the effect of formulation composition on the physical characteristics and drug release behavior of controlled-release formulations made by roller compaction. The authors used mixture experimental design to study the effect of formulation components using diclofenac sodium as the model drug substance and varying relative amounts of microcrystalline cellulose (Avicel), hydroxypropyl methylcellulose (HPMC), and glyceryl behenate (Compritol). Dissolution studies revealed very little variability in drug release. The t₇₀ values for the 13 formulations were found to vary between 260 and 550 min. A reduced cubic model was found to best fit the t₇₀ data and gave an adjusted r-square of 0.9406. Each of the linear terms, the interaction terms between Compritol and Avicel and between all three of the tested factors were found to be significant. The longest release times were observed for formulations having higher concentrations of HPMC or Compritol. Tablets with higher concentrations of Avicel showed reduced ability to retard the release of the drug from the tablet matrix. Crushing strength showed systematic dependence on the formulation factors and could be modeled using a reduced quadratic model. The crushing strength values were highest at high concentrations of Avicel, while tablets with a high level of Compritol showed the lowest values. A predicted optimum formulation was derived by a numerical, multiresponse optimization technique. The validity of the model for predicting physical attributes of the product was also verified by experiment. The observed responses from the calculated optimum formulation were in very close agreement with values predicted by the model. The utility of a mixture experimental design for selecting formulation components of a roller compacted product was demonstrated. These simple statistical tools can allow a formulator to rationally select levels of various components in a formulation, improve the quality of products, and develop more robust processes.     

Thermal instability in a micropolar fluid layer subject to a magnetic field

In the present paper we have considered thermal instability in a heat conducting micropolar fluid layer under the influence of a transverse magnetic field. Assuming the bounding surfaces to be rigid the eigenvalue problem is solved using finite-difference and Wilkinson's iteration techniques. Here it is seen that the instability sets in not only for adverse temperature gradient but also for positive temperature gradient. Both the microtation and the magnetic field are seen to stabilize the fluid layer. However, the stabilizing effect of microrotation becomes less significant when the strength of the magnetic field is large. In the case of heating from below, the critical wave number is seen to be insensitive to increase in the strength of the magnetic field, while it increases significantly when the fluid is heated from above.     

Kinetics of pyrolysis of pure and doped cobalt oxalate

The object of the present work was to illustrate the effect of impurities on the kinetics and energetics of the thermal decomposition of pure cobalt oxalate. Cationic impurities like Mg²⁺, Mn²⁺, Fe²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Zr⁴⁺ have been introduced into pure cobalt oxalate dihydrate and differential thermal analysis has been used to determine the enthalpy and energy of activation for the decomposition reaction of pure and doped samples.     

Microstructural and magnetic studies on P/M processed (Nd14.9Dy1.9)(Fe65.0Co8.0Cu1.0Ga1.0Nb0.7) B7.5 alloy

Sintered samples of (Nd_14.9 Dy_1.9) (Fe₆₅ Co₈ Cu_1.0 Ga_1.0 Nb_0.7)B_7.5 were prepared and subjected to stepwise annealing in the temperature range 875 K–675 K. The XRD and metallographic (optical and electron microscopy) studies reveal a multi-phase microstructure with each phase showing different solubility of the alloying additions. This alloy has T _C of 705 K with an intrinsic coercivity of 1000 kA/m and energy product of 250 kJ/m³ at RT. Solubility of Co into the matrix phase and that of Ga and Cu into the Nd-rich grain boundary phase are considered to be the main contributing factors for the significant enhancement in T _C and H _ci respectively of the multi-component alloy when compared to those of ternary NdFeB, wherein H _ci = 720 kA/m and T _C = 585 K.     

Fluorescence properties and energy transfer mechanism of Sm ion in lead telluroborate glasses

We report the fluorescence properties of Sm³⁺-doped lead telluroborate glasses of composition PbF₂.TeO₂.H₃BO₃.Sm₂O₃ as a function of Sm³⁺ concentration. A Judd-Ofelt scheme was used to determine the intensity parameters and radiative properties of Sm³⁺ ion. The emission and decay measurements were carried out at 402 nm excitation. Beyond 1.0 mol% Sm³⁺ concentration, the luminescence quenching is observed. The decay curves of ⁴G_5/2 level are well fitted to a single exponential function. The evaluated radiative properties suggest that the ⁴G_5/2 → ⁶H_7/2 transition is responsible for reddish-orange luminescence which might be used in the development of visible lasers.     

Ionic conduction in polyether-based lithium arylfluorosulfonimide ionic melt electrolytes

We report synthesis, characterization and ion transport in polyether-based ionic melt electrolytes consisting of Li salts of low-basicity anions covalently attached to polyether oligomers. Purity of the materials was investigated by HPLC analysis and electrospray ionization mass spectrometry. The highest ionic conductivity of 7.1 × 10⁻⁶ S/cm at 30 °C was obtained for the sample consisting of a lithium salt of an arylfluorosulfonimide anion attached to a polyether oligomer with an ethyleneoxide (EO) to lithium ratio of 12. The conductivity order of various ionic melts having different polyether chain lengths suggests that at higher EO:Li ratios the conductivity of the electrolytes at room temperature is determined in part by the amount of crystallization of the polyether portion of the ionic melt.