Non-isothermal crystallisation kinetics of self-assembled polyvinylalcohol/silica nano-composite

A novel polyvinylalcohol/silica (PVA/SiO₂) nano-composite is prepared with the self-assembly monolayer (SAM) technique. The SiO₂ nano-particles are homogenously distributed throughout the PVA matrixes as nano-clusters with an average diameter ranged from 15 to 240 nm depending on the SiO₂ contents. Using differential scanning calorimetry (DSC), the non-isothermal crystallisation behaviour and kinetics of the PVA/SiO₂ nano-composites are investigated and compared to those of the pure PVA. There are strong dependences of the degree of crystallinity (X_c), peak crystallisation temperature (T_p), half time of crystallisation (t_1/2), and Ozawa exponent (m) on the SiO₂ content and cooling rate. The crystallisation activation energy (E) calculated with the Kissinger model is markedly lower when a small amount of SiO₂ is added, then gradually increases and finally becomes higher than that of the pure PVA when there is more than 10% SiO₂ in the composite.

Consistent model predictions for isothermal cure kinetics investigation of high performance epoxy prepregs

An accurate kinetics model is essential for understanding the curing mechanism and predicting the end properties of polymer materials. Graphite/epoxy AS4/ 8552 prepreg is a recent high-performance thermosetting composite modified with thermoplastic, which is being used in the manufacture of aircraft and military structures. The isothermal cures of this system along with another thermoplastic toughened high-performance prepreg, the T800H/3900-2 system, were investigated by real-time Fourier transform infrared (FTIR) spectroscopy. The cure rate was quantitatively analyzed based on the concentration profiles of both the epoxy and primary amine groups. Three autocatalytic models were used to determine kinetics parameters for both composite systems. The model which utilizes an empirical term, the final relative conversion (at different isothermal curing temperatures), describes the experimental data of both systems more satisfactorily than the model which applies a diffusion factor. The modeling results suggest that the curing of epoxy within both prepregs can be assumed to be a second order process.

Effect of isothermal dissolution and re-precipitation of austenite on the mechanical properties of duplex structures

The hot deformation behaviour of a duplex ferritic/austenitic stainless steel was studied after different deformation conditions. The results showed a strange and interesting behaviour in the strength of the material during post-deformation studies. For most deformation conditions, the flow stress of the material was un-expectedly increased after annealing of deformed structures. This phenomenon implied that microstructural hardening occurred in the material during the interpass annealing rather than the expected softening. Also, an interesting change was observed where the morphology of the austenite phase changed from stringers or layers of austenite to a widmanstätten structure. The microstructural studies suggest that the austenite was dissolved and re-precipitated during the annealing process and the hardening was mostly associated with the change in the morphology of austenite.

Determining binding constants from 1H NMR titration data using global and local methods : a case study using [n]polynorbornane-based anion hosts

From data generated using 1H NMR titrations, different methodologies to calculate binding constants are compared. The ‘local’ analysis method that uses only a single isotherm (only one H-bond donor) is compared against the ‘global’ method (that includes many or all H-bond donors). The results indicate that for simple systems both methods are suitable, however, the global approach consistently provides a K a value with uncertainties up to 30% smaller. For more complex binding, the global analysis method gives much more robust results than the local methods. This study also highlights the need to explore several different modes when data do not fit well to a simple 1:1 complexation model and illustrates the need for better methods to estimate uncertainties in supramolecular binding experiments.

Effect of silicon and prior deformation of austenite on isothermal transformation in low carbon steels

Isothermal transformation (TTT) behavior of the low carbon steels with two Si contents (0.50 wt pct and 1.35 wt pct) was investigated with and without the prior deformation. The results show that Si and the prior deformation of the austenite have significant effiects on the transformation of the ferrite and bainite. The addition of Si refines the ferrite grains, accelerates the polygonal ferrite transformation and the formation of M/A constituents, leading to the improvement of the strength. The ferrite grains formed under the prior deformation of the austenite become more homogeneous and refined. However, the influence of deformation on the tensile strength of both steels is dependent on the isothermal temperatures. Thermodynamic calculation indicates that Si and prior deformation reduce the incubation time of both ferrite and bainite transformation, but the effiect is weakened by the decrease of the isothermal temperatures.

Textures and compressive properties of ferromagnetic shape-memory alloy Ni48Mn25Ga22Co5 prepared by isothermal forging process

A ferromagnetic shape-memory alloy Ni₄₈Mn₂₅Ga₂₂Co₅ was prepared by the induction melting and isothermal forging process. Dynamic recrystallization occurs during the isothermal forging. The deformation texture was studied by the neutron diffraction technique. The main texture components consist of (110)[112] and (001)[100], which suggested that in-plane plastic flow anisotropy should be expected in the as-forged condition. The uniaxial compression fracture strain in the forged alloy reaches over 9.5%. The final room-temperature fracture of the polycrystalline Ni₄₈Mn₂₅Ga₂₂Co₅ is controlled mainly by intergranular mode.

A tabular approach to titration calculations

Titrations are common laboratory exercises in high school and university chemistry courses, because they are easy, relatively inexpensive, and they illustrate a number of fundamental chemical principles. While students have little difficulty with calculations involving a single titration step, there is a significant leap in conceptual difficulty when “scaling-up” to more involved titration calculations with two or more steps. Currently, there is no alternative approach for students who are unable to follow the standard textbook method for titration calculations. This paper presents a new method of setting out the titration calculations, which helps these weaker students to better organize the data. The connection between the new method and current models of learning is discussed to explain why the tabular approach is successful for students who have difficulty following the standard textbook method.

Nurse-led titration of angiotensin converting enzyme inhibitors, beta-adrenergic blocking agents and angiotensin receptor blockers for patients with left ventricular systolic dysfunction

This is the protocol for a review and there is no abstract. The objectives are as follows:

To assess the effects of nurse-led titration of ACEIs, beta-adrenergic blocking agents and ARBs in patients with left ventricular systolic dysfunction in terms of safety and patient outcomes.