Heat Treatments

AlSi8Cu3Fe alloy is a general purpose die casting alloy widely used to manufacture automotive parts. Forming of this alloy in the semi-solid state could largely eliminate problems inherent in die casting process and thus offers a number of advantages. Low superheat casting was employed in the present work to produce non-dendritic AlSi8Cu3Fe alloy feedstock. The ingots thus obtained were thixoformed in a laboratory press after they were held at 570 °C for 5 min, yielding a microstructure with predominantly α-Al globules and interglobular Si particles. The thixoformed parts attain hardness values as high as 125 HB after T6 heat treatment, implying a considerable age hardening potential. However, with a reheating temperature range of 568–572 °C, thixoforming of AlSi8Cu3Fe alloy components under industrial conditions may be challenging.

Lead zirconate titanate (PZT) fibers are prepared by the sol–gel method using acetic acid and methacrylic acid to control the pH of the PZT precursor sol. The chemical evolution of the precursors, the thermal and crystallization behavior of the PZT gel fibers, and the microstructure of the samples with and without acid addition are analyzed and compared. It is observed that the properties of the fibers are improved when acids are used; particularly longer PZT ceramic fibers (4–5 cm) are obtained after heat treatment and a single perovskite phase is obtained at 550°C when using methacrylic acid. The mechanisms of the acid effect on the strengthening and crystallization of PZT fibers are discussed.

The metastable zone width (MSZW), induction time and primary nucleation kinetics have been measured and estimated for simultaneous anti-solvent and cooling crystallization of paracetamol in iso-propanol/water solution. ATR-FTIR spectroscopy and laser back-scattering are used to measure the solute concentration and primary nucleation event, respectively. Response surface analysis was applied to find the contribution of the crystallization mechanism on the MSZW and obtain a statistical model for quick estimation of the MSZW. Two theoretical approaches for the estimation of nucleation rate kinetic parameters from experimental data are presented. The methods are obtained by modifying the classical Nyvlt's correlation for simultaneous cooling/anti-solvent crystallizations. The nucleation order n for primary nucleation was deduced from the slope of a linear plot of log(MSZW) vs. log(cooling and anti-solvent rates). The induction time was also estimated by changing the classical methods for combined cooling and anti-solvent crystallization.

In this study, effects of stirring time and stirring speed on the microstructure of semisolid rheocast (SSR) Al–7.1 wt.%Si were examined. The results demonstrated that the non-dendritic structure could be formed by a short stirring period below liquidus temperature and further stirring had little impact on the final morphology of the primary particles. Stirring was shown, however, to affect the average particles size mainly during the initial stages of solidification. Although the average shape factor of primary particles was relatively insensitive to large variations in the stirring speed, higher stirring speeds made the shape and size of the primary particles more uniform. Higher stirring speeds also rendered smaller and more rounded agglomerates of primary particles. The results of two stability models employed suggest that, in general, the primary particles generated in the initial stages of solidification can attain growth stability before pouring and maintain this stability during the secondary cooling stage.

The behaviors of thermally stimulated electron emission from pyroelectric monodomain lithium niobate single crystal (LiNbO 3) were investigated by utilizing a Si p-n junction photodiode as electron detector and a receptive electron beam resist (E-beam resist) as electron collector. In high vacuum (10 -6 Torr), the pyroelectric electron emission (PEE) was found to depend on the exposed emitting polar crystal surface (+ Z face or - Z face) and was significantly influenced by the emitter-electron receiver gap distances. Thus, the PEE from + Z face was detected during heating and was activated, in small gaps (<2 mm), by field emission effect on which was superposed an intense field ionization effect that primed intermittent runway ionizations (plasma breakdown into a glow discharge). In large gaps (>2 mm) the emission was simply mastered by field emission effect. Whereas, The PEE from - Z face was detected during cooling and was solely due to the field ionization effect. Therewith, for small gaps (<2 mm) the emission was governed by intermittent runway ionization ignitions resulting from a high ionization degree leading to dense plasma formation, and for large gaps (>2 mm) PEE was governed by field ionization generating a soft and continuous plasma ambient atmosphere. Significant decrease of electron emission current was observed from + Z face after successive thermal cycles. A fast and fully emission recovery was established after a brief exposure of crystal to a poor air vacuum of 10 -1 Torr.

Nanocrystalline metal molybdates [i.e., AMoO4, where A=Ca(II), Co(II), Cu(II), Ni(II), and Zn(II)] powders have been prepared from the complete evaporation of a polymer-based metal-complex precursor solution. The metal ions are in aqueous solution through complexion with triethanolamine (TEA) and are dispersed in a polymeric reagent composed of an aqueous solution mixture of sucrose and polyvinyl alcohol (PVA). The mesoporous carbon-rich precursor powders has been obtained on complete dehydration of the precursor solution and generates the respective metal molybdate phase after complete removal of carbonaceous residue at a heat treatment temperature less than 500 °C. X-ray diffractometry (XRD), Differential Thermal Analysis and Thermogravimetric Analysis (TG/DTA), and Transmission Electron Microscopy (TEM) have been used to characterize the preprecursors and the heat-treated final powders. The average particle sizes as measured from X-ray line broadening and transmission electron mi...

Environmental factors significantly influence concrete surfaces. Infrastructures
are affected by variety climatic conditions including: extreme temperatures,
droughts, moist and humid conditions or even inundation, and they are more likely to
experience negative influences on their concrete surfaces. Thus, this research aims to
identify sustainable solutions to decrease the vulnerability of concrete exposed to
climatic and environmental influences by assessing the response of concrete surfaces
to high solar radiation, high temperatures, and wet weather conditions.
Our results within warm and tropical regions show that temperature fluctuations
lead to expansion and shrinkage of concrete, particularly in buildings with poor
thermal insulation. Including iron components are prone to these shrink-swell
processes, causing crack development and expansion over time. Then, this study is
suggested some responding solutions including; plant covering over concrete surfaces
of the structures as well as use of some light-coloured silicates to reduce solar
radiation absorption.
Another focus of this study is to analyse the roles of some environmental factors
including salinity, humidity, rain, and snow that may influence the concrete surfaces,
particularly within wet and coastal regions. Previous studies show that the
permeability of concrete surfaces increase the Infiltration of water which can lead corrosion of iron components, and salt accumulation within cavities, particularly
affecting coastal-zone infrastructures. Thus, a suggestion of high-density, low-porous
concrete to be used to prevent the diffusion of water into concrete surfaces.
The concrete surface problems that are occurring due to various environmental
factors can cause severe damage. The corrosions including peeling process is an
example of such damage that often is not-repairable. Notably, if peeling occurs within
the primary reinforcing structure, the metal bodies are likely exposed to corrosion,
which then requires a greater response to be fixed. Thus, the information provided in
this study yield base suggestions which can support informed decision-making during
planning and construction stages to sustain longer-lasting concrete surfaces under
different environmental conditions. Additionally, the concrete material industry can
benefit from this research, as the findings provide guidance to the use of more suitable
materials for improved structural integrity under various climatic conditions.

Cold-rolled steels based on 0.15C–1.5Mn–1.5Si–0.5Cu containing Cr or/and Ni were prepared, and intercritical annealing and isothermal treatment, were carried out. The addition of Cu or Cu+Ni resulted in a large increase of the retained austenite volume fraction as well as an improvement of elongation and the strength-ductility balance. However, the addition of Cr or Cu+Ni showed a dual-phase deformation behavior having higher tensile strength and lower elongation.

Various heat-treatment schedules have been applied to the optimization of Tc and Jc,m in bulk MgB 2. Samples were prepared by first mixing in a ‘V’ shaped mixer and then planetary milling a stoichiometric mixture of Mg and B powders. These powders were then compacted and heat-treated at different schedules under 200 Torr of Ar. The heat-treating schedules investigated involved different time-temperatures, heating rates, and cooling rates. Magnetic critical current densities (at 20 K) of more than 2 × 10 5 A/cm 2 in 10 kOe and 4 × 10 5 A/cm 2 in 5 kOe were obtained. The influence of sodium silicate additions on the bulk properties has been studied.