Extensive Annealing Research Articles

The Impact of Annealing Methods on the Encapsulating Structure and Storage-Stability of Freeze-Dried Pellets of Probiotic Bacteria

ObjectiveThis paper investigates the critical role of material thickness in freeze-dried pellets for enhancing the storage stability of encapsulated bacteria. Freeze dried material of varying thicknesses obtained from different annealing durations is quantified using Scanning Electron Microscopy (SEM) and X-ray microtomography (μCT), the material thickness is then correlated to the storage stability of the encapsulated cells.MethodsA formulation comprising of sucrose, maltodextrin, and probiotic cells is quenched in liquid nitrogen to form pellets. The pellets undergo different durations of annealing before undergoing freeze-drying. The material thickness is quantified using SEM and μCT. Storage stability in both oxygen-rich and oxygen-poor environments is evaluated by measuring CFU counts and correlated with the pellet structure.ResultsThe varying annealing protocols produce a range of material thicknesses, with more extensive annealing resulting in thicker materials. Storage stability exhibits a positive correlation with material thickness, indicating improved stability with thicker materials. Non-annealed pellets exhibit structural irregularities and inconsistent storage stability, highlighting the impracticality of avoiding annealing in the freeze-drying process.ConclusionsExtensive annealing not only enhances the storage stability of probiotic products but also provides greater control over the freeze-drying process, ensuring homogeneous and reproducible products. This study underscores the importance of material thickness in freeze-dried pellets for optimizing storage stability for probiotic formulations, and emphasize the necessity of annealing as a critical step in freeze-drying quenched pellets to achieve desired structural and stability outcomes.

Fold, Twist, and Draw – Techniques of Copper Alloy Wire Production from Hellenistic Jebel Khalid

Abstract Copper alloy wire fragments were examined using XRF, optical light microscopy and SEM-EDS. The specimens come from archaeological excavations at Jebel Khalid in Syria, dating from the 3rd century BCE (the Hellenistic period) to the Roman period. Our results show that several techniques were employed to make the wires: forging, folding, strip twisting, and possibly ‘strip drawing’. We investigated the morphologies, treatments, and fabrications attributed to making wire from copper alloys compared to more ductile materials such as gold and silver. Evidence of extensive annealing and non-uniform, sub-round profiles, and uneven and faceted surfaces represent the challenges of working with the material. There is no obvious evidence of solid wire drawing. The metalworkers used different copper alloys to make wire, some with high levels of lead (Pb). Subtle joins were observed in some samples, whereas others had evident folds and directional structures. The findings contribute new evidence to enhance our understanding of base-metal wire development in antiquity.

Influence of Melt‐Peridotite Interactions on Deformation and Seismic Properties of the Upper Mantle Beneath a Destroyed Craton: A Case Study of the Damaping Peridotites From the North China Craton

AbstractExtensive melt‐peridotite interactions had been documented in the lithospheric mantle beneath the North China Craton (NCC), a prime example of destroyed cratons in the world. Yet the impacts of melt‐peridotite interactions on the deformation and seismic anisotropy of the NCC upper mantle remain unclear. Here we studied in detail the microstructure, crystallographic preferred orientation (CPO) of minerals, and seismic properties of 26 peridotite xenoliths from the Damaping area of the NCC. The studied samples can be classified into two groups: weakly to nonfoliated and strongly foliated. Petrographic and microstructural observations suggest that multiple melt‐peridotite interactions and at least two stages of deformation had influenced samples from both microstructural groups. Dislocation creep in response to a transpression deformation led to the [010]‐fiber type olivine CPOs in most samples. Variable degrees of annealing followed the last stage of deformation. Due to a higher degree of melt‐peridotite interactions, which had promoted nondislocation creep, and more extensive annealing, olivine and pyroxene in the strongly foliated samples developed weaker CPOs. This in turn leads to weaker maximum P wave propagation anisotropy and S wave polarization anisotropy for this microstructural group. Our data, therefore, cast light on a strong control of intensity of melt‐peridotite interactions on deformation and seismic properties of the upper mantle beneath the NCC. If foliation and lineation are vertical and horizontal, respectively, the measured SKS splitting parameters can be well explained by the “fossil” anisotropy frozen in the lithospheric mantle, with no need to invoke asthenospheric flow as a source of the anisotropy.

High β‐phase Poly(vinylidene fluoride) Using a Thermally Decomposable Molecular Splint

AbstractAn additive, 1,4‐butadiene sulfone (BDS), which generates H2SO3 by in situ thermal retro‐Diels‐Alder decompositions, is used for preparing high β‐phase polyvinylidene fluoride (PVDF) films. Because of preferential multiple non‐covalent interactions of H2SO3 with all‐trans configuration of PVDF, β‐phase PVDF is spontaneously induced without mechanical drawing and/or extensive thermal annealing process. PVDF films cast from PVDF/BDS/water solutions exhibit high β‐phase content (fβ = 95%) when the BDS concentration is only cBDS = 1.0 wt%, which is confirmed by polarized optical microscopy (POM), SEM, Fourier transform infrared spectroscopy (FT‐IR), differential scan calorimetry (DSC), and 2D grazing incidence wide‐angle X‐ray scattering (GIWAXS). Because of the high β‐phase content, PVDF films prepared by using BDS exhibit excellent ferroelectric and piezoelectric properties (Ec = 50 MV/m, Pr = 5 µC/cm2, and d33 = ≈‐25 pm/V). Furthermore, a triboelectric nanogenerator (TENG) developed with high β‐phase PVDF film exhibits enhanced performance as 2.5 times higher than neat PVDF film in output charge density, allowing reliable operation of conventional electronic devices.

Structural Investigations of Polycarbonates whose Mechanical and Erosion Behavior Can Be Controlled by Their Isomer Sequence

One of the challenges in materials science is to design functional, synthetic polymers that match the desired properties of a specific application. Achieving high stiffness and strength under physiological conditions while maintaining the proper erosion profile is particularly difficult. This challenge is addressed here by synthesizing polymers with sequence control followed by optimal processing of the polymer. A new class of biodegradable, aromatic–aliphatic polycarbonates based on tyrosol, a naturally derived (hydroxy)alkyl phenol with an alternating (altTyPC) or scrambled (scrTyPC) sequence, is reported. AltTyPC contained strictly alternating sequences of diaryl (head-to-head, HH) and dialkyl (tail-to-tail, TT) carbonate backbone isomers; this was accomplished by using preprogrammed diaryl carbonate diol and triphosgene in polycondensation. The scrambled sequence (scrTyPC) of HH, TT, and the aryl-alkyl (head-to-tail, HT) carbonate isomers was obtained by direct polymerization of tyrosol. The isomer sequence had a large effect on the thermal behavior: altTyPC rapidly transitioned from the amorphous phase into a 1D mesophase at 90 °C and then into a 3D crystalline phase at 150 °C before melting at 204 °C; in contrast, scrTyPC remained in a 1D mesophase after extensive annealing at 100 °C for 20 h and melted at 149 °C. The modulus of the oriented, semicrystalline altTyPC films was higher than that of the similarly processed scrTyPC films (5.4 ± 0.3 vs 3.8 ± 0.2 GPa). The erosion behavior was also different: AltTyPC showed more rapid mass and thickness loss over time than scrTyPC. Thus, a combination of sequence control and processing optimization in aromatic–aliphatic polycarbonates gives rise to a new platform of tunable polymers for numerous applications.

Geochemical evolution of the lithospheric mantle beneath the Styrian Basin (Western Pannonian Basin)

The Styrian Basin is located at the westernmost part of the Carpathian-Pannonian region, in the transition zone between the Pannonian Basin and the Eastern Alps. The lithospheric mantle beneath the Styrian Basin (SB) was sampled by Plio-Pleistocene alkali basalts, which brought mantle xenoliths to the surface. Mantle xenoliths from the SB are mostly coarse granular, amphibole-bearing spinel lherzolites with microstructures indicating extensive annealing. Three geochemical events were recorded in the SB xenoliths. The initial, ancient partial melting event was followed by an old metasomatism, which formed lithological heterogeneities (e.g. websterite, dunite) occurring as veins, bands and layers. The most recent geochemical event recorded in the SB xenoliths is the migration of a hydrous alkaline melt originating from a nephelinitic melt source. This melt migrated from the asthenosphere, forming melt channels in the lithospheric mantle. Close to the channels, the metasomatic agent caused extensive amphibole and sparse phlogopite formation. This particular pargasite-phlogopite equilibrium mineral assemblage in the spinel facies was not described before in the literature based on our knowledge. The reaction caused significant enrichment in basaltic elements (such as Ti, Fe), K, light rare earth elements and incompatible trace elements such as Zr and Hf. Further from the channels, the metasomatic melt became enriched in volatiles (mainly H2O and CO2) and fluid mobile elements (e.g. U, Pb, Cl and P), but depleted in basaltic elements, K and LREE, which resulted in modal decrease of amphiboles. Previous studies suggested a dehydrating subducted slab beneath the Styrian Basin, however geochemical fingerprints of subducted slab derived fluids were recognized only in one xenolith. Mantle portions with different geochemical characteristics developed in the lithosphere laterally, however metasomatic fingerprints were erased later due to annealing and chemical re-equilibration at ambient mantle conditions. The Neogene evolution of the lithosphere overwrote the previous state of the upper mantle beneath the region, thus the signs of the most recent metasomatism by nephelinitic melts could have been only preserved due to this extensive annealing event.

Comparison of D-Wave Quantum Annealing and Classical Simulated Annealing for Local Minima Determination

Restricted Boltzmann Machines trained with different numbers of iterations were used to provide a diverse set of energy functions each containing many local valleys (LVs) with different energies, widths, escape barrier heights, etc. They were used to verify the previously reported possibility of using the D-Wave quantum annealer (QA) to find potentially important LVs in the energy functions of Ising spin glasses that may be missed by classical searches. For classical search, extensive simulated annealing (SA) was conducted to find as many LVs as possible regardless of the computational cost. SA was conducted long enough to ensure that the number of SA-found LVs approaches that and eventually significantly exceeds the number of the LVs found by a single call submitted to the D-Wave. Even after a prohibitively long SA search, as many as 30-50% of the D-Wave-found LVs remained not found by the SA. In order to establish if LVs found only by the D-Wave represent potentially important regions of the configuration space, they were compared to those that were found by both techniques. While the LVs found by the D-Wave but missed by SA predominantly had higher energies and lower escape barriers, there was a significant fraction having intermediate values of the energy and barrier height. With respect to most other important LV parameters, the LVs found only by the D-Wave were distributed in a wide range of the parameters' values. It was established that for large or small, shallow or deep, wide or narrow LVs, the LVs found only by the D-Wave are distinguished by a few-times smaller size of the LV basin of attraction (BoA). Apparently, the size of the BoA is not or at least is less important for QA search compared to the classical search, allowing QA to easily find many potentially important (e.g., wide and deep) LVs missed by even prohibitively lengthy classical searches.

Room‐Temperature Partial Conversion of α‐FAPbI3Perovskite Phase via PbI2Solvation Enables High‐Performance Solar Cells

AbstractThe two‐step conversion process consisting of metal halide deposition followed by conversion to hybrid perovskite has been successfully applied toward producing high‐quality solar cells of the archetypal MAPbI3hybrid perovskite, but the conversion of other halide perovskites, such as the lower bandgap FAPbI3, is more challenging and tends to be hampered by the formation of hexagonal nonperovskite polymorph of FAPbI3, requiring Cs addition and/or extensive thermal annealing. Here, an efficient room‐temperature conversion route of PbI2into the α‐FAPbI3perovskite phase without the use of cesium is demonstrated. Using in situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) and quartz crystal microbalance with dissipation (QCM‐D), the conversion behaviors of the PbI2precursor from its different states are compared. α‐FAPbI3forms spontaneously and efficiently at room temperature from P2(ordered solvated polymorphs with DMF) without hexagonal phase formation and leads to complete conversion after thermal annealing. The average power conversion efficiency (PCE) of the fabricated solar cells is greatly improved from 16.0(±0.32)% (conversion from annealed PbI2) to 17.23(±0.28)% (from solvated PbI2) with a champion device PCE > 18% due to reduction of carrier recombination rate. This work provides new design rules toward the room‐temperature phase transformation and processing of hybrid perovskite films based on FA+cation without the need for Cs+or mixed halide formulation.

WO2 triggered nucleation and growth of ultra-long W18O49 structures, from nanobundles to single-crystalline microrod

W18O49 has exceptional electronic and electro-chromic properties and has been synthesized in various morphologies for applications in nanodevices. Nevertheless, the controlled growth of nanostructured W18O49 with desirable morphology is not yet achieved, and the growth mechanism is not yet clear. In this work, we synthesized ultra-long single-crystalline W18O49 micron-rods via heating W matrix under an atmosphere-Ar flow, and systematically investigated the nucleation and growth by detailed microstructural characterization. The presence of WO2 interlayer above the W matrix was reported for the first time, which was confirmed to play a key role in the epitaxial nucleation of W18O49. Extensive annealing led to the growth of WO2 grain and W18O49 nanostructures into micron-rods, which suggests that W18O49 diameter is controlled by WO2 grain size. This study is helpful in the design of W18O49 nanostructures for various applications.

Fluid‐Enhanced Annealing in the Subcontinental Lithospheric Mantle Beneath the Westernmost Margin of the Carpathian‐Pannonian Extensional Basin System

AbstractMantle xenoliths from the Styrian Basin Volcanic Field (Western Pannonian Basin, Austria) are mostly coarse granular amphibole‐bearing spinel lherzolites with microstructures attesting for extensive annealing. Olivine and pyroxene CPO (crystal‐preferred orientation) preserve nevertheless the record of coeval deformation during a preannealing tectonic event. Olivine shows transitional CPO symmetry from [010]‐fiber to orthogonal type. In most samples with [010]‐fiber olivine CPO symmetry, the [001] axes of the pyroxenes are also dispersed in the foliation plane. This CPO patterns are consistent with lithospheric deformation accommodated by dislocation creep in a transpressional tectonic regime. The lithospheric mantle deformed most probably during the transpressional phase after the Penninic slab breakoff in the Eastern Alps. The calculated seismic properties of the xenoliths indicate that a significant portion of shear wave splitting delay times in the Styrian Basin (0.5 s out of approximately 1.3 s) may originate in a highly annealed subcontinental lithospheric mantle. Hydroxyl content in olivine is correlated to the degree of annealing, with higher concentrations in the more annealed textures. Based on the correlation between microstructures and hydroxyl content in olivine, we propose that annealing was triggered by percolation of hydrous fluids/melts in the shallow subcontinental lithospheric mantle. A possible source of these fluids/melts is the dehydration of the subducted Penninic slab beneath the Styrian Basin. The studied xenoliths did not record the latest large‐scale geodynamic events in the region—the Miocene extension then tectonic inversion of the Pannonian Basin.

Metal-insulator transition and nonlinear optical responseof sputter-deposited V3O5 thin films

The compound V3O5, a member of the vanadium oxide Magnéli series, exhibits a metal-insulator transition near 430 K, the highest known temperature value among all vanadium oxides. It has been studied before mainly in single-crystal form, and for the very few cases in which thin films have been fabricated before, the procedure has required extensive post-deposition annealing of other oxides or vanadium metal at high temperatures in tightly controlled atmospheres. For the present work, V3O5 films were deposited directly on SiO2 glass substrates, without subsequent annealing, by DC magnetron sputtering. X-ray diffraction study of the samples evidenced oxygen deficiency, accommodated by oxygen vacancies. Resistivity measurements from 300 to 500 K revealed the metal-insulator transition by Tc ∼ 430 K, with an associated resistivity change by a factor of 20, and no detectable hysteresis in heating-cooling cycles, in agreement with most single-crystal studies. Resistivity values obtained were, however, lower than published results for bulk crystal values, particularly at temperatures below Tc. This was attributed to conduction electrons generated by the oxygen vacancies. Gradual resistivity increase in a very thin sample, through heating in air at temperatures up to 500 K, lends support to this argument. Using a pump-probe scattering technique, the V3O5 films were also probed for ultrafast nonlinear optical response. A reduction in the transient relative scattered light signal was recorded, which reached –10% within ∼800 fs. This observed response, likely related to the photoinduced insulator-to-metal phase transition, should stimulate additional interest in this material.

Sol-gel hot injection synthesis of ZnO nanoparticles into a porous silica matrix and reaction mechanism

Despite the enormous interest in the properties and applications of porous silica matrix, only a few attempts have been reported to deposit metal and metal oxide nanoparticles (NPs) inside the porous silica matrix. We report a simple approach (i.e. sol-gel hot injection) for insitu synthesis of ZnO NPs inside a porous silica matrix. Control of the Zn:Si molar ratio, reaction temperature, pH value, and annealing temperature permits formation of ZnO NPs (≤10nm) inside a porous silica particles, without additives or organic solvents. Results revealed that a solid state reaction inside the ZnO/SiO2 nanocomposites occurs with increasing the annealing temperature. The reaction of ZnO NPs with SiO2 matrix was insignificant up to approximately 500°C. However, ZnO NPs react strongly with the silica matrix when the nanocomposites are annealed at temperatures above 700°C. Extensive annealing of the ZnO/SiO2 nanocomposite at 900°C yields 3D structures made of 500nm rod-like, 5–7μm tube-like and 3–5μm needle-like Zn2SiO4 crystals. A possible mechanism for forming ZnO NPs inside porous silica matrix and phase transformation of the ZnO/SiO2 nanocomposites into 3D architectures of Zn2SiO4 are carefully discussed.

Microstructural evolution and thermal stability of Fe–Zr metastable alloys developed by mechanical alloying followed by annealing

The effect of Zr (up to 1 at.%) addition on the formation of Fe–Zr metastable alloys and their thermal stability were investigated for their possible nuclear applications. Fe–xZr (x = 0.25, 0.5, 1%) alloys were synthesised by mechanical alloying under a high-purity argon atmosphere using stainless steel grinding media in a SPEX 8000M high energy mill. The milling was conducted for 20 h with a ball-to-powder weight ratio of 10:1. The formation of metastable solid solutions after milling was confirmed from the change in the Gibbs free energy analysis as per Miedema’s model. The microstructural characterisation was carried out by analysis of X-ray diffraction, atomic force microscopy and transmission electron microscopy. The effect of Zr on the thermal stability of Fe–Zr alloys was investigated by extensive annealing experiments followed by microstructural analysis and microhardness measurements. The stabilisation was found to occur at 800 °C and thereafter, no significant change in the crystallite size was observed for the samples annealed between 800 and 1200 °C. The supersaturated solid solution, especially 1% Zr alloy, found to be highly stable up to 800 °C and the microhardness value of the same measured to be as high as 8.8 GPa corresponding to a crystallite size of 57 nm. The stabilisation effect has been discussed in the light of both the thermodynamic and kinetic mechanisms and the grain size stabilisation is attributed to the grain boundary segregation of Zr atoms and/or Zener pinning by nanoscale precipitation of the Fe2Zr phase.

Surfactant stabilisation of colloidal lignin microparticulates produced through a solvent attrition process

Abstract The stabilisation of insoluble lignin microparticulates produced through solvent attrition in aqueous media containing surfactants has been investigated. In the absence of added surfactants, addition of solvent solubilised lignin to water caused extensive precipitation and annealing of lignin, leading to the formation of large, agglomerated structures in the approximate size range of 20–200 μm. Addition of high HLB non-ionic surfactants (Polysorbate 20/sucrose ester) to the aqueous solution prior to lignin precipitation had only limited effect on the size of agglomerates produced, with a partial decrease in mean aggregate size at elevated surfactant concentrations, and no observed effect at low surfactant concentrations. In contrast, addition of either negatively (SDS) or positively (CTAB) charged ionic surfactants at concentrations Findings indicate that adsorption of charged surfactants to the surface of lignin particles during precipitation is able to provide effective electrostatic stabilisation; however, no such stabilising effect is provided by non-ionic surfactants. Furthermore, it appears that the size and stability of the particles produced is dependent on the conditions within the aqueous phase during precipitation. In this way, it may be possible to produce lignin microparticles with tailored particle distributions.

Absorption spectroscopy of heavy alkaline earth metals Ba and Sr in rare gas matrices--CCSD(T) calculations and atomic site occupancies.

Isolation of the heavier alkaline earth metals Ba and Sr in the solid rare gases (RGs) Ar, Kr, and Xe is analysed with absorption spectroscopy and interpreted partly with the assistance of ab initio calculations of the diatomic M ⋅ RG ground state interaction potentials. The y(1)P ← a(1)S resonance transitions in the visible spectral region are used to compare the isolation conditions of these two metal atom systems and calcium. Complex absorption bands were recorded in all three metal atom systems even after extensive sample annealing. Coupled cluster calculations conducted on the ground states of the nine M ⋅ RG diatomics (M = Ca, Sr, and Ba; RG = Ar, Kr, and Xe) at the coupled cluster single, double, and non-iterative triple level of theory revealed long bond lengths (>5 Å) and shallow bound regions (<130 cm(-1)). All of the M ⋅ RG diatomics have bond lengths considerably longer than those of the rare gas dimers, with the consequence that isolation of these metal atoms in a single substitutional site of the solid rare gas is unlikely, with the possible exception of Ca/Xe. The luminescence of metal dimer bands has been recorded for Ba and Sr revealing very different behaviours. Resonance fluorescence with a lifetime of 15 ns is observed for the lowest energy transition of Sr2 while this transition is quenched in Ba2. This behaviour is consistent with the absence of vibrational structure on the dimer absorption band in Ba2 indicating lifetime broadening arising from efficient relaxation to low-lying molecular states. More extensive 2D excitation-emission data recorded for the complex site structures present on the absorption bands of the atomic Ba and Sr systems will be presented in future publications.

Polymer Soft-Landing Isolation of Acetylene on Polystyrene and Poly(vinylpyridine): A Novel Approach to Probing Hydrogen Bonding in Polymers.

Hydrogen-bonded complexes of acetylene (Ac) with the polymers polystyrene (PS), poly(4-vinylpyridine) (P4VP), and poly(2-vinylpyridine) (P2VP) have been characterized for the first time at 16 K in a "polymer soft-landing isolation" experiment which is being pioneered in our research laboratory. In particular, changes in vibrational modes of Ac provide ample evidence for hydrogen-bonded complexes between Ac and the phenyl groups of PS or the pyridyl groups of P4VP and P2VP. With PS, the proton on the top Ac molecule of the classic T-shaped Ac dimer interacts with the π cloud of the benzene (Bz) ring to form a C-H---π interaction, while the π cloud of the lower Ac forms a second C-H---π interaction with a proton on the Bz ring. An analogous (ring)1-(Ac)2 double interaction occurs between an Ac dimer and the pyridine (Pyr) rings on both P2VP and P4VP, yielding a C-H---N and C-H---π interaction. With P4VP and P2VP a second bridged (ring)2-(Ac)2 product is formed, with the Ac dimer forming nearly collinear C-H---N hydrogen bonds to adjacent Pyr rings. On P2VP this bridged product is the only one after extensive annealing. These complexes in which Ac acts as both proton donor and acceptor have not previously been observed in conventional matrix isolation experiments. This study is the second from our laboratory employing this method, which represents a slight modification of the traditional matrix isolation technique.

A neutron spin echo resolved grazing incidence scattering study of crystallites in organic photovoltaic thin films

Neutron spin echo resolved grazing incidence scattering (SERGIS) was used to probe crystallites of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) produced by extensive thermal annealing of a poly(3-hexylthiophene-2,5-diyl)(P3HT):PCBM organic photovoltaic layer. After annealing a thin film of P3HT:PCBM, PCBM crystallites appear on the sample surface, and a strong SERGIS signal is observed superimposed on the specular reflection. Features in the data can be readily correlated with length scales of the crystallites determined using atomic force microscopy and indicate that in such cases the SERGIS signal may be interpreted as a form of small angle neutron scattering.

Beneficiation of coal fly ashes by oxygen chemisorption

This paper addresses the issue of unburnt carbon in fly ashes from coal-fired power stations. It has been shown that carbon-in-ash has much lower combustion reactivity than the original coal, because of the extensive thermal annealing experienced in the boiler. Thermal annealing reduces the rate of the first reaction step of which carbon combustion is composed, namely oxygen chemisorption. In the present work experiments have been carried out in order to verify if a preconditioning stage consisting of mild pre-oxidation with air is able to promote oxygen chemisorption thus increasing the combustion reactivity of ashes. Fly ashes with high LOI have been exposed to air at temperature <400°C for times up to 300min. Results show that a satisfactory extent of oxygen chemisorption can be attained at 300–400°C with 1–2h holding time. After this conditioning, samples have been tested to check their combustion reactivity by means of non isothermal thermogravimetric analysis. Additionally, combustion experiments have been carried in a purposely designed suspension reactor at temperatures up to 1000°C. Results confirm that ash pre-conditioning reduces the burn-out time of carbon in ash. The concept has been finalized into an international patent application.

Thermodynamic feasibility of solid solubility extension of Nb in Cu and their thermal stability

A series of Cu–xNb (x = 1–15 at.%2) alloys have been investigated to study the metastable solid solubility extension of Nb in Cu by mechanical alloying. Analysis of X-ray diffraction and Gibbs free energy change confirmed that 7.5% of Nb was metastably dissolved in Cu after 8 h of milling at room temperature although Cu–Nb is a system with positive heat of mixing. The solid solubility could be extended up to 10% after enhancing milling duration to 16 h. Detailed thermodynamic analysis revealed that the additional energy stored during mechanical alloying could overcome the required energy barrier as per Miedema's model for the formation of disordered solid solution. The extended solid solubility has been explained along with the other possible mechanisms. Extensive annealing experiments and structural investigation revealed that the supersaturated solid solution is completely stable up to 400 °C. The matrix grains were stabilized and retained their size, ∼25 nm, even after annealing at 600 °C. Microhardness measurement and grain size analysis show that the dissolution of Nb in Cu has a larger strengthening effect than that of free Nb in the compositions.

Optical property improvement of InAs/GaAs quantum dots grown by hydrogen-plasma-assisted molecular beam epitaxy

An order-of-magnitude increase of photoluminescence (PL) efficiency at room temperature has been observed in the GaAs/InAs quantum dots (QDs)-in-a-well structure grown with in situ irradiation of atomic hydrogen supplied by a radio-frequency hydrogen-plasma source. The enhancement in PL intensity rapidly increases with the hydrogen flow rate and is stable with a variation of excitation power in the radio-frequency plasma source. Extensive thermal annealing of grown samples up to 634 °C did not show any significant degradation of photoluminescence intensity compared with the reference sample. The reduction of nonradiative recombination centers in the as-grown sample causes the greatly enhanced luminescence property. In addition to PL enhancement the authors observed that the H-assisted growth of InAs QDs has suppressed bimodal distribution of QD shape. In contrast to the hydrogen-plasma-assisted growth, irradiation by hydrogen in molecular form has a detrimental effect on the optical properties of similar structures. The high thermal stability of improved optical properties suggests that the formation of the defects which are responsible for nonradiative recombination channels is suppressed during H-assisted epitaxy although in situ defect passivation by atomic hydrogen cannot be completely ruled out.