Effect of quenching temperature on the structure of isotactic polypropylene films

Films of isotactic polypropylene (iPP) were quenched at different temperatures. Wide-angle x-ray diffractograms for these samples show the presence of the smectic form of iPP at low quenching temperatures and the appearance of mono-clinic form on increasing the thickness of the substrate and the quenching temperature. A quenching temperature higher than 80°C produces only the monoclinic form of iPP, whereas at intermediate temperatures we obtain three-phase amorphous-smectic-crystalline systems. Except for the two-phase amorphous-crystalline system obtained at high temperatures, density values alone do not allow us to obtain the three-phase fractions. We studied the transport properties, sorption, and diffusion of CH₂Cl₂ vapor in these systems to investigate the thermodynamic state of the amorphous component. The behavior of the amorphous component with respect to the diffusion of CH₂Cl₂, which proved identical in all the samples, led us to conclude that at low penetrant activity the smectic phase is not permeable, and therefore we were able to obtain the amorphous fraction in each sample. This value together with density values allowed the determination of the complete composition in terms of three phases for every sample. The crystalline fraction expressed as % mono-clinic form is very well correlated with the reciprocal of the half-height broadening of the (110) diffraction peak at about 2e = 14°.     

Fabrication and analysis of the structural phase transition of ZrO2 nanoparticles using modified facile sol–gel route

The synthesis of zirconia nanoparticles is achieved through a modified facile sol–gel route. The as-prepared gel is analyzed thermally using TGA and DTA techniques to spot the crystallization process of zirconia nanoparticles. The prepared gel is then annealed at different temperatures and the structure was found to change between tetragonal and monoclinic crystal systems. The first stable tetragonal phase is achieved after annealing for 2?h at 400°C. The annealed powders between 600°C and 800°C demonstrate mixed tetragonal/monoclinic phases. Annealing at 1000°C and higher temperatures up to 1200°C resulted in pure monoclinic phase. Cubic phase was not detected within the annealing temperature range in this study. The elemental analysis of the annealed powder confirmed the formation of zirconia nanoparticles with the chemical formula ZrO₂. The FTIR spectra of the annealed samples introduced a variation in the vibrational bands especially around the phase transition temperature. HR-TEM images reported the formation of nano-zirconia crystals with apparently large particle sizes. The optical energy gap of zirconia nanoparticles is investigated and determined.     

In situ confocal micro‐Raman spectroscopic investigation of rearrangement kinetics and phase evolution of UHMWPE during annealing

Ultrahigh molecular weight polyethylene was investigated using in situ confocal micro‐Raman spectroscopy during annealing at 110.0 °C. Based on the Raman spectra, crystalline, amorphous, and all‐trans noncrystalline fractions were recognized to evaluate rearrangement kinetics during isothermal annealing at 110.0 °C and phase evolution during cooling from 110.0 to 30.0 °C. For the crystalline fraction, a substantial increase from 0.600 ± 0.001 to 0.639 ± 0.008 was observed during the first 24.2 min of annealing; a very gradual increase from 0.639 ± 0.001 to 0.679 ± 0.001 occurred during the following 114.6 min. For the amorphous phase fraction, conversely, a sharp decrease from 0.240 ± 0.000 to 0.213 ± 0.004 was exhibited during the first 24.2 min of annealing, and then, a flat decrease happened from 0.213 ± 0.004 to 0.192 ± 0.001 as time expanded to 138.8 min. For the all‐tans noncrystalline fraction, a gradual decrease was shown from 0.160 ± 0.000 at 0.0 min to 0.128 ± 0.001 at 138.8 min. The rearrangement rate constant K was obtained to be 0.632 by an Avrami equation. During cooling from 110.0 to 30.0 °C, there were two phase evolution regions: region 1 from 110.0 to 90.0 °C and region 2 from 90.0 to 30.0 °C. The crystal lamella thickened faster in region 1 than in region 2. The amorphous layer continually decreased in content in the combined region of 1 and 2. The all‐trans noncrystalline phase obviously decreased in region 1 and then almost maintained a constant level in region 2. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of composition on hyperfine interactions in FeMoCuB nanocrystalline alloy

Influence of varying Fe/B ratio upon hyperfine interactions is investigated in the Fe_91?x Mo₈Cu₁B_x rapidly quenched alloys. They are studied both in the as-quenched (amorphous) state as well as after one-hour annealing at different temperatures ranging from 330 °C up to 650 °C. Such a heat treatment causes significant structural changes featuring a formation of nanocrystalline bcc-Fe grains during the first crystallization step. At higher annealing temperatures, a grain growth of bcc-Fe and occurrence of additional crystalline phases are observed. The relative fraction of the crystalline phase governs the development of magnetic hyperfine fields in the residual amorphous matrix even if this was fully paramagnetic in the as-quenched state. The development of hyperfine interactions is discussed as a function of annealing temperature and composition of the investigated alloys. ⁵⁷Fe Mössbauer spectrometry was used as a principal analytical method. Additional information related to the structural arrangement is obtained from X-ray diffractometry. It is shown that in the as-quenched state, the relative fraction of magnetic hyperfine interactions increases as the amount of B rises. In partially crystalline samples, the contribution of magnetic hyperfine interactions inside the retained amorphous matrix increases with annealing temperature even though the relative fraction of amorphous magnetic regions decreases.     

Structural study of TiO2 thin films by micro-Raman spectroscopy

The Raman spectroscopy method was used for structural characterization of TiO₂ thin films prepared by atomic layer deposition (ALD) and pulsed laser deposition (PLD) on fused silica and single-crystal silicon and sapphire substrates. Using ALD, anatase thin films were grown on silica and silicon substrates at temperatures 125–425 °C. At higher deposition temperatures, mixed anatase and rutile phases grew on these substrates. Post-growth annealing resulted in anatase-to-rutile phase transitions at 750 °C in the case of pure anatase films. The films that contained chlorine residues and were amorphous in their as-grown stage transformed into anatase phase at 400 °C and retained this phase even after annealing at 900 °C. On single crystal sapphire substrates, phase-pure rutile films were obtained by ALD at 425 °C and higher temperatures without additional annealing. Thin films that predominantly contained brookite phase were grown by PLD on silica substrates using rutile as a starting material.     

Microstructures and soft magnetic properties of Fe80P20-xSix (x = 4.5–6.5) amorphous ribbons

Fe-based amorphous ribbons with excellent soft magnetic properties and mechanical properties were prepared in the Fe–Si–P ternary system. Enhanced soft magnetic properties could be achieved through annealing treatment of the ribbons for 1 h at 325 °C, which is far below the glass transition temperatures (462–474 °C). Icosahedral medium-range ordering with a size range of around 2 nm occurred throughout the amorphous matrix during the low-temperature annealing treatment. The annealed ribbons exhibited improved magnetic saturation of over 185 emu/g while maintaining good mechanical flexibility. During icosahedral ordering, the distance between the Fe atoms and the coordination number within the amorphous ribbon can be optimised for achieving high magnetic saturation. However, nanocrystallisation of the SiP and Fe₂P transition phases embedded within the amorphous matrix occurred after the annealing treatment for 1 h at 385 °C, which caused deterioration of the soft magnetic properties and mechanical flexibility of the ribbons. Therefore, the combination of high magnetic saturation and mechanical flexibility of the amorphous ribbons could be optimised through low-temperature annealing treatment without any nanocrystallisation.     

Recrystallization of hexagonal silicon carbide after gold ion irradiation and thermal annealing

Silicon carbide (SiC) single crystals with the 6H polytype structure were irradiated with 4.0-MeV Au ions at room temperature (RT) for increasing fluences ranging from 1?×?10¹² to 2?×?10¹⁵ cm^?2, corresponding to irradiation doses from ~0.03 to 5.3 displacements per atom (dpa). The damage build-up was studied by micro-Raman spectroscopy that shows a progressive amorphization by the decrease and broadening of 6H-SiC lattice phonon peaks and the related growth of bands assigned to Si–Si and C–C homonuclear bonds. A saturation of the lattice damage fraction deduced from Raman spectra is found for ~0.8?dpa (i.e. ion fluence of 3?×?10¹⁴ cm^?2). This process is accompanied by an increase and saturation of the out-of-plane expansion (also for ~0.8?dpa), deduced from the step height at the sample surface, as measured by phase-shift interferometry. Isochronal thermal annealing experiments were then performed on partially amorphous (from 30 to 90%) and fully amorphous samples for temperatures from 200 °C up to 1500 °C under vacuum. Damage recovery and densification take place at the same annealing stage with an onset temperature of ~200 °C. Almost complete 6H polytype regrowth is found for partially amorphous samples (for doses lower than 0.8 dpa) at 1000 °C, whereas a residual damage and swelling remain for larger doses. In the latter case, these unrelaxed internal stresses give rise to an exfoliation process for higher annealing temperatures.     

Phase transformation of ZrO2 nanoparticles produced from zircon

This article focuses on the phase transformation of zirconia (ZrO₂) nanoparticles produced from zircon using a bottom-up approach. The influence of mechanical milling and thermal annealing on crystalline phase transformation of ZrO₂ nanoparticles was explored. It was found that the iron oxide, as an inherent impurity present in ZrO₂ nanoparticles, produced from zircon stabilises the cubic phase after calcination at 600°C. The stabilised cubic phase of ZrO₂ nanoparticles was disappeared and transformed into partial tetragonal and monoclinic phases after mechanical milling. The phase transformation occurred on account of the crystal defect induced by high-energy mechanical milling. The destabilisation of cubic phase into monoclinic phase was observed after the thermal annealing of ZrO₂ nanoparticles at 1000°C. The phase transitions observed are correlated to the exclusion of iron oxide from the zirconia crystal structure.     

Transport properties of mesomorphic syndiotactic polystyrene

Amorphous syndiotactic polystyrene (sPS) films were annealed at 110° and 115°C for 24 h. The annealing at the higher temperature produced the mesomorphic form of sPS, characterized by conformational order, as shown both by the presence of the zigzag band in the infrared spectrum and by the presence of characteristic peaks in the x-ray diffractogram. The crystalline form was not formed at the investigated temperatures. Differential scanning calorimetry of the mesomorphic sample shows that the transformation of the mesophase into the crystalline phase occurs during the heating run. The transport properties of dichloromethane show that the mesophase is impermeable to the vapors at low activity and becomes permeable at higher activities. At low activity it is therefore possible to derive the fraction of impermeable phase, which corresponds to the fraction of mesophase. This fraction was about 50%.     

Evolution of the spectral response of amorphous europium molybdate under annealing

The phase transformations occurring in amorphous europium molybdate Eu₂(MoO₄)₃ during annealing at atmospheric pressure are studied using optical spectroscopy and x-ray diffractometry. It is established that the metastable β phase is formed at a temperature of ～550°C, whereas the transition to the stable equilibrium α phase takes place at higher temperatures T ≥ 700°C. The spectral characteristics of the α phase, which differ substantially from those of the amorphous state and the β phase, are measured for the first time.     

Secondary defects in low-energy As-implanted Si

14 /cm² dose of As ions followed by both isochronal and isothermal annealing. The elementary defects generated first during solid-phase epitaxial recovery of implantation-induced amorphous layers at temperatures of 550 °C and/or 600 °C are {311} defects 2–3 nm long. They are considered to be transformed into {111} and {100} defects after annealing at temperatures higher than 750 °C. These secondary defects show the opposite annealing behavior to the dissolution and growth by the difference of their depth positions at 800 °C. This phenomenon is explained by the diffusion of self-interstitials contained in defects. With regard to the formation and dissolution of defects, there is no significant difference between the effects of rapid thermal annealing (950 °C for 10 s) and furnace annealing (800 °C for 10 min). Received: 14 November 1997/Accepted: 16 November 1997     

Phase transformation of Ni/Si thin films induced by nanoindentation and annealing

Thin Ni/Si films are prepared by depositing a Ni layer with a thickness of 100 nm on a Si (100) substrate. The as-deposited thin-film specimens are indented to a maximum depth of 500 nm using a nanoindentation technique and are then annealed at temperatures of 200°C, 300°C, 500°C and 800°C for 2 min. The microstructural changes and phases induced in the various specimens are observed using transmission electron microscopy (TEM) and micro-Raman scattering spectroscopy (RSS). Based on the load-displacement data obtained in the nanoindentation tests, the hardness and Young’s modulus of the as-deposited specimens are found to be 13 GPa and 177 GPa, respectively. The microstructural observations reveal that the nanoindentation process prompts the transformation of the indentation-affected zone of the silicon substrate from a diamond cubic structure to a mixed structure comprising amorphous phase and metastable Si III and Si XII phases. Following annealing at temperatures of 200∼500°C, the indented zone contains either a mixture of amorphous phase and Si III and Si XII phases, or Si III and Si XII phases only, depending on the annealing temperature. In addition, the annealing process prompts the formation of nickel silicide phases at the Ni/Si interface or within the indentation zone. The composition of these phases depends on the annealing temperature. Specifically, Ni₂Si is formed at a temperature of 200°C, NiSi is formed at a temperature of 300°C and 500°C, and NiSi₂ is formed at 800°C.     

Phase transformations and crystallization kinetics in electrospun TiO2 nanofibers in air and argon atmospheres

The effects of atmospheric air and argon environments on thermal-induced phase transformations in electrospun TiO₂ nanofibers have been investigated in situ using synchrotron radiation diffraction. Diffraction results showed that the as-synthesized TiO₂ nanofibers were initially amorphous, but crystallized to form anatase and rutile after thermal annealing in air or argon at elevated temperatures. The crystallization temperature of anatase was delayed by 100 °C in argon relative to in air, and the transformation of anatase into rutile occurs faster in argon atmosphere than in air due to the formation of oxygen vacancies. Non-linear strains formed in both polymorphs and the substantial elevation of rutile thermal expansion pointed to strain anisotropy in the rutile phase and the concomitant fibre breakage.     

Structural characterisation of the silica and alumina Zener pinning phases in nanocrystalline CeO2 by 29Si and 27Al nuclear magnetic resonance

Nanocrystalline CeO₂ samples have been manufactured using sol-gel techniques, containing either 15 % silica or 10 % alumina by weight to restrict growth of the ceria nanocrystals during annealing by Zener pinning. ²⁹Si and ²⁷Al MAS NMR have been used to investigate the structure of these pinning phases over a range of annealing temperatures up to 1000 °C, and their effect on the CeO₂ morphology has been studied using electron microscopy. The silica pinning phase resulted in CeO₂ nanocrystals of average diameter 19 nm after annealing at 1000 °C, whereas the alumina pinned nanocrystals grew to 88 nm at the same temperature. The silica pinning phase was found to contain a significant amount of inherent disorder indicated by the presence of lower n Qⁿ species even after annealing at 1000 °C. The alumina phase was less successful at restricting the growth of the ceria nanocrystals, and tended to separate into larger agglomerations of amorphous alumina, which crystallised to a transition alumina phase at higher temperatures.     

Relaxation of the state with induced transverse magnetic anisotropy in the soft magnetic nanocrystalline alloy Fe73.5Si13.5Nb3B9Cu1

The residual lattice strains of nanocrystals, which are responsible for the formation of states with transverse magnetic anisotropy in samples of the Fe-Si-Nb-B-Cu alloys (Finemets) subjected to annealing under tensile loading with the subsequent relaxation annealing at temperatures in the range from 500 to 600°C, have been measured using X-ray diffraction. The relative extension and compression of interplanar spacings have been compared with the induced magnetic anisotropy constants determined from the magnetic hysteresis loops. It has been shown that, during the relaxation annealing at the nanocrystallization temperature (500?C540°C), the observed decrease in the residual strains is accompanied by a decrease in the transverse magnetic anisotropy constant. A linear correlation between the relative extension and compression of the interplanar spacings for different crystallographic planes and magnetic anisotropy constant has been revealed. The deviation from linearity is observed after annealing at a temperature of 600°C, which is explained by a possible increase in sizes of nanocrystals, changes in their structure, and partial crystallization of the amorphous matrix.     

Nanocrystal formation in gas-atomized amorphous Al85Ni10La5 alloy

An Al₈₅Ni₁₀La₅ amorphous alloy, produced via gas atomization, was selected to study the mechanisms of nanocrystallization induced by thermal exposure. High resolution transmission electron microscopy results indicated the presence of quenched-in Al nuclei in the amorphous matrix of the atomized powder. However, a eutectic-like reaction, which involved the formation of the Al, Al₁₁La₃, and Al₃Ni phases, was recorded in the first crystallization event (263°C) during differential scanning calorimetry continuous heating. Isothermal annealing experiments conducted below 263°C revealed that the formation of single fcc-Al phase occurred at 235°C. At higher temperatures, growth of the Al crystals occurred with formation of intermetallic phases, leading to a eutectic-like transformation behaviour at 263°C. During the first crystallization stage, nanocrystals were developed in the size range of 5 ～ 30 nm. During the second crystallization event (283°C), a bimodal size distribution of nanocrystals was formed with the smaller size in the range of around 10 ～ 30 nm and the larger size around 100 nm. The influence of pre-existing quenched-in Al nuclei on the microstructural evolution in the amorphous Al₈₅Ni₁₀La₅ alloy is discussed and the effect of the microstructural evolution on the hardening behaviour is described in detail.     

Phase behavior of DODAB aqueous solution

Phase behavior of DODAB aqueous solution, prepared without sonication, was studied by adiabatic scanning calorimetry. Measurements revealed four phase transitions with the temperatures 35.2, 39.6, 44.6, and 52.4°C at heating and one transition at the temperature 40.4°C at cooling. The first three transitions at heating occur in unilamellar vesicles. The first and third transitions correspond to the subgel-gel and gelliquid phase transitions, corresponding enthalpy jumps are equal to 33 and 49 kJ/mol. The second transition appears after some aging and is similar to gel-ripple phase transition in a DPPC solution, with the enthalpy jump under the transition exceeding 7.4 kJ/mol. The transition occurs in unilamellar vesicles. The transition at the temperature 52.4°C occurs in another subsystem of the solution, which we believe to be multilamellar vesicles. The enthalpy jump at this transition is equal to 97 kJ/mol, and data analysis suggests that this is a subgel-liquid transition. The phase transition at cooling is the liquid-gel transition in unilamellar vesicles. During the measurements, a slow evolution of the solution occurs, consisting in a change of concentrations of unilamellar and multilamellar vesicles. This transformation mainly occurs at low temperatures.     

Broad-line NMR investigation of the amorphous component of poly(trans-1,4-butadiene) and poly(4-methyl pentene-1) crystals wetted by carbon disulfide

Broad-line (proton) NMR measurements were made at temperatures from -15 to -96°C on crystals of poly(4-methyl pentene-1) wetted with a nonprotonated solvent, CS₂. The mobile fraction, A_n, is found to depend on the crystal morphology and subsequent annealing treatments of dried crystals. A_n varies with temperature in the -30 to -70°C region; changes in the slope of the A_n vs temperature plot in this region with annealing treatment are interpreted in terms of changes in the amorphous portions of the lamellae. Previous NMR results for poly(trans-1, 4-butadiene) have been reanalyzed and the new A_n values obtained are given; annealing dry PTBD crystals at 80°C is shown to bring about a significant decrease in A_n.     

Electrical activation of boron-implanted silicon during rapid thermal annealing

The electrical activation of boron implanted in crystalline and preamorphized silicon has been investigated during rapid thermal annealing performed with halogen lamps. Samples implanted with B⁺ fluences ranging between 5×10¹⁴ and 1×10¹⁶cm⁻² and treated at temperatures between 900°C and 1100°C have been examined. When boron is implanted in crystalline Si, activation proceeds slowly atT<1000°C and cannot be completed in times typical of rapid thermal annealing (a few tens of seconds). The analysis of carrier profiles indicates that the time constant for activation is strongly affected by local damage and dopant concentration. If the total boron concentration exceeds equilibrium solubility, precipitation occurs concomitant to activation, even if the substitutional boron fraction is still lower than equilibrium solubility. ForT≧1000°C complete activation is obtained in times of about 10 s. In the case of preamorphized Si the activation occurs very quickly, during the recrystallization of the amorphous layer, for all the examined temperatures.     

KTN thin films prepared by pulsed laser deposition on transparent single crystal quartz(100)

Using the Sol-Gel method to produce the KTN ultrafine powder and the sintering technique with K2O atmosphere to prepare KTN ceramics as the targets instead of the KTN single crystal, highly oriented KTN thin films were produced on the transparent single crystal quartz (100) by the pulsed laser deposition (PLD). Since the thermal stress sustained by the quartz is relatively small, the limit temperature of the quartz substrates (300℃) is much lower than that of the P-Si substrates (560℃); the prepared thin film is at amorphous state. Increasing the pulsed laser energy density in the process incorporated with annealing the film after deposition at different temperatures converts the amorphous films into crystal. The optimal pulsed laser energy density and annealing temperature were 2.0 J/cm2 and 600℃, respectively. A discussion was made to understand the mechanism of film production at relatively low substrate temperature by PLD and effects of the annealing temperatures on the forming of the perovskite p