Thermally-induced Transformations Research Articles

Role of point defects in stress-induced martensite transformations in NiTi shape memory alloys: A molecular dynamics study

Shape-memory properties of equiatomic NiTi rely on the thermal- or stress-induced reversible martensitic phase transformation between the $B2$ and $B{19}^{\ensuremath{'}}$ phases. Irradiation defects suppress thermal-induced transformations, but their effects on stress-induced transformations are poorly understood. We use molecular dynamics to investigate the effect of vacancies, vacancy clusters, interstitials, and antisite defects on stress-induced transformations. All defects suppress the transformation, but vacancy clusters do so to the greatest extent, while antisite defects do so to the least extent. The responsible mechanisms are grain boundary pinning and chemical disordering.

Effect of high temperatures on the magnetic susceptibility of loess.

Coal fires refer to fires generated by the self-combustion of coal seams, which have a maximum temperature of 1000 °C. Such fires can significantly alter the properties of surrounding rock and soil. However, in Northern Shaanxi, China, coal resources are abundant, and the buried depth of coal seams is shallow; therefore, coal fires often occur. Because Northern Shaanxi is located in China's Loess Plateau, there is a large amount of loess accumulation on the surface. For this reason, it is imperative to study the effects of high temperatures on loess. In this paper, the loess samples are heat treated at different temperatures (200-1000 °C), and their surface redness (a*) and mass magnetic susceptibility (χ) are measured to simulate the high-temperature effects of coal fires on the loess in northern Shaanxi, and also study its chromaticity changes and abnormal magnetic properties. The results show that (1) the loess χ value is affected by the heat-treatment temperature; at 600 °C, the χ value decreases, increasing rapidly above after 850 °C. Further, the magnetic susceptibility changes significantly. (2) The thermal-induced transformation of ferromagnetic minerals and the buried depth of loess are the main reasons for these changes in magnetic susceptibility and red chroma of loess.

Thermal-induced transformation of glutamic acid to pyroglutamic acid and self-cocrystallization: a charge-density analysis.

Thermal-induced transformation of glutamic acid to pyroglutamic acid is well known. However, confusion remains over the exact temperature at which this happens. Moreover, no diffraction data are available to support the transition. In this article, we make a systematic investigation involving thermal analysis, hot-stage microscopy and single-crystal X-ray diffraction to study a one-pot thermal transition of glutamic acid to pyroglutamic acid and subsequent self-cocrystallization between the product (hydrated pyroglutamic acid) and the unreacted precursor (glutamic acid). The melt upon cooling gave a robust cocrystal, namely, glutamic acid-pyroglutamic acid-water (1/1/1), C5H7NO3·C5H9NO4·H2O, whose structure has been elucidated from single-crystal X-ray diffraction data collected at room temperature. A three-dimensional network of strong hydrogen bonds has been found. A Hirshfeld surface analysis was carried out to make a quantitative estimation of the intermolecular interactions. In order to gain insight into the strength and stability of the cocrystal, the transferability principle was utilized to make a topological analysis and to study the electron-density-derived properties. The transferred model has been found to be superior to the classical independent atom model (IAM). The experimental results have been compared with results from a multipolar refinement carried out using theoretical structure factors generated from density functional theory (DFT) calculations. Very strong classical hydrogen bonds drive the cocrystallization and lend stability to the resulting cocrystal. Important conclusions have been drawn about this transition.

Influence of annealing on microstructures and mechanical properties of arc-deposited AlCrTiSiN coating

A AlCrTiSiN nanomultilayered coating, mainly consisting of fcc-AlCrTiSiN solid solution and some hcp-clusters at fcc-AlCrTiSiN nanotwin boundaries, was isothermally annealed at 800–1100 °C. Thermal stability and changes in microstructure were studied carefully to illustrate its thermal dissolution mechanism. A thermal induced transformation of hcp to fcc is observed by emission of partial dislocation at hcp/fcc interfaces when annealed at 800 °C. Furthermore, we observe the onset of decomposition of fcc-AlCrTiSiN solid solution to coherently Al-rich and TiCr-rich fcc domains at 1000 °C via spinodal mechanism, accompanied by the precipitation of semi-coherent hcp-clusters within Al-rich fcc sublayers by nucleation mechanism. This transformation results in a notable hardening due to the refinement of grains and the coherency strains caused by spinodal decomposition and the formation of semi-coherent hcp-clusters. Later, annealing at 1100 °C promotes the dissolution of layered structures by pinching off of hcp sublayers, the transformation of fcc-AlCrTiSiN solid solution to Cr, Cr2N and hcp-AlN particles and the coarsening of hcp-AlN particles, resulting in a notable loss in hardness.

Effect of various technological parameters on particle morphology and uniformity of α-Ni(OH)2 synthesized via surfactant-free hydrothermal route

Hierarchical microspheres of α-Ni(OH)2, uniform in size and shape, have been synthesized through a facile surfactant-free hydrothermal route. Experimental parameters such as reaction time, temperature and reactant concentration were systematically optimized to produce monodispersed particles. SEM analysis confirmed that the particles synthesized from a recipe containing 2.65 × 10−2 mol. L−1 nickel chloride and 5.6 × 10−1 mol. L−1 urea aged at 85 °C for 2 hours were uniform in size and morphology. HR-TEM results showed that the hierarchical microspheres are made up of thin sheet-like units. The crystal structure of the α-Ni(OH)2 microspheres was investigated by XRD which showed (003) as the preferred orientation plane having 7.369 Å interplanar spacing and crystallite size of 21 nm. The intercalation of CO3 −2 and OCN− species was revealed by FT-IR spectroscopy. The average activation energy (41.23 KJ mol−1) for thermal-induced transformation reaction was determined based on the TG/DTA data recorded at three heating rates. The present green and facile route could be extended to synthesize monodispersed systems of other metal compounds.

Quartz paramorphs after former stishovite in UHP eclogite from the South Altyn Tagh, Western China and its Significance

AbstractThe long prism/needle‐shaped polycrystalline quartz aggregates and square/parallelogram‐shaped singlephase quartz inclusions in omphacite and garnet of ultrahigh pressure eclogite were first discovered from the Jiangalesayi area, South Altyn UHP belt. Based on their morphology, these quartz inclusions are quartz paramorphs after stishovite. The minimum peak pressure of the eclogite is estimated to be >8–9 GPa at 800– 1000 °C based on the stability field of stishovite. This new evidence, together with previous stishovite exsolution microstructure in the gneiss from the same region, suggests an ultra‐deep subduction and exhumation of the South Altyn continental rocks to/from mantle depths in stishovite stability field. Evidence of ultra‐deep subduction of continental materials might be more common and diverse than previous thought.Exhumation of subducted continental rocks from≥300 km has been considered impossible because they are denser than mantle at these depths. How did the stishovite bearing continental rocks of the South Altyn exhumated?As we all know, the densities of stishovite (4.3 g/cm3) are much higher than coesite (2.9 g/cm3), and stishovite transforms into coesite with temperature increases. Density calculations were performed for subducted continental rocks along phase transition of stishovite to coesite, using the third‐order Birch‐Murnaghan equation of state based on mineral fractions obtained from experiments and Perple_X. The results show that the density of Siliceous rocks decrease remarkably, lower than the surrounding mantle in coesite stability field, whereas the density of Oligosiliceous and Silicon unsaturated rocks is higher than surrounding mantle.Thus, we propose that the thermal induced transformation could provide an initial driven force for the exhumation of ultra‐deep subducted silica‐enriched felsic continental rocks. Temperature increase could be derived from an increased geothermal gradient from convective mantle or mantle plume. Mafic to ultra‐mafic rocks and silica‐deficient rocks may be captured by the upwelling subducted continental rocks and exhumated together.

Postshock Thermally Induced Transformations in Experimentally Shocked Magnetite

AbstractWe studied the effect of 973 K heating in argon atmosphere on the magnetic and structural properties of a magnetite‐bearing ore, which was previously exposed to laboratory shock waves between 5 and 30 GPa. For this purpose magnetic properties were studied using temperature‐dependent magnetic susceptibility, magnetic hysteresis and low‐temperature saturation isothermal remanent magnetization. Structural properties of magnetite were analyzed using X‐ray diffraction, high‐resolution scanning electron microscopy and synchrotron‐assisted X‐ray absorption spectroscopy. The shock‐induced changes include magnetic domain size reduction due to brittle and ductile deformation features and an increase in Verwey transition temperature due to lattice distortion. After heating, the crystal lattice is relaxed and apparent crystallite size is increased suggesting a recovery of lattice defects documented by a mosaic recrystallization texture. The structural changes correlate with modifications in magnetic domain state recorded by temperature‐dependent magnetic susceptibility, hysteresis properties and low‐temperature saturation isothermal remanent magnetization. These alterations in both, magnetic and structural properties of magnetite can be used to assess impact‐related magnetic anomalies in impact structures with a high temperature overprint.

Analysis of thermally-induced transformations of silica rocks after high temperature heat treatment

Analysis of thermally-induced transformations of silica rocks after high temperature heat treatment

Thermal properties of iopamidol

Three crystal forms of iopamidol, an iodinated contrast media used in radiology, have been so far elucidated: an anhydrous, a monohydrate and a pentahydrate form (labeled hereafter as W0, W1 and W5, respectively), which showed the occurrence of different conformations, atropisomeric in nature. Specifically, the anhydrous and monohydrate forms contain iopamidol with a “syn” conformation of the two symmetric sidearms, while an “anti” conformation was found in the pentahydrate, making it a conformational (pseudo)-polymorph of the first two. The three crystal forms have been here investigated by means of DSC, variable temperature X-ray powder diffraction and Raman spectroscopy. This study enabled us to highlight the thermal-induced transformations, leading to the discovery of new crystal forms, for a total of four hydrated and four distinct anhydrous phases. In particular, the DSC curve of W0 revealed only a reversible solid–solid transition at around 180 °C before melting, with subsequent degradation above 300 °C. W1, after the loss of lattice water around 100 °C, shows a characteristic split peak at about 250 °C, which is attributed to melting. Below 150 °C, powder diffraction of W1 suffers of minor changes, with a smooth variation of the lattice parameters, in agreement with a progressive loss of water in a reversible event, monitored also by DSC. At variance, W5 evidenced an irreversible loss of water in three distinct steps, for three, one and one H2O molecules each, respectively; subsequent transitions occur at 140 and 180 °C, before melting at 240 °C. Three clearly visible transformations were also detected by variable temperature powder diffraction measurements, where the loss of three molecules of water in a single step, generating a bis-hydrated species (W2), is followed by a second dehydration process leading, above 75 °C, to a new monohydrate phase W1′, different from the known W1 form. The Raman spectra of the three crystal forms, measured upon heating up to 160 °C, evidenced changes in spectral regions of amides that, according to our simulations of the vibrational properties, can be attributed to changes of the hydration properties and, more significantly, in terms of the “syn” and “anti” conformations.

Thermal-induced transformation of wetting behaviors on laser-textured SiC surfaces

Thermal-induced transformation of wetting behaviors on laser-textured silicon carbide (SiC) surfaces was discussed in this work. To investigate the transformation, a quenching experiment was conducted and an X-ray diffractometer was used to measure the residual stress. The experimental results demonstrate that the significantly enhanced hydrophilicity was induced by the increasing thermal residual stress of SiC materials after the aqueous quenching. It was found that the decrease in the contact angle increased with the increasing quenching temperature. Quenching at 350°C led to the change of contact angle from 89.28° to 70.88° for the smooth surface, while from 72.25° to 33.75° for the laser-textured surface with depth 8 μm. Further, the surface hydrophobicity was enhanced by the release of thermal residual stress after quenching, thereby leading to an increase in the contact angle over time. The transformation of wetting behaviors on laser textured SiC surfaces can be achieved mutually by the aqueous quenching method.

Solution deposition of ultrasmooth alumina on long-length metallic substrate for 2G superconducting tapes

Chemical solution deposition of smooth amorphous Al2O3 thin films has been successfully used for planarization of long-length metallic substrates for 2G HTS superconducting wires production. A series of metal-organic precursors based on Al(iPrO)3, Al(acac)3, acetic acid, monoethanolamine (MEA) and diethylenetriamine (DETA) was developed. Correlations between the precursor composition and the features of its two-step thermal-induced transformation to amorphous Al2O3 were studied by 1H NMR, IR spectroscopy and thermal analysis. Utilizing the solutions of {Al(iPrO)3+2.5MEA+6HAcet} in iPrOH and {Al(acac)3+nDETA} in HAcet (n=1−3) as precursors for dip-coating, we obtained the long-length Hastelloy C276 substrate covered by uniform amorphous 50–550nm thick alumina films with surface roughness of about 0.5–1.5nm. A 20m long sample of 2G HTS wire with a commercial level of superconducting critical current of up to 300A was prepared based on Hastelloy substrate tape planarized with Al2O3.

Peak-bridges due to in-column analyte transformations as a new tool for establishing molecular connectivities by comprehensive two-dimensional gas chromatography–mass spectrometry

Comprehensive two-dimensional gas chromatography–mass spectrometry (GC×GC–MS) has been shown to permit for the unprecedented chromatographic resolution of volatile analytes encompassing various families of organic compounds. However, peak identification based on retention time, two-dimensional mapping, and mass spectrometric fragmentation only, is not a straightforward task yet. The possibility to establish molecular links between constituents is of crucial importance to understand the overall chemistry of any sample, especially in natural extracts where biogenetically related isomeric structures are often abundant. We here present a new way of using GC×GC that allows searching for those molecular connectivities. Analytical investigations of essential oil constituents by means of GC×GC–MS permitted to observe in real time the thermally-induced transformations of various sesquiterpenic derivatives. These transformations generated a series of well-defined two-dimensional peak bridges within the 2D-chromatograms connecting parent and daughter molecules, thus permitting to build a clear scheme of structural relationship between the different constituents. GC×GC–MS appears here as a tool for investigating chromatographic phenomena and analyte transformations that could not be understood with conventional GC–MS only.

Thermodynamics of nanoalloys.

This article reviews recent advances in our understanding of how temperature affects the structure and the phase of multimetallic nanoparticles. Focusing on bimetallic systems, we discuss the interplay of size, shape and chemical order on the stable configurations at thermal equilibrium. Besides some considerations about experimental evidence for thermally-induced transformations, most insight is generally gained from theory and computation. The perspectives offered by mesoscopic approaches (i.e. corrected from the bulk) and atomistic simulations complement each other and often provide detailed information about the respective roles of coordination, composition and more generally surface effects to be evaluated. Order-disorder transitions and the melting phase change are strongly altered in nanoscale systems, and we describe how they possibly impact entire phase diagrams.

Backbone Modified Small Bite-Angle Diphosphines: Synthesis, Structure, Fluxionality and Regioselective Thermally-Induced Transformations of Ru3(CO)10{µ-Ph2PCH(Me)PPh2}

The synthesis of Ru3(CO)10{µ-Ph2PCH(Me)PPh2} (1) has been achieved from the radical-catalysed reaction of Ru3(CO)12 with 1,1′-bis(diphenylphosphino)ethane and the fluxionality, protonation and regioselective thermally-induced on-metal transformations of the small bite-angle diphosphine have been studied. Cluster 1 is fluxional in solution and variable temperature 13C{1H} NMR spectroscopy shows that the six carbonyls on the phosphine-bound metal centers interconvert rapidly on the NMR timescale. Protonation of 1 is facile at room temperature and affords the cationic-hydride [Ru3(CO)10{µ-Ph2PCH(Me)PPh2}(μ-H)][BF4] (1H +) which is fluxional, the hydride migrating between bridged and non-bridged ruthenium–ruthenium vectors, location across an unbridged metal–metal bond being thermodynamically favoured. Thermolysis of 1 in heptane affords moderate amounts of the expected benzene-CO elimination product, Ru3(CO)8(µ-CO){µ3-PhPCH(Me)PPh(C6H4)} (2), along with smaller amounts of Ru3(CO)10{μ-PhP(CHMe)(C6H4)PPh} (3) containing a novel doubly-bridged diphosphine ligand. Hydrogenation of 1 in refluxing cyclohexane affords the hydride cluster Ru3(CO)9{μ3-PhPCH(Me)PPh2}(μ-H) (4), the same species also being obtained when 2 was treated with hydrogen under similar conditions. All thermally-induced transformations are regioselective, with only a single isomer being generated. In light of the observed regioselectivity a mechanism is proposed for the formation of 2 from 1 which results from an intermediate in which the methyl-group is held over the triruthenium framework. Cluster Ru3(CO)10{µ-Ph2PCH(Me)PPh2} has been synthesized from the radical-catalysed reaction between Ru3(CO)12 and 1,1′-bis(diphenylphosphino)ethane and the fluxionality, protonation and regioselective thermally-induced on-metal transformations of the small bite-angle diphosphine have been investigated.

Monitoring polymorphic transformations by using in situ Raman hyperspectral imaging and image multiset analysis

Polymorphism is often encountered in many crystalline compounds. To control the quality of the products, it is relevant knowing the potential presence of polymorph transformations induced by different agents, such as light exposure or temperature changes. Raman images offer a great potential to identify polymorphs involved in a process and to accurately describe this kind of solid-state transformation in the surface scanned.As a way of example, this work proposes the use of multiset analysis on the series of Raman hyperspectral images acquired during a thermal induced transformation of carbamazepine as the optimal way to extract useful information about polymorphic or any other kind of dynamic transformation among process compounds. Image multiset analysis, performed by using Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS), will furnish pure spectra and distribution maps of the compounds involved in the process and, hence, will allow the identification of polymorphs and, more important, the description of the process evolution at a global and local (pixel) level. Thus, process will be defined from a spatial point of view and by means of a set of global process profiles dependent on the process control variable. The results obtained confirm the power of this methodology and show the crucial role of the spatial information contained in the image (absent in conventional spectroscopy) for a correct process description.

Thermal stability of electrodeposited platinum nanowires and morphological transformations at elevated temperatures

Pt nanowires were prepared by template electrodeposition using ion track etched polymer membranes and analysed with respect to their thermal stability. Driven by Rayleigh instability, the polycrystalline Pt nanostructures experienced structural transformations and finally fragmented into linear chains of nanospheres at temperatures much below the melting point of bulk Pt. Morphological changes were systematically studied by electron microscopy and compared with previously reported results on other metal nanowires and theoretical predictions. In addition, nanowires could readily be interconnected to two-dimensional assemblies by taking advantage of the rapid diffusion processes. This study will help to predict the durability of integrated nanowires and contributes to the understanding of thermal-induced transformations for polycrystalline nanowires.

Synthesis, characterizations, and thermal induced structural transformation of silver-fullerene C60 nanocomposite thin films for applications in optical devices

Nanocomposite thin films of fullerene C60 containing Ag nanoparticles (NPs) were synthesized by thermal codeposition. The surface plasmon resonance (SPR) band of the nanocomposite film was observed in the region 450–550 nm, showing a large redshift with increasing metal concentration. This is explained by the Maxwell–Garnett effective medium theory considering the absorbing nature of fullerene C60. The C60–Ag nanocomposite thin film with lowest Ag concentration was annealed at increasing temperatures in neutral atmosphere. The SPR band showed first a small redshift after annealing at small temperature then progressive blueshift at higher temperature. This behavior of SPR is explained by the increased particle–particle interaction due to the compaction of the fullerene C60 film upon annealing at low temperature and the transformation of fullerene C60 matrix into amorphous carbon at higher temperature. Rutherford backscattering spectrometry and transmission electron microscopy were used to quantify Ag metal content and the microstructural evolution of Ag NPs in the nanocomposite films, respectively. Thermal induced structural transformations of fullerene C60 molecules of host matrix were investigated by Raman spectroscopy.

Low Dimensional Approximations to Ferroelastic Dynamics and Hysteretic Behavior Due to Phase Transformations

In this paper, a low dimensional model is constructed to approximate the nonlinear ferroelastic dynamics involving mechanically and thermally-induced martensite transformations. The dynamics of the first order martensite transformation is first modeled by a set of nonlinear coupled partial differential equations (PDEs), which is obtained by using the modified Ginzburg–Landau theory. The Chebyshev collocation method is employed for the numerical analysis of the PDE model. An extended proper orthogonal decomposition is then carried out to construct a set of empirical orthogonal eigenmodes of the dynamics, with which system characteristics can be optimally approximated (in a specified sense) within a range of different temperatures and under various mechanical and thermal loadings. The performance of the low dimensional model is analyzed numerically. Results on the dynamics involving mechanically and thermally-induced phase transformations and the hysteresis effects induced by such transformations are presented.

Compressive stresses and stabilisation in Cu-Al-Ni single crystals

Cu-Al-Ni single crystals which present β-β' (quenched samples) or β-γ' (aged at 570K samples) thermally induced martensitic transformations, were submitted to compressive stresses at different temperatures. The test temperatures were chosen in order to have martensite-martensite stress induced transformations. The characteristics of the martensitic transformation and structural changes before and after the compression tests have been studied by means of calorimetry (DSC) and TEM. The obtained results show that when applying compressive stresses in both ensembles of samples, a non-twinned γ' martensite appears. In the quenched samples it is formed through the β' phase already present at room temperature. In the aged samples the non twinned γ' phase is stress induced from the γ' thermally formed (internally twinned). The amount of non twinned γ' phase increases with the applied deformation, for low strain values it coexists with the β' or y' (twinned) phases and is the only present phase for higher applied strain values. In all the cases a notable martensite stabilisation is observed in the first thermal induced transformation after the mechanical test only when the stress-strain loops are not closed, that means when a permanent strain remains in the material after unloading. The degree of mechanical stabilisation is more important as higher is the applied deformation and as much amount of γ' phase mechanically formed (non twinned) is still present in the material and it is slightly dependent on the test temperature if lower than Af. The stress induced stabilisation mechanism is related to the presence of this non twinned martensite and its difficult retransformation to the parent phase.

Thermally-Induced Transformations of Gallium and Indium Alkyl Phosphido Complexes: Dealkylsilylation Routes to MP (M = Ga, In)

The dehalosilylation reaction of nBu2GaCl with 1 equiv of P(SiMe3)3 provided [nBu2GaP(SiMe3)2]2 (1) in good yield. A similar reaction between nBuGaCl2 and P(SiMe3)3 gave [nBu(Cl)GaP(SiMe3)2]2 (2). Compound 1 was characterized by X-ray crystallography and possesses an approximately square planar Ga2P2 molecular core. Both the P and the Ga centers are in distorted tetrahedral environments. Thermolysis of 1, at 400 °C, produced GaP and BuSiMe3 and no other crystalline products, as confirmed by thermogravimetric and spectroscopic analysis. The indium analogue of 1, [(nBu)2InP(SiMe3)2]2 (3), was prepared from the reaction of (nBu)2InCl with P(SiMe3)3. The thermolysis of 3 at 400 °C under nitrogen produced butene, butane, and butyltrimethylsilane as organic products and a dark grey solid. Powder X-ray diffraction of this solid revealed it to consist of InP and metallic indium. Combination of In(nBu)3 with P(SiMe3)3 produced the monomeric adduct (nBu)3In·P(SiMe3)3 (4). The thermal reactivity of complex 4 was investigated at various temperatures. At 130 °C in a sealed tube, the products of thermolysis are [(nBu)2InP(SiMe3)2]2 (3) and In0. While complex 1 is a potential precursor to GaP via a dealkylsilylation mechanism, the indium analogue 3 and the adduct 4 appear to have a more facile β-hydrogen elimination pathway which makes them less suitable for the production of pure InP.