Temperature-resolved X-ray Diffraction Research Articles

Synthesis of acetonitrile from NH3/syngas mixtures on molybdenum nitride: Insights into the reaction mechanism

Owing to their metallic-like surface electronic properties and their capacity to act as reservoirs and solid transfer agents for active nitrogen, transition metal nitrides are interesting as solid catalysts for C-C and C-N coupling reactions for the bottom-up production of higher (C2+) nitrogenated chemicals from unconventional carbon resources. The catalytically active state and reaction mechanism for the direct synthesis of acetonitrile from syngas/ammonia mixtures are studied on an unsupported Mo catalyst from complementary experimental and computational approaches. Temperature resolved X-ray diffraction and X-ray photoemission spectroscopy verify that an oxidic MoO3 catalyst precursor undergoes in situ (near-surface) nitridation, upon exposure to reaction conditions at 723 K, rendering Mo2N the actual working catalyst. Density Functional Theory mechanistic investigations on a γ-Mo2N(100) model surface point to a hydrogen-assisted CO dissociation on the nitride surface. Moreover, surface oxygen, evolved from CO dissociation, is predicted to play a central role as hydrogen acceptor, to enable the dehydrogenative NH3 dissociation. Direct condensation of CH and N adspecies proceeds with a low energy barrier of 33 kJ mol−1, which makes C-N coupling preferred over full hydrogenation of CHx species, in agreement with the experimental modest selectivity to methane (ca. 10 %). Both experimental and computational results indicate that HCN is a major intermediate product along the reaction pathway to acetonitrile. No energetically feasible associative reaction pathways could be identified for C-C coupling from HCN. The dissociation of the latter intermediate product is predicted to precede the reaction of CN adspecies to CHx. Similarly to NH3 dissociation, dehydrogenative HCN activation on the Mo2N surface is predicted to be facilitated through hydrogen abstraction by surface oxygen species, yet subjected to a comparatively higher energy barrier (>120 kJ mol−1), therefore likely to control the overall kinetics. These findings suggest that the enhancement of HCN dissociation is a central design objective towards Mo2N-based catalysts with advanced performance.

Phase transitions in germanium telluride nanoparticle phase-change materials studied by temperature-resolved x-ray diffraction

Germanium telluride (GeTe), a phase-change material, is known to exhibit four different structural states: three at room-temperature (one amorphous and two crystalline, α and γ) and one at high temperature (crystalline, β). Because transitions between the amorphous and crystalline states lead to significant changes in material properties (e.g., refractive index and resistivity), GeTe has been investigated as a phase-change material for photonics, thermoelectrics, ferroelectrics, and spintronics. Consequently, the temperature-dependent phase transitions in GeTe have been studied for bulk and thin-film GeTe, both fabricated by sputtering. Colloidal synthesis of nanoparticles offers a more flexible fabrication approach for amorphous and crystalline GeTe. These nanoparticles are known to exhibit size-dependent properties, such as an increased crystallization temperature for the amorphous-to-α transition in sub-10 nm GeTe particles. The α-to-β phase transition is also expected to vary with size, but this effect has not yet been investigated for GeTe. Here, we report time-resolved x-ray diffraction of GeTe nanoparticles with different diameters and from different synthetic protocols. We observe a non-volatile amorphous-to-α transition between 210 °C and 240 °C and a volatile α-to-β transition between 370 °C and 420 °C. The latter transition was reversible and repeatable. While the transition temperatures are shifted relative to the values known for bulk GeTe, the nanoparticle-based samples still exhibit the same structural phases reported for sputtered GeTe. Thus, colloidal GeTe maintains the same general phase behavior as bulk GeTe while allowing for more flexible and accessible fabrication. Therefore, nanoparticle-based GeTe films show great potential for applications such as in active photonics.

Multi-scale thermal stability study of commercial lithium-ion batteries as a function of cathode chemistry and state-of-charge

This paper takes a critical look at the materials aspects of thermal runaway of lithium-ion batteries and correlates contributions from individual cell components to thermal runaway trends.An accelerating rate calorimeter (ARC) was used to evaluate commercial lithium-ion cells based on LiCoO2 (LCO), LiFePO4 (LFP), and LiNixCoyAl1-x-yO2 (NCA) at various states of charge (SOC). Cells were disassembled and the component properties were evaluated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and temperature-resolved X-ray diffraction (TR-XRD).The whole cell thermal runaway onset temperature decreases and peak heating rate increases with SOC due to cathode destabilization. LCO and NCA cathodes are metastable, with NCA cells exhibiting the highest thermal runaway rates. By contrast, the LFP cathode is stable to >500 °C, even when charged. For anodes, the decomposition and whole cell self-heating onset temperature is generally independent of SOC. DSC exotherm onset temperatures of the anodes were generally within 10 °C of the onset of self-heating in whole cell ARC. However, onset temperatures of the cathodes were typically observed above the ARC onset of whole cell runaway. This systematic evaluation of component to whole cell degradation provides a scientific basis for future thermal modeling and design of safer cells.

Thermal Stability Study of Commercial Lithium-Ion Batteries As a Function of Cathode Chemistry and State-of-Charge

The safety of lithium-ion batteries is mainly quantified by thermal runaway characteristics such as onset temperature, peak heating rate (HR), and maximum pressure release. This talk evaluates the materials aspects of thermal runaway of commercial lithium-ion batteries by correlating the contributions from individual cell components to thermal runaway trends. An accelerating rate calorimeter was used to define the thermal runaway behavior of three commercial 18650 lithium-ion batteries (LiCoO2, LiFePO4, and LiNixCoyAl1-x-y­O2) at various states of charge (SOC). Cells were also disassembled and the thermal properties of their component materials was evaluated by thermogravimetric analysis, differential scanning calorimetry, and temperature-resolved X-ray diffraction. Broadly, lithium-ion battery thermal runaway process begins with solid-electrolyte interface and negative active material decomposition followed by the positive active material breakdown. The experimental results show that the onset temperature is generally independent of SOC and peak HR increases with SOC as a result of cathode destabilization. Overall, LiNixCoyAl1-x-yO2 decomposes readily, and charged LiCoO2 is also metastable, although it decomposes more gradually than LiNixCoyAl1-x-y. Contrary to the layered transition metal oxides, LiFePO4 is stable to > 500oC, even when charged. The results are aimed at informing future engineering and fire protection of commercial lithium-ion batteries. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2018-3360 A

Thermal Stability Study of Commercial Lithium-Ion Batteries As a Function of Cathode Chemistry and State-of-Charge

The safety of lithium-ion batteries is mainly quantified by thermal runaway characteristics such as onset temperature, peak heating rate (HR), and maximum pressure release. This talk evaluates the materials aspects of thermal runaway of commercial lithium-ion batteries by correlating the contributions from individual cell components to thermal runaway trends. An accelerating rate calorimeter was used to define the thermal runaway behavior of three commercial 18650 lithium-ion batteries (LiCoO2, LiFePO4, and LiNixCoyAl1-x-y­O2) at various states of charge (SOC). Cells were also disassembled and the thermal properties of their component materials was evaluated by thermogravimetric analysis, differential scanning calorimetry, and temperature-resolved X-ray diffraction. Broadly, lithium-ion battery thermal runaway process begins with solid-electrolyte interface and negative active material decomposition followed by the positive active material breakdown. The experimental results show that the onset temperature is generally independent of SOC and peak HR increases with SOC as a result of cathode destabilization. Overall, LiNixCoyAl1-x-yO2 decomposes readily, and charged LiCoO2 is also metastable, although it decomposes more gradually than LiNixCoyAl1-x-y. Contrary to the layered transition metal oxides, LiFePO4 is stable to > 500oC, even when charged. The results are aimed at informing future engineering and fire protection of commercial lithium-ion batteries. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2018-3360 A

The importance of specific surface area in the geopolymerization of heated illitic clay

Geopolymers are inorganic binders formed by adding alkaline (hydroxide) solution to silicates such as blast furnace slag, fly ash or calcined clay to dissolve Si and Al that polymerizes and precipitates while hardening. The most common clay used as geopolymer raw material is kaolin. The aim of this study was to investigate the suitability of clays dominated by 2:1 dioctahedral layer silicates using the example of Friedland clay as a cheaper alternative to kaolin and determine the necessary preparation steps required to produce an effective geopolymer binder material. After a Rietveld-based quantification of the raw clay, the successive thermal modifications of the mineral phases were analyzed using simultaneous thermal analysis coupled with mass spectrometer (STA-MS), temperature-resolved X-ray diffraction (TXRD), and 27Al solid-state nuclear magnetic resonance spectroscopy (NMR) measurements. Friedland clay heated to 875°C was found to produce a geopolymer with the highest compressive strength, but in contrast to the literature, the Si:Al ratio and the amount of 5-fold coordinated Al were not found to be the key parameters that determined the success of geopolymer synthesis. The specific surface area and the amount of Si and Al dissolved are here reported to be the key factors determining the suitability of clays dominated by 2:1 dioctahedral layer silicates as raw materials for geopolymer production.

Room-temperature stabilization of nanoscale superionic Ag2Se

Superionic materials are multi-component solids in which one sub-lattice exhibits high ionic conductivity within a fixed crystalline structure. This is typically associated with a structural phase transition occurring significantly above room temperature. Here, through combined temperature-resolved x-ray diffraction and differential scanning calorimetry, we map out the nanoscale size-dependence of the Ag2Se tetragonal to superionic phase transition temperature and determine the threshold size for room-temperature stabilization of superionic Ag2Se. For the first time, clear experimental evidence for such stabilization of the highly ionic conducting phase at room temperature is obtained in ∼2 nm diameter spheres, which corresponds to a >100 °C suppression of the bulk phase transition temperature. This may enable technological applications of Ag2Se in devices where high ionic conductivity at room temperature is required.

Design and Synthesis of Copper–Cobalt Catalysts for the Selective Conversion of Synthesis Gas to Ethanol and Higher Alcohols

Combining quantum-mechanical simulations and synthesis tools allows the design of highly efficient CuCo/MoO(x) catalysts for the selective conversion of synthesis gas (CO+H2) into ethanol and higher alcohols, which are of eminent interest for the production of platform chemicals from non-petroleum feedstocks. Density functional theory calculations coupled to microkinetic models identify mixed Cu-Co alloy sites, at Co-enriched surfaces, as ideal for the selective production of long-chain alcohols. Accordingly, a versatile synthesis route is developed based on metal nanoparticle exsolution from a molybdate precursor compound whose crystalline structure isomorphically accommodates Cu(2+) and Co(2+) cations in a wide range of compositions. As revealed by energy-dispersive X-ray nanospectroscopy and temperature-resolved X-ray diffraction, superior mixing of Cu and Co species promotes formation of CuCo alloy nanocrystals after activation, leading to two orders of magnitude higher yield to high alcohols than a benchmark CuCoCr catalyst. Substantiating simulations, the yield to high alcohols is maximized in parallel to the CuCo alloy contribution, for Co-rich surface compositions, for which Cu phase segregation is prevented.

Recrystallization in a low-density low-alloy Fe–Mn–Al–C duplex-phase alloy

The recrystallization behaviour of a cold-rolled, low-density, low-alloy duplex-phase alloy (Fe–6.57Al–3.34Mn–0.18C, wt.%) has been studied. Temperature-resolved X-ray diffraction and dilatometry showed that the alloy recrystallizes at 850 °C during continuous heating. However, electron back-scattered diffraction investigations using Kernel average misorientation revealed that during annealing ferrite recrystallizes at lower temperatures while austenite remains strained up to 1200 °C. This study underlines the complexity of recrystallization of a microstructure comprising of constituents with high and low stacking fault energy.

Thin film Ni-Si solid-state reactions: Phase formation sequence on amorphized Si

The phase formation sequence during the thermally induced solid-state reaction of a 10-nm-thick magnetron-sputtered Ni film with a Si(001) substrate amorphized by ion implantation (a-Si) is investigated using a combination of in situ temperature-resolved x-ray diffraction and ex situ x-ray pole figure analyses, transmission electron microscopy, and Rutherford backscattering spectrometry. Our results reveal (1) that the metastable θ-phase grows from δ-Ni2Si and directly transforms into NiSi and (2) that cleaving the as-prepared, amorphized samples are often subject to a spontaneous reaction possibly resulting from cleaving. In the spontaneously reacted samples, a mixture of θ and NiSi is observed from the beginning of the thermal treatment. The θ phase exhibits a (110) fiber texture with a ±10° misorientation, which is then inherited by NiSi. The rest of the phase sequence is the same as for nonreacted samples, the NiSi2 growing from 390 °C if the amorphized Si is not completely consumed.

Phase stabilization in plasma sprayed BaTiO3

Abstract This paper presents a comparison of properties of BaTiO3 ceramics prepared by two different production methods: gas-stabilized plasma spraying (GSP) and spark plasma sintering (SPS). Samples of both materials were evaluated by various techniques, the goal being to detect the Curie temperature of the ferroelectric transformation between the tetragonal and the cubic phase. All tests, resonant ultrasound spectroscopy, dielectric measurements, differential scanning calorimetry and temperature-resolved X-ray diffraction (XRD), used in combination, proved the absence of this transformation in the case of GSP coating up to 500 °C. Similarly, the tetragonal-to-orthorhombic transition temperature is shifted downwards, this transition probably taking place in a small fraction of the volume of coating. The SPS samples exhibit several anomalies, such as a strong anisotropy of relative permittivity, but their phase transformations were detected in the usual temperature ranges.

Identification of the Curie point in Fe-based metallic glasses using in situ hard x-ray diffraction

In situ temperature-resolved x-ray diffraction was used to follow structural changes of amorphous Fe(73.5−x)MnxSi13.5Cu1Nb3B9 (x = 1, 3, 5, 7 and 9) during constant rate heating experiments. Analysing diffraction patterns in reciprocal space by tracing the position of the first sharp diffraction peak provided information about the thermal expansion behaviour on atomic scale. Two distinct zones showing different slopes were identified for all expansion curves in the temperature range between 40 and 450 °C. The temperatures at which the expansion curves change their slopes are in good accordance with the Curie temperatures determined from thermomagnetic curves. Therefore, it is concluded that the in situ high-energy x-ray diffraction enables detection of the transition from a ferromagnetic to a paramagnetic state in the case of Fe-based metallic glasses.

In situ studies of CeO2-supported Pt, Ru, and Pt–Ru alloy catalysts for the water–gas shift reaction: Active phases and reaction intermediates

The activity and structure of three CeO2-based catalysts (Pt–CeO2, Ru–CeO2, and Pt–Ru alloy-CeO2) active for water–gas shift reaction (WGSR) are studied by in situ X-ray diffraction (XRD), operando X-ray absorption near edge spectroscopy (XANES), operando diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS), and high-resolution transmission electron microscopy (HRTEM) in order to understand and thus correlate both bulk and surface dynamics with performance. All systems investigated displayed a high WGS activity. Temperature-resolved XRD (under CO or H2 environment) indicated an additional expansion of the CeO2 crystal lattice at 100–250°C for the catalysts compared to pure CeO2. This extra lattice expansion is due to additional oxygen removal from CeO2 promoted by the deposited Pt, Ru, or Pt–Ru alloy particles; CO showed an accelerated expansion when compared to that of H2. DRIFTS spectra revealed the formation of substantial amounts of formates (HCOO–) on Pt–CeO2 during WGSR, while formates on PtRu–CeO2 and Ru–CeO2 were at a much lower level. For all catalysts, formate species totally disappeared by 350°C. The inhibition of formate formation on PtRu–CeO2 points to a modification of the chemical properties of Pt by alloying with Ru. The fact that the inhibition of Pt-bound formate species does not affect the catalytic activity implies that they are probably merely spectators on Pt, or at least not involved in the main reaction pathway. While the Pt–Ru alloy was not more active than Pt–CeO2, the alloyed catalyst did show a reduced generation of methane under WGSR conditions compared to Ru–CeO2. Pt XANES data confirmed the reduction of Pt in both Pt–CeO2 and PtRu–CeO2 with increasing temperature in the WGSR environment. HRTEM showed that the reduced PtRu–CeO2 catalyst was composed of a Pt–Ru alloy with a mean particle size of 2nm well dispersed over the CeO2 support. Overall, the work indicates that a Pt–Ru alloy supported on CeO2 is an active and selective catalyst for WGSR.

Investigations on the thermal behaviour of [Ni(NH3)6](NO3)2 and [Ni(en)3](NO3)2 using TG–MS and TR-XRD under inert condition

Thermal behaviour of hexaamminenickel(II) nitrate and tris(ethylenediamine)nickel(II) nitrate have been investigated by means of simultaneous thermogravimetry/DTA coupled online with mass spectral (MS) studies and temperature resolved X-ray diffraction (TR-XRD) techniques under inert atmospheric condition. Both the complexes produce highly exothermic reactions during heating due to the oxidation of the evolved ammonia or ethylenediamine by the decomposition products of Ni(NO3)2. Evolved gas analysis by MS studies detected fragments like NH2 and NH ions with weak intensity. The decomposition of nitrate group generates N, N2, NO, O2 and N2O species. Ethylenediamine (m/z 60) is fragmented to H2 (m/z 2), N (m/z 14), NH3 (m/z 17) and CH2=CH2/N2 (m/z 28) species. The formation of the intermediates was monitored by in situ TR-XRD. The residue of thermal decomposition for both the complexes was found to be crystalline NiO in the nano range.

Thermal and X-ray analysis of racemic bupivacaine hydrochloride

An amide-type local anesthetic drug, bupivacaine hydrochloride (BupiHCl), in the form of racemate is listed in the European and American pharmacopoeias and continues to be used in medicine. Thermal and X-ray analysis of commercial BupiHCl monohydrate was performed by differential scanning calorimetry with thermogravimetry, hot stage microscopy, and X-ray diffraction. Endothermic dehydration occurs at the temperature range of 73–130 °C for DSC–TG 111 (Setaram) and at 83–150 °C for DSC 404 (Netzsch). Both curves at 2 and 10 °C min−1 clearly reflect phase transformation of anhydrous Form I into II before reaching the melting point. A well-defined exothermic phase transition of BupiHCl was detected at a lower heating rate. Temperature-resolved X-ray diffraction in conjunction with DSC led to determining a similarity between the obtained thermal events. Microscopic investigation also confirmed the above-mentioned transformations.

Kinetic Study of the Graphite Oxide Reduction: Combined Structural and Gravimetric Experiments under Isothermal and Nonisothermal Conditions

The mechanisms involved in the thermal reduction of graphite oxide (GO) are not yet clear. In the present study, the thermal reduction of GO, obtained by a Brodie-based method, is monitored by means of time- and temperature-resolved X-ray diffraction (XRD), thermogravimetric analysis (TGA), and TGA/mass spectrometry (MS) in dynamic (nonisothermal) and static (isothermal) modes. Two distinct mechanisms were well resolved by the fitting of isothermal TGA data to 2D diffusion and autocatalytic models, which provides new insights on the thermal behavior of GO. The combined TGA and XRD results in isothermal mode suggest that the 2D diffusion mechanism mainly occurs in the interlayer, whereas the autocatalytic mechanism occurs in the external surface. The latter overcomes the former when GO has lost about 10 wt %. The results are compared to previous studies on the thermal reduction of GO. The differences found could be attributed to the synthetic method used to obtain GO.

Thermal decomposition studies of [Ni(NH3)6]X2 (X = Cl, Br) in the solid state using TG-MS and TR-XRD

Detailed investigation on the thermal behaviour of hexaamminenickel(II) chloride and hexaamminenickel(II) bromide has been carried out by means of simultaneous TG/DTA coupled online with mass spectroscopy (TG-MS) and temperature-resolved X-ray diffraction (TR-XRD). Evolved gas analyses by TG-MS revealed the presence of NH2, NH, N2 and H2 fragments in addition to ammonia during the deamination process. These transient species resulted due to the fragmentation of the evolved ammonia during pyrolysis. The intermediates formed during the thermal deamination stages were monitored by in situ TR-XRD. The final product of the decomposition was found to be nano size metallic nickel in both cases. Morphology of the complexes, intermediates and the residue formed at various decomposition stages was analysed by scanning electron microscope (SEM). Kinetic analyses using isoconversional method for deamination and dehalogenation reaction show that the activation energies vary with the extent of conversion, indicating the multi-step nature of these solid state decomposition reactions.

Thermoanalytical investigations of tris(ethylenediamine)nickel(II) oxalate and sulphate complexes

Investigations on the thermal behaviour of [Ni(en)3]C2O4·2H2O and [Ni(en)3]SO4 have been carried out in air and helium atmosphere. Simultaneous TG/DTA coupled online with mass spectroscopy (MS) in helium atmosphere detected the presence of H2, O, CO, N2/CH2=CH2 and CO2 fragments during the decomposition of tris(ethylenediamine)nickel(II) oxalate and H2, O, NH, NH2, NH3 and N2/CH2=CH2 fragments for tris(ethylenediamine)nickel(II) sulphate complex. The thermal events during the decomposition were monitored by temperature-resolved X-ray diffraction. In air, both the complexes give nickel oxide as the final product of the decomposition. In helium atmosphere, tris(ethylenediamine)nickel(II) oxalate gives nickel as the residue, whereas tris(ethylenediamine)nickel(II) sulphate gives a mixture of nickel and nickel sulphide phases as the final residue. Kinetic analyses of these complexes by isoconversional methods are discussed and compared.

Melting of Nanostructured Drugs Embedded into a Polymeric Matrix

The melting behavior of nanostructured organic materials (drugs) embedded into a cross-linked polymeric matrix was studied for the first time. The complex microstructure of these nanocomposites, yielded by the polymer matrix in which molecular clusters and nanocrystals of drug plus a cospiquous fraction of water are confined, demanded synergic application of thermal analysis and temperature resolved X-ray diffraction. A relevant depression of the melting point of the embedded drug with respect to the bulk drug was experimentally demonstrated. The coherent domain size of the embedded drug nanocrystals was independently evaluated by thermal and diffraction data and results were in agreement. This indicates that the adopted thermodynamic melting model, based on Laplace and Gibbs−Duhem equations and developed for simpler systems, can be successfully assessed for describing drug/polymer nanocomposites, and, potentially, other classes of organic nanocomposites.

The reaction of ceria coatings on mica with H 2S : An in-situ X-ray diffraction study

Thin layers of ceria were deposited on the surface of mica platelets in solution. The reaction of such particles with hydrogen sulfide yields a red colored special effect pigment. The ceria layer reacts with H 2S to produce a variety of sulfide and oxysulfide phases. The reaction path discovered in situ by time and temperature resolved X-ray diffraction is CeO 2→CeS 2→C-Ce 2S 3→Ce 10S 14O. The reaction itself is extremely variable depending on gas flow, heating rates and decomposition atmospheres. Effects on the thin film are recorded by scanning electron microscopy (SEM) and revealed a destruction of the layer once red Ce 10S 14O was formed. The product layer then reveals the typical nonwetting behaviour of a liquid on a surface.