Vapor-solid Reaction Research Articles

Crystal and magnetic properties of 57Fe doped MnAs for magnetic refrigeration application

The Mn1−x 57Fe x As (x = 0.001, 0.003, 0.005) compounds for magnetic refrigeration application were synthesized by using a solid-vapor reaction method. We have investigated the crystallographic and magnetic properties of Mn1−x 57Fe x As (x = 0.001, 0.003, 0.005) samples by using x-ray diffractometer (XRD), vibrating sample magnetometer (VSM), superconducting quantum interference device (SQUID), and Mossbauer spectrometer. The XRD patterns, revealed that all samples exhibited hexagonal space group P63/mmc below Curie temperature (T C ), while above T C they belong to the orthorhombic space group Pnma. The temperature-dependent magnetization curves under 200 Oe between 4.2 and 320 K showed a large hysteresis in the magnetization as a function of the temperature. To analyze the meagnetocaloric effect, the value of magnetic entropy (−ΔS M ) was calculated from the isothermal initial curves up to 5 T at various temperatures. Mossbauer spectra of Mn0.997 57Fe0.003As sample were taken at various temperatures ranging from 4.2 to 315 K.

The effects of sintering temperature on the morphology and physical properties of in situ Si3N4 bonded MgO–C refractory

Si3N4 bonded MgO–C refractory was formed in situ using silicon powder as a raw material through the nitriding processing. The effects of sintering temperature on the microstructural evolution and physical properties of the in situ formed Si3N4 bonded MgO–C refractory were investigated. The results showed that α–Si3N4 and β–Si3N4 were generated from the reaction of Si–N2 in MgO–C refractories at 1450°C. The β–Si3N4 phase was the major ceramic bonding phase which connects neighbouring MgO and graphite particles. Rod–like β–Si3N4 crystals with conical tips were formed by the direct nitriding of liquid silicon following a vapor-liquid-solid growth mechanism in the initial stage which was followed by a vapor-solid reaction at elevated temperatures. Based on the determined characteristic properties of the specimens, 1500°C is the best sintering temperature for the in situ formation of Si3N4 in MgO–C refractory.

Evolution of the novel C/SiO2/SiC ternary aerogel with high specific surface area and improved oxidation resistance

A novel C/SiO2/SiC ternary aerogel is derived from catechol-formaldehyde/silica hybrid aerogel (CF/SiO2) via a one-step sol-gel method followed by carbonization and carbothermal reduction processes under flowing argon. The effects of the carbon/silica molar ratios on the physicochemical properties of the C/SiO2 binary and C/SiO2/SiC ternary aerogel are investigated. The mechanism of the textural and structural evolution for the novel C/SiO2/SiC ternary aerogel is further discussed based on the experimental results and the calculated Gibbs free energy changes at different SiO partial pressure. The SiC layer is first formed on the surface of the composite aerogel via the solid-vapor reaction at 1400°C while SiC nanoparticles form at 1500°C. The C/SiO2/SiC ternary aerogel possesses a rather high specific surface area (746.87m2/g), a high micropore volume (0.2279cm3/g) and a high porosity (89.10%). The oxidation resistance is improved for 100°C when compared with the carbon based aerogel. The ternary aerogel obtains a high compressive strength (1.86MPa) and a low thermal conductivity (0.053W/m*K), which is suitable for high efficient thermal insulation uses both in inert and oxidative atmosphere.

Visualization of Protonation/Deprotonation of Active Pharmaceutical Ingredient in Solid State by Vapor Phase Amine-Selective Alkyne Tagging and Raman Imaging

Here, we report a simple and direct method to visualize the protonation/deprotonation of an amine active pharmaceutical ingredient (API) in the solid state using a solid-vapor reaction with propargyl bromide and Raman imaging for the assessment of the API during the manufacturing process of solid formulations. An alkyne tagging occurred on the free form of solid haloperidol by the vapor phase reaction, and a distinct Raman signal of alkyne was detected. Alkyne signal monitoring by Raman imaging enabled us to visualize the distribution of the free-form haloperidol in a solid formulation. On the other hand, haloperidol hydrochloride did not react with propargyl bromide in the solid-vapor reaction, and the alkyne signal was not observed. Using the difference in reactivity, the protonation/deprotonation of the amine API in the solid state could be visualized. As an example of application, we tried to visually assess the protonation/deprotonation state when the free-form haloperidol was ground with acids using the solid-vapor reaction and Raman imaging and found that haloperidol was partially protonated when ground with 2 equivalents of hydrogen chloride. Furthermore, we demonstrated the relationship between the degree of protonation and the amount of water added as a medium for grinding haloperidol with succinic acid.

Effect of NOx on AgI formation in Ag-mordenite

Ag loaded mordenite can be used as a trap for radio-iodine arising from nuclear reprocessing operations. Typically, iodine is trapped in the Ag loaded mordenite by the formation of AgI in the pores of the mordenite, through a solid-vapour reaction. In the presence of NOx and water vapour, AgI is most likely formed by liquid-vapour reaction between AgNO3 and I2. This reaction results in the formation of large aggregates of AgI crystals on the surface of the mordenite, also leading to a yellow colouration of the mordenite, which is not observed when NOx and water vapour is absent.

Facile fabrication of ultralong organic nanowires with enhanced phosphorescence

The development of organic micro/nanomaterials plays a major role in emerging organic optoelectronic applications. In the present work, the ultralong organic nanowires with high aspect ratio (>256) were firstly fabricated by a green vapor-solid reaction strategy. The organic nanowires reveal improved phosphorescent performance, which is attributed to high aspect ratio of nanowires, and/or morphological anisotropy of larger bundles made of nanowires. The importance of this work evidences that the vapor-solid reaction can facilely fabricate organic nanowire materials.

Enhanced ZT of InxCo4Sb12-InSb Nanocomposites Fabricated by Hydrothermal Synthesis Combined with Solid-Vapor Reaction: A Signature of Phonon-Glass and Electron-Crystal Materials.

A rapid route of synthesizing pristine Co4Sb12 at relatively low temperature was previously developed. However, filling the voids using the same procedure is not successful. We develop a new route to fabricate In-filled cobalt skutterudites with InSb nanoinclusions InxCo4Sb12-(InSb)y via solid-vapor reaction between hydrothermally synthesized Co4Sb12 powder and the indium chunk. The nanocomposites are characterized using powder X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS). With the success of partial filling of In into the voids and InSb nanoinclusions, the power factor of the InxCo4Sb12-(InSb)y nanocomposites is significantly enhanced, and the thermal conductivity is lowered as compared with the pristine Co4Sb12. As a result, ZT with its highest value of 1.0 is attained for the hierarchical structured In0.04Co4Sb12-(InSb)0.05 nanocomposite at 575 K. The attained ZT value is among the highest ever reported value at T ≤ 575 K for In-filled cobalt skutterudites.

Improved photoelectrochemical performance of bismuth vanadate by partial O/F-substitution

Fluorine-containing bismuth vanadate (F:BiVO4) powder was synthesized using a new, clean, and simple solid-vapor reaction. Incorporation of fluorine mainly leads to the formation of cation vacancies. Electrodes were fabricated from the pre-synthesized powder samples by electrophoretic deposition onto fluorine-doped tin oxide coated glass slides and subsequent calcination. The photoelectrochemical performance concerning the water oxidation reaction was investigated and compared to pristine BiVO4 revealing strongly enhanced photoelectrochemical behavior for the F-containing BiVO4.

Microstructure and property of porous mullites with a whiskers framework obtained by a sol–gel process

Porous mullites with a whiskers framework and high porosities were fabricated by the reaction sintering (1100 to 1600°C, 1h, in an airtight container) of an aerogel block shaped by the sol–gel transition of a mullite precursor composed of SiO2 sol, Al2O3 and AlF3 powders (as reaction catalyst). The effect of heating temperatures on porosity, whisker formation, microstructure feature and compressive strength of the porous mullites was determined by XRD, SEM and compressive test. The results indicate that after heating at temperatures from 1100 to 1600°C, the porosities of the mullites varied within the range of 84.1–80.2%. The whiskers in the framework well lap-jointed each other to form the large space and became elongated and smooth at high temperatures due to the accelerated vapor–solid reaction rate. A maximum compressive strength of 16.1MPa was obtained for the whiskers framework heated at 1600°C; this strength was attributed to the strong bonding among the smooth whiskers.

Towards a uniform and large-scale deposition of MoS2 nanosheets via sulfurization of ultra-thin Mo-based solid films

Large-scale integration of MoS2 in electronic devices requires the development of reliable and cost-effective deposition processes, leading to uniform MoS2 layers on a wafer scale. Here we report on the detailed study of the heterogeneous vapor–solid reaction between a pre-deposited molybdenum solid film and sulfur vapor, thus resulting in a controlled growth of MoS2 films onto SiO2/Si substrates with a tunable thickness and cm2-scale uniformity. Based on Raman spectroscopy and photoluminescence, we show that the degree of crystallinity in the MoS2 layers is dictated by the deposition temperature and thickness. In particular, the MoS2 structural disorder observed at low temperature (<750 °C) and low thickness (two layers) evolves to a more ordered crystalline structure at high temperature (1000 °C) and high thickness (four layers). From an atomic force microscopy investigation prior to and after sulfurization, this parametrical dependence is associated with the inherent granularity of the MoS2 nanosheet that is inherited by the pristine morphology of the pre-deposited Mo film. This work paves the way to a closer control of the synthesis of wafer-scale and atomically thin MoS2, potentially extendable to other transition metal dichalcogenides and hence targeting massive and high-volume production for electronic device manufacturing.

Synthesis of Silicon Microspheres

The synthesis of silicon microspheres is of outmost importance, especially for the production of optical and electrical devices due to their unique properties displayed by this material. In this paper, we review the research on the synthesis of silicon microspheres, including one physical method, the drop method and several chemical methods, such as vapor-phase reaction, vapor-solid reaction, liquid phase reaction and magnesio-thermal reduction method. The formation mechanisms for silicon microsphere particles are also summarized.

Large-area, high-quality organic–inorganic hybrid perovskite thin films via a controlled vapor–solid reaction

Large-area high-quality MAPbI3 films were fabricated via a controlled vapor–solid reaction monitored by in situ resistance measurement.

Coordination polymer flexibility leads to polymorphism and enables a crystalline solid-vapour reaction: a multi-technique mechanistic study.

Despite an absence of conventional porosity, the 1D coordination polymer [Ag4(O2C(CF2)2CF3)4(TMP)3] (1; TMP=tetramethylpyrazine) can absorb small alcohols from the vapour phase, which insert into Ag–O bonds to yield coordination polymers [Ag4(O2C(CF2)2CF3)4(TMP)3(ROH)2] (1-ROH; R=Me, Et, iPr). The reactions are reversible single-crystal-to-single-crystal transformations. Vapour-solid equilibria have been examined by gas-phase IR spectroscopy (K=5.68(9)×10−5 (MeOH), 9.5(3)×10−6 (EtOH), 6.14(5)×10−5 (iPrOH) at 295 K, 1 bar). Thermal analyses (TGA, DSC) have enabled quantitative comparison of two-step reactions 1-ROH→1→2, in which 2 is the 2D coordination polymer [Ag4(O2C(CF2)2CF3)4(TMP)2] formed by loss of TMP ligands exclusively from singly-bridging sites. Four polymorphic forms of 1 (1-ALT, 1-AHT, 1-BLT and 1-BHT; HT=high temperature, LT=low temperature) have been identified crystallographically. In situ powder X-ray diffraction (PXRD) studies of the 1-ROH→1→2 transformations indicate the role of the HT polymorphs in these reactions. The structural relationship between polymorphs, involving changes in conformation of perfluoroalkyl chains and a change in orientation of entire polymers (A versus B forms), suggests a mechanism for the observed reactions and a pathway for guest transport within the fluorous layers. Consistent with this pathway, optical microscopy and AFM studies on single crystals of 1-MeOH/1-AHT show that cracks parallel to the layers of interdigitated perfluoroalkyl chains develop during the MeOH release/uptake process.

Heterogeneous Catalyst Deactivation and Regeneration: A Review

Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.

Vapor growth of typical II-VI wide-gap semiconductor crystals directly from the constituent elements

Three ZnE (E=Se, Te) single crystals were successfully grown directly from Zn-E (E=Se, Te) system with the assistance of I2 or NH4Cl as the transport agents via a modified chemical vapor transport (CVT) method by avoiding the kinetics limitations of the congruent sublimation of ZnE compound. As-grown ZnE crystals exhibit different crystalline appearance due to various growth conditions. The structure, growth habit and morphologies of as-grown ZnE crystals are investigated by XRD, RO-XRD, SEM and optic microscope. ZnE crystals with NH4Cl transport agent look like the platelets with an interesting growth habit, while ZnE crystal with I2 transport agent has high crystalline quality with a conical shape. Contrasting investigation between different growth results offers us an opportunity to understand the vapor-free-growth mechanism of ZnE crystals in closed-space CVT system, indicating that the free-growth habit of ZnE crystals depends on the growth parameters, which can be essentially attributed to their growth mechanism and the main vapor–solid reactions on the interfaces.

Morphology-controllable fabrication of organic microcrystals by solid-phase reactions: revealing morphology-sensitive highly efficient phosphorescence and enhanced near-infrared absorption

The vapor-solid reaction induced hexangular microflakes exhibit high phosphorescence quantum yield and enhanced NIR absorption.

Phase Formation and Morphology of Nickel Silicide Thin Films Synthesized by Catalyzed Chemical Vapor Reaction of Nickel with Silane

The synthesis of nickel silicide thin films via a vapor–solid reaction has been studied by exposing thin (10 nm) Ni films to silane (SiH4). The crystalline phases, the Ni/Si stoichiometric ratios, as well as the surface and interface properties of the resulting silicide films were investigated as a function of the growth parameters such as the SiH4 partial pressure, the reaction temperature, and the exposure time. At low temperature (300 °C), SiH4 exposure led to the self-limiting deposition of Si on Ni by catalytic decomposition of SiH4 but not to silicate formation. Between 350 and 400 °C, phase pure orthorhombic NiSi films were obtained that were formed directly without any apparent intermediate Ni-rich silicide phases. A transformation to NiSi2 occurred at 450 °C and above, and at 500 °C phase pure NiSi2 was obtained. Here, the transient formation of NiSi was observed that transformed into NiSi2 for prolonged SiH4 exposure. The results indicate that the Si solubility governs the phase formation sequen...

Formation mechanism of periodic layered structure in Ni3Si/Zn system

The formation of periodic layered structure in Ni3Si/Zn diffusion couples with Zn in vapor or liquid state was investigated by SEM-EDS, FESEM and XRD. The results show that the diffusion path in solid–liquid reaction is Ni3Si/(T+γ)/γ/…T/γ/Ni4Zn12Si3/γ/…Ni4Zn12Si3/γ/Ni4Zn12Si3/δ…/Ni4Zn12Si3/δ/liquid-Zn, and the diffusion path in solid–vapor reaction is Ni3Si/θ/(T+γ)/γ/…/T/γ/…T/γ/vapor-Zn. With increasing Zn diffusion flux, the diffusion reaction path moves toward the Zn-rich direction, and the distance from the Ni3Si substrate to the periodic layer pair nearest to the interface decreases. In the initial stage of both reactions, γ phase nucleates and grows within T matrix phase at first, and then conjuncts together to form a band to reduce the surface energy. Based on the experimental results and diffusion kinetics analysis, the microstructure differences were compared and the formation mechanism of the periodic layered structure in Ni3Si/Zn system was discussed.

Thermodynamic analysis and growth of ZnSe single crystals in Zn-Se-I2 system

A modified chemical vapor transport system is developed to grow ZnSe single crystals from zinc–selenium source materials, where iodine serves as the chemical transport agent to avoid the kinetics limitations of the congruent sublimation conditions. ZnSe crystals with different crystalline quality are obtained under various growth conditions. The thermodynamic properties of Zn-Se-I2 system are studied by combining the mass conservation with the vapor-solid reactions related to crystal growth. The mass transport is analyzed by using the diffusion-convection mathematical model. Depending on initial iodine concentration and the designed temperature difference between source zone and growth zone, the optimum growth conditions can be predicted based on the calculated maximum growth rate. Comparing growth results with theoretical analysis indicates that Zn-Se-I2 system affords a feasible route to grow ZnSe crystals. High quality ZnSe crystal can be achieved under the theoretically optimized growth conditions.

Effects of Oxygen Doping on the Transport Properties of Hg&lt;sub&gt;0.82&lt;/sub&gt;Re&lt;sub&gt;0.18&lt;/sub&gt;Ba&lt;sub&gt;2&lt;/sub&gt;Ca&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;8+d&lt;/sub&gt; Superconducting Polycrystals

Hg0.82Re0.18Ba2Ca2Cu3O8+dpolycrystalline ceramic samples were prepared using a solid-vapour reaction technique. First, the ceramic precursor was prepared from a mixture of Ba2Ca2Cu3Oxand ReO2powders in a molar ratio of 1:0.18. The precursor material was annealed under three different partial pressures of oxygen that consisted of a mixture of oxygen/argon in the following ratios: 5/95 (sample A), 10/90 (sample B) and 15/85 (sample C). Secondly, the precursors prepared at different O2partial pressures were blended with HgO at a molar relationship of 1:0.82. The synthesis was carried out at 865 °C for 72 h. Moreover, analyses using X-ray powder diffraction, Scanning Electron Microscopy (SEM), and Energy Dispersion X-ray spectroscopy (EDS) were performed. These results demonstrated a similarity in the grain morphology within the samples. Using SEM images, a histogram of grain-boundary size was produced where the average junction size is represented by a gamma density distribution function. Finally, the samples were submitted to ac electrical resistivity ρ (T) under a low applied magnetic field (up to 400 Oe). Samples cut into bars approximately 7 × 1 × 1 mm3in size were studied using a four-probe technique. The zero-resistance critical temperatures (Tcj) were determined from ρ (T) curves. The results are compared and qualitatively explained in the framework of flux trapping by superconducting grains. In our opinion, the oxygen partial pressure has a strong influence on the grain junctions and causes island structures that form defects at the grain boundaries.