High-temperature IR Research Articles

Structural and opto-electrical properties of Y2O3 nanopowders synthesized by co-precipitation method

The synthesis-dependent structural-optical characteristics of nanomaterials have induced the critical optimization of parameters for nanoparticle synthesis. Considering the potential applications of yttria (Y2O3) in high-temperature IR windows and electro-optic devices, the present study describes the preparation of yttria nanopowders (YNPs) through co-precipitation method. Some special morphological and opto-electrical properties have been observed with a change in the precipitating agent concentration (R = NH5CO3/Y3+ = 1.5–5.5) without using any surfactant. Rietveld refinement confirmed the body-centered cubic (Ia-3 space group) structure of YNPs. Surface functionalities have been determined by Fourier transform infrared (FTIR) spectroscopy. Electron microscopy results confirmed the formation of agglomerated YNPs with R-dependent morphological modifications from flake-like shape to pseudo-spherical and rod-like particles. UV–visible and fluorescence (FL) spectroscopy confirmed the R-dependent optical absorption and emission (indigo, blue and green) characteristics. The dielectric measurement also confirmed the R-dependent variation in the dielectric constant values in the lower frequency range.

Preparation of novel silver borates by soft hydrothermal synthesis in sealed tubes: New representatives of larderellite and veatchite families

New silver-based representatives of the larderellite and veatchite families, Ag2B10O14(OH)4∙H2O (1) and Ag2B5O8(OH)∙H2O (2) respectively, have been prepared using a soft hydrothermal synthetic approach inside a sealed silica tube. Both structures are built of the pentaborate groups yet exhibit various dimensionality: 2D for 1 and 1D for 2. The silver atoms in 1 exhibit noticeable anharmonicity approximated using Gram–Charlie approach. 1 was additionally characterized by thermal analysis, high-temperature X-ray powder diffraction and IR spectroscopy. Thermal expansion of 1 is strongly anisotropic (α11 = 38, α22 = −13, α33 = 14 × 10−6 °С−1) which is related with the hinge mechanism of the larderellite chains from corner-sharing pentaborate groups. Topology and complexity analysis of these compounds within the larderellite and veatchite families is presented.

Transformation of Specific Dispersion Interactions between Cellulose and Polyacrylonitrile in Solutions into Covalent Interactions in Fibers.

Morphological transformations in emulsions of cellulose and polyacrylonitrile (PAN) ternary copolymers containing acrylonitrile, methyl acrylate, and methylsulfonate comonomers in N-methylmorpholine-N-oxide were studied over the entire range of concentrations depending on temperature and intensity of the deformation action. Based on the morphological and rheological features of the system, the temperature-concentration range of spinnability of mixed solutions was determined, and composite fibers were spun. The fibers are characterized by a heterogeneous fibrillar texture. Studies of the structure of the fibers, carried out using X-ray diffraction analysis, revealed a decrease in cellulose crystallinity with an increase in the content of PAN. The study of the thermal properties of the obtained fibers, carried out using DSC, and chemical transformations in them in a wide temperature range by high-temperature diffuse reflection IR spectroscopy made it possible to reveal a new intense exothermic peak on the thermograms at 360 °C, which according to the IR spectra corresponds to the transformation of intermacromolecular physical interactions of the PAN and cellulose into covalent bonds between polymers. In addition, the ester groups found during the thermal treatment of the PAN part of the composite fibers in the pyrolysis zone can have a key effect on the process of their further carbonization.

Superior corrosion resistance of high-temperature Ir–Ni–Ta–(B) amorphous alloy in sulfuric acid solution

In this work, the corrosion behaviors and underlying mechanisms of high-temperature Ir-based amorphous alloys in an acidic solution were investigated systematically. The Ir-Ni-Ta-B amorphous alloy exhibits a crevice corrosion behavior with a superior corrosion resistance characterized by a low passive current density and a wide passive potential range. It is found that the high-exchange current density of H+ and H2 couple on the metalloid constituent can accelerate the active precipitation of passivation elements, leading to rapid formation of passive film. In sulfuric acid solutions, the formed passive film containing Ir, Ta5+ and Ni3+ oxides significantly increase the corrosion resistance.

Superior Corrosion Resistance of High-Temperature Ir–Ni–Ta–(B) Amorphous Alloy in Sulfuric Acid Solution

Superior Corrosion Resistance of High-Temperature Ir–Ni–Ta–(B) Amorphous Alloy in Sulfuric Acid Solution

Conversion of dimethyl ether to liquid hydrocarbons on zeolite catalysts: Influence of a base admixture in the zeolite

This paper presents comparative data on the selectivity and gasoline fraction composition for commercial catalysts based on Zn- and Pd-modified zeolites with the same MFI structural type, but produced by different manufacturers. The data are obtained in the operation of a two-reactor micropilot unit in a flow circulation mode. The relationship and differences between the character and type of Brønsted acid site were investigated using in situ high-temperature diffuse reflectance IR spectroscopy during annealing of the catalysts in dry argon, hydrogen, and dimethyl ether flows. It was found that catalysts contain organic ammonium cations with different structures of organic substituents, which decompose to give a very strong nitrogen-containing acid site. This site can promote the formation of branched paraffins and light aromatics from dimethyl ether. Under the action of these sites, methanol can be rapidly converted to DME, which is more reactive towards the production of gasoline fraction.

Features of the Mechanism of the Dimethyl Ether to Light Olefins Conversion over MgZSM-5/Al2O3: Study by Vibrational Spectroscopy Experimental and Theoretical Methods

Features of the mechanism of dimethyl ether (DME) conversion to olefins over ZSM-5 zeolite catalysts were studied using experimental and theoretical methods of vibrational spectroscopy. A catalytic activity comparison of the catalysts Mg-HZSM-5 without a binder and Mg-HZSM-5/Al2O3 containing 1% Mg (by weight) and 33% Al2O3 (by weight) as a binder in the DME conversion was carried out. Using high-temperature diffuse reflectance IR (DRIR) spectroscopy in situ combined with quantum-chemical simulations in the temperature range of 25–450 °C in a stream of dry Ar and DME, the bands corresponding to OH bonds, including BAS and H3O+, were interpreted. Depending on the temperature and the presence of magnesium and a binder in the catalyst composition, the intensity and position of these bands maxima vary greatly. The intermediates of the catalytic DME conversion were discovered and identified. At low temperatures (below 200 °C), in a DME stream, methoxy groups (CH3O-Al-), ketene (CH2 =C=O), and a carbocation (CH3 +) were formed on the surface of the catalysts. As the temperature rises (above 300° C), the bands from ketene completely disappear in the spectra of catalysts, and bands from oxonium cations or ylide particles appear, leading the process of DME conversion by the oxonium-ylide mechanism. In the presence of H3O+, the conversion of DME on the zeolite catalyst surface was more effective; however, selectivity for olefins was lower.

Reliable Mircohotplate Design for High temperature Gas Sensing and IR Source

While Microhotplates (MHPs) keeps very important place in many critical applications such as high temperature gas sensing and building IR source, they still suffer from short term reliability due to high thermal stress at relatively high temperatures. Here we demonstrate low thermal stress design at high temperatures by combining the advantages of spring type structure and compatible materials in terms of thermal expansion constant. FEM results demonstrated that, the main mechanism behind achieving low thermal stress is using compatible materials. A low thermal stress of 180 MPa at 2119 K was achieved by using SiN/Polysilicon/SiN stack with a spring type design via FEM tool. The response time required to reach 2076 K was calculated as 200 ms with 3.47mW power consumption.

Zr- and La-containing Catalysts in Synthesis of Methanol and Dimethyl Ether

Zirconium oxide samples synthesized and modified with Al, Si, W oxides were studied as dehydrating components of bifunctional catalysts for synthesis of dimethyl ether. ZrO2 modified with Al and Si oxides is inactive in the dehydration of methanol, but its dehydrating activity becomes comparable with the activity of γ-Al2O3 upon introduction of WO3. According to the data on methanol adsorption at 46°C, the adsorption capacity of ZrO2 modified with SiO2 is comparable with the capacity of γ-Al2O3, and that of ZrO2 modified with WO3 is four times lower. The difference in the catalytic and adsorption behavior of the samples is accounted for by the data of in situ high-temperature diffuse reflection IR spectroscopy. A high content of weak Bronsted acid centers is observed on the ZrO2 surface, with the interaction of these with methanol resulting in the methoxylation of the catalyst surface. When W oxide is deposited onto zirconium oxide, the surface has strong Bronsted centers involved in the reaction of methanol dehydration. A coprecipitation from solution of nitrate salts of Cu, Zn, La with Na carbonate, followed by the procedures of filtration, washing, and thermal treatment, yielded a catalyst for synthesis of methanol, the activity of which is close to that of the industrial catalyst.

High-temperature X-ray diffraction, Raman and IR spectroscopy on serandite

We collected in situ high-temperature powder X-ray diffraction (XRD) patterns, as well as Raman and Fourier transform infrared (FTIR) spectra on a natural serandite sample. The volumetric thermal expansion coefficient αV (K−1) is determined as a linear function of T (K): 37.6(5) × 10−9 × T + 11.1(3) × 10−6, with an averaged value of 31.7(10) × 10−6 K−1, while the anisotropy of axial thermal expansivities shows the order of αa > αb > αc. The isobaric Gruneisen parameters γiP are constrained as: 0.2–1.6 for most of the lattice vibrations below 500 cm−1; while 0–0.6 for the O–Si–O bending and Si–O stretching modes inside the Si3O9 chains above 500 cm−1. As compared with common silicate phases in the upper mantle and the transition zone, the γiP parameters for the internal vibrations are significantly smaller in silicate chains (serandite, enstatite) than those in Si2O7 groups (wadsleyite) and isolated SiO4 units (forsterite, pyrope), since the rotation of the bridging O atoms (in the direction perpendicular to Si–O–Si) could relax the SiO4 tetrahedra at elevated temperature. The OH-bending vibration of serandite is observed in both Raman-active (1378 cm−1) and IR-active (1389 cm−1) modes, with a temperature-dependence of − 0.07 and − 0.09 cm−1/K, respectively. The red-shift of these OH-bending modes with increasing temperature indicates that the hydrogen bond gets weaker as the O3…O4 distance becomes larger during thermal expansion. Additionally, our polarized FTIR spectra confirm that the stretching mode of the very strong hydrogen bond, a broad absorption region (1400–3300 cm−1), is polarized in the direction of E//b, as reported by Hammer et al. (Am Mineral 83:569–576, 1998).

Optical and thermo-mechanical properties of fine-grained transparent yttria ceramics fabricated by hot-press sintering for infrared window applications

In this work, highly transparent yttria ceramics Φ = 55 mm in size were fabricated by a hot-pressing method with 1 at.% ZrO2 or 12 at.% La2O3 as a sintering additive. For a 4-mm-thick specimen doped with ZrO2, the in-line transmittance reaches 71.1% at 400 nm and 80.9% at 1100 nm, and the transmittance of the La2O3-doped specimen is comparable to that of the ZrO2-doped specimen. By means of the relatively low sintering temperature of 1600 °C, the present samples exhibited very fine microstructures (<2 μm), giving rise to excellent mechanical strength levels (∼200 MPa). With regard to the 1 at.% ZrO2-doped specimen, the combination of high strength and high thermal conductivity (∼10 W/m K) substantially improved parameters related to the thermal shock resistance. The results of this study indicate that the hot-pressed transparent yttria ceramic doped with 1 at.% ZrO2 is optically, mechanically, and thermally suitable for high-temperature IR window applications.

The fate of ammonium in phengite at high temperature

Nitrogen (N) is the main component of the atmosphere and is largely considered as a volatile element. However, most researchers now agree that a significant amount of N, in the form of ammonium (NH4+) substituting for K+ in some K-bearing minerals such as clays, micas, and feldspars, can be transferred to the deep Earth through subduction. The fate of ammonium in those minerals during subduction is still poorly known but is likely controlled by temperature and pressure pathways. In an attempt to contribute to understanding the fate of N during high-temperature processes, we carried out in situ high-temperature IR and Raman spectra measurements to investigate the rate and mechanism of NH4+ loss in phengite. We observed that a new OH band at 3425 cm−1 became prominent above 400 °C, and did not change with times during isothermal annealing at 500 and 700 °C. The N-H stretching band shifted to higher wavenumbers in the temperature interval from −150 to 20 °C, while linearly shifted to lower wavenumbers in the temperature interval from 20 to 500 °C and remained stable above 500 °C. The N-H bending band linearly shifted to lower wavenumbers in the temperature interval from −150 to 400 °C and remained stable. The K-O stretching frequency decreased with increasing temperature to 600 °C, and then remained stable. These processes were reversible until dehydration and ammonium loss from phengite starting at 800 °C. The results suggest that (1) at low temperatures, ammonium is ordered and hydrogen bonding between ammonium and the framework evolves during cooling; (2) at high temperatures, the N-H interatomic distance of NH4+ lengthens with increasing temperature until 500 °C. N-H bond subsequently no longer lengthens, accompanied by H transferring from N to neighboring O and forming a new OH band at 3425 cm−1. At 800 °C, H+ starts breaking from N and leaving others to form NH3 and OH−. This study has implications for evaluating the extent to which these minerals can preserve information regarding nitrogen behavior during high-temperature processes.

Monitoring High Temperatures in Industrial Applications

AbstractState of the art IR cameras in the near infrared spectral range for monitoring high temperatures in industrial applications are characterized by a number of small measurement ranges. Scenes with a high temperature contrast require several measures switching between these ranges and result in pictures with under‐ or overexposed parts, respectively.New developed high temperature IR cameras with high‐dynamic silicon detectors are using a spectral range in the near infrared and a very special signal processing. A continuous temperature measurement range from 600 up to 1,500 °C or optional 1,400 to 3,000 °C is realized with a resolution of 512 × 384 or 768 × 576 pixels and a measuring frequency of 60 or 50 Hz. Using a InGaAs high‐dynamic detector with 320 × 256 pixels, a continuous temperature measurement range from 300 to 1,200 °C is realized (measuring frequency 100 Hz). Each resulting image contains the full dynamic range and is transmitted via a Gigabit‐Ethernet interface in real time.

Phase states of hydrous–hydrocarbon fluids at elevated and high temperatures and pressures: Study of the forms and maximal depths of oil occurrence in the Earth’s interior

Based on synthetic fluid inclusions in quartz grown at 240–490°C and 7–150 MPa in aqueous–oil solutions, the behavior, composition, and phase states of liquid, gaseous, and solid hydrocarbons (HC) were studied. Investigations were performed using common and fluorescent microscopy, microthermometry, local common and high-temperature IR Fourier spectroscopy, Raman spectroscopy, chromatography, and X-ray and microprobe analysis. The data obtained allowed us to understand the influence of thermobaric conditions and volume proportions of the oil, aqueous, and gaseous phases on the composition, phase state, and behavior of hydrous–hydrocarbon fluids and estimate the forms and probable maximal depths of the origin of oil in the Earth’s interior.

Surface reactions of dimethyl ether on γ-Al2O3

The surface reactions of dimethyl ether (DME) on industrial alumina (γ-Al2O3) were studied by chromatographic analysis of the products at the outlet of the flow reactor and (independently) by diffuse reflectance IR spectroscopy. The major products of the reactions at 250°С were found to be methanol formed in the reaction of DME with hydroxyl groups (the 3720 and 3674 cm–1 bands in the diffuse reflectance spectrum) and various methoxy groups (the 1121, 1070, 695, and 670 cm–1 bands in the differential spectra). The presence of molecularly adsorbed methanol was confirmed by experiments with methanol fed in a high-temperature IR cell. The interaction of the resulting methanol molecule with the hydroxyl group led to the formation of a water molecule in the gas phase and a methoxy group on the oxide surface. Strong adsorption of molecular DME was revealed, which was favored by an increase in the temperature of the preliminary calcination of oxide from 250 to 450–500°С; treatment of alumina with water vapor after its preliminary contact with DME led to a recovery of the hydroxyl coating and a replacement of molecularly adsorbed DME with hydroxyl. The thermal effect recorded in a flow reactor was positive during the adsorption of DME and negative during the desorption of weakly bonded DME. Schemes of formation of methoxy groups in the interaction of DME and methanol with surface hydroxyls were suggested.

Synthesis and study of manganese and cobalt triuranates MIIU3O10·6H2O

A procedure was developed for preparing Mn(II) and Co(II) triuranates MIIU3O10·6H2O by the reaction of schoepite UO3·2.25H2O with aqueous solutions of Mn(II) and Co(II) nitrates. Methods of hightemperature X-ray diffraction, IR spectroscopy, thermal analysis, and chemical analysis were used for determining the composition and structure of the compounds and for studying their dehydration and thermal decomposition.

Synthesis and study of magnesium triuranate hexahydrate, MgU3O10·6H2O

A procedure was developed for preparing magnesium triuranate hexahydrate, MgU3O10·6H2O, by the reaction of hydrated uranium(VI) oxide UO3·nH2O with an aqueous solution of magnesium nitrate under hydrothermal conditions at 200°C. The composition and structure of MgU3O10·6H2O were determined by high-temperature X-ray diffraction, IR spectroscopy, and thermal and chemical analyses; the dehydration and thermal decomposition of the compound were studied.

High temperature Ir segregation in Ir–B ceramics: effect of oxygen presence on stability of IrB2 and other Ir–B phases

The formation of IrB2, IrB1.35, IrB1.1 and IrB monoboride phases in the Ir–B ceramic nanopowder was confirmed during mechanochemical reaction between metallic Ir and elemental B powders. The Ir–B phases were analysed after 90 h of high energy ball milling and after annealing of the powder for 72 h at 1050°C in vacuo. The iridium monoboride (IrB) orthorhombic phase was synthesised experimentally for the first time and identified by powder X-ray diffraction. Additionally, the ReB2 type IrB2 hexagonal phase was also produced for the first time and identified by high resolution transmission electron microscope. Ir segregation along disordered domains of the boron lattice was found to occur during high temperature annealing. These nanodomains may have useful catalytic properties.

Measurement of Thermo-Radiation Characteristics of IR Window Materials

When aircrafts have hypersonic flights in the atmosphere, high-temperature IR windows become the main factor of complicated aero-thermo-radiation effects, which reduce the performance of IR detection systems, or even make these detection systems fail. Consequently, measuring thermo-radiation characteristics of IR window material is essential for the assessment of aero-thermo-radiation effect. By analyzing thermal radiation transfer in IR windows, a method is proposed to measure thermo-radiation characteristics of IR window materials, and an experimental platform is established. Based on the platform, thermo-radiation characteristics of a sapphire IR window of a MWIR detection system in a hypersonic vehicle are measured. The results indicate that, the thermo-radiation characteristics of the sapphire IR window material in 3.7μm-4.8μm have an approximate cubic relationship with temperature at 100~350. With the rise of temperature, the transmittance of the sapphire material decreases, while the self-radiation increases. Subsequently, the self-radiation can drive detector into saturation easily, of which the influence on the MWIR detection system is bigger than that of the transmittance. And, with thickness increasing, transmittance decreases exponentially, and self-radiation increases, but the increment decreases exponentially. Consequently, as IR windows’ thickness or temperature increases, SNR of the MWIR detection system declines, saturation of IR detectors occurs easily.

Gas separation properties of new thermoplastic polyimides with phenylamide groups in diamine moiety: Effect of polymer structure

3,5-Diamino-N-phenylbenzamide has been synthesized and thermoplastic polyimides prepared on its basis. Analysis of the gas transport and physicochemical properties of the obtained polymers has shown that the introduction of the phenylamide group into the diamine moiety of rigid- and flexible-chain polyimides has opposite effects on their properties. The observed effects can be explained by the formation of hydrogen bonds in the case of the more flexible polymer, as has been proved by high-temperature IR spectroscopy data. Thus, the properties of polyimides based on 3,5-diamino-N-phenylbenzamide are determined by intermolecular interaction of the side phenylamide groups, opening new opportunities for the synthesis of membrane materials with active polar groups.