High-temperature Thermal Treatment Research Articles

Effect of high-temperature quenching on the magnetostructural transformations and the long-range atomic order of Ni–Mn–Sn and Ni–Mn–Sb metamagnetic shape memory alloys

The influence of high-temperature thermal treatments on the martensitic transformation and the magnetic properties of Ni–Mn–Sn and Ni–Mn–Sb metamagnetic shape memory alloys have been investigated by calorimetric and magnetic measurements. Contrary to Ni–Mn–Ga and Ni–Mn–In systems, the martensitic transformation and Curie temperatures of Ni–Mn–Sn and Ni–Mn–Sb alloys are found to be unaffected by the increasing quenching temperature. Neutron diffraction measurements confirm the null effect of quenching on the next-nearest-neighbors atomic order due to the negligible L21 atomic disorder achieved with high-temperature annealings. The analysis of long-range order also suggests that no L21–B2 ordering transition takes place in the studied alloys, thus indicating an unusually high stability of the L21 structure. The obtained results show that the magnetostructural properties of Ni–Mn–Sn and Ni–Mn–Sb alloys cannot be properly tuned by means of standard thermal treatments.

A Multiwalled‐Carbon‐Nanotube‐Based Biosensor for Monitoring Microcystin‐LR in Sources of Drinking Water Supplies

AbstractA multiwalled carbon nanotube (MWCNT)‐based electrochemical biosensor is developed for monitoring microcystin‐LR (MC‐LR), a toxic cyanobacterial toxin, in sources of drinking water supplies. The biosensor electrodes are fabricated using vertically well‐aligned, dense, millimeter‐long MWCNT arrays with a narrow size distribution, grown on patterned Si substrates by water‐assisted chemical vapor deposition. High temperature thermal treatment (2500 °C) in an Ar atmosphere is used to enhance the crystallinity of the pristine materials, followed by electrochemical functionalization in alkaline solution to produce oxygen‐containing functional groups on the MWCNT surface, thus providing the anchoring sites for linking molecules that allow the immobilization of MC‐LR onto the MWCNT array electrodes. Addition of the monoclonal antibodies specific to MC‐LR in the incubation solutions offers the required sensor specificity for toxin detection. The performance of the MWCNT array biosensor is evaluated using micro‐Raman spectroscopy, including polarized Raman measurements, X‐ray photoelectron spectroscopy, cyclic voltammetry, optical microscopy, and Faradaic electrochemical impedance spectroscopy. A linear dependence of the electron‐transfer resistance on the MC‐LR concentration is observed in the range of 0.05 to 20 μg L−1, which enables cyanotoxin monitoring well below the World Health Organization (WHO) provisional concentration limit of 1 μg L−1 for MC‐LR in drinking water.

Thermodynamic and structural properties of water adsorbed film on MgO (100) ionic surface

We have investigated by adsorption isotherms and neutron diffraction measurements, respectively the thermodynamic and structural properties of water physisorbed film on MgO (100) powder. Thanks to a high temperature thermal treatment, under vacuum, our MgO powder samples are characterized by a highly homogeneous (100) MgO surface. We have determined the structure of the (2D) water film physisorbed on such an ionic surface. This one is a commensurate P(2×3) structure which is very similar to the (110) planes of ice-VII. Recall that ice VII, which is stable at very high pressure, is characterized by a quite large density (d = 1.6).

Long-Range Ordering of Block Copolymer Cylinders Driven by Combining Thermal Annealing and Substrate Functionalization

This work presents a new method for forming well-defined nanostructured thin films from self-assembled polystyrene-block-poly(l-lactide) (PS-PLLA) on Si wafers with a functionalized SiO2 surface. Large, well-ordered, perpendicular PLLA cylinders in PS-PLLA thin films can be formed using the functionalized substrate. In contrast to random copolymers, a neutral substrate for the PS and PLLA blocks is formed by functionalizing a substrate with hydroxyl-terminated PS (PS-OH) followed by hydroxyl-terminated PLLA (PLLA-OH). The heterogeneous grafting of PS-OH and PLLA-OH can be substantially alleviated using this two-step functionalization. Accordingly, the surface properties can be fine-tuned by controlling the ratio of grafted PS-OH to PLLA-OH to control the orientation of the PLLA cylinders on the functionalized SiO2. Nevertheless, the orientation that is driven by the neutral substrate is surprisingly limited in that the effective length of orienting cylinders is less than twice the interdomain spacing. Thermal annealing at high temperature can yield a neutral air surface, rendering perpendicular PLLA cylinders that stand sub-micrometers from the air surface. Consequently, the neutral substrate can be used to enable truly film-spanning perpendicular cylinders in films to be fabricated using the high-temperature thermal treatment. In addition, the perpendicular cylinders can be laterally ordered by further increasing the annealing temperature. The ability to create these film-spanning perpendicular cylinders in films with a well-ordered texture and sub-micrometer thickness opens up possible applications in nanotechnology.

Temperature Dependent Photoluminescence from Polysilsesquioxane Xerogels

Polysilsesquioxane xerogels have been prepared via hydrolysis and condensation of the sole precursor N-(3-Trimethoxysilylethyl)ethylenediamine (TMSEEDA) with no acid or base catalyzed sol–gel processing. Complex siloxane matrix is formed along with abundant and covalently linked ethylenediamine (EDA). After high temperature thermal treatment over 500 °C, EDA groups are completely decomposed. The as-synthesized sample exhibits strong blue emission at room temperature (RT), which is shifted to green and red bands when encountered high temperature annealing treatment (in air), promising potential applications in opto-electronics and sensor. Moreover, the PL mechanism is also discussed in details.

ChemInform Abstract: Influence of Long‐Range Atomic Order on the Structural and Magnetic Properties of Ni—Mn—Ga Ferromagnetic Shape Memory Alloys

AbstractReview: 67 refs.

Effect of thermal treatment and moisture content on the charge of silica particles in non-polar media

Surfactants, such as Aerosol-OT (AOT), are known to impart charge on particles in non-polar media and make them colloidally stable. Previous studies on the charge of silica particles, which are one of the most widely used and studied colloids in non-polar media, have shown significant inconsistencies in the observed charging behaviour. While some studies have shown that silica becomes positively charged with AOT, others have shown that silica gains a net negative charge with the same surfactant. In addition, we have noticed differences in the charge state of colloidal silica from different suppliers. To determine the possible origin of these discrepancies, the effect of surface chemistry and moisture on the charge of silica in AOT–toluene is examined. The surface chemistry of silica is altered by thermal treatment at temperatures up to 1000 °C, while the amount of water in silica dispersions is controlled by keeping them at three different relative humidities. We use Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and quartz crystal microbalance (QCM) to gain insight into the effect of thermal treatment and moisture on the charging of silica in non-polar media. Changes in the surface chemistry of silica particles are found to have a significant effect on their charge in AOT–toluene solution. In addition, an increase in the moisture content of silica dispersions is shown to adversely affect the charge in AOT–toluene and, in some cases, induce charge inversion. Our results show that the surface chemistry of silica as well as moisture content are crucial parameters that influence the charging of silica in non-polar media and that these parameters should be carefully controlled to enhance the reproducibility of surface charge measurements in non-polar media. Furthermore, both high temperature thermal treatment and moisture content could serve as control parameters to change the charge of silica in non-polar media.

Controlled interlayer spacing of scrolled reduced graphene nanotubes by thermal annealing

We have demonstrated the ability to control the interlayer spacing of scrolled reduced graphene nanotubes through a high-temperature thermal treatment. The thermal annealing-induced variation of the interlayer spacing from 0.385 to 0.339 nm allowed us to study the change in the electronic and transport properties of the scrolled tubes.

Inorganic nanoparticle multilayers using photo-crosslinking layer-by-layer assembly and their applications in nonvolatile memory devices

We introduce a general and facile method for the preparation of organic/inorganic nanoparticle (NP) nanocomposite multilayer films that allows vertical growth of various NP layers (i.e., metal or transition metal oxide NPs) in a densely packed structure. Our approach is based on the successive photo-crosslinking layer-by-layer (LbL) assembly between hydrophobic ligands onto a NP surface and photoinitiator (PI) molecules. Therefore, our approach requires neither the additional surface modification needed for well-defined NPs synthesized in organic media nor the deposition step that inserts a polymer layer bridge between adjacent inorganic NP layers in the preparation of traditional LbL-assembled NP films. We also demonstrate that photo-crosslinking LbL-assembled (metal oxide NP)n films could be used as a nonvolatile memory layer without a high-temperature thermal treatment, unlike conventional vacuum-deposition- or sol-gel-derived memory devices, which require thermal treatments at temperatures greater than 200 °C. This robust method could open a facile route for the design of functional NP-based electronic devices.

A hierarchically structured graphene foam and its potential as a large-scale strain-gauge sensor

A hierarchically structured thermal-reduced graphene (ReG) foam with 0.5 S cm(-1) electrical conductivity is fabricated from a well-dispersed graphene oxide suspension via a directional freezing method followed by high-temperature thermal treatment. The as-prepared three-dimensional ReG foam has an ordered macroporous honeycomb-like structure with straight and parallel voids in the range of 30 μm to 75 μm separated by cell walls of several tens of nanometers thick. Despite its ultra-low density, the ReG foam has an excellent compression recovery along its in-plane direction. This property of the ReG foam can be attributed to its hierarchically porous structure, as demonstrated by the compression test. The excellent compression recovery and high conductivity provide the ReG foam with exceptional piezoresistive capabilities. The electrical resistance of the ReG foam shows a linearly decreasing trend with compressive strain increments of up to 60%, which cannot be observed in conventional rigid material-based sensors and carbon nanotube-based polymer sensors. Such intriguing linear strain-responsive behavior, along with the fast response time and high thermal stability, makes the ReG foam a promising candidate for strain sensing. We demonstrated that it could be used as a wearable device for real-time monitoring of human health.

CO2 splitting via two step thermochemical reactions over doped ceria/zirconia solid solutions

Thermochemical CO2 splitting was carried out over Ni-, Fe-, Mg- and Mn-doped ceria/zirconia solid solutions, where the sample was thermally reduced at 1400 °C under inert atmosphere followed by the re-oxidization of CO2 to generate CO at 1100 °C in the subsequent step. Compared with the undoped sample, all the doped ceria/zirconia had a high reduction yield in the first thermal reduction step. Due to the low thermal stability, Ni-, Fe- and Mn-doped samples showed lower CO production in the CO2 splitting step than the stoichiometric amounts. In contrast, the Mg-doped sample produced more CO with the volumes of 5.64 and 5.17 mL g−1 during the two thermochemical cycles. Moreover, a 10% Mg-doped sample prepared via hydrothermal treatment with P123 showed a more stable reactivity during cycling due to the relatively stable microstructure under the successive high temperature thermal treatment.

Research on up- and down-conversion emissions of Er3+/Yb3+ co-doped phosphate glass ceramic

By high-temperature melting method and thermal treatment technology, Er3+/Yb3+ co-doped phosphate glass and glass ceramic samples were prepared. The luminescence spectra of the glass and glass ceramic samples were studied under 975nm excitation. In visible and near-infrared bands, the emission intensity of the glass ceramic is stronger than that of the glass. The glass ceramic can comprehensively improve the luminous characters of the precursor glass. The phosphate glass ceramic will be valuable luminescence materials.

Influence of high temperature thermal treatment on grain stability and mechanical properties of medium strength aluminium alloy friction stir welds

A heat treatment of 2h at 535°C was applied to 6082T6 friction stir welds. One of the effects of post-welding heat treatment on microstructure was abnormal grain growth. The presence, in the same nugget, of zones with different grain size, is the key factor to understand why, after exposure at 535°C for 2h, abnormal grain growth is locally observed. The ductility substantially increased and tensile strengths remained comparable to those of as-friction stir welded samples. Particle evolution influenced microhardness values and determined deformation to fracture, even if abnormal grain growth appeared in the nuggets.

Thermal Treatment of New Inorganic Thermal Insulation Board Based on Expanded Perlite

A new lightweight thermal insulation board, containing expanded perlite and inorganic silicate binder with corresponding industrial production procedure was developed. The industrial technology was developed in cooperation between company Trimo d.d. and Faculty of chemistry and chemical technology Ljubljana and among others includes mixing of raw materials, molding, microwave drying and high temperature treatment of the dried board. A new product has low density (130 – 160 kg/m3), good mechanical properties and durability and can be used in various fields where inorganic thermal insulation is required. The current work presents the experimental study of the final process during plate production – high temperature treatment with sintering. During thermal treatment of the board, certain shrinkage is required to obtain sufficient mechanical properties and durability. Controlling the process of high temperature thermal treatment is the key to achieve the right balance between low final density of the board and its good mechanical properties.

Moderately reduced graphene oxide as transparent counter electrodes for dye-sensitized solar cells

Moderately reduced graphene oxide (GO) films were fabricated by simple and fast thermal treatment of solution processed GO, and their application as an alternative to conventional Pt counter electrode in dye-sensitized solar cells (DSSCs) was investigated. GO without thermal treatment and thermally treated GO at 150°C showed low efficiency of ∼0.5%, whereas cell performance was significantly improved by applying thermal treatment over 250°C. In particular, the DSSC with GO thermally treated at 350°C exhibited the highest performance with open-circuit voltage (VOC) of 0.66V, short-circuit current density (JSC) of 16.35mA/cm2, F.F. of 33.33%, and overall power conversion efficiency (PCE) of 3.60%. Moderate reduction of GO by simple thermal treatment over 250°C was confirmed through the measurements of X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). Enhancement of efficiency after high temperature thermal treatment might be attributed to the improved electrical conductivities and higher catalytic activities, resulting from the reduction of GO.

TM7TM′6B8(TM= Ta, Nb;TM′ = Ru, Rh, Ir): New Compounds with [B6] Ring Polyanions

The ternary boron compounds TM(7)TM'(6)B(8) (TM = Ta, Nb; TM' = Ru, Rh, Ir) were prepared by high-temperature thermal treatment of mixtures of the elements. An analysis of the chemical bonding by the electron density/electron localizability approach reveals formation of covalently bonded polyanions [B(6)] and [TM'(6)B(2)]. The cationic part of the structure contains separated TM cations. In agreement with the chemical bonding analysis and band structure calculations, all TM(7)TM'(6)B(8) compounds are metallic Pauli-paramagnets (TM' = Ru, Rh) or diamagnets (TM' = Ir).

Investigation on Yb3+/Er3+/Tm3+ tri-doped phosphate glass ceramic for white-light-emitting diode

Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramics were prepared by a high-temperature melting method and thermal treatment technology. Upconversion (UC) emissions of the Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramic samples were studied under 975 nm excitation. The glass ceramic samples can simultaneously generate blue, green, and red emissions. The multicolor emission obtained was tuned to white light by adjusting the Er3+ ion concentration. The emission color of the sample doped with 8 mol.% Er3+ ion is white to the naked eye, and CIE coordinates (x=0.316, y=0.354) of the sample are close to the standard equal energy white-light illumination (x=0.333, y=0.333). The material will be useful in developing the white-light-emitting diode.

Effects of reduction process and carbon nanotube content on the supercapacitive performance of flexible graphene oxide papers

The effects of the reduction process and carbon nanotube (CNT) content on the supercapacitive behavior of electrodes made from flexible, binder-free thick graphene oxide (GO) papers are studied. It is found that the supercapacitive performance depends on several factors, including the presence of oxygenated functional groups after reduction, the interlayer spacing of the GO papers and their wettability with electrolyte. A moderate reduction of GO papers using hydrazine or annealing at a low temperature of 220°C in air is proven to be more beneficial to achieve a high capacitance than the heavy reduction using a hydrazine vapor or a high temperature thermal treatment. The addition of a small amount of CNT, typically 12.5wt.%, to form thick GO/CNT sandwich papers gives rise to an excellent specific capacitance of 151Fg−1 at a current density of 0.5Ag−1, as well as a retention ratio of 86% of the initial value after 6000 charge/discharge cycles at 5Ag−1. These improvements arise from the synergistic effects of the increased electronic conductivity and effective surface area associated with large electrochemical active sites due to the presence of intercalated CNT.

A facile method for the synthesis of tapered ZnO:Cu nanorod arrays and its secondary growth

A facile thermal diffusion method has been employed to synthesize tapered ZnO:Cu nanorod arrays. The plain hexagonal ZnO nanorods gradually turned into round cylinder and then tapered nanorods during thermal treatment. The shape evolution was explained by the terrace–ledge–kink model. Moreover, a small amount of copper has been incorporated into the nanorods during high temperature thermal treatment. Both X-ray photoelectron spectrum and photoluminescence results indicated that a number of oxygen vacancies exist in copper diffused samples. In addition, a catalyst free secondary growth was achieved on the tapered ZnO:Cu nanorod arrays. High resolution transmission electron microscope result showed that the tapered nanorods after secondary growth remained as a single crystal and the thinner section was epitaxially grown on the tip.

The thermal stability of atomic layer deposited HfLaOx: Material and electrical characterization

HfLaOx based Metal–oxide–semiconductor capacitors were fabricated by atomic layer deposition in this work. The material and electrical properties of the films along with the high temperature thermal treatment were investigated. It was found that samples undergoing annealing at 900 °C exhibited the best performance. The film was found to be crystallized to a cubic structure at 900 °C, and the roughness of the films was estimated to be 0.332 nm. For electrical characterization, the C–V curve of the film is in good agreement with the corresponding simulated curve, and the capacitor does not show any hysteresis. Moreover, the Dit near the center of silicon band gap exhibits lowest value, and it was calculated to be 2.28 × 1011 eV−1 cm−2.