Subsequent High-temperature Treatment Research Articles

Sn-V centers in diamond activated by ultra high pressure and high temperature treatment

We investigate the activation of Sn-V centers in diamond through ions implantation and the subsequent high pressure and high temperature (HPHT) treatment at 15 GPa and 2300 °C. Sn ions is implanted at fluences greater than 2 × 1014 cm−2 by varying the acceleration voltage up to 180 kV, which results in a Sn distribution with a uniform concentration of 1 × 1020 cm−3 down to a depth of 50 nm from the surface. The subsequent HPHT treatment recovers the transparent appearance and preserves the introduced Sn ions. The sample shows emission peaks composed of four levels that originate from the Sn-V centers. The two distinct emission peaks from the lower excited states to the split ground states are stable up to 77 K. At 10 K, these peaks are clearly observable at excitation powers spanning two orders of magnitude, which suggests the preferential carrier capture at these centers.

Electrostatic self-assembly design of core@shell structured Al2O3@C nanospheres towards high-efficiency and damage-free polishing sapphire wafer

A novel core@shell structured nanocomposite particles with carbon as soft shell and nanoAl2O3 as hard core were prepared by electrostatic self-assembly, and the subsequent hydrothermal and high temperature treatment. By adjusting concentration of nanoAl2O3, the average size of the composite particles vary from 750 nm to 150 nm, the corresponding to the thickness of the carbon shell in the range of 355–55 nm. On the basic of the TEM and Raman results, the shell materials were composed of the amorphous carbon. As confirmed by XPS, the Al2O3 @C composite particles had a stable structure, owing to the formation of the interfacial bonding between carbon shell and nanoAl2O3 after the carbonization process. Moreover, the nanoAl2O3 @carbon composite abrasive could lead to a decrease in the surface damage and roughness of the sapphire wafer compared with the nanoalumina abrasive, owing to the elastic effect coming from the amorphous carbon shell.

Chemical Vapor Deposition of an Iridium Phase on Hafnium Carbide and Tantalum Carbide

Nanocrystalline iridium coatings on hafnium carbide and tantalum carbide substrates are prepared by chemical vapor deposition (MOCVD) at 600°С. Subsequent high-temperature treatment at 1100°С gives rise to chemical reactions between iridium and hafnium carbide or tantalum carbide to yield nanosized substitutional intermetallic solid solutions MIr3 – x and evolve free carbon. The occurrence of intermetallic interaction is proved by X-ray photoelectron (XPS) spectroscopy.

Micro-powder Ca3Sc2Si3O12:Ce silicate garnets as efficient light converters for WLEDs

A novel synthesis method of Ca3Sc2Si3O12:Ce micropowder with very bright photo-luminescence (PL) has been developed. The conventional solid-state reaction has been modified for Ca3Sc2Si3O12:Ce microparticle crystallization. Pre-synthesis of metal and silicon oxide blends with subsequent high-temperature treatment in reducing (H2/N2) atmosphere enables obtaining Ca3Sc2Si3O12:Ce micropowder with a high PL quantum yield of about 60–70% at Ce3+ content in the 2.5–5 at.% range, which is highly attractive for LED technology. Additionally, the Ca3Sc2Si3O12:Ce phosphors with Ce concentration in the 0.5–2.5% range display higher thermal stability of photoluminescence in comparison with a commercial YAG:Ce phosphor.

Ensuring industrial safety of pipelines with developed hard sections

Oil refining and petrochemicals have a wide demand for pipelines from heat resistant chromium steels. One of the main reasons for frequent failures of more stressed joints may be the presence of wide solid and brittle layers having significant areas in metal volume with maximum clusters of imperfections of metal structure and creating excessive concentration of additional residual deformations and stresses in welded joints, which are most saturated with defects inherent in welded joints. Presence of such extended sections leads to reduction of process strength of welded joints, increases tendency to formation of cold cracks and sharply limits time of laying of thick-walled welded joints of pipelines before subsequent high-temperature thermal treatment. The work carried out studies on welding pipe blanks in order to compare different methods of 5CroMo16 steel treatment during welding and determine the most efficient mode. Regularities of stressed state of different-module structural elements with wide solid layers are established.

Studying the Grain Structure of SmS Targets Manufactured under Variable Conditions

The grain structure of samarium sulfide (SmS) targets manufactured by pressing with or without subsequent high-temperature treatment by high-frequency current (HFC) at various pressures has been studied. The density of samples manufactured in various regimes was determined and the optimum technological conditions for obtaining high-quality SMS targets were selected. In particular, the HFC annealing upon pressing at 5 t/cm2 proved to be more effective than the analogous treatment at 4 t/cm2. It is established that the samples obtained by pressing at 5 t/cm2 without high-temperature HFC annealing contain significant amounts of unbound metallic samarium.

Layered Confinement Reaction: Atomic-level Dispersed Iron-Nitrogen Co-Doped Ultrathin Carbon Nanosheets for CO2 Electroreduction.

High electrochemical over-potential and low product selectivity are regarded as the main limitations of electroreduction of CO2 . Here, we proposed a new strategy to synthesize metal porphyrin-hybridized porous and ultra-thin carbon nanosheets (MPPCN) by the confinement function of the layered template. The layered confinement reaction protects the coordination structure of metal and nitrogen atoms during subsequent high-temperature treatment while ensuring the formation of ultra-thin structures. This method effectively prevents the aggregation of metal atoms, so that the metal atoms exhibit a dispersed state of a single atomic level. MPPCN exhibit unexpected catalytic activity for electroreduction of CO2 , and the catalytic reaction can be carried out at an over-potential of 0.39 V. The faradaic efficiency of CO can reach 95.9 % at the potential of -0.7 V versus the reversible hydrogen electrode.

Effect of Liquid Crystalline Texture of Mesophase Pitches on the Structure and Property of Large-Diameter Carbon Fibers.

Two types of carbon fibers with a large diameter of ∼22 μm, derived from unstirred and vigorously stirred mesophase pitch melts with different liquid crystalline mesophase textures, were prepared by melt-spinning, stabilization, carbonization, and graphitization treatments. The morphology, microstructure, and physical properties of the carbon fibers derived from the two kinds of mesophase precursors after various processes were characterized in detail. The results show that the optical texture (i.e., size and orientation) of the liquid crystalline mesophase in the molten pitch is obviously modified by thermomechanical stirring treatment, which has a significant effect on the texture of as-spun pitch fibers, and finally dominates the microstructure and physical properties of the resulting carbon and graphite fibers. These large-diameter fibers expectedly maintain their morphological and structural integrity and effectively avoid shrinkage cracking during subsequent high-temperature heat treatment processes, in contrast to those derived from the unstirred pitch. This is due to the smaller crystallite sizes and lower orientation of graphene layers in the former. The tensile strength and axial electrical resistivity of the 3000 °C-graphitized large fibers derived from the unstirred pitch are about 1.8 GPa and 1.18 μΩ m, respectively. In contrast, upon melt stirring treatment of the pitch before spinning, the resulting large-diameter graphite fibers possess the corresponding values of 1.3 GPa and 1.86 μΩ m. Despite the acceptable decrease of mechanical properties and axial electrical and thermal conduction performance, the latter possesses relatively high mechanical stability (i.e., low strength deviation) and ideal morphological and structural integrity, which is beneficial for the wide applications in composites.

Interface self-assembly preparation of multi-element doped carbon nanobowls with high electrocatalysis activity for oxygen reduction reaction

Developing an efficient, stable and low cost oxygen reduction reaction electrocatalyst is desirable for fuel cells and metal-air batteries. Here, we have successfully prepared multi-element doped carbon nanobowls by simply mixing the porous carbon nanobowls and sulfur doped graphitic carbon nitride quantum dots in FeCl3 solution and subsequent high temperature treatment processes. Compared with the commercial Pt/C electrocatalyst, the multi-element doped carbon nanobowls display a comparable half-wave potential of 0.82 V, much larger limiting diffusion current density (0.4–0.8 V), better methanol-tolerance and higher long-term stability for the oxygen reduction reaction in alkaline media. The robust three-dimensional porous structure of carbon nanobowls and multiple active centers derived from Fe, N, S and O co-doping are responsible for the excellent performance. This work suggests that such multi-element doped carbon nanobowls can be a promising alternative for Pt-based catalysts in fuel cells.

Facile Fabrication of N-Doped Magnetic Porous Carbon for Highly Efficient Mercury Removal

N-doped magnetic porous carbon (N-MPC) is an emerging adsorbent for water pollution control. However, high cost and multisteps procedure make the direct fabrication of N-MPCs difficult until now. Herein, highly dispersed N-MPCs were synthesized by a facial one-pot solid-state pyrolysis strategy. Heating the mixture of ZnO, Co(OH)2, and 2-methylimidazole (HmIm), Zn/Co bimetallic ZIFs formed at the initial stages, being the primary self-template to produce N-MPCs during subsequent high-temperature treatment. By altering the pyrolysis temperature and the molar ratio of ZnO/Co(OH)2 in the precursor, the magnetism, nitrogen content, and surface areas of N-MPCs can be easily controlled. Due to its high special surface areas and the decoration of abundant nitrogen functional groups (pyrrole-N and pyridinic-N), the optimized N-MPC-700-7/3 exhibited a superior adsorption performance for Hg2+ uptake (489 mg g–1). Moreover, the N-MPCs exhibited fast dynamics in adsorption (K2 = 0.47 g mg–1 min–1) and good chemical s...

Recovery of Thermally Compressed Scots Pine (Pinus sylvestris L.) Wood

Heartwood and sapwood samples of Scots pine were subjected to densification and thermal compression (180 °C to 220 °C) using a hot press, and their recovery behaviors and the involved mechanisms were investigated. Compressed wood (CW) showed poor recovery after water uptake. This deformation effectively was fixed by the subsequent high temperature treatment. To explain the phenomenon, the sorption properties of wood before and after modification by the adsorption isotherms were evaluated. The model of Hailwood and Horrobin gave the changes of the monolayer and multilayer sorption of each group samples and the relationship with wood deformation. By analyzing hygroscopic hysteresis, it was found that the removed elastic components from wood under elevated temperature had an inescapable impact on hysteresis ratio and recovery, even if it was not the only cause. In other words, the modified wood’s plasticity was responsible for its recovery.

New method for the growth of single-walled carbon nanotubes from bimetallic nanoalloy catalysts based on Prussian blue analog precursors

Catalyst engineering is a key point for selective growth of single-walled carbon nanotubes (SWCNT) with chemical vapor deposition (CVD). Here, we develop a new general synthesis method able to produce a wide range of homogenous bimetallic catalyst nanoparticles with controlled stoichiometry and sizes. The basics of this catalyst synthesis is to use preformed stoichiometric bimetallic Prussian blue analog (PBA) nanoparticles. Catalyst nanoparticles are then prepared in-situ in a hot filament CVD reactor with subsequent high temperature treatment in reducing atmosphere prior to SWCNT growth. The capabilities of the synthesis route are demonstrated by testing five PBA systems involving various transition metals. Transmission electron microscopy (TEM), scanning TEM and energy dispersive X-ray spectroscopy (STEM-EDX), and in-situ X-ray photoelectron spectroscopy (XPS) measurements are used to finely follow the size and composition of the catalyst at each step of the process. Each system yields small size catalysts with a narrow distribution, which act as efficient catalysts for SWCNT growth with a good yield and small diameter distribution. The versatility of the PBA family paves a new way for a fine tuning of the catalyst properties monitored by the metal involved in the PBA, and for opening routes to more selective SWCNT synthesis.

Synthesis of high-purity aluminum oxide from hydrothermally produced boehmite by high temperature vacuum treatment

In this study a simple and environmentally benign method for conversion of technical purity Al into high-purity alumina is described. The method is based on hydrothermal oxidation of aluminium producing boehmite as intermediate product and its subsequent high temperature treatment. It has been shown that by proposed method the Al powder of technical purity (99.8 wt.%) is converted into alumina with high-purity (up to 99.999 wt.%).

Synthesis of rutile titanium dioxide from Russian raw materials

The conditions of the structure formation of rutile titanium dioxide from titanium dioxide (anatase) and titanium hydroxide isolated by thermolysis from the titanium compound (NH4)2TiO(SO4)2 · H2O and by thermal hydrolysis of a titanium sulfate(IV) solution, respectively, were studied. It was shown that the mechanical activation of the studied powders causes, in addition to a decrease in the initial grain size, deep destructuring with the formation of the transition phase, which, in the process of the subsequent high-temperature treatment, functions as a matrix for the formation of rutile. The research results will be used for the development of a new variant of the technology for the synthesis of titanium dioxide, which is an important component of compositions for polymeric materials—in particular, the K-300-61 and K-153 adhesives.

A new method for developing defect-rich graphene nanoribbons/onion-like carbon@Co nanoparticles hybrid materials as an excellent catalyst for oxygen reactions.

Herein, a novel material with an excellent electrocatalytic activity for the oxygen reduction reaction (ORR), composed of onion-like carbon@Co nanoparticles (NPs) incorporated on defect-rich N-doped graphene nanoribbons (C@Co-NGR), is prepared via a combination of nitric acid etching and subsequent high-temperature treatment of the as-synthesized C@Co-N doped carbon nanotubes. The as-prepared C@Co-NGR exhibits excellent electrocatalytic activity for the ORR in 0.10 M KOH with a half-wave potential of 0.830 V (vs. a reversible hydrogen electrode, RHE), which is 21 mV more positive than that of a commercial 20 wt% Pt/C catalyst. Moreover, it shows a higher stability and better methanol tolerance than the commercial Pt/C catalyst in alkaline solution, with almost no shift in the ORR polarization curve after 3000 cycles and no change of the ORR peak in the cyclic voltammogram in the presence of 1.0 M methanol. Most importantly, the C@Co-NGR also exhibits a comparable activity for the oxygen evolution reaction (OER) in 0.10 M KOH solution, in which the overpotential needed to achieve a current density of 10 mA cm-2 is 410 mV, comparable to that of the state-of-the-art commercial RuO2 catalyst (370 mV, vs. RHE). This makes the C@Co-NGR one of the best non-precious-metal catalyst for OER and ORR in alkaline solution ever reported.

Diamond drumhead crystals for X-ray optics applications

Thin (<50 µm) and flawless diamond single crystals are essential for the realization of numerous advanced X-ray optical devices at synchrotron radiation and free-electron laser facilities. The fabrication and handling of such ultra-thin components without introducing crystal damage and strain is a challenge. Drumhead crystals, monolithic crystal structures composed of a thin membrane furnished with a surrounding solid collar, are a solution ensuring mechanically stable strain-free mounting of the membranes with efficient thermal transport. Diamond, being one of the hardest and most chemically inert materials, poses significant difficulties in fabrication. Reported here is the successful manufacture of diamond drumhead crystals in the [100] orientation using picosecond laser milling. Subsequent high-temperature treatment appears to be crucial for the membranes to become defect free and unstrained, as revealed by X-ray topography on examples of drumhead crystals with a 26 µm thick (1 mm in diameter) and a 47 µm thick (1.5 × 2.5 mm) membrane.

Porous Li-Rich Cathode Material with Carbonaceous Modified Surface for High Performance Lithium Ion Batterie

Li-rich layered oxides (Li1+zMnx NiyCo1-x-y O2) are considered as a most promising family of intercalation cathode materials for rechargeable lithium batteries, due to the advantages of high discharge capacity and high specific energy. Coupled with other benefits like high safety, low toxicity and costs, Li-rich materials are currently significantly attractive for high-power applications. However, weaknesses like intrinsic poor rate capability, dramatically decrease in the discharge potential plateau, irreversible volume expansion and capacity fade during long-term cycling are bringing up concerns about their practical utilization, which need to be surmounted. Morphology tailoring is considered to be an efficient way to address these issues. It has been proved that the particle size, crystallinity and structural morphology have obvious effects on electrochemical performance of electrode materials. In order to improve the electrochemical performance of Li-rich, the special morphology of the material, with extra space between particles to buffer the volume change and the modified surface to enhance the electronic conductivity, was synthesized in this work. Specifically, high crystallinity Li1.2Mn0.56Ni0.16Co0.08O2 Li-rich porous materials integrating with an in-situ formed surface containing carbonaceous compounds are obtained through a novel facile approach. The rationally designed procedure involves the formation of a specific morphology of a hydroxide precursor assisted by a self-made template and subsequent high temperature treatment. The porous morphology is investigated using field-emission scanning electron microscopy and its surface area quantitatively examined by gas sorption analysis couple with the Brunauer-Emmett–Teller method. The porous morphology can be viewed from SEM image (Figure 1a), and it owns large surface area which is five time more than the sample in the normal shape. The crystallinity is characterized by X-ray diffraction and high-resolution transmission electron microscopy. X-ray photoelectron spectroscopy, CHN element analysis confirm the presence of the carbonaceous compounds in the surface composition. The prepared material exhibits superior discharge rate capability and excellent cycling stability. It shows minor capacity loss after 100 cycles at 0.5 C and maintains 94.9% of its initial capacity after 500 cycles at 2 C. Even more notably (Figure 1b), the “voltage decay” during cycling is also significantly decreased. It has been found that carbonaceous compounds play a critical role for reducing the layered to spinel structural transformation during cycling. Therefore, the present porous Li-rich material with surface modified a carbonaceous compounds represents an attractive material for advanced Lithium-ion batteries. Figure 1

Near-infrared optical properties of a porous alumina ceramics produced by hydrothermal oxidation of aluminum

The measured spectral normal–hemispherical reflectance of an optically thick sample of porous alumina ceramics produced by hydrothermal oxidation of aluminum and subsequent high-temperature treatment of boehmite (or böhmite), AlO(OH), is used in a combination with the published data for absorption coefficient of alumina to retrieve the near-infrared optical properties of the alumina ceramics at both room and elevated temperatures. The spectral emissivity of porous alumina ceramics is also determined. An approximate model based on the Mie theory for single grains is suggested to estimate the transport scattering coefficient and the radiative conductivity of the material at high temperatures.

Synthesis of Few-Atomic-Layer BN Hollow Nanospheres and Their Applications as Nanocontainers and Catalyst Support Materials.

In this work, few-atomic-layer boron nitride (BN) hollow nanospheres were directly synthesized via a modified CVD method followed by subsequent high-temperature degassing treatment. The encapsulated impurities in the hollow nanospheres were effectively removed during the reaction process. The BN shells of most nanospheres consisted of 2-6 atomic layers. Because of the low thickness, the obtained BN hollow nanospheres presented excellent performance in many aspects. For instance, they were demonstrated as useful nanocontainers for controllable multistep release of iodine, which could diffuse and be encapsulated into the few-layer BN hollow nanospheres when heating. They were also promising support materials that could markedly increase the photocatalytic activity of TiO2 nanocrystals.

Template-assisted synthesis of hierarchically porous Co3O4 with enhanced oxygen evolution activity

Oxygen evolution reaction (OER) is one of the most important reactions in the energy storage devices such as metal–air batteries and unitized regenerative fuel cells (URFCs). However, the kinetically sluggishness of OER and the high prices as well as the scarcity of the most active precious metal electrocatalysts are the major bottleneck in these devices. Developing low-cost non-precious metal catalysts with high activity and stability for OER is highly desirable. A facile, in situ template method combining the dodecyl benzene sulfuric acid sodium (SDBS) assisted hydrothermal process with subsequent high-temperature treatment was developed to prepare porous Co3O4 with improved surface area and hierarchical porous structure as precious catalysts alternative for oxygen evolution reaction (OER). Due to the unique structure, the as-prepared catalyst shows higher electrocatalytic activity than Co3O4 prepared by traditional thermal-decomposition method (noted as Co3O4-T) and commercial IrO2 catalyst for OER in 0.1 M KOH aqueous solution. Moreover, it displays improved stability than Co3O4-T. The results demonstrate a highly efficient, scalable, and low cost method for developing highly active and stable OER electrocatalysts in alkaline solutions.