Nitride synthesis using ammonia and hydrazine—a thermodynamic panorama

Because of the wide variety of projected applications of ultrapure nitrides in advanced technologies, there is interest in developing new cost-effective methods of synthesis. Explored in this study is the use of ammonia and hydrazine for the synthesis of nitrides from oxides, sulfides and chlorides. Even when the standard Gibbs energy change for the nitridation reactions involved are moderately positive, the reaction can be made to proceed by lowering the partial pressure of the product gas below its equilibrium value. Use of a metastable form of precursor in the nanometric size range is an alternative method to facilitate nitridation. Ellingham-Richardson-Jeffes diagrams are used for a panoramic presentation of the driving force for each set of reactions as a function of temperature. Oxides are the least promising precursors for nitride synthesis; sulfides offer a larger synthetic window for many useful nitrides such as BN, AlN, InN, VN, TiN, ThN and Si₃N₄. The standard Gibbs free energy changes for reactions involving chlorides with either ammonia or hydrazine are much more negative. Hydrazine is a more powerful nitriding agent than ammonia. The metastability of hydrazine requires that it be introduced into a reactor through a water-cooled lance. The use of volatile halides with ammonia or hydrazine offers the potential for synthesis of pure and doped nanocrystalline nitrides. Nitride thin films can also be prepared by suitable adaptations of the chloride route.     

Flux synthesis of cubic potassium antimonate

Although the compound KSbO₃ has been reported to occur in a high temperature cubic polymorph, only the rhombohedral ilmenite phase was obtained in this study for pure material at ambient pressure and temperatures up to about 1350°C in open Pt crucibles or sealed Pt tubes. With the addition of about 2 mole percent SiO₂, B₂O₃ or other oxides of small cations a primitive cubic phase was found with $\text{a}\text{?9.578}\text{A}$. Small single crystals of a body centered cubic phase (a=9.605A) were easily synthesized by a flux evaporation technique at about 1000°C in an open Pt crucible from a composition of about 5 mole % Sb₂O₄:95 mole % KF. The exact composition and structure of this phase (presumably K_1?xSbO_3?xF_x, 0<x≤0.5) is now under investigation.     

New catalysts for the high pressure synthesis of cubic BN

The catalytic effect of water on the high pressure synthesis of cubic BN from hexagonal BN is studied in further detail. An amorphous substance is found to coexist with cubic BN thus prepared and is tentatively identified as anhydrous ammonium borate. The idea that a melt of ammonium borate which is formed by the reaction of hexagonal BN and water at high pressures and temperatures might act as a flux for the conversion from hexagonal BN to cubic BN, leads to the discovery of new catalysts, Urea, Ammonium borate, Ammonium nitrate, etc. It is also found that cubic BN can be synthesized from Boron and Urea or Ammonium nitrate under the same pressures and temperatures. The results open more efficient ways of synthesizing cubic BN.     

Hydrothermal synthesis of cubic ferric oxide particles

Single crystalline α-Fe₂O₃ cubic particles of narrow size distribution were prepared by a hydrothermal synthesis at 130 °C from a solution of urotropine ((CH₂)N₄) and ferric chloride. About 400 nm faultless cubic particles were observed. Spheres with rough surface were synthesized at 80 °C, while pseudo cubes and some spheres were prepared at 100 °C. For the preparation of α-Fe₂O₃ cubes, 130 °C is the appropriate temperature.     

Catalytic effect of water on the synthesis of cubic BN

The transition pressure and temperature of graphitic hexagonal boron nitride to the dense cubic form is drastically reduced by the presence of water in the starting material. A water content of about 40 wt% reduces these conditions to about 50 kb and 600°C. Cubic BN obtained under such conditions is extremely small in crystal size, which was estimated by the broadening of x-ray powder diffraction lines.     

Solid-state synthesis of cubic ZnTe nanocrystals using a microwave plasma

Cubic ZnTe nanocrystals were produced from 1:1 and 1.8:1 molar ratios of Zn:Te by a 900 W microwave plasma. The phase was detected using X-ray diffraction (XRD), which are in accordance with those of the simulations, and selected area electron diffraction (SAED). Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the products were nanocrystals with different orientations, including three longitudinal optical (LO) vibrations at 205, 410 and 620 cm^? 1 and a transverse optical (TO) vibration at 166 cm^? 1. Their green emissions were detected at 562 nm (2.21 eV) using luminescence spectrophotometry.     

High pressure synthesis of cubic boron nitride from amorphous state

Cubic-zincblende-type boron nitride was synthesized from amorphous state at pressures higher than 6 GPa and at temperatures higher than 800°C, without any planned addition of catalysts. Also, wurtzite type boron nitride was formed although the amount was small.     

Solvent effects of fluorides in cubic BN high pressure synthesis

Cubic BN can be synthesized under high pressure by using various fluorides as solvents. When NH₄F solvent is used, synthesis conditions are pressures above 4.0 GPa and temperatures above 800°C at 6.0 GPa. However, there exists a lower pressure limit for the synthesis, as in the case of water solvent. Synthesized cubic BN is a colorless tetrahedral crystalline powder with crystal size varying from 0.2 – 1 μm. Spark ion source mass spectrography revealed that the resulting cubic BN and hexagonal BN contain fluorine. This indicates that fluorine plays a role in the shift of the cubic-hexagonal BN equilibrium line to the higher pressure side, creating a pressure limit for the synthesis.     

Direct synthesis of shaped carbon nanoparticles with ordered cubic mesostructure

Shaped, mesoporous carbon nanoparticles (MSP-3) were prepared in high yield by a simple direct synthesis using a block copolymer surfactant as the mesopore-directing agent and a colloidal crystal to mold the external shape of the particles. The product consisted of monodisperse nanocubes and uniform nanospheres or tetrapods. The nanocubes contained regularly spaced, cagelike mesopores. The orientation of the cubic unit cell describing the mesopore symmetry coincided with the templated external cube faces.     

Rapid synthesis of cubic Pt nanoparticles and their use for the preparation of Pt nanoagglomerates

We report the synthesis of hexadecyltrimethylammonium bromide (CTAB)-stabilized cubic Pt nanoparticles by NaBH4 reduction of H2PtCl6 in aqueous CTAB solution. These Pt nanoparticles (average size of 7 nm) were well dispersed in aqueous solution and stable at least for 2 months. Addition of a trace amount of AgNO3 can alter the morphology of these Pt nanoparticles. More interestingly, the as-prepared uniform Pt nanoparticles were further developed into bigger Pt nanoagglomerates (approximately 20 to 47 nm) by a seed-mediate growth process. Dentritic and spherical Pt nanoagglomerates can be synthesized by altering the incubation time and their size can be tuned by controlling the amount of the seeds added.     

口腔全景X射线摄影机检定实践

针对口腔全景X射线摄影机的特点,特别是用半导体探测器检定时遇到的问题,通过实验,研究其主要参数的测量,为解决口腔全景X射线摄影机相关参数的量值溯源提供可参考的数据依据。     

Nanocomposite for methanol oxidation: synthesis and characterization of cubic Pt nanoparticles on graphene sheets

Abstract

We present our recent results on Pt nanoparticles on graphene sheets (Pt-NPs/G), a nanocomposite prepared with microwave assistance in ionic liquid 2-hydroxyethanaminiumformate. Preparation of Pt-NPs/G was achieved without the addition of extra reductant such as hydrazine or ethylene glycol. The Pt nanoparticles on graphene have a cubic-like shape (about 60 wt% Pt loading, Pt-NPs/G) and the particle size is 6 ± 3 nm from transmission electron microscopy results. Electrochemical cyclic voltammetry studies in 0.5 M aqueous H₂SO₄ were performed using Pt-NPs/G and separately, for comparison, using a commercially available electrocatalyst (60 wt% Pt loading, Pt/C). The electrochemical surface ratio of Pt-NPs/G to Pt/C is 0.745. The results of a methanol oxidation reaction (MOR) in 0.5 M aqueous H₂SO₄ + 1.0 M methanol for the two samples are presented. The MOR results show that the ratios of the current density of oxidation (I_f) to the current density of reduction (I_b) are 3.49 (Pt-NPs/G) and 1.37 (Pt/C), respectively, with a preference by 2.55 times favoring Pt-NPs/G. That is, the tolerance CO poisoning of Pt-NPs/G is better than that of commercial Pt/C.     

Mixed nitrogen source effect in the hydrothermal synthesis of cubic BN

Mixed nitrogen source effect was applied in the synthesis of boron nitride (BN) by hydrothermal method. The experimental results revealed that, compared to those obtained by using only two kinds of nitrogen sources, when three kinds of nitrogen sources were used during the synthesis of BN, it was more easier to obtain BN samples with cBN as the dominant phase. Furthermore, if this effect was applied together with the two-step reaction method, nearly pure cBN can be obtained. The results of X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), transmission electron microscopy (TEM), selective area electron diffraction (SAED), high-resolution transmission electron microscope (HRTEM) and X-ray photoelectron spectroscopy (XPS) measurements proved that the major phases in the samples are cBN.     

Quick high-temperature hydrothermal synthesis of mesoporous materials with 3D cubic structure for the adsorption of lysozyme

Abstract

Three-dimensional cage-like mesoporous FDU-12 materials with large tuneable pore sizes ranging from 9.9 to 15.6 nm were prepared by varying the synthesis temperature from 100 to 200 °C for the aging time of just 2 h using a tri-block copolymer F-127(EO₁₀₆PO₇₀EO₁₀₆) as the surfactant and 1,3,5-trimethyl benzene as the swelling agent in an acidic condition. The mesoporous structure and textural features of FDU-12-HX (where H denotes the hydrothermal method and X denotes the synthesis temperature) samples were elucidated and probed using x-ray diffraction, N₂ adsorption, ²⁹Si magic angle spinning nuclear magnetic resonance, scanning electron microscopy and transmission electron microscopy. It has been demonstrated that the aging time can be significantly reduced from 72 to 2 h without affecting the structural order of the FDU-12 materials with a simple adjustment of the synthesis temperature from 100 to 200 °C. Among the materials prepared, the samples prepared at 200 °C had the highest pore volume and the largest pore diameter. Lysozyme adsorption experiments were conducted over FDU-12 samples prepared at different temperatures in order to understand their biomolecule adsorption capacity, where the FDU-12-HX samples displayed high adsorption performance of 29 μmol g^?1 in spite of shortening the actual synthesis time from 72 to 2 h. Further, the influence of surface area, pore volume and pore diameter on the adsorption capacity of FDU-12-HX samples has been investigated and results are discussed in correlation with the textural parameters of the FDU-12-HX and other mesoporous adsorbents including SBA-15, MCM-41, KIT-5, KIT-6 and CMK-3.     

Quick high-temperature hydrothermal synthesis of mesoporous materials with 3D cubic structure for the adsorption of lysozyme

Three-dimensional cage-like mesoporous FDU-12 materials with large tuneable pore sizes ranging from 9.9 to 15.6 nm were prepared by varying the synthesis temperature from 100 to 200 °C for the aging time of just 2 h using a tri-block copolymer F-127(EO₁₀₆PO₇₀EO₁₀₆) as the surfactant and 1,3,5-trimethyl benzene as the swelling agent in an acidic condition. The mesoporous structure and textural features of FDU-12-HX (where H denotes the hydrothermal method and X denotes the synthesis temperature) samples were elucidated and probed using x-ray diffraction, N₂ adsorption, ²⁹Si magic angle spinning nuclear magnetic resonance, scanning electron microscopy and transmission electron microscopy. It has been demonstrated that the aging time can be significantly reduced from 72 to 2 h without affecting the structural order of the FDU-12 materials with a simple adjustment of the synthesis temperature from 100 to 200 °C. Among the materials prepared, the samples prepared at 200 °C had the highest pore volume and the largest pore diameter. Lysozyme adsorption experiments were conducted over FDU-12 samples prepared at different temperatures in order to understand their biomolecule adsorption capacity, where the FDU-12-HX samples displayed high adsorption performance of 29 μmol g⁻¹ in spite of shortening the actual synthesis time from 72 to 2 h. Further, the influence of surface area, pore volume and pore diameter on the adsorption capacity of FDU-12-HX samples has been investigated and results are discussed in correlation with the textural parameters of the FDU-12-HX and other mesoporous adsorbents including SBA-15, MCM-41, KIT-5, KIT-6 and CMK-3.     

Binary and ternary compounds in the Mg-Sb-B and Mg-Bi-B systems as catalysts for the synthesis of cubic BN

We have studied the phase relations in the Mg-Pn and Mg-B-Pn (Pn = Sb, Bi) systems, synthesized the magnesium pnictides Mg₃Sb₂ and Mg₃Bi₂ and the new magnesium boropnictides Mg₃Pn₂(B₂), and determined their structure and unit-cell parameters. The synthesized compounds have been investigated at high pressures (4.0–6.5 GPa) and temperatures (700–1400°C). All of them have been found to promote the hexagonal-to-cubic phase transformation of boron nitride.     

The research and synthesis of the cubic 2MnCO3@ZnO applied as cathode material for zinc ion battery

Journal of Materials Science: Materials in Electronics - In this paper, 2MnCO3@ZnO was synthesized by a hydrothermal method as a cathode material for Zn-ion batteries. In order to synthesize the...