Phase transformation of melamine at high pressure and temperature

Yu, Dongli; He, Julong; Liu, Z. Y.; Xu, Bin; Li, D. C.; Tian, Yongjun

doi:10.1007/s10853-007-2148-y

Cited by 60 publications

(36 citation statements)

References 21 publications

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“…The N 1s XPS spectra for different nitrogen doping temperatures showed clear differences. For a nitrogen‐doping temperature of 750–800 °C, nitride‐like species occurred for the first time, which could be attributed to the formation of g‐CN x from melamine pyrolysis . Furthermore, compared with Fe‐CNTs, the content of pyridinic‐N in Fe‐N‐CNT750 and Fe‐N‐CNT800 increased, mainly because of the cyclization reactions of O‐containing compounds (produced from nitric acid leaching) reacting with N‐containing intermediates derived from melamine pyrolysis (such as NH 3 ) .…”

Section: Resultsmentioning

confidence: 99%

“…For an itrogendoping temperature of 750-800 8C, nitride-like species occurred for the first time, which could be attributed to the formation of g-CN x from melamine pyrolysis. [28] Furthermore, com-pared with Fe-CNTs, the content of pyridinic-N in Fe-N-CNT750 and Fe-N-CNT800i ncreased, mainly because of the cyclization reactions of O-containing compounds (produced from nitric acid leaching) reacting with N-containing intermediates derived from melaminep yrolysis (such as NH 3 ). [29] However, with af urtheri ncrease in the dopingt emperature, the relatively active nitrogen groups, such as nitride-like species and pyridinic-N, decreased.…”

Section: Resultsmentioning

confidence: 99%

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Preparation of Iron‐ and Nitrogen‐Codoped Carbon Nanotubes from Waste Plastics Pyrolysis for the Oxygen Reduction Reaction

et al. 2020

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A novel method for the preparation of iron‐ and nitrogen‐codoped carbon nanotubes (Fe‐N‐CNTs) is proposed, based on the catalytic pyrolysis of waste plastics. First, carbon nanotubes are produced from pyrolysis of plastic waste over Fe‐Al2O3; then, Fe‐CNTs and melamine are heated together in an inert atmosphere. Different co‐pyrolysis temperatures are tested to optimize the electrocatalyst production. A high doping temperature improves the degree of graphite formation and promotes the conversion of nitrogen into a more stable form. Compared with commercial Pt/C, the electrocatalyst obtained from pyrolysis at 850 °C shows remarkable properties, with an onset potential of 0.943 V versus RHE and a half‐wave potential of 0.811 V versus RHE, and even better stability and anti‐poisoning properties. In addition, zinc–air battery tests are performed, and the optimized catalyst exhibits a high maximum power density.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Preparation of Iron‐ and Nitrogen‐Codoped Carbon Nanotubes from Waste Plastics Pyrolysis for the Oxygen Reduction Reaction

et al. 2020

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“…Synthesis of C-N nanotubes was also observed in high-pressure catalytic pyrolysis of melamine with NaN 3 -Fe-Ni at 35 MPa and 650 • C [11]. Interestingly, another recent high-pressure pyrolysis experiments at 5 GPa and 800 • C showed formation of a different molecular crystalline monoclinic solid [12].Given the complexity of coupled high temperature and pressure pyrolysis, a good starting point for understanding the reaction potential of melamine is through a thorough examination of the compression mechanism. One of the first high-pressure studies of melamine to 4.0 GPa utilized infrared spectroscopy [13], and while noting number of important band frequency shifts, it did not report any discontinuous changes in the compression behavior.…”

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confidence: 84%

Evolution of Interatomic and Intermolecular Interactions and Polymorphism of Melamine at High Pressure

2018

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Melamine (C 3 H 6 N 6 ; 1,3,5-triazine-2,4,6-triamine) is an aromatic substituted s-triazine, with carbon and nitrogen atoms forming the ring body, and amino groups bonded to each carbon. Melamine is widely used to produce laminate products, adhesives, and flame retardants, but is also similar chemically and structurally to many energetic materials, including TATB (2,4,6-triamino-1,3,5trinitrobenzene) and RDX (1,3,3,. Additionally, melamine may be a precursor in the synthesis of superhard carbon-nitrides, such as β-C 3 N 4 . In the crystalline state melamine forms corrugated sheets of individual molecules, which are stacked on top of one another, and linked by intra-and inter-plane N-H hydrogen bonds. Several previous high-pressure X-ray diffraction and Raman spectroscopy studies have claimed that melamine undergoes two or more phase transformations below 25 GPa. Our results show no indication of previously reported low pressure polymorphism up to approximately 30 GPa. High-pressure crystal structure refinements demonstrate that the individual molecular units of melamine are remarkably rigid, and their geometry changes very little despite volume decrease by almost a factor of two at 30 GPa and major re-arrangements of the intermolecular interactions, as seen through the Hirshfeld surface analysis. A symmetry change from monoclinic to triclinic, indicated by both dramatic changes in diffraction pattern, as well as discontinuities in the vibration mode behavior, was observed above approximately 36 GPa in helium and 30 GPa in neon pressure media. Examination of the hydrogen bonding behavior in melamine's structure will allow its improved utilization as a chemical feedstock and analog for related energetic compounds. Crystals 2018, 8, 265 2 of 20stacked on top of one another. When used as a salt or mixed with resins, melamine is an effective fire retardant, in part due to the release of flame-smothering nitrogen gas when burned [2]. When combined with formaldehyde, melamine forms a very durable thermosetting plastic used in a broad variety of kitchenware and household goods [3]. Despite its stability and flame-retardant properties, melamine is also very closely related, both structurally and chemically, to the widely used molecular explosives RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), TATB (2,4,6-triamino-1,3,5-trinitrobenzene), and to 2,4,6-trinitro-1,3,5-triazine, a hypothetical new explosive [4] which has not yet been successfully synthesized [5,6]. As a curiously stable cousin of these explosives, melamine is a worthwhile target of investigation in the search for new energetic materials with enhanced safety and stability while maintaining sufficient explosive potential [7].The primary motivation for studying the high-pressure behavior of melamine ultimately stems from its intermediate position between energetic species and ultra-hard materials; for instance, melamine may be a functional precursor for synthesis of a hypothetical β-C 3 N 4 phase, with a β-Si 3 N 4 structure, predicted to be a super-hard materia...

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“…The second peak (N2), located at ~399.8 eV is attributed to the ammine groups bonded to carbon atoms in the hexagonal ring of the melamine molecule. The lower intensity of the N2 peak with respect to the N1 peak confirms the lower amount of ammine groups due to the decomposition of melamine after the high temperature treatment [6]. The absence of the peak at 401 eV in the N 1s spectrum, related to graphitic nitrogen in the sp 2 bonding, together with the fact that the melamine peaks are clearly identified from the graphene peaks on the XPS spectra, suggest that the melamine is merely weakly bonded to graphene (physicsorption).…”

Section: Xpsmentioning

confidence: 76%

“…The peak, located at 287.6 eV (C4), is attributed to the carbon with two CN bonds and one C=N bond, consistent with the peak found for the carbon atom in the melamine structure. Finally, the peak, located at 286.1 eV, can be attributed to the nitrogen in the partially decomposed melamine molecules after the high temperature treatment under which the ammine groups (-NH 2 ) are broken from the hexagonal ring of the melamine molecules [6]. It is also important to notice the absence of the peak at about 289 eV, attributed to the C=O bonds.…”

Section: Methodsmentioning

confidence: 94%

Defect Engineering for Graphene Tunable Doping

2011

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Here we describe a doping approach that enables selective and variable doping on graphene. The doping level reflected in the successive shift of the Raman G mode can be progressively changed by varying the coverage of molecular adsorption on graphene. We make use of lattice defects which serve as anchor groups for the non-covalent functionalization on graphene to enhance molecule adsorption on defective sites at the elevated processing temperatures and also orbital overlap between graphene and adsorbates (melamine). Low density of defects, which can be monitored by seeing the intensity ratio of the D to G mode in the Raman spectra, was generated by exposing graphene to short Ar plasma pulses, followed by dopant adsorption. The controllable creation of defects makes the precise doping on graphene feasible. Systematic characterizations by Raman scattering show that holes are transferred to graphene, with the doping level depending on the surface coverage of melamine. The charge transfer is also identified by the downshift of the charge neutrality point in the transfer characteristics.

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Phase transformation of melamine at high pressure and temperature

Cited by 60 publications

References 21 publications

Preparation of Iron‐ and Nitrogen‐Codoped Carbon Nanotubes from Waste Plastics Pyrolysis for the Oxygen Reduction Reaction

Preparation of Iron‐ and Nitrogen‐Codoped Carbon Nanotubes from Waste Plastics Pyrolysis for the Oxygen Reduction Reaction

Evolution of Interatomic and Intermolecular Interactions and Polymorphism of Melamine at High Pressure

Defect Engineering for Graphene Tunable Doping

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