Size Effects on Surface Chemistry and Raman Spectra of Sub-5 nm Oxidized High-Pressure High-Temperature and Detonation Nanodiamonds
Štěpán StehlíkMichel MermouxBernhard SchummerOndřej VaněkKateřina KolářováPavla ŠtenclováAleš VlkMartin LedinskýRene PfeiferO. RomanyukIvan GordeevFrancine Roussel-DherbeyZuzana NěmečkováJiří HenychPetr Bezdic̆kaAlexander KromkaBohuslav Rezek
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Understanding materials with dimensions down to a few nanometers is of major importance for fundamental science as well as prospective applications. Structural transformation and phonon-confinement effects in the nanodiamonds (NDs) have been theoretically predicted below 3 nm in size. Here, we investigate the effect of size on the surface chemistry, microscopic structure, and Raman scattering of high-pressure high-temperature (HPHT) and detonation nanodiamonds (DNDs) down to 2–3 nm. The surface and size of NDs are controlled by annealing in air and ultracentrifugation resulting in three ND fractions. Particle size distribution (PSD) of the fractions is analyzed by combining dynamic light scattering, analytical ultracentrifugation, small-angle X-ray scattering, X-ray diffraction, and transmission electron microscopy as complementary techniques. Based on the obtained PSD, we identify size-dependent and synthesis-dependent differences of ND properties. In particular, interpretation of Raman scattering on NDs is revisited. Comprehensive comparison of detonation and pure monocrystalline HPHT NDs reveals effects of diamond core size and defects, chemical and temperature (in)stability, and limitations of current phonon confinement models. In addition, low-frequency Raman scattering in the 20–200 cm–1 range is experimentally observed. The size dependence of this signal for both HPHT NDs and DNDs suggests that it may correspond to confined acoustic vibrational, "breathing-like" modes of NDs.Keywords:
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Abstract As a promising method for synthesizing nanosized materials, detonation method was used to prepare TiO 2 nanoparticles. A new method for predicting the Chapman‐Jouguet (C‐J) detonation parameters of C a H b O c N d Ti e explosives, such as detonation heat, detonation temperature, and detonation pressure, was introduced according to the approximate reaction equations of detonation. The coefficient of oxygen balance of explosive was also calculated according to the specific detonation synthesis experiment. The calculation method was more useful in predicting the formation processes of detonation products and optimizing the experimental procedure. It could also support theory foundation for further experiments to some extent.
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WT5”BZ]The comparative experimental study on the single detonation wave of an ethyne air mixture under various conditions was made.The effect of the detonation chamber closeness on the detonation wave formation was studied.It was found that the developed detonation wave (CJ detonation) was produced when the detonation chamber was completely closed,but the strength of the detonation wave was obviously decreased when one end of the detonation chamber was closed and the other end was open. [WT5”HZ]
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Abstract For the experimental determination of detonation parameters (such as detonation velocity, detonation pressure, detonation products mass velocity, detonation temperature, etc.) of an explosive, various dynamic methods, based on different physical principles, are applied. For this purpose, various experimental methods, as well as testing apparatuses and procedures, are used. At the same time, due to unusual (extreme) values of detonation parameters (detonation velocity reaches 10 mm/μs, detonation pressure up to 400 kbar, detonation temperature ranges from 2000 to 5000 K, duration time of the chemical reactions in the reaction zone is of the order of microseconds, and the width of the chemical reaction zone ranges from tenths of a micrometer to several millimetres), it is very difficult to achieve an entirely reliable experimental determination of some detonation parameters. Detonation velocity is one of the most important parameters of an explosive, which nowadays can be measured very accurately. Its measurement is based on the application of some detonation wave properties and various ultrafast signal recording techniques. This paper summarises research work done in this field.
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