Using the tracer method to study detonation processes

The tracer method was used to study the synthesis of nanodiamonds during detonation of composite explosives. Alloys of TNT with RDX, HMX, PETN, and benzotrifuroxan were studied. It was shown that, in all cases, most nanodiamonds were formed from TNT carbon. It was concluded that during the chemical reaction in the detonation wave propagating in heterogeneous explosives, equilibrium parameters were not established. In homogeneous TNT/PETN mixtures, individual components react with each other to form common products. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 6, pp. 92–98, November–December, 2008.     

Detonation of nanosized explosive: New mechanistic model for nanodiamond formation

While nanodiamonds are synthesized by detonation of microstructured explosives since 50 years ago, we developed a novel approach to synthesize these particles by using nanostructured explosives. This new synthesis method leads to novel results not only in the control of the size, but also in the understanding of the nanodiamond synthesis and the detonation mechanisms. The use of explosive particles with size down to 40 nm results in the formation of detonation nanodiamonds with a mean size of 2.8 nm. In the light of these experiments, a model based on the size of the material involved during the detonation process has been developed to explain the size of the obtained nanodiamond. According to hypotheses based on the number of the nanodiamond nucleation sites, the experimental results are in favor of a decrease in the size of the nanodiamonds formed when the size of the explosive particles used during detonation is decreased.     

Surface electronic structure of detonation nanodiamonds after oxidative treatment

X-ray absorption spectroscopy has been used for comparative study of electronic structure of detonation nanodiamonds (ND) purified using different oxidative treatments. The treatment of detonation soot with a mixture of nitric and sulphuric acids followed by ion exchange and ultrafiltration of hydrosol obtained was found to result in developing of ND surface coverage consisting of oxidized carbon species, which electronic state is close to that of strongly oxidized graphite. The deeper purification of ND was demonstrated to allow cleaning of ND particles from most of the oxidized carbon contaminations.     

Pressure induced changes in fractal structure of detonation nanodiamond powder by small-angle neutron scattering

The results of the experiments on small-angle neutron scattering from the industrial detonation nanodiamond powder under a pressure in the range of up to 1000 MPa are reported. It is shown that at a scale of 10–100 nm the scattering is determined by the fractal pore structure within aggregates of nanodiamonds. Its fractal dimension monotonously decreases with pressure from 1.8 to 1.2, which indicates the recombination of pores as a result of mobility of nanodiamonds in the powder under pressure. The mean pore size under the highest pressure (6 nm) is close to the characteristic size of nanodiamonds in the sample (5 nm) found from the width of X-ray diffraction peaks. The difference can be explained by the existence of a non-diamond carbon shell around diamond crystallites.     

An efficient purification method for detonation nanodiamonds

This article reports the purification process of detonation soot to obtain pure nanodiamond powder. Nanodiamonds are synthesized by detonation using a high explosive mixture composed of trinitrotoluene and hexogen. The detonation of the charge leads to a powder containing nanodiamonds as well as metallic impurities and sp² carbon species. Further, to remove metallic particles, an unusual acidic treatment (hydrofluoric/nitric acids; i.e. fluorinated aqua regia) was set up. To eliminate sp² carbon species such as graphite and amorphous carbon, a thermal oxidation treatment was performed at 420 °C under air in a furnace during several hours. Transmission Electronic Microscopy, Raman spectroscopy, X-ray diffraction and Thermo-Gravimetric Analysis showed that this purification process is very efficient. From TGA measurements, a model of the carbon grain combustion was developed by considering graphitic shells surrounding the nanodiamond particles, and was used to demonstrate that the selective oxidation of graphite was experimentally realistic. Moreover, another model was set up from specific area measurements to evaluate the thickness of the functional groups surrounding the nanodiamonds after the oxidation of sp² carbonaceous species. The treatment described herein was achieved on several tens of grams of product and could be easily adapted to the industrial scale.     

Specific Features of Synthesis of Detonation Nanodiamonds

It is demonstrated that the Chapman-Jouguet parameters for high explosives used in nanodiamond synthesis are located in the region of liquid nanocarbon; therefore, the chemical reaction zone of the detonation wave involves formation of carbon nanodroplets, which are later crystallized into nanodiamonds on the segment of the isentrope of expansion of detonation products, passing through the region of stability of nanodiamonds in the pressure range of 16.5–10 GPa and the temperature range of 3400–2900 K. Soot in the resultant mixture is the product of amorphization of nanodroplets rather than graphitization of ultrafine diamonds. The influence of detonation conditions of high-explosive charges in an explosive chamber on nanodiamond synthesis is analyzed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 104–116, September–October, 2005.     

Preparation of composite electrochemical nickel–diamond and iron–diamond coatings in the presence of detonation synthesis nanodiamonds

In the work it is shown that addition of individual pure detonation synthesis nanodiamonds to nickel- and iron-plating electrolytes results in an increase in microhardness (2–3.5 times) and wear-resistance (3–6 times) and a decrease in porosity (3–4 times) of a coating. The use of nanodiamonds as a component of diamond-containing blend (a semi-product of synthesis of the nanodiamonds) results in deterioration of all of the above properties for a nickel–diamond coating and great improvement of the same properties for an iron–diamond coating.     

Where and when are nanodiamonds formed under explosion?

The formation of nano-sized diamonds during the detonation of a TNT/RDX explosive with 50/50 composition was investigated experimentally in situ by means of small-angle X-ray scattering using synchrotron radiation with nanosecond time resolution. No nanodiamonds were observed immediately after the detonation front, as only the nucleation of nanodiamonds takes place at this moment. The increase in small-angle X-ray scattering which was observed during 2 μs was the cause of the dynamic growth of nanodiamonds. The inclusion of a very thin shell around the explosive causes a significant increase in this time, because the kinetic of nanodiamonds growth was changed.

In another set of experiments, the nanodiamonds were artificially introduced into different explosives before explosion. The nanodiamonds were not destroyed in RDX immediately after the detonation front, but burned in an oxidants with some delay. In TNT, the nanodiamonds were not destroyed at all.     

低温等离子体除苯过程中臭氧的演变与作用

大气污染物中,挥发性有机化合物(VOCs)已超越NOx和SO_2成为排放量最高的气态污染物,对人体健康和环境的影响已引起广泛关注。相比传统去除VOCs的技术,低温等离子体法具有高效率、低能耗、易操作等优势,但有产生臭氧(O_3)等副产物的问题。本研究选择苯作为VOCs的代表污染物,采用线管式介质阻挡放电反应器,考察电压、电流等放电参数对苯去除率、副产物臭氧浓度和CO_2选择性的影响,重点分析臭氧的演变、机理及其作用。结果表明,影响臭氧浓度的直接因素是输入功率:随着输入功率的上升,苯去除率逐渐上升,臭氧浓度先上升后下降。其原因在于高功率下生成更多低能电子,使得臭氧分解为氧气。等离子体产生的臭氧无法直接氧化苯,但可以氧化苯的中间产物CO完全转化为CO_2。     

Polymer composite materials based on thermoset epoxy binders modified with diamond-containing nanofillers

Structural features and physicochemical properties of promising diamond-containing modifier fillers for industrial polymers, namely, detonation nanodiamonds and nanodiamond soot, are considered. Experimental results demonstrating the possibility to create prepregs with the use of the carbon fabric 1.5 К and a detonation-diamond soot-modified binder based on the epoxy-resin mixture Epikote828/Epikote154 with an anhydride-type curing agent are presented. The rheological characteristics of the diamond-sootmodified binder remain practically the same after storage for 2 or 3 days at room temperature. The dependence of the glass-transition temperatures of the binders on the content of diamond soot in the concentration range 0.025–0.1 wt % is studied, and the correlation between these results and the mechanical characteristics (breaking strength, flexural strength, and crack resistance) of the cured binders is ascertained. Within the entire range of diamond-soot concentrations, the parameters of gelation are determined and the activation energies of this process are calculated.     

Extraterrestrial,terrestrial and laboratory diamonds — Differences and similarities

Characterization tools such as confocal Raman micro-spectroscopy, Laser Ablation (LA-ICP-TOF-MS) and SEM-EDS were used to characterize meteorites: primitive achondrite — not classified NWA XXX ureilite found in 2006 in Morocco and the graphite nodula from the Canyon Diablo iron meteorite. The presence of diamond was confirmed in both samples.There are two kinds of meteoritic diamonds: diamonds of the sizes of microns up to millimeters are most probably of impact origin, nanodiamonds of the sizes of 1–3 nm, called presolar diamonds because of the isotopic anomalies, are believed to be formed before our Solar System was formed. There are many theories concerning presolar diamonds formation, among them: impact shock metamorphism driven by supernovae or chemical vapor deposition (CVD) from stellar outflows.We examined the properties of diamond nanopowders obtained by the PA CVD and detonation methods. Nanodiamonds obtained by the detonation method, called ultradispersed detonation diamonds (UDD), are of the same range of sizes as presolar diamonds.The results show both differences and similarities among meteoritic, terrestrial and laboratory diamonds. The comparison will help to understand the processes during presolar nanodiamonds formation.     

Experimental characterization of the role of hydrogen in CVD synthesis of MWCNTs

An experimental study was conducted to examine the role of hydrogen in the chemical vapor deposition (CVD) synthesis of multiwalled carbon nanotubes (MWCNTs) in a flow tube reactor using xylene as a carbon source and ferrocene as a catalyst. Ferrocene was introduced into the reactor by two methods. In a single step method, the catalyst was dissolved in xylene and the mixture was introduced using a syringe pump. A two step method was also used where the ferrocene powder was placed in the preheated zone for a certain time to deposit iron catalyst particles on the reactor wall prior to introducing the pure xylene into the reactor. CVD synthesis of carbon products was performed as a function of hydrogen input under constant flow conditions using both methods. SEM and TEM images of the carbon products were examined. The results revealed a competition between the formations of the different carbon products (soot, carbon fibers and CNTs) that altered by the addition of hydrogen. The role of hydrogen is suggested to reduce the rate of carbon production by dehydrogenation so that the more ordered and thermodynamically stable MWCNTs can be produced rather than less ordered and thermodynamically stable soot and carbon fibers.     

Nanodiamonds with novel properties: A biological study

This paper discusses the prospects for using modified detonation nanodiamonds with novel properties as a new promising material for the development of nanotechnologies intended for biological and medical purposes. The authors report that nanodiamonds synthesized by detonation can be used to further purify commercial protein preparations and that enzymes adsorbed on diamond nanoparticles retain their activity. The paper presents results of in vivo experiments with nanodiamonds administered to animals via different routes.     

Cold plasma functionalization of nanodiamond particles

Functionalization of three different types of detonation nanodiamonds was performed using a cold plasma discharge generated with fluorine containing gas. The chemical bonds formed between the reactive species generated in the plasma and nanodiamond particle surfaces were confirmed by FTIR and XPS analysis. From results of FTIR and XPS characterization, it was concluded that initial type of nanodiamond has little overall effect on the degree of fluorination. Fluorination of nanodiamonds allowed for the previously unavailable colloidal suspension in anisole.     

Effect of nanodiamond surface functionalization using oleylamine on the scratch behavior of polyacrylic/nanodiamond nanocomposite

Addition of hard particles such as nanodiamonds to polymers to improve their physical and mechanical properties is very common. However, nanodiamonds are usually hydrophilic so their tendency to form agglomerates in a polymeric matrix is quite strong. In this study, the effect of nanodiamond surface modification on its uniform dispersion in a polymeric matrix such as polyacrylic-base polymer clear coat was investigated. For this purpose, detonation nanodiamond (DND) with an average particle diameter of 4–6 nm was used. To improve dispersion of as-received DND (AR-DND) in the polymeric matrix, the surfaces of the particles were modified by heat treatment (oxidation) in air and followed by functionalization using oleylamine (OLA) as surfactant. So, nanocomposites with different contents of AR-DND, HT-DND and OLA treated HT- DND (OLA-HT-DND) particles were produced. Their characterizations were investigated by employing many analytical methods such as: Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermo-gravimetry analysis (TGA). Scratch resistance test and study of coating surfaces, using scanning tunneling microscopy (STM), were carried out on the polymeric nanocomposites. The results showed that the surface-functionalized nanodiamonds are highly dispersive and stable in the polymeric matrix. In addition, scratch resistance was increased with the addition of nanoparticles.     

Influence of HMX particle size on the synthesis of nanodiamonds in detonation waves

The effect of the particle size of HMX in alloys with TNT on the synthesis of nanodiamonds in a detonation wave was studied experimentally. Mixtures with a TNT content of 40 to 90% and the specific surface area of HMX varied in the range of 5–510 m²/kg were investigated. For all mixtures, an increase in the particle size of HMX was found to lead to an increase in the yield of nanodiamonds with the maximum yield shift toward alloys with increased TNT content. The results are explained using a model based on the absence of thermodynamic equilibrium between the components of the heterogeneous explosive during detonation. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 79–84, March–April, 2008.     

Microwave induced carboxylation of nanodiamonds

Microwave-assisted chemical functionalization of detonation nanodiamonds (NDs) is reported for the first time. The diamond core is not a microwave absorber, and consequently NDs required relatively long reaction times. Fourier transform infrared spectroscopy (FTIR) confirmed the successful grafting of carboxylic group on the NDs surface while X-ray diffraction (XRD) showed that the NDs core was unaffected by microwave treatment. The carboxylation led to altered colloidal behavior in terms of reduced in agglomeration in both aqueous and polar organic solvents, which was accompanied by increased solubility.     

Kinetic Modeling of Ozone Generation via Dielectric Barrier Discharges

A mathematical model combining chemical kinetic and reactor geometry is developed for ozone synthesis in dry O₂ streams with a wire-tube dielectric barrier discharge (DBD) reactor. Good agreement is found between the predicted ozone concentrations and experimental data. Sensitivity analysis is conducted to elucidate the relative importance of individual reactions. Results indicate that the ground-state oxygen atom is the most important species for O₃ generation; however, ozone generation will be inhibited if the O atom is overdosed. The excited species, that is, O(¹ D) and O₂(b ¹Σ), can decompose O₃ and suppress ozone synthesis. The model developed is then applied to modify the original DBD reactor design for the enhancement of ozone yield. With a thinner dielectric thickness, more than 10% increase of ozone concentration is achieved.     

超硬材料合成方法、结构性能、应用及发展现状

为了对超硬材料有更深入的了解,对以金刚石和立方氮化硼为主的超硬材料的合成方法、发展历程、结构与性能及应用领域进行了综述.金刚石的合成方法主要有静压触媒高压高温法、化学气相沉积法、动压爆炸法或爆轰法.经过几十年的发展,我国超硬材料制造技术和装备已经处于国际先进水平.超硬材料除了硬度高之外,还有许多优良的物理力学和化学性能...     

The effects of surface oxidation on luminescence of nano diamonds

In this work we quantify and characterise the effects of air-oxidation on nitrogen-vacancy defect luminescence in both high-temperature-high-pressure and detonation synthesized nanodiamonds using Raman and luminescence spectroscopies. We find that oxidation treatments result in an increased nitrogen-vacancy centre excited state lifetime from 13 ns to 25 ns and in 5-nm diamonds the intensity of this luminescence increases by at least 5-fold. At the same time, in 5-nm diamonds, short lived surface-defect related luminescence is reduced by 10-fold. Furthermore we find that air oxidation reduces the sp² and disordered carbon fraction of nanodiamonds by up to 5-fold in 5-nm nanodiamonds. Based on these results, the authors suggest that the disordered-carbon and graphite shell of 5-nm nanodiamonds quenches nitrogen-vacancy luminescence, and that this quenching can be partially reduced by surface oxidation. These findings provide useful insights into the role of the graphite and disordered carbon shell in quenching luminescence, and have implications for the applicability of 5-nm nanodiamonds to bio- and quantum physics applications.