Synthesis of alumina-bonded polycrystalline diamond by detonation

In this study, nanodiamond, aluminum isopropoxide, and hexogen (RDX) were used as starting materials to synthesize alumina-bonded polycrystalline diamond materials under high-temperature and high-pressure conditions generated by the detonation of the explosive. During detonation, the surface of the nanodiamond is coated with boron, silicon, and chromium through vacuum diffusion. Carbides of boron, silicon, and chromium referred as “bridges” are formed at the diamond/metal interface during the carbonization reaction. The "bridge" formed between diamond and nanoalumina considerably reduced the possibility of oxidation of nanodiamond as well as its graphitization during the detonation reaction. The phase, morphology, microstructure, and elemental composition of the detonation products were characterized by X-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The results revealed that the explosion causes alumina and diamond to bond tightly to form alumina-bonded polycrystalline diamond composites. The thermal stabilities of the nanodiamond particles coated with boron, silicon, and chromium were found to be markedly higher, and the diamond phase remained intact even after heating at elevated temperatures. Thus, boron, silicon, and chromium reduced the wetting angle of diamond and alumina and improved the degree of bonding between them. Furthermore, boron facilitated the bonding between nanodiamond and alumina. In contrast, the bond was weaker in the case of silicon. Chromium also aided the bonding of the nanodiamond and alumina but introduced a large amount of oxygen into the composite.     

Shock densification of ultradispersed diamond

The production of densified ultradispersed diamonds is examined. Methods for preliminary removal of impurities from samples and shock densification are proposed which make it possible to obtain compact materials with durability comparable to that of AS2 synthetic diamond. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 143–145, May–June 1999.     

Chemical aspect of ultradispersed diamond formation

On the basis of analysis of ultradispersed diamond optical (infrared and ultraviolet) spectra it was suggested to consider chemical part of detonation processes as superposition of three basic processes such as destruction of ‘explosophoric groups’, the endothermic reactions and the exothermic reactions.     

Deaggregation of ultradispersed diamond from explosive detonation by a graphitization–oxidation method and by hydroiodic acid treatment

The deaggregation of ultradispersed diamond (UDD) from explosive detonation has been carried out by a graphitization–oxidation method and by a hydroiodic acid (HI) treatment. The first method is used to break the crystalline bridge between the diamond primary particles, and the second one is employed to break down C–O–C ethereal linkages formed between the diamond crystallites. The samples after the above-mentioned chemical treatments were suspended in water by ultrasonic waves and the resulted suspensions were examined by a dynamic laser scattering method to obtain particle size distributions of samples in water. Experimental results show that after graphitization–oxidation treatment, nearly 35% of the particles, and after further HI treatment 43% of the diamond aggregates were reduced to less than 50 nm, and the particle size of nearly 98% of the aggregates is less than 200 nm in diameter. Thus, these two methods are useful for the deaggregation of UDD from detonation. But it is evident that the results obtained are far from the monodispersion state of UDD. In order to reach an even higher level of deaggregation, further study to improve treating methods is needed.     

Synthesis of diamond from the carbon in the detonation products of explosives

Chelyabinsk. Translated from Fizika Goreniya i Vzryva, Vol. 26, No. 3, pp. 123–125, May–June, 1990.     

Synthesis and properties of single phase diamond ceramics

We report on the synthesis of single phase diamond ceramics and its microstructural and physical characterization. The most relevant physical properties are listed and are compared to natural diamond. The ceramic solid has been fabricated from chemically treated micro crystalline diamond powder, where oxy-functional groups have been attached to the surface. The special surface treatment is considered essential to achieve direct atomic bonding between adjacent grains.The hot isostatic pressing method (HIP) has been applied for materials processing that pertains to the stability region of the related carbon phase diagram. No further additives have been used for preparation. Transmission and scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction and Raman spectroscopy have been used for the micro structural analysis. The achievable density is close to that of natural diamond, revealing porosity values of <3%. The micro structural analyses indicated the presence of small amounts of isolated diamond micro crystals, embedded into a matrix of polycrystalline diamond with a very small grain size. The grains are much smaller than the originally used micro crystalline source material, indicating crystal break-up and atomic rebonding during the sintering process. Also traces of sp²-hybridized carbon have been identified, located primarily at grain boundaries. Fracture of the material appears mostly transgranular. Relevant physical properties as thermal and electrical conductivity, hardness and Young's modulus approach those of natural diamond.     

Spherical nanometer-sized diamond obtained from detonation

Ultrafine diamond (UFD) was synthesized under high pressure and high temperatures generated by explosive detonation. The structure, composition, surface and thermal stability of UFD were studied by use of XRD, TEM, Raman Spectroscopy, FTIR, etc. The influences of the synthesis conditions and purification conditions on the properties of UFD were analyzed. The UFD had an average size of 4–6 nm, commonly exhibiting a spherical shape. The highest yield was of up to 10 mass% of the explosive. Attempts were made to use UFD as an additive to metal–diamond sintering and as crystallite seeds of CVD diamond films. The results show that UFD can decrease the coefficient of friction of the composite by 30%, and raise the nucleation density in CVD diamond films by 2–3 times.     

Partially oxidized potassium intercalate of ultradispersed diamond: A cautionary note

Direct reaction of gray ultradispersed diamond (UDD) powder with molten potassium metal gives K/UDD intercalate as a black powder. Upon prolonged storage in glass vials, presumed partial oxidation of this black powder by diffused air occurs giving a partially oxidized K/UDD gray powder. Powder XRD data indicate likely formation of undetermined amounts of KO₂ and stage-3 potassium graphite intercalate. Exposure of this gray powder to ambient atmosphere initiates a violent detonation (or rapid oxidation) having sufficient force to pulverize glass vial containers. It is recommended that handling of any partially oxidized carbonaceous potassium intercalate material should be conducted with extreme caution. Partially oxidized K/UDD powder appears to be stable to mild mechanical shock and could possibly be of interest as a secondary explosive activated by direct exposure to ambient atmosphere.     

The effect of temperature on the growth of ultradispersed diamonds at a detonation front

Experimental data verify that particles of ultradispersed diamond produced during the detonative decomposition of an explosive material can grow in the solid crystalline state. A method is proposed, and increasing the size of particles of ultradispersed diamond by raising the temperature at the detonation front is shown to be feasible.Biisk. Scientific and Technical Council, Almai. Translated from Fizika Goreniya i Vzryva, No. 1, pp. 109–112, January–February, 1995.     

Improvement of thermal stability of diamond by adding Ti powder during sintering of diamond/borosilicate glass composites

Oxidization of diamond in the sintering process of diamond/glass composites results in thermal degradation of diamond and uncontrolled expansion of the bulk composites with many irregular pores, causing low bending strength of the composites. In this paper, Ti powder was used as oxygen getter due to its excellent affinity with oxygen. The results showed the diamond grits got good protection from oxidation during sintering due to the prior reaction of Ti powder with oxygen. As a result, expansion phenomenon was inhibited and bending strength was improved for the composites due to the Ti additives. TiO₂, as oxidization product of Ti, could enter into the glass network. The maximum bending strength and minimum volume expansion values were obtained for the composites with 6 wt.% Ti powder. This content resulted in a decrease of volume expansion from 22.78% to −25.0%, and an increase in bending strength from 28.49 MPa to 100.54 MPa.     

Electron paramagnetic resonance spectra in fullerite and detonation diamond

An examination of electron paramagnetic resonance spectra in samples of ultra disperse detonation diamond showed that they contain fullerite as impurity. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 4, pp. 100–101, July–August 1999.     

Two-stage combustion of an ultradispersed aluminum powder in air

Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 26, No. 2, pp. 71–72, March–April, 1990.     

Surface stress distribution in diamond crystals in diamond–silicon carbide composites

Diamond–silicon carbide composites were sintered at high temperature, up to 2273 K, and high pressure, up to 10 GPa. Raman microscopy was used to map stress distribution in diamond crystals on surfaces of the composites. Splitting of the triple degenerate band of diamond and frequency shifts of its components were used to calculate the magnitudes of stress. Those magnitudes varied with location and reached maximum values near crystals boundaries. Stress depended on the sintering temperature, pressure, and the crystal size and was attributed to differences in thermal expansion coefficients and bulk moduluses of diamond and silicon carbide.     

Origination of detonation during multistage self-ignition

Conclusion The analysis performed shows that multistage self-ignition under known conditions can display the reason for strong shock and detonation wave generation. The wave excitation mechanism is associated with flame self-acceleration as, during the transition of combustion into detonation in tubes and consists of self-consistent motion of pressure and ignition waves. Realization of such a mechanism is quite probable in application to detonations in engines. The high-speed photography of a detonation explosion in an engine [11] actually, discloses the existence of self-ignition waves and records shock generation in local volumes of unburned parts of the charge.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 25, No. 4, pp. 93–100, July–August, 1989.     

Laser-induced phase transitions in ion-implanted diamond

Results are reported on the study of phase transformations in D⁺ (deuterium) ion-implanted diamond single crystals induced by nanosecond pulses of a KrF excimer laser (λ=248 nm). Multipulse laser irradiation at fluences lower than the graphitization thresholds resulted in progressive annealing, pronounced in an increase of the optical transmission and surface contraction. A non-linear defect distribution in a near-surface layer was found to strongly affect the annealing and graphitization processes; higher annealing efficiency and higher graphitization thresholds were observed under irradiation conditions when a laser beam was incident onto a buried defective layer through diamond, i.e., onto a ‘back’ side of the diamond sample opposite to the ion-implanted side. The influence of non-uniform laser-induced heating of defective diamond material on characteristic features of the phase transitions is discussed.