Experimental Etching of Diamonds: Extrapolation to Impact Diamonds from the Popigai Crater (Russia)

Diamond etching in high-temperature ambient-pressure experiments has been performed aimed to assess possible postimpact effects on diamonds in impact craters, for the case of the Popigai crater in Yakutia (Russia). The experiments with different etchants, including various combinations of silicate melts, air, and inert gases, demonstrated the diversity of microstructures on {111} diamond faces: negative or positive trigons, as well as hexagonal, round, or irregularly shaped etch pits and striation. The surface features obtained after etching experiments with kimberlitic diamonds are similar to those observed on natural impact diamonds with some difference due to the origin of the latter as a result of a martensitic transformation of graphite in target rocks. Extrapolated to natural impact diamonds, the experimental results lead to several inferences: (1) Diamond crystals experienced natural oxidation and surface graphitization during the pressure decrease after the impact event, while the molten target rocks remained at high temperatures. (2) Natural etching of diamonds in silicate melts is possible in a large range of oxidation states controlled by O2 diffusion. (3) Impact diamonds near the surface of molten target rocks oxidized at the highest rates, whereas those within the melt were shielded from the oxidizing agents and remained unchanged.

THE EFFECT OF IRON ON THE SURFACE GRAPHITIZATION OF SILICON CARBIDE

In order to decrease the decomposition temperature of SiC, 12[Formula: see text]nm Fe thin film is applied on SiC substrates as a catalyst layer using electron beam (e-beam) deposition. To investigate the mechanism of Fe-treated SiC decomposition, local Fe regions are formed through dewetting of the catalyst layer by hydrogen annealing. The results show that Fe decreases the decomposition temperature of SiC effectively and increases the kinetics of the graphitization. Studies showed that depending on the amount of Fe, crumpled and ordered graphene films can be synthesized simultaneously on SiC by using this method.

Friction-reducing effect and damage mechanism of laser micro-texture on diamond films during friction

Diamond films are often applied in places where there is intense friction. The use of lasers to fabricate textured arrays on diamond films can effectively reduce the friction coefficient. In this paper, we use a UV nanosecond laser to produce periodic linear and pit micro-textures over the areas of [Formula: see text]. Laser irradiation was below the single-pulse ablation threshold corresponding to the conditions of surface graphitization during the multi-pulse irradiation. Irradiated graphitization can be detected by Raman spectroscopy, and at the same time, lattice distortion and crack initiation that accompany graphitization can be obtained by XRD and SEM, respectively. The shape of the texture also has a great influence on the residual stress. Grooved texture released the residual stress, but pit texture gave rise to uneven stress, as shown in the test result. SEM was used for observing morphological change at the edge of texture and the mechanism of internal stress changes is analyzed. Detection of texture antifriction performance by reciprocating friction and wear tester. After rubbing, the layered shedding marks of the edge of the texture were observed, and the influence of the superposition of residual stress and external stress on the texture damage was proved based on this.

Impulse laser effect on graphitized surface of Y‒TZP-ceramics

Using the original technique, the role of the graphite layer under impulse laser effect on the surface of ceramics based on tetragonal zirconia, partially stabilized by yttrium oxide (Y‒TZP-ceramics), was studied. It has been established that surface graphitization increases the fraction of absorbed laser radiation, as a result of which heating, melting and evaporation of Y‒TZP-ceramics occur under less intense modes, which favorably affects the use of impulse laser radiation to modify its surface. Ill. 6. Ref. 18.

Study on High Pressure Sintering of Nanocrystalline Diamond with Nano Silicon as Additives

In this paper, nanocrystalline diamond with the average grain size of 50nm was prepared under different sintering pressure, temperature and sintering time. The microstructure of the sample was analyzed by SEM, EDS and XRD, and the mechanical properties tested by micro-hardness tester and wear ratio instrument. The results show that the sample sintered under the optimum conditions of oil pressure 87MPa, heating power 4000W and sintering time 120s possessed hardness of 706.41HV and wear ratio of 3280. It indicated that high performance n-PCD sintered from nanodiamond and silicon system can be formed hardly with diamond to diamond bonding but can be formed with diamond to silicon carbide bonding. The poor mechanical properties of the samples were due to the surface adsorption groups and surface graphitization of nanodiamond during high pressure sintering.