Abstract Generated abstract
The paper reports the laboratory synthesis of polycrystalline diamond formations of the carbonado type, distinguished from previously synthesized ballas by a much finer grained structure and an X-ray diffraction halo resembling that of natural carbonado. The authors compare the microstructures of natural carbonado, artificial ballas, and newly obtained specimens, arguing that the synthesized material closely matches natural carbonado in both microstructure and diffraction features. They note that synthesis conditions can convert the whole reaction volume into diamond, allowing specimens to be produced in prescribed shapes, and suggest practical value for machining ceramics and hard alloys.
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PHYSICS
Academician L. F. VERESHCHAGIN, E. N. YAKOVLEV, T. D. VARFOLOMEEVA,
V. N. SLESAREV, L. E. SHTERNBERG
SYNTHESIS OF DIAMONDS OF THE “CARBONADO” TYPE
It was recently reported (¹) that polycrystalline diamond formations of the “ballas” type had been synthesized. Some properties of these diamonds are discussed in (²). It is known that diamonds of the “carbonado” type occur in nature. According to the modern classification, ballas is defined as a polycrystalline spherical aggregate of fine-grained structure, whereas carbonado consists of still finer-grained diamond formations, which on X-ray diffraction patterns give a halo, as do amorphous bodies (³). The typical microstructure of ballases synthesized under laboratory conditions is shown in Fig. 1. Here the light field is diamond, and the dark field is inclusions. Natural carbonados have the microstructure shown in Fig. 3a.
Fig. 1. Microstructure of artificial ballas. 450×
Fig. 2. Carbonado grown in the form of a cylinder, \(h = 4\) mm
As far as we know, we have for the first time synthesized diamond polycrystalline formations having a microstructure similar to that of natural carbonados. The similarity of the microstructures of the obtained specimens (Fig. 3b, c) to the microstructure of natural carbonado makes it possible to call the obtained specimens diamonds of the carbonado type. In the X-ray diffraction pattern taken by us of artificial carbonado, the internal halo characteristic of carbonado is visible (⁴). It should be noted that, in synthesizing artificial carbonado, conditions can be chosen under which the entire reaction volume is transformed into diamond; consequently, the obtained specimens may have a prescribed shape that repeats the shape of the reaction volume. This is of great practical significance. Figure 2 presents a photograph of cylindrical carbonado.
Fig. 3. Microstructure of carbonado: natural (a) and synthesized (b and c). 450×
In conclusion, it may be noted that cutters made of artificial carbonado can machine, with high purity, such materials as ceramics and hard alloys.
Institute of High-Pressure Physics
Academy of Sciences of the USSR
Received
11 XI 1968
REFERENCES
- Ya. A. Kalashnikov, L. F. Vereshchagin et al., DAN, 172, No. 1 (1967).
- I. V. Nikolskaya, L. F. Vereshchagin et al., DAN, 182, No. 1 (1968).
- Yu. L. Orlov, Morphology of Diamonds, Publishing House of the Academy of Sciences of the USSR, 1963.
- S. I. Fuergendler, Candidate’s Dissertation, VSEGEI, 1964.