[en] In this paper a technique for the determination of free carbon in boron carbide was studied. This technique consists in the treatment of the carbide samples with hot sulfocromic mixture, to the free carbon oxidation. The released gases are then circulated in barium hydroxide solutions, whose concentrations are previously determined and by titration the remain quantity of hydroxide in solution is determined. From convenient calculations the amount of free carbon present initially in the samples is then obtained, and these results are here evaluated. (author)

No abstract available

[en] Published in summary form only

[en] The spectral moment's method combined with a force constant model is used to calculate the polarized infrared spectra in single-walled BC₃ nanotubes. We discuss the evolution of these spectra as a function of the diameter, chirality and length of nanotubes. Our work provides benchmark theoretical data for the assignment of experimental infrared spectra.

[en] The invention relates to the manufacture of boron carbide powder. It is well known that boron carbide, formula B4C, has many industrial applications because of its hardness. It is thus used in powder form as an abrasive, especially for lapping and polishing hard metals and carbides, whereas in the pressed and sintered condition it is very suitable for manufacturing parts subjected to a high rate of wear, e.g., sanding nozzles, dies, or bearings. Other applications exist in the nuclear field, when the B 10 isotope, which is a neutron absorber, is present

[en] Published in summary form only

[en] Plate-impact experiments were performed on boron carbide specimens, having different porosities, in order to measure their Hugoniot elastic limit (HEL) values. The measurements were performed with commercial manganin gauges embedded at the back surface of the specimen and backed by a thick Plexiglas disk. The measured values show an almost linear decrease in the HEL values between 194 kbar (For the fully dense material) to 96 kbar for a specimen with 16.3% porosity. These values were compared with a theoretical model [suggested by D. Steinberg (LLL report LLL-UCID-16946, 1975)] which accounts for the dependence of the HEL on porosity, and the agreement is shown to be good

[en] A method has been developed for fabricating long, cylindrical rubber-mill rolls of boron carbide for use with abrasive materials. The technique consisted of initially hot pressing the boron carbide (to 90% of the theoretical density) to short, hollow cylinders having a length-to-diameter ratio of about one. This initial hot-press operation was followed by a second hot press to join or bond, and further densify, the short sections into a final compact having a length-to-diameter ratio of three. Flexural-strength data show that the integrity of the bond is comparable to that of the base material

[en] Hot-pressing techniques have been developed to economically fabricate artefacts of such widely different materials as boron carbide, europium hexaboride, europia and zirconia, over a wide range of temperature, using HF heating. Using specially-designed multibore graphite dies, and a method whereby several specimens were pressed simultaneously in each bore, 48 specimens could be fabricated in a single operation. Experience gained resulted in the design and operation of a continuous hot-pressing facility, which consists essentially of a vertical column of interlocking dies, so arranged that each die acts as either a top or bottom punch in addition to its normal function as a die. The column as a whole moves downwards in a series of intermittent pulses, and is enclosed in silica shielding which allows only a small ingress of air. The use of multi-bore dies and expendable bore liners increased the efficiency of the system and replacement of the self-generated carbon monoxide atmosphere by a non-explosive argon/hydrogen mixture extended the lifespan of the graphite components. Silicon carbide dies are currently being tested with materials, particularly oxides, that show reaction with graphite. (author)

[en] The special physical characteristics of boron carbide (B₄ C) allow its use in a wide range of application in engineering design. Despite of this, the densification during sintering step became the main drawback of the development of ceramics components. The present work deals with the role of sintering aids on the densification of boron carbide ceramics produced through pressureless and hot-pressing sintering. The applied sintering aids were, C+B₂ O₃+ Al₂ O₃, Ni and/or Ti. Dilatometry was used to assist hot-pressing and, C+B₂ O₃ + Al₂ O₃ were the sintering aids. In the both cases the sintering temperature was lowered to 2200 K and 2073 K, pressureless and hot pressing respectively. The results of hardness of about 35 GPa and densification of 99% theoretical density for hot-pressed material show the effectiveness of these sintering aids. So far as the obtained data from this work is concerned we may believe that is possible to produce boron carbide ceramics components with both high density and hardness with lower cost by lowering sintering temperatures, that is, 200 K for pressureless sintering and 350 K for hot-pressing. (author)