Cemented diamond compositions

In 1958, Hall [141] discussed the desirability of preparing a cemented diamond composition analogous to WC and hinted that experiments to produce polycrystalline diamonds were underway. But it was not until 1970, when he reported details of his procedures [142], that he established experimentally practical pressure and temperature fields where pure diamond powder can be sintered within times ranging from several days down to about one second. He mentions hard refractory materials like borides, carbides, nitrides and oxides as suitable binders. 

SEM images of the SiC-coated diamond-dispersed cemented carbide composite (a) polished surface, (b) crack propagation. 

MWCNTs have been tested to reinforce various matrices because they have many unique mechanical and physical properties.14,15 However, these nanotubes become corroded with metals (such as iron, cobalt, and aluminum) at temperatures above 850°C. These shortcomings limit the applications of MWCNTs as nano-reinforcements. The SiC coating can effectively protect the diamond from molten cobalt, thus allowing dense SiC-coated diamond-dispersed cemented carbide composites to be successfully fabricated at lower pressures. If MWCNTs can be coated with the same SiC layer, more stable MWCNTs would be produced and expected to be used as nano-reinforcements for various matrices. The development of SiC-coated MWCNTsAVC-Co composites has potential to extend functions of both MWCNTs and WC-Co. 

While we have not yet carried out detailed kinetic measurements on the rate of photocorrosion, our impression is that the process is relatively insensitive to the specific composition of the strontium titanate. Trace element compositions, obtained by spark-source mass spectrometry, are presented in Table I for the four boules of n-SrTi03 from which electrodes have been cut. Photocorrosion has been observed in samples from all four boules. In all cases, the electrodes were cut to a thickness of 1-2 mm using a diamond saw, reduced under H2 at 800-1000 C for up to 16 hours, polished with a diamond paste cloth, and etched with either hot concentrated nitric acid or hot aqua regia. Ohmic contacts were then made with gallium-indium eutectic alloy, and a wire was attached using electrically conductive silver epoxy prior to mounting the electrode on a Pyrex support tube with either epoxy cement or heat-shrinkable Teflon tubing. 

Dense composites of cemented carbide containing SiC-coated diamond particles can be fabricated without conversion of diamond to graphite. The fracture toughness of the composite is double that of cemented carbide due to the deflection and blocking effects against crack propagation by the dispersed diamond particles. 

S. Diamond Considerations in image analysis as applied to investigations of the ITZ in concrete. Cement and Concrete Composites 23(2-3) 171-178. (2001)... 

Bentur, A., and Diamond, S. (1987) Direct incorporation of silica fume into glass fibre strands as a means for developing GRCF composites of improved durability. International Journal of Cement Composites and Lightweight Concrete 9,214-222. 

Of particular importance is the machining of aluminum alloys now widely used in automobiles and other areas. These alloys are difficult to machine with carbides, especially if a good finish is required, and diamond has shown to be the best machining material. Diamond is used extensively in machining abrasive materials, such as fiber composites, ceramics, cemented carbides, graphite, concrete, and silicon. A major application is the cutting of architectural stones. 

Cohen, E. B., Diamond, S. (1975) Validity of flexural strength reduction as an indication of alkali attack on glass in fibre-reinforced cement composites , Proc. RILEM Symp. Fibre-reinforced Cement and Concrete, Sheffield, pp. 315-25. 

Among composites produced by modern technology there exist diamond-bearing composite materials (DCM) consisting of a homogeneous cemented carbide matrix and grains of natural or synthetic diamond stochastically distributed in it (5) ... 

Novikov, N.V., Tsypin, N.V. and Maistrenko A.L., Composite diamond-bearing materials based on cemented carbides. Sverkhtverdye materialy. 1983> 2, 3 5 (in Russian). 

A. Bentur, Mechanisms of potential embrittlement and strength loss of glass fibre reinforced cement composites , in S. Diamond (ed.) Proceeding- Durability of Glass Fiber Reinforced Concrete Symposium, Prestressed Concrete Institute, Chicago, IL, 1986, pp. 109-123. 

A. Bentur and S. Diamond, Aging and microstructure of glass fibre cement composites reinforced with different types of glass fibres , Durab. Bldg. Mat. 4, 1987, 201-226. 

X. Ein, D.M. Silsbee and D.M. Roy, The microstructure of wood fiber reinforced cementitious composites , in S. Diamond, S. Mindess, F.P. Glasser, L.W. Roberts, J.P. Skalnyand E.D. Wakeley (eds) Microstructure of Cement-Based Systems/Bonding and interfaces in Cementitious Materials, Materials Research Society Symp. Proc. Vol. 370, Materials Research Society, Pittsburgh, PA, pp. 487-495. 

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