Tensile strength of synthetic chemical-vapor-deposited diamond

Abstract

Pressure burst tests gave measured tensile strengths between 230 and 410 MPa for a total of six chemical-vapor-deposited (CVD) diamond disks in both transparent ‘‘white’’ and opaque ‘‘black’’ forms obtained from three different sources. The disks were nominally 0.635 cm in diameter and 254 μm thick. These strengths are explained by a theoretical model using a Young’s modulus of 1.05×106 MPa and a fracture surface energy of 5.3 J/m2, appropriate for natural diamond, and with critical crack lengths between 33 and 105 μm. The latter lengths can fit, either on or inside, the tapered columnar crystal grains that grow vertically in synthetic CVD diamond films. The model is consistent with the observed inverse dependence of measured tensile strength on film thickness and with tensile strengths between 180 and 5190 MPa reported by other workers for synthetic CVD diamond.

The mechanical properties of various chemical vapor deposition diamond structures compared to the ideal single crystal

“…The fracture strength of polycrystalline diamond has been studied by pressure burst tests, 91,92 three-point bending, 90,93 and four-point bending 90,94 experiments. The fracture strength of the fine-grained nucleation side was consistently higher than that of the coarse-grained growth side, 90,91,93 with values typically below 1 GPa, as discussed above.…”

Applications of advanced materials technologies to vacuum electronic devices

“…The advantage of CVD diamond in this scenario arises from its high bending strength, which is in the range of 200-500 MPa and is a factor of two to three times higher than BeO [12]. Thus, windows composed of high-strength diamond can be made thinner than those of BeO, which will reduce reflections in unmatched window applications and increase the bandwidth in pillbox configurations [11].…”

“…For the case of turbulent flow in a tube, the Nusselt number is approximately given by the Petukhov-Kirillov [39] correlation (12) In this equation is the Reynolds number, is known as the Prandtl number, is the fluid flow velocity, is the mass density, is the viscosity, and is a friction factor approximated by (13) For flow in a tube, a Reynolds number above 10 is considered fully turbulent. To illustrate the foregoing equations in a practical example, consider a single water-filled cooling tube, such as those in Fig.…”

“…Under these conditions, the window can be assumed to be simply supported along its edge. The bending stress in a such a thin disk of diameter and thickness , under uniform surface pressure , is given by (1) where is Poisson's ratio [12], [13]. Poisson's ratio varies between 0.1 and 0.2 for different types of diamond; the effect is weak since is added to three.…”

Vertically Aligned Carbon Nanotubes as a Unique Material for Biomedical Applications

“…Specifically, the sp 2 hybridized orbital brings about extremely strong bonds giving CNT its high tensile strength (>100 GPa) . This is stronger than diamond (5.19 GPa), which has weaker bonds from its sp 3 orbitals . These bonds are also very stiff and efficiently transmit lattice vibrations, making CNT thermally conductive (up to 6600 W/mK at 20 °C). , Furthermore, the sp 2 orbitals in CNT give rise to a single π bond and, consequently, a delocalized electron, enabling conductivity as high as 10 7 S/m .…”