Applications of Polycrystalline Diamond (PCD) Materials in Oil and Gas Industry

Polycrystalline diamond possesses high hardness and wear resistance, among other superior properties, such as low coefficient of friction, high thermal conductivity, high corrosion resistance and low electrical conductivity. Some of these properties favor the application of polycrystalline diamond in oil & gas industry. PDC cutters are the primary and key components in the PDC drill bits to cut various formations. However, drilling very hard and highly abrasive formations poses a big challenge for today’s PDC drill bits. The weakness in the current technology is due to the unavoidable use of metallic catalysts to bond the diamond grains that comprise the PDC cutters in traditional high-pressure and high-temperature (HPHT) manufacturing. Development of catalyst-free PDC cutters would be a game changing technology for drill bits to potentially realize the goal of “One Run to Total Depth” in drilling technology. This chapter will cover the development and applications of both catalyst-synthesized and catalyst-free polycrystalline diamonds in oil and gas industry including latest breakthrough on ultra-HPHT manufacturing technology to make the hardest diamond on earth for drilling and completion. Besides the application of polycrystalline diamond as PDC cutters, this chapter will also cover its applications in bearing or drilling system

Self-concept mediates the relationships between childhood traumatic experiences and adolescent depression in both clinical and community samples

Background: Childhood trauma is a pivotal risk factor for adolescent depression. While the association between childhood trauma and depression is well-established, the mediating role of self-concept has not been acknowledged. Specifically, limited attention has been paid to how childhood maltreatment impacts adolescent depression through physical and social self-concept, both in clinical and community samples. This study aims to investigate how distinct and cumulative childhood trauma affects adolescent depression, as well as the potential mediating role of self-concept in their relationships. Methods: We recruited 227 depressed adolescents (dataset 1, 45 males, age = 15.34 ± 1.96) and 574 community adolescents (dataset 2, 107 males, age = 16.79 ± 0.65). Each participant was assessed on five subtypes of childhood trauma severity, cumulative trauma index, physical and social self-concept, and depression. Mediation models were tested separately in the clinical and community samples. Results: Clinically depressed adolescents experienced a higher level of trauma severity, a greater number of trauma subtypes, and had lower levels of physical and social self-concept compared to community adolescents. Analyses on childhood trauma severity and cumulative trauma index jointly indicated that physical and social self-concept played mediation roles in the relationships between childhood trauma experiences and depression. Moreover, the mediating effects of self-concept were stronger in depressed adolescents when compared to community samples. Conclusions: Our findings suggest that physical and social self-concept play mediating roles in the pathway linking childhood trauma and adolescent depression, particularly in clinically depressed individuals

Polycrystalline {\gamma}-boron: As hard as polycrystalline cubic boron nitride

The Vickers hardness of polycrystalline {\gamma}-B was measured using a diamond indentation method. The elastic properties of polycrystalline {\gamma}-B (B=213.9 GPa, G=227.2 GPa, and E=503.3 GPa) were determined using ultrasonic measurement at ambient condition. Under the loading force up to 20 N, our test gave an average Vickers hardness in the asymptotic-hardness region of 30.3 GPa. The average fracture toughness was measured as 4.1MPa m1/2. Additionally, We also measured the hardness and elastic properties of polycrystalline {\beta}-B and PcBN for comparison. The hardness and elastic properties for polycrystalline {\gamma}-B was found to be very close to that of PcBN. Our results suggest that the polycrystalline {\gamma}-B could be a superhard polycrystalline material for industrial applications.Comment: 16 page

The mystery of abnormally large volume of PbCrO

PbCrO3 is found experimentally to be a cubic perovskite with an abnormally large lattice constant of about 4.00 Å. To date, no successful first principle calculations have been carried out for cubic PbCrO3 perovskite. Combining the generalized-gradient approximations and a structurally consistent Hubbard U approach, the crystal, electronic and magnetic structures of PbCrO3 are calculated to explore the mystery of abnormally large volume of PbCrO3 in cubic structure. The crystal structure, magnetic order and half-metallic properties of PbCrO3 are determined. For the first time, a structurally consistent Hubbard Ueff of about 8.28 eV for PbCrO3 is calculated based on linear-response approach. With the structurally consistent U obtained by first principles, a \hbox{$Pm\overline 3 m$} cubic structure with a lattice constant of about 3.98 Å for PbCrO3 is obtained successfully. Moreover PbCrO3 is found to be half-metallic ferromagnet with an integral magnet moment of 2.00μB per unit cell. The anomalously large volume of PbCrO3 in cubic structure results from the strongly correlated electron interaction. The results obtained agree well with experimental data

Optimization of Tungsten Carbide Opposite Anvils Used in the In Situ High-Pressure Loading Apparatus

In order to optimize the structure of anvils, finite element method is used to simulate two kinds of structures, one of which has a support ring but the other one does not. According to the simulated results, it is found that the maximum value of pressure appears at the center of culet when the bevelled angle is about 20°. Comparing the results of these two kinds of structures, we find that the efficiency of pressure transformation for the structure without support ring is larger than that for the structure with support ring. Considering the effect of von Mises stress, two kinds of tungsten carbide opposite anvils have been manufactured with bevelled angle of 10°. The experimental results for these two anvils are in good agreement with the simulation

Novel substantial reductions in sintering temperatures for preparation of transparent hydroxyapatite bioceramics under ultrahigh pressure

A novel method for preparing highly transparent hydroxyapatite bioceramics at relatively low temperatures (325-450 degrees C), i.e. about 60% lower compared with other commonly used preparation methods, has been developed under ultrahigh pressure (UHP; 2.0-5.0 GPa). UHP can remarkably restrain grain growth, enhance density and microhardness and we have characterized the morphology, density and mechanical properties of the prepared ceramics. We reason that these bioceramics are highly transparent due to the negligible light scattering from the nanosized grains and pores in the samples. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

The strength of ruby from X-ray diffraction under non-hydrostatic compression to 68 GPa

Polycrystalline ruby (alpha-Al2O3:Cr3+), a widely used pressure calibrant in high-pressure experiments, was compressed to 68.1 GPa at room temperature under non-hydrostatic conditions in a diamond anvil cell. Angle-dispersive X-ray diffraction experiments in a radial geometry were conducted at beamline X17C of the National Synchrotron Light Source. The stress state of ruby at high pressure and room temperature was analyzed based on the measured lattice strain. The differential stress of ruby increases with pressure from similar to 3.4 % of the shear modulus at 18.5 GPa to similar to 6.5 % at 68.1 GPa. The polycrystalline ruby sample can support a maximum differential stress of similar to 16 GPa at 68.1 GPa under non-hydrostatic compression. The results of this study provide a better understanding of the mechanical properties of this important material for high-pressure science. From a synthesis of existing data for strong ceramic materials, we find that the high-pressure yield strength correlates well with the ambient pressure Vickers hardness