Diamond capacitors

Static Pressure Synthesis. Diamond can form direcdy from graphite at pressures of about 13 GPa (130 kbar) and higher at temperatures of about 3300—4300 K (7). No catalyst is needed. The transformation is carried out in a static high pressure apparatus in which the sample is heated by the discharge current from a capacitor. Diamond forms in a few milliseconds and is recovered in the form of polycrystalline lumps. From this work, and studies of graphite vaporization/melting, the triple point of diamond, graphite, and molten carbon is estimated to He at 13 GPa and 5000 K (Fig. 1)... 

Most PCBs were added to reduce the flammability and increase the stability in mineral oils used as dielectric fluids in electrical transformers and capacitors, including the small transformers in fluorescent light fixtures (see Diamond et al, 2009, among others). PCBs also saw widespread use as plasticizers in sealants in about one quarter of the many buildings built during the post-WWII construction boom in Europe and North America, as flame retardants in electrical wiring, and as a preservative in exterior paints and interior floor... 

Because of the high breakdown voltage, wide band-gap material can and have been used as electrical insulators. There has been a great deal of interest in pressed nanophase SiC and diamond powders as an electrical insulator for capacitors. 

Barium and strontium have been incorporated in new materials research. Barium titanate (BaTi03) is used in ceramic capacitors and, when incorporated in tin, makes a material harder than diamond. Crystals of barium titanate are also used in optical materials. Strontium titanate (SrTi03) has such a high refractive index that it sparkles like diamond and is used in less expensive jewelry. 

Electro-Deposited (ED) films were prepared on Indium Tin oxide (ITO) coated slides closely following the procedure described in ref. [7]. ED films were allowed to dry in a constant 12% relative humidity (R.H.) chamber for 24 hrs prior to the completion of the capacitive cell which consisted of vacuum evaporation of 5000 A of polyethalene (PE) and 50 to 90 A of Pt. Typical capacitor areas were from 50 to 80 mm. Capacitances ranged from 600pf to 1,2 nf, as measured with a B K Precision digital capacitance meter. Film thicknesses were measured with a Talysurf apparatus, which probes the film surface with a fine diamond tip coupled to a mechanic-electric transducer. Typical values ranged from 3 to 6 m i ( 40 A). A schematic illustration of a finished capacitor is presented in figure 1. 

The lanthanides are also used in the electronics industry in the form of YAG (yttrium-aluminum-garnet) crystals, which are used as microwave filters and control devices. When doped with small quantities of Nd or Er, the garnets can be used as lasers. These garnets have a brilliance similar to diamond and are used as gem stones. Lanthanides are also used to a limited degree in the miniturization of capacitors and the production of thermistors. 

In this Section, a functional sp -sp carbon composite material using this nano-porous diamond film (NANO) has been introduced. The electrochemical interface on this composite surface was designed such that the sp2 portion, which was composed of carbon nanotubes (CNT), and the sp portion operate as a Li+ ion battery and a double-layer capacitor, respectively. 

However, our interest here is more related to the electrochemical characteristics. The often cited intrinsic electrochemical characteristics of diamond, including extreme stability, low background current and large potential working range, are also advantages for the fundamental study of the electrochemical characteristics of solid materials. The electroanalytical applications of electrochemical metal deposition will be treated in Chapter 16. The materials of interest in the present chapter are those with applications as battery electrodes, capacitor electrodes and electrocatalysts. There may even be cases in which diamond can play a role as a practical support material. 

One of the first metal oxides to be examined electrochemically on a diamond substrate was ruthenium dioxide [115, 116]. This material is important both for electrochemical capacitor and electrocatalytic applications (chlorine evolution). Another example is cobalt hydrous oxide, which has catalytic activity for oxygen evolution [117]. A very recent example is lead dioxide [118]. A metal oxide (V2O3) has also been supported on particulate diamond as a catalyst for an organic gas-phase reaction [119]. 

Impedance Characteristics of the Nano-porous Honeycomb Diamond and Application as an Electrical Double- Layer Capacitor... 

Cyclic voltammetry - Because the advantage of diamond in the double-layer capacitor application is its wide working potential window, we have examined the current-potential behavior for the honeycomb films (Figure 19.2A). Interestingly, the working potential window for the honeycomb films remained essentially the same as that for the as-deposited film, even after extended oxygen plasma treatment. 

---