Properties Of Diamond Crystals Research Articles

Paramagnetic Properties of Synthetic Diamond Crystals Obtained in Ni-Mn-C System with Iron Doping

Diamond crystals were synthesized at 4.5GPa and 1300°C in a Ni-Mn-C system with and without Fe doping. The reactive mixture was prepared with 50 wt% graphite and 50 wt% Ni-Mn followed by doping of 2 to 5wt% of pure iron. The synthesis was performed inside an anvil type high pressure device. After extraction and purification, the paramagnetic properties of the diamond crystals were evaluated by specific techniques at room temperature. It was found that the diamond synthesized with different iron content exhibit different paramagnetic properties. The data obtained by infrared spectroscopy and electron spin resonance (ESR) spectroscopy are coincident for radiation defects and different for nitrogen centers. The spectra of the electron spin resonance exhibited broad lines produced by residual impurities of Fe compounds together with catalyst alloy and were accompanied by a distortion of the spectrum of paramagnetic nitrogen in the form of a tilt of the ESR spectra with respect to the zero line.

Design of an adaptive controller in constant pressure grinding of natural diamond cutters

Natural diamond cutters are critical cutting tools applied in nano science and technology fields. The properties of diamond crystal, which are advantages for making high precision cutters, also bring difficulties to the cutter grinding process. In this paper, an adaptive control method is described based on principles of predictive functional control (PFC) method. With this method, an adaptive controller was designed in order to implement constant pressure grinding of natural diamond cutters. Firstly, a real-time grinding process model was constructed, taking account of time-variant characteristic of the wheel-cutter contact and the low stiffness of flexible stage in the practical grinding system. Then, parameters of PFC controller was calculated according to this model. Controller performances were simulated under three conditions of non-disturbance, model parameter mismatch, and time-variant disturbance. Simulation results show that performance of the designed controller is as good as desired, and the controller has enough capability to fit practical diamond cutter grinding process which has characteristics of non-linear and time variance.

New data of typomorphic features of diamonds from placers in North Timan

The morphological and spectral-optical properties of diamond crystals from placers in North Timan rivers have been studied with IR-spectroscopy and cathode luminescence methods. As a result, correlation between external characteristics of diamonds (size and degree of mechanical damage) and number of optically active centers has been revealed. The habit and the type of distribution of structural defects in diamond crystals studied are comparable with those in diamonds from the Archangelsk Region and North Timan’s placers. Based on the obtained data, origin issues and possible primary sources of diamonds from North Timan’s placers are discussed.

Design and characterization of a tissue-equivalent CVD-diamond detector for clinical dosimetry in high-energy photon beams

New solid-state detectors, based on chemical vapour deposited (CVD) polycrystalline diamonds produced by hot-filament (HF) or microwave plasma (MW) assisted deposition methods, were constructed for radiation therapy dosimetry. Properties of diamond crystals, such as high radiation sensitivity, resistance to radiation damage and tissue-equivalence giving a low-energy dependence are very advantageous for clinical dosimetry. Therefore the encapsulation was specially designed for these detectors to have as little influence as possible on the radiation response. The prototypes were irradiated with use of a wide range of photon beam qualities ( 60Co γ-rays, 6 and 18 MV X-rays). The radiation sensitivity varied considerably between samples deposited with HF (9 nC Gy −1 mm −3) and MW (66 and 144 nC Gy −1 mm −3) methods. For all detectors the leakage current was of the order of 10% of the radiation-induced current (bias voltage 100 V, dose rate 0.3 Gy/min). When irradiated with 60Co γ-rays, the detectors showed a dose-rate linearity with an exponential Δ parameter close to unity. However, a difference of 8% was found between Δ values for the different beam qualities. A small energy dependence was observed, for which the most probable sources are interface effects due to the silver electrodes and partly the geometry of the encapsulation which needs to be further optimized. Despite some limitations in the performance of present prototype detectors, with an improved CVD technique producing crystals of better electrical and dosimetric properties, and with a well-designed tissue-equivalent encapsulation, CVD-diamonds could serve as very good dosimeters for radiotherapy.

Constraints on diamond genesis from the study of the dependence of diamond properties on the composition of kimberlites and lamproites

It was shown that the crystal morphology, content, and size of diamonds depend on the concentrations of silica, magnesium, calcium, and carbon dioxide in the host kimberlites and lamproites. The character of this dependence suggests that the viscosity of the initial melts of these rocks was the main control of the morphology and properties of diamond crystals and indicates a magmatic genesis for this mineral. Two genetic varieties of diamond crystals were distinguished: larger residual grains coeval with the formation of the sources of kimberlite and lamproite magmas during the slow high-pressure fractionation of the near-bottom peridotite layer of the global magma ocean and smaller early magmatic grains, which crystallized during the decompression-friction transformation of kimberlite and lamproite protoliths into magmas.

Effect of Low Neutron Doses on the Properties of Synthetic Diamond Crystals

The effect of neutron irradiation on the properties of diamond crystals prepared in the Mn–Ni–C system (5.5 GPa, 1620–1670 K, 120–300 s) was studied. The results indicate that irradiation increases the strength of the crystals and reduces the concentration of paramagnetic centers. The observed changes are interpreted in terms of interaction between intrinsic defects and impurities.