Структурные и оптические характеристики синтетических алмазов в нано-, микро- и миллиметровом масштабе

Synthetic diamonds are the subject of research in many different implementations. Recognition of the properties of materials with dimensions near the nanometre scale is of great importance for essential science and multiple applications. Microdiamonds synthesised by the HPHT method and nanodiamonds made by detonation were evaluated using XRD, SEM, TEM and Raman spectroscopy. UV-VIS luminescence measurements were performed and compared with each other to assess the surface defects and grain size influence on their optical properties.

Trevor Evans. 26 April 1927 — 10 October 2010

Trevor Evans was responsible for revealing the main physical processes which take place in natural diamond both in the upper mantle of the earth, where it is stabilized by high pressure and temperature, and as it is ejected by volcanic action to the surface. By measuring the activation energies required for graphitization, he clarified the reason for its very long life as a metastable crystal, valuable both as a gemstone and as an industrial abrasive. He learned how to make diamond specimens for examination in the transmission electron microscope, which enabled his discovery of dislocation loops and platelet precipitates in nitrogen-containing (type 1) stones. In a series of exacting laboratory experiments under geologically relevant conditions he pioneered the study of the emergence of nitrogen from solution to precipitation during the ejection process. In synthetic diamonds, using high-energy electron irradiation, he was able to reproduce the sequence of all the various types of nitrogen aggregation found in natural diamond. His work played a major role underpinning the characterization of gemstones, explaining many features of their colour. For many years he led diamond research in the UK, supported by De Beers. His work stimulated and has been confirmed by research in many other laboratories around the world.

Engineering of defects in fast neutron irradiated synthetic diamonds

Chemical vapor deposited (CVD) diamonds have been irradiated with fast reactor neutrons at fluencies F = 1·1018 and 3 · 1018 cm-2 and then heated at temperatures up to 1600 °C. The processes of annealing in and annealing out of various complexes of intrinsic defects responsible for vibrational and electron-vibrational bands in the IR absorption spectra have been studied in detail. Some tens of local vibrational modes and zero-phonon lines with rather small width caused by numerous complexes of intrinsic defects were observed in the 400-11000 cm-1 range.

Gemological Characteristic Difference between Colorless CVD Synthetic Diamonds and Natural Diamonds

CVD synthetic diamond plays an important role in the jewelry market due to its excellent performance and low cost. In this paper, colorless CVD synthetic diamonds produced by a Chinese company were investigated in detail with their gemological, spectroscopic, and luminescent properties compared with natural colorless diamonds. Compared with natural diamonds, CVD synthetic diamonds have high-order interference color and more apparent abnormal birefringence. The results of infrared spectra indicate that all the CVD samples are classified as type IIa, while the natural samples belong to type Ia. The CVD samples show lamellar growth and mottled luminescence pattern and have blue, orange red, purple red, and blue fluorescence, respectively, while most of the natural samples show blue fluorescence. CVD diamonds show lamellar growth structure, and natural diamonds show irregular ring-like growth structure. Thus, multiple methods combined with analysis are required to distinguish synthetic diamonds from natural diamonds. This work provides an experimental basis for the identification of CVD synthetic diamonds.

Identification of Pink-Coloured CVD Synthetic Diamonds from Huzhou Sino-C Semiconductor Co. in China

In recent years, increasing numbers of pink-coloured CVD synthetic diamonds have appeared on the market. One of the major sources is Huzhou SinoC Semiconductor Science and Technology Co., Ltd., Zhejiang province of China. In this article, seven pink-coloured CVD-grown diamonds produced in the last two years by Huzhou have been investigated and identified, including their gemological and spectroscopic characteristics. In DiamondView, they fluoresced orange–red, with an obscure striated growth structure, which is common for CVD synthetics. The mid-IR absorption spectra of these samples showed some single nitrogen and hydrogen-related features (1130, 1344, 3123, 3323 cm−1), which indicated that the diamonds were type Ib and were CVD-grown diamonds. The H1a defect annealed out at approximately 1400 °C, whereas the 3107 cm−1 defect was produced by annealing above 1700 or 1800 °C. This implied that the samples had undergone two separate heat treatments: first, a high-temperature anneal (possibly an HPHT treatment to reduce any brown colour), which would have produced the 3107 cm−1 defects and a small number of A centres, followed by irradiation, followed by annealing above 800 °C to make the vacancies mobile. The UV–Vis–NIR absorption spectra showed distinct NV-related features (575 and 637 nm), the main reason for the pink colour. Photoluminescence spectra obtained at liquid nitrogen temperature recorded radiation-related emissions (388.9, 503.5 nm), a strong N-V centre, H3 and H2 defects, and many unassigned emissions. These pink CVD products can be separated from natural and treated pink-coloured diamonds by a combination of optical spectroscopic properties, such as fluorescence colour, and absorption features in the infrared and UV–Vis regions.

From Ashes to Diamonds

This article examines the making and makers of “memorial diamonds.” These are “natural” diamonds identical to gemstones found in nature but produced in laboratories with carbon sourced from genetic material (cremation ashes) or other objects of symbolic and emotional value. Threading corporality and objectified life forms, we examine the transformation from ashes to the “afterlife” of these “living” objects that are at once synthetic and organic. We ask, first, what material and affective properties distinguish synthetic diamonds from those extracted from nature? Second, how are these living and memorialized representations of inert substances – in continuity with bodily elements of the deceased – valued and mediated through “real” human, though artificially grown, natural objects? Drawing from research with the leading companies in the memorial diamond business in Switzerland and the United States, this article suggests that these diamonds’ singular connection to the human body offer a window into the transmutations between nature and the artificial, memory and material likeness, life and death.

EXCESSIVE ENERGY OF DETONATION NANODIAMONDS

Алмазы детонационного синтеза (ДНА) отличаются набором уникальных свойств, связанных с существенно неравновесными условиями их получения. Исследование их свойств продолжает оставаться актуальным в последние годы. Наноалмазы находят применение в полировальных составах, при модификации каучуков, резин, полимеров, металлов, создании новых композиционных материалов, в качестве добавок к топливу, адсорбентов и катализаторов, в биологии и в медицине. Интерес представляет энергетическая насыщенность наноалмазов. В данной работе проведено теоретическое и экспериментальное исследование избыточной энергии алмазов детонационного синтеза. Доказано, что ДНА обладают избыточной энергией по сравнению с природными и синтетическими алмазами. Рассмотрены возможные источники возникновения избыточной энергии. Исследованы образцы ДНА, полученные в различных условиях синтеза. На основе данных по термогравиметрическому анализу образцов ДНА представлены результаты анализа избыточной энергии образцов и ее зависимости от площади удельной поверхности частиц. Площадь удельной поверхности порошков получена методом БЭТ. Установлено, что чем больше поверхность частиц, тем больше тепла затрачено на её получение и выделилось при сжигании. Однако зависимость избыточной энергии от площади удельной поверхности частиц обратная. Экспериментально полученные нами величины плотности избыточной энергии на 1-2 порядка выше теоретически полученных значений для природных алмазов и для наноалмазов, что подтверждает наличие большой избыточной энергии ДНА. Такое свойство детонационных наноалмазов может найти применение в новых технологиях, в частности, при использовании наноалмазов в роли сорбентов. Detonation synthesis diamonds (DNDs) are distinguished by a set of unique properties associated with substantially nonequilibrium conditions for their production. The study of their properties continues to be relevant in recent years. Nanodiamonds are used in polishing compositions, in the modification of rubbers, polymers, metals, the creation of new composite materials, as additives to fuel, adsorbents and catalysts, in biology and medicine. The energy saturation of nanodiamonds is of interest. In this work, a theoretical and experimental study of the excessive energy of detonation synthesis diamonds is carried out. It has been proven that DNDs have excessive energy in comparison with natural and synthetic diamonds. Possible sources of excess energy are considered. Samples of DND obtained under various synthesis conditions have been investigated. Based on the data on thermogravimetric analysis of DND samples, the results of the analysis of the excessive energy of the samples and their dependence on the specific surface area of ​​the particles are presented. The specific surface area of ​​the powders was obtained by the BET method. It was found that the larger the surface of the particles, the more heat is spent on its production and released during combustion. However, the dependence of the excessive energy on the specific surface area of ​​the particles is inverse. The experimentally obtained values ​​of the excessive energy density are 1–2 orders of magnitude higher than the theoretically obtained values ​​for natural diamonds and for nanodiamonds, which confirms the presence of a large excess excessive of DND. This property of detonation nanodiamonds can find application in new technologies, in particular, when nanodiamonds are used as sorbents.

MODELING THE INFLUENCE OF METAL PHASE IN DIAMOND GRAINS ON SELF-SHARPENING OF GRINDING WHEELS ON CERAMIC BONDS

The article presents the results of theoretical studies using finite element modeling, which made it possible to determine the rational characteristics of diamond wheels based on ceramic and polymer bonds. The effect of the parameters of the diamond-bearing layer on the change in its stress-strain state in the process of microcutting of hard alloys and superhard materials has been studied. It is established that the determining factor in the occurrence of critical stresses during grinding is the temperature in the cutting area, the increase of which in the presence of metal phase inclusions in diamond grains with high values of thermal expansion coefficient can lead to destructive stresses in grains and, consequently, their premature destruction. It is advisable to use diamond grains with a minimum content of metal phase and the use in the manufacture of synthetic diamonds solvent metals with a low value of this coefficient, which will significantly increase the use of potentially high resource diamond grains.

Sintering of composite materials for tool appointment, based on impact diamonds, under high pressure and temperatures

The article presents the results of a study of composite materials based on diamond-lonsdaleite abrasive (DLA) and various binders (Fe–Ti mechanocomposite, silicon carbide SiC). A metal-matrix composite material with a multimodal nano- and microlevel structure, characterized by increased adhesion of diamond grains to the binder, is obtained on the basis of impact diamonds and a Fe–Ti nano-mechanical composite. It is shown that the use of impact diamonds in comparison with synthetic diamonds makes it possible to reduce the pressure of thermobaric treatment by 30–50 % at the same sintering temperatures. The use of Fe–Ti–DLA composites in the process of magnetic-abrasive polishing (MAP) makes it possible to increase the removal rate of material based on silicon by 1.5–2 times and reduce the processing time by 30 % compared to ferroabrasive powder (FAP) based on synthetic diamonds. The effect of adding of silicon carbide on the process of obtaining a superhard composite material impact diamond – SiC is investigated. It is found that adding of SiC helps to reduce the defectiveness of the material and increase the homogeneity of its structure in comparison with the material without adding of a binder. In this case, an increase in the content of SiC and Si also leads to an inversion of the structure type of the superhard composite from polycrystalline to matrix. It is found that the additional use of amorphous soot and boron affects the refinement of the matrix structure of the composite material due to the formation of boron carbide and secondary finely dispersed silicon carbide.