Improving dispersion of nanometer-size diamond particles by acoustic cavitation

A novel acoustic-dispersion method for fine diamond particles was developed. Two samples of nanometer-sized diamond particles were used. They had primary particle sizes of 5 nm (ND5) and 150 nm (ND150). Disaggregation of agglomerated particles using ultrasound and surface modification of ND5 and ND150 were investigated. The ND5 and ND150 particles aggregated to secondary particles, having sizes on the order of micrometers. The surfaces of ND5 and ND150 particle were modified due to chemical reactions and the particles were disaggregated by acoustic cavitation. The ND5 particles were disaggregated to give an average particle size of about 100 nm by ultrasound exposure with average acoustic intensities higher than 800 W/m(2). The agglomerated ND150 particles with size of 15 microm were disaggregated to reach an average particle size of about 300 nm by ultrasound exposure with an average acoustic intensity higher than 2000 W/m(2). The surfaces of ND5 and ND150 particles were found to be modified with hydroxyl groups resulting from acoustic cavitation. This could lead to a well dispersed solution of nanometer-sized diamond particles in water.     

To the synthesis of polycrystalline diamond

Abstract

The sintering system “Diamond-Graphite-Cobalt” is investigated by means of a High Pressure - High Temperature - Belt - Apparatus. Described are the sintering conditions used and some of the properties of the compacts obtained. Good sintering structures and hard PCD (up to 50 GPa) were obtained at 7,5 GPa and 1500°C.     

人工合成金刚石研究进展

1796年英国科学家S.Tennant的精确燃烧实验,首次揭示金刚石是由纯碳构成的宝石,从此人类开始了漫长的人工合成金刚石的探索.金刚石通常只能在极端条件下形成,因此,合成技术的突破是人类合成水平提高的一个重要标志,文章对这一领域一些重要工作做了简单回顾,也讨论了作者在合成金刚石方面的工作.我们在440℃的低温条件下,用碱金属（Li,Na,K）还原超临界CO2,得到透明、大尺寸的金刚石晶体,首次实现了金刚石燃烧实验的逆过程,即把低能、直线型CO2分子变成了碳-碳四面体连接的金刚石,开辟了人工合成金刚石的新途径.也讨论了它与天然金刚石起源之间的可能联系.     

人工合成金刚石研究进展

1796年英国科学家S．Tennant的精确燃烧实验，首次揭示金刚石是由纯碳构成的宝石，从此人类开始了漫长的人工合成金刚石的探索．金刚石通常只能在极端条件下形成，因此，合成技术的突破是人类合成水平提高的一个重要标志，文章对这一领域一些重要工作做了简单回顾，也讨论了作者在合成金刚石方面的工作．我们在440℃的低温条件下，用碱金属(Li，Na，K)还原超临界CO2，得到透明、大尺寸的金刚石晶体，首次实现了金刚石燃烧实验的逆过程，即把低能、直线型CO2分子变成了碳-碳四面体连接的金刚石，开辟了人工合成金刚石的新途径．也讨论了它与天然金刚石起源之间的可能联系．     

Hydrodynamic cavitation: A feasible approach to intensify the emulsion cross-linking process for chitosan nanoparticle synthesis

Chitosan nanoparticles (NPs) exhibit great potential in drug-controlled release systems. A controlled hydrodynamic cavitation (HC) technique was developed to intensify the emulsion crosslinking process for the synthesis of chitosan NPs. Experiments were performed using a circular venturi and under varying operating conditions, i.e., types of oil, addition mode of glutaraldehyde (Glu) solution, inlet pressure (P_in), and rheological properties of chitosan solution. Palm oil was more appropriate for use as the oil phase for the HC-intensified process than the other oil types. The addition mode of water-in-oil (W/O) emulsion containing Glu (with Span 80) was more favorable than the other modes for obtaining a narrow distribution of chitosan NPs. The minimum size of NPs with polydispersity index of 0.342 was 286.5 nm, and the maximum production yield (P_y) could reach 47.26%. A positive correlation was found between the size of NPs and the droplet size of W/O emulsion containing chitosan at increasing P_in. Particle size, size distribution, and the formation of NPs were greatly dependent on the rheological properties of the chitosan solution. Fourier transform infrared spectroscopy (FTIR) analysis indicated that the molecular structure of palm oil was unaffected by HC-induced effects. Compared with ultrasonic horn, stirring-based, and conventional drop-by-drop processes, the application of HC to intensify the emulsion crosslinking process allowed the preparation of a finer and a narrower distribution of chitosan NPs in a more energy-efficient manner. The novel route developed in this work is a viable option for chitosan NP synthesis.     

Hydrogen-free CVD diamond synthesis

A wide band gap semiconductor, diamond, has recently emerged as an important and promising material for a wide field of optoelectronic and electronic applications. In traditional CVD diamond synthesis, we thought that hydrogen radicals were inevitable. But, in this work, we are trying to synthesize diamond particles without hydrogen, in a process we call “hydrogen-free diamond synthesis”. Graphite rods were used as heaters and, at the same time, carbon sources. In argon or helium atmospheres, completely free from hydrogen, diamond particles were synthesized and confirmed with SEM photographs and Raman spectra for the first time. OES (Optical Emission Spectroscopy) results will be presented.     

单空泡溃灭辐射噪声的实验研究

对空泡在自由面或固壁面附近溃灭辐射噪声的规律进行了实验研究,不仅讨论了自由面及固壁面对辐射噪声的影响,还讨论了空泡中心距边界面的距离对辐射噪声的影响。其中空泡是应用调Q-YAG脉冲激光器产生,该方法在国内尚属首次,得到的实验结果与经典Vogel激光实验结果及作者的数值结果相吻合。     

Experimental study of the cavitation noise spectral line breadth

Results of the experimental study of the cavitation noise spectral line breadth are presented. It was found, that the power spectrum varies as 1/|f| in the vicinity of spectral lines. A possible qualitative explanation of the phenomenon is given on the basis of the theory of group pulse processes. However, this theory fails to explain the observed facts quantitatively.The hydrophone used in this work was designed and constructed by Ing. P. Janeek with a kind help of Dr. A. Boleslav.     

Ultrasonic synthesis of hydroxyapatite in non-cavitation and cavitation modes

The size control of materials is of great importance in research and technology because materials of different size and shape have different properties and applications.This paper focuses on the synthesis of hydroxyapatite in ultrasound fields of different frequencies and intensities with the aim to find the conditions which allow control of the particles size. The results are evaluated by X-ray diffraction, Transmission Electron Microscopy, morphological and sedimentation analyses. It is shown that the hydroxyapatite particles synthesized at low intensity non-cavitation regime of ultrasound have smaller size than those prepared at high intensity cavitation regime. The explanation of observed results is based on the idea of formation of vortices at the interface between phosphoric acid and calcium hydroxide solution where the nucleation of hydroxyapatite particles is taken place. Smaller vortices formed at high frequency non-cavitation ultrasound regime provide smaller nucleation sites and smaller resulting particles, compared to vortices and particles obtained without ultrasound. Discovered method has a potential of industrial application of ultrasound for the controlled synthesis of nanoparticles.     

Experimental and numerical studies on the cavitation in an advanced rotational hydrodynamic cavitation reactor for water treatment

Hydrodynamic cavitation (HC) has emerged as one of the most potential technologies for industrial-scale water treatment. The advanced rotational hydrodynamic cavitation reactors (ARHCRs) that appeared recently have shown their high effectiveness and economical efficiency compared with conventional devices. For the interaction-type ARHCRs where cavitation is generated from the interaction between the cavitation generation units (CGUs) located on the rotor and the stator, their flow field, cavitation generation mechanism, and interaction process are still not well defined. The present study experimentally and numerically investigated the cavitation flow characteristics in a representative interaction-type ARHCR which has been proposed in the past. The cavitation generation mechanism and development process, which was categorized into “coinciding”, “leaving”, and “approaching” stages, were analyzed explicitly with experimental flow visualization and computational fluid dynamics (CFD) simulations. The changes in the cavitation pattern, area ratio, and sheet cavitation length showed high periodicity with a period of 0.5 ms/cycle at a rotational speed of 3,600 rpm in the flow visualization. The experimental and CFD results indicated that sheet cavitation can be generated on the downstream sides of both the moving and the static CGUs. The sheet cavitation was induced and continuously enlarged in the “leaving” and “approaching” stages and was crushed after the moving CGUs coincided with the static CGUs. In addition, vortex cavitation was formed in the vortex center of each CGU due to high-speed rotating fluid motion. The shape and size of the vortex cavitation were determined by the compression effect produced by the interaction. The findings of this work are important for the fundamental understanding, design, and application of the ARHCRs in water treatment.     

Mössbauer study of the amorphization process in diamond

⁵⁷Co is implanted at different doses in diamond and graphite. The⁵⁷Fe Mössbauer spectrum is studied under various heat treatments. It is found that, in contrast with the measurements of⁵⁷Co implanted Si and Ge, the damage production in diamond can not be described by a direct amorphization model. At lower implantation doses, the defects in diamond can be partly annealed, when the sample is heated after or during implantation. At higher implantation doses graphitization occurs.     

金刚石砂轮在精密光学加工中的应用技术

在精密光学加工中,金刚石砂轮被广泛应用于精磨各种硬脆性材料。为了提高光学零件的表面质量,降低亚表面损伤,精密金刚石砂轮的制造及其光学加工工艺受到广泛的关注。综述了金刚石砂轮的结构、装夹方式、结合剂及基体的选用情况,对金刚石砂轮的静平衡和动平衡进行了分析,并提出了解决方案,运用该方案加工出的非球面零件面形精度Rt1 m,Ra＜0.3 m。实践证明,运用该方法加工出的零件达到了超精磨的水平,大大提高了后道工序的加工效率。     

Power spectrum of fluctuation for ultrasonic cavitation process in glycerin

Experiments were carried out on ultrasonic cavitation in glycerin. The zone near the emitter has a structure from interacting gas-vapor bubbles; this structure takes the form of fractal clusters. The photometry of passed laser emission was the tool for studying dynamics of fluctuations. In transitive mode, the power spectrum of fluctuation varies by the law inversely proportional to frequency. Distributions of local fluctuations are different from Gaussian and exhibit the property of scale invariance. The qualitative behavior of the frequency dependence of the spectral fluctuation density was tested while varying the power of the ultrasonic emitter. It was demonstrated that the growth of the high-frequency margin of flicker-type behavior evidences for growing instability and can be considered as a forerunner of possible large-scale outbursts. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 05-08-01320a).     

Experimental investigation of time-dependent cavitation in an oscillatory squeeze film

The occurrence of time-dependent cavitation and tensile stress in an oscillatory oil squeeze film were investigated experimentally. The test apparatus was a simple thrust bearing consisting of two parallel circular plates separated by a thin viscous oil film. During the test, one plate was at rest while the other (transparent) oscillated in a direction normal to its surface. This test configuration was chosen to avoid the rotational motion and complicated geometry of a squeeze film journal bearing. The frequency of oscillation was in the range of 5 to 50 Hz and was controlled by an electro-magnetic exciter. The process of cavity formation and its subsequent development was recorded by a high-speed video camera. Concomitant pressure in the oil film was measured both within and without the cavitation region. It was found that both tensile stress and cavities existed in a squeeze film under certain working conditions.     

Influence of the nucleation behaviour on the synthesis of diamond

Abstract

Using a solid state nucleation model the influence of different carbon types on the nucleation number of diamond has been studied, keeping constant the synthesis parameters p, T, t. The carbon types used have been investigated concerning their mechanical, electrical and chemical properties; the graphite content and the lattice perfection of the graphite are also determined. As a experimental result the nucleation number shows a significant dependence on the carbon type used, particularly on the amount of crystalline graphite.

The results show the possibility to influence certain steps of the diamond synthesis process.