cBN Synthesis Research Articles

RESEARCH ON THE STRUCTURE OF THE MATERIAL BASED ON NANO-AND MICRO-SIZED CUBIC BN SYNTHESIZED FROM MECHANICALLY ACTIVATED GRAPHITE-LIKE BN WITH THE ADDITION OF ALUMINUMUNDER HPHT CONDITIONS

In the article the structure and phase composition of the material based on nano-and micro-sized cubic boron nitride (cBN) obtained under high pressure and high temperature conditions from mechanically activated graphite-like boron nitride (hBN) in the presence of aluminum (Al), which plays the role of an initiator for the phase transformation hBN → cBN, are investigated. It has been shown that the use of mechanical activation contributes to the formation of cBN nuclei in hBN, which makes it possible to increase the dispersion of the final product. The technological parameters of the cBN synthesis and the amount of Alhave a significant effect on the structure of the material as well as the content of the cubic BN phase in it. The increase in the pressure for the hBN (MA) -10% Al system from 2.5 to 5.5 GPa and the temperature from 1550 °C to 1750 °C contributes to the increase of the content of the cBN phase from 10-15% to 90%. In this case, the size of cBN grains synthesized at pressures of 2.5 and 5.5 GPa is in the range of 200-500 nm and 40-120 nm, respectively. The increase in the amount of Al, temperature and duration for the cBN synthesis leads to the formation of large cBN grains with a size of about 10-50 μm.

Facile preparation of Cucurbit[6]uril modified melamine sponge for efficient oil spill cleanup

Herein, as a part of a circular economy, we have utilized Cucurbit[6]uril CB6 (a major product formed during the synthesis of CBn), to convert commercial hydrophilic melamine sponge (MS) into hydrophobic CB6 coated melamine sponge (abbreviated as CB6@MS). A facile, cost-effective, and rapid one-step dip-coating method without using the toxic and expensive modifying agents for the preparation of CB6@MS at ambient conditions is described. The prepared modified sponge is characterized using Fe-SEM, FT-IR, TGA, and PXRD. Self-assembly of CB6 on the skeleton of MS by hydrogen bonding/electrostatic interactions enhanced MS surface roughness and improved MS stability by maintaining its original 3D porous structure. The CB6@MS hydrophobic sponge had excellent oil absorption potential for many oils and organic solvents (53–112 g/g). The absorbed oil or solvents could be recycled in the simple squeezing process because of structural stability and strong elasticity of CB6@MS sponge, and absorption performance was nearly unchangeable after 15 absorptions/squeezing cycles. The resultant sponge can also continuously absorb and extract oil from the pollutant water through a vacuum pump. Thus, the utilization of the major undesired product, simple preparation, economical, and excellent oil separation would give this approach great potential to develop various CB-based applied materials.

In situ synthesis of polycrystalline cubic boron nitride in cBN–Al–Ti system with different Gd2O3 additions

Polycrystalline cubic boron nitride was sintered under high temperature (1400 °C) and high pressure (5.5 GPa) using an in situ synthesis method. The composition, microstructure, relative density and mechanical properties of the polycrystalline cubic boron nitride (PcBN) with different contents of Gd2O3 were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results show that the phases of TiB2, TiN, AlN, AlTi2N and GdB6 are formed through in situ synthesis of cBN–Al–Ti–Gd2O3 system. With the Gd2O3 content increasing, the relative density increases and mechanical properties of PcBN begin to increase and then decrease. Proper amount of Gd2O3 can advance the formation of TiB2 and improve the aspect ratio of TiB2. When Gd2O3 content is 1.0 wt%, the PcBN exhibits optimal comprehensive mechanical properties, with a microhardness of 33.35 GPa and a flexural strength of 972.37 MPa.

Deposition of cubic boron nitride films by anode layer linear ion source assisted radio frequency magnetron sputtering

Anode Layer Linear Ion Source (ALLIS) can improve the ionization rate of working gases and enhance the activity of gas molecules. In the present work, the ALLIS assisted Radio Frequency Magnetron Sputtering (RFMS) method was proposed to deposit cubic boron nitride (cBN) films, and the effect of ALLIS on the microstructure and mechanical properties of the deposited cBN films was investigated. The phase component, chemical composition, bonding states, surface topography, deposition rate and nanohardness of the cBN films were characterized respectively by Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and nanoindentation. The results indicated that the sp3 phase content in cBN films increased at first and then decreased with the increase of ALLIS power, and the maximum value was 83% when the ALLIS power was 200 W, the surface quality and growth rate of cBN films were enhanced markedly. The hardness and elastic modulus exhibited the same trend to variation of cubic phase content. Finally, the effect of ALLIS on the cBN synthesis was discussed systematically.

Preparation of Nanocrystalline Cubic Boron Nitride Coating by Magnetron Sputtering Method

Cubic Boron Nitride (cBN) has wide application prospect in the field of high performance cutting tool, for its outstanding mechanical properties. In this paper, the cBN coating was synthesized on cement carbide by chemical vapor deposition nanocrystalline diamond interlayer in radio frequency magnetron sputtering system. The SEM, FTIR and AFM were used to investigate the microstructure, purity and morphology of the cBN film. The research was carried out on the effect of the deposition parameters on the cBN content in the film. High temperature and high pressure locally in the substrate is an important factor of transformation of cubic phase BN from hexagonal phase BN. There is a narrow optimization parameters window in cBN synthesis by ion bombardment assist radio frequency magnetron sputtering method. The good quality of cBN film can be obtained by a combination of moderate substrate bias voltage and gas pressure, high substrate temperature and a certain N2 partial pressure.

Thermodynamic Analysis of the V-Shaped Area of High Pressure and High Temperature in Cubic Boron Nitride Synthesis with Li3N as a Catalyst

The possibilities of different phase transitions to cBN with Li3N as catalyst at high temperature and high pressure (1600–2200 K, 4.8–6.0 GPa) are analyzed, in the framework of the second law of thermodynamics. The Gibbs free energy (∆G) of three reactions which may happen in the Li3N-BN system: hBN + Li3N→Li3BN2, hBN→cBN, and Li3BN2→cBN + Li3N, is calculated, with the influence of high temperature and high pressure on volume included. We show that ∆G of hBN + Li3N→Li3BN2 and hBN→cBN are between −35~−10 KJ·mol−1 and −25~−19 KJ·mol−1, respectively. However, ∆G of Li3BN2→cBN + Li3N can be positive or negative. The area formed by the positive data is a V-shaped area, which covers the most part of the cBN growing V-shaped area. It confirms that Li3BN2 is stable in the P-T area of cBN synthesis, and cBN is probably transformed directly from hBN. Analysis suggests that Li3BN2 promotes the transition from hBN to cBN.

In situ synthesis of cBN–Ti3AlC2 composites by high‐pressure and high‐temperature technology

In this paper, titanium aluminum carbide (Ti3AlC2) was studied as the binder of polycrystalline cubic boron nitride (PCBN) to overcome the weaknesses of traditional metal binders and ceramic binders. The composites of cubic boron nitride (cBN) and Ti3AlC2 were in situ synthesized from the mixtures of Ti, Al, TiC and cBN powders at high temperature (1050°C–1250°C) and under high pressure (4.5GPa) (HTHP). The Ti3AlC2 proportion in as-prepared composites increased as the processing temperature increased from 1050°C to 1150°C. At 1200°C, part of Ti3AlC2 decomposed to form new TiC. At 1250°C, cBN transformed to hBN and reacted with other materials. The composites processed at 1200°C had the optimal mechanical properties, including friction coefficient, hardness and mass loss of worn Si3N4 ball. From the microstructure of as-prepared composites, agglomeration of cBN particles existed; however, the cBN particles, in general, were evenly distributed in the matrix of Ti3AlC2. The cBN particles strongly bonded with the matrix with a clear interface.

Materials with extreme properties: Their structuring and applications

This article is a brief review on syntheses of materials with extreme properties and their modification by plasma processes to obtain different morphological structures. First we illustrate general methodologies on preparation of polycrystalline diamond (PD), nanocrystalline diamond (ND), cubic boron nitride (cBN), diamond/cBN multilayer films by low pressure methods. Since cBN synthesis is more challenging, we place more attention to cBN including its growth, structuring and doping. The structural compatibility of cBN and diamond enables the fabrication of multilayer (superlattices); and we describe such an approach to produce composite materials with even more extreme properties. The superior hardness, extreme thermal conductivity and high chemical stability make diamond and cBN well suited for cutting tool and tribological applications. Although doping of these wide bandgap materials for p- and n-type conductivity is difficult, recent works indicate considerable advancement. The combination of high chemical stability and thermal conductivity with attractive electronic properties makes diamond and cBN suitable for construction of high power electronic devices operating in harsh environments. The development of these applications relies on the ability to design patterns and control the film conductivity. We illustrate that despite diamond and cBN are chemically stable and inert against many chemicals, film patterning and device fabrication is possible with the use of plasma processing. Further, we discuss the fundamental issues involved and demonstrate feasibility for the design of practical applications such as deep-ultraviolet (DUV) detectors and surface acoustic wave (SAW) devices. Finally we discuss the existence of other composite materials with extreme properties that have been only barely investigated, and that present promising alternatives for the future commercial applications.

Effects of additive LiF on the synthesis of cBN in the system of Li 3N–hBN at HPHT

High-quality cBN single crystals were successfully synthesized in the system of Li 3N–hBN with additive LiF at high pressure and high temperature (HPHT). The lowest synthetic conditions of cBN decreased to 4.6 GPa, 1320 °C by employing 3 wt.% LiF, and it didn't change anymore though more than 3 wt.% LiF had been added. The quality of cBN crystals improved markedly. The cBN crystals and other products were examined by X-Ray diffraction and scanning electron microscopy. The X-Ray analysis reveals that the “graphitization index” (GI) of hBN increased by adding 3 wt.% LiF into the system of Li 3N–hBN at HPHT. The SEM photographs show that different growth steps were formed on the cBN crystal surface in systems of Li 3N–hBN and Li 3N–LiF–hBN, respectively.

Quantitative linear correlations between the cBN synthesis parameters and the structural features of the hBN precursor

Seven selected hBN powders previously characterized by X-ray diffraction were subject to cBN synthesis tests at 1500 °C and 5.2GP using MgB 2 as a solvent-catalyst. Attempts have been made to establish quantitative linear correlations involving the conversion yield and the kinetic parameters (nucleation rate and linear growth rate) obtained in the cBN synthesis and the X-ray revealed features of the hBN precursor to disclose definite hereditary influences in the hBN → cBN conversion. The aspect ratio of the hBN crystallites seems to have an influence on the conversion yield and nucleation rate only if considered jointly with the graphitizing index and special lattice defects such as nanoarches and mid-plane point defects of chemical origin. The model of Sung and Tai for the catalytic synthesis of diamond was used to explain the obtained correlations.

An attempt to identify the presence of polytype stacking faults in hBN powders by means of X-ray diffraction

X-ray diffraction techniques have been used to characterize the three-dimensional order and the crystallite size for 17 hBN powders intended to be used as precursors in the cBN synthesis. Six hBN powders (group A) were obtained by the amidic method (borax + urea) purposely for this research and the remaining 11 hBN powders (group B) were commercial products of recognized companies. Attempts have been made to establish linear correlations between the X-ray revealed parameters of the hBN powders. An explanation sustained on experimental basis is proposed for the different linear correlation between the graphitizing index G.I. and order parameter p 3 in the two groups, that points to the existence of polytype stacking faults in hBN depending on the way of fabrication.

Transformação do nitreto hexagonal de boro em nitreto cúbico de boro com o catalisador magnésio

A importância do Nitreto cúbico de Boro (cBN) reside em processos de usinagem de metais ferrosos de elevada dureza. Apesar do cBN ser superado pelo diamante em termos de dureza, ele é mais resistente a oxidação provocada pelo ferro sob altas temperaturas em torno de 700ºC. Os cristais de cBN podem ser obtidos pela síntese a partir da mistura de Nitreto hexagonal de Boro (hBN), aplicando altas pressões e altas temperaturas (HPHT), durante um determinado tempo. Para facilitar os processos de transformação do hBN em cBN, podem ser utilizados um ou mais catalisadores, tais como o magnésio, lítio e bário e outros. No presente trabalho o magnésio na forma de partículas de até 53µm foi utilizado como catalisador nas tentativas de síntese de cBN. Com o objetivo de identificar os parâmetros de síntese (HPHT) que possibilitam a obtenção de partículas de cBN, foram feitas calibrações de temperatura e pressão na prensa hidráulica de 630 toneladas utilizada nos experimentos. As sínteses foram realizadas, utilizando a mesma temperatura para quatro pressões de 5,0; 6,0; 7,0; e 8,0 GPa, durante 5 minutos. E logo após as sínteses foram obtidas imagens por microscopia eletrônica de varredura (MEV) de cada amostra fraturada, o que mostrou algumas formações de cBN.

The influence of hBN crystallinity and additive Lithium hydride on cBN synthesis in Li 3N–hBN system

In this paper, the influence of hBN crystallinity and additive Lithium hydride (LiH) on cBN synthesis with Lithium nitride (Li 3N) as catalyst was investigated under the pressure of 4.5–5 GPa and the temperature of 1500–1700 °C. hBN with different crystallinities was obtained by the same hBN. Some were explored to high pressure and high temperature, and others were subjected to heat treatment with alkali. X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectronic spectroscopy (XPS) were used to characterize the property of the starting materials. The synthesized samples were observed by optical microscopy (OM). The results indicated that besides the crystallinity of hBN, which is a general parameter for controlling the structural quality of hBN powders, some other factors such as the content of B + at the surface of hBN and additive LiH all strongly influence the synthesis of cBN.

In situ FTIR investigation on phase transformations in BN nanoparticles

Fourier transformation infrared spectrum (FTIR) was employed to investigate phase transformation of nanoparticle BN, containing eBN, rBN, wBN and cBN, in which eBN and rBN are the main components. We found that part of eBN was converted into rBN at 200–350°C. At and above 400°C, eBN transformed into wBN, and some of wBN were converted into cBN simultaneously. This conclusion is supported by the results from high-resolution transmission electron microscopic (HRTEM) and Raman spectroscopic measurements. In this work, the converting processes between different BN phases were continuously monitored by in situ FTIR spectroscopy. The results will be helpful for synthesis of cBN at moderate conditions.

Hydrothermal synthesis of cubic boron nitride crystals

Cubic boron nitride (cBN) crystals have been successfully synthesized by in situ hydrothermal method. In order to obtain cBN pure phase crystals, two comparative experiments were carried out. The experimental results indicated that compared to one-step in situ hydrothermal method, multi-step in situ hydrothermal method was beneficial to the synthesis of cBN. It is believed that the multi-step in situ hydrothermal method is the optimal route to synthesize pure cBN bulk crystals.

CBN synthesis in the system of hBN–Mg and bonded water

The growing behavior of cubic boron nitride (cBN) crystal in the system of hBN–Mg with bonded water ((HO) 2) was investigated at 5.0 GPa and 1100–1500 °C. The results show that, with the existence of bonded water, the grown cBN crystals can appear different color and the growth temperature decreases approximately 300 °C with the pressure fixed at 5.0 GPa by contrast with that in the hBN–Mg system. In addition, the cBN synthesis process is quite different from that when bonded water is absent or that when magnesium is absent.

The parameters of equilibrium between oxygen solid solutions in cubic and graphite-like hexagonal boron nitrides

Abstract A decrease in the onset temperature of the cBN-to-hBN solid-phase transformation with increase in the oxygen content of cBN samples has been found experimentally. This dependence might be attributable to the existence of oxygen solid solutions in cBN and hBN. From the experimental data and taking into account the kinetics of solid-phase transformations, the equilibrium onset temperature of the cBN-to-hBN transition has been derived for samples with different oxygen contents. In the framework of phenomenological thermodynamics, the model parameters have been determined and the lines of equilibrium between oxygen solid solutions in cubic and graphite-like hexagonal boron nitride have been calculated. It has been shown that a decrease in the oxygen content of the boron nitride–solvent system usually used for cBN synthesis should induce an increase in the thermodynamic stimulus to the hBN-to-cBN transformation at high pressures.

Boron Nitride Revisited.

The phase diagram published by Bundy & Wentorf [2] already shows cBN to be the stable fonn of boron nitride, in contrast to similar diagrams used today. This picture is supported by theoretical calculations by Maid et al. [5] and Solozhenko [6]. Results of compressibility measurements for cBN and hBN are presented . To clarify the picture of the phase diagram the transformation from hBN to cBN has been studied in a series of time dependent diffraction experiments using synchrotron radiation. The crystallization is found to go through the melt. In a second series of experiments the back-transformation of cBN to hBN was studied . Finally the experimental conditions for high pressure! high temperature synthesis of cBN could be lowered to 2. 5 GPa at 1800°C using amorphous boron nitride as starting material.

ダイヤモンドの高圧合成 ｃＢＮ単結晶の高圧合成

ダイヤモンドの高圧合成 ｃＢＮ単結晶の高圧合成

The phase transition of hBN-cBN in the B-N-H-O system

The physical-chemical processes are responsible for hBN-cBN conversion in the B-N-H-O system were studied in region of pressure 3.5–7.2 GPa and temperature up to 1400°C by means of in situ differential thermal analysis (DTA) and the quenched method. The absence of intermediate solid phases in products of the interaction of hBN with melts of anhydrous ammonium borates has confirmed the supposition about the activating effect of these melts on the kinetic of the conversion. A scheme of the part of T,c phase diagram on the (NH 4) 2O-B 2O 3 line was built at 6 GPa. Three peritectics corresponding to the dissociation of proposed NH 4BO 2, (NH 4) 2B 4O 7 and (NH 4) 4B 10O 17 were found. The connection of the lower-temperature limits of cBN synthesis regions with the found peritectics in the range of 5.5–7.2 GPa was established. The formal critical composition of the melt was 3(NH 4) 2O:7B 2O 3, because the appearance of cBN was fixed in the product beginning with just this composition. However, the question about critical melt composition activating hBN-cBN conversion has no correct solution without information about short-range order structure and relaxation kinetics of the melts. Two unknown anhydrous ammonium borates were found in HPHT products. One of these compounds was determined to be (NH 4) 4B 10O 17. It crystallizes in a orthorhombic cell with a=12.82 Å, b=11.30 Å, c=9.52 Å, a measured density of 2.10 g cm −3, a calculated density of 2.21 g cm −3 at Z=4. At normal conditions (NH 4) 4B 10O 17 is metastable but it can be preserved a long time in a “dry” atmosphere.