BN Content Research Articles

Chemical stability of a composite material based on silicon and boron nitrides

Results of a study of the chemical resistance of a composite Si3N4 — BN material to the action of acids and alkalis are presented. Independently of the content of BN and the porosity the material resists the action of HC1, HNO3, H2SO4, and KOH. Hydrofluoric acid has a strong effect on the composite material with over 30% BN even after only 10 days of contact. It is shown that the decomposition of the material obeys the rule “glass phase → Si3N4” and is selective; BN is more chemically stable than Si3N4.

Dielectric Properties of Ta 2O 5–BN Polycrystalline Ceramics

The dielectric properties of (Ta 2O 5) 1−x(BN) x polycrystalline ceramics are reported for 0.0 < x < 0.25. Measurements were made at 1 MHz and temperatures between 0 and 100°C. The dielectric constant is moderately enhanced in the high temperature tantalum oxide phase at low BN concentrations; it then decreases to an essentially composition-independent value at higher concentrations where the low temperature form of tantalum oxide is stabilized. In the low temperature form, above x = 0.05, there is a significant decrease in the temperature coefficient of the dielectric constant with increasing BN content.

Contact‐Induced Transverse Fractures in Brittle Layers on Soft Substrates: A Study on Silicon Nitride Bilayers

An analysis of transverse cracks induced in brittle coatings on soft substrates by spherical indenters is developed. The transverse cracks are essentially axisymmetric and geometrically conelike, with variant forms dependent on the location of initiation: outer cracks that initiate at the top surface outside the contact and propagate downward; inner cracks that initiate at the coating/substrate interface beneath the contact and propagate upward; intermediate cracks that initiate within the coating and propagate in both directions. Bilayers consisting of hard silicon nitride (coating) on a composite underlayer of silicon nitride with boron nitride platelets (substrate), with strong interfacial bonding to minimize delamination, are used as a model test system for Hertzian testing. Test variables investigated are contact load, coating/substrate elastic‐plastic mismatch (controlled by substrate boron nitride content), and coating thickness. Initiation of the transverse coating cracks occurs at lower critical loads, and shifts from the surface to the interface, with increasing elastic‐plastic mismatch and decreasing coating thickness. This shift is accompanied by increasing quasi‐plasticity in the substrate. Once initiated, the cracks pop in and arrest within the coating, becoming highly stabilized and insensitive to further increases in contact load, or even to coating toughness. A finite element analysis of the stress fields in the loaded layer systems enables a direct correlation between the damage patterns and the stress distributions: between the transverse cracks and the tensile (and compressive) stresses; and between the subsurface yield zones and the shear stresses. Implications of these conclusions concerning the design of coating systems for damage tolerance are discussed.

Temperature evaluation of cutting tools during machining of hardened bearing steel.using polycrystalline cubic boron nitride and ceramic cutting tools

In this work some of the most popular techniques used to evaluate the temperature in cutting tools during machining are briefly reviewed. The experimental work used two different techniques to assess the temperature generated during turning of hardened bearing steel using polycrystalline cubic boron nitride and ceramic cutting tools: the thermal radiation method and the implanted thermocouple method. Additionally, a finite volume analysis was conducted to estimate the temperature distribution in the cutting tool. The results suggested that the temperature increased with the cutting speed, feedrate, depth of cut, and tool wear, and an increase in the thermal conductivity of the tool material caused an elevation in the temperature of the cutting tool and a reduction in the temperature of the chip. Temperatures as high as 1550°C were estimated in the cutting zone when finish turning using a high cubic boron nitride concentration cutting tool.

Infrared ellipsometry on hexagonal and cubic boron nitride thin films

Infrared spectroscopic ellipsometry (IRSE) over the wavelength range from 700 to 3000 cm−1 has been used to study and distinguish the microstructure of polycrystalline hexagonal and cubic boron nitride thin films deposited by magnetron sputtering onto (100) silicon. The IRSE data are sensitive to the thin-film layer structure, phase composition, and average grain c-axes orientations of the hexagonal phase. We determine the amount of cubic material in high cubic boron nitride content thin films from the infrared optical dielectric function using an effective medium approach.

A study of the composition and properties of EB-ion plating TiBN coatings

TiBN coatings were deposited on W 18Cr 4V high speed steels by using EB-ion plating with different boron contents. The chemical compositions of the coating are Ti, B and N. It was found that Ti, B and N in the coating are homogeneous, but there exists a diffusion zone at the coating/substrate interface on the basis of the results of ion probe microanalysis and Auger electron spectrometry. The boron content of the coating is 3–16 at.% given by nuclear reaction analysis. The ratio of nitrogen to titanium of the coating is about 1 given by electron probe microanalysis. The microhardness (HV) of the coating is 35–45 GPa (load of 0.25 N). The critical load of the coating using the scratch test is 12–14 N. The sliding friction coefficient of the coating on diamond stylus is 0.086–0.097 (load of 8.8 N). X-ray diffraction measurement shows that the coating consists of f.c.c. TiN, simple orthorhombic TiB, cubic BN and simple hexagonal TiBN phases. As expected, the higher the boron content, the higher the content of cubic BN and TiB phases; and the higher the microhardness, the lower the adhesion.

Laser-induced reactive crystallization of metastable BN from copper implanted with B+ and N2+ ions

Abstract Ion implantation followed by an excimer laser irradiation was used for the crystallization of metastable boron nitride (BN) films. Plates of polycrystalline copper (3 mm diameter) thinned locally to permit their observation in the transmission electron microscope (TEM) were implanted with boron ions (B + ) and nitrogen ions (N 2 + ). The ions were implanted with an ion energy of 100 keV and ion dose of 1.0 × 10 18 ions cm −2 . The as-implanted copper specimens were subsequently irradiated with nanosecond pulsed XeCl excimer laser of beam energy of 43 mJ, wavelength 308 nm pulse duration of 10 ns. The penetration depth of the implanted ions was estimated roughly at R L = 700 nm for B + ions and R L = 200 nm for N 2 + ions. TEM examinations have indicated that the layers thus formed were boron nitride (BN) films. Results have shown that the phase content of boron nitride crystallized appeared to depend largely on the sequence of ion implantation. When boron ions were implanted, first BN of the wurtzite (w-BN) type and then E-BN phases were formed, whereas when nitrogen ions were implanted first only the E-BN phase was crystallized.

Phase and Property Studies of Boron Carbide–Boron Nitride Composites

Boron carbide–boron nitride particulate composites were fabricated by vacuum hot‐pressing. Near‐theoretical densities of B4C were obtained, but percent theoretical densities decreased with increasing amounts of BN. The grain size of B4C and BN was not affected by composition, but the amount of twinning in B4C decreased with increasing BN content. No third phase was found at the B4C–BN interface by analytical STEM analysis. Lattice parameter measurements indicated slight solubility of B4C in BN, but no solubility of BN in B4C for samples hot‐pressed at 2250°C. Room‐temperature flexural strength measurements revealed a sharply decreasing strength with increasing BN content up to 40% BN, and then relatively constant values with greater amounts of BN.

Fracture Toughness and Thermal Shock Behavior of Silicon Nitride–Boron Nitride Ceramics

Fracture toughness behavior, stress–strain behavior, and flaw resistance of pressureless‐sintered Si3N4‐BN ceramics are investigated. The results are discussed with respect to the reported thermal shock behavior of these composites. Although the materials behave linear‐elastic and exhibit no R‐curve behavior, their flaw resistance is different from that of other linear‐elastic materials. Whereas the critical thermal shock temperature difference (ΔTc) is enhanced by adding BN, the content of BN has no influence on the strength loss during severe thermal shocks.

Measurement of thermal diffusivity of filler‐polymide composites by flash radiometry

AbstractThermal diffusivity D of filler‐polyimide composites was investigated using flash radiometry. The fillers used were: diamond, alumina, boron nitride, aluminium nitride, silicon carbide, and silicon carbide whiskers, Composite films were prepared by casting a polyamic acid solution with dispersed filler on a glass plate and then annealing. The effects of filler type, size, content, and shape on D were studied. D increased with increasing average filler particle diameter and filler content. For the composite filled with fine Al2O3 whose average particle diameter is about 0.2 μm, aggregates of filler were observed with dimensions up to a few microns. The formation of thermal paths through this aggregate enhances thermal diffusion. For the composites filled with high thermal conductivity filler such as BN and AIN, there was a strong increase in D above a filler content of 20 vol %. D was ten times larger than that of unfilled polyimide when the BN content was 54 vol %. D of the SiC‐whisker composite increased strongly up to a filler content of 18 vol %. Above this content D significantly decreased, probably because of interconnected voids formed by mold shrinkage.

Phase and Property Studies of SiC-BN Composites

Phase composition and solid solubility in SiC-BN composites were studied using cubic SiC, and cubic and graphitic BN with consolidation by uniaxial and isostatic hot-pressing techniques. Results revealed that SiC and BN were the only phases present. When BN is the major phase, cubic SiC is the major SiC phase, and some hexagonal polytypes are sometimes found. For samples hot isostatically pressed to 2,000{degree}C, cubic BN transformed to graphitic BN, and a solubility of 0.5 to 1 mol% BN in cubic SiC was indicated. Electron microscopy revealed that the cubic and highly cubic polytypes (i.e., those with a large fraction of ABCABC-type stacking arrangements) appeared adjacent to the BN phase and to be stabilized by it. Young's modulus of hot-pressed composites decreased nonlinearly with increasing BN content.

Dynamic Characteristics of the Landslide Surface of the Frictional Type and Their Measurement

It was reported that the landslide surface can be classified into the shearing type and the frictional type.This report describes the measurement of friction angle (friction coefficient) and the relation between the friction angle and the physical properties. The friction angle can be measured, using the direct shear apparatus a friction plate in it.The relationship between the friction angle φf and the content of Bentonite Bn is shown as follows, φf=φf0exp(-Af·Bn)where φf0 and Af are constants determined by the kinds of the clay minerals contained.

Determination of free graphite in textured samples of boron carbide and boron carbide-silicon carbide composites

The common X-ray diffractometer powder techniques used to determine the amount of free graphite in boron carbide usually do not include any corrections for grain orientation. It has also been shown that the preparation of the samples by grinding and the addition of plate-like graphite powder induces a preferential orientation of the grains. The texturation phenomenon was also detected in the case of dense samples when secondary recrystallization occurred during sintering. A new X-ray diffraction method has thus been optimized for a correct quantitative analysis in the presence of textured products (graphite in boron carbide or in boron carbide-silicon carbide composites). The accuracy of this new method made it possible to determine both the free graphite and free boron nitride content in a commercial boron carbide powder.

Thermal Diffusivity Anisotropy of SiC/BN Composites

The thermal diffusivity of hot‐pressed SiC /BN composites is shown to exhibit a high degree of anisotropy with respect to the hot‐pressing direction as a result of preferred orientation of the BN phase. This effect is particularly pronounced at the higher BN contents at both room and elevated temperatures.

The Relation between the Constants of Shear Strength and the Clay Minerals on the Landslide Surface

This paper describes the experimental results that the angle of internal friction of the landslide clay on the slide surface is not affected very much by grain size distribution, but contens of clay minerals are in flueced considerably and the content of montmorillonite has the greatest influence.The relationship between the angle of internal friction φ' and the content of montmorillonite Bn is shown as follows.φ=φ0;exp (-A·Bn)Bn≤40%where φ0 and A are the constants determined by the kinds of the minerals contained (excluding clay minerals).The experimental results can be applied to the exploration of slide surface and the estimated values of angle of internal friction on the slide surface.

High/Low Modulus Si3N4‐BN Composite for Improved Electrical and Thermal Shock Behavior

High‐density Si3N4+6% CeO2 composites with 5 to 50% BN were fabricated by hot‐pressing. BN remained as a discrete phase. Dielectric constants were 4 to 8 and loss tangents were 0.0008 to 0.06 for the room temperature to 1100°C range for compositions with 10 to 50% BN. Thermal‐expansion values perpendicular to the hot‐pressing direction were somewhat less than those of hot‐pressed Si3N4+6% CeO2. Flexure strengths at room temperature were considerably lower than those of hot‐pressed Si3N4+6% CeO2 but values at 1000°, 1250°, and 1400°C in air were only slightly lower. Young's modulus values were found to decrease with increasing BN content at all temperatures. Better thermal shock resistance was found than for commercial hot‐pressed Si3N4.

Chromatium purpuratum, sp. nov., a new species of the Chromatiaceae

Enrichment cultures inoculated with fragments of the sponge Ircinia spec, under autotrophic culture conditions and with thiosulfate as sole electron donor yielded the predominant development of a small cell Chromatium strain, which is described herein as the new species Chromatium purpuratum. Autotrophically grown cells are 1.2–1.7 μm wide and 3–4 μm long. The cells are motile by means of one single polar flagellum. Intracytoplasmic membranes are present as vesicles as in the other Chromatium species. Multiplication occurs by binary fission. The photopigments are bacteriochlorophyll a and carotenoids of the okenone series. The G + C content of the type strain BN 5500 is 68.9 mole%. Chromatium purpuratum grows well photoautotrophically with sulfide or thiosulfate as electron donor. Photoheterotrophic growth is possible with various fatty acids serving as electron donor and carbon source. The new species is a marine isolate with an optimal salinity of 5% NaCl. It is compared with other known species of the genus Chromatium.

Dependence of the oxygen content of boron nitride on heat-treatment temperature and its effect on the structure and strength characteristics of this compound

1. A method is described for determining oxygen in active boron nitride powders by neutron activation analysis. 2. It is shown that raising the heat treatment temperature from 1300 to 1500°C decreases the oxygen content of boron nitride synthesized at 900°C from boric acid and urea in an ammonia stream by about three quarters; at the same time, the crystal lattice structure of the compound becomes transformed from turbostratic to mesographitic. 3. The hypothesis is advanced that the imperfect structure of boron nitride is caused by oxygen implanted in its crystal lattice. 4. At the drying temperature water-containing boron nitride undergoes hydrolysis, with the formation of various oxygen-containing compounds, including B2O3. 5. Use of neutron activation analysis may in many cases enable a materials (elements) balance sheet to be drawn up.

希土類元素とB添加による高張力鋼の大入熱溶接ボンド部の組織と靱性の改良

For the purpose to improve the weld bond toughness through ferrite grain refinement in 40-60kg/mmmm2 tensile strength steels, the effects of various alloying elements on the grain structure and notch toughness in the weld bond were investigated. Of the alloying elements investigated, small additions of both rare earth metal (REM) and boron (B) were found to accelerate the formation of fine ferrite grains inside prior austenite grains, resulting in a remarkable improvement weld bond thoughnss.The main results obtained are summarized as follows:(1) The optimum concentration range of REM and B are 0.020-0.040% and 0.0020-0.0035%, respectively.(2) With an increase of BN content, the number of fine ferrite grains increases remarkably.(3) The amount of BN re-precipitated during welding thermal cycle is larger in REM-B steel than in B steel.(4) Spherical inclusions are frequently observed in the center of ferrite grains or adjacent to them and many of them identified as Ce2O2S and BN.(5) According to the observation by IMMA, the location of B+-images is in good accordance with that of both Ce+-and N+-images.By the use of commercial heats of REM-B steel, brittle fracture tests were conducted and good results were obtained.

Physical and technical properties of alloys of the system W - BN

1. A technique has been developed for the preparation of W-BN system alloys with various boron nitride contents. 2. Using x-ray diffraction, metallographic, and chemical analyses, a study was made of the character of reaction between tungsten and boron nitride over the temperature range 2060–2260°C; it was established that reaction between the components of these alloys leads to the formation of the following phases: a solid solution of boron in tungsten and the tungsten borides W2B andα-WB. 3. It is concluded that tungsten in contact with boron nitride is not suitable for engineering applications at temperatures of 2260°C.