Hexagonal Nitride Research Articles

Investigation of the effects of room-temperature nitrogen implantation on the precipitation of aluminium nitride

Aluminium single- and polycrystalline bulk material has been implanted with doses from 10 17 to 1.06 × 10 18 N/cm 2 at energies ranging from 25 to 75 keV. Implantation of polycrystalline material led to the formation of both hexagonal and cubic AlN. This precipitation was accompanied by the presence of bubbles at the surface, whose dimensions were dependent on the energy of implantation. The single-crystal material exhibited precipitation of (002) preferentially oriented hexagonal nitride, only for implantation along specific crystalline directions. The extent of bubble formation was also dependent on the relative substrate orientation.

Reaction-Bonded Boron Nitride-Aluminum Nitride Ceramic Composites

Hexagonal boron nitride-aluminum nitride (h-BN-AlN, 75-25 wt%) ceramic composites are synthesized by reaction bonding. Metallic component-free, relatively dense composites are obtained by using h-BN and Al as starting materials and by optimizing sintering conditions. In comparison with reaction-bonded BN, higher bending strength, 98 MPa, and higher thermal conductivity, 66 W/(m·K), are attained for a Y2O3-added BN-AlN composite. A low thermal expansion coefficient of 2.6×10-6/K is also achieved.

Thermodynamic properties of ni nitrides and phase stability in the Ni-N system

The thermodynamics of the Ni-N system is poorly known from experiments, and there is a need of information on the stability of the various nitride phases and the Ni-N phase diagram. This kind of information has been obtained by us, by combining the few measurements available with predictions, based on recently reported regularities in bonding properties and vibrational entropy of 3d transition metal compounds. A calculated Ni-N phase diagram is presented. A certain range of homogeneity for the hexagonal nitride phase is obtained, which is comparable to that of other 3d transition metal-nitrogen systems. The question of the possible existence of a stable “Ni4N” phase is examined. According to our results, Ni4N is metastable in the Ni-N system.

On Fermi's surfaces of hexagonal carbides and nitrides

The reason the anomalously low momentum matrix element between the wave functions of the degenerate state is discussed. The dHvA-measurements for the WC has been interpreted.

Hot-Pressed BN–AlN Ceramic Composites of High Thermal Conductivity

Hexagonal boron nitride-aluminum nitride (75–25 wt%) ceramic composites are synthesized by uniaxial hot pressing. High thermal conductivity, 247 W/(m·K), is attained for the perpendicular direction of the hot-pressing axis of the sintered body, by optimizing the amount of added sintering aid, calcium carbide. The composites have remarkable anisotropy with respect to structure and thermal conductivity. The revelation mechanism of high thermal conductivity is discussed.

Investigation of laser-induced plasma deposition of boron nitride

Laser ionization mass spectrometry (LIMS) was applied to the investigation of the composition of laser plasmas of three different boron nitride modifications (hexagonal α-boron nitride with graphite structure, cubic β-boron nitride with diamond structure and hexagonal γ-boron nitride resembling the wurtzite type). Thin films in the 10 nm range were produced in the ion source of the laser mass spectrograph by laser-induced plasma deposition. So we could carry out the plasma diagnostic and the preparation of thin films under the same condition. The cluster distribution in laser plasma is independent of the structure of the BN target. An explanation of laser-induced plasma deposition of boron nitride from the results of mass spectrometric analysis of laser plasmas and of the analysis of deposited thin films (TEM, EELS) was derived.

Hexagonal iron nitride thin films prepared by plasma reaction

Hexagonal iron nitride thin films prepared by plasma reaction

Property Changes of Fe-N Prepared by Reduction-Sintering Method with Quenching

A process of reduction from ?-Fe 2 O 3 , nitrification in ammonia and sintering was used to obtain dense single-phase Fe 4 N, and changes in the material thus obtained with quenching were investigated. It was found that quenching from temperatures of 550°C and above brings about a slight decrease in saturation magnetization, due to intermixing of hexagonal iron nitride. In attempts to lower the nitrogen content, the ammonia pressure was lowered and samples quenched from 650°C; this also resulted in lower saturation magnetization, and the division of the Fe 4 N into hexagonal iron nitride and ?-Fe.

Ab initio study of the autocorrelation function for lithium nitride.

The autocorrelation function B(r\ensuremath{\rightarrow}) is the convolution of the density matrix \ensuremath{\rho}(r\ensuremath{\rightarrow}', r\ensuremath{\rightarrow}'+r\ensuremath{\rightarrow}), and can be obtained experimentally by taking the Fourier transform of directional Compton profiles. The different terms that contribute to B(r\ensuremath{\rightarrow}) are discussed here in general and carefully analyzed in the case of hexagonal lithium nitride (${\mathrm{Li}}_{3}$N). The results of different Hartree-Fock calculations are compared with recent very detailed experimental data in the basal plane of lithium nitride. It is shown that, while a minimal basis set gives quite wrong results, satisfactory agreement with experiment is obtained with the use of an extended basis set, comprising 28 atomic orbitals per unit cell, and that there is room for further improvements within the Hartree-Fock approximation. Overcoming some limitations of the present experimental technique would make the autocorrelation function a most valuable means for checking the accuracy of calculated wave functions for crystalline systems, and for assessing the adequacy of the employed basis set.

TEM study of the structural changes of nitrogen implanted iron alloys

Pure iron and simple iron alloys (iron-chromium, iron-nickel, iron-chromium-nickel) were implanted at room temperature with nitrogen ions at an energy of 40 keV with fluences from 10 17 ions cm −2 to 6 × 10 17 ions cm −2. The microstructural changes (nitride formation and lattice transformations) were studied by transmission electron microscopy and selected area diffraction. The four chosen alloys had different initial structures (α-ferrite, α 2 metastable martensite, γ-austenite) that allowed us to investigate the lattice transformations caused by nitrogen implantation. Additionally, the formation of hexagonal nitrides was observed.

Nitriding of tantalum

1. The diffusion of nitrogen in tantalum in the nitriding process at 600–1000°C occurs with the formation of nitride phases and the subsequent growth of their layers. The hexagonal nitrides TaN and Ta2N form on the surface of the nitrided metal, and a zone of the solid solution of nitrogen in tantalum forms at greater depths. 2. The temperature dependence of the thickness of the diffusion zone located beneath the nitride layer is altered at nitriding temperatures above 850°C (the hardness decreases); this is explained by the formation of various modifications of the outer nitride; tantalum should therefore be nitrided at temperatures no higher than 850°C to obtain the required diffusion zone.

High-chromium steels alloyed with nitrogen

1. The addition of 0.5% N to high-chromium steel produces an economically alloyed corrosion-resistant high-strength steel suitable for operation at moderately low temperatures. The steel consists of austenite+ferrite or austenite alone. 2. The best combination of properties of high-strength corrosion-resistant high-chromium steel alloyed with nitrogen in amounts exceeding its normal solubility is obtained with ≥3–5%N. Both the strength and corrosion resistance increase with rising nitrogen concentrations. 3. Hexagonal nitride Cr2N is precipitated during air cooling of the nitrogen-containing steel after heating at 900–1200°. In nickel-free steel of the Kh25A type, especially in the presence of molybdenum, colonies of eutectoid pearlitelike structure consisting of thin interlayers of Cr2N and austenite are found along with boundary precipitates of Cr2N. In steels of the Kh25N3(5)AM3 type a similar structure is formed only with furnace cooling or after tempering at 750–800°. 4. The corrosion resistance and strength of these steels depend not on the ratio of ferrite and austenite but largely on the nitrogen concentration and the form in which it exists (solid solution, excess phase). Formation of pearlitelike structure lowers the ductility, fracture toughness, and corrosion resistance to a larger extent than formation and precipitation of nitrides with the usual petallike lamellar shape.

Formation of cubic tantalum nitride by heating hexagonal tantalum nitride in a nitrogen-argon plasma jet

Formation of cubic tantalum nitride by heating hexagonal tantalum nitride in a nitrogen-argon plasma jet

Morphologies des nitrures β-Nb 2N et γ-Ta 2N. Relations d'orientation avec la matrice α-Nb(N); α-Ta(N)

Thin foils of niobium and tantalum have been nitrided by heating in a flow of gaseous ammonia over the temperature range 600–700°C. The three phases β-Nb 2N, β-Ta 9N and γ-Ta 2N formed have been studied by electron microscopy and diffraction. The two hexagonal nitrides, β-Nb 2N and γ-Ta 2N, appeared as twinned precipitates with a (011̄1) cph twinning plane parallel to one of the matrix α-Nb(N) or α-Ta(N) {110} bcc planes. The angle between the close-packed (0001) cph and (110) bcc planes is ~2°. A similar relationship has been observed by Potter between the V 3N phase and the α-V(N) phase. However, some precipitates of γ-Ta 2N are in a different orientation with respect to the matrix and are best described by the relationship of Pitsch and Schrader. The crystal structures of the nitrides are in agreement with previous results.

Phase equilibria in the metal-rich side of the Ta-N system

The region of the Ta−N system with nitrogen content less than 20 at. pct and temperature between 350° and 1200°C was investigated using electron microscopy and diffraction and X-ray diffraction. For temperatures above 790°C, the hexagonal nitride Ta2N was observed to form. Below this temperature two interstitially ordered cubic nitrides were observed. The higher temperature cubic nitride was found to be an equilibrium phase of approximate composition Ta9N2; a crystal structure, for this phase consistent with the data is presented. The terminal solubility was measured, and a partial phase diagram is given. In addition, the precipitation of these nitrides from supersaturated solution is described.

Magnetic Study on Hexagonal Nitrides of 3d Transition Metals

Magnetic and Mössbauer effect measurements on the nitrides with hcp metal lattice of V, Cr, Mn and Fe are carried out as a function of composition. Hexagonal VN x and hexagonal CrM x are Pauli paramagnetic. Hexagonal MnN x shows antiferromagnetism, while both hexagonal and orthorhombic FeN x show ferromagnetism at low temperatures. In these Phases, nitrogen atoms suppress magnetic ordering in consequence of the reduction of magnetic moments. As a whole, the observed types of magnetism of hexagonal nitrides resemble those of their metals in spite of the difference in crystal structures. Type II superconductivity is found in hexagonal VN x although it is not yet conclusive.

The crystal growth of transition metal interstitial compounds by a floating zone technique

A floating zone technique for the preparation of large high purity crystals of vanadium carbide, oxide and nitride with controlled stoichiometry is described. An essential feature of the process is the provision of a facility which enables growth under positive ambient gas pressures (up to 20 atm) to be carried out. Inert gas atmospheres are used to reduce vanadium vaporisation losses in vanadium carbide and oxide and so enable closer compositional control to be achieved, while the nitrides are grown under similar pressures of nitrogen and helium to reduce nitrogen losses. Zone levelling has enabled large single crystals of vanadium monocarbide (VC) with differing and closely controllable compositions to be produced. Vanadium monoxide crystals were grown over the whole cubic stoichiometry range but in the vanadium nitrogen system single phase cubic vanadium mononitride (VN) could not be produced and the microstructure of the alloy of highest nitrogen content consisted of a eutectic of the cubic VN and the hexagonal divanadium nitride (V2N) phases.Finally, in addition to the usual chemical and optical microstructural examination, electron microscopy and electron diffraction have been used to characterise the type and extent of the defect structures which are present in all three alloy systems studied.

NMR of hexagonal and cubic boron nitride

NMR of hexagonal and cubic boron nitride

Investigation of hexagonal and cubic boron nitrides by the electron paramagnetic resonance method

Investigation of hexagonal and cubic boron nitrides by the electron paramagnetic resonance method

A study of the system Fe-V-C-N with a view to the precipitation hardening process

The paper deals with the analysis of the precipitate composition and the precipitation mechanism in the system Fe-V-C-N. The aim of this paper is also to discuss the way of vanadium carbide hardening in commercial type CrMoV steel. Further, the paper quotes data on hexagonal vanadium nitride V2N which becomes an important element in the development of high-strength steels.