Solubility Of Boron Research Articles

Microstructures of rapidly solidified powder and extruded rod of Ni 3Ge

Rapidly solidified powders and extruded rods of Ni 3Ge with and without 0.06at.% boron were characterized using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The powders were generally spherical and exhibited both dendritic and lamellar structures. The increase in lattice parameter per atom fraction of boron, ε, was estimated to be 0.33. Extrusion of the powders produced fine grains of about 2μm in diameter. The extruded materials were partially recrystallized and showed a minor preference for {111} orientation. Annealing at 950 °C resulted in a fully recrystallized structure and a nearly random orientation. The addition of 0.06at.% boron had no observable effect on the morphology, microstructure, and texture. Precipitates of borides were observed in the annealed boron-doped alloy, suggesting that the solubility of boron in Ni 3Ge may be below about 0.06at.%.

A Model for Boron Diffusion Through Patterned Silicon

It has been reported earlier that in the case of boron diffusion into silicon, the value of sheet resistance observed on plain check slices is almost always considerably smaller than the sheet resistance calculated from diffused resistors. The actual value of the discrepancy depends upon the size of the window, the surrounding masking oxide geometry, and the process parameters. These observations add another important factor in 2‐D simulation for diffusion processes. Further investigations have therefore been made in an attempt to present a theoretical model to explain the experimental observations. The results of a careful series of experiments using multilayered mask structures consisting of thermal oxide, silicon nitride, and silox ( deposited using chemical vapor deposition process with silane) have been presented. On the basis of these experiments, it is suggested that most of the experimental observations may be explained with the help of a theoretical model based on “surface diffusion” of boron over silicon and silicon dioxide. The model assumes a high solubility of boron in oxide and a high surface diffusion coefficient. Numerical calculations demonstrate the capability of the model to explain most of the experimental observations.

Growth Temperature Dependence of Boron Surface Segregation and Electrical Properties of Boron Delta-Doped Structures Grown by Si Molecular Beam Epitaxy

Reflection high-energy electron diffraction (RHEED) intensity oscillation showed a 4-monolayer (ML) period in the early stage of Si molecular beam epitaxy (MBE) on a 1 ML boron preadsorbed Si(111) surface, as long as the surface-segregated boron coverage was more than 1/3 ML. Temperature dependence of the boron surface segregation was investigated from the duration of the 4-ML-period oscillation. Effective solubility of boron in Si was one order higher than those reported for 1/3 ML boron preadsorbed cases. Crystallinity of the Si overlayer was satisfactory when the growth temperature was equal to or above 450° C, and 2/3 of the initially adsorbed boron atoms were confined to within about 10 ML (about 16 Å) of the Si overlayer at 450° C. Boron preadsorption was found to saturate at 1 ML, and the temperature dependence of the peak carrier concentration showed the same tendency as that of the effective solubility.

Chemistry and structure analysis in the Li 4 + xB xSi 1 − xO 4 solid solution

The crystal chemistry of the Li 4SiO 4-based solid solution Li 4+ x B x Si 1− x O 4 is presented. Synthesis was carried out using LiOH·H 2O or Li 2CO 3 as starting materials. Stoichiometric mixtures with 0≤ x≤0.7 were fired at temperatures ranging from 670 to 850 °C. A CO 2-free atmosphere is required to avoid the presence of Li 2CO 3 in the remaining solid. Small amounts of LiOH are detected in samples prepared from LiOH·H 2O. The solubility of boron in the solid solution is also discussed in terms of crystal structure analysis. The lithium insertion is accompanied with a continuous slight increase in the unit-cell volume. x=0.5 is the maximum composition above which Li + insertion should be accompanied with a modification of the Li 4SiO 4-based structure.

A critical assessment and thermodynamic calculation of the boron-carbon-titanium (B-C-Ti) ternary system

The B-C-Ti system has been critically assessed and calculated in the temperature region of 1400 °C up to the melting range employing the Thermocalc program system. The liquid phase is described using a substitutional model. The ternary solid solubility of boron in titanium carbide has been taken into account by using a two-sublattice model (Ti)1(B,C,Va),. The calculated isotherms and isopleths are presented and compared with the experimental information. The B-C-Ti reaction scheme is presented including the Ti3B4 phase.

Electrical characterization of an ultrahigh concentration boron delta-doping layer

We report a boron δ-doping layer in crystalline silicon with an electrically active concentration of 1×1022 cm−3 and a mobility of ∼20 cm2/V s. This structure was fabricated by low-temperature molecular-beam epitaxy with boron confined to 3 monolayers in the silicon growth direction. Complete electrical activation is observed, showing metallic conduction down to 4 K. This two-dimensional doped layer, incorporated into the crystal lattice, represents a volume concentration exceeding the solid solubility of boron in silicon by two orders of magnitude. These high-concentration structures fill an unexplored region of the mobility versus concentration curve.

The role of atom-probe field ion microscopy in alloy development and phase transformation studies

One of the important parameters in the design of new materials is the distribution of the alloyingelements in the microstructure and whether these elements are involved in the formation of precipitates or in segregation to internal interfaces such as grain boundaries. The atom probe field ion microscope is an extremely effective tool for these types of fine scale characterizations. Recently, therehas been a large effort to develop new, more efficient materials for high temperature applications such as gas turbines. A candidate material for this application is NiAl. However, the low temperature ductility of NiAl is extremely small and hinders fabrication. Therefore, attempts have been made to alleviate these problems with the use of microalloying additions such as boron. The atom probe has beenused to determine the location of boron in the microstructure and correlate its distribution with themechanical properties. Atom probe analyses have revealed that the solubility of boron in NiAl is extremely low and most of the excess boron is precipitated in the form of ultrafine MB2 precipitates as shown in Fig. 1. In addition, boron segregation to the grain boundaries has been observed, Fig. 2. Theobserved increase in the yield strength is therefore primarily due to a precipitation hardening mechanism with a contribution from solid solution hardening and this offsets the beneficial effect of the boron at the grain boundaries.

Mathematical simulation of borating of iron. Diffusional approximation

The growth of ferroborides on borating and diffusional annealing is investigated within the framework of the diffusional approximation. The solubility of boron in Fe2B, FeB is evaluated from comparison of calculated and experimental data.

NiAlにおけるボロンの固溶限と固溶強化

With boron-doped NiAl alloys, the solubility of boron, the composition and structure of the precipitated boride and the change in fracture mode due to boron addition have been studied. The solubility of boron is very small on the Ni-rich side of the alloys with a slight increase in its magnitude with deviation from the stoichiometric composition of the alloys, while the solubility of boron on the Al-rich side can be neglected. The structure of the precipitated boride on the Ni-rich side of the NiAl(45 at%Al) alloy is a Cr23C6 type compound, where composition is Ni60Al10B30 and the lattice parameter of which is 1.0542 nm.The fracture mode for the alloys changes from the intergranular to the transgranular type of fracture as an increase in boron concentration for both sides of Ni- and Al-rich compositions. However, the critical concentration of boron to the mode change in fracture mode is 0.003 mass% on the Ni-rich side, whereas it is 0.02 mass% on the Al-rich side.

Dispersion and reaction of TiB2in liquid iron alloys

AbstractThe degree of reaction and dispersion achieved when TiB2 powders are melted in contact with liquid iron based alloys has been assessed via a levitation dispersion test which had been developed earlier. Both Fe2B and TiC were observed to form as a result of dissolution and reaction of TiB2. The formation of TiC occurs during the reaction of commercial grade TiB2 with liquid iron alloys containing as little as 0·08 wt-%C. The reaction of high purity TiB2 with liquid iron alloys containing 0·24 wt-%C does not however lead to TiC formation. The formation of Fe2B was observed for all conditions tested, owing to the effectively zero solubility of boron in solid iron. The TiB2 remaining after dissolution and reaction was found to produce relatively good dispersions in the iron matrix and therefore additions of TiB2 to liquid iron alloys may provide a means of producing Fe–TiB2 composite materials. However, the brittle properties of Fe2B will mean that, whereas such materials may be very hard, they are li...

The application of track autoradiography for studying diffusion of boron in iron

Abstract An investigation of the results of diffusion of boron in low-carbon (30 ppm C) iron with the application of a high-sensitivity method of track autoradiography on polymetric detectors was conducted. It is shown that the diffusive boron mass-transport in body-centred cubic iron is carried by vacancy diffusion, and in face-centred cubic iron—by interstitial diffusion. The diffusion of boron in iron is accompanied by formation of a high density of dislocations, and distribution of boron in the diffusion layer is characterized by the presence of the “concentrational step” on the boundary between the two solid solutions with different dislocation density. The solubility of boron in low-dislocation density iron is very small and its temperature dependence is slight.

Contact interaction of lanthanum hexaboride with metallic melts

According to the current views, wetting of the solids by metallic melts is determined by the intensity of the chemical reaction which takes place at the contact boundaries [3]. in this work, we examined wetting of lanthanum hexaboride by metals of the iron group, platinum and palladium, as well as copper, gold, germanium, and tin. ~ The selected metals are characterized by different intensities of interaction with the components of the solid phase lanthanum and boron. The metals of the iron group interact with lanthanum, and in the liquid and solid states are characterized by high solubility of boron in them with the formation of chemical compounds. Gold, copper, tin, and germanium do not interact with boron, whereas the binding energy of these metals with lanthanum increases in the sequence Cu-Au-Sn-Ge. The wetting effect was examined by the sessile droplet method in vacuum using the method described in [3]. The substrate was represented by single-crystal lanthanum hexaboride produced by zone melting. The surface of the substrate was polished to the tenth surface grade finish. Melts were produced from V-3 grade copper, iron (purity of the main element 999), semiconductor purity germanium, palladium ~j,~ platinum ~),~ as well as carbonyl iron, cobalt and nickel, premelted in vacuum by electron beam heating. We determined the variation of the contact wetting angle with time for several isothermal holding periods, and also inspected the variation of the diameter of the wetting droplet. The contact interaction was examined using metaiiographic and x-ray spectrum microanaiysis methods. Sections for examination were cut out in the direction normal to the wetting plane. The data on wetting of lanthanum hexaboride are presented in Table i. The temperature of formation of the liquid phase of all metals of the iron group and platinoids in heating contact with lanthanum hexaboride is considerably lower than the melting point of the pure metals, in melts of cobalt and nickel the liquid phase wets the substrate with the angle close to zero. For iron this angle equals 30 ~ . The wetting angles of the melts of tin, germanium, gold, and copper greatly decrease with increasing temperature and no contact melting is detected. The results show that the metals of the iron group intensively interact *A. V. Gorbach took part in the investigations.

Glass fiber surface effects in silane coupling

Glass fibers with the nominal E-glass composition were synthesized with 0, 2, 4, or 6% B2.O3. The influence of the H2O3 content on aminosilane adsorption was evaluated using X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. The water adsorption capacity of the silane-treated fibers was measured using a gravimetric technique. It was found that the presence of B2O3 enhanced the adsorption of aminosilane, but, more significantly, it greatly increased the water adsorption capacity of the silane-treated fibers. This effect of the B2,O3 on water adsorption was considerably less evident in the untreated fibers. The solubility of boron and aluminum appears to play a role in determining the chemical and physical structure of the silane overlayer.

Temperature dependence of incorporation processes during heavy boron doping in silicon molecular beam epitaxy

Boron doped layers were grown by silicon molecular beam epitaxy to establish incorporation processes at temperatures between 900 and 450 °C. For temperatures exceeding 650 °C a surface accumulated phase of boron was formed when doping levels exceeded solid solubility limits. The properties of this surface phase were used to determine solubility limits for boron in silicon. Above 750 °C, the measured equilibrium solubility limit was in the 1019-cm−3 range in good agreement with previously published annealing data and showing a gradual decrease with decreasing temperature. Below 650 °C, the processes leading to the formation of the surface phase were kinetically limited, manifested by a sharp increase in boron solubility limit, with completely activated levels above 1 × 1020 cm−3 realized. At intermediate growth temperatures the degree of dopant activation was found to be dependent on growth rate. The stability of fully activated highly-doped boron layers, grown at low temperatures, to ex situ annealing is also discussed.

Non-equilibrium solidification in undercooled NiB alloys

Electromagnetic levitation has been used to melt and undercool Ni 100− x B x alloys ( x = 0.7, 1.0). Dendrite growth velocities in the levitated droplets have been measured as a function of undercooling. Owing to the extremely small solubility of boron in solid nickel, the growth velocities in the alloys are much lower than those in pure nickel. At a critical undercooling ΔT ∗ a sudden rise in the growth velocities with increasing undercooling is observed, indicating a transition from growth controlled both by solutal and thermal diffusion to a purely thermally controlled and segregation free growth of the supersaturated NiB dendrites.

Analysis of hardenability effect of boron

AbstractThe effect of boron on the hardenability of steels depends on the contents of such elements as aluminium, titanium, nitrogen, and boron and on the austenitising temperature. An attempt has been made to calculate the solubility of boron in the presence of aluminium, titanium, and nitrogen in steels. Three systems, Ti–B–Al–N, Ti–B–N, and B–N, were derived according to the thermodynamic state of each steel and the soluble boron contents were calculated. It was found that the maximum boron factor was achieved at 0·0004–0·0005% soluble boron. The fact that aluminium content in the range 0·018–0·050 wt-% investigated in this study has little effect on the boron hardenability factor can be explained from the results of the thermodynamic calculation.MST/1025

Improved ductility of Ni3Si by microalloying with boron or carbon

The effects of boron and carbon additions on the tendency for intergranular fracture in trinickel silicide intermetallics are reported. Melt spinning of Ni77Si23 alloyed with 0.1 at. pet boron results in full bend ductility and complete transgranular fracture compared with brittle intergranular fracture for the unmodified compound. Alloying with 0.1 at. pet carbon also produces full bend ductility but a mixed mode failure (≈30 pct transgranular). For both carbon and boron additions, reducing the Ni concentration of the base compound results in a greater percentage of intergranular fracture. The boron solubility limit depends on the Ni concentration of the base compound. For Ni77Si23, the solubility limit is between 0.1 and 0.2 at. pet boron. For compounds with silicon concentrations of 23.5 and 24.0 at. pct, the solubility limit is less than 0.1 at. pct boron. Boron additions above the solubility limit result in Ni3B precipitates which degrade the bend ductility and increase the percentage of integranular fracture. Alloying with carbon above the solubility limit (<0.1 at. pct) produces graphite precipitation. For Ni77Si23, increasing the carbon concentration from 0.1 to 1.0 at. pct resulted in no change in the ductility. Auger examination of the grain boundary composition showed strong segregation of both boron and carbon. Enrichment in silicon concentration was also observed.

Role of point defects in the transient diffusion and clustering of implanted boron in silicon

The influence of a supersaturation of point defects on the diffusion and clustering of boron in crystalline silicon is discussed. It is shown that, with suitable approximations, a generalized boron solubility can be derived which is an inverse function of the diffusion enhancement. This concept is applied to the problem of anomalous transient boron diffusion after medium dose implantation, where the observed boron profile consists of a relatively static peak and a mobile diffusion tail. The model predicts that diffusion starts first in the low concentration part of the boron profile, developing more slowly at higher concentrations as the point defect supersaturation relaxes towards equilibrium. Previous models have assumed that anomalous boron profile shapes arise from the spatial distribution of implant damage or channelled ions. The new model provides a more promising interpretation of recent experiments in which the damage profile has been separated from the boron-doping profile.

Enhanced Boron Diffusion Through Thin Silicon Dioxide in a Wet Oxygen Atmosphere

Boron diffusion through a 5 nm silicon dioxide film from heavily boron‐doped polysilicon was investigated at temperatures below 1000°C in nitrogen or a wet oxygen atmosphere. The boron concentration at the silicon substrate surface,Ns, which was enhanced by the boron penetration through the thin oxide film, was estimated from MOS‐CV curves. The boron diffusion coefficient in silicon dioxide, Dox, and boron concentration at the oxide surface, Nox, were calculated using Ns. It was observed that there is a limit to boron solubility in oxide. It was found, moreover, that the limit, as well as the boron diffusivity in oxide, is higher in wet oxygen than in nitrogen, which enables a large amount of boron to pass through the oxide.

The effect of boron on the microstructure and physical properties of chemically vapour deposited nickel films

The solid solution addition of boron greatly enhances the strength and hardness of chemically vapour deposited (CVD) nickel while dramatically changing the microstructure. The solid solubility of boron in nickel is limited, and single-phase alloys containing in excess of 0.3 at% B are supersaturated with respect to the formation of one or more intermetallic boride phases. Single-phase Ni-B alloys containing 0 to 13.0 at% B were produced by CVD on polycrystalline copper substrates at 155° C in an atmospheric pressure process. The microstructure, mechanical and physical properties were characterized for the alloys both as-deposited and after various thermal treatments by using optical microscopy, transmission electron microscopy, X-ray diffraction and micro-indentation hardness testing with a diamond pyramid indentor. The grain size of the alloy was found to decrease sharply with rising boron content. Concomitantly, the defect density of the material rose significantly, the microhardness increased and the ductility decreased. With annealing at a temperature of 300° C or greater, precipitation of the Ni3B intermetallic phase, recovery and grain growth occurred.