Diffusion Coefficient Of Boron Research Articles

Diffusion coefficients of boron in vitreous silica at high temperatures

The diffusion of boron in yB2O3(1-y)SiO2 glasses with up to 8 mol% B2O3 was investigated by annealing doped layers on the inner surface of quartz glass tubes between 1700°C and 2000°C and measuring radial doping profiles by X-ray microprobe analysis and refractive index profiling subsequent to the tube collapse. By comparison with calculated profiles, diffusion coefficients could be determined and fitted by an Arrhenius function, where the preexponential D0 = 100.38 cm2s−1 is constant, but the activation energy decreases with increasing concentration according to E = (449-4.8∙c1.06) kJ∙mol−1 (c[mol% B2O3] = 100y).

Diffusion of Hard Coatings on Ductile Cast Iron

ABSTRACTThis work estimate the growth kinetics of Fe2B coatings created on surface nodular cast iron ASTM A-536 class 80-56-06. The Fe2B coatings were formed by power packaging boriding process, considering three temperatures and exposure times different treatment. The hard coatings were evaluated through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The model of diffusion employs the mass balance equation at the (Fe2B/substrate) interface to evaluate the boron diffusion coefficient in the Fe2B coatingDFe2B, an expression of the parabolic growth constant, the instantaneous velocity of the Fe2B/substrate interface, and the weight gain in the boriding sample were establish as a function of the parameter ε(T) and η(T), dependents of boriding process in function of the temperature related and the time of boridingt0(T), respectively in the Fe2B coating. Model validation was extended considering the treatment of 1273 and 1123 K for 10 h respectively, obtaining a good correlation with experimental data.

The effective boron diffusion coefficient in Fe2B layers with the presence of chemical stresses

The effective boron diffusion coefficient in Fe2B layers with the presence of chemical stresses

Kinetics and Boron Diffusion in the FeB/Fe2B Layers Formed at the Surface of Borided High-Alloy Steel

In the present study, boron diffusion in the surface layers of AISI M2 borided steels and the growth kinetics of the FeB/Fe2B layers were estimated. The boriding of AISI M2 steel was performed according to the powder-pack method and was conducted at 1173-1323 K and at various exposure times. As a result of the boriding process, the diffusion-controlled growth of the FeB/Fe2B layers was obtained at the surface of the high-alloy steel, and the kinetics of the growth process changed parabolically over time. The boron diffusion coefficients were estimated by solving two simultaneous equations based on the limits of the boron concentration in each layer, the boride incubation time, and the parabolic growth constant. With the proposed diffusion model, an expression, which describes the evolution of the FeB/Fe2B layers, was obtained. Moreover, the proposed model and diverse empirical models presented in the literature provided a good fit to the experimental data obtained for 10 h of exposure and different boriding temperatures.

Diffusion model for growth of Fe2B layer in pure iron

A simple diffusion model is proposed to estimate the growth kinetics of Fe2B layers created at the surface of pure iron. This model employs the mass balance equation at the Fe2B/substrate interface to evaluate the boron diffusion coefficient (DFe2B) in the boride layer. The Fe2B layers were formed using the paste boriding process, at four temperatures with different exposure times. Analysing the results, the evolution of the parabolic growth constant (k) of the Fe2B layer is presented as a function of boron concentration and boride incubation time [t0(T)]. Furthermore, the instantaneous velocity of the Fe2B/substrate interface and the weight gain of borided pure iron were estimated for different boriding temperatures. Finally, to validate the diffusion model, the boride layer thicknesses were predicted and experimentally verified for two boriding temperatures and for different treatment times.

Nitrogen doped silicon films heavily boron implanted for MOS structures: Simulation and characterization

In this work we study the boron diffusion and its activation into recrystallized nitrogen doped silicon thin films (NIDOS) and we also discuss the influence of the chemical interaction between boron and nitrogen in NIDOS films. These films are deposited by low pressure chemical vapor (LPCVD) for the development of a P + polysilicon gate for MOS structures. The reduction of boron diffusion with increasing nitrogen content is observed by SIMS profiles. SUPREM IV software is used in order to estimate the boron diffusion coefficients in NIDOS films. FTIR analyses show the appearance of a B–N complex whose density strongly depends on the annealing treatment in terms of temperature and duration. It is deduced through resistivity measurements and SEM observation that the formation of B–N complexes tends to degrade the electrical properties of polysilicon thin layers through the decrease of both electrically active boron and polycrystalline grains growth.

Simulation of the growth kinetics of the (FeB/Fe 2B) bilayer obtained on a borided stainless steel

The present work is an attempt to simulate the growth kinetics of the (FeB/Fe 2B) bilayer grown on a substrate made of AISI 316 stainless steel by the application of the powder-pack boriding process, and using four different temperatures (1123, 1173, 1223 and 1273 K) and five exposure times (2, 4, 6, 8 and 10 h). The adopted diffusion model solves the mass balance equation at each growth front: (FeB/Fe 2B or FeB/substrate) under certain assumptions and without considering the diffusion zone. To consider the effect of the incubation times for the borides formation, the temperature-dependent function ϕ( T) was incorporated in the model. To validate this model, a computer code written in Matlab (version 6.5), was developed with the purpose of simulating the kinetics of the boride layers. This computer code uses the following parameters as input data: (the boriding temperature, the treatment time, the upper and lower limits of boron concentration in each iron boride, the diffusion coefficients of boron in the FeB and Fe 2B phases as well as the ϕ( T) parameter). The outputs of the computer code are the parabolic growth constant at each growth front and the thicknesses of the FeB and Fe 2B layers. A good agreement was obtained between the experimental parabolic growth constants taken from a reference work [I. Campos-Silva et al., Formation and kinetics of FeB/Fe 2B layers and diffusion zone at the surface of AISI 316 borided steels, Surf. Coat Technol., 205 (2010) 403–412] and the simulated values of the parabolic growth constants ( k FeB and k 1). The present model was also able to predict the thicknesses of the FeB and Fe 2B layers at a temperature of 1243 K during 3 and 5 h. In addition, the mass gain at the material surface was also estimated as a function of the time and the upper boron content in each iron boride phase. It was shown that the simulated values of the generated mass gain are very sensitive to the increase of both temperature and the upper boron contents in the FeB and Fe 2B phases.

Formation and kinetics of FeB/Fe 2B layers and diffusion zone at the surface of AISI 316 borided steels

The kinetics of the FeB/Fe 2B layers and diffusion zone at the surface of AISI 316 steels exposed to the powder-pack boriding process were studied in this work. FeB/Fe 2B layers and diffusion zone measurements were taken at different temperatures and exposure times to validate diffusion-controlled growth during the boriding process. In order to obtain the boron diffusion coefficients at the FeB/Fe 2B layers and diffusion zone, a mathematical model based on the mass balance at the growing interfaces was proposed. The activation energy values estimated for the FeB and Fe 2B layers were 204 and 198 kJ mol − 1 respectively. In addition, the activation energy value obtained for the diffusion zone was 116 kJ mol − 1 . The diffusion model was extended to estimate the FeB/Fe 2B layer thicknesses, and the depth of the diffusion zone at the temperature of 1243 K with 3 and 5 h of exposure, based on the experimental parameters ascribed to the boriding process. Finally, the effects of the FeB/Fe 2B growth and diffusion zone, on the weight gain of borided steels and on the instantaneous velocity of the interfaces were incorporated in the model.

Dependence between the Boron Surface Concentration and the Growth Kinetics of Boride Layers in AISI 4140 Steels

The present work estimated the growth kinetics of Fe2B layers formed at the surface of AISI 4140 steels. The thermochemical treatment was applied in order to produce the Fe2B phase, considering temperatures of 1123, 1173, 1223 and 1273 K with five exposure times (2, 4, 5, 6, and 8 h), using a 4 mm thick layer of boron carbide paste over the material surface. The growth of boride layers was described by the mass balance equation between phases in thermodynamic equilibrium, assuming that the growth of boride layers obeys the parabolic growth equation and the boron concentration at the interfaces remains constant. Also, the boron diffusion coefficient at the Fe2B ( ) was established as a function of boriding temperature. Likewise, the parabolic growth constant (k), the instantaneous velocity (v) of the Fe2B/substrate interface and the weight-gain of borided steels were established as a function of the parameters and , which are related to the boride incubation time ( ) and boron surface concentration ( ), respectively.

Modelling the growth of Fe<SUB align=right>2B layers obtained by the paste boriding process in AISI 1018 steel

This study evaluated the growth kinetics of Fe2B hard coatings obtained by the paste boriding process at the surface of AISI 1018 steels. The treatment was carried out at temperatures of 1123, 1173, 1223 and 1273 K with different exposure times for each temperature using a 4 mm thick layer of boron carbide paste over the material surface. The boron diffusion coefficient was determined by the mass balance equation at the Fe2B/substrate interface, assuming that the growth of Fe2B layers obey the parabolic growth law. Likewise, the growth constant was related as a function of the boride incubation time, the boron surface content and the boron diffusion coefficient, in order to estimate the weight gain in the borided samples and the instantaneous velocity of the Fe2B/substrate interface.

Kinetics of the formation of Fe 2B layers in gray cast iron: Effects of boron concentration and boride incubation time

The growth kinetics of Fe 2B layers formed at the surface of gray cast iron were evaluated in this study. The pack-boriding process was applied to produce the Fe 2B phase at the material surface, and the variables included three temperatures (1173, 1223 and 1273 K) and four exposure times (2, 4, 6 and 8 h). Taking into account the growth fronts obtained at the surface of the material and the mass balance equation at the Fe 2B/substrate interface, the boron diffusion coefficient on the borided phase was estimated for the range of treatment temperatures. Likewise the parabolic growth constant, the instantaneous velocity of the Fe 2B/substrate interface, and the weight gain in the borided samples were established as a function of the parameters τ( t) and α( C), which are related to the boride incubation time ( t 0( T)) and boron concentration at the Fe 2B phase, respectively. Observation of the growth kinetics of the Fe 2B layers in gray cast irons suggest an optimum value of boron concentration that is in good agreement with the set of boriding experimental conditions used in this work.

Determination of Boron Diffusion Coefficients in Borided Tool Steels

The boron diffusion in the Fe2B and FeB borided phases formed at the surface of AISI H13 tool steels during the paste boriding process was estimated. The treatment was carried out at temperatures of 1173, 1223 and 1273 K with 2, 4, 6 and 8 h exposure times for each temperature using a 4 mm layer thickness of boron carbide paste over the material surface. The boride layers were characterized by the GDOES technique to determine in quantitative form the presence of the alloying elements on the borided phases. The boron diffusion coefficients and were determined by the mass balance equation and the boride incubation time assuming that the boride layers obey the parabolic growth law. Also, the mass gain produced by both boride layers at the surface of the tool steels was determined. Finally, the boron diffusion coefficients were interpreted as a function of the treatment temperature, obtaining the activation energy values for the diffusion controlled growth of Fe2B and FeB hard coatings.

Investigation of the parameters of layers prepared through diffusion of boron and gadolinium from silicate and hybrid films into silicon wafers

This paper reports on the results of investigations into the main electrical parameters of diffusion layers formed in silicon due to the annealing of films containing boron and gadolinium. The sources for boron and gadolinium diffusion are silicate and hybrid organic-inorganic films prepared by the sol-gel method. It is demonstrated that small amounts (0.5–2.0 wt %) of organic additives, i.e., polyols with different structures and different molecular weights, favor the formation of layers with the highest possible concentration of the boron dopant at a level of the boron solubility limit in silicon (Ns = 5−7 × 1020 cm−3) with a diffusion layer depth ≥4 μm. The electrical parameters determined for the diffusion layers with the use of the Irwin concentration curves and the data obtained by secondary ion mass spectrometry are compared. The diffusion coefficients of boron and gadolinium are calculated. These data for gadolinium are obtained for the first time. It is revealed that the process of boron diffusion is retarded when boron is introduced in combination with gadolinium.

Immobilization of simulated evaporator concentrate waste in low density polyethylene

Simulated evaporator concentrate was prepared by pre-treating sodium borate with calcium hydroxide to produce an insoluble, ulexite-like borate salt. The resultant solid waste was blended by extrusion with virgin and recycled low density polyethylene (LDPE) at 30 and 50 wt% load. Samples were evaluate to homogeneity by density determinations (ASTM D792-91), compressive strength (ASTM D695-91) and leaching behavior by accelerated leaching tests (ASTM C1308-95). Coefficient of variation of density was lower than 5% for all evaluated waste forms, indicating a satisfactory homogeneity. Compressive strengths have complied to U.S.NRC standard and were above CNEN standard limit for cement waste products if 5% strain could be considered a reasonable limit to assure the structural integrity of the material. Cumulated fraction leached after 11 days of accelerated leach test was found to be lower than 10%, and diffusion coefficients of boron have varied between 3.86 × 10 −10 and 9.06 × 10 −10 cm 2/s. Boron concentrations for all materials have shown a tendency to reach an asymptotic value at the end of the test (around 0.25 and 0.7 mg/L for 30 and 50% waste load, respectively). Measured cumulated fraction leached (CFL) data with time have shown a tendency of becoming asymptotic sooner than it was predicted by the diffusion model.

Growth Kinetics of Boride Layers: A Modified Approach

This study evaluates the boron diffusion in the Fe2B phase formed at the surface of AISI 1018 steels during the paste boriding process. The treatment was carried out at temperatures of 1123, 1173, 1223 and 1273 K with 2, 4, 5, 6 and 8 h exposure times for each temperature using a 4 mm layer thickness of boron carbide paste over the material surface. The boron diffusion coefficient Fe2B D was determined by the mass balance equation and the boride incubation time assuming that the boride layers obey the parabolic growth law, while the boron concentration profile along the interphase Fe2B/substrate was unknown. The boron diffusion coefficient was interpreted as a function of the treatment temperature, obtaining the activation energy value for diffusion controlled growth of Fe2B boride phase.

Reduced boron diffusion under interstitial injection in fluorine implanted silicon

Point defect injection studies are performed to investigate how fluorine implantation influences the diffusion of boron marker layers in both the vacancy-rich and interstitial-rich regions of the fluorine damage profile. A 185keV, 2.3×1015cm−2 F+ implant is made into silicon samples containing multiple boron marker layers and rapid thermal annealing is performed at 1000°C for times of 15–120s. The boron and fluorine profiles are characterized by secondary ion mass spectroscopy and the defect structures by transmission electron microscopy (TEM). Fluorine implanted samples surprisingly show less boron diffusion under interstitial injection than those under inert anneal. This effect is particularly noticeable for boron marker layers located in the interstitial-rich region of the fluorine damage profile and for short anneal times (15s). TEM images show a band of dislocation loops around the range of the fluorine implant and the density of dislocation loops is lower under interstitial injection than under inert anneal. It is proposed that interstitial injection accelerates the evolution of interstitial defects into dislocation loops, thereby giving transient enhanced boron diffusion over a shorter period of time. The effect of the fluorine implant on boron diffusion is found to be the opposite for boron marker layers in the interstitial-rich and vacancy-rich regions of the fluorine damage profile. For marker layers in the interstitial-rich region of the fluorine damage profile, the boron diffusion coefficient decreases with anneal time, as is typically seen for transient enhanced diffusion. The boron diffusion under interstitial injection is enhanced by the fluorine implant at short anneal times but suppressed at longer anneal times. It is proposed that this behavior is due to trapping of interstitials at the dislocation loops introduced by the fluorine implant. For boron marker layers in the vacancy-rich region of the fluorine damage profile, suppression of boron diffusion is seen for short anneals and then increased diffusion after a critical time, which is longer for inert anneal than interstitial injection. This behavior is explained by the annealing of vacancy-fluorine clusters, which anneal quicker under interstitial injection because the injected interstitials annihilate vacancies in the clusters.

Paste boriding process: evaluation of boron mobility on borided steels

The present study evaluates the boron mobility at the material surface of borided steels AISI 1045 and M2 during the paste boriding process. This surface hardening technique produces two characteristic phases on the material, FeB, Fe2B and a transition zone, denominated diffusion zone, in the layer/substrate interface. The thermochemical treatment was performed at three different temperatures: 1193, 1223, 1273 K and two treatment times: 2 and 6 h for the 1045 steel, and 1223, 1253 and 1273 K with the same treatment times for M2 steel, modifying the boron potentials in equilibrium at the substrates surfaces. By using the mass balance equation, and assuming a linear concentration profile at the interfaces, the new model determined the diffusion coefficients of boron in the phases formed at the surface of the substrates, included the diffusion zone for both steels.

Effect of fluorine on boron diffusion under interstitial injection from the surface

In this paper, a point defect injection study is performed to investigate the effect of fluorine on boron diffusion when interstitials are injected from the surface. 185keV, 2.3×1015cm−2 F+ is implanted into silicon with a boron marker layer located at about Rp/2 of the fluorine implant. This is followed by rapid thermal annealing at 1000°C for times 15–120s in an oxygen ambient. The wafers are covered with different layers prior to anneal to introduce different point defect injection effects. When interstitials are injected from the surface, fluorine strongly suppresses boron diffusion for anneal times of 15 and 30s. For longer anneal times, fluorine becomes progressively less effective and the boron diffusion coefficient approaches the value obtained in samples without fluorine. This effect of fluorine on boron diffusion suppression correlates with the presence of a shallow SIMS fluorine peak at ∼Rp/2. These results support earlier work showing that vacancy–fluorine clusters at ∼Rp/2 are responsible for the suppression of boron diffusion and that these clusters anneal out during long anneal times. An issue of boron cross contamination during the fluorine implant is also identified.

FeB/Fe 2B phase transformation during SPS pack-boriding: Boride layer growth kinetics

The iron boride layer growth kinetics in mild steel through the spark plasma sintering (SPS) pack-boriding technique is investigated at 850 °C with different boriding durations (maximum 240 min). Results show that both FeB and Fe 2B layers form and grow on the mild steel surface with the FeB layer on the top of Fe 2B sublayer in the samples with boriding duration less than 90 min. However, at longer boriding duration, the top FeB layer eventually ceases growing, starts to diminish, and, finally disappears completely by transforming into the Fe 2B phase. Numerical simulation is implemented to explain this phenomenon. Subsequently, the diffusion coefficient of boron in FeB and Fe 2B phase is obtained through fitting the experimental results into the model. The simulation results are found to be in good agreement with the experimental results, and the estimated diffusion coefficients of boron in FeB and Fe 2B phases as 2.33 × 10 −9 and 4.67 × 10 −9 cm 2/s, respectively. Both the simulation and experimental results reveal that the Fe 2B mono-phase layer can be obtained through the transformation of FeB to Fe 2B phase due to the depletion of boron concentration in the boriding medium, and is indifferent to the formation of FeB phase at the very onset of the boriding process. This provides a new approach to overcome the side effect of FeB formation in borided components.

Effect of boron paste thickness on the growth kinetics of Fe 2B boride layers during the boriding process

Through this work we study the influence of the thickness of boron paste in the growth of Fe 2B boride layer during the paste boriding thermochemical treatment applied on AISI 1045 steel. Different thickness of boron paste over the material surface with constant temperature and time show the variability of the diffusion coefficient of boron in Fe 2B phase depending, basically, on the boron potential at the external surface of the substrate. The mobility of boron in the formed phase is determined by the balance mass equation that considers the concentration profiles in the corresponding interphases layer–substrate, the thermodynamic equilibrium in the growth of the iron boride layer and the experimental results obtained during the process.