Diffusion Coefficients Of Chromium Research Articles

Study on diffusion kinetics of chromium and nickel electrochemical co-deposition in a NaCl–KCl–NaF–Cr2O3–NiO molten salt

Abstract The process of preparing surface composite by molten salt co-deposition is the result of the mass transfer of active particles in molten salt, electrochemical reduction, and solid diffusion. In this study, we prepared Cr–Ni alloy/low-carbon steel surface composites in NaCl, KCl, NaF, Cr2O3, and NiO melt salt system successfully, and analyzed the entire diffusion dynamics process, aiming to find out the limiting links and provide ideas for further improving the preparation efficiency. The results show that chromium and nickel ions are simultaneously reduced on the cathode surface through two and one steps, respectively. And an alloy layer with Fe content of 64.52 wt%, Ni content of 28.96 wt%, and Cr content of 6.52 wt% is formed on the surface of low-carbon steel substrate. The average diffusion coefficients of chromium and nickel atoms in the surface composites are 1.16 × 10−14 and 1.44 × 10−14 m2·s−1. The mass transfer process in molten salt is the limiting link in the whole preparation process.

Study on Diffusion Kinetics and Law of Chromium on the Surface of Low-Carbon Steel

Cr/low-carbon steel surface composites were prepared by aqueous solution co-deposition and high-temperature solid-state diffusion technology, and the macro rule of the solid-state diffusion of chromium on the surface of low-carbon steel was analyzed. The molecular dynamics (MD) method was used to simulate and calculate the diffusion process of the Cr/Fe interface, and the macro and micro diffusion mechanisms were analyzed. The results show that the diffusion of the chromium in iron is the combined action of the temperature, crystal structure and lattice distortion, and the diffusion coefficients of chromium in α-Fe and γ-Fe have little difference. The vacancy diffusion mechanism of the first adjacent transition is the main diffusion mode. In practice, chromium atoms diffuse along the grain boundaries of the low-carbon steel matrix and provide pinning at the grain boundaries to prevent grain growth. The simulation law is in good agreement with the experimental law. The variation law of the average diffusion coefficient of chromium atoms with temperature is obtained. The diffusion rate of chromium in the bcc crystal structure is obviously higher than that in the fcc crystal structure. In the same crystal structure, the diffusion coefficient of chromium increases with the increase in temperature. However, in the lattice transition temperature region, the diffusion coefficient of chromium gradually decreases with the increase in temperature until the end of the transformation.

THE CHROMIUM AND COBALT DISTRIBUTION IN THE DIFFUSION LAYER OF STEEL X35CrNi2-3 DURING THERMОDIFFUSION SATURATION

For parts of machines and equipment operating under the influence of aggressive media, abrasive, high temperatures, the creation of a hard, wear-resistant surface is an urgent task. Cobalt is used as a binder to create hard alloy materials that work under these conditions. It was of interest to evaluate the possibility of using cobalt as an additive in complex thermal diffusion chromium plating of structural steel. The article describes the features of thermal diffusion saturation of steel X35CrNi2-3 with chromium and cobalt at a temperature of 1000°C. A technique for analyzing the obtained coating is presented, based on the possibilities of X-ray spectral microanalysis of the diffusion layer on transverse microsections of the obtained samples. The elemental composition of the diffusion layer was monitored using the JEOL JSM-6460 LV universal scanning (scanning) electron microscope. The microstructure was studied using the optical metallographic microscope Axio Observer D1.m. The X-ray phase analysis was carried out with the Rigaku Ultima IV diffractometer. The hardness measurement was carried out with the FM-800 microhardness tester at a load of 50 g. Data were obtained on the distribution of chromium and cobalt in the surface layer of steel. It is shown that the resulting thermal diffusion coating consists mainly of a substitutional solid solution based on Cr‒Fe‒Co with bcc lattice and chromium carbides. The average diffusion coefficients of chromium in the α-phase of chromium were determined to be DCr = 3,22·10‒15 м2/с; in the γ-phase of iron DCr = 9,41·10‒15 м2/с. The diffusion coefficient of cobalt in the γ-phase of iron DCo = 7,89·10‒15 м2/с. The depth of the outer coating on the sample was about 15–20 µm, the depth of the diffusion layer of chromium in the base metal was about 70 µm, and that of cobalt was about 40 µm. The maximum hardness of the outer surface layer was 1740 HV, the diffusion layer in the base metal was 900–560 HV, and the base metal was about 510 HV.

ИССЛЕДОВАНИЕ РАСПРЕДЕЛЕНИЯ ХРОМА В ДИФФУЗИОННОМ СЛОЕ ПРИ ХРОМИРОВАНИИ СТАЛИ 35Х2Н3

The analysis of scientific literature has shown the diffusion saturation of two and more chemical elements of the surface of alloys remains understudied due to the complexity of sample preparation and subsequent analysis of samples. This remains a relevant objective of modern science. Using of a new technique for determining the concentration of a chemical element during chemical-thermal treatment of alloys will greatly facilitate the theoretical studying of diffusion processes in alloys and the practical application of diffusion saturation. The article describes a new method of determining the concentration of chromium during diffusion chromium plating of steel. The possibilities of the new technique are shown on the example of diffusion saturation with chromium of X35CRNI2-3. The principle of the technique – the obtained samples after chromium plating of steel are cut across the axis, thin sections are made, the diffusion layer is examined from the end of the sample using an electron microscope. In this work the analysis technique is based on the capabilities of scanning electron microscopy, X-ray spectral microanalysis of diffusion layers across a section (local determination of the chemical composition of the material). The chemical composition of the diffusion layer was monitored using a universal scanning electron microscope JEOL JSM-6460 LV. Chromium diffusion saturation of steel X35CRNI2-3 has done. A dense (pore-free) surface layer containing 100 to 2% chromium, to 62 microns thick, has obtained. The diffusion coefficient of chromium has calculated: α-phase – DCr = 6.3·10–14 m2/s, γ-phase – DCr = 3.7·10–15 m2/s. The microhardness of the chromiumplated layer has determined, which averaged 1369 HV300.

РАСПРЕДЕЛЕНИЕ ХРОМА И ВАНАДИЯ В ДИФФУЗИОННОМ СЛОЕ СТАЛИ 35Х2Н3 ПРИ СОВМЕСТНОМ ТЕРМОДИФФУЗИОННОМ НАСЫЩЕНИИ

Termodiffusion saturation of the surface of alloys with two or more elements remains poorly understood despite the great practical and scientific interest that this method of chemical-thermal treatment represents. The simultaneous introduction of several elements can significantly reduce the processing time of products and obtain a multiphase composition on the surface of the product, which opens up wide opportunities for imparting unique technological and operational properties to products. The article describes the features of the distribution of chromium and vanadium during joint thermal diffusion saturation of steel X35CrNi2-3 at a temperature of 1000 °C. The proposed analysis technique is based on the possibilities of X-ray spectral microanalysis of diffusion layers on transverse microsections of the obtained samples. The elemental composition of the diffusion layer was monitored using a JEOL JSM-6460 LV universal scanning electron microscope. The microstructure was studied on an optical metallographic microscope Axio Observer D1.m. X-ray phase analysis was carried out on a Rigaku Ultima IV diffractometer. The hardness measurement was carried out on an FM-800 microhardness tester at a load of 100 g. Data were obtained on the qualitative and quantitative distribution of chromium and vanadium in the surface layer of steel. It is shown that the emerging diffusion coating has the following structure: a structureless outer layer, consisting mainly of chromium, vanadium carbides → a region of columnar crystals (experiencing γ→α transformation upon cooling), consisting mainly of their Cr1.0V0.4Fe0.3 solid solution → partially decarburized α-phase → base metal. The diffusion coefficients of chromium and vanadium are determined: in the α-phase DCr = 1.3·10–15 m2/s; DV = 1.8·10–14 m2/s; in the γ-phase DCr = 1.13·10–15 m2/s; DV = 1.3·10–15 m2/s. The microhardness of the outer surface layer was 1400–1980 H, the diffusion layer in the base metal was 630–790 HV, and the base metal was about 540–510 HV.

РАСПРЕДЕЛЕНИЕ ХРОМА И МОЛИБДЕНА В ДИФФУЗИОННОМ СЛОЕ СТАЛИ 35Х2Н3 ПРИ СОВМЕСТНОМ ТЕРМОДИФФУЗИОННОМ НАСЫЩЕНИИ

Known methods of chemical-thermal treatment of structural parts, such as carburizing, nitriding, diffusion metallization technologies, make it possible to obtain a unique combination of surface and core properties of the product. The positive experience of using methods of multi-element diffusion saturation opens up prospects for the development of methods for complex saturation. The article describes the technology of thermal diffusion saturation of steel X35CrNi2-3 with chromium and molybdenum at a temperature of 1000 °C. A technique for analyzing the obtained coating is presented, based on the possibilities of X-ray spectral microanalysis (XMS) of the diffusion layer on transverse microsections of the obtained samples. The elemental composition of the diffusion layer was monitored using a JEOL JSM-6460 LV universal scanning (scanning) electron microscope. The microstructure was studied on an optical metallographic microscope Axio Observer D1.m. X-ray phase analysis was carried out on a Rigaku Ultima IV diffractometer. The hardness measurement was carried out on an FM-800 microhardness tester at a load of 100 g. Data were obtained on the qualitative and quantitative distribution of chromium and molybdenum in the surface layer of steel. It is shown that the resulting thermal diffusion coating consists mainly of a substitutional solid solution based on Cr–Fe–Mo with a bcc lattice and chromium and molybdenum carbides. The depth of the outer coating on the sample was about 20 μm, the depth of the diffusion layer in the base metal was about 25 μm. The absence of a decarburized area in the surface layer of the base metal was noted. The average diffusion coefficients of chromium and molybdenum in the α-phase of chromium were determined DCr = 6.6·10–15 m2/s and DMo = 4.35·10–16 m2/s respectively; in the γ-phase of iron DCr = 2.95·10–15 m2/s, DMo = 2.48·10–16 m2/s respectively. The microhardness of the outer surface layer was 1400–1980 H, the diffusion layer in the base metal was 1000–600 HV, and the base metal was about 540–510 HV.

РАСПРЕДЕЛЕНИЕ ХРОМА И ВОЛЬФРАМА В ДИФФУЗИОННОМ СЛОЕ СТАЛИ 35Х2Н3 ПРИ СОВМЕСТНОМ ТЕРМОДИФФУЗИОННОМ НАСЫЩЕНИИ

Chemical-thermal treatment (CHT) of structural parts operating under conditions of wear, friction, shock loads make it possible to obtain a unique combination of surface and core properties of the product. However, such traditional CTO methods as carburizing and nitriding, while improving the mechanical characteristics of the surface, are not suitable for all types of steels. Diffusion metallization methods, in particular, thermal diffusion chromium plating, are more effective in terms of the achieved set of properties. Currently, chromium plating is carried out both by saturation of the metal with one element – chromium, and by multi-element mixtures. The article describes the technology of thermal diffusion saturation of steel X35CrNi2-3 with chromium and tungsten at a temperature of 1000 °С. A technique for analyzing the obtained coating is presented, based on the possibilities of X-ray spectral microanalysis (XMS) of the diffusion layer on transverse microsections of the obtained samples. The elemental composition of the diffusion layer was monitored using a JEOL JSM-6460 LV universal scanning (scanning) electron microscope. The microstructure was studied on an optical metallographic microscope Axio Observer D1.m. X-ray phase analysis was carried out on a Rigaku Ultima IV diffractometer. The hardness measurement was carried out on an FM-800 microhardness tester at a load of 100 g. Data were obtained on the qualitative and quantitative distribution of chromium and tungsten in the surface layer of steel. It is shown that the resulting thermal diffusion coating consists of a substitutional solid solution based on Cr–Fe with a bcc lattice, chromium and tungsten carbides. The depth of the outer coating on the sample was about 20 μm, the depth of the diffusion layer in the base metal was 50–55 μm. The absence of a decarburized area in the surface layer of the base metal was noted. The average diffusion coefficients of chromium in the α-phase of chromium were determined to be DCr = 3,58·10–13 m2/s; in the γ-phase of iron DCr = 2,83·10–15 m2/s. The microhardness of the outer surface layer was 1800–2000 HV, the diffusion layer in the base metal was 1300–550 HV, and the base metal was about 540–510 HV.

Investigation of transient metal vapour transport processes in helium arc welding by imaging spectroscopy

In order to understand the transient transport mechanisms of metal vapour in an arc plasma, imaging spectroscopy was performed for helium arc plasmas burning on pure metals. The measured images were converted into the spectral intensity distributions at the central cross-section of the arc plasma by image processing and Abel inversion. The transient transport process of metal vapours inside the arc plasma are discussed in terms of the diffusion coefficients of metal vapour. The metal vapour generated from the weld pool surface was transported into the arc plasma and to the region near the tungsten electrode within a few seconds. As time passed, the metal vapour spectral intensities gradually increased near the weld pool surface, near the electrode and in the intermediate region. In contrast, the He I spectral intensity was weak and the He I distribution shrunk toward the centre of the arc. This is because the helium arc plasma was cooled by the strong radiation from metal vapour. For an arc burning on pure chromium, chromium ions reached to centre of the arc after about 40 s. In contrast, on pure iron, iron ions did not reach to the centre of the arc. This is because the helium arc plasma on pure chromium was cooled to a temperature at which the electric field and ordinary diffusion coefficients of chromium are largest, whereas the temperature of the plasma on pure iron remained high. Two factors contributed to this; the higher boiling point of iron, which reduces the iron vapour concentration, and the lower radiative emission coefficient of iron.

Investigation of the diffusion of alloying elements in multicomponent alloy using the photometric analysis of the radiation brightness spectrum

In this paper we consider the results of studying the diffusion of molubdenum and boron in the alloy G 35 (USA), in the chemical composition of which there were 12 elements, with the help of the method of photometric analysis of structural images (PHASI), developed in IMET RAS. PHASI method is based on comparison according to the differential scheme of the spectra of the brightness of the reflection of visible light from the fragments of the surface of the object under study and their images before, during and after heating. The study was performed in situ in a high temperature metallographic microscope. The digital camera allowed in a periodic mode to register the image of the investigated fragment of the sample surface. Analysis of the data obtained by the PHASI method made it possible to establish the time and radial dependencies of the partial derivatives of the concentrations of the first and second order alloying elements that appear in the diffusion equation. A complete analysis of the obtained experimental data made it possible to obtain temperature dependencies of the diffusion coefficients of chromium and boron.

Diffusivities of metal acetylacetonates in liquid ethanol and comparison with the transport behavior in supercritical systems

Diffusion coefficients of chromium(III) acetylacetonate, palladium(II) acetylacetonate, nickel(II) acetylacetonate, vanadyl(II) acetylacetonate, and titanium(IV) oxyacetylacetonate in liquid ethanol were measured by chromatographic peak broadening method (CPB) over the range of temperature 303.15–333.15 K at atmospheric pressure. The dependencies of D12 upon temperature and Stokes–Einstein coordinates were examined in detail. Moreover, the experimental data were modeled using nine equations from the literature to test their accuracy and prediction ability. The lower deviations were achieved by the 2-parameter correlation of Dymond-Hildebrand-Batschinski (0.32–2.17 %), the 1-parameter correlation of Tracer Liu-Silva-Macedo (1.58–3.88 %), and the 2-parameter correlations of Magalhães et al. (0.55–2.32 %). Finally, the proposed correlation based on hydrodynamic approach was found to well represent palladium(II) acetylacetonate and chromium(III) acetylacetonate systems in supercritical carbon dioxide and liquid ethanol, with the average absolute relative deviation of 3.15 and 5.02 %, respectively.

Measurement and correlation of the diffusion coefficients of chromium(III) acetylacetonate at infinite dilution in supercritical carbon dioxide and in liquid ethanol

The diffusion coefficients of chromium(III) acetylacetonate (Cr(acac)3) were measured at infinite dilution in supercritical carbon dioxide and in liquid ethanol. The diffusion measurements in supercritical carbon dioxide were carried out at five different temperatures varying from T=(308.15 to 343.15)K and at pressures up to 40.00MPa by using the chromatographic impulse response (CIR) method. And the measurements in liquid ethanol were also made by the Taylor dispersion method at five temperatures in the range from T=(299.15 to 333.15)K and 0.10MPa. The determined diffusion activation energies in supercritical carbon dioxide were Ea=(22.9–11.2)kJ·mol−1 at p=(13.00–35.00)MPa, respectively, and that in liquid ethanol was 15.9kJ·mol−1 at 0.10MPa. All the diffusion coefficients of Cr(acac)3 in supercritical and in liquid states can be correlated by the hydrodynamic equation as a function of temperature and fluid viscosity with average absolute relative deviation (AARD) of 4.6% over a wide viscosity range from η=(3.036·10−5 to 1.113·10−3)Pa·s for 85 data points.

Low-pressure diffusion chromising of thin low-carbon steel sheet for improved surface and bulk properties

Multi-component alloying of thin metal sheets offers the particular possibility to produce novel materials with adjusted bulk and surface performance characteristics. Its application is of great interest for the development of advanced materials with tailored properties such as steel based materials for the use as bipolar plates for proton exchange membrane fuel cells. Within this work 0.13-mm thick cold-rolled sheets of low-carbon steel EN 1.0338 were double-sided chromised by means of low-pressure diffusion metallization method. Samples with chromium diffusion coatings as well as bulk-chromised samples, i.e., samples fully chromised over the whole strip thickness, were prepared. For the diffusion coefficient of chromium in γ-iron phase at 1423 K a value of 1.80·10−14 m2 s−1 was determined. As long as the samples did not reach the bulk-chromised state, the chromium concentration remained less than 12.5 wt%. The bulk-chromised sheets with surface chromium concentration of approximately 22 wt% showed the best corrosion resistance in 0.5% sodium chloride and 0.05 M sulphuric acid solutions electrochemical tests. Moreover, they exhibited the smallest interfacial contact resistance of approx. 31 mΩ cm2 at a contact pressure of 140 N cm−2.

Using a Tm:YLF laser to determine the diffusion coefficient of chromium in ZnSe

This paper presents an express technique for determining the diffusion coefficients of chromium in ZnSe, using a Tm:YLF laser that emits at 1.908 ?m. The diffusion coefficients of chromium in ZnSe obtained by deposition from the vapor phase are determined to be D=(9.5±0.6)×10?9??cm2/s and D=(1.0±0.1)×10?9??cm2/s at 1100°C and 900°C, respectively. The absorption cross section of Cr2+ ions in zinc selenide at 1.908 ?m was 4.6×10?19??cm2.

Chromium and cobalt diffusion in a ZnSe1 − x S x solid solution

ZnSe1 − xSx (1 ≥ x ≥ 0) crystals are grown from the vapor of binary components in a closed horizontal system. The ZnSe1 − xSx crystals doped with chromium and cobalt are prepared by post-growth diffusion. Their absorption spectra are studied depending on the composition of the solid solution and the doping level. The diffusion coefficients of chromium and cobalt at the temperature 1040°C and their dependence on composition are determined.

Hot Deformation Characteristics of Functionally Graded Steels Produced by Electroslag Remelting

In this work, functionally graded steel has been produced via diffusion of the alloying elements during electroslag refining. As the alloying element diffuses, it creates alternating regions with different transformation characteristics. Thus, it is possible to obtain steel composites with various combinations of ferrite, bainite, martensite, and austenite phases. By choosing the appropriate thickness of the slices used to set up the consumable electrodes and subsequent heat treatment, different functionally graded phases may be produced. The diffusion coefficients of chromium, nickel, and carbon atoms at temperatures just above the melting point of iron were estimated. Also, the thicknesses of the emerging bainite and martensite phases were determined and are in good agreement with the experimental results.

Diffusion of hexavalent chromium in chromium-containing slag as affected by microbial detoxification

An electrochemical method was used to determine the diffusion coefficient of chromium(VI) in chromium-containing slag. A slag plate was prepared from the original slag or the detoxified slag by Achromobacter sp. CH-1. The results revealed that the apparent diffusion coefficient of Cr(VI) was 4.4 × 10 −9 m 2 s −1 in original slag and 2.62 × 10 −8 m 2 s −1 in detoxified slag. The results implied that detoxification of chromium-containing slag by Achromobacter sp. CH-1 could enhance Cr(VI) release. Meanwhile, the results of laboratory experiment showed that the residual total Cr(VI) in slag decreased from an initial value of 6.8 mg g −1 to 0.338 mg g −1 at the end of the detoxification process. The Cr(VI) released from slag was also reduced by Achromobacter sp. CH-1 strain since water soluble Cr(VI) in the leachate was not detected after 4 days. Therefore, Achromobacter sp. CH-1 has potential application for the bio-detoxification of chromium-containing slag.

Interaction of the oxyfluoride melts of Ca, Al, Mg, Si, Ba, and Cr with refractories based on alumina and magnesia

The interaction of slags consisting of the oxides and fluorides of Ca, Al, Mg, Si, Ba, and Cr with refractories based on Al2O3, MgO, and MgO · Al2O3 is experimentally studied at 1600–1700°C and p Ar = 0.3 MPa. Laser emission microprobe analysis is used to study the fracture surfaces in the slag-crucible contact zone, to analyze the depth profile of the chromium concentration in the bulk of the refractory material, and to determine the diffusion coefficient of chromium. The values of the diffusion coefficient are related to the slag melt composition. These relations are established using the optical basicity of the slag.

Ti-13Cr-1Fe-3Al 合金の機械的性質に及ぼす冷却速度の影響

By their high specific strength and good cold workability, β titanium alloys have been used for various applications, e.g. parts of airplanes and eyeglass frames. Generally, β titanium alloys contain vanadium and molybdenum as alloying elements. However, the official quotations of vanadium and molybdenum are unstable. Therefore, use of those alloying elements is limited. Chromium and iron are attractive element as β stabilizer due to more stable official quotations than vanadium and molybdenum. Ti-13Cr-1Fe-3Al alloy was developed and some properties of that alloy were reported by present authors. It is very important to investigate the influence of cooling rate on mechanical properties of that alloy because of higher diffusion coefficient of chromium and iron. In this study, effect of cooling rate on tensile properties of Ti-13Cr-1Fe-3Al alloy was investigated by measurement of Vickers hardness, X-ray diffraction, optical and scanning electron microscope observations and tensile tests. The results obtained are as follows. Tensile strength and reduction in area of Ti-13Cr-1Fe-3Al alloy cooled at 0.02 K/s (show furnace cooling) showed about 860 MPa and about 45%, respectively. Reduction in area at 0.02 K/s is slightly lower than that at other cooling rate. It is considered that α precipitation on cooling at 0.02 K/s causes that decrease. Therefore, cooling rate above 0.02 K/s is recommended in Ti-13Cr-1Fe-3Al alloys, though tensile properties at 0.02 K/s is not bad.

Simulation of alloying-element diffusion during electrodiffusion heat treatment of steels

The effect of an electric current on the diffusion of alloy-forming components and vacancies in alloy steels subjected to electrodiffusion heat treatment has been studied. The diffusion coefficients of chromium, silicon, and aluminum are shown to increase by one to three orders of magnitude as compared to the reported data.

Estimation of diffusion coefficient of chromium in colloidal silica using digital photography.

In order to study the effectiveness of using colloidal silica, NYACOL DP5110, to stabilize chromium-contaminated soil, the diffusion of chromium in colloidal silica gel was estimated from laboratory experiments. To measure diffusion coefficients of chromium in the colloidal silica gel, a new measurement method based on digital photography was introduced. A series of experiments were designed and conducted to validate this new method and to estimate the diffusion coefficients of chromium in the colloidal silica gel. Accuracy of the proposed method was evaluated by several differentways. It was found that the apparent diffusion coefficient of chromium in colloidal silica gel ranged from 1.76 to 8.48 x 10(-10) m2/s depending mainly on the concentration of silica in the gel with chromium concentration less than 10(-2) M. Higher silica concentrations yielded lower diffusion coefficients due to the obstruction to the free movement of chromium. The adsorption isotherm of chromate to colloidal silica gel was found to be linear at pH 7; the partition coefficient was calculated to be 0.549 L/g. Mass balance calculations were performed to evaluate the accuracy of the proposed method and found that the measuring error was less than 6.5%. Based on the test data, the estimation of diffusion coefficients for chromium in colloidal silica gel using digital photography seems to be accurate and precise. This method is suitable for analyzing colored chemicals inside clear/white gels. From the results, it can be concluded that the gel behaves as a porous material with silica network forming continuous solid phase and its pore space saturated with water. The chromium ions diffuse in porous silica gel on a tortuous path. Therefore, the bulk diffusion dominates. Thus, the silica can be represented as a fix and impenetrable immersion in the solution. The presence of these motionless silica chains leads to an increase in the mean path of the diffusing molecules between two points in the system. On the basis of the test results, it can also be concluded that colloidal silica, NYACOL DP5110, for in-situ treatment of chromium-contaminated soils seems to be ineffective. Further research of more realistic simulation of diffusion and refined gel formulation with the capacity to convert the chromium to an immobile form is recommended.