Composition Of Reaction Layer Research Articles

Interface Reactions Responsible for Run-Out in Active Brazing: Part 4

This study examined the interface reaction between Ag-xAl filler metals h˜ving x = 0.2, 0.5, or 1.0 wt-% and Kovar™ base materials. The present investigation used the braze joint test sample configuration. The brazing conditions were 965°C (1769°F), 5 min; 995°C (1823°F), 20 min, and a vacuum of 10–7 Torr. Run-out was absent from all test samples. Combining these results with those of the Part 2 study that used high-Al, Ag-xAl filler metals (x = 2.0, 5.0, and 10 wt-%) established these conditions for run-out: Ag-xAl filler metals having x ≥ 2.0 wt-% Al, which result in reaction layer compositions, and (Fe, Ni, Co)yAlz, having z ≥ 26 at.-% Al. The limited occurrences of run-out lobes resulted from the surface tension effect that quickly reduced the driving force for additional run-out events. The interface reactions were controlled by a driving force that was an expressed function of filler metal composition (Ag-xAl) and brazing temperature, as opposed to simply thermally activated rate kinetics. The differences of reaction layer composition and thickness confirmed that the interface reactions differed between the braze joint and sessile drop configurations. Collectively, the findings from the Parts 1–4 investigations concluded that the most-effective means to mitigate run-out is to place a barrier coating on the Kovar base material that will prevent formation of the (Fe, Ni, Co)yAlz reaction layer.

Interface Reactions Responsible for Run-Out in Active Brazing: Part 3

This study examined the interface reaction between sessile drops of the Ag-xAl filler metals having x = 0.2, 0.5, and 1.0 wt-% and KovarTM base material as an avenue to understand the run-out phenomenon observed in active filler metal braze joints. The brazing conditions were combinations of 965°C (1769°F) and 995°C (1823°F) temperatures and brazing times of 5 and 20 min. All brazing was performed in a vacuum of 10–7 Torr. Microanalysis confirmed that a reaction layer developed ahead of the filler metal to support spontaneous wetting and spreading activity. However, run-out was not observed with the sessile drops because the additional surface energy created by the sessile drop free surface constrained wetting and spreading. The value of z in the reaction layer composition, (Fe, Ni, Co)yAlz, increased with x of the Ag-xAl sessile drops for both brazing conditions. Generally, the values of z were lower for the more severe brazing conditions. Also, the reaction layer thickness increased with the Al concentration in the filler metal but did not increase with the severity of brazing conditions. These behaviors indicate that the interface reaction was controlled by the chemical potential rather than the rate kinetics of a thermally activated process. The determining metrics were filler metal composition (Ag-xAl) and brazing temperature. The findings of the present study provided several insights toward developing potential mitigation strategies to prevent run-out.

The effect of reaction layer composition on Pt/NiO function for glucose oxidation reaction in neutral media.

This study shows the application of carbon supported electrodes containing Pt/NiO nanoparticles to catalyze the electrochemical oxidation of glucose in neutral media. In particular, this study describes the effect of the Pt content and type of carbon (carbon black, expanded graphite, or charcoal active) in the reaction layer on this oxidation process in neutral media. Pt/NiO nanoparticles were synthesized by a simple hydrothermal method, and further characterized by scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), and cyclic voltammetry. These nanoparticles were used to modify carbon electrodes. The effectiveness of these electrodes for electrochemical glucose oxidation was evaluated. The results revealed that the catalytic activity of the electrodes depends on the content of Pt/NiO nanoparticles and the type of carbon. The 10% Pt/NiO with 90% loading (use of activated charcoal in the reaction layer) as optimum electrode indicated good stability after 1200 voltammetry cycles. This modified electrode was highly active for glucose oxidation in neutral media, which could be attributed to the presence of Pt/NiO nanoparticles as catalyst and high surface area of activated charcoal on the electrode surface.

The Composition of Reaction Layers on Rolling Bearings Lubricated with Gear Oils and Its Correlation with Rolling Bearing Performance

Various commercially available gear oils with similar viscosity were subjected to bearing life tests under identical mixed lubrication conditions. The test results revealed that bearing performance varied significantly depending on the chemistry of the gear oil used. Surface analysis with secondary neutral mass spectrometry (SNMS) techniques showed that the best-performing gear oil with respect to bearing life formed a reaction layer that was mainly composed of oxygen with a low concentration of sulfur and phosphorus and the worst-performing gear oil formed a reaction layer that was mainly composed of sulfur and phosphorus with significantly less oxygen. In this article, a semi-empirical equation is proposed to correlate the composition of the reaction layer (i.e., the oxygen, phosphorus, and sulfur concentration profile) with bearing performance. Plausible mechanisms of the observed correlation are discussed.

Microstructure and tensile properties of dissimilar metal gas tungsten arc welding of aluminium to titanium alloy

Commercially pure aluminium and titanium alloy Ti–6Al–4V were welded by gas tungsten arc welding (GTAW) process using AA 4047 Al–Si filler material. The chemical composition of reaction layer at the interface of titanium alloy and weld zone was determined by electron probe microanalyser (EPMA) showing that continuous layer of intermetallic compound of TiAl base phase was formed and aluminium is partly replaced by silicon. Transmission electron microscopic examination confirmed formation of (AlSi)3Ti intermetallic compound formed at the interface of Ti alloy and weld. In the weld zone, intermetallic phases containing Fe and Si were identified by EPMA analysis. These intermetallics were confirmed by X-ray diffraction technique. No intermetallic compound was found at the interface of weld and aluminium. Optical microscopy, scanning electron microscopy, microhardness, and tensile testing of the joints were used to characterise the resulting joints. The transverse strength of the weld joint is higher than that of the aluminium.

PTLPB of Si3N4 to FA-129 using nickel as a core interlayer

Partial transient liquid phase bonding was applied to a silicon nitride/iron aluminide alloy (FA-129) joint. This joint was composed of two independent joining systems. The joint configuration was Si 3 N 4 /75Cu–25Ti/Cu/Ni/Al/FA-129. The results demonstrate that homogenization has no effect on the kinetic of the reaction layer formation between the ceramic and the nickel core due to a previous dissolution reaction. The reaction layer composition evolves from a TiN–Ti 5 Si 3 layer system after reaction during the first soaking time, to a single TiN layer after the complete cycle. The dissolution of the Ti 5 Si 3 layer in the Ni core becomes the driving factor influencing the properties of the joint. The composition of the copper–nickel alloy interlayer changes with homogenization treatment, passing from a maximum of 70–20 wt% Cu, depending on the conditions. NiAl and Ni 3 Al intermetallics were observed at the interface between the nickel and the FA-129 and their thicknesses varies with the homogenization conditions. The strength values obtained were within the range of 80 MPa, with the ceramic reaction layer being the region where all failures occurred.

PTLPB of Si 3N 4 to FA-129 using nickel as a core interlayer

Partial transient liquid phase bonding was applied to a silicon nitride/iron aluminide alloy (FA-129) joint. This joint was composed of two independent joining systems. The joint configuration was Si 3N 4/75Cu–25Ti/Cu/Ni/Al/FA-129. The results demonstrate that homogenization has no effect on the kinetic of the reaction layer formation between the ceramic and the nickel core due to a previous dissolution reaction. The reaction layer composition evolves from a TiN–Ti 5Si 3 layer system after reaction during the first soaking time, to a single TiN layer after the complete cycle. The dissolution of the Ti 5Si 3 layer in the Ni core becomes the driving factor influencing the properties of the joint. The composition of the copper–nickel alloy interlayer changes with homogenization treatment, passing from a maximum of 70–20 wt% Cu, depending on the conditions. NiAl and Ni 3Al intermetallics were observed at the interface between the nickel and the FA-129 and their thicknesses varies with the homogenization conditions. The strength values obtained were within the range of 80 MPa, with the ceramic reaction layer being the region where all failures occurred.

Bioactive Ceramic And Model Surfaces Adsorb Ligands and Factors That Stimulate Cellular Function

Abstract Microscopy and microanalysis techniques have played an important role in our understanding of how biomaterials interact with their environment. In first part of this study, we will focus on the behavior of bioactive glass, whereas in the second a model surface will be investigated. Upon implantation bioactive glass undergoes a series of reactions that leads to the formation of a calcium phosphate-rich layer. Most in vitro studies of the changes that occur on the surface of bioactive glass have employed the use of buffer solutions with compositions reflecting the ionic composition of interstitial fluid. Although these studies have documented the physical and chemical changes associated with bioactive glass immersed in aqueous media, they do not reveal the effect of serum proteins and cells which are present at the implantation site. In the present study, we document, using atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS), significant differences in reaction layer composition, thickness, morphology and kinetics of formation arising from the presence of serum proteins.

Formation of reaction layers in steel machining: impact on surface treatment processes

During production and machining, metal parts come into contact with cooling lubricants which protect the tool from wear. Cooling lubricants are responsible for heat and swarf removal as well as for friction reduction. For this reason they contain additives which form reaction layers not only at the tool surface, but also on the surface of the workpiece. Residues of cooling lubricants are thought to cause problems in surface treatment processes if they are not removed by efficient cleaning/degreasing. This is hardly practicable as long as it is unknown what contamination (and how much of it) has to be removed to obtain a desired physicochemical surface condition. Thus it is necessary to identify the composition of reaction layers and to determine critical surface concentrations which must not be exceeded if the surface treatment process is to function properly. Reaction layers have been prepared on steel by milling using different cutting oils, consisting of a mineral or synthetic base oil and additives in different concentrations. X-ray photoelectron spectroscopy was used to analyse surface composition after milling, and electrochemical measurements were carried out to establish the condition of the metal surfaces. Gas nitriding was used as a model surface treatment process to examine the impact of these reaction layers on the reactivity of a steel surface.

Biotite dissolution at 25°C: The pH dependence of dissolution rate and stoichiometry

The rate and stoichiometry of biotite dissolution were studied in the pH range 2–10 using thin-film continuous flow reactors. The release of interlayer K is relatively fast and becomes diffusion-controlled within a few days. The release rates of framework ions (Mg, Al, Fe, Si) are much slower and reach an apparent steady-state within ten days. The stoichiometry and rate of dissolution vary greatly with pH. Consistent with surface reaction control of release rates, an empirical rate law, R + k H[H +] m + k 0 + k OH[H +] n (moles m −2 h −1) describes proton- and hydroxyl-catalysed dissolution for each ion. Si Fe Mg Al log k H −4.45 −5.10 −4.93 −5.31 m 0.91 0.51 0.57 0.40 log k 0 −7.31 log k OH −11.29 −15.36 −10.57 −12.58 n −0.48 −0.81 −0.29 −0.54 Rapid K + release provides a tracer for the extent of the hydrated reacting layer on the biotite surface and within interlayers. An altered reaction layer composition, calculated from mass balances for released ions, results from preferential leaching of some ions and is consistent with that of vermiculite. X-Ray powder diffractometry confirmed the formation of both vermiculite and kaolinite during the weathering reaction. The pH dependence of release rates, normalised to the corresponding ion concentrations in the reacting layer, correlate with those for the respective binary oxides (SiO 2, Al 2O 3, Fe 2O 3, MgO). Release rates for Al, Mg, and Fe at neutral pH are much slower when the mineral has been previously reacted at low pH where these ions are released rapidly. Model simulations suggest that, for ions that initially dissolve rapidly, release rates will decrease as the ion is depleted in the reacting layer. Rates will eventually approach those of the most slowly dissolving ion. At 25°C and pH 7, this process would lead to stoichiometric dissolution within 50 y.

An investigation of surface reactions of extreme pressure additives by the single-pulse heating method

The chemical composition of reaction layers formed with isogeometrical extreme pressure-antiwear additives in polyalphaolefin in the absence of mechanical stimulation is investigated using the single-pulse heating method in the temperature range 25 – 720 °C. The influence of the chemical structure of the additives on their reactivity is studied with Auger electron spectroscopy and photoelectron spectroscopy. Three temperature domains can be distinguished as the temperature increased: oxidation of the surface, reaction of the additive and decomposition of the solvent. The thermally activated reaction of the sulphur-containing phosphate esters leads to the formation of reaction layers several nanometres thick containing iron sulphide and iron phosphate. The composition of reaction layers formed differs from that found under wear test conditions where the metallic surface reacts directly with the additive. For thermally activated immersion tests, however, the additive apparently reacts with a previously oxidized surface.

X-ray Diffraction/Electron Microprobe Analysis of Surface Films Formed on Alloys During Hydrothermal Reaction with Geologic Materials

AbstractX-ray diffraction and electron microprobe analysis were used in combination to identify reaction phases that formed on the surfaces of low-carbon steel specimens reacted with a 75% basalt-25% bentonite mixture and anion-doped water in sealed pressure vessels at 100°C and 250°C. Reaction phases on specimen surfaces and in adhering geologic material were identified by conventional X-ray diffraction scans of entire specimens with intact reaction layers. Comparison of results from adhering geologic material and scans of selectively removed layers allowed establishment of approximate reaction gradients in the adhering packing material. Electron microprobe analysis of specimens in cross-section provided quantitative chemical analyses of adhering reaction phases, and identification of reaction layer composition gradients and thicknesses. Magnetite formed on the surface of specimens reacted at 250°C for 4 weeks. Iron-enriched clay was also observed on specimen surfaces and in the adjacent basalt-bentonite mixture. The 100°C experiments yielded surface films of a siderite-structure phase, (Fe,Ca,Mn)CO3, that were not observed in previous experiments with synthetic ground-water. Less extensive iron enrichment of the adjacent clays compared to that seen in the 250°C experiments was observed. The siderite-structure phase generally formed when no carbonate ion was present in the initial solution, implying dissolution of impurity calcite in the bentonite as the controlling factor in the reaction. The results demonstrate the utility of combining X-ray diffraction and electron microprobe analysis for characterization of reaction phases on alloys reacted with complex geologic materials.

Study of solid-state reactions in the NiO/Fe2O3 system

Solid-state reactions in the NiO/Fe2O3 system have been investigated in the temperature range 1100 to 1300° C, The optical microscope and the electron probe microanalyser were used. Kinetic parameters of the calcination process of this system: the reaction rate, time exponent and activation energy, have been determined by observing the changes in the reaction layer thickness with time and temperature. The analysis of the reaction layer composition was the basis for discussion concerning the possible mechanism of this reaction.