Oxidative Cleaning Research Articles

Real-time observation of cathodic cleaning during variable-polarity gas tungsten arc welding of aluminium alloy

Online observation is expected to provide a better understanding of the cathodic cleaning of oxides from the molten pool during variable-polarity gas tungsten arc welding (VP GTAW) of aluminium alloys. In this paper, a machine-vision system with appropriate illumination and filtering is used to monitor in real time the effect of different process parameters on the cleaning of oxides from the molten pool during VP GTAW of Al 6061. Based on the observations, the process conditions under which a clean molten pool can be achieved are determined. In addition, the control of the welding process to maintain the consistency of cathodic cleaning is discussed. The results showed that in order to have an oxide-free molten pool, the solid surface in front of the molten pool should be cleaned from oxides by the electric arc. The choice of process parameters to satisfy this condition has been discussed. It was found that the percentage of direct current electrode positive (DCEP) polarity in the cycle of current has the highest impact on the cathodic cleaning, with the arc current having less influence, and the welding speed showing the least effect. Furthermore, in order to keep the consistency of oxide cleaning, process parameters should be set or controlled to maintain the cleaned zone larger than the molten pool.

Chemical Functionalization of Water-etched Si(100)

AbstractEtching of hydrogen-terminated Si(100) in deoxygenated water produces surfaces with a regular nanoscale topography. Surface infrared spectroscopy provides detailed information about this topography via interrogation of the silicon hydride species that populate this highly ordered surface. Here we investigate the feasibility of using siloxane chemistry to functionalize this surface while preserving the initial topography. The critical step in silanization to form high-quality organic layers is oxidative cleaning of the surface. By re-etching oxidized surfaces in hydrofluoric acid, we can repopulate surface hydride species and examine any apparent changes in topography that resulted from the oxidation step. We compare three different oxidation protocols and find that an SC-2 clean results in the least perturbation of the original topography. Preliminary results using both dynamic contact angle and atomic force microscopy suggest that the SC-2 oxidized surface can be functionalized with alkylsilane reagents to create a functionalized surface with regular, nanoscale topography, with all surface processing carried out under ambient conditions at or near room temperature.

Mg/Ca in the benthic foraminifera Cibicidoides wuellerstorfi and Cibicidoides mundulus: Temperature versus carbonate ion saturation

Magnesium/calcium (Mg/Ca) ratios in two widely used benthic foraminiferal species, Cibicidoides wuellerstorfi and Cibicidoides mundulus ( Cibicidoides kullenbergi), picked from global ocean core-tops and from six cores in the North Atlantic Ocean have been measured to investigate Mg/Ca variability, cleaning effect, and influences from bottom water temperature (BWT) and deep water carbonate ion saturation (Δ[CO 3 2−]). Replicate measurements of the two species reveal Mg/Ca variability of 0.07 ± 0.07 mmol/mol. Compared with Mg/Ca in samples cleaned by oxidative cleaning, Mg/Ca ratios are significantly lowered, by 0.10 ± 0.09 mmol/mol, in samples cleaned by reductive cleaning, likely due to preferential leaching during the reductive cleaning step. The cleaning influence is large relative to glacial–interglacial Mg/Ca changes (0.05–0.31 mmol/mol by this study). Regression of core-top data from a wide range of locations show that C. wuellerstorfi Mg/Ca is strongly affected by deep water Δ[CO 3 2−] with a sensitivity of ~ 0.009 mmol/mol per µmol/kg. When BWT is included in regressions, the correlation is slightly more significant with a weak BWT sensitivity on Mg/Ca of between 0.03 ± 0.01 and 0.07 ± 0.02 mmol/mol per °C. Because Δ[CO 3 2−] and BWT co-vary for most core-top samples, an alternate method of separating the two effects was made by comparing glacial to interglacial changes in Mg/Ca from a depth transect of North Atlantic cores where the BWT and carbonate ion histories since the last glacial period have been well constrained. Results from this transect suggest that the BWT effect is < 0.03 mmol/mol per °C, weaker than inferred from the core-top study. Therefore, core-top and down core data suggest that C. wuellerstorfi Mg/Ca is insensitive to BWT changes. The weak BWT effect, when compared with natural variability, complicates the use of Mg/Ca in this species to reconstruct past BWT. Taking all measured samples from various environments into account, C. mundulus Mg/Ca ratios show no correlation with BWT or deep water Δ[CO 3 2−].

Influences of organic matter and calcification rate on trace elements in aragonitic estuarine bivalve shells

A suite of elements (B, Na, Mg, S, K, Ca, V, Mn, Cr, Sr, and Ba) was measured in aragonitic shells of the estuarine bivalve Corbula amurensis, the Asian clam, using the Sensitive High-Resolution Ion MicroProbe with Reverse Geometry (SHRIMP RG). Our initial intent was to explore potential geochemical proxy relationships between shell chemistry and salinity (freshwater inflow) in northern San Francisco Bay (SFB). In the course of this study we observed variations in shell trace element to calcium ([M]/Ca) ratios that could only be attributed to internal biological processes. This paper discusses the nature and sources of internal trace element variability in C. amurensis shells related to the shell organic fraction and shell calcification rates. The average organic content of whole C. amurensis shells is 19%. After treating whole powdered shells with an oxidative cleaning procedure to remove organic matter, shells contained on average 33% less total Mg and 78% less total Mn. Within our analytical uncertainty, Sr and Ba contents were unchanged by the removal of organic matter. These results show that aragonitic C. amurensis shells have a large component of non-lattice-bound Mg and Mn that probably contribute to the dissimilarity of [M]/Ca profiles among five same-sized shells. Non-lattice-bound trace elements could complicate the development and application of geochemical proxy relationships in bivalve shells. Because B, Ba and Sr occur exclusively in shell aragonite, they are good candidates for external proxy relationships. [M]/Ca ratios were significantly different in prismatic and nacreous aragonite and in two valves of the same shell that had different crystal growth rates. Some part of these differences can be attributed to non-lattice-bound trace elements associated with the organic fraction. The differences in [M]/Ca ratios were also consistent with the calcification rate-dependent ion transport model developed by Carré et al. [Carré M., Bentaleb I., Bruguier O., Ordinola E., Barrett N. T. and Fontugne M. (2006) Calcification rate influence on trace element concentrations in aragonitic bivalve shells: evidences and mechanisms. Geochim. Cosmochim. Acta 70, 4906–4920] which predicts that [M]/Ca ratios increase as calcification rates increase and Ca 2+ channel specificity decreases. This result, in combination with the possibility that there were ontogenetic variations in growth rates among individuals younger than 2 years, underscores the need to develop an independent age model for C. amurensis shells. If growth-rate effects on lattice-bound [M]/Ca ratios can be constrained, it may yet be possible to develop high-resolution geochemical proxies for external solution chemistry in low-salinity regions of SFB.

Strain Behaviors of Si[sub 1−x]Ge[sub x] Grown on Oxidized and Etched Si[sub 1−x]Ge[sub x

The strain of Si 1-x Ge x (x = 0.15) was controlled by oxidation temperature, time, and initial Ge fraction in underlying Si 1-x Ge x . Followed by oxidation and HF cleaning of Si 1-x Ge x , epi-Si 1-x Ge x (x = 0.15) films were deposited on the Ge pileup layer, which is formed by the ultrahigh-vacuum chemical vapor deposition technique at 550°C. Through the X-ray rocking curve measurements and Raman scattering measurements, the strain-shift coefficient [b(x)] was evaluated. By using oxidized and etched Si 1-x Ge x for the substrate, the strain of deposited Si 1-x Ge x was changed from the partially relaxed to the tensile-strained state, a method for growing relaxed Si 1-x Ge x .

Mixing and Oxide Cleanness in Sequence Casting of Heats of Differing Compositions

For a two‐strand slab caster and a tundish capacity of 50 t the transition zone between two heats of different chemical composition was experimentally defined. The distribution of various elements was measured. The transition curves also show the penetration depth of the casting stream using a bifurcated submerged nozzle. This is basic information for the calculation of the mixing zone. Knowledge of the permissible composition ranges permits optimisation of the usable length of the strand. The impact of ladle change on oxide cleanness is analysed as well.

Calibrations for benthic foraminiferal Mg/Ca paleothermometry and the carbonate ion hypothesis

Benthic foraminiferal magnesium/calcium ratios were determined on one hundred and forty core-top samples from the Atlantic Ocean, the Norwegian Sea, the Indian Ocean, the Arabian Sea and the Pacific Ocean, mostly at sites with bottom water temperatures below 5 °C. Mg/Ca ratios are consistently lower, by ∼ 0.2 mmol/mol, in samples cleaned using oxidative and reductive steps than using oxidative cleaning. Differences between Cibicidoides species have been identified: Mg/Ca of Cibicidoides robertsonianus > Cibicidoides kullenbergi > Cibicidoides wuellerstorfi. Comparison with bottom water temperatures support observations of lowered Mg/Ca of C. wuellerstorfi at temperature below ∼ 3 °C compared with values predicted by published calibrations and from other Cibicidoides species. Hydrographic data shows that carbonate ion saturation (Δ[CO 3 2−]) decreases rapidly below this temperature. An empirical sensitivity of Δ[CO 3 2−] on Mg/Ca has been established for C. wuellerstorfi of 0.0086 ± 0.0006 mmol/mol/μmol/kg. A novel application using modern temperatures and Last Glacial Maximum temperatures derived via pore fluid modelling supports a carbonate ion saturation state effect on Mg incorporation. This may significantly affect calculated δ 18O seawater obtained from foraminiferal δ 18O and Mg/Ca temperature.

Influence of Deformation Degree on the Evaluation of Macroscopic Oxide Cleanness

The demand for cleaner steels requires reducing the number of macroscopic non-metallic oxide inclusions. A major problem of clean is the measurement and evaluation of the rare large inclusions which exceed a critical size harmful to the product. To this end, volumetric methods of evaluating macro-inclusions in the three-dimensional steel matrix are necessary to qualify steel heats or continuous cast slabs and to check if the refining and casting processes are stable and have been improved. Ultrasonic scans are a powerful tool to assess the quality of the volume. In order to activate macroscopic oxide inclusions for the reflexion of the ultrasound, as-cast material is deformed by hot rolling. The aim of the present research work was to find out the most effective hot rolling practice with respect to ultrasonic detection of the rare large oxide inclusions. For this purpose, heavily contaminated neighbouring slab samples, corresponding to a severe incidence of ladle slag carryover, were hot rolled in a different manner. The 23-kg-samples were either elongated by a ratio λ = 2, 3, 10 or 15, or alternatively cross-rolled, e.g. spread and stretched by ratios 2 x 5 or 3.2 x 3.2. The best compromise to quantify macroscopic steel cleanliness under consideration of cost and time requirements is based on the pure 10fold elongation or the cross-rolling by 2fold x Sfold. It likewise became clear that rare large oxides can be detected with good sensitivity, as long as the hot rolling reduction ratio is large enough.

Surface activation of thin silicon oxides by wet cleaning and silanization

Silanization protocols for glass slides and silicon oxide substrates usually include acid rinsing steps to activate the surfaces prior to silanization. In our group, field-effect transistor devices and electrolyte–insulator–semiconductor structures are used to electronically record signals from cells or to detect biomolecular interactions at the solid–liquid interface. A miniaturized, high sensitive, field-effect-based semiconductor device should expose at its input stage just a thin oxide (< 10 nm) to the electrolyte solution. Therefore, silanization protocols are needed, which do not alter the thin oxide layers in terms of topology changes or thickness loss. In this article we evaluated different protocols for wet cleaning and activation of thin silicon oxides. The efficiency of the cleaning methods was verified with Contact Angle Measurements, Atomic Force Microscopy, and Fourier-Transform Infrared Spectroscopy. Furthermore, X-ray Photoelectron Spectroscopy was used to characterize the oxides after the cleaning and silanization procedures. (3-aminopropyl)triethoxysilane was used to functionalize the oxide surfaces for further attachment of biological molecules (e.g. proteins, DNA). Thicknesses and uniformity of the silane coatings were evaluated by Imaging Ellipsometry.

Effect of pulsing parameters on laser ablative cleaning of copper oxides

The characteristics of copper oxide removal are comparably investigated under different pulsing strategies. A two-dimensional model is utilized to numerically simulate the laser ablative cleaning process. In the model, property discontinuity and Stephan and kinetic boundary conditions are taken into account, and the moving phase interface in the material is evaluated with the enthalpy method. Experiments are carried out on copper samples having different oxide layer thicknesses. The copper oxide layer thicknesses determined by ellipsometer and the chemical constituents of the copper oxide layer determined via x-ray photoelectron spectroscopy are incorporated into this numerical model. Under the single-pulse irradiation strategy, a higher laser intensity threshold is determined by the model based on the criterion of removing the oxide film as much as possible without damaging the substrate. Under the multipulse irradiation strategy, a lower threshold is employed to remove the oxide layer, while the appropriate pulse numbers under different laser intensities and different laser pulse repetition rates are the key issues investigated. A reasonable agreement is obtained between the experimental and simulated results.

Thermodynamics and Kinetics of Oxidation of Pure Indium Solders

ABSTRACTMicroElectroMechanical System (MEMS) devices often require low-temperature, fluxless soldering techniques due to their high temperature sensitivity and performance requirements of the components. While seeking the development of a soldering technology using pure indium, the major focus of this study is to assess the thermodynamics and kinetics of indium oxidation at various solder reflow environments that will ultimately provide a processing window for solder reflow and surface oxide cleaning. With a glove box employed to generate reducing environments, oxygen, moisture, and hydrogen contents were varied to examine their effects on oxidation and reduction behavior of indium. We also explored oxidation mechanisms at different regimes of temperature and time. In particular, electron transport from indium to indium oxide is shown to be the rate controlling mechanism under specific oxidizing conditions. For accurate thickness measurements, a spectroscopic ellipsometer was employed. In addition, the effect of indium oxidation on solder joint reliability was observed via wetting angle and interfacial shear strength measurements.

Application of nanoscale probes for the evaluation of the integrity of ultrafiltration membranes

The consequences of chemical cleaning of ultrafiltration membranes should not be interpreted solely in terms of flux recovery. It is important to evaluate the nature of the interactions between the cleaning agent and the membrane surface and to determine whether the introduction of the agent acts solely to improve the flux recovery or whether it also alters the membrane skin layer. Despite the important consequences of this information, only very limited data have been reported to date about the permeability-treatment relationships. Studies on membranes have mainly considered changes in streaming potential, FTIR spectra and hydrophobicity of the membrane surface. The present report uses an additional tool, probes of gold nanoparticles or dye-labeled MS2 bacteriophages, to trace gradual disintegration of the membrane skin layer during chemical cleaning. The new type of probe allowed us to follow two-stage deformation kinetics of the membranes during oxidative cleaning. The first stage involved the formation of holes with an average diameter of 20–30 nm, and the second stage, the rapid growth of the holes, leading to disintegration of the skin layer. The two-phase transition was followed using bubble-point measurements, ATR-FTIR spectroscopy, and SEM micrography. A second aim of the current article is to demonstrate the usefulness of a newly introduced tool—monodispersed nanoprobes—to trace membrane damage.

Non-river flood barium signals in the skeletons of corals from coastal Queensland, Australia

Two corals from coastal Queensland (Cow and Calf Islands, and Orpheus Island) have been analysed for a suite of trace elements by laser-ablation ICP-MS (LA-ICP-MS). Barium signals in these two corals are ‘anomalous’ in comparison with Ba behaviour seen in other near-shore corals from this region. The two corals display large sharp peaks in spring which do not correlate with markers of river discharge (Y/Ca and fluorescence). This Ba pattern contrasts with ‘normal’ behaviour—characterised here by the patterns previously published for two other coastal Queensland corals (King Reef and Pandora Reef), which display Ba peaks in summer associated with flooding of nearby rivers [1] [D.J. Sinclair, M.T. McCulloch, Corals record low mobile barium concentrations in the Burdekin River during the 1974 flood: evidence for limited Ba supply to rivers?, Palaeogeogr. Palaeoclimatol. Palaeoecol. 214 (1–2) (2004) 155–174]. Similarities are observed between the anomalous Ba in the Queensland corals and other published patterns of Ba behaviour in corals from South Africa and the Arabian Sea. This non-river flood Ba behaviour is characterized by large sharp spikes of Ba which are resistant to oxidative cleaning and form a continuous horizon within the coral. Curiously, not all corals from a region display anomalous Ba behaviour despite being in similar environments. The timing of anomalous Ba is consistent within a coral, but may vary from one location to the next. Anomalous Ba spikes are too large to be caused by Ba-rich upwelling, and no single environmental forcing function seems to be able to account for their timing. This combination of observations argues against an exogenous abiotic source for the anomalous Ba signal; instead, it may result from a biological event triggered by a combination of environmental parameters. Three hypotheses are presented, and critically tested against the observations: barite inclusion following phytoplankton blooms, decaying blooms of the blue-green algae Trichodesmium, and physiological perturbations associated coral mass spawning. None of the three hypotheses are fully consistent with all of the observations and it is concluded that no satisfactory explanation currently exists for the anomalous Ba spikes.

Centre Segregation, Soft Reduction and Oxide Cleanness for Large Diameter Line Pipe with Highest Demands on HIC

Starting material to meet maximum demands requires low centre segregation and excellent oxide cleanness. Comparative tests were performed for this purpose on an oval‐bow caster with a 5 m radius and a vertical bending machine with a 3 m vertical section and a 9 m radius. Both types of machine are capable of producing an excellent strand‐centre quality provided strand support system settings are well monitored. Oxide cleanness is superior in slabs cast on the vertical bending machine; the inclusion band is further from the surface than on the bow caster. Sulphur prints are not suitable for inspection purposes, whereas MIDAS (Mannesmann Inclusion Detection by Analysing Surfboards) is able to detect macroscopic inclusions with certainty.

Combined in situ and ex situ analysis of hydrogen radical and thermal removal of native oxides from (001) GaAs

We are currently involved in the study of regrowth of InAs on nanopatterned GaAs surfaces. The nanopatterning is accomplished through the movement of the sample while in contact with a diamond tip maintained at a constant load. Native oxides present on these surfaces introduce an obstacle to the subsequent regrowth. Therefore, the removal of this oxide is a prerequisite step for the study of the subsequent regrowth on these patterned surfaces. In this study we used in situ spectroscopic ellipsometry (SE) and reflection high energy electron diffraction (RHEED) as well as ex situ atomic force microscopy to follow the hydrogen cleaning and thermal removal of the native oxides from the GaAs surface. SE and RHEED were used to follow the oxide desorption process in situ and were used to determine when the surface was clean. Post AFM analysis indicated that the thermally desorbed oxide surface contained pits which were approximately 100 Å deep and covered 15% of the surface. Hydrogen radical cleaning was studied at substrate temperatures between 400–535 °C using a pressure of approximately 1×10−6Torr and a cracking thermocouple reading of 900 °C. The time to produce a clean surface was found to decrease as the temperature was increased. At the highest temperatures, cleaning took less than 10 min. AFM analysis indicated smooth surfaces were produced up to 500 °C. Above 500 °C, pitting was seen to occur similar to that observed for thermal oxide desorption. It was found that the onset of this pitting coincided with time at which spectroscopic ellipsometry indicated a change in the oxide layer.

Novel One-Step Aqueous Solutions to Replace Pregate Oxide Cleans

We have developed a number of novel solutions to use for one-step pregate oxide cleaning; they are based on tetraalkylammonium hydroxides of varying alkyl chain lengths, namely tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH). We added these surfactants together with ethylenediaminetetraacetic acid (EDTA) into the RCA SC-1 cleaning solution to enhance the efficiency of cleaning. With the exception of the TBAH solution, the cleaning efficiency of these solutions toward particles was 4%-7% higher than that of the conventional RCA method. Our cleaning methods have better efficiency toward the removal of Fe, Na, Ca, Cu, and Mn contaminants. We found that the conventional RCA method results in 10/sup 9/-10/sup 10/ atoms/cm/sup 2/ of Cu and Mn after cleaning. The electrical breakdown field of MOS capacitors was enhanced when using the new cleaning method. The literature model for surface adsorption and double-layer formation explains the cleaning behavior of the tetraalkylammonium ion-containing solutions. The removal of surface particles and metallic contaminants and the degree of surface roughness agree with the model's predictions. We believe that the best solution for use in one-step cleaning-one that comprises EDTA and TPAH-can replace the traditional RCA cleaning method. This new method has great potential for pregate oxide cleaning because it has the advantages of faster cycle times, lower costs, and greater efficiency.

Improving oxide cleanness on basis of MIDAS method

The MIDAS method (Mannesmann inclusion detection by analysing surfboards) was established in 1987 and enabled steelmakers to detect less frequent macroscopic inclusion particles in large volumes of steel. The basic idea of MIDAS is the flat cross-rolling of a strand sample perpendicular to the casting direction. Improvements in secondary metallurgy and casting technology have been achieved, since it became possible to define macrocleanness in exact numbers. In this paper, MIDAS results are presented for various strand sections: billets, blooms, jumbo blooms, round strands, conventional slabs and thin slabs. The variation of cleanness during sequence casting, at the front portion and end portion of heats, at ladle change and during steady state casting is investigated. The effect of teeming disturbances and accidental casting events on macrocleanness is studied. Selection of clean material can be optimised by adjusting the cutting length and downgrading critical casting portions. Detected inclusion particles in ultrasonic tested 'surfboard' samples are subsequently identified by metallography and by SEM or EPMA. The exogenous sources of contaminations and the formation mechanisms of inclusion particles are elucidated. Fundamental aspects, such as flotation due to buoyancy forces, coagulation of liquid particles, agglomeration of solid particles due to turbulent fluid flow, and the emulsification of slag droplets from ladle, tundish or mould, are now more deeply understood and enable progressive steps towards clean steel practice. MIDAS results correlate with material behaviour and properties at manufacturing and end-use of long and flat steel products. Future objectives should stress the stabilisation of optimised steady state conditions to realise a higher consistency and reproducibility of properties. Revamping of older continuous casting machines with curved moulds and the introduction of vertical sections are most essential for clean steelmaking. To avoid subsurface inclusions at the midwidth of the strand, submerged entry nozzle design and fluid flow pattern in the mould and liquid pool of continuous cast slabs should be reconsidered.

Process Technological Develpoments for Improvement of the Castability of High-Carbon Steels

Steels for rail-making involve standard requirements concerning oxide cleanness. Castability problems do not generally occur. Due to the extremely high demands on cleanness, roller-bearing steel 100Cr6 is cast using narrow SENs, which are extremely susceptible to clogging. Problems caused by clogging occur despite the fact that these heats are deoxidized using C, Si and Mn, with no addition of Al. Castability improved significantly after conversion to low-Al ferrosilicon for deoxidation and rinsing of ladles with carbon-deoxidized preceding heats. Casting temperature with a superheat of 30 °C and a reduction in Al content to less than 20 ppm made it possible to increase sequence length to three heats.

Simulation of the Behavior of Dioxins under the Conditions of Electron-Beam Gas Cleaning of Sulfur and Nitrogen Oxides

The efficiency of the electron-beam treatment of gases for the removal of sulfur and nitrogen oxides was examined as applied to dioxins. The gas-phase and liquid-phase degradation of dioxins and the oxidation of condensed carbon to form dioxins were taken into account in a model for the behavior of dioxins under the action of ionizing radiation. It was found that the formation of dioxins can significantly decrease the removal efficiency. Under certain conditions, the initial concentration of dioxins can increase.

Pt–M (M=Fe, Co, Ni and Cu) electrocatalysts synthesized by an aqueous route for proton exchange membrane fuel cells

Nanostructured Pt–M (M=Fe, Co, Ni, and Cu) alloy catalysts synthesized by a low temperature (70 °C) reduction procedure with sodium formate in aqueous medium have been investigated for oxygen reduction in sulfuric acid and as cathodes in single proton exchange membrane fuel cells (PEMFC). The Pt–M alloy catalysts show improved catalytic activity towards oxygen reduction compared to pure platinum. Among the various alloy catalysts investigated, the Pt–Co catalyst shows the best performance with the maximum catalytic activity and minimum polarization occurring at a Pt:Co atomic ratio of around 1:7. While mild heat treatments at moderate temperatures (200 °C) improve the catalytic activity due to a cleaning of the surface oxides, annealing at elevated temperatures (900 °C) degrade the activity due to an increase in particle size.