Prior Surface Treatment Research Articles

Simultaneous Segment Orientation and Anchoring for Robust Hydrogel Coating with Underwater Superoleophobicity

AbstractUnderwater adhesive superoleophobic coatings are in high demand for underwater activities. However, hydrogel coatings have limited adhesiveness for long periods. In this work, a novel approach is presented that employs synergistic segment orientation and covalent anchoring strategies to fabricate superoleophobic hydrogel coatings on different substrates without prior surface treatments. The coating demonstrated remarkable long‐lasting superoleophobic properties even in extreme underwater environments. It also exhibited strong adhesion with a shear strength of up to 5 MPa and antiswelling and antibiofouling properties, making it highly effective for applications in antiliquid adhesion, crude oil self‐cleaning, and antibiofouling. The simplicity, ease of preparation, and exceptional performance of the hydrogel coating provide a notable example for the synergistic segment orientation and covalent anchoring of hydrogel‐based underwater coatings. Therefore, this study provides a new paradigm for designing straightforward surface‐functional materials.

Anodic Behaviour of NixFeyCu5 and NixFeyCu20 in Potassium-Rich Naf-KF-AlF3-Al2O3 Melts

Using inert anode technology to produce aluminium would substantially reduce the aluminium industry's carbon footprint. Replacing the Hall-Héroult process with an alternative process based on vertical electrode cell (VEC) design using inert anodes and wettable cathodes is a promising alternative, but must be developed to be economically viable at scale. Three material types have been explored as inert anodes: metals, cermets and ceramics. Metallic anodes have been widely studied for their attractive properties, such as superior mechanical strength, high electrical conductivity and ease of fabrication. Of metallic anodes, Cu-Al, Ni-Fe and Ni-Fe-Cu-based alloys are the most commonly examined alloy systems for anode applications. It is also necessary to use low-temperature melts during the electrolysis process to ensure that the anodes are not damaged. In NaF-KF-AlF3 melts, increasing the KF content in the mixture would reduce the liquidus temperature and increase the alumina solubility in the melt.In this work, we examine the anodic behaviour of NixFeyCu5 and NixFeyCu20 electrodes, without prior surface treatment, in potassium-rich NaF-KF-AlF3 melts at 770°C. The cryolite ratio (xNaF+xKF/xAlF3) and potassium ratio (xKF/xKF+xNaF) of the melt used for the studies are 1.3 and 0.7, respectively. Electrochemical techniques such as chronopotentiometry, chronoamperometry and linear sweep voltammetry were performed to examine the anodic behaviour of these metallic anodes under an N2 atmosphere.Figure 1 shows the steady-state anodic polarisation curves on NixFeyCu5 and NixFeyCu20 anodes before and after galvanostatic polarisation with an applied current density of 0.5 Acm-2 for 120 minutes. It can be noted that the anodic potential at the same current density is more for the polarised anode compared to the non-polarised in both cases. This is due to the formation of a stable oxide layer during the galvanostatic polarisation of the anode. Oxidation of the anode is expected instead of fluoridation when the melt is saturated with alumina. The stabilisation of anodic current can be seen between 1.9 and 2.4 V. This stabilisation corresponds to the passivation of anodes due to the oxide layer formation. A rapid increase in the current after 2.4 V is due to the oxygen evolution reaction. The anodic current density in the passive region is much lower in anodes with Cu 20%, meaning a more protective layer is formed. After the galvanostatic polarisation of the anode, anodes were examined using scanning electron microscopy to understand the oxide layer composition. Anodes performed stably in potassium-rich melts, and Cu content plays a vital role in the anode's performance. Figure 1. Stationary state polarisation curves of NixFeyCu5 and NixFeyCu20 anodes before and after the polarisation at 0.5 A cm-2 Figure 1

Feasibility of Ecofriendly Mortars with Different Hemp Additions for Use in Building Sector

Cement mortars are commonly used in building works for the execution of enclosures and exterior rehabilitation of facades. The incorporation of plant-based additives enables the development of ecofriendly construction materials. In this work, a physical and mechanical characterisation of cement mortars with the incorporation of hemp in three morphologies (fibre, powder and pellet) was conducted. The results show how the additions of hemp powder and pellets with a partial replacement of natural aggregate reduce the final density of cement mortars and their thermal conductivity by more than 16% and 19%, respectively. On the other hand, the addition of hemp fibres reduces shrinkage during the setting of cement mortars, improving their flexural strength and increasing their durability. For this reason, it is possible to recommend the use of these mortars with the addition of natural hemp fibres without prior surface treatment to improve the physical-mechanical properties of these construction materials and extend their application field as ecofriendly materials for masonry work.

Effect of Filler Content on the Morphology and Physical Properties of Poly(Lactic Acid)-Hydroxyapatite Composites.

The effect of hydroxyapatite (HAp) synthesized by the chemical precipitation process on the morphology and properties of composites based on poly(lactic acid) (PLA) was investigated at various filler content ratios, i.e., 5, 10 and 15 wt%. Both neat PLA and PLA-based composites were first prepared using the solvent casting method, followed by melt compounding in an internal mixer, whereas tensile specimens were obtained by thermo-compression. The study revealed that the addition of 5 wt% of HAp into the PLA led to a slight improvement in both the thermal stability and tensile properties of the composite material in comparison with neat PLA and other composite samples. Indeed, the values of the tensile strength and modulus increased from approximately 61 MPa and 2.9 GPa for the neat PLA to almost 64 MPa and 3.057 GPa for the composite sample, respectively. Moreover, the degradation temperature at a 5 wt% mass loss also increased by almost 5 °C compared to other samples, due probably to a finer dispersion of the HAp particles in the PLA, as observed under a scanning electron microscope. Furthermore, the FT-IR spectra displayed some changes in the chemical structure of the PLA/HAp (5 wt%), indicating the occurrence of filler-matrix interactions. At a higher filler content ratio, a decrease in the properties of the PLA/HAp composites was observed, being more pronounced at 15 wt%. The PLA composite containing 5 wt% HAp presents the best compromise among the investigated properties. The study highlighted the possibility of using HAp without any prior surface treatment as a reinforcement in PLA composite materials.

Comparison of microleakage of different surface pre-treatment modalities of ionoseal® pit and fissure sealant in primary teeth: An in vitro study.

Pit and fissure sealing is an evidence-based preventive measure against dental caries, especially in primary teeth which possess high caries risk, and to give the required benefits of the sealant, a good adaptation, and sealing ability should be present. This study aimed to assess and compare the microleakage score of Ionoseal® pit and fissure sealant, when used either alone or with prior surface treatment of erbium-doped yttrium aluminum garnet (Er: YAG) laser, acid etching, or their combination, in primary teeth. Forty healthy human molar teeth were randomly chosen and allocated into four study groups according to the surface pretreatment: group I, no surface pretreatment; Group II, 2W Er: YAG laser etching, Group III, combined laser etching and acid etching group, and Group IV, 37% phosphoric acid etching. After surface pretreatment procedures were conducted, the teeth were sealed with Ionoseal®. Subsequent microleakage was assessed through dye penetration under a stereomicroscope. One sample from each group was randomly selected, and scanning electron microscopy (SEM) was carried out on the central slice of the three obtained slices of the samples. Chi-square test revealed a high statistically significant difference between groups (P = 0.00). Similarly, all pairwise comparisons revealed a statistically significant difference. Group I showed the greatest mean of microleakage score (1.5), followed by Group IV (1.4), Group II (0.7), and Group III which showed the least microleakage score (0.6). These findings were supported by the SEM examination results. Using Ionoseal with prior surface treatment by combined 2 W Er: YAG laser etching and 37% phosphoric acid etching can result in the best sealing ability which would significantly enhance the long-term success of pit and fissure sealing in primary teeth.

Facile Preparation of PANI-Sr Composite Flexible Thin Film for Ammonia Sensing at Very Low Concentration

Conducting polymers, are still fascinating the industrial applications area since their discovery, particularly in the field of chemical sensors. For this purpose, flexible and highly sensitive based polyaniline-strontium (PANI-Sr) films were successfully prepared via a facile in-situ chemical polymerization process of aniline in presence of Sr (NO3)2 deposited on biaxially oriented polyethylene terephthalate (BOPET) flexible substrates with prior surface treatment using (3-aminopropyl) trimethoxysilane. Spectral, structural, morphological, and surface behavior characterizations were carried out using Fourier transform infrared spectroscopy (FTIR-ATR), X-ray fluorescence (XRF), raman spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and surface wettability. The electrical conductivity was measured by the usual four probes technique. Noticeably, the prepared films with Sr (NO3)2 ∼2 M have shown a highest conductivity of 0.3 S·cm−1 over the other samples. This conductivity feature has been exploited to test the sensitivity and the performances of the obtained films toward different type of gas. The PANI-Sr sensor demonstrates an outstanding selectivity and an excellent sensitivity towards the ammonia (498% response to 100 ppm) within a detection limit of 0.013 ppm, and a fast response/recovery time (1 s /42 s) toward 50 ppm at room temperature. The PANI-Sr sensor also showed a good reproducibility during five cycles. The interaction mechanism of PANI-Sr sensor film and the NH3 vapors was discussed basing on the impedance spectroscopy analysis results. The obtained results highlight the paramount role played by the strontium particle in enhancing the ammonia detection performances, when they are imbedded into PANI matrix through facile preparation process, and they emphasize their prominence over the similar study.

The skin microbiome of Xenopus laevis and the effects of husbandry conditions

BackgroundHistorically the main source of laboratory Xenopus laevis was the environment. The increase in genetically altered animals and evolving governmental constraints around using wild-caught animals for research has led to the establishment of resource centres that supply animals and reagents worldwide, such as the European Xenopus Resource Centre. In the last decade, centres were encouraged to keep animals in a “low microbial load” or “clean” state, where embryos are surface sterilized before entering the housing system; instead of the conventional, “standard” conditions where frogs and embryos are kept without prior surface treatment. Despite Xenopus laevis having been kept in captivity for almost a century, surprisingly little is known about the frogs as a holobiont and how changing the microbiome may affect resistance to disease. This study examines how the different treatment conditions, “clean” and “standard” husbandry in recirculating housing, affects the skin microbiome of tadpoles and female adults. This is particularly important when considering the potential for poor welfare caused by a change in husbandry method as animals move from resource centres to smaller research colonies.ResultsWe found strong evidence for developmental control of the surface microbiome on Xenopus laevis; adults had extremely similar microbial communities independent of their housing, while both tadpole and environmental microbiome communities were less resilient and showed greater diversity.ConclusionsOur findings suggest that the adult Xenopus laevis microbiome is controlled and selected by the host. This indicates that the surface microbiome of adult Xenopus laevis is stable and defined independently of the environment in which it is housed, suggesting that the use of clean husbandry conditions poses little risk to the skin microbiome when transferring adult frogs to research laboratories. This will have important implications for frog health applicable to Xenopus laevis research centres throughout the world.

Analysis of surface treatment of ASTM A516 Grade 70 using Salt spray method

Conversion coating is an effective way to safeguard against corrosion. It is performed on a number of materials inhibiting the surface layer to corrosive attack. In this work surface engineering is carried out on test material ASTM A 516 Grade 70 which is widely used for constructional purposes. During the passivation process samples were given a hot alkaline oxide bath in sodium hydroxide and sodium nitrate. The corrosion resistance was then analyzed using advanced testing procedures. Salt spray test was used as a yard stick in making a comparative analysis of different samples including unpassivated samples, passivated samples and passivated samples with prior surface treatment. Results have shown that mechanical surface treatment improves material life by 3% whereas passivation with prior surface treatment can increase life by 18%.

Thermo-mechanical fatigue evaluation of a thermal barrier coating bond-coatless system

Thermal barrier coating systems are often subjected to complex thermo-mechanical loading involving a combination of mechanical stresses under complex thermal gradients, in addition to the contribution of oxidation to the damage processes. Recently, a thermal-barrier coating bond-coatless system has been developed using prior-surface treatments. Atmospheric plasma spray (APS) Yttria-Stabilized-Zirconia (YSZ) is deposited on the AM1 nickel-based single crystalline superalloy substrate. The substrate has been either grit-blasted or laser textured before thermal spraying. The durability of these systems are investigated performing out-of-phase load controlled thermo-mechanical fatigue (TMF) tests in the 500–1100 °C and 120–700 MPa temperature and stress ranges. The contribution of a prior thermal over-aging of 200 h at 1100 °C has also been investigated. The damage mechanisms during out-of-phase TMF of the different TBC bond-coat-less systems have been studied and compared to the ones obtained during isothermal creep at 1100 °C/120 MPa. It is shown that a prior thermal over-aging favors cycling ratcheting during TMF cycling due to the degradation of the substrate microstructure. In addition, the coating damage mechanisms are observed to depend on the prior-surface treatment and thermal over-aging. Cracks perpendicular to the interface in the top coat have been observed whatever the specimens and microstructural state. Top coats are debonded for grit-blasted substrates while crack bifurcation above key holes is observed for laser textured substrates, leading to a better top coat TMF durability.

Template-assisted bottom-up growth of nanocrystalline diamond micropillar arrays

Micro-patterned diamond has been investigated for numerous applications, such as biomimetic surfaces, electrodes for cell stimulation and energy storage, photonic structures, imprint lithography, and others. Controlled patterning of diamond substrates and moulds typically requires lithography-based top-down processing, which is costly and complex. In this work, we introduce an alternative, cleanroom-free approach consisting of the bottom-up growth of nanocrystalline diamond (NCD) micropillar arrays by chemical vapour deposition (CVD) using a commercial porous Si membrane as a template. Conformal pillars of ~4.7 μm in height and ~2.2 μm in width were achieved after a maximum growth time of 9 h by hot-filament CVD (2% CH4 in H2, 725 °C at 10 mbar). In order to demonstrate one of many possible applications, micropillar arrays grown for 6 h, with ~2 μm in height, were evaluated as moulds for imprint lithography by replication onto hard cyclic olefin copolymer (COC) and onto soft polydimethylsiloxane (PDMS) elastomer. The results showed preserved mechanical integrity of the diamond moulds after replication, as well as full pattern transfer onto the two polymers, with matching dimensions between the grown pillars and the replicated holes. Prior surface treatment of the diamond mould was not required for releasing the PDMS replica, whereas the functionalisation of the diamond surface with a perfluorododecyltrichlorosilane (FDDTS) anti-stiction layer was necessary for the successful release of the COC replica from the mould. In summary, this paper presents an alternative and facile route for the fabrication of diamond micropillar arrays and functional micro-textured surfaces.

Exploring environment friendly nickel electrodeposition on AZ91 magnesium alloy: Effect of prior surface treatments and temperature of the bath on corrosion behaviour

The nickel electroplating of AZ91 magnesium alloy was explored with and without employing surface pretreatment. The plating process refrained from using hazardous elements namely fluoride, chromium and copper or zinc undercoat. The electroplating was achieved at 25–70 °C and 25 mA cm−2 after applying surface pretreatments and Ni-P interlayer. Electrochemical and salt spray tests revealed large enhancement in corrosion resistance of 15 μm thick coating obtained at 70 °C bath temperature. The pretreatment involved phosphoric acid followed by NaOH produced superior coating to nickel carbonate followed by carbonate silicate bath, which is explained based on the porosity and hydrogen activity on the surface.

Study of apatite layer formation on SBF-treated chitosan composite thin films

Surface modifications of thin films based on chitosan (Ch), pure Ch and either Ch/montmorillonite (MMT) or Ch/nanoclay composites, were characterised by infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Biomineralisation of the Ch-based materials without any prior surface treatment was evaluated by immersing films in simulated body fluid (SBF) at 37 °C for 14 days. Samples were compared before and after soaking. Results obtained from SEM-EDX, AFM, and infrared spectroscopy (ATR-FTIR) were compared, and all prepared films showed growth of a new phase containing calcium. The composition of thin films influenced the amount of new phase formed as well as the degree of crystallinity of the newly formed phase. The largest increase was observed for the Ch composite with modified nanoclay. Moreover, increased growth of the new phase on the surface of films after immersion in SBF solution significantly influenced the thermal properties of the materials.

Fabrication of Si and Ge nanoarrays through graphoepitaxial directed hardmask block copolymer self-assembly

Films of self assembled diblock copolymers (BCPs) have attracted significant attention for generating semiconductor nanoarrays of sizes below 100 nm through a simple low cost approach for device fabrication. A challenging abstract is controlling microdomain orientation and ordering dictated by complex interplay of surface energies, polymer–solvent interactions and domain spacing. In context, microphase separated poly (styrene-b-ethylene oxide) (PS-b-PEO) thin films is illustrated to fabricate nanopatterns on silicon and germanium materials trenches. The trenched templates was produced by simple electron beam lithography using hydrogen silsesquioxane (HSQ) resist. The orientation of PEO, minority cylinder forming block, was controlled by controlling trench width and varying solvent annealing parameters viz. temperature, time etc. A noticeable difference in microdomain orientation was observed for Si and Ge trenches processed under same conditions. The Ge trenches promoted horizontal orientations compared to Si due to difference in surface properties without any prior surface treatments. This methodology allows to create Ge nanopatterns for device fabrication since native oxides on Ge often induce patterning challenges. Subsequently, a selective metal inclusion method was used to form hardmask nanoarrays to pattern transfer into those substrates through dry etching. The hardmask allows to create good fidelity, low line edge roughness (LER) materials nanopatterns.

Cold Gas-Sprayed Deposition of Metallic Coatings onto Ceramic Substrates Using Laser Surface Texturing Pre-treatment

Cold spraying enables a variety of metals dense coatings onto metal surfaces. Supersonic gas jet accelerates particles which undergo with the substrate plastic deformation. Different bonding mechanisms can be created depending on the materials. The particle–substrate contact time, contact temperature and contact area upon impact are the parameters influencing physicochemical and mechanical bonds. The resultant bonding arose from plastic deformation of the particle and substrate and temperature increasing at the interface. The objective was to create specific topography to enable metallic particle adhesion onto ceramic substrates. Ceramic did not demonstrate deformation during the impact which minimized the intimate bonds. Laser surface texturing was hence used as prior surface treatment to create specific topography and to enable mechanical anchoring. Particle compressive states were necessary to build up coating. The coating deposition efficiency and adhesion strength were evaluated. Textured surface is required to obtain strong adhesion of metallic coatings onto ceramic substrates. Consequently, cold spray coating parameters depend on the target material and a methodology was established with particle parameters (diameters, velocities, temperatures) and particle/substrate properties to adapt the surface topography. Laser surface texturing is a promising tool to increase the cold spraying applications.

A Simple Nanocellulose Coating for Self‐Cleaning upon Water Action: Molecular Design of Stable Surface Hydrophilicity

AbstractCoating solid surfaces with cellulose nanofibril (CNF) monolayers via physical deposition was found to keep the surfaces free of a variety of oils, ranging from viscous engine oil to polar n‐butanol, upon water action. The self‐cleaning function was well correlated with the unique molecular structure of the CNF, in which abundant surface carboxyl and hydroxy groups are uniformly, densely, and symmetrically arranged to form a polar corona on a crystalline nanocellulose strand. This isotropic core–corona configuration offers new and easily adoptable guidance to design self‐cleaning surfaces at the molecular level. Thanks to its excellent self‐cleaning behavior, the CNF coating converted conventional meshes into highly effective membranes for oil–water separation with no prior surface treatment required.

A Simple Nanocellulose Coating for Self-Cleaning upon Water Action: Molecular Design of Stable Surface Hydrophilicity.

Coating solid surfaces with cellulose nanofibril (CNF) monolayers via physical deposition was found to keep the surfaces free of a variety of oils, ranging from viscous engine oil to polar n-butanol, upon water action. The self-cleaning function was well correlated with the unique molecular structure of the CNF, in which abundant surface carboxyl and hydroxy groups are uniformly, densely, and symmetrically arranged to form a polar corona on a crystalline nanocellulose strand. This isotropic core-corona configuration offers new and easily adoptable guidance to design self-cleaning surfaces at the molecular level. Thanks to its excellent self-cleaning behavior, the CNF coating converted conventional meshes into highly effective membranes for oil-water separation with no prior surface treatment required.

A Seismic Strengthening Technique for Reinforced Concrete Columns Using Sprayed FRP.

Conventional methods for seismic retrofitting of concrete columns include reinforcement with steel plates or steel frame braces, as well as cross-sectional increments and in-filled walls. However, these methods have some disadvantages, such as the increase in mass and the need for precise construction. Fiber-reinforced polymer (FRP) sheets for seismic strengthening of concrete columns using new light-weight composite materials, such as carbon fiber or glass fiber, have been developed, have excellent durability and performance, and are being widely applied to overcome the shortcomings of conventional seismic strengthening methods. Nonetheless, the FRP-sheet reinforcement method also has some drawbacks, such as the need for prior surface treatment, problems at joints, and relatively expensive material costs. In the current research, the structural and material properties associated with a new method for seismic strengthening of concrete columns using FRP were investigated. The new technique is a sprayed FRP system, achieved by mixing chopped glass and carbon fibers with epoxy and vinyl ester resin in the open air and randomly spraying the resulting mixture onto the uneven surface of the concrete columns. This paper reports on the seismic resistance of reinforced concrete columns controlled by shear strengthening using the sprayed FRP system. Five shear column specimens were designed, and then strengthened with sprayed FRP by using different combinations of short carbon or glass fibers and epoxy or vinyl ester resins. There was also a non-strengthened control specimen. Cyclic loading tests were carried out, and the ultimate load carrying capacity and deformation were investigated, as well as hysteresis in the lateral load-drift relationship. The results showed that shear strengths and deformation capacities of shear columns strengthened using sprayed FRP improved markedly, compared with those of the control column. The spraying FRP technique developed in this study can be practically and effectively used for the seismic strengthening of existing concrete columns.

Growth of Ag nanostructures on high-index Si (5 5 12) surfaces under UHV conditions: effect of prior surface treatment before deposition

High-index substrates, such as Si (5 5 12), provide self-assembled one-dimensional periodic array of structures upon reconstruction and can be used as templates for growth of aligned nanoscale structures. Crystalline quality of Ag nanostructures grown under UHV conditions using a molecular beam epitaxy system on reconstructed Si (5 5 12) surface is compared with those structures grown on HF-treated and native-oxide-covered Si (5 5 12) surfaces. These have been characterized by using reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM) and in situ scanning tunneling microscopy methods. The RHEED and TEM studies confirm the polycrystalline, textured and crystalline nature of the Ag nanostructures grown on Si (5 5 12) with native oxide, HF-treated, and reconstructed surfaces, respectively. The crystalline quality of Ag nanostructures on HF-treated substrate was found to improve at higher substrate temperatures during growth.

Laser surface patterning to enhance adhesion of plasma sprayed coatings

In thermal spraying, adhesive bond strength is a feature of surface properties. An adapted surface is studied with prior-surface treatments to enhance interface energy. This study deals with Ni–Al coatings on 2017 aluminum alloy substrate produced by atmospheric plasma spraying. The adherence was evaluated with several controlled surface topographies obtained by grit-blasting and laser surface texturing technique. Adherence has been tested with two different techniques: pull-off test and LASer Adhesion Test. They induce different stresses at the interface. The results showed that the adhesive strength is mostly controlled by a contact adhesion area. A large contact area increases the energy release rate at the interface during coating failures. The bond strength tendency for the two adherence tests is similar: apparent adherence is tripled thanks to laser surface patterning. Fracture propagation is stopped nearby laser-induced holes due to the complex shape and has to deviate inside the coating to maintain crack propagation (inter-splat cracks). The energy at the interfaces being stored locally due to pattern: pattern morphology, pattern localization and powder feed rate are important factors that control the adhesion strength of the thermally sprayed coatings.

Interactions of Hydrogen, CO, Oxygen, and Water with Molybdenum-Modified Pt(111)

Modification of Pt group catalysts by molybdenum is known to improve catalyst performance in a number of important chemical reactions. To investigate fundamental mechanisms responsible for the promoting effect of Mo, temperature-programmed desorption (TPD) and low energy electron diffraction (LEED) experiments were performed to examine the adsorption of O2, D2, CO, and water on Pt(111) modified with submonolayer quantities of molybdenum. Auger electron spectroscopy (AES) was used to detect and quantify the Mo coverage and X-ray photoelectron spectroscopy (XPS) was employed in conjunction with density functional theory (DFT) calculations to identify Mo species present following various surface treatments. The state of Mo on the surface was found to vary depending on prior surface treatment. Treatment with oxygen resulted in a surface molybdenum oxide, whereas treatment with hydrogen resulted in a reduced bimetallic surface. XPS results indicate that high pressures of oxygen create a higher valent oxide tha...