Different Degrees Of Surface Oxidation Research Articles

Comparing lead and copper activation on pyrite with different degrees of surface oxidation

Copper ions are often added in the flotation of gold-bearing pyrite to activate pyrite so that high gold and pyrite recoveries can be achieved. However, the residual copper ions are problematic in subsequent cyanidation by consuming cyanide. There is a great need to replace copper ions by lead ions which are beneficial to cyanidation. This study compared lead and copper activation on pyrite with different degrees of surface oxidation at pH 5.0. Flotation tests indicated that lead and copper ions were equally efficient in activating slightly oxidised pyrite and both produced a high pyrite recovery. For moderately oxidised pyrite, copper ions were superior to lead ions in activating pyrite. However, for severely oxidised pyrite, lead ions prevailed over copper ions in activating pyrite. By Cryogenic X-ray photoelectron spectroscopy analysis, it was found that the different behaviour of lead and copper ions in activating pyrite was governed by the lead and copper species adsorbed on pyrite surface. In general, pyrite oxidation generated iron and sulphur oxidation species which inhibited the adsorption of lead and copper ions on pyrite surface. Lead ions had stronger affinity to oxidised pyrite than copper ions but pyrite flotation required a higher amount of lead-activating products than copper-activating products.

The interplay between atmospheric corrosion and antimicrobial efficiency of Cu and Cu5Zn5Al1Sn during simulated high-touch conditions

The interplay between atmospheric corrosion and antimicrobial efficiency of bare Cu and Cu5Zn5Al1Sn was studied upon exposures simulating high-touch surface conditions. The survival of the bacteria Bacillus subtilis during surface contact with Cu and Cu5Zn5Al1Sn was examined under different degrees of surface oxidation, tarnishing, wettability and copper ion release. Depending on surface conditions complete bacteria inhibition was obtained within 4 min on Cu and within 6–10 min on Cu5Zn5Al1Sn. The antibacterial efficiency increases slightly with copper release rate and is governed by complex interactions between the corroded metal surface, bacteria and extracellular polymeric substances produced by the bacteria.

Quantification of microplastics along the Caribbean Coastline of Colombia: Pollution profile and biological effects on Caenorhabditis elegans

The Caribbean Coast of Colombia has a flourishing plastic industry with weak and insufficient waste management policies and practices, leading to plastic pollution along its touristic beaches. In this work, primary and secondary microplastics (MPs) were surveyed at four different locations along the Colombian Caribbean Coast. Primary microplastics, specifically white new plastic pellets, represented the largest amount of MPs found, with densities decreasing in the order Cartagena > Coveñas > Puerto Colombia > Riohacha. This distribution was connected to the vicinity of MPs sources, marine currents and wind direction. The presence of secondary MPs was associated with urban centers and proximity to river mouths. The FTIR characterization showed polyethylene as the predominant resin type, with different degrees of surface oxidation. Aqueous extracts from sampled MPs were tested on Caenorhabditis elegans. Secondary MPs elicited greater toxicological responses than pellets, especially those from Cartagena Bay, suggesting MPs act as carriers for biologically-active pollutants.

A new experimental apparatus for emissivity measurements of steel and the application of multi-wavelength thermometry to continuous casting billets.

An experimental apparatus has been designed for measuring the emissivity of a steel surface in both vacuum and oxidation atmosphere. The sample is heated with the method of electromagnetic induction in order to ensure the temperature uniformity. The radiance emitted from a sample is measured using a fiber-optic Fourier transform infrared spectrometer. Using this unique apparatus, we investigated the spectral (2-6 μm) and directional (0°-86°) emissivity of stainless steel 304 with different degrees of surface oxidation at temperatures ranging from 800 to 1100 °C. The experimental results show that the emissivity increases slightly with increasing temperature, which accords with the Hagen-Rubens relation. The emissivity increases rapidly at the initial stage of oxidation, but gradually reaches to a constant value after 20 min. In addition, the directional emissivity has a maximum value at the measuring angle of about 75°. The maximum uncertainty of emissivity is only 3.0% over all the measuring ranges, indicating that this experimental apparatus has a high reliability. In order to measure the surface temperature of casting billets based on multi-wavelength thermometry, the bivariate emissivity function with the two variables, wavelength and temperature, is determined. Temperature measurement results based on our technique are compared with those from common dual-wavelength radiation thermometry. Our approach reduces the measured temperature fluctuation from ±20.7 °C to ±2.8 °C and reflects the temperature variation with the changes of production parameters in real time.

The effect of saline water on the critical degree of coal surface oxidation for coal flotation

In this work, the effects of water with different salinities on the flotation of oxidized coals were studied and the underlying mechanisms were revealed. Flotation tests were conducted using coal samples with different degrees of surface oxidation and in water of different salinities. A critical degree of coal surface oxidation, above which the coal particles cannot be recovered by true flotation, was observed in flotation with all types of water. It is interesting to find that the critical degree of surface oxidation increased with water salinity, suggesting that coal flotation in saline water had a better tolerance for surface oxidation. The effects of water salinity on the flotation of oxidized coals were studied by investigating the change of coal surface properties and froth stability. On one hand, the surface hydrophobicity of oxidized coals decreased in saline water, which was unfavorable for coal flotation. On the other hand, the compression of the electric double layer in saline water could increase the flotation efficiency by reducing the electrostatic repulsion between particle and bubble. In addition, smaller bubbles and a higher stability froth were generated in saline water, which could also increase the flotation efficiency.

Understanding and improving the flotation of coals with different degrees of surface oxidation

In this study, the research was designed to answer two questions: how does the degree of surface oxidation affect coal flotation and how to improve the flotation of coals with different degrees of surface oxidation? The degree of coal surface oxidation was quantified as the percentage of oxidized carbon by X-ray photoelectron spectroscopy (XPS), and flotation tests were conducted to determine the flotation behavior of coals with different degrees of surface oxidation. It was found that coal flotation performance decreased with an increase in the degree of surface oxidation. A critical degree of coal surface oxidation was observed in flotation and, above it, the true flotation of coals was impossible. To improve the flotation of oxidized coals, diesel (a nonpolar collector) and Triton X-100 (a polar collector) were mixed as a composite collector to enhance the hydrophobicity of both un-oxidized and oxidized coal surfaces simultaneously. Flotation tests demonstrated a significant increase in the flotation of oxidized coals after the addition of X-100. A close relationship between the degree of coal surface oxidation and the proportion of X-100 in the composite collector used to achieve the optimal coal flotation was identified: the higher the degree of coal surface oxidation, the higher the proportion of X-100 required. This study indicates that the best composite collector used to float an oxidized coal may be formulated based on the degree of surface oxidation.

Study on the Multi-wavelength Emissivity of GCr15 Steel and its Application on Temperature Measurement for Continuous Casting Billets

A method for measuring the multi-wavelength emissivity of a steel surface is proposed, and an applicable experimental apparatus is designed. Multi-wavelength radiant energy emitted from a sample was measured using a fiber-optic spectrometer and its temperature measured using a NiCrSi/NiSiMg thermocouple. Utilizing the unique vacuum control and background noise-shielding systems, we investigated the multi-wavelength emissivity of GCr15 steel at three different degrees of surface oxidation at temperatures ranging from 1000 \(^{\circ }\)C to \(1100\,^{\circ }\)C. The experimental results show that the multi-wavelength (0.7 \(\upmu \)m–0.9 \(\upmu \)m) emissivity increased substantially, from 0.409–0.565 to 0.609–0.702, once the steel was oxidized. In addition, the emissivity increased slightly with increasing temperature, but the trends for emissivity and wavelength were similar. To measure the surface temperature of casting billets based on multi-wavelength thermometry, the functional relationships between emissivity and wavelength at different extents of oxidation were determined. Temperature measurements based on our technique were compared with those from common colorimetric thermometry. Our approach reduced the temperature fluctuation from \(\pm 23\,^{\circ }\)C to \(\pm 3.5\,^{\circ }\)C, indicating that a reliable measurement of the multi-wavelength emissivity of GCr15 steel is obtained using this experimental apparatus.

The influence of sterilization on nitrogen-included ultrananocrystalline diamond for biomedical applications

Diamond has shown great potential in different biomedical applications, but the effects of sterilization on its properties have not been investigated. Here, we studied the influence of five sterilization techniques (solvent cleaning, oxygen plasma, UV irradiation, autoclave and hydrogen peroxide) on nitrogen-included ultrananocrystalline diamond. The chemical modification of the diamond surface was evaluated using X-ray photoelectron spectroscopy and water contact angle measurements. Different degrees of surface oxidation and selective sp2 bonded carbon etching were found following all sterilization techniques, resulting in an increase of hydrophilicity. Higher viabilities of in vitro mouse 3T3 fibroblasts and rat cortical neuron cells were observed on oxygen plasma, autoclave and hydrogen peroxide sterilized diamond, which correlated with their higher hydrophilicity. By examination of apatite formation in simulated body fluid, in vivo bioactivity was predicted to be best on those surfaces which have been oxygen plasma treated and lowest on those which have been exposed to UV irradiation. The charge injection properties were also altered by the sterilization process and there appears to be a correlation between these changes and the degree of oxygen termination of the surface. We find that the modification brought by autoclave, oxygen plasma and hydrogen peroxide were most consistent with the use of N-UNCD in biological applications as compared to samples sterilized by solvent cleaning or UV exposure or indeed non-sterilized. A two-step process of sterilization by hydrogen peroxide following oxygen plasma treatment was then suggested. However, the final choice of sterilization technique will depend on the intended end application.

ВЛИЯНИЕ ОКИСЛИТЕЛЬНОЙ ОБРАБОТКИ НА СВОЙСТВА УГЛЕРОДНЫХ МАТЕРИАЛОВ ИЗ МИКРОКРИСТАЛЛИЧЕСКОЙ ЦЕЛЛЮЛОЗЫ

Модифицирование поверхности карбонизованной при 450 °С микрокристаллической целлюлозы (МКЦ-450) растворами окисляющих агентов различной силы: 30% H2O2, 3N H2SO4, олеумом и хлорсульфоновой HSO3Cl кислотой приводит к получению углеродных материалов (УМ) с различной степенью окисления поверхности. Полученные УМ были охарактеризованы методами ИК-спектроскопии, БЭТ, элементного и рентгеноспектрального анализа (РСА). Результаты показали, что больше карбоксильных и гидроксильных поверхностных групп вводятся в состав УМ в результате окисления олеумом и HSO3Cl, чем окисляющими растворами Н2О2 и 3N H2SO4. Установлено, что в образцах МКЦ/олеум и МКЦ/ HSO3Cl значительная часть кислорода входит в состав НSO3- поверхностных частиц, содержание серы в которых составляет около 2,3–2,5% ат. Выяснено, что окисленный образец МКЦ/олеум проявляет активность в тестовых реакциях каталитического гидролиза целлюлозы и этерификации уксусной кислоты с этанолом.

Influence of Functional Groups on Desorption of Organic Compounds from Carbon Nanotubes into Water: Insight into Desorption Hysteresis

Adsorption-desorption of nitrobenzenes, phenols, and anilines on five multiwalled carbon nanotubes (MWCNTs) with different degrees of surface oxidation were investigated to examine the influence of functional groups of both organic chemicals and CNTs on desorption hysteresis. Desorption hysteresis was not observed for nitrobenzenes, phenols, and 4-nitroaniline from all MWCNTs. Significant desorption hysteresis was observed for aniline and 4-methylaniline on surface-oxidized MWCNTs but not on unoxidized MWCNTs. Formation of an irreversible amide bond (i.e.,-CONH-) by amidation reaction of amino group of anilines with oxygen-containing groups (i.e., carboxyl or lactonic groups) on MWCNTs was observed. We proposed that desorption hysteresis could be attributed to the immobilization of organic compounds on the surface of CNTs resulting from the irreversible chemical reaction/binding. The irreversible chemical immobilization is compound functional group selective and dependent on the surface oxygen-containing groups of CNTs. Hysteresis index (HI) values of aniline or 4-methylaniline on MWCNTs increased with the amounts of oxygen-containing groups on MWCNTs. Moreover, HI values of anilines on a given oxidized MWCNT followed an order of 4-nitroaniline < 4-chloroaniline < aniline < 4-methylaniline.

Influence of Surface Oxidation on the Aggregation and Deposition Kinetics of Multiwalled Carbon Nanotubes in Monovalent and Divalent Electrolytes

The aggregation and deposition kinetics of two multiwalled carbon nanotubes (MWNTs) with different degrees of surface oxidation are investigated using time-resolved dynamic light scattering (DLS) and quartz crystal microbalance with dissipation monitoring (QCM-D), respectively. Carboxyl groups are determined to be the predominant oxygen-containing surface functional groups for both MWNTs through X-ray photoelectron spectroscopy (XPS). The aggregation and deposition behavior of both MWNTs is in qualitative agreement with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The critical coagulation concentration (CCC) of the highly oxidized MWNTs (HO-MWNTs) is significantly higher than the lowly oxidized MWNTs (LO-MWNTs) in the presence of NaCl (210 and 53 mM, respectively) since HO-MWNTs have a higher surface charge density. In contrast, the aggregation inverse stability profiles of HO-MWNTs and LO-MWNTs are identical and yield comparable CCCs (0.9 and 1.0 mM, respectively) in the presence of CaCl(2). Similar to the results obtained from the aggregation study, HO-MWNTs are considerably more stable to deposition on silica surfaces compared to LO-MWNTs in the presence of NaCl. However, both MWNTs have the same propensity to undergo deposition in the presence of CaCl(2). The remarkable similarity in the aggregation and deposition kinetics of HO-MWNTs and LO-MWNTs in CaCl(2) may be due to Ca(2+) cations having a higher affinity to form complexes with adjacent carboxyl groups on HO-MWNTs than with isolated carboxyl groups on LO-MWNTs.

Characterization of the thrombogenic potential of surface oxides on stainless steel for implant purposes

Marketed stents are manufactured from various metals and passivated with different degrees of surface oxidation. The functional surface oxides on the degree of antithrombotic potential were explored through a canine femoral extracorporeal circuit model. Related properties of these oxide films were studied by open-circuit potential, current density detected at open-circuit potential, the electrochemical impedance spectroscopy, transmission electron microscopy, Auger spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. Experimental evidences showed that blood clot weight after a 30-min follow-up was significantly lower for the stainless steel wire passivated with amorphous oxide (AO) compared to the wire passivated with polycrystalline oxide (PO) or commercial as-received wire coils (AS). Surface characterizations showed that a stable negative current density at open-circuit potential and a significant lower potential were found for the wire surface passivated with AO than for the surface passivated with PO. Time constant of AO is about 25 times larger than that of polycrystalline oxide. Significant difference in oxide grain sizes was found between PO and AO. Surface chemistries revealed by the AES and XPS spectra indicated the presence of a Cr- and oxygen-rich surface oxide for AO, and a Fe-rich and oxygen-lean surface oxide for PO. These remarkable characteristics of AO surface film might have a potential to provide for excellent antithrombotic characteristics for the 316L stainless steel stents.

Characterisation of surface oxides on carbon and their influence on dynamic adsorption

The aim of this work is to gain a better fundamental understanding of the nature of surface oxide sites present on carbon surfaces, and their role in the adsorption process. A number of model carbon substrates with different degrees of surface oxidation and similar textural properties were prepared using a wide range of solution and gaseous phase oxidation techniques. Some of the carbons were characterised using established techniques including flow microcalorimetry, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The results showed that both carboxylic acid (–CO 2H) and ether/hydroxyl (C–O) surface oxygen complexes were introduced to all of these carbons as a result of the oxidation processes. The number, strength and thermal stability of the surface groups formed were dependent on the nature of the base material and the oxidation conditions employed. The dynamic adsorption performance of the carbons against hexane, under humid conditions, was found to be mainly determined by the quantity of acidic surface functional groups. However, the location, strength of interaction and availability of the surface oxygen complexes to the adsorbate molecules, are also thought to affect the breakthrough characteristics of the carbons used in this work.

Catalytic oxidation of Fe(II) by activated carbon in the presence of oxygen.: Effect of the surface oxidation degree on the catalytic activity

The catalytic oxidation of Fe(II) species in aqueous solution by activated carbons with different degrees of surface oxidation is described. The parent activated carbon was oxidized with aqueous solutions of nitric acid or hydrogen peroxide, and submitted to thermal treatment at 373, 523 and 773 K. The activated carbons prepared were characterized by N 2 adsorption and temperature-programmed desorption, and their catalytic behavior was determined by measuring the oxidation rate of Fe(II) to Fe(III) and the generation of hydrogen peroxide. Catalytic activity is a function of the nature of oxygen surface groups generated by oxidation.

Study of Water Adsorption on Activated Carbons with Different Degrees of Surface Oxidation

A carbon of wood origin was oxidized with different oxidizing agents (nitric acid, hydrogen peroxide, and ammonium persulfate). The microstructural properties of the starting material and the oxidized samples were characterized using sorption of nitrogen. The surface acidity was determined using Boehm titration and potentiometric titration. The changes in the surface chemistry were also studied by diffuse reflectance FTIR. Water adsorption isotherms were measured at three different temperatures close to ambient (relative pressure from 0.001 to 0.3). From the isotherms the heats of adsorption were calculated using a virial equation. The results indicated that the isosteric heats of water adsorption are affected by the surface heterogeneity only at low surface coverage. In all cases the limiting heat of adsorption was equal to the heat of water condensation (45 kJ/mol).

The effect of surface treatment on the interfacial properties in carbon fibre/epoxy matrix composites

Carbon fibres with different degrees of surface oxidation, as well as epoxy-sized fibres, were used to prepare epoxy composites in order to compare the effects of the fibres surface chemistry on the interfacial properties. X-ray photoelectron spectroscopy, water vapour adsorption measurements and contact angle examination were applied to characterize the carbon fibre surfaces. A correlation was found between the content of primary adsorption sites on the fibre surface and interlaminar shear strength (ILSS) of the composites. Higher values of ILSS obtained for the oxidized fibres containing composites are proposed to be due to the higher concentration of carboxylic groups created on the oxidized fibres surface and to the creation of chemical bonds at the fibre/epoxy matrix interface. Enthalpy of cure, reaction peak temperature and glass transition temperature of the composites were determined by differential scanning calorimetry.

Evaluation of interfacial properties between carbon fibres and semicrystalline thermoplastic matrices in single-fibre composites

The interfacial properties between pitch-based carbon fibre and semicrystalline thermoplastic matrices have been investigated by using the fragmentation test on single-fibre composites. For this purpose, fibres with seven different degrees of surface oxidation were prepared. From the fragmentation test, it was found that oxidization of carbon fibre reduces the fibre fragment length. Further, the length is also influenced by the nature of resin used as matrix. The morphology of crystallites formed on the fibres has been studied. Based on these results, the interfacial properties of carbon fibre and thermoplastic resins are discussed.