Enhanced localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel in high-concentration hydrochloric acid solutions at room temperature

The localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel (NC-304SS) produced by severe rolling technique, and its conventional polycrystalline 304 stainless steel (CC-304SS) counterpart, were investigated in high-concentration hydrochloric acid solutions at room temperature. NC-304SS can scarcely suffer from localized corrosion in 4 mol/L and 5 mol/L HCl solutions during 5-day immersion tests, and in 1–3 mol/L HCl solutions during thirty-five-day immersion tests. The corrosion rate of NC-304SS was also less than that of CC-304SS during these immersion tests. The improved localized and uniform corrosion resistances of NC-304SS were explained in terms of the adsorption and chemical activity of Cl^? on NC-304SS and CC-304SS characterized by X-ray photoelectron spectroscopy, and the valence electron configurations of NC-304SS and CC-304SS were characterized by ultra-violet photoelectron spectroscopy rather than conventional electrochemical results.     

The effects of binding type on luminescence LED phosphor based on GGG/Ce3+

Luminescence and reflectance spectra of coatings based on gadolinium gallium garnet doped by cerium (GGG/Ce³⁺) with silicone resin or potassium liquid glass compound were analyzed depending on concentration. It was established that the maximum emissions of the coatings at 75 wt.% compound concentration have luminescence band at 570 nm and absorption band at 470 nm. Both bands were detected by absorption or emission of cerium ions in gadolinium gallium garnet. Ce³⁺ ion transition into Ce⁴⁺ ion was observed upon quantum absorption, and the reverse transition was observed upon quantum emission.     

NaCl-induced accelerated oxidation of 304 stainless steel and Fe-Mn-Al alloy at 900°C

The high-temperature corrosion behavior of cold-rolled and annealed 304 stainless steel (304SS) and Fe-29Mn-8Al-2.5Si-2Cr-0.74C alloy coated with 0.002 g cm^–2 NaCl initially were studied at 900°C in air. The corrosion kinetics of the two alloys follow the parabolic rate law. The initial NaCl coating accelerates oxidation of these alloys by oxychlorination and chlorination/oxidation cyclic reactions, and catalytic actions of chloride or chlorine are thought to be the principal causes. A bulky, layered scale as well as some intergranular attack is noted on the annealed 304SS, and intergranular attack distributes over the alloy substrate of the cold-rolled 304SS during a 144 h exposure. With the formation of a compact Al₂O₃ scale to decrease further chlorine attack, the corrosion resistance of Fe-Mn-Al alloy is superior to that of 304SS in this study.     

Hydrothermal synthesis and photoluminescence properties of cerium-doped cadmium tungstate nanophosphor

The present paper reports synthesis and photoluminescence studies of cadmium tungstate (CdWO₄) and cerium-doped cadmium tungstate. The samples were synthesised by low cost and low temperature hydrothermal method and characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and photoluminescence analysis. XRD pattern reveals that the CdWO₄ has monoclinic wolframite structure. The FTIR spectrum of cerium-doped CdWO₄ exhibits broadband below 700 cm^?1 which is due to the δ (Ce–O–C) mode. The TEM images show that size of particle is approximately 60–120 nm in both samples. A broad intense peak was observed at 474 nm when the samples were excited with 263 nm. A broad intense peak was observed at 475 nm when the samples were excited with 600 nm. The intensity of the 474 nm peak decreases with increase in cerium doping concentration. The observation of 475 nm peak when excited with 600 nm is upconversion luminescence. This upconversion emission is due to energy transfer upconversion process involving Cd²⁺ ions and [WO₆]^6? ions. Ce³⁺ ion is responsible for the peak shift of 6 nm.     

Luminescence properties and preparation of Lu<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> powder doped with Ce and Pr ions

Lu₃Al₅O₁₂:Ce³⁺ phosphor powder, which exhibits green emission band, was synthesized by the high-temperature solid-state reaction method with a flux BaF₂. X-ray diffraction (XRD), photoluminescence (PL) spectra, and fluorescent lifetime spectra were used to characterize the structure and luminescent properties of the sample. The XRD patterns indicated that when prepared at 1550 °C for 3 h with 4 wt% flux, Lu₃Al₅O₁₂:Ce³⁺ phosphors powder is the garnet cubic crystal system structure. Photoluminescence (PL) spectra showed that the Lu₃Al₅O₁₂:Ce³⁺ phosphor powder can be effectively excited by near ultraviolet and blue light, emitting broad band peaking at 505 nm, which is attributed to ²F_5/2?→?²D_5/2 transition. The self-concentration quenching mechanism of Ce³⁺ is the dipole–dipole interaction. Small amount of Pr³⁺ increased red light emission at 610 nm. Photoluminescence (PL) spectra and fluorescent lifetime spectra indicated that there was an efficient energy transfer process between Ce³⁺ and Pr³⁺.     

Synthesis,characterization and electrical property of nanocrystalline Cu0.5Ni0.5Ce3O5

Nanocrystalline Cu_0.5Ni_0.5Ce₃O₅ with particle size of about 28 nm was directly synthesized by sol–gel auto-combustion method at room temperature. The overall process involves three steps: formation of homogeneous sol; formation of dried gel; and combustion of the dried gel. Experiments revealed that Cu_0.5Ni_0.5Ce₃O₅ dried gel derived from glycine and nitrate sol exhibits self-propagating combustion at room temperature once it is ignited in air. After auto-combustion, the desired nanocrystalline Cu_0.5Ni_0.5Ce₃O₅ was acquired and further calcination was needed. The auto-combustion was considered as a heat-induced exothermic oxidation–reduction reaction between nitrate ions and carboxyl group. The synthesized powder was characterized by XRD, TG/DTA, SEM and TEM. Nanocrystalline Cu_0.5Ni_0.5Ce₃O₅ was p type semiconducting material. Shapes of the particles are nanocoralloids in nature. The I–V characteristic and electrical properties of the nanocrystalline Cu_0.5Ni_0.5Ce₃O₅ were studied.     

Synthesis and structure of cerium-substituted hydroxyapatite

The aim of this study was to explore the effect of cerium ions on the formation and structure of hydroxyapatite (HAP). All particles, prepared by hydrothermal method, were synthesized at varied X_Ce = Ce/(Ca + Ce) (from 0 to 10%) with the atomic ratio (Ce + Ca)/P fixed at 1.67. Their morphology, composition and crystal structure were characterized by TEM, EPMA, XRD and FTIR. The results showed that in this composition range the apatite structure is maintained, Ce^{3 +} ions could enter the crystal lattice of apatite and substitute Ca^{2 +} ions. The doping of Ce^{3 +} ions resulted in the decrease of the crystallite size with increase in X_Ce. The HAP particles without doping were short rods having a diameter from 10 to 20 nm and a length from 30 to 50 nm. They grew into long needles upon increasing X_Ce.     

304不锈钢表面纳米铝改性有机硅涂层的高温氧化和电化学行为

研究了纳米铝改性有机硅高温涂层的固化、抗650℃高温氧化性能和耐3.5% NaCl水溶液电化学腐蚀性能。当聚氨酯:有机硅的质量分数达到1:3或更高时,有机硅涂料可以在24 h内完成常温固化。制备出的纳米铝改性有机硅高温涂层表面致密,没有微观裂纹等缺陷。纳米铝改性的有机硅涂层显著提高了304不锈钢抗氧化性能,经1028 h氧化实验,基体几乎没有发生氧化,涂层没有出现开裂和剥落。纳米铝改性的有机硅涂层还显著提高了氧化后的304不锈钢耐氯化钠水溶液腐蚀性能,无涂层的304不锈钢氧化后形成的氧化膜低频阻抗仅3.2 Ω·cm²,而涂装涂层的不锈钢的低频阻抗约为1.1×10⁵ Ω·cm²。     

A facile synthesis of silver nanoparticle with SERS and antimicrobial activity using Bacillus subtilis exopolysaccharides

In this study, we report a facile synthesis of silver nanoparticle having SERS and antimicrobial activity using bacterial exopolysaccharide (EPS). Bacillus subtilis (MTCC 2422) was grown in nutrient broth and the extracellular EPS secreted by the organism was extracted and purified. The purified EPS was used for the synthesis of silver nanoparticles. The kinetics of silver nanoparticle synthesis was deduced by varying the exposure time and the concentration of EPS. The rate constant (k) for the synthesis of silver nanoparticle was calculated from the slope of ln(A^∞ ? A^t) versus time plot. The k value was found to be 3.49 × 10^?3, 5.81 × 10^?3 and 5.03 × 10^?3 per min for particle synthesis using 2, 5 and 10 mg/mL EPS, respectively. The nanoparticles synthesised had an average particle size of 5.18 ± 1.49 nm, 1.96 ± 0.77 nm and 2.08 ± 0.88 nm for 2, 5 and 10 mg/mL EPS, respectively. The synthesised particles were characterised using UV-Vis absorbance spectroscopy, high-resolution transmission electron microscopy (HRTEM) attached to EDS (energy dispersive spectroscopy), Fourier transform infrared spectroscopy (FTIR), surface enhanced Raman spectroscopy (SERS) and zeta potential analyser. To our knowledge, this is the first study to report SERS activity of microbial Bacillus subtilis EPS-based synthesis of silver nanoparticle. HRTEM images showed silver nanoparticle entrapped in polysaccharide nanocages. Silver nanoparticle showed higher adherence towards the bacterial surface, with good bactericidal activity against Pseudomonas aeroginosa and Staphylococcus aureus.     

Room-Temperature Ferromagnetism in Chemically Synthesized Ce0.97Cr0.03O2−δ Nanopowders

In this paper, we study structural and magnetic properties of undoped (CeO_2?δ ) and Cr-doped (Ce_0.97Cr_0.03O_2?δ ) cerium oxide nanopowders synthesized by a sol-gel-based method. We estimate the crystallite sizes calculated from X-ray diffraction measurements to be around 9.4±0.3 nm for both CeO_2?δ and Ce_0.97Cr_0.03O_2?δ samples. Raman measurements indicate that microstructural defects are generated when Cr substitutes the Ce in the CeO₂ crystal lattice. Magnetic measurements of the Ce_0.97Cr_0.03O_2?δ sample at 300 K indicate ferromagnetic behavior, with a coercive field of 34.27 Oe and a saturation magnetization of 5.8×10^?4 emu/g. We interpret the nature of room-temperature ferromagnetism by taking into account the exchange interaction between Cr³⁺ ions and oxygen vacancies in CeO₂.     

Production of FeCrAlY and CoCrAlY coatings by laser surface fusion and their oxidation behavior

In this paper the results of a study aimed at coating large areas with FeCrAlY and CoCrAlY alloys by laser surface fusion are described. Metallurgical characteristics and oxidation behavior of the coatings are discussed.The results indicate that fusion of the coating materials was complete and a metallurgical bond was formed between the coatings and the type 304 stainless steel (SS) substrate as a result of laser processing. Some dilution of the coating alloys, in particular the aluminum content, was noticed due to melting of a portion of the substrate. Some small cracks, observed in the CoCrAlY coating, were formed as a result of shrinkage during solidification.Oxidation studies were performed at 1000–1185 °C in air for various times. The coatings, although diluted, showed excellent oxidation resistance and protection, while the type 304 SS substrate deteriorated rapidly. The effect of the thermal and oxidation treatment on the microstructural and chemical stabilities of the coatings are discussed.     

Insights into structure and high-temperature oxidation behavior of plasma electrolytic oxidation ceramic coatings formed in NaAlO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>CrO<Subscript>4</Subscript> electrolyte

Plasma electrolytic oxidation (PEO) ceramic coatings were formed on Ti₂AlNb alloy in various NaAlO₂ electrolytes containing 2 g L^?1, 4 g L^?1, and 6 g ^?1 Na₂CrO₄ additive, respectively. The influence of Na₂CrO₄ additive in NaAlO₂ electrolyte on structure and high-temperature oxidation behavior at 800 °C was investigated. The Na₂CrO₄ additive in the NaAlO₂ electrolyte not only promotes the formation of γ-Al₂O₃ phase and densification of ceramic coatings, but also participates directly in the growth of ceramic coating to form new Cr₃O and (Al_0.948Cr_0.052)₂O₃ phases. The PEO ceramic coatings formed in NaAlO₂ electrolytes with 2 g L^?1 and 4 g L^?1 Na₂CrO₄ additive show better oxidation resistance than those PEO coatings formed in a NaAlO₂ basic electrolyte based on isothermal oxidation tests at 800 °C up to 150 h. A thin and uniform isothermally oxidized layer is formed in the interlayer adjacent the substrate, which protects the substrate from the inward diffusion of oxygen and the outward diffusion of metallic elements. The PEO ceramic coatings formed in NaAlO₂ electrolyte with 4 g L^?1 Na₂CrO₄ additive exhibit the least mass gain among all the specimens, which is only a half of the ceramic coating formed in a NaAlO₂ basic electrolyte without any Na₂CrO₄ additive.     

Combustion synthesis and photoluminescence study of UV emitting LaBaB<Subscript>9</Subscript>O<Subscript>16</Subscript> phosphors

The borate phosphor LaBaB₉O₁₆ doped with Ce³⁺ ion intentionally and successfully synthesized using solution combustion rout using metal nitrates as precursors and urea as fuel. The phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy and photoluminescence spectroscopies. The XRD patterns of the phosphor confirmed the successful crystallization of LaBaB₉O₁₆. The average crystallite size calculated using the Debye Scherer equation. The PL excitation spectra of LaBaB₉O₁₆ exhibited broad spectra peaking at 275 nm. Upon excitation with ultraviolet (UV) radiation at 274 nm the phosphor exhibited a broad band UV emission peaking at a wavelength of 335 nm corresponding to the 4f⁰5d¹??4f¹ transition of the Ce³⁺ ion. Moreover the influence of concentration of Ce³⁺ ion on luminescence properties has also been studied. Optimum concentration of Ce³⁺ ions in the prepared phosphor was found to be 0.05 mol. For this concentration the critical distance R₀ was calculated to be 22.04 Å. Finally, the Stokes shift for the synthesized phosphor was calculated to be 6512 cm^??1 using corresponding excitation and emission.     

Efficiency issues in Ce doped YAG nanocrystals

Nanoparticles of Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺, 1%) were synthesized via the glycothermal method. The particle sizes were estimated by transmission electron microscopy, X-ray diffraction, surface area determination and by dynamic light scattering. We found primary particles of 10–14 nm in diameter, which form agglomerates of approximately 100 nm. For the 4f → 5d transition of Ce³⁺ an internal quantum efficacy of up to 46% was measured. The particles consist of 6–10% of 1,4-butanediol attached on the surface, as determined by carbon content measurements in combination with IR and absorption spectroscopy. In particular, limiting drawbacks due to inevitable surface coatings for glycothermal syntheses and nanoscale associated scattering are elucidated.     

Synthesis of nanometer-sized ceria particles by alternating current electrolysis of aqueous solution

Ceria particles in an average size range from 8 to 70 nm were synthesized from cerium nitrate solutions by electrolysis at AC 0.1–10 Hz using platinum wire electrodes at 25–80 °C. The produced ceria particles dissolved in low pH solutions (pH 1.1–2.7) at a longer electrolysis time (>12 h), which caused the decrease of particle size. Increase of the concentration of Ce³⁺ ions and increase of the electrolysis temperature were effective to enhance the particle yield. Small growth of particles (10–20 nm) was measured when the electrolysis temperature was increased to 60–80 °C. When the applied frequency was increased, the particle size decreased. A theoretical equation of particle size as functions of Ce³⁺ ion concentration, electrolysis temperature and applied frequency was derived. The experimental results were in accordance with the prediction from the theoretical model.     

Thermal stability and oxidation behavior of Al-containing nanocrystalline powders produced by cryomilling

Al-containing nanostructured coatings provide excellent protection from high temperature corrosion. Aluminum oxide scales generally provide better oxidation resistance and yield lower oxidation rates than other oxide scale compositions. In this study, nanocrystalline 316L stainless steel containing 6 wt.% Al was synthesized using cryogenic milling (cryomilling). Complete alloying was obtained after 32 h of milling and the average grain size was found to be 7 nm. High temperature thermal stability and oxidation kinetics of the alloyed powders were examined. The powder demonstrated good grain growth stability at 500 °C, at which point, the powders had been heat treated for 120 h and the average grain size was found to be 11.4 nm. The oxidation kinetics of the powder were studied for 48 h at 500, 800, and 1,000 °C, respectively. For comparison, conventional 316LSS powder was also tested. Nanocrystalline 316LSS-6 wt.% Al showed lower weight gain than the conventional 316LSS powders. During the oxidation of nanocrystalline 316LSS-6 wt. % Al at 500 °C, protective aluminum oxide scale formed at the surface. At 800 °C and 1,000 °C, most of the nanocrystalline 316LSS-6 wt.% Al particles showed completed outer aluminum oxide scale. However, at 800 and 1,000 °C, some particles showed growth of chromium oxide scale underneath the aluminum oxide scale. In those samples, Al depletion was also observed due to a non-homogenous distribution of Al during cryomilling. The activation energy of the oxidation reaction was calculated and was found to be affected by the enhancement of the grain boundary diffusion in nanostructured particles.     

Characterization and Performance of AlTiN,AlTiCrN, TiN/TiAlN PVD Coated Carbide Tools While Turning SS 304

This study presents the physical, mechanical properties and dry turning performance of AlTiN, AlTiCrN, and TiN/TiAlN coatings produced on K-grade tungsten carbide insert by advanced physical vapor deposition technique. Scanning electron microscopy, microhardness tester, and scratch tester were used to examine surface morphology, coating thickness, microstructure, microhardness, and adhesion of coating. The performance in terms of cutting force and temperature of AlTiN, AlTiCrN, and TiN/TiAlN coated inserts was evaluated while dry turning of SS 304 steel. SS 304 is considered as “difficult-to-cut” material due to its exotic properties. The experiments were conducted at cutting speed of 140, 200, 260, and 320 m/min. Feed and depth of cut were kept constant and their values were 0.20 mm/rev and 1 mm, respectively. Experimental observations depicts that AlTiCrN coated insert demonstrated better performance because of its good adhesion and high oxidation resistance followed by TiN/TiAlN coated insert. TiN/TiAlN coated insert exhibited higher cutting temperature than AlTiCrN and AlTiN coated inserts. The findings of the study should also provide economic machining solution in case of dry turning of SS 304 stainless steel.     

Electrodeposited cerium film as chromate replacement for tinplate

The cerium film was prepared on tinplate by electrodeposition method. Sulfide-stain resistance of the Ce-passivated, unpassivated and Cr-passivated tinplates was evaluated using a cysteine tarnish test. Corrosion behavior of these tinplates in contact with 3.5% NaCl solution and 0.1 M citric-citrate buffer solution was investigated using Tafel measurement and electrochemical impedance spectroscopy measurement, respectively. The adhesion of epoxyphenolic lacquer to the Ce-passivated tinplate was checked using a cross hatch cutter. The morphology, composition and thickness of the cerium film were studied by atomic force microscopy, X-ray photoelectron spectroscopy and X-ray fluorescence spectrometry. According to the results, the Ce-passivated tinplate shows the best sulfide-stain resistance and the best corrosion protection property compared with the unpassivated and Cr-passivated tinplates. The adhesion of epoxyphenolic lacquer to the Ce-passivated tinplate is good. The cerium film is composed of the closely packed particles of about 50-200 nm in diameter. The film mainly consists of cerium and oxygen, which mainly exist as CeO₂, Ce₂O₃ and their hydrates such as Ce(OH)₄, Ce(OH)₃. The total cerium amount of the film is about 0.110 g/m².     

Synthesis and luminescence of Sr3Al2O6:Ce3+ powders synthesized by solid state reaction method with addition of H3BO3

Sr₃Al₂O₆:Ce³⁺ powders were synthesized using a solid state reaction method in air with addition of H₃BO₃. The effects of Ce³⁺ dopant concentrations and the weight ratio (wt) of H₃BO₃ to total raw materials weight on the formation of Sr₃Al₂O₆:Ce³⁺ samples were investigated. Single-phase and well-crystallized Sr₃Al₂O₆:Ce³⁺ samples can be obtained when the addition of H₃BO₃ is lower than 7 wt%. The excitation spectrum indicates that Sr₃Al₂O₆:Ce³⁺ phosphor powders exhibit two excitation bands centered at 345 and 462 nm. The emission spectrum shows that Sr₃Al₂O₆:Ce³⁺ phosphor powders exhibit an emission band peaked at 536 nm when excited at 462 nm. Sr₃Al₂O₆:Ce³⁺ sample at the Ce³⁺ concentration of 5 mol% shows the strongest emission intensity. The addition of H₃BO₃ has obvious influence on phase and emission intensity of Sr₃Al₂O₆:Ce³⁺ phosphors. The results show that the Sr_2.95Ce_0.05Al₂O₆ sample with the 7 wt% addition of H₃BO₃ has the highest emission intensity and the longest lifetime.     

Influence of multi-interfacial structure on mechanical and tribological properties of TiSiN/Ag multilayer coatings

The TiSiN/Ag multilayer coatings with bilayer periods of ~50, 65, 80, 115, 150, and 410 nm have been deposited on Ti6Al4 V alloy by arc ion plating. In order to improve the adhesion of the TiSiN/Ag multilayer coatings, TiN buffer layer was first deposited on titanium alloy. The multi-interfacial TiSiN/Ag layers possess alternating TiSiN and Ag layers. The TiSiN layers display a typical nanocrystalline/amorphous microstructure, with nanocrystalline TiN and amorphous Si₃N₄. TiN nanocrystallites embed in amorphous Si₃N₄ matrix exhibiting a fine-grained crystalline structure. The Ag layers exhibit ductile nanocrystalline metallic silver. The coatings appear to be a strong TiN (200)-preferred orientation for fiber texture growth. Moreover, the grain size of TiN decreases with the decrease of the bilayer periods. Evidence concluded from transmission electron microscopy revealed that multi-interfacial structures effectively limit continuous growth of single (200)-preferred orientation coarse columnar TiN crystals. The hardness of the coatings increases with the decreasing bilayer periods. Multi-interface can act as a lubricant, effectively hinder the cracks propagation and prevent aggressive seawater from permeating to substrate through the micro-pores to some extent, reducing the friction coefficient and wear rates. It was found that the TiSiN/Ag multilayer coating with a bilayer period of 50 nm shows an excellent wear resistance due to the fine grain size, high hardness, and silver-lubricated transfer films formed during wear tests.