Investigations on a nitriding process of molybdenum thin films exposed to (Ar-N2-H2) expanding microwave plasma

Nitriding treatments using various (Ar-N₂-H₂) gas mixtures are performed on thin molybdenum films coated on Si (100) substrates, in an expanding microwave plasma reactor.The electron density measured in (Ar-25%N₂-30%H₂) and (Ar-8%N₂-10%H₂) plasma as well as the electron energy distribution function (EEDF) vary with the distance from the centre of the discharge and are large compared to the corresponding parameters found in (Ar-30%N₂-12%H₂) gas mixture and pure N₂ gas. In such ternary gas mixtures, the mean electron energy ranges between 0.5 and 0.7 eV. A nitride compound of tetragonal-like structure is formed in the whole film thickness of molybdenum heated at 873 K and exposed to (Ar-25%N₂-30%H₂) and (Ar-8%N₂-10%H₂) gas mixtures for exposure times of 20 min duration. It consists of small columnar grains ranging in size from 20 to 30 nm in the growth direction. The nitrogen diffusion profiles are fitted to the Fick's second law by introducing a diffusion coefficient ranging between 5 × 10^− 10 and 5 × 10^− 9 cm²s^− 1 within the accuracy of the method. The diffusion coefficient found from previous measured pressure transients is equal to about 10^− 10 cm²s^− 1. The plasma composition as well as the distance from the centre of the discharge seems to play a role on the reduction of oxides, only. An (Ar-25%N₂-30%H₂) nitriding treatment carried out at 8 cm from the centre of the discharge leads to oxide amount twice lower than the one measured after an (Ar-8%N₂-10%H₂) nitriding treatment carried out at 12 cm from the centre of the discharge. Because of the low ion energies, the reduction of oxides is probably mainly confined to hydrogen species.     

Cementite decomposition and coke gasification in He and H2-He gas mixtures

Cementite decomposition and coke gasification were investigated by first carburisation of iron samples at 700 °C in a 50%CO-49.81%H₂-0.19%H₂O gas mixture for 4 h and then further treatment in He and He-H₂ gas at the same temperature for different time periods. After carburisation cementite is formed at the iron surface covered by a coke layer. Scanning electron microscopy (SEM) shows carbon filaments and columnar layered bulk graphite in the carbon deposits. X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveal only cementite as the iron-containing phase in the coke. Cementite in the iron specimen and cementite in the coke show a different decomposition behaviour during treatment in He and He-H₂ gases. In the iron specimen cementite decomposition proceeds fast and is comparable in both He and He-H₂ gases. However, cementite in the coke is much more stable than that at the sample surface especially in the case of only He gas. By using thermogravimetric analysis (TGA) no gasification is detected in He gas but very significant gasification in He-H₂ gas mixture until all the coke is removed. By adding some H₂O into the He-H₂ gas the gasification process is accelerated.     

Ni/Cu定向结构涂层在不同浓度H2SO4中的耐蚀性能

为了研究Cu元素对Ni基合金定向结构涂层耐腐蚀性能的影响,向Ni60合金粉末中添加了5%Cu(质量分数,下同),制备了定向结构Ni60/Cu复合涂层。采用电化学试验和浸泡试验,评估了涂层在不同浓度H₂SO₄溶液中的电化学腐蚀特性和浸泡腐蚀性能,探讨了涂层在不同浓度H₂SO₄溶液中的腐蚀行为。结果表明,涂层在不同浓度H₂SO₄溶液中的腐蚀均表现为活化-钝化-过钝化的过程,电化学阻抗谱在整个时间常数内具有典型的容抗特征,H₂SO₄溶液浓度从5%增至80%时,电荷转移电阻先减小后增大,涂层的耐腐蚀性呈现先降低后升高的趋势。随着H₂SO₄溶液浓度的增加,涂层表面的腐蚀程度先加剧后逐渐减缓,且在H₂SO₄溶液浓度为40%时,腐蚀电位移至最负,腐蚀电流密度增至最大。但在H₂SO₄溶液浓度达到80...     

Investigation of reaction between LiNH2 and H2

The reactions for LiNH₂ under a H₂ and an Ar flow were investigated, respectively. The results showed that LiNH₂ can be converted into LiH and NH₃ by reacting with H₂ under a H₂ flow condition, whereas LiNH₂ is converted into Li₂NH and NH₃ by decomposition under an Ar flow. Moreover, the reaction between LiNH₂ and H₂ can be accelerated by mixing LiNH₂ with LiH as well as doping LiNH₂ with TiCl₃. The confirmation of reaction between LiNH₂ and H₂ is helpful for the deeper insight in the systems of Li–N–H and Li–Mg–N–H for hydrogen storage materials.     

Corrosion characteristics of LiBH4 film exposed to a CO2/H2O/O2/N2 mixture

LiBH₄ films were prepared by pulsed laser deposition using a LiB target in a background pressure of hydrogen. The corrosion characteristics of LiBH₄ films were measured by exposing them to a gas mixture of CO₂/H₂O/O₂/N₂ at ambient temperature for 1–24 h. Scanning electron microscopy images show some cracks on the surface of corrosion films, which could act as easy paths for H₂O and CO₂ to further react with Li⁺ and B³⁺. The X-ray photoelectron spectroscopy results and theoretical analysis show that LiBH₄ tends to react with H₂O and CO₂ to form Li₂B₄O₇, Li₂CO₃ and LiOH during the corrosion process.     

Parallelogram-like microparticles of calcium dihydrogen phosphate monohydrate (Ca(H2PO4)2·H2O) obtained by a rapid precipitation route in aqueous and acetone media

Calcium dihydrogenphosphate monohydrate (Ca(H₂PO₄)₂·H₂O) was prepared by a rapid and simple precipitation method using CaCO₃ and H₃PO₄ in aqueous and acetone media at ambient temperature. The thermal transformation of the synthesized Ca(H₂PO₄)₂·H₂O at 500 °C was obtained to be CaP₂O₆ occurred through the dehydration and the phosphate condensation reactions, as revealed by thermoanalytical techniques (TG/DTG/DTA). The synthesized Ca(H₂PO₄)₂·H₂O and its decomposition product CaP₂O₆ were characterized by X-ray powder diffraction (XRD), Fourier transfer infrared (FTIR) spectroscopy and scanning electron microscope (SEM). Thermal behavior and the morphology of the synthesized Ca(H₂PO₄)₂·H₂O in aqueous and acetone media are compared with those of other works. The SEM micrograph of Ca(H₂PO₄)₂·H₂O show parallelogram-like microparticles containing small and large grain sizes. The aqueous and acetone media are proposed to play an important role in the synthetic process of calcium phosphates in exhibiting different physical properties, which are important for specific applications.     

Study of Conductivity of K41X Chromia Forming Alloy in High Temperature Electrolysis Environment

Alloy K41X has been proposed as interconnect material for high temperature vapor electrolysis (HTVE) devices. This chromia forming alloy (alloy K41X) was oxidized at 800 °C in a thermobalance in oxidizing (synthetic air) and reducing (Ar–1 %H₂–9 %H₂O) environments for 250 h. The evolution of the contact resistance was evaluated using a dedicated device under the same conditions. There were higher oxidation kinetics rate in air than in Ar–1 %H₂–9 %H₂O but surprisingly, the corresponding area specific resistance (ASR) values were 20 times higher in Ar–1 %H₂–9 %H₂O mixture than in air. Additional tests and analyses (exposure in Ar–D₂–H₂O environment, GD-OES and SIMS analyses) clearly showed that the higher ASR value can be attributed to the presence of hydrogen in the oxide scale when exposed in Ar–H₂–H₂O mixture. In situ changes of atmosphere during ASR measurement showed the rapid kinetics for hydrogen desorption.     

Comparative studies of the electrochemical behaviour of aluminium in 1 M H2SO4/water and in 1 M H2SO4/dimethylformamide (anhydrous)

Anodic current potential curves of Al (99.999%) in H₃O/1 M H₂SO₄ are quite different from that in anhydrous DMF/1 M H₂SO₄. Al is active in DMF/H₂SO₄, and at a potential of 0.4 V (SCE) gives a constant current-time curve, where in H₂O/H₂SO₄ the current decreases in the same time to a low value. In DMF, it decreases also at a later step. This happens when the solution is saturated with anhydrous Al₂(SO₄)₃ (0.18 g l^?1). Comparison of cut-off curves after polarization to 0.4 and 3 V (SCE) shows that the curves are similar, but the potential decreases more slowly in DMF/H₂SO₄ than in H₂O/H₂SO₄. This proves that the space charge of Al with a Al₂(SO₄)₃ layer in anhydrous DMF has a much higher half-time of potential decay than that of Al with an oxide layer in water. This can be explained on the basis that the oxide layer in water has incorporated water molecules and perhaps H⁺ or OH^?, whereas the anhydrous Al₂(SO₄)₃ layer is free from solvent molecules, and the ionic conductivity of Al₂(SO₄)₃ itself is very low. The high space charge in DMF/H₂SO₄ could also be shown by potentiostatic measurements using an interrupter. The different behaviour of Al, when passivated by salt layers on the one hand or by oxide layers on the other, is discussed.     

稀硫酸溶液清洗电镀铜晶种(英文)

采用稀硫酸溶液清洗以除去在铜晶种表面形成的氧化物。将通过溅射沉积在Ti/Si(100)薄片上生成的铜晶种暴露在空气中来生长原生铜氧化物。用稀硫酸溶液和TS-40A碱性清洗剂除去原生铜氧化物。先用TS-40A碱性清洗剂预处理以除去铜晶种表面的有机物,再用稀硫酸溶液除去铜氧化物(Cu2O和CuO)以及有机物和Cu(OH)2。     

Oxidation kinetics of Y‐doped FeCrAl‐alloys in low and high pO2 gases

A model Fe‐20Cr‐5Al‐0.05Y alloy was oxidized in Ar‐20%O₂ and Ar‐4%H₂‐7%H₂O at 1200–1300 °C. Two‐stage oxidation experiments using oxygen isotope tracers showed that inward oxygen diffusion was predominant in both gases, but more isotope exchange was observed in the H₂/H₂O gas reaction. The alumina scales formed in both gases were composed of columnar grains, the lateral size of which increased linearly with depth beneath the scale surface. Thermogravimetric measurement of oxygen uptake revealed kinetics which were intermediate to parabolic and cubic kinetic rate laws. A model based on grain boundary diffusion control coupled with competitive oxide grain growth accounts satisfactorily for the results when the requirement for a divergence‐free flux within the scale is imposed. This treatment shows that the oxide grain boundary diffusion coefficient is lower when H₂O is the oxidant. It is concluded that hydrogen slows the grain boundary diffusion process by altering the nature of the diffusing species.     

Corrosion behaviour of cermet-based coatings with a bond coat in 0.5 M H2SO4

The corrosion behaviour of an HVOF Ni–5Al/WC–17Co coating on Al-7075 is investigated in 0.5 M H₂SO₄. In the temperature range of 25–45 °C, the coating exhibits pseudopassivity that effectively protects from localized corrosion. At 25 °C, pseudopassivity proceeds via three stages: during the first stage, oxidation of W in the binder phase occurs. The second stage is characterized by oxidation of W in both the binder and the carbide particles. The third stage is characterized by intensive hydration of WO₃ and formation of Co₃O₄. During the second and third pseudopassive stages, the formation of a bi-layer surface film is postulated. The inner layer, consisting of anhydrous oxides, has a barrier character. The outer layer, composed of WO₃ · xH₂O, is unstable. In case of surface film disruption, the bond coat successfully hinders corrosion propagation into the Al-alloy. Higher electrolyte temperatures lead to faster corrosion kinetics and higher tendency for pitting.     

Fabrication of V3O7·H2O@C core-shell nanostructured composites and the effect of V3O7·H2O and V3O7·H2O@C on decomposition of ammonium perchlorate

V₃O₇·H₂O@C core-shell materials have been synthesized using V₃O₇·H₂O nanobelts as the cores and glucose as the source of carbon via an environmental hydrothermal method. The as-obtained V₃O₇·H₂O@C core-shell materials were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), elemental analysis (EA), Fourier transform infrared spectroscopy (FT-IR) and Raman spectrum. The influences of the reaction temperature, concentration of glucose and reaction time on the morphologies of the samples were respectively discussed in detail. The possible formation mechanism of V₃O₇·H₂O@C was proposed according to our experimental results. Furthermore, the effect of V₃O₇·H₂O and V₃O₇·H₂O@C on the thermal decomposition of ammonium perchlorate (AP) were investigated by thermal gravimetric analyzer (TG) and differential thermal analysis (DTA). The thermal decomposition temperatures of AP in the presence of V₃O₇·H₂O and V₃O₇·H₂O@C were reduced by 70 and 89 °C, respectively, which indicates that V₃O₇·H₂O@C core-shell composites have higher activity than V₃O₇·H₂O.     

Influence of H2-N2 atmosphere composition and annealing duration on the selective surface oxidation of low-carbon steels

The selective surface oxidation of the Ti-stabilized interstitial free (Ti-IF) and dual phase (DP) steel during recrystallization annealing at 820 °C under the variety of exposure time and composition of protective H₂-N₂ atmosphere at low dew point (−40 °C) was examined. It was found that Mn, Al, Si and Cr oxides are formed in all cases, but higher Mn and Si concentration in DP steel leads to an increase in a density of coarse nonwettable MnSiO₃ particles. An increase in annealing time enhances surface coverage with oxides, while increased H₂ content in gas atmosphere results in less coverage with external oxides improving the wettability. The influence of the stronger reducing atmosphere is more exhibit on Ti-IF steel where after 120 s of annealing in 15vol.%H₂-85vol.%N₂ atmosphere the wetting angle θ stabilized to a value of the order of 6°. The presence of surface BN and the TiN particles also affects the full surface coverage by external oxides.     

Hydrogen diffusion in Sm2Fe17 and Sm2Fe14Ga3 compounds

The short-range and long-range diffusion of hydrogen in Sm₂Fe₁₇ and Sm₂Fe₁₄Ga₃ compounds was investigated by magnetic after-effect (MAE) and thermal desorption spectroscopy (TDS). The substitution of iron by gallium greatly reduces the uptake and diffusion of hydrogen in these compounds. After charging in a high-purity H₂ atmosphere of 0.13 MPa at 570 K for 1 h the H content was determined to be Sm₂Fe₁₇H₅ and Sm₂Fe₁₄Ga₃H_1.3. Sm₂Fe₁₇ shows a hydrogen-induced MAE relaxation maximum at 190 K with a mean activation enthalpy of Q=(0.48±0.02) eV and a pre-exponential factor of

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s. In the case of the Ga-substituted compound this maximum is replaced by a double maximum at 200 and 250 K corresponding to activation ethalpies of (0.52±0.02) eV and (0.64±0.02) eV with a pre-exponential factor of

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s. These relaxation maxima are attributed to the short-range diffusion of hydrogen, since they are absent in the degassed compounds. TDS measurements of Sm₂Fe₁₇H₅ and Sm₂Fe₁₄Ga₃H_1.3 were performed in the temperature range from 291 to 515 K yielding activation enthalpies of Q=(0.59±0.02) eV and Q=(0.75±0.03) eV, respectively. The results are explained by different interstitial sites for hydrogen and the impact on the hydrogen disproportionation process is discussed.     

P110钢在CO2／H2S环境中的适用性研究

采用高温高压实验设备辅以失重法,研究了CO2／H2S腐蚀环境中P110钢的腐蚀性能,用SEM、EDS和XRD等分析了腐蚀产物．分别用电化学充氢及NACE TM0177A法对P110钢进行耐氢损伤试验．结果表明,虽然P110钢在试验环境中的均匀腐蚀速率很小,未发生点蚀,但随着充氢量的增加,强度、伸长率及断面收缩率均降低．...     

Plasma electroplating Ni coating on pure copper sheet—the effects of H2SO4 concentration on the microstructure and mechanical properties

Nanocrystalline Ni coatings were fabricated by plasma electroplating on pure copper sheets. The influence of H₂SO₄ concentration of the plating solution on the arc starting voltage and current value was studied. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-Ray diffractometry (XRD) were used to investigate the coating microstructures. The results indicated that the Ni coating prepared in 40–80 g/L H₂SO₄ solutions had the grain sizes of 50–70 nm. In addition, the maximum values of microharness and coating adhesion were ~ 280 HV and 80 N, respectively. The formation mechanism of Ni coating prepared using different H₂SO₄ concentration was discussed.     

Impact of oxyfuel atmospheres H2O/CO2/O2 and H2O/CO2 on the oxidation of ferritic–martensitic and austenitic steels

In future power plant technologies, oxyfuel, steels are subjected to steam rich and carbon dioxide rich combustion gases. The effect of simulated combustion gases H₂O/CO₂/O₂ (30/69/1 mol%) and H₂O/CO₂ (30/70 mol%) on the corrosion behavior of low alloyed steels, 9–12% chromium steels and an austenitic steel were studied. It was discovered that the formation of protective chromium rich oxides is hampered due to the carburization of the base material and the formation of chromium rich carbides. The kinetics of corrosion and carburization are quantified. The effect of temperature and the effect of gas pressure are analyzed statistically.     

Oxidation of 310 steel in H2O/O2 mixtures at 600 °C: the effect of water-vapour-enhanced chromium evaporation

The oxidation of type 310 stainless steel was investigated at 600 °C in the presence of O₂ and O₂+10% and 40% H₂O. The effect of gas velocity was studied. The oxidized samples were investigated by grazing angle X-ray diffraction, SEM/EDX and SAM. The addition of H₂O to O₂ resulted in a change of oxidation behaviour. A strong dependence on flow rate was observed in O₂/H₂O mixtures. At low flow rates a thin (30-50 nm) protective α-(Cr,Fe)₂O₃ formed, the outer part being depleted in chromium. When the flow rate was increased beyond a critical value the protective oxide failed. Under these conditions ?5 μm thick α-Fe₂O₃/(Cr,Fe)₃O₄, oxide islands formed on the part of the surface corresponding to the centre of the alloy grains. The effect of water vapour is attributed to the water-vapour-assisted evaporation of chromium from the oxide, in the form of a chromium oxide hydroxide, probably CrO₂(OH)₂. The oxidation behaviour is rationalized using a qualitative mechanism proposed previously and parallels that of the 304L alloy.     

Theoretical study of H2O and O2 adsorption on Au small clusters

Hybrid Density functional calculations have been carried out for Au₁₀, Au₁₀-H₂O, Au₁₀-O₂, and Au₁₀-H₂ O-O₂ model clusters. The results show that all the Au₁₀ clusters examined have a weak interaction with H₂O and neutral and negatively charged Au10 clusters have a weak interaction with O₂. Moreover, it is also found that the negative charge densities of O₂ were greatly increased in the case of the coadsorption of O₂ and H₂O on the surface of the negatively charged Au₁₀. These findings suggest that the presence of H₂O enhances the activation of O₂ on the surface of an Au cluster.     

The influence of CO2, AlCl3 · 6H2O, MgCl2 · 6H2O, Na2SO4 and NaCl on the atmospheric corrosion of aluminum

The influence of salt deposits on the atmospheric corrosion of high purity Al (99.999%) was studied in the laboratory. Four chloride and sulfate-containing salts, NaCl, Na₂SO₄, AlCl₃ · 6H₂O and MgCl₂ · 6H₂O were investigated. The samples were exposed to purified humid air with careful control of the relative humidity (95%), temperature (22.0 °C), and air flow. The concentration of CO₂ was 350 ppm or <1 ppm and the exposure time was four weeks. Under the experimental conditions all four salts formed aqueous solutions on the metal surface. Mass gain and metal loss results are reported. The corroded surfaces were studied by ESEM, OM, AES and FEG/SEM equipped with EDX. The corrosion products were analyzed by gravimetry, IC and grazing incidence XRD. In the absence of CO₂, the corrosivity of the chloride salts studied increases in the order MgCl₂ · 6H₂O < AlCl₃ · 6H₂O < NaCl. Sodium chloride is very corrosive in this environment because the sodium ion supports the development of high pH in the cathodic areas, resulting in alkaline dissolution of the alumina passive film and rapid general corrosion. The low corrosivity of MgCl₂ · 6H₂O is explained by the inability of Mg²⁺ to support high pH values in the cathodic areas. In the presence of carbon dioxide, the corrosion induced by the salts studied exhibit similar rates. Carbon dioxide strongly inhibits aluminum corrosion in the presence of AlCl₃ · 6H₂O and especially, NaCl, while it is slightly corrosive in the presence of MgCl₂ · 6H₂O. The corrosion effects of CO₂ are explained in terms of its acidic properties and by the precipitation of carbonates. In the absence of CO₂, Na₂SO₄ is less corrosive than NaCl. This is explained by the lower solubility of aluminum hydroxy sulfates in comparison to the chlorides. The average corrosion rate in the presence of CO₂ is the same for both salts. The main difference is that sulfate is less efficient than chloride in causing pitting of aluminum in neutral or acidic media.