Oxidation of nano-multilayered AlTiSiN thin films between 600 and 1000 degrees C in air

Multilayered AlTiSiN films with a composition of 32.0Al-12.4Ti-4.9Si-50.7N (at.%) were deposited on a steel substrate in a nitrogen atmosphere by cathodic arc plasma deposition. The films consisted of crystalline approximately 8 nm-thick AISiN nanolayers that originated from the Al-Si target and approximately 3 nm-thick TiN nanolayers that originated from the Ti target. Their oxidation characteristics were studied between 600 and 1000 degrees C for up to 20 h in air. They displayed good oxidation resistance due to the formation of a thin, dense Al2O3 surface scale below which an (Al2O3, TiO2, SiO2)-intermixed inner scale existed. They oxidized slower than TiN films because protective Al2O3-rich scales formed on the surface. However, they oxidized faster than CrN films because impure Al2O3 scale formed on the AlTiSiN film. Their oxidation progressed primarily by the outward diffusion of nitrogen and substrate elements, combined with the inward transport of oxygen that gradually reacted with Al, Ti, and Si in the film.     

Preparation and sorption properties of materials from paper sludge

Three materials were prepared from paper sludge (PS) using different treatment processes and their sorption abilities for phosphate and methylene blue (MB) were determined. The samples were a powder sample prepared by heating PS in air (sample C), a pellet prepared by grinding, forming and heating PS in air (sample G) and a powder prepared by physical activation of PS in flowing wet nitrogen (sample A). The three samples were heated at 600-900 degrees C for 6h. On heating at 700-800 degrees C, the organic fibers, limestone (CaCO3), kaolinite (Al2Si2O5(OH)4) and talc (Mg3Si4O10(OH)2) in the original PS were converted to amorphous CaO-Al2O3-SiO2 (CAS) and talc in sample C, while CAS was formed in sample G and activated carbon, CAS and talc was formed in sample A. On heating at 900 degrees C the CAS converted to gehlenite (Ca2Al2SiO7) and anorthite (CaAl2Si2O8). The specific surface areas (SBET) of the three samples achieved maximum values of 23, 37 and 70 m2/g upon heating at 700, 600 and 600 degrees C, respectively. The SBET value of the activated sample A was distinctly lower than usually reported for activated carbon. The samples C, G and A achieved maximum phosphate sorption capacities of 2.04, 1.38 and 1.70 mmol/g, calculated from the Langmuir model, upon heating at 700, 700 and 800 degrees C, respectively. The maximum sorption capacity for phosphate in sample C is attributed to the sorption by CAS, namely, adsorption on the alumina component and precipitation as Ca-phosphates. The MB multifunctional sorption capacity of sample A was 0.11 mmol/g. The phosphate and MB sorption rates show better correlation with a pseudo-second order model than with other models.     

Oxidation Behaviour of Sputtered Ni-3Cr-20Al Alloy

1. IntroductionNi-base superalloys are the important materialsused at high temperature and greatly rely on the presence of Cr and/or Al to form a protective scale ofCrook or Allot. Therefore, the investigation of oxidation of the simple Ni-Cr-Al ternary alloys is beneficial to the understanding of oxidation patterns of complex Ni-base superalloys. Some works have been conducted on the Ni-Cr-Al alloys with normal grain sizeand the results indicated that different oxides couldbe formed accor…     

The effects of substrate and annealing on structural and electrochemical properties in LiCoO2 thin films prepared by DC magnetron sputtering

LiCoO2 thin films were fabricated by direct current magnetron sputtering method on STS304 and Ti substrates. The effects of substrate and annealing on their structural and electrochemical properties of LiCoO2 thin film cathode were studied. Crystal structures and surface morphologies of the deposited films were investigated by X-ray diffraction and field emission scanning electron microscopy. The as-deposited films on both substrates have amorphous structure. The (104) oriented perfect crystallization was obtained by annealing over 600 degrees C in STS304 substrate. The LiCoO2 thin film deposited on Ti substrate shows the (003) texture after annealing at 700 degrees C. The electrochemical properties were investigated by the cyclic voltammetry and charge-discharge measurement. The 600 degrees C-annealed LiCoO2 film deposited on STS304 substrate exhibits the inithial discharge capacity of 22 uAh/cm2 and the 96% capacity retention rate at 50th cycles. The electrochemical measurement on annealed films over 600 degrees C was impossible due to the formed TiO2 insulator layer using Ti substrate. As a result, it was found that the STS304 substrate seems to be more suitable material than the Ti substrate in fabricating LiCoO2 thin film cathode.     

Morphological changes induced by thermal anneals in NiFe/Ag multilayers; their relation to the resistive and magnetoresistive properties

(Ti, Al)N films have drawn much attention as alternatives for TiN coatings, which are oxidized easily in air above 500 °C. We have investigated the effect of Al content on the oxidation resistance of (Ti_{1 − x}Al_x)N films prepared by r.f. reactive sputtering.

(Ti_{1 − x}Al_xN films (O ≤ x ≤ 0.55) were deposited onto fused quartz substrates by r.f. reactive sputtering. Composite targets with five kinds of Al-to-Ti area ratio were used. The sputtering gas was Ar (purity, 5 N) and N₂ (5 N). The flow rate of Ar and N₂ gas was kept constant at 0.8 and 1.2 sccm, respectively, resulting in a sputtering pressure of 0.4 Pa. The r.f. power was 300 W for all experiments. Substrates were not intentionally heated during deposition. The deposited films (thickness, 300 nm) were annealed in air at 600 900 °C and then subjected to X-ray diffractometer and Auger depth profiling.

The as-deposited (Ti_{1 − x}Al_x)N films had the same crystal structure as TiN (NaCl type). Al atoms seemed to substitute for Ti in lattice sites. The preferential orientation of the films changed with the Al content of the film, x. Oxide layers of the films grew during annealing and became thicker as the annealing temperature increased. The thickness of the oxide layer grown on the film surface decreased with increasing Al content in the film. For high Al content films an Al-rich oxide layer was grown on the surface, which seemed to prevent further oxidation. All of the films, however, were oxidized by 900 °C annealing, even if the Al content was increased up to 0.55.     

Amorphous alumina coatings: processing, structure and remarkable barrier properties

Amorphous aluminium oxide coatings were processed by metalorganic chemical vapour deposition (MOCVD); their structural characteristics were determined as a function of the processing conditions, the process was modelled considering appropriate chemical kinetic schemes, and the properties of the obtained material were investigated and were correlated with the nanostructure of the coatings. With increasing processing temperature in the range 350 degrees C-700 degrees C, subatmospheric MOCVD of alumina from aluminium tri-isopropoxide (ATI) sequentially yields partially hydroxylated amorphous aluminium oxides, amorphous Al2O3 (415 degrees C-650 degrees C) and nanostructured gamma-Al2O3 films. A numerical model for the process allowed reproducing the non uniformity of deposition rate along the substrate zone due to the depletion of ATI. The hardness of the coatings prepared at 350 degrees C, 480 degrees C and 700 degrees C is 6 GPa, 11 GPa and 1 GPa, respectively. Scratch tests on films grown on TA6V titanium alloy reveal adhesive and cohesive failures for the amorphous and nanocrystalline ones, respectively. Alumina coating processed at 480 degrees C on TA6V yielded zero weight gain after oxidation at 600 degrees C in lab air. The surface of such low temperature processed amorphous films is hydrophobic (water contact angle 106 degrees), while the high temperature processed nanocrystalline films are hydrophilic (48 degrees at a deposition temperature of 700 degrees C). It is concluded that amorphous Al2O3 coatings can be used as oxidation and corrosion barriers at ambient or moderate temperature. Nanostructured with Pt or Ag nanoparticles, they can also provide anti-fouling or catalytic surfaces.     

Improvement on the Oxidation Resistance of a Ti3Al Based Alloy by Cr1-xAlxN (0≤x≤0.47) Coatings

Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900 ℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3 Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the Al content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.     

Microstructure evolution and oxidation behaviour of Tif/TiAl3 composites

In this paper, Ti_f/TiAl₃ composites were fabricated by infiltration–in situ reaction method and its oxidation behaviours were investigated by cyclic oxidation testing at 700 °C, 800 °C and 900 °C. The microstructure evolution and oxidation of Ti_f/TiAl₃ composites were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray diffraction (EDX). The reaction between Ti₃Al particles and Al was more violent than that of Ti fibres and Al. Ti₃Al/Al reaction consumed a large amount of Al and inhibited the reaction of Ti fibres indirectly. Reactant of Ti fibres was TiAl₃ at 700 °C, and four reaction layers surrounding Ti fibre (Ti₃Al, TiAl, TiAl₂ and TiAl₃ from inner to outside) were observed above 800 °C. The thickness of the total reaction layers increased little with temperature and time, while the thickness of inner reaction layers increased remarkably. A model corresponding to the microstructure evolution process was drawn schematically. Oxidation resistance of Ti_f/TiAl₃ composites decreased with increasing of temperature, and changed from cubic law at 700 °C to parabolic law at 900 °C. The oxidation weight gain of Ti_f/TiAl₃ composite was dominated by the exposed Ti fibres. Due to outward diffusion of Ti and Al element, the oxide of Ti fibre at 900 °C changed to mushroom-shape. Fortunately, when TiAl₃ was oxidized, a thin and continuous Al₂O₃ layer was formed, protecting matrix from further oxidation.     

Uptake properties of Ni2+ by nCaO.Al2O3.2SiO2 (n=1-4) prepared from solid-state reaction of kaolinite and calcite

A series of nCaO.Al2O3.2SiO2 samples (n=1-4) were prepared by solid-state reaction of mechanochemically treated mixtures of kaolinite and calcite fired at 600-1000 degrees C for 24 h. All the samples were X-ray amorphous after firing at 600-800 degrees C but had crystallized by 900 degrees C. The main crystalline phases were anorthite (n=1), gehlenite (n=2 and 3) and larnite (n=4). The uptake of Ni2+ by nCaO.Al2O3.2SiO2 samples fired at 800 and 900 degrees C was investigated at room temperature using solutions with initial Ni2+ concentrations of 0.1-50 mmol/l. Amorphous samples (fired at 800 degrees C) showed a higher Ni2+ uptake capacity than crystalline samples (fired at 900 degrees C). Ni2+ uptake was found to increase with increasing of CaO content. Amorphous 4CaO.Al2O3.2SiO2 showed the highest Ni2+ uptake capacity (about 9 mmol/g). The Ni2+ uptake abilities of the present samples are higher than those of other materials reported in the literature. Since the sorbed Ni2+/released Ca2+ ratios of these samples are close to unity, ion replacement of Ni2+ for Ca2+ is thought to be the principal mechanism of Ni2+ uptake by the present samples.     

Improvement on the Oxidation Resistance of a Ti3Al Based Alloy by Cr1-xAlxN （0≤x≤0.47） Coatings

Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3＋Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the AI content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.     

Formation and Oxidation Behavior of Al—Cu—Fe Quasicrystal

Al62.5Cu25Fe12.5 alloy was prepared by arc melting .It was found that the formation of quasicrystalline phase is related to the condition of annealing,such as temperature and duration.Weight gain of Al-Cu-Fe quasicrystal during the oxidation at 700 and 800℃ in dry air was measured by means of thermal balance.The oxidation kinetics showed that the quasicrystal has good oxidation resistance.Only α-Al2O3 was formed on Al62.5Cu25Fe12.5 quasicrystal.The surface morphologies of Al-Cu-Fe quasicrystal after isothermal oxidation for different times were observed.     

Influence of sol–gel derived Al2O3 film on the oxidation behavior of a Ti3Al based alloy

Al₂O₃ thin films were deposited on a Ti₃Al based alloy (Ti–24Al–14Nb–3V–0.5Mo–0.3Si) by sol–gel processing. Isothermal oxidation at temperatures of 900–1000 °C and cyclic oxidation at 800–900 °C were performed to test their effect on the oxidation behavior of the alloy. Results of the oxidation tests show that the oxidation parabolic rate constants of the alloy were reduced due to the applied thin film. This beneficial effect became weaker after longer oxidation time at 1000 °C. TiO₂ and Al₂O₃ were the main phases formed on the alloy. The thin film could promote the growth of Al₂O₃, causing an increase of the Al₂O₃ content in the composite oxides, sequentially decreased the oxidation rate. Nb/Al enriched as a layer in the alloy adjacent to the oxide/alloy interface in both the coated and uncoated alloy. The coated thin film decreased the thickness of the Nb/Al enrichment layer by reducing the scale growth rate.     

The influences of rapid-thermal annealing on the characteristics of Sr0.6Ba0.4Nb2O6 thin film

The Sr0.6Ba0.4Nb2O6 (SBN) thin films were successfully prepared on Pt/Ti/Si and SiO2/Si/Al substrates and crystallized subsequently using rapid thermal annealing (RTA) process in ambient atmosphere for 1 min. The surface morphologies and thicknesses of as-deposited and annealed SBN thin films were characterized by field emission scanning electron microscopy, and the thickness was about 246 nm. As compared with the as-deposited SBN thin films, the RTA-treated process had improved the crystalline structures and also had large influence on the crystalline orientation. When the annealing temperatures increased from 700 degrees C to 900 degrees C, the diffraction intensities of (410) and (001) peaks apparently increased. Annealed at 900 degrees C, the (001) peak had the maximum texture coefficient and SBN thin films showed a highly c-axis (001) orientation. The influences of different RTA-treated temperatures on the polarization-applied electric field (P-E) curves and the capacitance-voltage (C-V) curves were also investigated.     

Effect of temperature on the oxidation of Fe-7.5A1-o.65C alloy

An alloy with the chemical composition Fe-7.5A1-0.65C was employed to investigate the effect of temperature on oxidation between 600 and 900° C in dry air. Kinetic curves were determined by thermogravimetry analyses (TGA). Optical metallography and electron probe microanalysis (EPMA) were used to examine the oxide scales. At 600°C, the initial stage of oxidation followed a parabolic rate law, and oxidation subsequently, increased dramatically. Internal oxidation occurred beneath the nodule formed on the present alloy at 600°C. In contrast, no internal oxidation could be found in specimens of the Fe-7.5A1-0.65C alloy after oxidizing at 700, 800 and 900°C. The kinetic results have two distinct parabolic rates for the present alloy.     

Oxidation behavior of (Ti1 − xAlx)N films perpared by r.f. reactive sputtering

(Ti, Al)N films have drawn much attention as alternatives for TiN coatings, which are oxidized easily in air above 500 °C. We have investigated the effect of Al content on the oxidation resistance of (Ti_{1 − x}Al_x)N films prepared by r.f. reactive sputtering.(Ti_{1 − x}Al_xN films (O ≤ x ≤ 0.55) were deposited onto fused quartz substrates by r.f. reactive sputtering. Composite targets with five kinds of Al-to-Ti area ratio were used. The sputtering gas was Ar (purity, 5 N) and N₂ (5 N). The flow rate of Ar and N₂ gas was kept constant at 0.8 and 1.2 sccm, respectively, resulting in a sputtering pressure of 0.4 Pa. The r.f. power was 300 W for all experiments. Substrates were not intentionally heated during deposition. The deposited films (thickness, 300 nm) were annealed in air at 600 900 °C and then subjected to X-ray diffractometer and Auger depth profiling.The as-deposited (Ti_{1 − x}Al_x)N films had the same crystal structure as TiN (NaCl type). Al atoms seemed to substitute for Ti in lattice sites. The preferential orientation of the films changed with the Al content of the film, x. Oxide layers of the films grew during annealing and became thicker as the annealing temperature increased. The thickness of the oxide layer grown on the film surface decreased with increasing Al content in the film. For high Al content films an Al-rich oxide layer was grown on the surface, which seemed to prevent further oxidation. All of the films, however, were oxidized by 900 °C annealing, even if the Al content was increased up to 0.55.     

含硅合金熔体对TiAl基合金表面改性的研究

使用含硅合金熔体对TiAl基合金进行了表面渗硅处理，渗硅处理温度范围是：913－1053K，实施发现，TiAl基合金与Al-Si熔体之间发生了界面反应，界面生成以Si,Ti,Al三元素为主的灰白色基体和条状，小块状黑色相。表面处理后样品经1173K／100h高温氧化后，表层形成了Al2O3,SiO2等致密的氧化膜，并保留有稳定的Si-Ti-Al相，因而改善了表面氧化层结构，大大增强了TiAl基合金的高温抗氧化能力。     

Nano-polycrystalline vanadium oxide thin films prepared by pulsed laser deposition

Nano-polycrystalline vanadium oxide thin films have been successfully produced by pulsed laser deposition on Si(100) substrates using a pure vanadium target in an oxygen atmosphere. The vanadium oxide thin film is amorphous when deposited at relatively low substrate temperature (500 degrees C) and enhancing substrate temperature (600-800 degrees C) appears to be efficient in crystallizing VOx thin films. Nano-polycrystalline V3O7 thin film has been achieved when deposited at oxygen pressure of 8 Pa and substrate temperature of 600 degrees C. Nano-polycrystalline VO2 thin films with a preferred (011) orientation have been obtained when deposited at oxygen pressure of 0.8 Pa and substrate temperatures of 600-800 degrees C. The vanadium oxide thin films deposited at high oxygen pressure (8 Pa) reveal a mix-valence of V5+ and V4+, while the VOx thin films deposited at low oxygen pressure (0.8 Pa) display a valence of V4+. The nano-polycrystalline vanadium oxide thin films prepared by pulsed laser deposition have smooth surface with high qualities of mean crystallite size ranging from 30 to 230 nm and Ra ranging from 1.5 to 22.2 nm. Relative low substrate temperature and oxygen pressure are benifit to aquire nano-polycrystalline VOx thin films with small grain size and low surface roughness.     

Thermal oxidation of Ti6Al4V alloy: Microstructural and electrochemical characterization

Thermal oxidation (TO) of Ti6Al4V alloy was performed at 500, 650 and 800 °C for 8, 16, 24 and 48 h in air. The morphological features, structural characteristics, microhardness and corrosion resistance in Ringer's solution of TO Ti6Al4V alloy were evaluated and compared with those of the untreated one. The surface morphological features reveal that the oxide film formed on Ti6Al4V alloy is adherent to the substrate at 500 and 650 °C irrespective of the oxidation time whereas it spalls off when the alloy is oxidized at 800 °C for more than 8 h. X-ray diffraction (XRD) measurement reveals the presence of Ti(O) and α-Ti phases on alloy oxidized at 500 and 650 °C, with Ti(O) as the dominant phase at 650 °C whereas the alloy oxidized at 800 °C exhibits only the rutile phase. Almost a threefold increase in hardness is observed for the alloy oxidized at 650 °C for 48 h when compared to that of the untreated one. Thermally oxidized Ti6Al4V alloy offers excellent corrosion resistance in Ringer's solution when compared to that of the untreated alloy.     

Oxidation Behavior of Pd-Modified Aluminide Coating at High Temperature

(Ni,Pd)Al coating, prepared by low pressure pack cementation on the Ni-base superalloy M38 where Pd-20 wt pct Ni alloy was predeposited, consists of a single β-(Ni,Pd)Al phase. The initial isothermal oxidation behavior of (Ni,Pd)Al coating was investigated by TGA, XRD, SEM/EDS at 800～1100℃. Results show that oxidation kinetics accord preferably with parabolic law at 800, 900 and 1100℃, but not at 1000℃.θ-Al2O3 was observed at 800～1100℃. It is found that Pd plays an important role in accelerating the diffusion of Ti from the substrate to the coating surface in the aluminide coating.     

Texture and sheet resistance of Al alloy thin films on Ti and TiN thin films

Ti films prepared by ionized physical vapor deposition (I-PVD) and TiN films prepared by metalorganic chemical vapor deposition (MOCVD) were examined as the underlayers of the Al interconnect films. The crystallographic texture of the Al films and the sheet resistance of the thin-film stacks were investigated at various thicknesses of the Ti or TiN thin film. The sheet resistance of the thin-film stacks was also measured after annealing at 400 °C in an N₂ ambient. For the I-PVD Ti underlayer, the excellent texture of the Al (1 1 1) was obtained even on a 5-nm thick Ti film. However, the sheet resistance of the multilayer structure increased after the annealing due to the reaction between Al and Ti. MOCVD TiN layers between the Ti film and the Al film could suppress the Al–Ti reaction without severe degradation of the Al (1 1 1) texture. Excellent texture of the Al film was obtained with thin MOCVD TiN films below 5 nm.