Uncoated Iron Research Articles

Oxidation of phosphated iron powders

The present work deals with the influence of phosphating treatment on the oxidation resistance of iron powders. Iron powders with particles diameter size of approximately 100 μm, have been immersed in phosphoric acid (0.102 mol l −1) in an acetone solution. After half an hour, a phosphate layer of less than 0.1 μm is formed at the metal surface. XRD spectrum is characteristic of an amorphous or nanocrystalline coating. The oxidation is performed by in situ thermogravimetric experiments in artificial air (20% O 2–80% N 2). For oxidation times of 24 or 48 h, between 350 and 700°C the kinetics are recorded for both untreated and phosphated powders. At all temperatures, the phosphate acts as a protective barrier layer. Between 350 and 450°C the coated powders present two parabolic stages in their oxidation kinetics and progressively with increasing temperature, the first stage disappears. On the other hand, uncoated iron powders show only one parabolic stage when oxidised. The oxidation constants k p were plotted for each stage of the curves vs. 1/ T. From each Arrhenius plot an activation energy is deduced. For the phosphated powders, an activation energy of less than 0.6 eV is found in the first stage while for the second stage the deduced value of approximately 1.8 eV is the same that for the uncoated iron. That second parabolic stage for the coated powders can be compared with the oxidation of cast iron while in the first stage another mechanism may be involved. XRD studies of the oxidised powders at 350°C for 48 h show that Fe 3O 4 and Fe 2O 3 are formed both on uncoated iron and on the coated powder. For phosphated powders, the amount of oxide is less important. As a result the phosphate layer acts as a diffusion barrier that slows down the oxidation of iron.

Novel Method for Coating Magnetic Iron Oxide Particles with Carbon Black

Magnetic particles with finer size, higher coercive force, higher blackness, and lower electrical resistance are required to produce better magnetic tape materials. A new method to coat iron oxide particles with carbon black using an adhesive agent is reported in this paper. Magnetic tapes prepared using the coated particles in the recording layer exhibit improvements in both light transparency and electrical resistance. A decrease in transparency of ∼20% and a reduction in electrical resistance of ∼1 order of magnitude relative to conventionally prepared tapes are achieved when ∼5% of the particle weight is carbon black. Surface smoothness and the orientation ratio are also improved because the dispersibility of these particles in magnetic lacquer is better than that of uncoated magnetic iron oxide particles. Higher electromagnetic performance relative to the conventionally prepared layers is also obtained. TEM photographs indicate that all the carbon black is firmly bound to the surface of the magnetic iron oxide particles in a distinct layer.

The delamination of polymeric coatings from steel. Part 1: Calibration of the Kelvinprobe and basic delamination mechanism

In the first part of this study are presented the theory and the experimental techniques which are necessary to investigate the delamination of model coatings on steel. It is shown that the electrochemical reactions taking place at the substrate/electrolyte and substrate/polymer interfaces are responsible for delamination. Due to the fact that the electrochemical reactions are accompanied by changes in the corrosion potential, it is possible to identify and follow the delamination by measuring the corrosion potential as a function of time and local position. Furthermore, it is demonstrated that the Volta-potential difference between a reference metal and the model polymer surface is determined by the corrosion potential, whereas the influence of the Donnan-potential is small and constant. By combining several experimental techniques, like the Scanning Kelvinprobe, Auger electron spectroscopy and mechanical de-adhesion tests, the delamination process is studied in detail and a model is presented, which is based on the existence of a galvanic element at the substrate/polymer interface. The uncoated iron is the local anode, where the iron dissolution predominates, whereas the delaminated part represents the local cathode and, within this area, only the oxygen reduction takes place. The second and third part of this paper deal with an experimental verification of this model.

Tribological behaviour of plasma-sprayed zirconia coatings

Various layers of zirconia, coated on cast iron plates and steel discs by plasma spraying, were studied to gain a better understanding of their tribological behaviour. Coatings selected for this investigation were zirconia-5% CaO, zirconia-8% yttria, zirconia-20% yttria and alumina-zirconia coatings. Wear tests were conducted under conditions of dry contact with reciprocating motion at a temperature of 200 °C. Measurements of friction and wear rate were made in association with sliding distance for various friction pairs: self-mated contact between zirconia-sprayed specimens, sprayed plate against chromium-plated disc, and uncoated cast iron plate against chromium-plated disc which represents the contact between cylinder liner and piston ring in diesel engines. To identify the wear mechanism, an X-ray diffractometer, scanning electron microscope, transmission electron microscope, surface roughness tester and micro-hardness tester were used. 92%-8% zirconia-yttria, 80%-20% zirconia-yttria and alumina-zirconia composite coatings exhibited excellent wear resistance. Wear debris were considerably involved in the wear process in the steady state. It is shown that the plastic deformation and forming of a smooth film by material transfer on the sliding surface strongly influenced the wear rate and friction coefficient. Phase transformation in the contact region was discussed. Phase transformation from the tetragonal to monoclinic phase was not noticeable but the transformation of the tetragonal phase to the t' tetragonal phase was observed to influence the tribological behaviour of the coatings.

Chemically vapor deposited diamond films grown on titanium nitride coated and uncoated iron substrates

The nature of the interfaces of chemically vapor deposited diamond films on Fe substrates with and without a protective TiN coating is investigated. For unprotected Fe substrates a thick graphitic soot containing 6.5% Fe grows upon the Fe in the first few minutes of exposure to the plasma and, once this soot completely covers the substrate, diamond can nucleate and grow upon it into an average quality unfaceted continuous diamond film. However, adhesion is poor, the weak link being the lack of structural integrity of the soot layer itself. A TiN coating is found to prevent soot formation, C diffusion into the Fe bulk, and Fe diffusion into the diamond films. In the initial stages of growth the TiN is covered with a thin layer of amorphous carbon (a-C), and it is on this layer that diamond nucleates and grows. Here, again, adhesion is not strong, with delamination occurring at the TiN/a-C interface.

A corrosion study of TiN (physical vapour deposition) hard coatings deposited on various substrates

Titanium nitride (TiN) coatings 2.8 υm thick, reactively deposited on various substrates by physical vapour deposition, were studied using electrochemical methods in combination with scanning electron microscopy and Auger electron spectroscopy. Three different substrates were used, namely stainless steel AISI 304, high speed ASP steel ASP 30 and stabilized iron CK 45. Multisweep cyclic voltammetry experiments in acetate buffer solution were performed in order to test the microporosity of the coatings. An Auger depth analysis performed on TiN coatings polarized at potentials more positive than 1.3 V in 0.5 M H 2SO 4 proves the formation of an oxidized layer, indicating the partial transformation of titanium nitride to a titanium oxynitride layer. A change in the corrosion behaviour associated with the presence of the TiN coating was observed in 0.5 M NaCl. Whereas the uncoated iron undergoes general corrosion, localized corrosion occurs on the TiN-coated iron. This localized corrosion is a consequence of the microdefects present in the coating.

Hydrogen ion-driven permeation in carbonaceous films

This paper presents the results of investigations into the permeation properties of amorphous carbonaceous, a-C: H, films produced by plasmachemical deposition techniques. Carbonaceous films on iron substrates with thickness ranging from 60 nm to 110 nm were subjected to high fluence implantations with mass analyzed D + 3 ions with energies ranging from 600 eV to 3000 eV and fluxes ranging from 5 × 10 14 D/ cm 2 s to 5 × 10 15 D/ cm 2 s, respectively. Deuterium re-emission upstream, deuterium permeation downstream and secondary ions sputtered from the implantation surface were measured as a function of implantation fluence for specimens at 420 K. The present studies indicate that the a-C : H film permeability is directly related to the time, hence the fluence, required to achieve isotopic replacement and saturation of the deuterium ion beam atoms stopped in the implant region. Once the deuterium saturation level is achieved in the layer, a significant fraction of the implanting ions can result in permeation. For the present experiment, this permeation factor was much higher than that for uncoated iron specimens subjected to similar beam conditions. Carbon sputter yields of 0.008–0.01 C/D were determined in this work for 1000-eV to 400-eV deuterium ions incident on a-C : H films.

The size distribution of interstellar grains

view Abstract Citations (3519) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The size distribution of interstellar grains. Mathis, J. S. ; Rumpl, W. ; Nordsieck, K. H. Abstract The observed interstellar extinction over the wavelength range 0.11 μm < λ < 1 μm was fitted with a very general particle size distribution of uncoated graphite, enstatite, olivine, silicon carbide, iron, and magnetite. Combinations of these materials, up to three at a time, were considered. The cosmic abundances ofthe various constituents were taken into account as constraints on the possible distributions of particle sizes. Excellent fits to the interstellar extinction, including the narrowness of the λ2160 feature, proved possible. Graphite was a necessary component of any good mixture, but it could be used with any of the other materials. The particle size distributions are roughly power law in nature, with an exponent of about -3.3 to -3.6. The size range for graphite is about 0.005 μm to about 1 μm. The size distribution for the other materials is also approximately power law in nature, with the same exponent, but there is a narrower range of sizes: about 0.025-0.25 μm, depending on the material. The number of large particles is not well determined, because they are gray. Similarly, the number of small particles is not well determined because they are in the Rayleigh limit. This power-law distribution is drastically different from an Oort-van de Hulst distribution, which is much more slowly varying for small particles but drops much faster for particles larger than average. The extinction was also fitted with spherical graphite particles plus cylinders of each of the other materials. Linear and circular polarizations were then determined for the cylinders on the assumption of Davis-Greenstein alignment. The extinction was quite satisfactory, but the linear polarization reached a maximum in the ultraviolet (about 1600 Å). This is because the mixture contains many small particles. Ifthe small particles are not elongated or aligned, the wavelength dependence of the polarization can be fitted, but the larger particles which are aligned do not provide enough polarization per magnitude of extinction. However, a fit to polarization and extinction can be achieved if the material responsible for the polarization contributes only a small part of the extinction but consists of fairly large particles and is very well aligned. Dielectric particles with coatings could also provide the polarization. Subject headings: interstellar : matter «— polarization — Publication: The Astrophysical Journal Pub Date: October 1977 DOI: 10.1086/155591 Bibcode: 1977ApJ...217..425M Keywords: Cosmic Dust; Interstellar Extinction; Interstellar Matter; Particle Size Distribution; Enstatite; Graphite; Magnetite; Olivine; Polarization Characteristics; Ultraviolet Astronomy; Astrophysics full text sources ADS | data products SIMBAD (1)

Bacterial Corrosion of Iron Encapsulated in Polyethylene Film

The effectiveness of unbonded polyethylene coatings, 0·20 mm in thickness, in protecting samples of iron immersed in cultures of sulphate-reducing bacteria has been studied. The corrosion (weight loss) rate was initially lower than that for uncoated controls, but later accelerated so that the weight loss after 12 weeks was about the same for coated and uncoated iron samples. The coatings were permeable to water and soluble sulphide, and underwent change in tensile strength during exposure to the bacterial cultures.

Bacterial Corrosion of Iron Encapsulated in Polyethylene Film

The effectiveness of unbonded polyethylene coatings, 0·20 mm in thickness, in protecting samples of iron immersed in cultures of sulphate-reducing bacteria has been studied. The corrosion (weight loss) rate was initially lower than that for uncoated controls, but later accelerated so that the weight loss after 12 weeks was about the same for coated and uncoated iron samples. The coatings were permeable to water and soluble sulphide, and underwent change in tensile strength during exposure to the bacterial cultures.