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- Ahlén, Niklas, 1970-
(author)
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Carbothermal synthesis of transition metal carbide and carbonitride whiskers via a Vapour-Liquid-Solid (VLS) growth mechanism
- 1999
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Doctoral thesis (other academic/artistic)abstract
- A route for the synthesis of TiC, TiCyN1-y, TaxTi1-xC and TaxTi1-xCyN1-y whiskers via a carbothermal Vapour-Liquid-Solid (VLS) growth mechanism, yielding 70-90 vol.% whiskers, has been established. The whiskers were uniform in diameter (0.3-0.6mm), and had a length of about 10-30mm. The starting materials consisted of TiO2 and/or Ta2O5, C, a catalyst metal (Ni or Fe) and NaCl. Carbon was added to reduce the oxides, and NaCl to provide chlorine in the formation of TiClx(g) and TaOxCly(g) species. The overall chemical reaction is a straightforward carbothermal reduction process. The optimum synthesis temperature was found to be 1250°C for TiCyN1-y, TaxTi1-xC and TaxTi1-xCyN1-y whisker, and 1400°C for TiC. The growth direction of the whiskers was found to be <100> for TaC and TaxTi1-xC and either <100> or <111> for TiC. Nitridation of TiC whiskers yielded TiCyN1-y whiskers with morphology and chemical composition different from those obtained by the carbothermal VLS growth mechanism. From oxidation studies it was found that TiC had the lowest oxidation resistance (onset temperature Ton=390°C) and that TaC had the highest (Ton=550°C). The oxidation onset temperature was found to increase with increasing x-value for both TaxTi1-xC and TaxTi1-xCyN1-y whiskers. Microscopy studies (SEM and TEM) showed that whiskers with a native diameter exceeding 0.3 mm split into two halves along their length when oxidised. It was found that the TiO2 particle size of oxidised TaxTi1-xC whiskers are markedly smaller than that obtained from oxidation of TiC whiskers, whereas the Ta2O5 particle size was the same as that observed for oxidised TaC whiskers.
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| 2. |
- Bauer, A. D., et al.
(author)
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Corrosion behaviour of monocrystalline titanium nitride
- 1997
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In: Surface and Coatings Technology. ; 91:3, s. 208-214
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Journal article (peer-reviewed)abstract
- The corrosion behaviour of monocrystalline and highly textured TiN films deposited onto single crystalline MgO has been investigated. It was found that films with high defect concentrations and elements of polycrystallinity had a reduced corrosion resistance. These films had low corrosion potentials and high critical and passive current densities. For high quality films the [110]- and [111]-orientations generally displayed better corrosion properties than films with [100]-orientation. Corrosion had different effects on films of different orientations: On [100]-oriented films loose rectangularly shaped flakes were observed. [110]-oriented films cracked because of compressive stresses, which in many cases caused the films to peel off during corrosion. On [111]-oriented films, finally, triangular pits were detected after corrosion. Films with high corrosion potentials had low values of critical and passive current densities. Non-destructive electrochemical analysis in combination with defect analysis can thus be used to predict the behaviour of these films on anodic polarisation.
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| 4. |
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| 5. |
- Elihn, K, et al.
(author)
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Nanoparticle formation by laser-assisted photolysis of ferrocene.
- 1999
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In: NANOSTRUCTURED MATERIALS. - 0965-9773. ; 12:1-4, s. 79-82
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Journal article (peer-reviewed)abstract
- Laser-assisted formation of iron-containing nanoparticles has been performed by photolytic dissociation of ferrocene vapour by a pulsed ArF excimer laser at 193 nm. The process was carried out at atmospheric pressure, either in an inert atmosphere of argo
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| 7. |
- Herranen, Merja, et al.
(author)
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Corrosion behaviour of Ti/TiN multilayer coated tool steel
- 1998
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In: SURFACE & COATINGS TECHNOLOGY. - 0257-8972. ; 99:1-2, s. 191-196
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Journal article (other academic/artistic)abstract
- The corrosion behaviour of Ti/TiN multilayer coated tool steel has been investigated by potentiodynamic measurements in 0.1 M H2SO4 and compared with single layer coatings of Ti and TiN, respectively. All the coatings had a total thickness of about 1 mu
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| 8. |
- Herranen, Merja, et al.
(author)
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Corrosion properties of thin molybdenum silicide films
- 1997
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In: Surface and Coatings Technology. ; 96:2-3, s. 245-254
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Journal article (peer-reviewed)abstract
- The corrosion properties of sputtered molybdenum and molybdenum silicide films in hydrochloric acid (HCl) have been studied by means of potentiodynamic measurements. Contributions from the substrate to the corrosion behaviour was avoided by depositing the films on inert aluminium oxide (Al2O3). The compositions studied were Mo, MoSi0.58, MoSi1.04, MoSi1.4 and MoSi1.9–2.1. Characterisation of the sampies was made by X-ray diffraction (XRD) and scanning electron microscopy (SEM) before and after corrosion. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to analyse the polarised films. Corrosion of M3Si was found in the molybdenum-rich samples (MoSi0.58) containing the two phases Mo3Si and Mo5Si3. Polarisation curves for these films showed one passivation peak at 228 mV vs. the saturated calomel electrode (SCE). The MoSi1.9–2.1 films had the best corrosion properties of the films studied. This composition had three passivation peaks, at about 154, 305 and 1850 mVSCE, respectively. In the silicon-rich samples, containing the phases MoSi2 and Mo5Si3, preferentiai corrosion of Mo5Si3 was found. All the samples containing the disilicide phase showed at least two passivation peaks. XPS and AES studies on the passive films formed on the samples at the two first passivation peaks indicate that both peaks are due to oxidation of silicon- and molybdenum-containing species. The amount of molybdenum in the outermost layer is increased after the second peak.
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| 9. |
- Herranen, Merja, et al.
(author)
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In situ scanning force microscopy study of TiN layers in sulphuric acid
- 1997
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In: JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B. - 1071-1023. ; 15:6, s. 1865-1870
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Journal article (peer-reviewed)abstract
- Morphological changes of sputter-deposited TiN films in 0.1 M sulphuric acid have been followed in situ with scanning force microscopy at different potentials. Disappearance of small structures was observed with increasing potential up to 1.2 V. A furthe
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| 10. |
- Heszler, Peter, et al.
(author)
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Amorphous carbon film deposition by laser induced C60 fragmentation
- 1997
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In: Applied Surface Science. ; 109, s. 457-461
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Journal article (peer-reviewed)abstract
- It is demonstrated that a pure carbon (fullerene) precursor, C60, is appropriate for laser-induced carbon film deposition. Amorphous carbon films were obtained on Si and SiO2 substrates upon ArF excimer laser induced fragmentation of gas phase C60. The depositions were performed in Ar and H2 ambient in a hot-wall reactor at 550°C. Strong C2 emission bands were observed by optical emission spectroscopy during the deposition process indicating that C2 dimers are used for film formation, however, thermal decomposition of C58, C56, etc. high-mass fragments may also contribute to the layer development. Raman and TEM studies showed amorphous (highly disordered, turbostratic) character of the films. Optical absorption spectroscopy indicated semiconductor feature of the layers with optical band gap of 0.7 and 0.9 eV for the films deposited in Ar and H2 ambient, respectively. For the films deposited in H2 atmosphere, changes in the Raman spectrum and an upshift of the optical band gap of the layer indicate amorphous hydrogenated film with diamond-like character, however, degree of the sp3 hybridisation was estimated to be low. The deposition rate was measured to be 200 Å/min at 500°C and 400 mJ/cm2 laser fluence. AFM measurements showed smooth films with low surface roughness, 1 nm on 1 μm scale length.
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