Surface O2 Content Research Articles

Wetting and bonding characteristics of selected liquid metals with a high–power diode–laser–treated alumina bioceramic

Changes in the wettability characteristics of an alumina bioceramic occasioned by high power diode laser (HPDL) surface treatment were apparent from the observed reduction in the contact angle. Such changes were due to the HPDL bringing about reductions the surface roughness, increases in the surface O2 content and increases in the polar component of the surface energy. Additionally, HPDL treatment of the alumina bioceramic surface was found to effect an improvement in the bonding characteristics by increasing the work of adhesion. An electronic approach was used to elucidate the bonding characteristics of the alumina bioceramic before and after HPDL treatment. It is postulated that HPDL induced changes to the alumina bioceramic produced a surface with a reduced bandgap energy which consequently increased the work of adhesion by increasing the electron transfer at the metal/oxide interface and thus the metal-oxide interactions. Furthermore, it is suggested that the increase in the work of adhesion of the alumina bioceramic after HPDL treatment was due to a correlation existing between the wettability and ionicity of the alumina bioceramic; for it is believed that the HPDL treated surface is less ionic in nature than the untreated surface and therefore exhibits better wettability characteristics.

CO2 laser modification of the wettability characteristics of a magnesia partially stabilized zirconia bioceramic

This paper describes the utilization of a 3 kW continuous wave CO2 laser to modify the wettability characteristics of the magnesia partially stabilized zirconia (MgO-PSZ) bioceramic and analyses the changes in the physical characteristics of the MgO-PSZ surface following the CO2 laser interaction. The measurement with a set of test liquids revealed that CO2 laser surface treatment of the MgO-PSZ brought about a reduction in the contact angles, θ, indicating that the wettability characteristics of the MgO-PSZ had been enhanced. It was subsequently deduced that the factors active in causing the observed modification in the wettability characteristics of the MgO-PSZ were the increase in the surface O2 content and the increase in the polar component of the surface energy, γsvp. Furthermore, it was noted that the considerable decrease in contact angle was disproportional to the increase in surface roughness, showing surface roughness plays a minor role in inducing changes of the wettability characteristics of the MgO-PSZ. The value of this paper is that establishes the CO2 laser as a controllable and flexible process for improving the surface properties of the MgO-PSZ bioceramic.

On the mechanisms of wetting characteristics modification for selected metallic materials by means of high power diode laser radiation

This work elucidates and analyzes the factors responsible for modifications to the wettability characteristics of metallic materials after high power diode laser (HPDL) treatment. It was found that interaction of EN3 and EN8 mild steel with HPDL radiation resulted in the wettability characteristics of the mild steels altering to various degrees depending upon the laser processing parameters. Such changes in the wettability characteristics of the mild steels were found to be due essentially to: (i) modifications to the surface roughness; (ii) changes in the surface O2 content; and (iii) the increase in the polar component of the surface energy. All of these factors were seen to influence the wettability characteristics of the mild steels, however, the degree of influence exerted by each was found to differ. Work was therefore conducted to isolate each of these influential factors, thereby allowing the magnitude of their influence to be determined. This analysis revealed that surface roughness was the primary influential factor governing changes in θ and hence the wettability characteristics of the mild steels. Surface energy, by way of microstructural changes, was also shown to influence to a lesser extent changes in the wettability characteristics, while surface O2 content, by way of process gas, was found to play a minor role in inducing changes in the wettability characteristics of the mild steels.

Wettability characteristics of polyethylene modified with CO2, Nd:YAG, excimer and high-power diode lasers

Interaction of CO2, Nd:YAG, excimer and high-power diode laser (HPDL) radiation with the surface of the biomaterial polyethylene (PE), was found to effect varying degrees of change to the wettability characteristics of the material depending upon the laser used. It was observed that interaction with CO2, Nd:YAG and HPDL effected very little change to the wettability characteristics of the PE. In contrast, interaction of the PE with excimer laser radiation resulted in a marked improvement in the wettability characteristics. After excimer laser treatment, the surface O2 content was found to have increased and the material was seen to be more polar in nature, resulting in a significant increase in the wettability characteristics. The work has shown that the wettability characteristics of the PE could be controlled and/or modified with laser surface treatment. However, a wavelength dependence of the change in the wetting properties could not be deduced from the findings of this work.

The characteristics of a high-power diode laser fired enamel coating on a carbon steel

Significant changes to the wettability characteristics of a common engineering carbon steel (EN8) were effected after high power diode laser (HPDL) surface treatment. These modifications have been investigated in terms of the changes in the surface roughness of the steel, the presence of any surface melting, the polar component of the steel surface energy and the relative surface O2 content of the steel. The morphological and wetting characteristics of the mild steel and the enamel were determined using optical microscopy, scanning electron microscopy, X-ray photoemission spectroscopy, energy-dispersive X-ray analysis and wetting experiments by the sessile drop technique. This work has shown that HPDL radiation can be used to alter the wetting characteristics of carbon steel so as to facilitate improved enamelling. Furthermore, standard mechanical, physical and chemical testing of the HPDL-fired enamel glaze revealed the glaze to possess similar properties to those of a conventionally fired enamel glaze in terms of bond strength, rupture/impact strength, wear and corrosion resistance. Such similar performance can be attributed to the two glazes possessing the same mechanical properties and similar amorphous structure, despite their very different firing techniques.

Wettability characteristics of a modified mild steel with CO2, Nd:YAG, excimer and high power diode lasers

Interaction of CO2, Nd:YAG, excimer and high-power diode laser radiation with the surface of a common mild steel (EN8) was found to effect changes in the wettability characteristics of the steel, namely changes in the measured contact angle of certain liquids. Such changes were identified as being due to modifications to (i) the surface roughness, (ii) changes in the surface oxygen content and (iii) changes in the surface energy of the mild steel. However, it was found that changes in the wettability characteristics of the mild steel were predominantly influenced by the surface roughness. To a much lesser extent surface O2 content is also thought to play a role. The work has shown that the wettability characteristics of the selected mild steel could be controlled and/or modified with laser surface treatment. Moreover, the findings of this work strongly indicate the existence of a relationship between the change of the wetting properties of the mild steel and the laser wavelength.

The effect of chromating on borohydride reduced iron powders

Iron powders with Hc between 350 Oe and 1000 Oe were prepared by borohydride reduction of ferrous sulfate. The powders were stabilized by a chromating procedure. This paper discusses the effect of the chromating as observed by: TEM, changes in surface area, O2 content, ESCA/Auger and adsorption. Chromating coats the surface of the particles with a layer of FeCr2O4. Oxygen content in chromated powders is generally ∼8% while in the unchromated powders, it varies between 11 and ≳16%. This increase in O2 can be correlated with a decrease in σs. Sheet-like impurities are observed in unchromated powders which have been identified as FeOOH. Chromating results in a reduction in surface area of the particles as measured by N2 adsorption. The stability of the powders is greatly improved with chromating. Powders subjected to 80% R.H. for 112 days showed that the unchromated powder lost 25% of its original magnetization, while the chromated powder lost only 3%. Simultaneously, a band of FeO and Fe2O3 formed around the particles. Adsorption studies of reference polymers have shown that chromating reduces the acidic surface sites of the powders.