Identification of the principal elements governing the wettability characteristics of ordinary Portland cement following high power diode laser surface treatment

The elements governing modifications to the wettability characteristics of ordinary Portland cement (OPC) following high power diode laser (HPDL) surface treatment have been identified. Changes in the contact angle, , and hence the wettability characteristics of the OPC after HPDL treatment were attributed to: reductions in the surface roughness of the OPC; the increase in the surface O2 content of the ceramic and the increase in the polar component of the surface energy, . What is more, the degree of influence exerted by each element has been qualitatively ascertained and was found to differ markedly. Surface energy, by way of microstructural changes, was found to be by far the most predominant element governing the wetting characteristics of the OPC. To a much lesser extent, surface O2 content, by way of process gas, was also seen to influence to a changes in the wettability characteristics of the OPC, whilst surface roughness was found to play a minor role in inducing changes in the wettability characteristics

The wear characteristics of a high power diode laser generated glaze on the ordinary Portland cement surface of concrete

The ordinary Portland cement (OPC) surface layer of concrete, which was glazed using a high power diode laser (HPDL), has been tested in order to determine the wear characteristics of the glaze. The work showed that the generation of a surface glaze resulted in the considerable enhancement of the wear characteristics over an untreated OPC surface of concrete. Within both normal and corrosive (detergent, NaOH and HNO3) environmental conditions the wear rate of the HPDL generated glaze was 3.5 mg.cm-2.h-1. In contrast, the untreated OPC surface of concrete exhibited a wear rate of 9.8 - 114.8 mg.cm-2.h-1 when exposed to the various reagents. Life assessment testing revealed that the laser glazed OPC surfaces effected an increase in actual wear life of 1.3 to 17.7 times over the untreated OPC surface of concrete, depending upon the corrosive environment. The reasons for these marked improvements in the wear resistance and wear life of the HPDL generated glaze over the untreated OPC surface of concrete can be attributed to firstly, the vitrification of the OPC surface after HPDL treatment which subsequently created a much more dense and consolidated surface, and secondly, the generation of a surface with improved microstructure and phase which is more resistant in corrosive environments

A comparative analysis of the wear characteristics of glazes generated on the ordinary Portland cement surface of concrete by means of CO2 and high power diode laser radiation

The wear characteristics of a glaze generated on the ordinary Portland cement (OPC) surface of concrete using a 2 kW high power diode laser (HPDL) and a 3 kW CO2 laser have been determined. Within both normal and corrosive environmental conditions, the wear rate of the CO2 and HPDL generated glazes were consistently higher than the untreated OPC surface of concrete. Life assessment testing revealed that surface glazing of the OPC with both the CO2 and the HPDL effected an increase in wear life of 1.3 to 17.7 times over an untreated OPC surface, depending upon the corrosive environment. The reasons for these marked improvements in the wear resistance and wear life of the CO2 and HPDL generated glazes over the untreated OPC surface of concrete can be attributed to the partial (CO2 laser) and full (HPDL) vitrification of the OPC surface after laser treatment which subsequently created a much more dense and consolidated surface with improved microstructure and phase characteristics which is more resistant in corrosive environments. In addition, the wear life and the wear rate of the HPDL glaze was found to be consistently higher than that of the CO2 laser glaze. This is due to the fact that CO2 and HPDLs have very different wavelengths; consequently, differences exist between the CO2 and HPDL beam absorption characteristics of the OPC. Such differences give rise to different cooling rates, solidification speeds, etc and are, therefore, the cause of the distinct glaze characteristics which furnishing each microstructure with its own unique wear resistance characteristics

The enamelling of concrete for improved performance characteristics by means of high power diode laser interaction

The contemporary 120 W high power diode laser (HPDL) has been successfully used for the first time to fire an enamel glaze onto the ordinary Portland cement (OPC) surface of concrete. The enamel glazes were generated with laser power densities as low as 1 kW/cm2 and at speeds of up to 780 mm/min, yielding a possible maximum coverage rate of 0.34 m2/h. The enamel glazes were typically 750 m in thickness and displayed no discernible microcracks or porosities. Owing to the wettability characteristics of the OPC, it proved necessary to laser treat the OPC surface prior to firing the enamel. Mechanical testing of the HPDL fired enamel glazes revealed that the average rupture strength was 2.8 J, whilst the rupture strength of the untreated OPC surface was some 4.3 J. The average bond strength of the glaze was recorded as 2.4 MPa as opposed to 6.3 MPa for the untreated OPC. The HPDL fired enamel glazes exhibited exceptional wear and corrosion resistance, wearing by only 3.3 mg/cm2 after 8 h and showing no discernible morphological or microstructural changes when exposed to acid, alkali and detergent. In contrast, the untreated OPC surface was attacked almost immediately by the reagents used and was worn by 78 mg/cm2 after 8 h. In addition, the HPDL fired enamel glaze afforded the concrete bulk complete resistance to water absorption. The findings of life assessment testing revealed that the HPDL fired enamel glaze effected an increase in the wear life of the concrete by 4.5 to 52.7 times over an untreated OPC surface, depending on the corrosive environment

The influence of shield gases on the surface condition of laser treated concrete

This work aims to elucidate the effects of using O2, Ar and He shield gasses during the treatment of the ordinary Portland cement (OPC) surface of concrete with a high power diode laser (HPDL). The findings showed a marked difference existed in the surface condition of the concrete after HPDL treatment depending on the shield gas used. The use of O2 as the shield gas was seen to result in glazes with far fewer microcracks and porosities than those generated with either Ar or He shield gases. Such differences were found to be due to the smaller O2 gas molecules dissolving molecularly into the open structure of the HPDL generated glaze on the OPC surface of concrete and react with the glass network to increase the fluidity of the melt. This in turn was also seen to affect the cooling rate and therefore the tendency to generate microcracks

Determination of the absorption length of CO2, Nd:YAG and high power diode laser radiation for a selected grouting material

The laser beam absorption lengths of CO2, Nd:YAG and a high power diode laser (HPDL) radiation for a newly developed SiO2/Al2O3-based tile grout have been determined through the application of Beer-Lambert’s law. The findings revealed marked differences in the absorption lengths despite the material having similar beam absorption coefficients for the lasers. The absorption lengths for the SiO2/Al2O3-based tile grout for CO2, Nd:YAG and HPDL radiation were calculated as being 23211 m, 1934 m and 1838 m respectively. Moreover, this method of laser beam absorption length determination, which has hitherto been used predominantly with lasers operated in the pulsed mode, is shown to be valid for use with lasers operated in the continuous wave (CW) mode, depending upon the material being treated

The influence of a high power diode laser (HPDL) generated glaze on the wetting characteristics and the subsequent HPDL enamelling of ordinary Portland cement

High power diode laser (HPDL) surface glazing of the ordinary Portland cement (OPC) surface of concrete was found to effect significant changes in the wettability characteristics of the OPC. This behaviour was identified as being primarily due to: (i) the polar component of the OPC surface energy increasing after HPDL glazing from 3.46 to 15.56 mJm-2, (ii) the surface roughness of the OPC decreasing from an Ra value of 21.91 to 2.88 m after HPDL glazing and (iii) the relative surface O2 content of the OPC increasing by 4.5at% after HPDL glazing. HPDL glazing was consequently identified as occasioning a decrease in the enamel contact angle from an initial value of 1090 to 310, thus allowing the vitreous enamel to wet the OPC surface

Augmentation of the mechanical and chemical resistance characteristics of an Al2O3-based refractory by means of high power diode laser surface treatment

Augmentation of the wear rate and wear life characteristics of an Al2O3-based refractory within both normal and corrosive (NaOH and HNO3) environmental conditions was effected by means of high power diode laser (HPDL) surface treatment. Life assessment testing revealed that the HPDL generated glaze increased the wear life of the Al2O3-based refractory by 1.27 to 13.44 times depending upon the environmental conditions. Such improvements are attributed to the fact that after laser treatment, the microstructure of the Al2O3-based refractory was altered from a porous, randomly ordered structure, to a much more dense and consolidated structure that contained fewer cracks and porosities. In a world economy that is increasingly placing more importance on material conservation, a technique of this kind for delaying the unavoidable erosion (wear) and corrosion that materials such as the Al2O3-based refractory must face may provide an economically attractive option for contemporary engineers

Surface treatment of an Al2O3-based refractory with CO2 and high power diode lasers for improved mechanical and chemical resistance characteristics

Within both normal and corrosive (NaOH and HNO3) environmental conditions, the wear rate and wear life characteristics of an Al2O3-based refractory were greatly enhanced by means of CO2 and high power diode laser (HPDL) surface treatment. Such improvements are attributed to the fact that after laser treatment, the microstructure of the Al2O3-based refractory was altered from a porous, randomly ordered structure, to a much more dense and consolidated structure that contained fewer cracks and porosities. What is more, resulting from the different rates of solidification brought about by differences in the wavelengths of the two lasers, dissimilar microstructures were subsequently generated. Indeed, despite the fact that the glaze thickness was less, the wear life of the HPDL treated surface exceeded that of the CO2 laser treated surface in all the test environments owing to its finer, more densely packed and less cracked microstructure

US Trade and Wages: The Misleading Implications of Conventional Trade Theory

Conventional trade theory, which combines the Heckscher-Ohlin theory and the Stolper- Samuelson theorem, implies that expanded trade between developed and developing countries will increase wage equality in the former. This theory is widely applied. It serves as the basis for estimating the impact of trade on wages using two-sector simulation models and the net factor content of trade. It leads naturally to the presumption that the rapid growth and declining relative prices of US manufactured imports from developing countries since the 1990s have been a powerful source of increased US wage inequality. In this study we present evidence that suggests the presumption is not warranted. We highlight the sensitivity of conventional theory to the assumption of incomplete specialization and find evidence that is not consistent with it. Since 1987, although US domestic relative effective prices in industries with relatively high shares of manufactured goods imports from developing countries have declined, effective unskilled-worker weighted prices have actually risen relative to skilled- worker-weighted prices. If anything this suggests pressures for increased wage equality. Also in apparent contradiction to theory, the (six-digit NAICS) US manufacturing industries with high shares of manufactured imports from developing countries are actually more skill-intensive than the industries with high shares of imports from developed countries. Finally, applying a two-stage regression procedure, we find that developing country import price changes have not mandated increased US wage equality. While these results conflict with standard theory, they are easily explained if the US and developing countries have specialized in products and tasks that are imperfect substitutes. If this is the case, the impact of increased trade with developing countries on US wage inequality is far more muted than standard theory suggests. Also methodologies such as the net factor content of trade using US production coefficients and simulation models assuming perfect substitution between imports and domestic products could be highly misleading.