Long-term Degradation Tests Research Articles

Long-term accelerated current operation of white light-emitting diodes

Long-term degradation tests regarding white light-emitting diodes based on InGaN were performed under accelerated current conditions, and the half-life of the light's output was estimated. An estimated mean half-life of 1.5×10 4 h was obtained under the recommended 20-mA operating condition. The change in the emission spectrum was found to be slight, and the color quality was considered generally satisfactory over the long term.

Estimation of the degradation of amorphous silicon solar cells

A long-term degradation test on amorphous silicon (a-Si) solar cells was performed under various light intensity and temperature conditions. We derived a basic equation for estimating the degradation of conversion efficiency and clarified the dependence of the level of degradation on these parameters. A unique phenomenon in which degradation was suppressed with increasing temperature was observed, and negative activation energies were obtained. The degraded characteristics of the solar cells recovered upon thermal annealing and the recovery characteristics were approximately using a stretched exponential function. The mechanisms by which degradation and recovery advance simultaneously with time are discussed.

Long-term degradation tests of amorphous silicon solar cells: Correlation between light- and current-induced degradation characteristics

Long-term degradation tests were conducted on amorphous silicon solar cells by light and current-induced technique. The correlation of the degradation patterns and the lifetime estimation data in these two methods have confirmed that mutual stress conversion of light intensity P L and current intensitiy I j is possible in estimating the lifetime of solar cells. The degradation tests are conducted at the same stress level which is expressed by the equation P L =B·I j ϵ. It has also been revealed that the short-circuit current of the cell,generated at light intensity P L is almost equal to the value obtained from the stress conversion of I J. Light-induced degradation is suppressed with increasing ambient temperature and is also same for current-induced degradation. The degradation and recovery mechanisms are common in both case.

Correlation between light and current induced degradationin a-Si solar cells

Long-term degradation tests were carried out on amorphous silicon solar cells by light irradiation and current injection. The correlation of the degradation patterns and the lifetime estimation data in these two methods have confirmed the mutual stress conversion of light and current intensity. It is possible to estimate the lifetime of solar cells.

Bioavailability of Pulp and Paper Mill Effluent Phosphorus

The aim of this study was to examine the stability and bioavailability of different phosphorus fractions of pulp and paper mill effluents in order to assess the environmental benefits of reducing their phosphorus discharges. Two types of effluent were studied: activated sludge treated bleached kraft mill effluent and activated sludge treated paper mill effluent. Phosphorus was characterized on the basis of its solubility and chemical reactivity. The stability of particulate phosphorus was studied in long-term (6-8 weeks) degradation tests. The bioavailability of different phosphorus fractions was measured by algal growth potential tests. In bleached kraft mill effluent (BKME) the proportion of dissolved phosphorus in relation to the total phosphorus was on an average 80%, and of this, approximately 80-90% was reactive phosphorus. During a 6-8 week incubation period some 60-70% of the particulate phosphorus in BKME was dissolved as soluble phosphorus, and most of it was of the reactive type. Approximately 90% of the dissolved phosphorus and 45% of the particulate phosphorus in BKME was biologically available phosphorus (BAP). Altogether some 80% of the total phosphorus in activated sludge treated BKME was available for algae either immediately or after inherent degradation. The percentages of dissolved and particulate phosphorus of paper mill effluent (PME) total phosphorus were of the same order of magnitude as those of BKME, but less than 20% of the dissolved phosphorus was of the reactive type. Approximately 50-60% of the particulate phosphorus in PME was dissolved in degradation tests, and 90% of it was biologically available.

Degradation effects of dilute polymer solutions on turbulent friction and heat transfer behavior

Long-term degradation tests for dilute polymer solutions flowing turbulently in circular pipes were conducted in a closed recirculatory flow loop at room temperature. The polymeric additives used were Polyox WSR-301 and Separan AP-273 at 200 ppm wt. in deionized water. The degradation run for Separan was conducted for 730 h, which is considerably longer than any of the earlier degradation studies reported in the literature. The degradation run for Polyox was conducted for only 22 h because of the extreme sensitivity of Polyox to shear degradation. Effects of degradation on turbulent friction and heat transfer coefficients are presented. It was found that dilute Polyox solution cannot be used in recirculatory systems because it degraded completely in less than 24 h. However, dilute Separan solution did not degrade completely under a typical flow shear condition but maintained a plateau value of about 25% friction reduction after the initial rapid degradation period. The existence of a plateau for the dilute Separan solution is an important finding because it implies that this solution may be a good candidate for use in practical closed-loop thermal systems.