| The use of fossil fuel lead to series of environmental problem such as acid rain, greenhouse effect etc, and depletion of this kind fuel itself raise question in front of the mankind development. Solar energy is without doubt the most extensive renewable energy in its class, and also is reseach on this field. Among different means of solar energy utilization, only photovoltaic and photothermal are performed in practice. Phtotovoltaic features high-cost and limited applicaition, while photothermal boost advantages of low-cost, easy scale-up, etc, especially solar thermal plant can provide electricity too. The receiver plays an important role in the solar thermal plant. Electricity generation demand the absorbing coating in the receiver performe in higher temperature, absorbs more and emmit less. Absorbing coating based on porous alumina features easy prepation and low energy consumption. Improvement of thermal stability and application of itself in constructing particular absorbing surface become two main development directions for this kind of absorber. Along this direction, focus is given on improving the absorber thermal stability based on a clear aware of the propety of porous alumina in this paper.In this paper, a necessary effort is given to analyze the influence of different parameters on the formation effect of AAO, including the pre-treatment of aluminum, electrolytes, concentration, applied potential, reaction temperature, etc. Optimization is done to the synthesis procedure in different electrolytes, and AAO of 40 nm 300 nm diameters, hundreds of nanometer to micrometers length is successfully manufactured on the high-purity aluminum at room temperature. Then, we try the effort to use commercial aluminum to produce AAO template. Through two-step anodic process, AAO film of 40 100 nm diameter, hundreds of nanometer to several micrometers length has been available.Following, optical charactaristic of AAO film with different diameter and depth as well as metal pigmented ones were studied; proper AAO film was selected for construction of selective absorber. Cu-Al2O3, Ni-Al2O3, Cu-Mo-Al2O, Ni - MoOx - Al2O3 was prepared through AC deposition in the AAO template. The best convertion efficiency was abtained on the Cu-Al2O3 film, with absorption?= 0.972,?= 0.105. Ni-Al2O3 film boasted the best thermal stability, optical properties was not changed after 100 h annealling at 300?in air, the absorption?reached 0.928,?< 0.10, which is applicable for the practical use. Metal alloy pigmented alumina was less effective both in optical efficiency and thermal stability compared with the former ones, resonable explanation was proposed.A new selective solar absorber coating of Cu–CuAl2O4 hybrids deposited in anodic aluminum oxide (AAO) on aluminum substrate has been prepared through an electrochemical process. The structure, composit and morphology was investigated by SEM, TEM, XPS, EDS, DRS, the CuAl2O4 belongs to spinel class, while Cu is crystallines. The filled Cu–CuAl2O4 hybrids was 600 700 nm length, 40 50 nm diameter, of which an overall optical performance of absorptance (?= 0.923) and emittance (?= 0.06) was achieved. The stability of the absorber was tested at high temperature and condensation at high humidity. While a decreased after annealing at 200 for 24h,?was slightly in?uenced; the absorber showed high selectivity (?/?) of 0.87/0.04. Even after exposing to 300?for 48h, the optical property did not change. XRD analysis showed that crystalline structure of the hybrids did not change after annealing treatment; probable reasons for the optical degradation are presented.Using electro-deposition technique to implement metal and metal-semiconductor composite into porous anodic alumina realize the easy control of nanorods size, which can favor the photo-thermal, photocatalytic effect of nano-size materials. It's more convenient for this technique to scale-up and to solve the immolization problem of catalyst, which contribute to the practical application of the nano materials. |
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