护环法在钢筋混凝土体系腐蚀评价中的可行性研究

采用普通三电极体系评价现场大钢筋混凝土结构时,辅助电极面积与钢筋表面积相差很大而导致极化电力线难以均匀分布在钢筋表面,极化面积不确定。为解决这一问题,采用护环电极(Guard Ring Elec-trode,GRE or GE)方法即在普通三电极法基础上添加一圆环形护环电极(GE),通过GE电流将辅助电极(CE)电流限制在CE投影面积内,试验中评价了不同腐蚀状态的钢筋,并与均匀极化法对比,结果表明:在正确的电流限制下,护环电极法能够较准确地评价钢筋腐蚀状态,该方法尤其适合已脱钝体系。

A n-Si/CoOx/Ni:CoOOH photoanode producing 600 mV photovoltage for efficient photoelectrochemical water splitting

n-Si,believed as a promising photoanode candidate,has suffered from sluggish oxygen evolution reaction(OER)kinetics and poor chemical stability when exposed to aqueous electrolyte.Herein,CoO_(x)/Ni:CoOOH bilayers were successfully deposited on n-Si substrate by atomic layer-deposition(ALD)and photoassisted electrochemical deposition(PED)for stabilizing and catalyzing photoelectrochemical(PEC)water oxidation.In comparison to the n-Si/CoO_(x)photoanode as reference,the prepared n-Si/CoO_(x)/Ni:CoOOH photoanode upon the optimized PED process presents a much improved PEC performance for water splitting,with the onset potential cathodically shifted to~1.03 V vs.reversible hydrogen electrode(RHE)and the photocurrent density much increased to 20 mA cm^(−2)at 1.23 V vs.RHE.It is revealed that the introduction of Ni dopants increases the work functions of the deposited Ni:CoOOH overlayers,which gives rise to the upward band bending weakened at the n-Si/CoO_(x)/Ni:CoOOH cascading interface while strengthened at the Ni:CoOOH/electrolyte interface(with the band bending shifted from downward to upward),contributing to the decreased and the increased driving forces for charge transfer at the interfaces,respectively.Then,the balanced driving forces at the interfaces would endow the n-Si/CoO_(x)/Ni:CoOOH photoanode with the best PEC performance.Moreover,PED has been evidenced superior to ED to dope Ni into CoOOH with the formed overlayer effectively catalyzing and stabilizing PEC water splitting.

Positive and negative shear lag behaviors of composite twin-girder decks with varying cross-section

In steel-concrete composite twin-girder decks, wide concrete slab would undergo significant shear lag warping effect, including positive and negative. Some researchers have investigated the positive shear lag of composite decks by means of one-dimensional line model, while the studies on the negative shear lag have not yet been reported until now. In this study, a new one-dimensional analytical model of composite twin-girder decks is first proposed based on the model proposed by Dezi et al. Besides slab shear lag effect and partial connection at slab-girder interface which have been included in the model of Dezi et al., the particularity of the proposed model relies on its ability to account for variation characteristic of cross-section. Verification of the analytical model is later conducted through comparison of results from the analytical analysis and elaborate FE analysis for a simply supported composite deck with increasing depth and a two-span continuous one with decreasing depth. Finally, three kinds of structural forms of composite twin-girder decks, including cantilever, simply supported and continuous decks, are selected to carry out the analysis of positive and negative shear lag behaviors by means of the analytical model. The influences of cross-sectional variation characteristic and load type on positive and negative shear lag behaviors are mainly investigated. Additionally, a new definition on effective width for considering simultaneously positive and negative shear lag behaviors is proposed. The results from the proposed analytical model and EC4 specification are compared to provide suggestions for designers and checkers. In this study, the proposed analytical model can provide a powerful numerical tool for researchers to conduct the further investigation, and the analysis on shear lag and effective width can assist in design analysis of composite twin-girder decks.

Surface-area-tuned, quantum-dot-sensitized heterostructured nanoarchitectures for highly efficient photoelectrodes

Harvesting solar energy to produce clean hydrogen from photoelectrolysis of water presents a valuable opportunity to find alternatives for fossil fuels. Three- dimensional nanoarchitecturing techniques can afford enhanced photoelectrochemical properties by improving geometrical and structural effects. Here, we report quantum-dot sensitized TiO2-Sb：SnO2 heterostructures as a model electrode to enable the optimization of the structural effects through the creation of a highly conductive pathway using a transparent conducting oxide （TCO）, coupled with a high surface area, by introducing branching and low interfacial resistance via an epitaxial relationship. An examination of various morphologies （dot, rod, and lamella shape） of TiO2 reveals that the rod-shaped TiO2-Sb：SnO2 is a more effective structure than the others. A photoelectrode fabricated using optimized CdS--TiO2-Sb：SnO2 produces a photocurrent density of 7.75 mA/cm2 at 0.4 V versus a reversible hydrogen electrode. These results demonstrate that constructing a branched heterostructure based on TCO can realize highperformance photoelectrochemical devices.