Cao Chunan

Study of double layer rare earth metal conversion coating on aluminum alloy LY12

The process of the double layer rare earth metal (REM) conversion coating on aluminum alloy LY12 (2024) was introduced in this paper. The corrosion resistance of REM conversion coating was examined by electrochemical impedance spectroscopy. The results showed that the coating increased the corrosion resistance (Rp) of the alloy surface, thus reducing the driving force of corrosion. The morphologies of the coating were studied by scanning electron microscope. The results revealed that the coating consisted of layers of spherical particles with different size, which grew gradually to cover the surface of aluminum alloy. The X-ray diffraction analysis revealed that the film was amorphous. The results of X-ray photoelectron spectroscopy indicated that the film consisted of cerium(III and IV) oxide and cerium(III and IV) hydroxide.

Corrosion behavior of rare earth metal (REM) conversion coatings on aluminum alloy LY12

The processes of the double layer rare earth metal (REM) conversion coating on aluminum alloy LY12 (2024) were introduced. The results of polarization tests showed that the corrosion resistance of the double layer REM conversion coating was superior to that of chromate conversion coating. The corrosion behavior of REM conversion coatings on LY12 alloy was studied with optical microscopy and energy dispersive spectroscopy (EDS). The results showed that in NaCl solution, pits initiated on the coatings formed on Cu-rich intermetalics. According to the equivalent circuit of pitting, a new method for analyzing the pit growth of REM conversion coatings was put forward by employing electrochemical impedance spectroscopy (EIS). Transmission line W in equivalent circuit could be neglected in short term exposure of REM conversion coatings to NaCl solution. This led to a formula for calculating the area fraction of pitting (F) on the surface of REM conversion coatings by simplifying the equivalent circuit

Application of rare earth metal salts in sealing anodized aluminum alloy

chinese acad sci, inst corros & protect met, state key lab corros & protect, shenyang 110015, peoples r china.;yu, xw (reprint author), chinese acad sci, inst corros & protect met, state key lab corros & protect, shenyang 110015, peoples r china

Theoretical errors of linear polarization resistance and a method for reducing them

Three types of linear polarization resistance (LPR) may provide an approximate value of polarization resistance (Rp) for estimating the corrosion current density icorr: an anodic LPR, Ra, a cathodic LPR, Rc and a bi-directional LPR, Rb. Theoretical errors of the LPSs depend upon two factors. One is related to the symmetric characteristic between anodic and cathodic branches of polarization curve and may be described by a parameter α = (βII)/(βI), where β denotes the Tafel slopes and the subscripts indicate smaller and larger values respectively. The other factor is related to the polarization measurement of the LPR and can be expressed by (| ΔE |;)/(βI), where | ΔE | is the absolute value of polarization in one direction. (1) For the same value of (| ΔE |)/(βI), the largest theoretical error for Rb will occur as a = 1 or α → ∞ whilst for Ra or Rc this will be as α → ∞ (2) The theoretical error of Rb is always less than that of Ra and Rc under the same conditions except in the case of α → 1. When α = 1, the value of all three types of LPR are equal to each other. (3) The theoretical errors of LPR values increase with increasing of the value of (| ΔE |)/(βI), but in most cases the increasing rate for Rb is far less than that for Ra or Rc. Based on the mathematical analysis, a method to reduce the theoretical error of Rb was proposed. If two measurements are made in succession with the polarization values ± | ΔE1 | and ±m |; ΔE1 |;, where 1 < m ⩽ 2 and | ΔE1 | ⩽ βI, and if the bi-directional LPRs thus measured are denoted by Rb1 and Rb2 respectively, then theoretical error of Rp(approx.) as estimated by the equation Rp(approx.) = (m2−1)Rb1 Rb2m2Rb2−Rb1 would be far less than that of Rb1 and Rb2.

Progress of Study on Erosion-corrosion

The current situation of study on erosion-corrosion mechanism and the influence of dif- ferent environmental factors and alloy properties on erosion-corrosion is reviewed in this paper. The erosion-corrosion is mainly composed of two parts: erosion wear and electrochemical corro- sion, of which the contribution to the total erosion-corrosion rate may depend upon the environmen- tal factors. To protect metallic materials from erosion-corrosion the following measures may be ef- fective: i.e. proper selection and addition of alloying elements, proper heat treatment and applied surface coatings as well. Meanwhile, the paper discusses the development of erosion-corrosion re- search in the future.

Discharge Performance of Alkaline Sulfide Fuel Cells Using Non-Precious Anode Catalysts

The choice of fuel is an important issue influencing the selection of catalyst, cost, and commercialization of fuel cells. Electrochemically-active and low-cost fuels that can be oxidized by non-precious catalysts are an attractive objective. The native electrochemical activity and low cost of sulfide make it a suitable candidate. Fuel cells using alkaline sulfide as a fuel were developed. At room temperature, a single cell containing non-precious anode catalysts achieves a maximum power density of 12.3 mW·cm-2 with a current density of 42.8 mA·cm-2. Life tests show that alkaline sulfide fuel cells exhibit good durability. Ion chromatography detected considerable amounts of thiosulfate, sulfite, and sulfate. The deep oxidation and high capacity of sulfide make it an attractive fuel candidate. Compared with other fuels, sulfide has the advantages of being inexpensive, easy to transport, possesses high electrochemical activity, and can be catalyzed by non-precious catalysts.

Stress corrosion cracking of AISI 321 stainless steel in acidic seawater

The stress corrosion cracking (SCC) of AISI 321 stainless steel in acidic in acidic seawater was studied by slow strain rate (SSR) technique and fracture mechanics method. The fractured surface was characterized by cleavage fracture. The inhibiting effects of KI on SCC behavior were also covered in this detailed study which showed that they were mainly attributable to their inhibition on anodic reaction. The SCC mechanism study supported the unified mechanism of SCC and corrosion fatigue cracking (CFC).