CORRELATION AMONG CORROSIVE FACTORS OF SOIL

In this paper, through the data treatment of correlation coefficients and the clustering technique of pattern recognition, both the matrix of correlation coefficients and the pedigree of factor clusters show that some factors affecting soil corrosivity are interrelated closely, and some independent relatively. The data analytical method used in this paper has certain assistance to the selection of major soil factors during the prediction and evaluation of soil corrosivity.

CORROSION OF 1Cr13 STAINLESS STEEL IN SOILS

The network of soil corrosion of China, initiated in 1989 a soil burial program in representative corrosive soils utilizing 2 stainless steels(1Cr13 and 1Cr18Ni9Ti), The test soil sites contained acid, neutral, and alkaline soils. This report contains the results of 1Cr13 stainless steel obtained for specimens buried in the soils for up to 1,3,5 years.The results shown, there is slight corrosion of 1Cr13 stainless steel in acid or neutral soils and severe pitting corrosion in alkaline soils. The total contents of Cl and SO 4 2 in soils was the most important factor determining the corrosion behavior of 1Cr13 stainless steel in soils. The weight loss of 1Cr13 increases with the growing of the total contents of Cl and SO 4 2 in soils.

Formation of Black Patina on Bronze Mirrors Caused by Humic Acid

The formation of black patina caused by soil humic acid under different conditions has been studied,and the black, grey and brown shiny surfaces prepared in laboratory have been analysed. The formation of tin-rich shiny black surface on mirrors was the product of the soil corrosion of the bronze mirrors. It is formed by reaction between the alloy and the humic acid in soil, and leaching of copper and lead oxides through a long period of time when the mirrors were buried under the ground. A dense cormsion-resistallt layer on the bronze mirrors consisted predominantly of stannic oxide.

Structure and Formative Mechanism of Black Patina on Bronze Mirrors

The formation of the black patina induced by soil humic asid under different conditions was studied, theblack, grey and brown colored shiny surfaces prepared in laboratory were analyzed. As a result the formation oftin-rich shiny black surface on bronze mirrors is the product of soil corrosion of the bronze mirrors. The patina isformed by reection between the alloy and the humic acid in soil, and leaching of copper and lead oxides through along period time when the mirrors were buried under the ground leaving a dense compact corrosion-resistant layerconsisted predominantly of stannic oxide microcrystal.

Simulated Corrosion Test of Q235 Steel in Diatomite Soil

Through the study of the corrosion behavior of Q235 steel in actual Yingtan soil and two simulated acidic soils with different water contents, the calculation of corrosion mass losses, and the analysis of the corrosion mor- phologies and products by means of scanning electron microscope （SEM） and X-ray diffraction （XRD）, the results demonstrated that the diatomite soil could simulate the corrosion in actual soil veritably. In both actual soil and simu- lated soil with 16.4% water content, the corrosion rates of Q235 steel were approximately 0.1 mm/a, the corrosion morphologies were mainly extension and connection of corrosion spots on sample surface, and the corrosion products were composed of a-FeOOH, γ-FeOOH, Fe3 O4 and Fe2O3. When other media conditions remained unchanged, the corrosion area of Q235 steel was larger in simulated soil with 34.5 % water content, and the corrosion rate reached 0.48 mm/a after 360 h of corrosion, which was nearly 5 times as the value in actual soil. Compared with the corro- sion products in actual soil, the proportion of γ-FeOOH in simulated soil with 34.5 % water content was higher, and the wα-FeOOH/wγ-FeOOH ratio was 1. 4, which was only 1/3 of the value in actual soil.

Galvanic Corrosion Behavior of Copper-Drawn Steel for Grounding Grids in the Acidic Red Soil Simulated Solution

The influence of pH and metallographic structure on the corrosion behavior of copper-drawn steel is studied with the simulated system.The effect of pH on the corrosion behavior of copper-drawn steel has been investigated using open-circuit potential,potentiodynamic polarization,galvanic current measurement,scanning electron microscopy and scanning vibrating electrode technique techniques.The steel is corroded as anode,while the corrosion of copper plate is protected as cathode.All the results revealed that pH and metallographic structure had a significant influence on the corrosion behavior of copper-drawn steel.With the decrease in pH value from 6 to 2.4,the corrosion rate of copper-drawn steel galvanic couple(Cu-Fe GC)obviously increased in the simulated solution of acidic red soil.The electric field formed by the Cu-Fe GC changes the direction of ion migration between the copper and drawn steel electrodes,which impacts the composition and microstructure of corrosion products formed on the electrode surface.

Corrosion behavior of low-carbon Cr micro-alloyed steel for grounding grids in simulated acidic soil

To improve the corrosion resistance of steels for grounding grids, a low-carbon Cr micro-alloyed steel was developed （C 1 steel）, and corrosion behavior of Q235 steel and newly developed C1 steel in simulated acidic soil was investigated. The corrosion rate was evaluated with the mass loss measurements, while the corrosion morphology of surface and cross section of rust layer was observed by scanning electron microscopy. The corrosion products were analyzed by energy- dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy, and the polarization curve was measured using potentiodynamic polarization method. Results indicated that C 1 steel displayed good corrosion resistance in the simulated acidic soil, of which the corrosion rate was only 30% of that of Q235 steel after corrosion for 360 h. The analysis of rust layer showed that lower carbon content in steel could reduce the tendency of micro cell corrosion and appropriate amount of chromium could improve the corrosion potential of metal matrix. Moreover, the analysis of X-ray photoelectron spectroscopy revealed that the chromium enriched in inner rust layer of C1 steel existed mainly in the form of Fe2CrO4, which facilitated the formation of Cr-goethite and improved the protection of corrosion products.

An Application of Dynamic Structure Model to SoilCorrosion Research

Soil corrosion is a complex system which is difficult to be simulated with mathematicalmodels. Taking the mountainous areas in western henan Province as an example, this paper describesthe application of dynamic structure model to soil corrosion analysis. The primary component factors ofthe soil corrosion system and the causality of the factors are determined in this paper. The interactiverelations of the systematic variables is established with delphi method. The dynamic structure modelis selected to make the forecast of the soil corrosion system, the analysis of sensitivity of the variablesand the analysis of the system control.

Crevice Corrosion of K60 in Dry Desertification Saline Soil

Corrosion products of K60crevice samples which were buried in Ordos area were analyzed by scanning electron microscopy and X-ray diffraction.The result showed that,the corrosion potential decreased differently in the crevice and a maximum negative existed at the bottom side;with pH value reduced,the dissolved oxygen was nearly exhausted in the crevice.When the opening side of the coupons was coupled with each other,the crevice corrosion in the crevice might be accelerated and the pH value gradually reduced;however,the oxygen was not completely exhausted.The unbalanced current density between anode and cathode was the main cause of blocked self-catalysis effect in the crevice,and was also the main cause of corrosion of alloys.Lumpy corrosion happened on the surface of metal,and rusty layer was composed of Fe3O4,Fe2O3,FeO,FeOOH and FeS which distributed in the opening of crevice.There were the reddish-brown corrosion products and white matter which distributed in the form of filiform and spotted in the center part of crevice.The analysis showed that the white matter might include oxide of Fe and NaHCO3.