This invention relates generally to studying crevice corrosion. More particularly, this invention relates to a multiple-reference electrode array for measuring open circuit potentials in artificial aerosol container crevices.
A common problem associated with commercial aerosol containers is that the metals (e.g., tinplated steel, aluminum or the like) used to form the containers are susceptible to corrosion. The potential for corrosion depends, at least partially, on both the material used to construct the container and the medium (e.g., solution) provided in the container. Generally, the materials used to construct such containers are subject to a uniform amount of corrosion along their inner surfaces. However, in cracks and crevices formed in the containers, there occurs non-uniform corrosion that manifests itself in the form of, for example, pitting. In addition, the non-uniform corrosion occurring in the cracks and crevices generally takes place at a faster rate than at exposed surfaces in the containers.
In order to determine the long-term viability of materials to be used in aerosol containers containing particular solutions, or other environments in which crevice corrosion is a factor, it is necessary to accurately predict the rate of corrosion that will occur within the crevices. However, traditional techniques for measuring corrosion on open/exposed surfaces are generally inadequate for predicting crevice corrosion.
Techniques have been developed to gage corrosion in artificial crevices of varying geometry in order to provide a model for what could be expected in an actual crevice due to the materials and solutions forming the crevice environment. In such conventional devices, an electrode is typically provided in the artificial crevice to measure electrical properties in the crevice that are indicative of corrosion. Alternatively, some devices employ a crevice formed in an electrode itself. Examples of devices employing these conventional techniques for measuring crevice corrosion are described in U.S. Pat. Nos. 3,633,099, 4,181,882 and 3,599,090.
Unfortunately, conventional devices for corrosion analysis in artificial crevices have certain drawbacks. In particular, the known devices typically measure only a general likelihood of corrosion in the entire crevice. Thus, the known devices only take into account corrosion effects due to the diffusion of solutions from the bulk of a container into a crevice as a whole. However, in real-world applications, diffusion of a solution not only occurs from the main cavity of a container into a crevice, but may also occur within the crevice. Thus, corrosion may occur at different rates at different positions within the crevice. Conventional devices are not equipped to measure varying corrosion rates within a continuous crevice.
Another drawback of conventional crevice-corrosion analysis is its inflexibility to simulate accurately varying real-world environments. Different lines of containers will have crevices of different dimensions. However, conventional devices are not equipped to take into account the different aspect ratios (i.e., the crevice depth divided by the crevice width) of crevices occurring in different lines of commercial containers.
This invention is directed to a device designed to overcome the problems of the conventional devices, by allowing for a plurality of measurements related to corrosion within a single crevice, to take into account the complexities of the dimensions of the crevice.
Typically, the invention relates to measuring crevice corrosion in a test cell designed to simulate the corrosive conditions that exist inside a container. The test cell can be filled with a particular test solution. An artificial crevice, formed of a particular test material, is exposed to the test solution in the test cell in order to simulate the corrosive conditions occurring in cracks and crevices of a container.
In one aspect, the invention is directed to a novel member used to simulate a crevice in a test cell. Preferably, the member is provided with a plurality of electrodes for measuring crevice corrosion in a more comprehensive and accurate manner than with known designs. In another aspect, the invention is directed to a test cell using the crevice simulation member discussed above.
More specifically, in a preferred aspect, the device of the present invention includes a non-conductive member having a face with a depression formed therein. When the face of the member is placed against a test surface, the depression forms a simulated crevice between the member and the test surface. A plurality of electrodes is embedded in the non-conductive member. Each of the plurality of electrodes has a portion exposed to the depression.
Preferably, this invention is directed to an electrode array device that includes a non-conductive member having a face. The member defines (i) an opening through the member, the opening passing through the face of the member, and (ii) a depression formed in the face and contiguous with at least a portion of the opening. The device also includes a plurality of electrodes embedded in the member. Each of the plurality of electrodes has a portion exposed from the member to the depression.
In another embodiment, the invention is directed to an electrode array for measuring corrosion in a crevice. The electrode array includes a ring-shaped non-conductive member and a plurality of electrodes. The ring-shaped non-conductive member has a first face and a second face, and defines an opening therethrough extending through the first face and the second face. The first face defines an annular depression that is contiguous with the opening in the non-conductive member. The plurality of electrodes is embedded in the non-conductive member. Each of the plurality of electrodes has a portion exposed from the non-conductive member in the depression of the first face.
This invention can also be directed to a test cell for measuring corrosion in a crevice. The test cell includes a container, an electrode array, and a test electrode. The container preferably includes a valve assembly opening into the container. The electrode array device includes a non-conductive member and a plurality of electrodes. The non-conductive member has a face, with the member defining (i) an opening through the member, the opening passing through the face of the member, and (ii) a depression formed in the face and contiguous with at least a portion of the opening. The plurality of electrodes is embedded in the member, with each of the plurality of electrodes having a portion exposed from the member to the depression. The test electrode is sealingly secured to the face of the non-conductive member and is spaced from a surface of the depression therein to form the crevice. The container, electrode array device, and test electrode are sealingly secured together such that the crevice and an interior of the container are in flow communication.
These and other objects, features and advantages of the invention will be made apparent from the following description with reference to the drawings, in which like reference numerals refer to like elements throughout.