The corrosion rate of copper in deaerated aqueous, sulfuric-acid solutions, with regard to the effect of strain, temperature and electrolyte concentration was studied. Copper in the form of wire was subjected to applied stresses of 1728, 8640, and 17,280 pounds per square inch. Five temperatures in the range 15°C to 75°C. were investigated for electrolyte concentrations of 0.1, 0.5 and 1.0 molar sulfuric acid. The rate of corrosion was followed by noting the rate of copper uptake by the solution through a polarographic analysis run periodically for up to 30 hours. Reproducible results were obtained, it was found that: 1. The rate of reaction for the dissolution of copper in sulfuric acid was first order with respect to cupric ion concentration. 2. Experimentally, the reaction rate was pseudo-first order with respect to hydrogen ion activity. 3. Stress, in general, increased the reaction rate slightly, the effect becoming less at higher temperatures. 4. The activation energy for unstressed corrosion was 10.6 Kcal. for the temperature range 15-75 degrees. 5. For 1.0M and 0.5M acid solutions, stress decreased the activation energy and hence increased the reaction rate. 6. The average increase in reaction rate for 10 degree changes in temperature between 15 and 75 degrees was about 1.5. 7. A diffusion controlled mechanism could be proposed for the dissolution of copper in sulfuric acid solutions. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

No / This is the second in a series of three papers from a project that has attempted to answer the question ‘does the application of agrochemicals accelerate the corrosion of archaeological metals in the top 50cm of the soil?’. We have approached it through a combination of field-based experiments, by establishing laboratory microcosms and by using geochemical modelling techniques to understand the processes involved. This paper reports on two different experimental approaches in the laboratory - a microcosm designed to mimic one of the burial sites (the ‘Lab Bin’ experiments), and a simpler one to understand the reaction between metal samples and concentrated aqueous solutions of the fertilizers and laboratory reagents used (the ‘Lab Beaker’ experiments). The bins were monitored for in situ corrosion and aqueous effluent collected for13 weeks, after which they were excavated and the metal coupons examined. The Lab Beakers were monitored for in situ corrosion for seven weeks, and then the coupons examined. We focus here on a sub-set of the data relating to the behaviour of the thinnest samples of copper in each case. As with the field data previously reported, the results are sometimes contradictory, but on balance this project has demonstrated that applied agricultural chemicals are likely to accelerate the rate of corrosion of metal objects within 50cm of the surface. In particular, it is likely that any fertilizers containing KCI will be particularly aggressive.

No / This is the third in a series of papers from a pilot project that has attempted to answer the question ‘does the application of agrochemicals accelerate the corrosion of archaeological metals in the top 50cm of the soil?’. We have approached it by a combination of field-based experiments, by establishing laboratory microcosms and by using geochemical modeling techniques to understand the processes involved. This paper reports on the geochemical modelling simulations that trace the potential corrosion pathways followed in two sets of laboratory microcosm experiments (‘Lab Beakers’ and ‘Lab Bins’) and one field experiment (at Palace Leas). This approach uses soil solution as the fluid mediating corrosion in the soil vadose zone. Soil solution was displaced following controlled exposure to fertilizers. Modelling using The Geochemists Workbench was carried out to mimic the experimental conditions, and predictions were compared with image analysis results, limited XRD analysis and published corrosion observations. We focus here on a sub-set of the data relating to the behaviour of the thinnest samples of copper in each case. As with the field and laboratory data previously reported, the results are sometimes contradictory, but on balance this project has demonstrated that applied agricultural chemicals are likely to accelerate the rate of corrosion of metal objects within 50cm of the surface. In particular, it is likely that any fertilizers containing KCI (‘potash’) will be particularly aggressive. Geochemical modeling generates plausible corrosion predictions based on post-depositional interaction between archaeological copper and soil solution, and appears to be useful in helping to simplify and understand corrosion pathways in naturally complex systems.

No / Part of a project that has attempted to answer the question ‘does the application of agrochemicals accelerate the corrosion of metals in the top 50cm of the soil? ’ is reported. We have approached the question by a combination of field-based experiments (on two sites), establishing laboratory microcosms (one involving simple aqueous systems and the other a series of simulated burial experiments) and by using geochemical modelling techniques to understand the processes involved. Two different experimental approaches in the field are documented — one using in situ monitoring of corrosion potentials and the other assessing the degree of induced corrosion using image analysis on recovered samples. The first was carried out on arable land close to the University of Bradford to which we applied different fertilizer regimes. The second was established on land owned by the University of Newcastle at Palace Leas, Morpeth, Northumberland, which has a documented field management regime extending back over one hundred years. We focus here on a sub-set of the data relating to the behaviour of the thinnest samples of copper in each case. There does seem to be some evidence of an effect resulting from the applied fertilizer, but the data are sometimes contradictory. We suggest a number of improvements for future field experiments that monitor in situ corrosion in the vadose zone.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Humanities, 1976. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND HUMANITIES. / Bibliography: leaves 68-72. / by Tania A. Krapchev. / B.S.

In this work, copper bimetallic corrosion and inhibition in ultra large scale interconnect fabrication process is explored. Corrosion behavior of physical vapor deposited (PVD) copper on ruthenium on acidic and alkaline solutions was investigated with and without organic inhibitors. Bimetallic corrosion screening experiments were carried out to determine the corrosion rate. Potentiodynamic polarization experiments yielded information on the galvanic couples and also corrosion rates. XPS and FTIR surface analysis gave important information pertaining inhibition mechanism of organic inhibitors. Interestingly copper in contact with ruthenium in cleaning solution led to increased corrosion rate compared to copper in contact with tantalum. On the other hand when cobalt was in contact with copper, cobalt corroded and copper did not. We ascribe this phenomenon to the difference in the standard reduction potentials of the two metals in contact and in such a case a less noble metal will be corroded. The effects of plasma etch gases such as CF4, CF4+O2, C4F8, CH2F2 and SF6 on copper bimetallic corrosion was investigated too in alkaline solution. It was revealed that the type of etching gas plasma chemistry used in Cu interconnect manufacturing process creates copper surface modification which affects corrosion behavior in alkaline solution. The learning from copper bimetallic corrosion studies will be useful in the development of etch and clean formulations that will results in minimum defects and therefore increase the yield and reliability of copper interconnects.

M.S.

Aluminum salts are used as the primary coagulants in the majority of United States drinking water treatment plants. Despite decades of practical experience, there are important knowledge gaps regarding the effects of residual Al on distribution system materials as well as specific types of solids formed. The first phase of this work examined the formation of aluminosilicate deposits in copper and lead pipes using water from Denver, Colorado. It was anticipated was that these deposits could form barrier films on the pipe, protecting it from corrosion. However, the deposits had slightly detrimental effects on leaching of metal to water, and higher levels of aluminosilicates could further worsen corrosion by-product release. The second phase of work attempted to extend understanding of aluminum solubility controls by accounting for effects of sulfate and formation of solids other than Al(OH)₃ during water treatment. Sulfate was found to destabilize small Al(OH)₃ colloids resulting in agglomeration into larger flocs from pH 5.0-6.2 . At pH 9.0 and above, Al-Mg, Al-Mg-Si and Al-Si solids were discovered to control Al solubility, while also having significant impacts on the precipitation of calcite in the presence of silica and overall softening effectiveness. This could be of considerable importance to water treatment practice. These solids also had some potential for removal of arsenic, TOC and boron. / Master of Science

In the first part of this dissertation, copper bimetallic corrosion and its inhibition in cleaning processes involved in interconnect fabrication is explored. In microelectronics fabrication, post chemical mechanical polishing (CMP) cleaning is required to remove organic contaminants and particles left on copper interconnects after the CMP process. Use of cleaning solutions, however, causes serious reliability issues due to corrosion and recession of the interconnects. In this study, different azole compounds are explored and pyrazole is found out to be a potentially superior Cu corrosion inhibitor, compared to the most widely used benzotriazole (BTA), for tetramethyl ammonium hydroxide (TMAH)-based post CMP cleaning solutions at pH 14. Micropattern corrosion screening results and electrochemical impedance spectroscopy (EIS) revealed that 1 mM Pyrazole in 8 wt% TMAH solution inhibits Cu corrosion more effectively than 10 mM benzotriazole (BTA) under same conditions. Moreover, water contact angle measurement results also showed that Pyrazole-treated Cu surfaces are relatively hydrophilic compared to those treated with BTA/TMAH. X-ray photoelectron spectroscopy (XPS) analysis supports Cu-Pyrazole complex formation on the Cu surface. Overall Cu corrosion rate in TMAH-based highly alkaline post CMP cleaning solution is shown to be considerably reduced to less than 1Å/min by addition of 1 mM Pyrazole. In the second part, a novel technique built in-house called multiple internal Reflection Infrared Spectroscopy (MIR-IR) was explored as a characterization tool for characterization of different low-k structures.In leading edge integrated circuit manufacturing, reduction of RC time delay by incorporation of porous ultra low-k interlayer dielectrics into Cu interconnect nanostructure continues to pose major integration challenges. The main challenge is that porous structure renders interlayer dielectrics mechanically weak, chemically unstable and more susceptible to the RIE plasma etching damages. Besides the challenge of handling weak porous ultra low-k materials, a lack of sensitive metrology to guide systematic development of plasma etching, restoration and cleaning processes is the major stumbling block. We explored Multiple Internal Reflection Infrared Spectroscopy and associated IR techniques as a sensitive (sub-5 nm) characterization tool to investigate chemical bonding modification across fluorocarbon etch residues and low-k dielectric interface after plasma etching, ashing, UV curing and post-etch cleaning. The new insights on chemical bonding transformation mapping can effectively guide the development of clean-friendly plasma etch for creating ultra low-k dielectric nanostructures with minimal dielectric damages.

Premise plumbing can contain copper and lead bearing fixtures, and although copper is considered primarily an aesthetic issue, the neurotoxic effects of lead present a significant public health concern. Utilities approach corrosion control in low alkalinity water by increasing the pH (>9) or adding a phosphate inhibitor at neutral pH. Phosphate inhibitors, pH and chlorine are known to affect lead and copper release through their direct action as corrosion inhibitors or oxidizing agents or through an indirect action via microbial growth. Biofilms are often an implied cause of premise plumbing corrosion, although little is known about their community structure or ability to store metals. The central hypothesis of this thesis is that biofilm contributes to lead and copper release in premise plumbing. This thesis addresses a unique gap in corrosion literature by integrating traditional corrosion chemistry methods with microbiological and molecular biology techniques. The experiments used three distinct approaches: (i). electrochemical cell experiments to determine the key factors in decreasing lead and copper corrosion in galvanically coupled systems while maintaining microbial control (ii). galvanic macrocells using premise plumbing components to examine the unintended consequences of adding a phosphate based corrosion inhibitor and (iii). an annular reactor study to examine the impacts of two commonly applied corrosion control strategies. In the electrochemical cell experiments, the pH 9.2 with zinc orthophosphate and chlorine treatment achieved both goals: decreased lead and copper release and limited microbial growth. In galvanic macrocells experiments with premise plumbing components, zinc orthophosphate addition was shown to be positively correlated with increased bulk water bacteria, biofilm growth and biofilm community structure as measured by DGGE. Biofilm was also observed to sorb 3-29% of lead and 3-16% of copper from the bulk water. The comparison of the two corrosion control strategies showed that the majority of lead released was in the particulate form, and the results further alluded to the potentially significant role lead particles play in biofilm formation.