Date of Award

Spring 5-23-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Zhang, Jianshun

Subject Categories

Chemistry | Engineering | Materials Science and Engineering | Mechanical Engineering | Physical Sciences and Mathematics

Abstract

The effects of moisture content, temperature, and pollutant mixture on atmospheric corrosion of copper and silver were investigated by exposing test specimens to different environmental conditions, followed by surface characterization using the coulometric reduction, Scanning Electron Microscopy, and Energy Dispersive Spectrometry (SEM/EDS). Printed circuit board test cards (PCBs) with bare copper were also used to investigate the effects of voltage bias on the PCBs on the corrosion rate. The test specimens were exposed to mixed flowing gases (MFG) environment with eight different combinations of the following five pollutants at the fixed concentration levels: 60 ppb O3, 80 ppb NO2, 40 ppb SO2, 2 ppb Cl2, and 10 ppb H2S. Temperature and relative humidity (RH) were varied from a reference condition (21°C and 50% RH which is within the current ASHRAE-recommended thermal envelope) to a higher value (28°C, 70% RH, or 80% RH) to increase the moisture content of the test environment. Test results revealed the dominating effect of Cl2 on copper corrosion and that of H2S on silver corrosion. Increasing the moisture content at 21°C caused more severe corrosion of copper when Cl2 was present, but not for silver. When the temperature was increased from 21°C to 28°C at 50% RH, it reduced the corrosion of copper, but not for silver. Voltage-biased PCBs had less effect on corrosion than PCBs without the voltage bias. A mechanistic model based on the multi-ion transport and chemical reactions was also proposed to predict the corrosion of copper due to Cl2-containing pollutant mixtures. The model's prediction of the effects of temperature and RH agreed well with the experimental results. These findings provided the basis for possible expansion of the ASHRAE-recommended thermal envelope for data centers when Cl2 and H2S are not present and limiting the thermal envelope when Cl2 or H2S is present. They also improved the understanding of the corrosion mechanisms for the copper when Cl2 is present in the data center environment.

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