Study of cathodic protection related to thermal desalination plant

This project comprised an in-depth study of the application of cathodic protection in thermal desalination plant and used as it's based on extensive cathodic protection system in multi stage flash units located at Dubai Aluminium Company in United Arab Emirates. A review of the literature confirmed that the Dubai cathodic protection system is unique since cathodic protection has seen only moderate application in desalination plant and this is particularly true of its application in respect of carbon steel components such as pipe-work. The practical work of the project included a detailed survey and assessment of the performance of the cathodic protection system in the multi stage flash units at Dubai. This confirmed that the system, even after some 15 years of operations, continues to successfully control corrosion in the inside of a wide range of carbon steel components. The examination of cathodically protected components clearly revealed the crucial role of calcareous deposition in the corrosion control process. The major part of the research comprised an in-depth experimental study of cathodic protection in a range of environmental conditions related to thermal desalination plant. This work involved some experiments on a relatively simple laboratory flow loop but with more emphasis on the utilization of a larger rig comprising a pipe 0.25 meter diameter and approximately 15 meter length attached to one of the multi stage flash units at Dubai. The results have provided substantial detailed evidence of the crucial role of calcareous scale deposition on the overall performance, and especially the current/time relations of cathodic protection systems and have significantly extended the knowledge available from previous studies which limited to conditions experienced on offshore installations. The work has involved the study of the influences of set potentials, temperature, flow conditions and cathodic protection control mode (potentiostatic or galvanostatic) on the performance of the cathodic protection system and the deposition characteristic of the calcareous scales. Doubled layered scale, comprises an inner Mg(OH)2 (brucite) and an outer zone of CaCO3 (aragonite) crystals have been identified over a range of conditions and tentative models for the mechanism of growth of the scales have been postulated. Since both phases of the research had confirmed the technical success of cathodic protection for protecting carbon steel components in thermal desalination plant, the final part of the work comprised a cost comparison study. This was focused on a pipe loop containing a number of fittings and the findings indicated that carbon steel protected by cathodic protection is considerably less costly then stainless steel for high temperature parts of multi stage flash plant but that glass reinforced epoxy pipes are likely to be cheaper than cathodically protected carbon steel unless modes of cathodic protection operation can be identified that successfully protect with lower capital cost

Cathodic Protection of Corroded Pre-stressed Tendons

The corrosion of reinforcement in concrete, whether conventional or pre-stressed, remains a significant cause for the loss of durability of reinforced concrete structures. Corrosion costs the UK economy between 3% to 4% of Gross National Product. This is, in turn, has resulted in the development of greatly enhanced methods of remediation and life extension. One possible approach is to use Cathodic Protection (CP) to control further deterioration. CP of reinforcing steel in concrete structures has proved to be effective for preventing or controlling corrosion and been used successfully for over 25 years. CP is able to stop corrosion in a reliable and economical way where the environment has caused reinforcement corrosion and subsequent concrete damage. However, concerns exist about the ability of CP to avert deterioration in pre-stressed structures due to hydrogen generation and subsequent embrittlement of the tendons. This research investigates the performance of pre-stressed steel tendon exposed to an impressed current cathodic protection (ICCP) at varying potentials on a long-term basis to establish its effect on strength and establish optimised criteria for CP that can be safely applied to deteriorated pre-stressed structures. Twelve timber moulds were manufactured for applying the pre-stressing technique to test specimens. Tendons measuring 5.4mm diameter were selected in both the galvanised and ungalvanised state. Two levels of pre-stressing have been investigated, namely low level (300-400 MPa) and high level (800-1200 MPa). Three different degrees of corrosion Stage I, II and III with target losses of cross-sectional of 0-1 %, 2-4 % and 4-7 % respectively, were employed to replicate in-situ conditions. The actual degree of corrosion was verified gravimetrically by weighing the tendons both before and after testing. The tendons were pre-stressed in two types of electrolyte, namely a saline solution and a sand/cement mortar representing mortar. Upon completion of the corrosion phase using an anodic impressed current method, Impressed Current Cathodic Protection (ICCP) was applied to the tendons at two levels of polarization, normal protection (ICCP-N) in the range of -650 to -750 mV vs Ag/AgCI/ 0.5M KCI and over protection (ICCP-O) ranging between -850 to -1300 mV vs Ag/AgCI/ 0.5M KCI for an extended period to both ungalvanised iv and galvanised pre-stressed steel tendons, to investigate its effect. The potentials of the pre-stressed steel tendon and potential decay resulting from the application of ICCP were monitored and analysed. The strain in the tendons was also monitored throughout the corrosion and ICCP phases to establish pre-stress losses. Finally, the mechanical properties were investigated and the tendon surfaces and fracture modes inspected using an Infinite Focus Microscope (IFM) and Scanning Electronic Microscope (SEM). The results confirmed that accelerated corrosion is a reliable technique for generating the corrosion of steel. ICCP can be used in the corroded pre-stressed tendons as the long-term application shows there is no significant effect on the surface or damage of the both types of tendons with low or high levels of pre-stress. There has been a long term loss in service stress which due to corrosion, due to ICCP or a combination of both. From the results, the loss is more likely to be corrosion induced rather than ICCP. A higher degree of corrosion leads to a higher loss in pre-stress in highly pre-stressed tendons, which is an additional loss that should be accounted for at the design stage

Transition metal oxide composite nanomaterials as anodes in Lithium-ion energy storage devices

The work in this thesis explores the use of a Continuous Hydrothermal Flow Synthesis (CHFS) method to create nano-sized transition metal oxides and carbon-metal oxide composites for use as anodic active materials in lithium-ion batteries (LIBs) and hybrid ion capacitors (HICs). In the first study, the novel use of a CHFS method to create the target nanomaterial TiNb2O7, (TNO) was investigated. The electrochemical properties in LIBs were explored. The CHFS TNO exhibited high capacity at low and high currents, good long term cycling stability and prominent levels of pseudocapacitive charge storage. The formation of a composite carbon/TNO material was also explored. This composite material was found to have improved capacity at all currents tested. The second investigation was a materials discovery study centering around tertiary mixed metal oxides. A library of V/Nb/Mo oxides were synthesised and characterised physically and electrochemically in LIBs. The relationships between composition, physical properties and electrochemical behaviour were studied. The novel material, V0.3Nb0.1Mo0.6 oxide (VNM316) was discovered, which showed high capacity at low and high currents. The third study built on the second and investigated the formation of carbon/metal oxide composite materials of the promising VNM composition. Nanoparticles of carbon-VNM316 were successfully synthesised by an assisted CHFS method. These materials showed a large improvement in capacity at high current and performed well as LIB and HIC anodes. Lastly, lessons learnt from previous studies were applied to a library of mixed metal oxides containing Fe, Mn, and Zn. Electrochemical and physical characterisation highlighted the composition Fe0.2Mn0.75Zn0.05. Carbon composite materials based on mixed Fe/Mn/Zn were then formed. The materials C(Fe0.66Mn0.21Zn0.11)-4HT and C(Fe0.72Mn0.17Zn0.09)-5HT displayed high capacities of 932 and 715 mAh g−1 at low current and 271 and 202 mAh g−1 at high current respectively. CV and EIS analysis indicated degradation over long-term cycling causing a drop in capacity retention