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By Sam X. Yao

The underwater concrete technology has historically evolved largely through a trial-and-error process of constructing marine works. Many outstanding examples exist of high quality concrete placed underwater. However, failures also occurred and led to excessive cost and/or schedule overruns. These failures were largely due to improper concrete mix design or improper placement. The problems may have occurred because proper underwater concrete construction techniques and experience have not been widely disseminated. This section focuses on technical issues of underwater concrete mix design, concrete production and placement, and quality control.

Jan 1, 2013

By Andrea Francioso, Roberto Folchi

In order to comply with the latest European Highway Standards, the highway Salerno - Reggio Calabria, in southern Italy, had do be widened and upgraded to reduce its vulnerability to earthquakes. Reinforced concrete viaducts, no longer needed for the new road, had to be demolished. Many bridges still to be used for the highway required refurbishment due to 50 years of wind, frost and salt corrosion. This re-furbishment and new construction had to be carried out simultaneously. To keep the highway open dur-ing the renewal process, all traffic was directed to one side of the road. Demolition was conducted ex-tremely close to operational roadways and viaducts, as close as only 2 cm (0.8 in). Care had to be taken to ensure that the stresses (vibration levels), resulting from the demolished pylons and decks hitting the ground, were below the no-damage thresholds for the nearby acceptors (structures receiving the vibra-tion stresses). These structures included bridges, houses and buried pipelines (water, oil and gas). In some cases, care also had to be taken to preserve the existing pylons supporting decks that were being demolished; since the same pylons were going to be used for the new viaducts (bridges). New continu-ous decks in weathering steel replaced the old reinforced concrete decks.

Jan 1, 2013

By Marco Lombard, Paulus Kapolo, Christopher J. Greet

"The conversion of a concentrator from one grinding media type to another is a major undertaking in terms of both financial and technical risk. So, a strategy of completing sufficient laboratory and field tests to mitigate this risk, and give the operation confidence that advancing to plant trial will give a high probability for success.The objectives of this paper are twofold: to provide the reader with a strategy for mitigating risk prior to undertaking a plant trial; and to provide a statistical basis for analysing plant trial data. That is, when employing an electrochemically inert grinding media in the primary grinding circuit it is possible to change the pulp chemistry of the system and improve the metallurgical response of the ore.This paper tracks the changes in pulp chemistry and metallurgical performance of Rosh Pinah Zinc Corporation’s silver/lead/zinc concentrator as the primary ball mill was converted from forged steel grinding media to high chrome grinding media. The changed in metallurgical performance are correlated to the shift in pulp chemistry.INTRODUCTIONTheoryBruckard et al (2011) recently published an article describe the effect of the grinding environment on the flotation of copper sulphides. While this paper confined its discussion to copper sulphides the arguments presented apply equally to other sulphide mineral systems. Broadly, these studies indicate that most sulphide minerals are more noble than the grinding media used during comminution. Therefore, the sulphide minerals are cathodic with respect to the forged steel grinding media, and the following reactions apply:Cathode (sulphide mineral): ½O2 + H2O + 2e- ? 2OH- (1)Anode (grinding media): Fe ? Fe2+ + 2e- (2)A galvanic couple between the grinding media and the sulphide mineral(s) exists, which increases the corrosion rate of the forged steel media. The corrosion products of the grinding media, iron oxy-hydroxide species, invariably precipitate on to the surfaces of the sulphide minerals thereby affecting their floatability (Johnson, 2002).The application of more electrochemically inert grinding media to “real” ore systems at an industrial level to improve metallurgical performance has not gained universal acceptance. The aim of this paper is to provide a protocol for conducting laboratory and plant test work that clearly demonstrate that metallurgical benefits are not only possible, but measureable, by way of example. In this case, the work conducted at Rosh Pinah Zinc Corporation in Namibia is described."

Jan 1, 2013

By L. Shoke

The aim of this study was to develop an in-house tensile testing procedure that would yield accurate and reproducible parameters as input material properties into computational models for numerical simulations of the mechanical behaviour of TM380 mild steel. To achieve this objective, we reviewed the ISO 6892:2009 tensile testing standard along with reported good practice guidelines. Tensile tests were conducted on a dog-bone shaped TM380 mild steel specimen with strain gauges attached on either side, to monitor alignment and measure strain, using three different types of tensile testing machines. Parameters quantified included yield stress, ultimate tensile strength, and modulus of elasticity. The values of these parameters were found to be in agreement with the values supplied by the manufacturer's specification and showed minimal variations between laboratories. Thus it can be concluded that the tensile test procedure used resulted in accurate and reproducible results. The strain values calculated as per standard were in disagreement with those determined from extensometer and strain gauges and resulted in lower elastic modulus values. This confirms that the current testing procedures require the use of long-range strain gauges or extensometer to determine the strain. A chemical analysis was conducted to verify the specification by the manufacturer. The specimen was found to be fairly homogeneous with minor sulphide inclusions. The micrographs reveal a pearlite and ferrite structure typical of mild steel, and the fractographs show a dimpled surface typical of ductile fracture, which is an attribute of mild steel.

Jan 1, 2013

By Liang Shen

The Cooper River Bridge, the longest cable-stayed bridge in North America, replaces two existing bridges along U.S. Highway 17 and connects the City of Charleston and the town of Mount Pleasant, South Carolina. Two diamond shaped towers support the 1,546 ft long main span over Cooper River and allows for a 1000 ft wide navigation channel. The Charleston high-level approach is 4351 ft long and provides a 250 ft wide navigation channel for Town Creek, while the Mount Pleasant high-level approach is 2,090 ft long. Due to the high seismicity in the region, potential vessel impact, and hurricanes, large lateral loads are expected. From various types of foundations, 10-foot diameter drilled shafts were selected for their high capacity against vertical and lateral loadings. The shafts are founded on a stiff to very stiff lightly cemented calcareous sandy clay or sandy silt layer, called Cooper Marl, which underlies the coastal sediments of the interbedded clays and sands. A group of 11 shafts supports each main tower, while a rock island protects it from vessel collision. A group of 4 to 8 shafts foundations support the other piers of the main span unit. A pair of shafts supports the High Level Approach piers. The shaft tip elevations vary from 120 ft to 230 ft below water line. An elaborate geotechnical investigation was conducted on the site, including a load test program on full-scale shafts under axial and lateral loads. The results of the tests were used to calibrate the lateral and axial soil resistance. The objective of this paper is to present the different aspects of the bridge foundation design.

Jan 1, 2013

By G. A. Slabbert

The paper describes work undertaken to identify the influence of the matrix structure on the metal dusting rate of stainless steel alloys. Specifically, the difference in metal dusting rate between austenitic and ferritic stainless steels of similar chromium contents was investigated. The alloys were exposed to metal dusting conditions and their performance compared by weight loss, optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The specific gas mixture used for all the tests were 18.9% CO-79.1% H2-2% H2O at 650°C. For austenitic stainless steels, Types 304, 321, 316, and 316Ti were compared to two ferritic grades, namely Types 430 and 441. The resistance of the ferritic grades was found to be significantly better than that of the austenitic grades. This was attributed to greater permeability of chromium through the matrix structure to maintain the protective oxide scale. The results will be used in the development of novel alloys to combat metal dusting.

Jan 1, 2013

By T. Johnson

Hydrometallurgical processes can be exceptionally corrosive. This is particularly true in acid leaching processes for copper, cobalt, nickel and rare earth elements. In the last five years, several large hydromet plants have been built in North America (Vale - Long Harbour, Baja Mining ? El Boleo and MolyCorp - Mountain Pass). Hundreds of storage tanks, extraction vessels and electrowinning cells along with miles of piping were designed and fabricated to withstand the aggressive environments inherent in these processes. One key element all three projects had in common was the extensive use of FRP in equipment design. As a material of construction, FRP provided equal if not improved durability relative to alternative corrosion resistant alloys at a considerably lower cost. This paper will highlight the extensive use of FRP in these three world scale projects and why it was chosen for each process.

Jan 1, 2013

By Thomas A. Printz

The wide use of carbon steel in construction and engineering projects makes this engineering material accountable for approximately 85% of the total annual steel production worldwide. Despite the lack of corrosion resistance of carbon steel, it is incorporated into the permanent work for marine applications, power plants, transportation projects, chemical processing, mining, petroleum production and refining, pipelines, mining and construction equipment. Corrosion is an electro-chemical process that occurs in the presence of water and air. When an electric current is introduced to water or soil, the rate of carbon steel corrosion increases rapidly. Gaseous atmospheric constituents that are capable of electrolytic activity can also increase the rate of corrosion. Corrosion tends to be more rapid in environments in which the steel is exposed to water, and then air, rather than being constantly submerged. The exposure to seawater increases steel pitting because the electrical conductivity is improved in salt water.

Jan 1, 2013

By A. Butler

This paper explains the politics of mine nationalization in contemporary South Africa. Nationalization and privatization typically occur in the oil, mineral resources, and state utilities sectors, and they tend to follow one another in a long-term cyclical pattern. The paper explains why the current international environment has encouraged demands for nationalization and other forms of ?resource nationalism? in the South African minerals sector. It goes on to describe how the resurgence of resource nationalism has been influenced by internal factional politics in the African National Congress. It concludes that nationalization is unlikely to be the outcome of current policy deliberations within the ANC.

Jan 1, 2013

Decision-making regarding plant-scale reagent dosage regimes and air rates is a topic of ongoing investigation and high importance. The current work explains some techniques that have proven useful in deciding on plant-scale flotation operating regimes. Specific focus has been placed on the reagents: frother and depressant, as well as some discussion around the control of air rate and froth depth. Air rate has been selected based on its effects on the froth phase. Froth velocity and froth height above the cell lip are the two variables measured and used to select the operating air rate. Pulp level is then adjusted to increase or decrease mass pull. A technique has been developed using the Anglo Platinum Bubble Sizer on an industrial flotation cell to determine the relationship between bubble size and frother concentration. This technique has been extended to measure the equivalent frother concentration or frothabilities of various streams on a rougher bank. A mass balance for frother was performed successfully, and this provided a better understanding of the way frother moved in the rougher bank. With this knowledge, more informed decisions can be made about frother addition required in subsequent flotation stages. For depressant, a new protocol for deciding on dosage rate has been developed. The depressant dosage should be based on the amount of fresh feed material reporting to a bank. Currently 400 g per ton of fresh feed has been assumed a reasonable starting point, with promising results. Improved froth stability and grades were observed. There is scope for more accurately defining the optimal dosage rate. Importantly, the combined effect of changing the chemistry and the hydrodynamics together has been demonstrated. A significant upward shift in the grade-recovery relationship for a cleaner bank was observed.

Jan 1, 2013

By Onuralp Yiicel, Ozlem Okur, Murat Alkan

"In this study, Co-Cr-Mo alloys were produced using a mixture of Co304, Cr203 and Mo03 powders with Al powders by a Self-propagating high temperature synthesis process. SHS is a process of material synthesis that has revealed a number of reactants combinations capable of much higher energy release than conventional explosives. Al203 is added to the mixture to decrease the adiabatic temperature of the system. The thermodynamic simulations and the calculations of adiabatic temperature were examined with FactSage 6.2. In the SHS experiments, different Co304/ Cr203/Mo03 ratios were examined, and their effects on the metal recovery and alloy compositions were carried out. The samples were characterized by using chemical analysis, XRD, XRF and SEM/EDS techniques.IntroductionSelf Propagating High Temperature Synthesis (SHS) has significant advantages compared to the high technology furnace applications, such as very short processing time, simple operation, low energy requirement and low cost [l, 2]. In a SHS process, the ignition starts the combustion and propagates throughout the reactant mixture yielding the desired product. However, the disadvantages of the process such as inhomogeneous or unreacted products due to undesirable reaction rates needs to be overcome by changing some parameters such as ignition temperature, particle size, additive, atmosphere etc. [3, 4]. This work aims to establish a scientific and engineering background in the production of some cast Co-Cr-Mo master alloys via SHS (Self Propagating High Temperature Synthesis) metallurgy which is attractive process technique regarding fast and low-cost production ability of cast alloys."

Jan 1, 2013

By Kimberlee Falkenstein, Volha Kibitkina, Jessica Steeves

A series of experiments were conducted to obtain site specific constants for the vibration produced by a single charge and by more charges detonating in sequence, using short delay intervals. All charges were placed in relatively long boreholes in granite without a free face other than the ground surface. The boreholes were filled with water to provide good coupling with the rock and to provide identical confinement for all the blasts. Vibrations were recorded close to each blast in the vertical direction by uniaxial high frequency geophones and far field using a triaxial geophone.

Jan 1, 2013

By R. Venugopal, Saxena. V. K., U. Sankrityayan

"There is a dire need of a technology which can break the mineral interfaces to enhance liberation with minimum energy consumption in mineral beneficiation processes. Understanding of mineral crystal system and interfaces is essential to develop such methodology. So, this study is carried out to find out the role of mineral crystallography in milling and liberation. Data related of mineral crystallography, Vickers Hardness Number, Bond Work Index and beneficiation processes were collected from literature and detailed statistical analysis has been carried out to establish a correlation among these parameters. It was found that atomic weight and cell parameters shown statistically significant relationship with Vickers Hardness Number of minerals, which controls the milling characteristics of ores. Liberation characteristics of five different kinds of ores were analyzed considering the types of interfaces between valuable and gangue minerals. It was found that phase interfaces play vita role in liberation and coarser liberation can be achieved in the minerals of incoherent crystal systems like manganese and zinc ores. Study of this subject can help us to understand the effect of stress wave propagation in solids and its effect on crystal interfaces. It can also help us to design a technology of future to break the mineral interfaces.INTRODUCTIONCommunition is energy intensive mineral processing operation and consumes up to 2% of the total electric power generated in the world. Energy consumption due to comminution is increasing every year as there is growing needs to exploit lower grade ore bodies and process rejects (Blazy et al., 1994; DOE, 2005). Low grade ores require crushing and grinding to liberate the valuable minerals which are further separated from gangues by various beneficiation methods like gravity separation, floatation, leaching etc. Currently, comminution methods are selected based on the reduction ratio and energy consumption but effect of grinding methods on subsequent processing methods specially on liberation also need to be studied to optimize the entire beneficiation process. Most of the attempts made in past to minimize the energy consumption in milling to enhance the mineral liberation were focused on compression mechanism, chemical additives, thermal treatment, microwave treatment and electric disintegration (Kilpelm and Austin, 1982; Norgate and Weller et al, 1994; Bearman et al., 1997; Kumar et al., 2010; Wang el al., 2011; Singh et al., 2012). But the role of mineral crystallography on milling and liberation behavior of minerals not fully explored yet."

Jan 1, 2013

By G. R. Lane

A large opencast gold mining company in Africa had just completed a feasibility study for an expansion of the operations. A traditional net present value project valuation methodology had been used that showed a very positive net present value (NPV). The project team had conducted a qualitative risk assessment that identified and logged all potential project risks and had subjectively incorporated 'risk' via the discount rate and other assumption contingencies around gold price expectations, operating parameters, etc. Management requested that an independent quantitative risk modelling approach be adopted to obtain a better understanding of the impact of risk on the overall project valuation and confidence level in the final valuation. A detailed project valuation model was configured in the Cyest Carbon Modelling Technology platform, and the stochastic modelling module used to perform the Monte Carlo simulations. Analysis of historical operational performance data relating to actual achievements versus planned and budget determined the historical variability of the underlying parameters as well as variance to budget. This was done at a detailed level for mining rates and costs, processing rate, costs and recovery, and other operational efficiency measures. External market assumptions relating to gold price, exchange rate, and inflation were modelled and the dependency between them modelled using a copula. This case study will demonstrate the approach taken to building and populating the quantitative risk model and the overall results of the Monte Carlo simulation. The final valuation demonstrated that the project had a 44 percent probability of an NPV less than zero i.e. a 44 percent chance of project finance loss.

Jan 1, 2013

By Dachun Liu, Baoqiang Xu, Bin Yang, Yong Deng, Heng Xiong, Xiumin Chen

"In this paper, vacuum distillation technology has been employed to study the possibility and regularity of separating copper and enriching lead, silver and other valuable metals from copper- based multi component alloys. The result of experiment indicated the practicability of vacuum distillation dealing with copper base complex multi-component alloy to separating lead and silver, when the vacuum distillation temperature was 1637K, distillation time was 60min; residual gas pressure was 20-30Pa, the removal rate of silver was 95.86%, of lead was 99.63%; the evaporation rate of copper was 0.745%. The removal rate of arsenic, antimony and tin respectively were 83.09%, 48.12% and 24.54%. Vacuum distillation method is applicable for dealing with the copper-based multi component alloys, silver and lead can realize effective recovery.IntroductionCopper generally go with lead mineral, therefore, to remove copper from lead becomes an inevitable link in lead smelting. Dross from removed copper usually contains lead, arsenic, antimony, tin and noble metal silver. In abroad, soda ash-iron dust is adopted to process copper dross of this kind. The outcomes of this process are lead matte, wet lead, scoria smoke dust etc[1~5] The dominant components of all the outcomes are copper and lead. Moreover, in the process of tin smelting, copper contained by-products are produced, such as, crude tin alloy, tin lead electrolytic anode slime and so on. Copper content of all the products are ranging from few percentages to several tens percentage. Those products, no matter merge into main producing process, or separate treatment cost losses of valuable metal. For one hand, the containing of copper of outcomes from pyrogenic attack is less than 50%, for the other hand, a lot of valuable metal need to be processed, which increase the cost of retrieve."

Jan 1, 2013

By F. M. L. Mulaudzi

Behaviour studies of metal dusting processes and associated filamentous carbon formation were undertaken on Alloys 600, 601, and 800 using a simulated metal dusting environment of 25C0-70H2-5H20 (vol.%) at 650°C. These samples were studied visually and by optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy with energy-dispersive X-ray spectroscopy (TEM-EDX) and x-ray diffraction (XRD). Visual examination and SEM surface observation showed that Alloy 800 suffered metal dusting attack at an early exposure reaction period. The coke deposit amounts increased significantly with reaction time from 168 hours to 336 hours in Alloys 600, 601, and 800. Alloy 800 showed pitting after 168 hours' exposure, and the degree of pitting increased after 336 hours. XRD showed all these alloys had a common austenitic phase, with Alloy 800 also having ferritic metal particles. Alloy 800 after 168 hours' exposure had a complex phase mixture on the surface, consisting of ferritic Fe and austenitic FeNi phases. For coke deposit, there were also Fe304, Fe3C and graphitic carbon. The existence of Fe, Ni, and Cr metal particles, and also graphitic carbon in coke deposits, was confirmed by EDX analyses.

Jan 1, 2013

By S. Burks

This paper develops the themes explored by the authors at the Fourth International Platinum Conference,. Optimization techniques can be used to significantly increase the value of mining businesses by enabling better long-term planning decisions. Open pit and underground mine design, mine scheduling, cut-off grade and blending, stockpiling, and the linking of these to flexible elements of the metallurgical recovery processes are all evaluated together. Transport or sale of intermediate products and the requirements of the product metal markets can also be considered. Experience shows that net present value (NPV) can potentially be increased by 5-35 per cent or more, usually even before the expenditure of significant amounts of project capital. The case studies presented include: > An existing operation with multiple open pits and PGM concentrators linked to offsite downstream processing facilities, and with infrastructure constraints for which the scheduling of current operations and the potential for expansion were investigated > An existing operation with an integrated portfolio of mines, concentrators, smelter, and refinery, for which the various possible sources of ore for processing were prioritized to match the downstream process plant constraints and the product markets > An underground operation in Zimbabwe for which the optimum mining width was calculated and expansion plans were evaluated > An underground mine with many separate mining sections, for which a revised schedule was developed aiming to keep the shaft system and processing plant at capacity with the highest net value material available at any time throughout the life of mine. In the concluding section of the paper, a few brief notes are included suggesting how the strategic recommendations from enterprise optimization studies may be implemented by the owner's team.

Jan 1, 2013

By Harsh Deep Chopra, Jason N. Armstrong, Susan Z. Hua

"Existence of anisotropic Curie temperature materials [E. R. Callen, Phys. Rev. 124, 1373 (1961); J. Appl. Phys. 32 S221 (1961)] is a longstanding prediction - materials that become paramagnetic at a lower temperature along certain crystal directions while remaining magnetically ordered in other directions up to a higher temperature. Validating Callen's theory, we show that all directions within the basal plane of monoclinic F e1Ss (pyrrhotite) single crystal remain ordered up to 603 K while the c-axis becomes paramagnetic at 225 K. Results prompt a re-evaluation of existing magnetic materials with a focus on magnetic characteristics along different crystal orientations above instead of below the ordering temperatures. Theoretical guidelines for identifying new materials with large anisotropy of Curie temperature are also given, and analysis protocol to characterize them in a self-consistent manner is discussed. Materials with such a large directional dependence of Curie temperature open the possibility for uniquely new devices and phenomena, including energy storage and spintronics devices.IntroductionThis paper is an overview of our recently published work on anisotropic Curie temperature materials [l]. As a background, ferromagnetic and ferrimagnetic materials are characterized by a critical temperature below which magnetic interactions prevail over thermal agitation, leading to the appearance of a spontaneous magnetization. Above this critical point, called the Curie temperature, thermal energy eventually overcomes magnetic interactions and the material becomes paramagnetic.It is less well known that the Curie temperature varies with the orientation of the crystal. In ordinary ferromagnets this orientation dependence of Curie temperature is negligible because of the vanishingly small ratio of anisotropy to exchange energy, i.e., the spherical or isotropic exchange term dominates. Thus Curie temperature in ordinary ferromagnets appears to be an isotropic property, and assigning it a single characteristic ordering temperature suffices. However, a 'small' difference is not equivalent to being the 'same', and under appropriate set of conditions the anisotropy of Curie temperature is predicted to become appreciable, as discussed in the following.In formulating the theory of 'anisotropic magnetization' [2, 3] E. R. Callen and H. B. Callen first discussed the ""interesting possibility"" of anisotropic Curie temperature [2] or ACT; Callen and Callen noted that it was W. J. Carr, Jr. who initially raised this question, and they discussed it in detail at the Conference on Magnetism and Magnetic Materials (NY, November 1960), see footnote on page 320 of Ref. [2]. Soon thereafter, E. R. Callen developed the theory underlying the anisotropy of Curie temperature and conditions conducive to its observation [4, 5]."

Jan 1, 2013

By Xinli Wang, Matthew Andriese, Jiann-Yang Hwang, Zhiwei Peng, Byoung-Gon Kim

"The microwave reflection loss (RL) of ferric oxide is studied in the temperature range from 297 to approximately 1400 Kat frequencies of 915 and 2450 MHz. It is shown that the maximum microwave absorption with RL of -38.46 and -35.97 dB can be obtained for ferric oxide having thicknesses of 0.03 and 0.01 m at 915 and 2450 MHz, respectively. The maximum absorption peak with RL below -10 dB is in a 250 K temperature range from 723 to 973 Kat 915 MHz, which shifts to the range between 823 and 1073 K at 2450 MHz. This migration is in good agreement with the variation of the dielectric loss tangent of ferric oxide.IntroductionMicrowave irradiation has distinguishing characteristics such as volumetric and selective heating compared with conventional methods, leading to extremely broad applications in materials heating and processing [1-5].The efficiency of microwave heating was found to be dependent on various factors, such as microwave power [6], frequency [7,8], radiation time [8], applicator geometry [8], sample microwave absorption properties and position as well as dimension [9-11 ], etc. Among these parameters, sample dimension plays an important role but is usually neglected by researchers in microwave processing of materials. In fact, although numerous studies have been directed toward the utilization of microwave energy to assist materials heating and processing, few reports were released on the effect of sample dimension [12,13].This is because all aforementioned factors influencing microwave heating generally exert interactive effects to each other during the heating process, making clarification of the effect of sample dimension difficult. Therefore, it is necessary to propose a parameter or concept for quantifying the effect of absorber dimension on microwave heating, increasing heating efficiency."

Jan 1, 2013

By I. A. Mwamba

Plain and alloyed titanium aluminides of composition Ti-47.5 at.% Al were prepared by melting commercial-purity titanium and aluminium with additions of 1 at.% precious metal. The as-cast alloys were subjected to potentiodynamic scans in 5, 15, and 25 wt% HCl aqueous solutions at room temperature and compared for their abilities to spontaneously passivate. Addition of precious metals resulted in a general improvement of corrosion resistance by increasing the open circuit potential to more noble values. Addition of 1 at.% gold or silver to titanium aluminide did not significantly increase the corrosion potential (Ecorr) above that of the plain titanium aluminide alloy, indicating that gold and silver are not sufficient cathodic modifiers to improve the corrosion resistance of titanium aluminide in all the solutions tested. However, platinum, palladium, and iridium additions shifted the corrosion potentials to the position of the passive region of plain TiAl for all solution concentrations. This indicated that TiAl alloyed with these platinum group metals would passivate spontaneously by cathodic modification. TiAl alloyed with palladium performed the best in 5 wt% HCl solution with the most positive corrosion potential. In 15 wt% HCl solution, alloys with platinum exhibited the most positive corrosion potentials, while alloying with iridium or palladium revealed more negative corrosion potentials. Thus, palladium alloying led to the best cathodic modification of titanium aluminide in low-concentration HCl solution, whereas platinum and iridium alloying additions resulted in the best cathodic modification of titanium aluminide in high-concentration HCl solutions.

Jan 1, 2013