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By Luciano E. Ramírez, Jesús L. Valenzuela, José R. Parga

"An innovative process for removing copper cyanide complexes including silver and zinc from cyanidation circuits has been developed. The technology was based on the inducing the nucleated precipitation of copper and silver in a tube serpentine reactor, using sodium sulfide as the precipitate and sulfuric acid as pH control. The results showed that pH had a great effect on copper cyanide removal efficiency and the optimum pH was about 3 to 3.5. At this pH value copper cyanide removal efficiency could be achieved above 97 and 99 % ,when influent copper concentration ions were 650 and 900 ppm respectively. In this process (sulphidizaton-acidification-recycle-thickening), the cyanide associated with the copper cyanide complexes is released as HCN gas under weakly acidic conditions, allowing it to be recycled back to the cyanidation process as free cyanide. This system was successfully commercial applied at Minera William in Mexico.IntroductionThe recovery of gold and silver from minerals and concentrates with cyanide is an important hydrometallurgical process, which has been studied for more than 124 years. Patented by MacArthur in 1888 [1], the process relies on the fact that gold dissolves in aerated cyanide solutions to produce the gold cyanide complex. The stoichiometry by wich this reaction occurs is known as the Elsner equation as shown here. Silver is accomplished in the same fashion."

Jan 1, 2012

By O. F. Brown

Excavation and loading are primary operations in the surface mine production chain, constituting a significant component of production costs. This makes excavation and loading important cost centers that need to be improved to lower production costs. Optimizing the design and use of excavators will improve energy efficiency in earthmoving operations, and this requires a thorough understanding of the soil-tool interaction process. Modeling the interaction process accurately is the key to this optimization. Experimental and analytical methods have provided limited information on the behavior of soils during excavation. Finite element (Fe) analysis of soil-cutting blade interaction produces some advantages over experimental and analytical methods. However, the soil constitutive equations used in most of the available Fe analyses fail to adequately model the plastic behavior of the soil. This work uses Fe modeling to study the behavior of formation-cutting blade interactions in dozer excavation. The formation is modeled as a nonlinear elastoplastic material using the modified cam-clay (mCC) model. The model accounts for soil-tool interface friction, and progressive and continuous cutting at the blade tip. The results provide soil forces, a progressive developed failure zone and soil displacement fields. The sensitivity analysis of changes in blade angle on cutting force shows that the cutting force increases with increasing blade angle. The cutting depth of the blade had a similar effect on blade cutting force. Increasing the depth of cut increases the required cutting force. Increasing the coefficient of friction at the soil blade interface increases the blade cutting force. Reducing the coefficient of friction at the soil blade interface from 0.3 to 0.05 reduces the cutting force by 22.3%. The percentage represents the maximum potential savings in blade cutting force. This research initiative advances the frontiers of soil-tool interactions during excavations to expand the limited knowledge in this critical area.

Jan 1, 2012

The accompanying supply/demand flow diagrams and 10-year tables for mineral and fuel commodities present essential data required by government, industry, and others to formulate policies and programs that can help assure an adequate and continuing supply of mineral raw materials. The 10-year data base terminates with 1975 figures because adequate world information was not available beyond that date. The selected mineral supply/demand tables and flow diagrams comprise but one "output" from the massive body of information and data collected and compiled by the Bureau of Mines on a continuing basis covering mineral production, consumption, prices, shipments, imports, exports, and stocks, as well as industry activities in all States and abroad.

Jan 1, 2012

By G. Deschênes

Located in North West Tanzania, Buzwagi is an underground narrow-vein gold mine owned by Barrick Gold. The plant was commissioned in 2000. The reserves are estimated to be more than 25 years. The ore, containing gold, silver and copper mineralization in sulphides, is processed at 3,300 tpd. This paper presents the results of an investigation to determine the performance of an ammonia-cyanide leaching approach to recover gold from two samples. Coarse gold was recovered by gravity prior to leaching. The gravity tailings had the following composition; 1.97 g/t Au and 0.31% copper for the medium cyanide soluble copper (MCSC) sample and 2.80 g/t Au and 0.53% Cu for the high cyanide soluble copper (HCSC) sample. Experiments were conducted for 72 hours in stirred tank reactors with monitoring and control of parameters. The straight cyanidation produced gold extractions of 76.1% for the MCSC sample and 84.6% for the HCSC sample. Associated cyanide additions were 6.1 kg/t and 11.5 kg/t respectively. The gold extraction of the MCSC sample was improved to 88.8% using 350 ppm NaCN and 700 ppm ammonia. The associated cyanide and ammonia additions were 2.5 kg/t and 1.7 kg/t respectively. For the HCSC sample, 82.5% gold extraction was obtained using 500 ppm NaCN and 600 ppm ammonia. The cyanide addition and ammonia additions were reduced to 3.8 kg/t and 1.0 kg/t respectively. No significant decrease in gold extraction was noticed when the cyanide and ammonia were reduced to 150 ppm and 500 ppm respectively. In the presence of ammonia, a significant amount of cyanide was oxidized to cyanate by the cupric ion. In the absence of ammonia, the formation of copper cyanide was the predominant reaction responsible for consumption of cyanide.

Jan 1, 2012

By Thys B. Johnson

The mine system analysis and evaluation study presented in this report was part of the U. S. Bureau of Nines' Tertiary channel project conducted under the Heavy Metals program. The Badger Hill pit, located on the west end of the San Juan Ridge area, near Nevada City, California, was the site of the Bureau's field work. The objectives of this study were: (1) Determine potential alternative mining systems for some of the large tertiary channel gold-bearing gravel deposits, and (2) Identify areas of technology where further investigation would be merited because of their potential inclusion in a mining system for such deposits, The study involved the development of a mineralized block inventory, an economic block inventory, determination of optimum ultimate mining limits and a preliminary economic mining system evaluation. Computer programs were developed and utilized for each of the study phases stated above. The sampling program conducted at Badger Hill by the Bureau Delineation Group together with confidential drill hole data provided by the San Juan Gold Co. formed the basic gold values and distribution information from which a deposit model was developed. The deposit was divided into minable block units and net economic values were assigned to each block for various configurations of both open-pit and underground mining methods based on cost and performance data provided by the various Bureau of Mines Research Centers. A number of controllable variables such as: (1) Mining method (open-pit and underground), (2) depth of mining cut, (3) production rate and (4) equipment type and capacity were evaluated. The prime measures of effectiveness on which the mining systems where judged were discounted cash flow rate of return and maximum utilization of natural resources. The analysis showed that underground mining of the Six-Mile Tertiary channel gold-bearing gravel deposit under consideration was uneconomical and did not permit maximum recovery of the resources within the channel. It was also apparent that mining the Six-Mile Deposit for gold alone is uneconomical or at best marginal at a gold price less than $80 per ounce. The analysis showed that the potential for an economic mining operation within the Six-Mile Deposit exists when the gravel resources of the channel are considered together with the gold. It was determined that the highest rate of return would be realized with a 20-year open-pit mining operation yielding 745,000 ounces of -gold and 55 million cubic yards of usable gravel.

Jan 1, 2012

By S. M. Bradshaw

In order to assess the requirements for online matching when using a transverse electric field (E-field) applicator to treat mineral ores continuously, the effect of varying load properties on matching has been investigated by simulation. The effective permittivity of the ore to be treated is expected to show variation on both short (< 1 s ) and long (minutes) time scales. By modelling the ore as a series of slices with alternating effective permittivity values, it was shown that permittivity variations on the scale of the expected particle size are attenuated significantly and matching is not required. For variations in permittivity on the length scale of the free-space wavelength, variations in reflected power are at most within ±10% of the mean. This is not considered operationally significant, as extreme permittivity variation over this length scale is unlikely, given the expected distribution of ore particle sizes to be treated. At typical ore transport speeds through the applicator, these variations occur on a time scale an order of magnitude shorter than the response time of typical industrial online matching equipment. This implies that online matching is neither required nor possible for short time scale variation. Long-term variations in dielectric properties can be adequately compensated for by current matching technologies. It is concluded that the transverse E-field applicator is robust to changes in the dielectric properties of crushed ores within the expected range of their variation.

Jan 1, 2012

By Truan-Sheng Lui, Li-Hui Chen, Hao-Wen Hsueh, Fei-Yi Hung

"Since Ag wires have similar hardness and bonding properties to Au wires, they can be applied in some pads. In the present study, the annealing effect (at 225°C~275°C for 30min) on the tensile mechanical properties of silver wires with f=23µm was investigated. In addition, the micro-structural characteristics and the mechanical properties before and after an electric flame-off (EFO) process were also studied. Experimental results indicate that with annealing temperatures of more than 250°C, the silver wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised significantly. Under the thermal effect of EFO, the necks of the Ag balls underwent recrystallization and grain growth was induced, and the annealed Ag wires had a shorter zone of HAZ (220µm). The bonding strength and the neck-strength of the Ag wires were more than 7gf and possessed excellent bonding properties.IntroductionThermosonic ball bonding is one of the preferred processes for electronic packaging to connect a semiconductor chip and a lead frame by a thin metal wire. At present, gold wire and copper wire are the preferred interconnect materials to bond with the aluminum metallized wafer pads [1, 2]. Since gold is expensive and the reliability of copper is poorer [3], the study of silver wire has attracted a lot of attention already. In addition, the inherent properties of high ductility and low hardness of silver as well as its workability effectiveness compared to gold, have made it a preferred alternative .[4, 5]"

Jan 1, 2012

By Raj Rajamani

In general, many past works examine mill load, mill power, shell lifter design etc with a view to improving the mill capacity. On the contrary, only a handful of papers have addressed the transport of fine slurry through the pulp lifters. We present the flow dynamics of pulp lifters via laboratory scale experiments, high speed photography and modeling with computational fluid dynamics. Next, the flow behaviour in ArcelorMittal?s Mont-Wright autogenous mill discharge flow is examined. In an effort to improve mill throughput, a comprehensive simulation and plant scale study of the mill was taken up with a focus on the shell and pulp lifter design. The shell lifter was found to be at its optimum limit for breakage of ore particles given the constraints of wear life and occupied volume. Next, the pulp lifter study was taken up with computational fluid flow code and discrete element code. The simulations directly showed that there was considerable carry-over of slurry. This effect was traced to the area restriction in the pulp lifter channels. Further, crash-stop studies confirmed slurry pooling within the mill. Thus it was readily apparent that mill throughput can be increased if the pulp-lifter could be redesigned. Consequently, the discharger section of the pulp-lifter was redesigned. First, this paper outlines the modeling in laboratory scale studies and plant scale studies leading up to the discharger design. Next, the discharge flow in seven different published mill surveys is predicted with computational fluid dynamics (CFD) methodology shown here. Finally, Mont-Wright mill circuit performance before and after the discharger redesign is described. The usefulness of fluid flow simulations in the design of pulp-lifters is emphasized.

Jan 1, 2012

By J. E. Nesset, F. Rosenblum, J. A. Finch, R. Payant

ABSTRACT Under certain conditions of moisture and oxygen, sulphides can spontaneously self-heat. We tested a hypothesis that galvanic interaction between some sulphides can promote self-heating. Galvanic interaction is controlled by the rest potential difference between sulphides and particle size. A series of binary sulphide mixtures was tested. Individual sulphides and mixtures with low rest potential difference did not self-heat, but mixtures of high rest potential difference did. When testing pyrite-sphalerite mixtures, self-heating increased inversely with particle size, with the fineness of the pyrite governing self-heating, indicating the rate-limiting step is the reduction reaction. The results support the hypothesis that galvanic interaction contributes to sulphide self-heating. A possible mechanism based on hydrogen sulphide as an intermediate product is proposed. The understanding gained will be of interest to those involved in storage, shipping, and disposal of sulphides.

Jan 1, 2012

By Roger Favreau, Patrice Favreau

The article reviews the aspects which contribute to the quality of the results from a blast with explosives, namely a good floor, no large blocks, easy mucking, and explains the mechanisms of the blasting process which decide on the quality of these aspects for a given blast method, and how these mechanisms can be simulated from basic principles. It proposes that good fragmentation size distribution can also be important if the rock is going to a crusher, e. g. for the ore in a mine and for the rock excavated in a quarry.

Jan 1, 2012

By R. Hammen, J. Lifton

"The purification of rare earth elements (REE) at mining operations is traditionally accomplished by multiple chemical phase-transfer processes including precipitation, solvent extraction, and ion exchange. We describe REE purification results with Solid Phase Extraction (SPE) columns that were developed to improve the speed and economy of REE purification. The SPE columns have the properties of enhanced equilibration kinetics, so that residence time of a few seconds will accomplish selective chemical transfers from solution phase to solid phase. We describe the separation of REE’s as a class from leach solutions and the further purification of REE salts. INTRODUCTIONHistorically the rare earths were first chemically separated from each other and purified by fractional crystallization. This slow, cumbersome, and laborious process was not suited to commercial production. Solvent Exchange (SX) technology was applied to the problem of separating and purifying the rare earth elements when it was determined in the late 1960s that there might be commercial uses for them individually. At the same time the very slow and expensive technique of ion exchange was applied either for ultra-purification of the desired “light” rare earths, or for the recovery and purification of the tiny amounts of higher atomic numbered, “heavy,” rare earths. Solvent Exchange (SX) has today become the standard for separating the rare earths across their atomic number spectrum. Whereas the separation of the light rare earths commercially may take 30 “cascades’ in a modern Chinese plant, the total separation of all of them from each other may take up to 80 such “cascades,” and is only even “practical’ with preconcentrated feed stocks, such as those produced in China by heap-leaching techniques performed in situ on very low grade radio-nuclide free ionic absorption clays.. Ultra-pure materials of all types are produced today by ion-exchange processing of ionic species already separated by solvent exchange.Hard rock deposits and refractory residues of tin mining and residues from uranium mining have been identified outside of China with very high ratios of dysprosium and other heavy rare earths to the majority lighter ones. Several issues face those who wish to process these materials so as to separate the heavy rare earths commercially:"

Jan 1, 2012

By E. Roman, M. Brissette

"For its end of life, Kemess Mine processed its difficult-to-treat hypogene ore from the east pit, which is a lower grade copper and higher pyrite content gold ore. Metallurgical testwork showed that improvement was possible with finer grinding. In July 2010, small grinding media were introduced into the regrind mill resulting to a nearly 50% decrease of the power draw with a finer grind, an increase of 1.1% in the final copper grade, an increase of 1.2% in copper and 2.9% in gold recoveries at the cleaners. The overall recoveries of copper and gold increased by 0.6% and 1.3% respectively.INTRODUCTION Kemess Mine was located at 430 km North West of Prince George in North Central British Colombia. Its production started in May 1998 by Royal Oak Mines and was acquired by Northgate Exploration in 2000. Kemess reached its end of life production with its last of production on March 9th, 2011. The concentrator nominal capacity was 56,000 TPD consisting of a primary gyratory crusher feeding two identical conventional SAB circuits totalizing 35,840 kW available for grinding. Rougher flotation consists of four parallel rows of eight 130 m³ tank cells to produce a concentrate of 2% Cu and 6 gr/t Au which was pumped to a 5 m x 10.8 m regrind ball mill. The regrind installed power was 4,480 kW to generate a final grind of 80% passing 40 microns. This product fed the two stage cleaner flotation circuit, first stage being two parallel rows conventional 17 m³ Denver cells and second stage, two 3.3 m x 11.0 m flotation columns in series, designed and constructed by Kemess, to produce a 22% copper concentrate grade. The cleaner flotation middlings were returned back to the regrind mill (Froehling, Mohns, Roman & Grady, 2005; Froehling, Mohns, Rajwani & Fullam, 2007). The large copper-gold porphyry deposit was composed of 15% of oxidized supergene and leach cap ore and 85% of hypogene ore having three major alteration zones, mainly characterized by their sulphur/sulphide content. Chalcopyrite is the main copper mineral species with minor bornite. Gold was mainly present as free gold or electrum. The first alteration zone consisted of a phyllic alteration characterized by moderate and intense sericite alteration which had the highest mill throughput and twice the mine grade when in contact with the supergene horizon. The second zone consisted of a potassic alteration characterized by more competent groundmass and moderate to intense quartz stockwork which had a slightly lower mill throughput. Finally, a third alteration found beneath and on the east side of the deposit having almost no quartz stockwork and hardened groundmass, sulphide content is two to four times more. This zone had the lower mill throughput with significant drop in the mine average gold and copper grade. Through its mine life, the average life of mine copper head grade was 0.21% Cu and 0.64 gr/t Au. Head grades began to decrease from 2008 to be substantially lower in 2011 as shown in Table 1."

Jan 1, 2012

By Brian Sandhuas, Robert McClure

All flyrock incidents have the potential to result in injuries or fatalities that can result in loss of company reputation, license to operate with clients, and bear the exposure to high cost liability. From 2007 to 2009, one North American Quarry and Construction Business experienced a series of flyrock incidents. In the spring of 2009, this business declared that the frequency and severity of Flyrock Incidents had reached an unacceptable level. A Flyrock Elimination Program was launched.

Jan 1, 2012

The Discrete Element Method (DEM) is a powerful tool for analysing the flow of charge, the energy consumption and the pattern of energy utilisation of a SAG mill. With the development of laser scanning measurement, the detailed internal working surfaces of a SAG mill can now be included in DEM models. Using scanned results for new and worn shell liners for a 32? (9.75 m) SAG mill, it is shown that the feed and discharge lifters have significant effect on the flow of the charge introducing significant threedimensionality. The effects of the resolution accuracy of liner geometry and the lower cut-off of the rock size distribution are explored. Finally, using a matched new and end of life worn liner and operating conditions taken from site surveys, the effect of wear on charge motion, distribution and energy utilisation are evaluated.

Jan 1, 2012

By M. Clotilde Apua, A. F. Mulaba-Bafubiandi

"The efficiency of hydrochloric acid (HCl) leaching of gold from low grade gold-bearing material has been investigated in the presence of sodium hypochlorite (NaOCl) to produce in situ chlorine gas which is an oxidizing agent able to oxidize gold metal to its soluble forms. The effect of concentrations of HCl, NaOCl, and mixtures of HCl + NaOCl was sought. Iron and potassium present in the feed were leached and consumed all the HCl. Gold found as inclusion in pyrite was not exposed to the lixiviant. Therefore, leaching of gold from low grade gold-bearing material in aqueous chlorine solution is not an effective process for now.INTRODUCTIONHydrometallurgy of gold is commonly based on cyanide leaching solution. Due to the environmental concerns related to cyanidation and mercury processes, and inefficiency of cyanide gold leaching to dissolve refractory ores, sustainable alternative lixiviant systems, capable of generating gold (I) and gold (III) complexes must be studied. Amongst non-cyanide gold lixiviants there is the chloride/chlorine system (Hilson and Monhemius, 2006; Senanayake, 2004; Pilsniak and Trochimczuck, 2007; Wang et al., 2007; Reeves et al., 1999; Khodadad et al., 2008).In practice, the most oxidizing agents utilized for the leaching of gold as chloride, are chlorine (Cl2) or hypochlorite (HOCl) which are either generated in situ by suitable reaction or added in solution (Adamson, 1972). The dissolution of gold concentrate using hydrochloric acid, sodium chloride and sodium hypochlorite (Cl-/HOCl system) were studied (Puvada and Murthy, 2006). The effect of NaOCl and NaCl concentrations were also investigated. The leaching was performed under the following conditions; time: 4h, solid–liquid ratio = 1:4, at room temperature. It was found that the increase of the NaOCl concentration from 25 to 75 g/L did not have any meaningful effect on the recovery of gold which was about 30% (experimental conditions; S/L ratio = 1:4, NaCl concentration: 25 g/L, HCl concentration: 0.35 M). It was also found that from 25 g/L to 200 g/L NaCl, the recovery of gold rose from 30% to 40% (experimental conditions; S/L ratio: 1:4, NaOCl concentration: 25 g/L, HCl concentration: 0.35 M)."

Jan 1, 2012

By Jorge Beim

Helical Piles are increasingly being used to support and rehabilitate structures subjected to compressive axial loads. Traditionally, empirical correlations between installation torque and load capacity of helical screw piles are used as the field quality control. Load tests, however, are always recommended to validate the installation process and design methodology. This paper describes a test program performed on helical piles installed at the National Geotechnical Experimentation Site of the University of Massachusetts - Amherst campus (UMass-Amherst), well known for its deep varved clay deposit. Seven of these piles were submitted to Dynamic Load Tests using the Pile Driving Analyzer® (PDA), and also to Static Load Tests. Good agreements were obtained between the results of the dynamic and static load tests, encouraging the use of the former testing method as a viable alternative to the latter for determining the compressive load capacity of helical piles installed in cohesive soils. The results of the load tests were also compared to the predictions based on torque correlations, resulting in correlation coefficients which were higher than the ones traditionally used.

Jan 1, 2012

By A. Pawelczyk, D. Hreniak, E. Zych, W. Strek, K. Grabas, A. Ostrowski

"Mongolia is a country rich in rare earth resources. In the experiments carried out samples of the Mongolian ore were processed to obtain a lanthanide concentrate. The concentrate underwent hydrometallurgical processing. At the same time radioactive elements were removed. The lanthanides were obtained in the form of hydroxides that were further processed in order to get concentrated products. As a result cerium, lanthanum and neodymium-praseodymium concentrates were separated in the process. Also a concentrate of remaining elements: samarium, europium, gadolinium, terbium, dysprosium, holmium and erbium was obtained. INTRODUCTIONAccording to the assessment of the US Geological Survey, Mongolia possesses 16.77 % of the world total rare earth (RE) resources (Daly, 2011); that is the second largest RE reserve in the world, estimated to be 31 million tonnes in terms of rare earth oxides (REO). In the face of Chinese RE trade restrictions, Mongolia emerged as an important economical partner in mining and exploitation of these critical raw materials. This country is recognized as having more than five large RE deposits in the southern provinces. The most important are Lugeengol (Lugin Gol), Mushgia Khudag, Khotgor and Khalzan Buregtei (Eurasia, 2010). The Mongolian government has taken measures to facilitate western investments, nevertheless the country is economically dependent on China, the basic trading partner, particularly where exports are concerned.In the late 1970s Hydromet Kowary Enterprise, Poland, took up, along with the Wroclaw University of Technology, research and technological study on lanthanides recovery from raw materials of Vietnamese and Mongolian origin and from Indian monazite sands (Kowalczyk, 1990; Kowalczyk & Mazanek, 1987; 1990). For that purpose, a rare earth processing plant had been constructed with the capacity of about 10 t/year of hydroxide concentrate. The facility included several technological operations like grinding, flotation, hydroxide concentrate production in the hydrometallurgical processing, particular RE separation, and production of commercial products in form of CeO2, La2O3, Nd2O3, Pr2O3, and misch metal. Additionally work had been carried out in Kowary on the manufacture of yttrium and europium oxides of high purity, which were intended for color TV picture tube production in Poland."

Jan 1, 2012

By Mansoor Barati, Shaghayegh Esfahani

"The slag from extraction of ferrous and non-ferrous metals is a potential heat source which if treated properly can contribute to recovery of a significant amount of energy. The waste heat of slag may be used to generate steam, synthetic fuel gas, or electricity. Although several technologies have been investigated for this purpose, very little has been achieved in terms implementing the technology in industry. In this article, the development and application of various granulation techniques are reviewed and the methods to recover energy from granulated slag are discussed.IntroductionEvery year, more than 422 million tons of slag is being produced around the world as a by-product of the metal manufacturing at temperatures of up to 1300-1600°C [1, 2]. Currently slags are either disposed of or treated by processes such as granulation. Through the granulation process, most slags can be converted into a material which may be fully used as a cement feedstock. Conventional cement production is an energy intensive process with large emissions of CO2; therefore, the replacement can both be energy saving and environmentally friendly. However, for this purpose, the slag should have what is known as a “glassy” content (i.e. it should be amorphous) which requires rapid cooling rates that are not easily achieved due to the very low thermal conductivity. The main challenge in all these processes is to granulate the slag at a high cooling rate while the heat is also being recovered."

Jan 1, 2012

By Mohammed Sakr

This paper presents the results of a full-scale axial compression and tension (uplift) testing program executed on large-capacity helical piles installed in very stiff to very hard clay till soils (i.e. cohesive soils). A total of ten tests including six axial compression tests and four tension (uplift) tests were carried out. The results of the axial compressive and tensile pile load tests and field monitoring of helical piles with either a single helix or double helix are presented in this paper. Helical piles are traditionally used to support light to medium loads (i.e. loads up to 500 kN or 56 tons). However the results of the present study confirmed that helical piles can support significantly higher axial compressive loads up to 2450 kN or 275 tons, which is about 5 times traditional design loads. The study also demonstrated the high tensile capacities of helical piles which was as high as 85% of their compressive capacity. Hence helical piles can provide a viable design option for foundations supporting relatively heavy loads.

Jan 1, 2012

By Peter Olubambi, Babatunde Obadele, Oluwagbenga Johnson

"The microstructure and corrosion behaviour of titanium carbide (TiC) reinforced duplex stainless steel matrix surface composites synthesized by laser melt injection technique was investigated. The surface melting operation was conducted using a 4.4 kW CW Nd:YAG laser with laser power of 1.5 kW, scanning speed of 0.4 to 1.0 m/min, beam size of 3 mm and argon shield gas flow rate of 4 L/min. The morphologies and microstructures of the coatings examined using field emission gun scanning electron microscope (FEGSEM) revealed homogeneous distribution of fine precipitates of TiC in the matrix, while X-ray diffraction (XRD) analysis confirm no phase change. TiC addition to the steels significantly increased hardness value to about 547 Hv0.1 but slightly decreased the corrosion resistance of the steels in 3.5% NaCl possibly due to the intergranular carbide coating that prevented chromium from forming continuous passive oxide layers.IntroductionComposite materials evolve from the idea of combining two basically dissimilar materials with different physical and mechanical properties to arrive at a product whose final properties are superior to those of the individual components [1]. Metal matrix composites (MMCs) are receiving much attention and are the focus of intense research and development worldwide for aerospace, automotive and other applications because of their excellent combination of ductility and toughness of the metallic matrix with high hardness and strength of carbides reinforced in the matrix [2]. Surface modification techniques such as laser, thermal spray, plasma spray, chemical vapour deposition have been use to fabricate MMCs. Laser melt injection (LMI) is a surface modification technique known since the 1980s [3] has been used to improve surface properties of metallic alloys such as aluminium, titanium and steels [4-6]. It involves the lateral injection of carbides, ceramics and cermets blown by a gas stream into a liquid metallic pool, created by laser irradiation of the top surface of the base material."

Jan 1, 2012