bluuebunny/crossref_metadata_2025 huggingface dataset:
EPS Production during Adaptation of Acidithiobacillus ferrooxidans to High Ferric Ion Concentration
Authors: Saavedra Albert , Pavez Beatriz , Diaz Mauricio , Gentina Juan Carlos
Published: October 2013

The ability ofAcidithiobacillus ferrooxidansto get its energy from the oxidation of ferrous iron and the inhibitory effect of high ferric iron concentrations on its growth behaviour has been extensively studied. Furthermore it is known thatA. ferrooxidansexudes organic substances called extracellular polymeric substances (EPS), which could play a role in its protection against adverse environmental conditions. In this context, the aim of this work was to study the production of EPS during adaptation ofA. ferrooxidansto high ferric ion concentrations. The experiments were performed in shake flasks of 250 mL at 30 °C, 200 rpm and at an initial pH of 1.8. In order to establish the natural tolerance of the strain, its growth behaviour was evaluated at high ferric iron concentrations by adding consecutively the equivalent of 9 g/L of ferrous iron each time it was depleted in the broth. Cell growth stopped once ferric iron concentration increased up to 38 g/L. The adaptation consisted in eight sub-cultures run in parallel at initial concentrations of ferrous iron of 18, 27 and 36 g/L. The EPS was quantified as micro volumes using confocal laser scanning microscopy (CLSM), labelling the cells with propidium iodide and EPS carbohydrates with wheat germ agglutinin (WGA). During the adaptation procedure it was observed an increase in the ferric ion volumetric productivity of subcultures run with 27 and 36 g/L, as a result of cell adaptation. The amount of EPS exuded by cells was higher along with those experimental conditions having higher ferric iron concentrations. It was not detected EPS on cells grown on 9 g/L of ferrous iron. This study found that the adapted strain showed higher production of EPS at high ferric ion concentrations and higher ferric ion tolerance than non-adapted ones.
Metagenomic Insights into the Microbial Community Diversity between Leaching Heap and Acid Mine Drainage
Authors: Hu Qi , Liang Yi Li , Yin Hua Qun , Guo Xue , Hao Xiao Dong , Liu Xue Duan , Qiu Guan Zhou
Published: October 2013

The leaching heap and acid mine drainage are two key nodes in a bioleaching system. This study aimed to investigate the microbial community structural and functional diversity between the two nodes in bioleaching system from Dexing copper mine in Jiangxi province, China. 16SrRNA gene cloning and metagenomic analysis consistently indicated that there were obvious differences on microbial community structural and functional diversity in the two nodes. In leaching heap, the dominant species was the heterotrophic bacterium Acidiphilium; while the dominant species was the autotrophic bacterium Acidithiobacillus in acid mine drainage. Seven bacteria species were found in both two nodes, while the unique bacteria species in leaching heap and acid mine drainage were eleven and eight, respectively. In relation to the microbial community function aspect, all contigs and singlets were annotated against the non-redundant protein database of NCBI and clustering analyzed with COG database. For the two nodes, the COG clustering results showed that the functional category abundances were different, though the functional categories were similar. And the great majority of ORFs were forecasted as function unknown. All the results meant that the microbial community structural and functional diversity of bioleaching system was not as simple as former thought. This study could provide a new meta-view of theoretical support to bioleaching process.
Novel Cell Envelope Proteins Related to Copper Resistance in Acidithiobacillus ferrooxidans
Authors: Almarcegui Rodrigo , Navarro Claudio , Paradela Alberto , von Bernath Diego , Jerez Carlos A.
Published: October 2013

The presence in At. ferrooxidans of canonical copper resistance determinants does not explain the extremely high copper concentrations this microorganism is able to tolerate. This suggests that At. ferrooxidans may have additional copper resistance mechanisms. New possible copper resistance determinants were searched by using 2D-PAGE and real time PCR (qRT-PCR). Results showed the up-regulation of RND-type Cus systems and different RND-type efflux pumps in At. ferrooxidans grown in the presence of copper, suggesting that these proteins may be implied in resistance to this metal. Furthermore, the up-regulation of putative periplasmatic disulfide isomerases was also seen in the presence of copper. These proteins are most likely involved in the formation and rearrangement of disulfide bonds in proteins in the periplasm. Copper ions catalyze the formation of incorrect disulfide bonds in proteins. However, the up-regulated disulfide isomerases found could restore native disufide bonds allowing cell survival. In conclusion, At. ferrooxidans may resist high copper concentrations by using additional copper resistance strategies in which cell envelope proteins are very important. This knowledge could be used to select the best fit members of the bioleaching community to attain more efficient industrial biomining processes.
Effect of Bioleaching Microorganisms and Solid Ore Particles on Formation of Interfacial Crud in Solvent Extraction Plants
Authors: Li Xiao Hui , Zhou Gui Ying , Huang Song Tao , Wen Jian Kang
Published: October 2013

Effect of microorganisms and nickel sulfide ore before and after bioleaching on the emulsification was investigated. The emulsion stability was evaluated by the disengagement time or the production rate of crud. The results indicate that no crud formed and the disengagement time of system was prolonged with increasing bacteria density. And a large number of bacteria dispersed at the water-oil interface and aqueous phase and rarely existed in organic phase. The influence of bacteria on the emulsion stability was attributed to the structural characteristics and the mass transfer viscosity. And the emulsion with nickel sulfide ore after bioleaching was more stable, characterized as higher production rate of crud and lower light transmittance of aqueous phase, because bacteria alter the surface properties of minerals and increase particles’ hydrophilicity.
Electrochemical Behavior of Carbon Paste Electrode with Gold-Bearing Pyrite in Bioleaching
Authors: Wu Zhi , Zhong Shui Ping , Wu Zeng Ling , Huang Zhong Sheng , Chan Brenda K.C.
Published: October 2013

The dissolution of gold-bearing pyrite plays an important role in bioleaching of gold. This paper describes a fundamental study on the electrochemical behavior and reaction mechanisms of gold-bearing pyrite leaching in the form of Carbon Paste Electrode (CPE) with and without microorganisms using Cyclic Voltammetry (CV) and polarization curve. A two step process was suggested from Cyclic voltammetry. Electrode passivation by elemental sulphur was observed below 700mV (vs. SCE), elemental sulphur was then oxidized to sulphate when the electrode potential further increased from 700mV. The polarization current density of CPE and the oxidation rate of pyrite are further enhanced by the presence of microorganisms. Analyses of EDS and XPS confirmed the formation of elemental sulphur and sulphate. This electrochemical method successfully showed its simplicity and reliability to measure oxidation rate of gold bearing pyrite.
Evaluation of Parameters in the Bio-Oxidation Process of Refractory Gold Minerals
Authors: Aguirre Paulina , Diaz Esvar , Gentina Juan C.
Published: October 2013

The mining districts located in the western mountain range in the south of Ecuador have gold minerals with refractory characteristics, which do not allow gold recovery by traditional methods used in Ecuador. Therefore, it is necessary to apply some technology that permits to obtain greater metal recovery. Bio-oxidation, as treatment of refractory ores that contain low grade of gold, offers an economic and sustainable alternative for this purpose. The objective of this research was to evaluate the effect of particle size, pulp density and concentration of inoculum and inducer (Fe+2) on the bio-oxidation of refractory gold minerals in order to maximize gold recovery of the bioleached minerals by means of a cyanidation process. The microbial consortium used in this work was collected and isolated from the Portovelo mining district corresponding mostly toAcidithiobacillus ferrooxidansandLeptospirillum ferrooxidansspecies. The Eh, final concentration of ferric ion, total iron and sulfates were measured. Finally, the bio-oxidized material was tested using cyanidation to determine the gold recovery. The results after the cyanidation tests showed that the highest gold recovery was obtained when the bio-oxidation step was conducted with 68-91 µm particle size, 15% pulp density, 20% v/v inoculum and 2 g/L of Fe2+as inducer. At those conditions, gold recovery was 68% compared to 26% obtained when no bio-oxidation step was performed, demonstrating that this process was favorable compared with traditional gold recovery processes
Proteo and Actinobacteria Diversity at a Sulfide, Salt and Acid-Rich Lake in the North of Chile
Authors: Davis-Belmar Carol S. , Pinto Eric , Demergasso Cecilia , Rautenbach George
Published: October 2013

The Salar de Gorbea, located at the hyperarid Atacama region of the north of Chile, is an unusual extreme environment. Its unique characteristics of high acidity and salt concentration as well as the presence of sulfide and hydrothermal alterations, makes it an unprecedented source of novel microbial communities with potential biotechnological prospects. Several lakes covering a wide range of chloride concentrations were sampled, characterized and enriched under acidic and high salt conditions. Site samples were characterized by the presence of novel Proteobacteria and Actinobacteria strains with closest relatives of the generaLeifsonia,Francisella,Novosphingobium,Mycobacterium,DunalielaandRickettsia. Several enrichments on diverse conditions and substrates (pyrite, elemental sulfur, ferrous iron and different organic compounds) were tested although few enrichments provided considerable and reproducible growth. Successful enrichments showed the presence and growth of novel strains of the generaAcidisomaandAlkalibacter, genera that have been identified as part of communities that prosper in acid mine drainage systems. The later enrichments were grown under mixotrophic conditions and gradually exposed to increasing concentrations of chloride.
Minimum Aeration in Acidithiobacillus ferrooxidans Cultures Required to Maintain Substrate Oxidation without Oxygen Limitation
Authors: Mandl Martin , Pakostova Eva , Poskerova Lenka
Published: October 2013

The volumetric oxygen transfer coefficient (kLa) was used to define the conditions necessary for minimum aeration and to eliminate potential oxygen limitation in bioleaching cultures ofAcidithiobacillus ferrooxidans. The Michaelis constants for oxygen were 1.07 and 0.71 μmol O2l-1for the oxidation of ferrous iron and elemental sulphur, respectively. The critical oxygen concentration, below which oxygen limitation occurred, was determined to be 6.25 and 3.125 μmol O2l-1for the oxidation of ferrous iron and elemental sulphur, respectively. The (kLa)critvalues required to maintain oxygen-unlimited substrate oxidation for ferrous iron and elemental sulphur were 7.70 and 4.88 h-1, respectively.
Molybdenite Bioleaching by Thermophilic Bacteria in a RELVA-ARBP Bioreactor
Authors: Rivera-Santillán Rosa Elva , Patricio-Ramírez Felipe , López-López Francisco Artuto
Published: October 2013

The biological technologies application in sulfide minerals leaching to the recovery of valuables metal is a very important technological advance. They are environmental friendly and favor the sustainability of metals production in the mining and metals industry. Nowadays there is not enough basic information on molybdenite bioleaching, as well as there isn`t equip capable to obtain efficient molybdenum extractions. The difficulty depends in part on microorganisms tolerance to the molybdenum. An 85% molybdenum extraction in 6 months has been reported. This work assesses the molybdenite bioleaching from a concentrate (MoS2) with thermophilic microorganisms, at a temperature of 65 °C, on a new reactor designed at the Faculty of Chemistry of the Universidad Nacional Autónoma de México, to obtain higher extractions of molybdenum. Since bioleaching an aerobic process, the oxygen transference is a difficult condition to achieve because its solubility in water is very low and in the air 20.9 %. In addition to homogenize and maintain constant the nutrients concentration, in this new bioreactor could be established the physical, chemical and biological conditions that lead to the microorganisms optimal growth, due to these are environmental sensitive. This new equip allows us mix the nutrients in a homogeneous way. Also is able maintain constant the nutrients concentration, and all controlled physical, biological and chemical parameters. Finally does not cause any microorganisms damage. The RELVA-ARBP bioreactor allows us the control of necessary conditions for a growth more efficient of the bacterial strains. This will allow leach more rapidly the ore, increasing the molybdenum extraction kinetics. The tests results of bioleaching molybdenite with a mixed strain of extreme thermophiles carried out at 65 °C in an orbital incubator and in the RELVA-ARBP bioreactor, show a better efficiency of the bioreactor used.
Microbial Community Composition on Lignite before and after the Addition of Phosphate Mining Wastes
Authors: Bellenberg Sören , Kalin Margarete , Sand Wolfgang
Published: October 2013

Empirical field tests in which phosphate mining wastes (NPR) were added to various sulphidic mining wastes resulted in neutral drainage. A biofilm was documented on waste rock covering the pyrite. This was likely the cause of the improved effluents. NPR was added to sterile columns containing pyritic lignite and spiked with granulated pyrite. The biological columns were inoculated with 108 cells/g of lignite-cultured microbes from Rio Agrio, Argentina. The microbes were maintained at 30°C using pyrite as sole energy source. The microbial populations were monitored with MPN before NPR addition and 2, 4 and 10 weeks later. After 45 days strong bioleaching was evident, as measured by electrical conductivity. Concurrently, a shift in the microbial populations took place. In the presence of NPR about 90% of populations consisted of heterotrophic neutrophiles covering the pyrite surfaces with a 10 μm thick biofilm, whereas without NPR, 99% of the populations were iron oxidizing acidophiles in mono-layered biofilms. These results are relevant to controlling processes in heap leaching and acid rock drainage.
The Effect of Ferrous Iron Addition during Tetrathionate Utilisation by Some Sulfobacillus Species
Authors: Shiers Denis W. , Ralph David E. , Watling Helen R.
Published: October 2013

Ferrous sulfate was added to batch cultures ofSulfobacillus (Sb.) acidophilus,Sb. thermosulfidooxidansandSb. sibiricusduring growth on tetrathionate. Soluble ferrous ion and polythionate concentrations were used as a measure of substrate utilisation.Sb. thermosulfidooxidansswitched from utilising polythionates to exclusively oxidising ferrous ions, only then oxidising the remainder of the polythionates.Sb. sibiricusandSb. acidophilusdid not cease polythionate oxidation but utilised both substrates concurrently after ferrous ion addition. None of the cultures tested exhibited preferential polythionate utilisation, even though they were utilising polythionate prior to the addition of ferrous ions.
The Influence of Pyrite on Galvanic Assisted Leaching of Chalcocite Concentrates
Authors: Wu Biao , Yang X.L. , Cai L.L. , Yao G.C. , Wen J.K. , Wang D.Z.
Published: October 2013

The dissolution of metal sulfides is controlled by their solubility product and valence bond theory, pyrite and chalcocite have different electronic nature of the valence energy band, with which the electrolyte may exchange electrons during dissolution reaction, so they have different principals of dissolution. Pyrite which has a higher rest potential is galvanically protected, while chalcopyrite which has a lower rest potential is preferentially leached. Pyrite is intentionally added to the leaching of chalcocite concentrates, we investigated the influence of pyrite to chalcocite weight ratio, solution pH , Eh and the presence of bacteria on assisted leaching of chalcocite concentrates. The leaching solution redox potential, pH, iron, copper and bacteria were monitored, leached residue was collected and analysed to understand leaching mechanism. We found that chalcocite leaching efficiency is enhanced with pyrite:chalcocite weight ratio increased.
Reduction and Complexation of Copper in a Novel Bioreduction System Developed to Recover Base Metals from Mine Process Waters
Authors: Hedrich Sabrina , du Plessis Chris , Mora Nelson , Johnson D. Barrie
Published: October 2013

An integrated bio-processing scheme was devised and tested in the laboratory for recovering copper, or other base metals, from pregnant leach solutions (PLS) using a two-step process involving both iron-reduction, and sulfate-reduction for H2S generation and sulfide precipitation, as a potential alternative to conventional SX-EW. Reduction of ferric iron in the PLS was achieved using iron-reducingAcidithiobacillusspp. andSulfobacillus thermosulfidooxidansin column reactors containing elemental sulfur as electron donor. Analysis of the column reactor effluents showed not only that most of the ferric iron was reduced to ferrous, but also that all of the copper (II) had been reduced to copper (I), i.e. cuprous copper. This copper (I) appeared to be complexed as it was not oxidized when exposed to ferric iron nor precipitated as a copper-sulfide when exposed to either sodium sulfide or H2S. The data suggested that copper (II) was reduced and the resulting copper (I) complexed, with both reactions probably mediated by sulfur oxy-anions produced indirectly by the bacteria, in the anoxic sulfur column bioreactors. It was also noted that copper (I) produced chemically by reduction of copper (II) by hydroxylamine was more toxic to axenic cultures ofAcidithiobacillusspp. andSb. thermosulfidooxidansthan was the copper (I) in the column effluent liquors.
Identification of a Bacterial Consortium with Biotechnological Potential for Arsenic Bioremediation
Authors: Moreira Mariana , de Queiroz Silva Silvana , Teixeira Mônica Cristina
Published: October 2013

The objective of this work was to identify one bacterial consortium adapted to the cultivation in the presence of trivalent arsenic (AsIII). Samples were cultured in flasks containing modified Postgate C liquid medium (selective for sulfate-reducing bacteria, SRB). Six different As concentrations were used: 0.5, 1.0, 2.0, 4.0, 8.0 and 16 mg l-1. The growth of sulfate reducing microorganisms was indirectly observed by the formation of an iron sulfide black precipitate and also by the Eh measures.100 ml aliquots of cultured media were centrifuged and stored at-20°C for DNA extraction by phenol/chloroform method. Universal primers 968F-GC 1392R (Bacteria domain) were used for 16S ribosomal DNA amplification. Microbial diversity was evaluated by denaturing gradient gel electrophoresis (DGGE). After DGGE analysis 7 different bands were selected, cut, sequenced and analyzed using the Ribosomal Database Project Release. Consortium microorganisms identified were: Pantoea agglomerans, Enterobacter sp, Citrobacter sp, Cupriavidusmetallidurans, Ralstonia sp, Burkholderia cepacia and Bacillus sp. Thus the microbial consortium here identified is a good candidate for bioremediation of arsenic contaminated areas and effluents.
A Novel Acidianus Strain Isolated from Copahue, Argentina Involved in the Sulphur Cycle of a Volcanic Environment
Authors: Nolasco Costanza , Chiacchiarini Patricia A. , Lavalle Teresa Laura , Giaveno Alejandra
Published: October 2013

The extremely thermophilic archaea have become a research hotspot in the recent years because of their extreme living conditions, physicochemical characteristics such as the oxidation of sulphur, metal sulphide ore and excellent leaching capability of metal sulphides. A novel thermoacidophilic archaea (ALE1 strain) of the genusAcidianus,CandidatusAcidianus copahuensis, was isolated from the Copahue Volcano area, in Neuquén, Argentina. This strain was able to metabolize different sulphur compounds under aerobic and anaerobic conditions. ALE1 strain was inoculated in M88, a selective medium for thermoacidophilic archaea recommended by DSMZ. Elemental sulphur (So) and potassium tetrathionate (T) were used alternatively as the energy source, while oxygen and iron (III) were the electron acceptors in the aerobic and anaerobic tests respectively. All systems were incubated at 70oC in shake flasks. The pH, Eh, [H+] and cell concentration were measured. The results from the aerobic test confirm that ALE1 strain was able to oxidize (So) and (T) decreasing the pH significantly, reaching the values 1 and 1.5, respectively. A light yellow precipitate was formed only in the inoculated systems in presence of (T). It was characterized by SEM and FTIR techniques showing that only sulphur atoms are bonded together in some way not confirmed yet. In the anaerobic tests, it was found that ALE1 was able to oxidize sulphur and tetrathionate ion transferring electrons to iron (III) acceptor. The Eh decreased in all inoculated systems from nearly 500mV to 300mV approximately. This work shows that ALE1 strain is helping to keep active the sulphur cycle in the Copahue volcanic environment; however the challenge is to elucidate the metabolism involved.
Molecular Identification of Iron Oxidizing Bacteria Isolated from Acid Mine Drainages in Peru
Authors: Abanto Michel , Pariona Nicolaza , Calderon Julio , Guerra Gregory , Ramirez Rina , Delacruz-Calvo Fernando , Ramirez Pablo
Published: October 2013

Acidophilic iron-oxidizing microorganisms are important in both environmental and biotechnological applications. These microorganisms are known to accelerate the dissolution of sulfur minerals such as pyrite (FeS2), leading to the acid mine drainage generation , a serious pollution problem, that makes these microorganisms essential to the commercial processing of minerals and sulfur. In order to answer this question, diversity of native acidophilic bacteria isolated from acid mine drainage of Peru was evaluated. The samples were collected from Yanacocha mining (3000 m.a.s.l.) located in the North of Cajamarca region, Yanamina mining (4440 m.a.s.l.) located in the middle of Huancavelica region; finally, SPCC mining (2000 m.a.s.l.) located in the South of Moquegua region. We isolated 11 strains from which three were identified asAcidithiobacillus ferrooxidans, two asAt. ferrivorans, two asAt. ferridurans,three asLeptospirillum ferrooxidansand one asAcidiphilium sp.by comparative sequencing of PCR-amplified 16S rRNA genes. Phylogenetic analysis of the 16S rRNA genes revealed that some of the strains isolated are closely related to other already known, but there are some with similarities lower than < 95 percent. Our results provide the first study on the diversity of iron-oxidizing bacteria isolated from acid mine drainage of Peru.
Precision Assembly Process with Augmented Reality Technology Support
Authors: Novak-Marcincin Jozef , Barna Jozef , Torok Jozef
Published: October 2013

This article presents possibilities of precision assembling process by using special tools of the augmented reality (AR) and logical procedures from related areas such as a Computer Aided Design and Planning. These possibilities are implemented in the virtual assembling environment of AR, where engineers and designers can see important information about an exact position and orientation of the single assembly element that creates a part of the entire assembly structure. By means of this the application of AR allows costumer to see the motion process of single assembly item according to its trajectory and prevents the possible mistakes in the assembling processes.
Experimental Investigation of Tool Breakage in Micro Drilling of EN AW-5083 Aluminium
Authors: Szalay Tibor , Patra Karali , Farkas Balázs Zsolt
Published: October 2013

Nowadays micro hole drilling is more and more applied machining operation. Because of less than 1 millimeter diameter, and of the relatively high thrust force, micro drills are more easily break than conventional ones. In this paper the experiences of micro drilling tests are summarize in order to demonstrate that measuring thrust force is efficient way to recognize the tool breakage. In order to evaluate the micro drill breakage monitoring method the authors carried out experimental measurements varying the cutting conditions, too.
Preliminary Study of Ozone Utilization in Elimination of Bacterial Contamination in Metalworking Fluids
Authors: Gerulova Kristina , Buranská Eva , Tatarka Ondrej , Szabova Zuzana
Published: October 2013

Metalworking fluids (MWFs) are used during machining to prolong the life of the tool, carry away debris, and protect the surfaces of work pieces. During their lifetime they are prone to intensive microbial deterioration. Microbial contamination can be a problem, primarily because of potentional adverse effect to the operators health and effect on a fluid quality, performance and economics. Bactericides are added to control the growth of micro-organisms. The paper deals with possible utilization of ozone for sterilization of MWFs to avoid presence of biocides. There were tested 16 MWFs for their reaction to ozone application in extreme conditions (concentration of MWF 1% (v/v), ozone concentration 15 g hour-1, application of ozone 4 hours). After, was realized pilot sanitation of selected in-use MWF for elimination of presence bacterias by applying lower concentration of O3, there were measured few parameters to control the quality of treatment fluid.
Precision Milling of Hardened Steel with CBN Tools
Authors: Matras Andrzej , Zębala Wojciech , Kowalczyk Robert
Published: October 2013

The paper presents research of milling tool inclination angle δ influence (in relation to the cutting surface) on the free surface roughness. Rotational tools with curved cutting edges (ball nose cutter) performed translation movements on the spherical surface of hardened steel work piece (hardness of 50, 62 and 65 HRC). Milling tool with diameter d=1 mm was made of CBN. Roughness measurements were performed in different places of the milling surface with the Taylor Hobson profilometer.
Application of Superfinishing to Curved Surfaces
Authors: Miura Kohichi , Yamada Takazo , Takahashi Masayuki , Lee Hwa Soo
Published: October 2013

It is well known that the superfinishing is a high efficient surface finishing method to cylindrical workpieces. In this method, grinding stones are pressed to the outside of cylindrical surfaces. Rotating cylindrical workpieces and making relative vibrations between grinding stones and ground surfaces in the directions of the center lines of workpiece rotations, the cylindrical surfaces are ground and mirror surfaces are realized relatively in short time. Therefore, this finishing method is widely applied to the finishing of precise machine elements. However, this method cannot be applied in case of that the workpiece which is not simple cylindrical geometries so far. In this study, a new application method of superfinishing to the cylindrical workpieces having curved parts is proposed and its performance is discussed experimentally.
Comparison of Round Insert's Lifetime when Milling Inconel 718
Authors: Mrkvica Ivan , Janoš Miroslav
Published: October 2013

This article focuses on the analysis of tool wear mechanisms in milling of Inconel 718. Inconel 718 is tough and highly temperature resistive material, which is used due to its excellent properties especially in aggressive corrosive medium. Machining of this alloy is still complicated. The feasibility of four inserts tested for milling of Inconel 718 has been shown in the work. Different cutting speeds and feeds were used. Experimental tests were performed in order to analyze wear patterns evolution. It was found influence of cutting conditions and type if insert in tool wear mode.
Influence of Welding Parameters to Quality of Welds from Structural Steel
Authors: Hatala Michal , Orlovský Imrich , Radchenko Svetlana
Published: October 2013

Welding is the most widely used technology of creating permanent joints in the engineering industry. Correct setting of welding parameters predisposes quality weld joint without unwanted defects. Article deals with the influence of fusion welding parameters on the final quality welds. Describes the thermal cycle of welding and its effects on the weld joint and theoretically describes used methods MIG / MAG. Core of the article is devoted to the description of the experiment and on the technological parameters of the welding process. Quality of weld is tested visually, metallographic and microhardness measurement of the weld joints.
Precision Manufacturing Process of Parts Realized by FDM Rapid Prototyping
Authors: Novakova-Marcincinova Ludmila , Novak-Marcincin Jozef , Janak Miroslav
Published: October 2013

Rapid Prototyping (RP) can be defined as a group of techniques used to quickly fabricate a scale model of a part or assembly using three-dimensional computer aided design (CAD) data. What is commonly considered to be the first RP technique, Stereolithography, was developed by 3D Systems of Valencia, CA, USA. In this contribution are presented basic characteristics and problems in area of technology of Rapid Prototyping with use of Fused Deposition Modelling. It belongs to methods of precision model creation based on geometry obtained from CAD environment. Chapters are focused on optimization of FDM technology preparation process with aim of maximal precision of the parts. There also is algorithm that leads to selection of suitable settings for these problems. There are outputs in form of graph and tables accumulating information directly affecting precision aspects of manufacturing.
Coherencies of Temperature and Surface Roughness by Milling Procedure
Authors: Fečová Veronika , Michalik Peter , Zajac Jozef , Hanisko Erik , Zajac Jan
Published: October 2013

This paper deals with coherencies of temperature and surface roughness by milling procedure. It explains the principle of up and down milling and also explains the fundamental differences between them. It also briefly describes the heat generated, too. A main part of this paper is realization of the experiment, description of the experiment and evaluation of results shown as the resulting values of temperature and subsequent surface roughness. The aim is to find coherencies of temperature and surface roughness by milling procedure.
Comparison of Theoretical and Real Surface Roughness in Face Milling with Octagonal and Circular Inserts
Authors: Felhő Csaba , Kundrák János
Published: October 2013

Various modeling techniques have applied by researchers to predict values of surface roughness parameters in different metal cutting processes. Some examples of these methods are briefly introduced. After this an analytical model and investigation method are presented which were used to make predictions of the expected values of surface roughness parameters. Cutting experiments were performed to obtain real roughness data and to validate the proposed and realised model by face milling of 42CrMo4 specimens with two different insert shapes. Conditions and results of these experimental investigations are presented in the subsequent part of the paper, and finally the determined approximation relations are introduced that can be used to calculate the expected roughness values from theoretical data.
Comparison of Roughness and Profile between ELID and Ground Surfaces
Authors: Novák Martin , Kasuga Hiroshi , Ohmori Hitoshi
Published: October 2013

This paper deals with surface roughness and surface profile in high precision methods of materials finishing. One of them is ELID process and the second method is grinding. There is surface profile and roughness compared of the three materials samples – carbide steel and two aluminium alloys. In the paper are shown results of surface measurement between ELID and ground surface. Both methods are very precision in the focus on surface roughness – measured units in nano scale. Paper shows possibilities in finishing methods for production, automotive, aerospace, medicine and cosmic industry.
Up to Date Mathematical Model for Analysing of Cylindrical Worm Power with Bevel-Gear
Authors: Balajti Zsuzsa , Toth Maria Nandorine
Published: October 2013

The developed general mathematical-kinematical model for examination of mating of cylindrical and conical helicoids and their tools - furthermore the helicoids surfaces are on identical axis -, which is suitable to deal with examination at the same time. This paper shows the newest mathematical-kinematical model to analyzing the mating of cylindrical worm gear with bevel gear.
Environmentally Conscious Manufacturing: The Effect of Metalworking Fluid in High Speed Machining
Authors: Hricova Julia
Published: October 2013

Environmentally conscious manufacturing is a new philosophy which focuses on the most efficient and productive use of raw materials and natural resources, and minimizes the adverse impacts on worker ́s health and safety and the environment. In this article, a set of experiments were designed and conducted on Al alloy to determine the effect of cutting fluid in high speed milling. The variables examined included cutting velocity, feed and tool geometry as well as milling with and without a cutting fluid.
Machining of Non-Homogeneous Composite Material with Natural Fibers Reinforcement and HDPE Matrix
Authors: Hutyrová Zuzana , Zajac Jozef , Fečová Veronika
Published: October 2013

Depending on expanding population and its increasing purchasing power we are forced to use more and more renewable resources for a production of materials. When compared to other types of fibres, the natural fibres have a lot of advantages: they are affordable (only 1/10 of a glass fibre price), non-abrasive, recyclable, with relatively high strength and rigidity, low density (and low weight in hollow profiles). When combined with plastic matrix the exceptional biomaterial, which is possible to describe as friendly environment, is created. It has high potential to succeed with a final customer. At present, a use of thermoplastic matrices (especially with WPC materials) is preferred. The final subject of this article is to point out considerable disadvantage from a perspective of machining inhomogeneity of the material (in full profiles).
Interactions of Self-Interstitials with Interstitial Carbon-Interstitial Oxygen Center in Irradiated Silicon: An Infrared Absorption Study
Authors: Murin Leonid I. , Svensson Bengt Gunnar , Markevich Vladimir P. , Peaker Anthony R.
Published: October 2013

The evolution of radiation-induced carbon-oxygen related defects with the fluence of MeV electrons and upon subsequent isochronal annealing (75-350 °C) in Si crystals with different carbon and oxygen content has been studied by means of Local Vibrational Mode (LVM) spectroscopy. In particular, the generation kinetics of the bands at 998 and 991 cm-1 is considered and additional arguments supporting their previous assignment to the I2CiOi and I3CiOi complexes are found. An annealing behaviour of the LVMs related to the C4 (ICiOi) defect has been studied in the various Si crystals irradiated with different particles. In all the samples studied the bands at 940 and 1024 cm-1 are found to disappear at about 200 °C while three new LVM bands, at 724 cm-1 (O-related) and at 952 and 973 cm-1 (both C-related) are emerging. Further increase in annealing temperature up to 250-275 °C results in a transformation of the latter bands into another set of LVM bands at 969 cm-1 (O-related) and at 951 and 977 cm-1 (both C-related). These bands disappear upon annealing in the temperature range 300-325 °C. The ratios of all the bands intensities as well as their transformation rates do not depend on the oxygen and carbon content in the Si samples nor on the kind of irradiation (2.5 and 10 MeV electrons, fast neutrons) and irradiation doses. These facts confirm our previous conclusion that all the above-mentioned LVMs arise from the C4 defect being in different configurations (ICiOi, ICiOi*, and ICiOi**).
PL and DLTS Analysis of Carbon-Related Centers in Irradiated P-Type Cz-Si
Authors: Raeissi Bahman , Ganagona Naveengoud , Galeckas Augustinas , Monakhov Edouard V. , Svensson Bengt Gunnar
Published: October 2013

Photoluminescence (PL) and deep level transient spectroscopy (DLTS) have been used to investigate carbon related defects in p–type Cz–Si induced by proton irradiation. The interstitial carbon–interstitial oxygen (CiOi) level in DLTS and the corresponding C–line (789.5 meV) in PL spectra are detected in as–irradiated samples. Formations of the so–called P–line at 767 meV in PL and a new defect level at about 0.39 eV above the valence band edge, Ev, in the DLTS spectra are observed in the annealed samples. The evolution of the CiOi and Ev+0.39 eV levels in DLTS and also the C– and P– lines in PL upon post–irradiation heat–treatment is investigated, showing that the intensity of the CiOi level decreases with heat–treatment, which is consistent with the PL data for the C–line. The intensity of the Ev+0.39 eV level is enhanced and then saturates with annealing duration. We tentatively assign this level to the interstitial carbon–oxygen dimer (CiO2i).
New Results on the Electrical Activity of 3d-Transition Metal Impurities in Silicon
Authors: Weber Jörg , Scheffler Leopold , Kolkovski Vladimir , Yarykin Nikolai
Published: October 2013

In silicon several electronic levels are known which can be attributed to transition metals. Ignorance persists however about the specific nature of the defect centers. Some progress was made recently on identifying electronic levels from substitutional or interstitial lattice sites and on identifying levels from defect complexes. The sensitive Laplace DLTS technique allows us to determine depth profiles or the influence of the electrical field on the emission rate with unparalleled accuracy. Three examples will be discussed in this short review: The identification of the CoB pair, a reinterpretation of the Ti DLTS spectrum and the complex formation of interstitial Cu with substitutional Cu as the nucleation site.
Metastable CuVO* Complex in Silicon
Authors: Yarykin Nikolai , Weber Jörg
Published: October 2013

The reaction of the mobile interstitial Cui atom and the A-center (vacancy-oxygen complex) was recently reported to produce at 350 K the rather stable CuVO complex. Chemomechanical polishing in a copper-contaminated slurry allowed to lower the copper in-diffusion temperature down to 295K. The development of the CuVO complex is shown to proceed via formation of the metastable precursor (CuVO*) which introduces two deep levels in the lower half of the band gap. The CuVO* defect is unstable at room temperature and transforms completely into the CuVO complex by a 30 min anneal at 350 K. The proposed structure for the CuVO* complex of a Cui atom trapped nearby the A-center is supported by recent ab-initio calculations.
External and Internal Gettering of Interstitial Iron in Silicon for Solar Cells
Authors: Macdonald Daniel , Liu An Yao , Phang Sieu Pheng
Published: October 2013

The removal of dissolved iron from the wafer bulk is important for the performance of p-type multicrystalline silicon solar cells. In this paper we review some recent progress in understanding both external and internal gettering of iron. Internal gettering at grain boundaries and dislocations occurs naturally during ingot cooling, and can also be driven further during cell processing, especially by moderate temperature anneals (usually below 700 °C). Internal gettering at intra-grain defects plays key a role during such precipitation annealing. External gettering to phosphorus diffused regions is crucial in reducing the dissolved iron concentration during cell processing, although its effectiveness depends strongly on the diffusion temperature and profile. Gettering of Fe by boron and aluminum diffusions is also found to be very effective under certain conditions.
Association of FeB Pairs under Illumination
Authors: Möller Christian , Laades Abdelazize , Lauer Kevin
Published: October 2013

It has been found that association of iron-boron (FeB) pairs takes place during illumination of iron contaminated boron-doped silicon. The established FeB pair model is interpreted with respect to the quasi-Fermi level position, the stability condition of FeB pairs and the steady state reaction between interstitial iron, electrons and boron. At an excess charge carrier density of Δn = 5.4·1014 cm-3, still 5 % of the interstitial iron associates to FeB pairs.
Proximity Gettering of Slow Diffuser Contaminants
Authors: Polignano Maria Luisa , Mica Isabella , Cazzini Elena , Ceresoli Monica , Codegoni Davide , Russo Felice , Moccia Giuseppe , Nardone Giancarlo , Alfonsetti Roberto , Polsinelli Giampaolo , D'Angelo Antonio Domenico , Patacchiola Antonio , Liverani Massimo , Pianezza Pio , Lippa Tiberio , Carlini Michele
Published: October 2013

In this paper, we test proximity gettering layers obtained by carbon or silicon implantation for their efficiency in molybdenum and tungsten gettering. DLTS was used to measure the impurity concentration in the solid solution and so to evaluate gettering efficiency. It was found that carbon implantation is effective in capturing these impurities, whereas silicon implantation is not. Extended defects seem not to play an important role in gettering these impurities. In addition, gettering was found to be most effective at high impurity concentration.
Light-Induced Boron-Oxygen Recombination Centres in Silicon: Understanding their Formation and Elimination
Authors: Voronkov Vladimir V. , Falster Robert
Published: October 2013

Lifetime-degrading recombination centres those that emerge in the presence of excess carriers in boron and oxygen containing silicon - show a peculiar dependence on the concentrations of the relevant impurities, B and O, and on the hole concentration p0 (net doping) in materials that contain compensating donors (phosphorus or Thermal Donors) or added Ga acceptors. The data indicate involvement of both substitutional (Bs) and interstitial (Bi) boron atoms in the major recombination centres observed in p-Si. A suggested model ascribes degradation to the presence of a BiBsO latent defect inherited from the thermal history in a recombination-inactive atomic configuration. In the presence of excess electrons, this latent defect reconfigures into a recombination-active centre. The defect concentration dependence on the material parameters is reduced, in some special cases, to a proportionality to p0 [2 or to [ [2. The essential feature is an involvement of a fast-diffusing species Bi in the defect. This species can be removed to the boron nanoprecipitates thus eliminating the defects responsible for the degradation.
Anisotropy of the Porous Layer Formation Rate in Silicon with Various Acceptor Concentrations
Authors: Astrova Ekaterina V. , Zharova Yuliya A.
Published: October 2013

The orientation dependence of porous Si formation rate has been studied by local anodization of p-Si wafers with a boron concentration NB = 3·1015 - 2·1019 cm-3 at various currents with the help of a wagon wheel technique. It is demonstrated that the etch rate diagram is drastically transformed as the dopant concentration in p-Si is changed. The highest etch rate is observed in the <100> direction for heavily doped p++-Si, whereas for p+-Si with NB < 2·1018 cm-3, <111> axis becomes the fastest direction. Further decrease in the doping level makes the anisotropy weaker, and at NB <2·1016cm-3, the anodization rate becomes nearly independent of the crystallographic orientation. For all the impurity concentrations in the substrate, the anisotropy is the strongest in the case of anodization at low currents and gradually decreases with increasing current density.
Direct Observation of Carrier Trapping Processes on Fe Impurities in mc-Si Solar Cells
Authors: Yoshida Yutaka , Tsukamoto Yoshinori , Ichino Masahiro , Tanaka Kiyotaka
Published: October 2013

n-situ Mössbauer studies on 57Fe solute atoms in Si solar cells are performed: (1) GeV-57Mn/57Fe implantation into Si solar cells, (2) 57Fe diffused n-type Si under light illumination; (3) 57Fe diffused solar cells under applying external voltages. The carrier trapping cross sections for the interstitial components with different charge states, Fei+ and Fei2+, can be successfully obtained by evaluating the dynamical charge fluctuations within a time scale of 100ns between Fei+ and Fei2+ which appear in the Mössbauer spectra of 57Fe doped mc-Si solar cells. We further measure the distributions of Fei+ and Fei2+ by a Mössbauer Microscope, which we have been developing. The present results provide us a possibility to clarify the carrier trapping process on an atomistic scale directly on the Fe impurities in Si-solar cells.
Properties of Strong Luminescence at 0.93 eV in Solar Grade Silicon
Authors: Krause Christoph , Arguirov Tzanimir , Seifert Winfried , Mankovics Daniel , Krause Hans Michael , Kittler Martin
Published: October 2013

We report on 0.93 eV luminescence observed in multicrystalline silicon. The spectral line is close to the well known D3 one, but its properties are different. The new feature shows a remarkable intensity at room temperature, exceeding the intensity of the band to band radiative transition. Moreover, it appears as a single line in the entire temperature range 10-300K, in contrast to the D3, which is usually accompanied by D4. Cathodoluminescence (CL) and electron beam induced current (EBIC) micrographs revealed that the centers causing 0.93 eV emission are irregularly distributed along certain grain boundaries. Electron backscattering diffraction examination showed that the 0.93 eV luminescence appears at grain boundaries characterized by a lattice rotation around a <344> axis. The EBIC contrast at those irregularities indicates strong total recombination. Based on an analysis of the temperature dependence of the CL intensity and the EBIC contrast we obtained an activation energy of about 120 meV.
The Impact of Financial Openness on the Size of Utility-enhancing Government
Authors: Erauskin Iñaki
Published: October 2013

In this paper, we employ a portfolio approach based on a two-country world to study the impact of financial openness on the size of government and on other key economic variables, including the consumption-wealth ratio, the growth rate of wealth, and welfare (assuming that public spending is utility enhancing). The model suggests that the size of government, the consumption-wealth ratio, and welfare should be greater in an open economy because of higher productivity and/or less volatility because of risk sharing. The theoretical results for the growth rate depend on differences in productivity and in consumption-wealth ratios. The empirical evidence — based on a sample of 49 countries from 1970 to 2009—broadly supports the main theoretical results of the model.