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Showing papers in "Materials Science Forum in 2016"


Journal ArticleDOI
TL;DR: In this paper, the current available 3D printing systems from literature and the respective materials that have been used thus far by various experts, industries for building and construction (B&C) purposes are summarized.
Abstract: 3D printing (3DP), commonly known as additive manufacturing (AM), is a promising technology that can fabricate three dimensional complex shape prototypes directly from computer-aided design (CAD) model without any tooling and human intervention. Owing to its peculiar characteristics, AM is widely used in many industries to assist in the design, manufacture and commercialization of a product. More recently, this technology has been extended to building and construction (B&C) application in order to mitigate some of the critical issues such as shortage of skilled labour, high production cost and construction time, health and safety concerns of the workers in the hazardous environment etc. However for successful implementation, proper selection of materials and their mix design is highly recommended, which is a challenging task. This paper summarizes the current available 3DP systems from literature and the respective materials that have been used thus far by various experts, industries for B&C purposes. Finally, the benchmarking properties of theses material and potential research directions are briefly discussed.

195 citations


Journal ArticleDOI
TL;DR: In this article, the selective laser melting (SLM) of pure copper powder was studied and the structure of fabricated specimens was studied by scanning electron microscopy of polished cross-sections.
Abstract: In this work the selective laser melting (SLM) of pure copper powder was studied. Because of low laser radiation absorption and high thermal conductivity it is very difficult to organize stable SLM process for copper. Five 10x10x5 mm specimens were fabricated by using different process parameters (scanning speed, point distance, exposure time, scanning strategy). The structure of fabricated specimens was studied by scanning electron microscopy of polished cross-sections. The tensile test was carried out for SLM regime with the lowest porosity.

81 citations


Journal ArticleDOI
TL;DR: In this paper, the setting time of fly ash-based geopolymer concrete is investigated. And the experimental results showed that fly ash particle size, CaO and MgO content, in addition to ratio of sodium silicate and sodium hydroxide in the alkali solution, molarity of NaOH, initial temperature of the mixture, curing temperature, and mix volume could potentially influence the set time of the geopolymers mixture.
Abstract: Fly ash is a waste from coal burning, that are generated with fluctuation both in its physical and chemical characteristics. This characteristics of fly ash when used in the making of geopolymer concrete will greatly affect the final products obtained. The pH value measured in fly ash, according previous research, can influence the setting time of geopolymer and fly ash with high pH values can cause flash-setting in the concrete. Understanding more clearly about the factors that affect the setting time of fly ash based geopolymer is important for further progress and development of the material. It was found that factors that influence the setting time of geopolymer was not only from the physical and chemical properties of the fly ash itself. Other factors such as composition and mix design, manufacturing process and environmental conditions can also affect its setting time. The experimental results showed that fly ash particle size, CaO and MgO content, in addition to ratio of sodium silicate and sodium hydroxide in the alkali solution, molarity of NaOH, initial temperature of the mixture, curing temperature, and mix volume could potentially influence the setting time of the geopolymer mixture.

52 citations


Journal ArticleDOI
TL;DR: A review on fly ash-based geopolymer concrete can be found in this article, where the authors mainly cover composition, mixing and curing process, benefits, limitations and applications of alkali activated fly ash based concrete.
Abstract: Due to environmental pollution form cement industries, some efforts for alternative construction material are increasing. Recently, geopolymer concrete has drawn attention of researchers and engineers because of its lower carbon print and better mechanical property over Portland cement concrete. According to previous studies, geopolymer concrete results almost up to 90% reduction in carbon dioxide (CO2) emission to atmosphere. Mechanical properties of geopolymer concrete such as compressive strength, durability, sulfate resistance, early strength and low shrinkage are better than Portland cement concrete. In addition, the appropriate usage of one ton of fly ash earns one carbon-credit redemption value of about 20 Euros, and hence earned monetary benefits through carbon-credit trade.Therefore, this paper presents a review on the fly ash-based geopolymer concrete. The paper mainly covers composition, mixing and curing process, benefits, limitations and applications of alkali activated fly ash based geopolymer concrete.

52 citations


Journal ArticleDOI
TL;DR: In this article, the growth of large diameter silicon carbide (SiC) crystals produced by the physical vapor transport (PVT) method is outlined, and methods to increase the crystal diameters, and to turn these large diameter crystals into substrates that are ready for the epitaxial growth of SiC or other non homogeneous epitaxially layers are discussed.
Abstract: The growth of large diameter silicon carbide (SiC) crystals produced by the physical vapor transport (PVT) method is outlined. Methods to increase the crystal diameters, and to turn these large diameter crystals into substrates that are ready for the epitaxial growth of SiC or other non homogeneous epitaxial layers are discussed. We review the present status of 150 mm and 200 mm substrate quality at Cree, Inc. in terms of crystallinity, dislocation density as well as the final substrate surface quality.

50 citations


Journal ArticleDOI
TL;DR: In this paper, an external Schottky barrier diodes (SBD) is used to suppress the conduction of the body diode of an MOSFET, which can reduce the total chip size of high voltage modules.
Abstract: External Schottky barrier diodes (SBD) are generally used to suppress the conduction of the body diode of MOSFET. A large external SBD is required for a high voltage module because of its high specific resistance, while the forward voltage of SBD should be kept smaller than the built-in potential of the body diode. Embedding SBD into MOSFET with short cycle length increases maximum source-drain voltage where body diode remains inactive, resulting in high current density of SBD current. We propose a MOSFET structure where an SBD is embedded into each unit cell and an additional doping is applied, which allows high current density in reverse operation without any activation of body diode. The proposed MOSFET was successfully fabricated and much higher reverse current density was demonstrated compared to the external SBD. We can expect to reduce total chip size of high voltage modules using the proposed MOSFET embedding SBD.

50 citations


Journal ArticleDOI
TL;DR: In this paper, a SiC UMOSFET is developed to cope with the trade-off between low on-resistance and extremely low gate oxide field, which is known as gate oxide protection.
Abstract: A critical issue with the SiC UMOSFET is the need to develop a shielding structure for the gate oxide at the trench bottom without any increase in the JFET resistance. This study describes our new UMOSFET named IE-UMOSFET, which we developed to cope with this trade-off. A simulation showed that a low on-resistance is accompanied by an extremely low gate oxide field even with a negative gate voltage. The low RonA was sustained as Vth increases. The RonA values at V g =25 V (E ox =3.2 MV/cm) and VG=20V (E ox =2.5 MV/cm), respectively, for the 3mm × 3mm device were 2.4 and 2.8 mΩcm2 with a lowest Vth of 2.4 V, and 3.1 and 4.4 mΩcm2 with a high Vth of 5.9 V.

45 citations


Journal ArticleDOI
TL;DR: In this article, the authors examined the possibility of utilizing clay brick waste as partial replacement for Portland cement in concrete and found that a significant improvement of the split tensile and compressive strength was achieved at 10% cement replacement, after which a decrease in strength with increasing ground clay brick content was recorded.
Abstract: With the increasing concerns on the impact of cement production on the environment and the need to protect the environment, the use of mineral additives as cementitious material to partially substitute cement is being considered as an effective option. One of such material is fired clay brick which can be sourced as generated waste from clay brick industry. This has an added advantage of reducing industrial waste and preserving the natural resources. The experimental objective of this study is to examine the possibility of utilizing clay brick waste as partial replacement for Portland cement in concrete. The clay brick was finely ground into powder size, and after grinding, the morphological characterization of the powder materials was carried out using scanning electron microscopy (SEM). Moreover, the chemical composition of the brick material was determined using X-ray fluorescence (XRF). Laboratory tests were carried out to determine the workability, split tensile and compressive strength properties of the concrete with 0%, 10%, 20%, 30% and 40% partial replacement of cement with ground clay brick (CB). From the test results, the chemical composition of the brick powder meets the standard requirements for pozzolanic material, with the SEM revealing an amorphous solid mass. The workability of the concrete reduces with increase in brick powder content. A significant improvement of the split tensile and compressive strength of the concrete was achieved at 10% cement replacement, after which a decrease in strength with increasing ground clay brick content was recorded. The use of ground clay brick of not more than 15% was recommended for concrete production.

42 citations


Journal ArticleDOI
TL;DR: In this article, a Super Junction (SJ) V-groove trench MOSFET was fabricated and demonstrated a low specific on-resistance (R on A) of 0.97 mΩcm2 and a blocking voltage (V b ) of 820 V.
Abstract: We have fabricated Super Junction (SJ) V-groove trench MOSFETs (VMOSFETs), demonstrated a low specific on-resistance (R on A) of 0.97 mΩcm2 and a blocking voltage (V b ) of 820 V. In the first trial, SJ structure in 4H-SiC have proved to be a good combination with MOS interface on (0-33-8) faces which keep high channel mobility in high doping concentration. We designed a protection structure called “upper p-pillar region” and demonstrated that V b lowering appeared according to its width.

41 citations


Journal ArticleDOI
TL;DR: In this paper, a finite element (FE) model of the flash-butt welding of railway rails was developed and implemented with the help of ESI's FE-software SYSWELD.
Abstract: Flash butt welding (FBW) of railway rails was investigated in this work. For this purpose samples of R260 rail steel and 60E1 profile were instrumented and subsequently welded on a Schlatter GAA 100 welding machine under industrial conditions. The intention is to gain in depth process knowledge by more accurately depicting thermal cycles for an entire welding sequence in the immediate proximity of the weld as well as in the heat affected zone (HAZ). A detailed characterization of the single stages of the heat up phase of the process is important. Additionally, the secondary welding voltage was measured simultaneously during the experiments to characterize the transient heat input. Moreover, these data were used in the analysis of the temperature signals to better cope with electrical interferences. Additionally, a finite element (FE) model of this FBW process was developed in the present work. Its implementation and solution is realized with the help of ESI’s FE-software SYSWELD. A strong coupled thermo-electrokinetical and metallurgical calculation routine was used. The model comprises the transition resistance at the welding surfaces as the main heat source to the process. Temperature dependent material properties and a corresponding metallurgical model based on an experimental CCT diagram of the rail steel R350HT are implemented in the simulation as well.

37 citations


Journal ArticleDOI
TL;DR: In this paper, the potential of plastic synthesized using bio-based starch was evaluated using Fourier transform infrared (FTIR), tensile strength tester and Thermogravimetric analysis (TGA).
Abstract: This study was carried out to evaluate the potential of plastic synthesized using bio-based starch. The method began with extraction of starch from chosen tubers with high content of starch; potato and yam. The samples were first grated, grinded and strained to obtain crude starch, which then centrifuged and rinsed to get pure starch. The starch was then reacted with hydrochloric acid to breakdown amylopectin to prevent the starch from becoming plastic-like. Finally, propan-1,2,3-triol was added as a plasticizer to increase the elasticity of the product. The chemical, mechanical, and thermal properties of the products were analyzed using Fourier transform infrared (FTIR), tensile strength tester and Thermogravimetric analysis (TGA). The FTIR spectra of the product displayed the presence of O-H, C-H, C=O and C-O absorption peaks, which indicate the formation of bioplastic has already occured. The tensile strength obtained for potato and yam starch-based bioplastic are 0.6 MPa and 1.9 MPa, respectively. The result gained from TGA showed that 50% weight loss occurred at 250°C for potato and 310°C for yam-based plastic. The highly biodegradability of the plastic was proven using soil burial test, which observed the percentage of soil biodegradation for potato and yam-based bioplastic in 1 week duration is 43% and 26%, respectively. These bio-based plastics have exhibited good thermal and mechanical properties with high biodegradability that makes them a suitable alternative for the existing conventional plastics.

Journal ArticleDOI
TL;DR: In this article, the authors present the findings of a study that aims at assessing the durability and strength properties of sustainable self-consolidating concrete (SCC) mixes in which Portland cement was partially replaced with fly ash.
Abstract: Fly ash is a sustainable partial replacement of Portland cement that offers significant advantages in terms of fresh and hardened properties of concrete. This paper presents the findings of a study that aims at assessing the durability and strength properties of sustainable self-consolidating concrete (SCC) mixes in which Portland cement was partially replaced with 10%, 20%, 30%, and 40% fly ash. The study confirms that replacing Portland cement with fly ash at all of the percentages studied improves resistance of concrete to chloride penetration. The 40% fly ash mix exhibited the highest resistance to chloride penetration compared to the control mix. Despite the relative drop in compressive strength after 7 days of curing, the 28-day compressive strength of 40% SCC mix reached 55.75 MP, which is very close to the control mix. The study also confirms that adding 1%, 1.5%, and 2% basalt fibers, respectively, to the 40% fly ash mix improves the resistance to chloride penetration compared to the mix without basalt fibers.

Journal ArticleDOI
TL;DR: In this article, the effect of borax addition to the high calcium fly ash-based geopolymer mixture to reduce the occurrence of flash setting was investigated, and it was found that the setting time can be extended significantly, with the addition of 5% borsax, by mass, of fly ash.
Abstract: Geopolymer that was made with high CaO content fly ash was found to have higher compressive strength than the low CaO fly ash, using the same mixture composition. This effect could be due to the physico-chemical properties of the fly ash, in respect to its particle size or the chemical composition. Although it was not widely published, the occurrence of flash setting of geopolymer was known to occur when using high CaO content fly ash as the precursor. Geopolymer paste may solidify within minutes after the addition of alkali activators, making it very difficult to cast in big volume. This paper investigate the effect of borax addition to the high calcium fly ash-based geopolymer mixture to reduce the occurrence of flash setting. It was found that the setting time can be extended significantly, with the addition of 5% borax, by mass, of fly ash. The addition of borax also have positive effect on increasing the compressive strength of geopolymer.

Journal ArticleDOI
TL;DR: In this article, specific polymer composites modified for the Fused Deposition Modelling (FDM) which is a 3D print technology are presented. But the main focus of this paper is on the accuracy of the semi-product formed into the filament shape.
Abstract: This article deals with specific polymer composites modified for the Fused Deposition Modelling (FDM) which is a 3D print technology. These two phase systems involve thermoplastic matrix filled with natural fibres. The crucial demand of this progressive technology is put on the accuracy of the semi-product formed into the filament shape. To reach the smooth production of 3D prototypes the filament should have a constant diameter. In the article, individual steps of the polymer composite pelletization and following pre-processing and processing activities are described. Among these steps the extrusion of the filaments belongs and subsequent print test on “RepRap” device accompanied by optimization of building parameters. Tensile specimens were chosen for print with regard to maps mechanical properties of this newly developed material which was the final stage of this work. Tensile test curves were then compared with those graphs which can be found for the material produced by conventional technologies such as injection moulding.

Journal ArticleDOI
TL;DR: In this paper, a method of increasing biological resistance and biological durability of buildings and constructions that are subject to destruction from the impact of microorganisms activity is considered, and the results of studies of innovative materials in the field of bioresistant building materials are presented.
Abstract: In this paper, we consider a method of increasing biological resistance and biological durability of buildings and constructions that are subject to destruction from the impact of microorganisms activity. This article presents the results of studies of innovative materials in the field of bioresistant building materials. Powders of milled quartz sand and limestone were the fillers for the composites. Limestone used for the experiments is from the Chechnya depostits. We have implemented optimization for the cement composites compositions using the methods of mathematical experiment design. We derived the dependences describing how the bioresistance coefficient, the elastic modulus and the water demand depend on the granulometric composition after 3 and 9 months of aging in the environment of filamentous fungi. We have found that the multifractional compositions have a higher bioresistance coefficient. We determined the fungal resist compositions.

Journal ArticleDOI
TL;DR: In this paper, the quantitative composition, the biocidal additive and gypsum content influence on the compressive and flexural strength and density of the composites of innovative materials for construction.
Abstract: The article considers innovative materials for construction. Using mathematical planning methods, we studied how the quantitative composition, the biocidal additive and gypsum content influence on the compressive and flexural strength and density of the composites. We found that the more gypsum in a composition the higher compressive and flexural strength of a specimen. So, with the greatest degree of compositions filling (fly ash – 20 mass fractions, gypsum – 11.2 mass fractions) maximum compressive strength is 72.5 MPa. We determined when the fly ash content rises up to 20 mass fractions per 100 mass fractions of clinker, flexural strength rises too and specimen density decreases. The developed compositions of biocidal cements recommended for use in the manufacture of materials, products and structures for buildings and constructions, operating in aggressive environments.

Journal ArticleDOI
TL;DR: In this paper, the double stop drill hole method can be used to increase the fatigue life of the cracked components and the results show that fatigue life extension caused by double stop hole method is significantly more than the conventional single stop-hole method, while the distance between the hole centers is the main parameter affecting the efficiency of this method.
Abstract: Drilling holes in the vicinity of the crack tip turns the crack into a notch and reduces the crack tip stress intensity factor. In this paper, a new idea is used in which instead of a single hole, two symmetric and interconnected holes are drilled at the crack tip. The main concept of double stop-hole method is to reduce the stress concentration at the edge of stop-holes in the cracked structural elements. The double stop drill hole method can be used to increase the fatigue life of the cracked components. The fatigue crack growth retardation is examined using an experimental investigation coupled with a stress analysis on the efficiency of proposed double stop-holes. The distance between the hole centers is considered as the main parameter affecting the efficiency of this method. The results show that the fatigue life extension caused by the double stop-hole method is significantly more than the conventional single stop-hole method.

Journal ArticleDOI
TL;DR: This paper offers an overview of high performance fabrics in armor systems, which are utilized to cover the living space in military vehicles such as helicopters and armored vehicles.
Abstract: High performance fabrics are preferable for armor systems due to their lightweight structure and flexibility. High performance fabrics are generally used in body armor design for personal protection. However, these fabrics are utilized to cover the living space in military vehicles such as helicopters and armored vehicles. Besides, pilot seats in combat helicopters are included in utilization area of high performance fabrics. On the other hand armor is defined as a defensive covering to protect body or something against attacking threats. Protection is provided by absorbing the kinetic energy of the attacking threats and stopping them before any damage occurs in the target. This paper offers an overview of high performance fabrics in armor systems.

Journal ArticleDOI
TL;DR: In this article, the physicico-mechanical and microstructure properties of geopolymers synthesized from metakaolin activated with sodium silicate solution were investigated using X-Ray diffraction (XRD) and the micro-structure of the paste and the interfacial transition zone (ITZ) between the aggregate and the matrix of a geopolymer were studied by using transmission Electron Microscope (TEM) and scanning Electron microscope (SEM).
Abstract: A research has been conducted to investigate the physico-mechanical and microstructure properties of geopolymers synthesised from metakaolin activated with sodium silicate solution. A wide range of physical and mechanical properties of geopolymers were studied such as bulk density, porosity, Vickers hardness, compressive strength, thermal expansion and thermal conductivity. It was found that these properties were directly related to geopolymers process variables such as Si:Al, Na:Al, Na2O:H2O, time and curing temperature. The structure of the resulting geopolymers was studied by using X-Ray diffraction (XRD) and the microstructure of geopolymers paste and the interfacial transition zone (ITZ) between the aggregate and the matrix of geopolymer were studied by using Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM). The results gave a new insight into the composition-microstructure-property relationship of geopolymers and paving the way to the production of geopolymers with improved performance in a variety of applications.

Journal ArticleDOI
TL;DR: In this article, an experimental study was conducted on the dry drilling of Ti-6Al-4V. The objective of this study was to establish the correlations between drilling parameters such as feed rate and spindle speed, and quality of machined surface which is evaluated in terms of drill hole diameter deviation, exit burr height and surface roughness.
Abstract: In past few decades, a lot of research has been done in the field of machining to improve the quality of machined surface. Out of these machining operations, drilling is widely used in the areas of marine and aerospace for assembly requirements. Titanium alloy Ti-6Al-4V, owing to its vast applications, is regarded as an important material for these industries. Ti-6Al-4V is categorized as difficult to machine material. Based on above stated facts, an experimental study was conducted on the dry drilling of Ti-6Al-4V. The objective of this study was to establish the correlations between drilling parameters such as feed rate and spindle speed, and quality of machined surface which is evaluated in terms of drill hole diameter deviation, exit burr height and surface roughness.

Journal ArticleDOI
TL;DR: In this paper, the authors report TDDB results on SiO2/SiC MOS capacitors fabricated in a matured production environment and demonstrate the absence of early failure out of over 600 capacitors tested.
Abstract: In this paper we report TDDB results on SiO2/SiC MOS capacitors fabricated in a matured production environment. A key feature is the absence of early failure out of over 600 capacitors tested. The observed field accelerations and activation energies are higher than what is reported on SiO2/Si of similar oxide thickness. The great improvement in oxide reliability and the deviation from typical SiO2/SiC observations are explained by the quality of the oxide in this study.

Journal ArticleDOI
TL;DR: In this paper, the role of TiO2 as the photocatalyst for the degradation of organic pollutants was discussed, and the possible approaches to enhance degradation via the nanoparticle along with existing bottlenecks have been also discussed.
Abstract: Heavy industrialization, specifically in the developing countries, has generated several unwanted environmental pollution. A variety of toxic organic compounds is produced in chemical and petroleum industries, which have resulted in collectively hazardous effects on the environment that needs immediate attention for remediation. Degradation of these pollutants has been tried through the various mechanism, out of which photocatalytic degradation seems to be one of the most promising approaches to reduce environmental pollution specifically in waste water treatment. Photocatalytic degradation has potential for the effective decomposition of organic pollutants due to efficiency to convert light energy into chemical energy. Additionally, the photocatalytic oxidation process is an advanced technique as it offers high degradation and effective mineralization at moderate temperature and specific radiation wavelength. Among various known photocatalysts, TiO2 is regarded as the one of the potential photocatalysts because of its hydrophilic property, high reactivity, reduced toxicity, chemical stability and lower costs. Therefore, the present chapter focuses on the role of TiO2 as the photocatalyst for the degradation of organic pollutants. The general mechanism of degradation of organic pollutants along with properties of TiO2 as the photocatalyst, existing mechanism of degradation via TiO2 was explained. The possible approaches to enhance degradation via TiO2 nanoparticle along with existing bottlenecks have been also discussed.

Journal ArticleDOI
TL;DR: In this article, the authors examined the possible reuse of waste glass crushed into fine and coarse aggregate sizes as partial substitute for natural fine aggregate in concrete and found that concrete mix made with 25% waste glass content compared significantly well with the control and can be suitably adopted for production of light weight concrete.
Abstract: Reusing of waste glass in concrete production is among the attractive option of achieving waste reduction and preserving the natural resources from further depletion thereby protecting the environment and achieving sustainability. This present study examines the possible reuse of waste glass crushed into fine and coarse aggregate sizes as partial substitute for natural fine and coarse aggregate in concrete. The variables in this study is both the fine and coarse aggregate while the cement and water-cement ratio were held constant. The crushed glass was varied from 0 – 100% in steps of 25% by weight to replace the both the natural fine and coarse aggregate in the same concrete mix. Concrete mixes were prepared using a mix proportion of 1:2:4 (cement: fine aggregate: coarse aggregate) at water-cement ratio of 0.5 targeting a design strength of 20 MPa. Tests were carried out on total number of 90 concrete cube specimens of size 150 x 150 x150 mm and 90concrete cylinder specimens of dimension 100 mm diameter by 200 mm height after 3, 7, 14, 28, 42 and 90 days of curing. Test results indicated that the compressive and split tensile strength of the hardened concrete decreases with increasing waste glass content compared with the control. However, concrete mix made with 25% waste glass content compared significantly well with the control and can be suitably adopted for production of light weight concrete.

Journal ArticleDOI
TL;DR: In this paper, features of application of the vacuum arc discharge for modification of surfaces are considered and the complexity of this process simulation due to its complexity and tight correlation between different parameters is explained.
Abstract: In this article features of application of the vacuum arc discharge for modification of surfaces are considered. The complication of o this process simulation due to its complexity and tight correlation between different parameters is explained. The mathematical model describing the interaction of a plasma flux with controlling system is offered. The need of cleaning plasma flux from drop fraction in the process of metal coatings deposition is shown. The properties of coatings received by means of a vacuum arc method are considered.

Journal ArticleDOI
TL;DR: In this paper, the effect of NO annealing on hole trapping characteristic of SiC metal-oxide-semiconductor (MOS) capacitors was evaluated by measuring flatband voltage (VFB) shifts during a constant negative gate voltage stress under UV illumination.
Abstract: We evaluated the effect of NO annealing on hole trapping characteristic of SiC metal-oxide-semiconductor (MOS) capacitor by measuring flatband voltage (VFB) shifts during a constant negative gate voltage stress under UV illumination. Under low stress voltages, the VFB shift due to hole trapping was found to be suppressed by NO annealing. However, the VFB shift of the NO-annealed device increases significantly with stress time under high stress voltage conditions, while the device without NO annealing showed only a slight shift. This result implies that NO annealing enhances generation of hole traps, leading to the degradation of SiC-MOS devices in long-term reliability.

Journal ArticleDOI
TL;DR: In this article, the extraction of vanadium and chromium from high chromium content vanadium slag by salt roasting and water leaching process has been investigated, which uses mixed sodium salts (Na2CO3 and NaOH) as additive agent in roasting process.
Abstract: The extraction of vanadium and chromium from high chromium content vanadium slag by salt roasting and water leaching process has been investigated, which uses mixed sodium salts (Na2CO3 and NaOH) as additive agent in roasting process. The mineralogical morphology was prospected by TG-DSC, XRD, SEM and EDS. The oxidation of slag and transversion of V/Cr-containing phase and sodium salts have been discussed. It has been demonstrated that the presence of NaOH contributes to decompose spinel and olivine phases, which is beneficial to reduce the roasting temperature and elevate V, Cr leaching ratio. The roasting parameters have been studied as a function of roasting temperature, roasting time and ratio of alkali, in which the roasting temperature is the most effective factor on the leaching rate of vanadium and chromium. Under the optimum condition, the leaching rates of V and Cr reached 95.8% and 97.6%, respectively.

Journal ArticleDOI
TL;DR: In this paper, Artificial Neural Networks were used to predict the silicon content through parameters of the reduction in blast furnace process, and this was verified by the precision of this model, which showed that theoretical flame temperature, pressure blow and Coke rate have a positive influence on silicon content in hot metal.
Abstract: The growing focus on the efficiency of the reduction process in blast furnace generates an alteration in the way they operate. This modifies the conditions of transfer of silicon for the hot metal and can cause problems in the added value of your product. To evaluate the changes of the operational parameters of the reduction on the conditions of transfer of silicon process a mathematical model based on artificial neural networks has been implemented. Through this model it was possible to predict the silicon content to determine the influence of each operational parameter. Artificial neural networks were able to predict the silicon content through parameters of the reduction in blast furnace process, and this was verified by the precision of this model. The ANN showed that Theoretical flame temperature, Pressure blow and Coke rate have a positive influence on the silicon content in hot metal, and the Hot metal rate is inversely proportional to the silicon content of the hot metal.

Journal ArticleDOI
TL;DR: In this article, the effect of loss of ignition, specific gravity, fineness, specific surface area and soluble fly ash to compressive strength of geopolymer paste was studied.
Abstract: The effect of loss of ignition, specific gravity, fineness, specific surface area and soluble fly ash to compressive strength of geopolymer paste were studied. Six fly ashes from two different sources and different time of collection were evaluated. Sodium hydroxide and sodium silicate were used as alkali activator. Concentration of sodium hydroxide and mass ratio of sodium hydroxide to sodium silicate were fixed 14M and one respectively. The result indicated that the improvement in compressive strength of geopolymer paste was more influenced by fineness, specific surface area and soluble content of fly ash. Soluble content of fly ash greatly affected the compressive strength of geopolymer paste compare to the compressive strength of cement paste with 20% fly ash replacement.

Journal ArticleDOI
TL;DR: In this paper, the performance of nanosilica and multi walled carbon nanotubes (MWCNT) as fluid loss additives in water-based drilling fluid with various nanoparticles concentration and temperature was evaluated.
Abstract: Nanoparticles are used to study the rheological characteristics of drilling fluids. Nanoparticles have high surface to volume ratio, therefore only small quantity is required to blend in the drilling fluid. This research evaluates the performance of nanosilica and multi walled carbon nanotubes (MWCNT) as fluid loss additives in water based drilling fluid with various nanoparticles concentration and temperature. The results show that plastic viscosity, yield point and gel strength of drilling fluid increases as the concentration of nanoparticles increased. Drilling fluid with nanosilica gives the highest filtrate loss of 12 ml and mudcake thickness of 10 inch at 1 g concentration at 300°F. However, drilling fluid with MWCNT shows a decreasing trend in fluid loss and mudcake thickness. The results also show that xanthan gum containing 1 g of MWCNT gives 4.9 ml fluid loss and mudcake thickness of 4 inch at 200°F. After aging, plastic viscosity, yield point and gel strength of mud containing nanoparticles decrease significantly especially for 1 g of nanosilica and 0.01 g MWCNT. Fluid loss and mudcake thickness increased when the mud is exposed to temperature above 250°F. The results showed that xanthan gum with MWCNT gives a better rheological performance.

Journal ArticleDOI
TL;DR: In this article, the threshold voltage instability of commercially available silicon carbide (SiC) power MOSFETs or prototypes from four different manufacturers under positive bias temperature stress (PBTS) was studied.
Abstract: We study the threshold voltage (Vth) instability of commercially available silicon carbide (SiC) power MOSFETs or prototypes from four different manufacturers under positive bias temperature stress (PBTS). A positive bias near the Vth causes a threshold voltage shift of 0.7 mV per decade in time per nanometer oxide thickness in the temperature range between-50 °C and 150 °C. Recovery at +5 V after a 100 s +25 V gate-pulse causes a recovery between-1.5 mV/dec/nm and-1.0 mV/dec/nm at room temperature and is decreasing with temperature. All devices show similar stress, recovery and temperature dependent behavior indicating that the observed Vth instabilities are likely a fundamental physical property of the SiC-SiO2 system caused by electron trapping in near interface traps. It is important to note that the trapping is not causing permanent damage to the interface like H-bond-breakage in silicon based devices and is nearly fully reversible via a negative gate bias.