Silicon Precipitation Research Articles

Effect of Modification of Rare Earth Elements on the Morphology of Silicon Precipitates in the ZnAl22Cu3Si Alloy

Properties of the Zn-Al-Cu alloys can be improved by partial or total replacement of the copper with silicon. The previous studies of the current authors have shown that in alloys with silicon addition its precipitates are not evenly distributed, which can lead to uneven wear of parts made of the Zn-Al-Cu alloy. The study of phenomena occurring during the crystallization of the ZnAl22Cu3Si alloy with ATD methods have shown that silicon does not form compounds and solid solutions with Zn and Al. In the examined alloy silicon is released as the primary even before the actual solidification of dendrites. It is not possible to reduce the irregular distribution of precipitates through heat treatment. Therefore it is important to assure the uniform distribution of precipitates of silicon already on the crystallization stage, e.g. by addition of rare earth elements. The purpose of this study was to determine the effect of rare earth elements on the morphology of silicon precipitates in the ZnAl22Cu3Si alloy. The investigated material were alloys containing 22 wt% Al, 3 wt % Cu and 1.5 wt% Si (Zn-remaining). The samples have been taken from the top, middle and bottom of the ingot. In order to determine the morphological characteristics of silicon precipitates a computer program: Met-Ilo developed in the Department of Materials Science, Silesian University of Technology was used. Changes of the area fraction and shape of precipitates in particular areas of the ingot were the subject of analysis in this work.

Effect of Modification of Rare Earth Elements on the Morphology of Silicon Precipitates in the ZnAl40Cu3Si Alloy

Properties of the alloys Zn-Al-Cu can be improved by partial or total replacement of copper with silicon. The previous studies of the current authors have shown that in alloys with silicon addition its precipitates are not evenly distributed. This can lead to uneven wear of parts made of the Zn-Al-Cu alloy. The study of phenomena occurring during the crystallization of the ZnAl40Cu3Si alloy with ATD methods have shown that silicon does not form compounds and solid solutions with Zn and Al. In the examined alloy silicon is released as the primary even before the actual solidification of dendrites. It is not possible to reduce the uneven distribution of precipitates through heat treatment. Therefore it is important to assure the uniform distribution of precipitates of silicon already on the crystallization stage, e.g. by addition of rare earth elements. The purpose of this study was to determine the effect of rare earth elements on the morphology of silicon precipitates in the ZnAl40Cu3Si alloy. The investigated material were alloys containing 40 wt% Al, 3 wt% Cu and 1.5 wt% Si (Zn - remaining). The samples have been taken from the top, middle and bottom of the ingot. In order to determine the morphological characteristics of silicon precipitates a computer program Met-Ilo developed in the Department of Materials Science, Silesian University of Technology was used. Changes of the volume fraction and shape of precipitates in particular areas of the ingot were the subject of analysis in this work.

Growth mechanism of primary silicon in cast hypoeutectic Al-Si alloys

The microstructural features of hypoeutectic Al-10%Si alloy were observed using optical microscopy and electron backscatter diffraction. The results show that primary silicon particles are frequently found in hypoeutectic alloys. Hence, the nucleation and growth mechanisms of the precipitation of primary silicon of hypoeutectic Al-10%Si alloy melts were investigated. It was discovered that Si atoms are easy to segregate and form Si-Si clusters, which results in the formation of primary silicon even in eutectic or hypoeutectic Al-Si alloys. In addition, solute redistribution caused by chemical driving force and large pile-ups or micro-segregation of the solute play an important role in the formation of the primary silicon, and the solute redistribution equations were derived from Jackson-Chalmers equations. Once Si solute concentration exceeds eutectic composition, primary silicon precipitates are formed at the front of solid/liquid interface.

Evaluation of the facilitated transport capabilities of nano- and micro-sized molecularly imprinted polymers (MIPs) in a bulk liquid membrane system

In this work, three types of molecularly imprinted polymers (MIP) containing atenolol selective sites were prepared by the methods of bulk polymerization, precipitation polymerization and suspension polymerization in silicon oil. Then, the MIP particles were used as the carrier elements in a bulk liquid membrane (BLM). Atenolol transport capabilities of different MIPs were compared with those of their relevant non imprinted polymers (NIP). It was shown that both nano- and micro-sized MIPs, obtained from suspension polymerization in silicon oil and precipitation polymerization, respectively, could transport atenolol more effective than the relevant NIPs. However, the nano-sized MIP was better than the micro-sized MIP for transportation of atenolol. Furthermore, the bulky MIP was not proper atenolol carrier in the BLM, since its transportation characteristic was similar to that of its relevant NIP. Moreover, the selectivity of the BLM containing different kinds of the MIPs obeyed the order of nano-MIP>micro-MIP>bulky MIP. The nano-MIP was adopted as the best atenolol carrier among the tested MIP-based carriers and then the effect of different factors on its transportation efficiency was evaluated. A kinetic model was proposed for the transportation of atenolol through the nano-MIP based BLM. It was found that the extraction of atenolol from the source to the membrane control the separation rate.

Precipitation in long term thermally aged high copper, high nickel model RPV steel welds

Copper precipitation in irradiated RPV steels is well known to have a deleterious effect on mechanical properties. In order to understand the contribution of thermal ageing to RPV embrittlement a high copper (0.44 at.%), high nickel (1.6 at.%) model RPV weld was thermally aged at 365 °C for times up to 90,000 h. Atom Probe Tomography (APT) was employed to study the precipitation of solutes, primarily copper, nickel, manganese and silicon within the matrix and at grain boundaries. As expected, a high number density of 1–4 nm radius copper rich precipitates was observed. Nickel, manganese and silicon were found at the precipitate matrix interface, and the evolution of the composition of this interface was investigated with ageing time. Segregation of solutes to grain boundaries particularly P, Mo and C was observed, along with enrichments of Ni, Mn and Si, which have not previously been reported in long term thermally aged RPV steels. Preliminary results on several large (>10 nm) Ni–Mn–Si rich features observed at a grain boundary are also presented. These features are rich in Ni (∼30%), Mn (∼15%) and Si (∼12%) and are virtually copper-free.

Precipitation of Si and its Influence on Mechanical Properties of Type 441 Stainless Steel

In this study the precipitation of silicon in Type 441 steel (18%Cr-0.4%Nb-0.5%Si) was investigated and its influence on strength properties were determined. To simulate high-temperature service conditions, heat treatments with various ageing times up to 120 hours and temperatures up to 800 °C were performed. Following the aging treatments, micro-and macro-hardness and tensile properties were measured. Microstructure and precipitation were analyzed using scanning electron microscopy and energy-dispersive spectroscopy. Predictions for equilibrium pericipitation were calculated using the Factsage software. According to observations, coarse titanium nitrides (TiN) and niobium carbides (NbC, Fe3Nb3C) were present in all specimens including non-aged ones. These precipitates did not coarsen during ageing, which implies that their growth already occurred in the sheet production process. However, silicon started to precipitate in the course of prolonged annealing. Si contributed to the formation of a secondary phase resembling the Laves-phase (FeNbSi) on grain boundaries. Hardness and yield strength were found to decrease with prolonged ageing at high temperatures. Factors affecting the silicon precipitation are discussed.

Silicon Precipitation via Photoinduced Reaction Using Femtosecond Laser

Silicon precipitation inside a glass is an important technique for silicon photonics. We successfully precipitated silicon inside silicate glasses containing an Al metal film using femtosecond laser irradiation. First, the Al-inserted sandwiched glass was fabricated by the direct bonding method. The results of a tensile test indicated that the adhesive strength of the sandwich structure reached approximately 4 MPa. Next, femtosecond laser pulses were focused at the Al/glass interface in the sandwich structure. A transmission electron microscopy photograph at the focus of the laser showed that the Al particles were dispersed into the glass substrate to a depth of approximately 2 microm from the initial Al layer. In addition, Raman spectra indicated that silicon had formed at the interface between the glass and Al film after the laser irradiation. The morphology or the particle size of the precipitated silicon was successfully modified by changing the repetition rate or the pulse energy of the laser.

Combinedab initioand classical potential simulation study on silicon carbide precipitation in silicon

Atomistic simulations on the silicon carbide precipitation in bulk silicon employing both, classical potential and first-principles methods are presented. The calculations aim at a comprehensive, microscopic understanding of the precipitation mechanism in the context of controversial discussions in the literature. For the quantum-mechanical treatment, basic processes assumed in the precipitation process are calculated in feasible systems of small size. The migration mechanism of a carbon $\ensuremath{\langle}1\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}0\ensuremath{\rangle}$ interstitial and silicon $\ensuremath{\langle}11\phantom{\rule{0.16em}{0ex}}0\ensuremath{\rangle}$ self-interstitial in otherwise defect-free silicon are investigated using density functional theory calculations. The influence of a nearby vacancy, another carbon interstitial and a substitutional defect as well as a silicon self-interstitial has been investigated systematically. Interactions of various combinations of defects have been characterized including a couple of selected migration pathways within these configurations. Most of the investigated pairs of defects tend to agglomerate allowing for a reduction in strain. The formation of structures involving strong carbon--carbon bonds turns out to be very unlikely. In contrast, substitutional carbon occurs in all probability. A long range capture radius has been observed for pairs of interstitial carbon as well as interstitial carbon and vacancies. A rather small capture radius is predicted for substitutional carbon and silicon self-interstitials. Initial assumptions regarding the precipitation mechanism of silicon carbide in bulk silicon are established and conformability to experimental findings is discussed. Furthermore, results of the accurate first-principles calculations on defects and carbon diffusion in silicon are compared to results of classical potential simulations revealing significant limitations of the latter method. An approach to work around this problem is proposed. Finally, results of the classical potential molecular dynamics simulations of large systems are examined, which reinforce previous assumptions and give further insight into basic processes involved in the silicon carbide transition.

Silicon Precipitation in Glass via Photoinduced Reaction Using Femtosecond Laser

We have succeeded in precipitation of silicon nanoparticles inside silicate glass containing Al metal film using femtosecond laser irradiation. The Al-inserted sandwiched glass was fabricated by direct bonding. Raman spectra indicated that silicon particles were formed at the interface between the glass and the Al film after the fs laser irradiation. In addition, the crystallinity of silicon particles was dramatically changed by changing the laser irradiation conditions; amorphous and crystalline silicon were formed by 1 kHz and 250 kHz fs laser irradiation, respectively. The deposited silicon was detected at an area 1 μm away from the focal point perpendicular to the direction of incident laser beam.

Formation of Silicon and Silicon-Based Semiconductor Materials via Photoinduced Reaction Using Femtosecond Laser

ABSTRACTWe have succeeded in silicon (Si) precipitation inside a glass/aluminum (Al) sandwich structure via photoinduced reaction using femtosecond (fs) laser irradiation. The sandwich structure was fabricated by direct bonding below 573 K. Raman spectra at the photomodified area indicated that Si crystals formed at the interface between the glass and metallic Al after the laser irradiation. In addition, the particle size of the precipitated Si could be changed by changing the pulse energy of the laser. Furthermore, we have also focused the laser pulses on Fe-Si film to trigger crystallization and phase transformation of FexSiy at the interface between Fe/Si multilayer and glass.

Tensile properties of AA6061 in different designated precipitation hardening and cold working

In most application of aluminum–magnesium–silicon alloys, both work hardening and precipitation strengthening are important contributors of strength. When these two mechanisms are combined, the additional strengthening mechanism takes place. In this study different designated precipitation hardening and cold working were employed. The 6061 aluminum alloy sheets were subjected to various amounts of reduction in area once or twice. In addition, different precipitation hardening cycles conducted after first and/or second cold rolling. Then tensile properties were evaluated in rolling direction. The results indicated that improvement in mechanical properties and negative or positive effect of pre-aging mainly depend on the amount of cold work. The changes in mechanical properties will be discussed by explanation of microstructural evolution due to precipitation hardening, strain hardening and work softening competition.

Chemical characterization of SiC and Si3N4 precipitates in multicrystalline silicon by NIR microscopy and ToF‐SIMS

AbstractDuring the crystallization process of multicrystalline silicon precipitates may be formed, which can cause electrical and mechanical problems in the later manufacturing process of solar cells. Typical precipitates in multicrystalline silicon (mc‐Si) ingots are SiC and Si3N4, the exact chemical composition is not known until now, especially regarding dopants. After localization with near infrared (NIR) microscopy, we used Time‐of‐Flight Secondary Ion Mass Spectrometry (ToF‐SIMS) for chemical investigations. Reproducible fingerprints of the elemental composition for several SiC and Si3N4 precipitates were determined and it is shown that characteristic polyatomic fragments can be assigned to each type of precipitate. Doping elements in the different precipitates explain the origin of the electrical conductivity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

X‐ray in situ observation of oxygen precipitation in silicon confirmed with ex situ detection methods

AbstractA focusing Laue diffractometer is used to analyze the strain field in silicon. The source for this so called strain field diffraction (SFD) setup is a high energy X‐ray tube. In the present work this setup is used to monitor the strain generated by growing oxygen precipitates (Bulk Micro Defects, BMDs) in situ at temperatures up to 1000 °C. By choosing appropriate thermal treatments a correlation of the SFD signal with BMD parameters gained with conventional analytic techniques (FT‐IR, infra red light scattering, TEM) is established. From this, the detection limit of the SFD setup for BMDs is determined at a diameter of 7 nm and a density of 1013 cm−3. This range is only covered by TEM so far. Further, the diffracted intensity provides a measure for the level of precipitation occurred.

Copper Precipitates in Multicrystalline Silicon for Solar Cells

In this paper, we have investigated the behaviors of Cu precipitation in multi-crystalline silicon by intentionally contaminating. It is found that, the Cu impurities are easily gettered at the structural defects, i.e. grain-boundaries and dislocations. However, in the defect-free region, the Cu impurities tend to form different kinds of precipitates, strongly dependent on the contamination level. The dot-like precipitates are often formed in the samples with low temperature contamination, and the star-like ones in the samples with high temperature contamination. The microwave photoconductivity decay measurements indicate that the Cu precipitates have strong recombination activity, significantly reducing the minority carrier lifetime.

Silicon crystal morphologies during solidification refining from Al–Si melts

To obtain a sound basis for further development of a refining process in which Si is precipitated from aluminium melts, a series of experiments have been performed in a Bridgman furnace. Compositions studied are in the range of 17–38% Si, and experiments have been carried out with the hot zone up and with the hot zone down to study the effects of flotation and sedimentation as well as those of different convection conditions on silicon precipitation. The similarity in density between liquid aluminium and silicon crystals implies that the melt convection is important for the possible separation of the crystals in a gravity field, but the crystal morphologies also have to be controlled to avoid aluminum inclusions.At lower silicon contents the silicon morphologies have a fish-bone or star-like shape but as the Si content increases the morphology changes to a plate-like structure, which becomes coarser with increasing Si concentration. The growth pattern for coarse plates growing as (111) platelets tend to form pockets of aluminium, which will end up as inclusions during dissolution of the matrix.

Kinetics of high-temperature precipitation in dislocation-free silicon single crystals

The defect structure of dislocation-free silicon single crystals has been calculated using the approximate solution of the Fokker-Planck partial differential equations. It has been demonstrated that the precipitation starts to occur near the crystallization front due to the disappearance of excess intrinsic point defects on sinks whose role is played by oxygen and carbon impurities.

Dilatometer Study of Aluminium-Silicon Based Alloys with Metastabile Structures

Aluminum-Silicon alloys are sought in a large number of automotive and aerospace applications due to their low coefficient of thermal expansion and high wear resistance. The fine structure of Si precipitates is controlled by forced solid solution structure obtainable by rapidly solidification techniques [1, 2, 3]. Present study focuses on precipitation of silicon in Al88Si12 as a function of temperature by dilatometer analysis. Different structures out of equilibrium have been obtained after casting in sand, black-lead and steel mould and by melt spinning. The average value of the activation energy for the precipitation of Si in steel mould casting of eutectic composition was found to be 47 kJ/mol. Our dilatometer studies were complemented by metallographic microscopy and XRD measurements.

Effect of vacancies on oxygen precipitation in germanium-doped Czochralski silicon

The effect of vacancies introduced by rapid thermal annealing (RTA) on the oxygen precipitation in germanium-doped Czochralski (GCZ) silicon has been investigated. GCZ silicon is annealed at 650–1050 °C to facilitate the precipitation of oxygen. It is observed that the oxygen precipitation in silicon is enhanced by both the vacancies introduced during RTA pretreatment and the doping of germanium. Especially, we find that the enhancement effect of vacancies on the precipitation of oxygen is larger than that of germanium atoms. In contrast to non-RTA pretreatments, RTA pretreatments lead to less significant oxygen precipitation in GCZ silicon than in conventional Czochralski (CZ) silicon at temperatures ranging from 850 to 950 °C. The mechanism for the interaction between vacancies and germanium atoms in CZ silicon is elucidated.

PHYSICOCHEMICAL TRANSFORMATIONS OF ALUMINUM AND QUARTZ POWDERS MIXTURE UNDER LOADING BY SPHERICAL CONVERGING SHOCK WAVES

The phase composition and structure of a mixture of aluminum and quartz powders taken in a ratio of 1:1 have been studied after loading by spherical converging shock waves. A number of concentric layers (zones) have been observed in the sample after shock-wave loading. The presence of several zones in the sample reflects the specific features of the processes occurring in different pressure ranges. It has been established that pressures below ~45 GPa cause only additional compacting of the material and deformation of aluminum and quartz. In this case, the quartz grain size substantially decreases up to the transition into the X-ray amorphous state. The attainment of a pressure of ~45 GPa initiates the solid-state reaction of SiO 2 decomposition, which leads to the precipitation of pure silicon and the evolution of oxygen. The beginning of the silicon precipitation and the chemical reaction of Al 2 O 3 formation are separated over the pressure scale. The critical pressure, which is necessary for the solid-state chemical reaction of the Al 2 O 3 formation, is about 50 GPa.

Photoluminescence Analysis of Iron Contamination Effect in Multicrystalline Silicon Wafers for Solar Cells

We investigated the effect of Fe contamination on the electronic properties of dislocation clusters in relation to oxygen precipitation in multicrystalline silicon (mc-Si). Photoluminescence (PL) spectroscopy and mapping were performed at room and liquid-He temperatures on mc-Si wafers before and after Fe contamination. PL spectra consisted of the band-edge emission, the 0.78-eV emission associated with oxygen precipitates, and the dislocation-related D-lines. The Fe contamination increased the electrically active dislocation clusters. Part of these clusters acted as preferential oxygen precipitation sites, and their electronic properties were not further influenced by the Fe contamination.