Crucible Research Articles

Research on the Mechanism Model of Carbon Composite Material Damaged by Erosion in the Thermal Field of Single Crystal Silicon Furnace

Aiming at the problem of the short service life of the carbon/carbon pot wall caused by continuous silicification during the pulling process of single crystal silicon, the paper analyzes the failure mode of the carbon/carbon pot wall and analyzes the influence of the pot wall in the single crystal silicon furnace thermal field. The mechanism of erosion damage. It is concluded from the use situation that the carbon/carbon composite crucible can be used in the field of Czochralski single crystal silicon, and its performance is far better than that of the graphite crucible, and the destruction mechanism of the carbon/carbon composite crucible is analyzed, and solutions are proposed. Through the analysis of the entire industry, carbon/carbon composite crucibles will replace graphite crucibles and become the preferred material for the thermal field of Czochralski silicon single crystals in the future.

Исследование процесса прессования и спекания шихты свинцово-сурьмянистого сплава ССу-3, полученной электроэрозионным диспергированием

The purpose of this study is to manufacture blanks from the charge obtained by the method of electroerosion dispersion, lead-antimony alloy - SSu3, under certain pressing and sintering parameters, to determine the effect of pressure on the density of the final blanks, as well as to find shrinkage dependencies during the sintering operation. Methods. To perform this study, a charge of lead-antimony alloy - SSu3, obtained by the method of electroerosive dispersion, was required. The pressing process was carried out in a mold specially designed for this study on a NORDBERG N3612 hydraulic floor press in two modes under load - 2.5 and 5 t. respectively, the holding time under pressure in both cases was 10 minutes. Sintering was carried out in a graphite crucible, which was placed in an oven for heating the molds EKPS - 10, where a constant temperature of 296 degrees is maintained for 120 minutes. Results. Experimentally, it was found that when the force is doubled, the density of the workpiece increases by 2%, which is due to a closer interaction between metal particles. It is noted that in order to create products with greater porosity, it is necessary to reduce the pressure during pressing, and to create products with greater hardness, more pressure is needed. The difference in the color of the workpieces is due to the degree of oxidation of the charge with oxygen during the cooling of the briquettes after pressing, the compounds of the alloy elements change during its oxidation with oxygen, oxides and lead peroxides are formed, which in turn affect the chemical properties of the alloy. Gray color has a low content of oxygen oxides, and brown, up to orange, is characterized by a high content of lead peroxides. Conclusion. The obtained results can be used for further study and improvement of the composition and structure of the alloy, as well as for the selection of optimal modes of pressing and sintering in further studies.

Nitrogen diffusion in silicate melts under reducing conditions

Abstract The behavior of nitrogen during magmatic degassing and the potential kinetic fractionation between N and other volatile species (H, C, O, noble gases) are poorly known due to the paucity of N diffusion data in silicate melts. To better constrain N mobility during magmatic processes, we investigated N diffusion in silicate melts under reducing conditions. We developed uniaxial diffusion experiments at 1 atm, 1425 °C, and under nominally anhydrous reducing conditions (fO2 ≤ IW-5.1, where IW is oxygen fugacity, fO2, reported in log units relative to the iron-wüstite buffer), in which N was chemically dissolved in silicate melts as nitride (N3–). Although several experimental designs were tested (platinum, amorphous graphite, and compacted graphite crucibles), only N diffusion experiments at IW-8 in compacted graphite crucibles for simplified basaltic andesite melts were successful. Measured N diffusivity (DN) is on the order of 5.3 ± 1.5 × 10−12 m2 s−1, two orders of magnitude lower than N chemical diffusion in soda-lime silicate melts (Frischat et al. 1978). This difference suggests that nitride diffusivity increases with an increasing degree of melt depolymerization. The dependence of N 3– diffusion on melt composition is greater than that of Ar. Furthermore, N3– diffusion in basalticandesitic melts is significantly slower than that of Ar in similarly polymerized andesitic-tholeiitic melts at magmatic temperatures (1400–1450 °C; Nowak et al. 2004). This implies that N/Ar ratios can be fractionated during reducing magmatic processes, such as during early Earth's magma ocean stages.

Distribution and behaviour of 233Pa in 2LiF-BeF2 molten salt.

Distribution and behavior of 233Pa, essential in the thorium–uranium nuclear fuel cycle, were studied in 2LiF–BeF2 (66 : 34 mole%, FLiBe) molten salt by γ-ray spectrometry. The experiments showed that 233Pa deposited slightly on the surface of graphite crucible. The addition of Hastelloy and metallic lithium decreased the 233Pa specific activity in the salt by 1 to 2 orders of magnitude rapidly. Analysis indicated that reductive deposition of 233Pa was responsible for the rapid decrease of 233Pa specific activity in the salt. Additional experiments strongly supported the mechanism of reductive deposition of 233Pa induced by Hastelloy and metallic lithium. In view of the large deposition of 233Pa on Hastelloy, the possible influence of fissile nuclide 233U produced from 233Pa decay on the operation of thorium-based molten salt reactor was discussed.

Utilization of waste graphite crucible for the fabrication of ex-situ AA1100/Graphite composite via stir casting route

This study presents the fabrication of aluminium alloy based ex-situ composite, where waste graphite crucible in the form of powder has been utilized as a reinforcement. X-ray diffractometer (XRD) has been employed for phase analysis and confirmed the presence of the carbon phase in the composite. Optical microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) have been employed for microstructural analysis and confirmation of Gr particles. OM reveals the existence of second phase graphite (Gr) particles which attribute the grain refinement of the matrix. SEM and EDX confirm the presence and distribution of Graphite particles. To illustrate the effect of graphite content on mechanical properties of composite, tensile strength, hardness, and percentage elongation have been evaluated. Three compositions with 0, 3, and 6 wt% (wt %) of graphite were prepared. Analysis of mechanical characteristics reveals that as Gr content increases till 3 wt% leads to improvement in the tensile strength as well as in hardness of composites but further enhancement in Gr content till 6 wt% shows a decrease in the tensile strength, while a very minor change in hardness of the composite.

Technical note: Effects of filter bags on neutral detergent fiber recovery and fiber digestion in vitro

Filter bags facilitate the measurement of amylase-treated neutral detergent fiber (aNDF) and in vitro (IV) undigested aNDF (uNDF) by eliminating the transfer of residues from beakers into filtration crucibles. The objectives of this study were to (1) determine effects of filter bags on recovery of aNDF and (2) evaluate effects of filter bags on IV uNDF. For study 1, 6 samples each of grass hay (GR), alfalfa (AL), and corn silage (CS) were selected. Large standard deviations (SD) of ash-free aNDF (aNDFom) for samples in each forage type indicated compositional diversity (15.1, 7.45, and 12.9% of DM for GR, AL, and CS, respectively), and starch SD for CS was 16.4% of DM. Samples were weighed into Berzelius beakers or filter bags [25-µm pores (F57) or 6-µm pores (F58); Ankom Technology, Macedon, NY] for measurement of aNDF and aNDFom. All samples were extracted with neutral detergent, thermostable α-amylase, and sodium sulfite, and then soaked in boiling water and then acetone. Residues from beakers were filtered through a sea sand-covered GF/D filter (Whatman, Marlborough, MA) in Gooch crucibles (CR). Filter bags were extracted in a pressurized chamber at 100°C. The aNDF values did not differ between F57 and CR, but F58 was greater than CR for CS and AL. For GR, F58 was greater than CR for aNDFom. For study 2, diverse samples with large SD of aNDFom (20.7, 7.45, and 12.9% of DM for GR, AL, and CS, respectively) were weighed as loose powder into medium bottles (LS) or F57 bags, which were weighted to prevent floating. Blended ruminal fluid from 3 steers fed a 30% aNDFom diet was used as inoculum. Three samples of 1 forage type were randomly assigned to 1 of 6 IV runs using both treatments (LS and F57), and 3 bottles of each sample-treatment combination were removed after 12 h and 2 were removed after 120 h to measure uNDF. For LS, residues were extracted as in study 1 for CR. For F57, bags were rinsed in cold water and extracted as described in study 1. After 12 h, uNDF of F57 was greater than LS in CS, AL, and overall types. Ash-free uNDF (uNDFom) after 12 h of F57 was greater than LS in CS and overall types. After 120 h, F57 was greater than LS for uNDF of CS, but no differences were detected for uNDFom. The SD of uNDFom, but not uNDF, was higher after 12 and 120 h for F57 compared with LS. From 6 to 96 h, overall gas production of F57 was less than LS, and F57 was less than LS for CS from 3 to 96 h. Overall, LS gave greater maximum and faster rates of gas production than F57, as did AL and CS, but lag did not vary. Results indicate that filter bags affected aNDF and aNDFom measurement and inhibited fermentation for some materials.

Investigation of the smelting reduction mechanism and of iron extraction from high-iron red mud

High-iron red mud presents a problem due to its alkalinity which leads to significant risks to the environment. In order to realize the harmless and large-scale utilization of high-iron red mud, the smelting reduction experiments were carried out to investigate the reaction mechanism for extraction iron from high-iron red mud. FactSage 6.4 software was used to conduct thermodynamic analysis of the carbon thermal reduction system. The results showed that the direct reduction with carbon involved a process of Fe2O3 → Fe3O4 → FeO → Fe, in which the theoretical required molar ratio of C/O (oxygen in Fe2O3) was 1:1. The maximum degree of iron extraction was 92.8% with anthracite as reductant and 88.8% without anthracite smelting at 1500 °C for 30 min in a graphite crucible. XRD was conducted to analyze the mineral phase of the samples and slags. The results showed that the minerals contained in high-iron red mud were hematite, quartz, rutile, and sodium aluminosilicate hydrate. The blank sample was consisted of hematite, nepheline quartz, and the reduced slag without quenching consisted of perovskite and gehlenite, indicating that the reaction processes occurred from sodium aluminosilicate hydrate to nepheline and then occurred from nepheline to gehlenite in slagging process. The overall smelting reduction process was described as three mass transfer steps and three chemical reaction steps. These results provide useful information for large-scale and harmless utilization of high-iron red mud.

A System Design for Large Scale Production of Elemental Boron by Electrochemical Deposition

In this study, a new electrolysis melt reactor for large-scale and low-temperature production amorphous elemental boron powders (ABP) equipped with a rotating star cathode electrode in a graphite crucible, which decreases the homogenization time of the boron salts is reported. The electrochemical deposition system has designed to produce high-purity ABP up to 25 kg capacity for a different combination of various salts in different percentage ranges in accordance with commercial production. One of the innovations of the system, the star type iron cathode is rotated bidirectionally and positioned up and down when desired, thanks to the movement transmission shaft. After the design of the melted reactor, ABP has produced using certain proportions of KCl, KBF4, and B2O3 salts. As a result, the melting time of KCl, KBF4, and B2O3 mixed salts was 3.7 h, and the production took place at a low temperature of 480 degrees. The highest cathode current density in production was measured as 1.083 A cm−2. The analyses revealed that an amorphous structured high purity (95.6%) elemental boron (B) particles were produced. The morphology and chemical composition of the highest purity B has characterized using XRD, SEM, EDS, and FTIR analysis.

Electrochemical Formation of RE–Ni Alloys (RE=Nd, Dy) in Molten CaCl2–RECl3

１． Introduction Rare earth elements (REs) were used in many industrial materials in the past few decades. Especially, the demand for Nd–Fe–B magnets has rapidly increased due to the popularization of electric vehicles (EVs) and hybrid electric vehicles (HEVs) in recent years. Since the magnets in motors need to work under high temperature environment, the addition of Dy to magnets is necessary to maintain their strong magnetic properties. However, the supply risk of Dy is high due to its insufficient reserves and uneven distribution. Based on this background, an efficient recycling process of Dy from Nd magnet scraps is a social demand.We proposed a separation / recovery method using the differences of the formation potential and formation rate of RE–Ni (RE=Nd, Dy) alloys [1]. In our previous reports, we have already studied on the formation of RE–Ni alloys and separation ratio of Dy/Nd in molten LiCl–KCl at 723 K [2], NaCl–KCl at 973 K [3] and LiF–CaF2 at 1123 K [4]. Although the higher separation ratio was achieved in the chloride systems at 723–923 K, alloy formation rate was higher in the fluoride system at 1123 K.In the present study, we focused on a low vapor pressure chloride salt CaCl2, to achieve both high separation ratio of Dy/Nd and high alloy formation rate. Electrochemical formation of RE–Ni alloys was investigated in CaCl2–RECl3 at 1123 K. ２． Experimental The experiments were conducted in a dry Ar atmosphere at 1123 K. Reagent-grade CaCl2 with 1 mol% NdCl3 or DyCl3 was loaded in a graphite crucible. The crucible was placed at the bottom of a stainless-steel vessel in an air-tight Kanthal container and dried under vacuum at 773 K for 24 h. Mo and Ni wires were used as the working electrodes. A carbon rod and a Ni2+/Ni electrode were used as the counter and reference electrodes, respectively. The potential was calibrated by the deposition potential of Ca metal on a Mo wire. Electrochemical formation behaviors of RE–Ni alloys were investigated by cyclic voltammetry. Samples prepared by potentiostatic electrolysis were analyzed by XRD and SEM/EDX. ３． Result and discussion Fig. 1 shows cyclic voltammograms at a Ni electrode measured before and after the addition of 1.0 mol% RECl3. The cathodic currents increase from around 1.0 V (vs. Ca2+/Ca) in both the NdCl3-added system and the DyCl3-added system, suggesting the formation of RE–Ni alloys. For the NdCl3 system, the cathodic current largely increases from 0.48 V, which is likely attributed to the formation of Nd–Ni intermetallic compound with a high Nd concentration. Several anodic current peaks probably correspond to the dissolutions of Nd from different Nd–Ni alloy phases. For the DyCl3 system, a steep increase of cathodic current is observed from 0.51 V, indicating the formation of Dy–Ni intermetallic compound with a high Dy concentration.To confirm the formation of RE–Ni alloys, potentiostaic electrolysis was conducted at a Ni plate at 0.50 V for 1 h in both the NdCl3 and DyCl3 systems. Fig. 2-a shows a cross-sectional SEM image of the sample obtained in NdCl3 system. An alloy layer with the thickness of approximately 10 μm was observed. From XRD and EDX results, the alloy layer was confirmed to be NdNi5. Fig. 2-b shows a cross-sectional SEM image of the sample obtained in DyCl3 system. Ni plate was completely alloyed with Dy and the thickness of plate increased from 100 μm to 200 μm due to the alloying. The formation of DyNi2 was confirmed by XRD and EDX. Based on these results, selective formation of Dy–Ni alloy can be expected at 0.50 V in molten CaCl2–NdCl3–DyCl3. Acknowledgement This work was supported by Grant-in-Aid for JSPS Fellows 19J20301.The present address of Kouji Yasuda is Graduate School of Engineering, Kyoto University. R eferences [1] T. Oishi, H. Konishi, T. Nohira, M. Tanaka and T. Usui, Kagaku Kogaku Ronbunshu, 36, 299 (2010).[2] H. Konishi, H. Ono, T. Nohira and T. Oishi, ECS Trans., 50, 463 (2012).[3] K. Yasuda, K. Kondo, S. Kobayashi, T. Nohira and R. Hagiwara, J. Electrochem. Soc., 163, D140 (2016).[4] T. Nohira, S. Kobayashi, K. Kondo, K. Yasuda, R. Hagiwara, T. Oishi and H. Konishi, ECS Trans., 50, 473 (2012). Figure 1

Dissolution Behavior of SiO2 and Electrochemical Reduction of Dissolved SiO2 in Molten Chlorides

1. Introduction The global production of photovoltaic (PV) cells has increased by a factor of approximately 360, i.e., 0.285 GW year−1 to 102.4 GW year−1, from the year 2000 to 2018 [1,2]. Among the many types of solar cells, crystalline Si solar cell accounted for 96.9% of the worldwide production in 2018 [3]. Therefore, crystalline Si would be most likely to remain as the main stream of the PV industry in the long term.Due to the high energy cost of the current production process of solar-grade silicon (SOG-Si), the next-generation production process for SOG-Si with low energy cost is required. For the past two decades, we have been studying the direct electrolytic reduction of solid SiO2 to Si in molten CaCl2 as a new production process of SOG-Si [4–6]. Recently, we have focused on electrochemical reduction of dissolved SiO2 in CaO-added molten salts [7].In this study, we selected eutectic molten NaCl–CaCl2 as the electrolyte, because its melting point is comparatively lower than that of single CaCl2 melt, which enables the investigation in a wide temperature range. The structure and electrochemical reduction of dissolved SiO2 were investigated in molten NaCl–CaCl2–CaO. 2. Experimental All experiments were conducted in a dry Ar atmosphere. The molten salts were prepared as follows: Firstly, NaCl and CaCl2 powders were mixed in a eutectic composition (NaCl:CaCl2 = 47.9:52.1 mol%), and then certain amounts of CaO (0–2.0 mol%) and SiO2 (0 or 1.0 mol%) powders were added to the molten eutectic mixture. For Raman spectroscopy, a platinum pan loaded with the mixed salt was placed in an air-tight high-temperature stage, and then heated to 1023 K.Then the structure of dissolved SiO2 was investigated by Raman spectroscopy. For electrochemical measurement, the mixed salts were loaded into a graphite crucible. A graphite plate was used as a working electrode. The counter and quasi-reference electrodes were a graphite rod and a Si rod, respectively. The potential was calibrated by the deposition potential of Na metal on a Mo wire. Samples obtained by the galvanostatic electrolysis were analyzed by XRD and SEM/EDX. 3. Result and discussion Fig. 1 shows Raman spectra of molten (a) eutectic NaCl–CaCl2, (b) NaCl–CaCl2–2.0 mol% CaO, and (c) NaCl–CaCl2–2.0 mol% CaO–1.0 mol% SiO2 at 1023 K. Within the wave number range of 700–1200 cm−1, a band at 845 cm−1 is observed only for molten salt (c), whereas no apparent bands for molten salts (a) and (b). The structure of dissolved SiO2 in molten salt (c) is considered as SiO4 4− ion, considering that the main Raman bands for the stretch vibration of SiO4 4−, SiO3 2−, and Si2O5 2− in silicate melts have been reported at around 850, 950, and 1100 cm−1, respectively [8]. Since the SiO4 4− ion is regarded as the dissolved species of Ca2SiO4, this ion is consistent well with the ratio of added CaO/SiO2 (2.0 mol% and 1.0 mol%).The galvanostatic electrolyses were also carried out at graphite plates at 50–200 mA cm−2 in molten NaCl–CaCl2–1.9 mol% CaO–0.97 mol% SiO2. From XRD and SEM/EDX analysis of the samples, deposition of Si was confirmed, which suggested the reduction of SiO4 4− ion as follows:SiO4 4− + 4 e− → Si(s) + 4 O2− (1)In the presentation, the effect of CaO concentration on the dissolution behavior of SiO2 and electrochemical reduction of dissolved SiO2 will be discussed. Acknowledgement The present address of Kouji Yasuda is Graduate School of Engineering, Kyoto University. R eferences [1] Photovoltaic Market 2017, RTS Corp., Tokyo, Japan (2017). [in Japanese][2] Industrial Rare Metal 2019, Arumu Publ. Co., Tokyo, Japan (2019). [in Japanese][3] Photovoltaic Market 2019, RTS Corp., Tokyo, Japan (2019). [in Japanese][4] T. Nohira, K. Yasuda, and Y. Ito, Nat. Mater., 2, 397 (2003).[5] K. Yasuda, T. Nohira, R. Hagiwara, and Y. H. Ogata, Electrochim. Acta, 53, 106 (2007).[6] T. Toba, K. Yasuda, T. Nohira, X. Yang, R. Hagiwara, K. Ichitsubo, K. Masuda, and T. Homma, Electrochemistry, 81, 559 (2013).[7] Y. Ma, K. Yasuda, and T. Nohira, s of The 51st Symposium on Molten Salt Chemistry, p. 24-25, Sapporo, Japan (2019).[8] B. O. Mysen, Structure and Properties of Silicate Melts, Elsevier, Amsterdam, Netherlands (1988). Figure 1

Shape control of the crystal-melt interface in the Bridgman method

The processes of silicon crystallization in flat-bottomed cylindrical graphite crucibles in the modes of conjugate convective heat transfer with allowance for latent heat are numerically investigated. The influence of hydrodynamics and heat transfer on the local shape of the crystal-melt interface has been studied. The hydrodynamics of a silicon melt is investigated in the modes of thermogravitational and thermal gravitational-centrifugal convection. First, the effect of the velocity of lowering the crucible into the cold zone was studied. Then, at the set crucible lowering velocity, the influence of the crucible angular velocity was studied. The problems were solved in a nonstationary formulation by the finite element method.

Effect of carbon addition and cooling rate on lamellar structure of peritectic TiAl-based alloy

The effect of carbon addition and cooling rate on the lamellar structure of peritectic Ti-46.5Al–5Nb-0.2B-0.2C (at.%) alloy was studied. The studied alloys with a carbon content of 0.2, 0.5, 0.7 and 1.0 at.% were prepared by vacuum induction melting in graphite crucibles. The as-cast samples were subjected to solution annealing in a single α (Ti-based solid solution) phase field followed by cooling at four constant rates ranging from 5 to 50 °C/min. The increase in carbon content leads to an increase in both start and finish α phase decomposition temperatures. During continuous cooling, the carbon atoms segregate along α2(Ti3Al)/γ(TiAl) lamellar interfaces and hinder lateral growth of γ lamellae. The interlamellar spacing decreases with increasing carbon content and increasing cooling rate. A relationship describing the complex influence of carbon content and cooling rate on α2-α2 interlamellar spacing λ is proposed. Vickers microhardness HVm increases with increasing both the carbon content and cooling rate. The Vickers microhardness depends on interlamellar spacing λ according to the Hall-Petch relationship.

Hardening of Silumin by Composite Particles Core/Shell Si@Mg

Aspects of increasing the strength of silumin due to the introduction of ultrafine silica powders into its melt are considered. The calculation of the surface energy of silicon oxide nanoparticles showed the promise of this modification. The method is proposed for increasing the adhesion of silicon to aluminum, due to the surface-active properties of magnesium and the high surface energy of nanoparticles, which contributes to the formation of chemical compounds of silicon with aluminum, and as a result, to hardening of the alloy. Due to the large difference in the surface energies of magnesium and silicon, the possibility of producing Si @ Mg core-shell nanoparticles in the one-step method under the action of an electron beam has been shown. The layout of substances in the graphite crucible, the dependence of the electron beam current to obtain Si @ Mg nanoparticles are presented.

Smelting Reduction of Spent Catalyst Containing Nickel: A Preliminary Study

The aim of this research was to study the recycling process and the feasibility to smelt the spent nickel catalyst for the production of nickel alloy or ferronickel. The smelting process was carried out in a laboratory induction furnace. The effects of SiO2/CaO for slag forming on metal recovery and smelting time were investigated. Petroleum coke was used as reductant. Mill scale was used as an iron resource for ferro-alloy production, while CaO was used as slag forming agent. The raw materials were mixed together and put into a graphite crucible, which was then placed in the induction furnace. After the melt was completed, the melt was poured into a mold to solidify. The chemical composition of the product was analyzed by XRF and XRD. It was found that the smelting time was decreased with increasing SiO2/CaO from 1.0 to 2.3. For nickel alloy production, increasing of SiO2/CaO increased the weight of metal product. For the ferronickel production, however, the weight of metal product was found not to vary with different ratio of SiO2/CaO.

Thermal Profile and Microstructure of Wrought Aluminium 7075 for Semisolid Metal Processing

Thermal analysis (TA) is a non-damaging and quick method to check the molten metal’s condition preceding to casting. This paper aims to present the relationship between fraction solid and temperature by utilising cooling curve analysis (CCA), to acquire correct processing parameters for wrought aluminium 7075 in semisolid condition. An induction furnace was used to heat a graphite crucible containing wrought aluminium 7075 alloy up to the temperature of 750 °C. A calibrated Chromel-Alumel K-type thermocouple was placed at the centre of the crucible and was submerged to 15 mm in the melt. The solidification temperature and time were measured by Data Logger GL-220. Normal, intermediate, and high cooling rate conditions were achieved when the crucible was left in an open atmosphere, in an open atmosphere with additional minimum airflow, and in an open atmosphere with the maximum airflow, respectively. It was found that the normal cooling rate was estimated at 2.23 °C/s, the intermediate cooling rate was calculated at 2.88 °C/s while the high cooling rate was recorded at 3.20 °C/s. The increase in cooling rate conditions has a significant effect on the changes of phases during solidification process where it leads to the decreased in liquidus, eutectic and solidus temperature. The microstructure feature was found to have a significant difference with the variation of cooling rates where higher cooling rate led to smaller primary grain size.

Directional solidification of photovoltaic silicon in re-useable graphite crucibles

Graphite crucibles are potentially interesting for the directional solidification processing of photovoltaic silicon, because, contrarily to standard silica crucibles, they can be used many times. In the present work, two types of graphite crucibles are studied: i) graphite directly coated with the Si3N4 powder classically used as a releasing layer for standard silica crucibles, and ii) graphite protected by a dense SiC layer before deposition of the releasing coating. In both cases, spontaneous detachment of the silicon ingot is observed to occur during cooling. Results are given and discussed concerning the impurities introduced in the silicon during the melting-solidification cycle, as well as their consequences on the photo-electrical characteristics of silicon. These results are compared with those obtained using the standard silica crucible. It is shown that re-useable SiC protected graphite crucibles lead to the same performances as standard silica. Reproducible results are found after four runs with the same crucible, and no degradation of the crucible is observed.

Eloboration of Methods for Determination on Content of the Oxygen, Nitrogen, Hydrogen Admixtures in Titanium Aluminides

Titanium intermetalides (TiAl and Ti3 Al) and alloys on theirs bases applies in air — and spacetechnology and automobile industry.
 Physical and mechanical properties there alloys is better, then at classical Ti — or Ni — alloys, that are utilized in aeroplanes and rocets.
 Alloys, based on TiAl and Ti3Al, are made with utilization vacuum — arc, plasma — arc, induction- garnisage, magnetoperating electroslag melting, electron — beam melting with intermediate capacity, electroslag melting in inert atmosphere under «active» fluxes with metallic calcium, induction melting in muchsectional crystallizator and cold crucible, argon — arc melting with unexpended tungsten electrode in copper watercooling crucible.
 For connection of the details, that were made from these alloys, there were used welding by pressure, contact, electron — beam, diffusion welding.
 Alloys, based on titanium aluminide, have essential defects — high brittleness and low plasticity, viscosity and resistance thermal impact strength.
 Autors a lot of articles explaines these descriptions by structural special features of titanium aluminides and alloys on their bases, but does not consider possibilities of the influence by oxygen nitrogen, hydrogen admixtures.
 In literature information about methods of determination gaseous admixtures (O, N, H) contents in titanium aluminides and alloys on their bases are absented.
 Methods of determination oxygen, nitrogen, hyd­rogen contents in titanium aluminides on ana­lysers TC436, RO316, TN114, RH402 are created. Parameters of these methods are described in this article (temperatures of heating on graphite crucibles, times, masses of analytical samples).

Effect of Temperature on the Formation of Stable and Metastable Aluminide Phases in Al‒Zr‒Nb Alloys

The conditions of the formation of stable and metastable aluminides Aln(Zr1 – xNbx) formed during the crystallization of superheated melts of the Al‒Zr‒Nb system are considered. Upon a close zirconium content in the alloys of 0.23–0.25 at %, the niobium content varies from 0.05 to 0.21 at %. Alloys are prepared in a resistance furnace at a temperature of 1230°C in an argon atmosphere in graphite crucibles. The alloys are cast into a bronze mold; the cooling rate is estimated as 200°C/s. The structural features, distribution, and morphology; the composition of matrix, dendritic cells, and aluminides; and the structural type of aluminides in the alloys are studied using scanning electron and optical microscopy, X-ray diffraction, and inductively coupled plasma atomic emission spectroscopy. It is shown that the growth forms of stable aluminides (D023 structural type) change from faceted to dendritic and primary metastable aluminides (L12 structural type) begin to form; in the process of the Al‒Zr‒Nb melt, overheating was 360–365°C above the liquidus temperature. Exclusively metastable aluminides with both polyhedral and dendritic growth forms are formed in the Al‒Zr‒Nb alloys when the overheating of their melt is 390–395°C (as well as at higher overheating) above the liquidus temperature. The near-peritectic niobium composition of the Al‒Zr‒Nb alloy and the zirconium content (more than seven times higher than peritectic) are crucial factors in the formation of a large fraction of metastable AlnZr aluminides having a cubic L12 structure. It is shown that, in accordance with the rules of isomorphism, Nb replaces Zr at equivalent positions of the aluminides crystal lattice. The intensity of isomorphism of the formed Al4(Zr0.79Nb0.21) aluminides increases with the increase in temperature of the melt overheating.

The ultrasound effects on the formation of the solidification structure of A356 ingots processed via a 2-zone induction melting furnace

To study the formation of the solidification structure including the columnar-to-equiaxed transition (CET) under the influence of ultrasound, a 2-zone furnace system and an ultrasound equipment were utilized. The 2-zone furnace system consists of an induction furnace with a top coil and a bottom coil, a graphite crucible, and. a water-cooled chill block located at the bottom of the crucible. By controlling both the top and bottom coil output power independently, the furnace can create various temperature gradients and cooling rates in different regions of the graphite crucible. The ultrasound probe was inserted at the top of the crucible. The top of the crucible was also thermally insulated. Temperature measurements were performed at different locations in the crucible. Optical microscopy was used to characterize the microstructure of the A356 cylindrical ingots. The effects of ultrasound on the microstructure formation during solidification of A356 alloy was studied. A numerical model was developed to compute the temperature gradients and mushy zone evolution in the crucible and to assist in developing of solidification maps.

Effect of temperature on the formation of stable and metastable aluminide phases in the Al-Zr-Nb alloys

The paper considers formation conditions for stable and metastable aluminides Al n (Zr 1-x Nb x ) obtained in the crystallization of superheated Al—Zr—Nb melts. At the close zirconium content in the alloys of 0.23—0.25 at.%, the niobium content varied from 0.05 to 0.21 at.%. Alloys were prepared in a resistance furnace at 1230 °C in an argon atmosphere in graphite crucibles. Alloys were cast into a bronze mold where the cooling rate was estimated at 200 °C per second. The structural features, distribution pattern, morphology, the composition of the matrix, dendritic cells and aluminides, as well as the structural type of intermetallics in the investigated alloys were studied using scanning electron and optical microscopy, X -ray phase analysis, X -ray diffraction analysis, electron microprobe analysis including inductively coupled plasma atomic emission spectroscopy. It was shown that the growth forms of stable aluminides (D0 23 structural type) change from the faceted to dendritic one, and primary metastable aluminides ( L 1 2 structural type) begin to form during the Al—Zr—Nb melt overheating at 360—365 °C above the liquidus temperature. Only metastable aluminides with both polyhedral and dendritic growth forms are formed in the alloys when overheated by 390 —395 °C and higher. The near-peritectic niobium composition of the Al—Zr—Nb alloy (at the zirconium content more than seven times higher than the peritectic one) are crucial factors in the formation of a large fraction of metastable Al n Zr aluminides having a cubic L 1 2 structure. It was shown that, in accordance with isomorphism rules, Nb replaces Zr at equivalent positions of the crystal lattice of aluminides. The intensity of isomorphism of the Al 4 (Zr 0.79 Nb 0.21 ) intermetallics formed increases with the increasing melt overheating temperature.