High Vacuum Furnace Research Articles

Enhanced reduction of silicon oxide thin films on silicon under electron beam annealing

Electron beam annealing is an interesting alternative to other annealing methods as it can provide high temperature, rapid heating and cooling and low level of impurity as it operates under high vacuum environment. Furthermore swamping the materials with electrons can lead to dramatic changes in the component valence states with the mechanism involving oxido-reduction reactions. This is illustrated in the present case with the enhancement of the reduction of SiO2. Commercial thermally grown 100 and 400nm SiO2 films on Si were annealed under three different environments: furnace annealing in open atmosphere with O2 flow, high vacuum furnace annealing and electron beam annealing. The reduction and oxidation of SiO2 films on Si are investigated using ion beam analysis. The validity of the measurement method was confirmed by measuring the oxidation rate through successive Rutherford backscattering spectrometry (RBS) measurements. The oxidation kinetics were observed to be in excellent agreement with literature values. At 1000°C reduction of the SiO2 film is observed only with electron beam annealing. A model is proposed to explain the effect of the electron beam.

Impurities, inclusions, and dislocations in multicrystalline silicon grown from well-mixed and poorly mixed melts

This paper presents an experimental study on the interaction between impurities, inclusions, and dislocations in multi-crystalline silicon ingots grown from well-mixed and poorly mixed melts. The ingots were grown in a high-vacuum induction furnace by the vertical Bridgman method and the degree of impurity mixing within the melt was modified by changing the growth rate. Vertical and horizontal slices were prepared from the ingots and analyzed by Fourier transform IR spectroscopy, as well as reflected-light and IR transmission microscopy to measure the axial carbon concentration and the distribution of dislocations or inclusions, respectively. The correlation between individual inclusions and dislocations has been investigated by correlative reflected-light/IR transmission and scanning electron microscopy. The influence of the melt mixing on the segregation of carbon is demonstrated and discussed with respect to the consequences for the formation of inclusions and dislocation clusters in multi-crystalline silicon.

다공성 티타늄 임플란트의 생리활성물질 담지특성에 관한 연구

Purpose: Surface modification is important techniques in modern dental and orthopedic implants. This study wasperformed to try embedding of bioactive materials in porous Ti implants.Methods: Porous Ti implant samples were fabricated by sintering of spherical Ti powders in a high vacuumfurnace. It’s diameter and height were 4 and 20 . Embedding process was used to suction and vacuum chamber.Loading properties of porous Ti implants were evaluated by scanning electron microscope(SEM), confocal laserscanning microscope(CLSM), and UV-Vis-NIR spectrophotometer.Results: Internal pore structure was formed fully open pore. Average pore size and porosity were 10.253and17.506%.Conclusion: Porous Ti implant was fabricated successfully by sintering method. Particles are necking strongly eachother and others portions were vacancy. This porous structure can be embedded to bioactive materials. Thereforebioactive materials will be able to embedding to porous Ti implants. Bioactive materials embedding in the porousTi implant will induced new bone faster.

Brazing of zirconia to titanium using Ag-Cu and Au-Ni filler alloys

Advanced ceramic is usually joined to metal by the well-known direct brazing process, where costly active filler alloys can be considered a limitation. Brazing using active-metal-free filler alloy as insert between the joint components is an attempt to overcome it. The active metal diffusion from the titanium member through the bulk of molten filler to the ceramic was responsible to produce an active filler alloy in loco and promote reduction of the zirconium oxide to improve wetting on the ceramic surface. Unalloyed titanium was joined in a high-vacuum furnace (<3x10-5 mbar) to yttria-tetragonal zirconia polycristals (Y-TZP) and zirconia partially stabilized with magnesia (Mg-PSZ), where commercial fillers Ag-28Cu and Au-18Ni with respective thermal cycles were evaluated. Helium gas leak detection test was performed at the ceramic/metal interface at room temperature; samples from reliable vacuum tight joints were examined by microstructural analysis techniques and energy dispersive X-ray analysis at the joint cross-section. Tight joints were produced with eutectic Ag-Cu filler, revealing an intermetallic layer and a dark reaction layer near the ceramic surface; titanium diffusion was efficient for superficial chemical interactions between individual components. Brazing joints were also tested using three-point flexure testing.

Transient liquid phase bonding of HfC-based ceramics

Transient liquid phase (TLP) bonding enables joining at lower temperatures than traditional bonding techniques and preserves the potential for high-temperature applications, making it particularly attractive for joining ultra-high-temperature ceramics (UHTCs) such as carbides and borides. The feasibility of a TLP joint between “pure” carbides has been recently demonstrated. The present study examines the interactions that occur between undoped HfC or MoSi2-doped HfC and a Ni/Nb/Ni multilayer interlayer during TLP bonding. Bonding is performed at 1400 °C for 30 min in a high-vacuum furnace. SEM–EDS characterization shows that the reaction layer formed at the interlayer/ceramic interface contains mixed carbides and depending upon the ceramic, Ni–Nb–Hf, or Ni–Nb–Hf–Si, or Ni–Nb–Si alloys. Nanoindentation tests traversing the reaction layer between the bulk ceramic and Nb foil midplane also show a clear transition zone across which the indentation modulus and hardness vary. Crack-free joints have been obtained with undoped HfC. The addition of 5 vol% MoSi2 introduces small (<5 μm long) isolated cracks within the reaction layer, whereas with 15 vol% MoSi2 added, cracking was pervasive within the reaction layer. When the reaction layer exceeds a critical thickness, as in the case of the bond obtained with HfC doped with 15 vol% MoSi2, residual stresses become sufficiently large to cause extensive cracking and bond failure. The results suggest a need to characterize and balance the positive role of additives on sintering with the potentially deleterious role they may have on joining.

Vacuum brazing of sapphire with Inconel 600 using Cu/Ni porous composite interlayer for gas pressure sensor application

In this research, sapphire as a ceramic was brazed to Inconel 600 as a metal with a commercially available Cusil ABA (63Ag–1.75Ti–35.25Cu) filler foil as braze alloy where Cu/Ni porous composite introduced as an interlayer so it could be used in a particular gas pressure sensor application. Several brazing processes were carried out in a high vacuum furnace in order to investigate the effects of brazing parameters on the joint interface and mechanical properties. The common brazing temperature and time were in the ranges of 830–900°C and 15–30min respectively, while vacuum pressure was remained constant at 1×10−4Pa. SEM-EDS and XRD analyses of the joint microstructure and interface composition revealed five distinct phases; Ni3Ti, AlNi, Cr1.97Ti1.07, Fe0.2Ni4.8Ti5, (TiO1.06)3.32. The brazing area formed two “ocean” structures near to Inconel and sapphire interfaces whereas a reaction layer was developed at the surface of Inconel 600. Under the mechanical property analyses the brazed joint at 900°C for 30min obtained the maximum shear strength of 58.5MPa which is adequate for particular gas pressure sensor application.

Influence of sintering parameters on the properties of powder metallurgy Ti–3Al–2.5V alloy

The processing of near net shape Ti–3Al–2.5V components using the conventional pressing and sintering route is addressed in this study. The Ti–3Al–2.5V starting powder was obtained considering both the blending elemental and the master alloy addition methods. The powders were uniaxially pressed and sintered in a high-vacuum furnace under various temperature–time combinations. The influence of the processing parameters on the relative density, microstructural features, amount of interstitials, mechanical behaviour, thermal conductivity and electrical resistivity of the sintered materials was evaluated. It was found that the relative density of the samples increases with processing temperature and time, and almost fully dense materials were obtained. The mechanical performance of the Ti–3Al–2.5V improves due to the reduction of the residual porosity and are, generally, of the same order of magnitude of those required for titanium biomedical products. Furthermore, the temperatures–times selected permit to obtain thermal and electrical properties similar to the wrought alloy.

Defect investigations of an iron-nickel meteorite

A sample from the Gibeon meteorite, an iron-nickel meteorite with the typical two-phase Widmanstätten structure, was investigated by positron annihilation techniques. A high mean positron lifetime was observed which derives from open volume defects. The meteorite samples were then gradually heated in a high-vacuum furnace and cooled down to room temperature. Upon temperature treatment a decrease of the mean positron lifetime was observed, as well as a gradual evolution of the 2-dimensional Doppler broadening spectra towards pure iron. This leads to the conclusion that the open volume defects are formed during slow cooling in the progress of the formation of the Widmanstätten structure. Upon re-heating these defects start to dissolve and do not re-appear due to fast cooling rates. We therefore attribute the open volume defects to misfit dislocations between the Kamacite (Ni-poor) and Taenite (Ni-rich) phases.

FFT アナライザの周波数応答関数による多孔質焼結材の振動減衰機構の同定

ABSTRACTIn the fields of an eco-friendly automobile, an advanced industrial machine, and a precision electronic device, controlling of vibrational behavior of the sintering parts obtained from powder metallurgy is required. In this paper, the vibration behavior of porous material made by powder metallurgy is investigated by a FFT analyzer. Pure Cu powders (Average particle size: 36 µm, 89 µm) are used as initial substances. The powder is compressed by a metal die with 100～200 MPa, and a plate shaped Cu compact is made. Using a high vacuum furnace, the green compact is heated from room temperature with 10 ˚C/min, and is sintered at 700～1000 ˚C for 1 hour. By changing the powder particle size, the compaction pressure, and the sintering temperature, some kinds of sintered Cu porous plates which had various microstructures, varied porosity, and different mechanical properties are sintered. For the sintered Cu porous plate obtained, microstructure observation, tensile test and vibration test are performed. The vibration behavior of the sintered Cu porous plates is analyzed from the frequency response function of the FFT analyzer. The damping coefficient of the sintered Cu porous plate depends on the porosity and the open pore ratio. The vibrational behavior of the sintered material is able to be easily measured by FFT analyzer.

Titanium and Ti-13Nb-13Zr Alloy Porous Implants Obtained by Space-Holder Technique with Addition of Albumin

Titanium and its alloys are the main metals studied as porous metallic implants by their excellent mechanical properties and biological interactions. Production methods of porous metallic materials are based on powder metallurgy (PM), because it allows the manufacturing of parts with complex shapes and dimensions close to the finals (near-net shape), and the addition of alloying elements reaching a satisfactory structural homogeneity, and porosity. The pore production by space-holder technique constitutes of mixing organic compounds with metal powder, which when removed by thermal treatment prior structures are kept in place. The objective of this study is to obtain porous implants of commercially pure titanium (cpTi) and Ti-13Nb-13Zr alloy by PM with space-holder technique and albumin as an additive. For the processing of the samples were used hydride titanium powder (TiH2) to obtain cpTi samples, and metal powders of Ti, Nb and Zr in the stoichiometric proportions for obtaining the alloy samples. The samples were prepared by mixing the metallic powder to the albumin (30wt%) and filling a silicone model that was pressed isostatically (140 MPa). The thermal treatment was performed in an oxidizing atmosphere (350°C/1h) for the decomposition of organic material. The sintering was performed at a temperature of 1300°C (1h/cpTi, 3h/Alloy) in high vacuum furnace (10-5 mBar) to all samples. The calculated porosity showed a significant difference between the samples cpTi (40%) and alloy (60%). The samples surface characterization showed very rough with high specific surface area. Samples of cpTi presented formation of necks arising from sintering. In the alloy samples were observed homogenous microstructure with the presence of α and β phases composing the Widmanstätten structure. It is possible to conclude that the same amount albumin allowed the formation of pores in the microstructure of cpTi and alloy although in different proportions, without harming the sintering of both and allowing diffusion of the alloy elements.

Magnesium silicide thin film formation by reactive diffusion

An industrial Rapid Thermal Processing has been used to grow nano-scale magnesium silicide (Mg2Si) thin films for thermoelectric applications, using reactive diffusion in vacuum. This formation is compared to that obtained by treatment in conventional high-vacuum furnace. Reaction between Mg and Si substrate occurs approximately at 200°C and its rate depends on the temperature and the heating rate of annealing, while the treatment duration determines the completeness of the reaction. These observations confirm the diffusion governed process of Mg silicidation. Two simultaneous processes occur in the films: Mg desorption from the surface and silicide formation at the Si/Mg interface. Applying the annealing temperature of 350°C is likely the sufficient condition to complete the reaction. The obtained films have shown stability regarding decomposition until the temperature of 450°C. However, in the presence of oxygen-contaminated atmosphere the Mg2Si tends to decompose at lower temperatures starting from circa 300°C and dissociated magnesium oxidizes. The rapid thermal annealing of Mg/Si layers allows to decrease the duration of silicide formation, while the risk of decomposition of Mg2Si film and surface oxidation due to high heating rate and presence of oxygen is increased. The optimum parameters for nano-scale Mg2Si thin films preparation have been proposed.

Dissimilar laser brazing of h-BN and WC-Co alloy in Ar atmosphere without evacuation process

Laser brazing with Ti as an active element in Ag-Cu alloy braze metal has been successfully applied to dissimilar joining of h-BN and WC-Co alloy in Ar (99.999% purity) gas flow atmosphere without any evacuation process. Good wettability of the braze metal with h-BN and WC-Co alloy were confirmed by the observation and structural analysis of the interface by electron probe micro-analysis and scanning acoustic microscopy. The oxidation of titanium was not observed and this showed that the laser brazing with titanium as an active element in braze metal could be performed even in an Ar gas flow atmosphere without an evacuation process using a high-vacuum furnace.

Study of Sol-Gel/Powder Metallurgy Technique for Processing Titanium Parts

The powder metallurgy processing of titanium devices for biomedical applications has complex steps. In order to introduce a new processing route, this work studied a sol-gel technique combined with powder metallurgy for producing porous titanium samples. The process involves the mixture of titanium powders with sodium alginate suspension, which undergoes reticulation by calcium salt solution contact, forming a titanium/calcium alginate hydrogel in granule shape. Later, the hydrogel granules were dried and sintered in a high vacuum furnace for titanium particles consolidation and calcium alginate removal. The samples characterization was performed by scanning electron microscopy, optical microscopy, metallographic analysis, semi-quantitative X-ray fluorescence spectroscopy and X-ray diffraction. The results showed that the methodology used is adequate for producing porous titanium parts, since the samples presented no contamination, a uniform shape, particle consolidation and interconnected porosity. The research continues aiming to obtain samples with different bulk morphology, like, discs or bars for surgical implant applications.

Brasagem da zircônia metalizada com titânio à liga Ti-6Al-4V

Zircônia tetragonal estabilizada com ítria foi mecanicamente metalizada com titânio e a condição de molhamento avaliada com as ligas convencionais Ag-28Cu e Au-18Ni. Estas dissolveram o revestimento de titânio para uma completa distribuição deste metal ativo na superfície cerâmica, gerando uma liga ativa in situ e possibilitando adequadas ligações químicas ao metal base na temperatura de união. Os melhores resultados de molhamento foram selecionados para brasagem indireta em forno de alto-vácuo nas juntas ZrO2/Ti-6Al-4V. Testes de detecção de vazamento de gás hélio foram realizados na interface de união das juntas; amostras removidas na seção transversal de juntas estanques foram examinadas por técnicas de análise microestrutural. Formou-se uma camada escura adjacente à cerâmica metalizada, responsável pelo molhamento ocasionado pela liga Ag-28Cu. Entretanto, o uso da liga Au-18Ni resultou em precipitação de intermetálicos e microtrincamento interfacial. Perfis de microdureza através da interface resultante até onde a zircônia mostrou típico escurecimento não indicaram alternância significativa entre medições consecutivas; os resultados dos ensaios de resistência mecânica à flexão-3p foram considerados satisfatórios.

High temperature annealing effects on low energy iron implanted SiO 2

15 keV Fe ions were implanted into a thermally grown silica film with a fluence of 1 × 10 16 at./cm 2 resulting in a near Gaussian concentration profile peaking at 8 at.% about 15 nm under the surface. High vacuum (∼10 −7 mbar) furnace annealing and electron beam annealing at high temperature resulted in diffusion of Fe inside the oxide film. Segregation of Fe atoms at the SiO 2 surface and SiO 2/Si interface was observed in both cases. EBA resulted in faster precipitation and lower out-diffusion of Fe. In-situ Rutherford Backscattering Spectrometry was performed during high vacuum annealing and is shown to be an appropriate method to investigate the diffusion rate. The differences observed between the methods are explained by the effect of excess electrons and ionization induced by the electron beam on the oxygen-vacancy mediated displacement mechanism and on the reduction of Fe oxides.

Taguchi Method for the Determination of Optimised Sintering Parameters of Titanium Alloy Foams

Sintering is a key step in the preparation of metal foams. The present work focuses on the sintering effects on the properties of titanium foam prepared using the slurry technique. Sintering affects the density as well as the mechanical properties of the sintered parts. To achieve a high density of the titanium alloy foam, the effects of various parameters including temperature, time profile and composition have to be characterized and optimized. This paper reports the use of the Taguchi method in characterizing and optimizing the sintering process parameters of titanium alloys. The effect of four sintering factors: composition, sintering temperature, heating rate and soaking time to the density has been studied. The titanium slurry was prepared by mixing titanium alloy powder, polyethylene glycol (PEG), methylcellulose and water. Polyurethane (PU) foam was then impregnated into the slurry and dried at room temperature. This was later sintered in a high temperature vacuum furnace. The various factors were assigned to an L9 orthogonal array. From the Analysis of Variance (ANOVA), the sintering temperature was found to give the highest percentage of contribution (34.73) followed by the composition of the titanium alloy powder (26.41) and the heating rate (0.64). The optimum density for the sintered titanium alloy foam was 1.4873±0.918 gcm-1. Confirmatory experiments have produced results that lay within the 90% confidence interval.

Carbon Nanotube Rubber Stays Rubbery in Extreme Temperatures

Extreme elastic: A new viscoelastic material has recently been developed from carbon nanotubes (CNT rubber; see picture). This material is similar to silicone rubber but maintains its viscoelasticity from −196 to 1000 °C in an oxygen-free environment. CNT rubber is promising for a wide range of applications, including use in high-vacuum furnaces and even aerospace vehicles that travel to the cold interstellar space.

High pressure and high temperature annealing on nitrogen aggregation in lab-grown diamonds

Diamond single crystals were grown by a high-pressure high-temperature gradient method using a molten Fe–Ni catalyst in a split-sphere apparatus at a pressure of 5.5 GPa and a temperature of 1473–1873 K. The as-grown crystals, ranging in size from 0.2 to 0.6 g, were generally deep yellow in color because of intake of nitrogen impurity during the process. Two different annealing methods were used to change their color to light and vivid yellow. One method involved annealing at 5.5 GPa and 2193–2473 K within the split-sphere apparatus. The other involved annealing of E-beam irradiated crystals at 1773 K in a high-vacuum furnace at 10−6 Torr. Distribution of C-center nitrogen, single substitutional nitrogen, and A-center nitrogen defects, a pair of nearest-neighbor nitrogen, were thoroughly studied by FT–IR spectroscopy. Upon annealing, C-center nitrogen defects decreased by 10–60%, while A-center nitrogen defects increased by 5–70%. It was confirmed that the irradiation process and intake of nickel impurity enhanced the nitrogen aggregation rate, which followed the second order kinetics. Measured activation energies were in the range of 2.88–3.01 eV, which were not strongly affected by the irradiation process. The results indicate that the nitrogen aggregation rate was enhanced by vacancies and interstitials introduced by E-beam irradiation.

Comparison of Epitaxial Graphene on Si-face and C-face 6H-SiC

ABSTRACTWe present atomic force microscopy (AFM), Hall-effect measurement, and Raman spectroscopy results from graphene films on 6H-SiC (0001) and (000-1) faces (Si-face and C-face, respectively) produced by radiative heating in a high vacuum furnace chamber through thermal decomposition. We observe that the formation of graphene on the two faces of SiC is different in terms of the surface morphology, graphene thickness, Hall mobility, and Raman spectra. In general, graphene films on the SiC C-face are thicker with higher mobilities than those grown on the Si-face.

NEW RUBBER BEATS HEAT AND COLD

CARBON NANOTUBES are taking rubbery behavior to new extremes. A novel rubberlike material made from long, tangled strands of single-, double-, and triple-walled carbon nanotubes (CNTs) maintains its viscoelasticity at temperatures as low as –196 °C and as high as 1,000 °C in an oxygen-free environment ( Science, DOI: 10.1126/science.1194865). Most rubbery materials, in contrast, turn brittle in the cold and degrade when things heat up. Because of its temperature-invariant viscoelasticity, the CNT-based material could find use in vehicles that travel to the cold reaches of interstellar space. It could also be used inside high-vacuum furnaces, where it could take the heat without running the risk of reacting with oxygen. A team led by Don N. Futaba, Kenji Hata, and Ming Xu of the Nanotube Research Center at Japan’s National Institute of Advanced Industrial Science & Technology (AIST) created the CNT-based material using a combination of water-assisted chemical vapor deposition, reactive ion etching of the ...