Inert Gas Fusion Method Research Articles

Characterization of Virgin, Re-used, and Oxygen-reduced Copper Powders processed by the Plasma Spheroidization Process

Fabrication of parts with high mechanical properties heavily depend on the quality of powder deployed in the fabrication process. Copper powder in three different powder types were spheroidized using radio-frequency inductively coupled plasma (ICP) spheroidization process (TekSphero-15 system). The characterized powders include virgin powder as purchased from the powder manufacturer, powder used in electron beam powder bed fusion (EB-PBF) process, and reconditioned powder, which was used powder that underwent an oxygen-reduction treatment. The goal of spheroidizing these powder types was to evaluate the change in powder morphology, the possibility of enhancing the powder properties back to their as-received conditions, and assess oxygen reduction of the powder lots given their initial oxygen contents. Also, to investigate the impact of re-spheroidization on powder properties, the second round of spheroidization was performed on the already used-spheroidized powder. The impact of powder type on powder sphericity and particle size distribution was evaluated using the image analysis of scanning electron microscope (SEM) micrographs and laser diffraction, respectively. The spheroidized powder showed higher sphericity and more uniform particle size distribution overall. Depending on the powder collection bin, second round of spheroidization affected the powder sphericity differently. The possibility of deploying the plasma spheroidization process as an alternative oxygen-reduction technique was also investigated through tracking the powders’ oxygen content using inert gas fusion method before and after the spheroidization. The plasma spheroidized powder showed less oxygen content than the hydrogen-treated powder. The second round of spheroidization caused no change in oxygen content. The correlation between oxygen-reduction and created cracks was discussed and compared between plasma spheroidization and hydrogen-treatment. The plasma spheroidization process created a powder with higher sphericity, uniform particle size, and less oxygen content.

Microstructural investigation of direct laser deposition of the Ti–6Al–4V alloy by different melt pool protection conditions

Abstract Titanium alloys require a special protecting atmosphere during the fabrication process due to their strong affinity with oxygen and nitrogen elements at high temperatures. In this study, the effects of different protection conditions on microstructure, phase characteristics, interstitial elements absorption and microhardness of additively manufactured Ti–6Al–4V alloy by direct laser deposition method have been investigated. Fabrication of specimens with similar laser parameters was carried out in three different protection conditions consist of air, closed box and argon shower. Characterization of samples was performed by utilization of OM, SEM, XRD, inert gas fusion method, micro-hardness and tensile strength analysis. Results indicated that fabrication of samples in an air atmosphere without proper protection leads to 2.5% spherical porosities, TiO2 and TiN formation in top layers, changing the c/a ratio from 1.59 to 1.61, absorption of 1870 and 500 ppm oxygen and nitrogen and 155 HV increment in micro-hardness value. Also, uncommon semi-globular microstructure in different locations of samples has been observed. The special protective atmosphere provided by argon shower led to 6.3% spherical porosities, negligible lattice parameter variation and martensite microstructure formation. It was found that in the optimal protection condition that was provided by a closed box, the typical basketweave microstructure with less than 1% porosity and 960 and 140 ppm oxygen and nitrogen absorption were achieved, which did not exceed the standard limits. In addition, the mechanical properties of UTS tensile strength, yield strength and elongation, were obtained 1042, 893 MPa and 13.2% respectively.

Glass forming ability of Zr48Cu36Al16-xAgx alloys determined by three different methods

This work was focused on the glass forming ability (GFA) of Zr48Cu36Al16-xAgx alloys (x = 0, 2, … 16) examination using three different methods. Critical diameters were determined by both discrete (classic) and continuous (cone test) methods. Several commonly used GFA thermal indicators were investigated as well. Due to oxygen contamination strong influence on the GFA of Zr-based alloys, oxygen content was measured in each prepared alloy by inert gas fusion method. Additionally, the authors discussed the alloy composition influence on the critical diameters and their respective thermal indicators values. These values were compared and their correlation with critical diameters was evaluated in terms of R2 correlation coefficient values. The best correlation was calculated for the θ indicator (R2 = 0.979).

Zirconium purity influence on the critical diameter and thermal indicators of the Zr48Cu36Al9Ag7 alloy

As it is known, the glass forming ability of Zr-based alloys is very sensitive to oxygen content. Oxygen contamination may come from raw zirconium and from alloy preparation stages as well. This work was focused on both factors. Using inert gas fusion method authors measured oxygen content in the zirconium delivered by five different providers as well as in five cone-shaped ingots after a full preparation process. Oxygen level influence on the critical diameter of Zr48Cu36Al9Ag7 alloy was quantitatively determined by cone test. Several common thermal indicators using characteristic temperatures were also calculated. They mostly exhibited high sensitivity to oxygen level as their correlation with the critical diameter was very high. Obtained results revealed that zirconium purity is not a relevant parameter in its quality description. The main GFA influencing factor is oxygen contamination level which should never be neglected. Moreover, an in-depth analysis including cost/quality aspects has been conducted in order to obtain practical guidelines for Zr-based bulk metallic glasses preparation.

Fast Simple Determination of Oxygen in Reduced Graphene Oxide by Inert Gas Fusion Method

AbstractA new method that combines inert gas fusion with infrared spectrometric detection for fast simple determination of total oxygen in reduced graphene oxide (RGO) has been established in this paper. The whole analyzing process was introduced, including calibration, temperature selection and sample weight selection. The equation of calculation the oxygen content of RGO in this method was given. The precision of the new method has been verified by measurement of a RGO sample. The RGO after measurement was characterized by X‐ray photoelectron spectroscopy (XPS). The relative standard deviation (RSD) of oxygen was 1.02%. The results were consistent with that obtained by the conventional classic method XPS. It has shown that the new method is accurate and efficient. The method of testing a RGO sample needs 140 s. The inert gas fusion‐infrared method is a fast simple method.

Pecularities of Gas Analysis in Al and Mg Powders

Abstract A new inert gas fusion method has been developed for determining oxygen and nitrogen in Al and Mg powders. The approach, the methods and some results are discussed. Dissociation of AlSi10Mg powder, 99.9 % Mg powder, Mg alloy powder and MgO p.a. are presented.

Measuring the effects of boron mass addition to V–Fe hydrogen storage alloys on their hydrogen absorbing–desorbing characteristics and loss of boron by hydrogenation by employing new analysis methods; hybrid of Sieverts' method, inert gas fusion method, and gravimetric method

(V0.85Fe0.15)100−xBx alloys (x = 0.5–15 atomic %) were synthesized by arc melting. 5 atomic % addition of boron to alloys markedly increased the hydrogen absorbing reaction rate to 50 times. However, the maximum hydrogen absorbing capacity decreased with the increasing boron addition. Even when it is very difficult to measure the exact amount of desorbed hydrogen by Sieverts' method, a new analysis method “iGFS hybrid method” which combines the inert gas fusion method with the Sieverts' method can estimate approximate amount of usable hydrogen HH/Musable rapidly. With this method, by only 0.5% addition of boron, HH/Musable increased significantly. The nature of hydrogen-alloy system was considered to change from “Compound type” to “Electron flow type” by only 0.5% addition of boron. We have designed a new analysis method “iGFG hybrid method” which combines the inert gas fusion method with the gravimetric method. With this iGFG method, the tendency of increasing boron evaporation by hydrogenation with the increasing boron addition may be observed, although quantitativity is not enough.

Deoxidation Limits of Titanium Alloys during Pressure Electro Slag Remelting

This paper focuses on deoxidation of titanium alloys produced by aluminothermic reduction (ATR) and subsequent homogenizing and alloying by vacuum induction melting (VIM). The main goal of the performed research work is to outline the deoxidation limit during pressure electro slag remelting (PESR) of the described material.To obtain electrodes for deoxidation, a Ti-24Al-16V masteralloy was produced by ATR and afterwards melted in a 0.5 litre calcium- zirconate (lab scale) or 14 litres high purity calcia (pilot scale) crucibles with continuous addition of Ti-sponge after reaching liquid state in order to obtain a final Ti-6Al-4V alloy. During melting, in both cases evaporation of calcium was noticed. The cast ingots were analysed for oxygen using inert gas fusion method, matrix and alloying elements were analysed by XRF.Results show oxygen levels between 0.5 and 0.95 wt.-% for the ingots which were melted in calcium-zirconate crucibles and approx. 1 - 1.2 wt.-% for the material produced by utilization of calcia crucibles. The subsequent deoxidation was carried out in lab and pilot scale electroslag remelting furnaces using a commercially pure calcium fluoride slag and metallic calcium as deoxidation agent. It could be shown, that deoxidation of the highly contaminated material is possible applying this method to a certain limit. Pilot scale trials showed a reduction of oxygen contents by 1500 - 3500 ppm. Oxygen levels in lab scale trials showed weaker deoxidation effects.In order to describe the achieved deoxidation effects in a quantitative way, the analyzed oxygen contents of the obtained ingots are compared with calculated data resulting from a mathematical kinetic model. The modelled datasets are in good agreement with experimental oxygen values.

Determination of free nitrogen in carbon steels by inert gas fusion method

The possibility to use hot extraction (thermal extraction in a carrier-gas flow) for fractional analysis of nitrogen in carbon steels is shown for cord and reinforcing-bar steels. A rapid procedure is developed for an analysis of free nitrogen in carbon steels. The validity of the analytical procedure is confirmed by high-temperature hydrogen extraction. The data obtained by the two methods correlate well with each other. A sample preparation procedure is developed for the determination of the content of dissolved nitrogen.

Y and Er minor addition effect on glass forming ability of a Ni–Nb–Zr alloy

Since the discovering of amorphous alloys in 1960, the actual causes of why some alloys can be easily formed into glasses while others cannot, are not clearly known, thus there is no universal theory to predict the glass forming ability in metallic systems. It is well known that the minor amount addition of proper rare-earth elements can greatly enhance the glass forming ability of some glass-forming alloys. In the present study, a selection criterion was successfully used to predict the glass forming ability improvement of Ni67.3Nb28.4Zr4.3 alloy with minor additions of Y or Er. The actual glass forming ability of the base alloy and rare-earth doped alloys were evaluated by the thermal parameter γm and the results agree very well with the tendency predicted by the calculation. The amorphous nature of alloys was mainly analyzed by X-ray diffraction and differential scanning calorimetry. This work also presents a brief and complementary consideration about oxygen contamination quantified by the inert gas fusion method.

Removal of gaseous impurities from terbium by hydrogen plasma arc melting

Terbium metal was melted by DC arc plasma using pure Ar and Ar + H2 mixture, respectively. The temperature distribution and the fluid flow during the melting process were simulated. Oxygen and nitrogen concentrations were examined by the inert gas fusion method. Experimental results show that the gaseous concentrations can be reduced more efficiently by hydrogen plasma arc melting (HPAM). Activated hydrogen atoms dissociated in high temperature plasma-arc probably take part in the refining reactions. The detailed behaviors of oxygen, nitrogen and hydrogen atoms are discussed systematically in this study.

Determination of oxygen in oxides with high dissociation pressure by inert gas fusion method

A procedure for determination of oxygen in oxides with high pressure of dissociation (NiO, CuO, CoO, Fe2O3, SnO2), including volatile (MoO3, WO3), by pulsed reductive fusion (evaporation) in carrier-gas flow at 2500 K in double graphite capsules (with Ni-Sn bath or graphite powder) on an apparatus with simultaneous IR detection of CO and CO2 is described. The validity of the protocol and its metrological characteristics were evaluated in a series of calibration experiments with a set of pure stoichiometric oxides, including a NiO certified reference material with certified oxygen content. The expanded uncertainty of analysis for the developed procedure was 0.1 wt %. The working range was 2–15 mg of oxygen.

Accuracy of a selection criterion for glass forming ability in the Ni–Nb–Zr system

Several theories have been developed and applied in metallic systems in order to find the best stoichiometries with high glass forming ability; however there is no universal theory to predict the glass forming ability in metallic systems. Recently a selection criterion was applied in the Zr–Ni–Cu system and it was found some correlation between experimental and theoretical data. This criterion correlates critical cooling rate for glass formation with topological instability of stable crystalline structures; average work function difference and average electron density difference among the constituent elements of the alloy. In the present work, this criterion was applied in the Ni–Nb–Zr system. It was investigated the influence of factors not considered in the calculation and on the accuracy of the criterion, such as unknown intermetallic compounds and oxygen contamination. Bulk amorphous specimens were produced by injection casting. The amorphous nature was analyzed by X-ray diffraction and differential scanning calorimetry; oxygen contamination was quantified by the inert gas fusion method.

Comparison of Oxidation and Microstructure of Warm-Sprayed and Cold-Sprayed Titanium Coatings

Thick titanium coatings were prepared by the warm spraying (WS) and cold spraying (CS) processes to investigate the oxidation and microstructure of the coating layers. Prior to the coating formations, the temperature and velocity of in-flight titanium powder particles were numerically calculated. Significant oxidation occurred in the WS process using higher gas temperature conditions with low nitrogen flow rate, which is mixed to the flame jet of a high velocity oxy-fuel (HVOF) spray gun in order to control the temperature of the propellant gas. Oxidation, however, decreased strikingly as the nitrogen flow rate increased. In the CS process using nitrogen or helium as a propellant gas, little oxidation was observed. Even when scanning electron microscopy or an x-ray diffraction method did not detect oxides in the coating layers produced by WS using a high nitrogen flow rate or by CS using helium, the inert gas fusion method revealed minor increases of oxygen content from 0.01 to 0.2 wt.%. Most of the cross-sections of the coating layers prepared by conventional mechanical polishing looked dense. However, the cross-sections prepared by an ion-milling method revealed the actual microstructures containing small pores and unbounded interfaces between deposited particles.

Determination of Oxygen Content in Magnesium and Its Alloys by Inert Gas Fusion-Infrared Absorptiometry

A method for the determination of the oxygen content in magnesium and magnesium alloys has been developed. Inert gas fusion-infrared absorptiometry was modified by introducing a multistep heating process; a sample containing oxygen is fused with tin to form an eutectic mixture at 900°C in a graphite crucible, followed by a subsequent gradual temperature increase of up to 2000°C, which enables the evaporation of magnesium from the mixture, and subsequent solidification at the rim of the crucible. Residual tin including magnesium oxide remained at the bottom of the crucible. The oxygen in the tin is measured by a conventional inert gas fusion (IGF) method. From a comparison with the results of charged particle activation analysis, the IGF method is considered to be an attractive candidate for measuring the oxygen content in Mg and its alloys.

A critical evaluation of the mode of incorporation of nitrogen in doped anatase photocatalysts

A range of sol-gel synthesis conditions were used to prepare high surface area N-doped TiO(2) in the anatase phase. The N dopant was derived either from NH(3) in solution or from NH(3) gas bubbled through solution. Bulk N doping levels were determined by an inert gas fusion method and were compared with surface N doping levels determined by X-ray photoelectron spectroscopy. Comparison was also made with the concentration of paramagnetic species measured by electron spin resonance spectroscopy. It was found that both surface and bulk doping levels were typically around 3 orders of magnitude higher than the concentration of paramagnetic N-containing species. All N-doped samples showed higher visible region (lambda > 395 nm) photocatalytic activity than undoped anatase itself. It is argued that catalytic activity is associated with the presence of nitrogen bound to lattice oxygen to give (NO)'O which can be photoexcited to give (NO)(O)(X).

Comparison of oxidation behavior of Ni–20Cr alloy and Ni-base self-fluxing alloy during air plasma spraying

Oxidation behavior of Ni–20Cr alloy and Ni-base self-fluxing (NiCrSiBC) alloy in atmospheric plasma spraying was studied experimentally. The in-flight particles were collected by quenching into liquid nitrogen. The oxygen contents in the collected particles and the coatings deposited on a substrate were analyzed by the inert gas fusion method. The oxide distribution, morphology and phase composition were analyzed using SEM, EDX, XRD, and AES. The results clearly show that the oxygen content in the NiCrSiBC coating was remarkably lower than that in the Ni20Cr coating by a factor of over 10. The formation of Cr 2O 3 and its vaporization primarily occurred during the flight of Ni20Cr particles, which dominated the oxidation in the coating. In contrast, little oxygen pickup occurred during flight for the NiCrSiBC alloy particles and a thin surface layer of 5 nm with rich in oxygen was found on the surface of NiCrSiBC splats. The mechanism of protecting NiCrSiBC alloy particles from oxidation is preferential oxidation of C, Si and B and simultaneous vaporization of the formed oxides.

Effect of nitridation on the properties of Na–Zn–P–O glasses

Phosphate glasses generally have a low melting temperature, a low glass transition temperature (Tg) and a high thermal expansion coefficient (α) [1–6]. These characteristics make them potential candidates for low temperature applications, such as the molding of optical elements [7] and sealing to high expansion metals [8]. However, the applications of phosphate glasses are greatly limited in practice by their poor chemical durability [6, 9]. It has been shown that the chemical durability of phosphate glasses could be significantly improved by nitridation and/or addition of appropriate additives, due to the increase of crosslink density and bonding strength in the glass network [9–18]. The effect of nitridation on the glass properties results in the two-coordinated oxygen atom being replaced by the three-coordinated nitrogen atom [19–22]. Either doping the melt with metal nitrides or remelting the glass in an ammonia atmosphere can lead to the incorporation of nitrogen atoms into the glass network [23–25]. Higher nitrogen contents can be obtained by the remelting method than by doping with metal nitrides [10, 24]. It has been shown that the nitrogen content of nitrided glasses would increase with increased remelting temperature and remelting time, but this may make melt volatilization more likely [10–12]. The purpose of this work is to improve the chemical durability of sodium-zinc phosphate (Na Zn P O) glasses by remelting the base glasses at a lower temperature and a shorter holding time under an ammonia (NH3) atmosphere. A base glass with composition 50P2O5–20Na2O– 30ZnO (mol%) was investigated in this study. The base glasses were prepared from mixtures of reagent grade sodium dihydrogen phosphate (NaH2PO4), zinc oxide (ZnO), and ammonium dihydrogen phosphate (NH4H2PO4). Well-mixed powders were melted in an alumina crucible in air at 850 ◦C for 1 h. The melts were quenched and crushed to frits. Then the crushed base glasses were nitrided in alumina boat crucibles under a flowing anhydrous ammonia atmosphere at 600 ◦C for different durations, from 0.5–5 h. The ammonia flow rate was kept at 300 cm3/min. After selected periods of time, the glass samples were removed and annealed in a preheated furnace under an air atmosphere. Then the oxynitride glass samples were cooled overnight to room temperature. Density measurements were carried out at room temperature, using the Archimedes method with deionized water as the immersion fluid. A micro-Vickers tester was used to measure the hardness with a 300 g load on polished glass samples. Glass powders were used for the differential thermal analysis (DTA) at a heating rate of 10 ◦C/min to determine the glass transition temperature (Tg). The relative chemical durability was estimated by measuring the dissolution rate of the polished glasses, which were immersed in deionized water for 24 h at 30 ◦C. The nitrogen content in the glasses was analyzed by an inert-gas fusion method, using an oxygen-nitrogen analyzer. X-ray photoelectron spectroscopy (XPS) spectra of N 1s core levels were recorded by a V. G. Scientific EscaLab 210 XPS spectrometer. The X-ray source was Mg Kα (hν = 1253.6 eV). The nitrogen contents of the nitrided glasses with various remelting times are shown in Fig. 1. The nitrogen content of the glasses increases with increasing remelting time, reaching a maximum value of 1.81wt% (2.9 at.%) for a remelting time of 5 h. The dissolution rate and concentration of nitrogen in the glass network are affected by glass composition and the remelting conditions. It was suggested that higher temperatures significantly accelerate nitrogen dissolution [11, 12, 26]. Alkali phosphorus oxynitride (Na P O N and Li P O N) and sodium alkalineearth metaphosphorus oxynitride glasses have been studied [10, 25, 26]. Lithium phosphorus oxynitride glasses that were prepared at 700 ◦C for 48 h had a maximum nitrogen content of 9.2 wt%, whereas those glasses that were prepared at 800 ◦C had a value of 12.6 wt% [12]. The nitrogen solubility in sodium alkaline-earth metaphosphorus oxynitride glasses decreased with increasing concentration of alkaline-earth oxides [26]. It was suggested that the divalent cations

Quantitative Analysis of Trace Bulk Oxygen in Silicon Wafers Using an Inert Gas Fusion Method

This paper describes a method for removing oxide film from the surface of silicon wafers using an inert gas fusion impulse furnace and precise determination of bulk oxygen within the wafer. A silicon wafer was cut to about 0.35 g (6 x 13 x 2 mm) and dropped into a graphite crucible. The sample was then heated for 40 s at 1300 degrees C. The wafer's oxide film was reduced by carbon and removed as carbon monoxide. The treated silicon sample was taken out of the graphite crucible and maintained again with the holder of the oxygen analyzer. The graphite crucible was then heated to 2100 degrees C. The treated silicon sample was dropped into the heated graphite crucible and the trace bulk oxygen in the wafer was measured using the inert gas fusion infrared absorption method. The relative standard deviations of the oxygen in silicon wafer samples with the removed surface oxide film were determined to be 0.8% for 9.8 x 10(17) atoms/cm3, and 2.7% for 13.0 x 10(17) atoms/cm3.

Simultaneous determination of nitrogen and oxygen in uranium nitride by an inert gas fusion method.

Simultaneous determination of nitrogen and oxygen in uranium nitride by an inert gas fusion method.