Amount Of Tungsten Research Articles

Adsorption of tungsten ion with a novel Fe-Mg type hydrotalcite prepared at different Mg2+/Fe3+ ratios

A novel Fe-Mg type hydrotalcite at different Mg2+/Fe3+ ratio (Fe-HT3.0 and Fe-HT5.0) were prepared, and their properties were investigated by scanning electron microscopy, X-ray diffraction analysis, electron probe microanalysis, specific surface area, and binding energy studies. In addition, the adsorption capability of tungsten onto Fe-HT3.0 and Fe-HT5.0 was evaluated. The amount of tungsten adsorbed onto Fe-HT3.0 and Fe-HT5.0 increased with increasing temperatures. The results of the adsorption isotherm studies suggested that tungsten adsorption can be well described by both the Freundlich (R2: 0.895–0.998) and Langmuir (R2: 0.890–0.998) equations. The tungsten adsorbed onto the adsorbent surface was confirmed by electron probe microanalysis and binding energy. The obtained data on thermodynamic parameters showed a decrease in ΔG with the increase in temperature, which indicated that tungsten adsorption was spontaneous. The adsorption of tungsten onto Fe-HT3.0 and Fe-HT5.0 reached equilibrium within 3 and 10h, respectively, and the adsorption kinetic data fit the pseudo-second-order kinetic model better than the pseudo-first-order kinetic model. The optimal pH condition for the adsorption of tungsten onto Fe-HT3.0 and Fe-HT5.0 is approximately 2.0. The results of this study indicate that the adsorption mechanism of tungsten onto Fe-HT3.0 and Fe-HT5.0 involves ion exchange, electrostatic attraction, and surface inner-sphere complex formation between tungsten ion and hydroxide ion. Finally, tungsten adsorbed onto the Fe-HT3.0 and Fe-HT5.0 surfaces was desorbed by sodium hydroxide solution at different concentrations. Collectively, these results suggest that Fe-HT3.0 and Fe-HT5.0 can be useful for the adsorption and recovery of tungsten from aqueous solutions.

Mechanical and magnetic properties of alloys near the concentration range of the existence of Co3(Al,W) intermetallic compound

An experimental study of the mechanical and magnetic properties of Co–8 at % Al–X at % W (where Х = 4.6; 6.8; 8.5; 10; 12) polycrystalline alloys has been carried out depending on the tungsten content. It has been shown that an increase in the tungsten content induces the following changes: Young’s modulus changes from 240 to 259 GPa and the microhardness HV changes from 290 to 413 MPa. The Curie temperature of the intermetallic γ' phase (L12) grows from 1025 to 1049 K, and the saturation magnetization of the alloys decreases. The value of the coercive force also increases, from 1 to 500 Oe. The calculations of the specific heat of the γ' (L12)–γ (dcc) phase transition has shown that the highest amount of heat (304 J/g) is absorbed upon the phase transition in the sample containing the largest amount of tungsten (12.6 at %). The results obtained indicate the diffusion character of the transition, the rate of which is controlled by the diffusion of the slowest component of the alloy (in this case, tungsten). It has been found that the solvus temperature of the γ' phase increases from 1009 to 1044°С with an increase in the tungsten content from 4.6 to 12.6 at %.

W-doped TiO2 mesoporous electron transport layer for efficient hole transport material free perovskite solar cells employing carbon counter electrodes

Abstract Doping of TiO2 by metal elements for the scaffold layer of the perovskite solar cells has been proved to be one of the effective methods to improve the power conversion efficiency. In the present work, we report the impact of doping of TiO2 nanoparticles with different amounts of tungsten (W) on the photovoltaic properties of hole transport material free perovskite solar cells (PSCs) that employ carbon counter electrode. Light doping with W (less than 1000 ppm) improves the power conversion efficiencies (PCEs) of solar cells by promoting the electron conductivity in the TiO2 layer which facilitates electron transfer and collection. With the incorporation of W, average efficiency of PSCs is increased from 9.1% for the un-doped samples to 10.53% for the 1000 ppm W-doped samples, mainly originates from the increase of short circuit current density and fill factor. Our champion cell exhibits an impressive PCE of 12.06% when using the 1000 ppm W-doped TiO2 films.

Structural incorporation of W6+into hematite and goethite: A combined study of natural and synthetic iron oxides developed from precursor ferrihydrite and the preservation of ancient fluid compositions in hematite

Hematite (a-Fe2O3) and goethite (a-FeOOH) can incorporate considerable amounts of tungsten (W). Although W concentrations up to several wt% in hematite and goethite have been reported in the literature, none of the proposed models for a structural incorporation has been generally accepted yet. Here, the first combination of X-ray absorption fine structure (XAFS) measurements with X-ray diffraction (XRD), Raman spectroscopy (RS), electron microprobe (EMPA) and total reflection X-ray fluorescence (TXRF) provides a general relation between W content and its structural incorporation into hematite and goethite.

A Simple Method for the Electrodeposition of WO3 in TiO2 Nanotubes: Influence of the Amount of Tungsten on Photoelectrocatalytic Activity

Although TiO2 is used in a wide range of photocatalytic applications, its activity can be improved considerably by coupling with a metal oxide, such as WO3, in a bicomponent systems. However, the amount of WO3 deposited onto TiO2 is of crucial importance because it may influence the optical and electrochemical properties and, consequently, the photocatalytic activity. In the present study, a series of modified electrodes were prepared by electrochemical deposition of different amounts of WO3 onto TiO2 nanotubes (TiO2-NTs). Energy dispersive X-ray analysis revealed that increasing amounts of W were deposited with increased deposition times between 5 and 60 min, and that electrodes EW5, EW10, EW15, EW30, EW45, and EW60 contained 0.74, 1.27, 1.60, 4.85, 10.10, and 13.30 at.% W, respectively. X-ray diffraction patterns confirmed the presence of the WO3 crystalline phase and the TiO2 anatase. Diffuse reflectance spectra of electrodes EW5, EW10, and EW15 exhibited the most intense absorbances, and their energy band-gap values were in the region of 2.90 eV, which is comparable with the value for TiO2-WO3 bicomponent. The photoactivities of electrodes EW5 and EW10 containing low amounts of W (~1 %) exhibited photocurrents that were, respectively, 13 and 25 % higher than that of the unmodified TiO2-NTs electrode. Electrodes containing larger amounts of W showed correspondingly reduced photocurrents. The application of electrodes E0 and EW10 on the photoelectrocatalytic oxidation of Bisphenol-A (BPA) revealed excellent removal rate which BPA was not detected after 30 min of reaction. The electrode EW10 achieved ~64 % of total organic carbon (TOC) in the end of degradation, more effective compared to the electrode E0 (58 %). These findings demonstrate that photoelectrocatalytic efficiency is strictly dependent on morphology and amount of WO3. Optimal deposition of WO3 favors the formation of WO3-TiO2 heterojunctions, thereby improving the performance of the semiconductor.

Preparation, Characterization and Photocatalytic Activity of Titania Nanotube Arrays Decorated with Tungsten Trioxide

Titania nanotube arrays decorated with WO 3 (WTN) were fabricated by a chemical bath deposition (CBD) technique in combination with a pyrolysis process. The products were uniform and the amount of tungsten can be easily adjusted by the deposition time. The resultant hybrid nanotubes arrays were characterized by SEM, EDX and XRD. Results show that titania nanotubes with an internal diameter of the tubes 90∼120 nm, an external diameter 120∼160 nm, wall thickness in the range of 30∼60 nm and a length of 39 μm are grown on titanium substrate by anodizing. The tungsten trioxide is i decorated on the titania nanotubes, which enhances the photocatalytic activity of the WTN, as indicated by the efficient removal of C.I. Sulphur Red 14. The resultant composite films show better photocatalytic activity than the non-decorated nanotube arrays (TN) under visible light illumination

The study of thermochromic and thermo-optical properties of sol–gel V1−x−y WxSiyO2 films by response surface method

Vanadium dioxide (VO2) is an attractive thermochromic material for smart windows attributed to its reversible phase transition between semiconductors to metal phase at its phase transition temperature. In this paper, various quantities of tungsten and SiO2 were mixed into VO2 sols to fabricate V1−x−y WxSiyO2 gels. The gels were spin coated on a sodium-free glass slide and subsequently calcined at 500 °C in an atmospheric control furnace under reducing gas flow (H2–Ar, 5%–95%). The comprehensive investigation was conducted on the corresponding thermochromic and thermo-optical characteristics of VO2 composite films by response surface methodology and ANOVA analysis. Results show that the addition of SiO2 has greatly inhibited the agglomeration of particles. Additionally, the thermal induced infrared filtering effect is found to be strongly dependent on the mixing ratios of SiO2/W. However, the optical parameters such as refractive index and extinction coefficient were temperature-dependent and less influenced by the doping contents of SiO2 and W. The phase transition temperature of the doped VO2 films containing both SiO2 and W was dropped to the room temperature (31 °C). Furthermore, the temperature dependent electrical–optical properties of VO2 of the as-prepared films were strongly correlated with the dopant concentrations of W and SiO2.

Arc erosion of full metal plasma facing components at the inner baffle region of ASDEX Upgrade

At the inner baffle of the AUG divertor massive polished inserts of tungsten and P92 steel were installed to measure the erosion by arcing. For tungsten most of the traces are less than 0.4µm deep and a similar amount of tungsten is deposited close to the traces. Few craters up to 4µm resulting in an average erosion rate of 2×1013 at cm−2s−1 are observed. The behaviour for P92 steel is quite different: most of the traces are 4µm deep, up to 80µm were observed. An average erosion rate of 400×1013 at cm−2s−1, i.e. more than a factor of hundred higher compared to tungsten, is found. Therefore, erosion by arcing has to be taken into account to determine the optimal material mix for future fusion devices.

Effect of tungsten loading on the physiochemical properties of nanocatalysts of Ni–Mo–W/carbon nanotubes for the hydrodesulfurization of thiophene

In this paper, trimetallic nanocatalysts of nickel–molybdenum–tungsten have been precipitated on multi walled carbon nanotubes and the effect of tungsten loading on structure and catalytic performance was studied. The prepared catalysts with different amounts of tungsten (0–3–6–9 wt.%) were tested as hydrodesulfurization catalyst in a stirred slurry-tank reactor at atmospheric pressure and 160 °C to eliminate thiophene. The catalyst with 6 wt.% had the highest thiophene removal and butane/butene ratio. Lower or higher loadings led to lower hydrodesulfurization activity and selectivity. To find the explanation, the prepared catalysts were examined by X-ray diffraction, field emission scanning electron microscopy, nitrogen adsorption Brunauer-Emmett-Telleranalysis, Fourier-transform infrared spectroscopy and thermogravimetric analysis. The characterization results indicated that in the catalyst with 6 wt.% tungsten, the smallest particles with average particle size of 31.9 nm and uniform distribution were observed. This catalyst showed the sharpest O–H peak in the Fourier-transform infrared analysis as well. The effect of thiophene concentration on the activity and selectivity of this catalyst was examined and the results showed less activity and lower butane/butene ratio in high thiophene concentrations. The examination of this catalyst after hydrodesulfurization also indicated no sintering and coke deposition.

Enhancement in Rate of Photocatalysis Upon Catalyst Recycling.

Recyclability is an important aspect for heterogeneous photo-catalysts. Ease of recovery and stability of the photo-catalyst in terms of efficiency over the number of cycles are highly desired and in fact it is ideal if the efficiency is constant and it should not decrease marginally with each cycle. Presented here is a seminal observation in which the photocatalytic activity is shown to improve with increasing number of catalytic cycles (it is 1.7 times better after the 1st cycle and 3.1 times better after the 2nd cycle). Specifically, nanorods of pure TiO2 and TiO2 doped with controlled amount of tungsten have been used to degrade two model pollutants: Phenol and Rhodamine B under exclusive visible light illumination. It was found that, in case of 1 mol.% W incorporation, rate of photocatalysis and also the range of visible light absorption of the photocatalyst increased after the photocatalysis as compared to before photocatalysis. This aspect is unique for doped TiO2 and hence provides an intriguing way to mitigate low photoactivity.

Composition and mechanical properties of B-C-W and B-C-Ti thin films prepared by pulse magnetron sputtering

In the present work, coatings in the material systems B-C-W and B-C-Ti have been synthesized by pulse magnetron sputtering, to exploit their potential as coatings for hard, wear resistant applications. These layers offer interesting properties, because of the possible amounts of carbides and borides that can form in the non-equilibrium deposition processes. Especially the amount of tungsten in the layers promises high wear resistance and corrosion protection at elevated temperatures.The B-C-W and B-C-Ti thin films have been deposited by pulsed magnetron co-sputtering in bipolar mode, using a boron carbide (B4C) target and a metal target (W or Ti) with a maximum total power input of 12.9W/cm2. The amount of metal in the layers has been varied by adjusting the sputtering pulse length of the respective target material. The influence of bias voltage on the properties of B-C-W coatings has been investigated and it was found out that bias voltages of −60V … −100V lower the hardness of the coatings.The hardness and the Young's modulus of the layers have been determined by nanoindentation. Whereas the majority of coatings exhibits hardness around 20GPa or lower, maximum hardness of 28GPa and Young's modulus of 420GPa are observed in a certain compositional range, in which coatings also distinguish by good thermal stability. Their composition has been analysed by using optical glow discharge emission spectroscopy (GD-OES) and Rutherford backscattering spectrometry (RBS).

Be/W and W/Be bilayers deposited on Si substrates with hydrogenated Fe-Cr and Fe-Cr-Al interlayers for plasma facing components

Be/W and W/Be bilayers, of interest in regard to the specific behavior of plasma facing components (PFCs) were deposited on Si substrates by thermionic vacuum arc, with Fe, Fe-Cr and Fe-Cr-Al interlayers. The interlayers, with compositions approaching the one of the reduced activation steels used in supporting PFCs, were subsequently annealed in hydrogen atmosphere. The multilayers were characterized with respect to morphologic, structural, diffusional and atomic intermixing aspects via XRD, XRR, X-ray photoemission spectroscopy and Mössbauer spectroscopy. All as-prepared samples present partially amorphous structures. A main α-Fe phase is observed, as well as (superparamagnetic) secondary Fe oxides, metallic Fe with Si, Cr, W and Be neighbors, Be-rich Fe-Be and Fe-Si phases. High amounts of tungsten and tungsten oxides were also evidenced in the Fe layer. The strong atomic intermixing of W and Be layers was indirectly supported by the unusual densities of W and Be layers and 57Fe Mössbauer spectroscopy results.

The New Examples of Tungsten Induced Codeposition Cu-W and Cu-Ni-W Alloys

Electrodeposition of new binary copper-tungsten alloys and ternary tungsten-copper-nickel alloys contradict the commonly assumed fact that tungsten cannot be electrocodeposited from aqueous solutions with other than iron-group (Co, Ni, Fe) metals [i]. This unusual electrodeposition behavior was named ‘induced codeposition’ by Brenner. The process of electrodeposition the new Cu alloys also can be also classified to this phenomenon [ii]. The obtained alloys, besides of their great potential of industrial applications, bring a new look into the induced codeposition phenomenon. It is commonly known that the binary Ni/Fe/Co-W alloys obtained under particular conditions of galvanic process form amorphous/nanocrystalline phases [iii]. This internal organization strongly influences their mechanical and corrosion behavior. Excellent values of the parameters, which are important in the industrial usage, such as hardness and thermal-, wear- and corrosion resistance make them advanced materials with a wide range of possible applications. The W-Ni/Fe/Co alloys can be used as a replacement for hard chrome coatings and as protective layers [iv]. The new obtained materials (Cu-W and Cu-Ni-W) exhibit similar properties, thus they may also find the applications analogous to the previously mentioned Ni/Fe/Co-W alloys. Both materials, Cu-W and Cu-Ni-W, were obtained via direct current electrodeposition from the citrate plating bath. Authors were able to obtain the materials with a wide range of elemental composition ratio. The required parameters to obtain the desired combination of composition and morphology were established and carefully investigated. The deposits were prepared on silver substrate, to avoid contamination of the deposited alloy with the substrate material; however; authors were also able to deposit the new alloys on other substrate materials such as stainless steel, copper, zinc and many others. All depositions were performed at elevated temperature (70 ◦C) in the presence of amorphous structure promoters such as boric acid and phosphoric acid in the bath. The Faradaic Efficiency of the deposition and its correlation with both: bath composition and current density was investigated in details. The process was optimized to obtain the material containing the high amount of tungsten with as low as possible number of surface defects. In comparison to the Ni/Fe/Co-W alloys, the best achieved CuW and CuNiW alloys exhibited less cracks and defects, what was probably caused by a decrease in the internal structure stress. Hardness of the layers was correlated with alloys composition. In the obtained alloys the content of W could reach up to 14 at.%. (Cu-W) or even 28 at.%. (Cu-Ni-W). The preliminary corrosion experiments revealed that the materials hardness and corrosion resistance changes significantly with W content. The internal structure of those materials was also investigated by using TEM microscopy of thin lamellas cut out from the layers and by SEM micrographs of the cross brakes and the cross-cuts. These investigations revealed peculiar and unique internal structure of the Cu-W alloy. Powder XRD and SEM with EDS measurements supported the existence of the nanocrystalline/amorphous tungsten rich phases which were decorated by polycrystalline, mesoscale-size excretions of metallic copper. The presented data enable new possibilities in electrodeposition of tungsten heavy alloys (WHAs). The same time they are significant contribution in investigations of phenomenon of tungsten (and molybdenum) codeposition. This work was financed by Polish NCN Grant 2015/17/N/ST5/03352 [i] Modern trends in tungsten alloys electrodeposition with iron group metals (Review); Tsyntsaru N., Cesiulis H., Donten M., Sort J., Pellicer E., Podlaha-Murphy E.J.; Surface Engineering and Applied Electrochemistry, Volume 48, Issue 6, 2012, Pages 491-520; [ii] Unusual example of induced codeposition of tungsten. Galvanic formation of Cu-W alloy Bacal P., Indyka P., Stojek Z., Donten M.; Electrochemistry Communications Volume 54, May 2015, Pages 28-31 [iii] Formation of nanofibers in thin layers of amorphous W alloys with Ni, Co, and Fe obtained by electrodeposition; Donten M.,Stojek Z. , Cesiulis H.; Journal of the Electrochemical Society, Volume 150, Issue 2, February 2003, Pages C95-C98; [iv] Structural, magnetic, and mechanical properties of electrodeposited cobalt-tungsten alloys: Intrinsic and extrinsic interdependencies; Tsyntsaru N., Cesiulis H. , Pellicer E., Celis J.P., Sort J.; Electrochimica Acta, Volume 104, 2013, Pages 94-103;

Reduction of Nitrogen Oxide by Ammonia over Vanadium Supported on Mixed Tungsten–Titanium-pillared Clays

New pillared clay catalysts, vanadium supported on mixed tungsten–titanium-pillared clays, were prepared with various amounts of tungsten and then characterized and tested as catalysts in the selective catalytic reduction of NO by NH3. It was found that only the mixed WTi-pillared clay that exhibited a uniform distribution of WTi-pillars between the clay layers, then doped with a small amount of vanadium, showed better catalytic performance in the selective catalytic reduction of nitrogen oxide by ammonia.

Hydrogen permeation through porous stainless steel for palladium-based composite porous membranes

Surface topography and hydrogen permeation properties of Porous Stainless Steel (PSS) substrates for thin films deposition of Pd-based hydrogen separation membrane were investigated. Hydrogen permeance through the as received PSS substrates demonstrated a wide range, despite a similar average surface pore size of ~15µm determined by SEM and confocal laser microscopy analyses. The surface pores of the PSS substrates were modified by impregnation of varying amounts of tungsten (W) powder. Maximum hydrogen flux reduction of 28% suggested that W has a limited effect on the hydrogen permeation through the PSS substrate. Therefore, it appears that hydrogen transport through PSS substrates is mainly controlled by the substrate geometrical factor (ετ), that is the ratio of the porosity to tortuosity. In addition, tungsten was shown to inhibit the iron inter-diffusion between the PSS substrate and the deposited Pd60Cu40 film at temperature as high as 800°C. Thus, tungsten layer also serves as an effective inter-diffusion barrier. The variation in the permeance between the nominally similar PSS substrates indicates the importance to independently assess the hydrogen transport characteristics of each of the components in a composite membrane.

Dye-sensitized solar cells based on tungsten trioxide-titanium dioxide nanotube nanocomposite photoanodes

The effect of tungsten trioxide doping on the photovoltaic efficiency of dye-sensitized solar cells (DSSCs) with anodized TiO2 nanotubes was investigated. Tungsten-doped TiO2 nanotubes with different amounts of tungsten were obtained directly by the electrochemical anodizing of titanium in a single-step process using sodium tungstate as the tungsten source. Nanocomposite films features were investigated by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and ultraviolet-visible spectroscopy. The photovoltaic efficiencies of fabricated DSSCs were characterized by a solar cell measurement system via the photocurrent-voltage (I–V) curves. It was found that the photovoltaic efficiency of DSSCs with tungsten-doped TiO2 nanotubes (sample WT2) was improved compared to DSSCs with as-prepared TiO2 nanotubes and WT samples fabricated using other tungsten concentrations. This improvement is ascribed to increased dye loading and photocurrent density.

The X-ray attenuation and the flexural properties of lead-free coated fabrics

In this paper, tungsten, bismuth, tin, and copper powders were used as additives in the fabric coating to obtain lead-free and flexible x-ray shielding material. The X-ray attenuation and the flexural properties of the coated fabrics were investigated considering the medical protection requirements. The results showed that tungsten additives in silicone rubber coating had better attenuation ratios than the samples that contain tungsten–tin, bismuth, and tungsten–copper, at same additive volume ratios. Moreover, the increment of tungsten volume ratios in coating blend resulted in higher shielding performance at same effective thicknesses and the lower silicone rubber amount in coating lead to compose thinner and lighter fabrics for equal protection level. In addition to that, the samples with tungsten–tin, bismuth, and tungsten–copper showed remarkable attenuation properties, and the results were found to be coherent with the theoretical values. The flex resistance and the flexural rigidity of the samples with tungsten content were also investigated. The coated fabrics with different powder loadings and thicknesses showed good resistance against repetitive folding; on the other hand, the results showed that the increment of tungsten amount in the coating resulted in stiffer fabrics.

Electroless Deposition of Cobalt-Tungsten-Boron Films from Glycine Containing Solutions As Barrier Layer Against Cu Diffusion

Electroless cobalt films have been demonstrated to produce high quality barrier and capping layers for Cu. The best barriers so far include, in addition to the cobalt, refractory metals ions (e.g., W, Mo, or Re), and either phosphorus or boron. Electroless cobalt and its alloys can be used in micro- and nano-technologies, e.g. for microelectro-mechanical systems (MEMS), as well as for ultra large-scale integration (ULSI) technology of integrated cicuits. In this work we present novel deposition solutions that is used to form cobalt-tungsten-boron films used morpholine borane as reducing agents. The films of cobalt that cointain small amounts of tungsten and boron were deposited by the electroless process. The cobalt-tungsten-boron coatings were deposited on the copper surface using a solutions containing (mol l-1): CoSO4 - 0.1, NH2CH2COOH (glycine) – 0.2, C4H8ONH·BH3 (morpholine borane) – 0.2, Na2WO4 – (0-0.02), C6H8O7 (citric acid) – 0.175. The bath operated at pH 7 and 60 ºC. The thickness of the compact cobalt-tungsten-boron coatings obtained under optimal operating conditions were ca. 0.5 µm. The morphology and strukture of the cobalt alloys were characterized by means of Field Emission Scanning Electron Microscopy. The composition of the cobalt-tungsten-boron films obtained was determined by means of X-ray Photoelectron Spectroscopy using an ESCALAB MKII spektrometer. To obtain depht profiles, the sample were etched in the preparation chamber by ionized argon at a vacuum of 5·10-4 Pa. The mikrostructure of the coatings changes with the intercorporation of tungsten into the coatings. The particles of cobalt-tungsten-boron films are larger and almost equilateral as compared with the cobalt-boron particles. XPS depth profile investigation does not show any significant diffusion of Cu atoms into cobalt after heat-treatment of the cobalt-tungsten-boron film. This fact confirms that the cobalt-tungsten-boron thin layer, deposited from glycine containing solutions, serves as a perfect diffucion barrier to prevent Cu diffusion. This research was funded by a Grant (No. TEC-06/2015) from the Research Council of Lithuania.

Towards Additive Manufacturing of Tungsten Carbide Using Renewable Resources

We present preliminary experiments leading to novel additive manufacturing of carbides. To this end, we shape and heat treat a biopolymer-metal oxide composite featuring Bingham plastic behavior. Extrusion of such composite at room temperature allows for layer-by-layer fabrication; with the rheology of the composite dictating the scale of fabrication, i.e. thin mixtures for millimetric features, and thicker composites for bigger structures. Upon heat treatment to 900 °C, the biopolymer carbonizes. Further increase in temperature leads to a reaction between this carbon and the metal oxide nanoparticles to form metal carbides1. Such manufacturing process could lead to a more energy-efficient route to complex carbides shapes. Renewable biopolymers replace petroleum-based ones as carbon source; and the temperature needed for carbide formation can be drastically reduced due the colloidal proximity of the reactants. Additive manufacturing of the composite that is precursor to carbides could enable complex shapes, which are challenging or impossible when using powder pressing or machining of bulk carbides. We developed and characterized water-based composites featuring iota-carrageenan (IC) and chitin as mixed with tungsten trioxide (WO3) nanoparticles. The initial target is tungsten carbide (WC). Iota carrageenan powder was mixed with chitin in a weight ratio of 1:4. Thermogravimetric analysis of this mixture yields a 10.85% carbon yield at 900 °C. Thus, WO3 nanoparticles were mixed with this biopolymer powder mixture to achieve a C:WO3molar ratio of 1:8, in accordance to the chemical reaction and providing an excess of carbon. Ultra-pure water was added to the biopolymer-metal oxide nanoparticle mixture and stirred manually to achieve a Bingham plastic composite. The biopolymer composite was loaded in a syringe and manually extruded into 3D spirals shapes of around 10 mm in height. The heat treatment protocol features a ramp of at 5°C/min, nitrogen flow, a dwell of half-hour at 300°C, and a dwell of 3 hours at different temperatures ranging from 750 °C to 1450 °C. Carbonaceous 3D shapes result in all cases. Resultant shapes are of similar geometry to the precursor ones but smaller due to shrinkage. SEM-EDS and XRD analysis were performed on the carbonaceous samples towards characterizing their composition and geometry at different temperatures. The WO3 reduces to different forms of tungsten oxide and finally to tungsten at 900 °C. With further increase of temperature, the reduced tungsten reacts with carbon to form tungsten carbide. It is observed in Figure 1 that tungsten carbide starts to form above 900 °C. Further increase of temperature increases the crystallinity of the tungsten carbide as WC peaks get higher with temperature as seen from the XRD pattern. Figure 2a and 2b show the grain structure before the carbide formation at 750 °C and 900 °C respectively. It can be observed that the grain size increases with temperature. Figure 2c and 2d show that porous carbide was synthesized at 1025 °C and 1150 °C. The carbides synthesized in this process have grain size ranging from tens of nanometers to 2 µm. From elemental analysis using EDS (Table 1), it is observed that the relative amount of tungsten with respect to carbon increases proportional to temperature. This supports the theory of carbonization of the biopolymer as well as the reduction of WO3with the increasing temperature. In EDS analysis, calcium and potassium were also found to be present as the impurities which may come from the water used for composite formation. Ongoing work is 1) investigating the effect of time, heating rate and heating environment on carbide formation and composition; 2) further understanding of shrinkage during heat treatment; and 3) implementing automated fabrication using a fused deposition modeling approach.

Effects of Alloying Elements on the Properties of Ni-Mo-Cr Superalloys with Low Thermal Expansion

The effects of alloying elements including tungsten, molybdenum and cobalt on the thermal expansion and mechanical properties of Ni-Mo-Cr superalloys were investigated. It was founded that cobalt had no influence on the thermal expansion properties of the alloys. The addition of proper amount of tungsten reduced the coefficient of thermal expansion and increased the mechanical properties of alloy both at room temperature and at high temperature. Reducing the amount of molybdenum and increasing the amount of tungsten were helpful to reduce the coefficient of thermal expansion of the alloys at high temperature and improved the performance consistency of the coefficient of thermal expansion from low to high temperature.