Hafnium Oxide in Tungsten Filaments

Liempt, J. A. M. van

doi:10.1038/115194b0

Cited by 10 publications

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“…Grain growth inhibitors can be added to W to pin the grain boundary motion and slow down grain growth. They are typically second-phase particles that are thermally stable in W matrix, such as Al 2 O 3 , [144,145,162] ZrO 2 , [48,163] HfO 2 , [117,164] rare earth oxide such as Y 2 O 3 , [47,71,75,133,135,142,143,147,149,156,158,[165][166][167] La 2 O 3 , [50,155,[168][169][170] CeO 2 , [146] and carbides such as TiC, [171][172][173][174][175][176] ZrC, [177][178][179][180][181] and HfC. [182,183] Figure 6c summarizes the grain size and density of several oxide dispersion strengthened (ODS) W from literature reports.…”

Section: Tungstenmentioning

confidence: 99%

Powder Metallurgy Route to Ultrafine‐Grained Refractory Metals

Zhang

et al. 2023

Advanced Materials

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Ultrafine‐grained (UFG) refractory metals are promising materials for applications in aerospace, microelectronics, nuclear energy, and many others under extreme environments. Powder metallurgy (PM) allows to produce such materials with well‐controlled chemistry and microstructure at multiple length scales and near‐net shape manufacturing. However, sintering refractory metals to full density while maintaining a fine microstructure is still challenging due to the high sintering temperature and the difficulty to separate the kinetics of densification versus grain growth. Here an overview of the sintering issues, microstructural design rules, and PM practices towards UFG and nanocrystalline refractory metals are sought to be provided. The previous efforts shall be reviewed to address the processing challenges, including the use of fine/nanopowders, second‐phase grain growth inhibitors, and field‐assisted sintering techniques. Recently, pressureless two‐step sintering has been successfully demonstrated in producing dense UFG refractory metals down to ≈300 nm average grain size with a uniform microstructure and this technological breakthrough shall be reviewed. PM progresses in specific materials systems shall be next reviewed, including elementary metals (W and Mo), refractory alloys (W‐Re), refractory high‐entropy alloys, and their composites. Last, future developments and the endeavor towards UFG and nanocrystalline refractory metals with exceptionally uniform microstructure and improved properties are outlined.

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Section: Tungstenmentioning

confidence: 99%

Powder Metallurgy Route to Ultrafine‐Grained Refractory Metals

Zhang

et al. 2023

Advanced Materials

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“…At temperatures higher than the transition temperature the reaction product is metallic tungsten (or a mixture of W and NaxWO3). Van Liempt (21) has proposed that the tungsten originates from the decomposition of sodium tungsten bronze according to the reaction The first product of electrolysis is the sodium tungsten bronze, irrespective of the melt temperature. When the temperature is higher than the transition temperature the bronze decomposition, (reaction [3]) gives rise to a metallic tungsten deposit.…”

Section: Eitect Of Temperature On Composition Of Deposit--atmentioning

confidence: 99%

Electrochemical Deposition of Sodium Tungsten Bronzes

Randin

1973

J. Electrochem. Soc.

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The electrochemical deposition of sodium tungsten bronzes (NaxWO3) from Na2V~O4/V~rO3 melts has been studied between 700 ~ and 900~The relation between the x-value in NaxWO3 and the concentration of WO~ in the melt is linear between 2 and 10 mole/liter WO~. Extrapolation of the linear section gives x = 1.0 at zero concentration of WO~. The current efficiency of the bronze deposition depends on both the applied current and the melt temperature. This dependence is attributed to the occurrence of simultaneous chemical dissolution of the bronze. A transition temperature has been found below which NaxWO3 is deposited, and above which W (or W + NaxWO3) is obtained. The nature of the deposit is a function of the melt composition and temperature. The slope of the (i),=const. vs. T -1 plot shows no break at, or near, the transition temperature, indicating that the rate-determining step for the deposition of NaxWO3 is the same as that for the deposition of W. The tungsten formation occurs most likely by decomposition of the previously deposited bronze. The content of platinum in a platinum-containing bronze is favored by a high temperature. The amount of platinum codeposited in the bronze is small compared to the amount of platinum dissolved from the anode. A relatively high concentration of platinum in the melt inhibits the bronze deposition. A nonelectrochemical reaction is believed to be responsible for the codeposition of platinum.The sodium tungsten bronzes are nonstoichiometric compounds of the general formula NaxWO3, where 0 < x --~ 1. They are chemically inert and have semimetallic properties, in particular, metallic luster and good electrical conductivity. Their properties have been reviewed recently (1-3).Two methods have been extensively used for the preparation of these bronzes. The first method involves a solid-state reaction between a mixture of fine powders of sodium tungstate, tungsten trioxide, and metallic tungsten, the latter acting as a reducing agent, at a temperature between 500 ~ and 1000~ in a nonoxidizing atmosphere. This reaction may be written asThe bronzes produced by this technique are in the form of fine powders (4, 5).The second method involves the electrolysis of a molten mixture of sodium tungstate and tungsten trioxide; it is essential when large single crystals are required. Crystal growth occurs at the cathode and oxygen evolution takes place at the anode, according to the over-all reactionThe growth of tungsten bronzes by fused salt electrolysis has been used by a number of investigators [see, for example (6-11)], but virtually no details about the actual growth method were reported until very recently. Banks, Fleischmann, and MeRes (12) performed polarographic experiments which revealed a polymeric character of the WO8 species reduced at the cathode for a melt concentration between 10 and 60 m/o (mole per cent) WO3 and a temperature of 750~ This work confirmed an earlier Raman spectroscopic investigation in which the formation of polyions in a Na~WO4/WO3 melt at 710~ was suggested (13)...

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“…Hafnium metal has important applications in gas and electric lights manufacturing, radiation control in nuclear reactors, refining oxygen and nitrogen, and in the durability improvement of refractory metals such as tungsten and tantalum. In regard to the environmental impacts of Hf, it is stated that its dust increases the risk of fire and explosion [27][28][29]. Until now, hafnium extraction has been performed in several ways such as liquid-liquid extraction [30], hydrogen plasma arc melting [31], resins [32,33] and hollow fiber renewal liquid membrane technique [24].…”

Section: Introductionmentioning

confidence: 99%

Investigation of experimental results and D-optimal design of hafnium ion extraction from aqueous system using emulsion liquid membrane technique

2020

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Hafnium metal is used in a wide range of industries such as microprocessor manufacturing, nuclear reactors and special alloys due to its physical, chemical and radiation properties. Emulsion liquid membrane (ELM) is an effective and efficient alternative for heavy metal separation compared to conventional methods due to high selectivity, energy-saving, high mass transfer and low operating capital. In this study, Cyanex 572 as a carrier, Span 85 as a surfactant, hydrochloric acid as an internal phase and kerosene as a diluent were used. In the first part of the study, the stability of the emulsions was investigated. The most stable emulsions were obtained by adding PIB polymer (3% w/v), Span 85 surfactant (3% w/v) and stirring for 15 min. In the second part, the separation of hafnium metal ions from aqueous solutions was investigated using ELM technique. The highest separation was obtained at 4% (v/v) as carrier concentration, 4% (w/v) as surfactant concentration, the membrane-to-feed volume ratio of 20/100 and W/O/W emulsion stirring rate and time equal to 400 rpm and 5 min, respectively. Moreover, to optimize the factors influencing the tests, the design of experiment (DOE) was performed using D-optimal method via Design Expert 10 software. Based on DOE results, the maximum extraction (> 99%) was achieved when the carrier concentration, the surfactant concentration, W/O/W emulsion stirring time, W/O/W emulsion stirring rate and emulsion volume/feed phase ratio were 4.49% v/v, 3.90% w/v, 11.49 min, 310.54 rpm and 2:1, respectively.

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Hafnium Oxide in Tungsten Filaments

Cited by 10 publications

References 0 publications

Powder Metallurgy Route to Ultrafine‐Grained Refractory Metals

Powder Metallurgy Route to Ultrafine‐Grained Refractory Metals

Electrochemical Deposition of Sodium Tungsten Bronzes

Investigation of experimental results and D-optimal design of hafnium ion extraction from aqueous system using emulsion liquid membrane technique

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