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Glasses
Published in Marvin J. Weber, and TECHNOLOGY, 2020
HMF glasses are typically prepared by melting batches of fluoride and/or oxide materials in platinum, gold, or vitreous carbon crucibles. When oxides are used ammonium bifluoride (NH4F.HF) is frequently employed as an in situ fluorinating agent. Melting is usually carried out under inert (N2, Ar, He etc.) and/or reactive (NF3, SF6, Cl2, etc.) atmospheres, the function of reactive atmosphere processing (RAP) being to facilitate the removal of residual oxide and hydride impurities and/or to prevent the reduction of some ionic species in the melt (e.g., Zr4+ to Zr3+).161 The optimum melting schedules and temperatures (typically 800–1000°C) are composition and batch size dependent. Significant compositional drift can occur by the preferential volatilization of constituents (e.g., ZrF4, InF3, and GaF3) if the melts are overheated.162
Process Applications and Challenges in Mineral Beneficiation and Recovery of Niobium from Ore Deposits – A Review
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Nnaemeka Stanislaus Nzeh, Samson Adeosun, Abimbola Patricia Popoola, Abraham Adeleke, Daniel Okanigbe
Since then, various studies have improved on this method and different new methods altogether have also been investigated and developed. This involved the digestion of the Nb and Ta minerals and effecting selective/stepwise separation of Nb and Ta from the same reaction complexes, putting into consideration; the reagent and energy consumption (Ribagnac et al. 2017), the recovery, cost, economic, environmental and waste management issues. Among the processes that have been utilized by researchers to achieve simultaneous decomposition of Nb-Ta minerals is the alkali fusion process. Others include alkali fusion-acid leaching, chlorination, ammonium fluoride (NH4F) or ammonium bifluoride (NH4HF2) fusion, direct sulfuric (H2SO4) acid dissolution or in a combination with hydrofluoric (HF) acid, alkaline solution dissolution (El-hussaini and El-hakam Mahdy 2002B; Gupta and Suri 1994; Wang et al. 2009; Yang et al. 2012a; Zhou, Zheng and Zhang 2005). More recently, the most successful used methods in processing and recovering Nb and Ta from their primary sources employs the initial halogenation and decomposition/dissolution in HF acid or a combination of mineral acids with HF acid or fluoride media like fluoride salts that forms oxy-fluorides complexes (El-hussaini and El-hakam Mahdy 2002A; Nete, Purcell and Nel 2016a, 2016b; Sanchez-Segado et al. 2015; Wang et al. 2010; Yang et al. 2013b, 2012a; Zhou, Zheng and Zhang 2005).
Removal and repair techniques for thermal barrier coatings: a review
Published in Transactions of the IMF, 2020
X. Yang, Jian Zhang, Z. Lu, H.-Y. Park, Y.-G. Jung, H. Park, D. D. Koo, R. Sinatra, Jing Zhang
Aqueous stripping with acid fluoride salt is a method8 used to remove the ceramic layer, such as yttria-stabilised zirconia (YSZ), from a substrate without damaging the bond coat. The ceramic layer is removed by exposure to the aqueous stripping solution containing an acid fluoride salt, such as ammonium bifluoride (NH4HF2) or sodium bifluoride (NaHF2), and a corrosion inhibitor. The acid fluoride can convert zirconia to zirconium, through a process for treating a zirconia-based material which comprises reacting the zirconia-based material with ammonium bifluoride, NH4F·HF. An ammonium fluorozirconic compound is produced.9 Also, the corrosion inhibitor could protect the metal substrate. The operating temperature is about 60–75°C, and the stripping time is about 4–5 h. This process could also be combined with ultrasonic treatment. The ultrasonic treatment can be continued until the TBC is completely removed or at least sufficiently loosened so that it can be removed by brushing or pressure spray rinsing, which could shorten the process time to 2–5 h.
Characterization of natural sand proppant used in hydraulic fracturing fluids
Published in Particulate Science and Technology, 2019
Abderraouf Kamel, Zineb Salem, Rachida Chemini, Mohamed Khodja, Khedidja Allia
The acid solubility test is used to determine the suitability of a proppant for use in applications where the proppant can come into contact with acids. A mixture of hydrofluoric acid and hydrochloric acid is used to estimate the effectiveness of mineral separation techniques in removing the softer and less desirable cementatious minerals from the quartz sand. The mixture acid solution of ammonium bifluoride (NH4F2), hydrochloric acid (HCl), and distilled water is added to (5 g/100 mL) dried proppant and is placed in a water bath during 30 min. After filtration, solubility (S) is expressed in percent (equation 2): where ms is the sample mass, mf the mass of filter, and mfs the dried mass of filter, expressed in grams.