{"title":"Synthesis of ultrafine NbB2 powder by rapid carbothermal reduction in a vertical tubular reactor","authors":"Hideaki Maeda, Tomohisa Yoshikawa, Katsuki Kusakabe, Shigeharu Morooka","doi":"10.1016/0925-8388(94)90829-X","DOIUrl":null,"url":null,"abstract":"<div><p>Niobium diboride (NbB<sub>2</sub>) powder was synthesized by carbothermal reduction of Nb<sub>2</sub>O<sub>5</sub>B<sub>2</sub>O<sub>3</sub>C precursor prepared with Nb<sub>2</sub>O<sub>5</sub>, H<sub>3</sub>BO<sub>3</sub> and cornstarch. The reaction was consecutive and Nb<sub>2</sub>O<sub>5</sub> was formed while NbC was consumed. The apparent activation energy of NbB<sub>2</sub> formation for the Nb<sub>2</sub>O<sub>5</sub>B<sub>2</sub>O<sub>3</sub>C system was about 360 kJ mol<sup>−1</sup>, which is in good agreement with that for the NbCB<sub>2</sub>O<sub>3</sub>C system. These results indicate that the rate-determining step of the carbothermal reduction was the formation of NbB<sub>2</sub> from NbCB<sub>2</sub>O<sub>3</sub>C mixture. For continuous production of NbB<sub>2</sub> particles a vertical tubular reactor was used in which the pulverized Nb<sub>2</sub>O<sub>5</sub>B<sub>2</sub>O<sub>3</sub>C precursor particles were entrained downwards with an argon gas flow. The size and purity of the NbB<sub>2</sub> formed were strongly dependent on the calcination temperature of the precursor, precursor size and temperature of carbothermal reduction. The carbonaceous material in the precursor particles was quite reactive when cornstarch was calcined at 400°C rather than 700°C. The smaller the precursor size, the longer the precursor particles could stay in the reaction zone, giving a better yield of NbB<sub>2</sub>. Sintering of NbB<sub>2</sub> particles occurred at 1800°C. Under optimum conditions the NbB<sub>2</sub> crystallites were as small as 40–50 nm and the residual carbon content was 2.65% by mass.</p></div>","PeriodicalId":344,"journal":{"name":"Journal of Alloys and Compounds","volume":null,"pages":null},"PeriodicalIF":5.8000,"publicationDate":"1994-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0925-8388(94)90829-X","citationCount":"32","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Alloys and Compounds","FirstCategoryId":"88","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/092583889490829X","RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
引用次数: 32
Abstract
Niobium diboride (NbB2) powder was synthesized by carbothermal reduction of Nb2O5B2O3C precursor prepared with Nb2O5, H3BO3 and cornstarch. The reaction was consecutive and Nb2O5 was formed while NbC was consumed. The apparent activation energy of NbB2 formation for the Nb2O5B2O3C system was about 360 kJ mol−1, which is in good agreement with that for the NbCB2O3C system. These results indicate that the rate-determining step of the carbothermal reduction was the formation of NbB2 from NbCB2O3C mixture. For continuous production of NbB2 particles a vertical tubular reactor was used in which the pulverized Nb2O5B2O3C precursor particles were entrained downwards with an argon gas flow. The size and purity of the NbB2 formed were strongly dependent on the calcination temperature of the precursor, precursor size and temperature of carbothermal reduction. The carbonaceous material in the precursor particles was quite reactive when cornstarch was calcined at 400°C rather than 700°C. The smaller the precursor size, the longer the precursor particles could stay in the reaction zone, giving a better yield of NbB2. Sintering of NbB2 particles occurred at 1800°C. Under optimum conditions the NbB2 crystallites were as small as 40–50 nm and the residual carbon content was 2.65% by mass.
期刊介绍:
The Journal of Alloys and Compounds is intended to serve as an international medium for the publication of work on solid materials comprising compounds as well as alloys. Its great strength lies in the diversity of discipline which it encompasses, drawing together results from materials science, solid-state chemistry and physics.