著者

国吉 実 村上 次雄 溝田 忠人

出版者

一般社団法人 資源・素材学会

雑誌

資源と素材 (ISSN:09161740)

巻号頁・発行日

vol.118, no.3,4, pp.191-196, 2002 (Released:2006-01-31)

参考文献数

10

被引用文献数

3 3

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Sodium bicarbonate is so unstable that the rate of decomposition is strongly affected by even trace amount of water in the powder. Variously hydrated species may be formed on the surface as decomposition products from sodium bicarbonate to sodium carbonate. In order to clarify the decomposition-mechanism and chemical-stability of the material, a method of quantitative analysis has necessarily been developed to determine the minute amount of free water and crystalline water related to variously hydrated salts. Preceded to the present work, therefore, four analytical methods established so far were examined to select the suitable method for the present object. The Karl-Fischer titration method combined with a moisture evaporator was finally selected by adding an analytical process, in which the dehydration amount-time profile is deconvoluted into several different peaks corresponding to the state of water. The fractional evaporation of various states of water enables the quantitative analysis without any pretreatment of the sample. This fractional quantitative analysis may be explained by the difference of thermal-stability among those of sodium bicarbonate, sodium carbonate hydrate and sodium sesquicarbonate.

著者

国吉 実 村上 次雄 溝田 忠人

出版者

The Mining and Materials Processing Institute of Japan

雑誌

資源と素材 : 資源・素材学会誌 : journal of the Mining and Materials Processing Institute of Japan (ISSN:09161740)

巻号頁・発行日

vol.118, no.7, pp.511-516, 2002-07-25

被引用文献数

2

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Sodium bicarbonate easily forms cakes during the storage and / or transport process after production, due to the influence of conditions such as humidity, temperature, compaction etc. Caking causes serious degradation of the material in the commercial value. To overcome the problem, the caking mechanism must be clarified first, and thereafter the effective treatment should be considered to avoid caking. Weak caking strength of sodium bicarbonate powder at the initial stage of caking was measured and evaluated in relation to amounts of various components and physical properties of the powder. Caking under the high humidity (RH80%) of sodium bicarbonate found to occur due to the bridging among particles during the process of changing of sodium carbonate to sodium sesquicarbonate. The caking under the conditions of low humidity (RH40%) and high temperature (40 ∼ 50 °C) however owes bridging accompanied by the change from sodium carbonate to Wegscheider's salt. Caking strengths measured for sodium bicarbonate samples with various particle sizes were correlated with contacting numbers among particles. The caking strength, <i>B_L</i>, was found to be expressed with the equation: <i>B_L</i> = <i>k</i>·<i>Sc</i>·<i>F</i>, where <i>Sc</i> is the contact area per unit surface area of sodium bicarbonate particles, and <i>F</i> is the formation quantity per the unit surface area, of the double salts such as sodium sesquicarbonate and Wegscheider's salt. We have found finally an effective method to avoid caking through the process of analyzing the caking mechanism of sodium bicarbonate.