Novel Synthesis Method of Ca3al2o6 Using an Ethanol Solution Technique

Journal of the Ceramic Society of Japan 118 [7] 617-619 2010 Note

Novel synthesis method of Ca3Al2O6 using an ethanol solution technique

Weining LIU*,** and Jiang CHANG*,³

*State Key Laboratory of High Performance Ceramics and Superﬁne Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, China **Graduate School of the Chinese Academy of Sciences, 319 Yueyang Road, Shanghai 200050, China

A novel method was developed for preparation of Ca3Al2O6 which is one composition of Portland cement-based mineral trioxide aggregate for endodontic treatment. OnlyAl(NO3)3·9H2O and Ca(NO3)2·4H2O as raw materials and ethanol as solvent were needed in the whole process. The consequent dry Ca3Al2O6 precursor was examined by thermal analysis and the as-burnt powders calcined at diﬀerent temperatures for 3 hours were measured by X-ray diﬀractometry. Pure phase Ca3Al2O6 with particlesize of 110 µm was obtained at 1100°C and highly pure Ca3Al2O6 (>99.5%) was obtained at 1350°C. Therefore, this method is usefulfor preparation of pure Ca3Al2O6 for biomedical applications. ©2010 The Ceramic Society of Japan. All rights reserved.

Key-words : Tricalcium aluminate, Synthesis, Ethanol, Pure phase, Biomedical applications

[Received November 24, 2009; Accepted April 15, 2010]

Al(NO3)3·9H2O and Ca(NO3)2·4H2O for the reaction, without 1. Introduction any aidof other components or repeated calcination for the Tricalcium aluminate (Ca3Al2O6) isanimportant constituent of synthesis. A combination of techniques (TG/DSC, XRD, SEM 1) Portland cement. Besides, Ca3Al2O6 isalso a major phase of and BET) was introduced to monitor and analyze Ca3Al2O6 mineral trioxide aggregate (MTA) which is a Portland cement- precursors, intermediate calcium aluminate compounds and final like biomaterial with numerous exciting clinical applications pure phase Ca3Al2O6. in endodontics, however, also with complex composition and consequent high cost.2)6) In order to form a simpified MTA, each 2. Experimental individual phase of MTA should be evaluated so that several All reagents were of analytical grade, purchased and used as principal phases which mostly contribute to the good physico- received without further purification. All experiments were chemical and biological properties of MTA will be selected. conducted under air atmosphere. The starting materials were Therefore, it is necessary to prepare individual phases of MTA Al(NO3)3·9H2O and Ca(NO3)2·4H2Owith an initial CaO/Al2O3 with high purity, like Ca3Al2O6, for further biomedical applica- molar ratioof 3 in order to obtain 3CaO·Al2O3 or Ca3Al2O6. tions. First, 0.02 mol Al(NO3)3·9H2O was added in excessive ethanol Ca3Al2O6 is conventionally formed by a solid-state reaction which afterwards turned into green under continuous stirring, between CaO and Al2O3 through high temperature and repeated followed by the addition of 0.03 mol Ca(NO3)2·4H2O. After calcinations. However, it becomes easy to fabricate pure phase achieving complete dissolution, the solution was maintained Ca3Al2O6 even at relatively low temperatures when wet chemical at 80°C for 24 h to form a very viscous gel precursor. Such methods are introduced, though some problems also exist. Ca3Al2O6 precursors derived from ethanol solutions were further 7),8) Stephan et al. prepared fine Ca3Al2O6 particles viaasolgel dried at 120°C overnight and then calcined at different temper- process, though 3 cycles of burning above 1260°C for up to 14 h atures between 700 and 1100°C for 3 h. The resultant powders with intermediate grindings were necessary. Lee et al.9) produced were ground and sieved through 300-mesh (<52 ¯m) for further Ca3Al2O6 through a solutionpolymerization route at 1200 characterizations. 1300°C for merely 2 h, though the additional aidof poly(vinyl The thermogravimetric analysis (TG) and differential scanning alcohol) was required. Yuan and Xu10) successfully synthesized calorimetric (DSC) curves were taken with a rising temperature Ca3Al2O6 using citrate precursor method at 1100°C for 2 h, rate of 10°C/min in flowing air by a STA 409/PC simultaneous though the extra combination of nitrate salts and citricacid was thermal analyzer (Netzsch, Germany) in order to monitor the needed as well as the subsequent ignition of resultant gels around decomposition and the oxidation process of Ca3Al2O6 precursors. 180°C. Therefore, further facile and economic methods are The as-prepared powders calcined at different temperatures were expected. In Yuan’s method, citricacid and aluminium nitrate examined by XRD (Geigerflex, Rigaku, Japan) with Cu (K¡) nonahydrate (Al(NO3)3·9H2O) were dissolved in ethylene glycol, radiation, operating at 40 kV and 100 mA. In addition, morpho- so it was likelytodissolve nitrate salts in ethanol which is fairly logical analysisof Ca3Al2O6 powders obtained at 1100°C was cheap and readily available. Thus, the aimof this study was to performed using a scanning electron microscope (SEM; JSM- explore the possibility offormation of the pure phase Ca3Al2O6 6700F, Japan) and the specific surface area of the powders at a relatively low temperature onlyusing ethanol to dissolve was determined by nitrogen absorption (BET, ASAP 2020M Analyzer, Micromeritics). Finally, the content offree CaO in ³ Corresponding author: J. Chang; E-mail address: jchang@mail. the samples calcined at different temperatures all for 3 h was sic.ac.cn determined by the glycolethanol method.11)

/ f l i f l Fig. 1. TG DSC curves o Ca3A 2O6 precursors der ved rom ethano Fig. 2. XRD patterns of various calcium aluminate compounds l i so ut ons. obtained at diﬀerent calcination temperatures for 3 h.

3. Results and discussion

The TGDSC curves of the dry Ca3Al2O6 precursor are shown in Fig. 1. The endothermic peak around 65°C in DSC accounting for about 2% of the initial weight loss in TG was assigned to the evaporation of residual ethanol. Thereafter, two endothermic peaks at 185 and 217°C in DSC, accompanied by the first sharp weight loss in the TG curve, were attributed to the dehydration of two different kinds of nitrate salts. The second step of weight loss from 217 to 556°C inTGmight be mainly caused by the formation of nitrite salts derived from corresponding nitrate salts, which accordinglyrelated to two endothermic peaks at 288 and 366°C in DSC, respectively. The last sharp weight loss from 556 to 695°C in TG resulted from the further and complete Fig. 3. SEM photograph of the as-prepared Ca3Al2O6 powders calcined decomposition of nitrite salts, which meantime led to the two at 1100°C for 3 h. endothermic peaks at 556 and 584°C in DSC. In addition, the other two exothermic peaks at 695 and 955°C in DSC with almost no change inweight loss were probablyarisen from the Table 1. BET specific surface area and free CaO contents of sample intermediate calcium aluminate compounds in the formation of powders l i l i ifi pure phase Ca3A 2O6, respect ve y, wh ch was ver ed by Temperature (°C) 1000 1100 1350 f ll i l f o ow ng XRD ana yses. There ore, 700°C was chosen as the 2/ ® a b ® i i i l i l BET (m g) 3.251 vs 3 n t a test temperature at wh ch the Ca3A 2O6 precursor was Content of CaO (%) 17.13 « 2.505 3.11 « 0.957 0.32 « 0.163 calcined for 3 h. aAs-prepared powders; bLee9) As shown in Fig. 2, the Ca3Al2O6 phase began to form at 1000°C accompanied by three other phases, namelyCa12Al14O33 (JCPDS 09-0413), Ca5Al6O4 (JCPDS 70-0801) and CaO. Then the pure phase Ca3Al2O6 (JCPDS 70-0839) could be obtained at Lee et al. (See Table1). In addition, Table 1 shows the content 1100°C onlywith a small overlapping peak both for Ca3Al2O6 offree CaO in powders by chemical analysis. In the case of a and free CaO. However, there was no evidence of the formation calcination temperature at 1000°C, large percentage (17.1%)of of Ca3Al2O6 below 1000°C in XRD patterns. After initially free CaO was found in the resultant powders. When the heating the Ca3Al2O6 precursor at 700°C for 3 h, Ca12Al14O33 calcination temperature increased to 1100°C, the Ca3Al2O6 with and CaO were identified in the pattern as well as CaAl12O19 little free CaO (only3%) formed, which was well crystallized as (JCPDS 32-0151) whose peak intensity was much lower relative shown in the XRD pattern (Fig. 2). When the calcination to other phases present. In the case of 850°C, a new phase of temperature was up to 1350°C, the obtained Ca3Al2O6 phase was Ca5Al6O4 appeared together with Ca12Al14O33 and CaO. There- highly pure, with very little amount offree CaO (0.32%). fore, three intermediate calcium aluminate compounds such as Previous studies have shown that,1),10),12) in the synthesisof Ca12Al14O33,Ca5Al6O4 and CaAl12O19 appeared herein in the Ca3Al2O6, some alumina-rich intermediate compounds rather crystallization process of Ca3Al2O6 below 1100°C, which was than Ca3Al2O6 first formed below 1100°C due to the fast 1),10) 2+ demonstrated by many other studies. conversion of alumina by diffusion of Ca to Ca12Al14O33 or Figure 3 illustrates the morphology of Ca3Al2O6 crystalline Ca5Al6O4.Since the diffusion is temperature dependant, certain powders obtained by calcination at 1100°C for 3 h. The particle amount of CaO exists when calcination temperature is low. With size was about 110 ¯m, which accordingly led to a relatively the increase of the calcination temperature, the diffusion of high BET specific surface area comparable to that reported by calcium ions through the layers of reaction products is enhanced,

618 Journal of the Ceramic Society of Japan 118 [7] 617-619 2010 JCS-Japan

and these intermediate calcium aluminate compounds slowly 12) 4. Conclusions converted to the final product Ca3Al2O6 by consuming CaO. 2+ However, previous studies have shown that the diffusion of Ca Pure phase Ca3Al2O6 was synthesized though a facile process became more and more difficultwith the increase oflayer of onlywith Al(NO3)3·9H2O and Ca(NO3)2·4H2Odissolved in reaction products, and little amount offree CaO still existed ethanol as precursor. The Ca12Al14O33 and Ca5Al6O14 were at 1100°C.9) In our study, we demonstrated that, when the identified as intermediate calcium aluminate compounds in the 2+ calcination temperature increased to 1350°C, the activity of Ca formation of Ca3Al2O6 by XRD measurement. The optimal further increased, and residual CaO was completely reacted. calcination temperature was determined at 1100°C and above, Therefore, the calcination temperature was criticalfor purity which led to the formation of relatively pure Ca3Al2O6 with of the as-prepared Ca3Al2O6. The pure phase Ca3Al2O6 was particlesize of 110 ¯m at 1100°C verified by XRD analysis and obtained by calcination at 1100°C verified by XRD analysis, and highly pure Ca3Al2O6 (>99.5%) at 1350°C verified quantita- highly pure Ca3Al2O6 (>99.5%) was obtained by calcination at tively by chemical analysis, suggesting that thissimple method 1350°C verified quantitatively by chemical analysis. can be used for preparation of Ca3Al2O6 inhigh purity for As iswell known, it is important to make cations of reactants biomedical or other industrial applications. homogeneouslydispersed within a short range in favor of the preparation of ceramic powders, especially the components of Acknowledgement This work is supported by the National Portland cement because the concentration of Ca2+ ions is much BasicScience Research Program of China (973 Program) (Grant higher than that of Al3+ or Si4+ ions, which is prone to No. 2005CB522704), Science and Technology Commission of appearance of unreacted CaO even at high temperatures.1),9) Shanghai Municipality (Grant No. 08JC1420800) and the funds of the Chinese Academy of Sciences for Key Topics in Innovation Therefore, the pure phase Ca3Al2O6 formed by a solidsolid Engineering (Grant No.: KGCX2-YW-207). reaction between CaO and Al2O3 usually needs high temperature and repeated calcinations. In this case, many efforts have been made to shorten the range of distances so as to achieve relatively Reference low crystalline temperature. Yuan and Xu10) took advantage of 1) C. Ghoroi and A. K. Suresh, AIChE J., 53, 502513 (2007). f i citricacidasfuel which facilitated the contact between cations 2) S. J. Lee, M. Monse and M. Torab nejad, J. Endod., 19, 541 of reactants so that the well-crystallized Ca Al O couldbe 544 (1993). 3 2 6 3) R. S. Schwartz et al., J. Am. Dent. Assoc., 130, 967975 obtained at 1100°C without any detectable amount ofimpurities l i ff (1999). by XRD ana ys s. However, the content o ree CaO was not 4) M. Torabinejad and N. Chivian, J. Endod., 25, 197205 f ifi i i l i l l i l 9) urther ver ed quant tat ve y by chem ca ana ys s. Lee et a . (1999). made use of PVA as polymer carrier which ensured the 5) H. W. Roberts et al., Dent. Mater., 24, 149164 (2008). homogenous distribution and full contact of the metalions from 6) J. Camilleri et al., Dent. Mater., 21, 297303 (2005). reactants in its polymeric network so that the resultant Ca3Al2O6 7) D. Stephan and P. Wilhelm, Z. Anorg. Allg. Chem., 630, 1477 powders exhibited relativelyhigh BET specific surface area 1483 (2004). as well as high reactivity at low calcining temperature. In the 8) D. Stephan and S. Wistuba, Cem. Concr. Res., 36, 20112020 present study, only ethanol was used as the disperse phase to (2006). l l 9) S. J. Lee, E. A. Benson and W. M. Kriven, J. Am. Ceram. Soc., prepare Ca3A 2O6 and the as-prepared Ca3A 2O6 powders i i i i lli 82, 2049 2055 (1999). exh b ted some good propert es, such as m crometer crysta ne i i i l i l i i l 10) X. Yuan, Y. B. Xu and Y. Y. He, Mater. Sc . Eng., A, 447, 142 d mens ons, re at ve yhgh pur ty at a ow temperature and 145 (2007). l ifi f i comparab e spec c sur ace areas w th that reported by Lee 11) F. M. Lea, “The Chemistry of Cement and Concrete,” 9) et al. Obviously, the method present here was simple and Chemical Society, New York (1971) p. 108. efficient for the synthesisof pure phase Ca3Al2O6, however, its 12) B. M. Mohamed and J. H. Sharp, Thermochim. Acta, 338, mechanism required further investigations. 105114 (2002).

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