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~ UTTEBWORTH I N E M A N N Mechanochemistry of zeolites: Part 2. Change in particulate properties of zeolites during ball milling Ruder Bo~kovig Institute, P.O. Box 1016, 41001 Zagreb, Croatia Mirko Stubi~ar and Anton Tonejc Cleo KosanoviE, Josip BroniE, Ankica Ci~mek, Boris SubotiE, and Ivan ~;mit Department of Physics, Faculty of Science, University of Zagreb, 41000 Zagreb, Croatia Change of particulate and morphological properties of the samples obtained during the highenergy ball milling
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    UTTEBWORTH I N E M A N N Mechanochemistry of zeolites: Part 2 Change in particulate properties of zeolites during ball milling Cleo KosanoviE Josip BroniE Ankica Ci~mek Boris SubotiE and Ivan ~;mit Ruder Bo~kovig Institute P.O. Box 1016 41001 Zagreb Croatia Mirko Stubi~ar and Anton Tonejc Department of Physics Faculty of Science University of Zagreb 41000 Zagreb Croatia Change of particulate and morphological properties of the samples obtained during the high- energy ball milling of zeolites A and X were studied by scanning-electron microscopy X-ray diffraction and determination of particle size distribution. It was found that decrease of crystal- linity is followed by considerable change of particulate properties during the milling but that the change of particulate properties and amorphization are two independent processes. Type of amorphization induced by ball milling was defined on the basis of the analysis of the change of effective crystallite size during the milling. KelnHords: Zeolites; amorphization; ball milling; particulate processes INTRODUCTION Although the most pronounced effects of mechanical treatment, including ball milling, are lowering of par- ticle size, increasing of specific surface area, and change in particle morphology, use of high-energy ball milling process can also result in the production of composite metal powders with a fine microstruc- ture and different amorphous materials.l'2 Mechanical treatment of zeolites and related natu- ral and synthetic aluminosilicates showed that the changes of particulate characteristics were in many cases followed by the structural changes of treated materials, s'4 Our previous study 5 showed that ball milling of zeolites A and X and synthetic mordenite causes their transformation to the fully X-ray amor- phous materials, for the long enough milling time. The loss of crystallinity, the decrease of cation- exchange capacity, and the increase of solubility were caused by breaking of external Si-O-Si and Si- O- AI bonds in the zeolite structure. 5 Scanning- electron micrographs of the sample obtained during the ball milling of synthetic mordenite showed that the ball milling resulted in the formation of polydis- persed powder with a markedly irregular particle shape. 5 Hence, one can assume that the structural changes of zeolites are followed by significant changes of the particulate and morphological prop- erties during their mechanical treatment. For this Address reprint requests to Dr. Subotic, Ruder Boskovic Insti- tute, P.O. Box 1016, Bijenicka 54, 41001 Zagreb Croatia Received 10 February 1994 Zeolites 15:247-252, 1995 © Elsevier Science Inc. 1995 655 Avenue of the Americas New York, NY 10010 reason our intention is to investigate the possible changes of particulate and morphological character- istics as well as the relations between them during the ball milling of zeolites A and X. EXPERIMENTAL Samples of hydrous zeolite 4A (22.8 wt% H20 ) and zeolite 13X (26.4 wt% H20), both products of Union Carbide Corp., were milled in a planetary ball mill (Fritsch Pulverisette type 05002) at room tempera- ture. For this purpose, 1 g of zeolite was put in an agate vessel containing 10 wolfram carbide balls (¢) = 10 mm) and the vessel was rotated (speed of rotation was 3000 rpm) for predetermined time, t,,. Depend- ing on the duration of milling, temperature of the samples can be increased to 40-60 ° Starting zeolite powders and the samples obtained by the ball milling were characterized as follows. Content of water in the samples was determined from the corresponding t.g. (thermogravimetry) curves. Thermal analysis of the samples were per- formed by a Netzch STA 409 thermal analysis appa- ratus. Scanning-electron micrographs of the samples were taken by a JEOL JSM-T330A scanning-electron microscope. The X-ray diffractograms of the samples were taken by Philips vertical goniometer PW 1820 mounted on PW 1300 X-ray generator. CuK,~ radia- tion was used. The weight fractions, fc of crystalline 0144-2449/95/ 10.00 SSDI 0144-2449(94)00022-K  Particulate properties of zeolites during ball milling: C Kosanovi6 et al and fa of amorphous phases, were calculated by the mixed method ° using the integral value of the broad amorphous halo 20 = 17-39 °) and the correspond- ing sharp peaks of crystalline phases. The average values of effective crystallite size were determined by the integral width of the diffraction peaks 622 20 = 23.99°), 642 20 = 27.12°), and 820 2e = 29.94 °) of zeolite A and by the integral width of the diffraction peaks 533 20 = 23.31°), 555 20 = 30.94°), and 642 20 = 26.65 °) of zeolite X. After subtracting the background and resolving the sharp maxima from broad amorphous halo, the profiles were corrected for instrumental broadening using the germanium diffraction profile of the 111 maxi- mum. The effective crystallite size was calculated by using the Scherrer formula. 7 Particle size distribution curves of the samples of zeolites 4A and 14X milled for different times, t m, were determined by a Disc Centrifuge with Photosed- imentometer Mark-III Joyce-Loebl). The mean hy- drodynamic particle diameter, D, geometric specific surface area, As, and specific number of particles particles/g), N s, were calculated from the corre- sponding particle size distribution curve as: = E ~iDi/E ~i 1) A s = 6 E ~i (Di)2/P y ~i (Di) s 2) N, = 6 E ~i/II p E ~i (Di) 3 3) where ~i is the number frequency of the particles having the hydrodynamic diameters between D and ~tD, D i = D + 0/2 and 9 is the density of the solid phase. Corresponding values of E rbi, E ~ i Oi, ~ I~ i Oi) 2, and E r~ (Di) ~ were calculated from the particle size distribution curves by the procedures described earlier. 8,9 RESULTS ND DISCUSSION Figures 1 through 4 and Tables 1 through 3 show that the ball milling of zeolites A and X causes significant changes of their particulate and morphological prop- erties. The starting, short-term milling tin = 10 min) caused a comminution of the srcinal crystals of zeo- lite A see Figure la) and zeolite X see Figure 2a) and formation of two different particulate systems: dam- aged, but recognizable crystals of zeolite A see Figure lb) and zeolite X see Figure 2b) and small particles of Figure 1 Scanning-electron micrographs of srcinal powder of zeolite A a) and of the samples obtained by ball milling of the zeolite A for t = 10 min b); t = 20 min c); and t = 75 min d). 248 Zeolites 15:247-252, 1995  Particulate properties of zeolites during ball milling: C Kosanovid et al Figure 2 Scanning-electron micrographs of srcinal powder of zeolite X a) and of the samples obtained by ball milling of the zeolite X for t,, = 10 min b); tm= 20 min c); and t,, = 75 min d). irregular shape. Because the solids obtained by the short-term milling of zeolites A and X contain about 30-40 of X-ray amorphous phase (see Figures 4 and 5 in Ref. 5), one can assume that the amorphous part of the system is represented by the small particles of irregular shape (see Figures lb and 2b . Further mill- ing of zeolite A (tin = 20 min) causes further decrease of particle size (see Figure lb, c and Table 1 and in- crease of irregularity of particle shape (see Figure lb, c geometric specific surface area, As (see Table 1 , specific number of particles (see Table 1 and fraction, f~, of the amorphous phase (fa = 0.75 for t m = 20 min; see Figure 4 in Ref. 5). In contrast to the sample obtained by milling of zeolite A for t,, = 20 min which does not contain recognizable crystals of zeolite A (see Figure lc, d , damaged, but recognizable crystals of ze- olite X together with an increased fraction of small particles of irregular shape can be shown in the sam- ple obtained by milling of zeolite X for t m = 20 min (see Figure 2c . A long enough milling (>60 min) re- sults in the formation of fully X-ray amorphous poly- dispersed powder with a markedly irregular particle shape (see Figures le and 2d . Figures ld and 2d (see also Figure 7b in Ref. 5) show that the larger particles are aggregates composed of smaller ones (below 1 I~m in size). Content of water in fully amorphized samples is lower (17.5 wt in the amorphized zeolite A and 15.5 wt in the amorphized zeolite X) than in the srcinal powders of zeolites A and X. The decrease of the water content can be explained by the desorption of water caused by warming of the treated materials during the milling. Although the rates of amorphiza- tion of zeolites A and X are almost the same (see Table 1 Changes in mean particle diameter, D, geometric spe- cific surface area, As, and specific number of particles, Ns, dur- ing the milling of zeolite A Z-A) and zeolite X Z-X) for different times,t m ~m) As m z g-l) Ns g-l) min) Z-A Z-X Z-A Z-X Z-A Z-X 0 5.07 3.86 0.28 0.62 2.3 x 109 1.2 × 10 l° 20 3.18 3.21 0.32 0.60 5.9 x 10 s 1.5 × 10 l° 45 3.05 - 0.66 - 1.8 x 101° - 60 - 3.03 - 0.64 - 1.8 × 101° 75 2.43 2.28 0.64 0.79 2.5 × 10 l° 3.8 x 101° Zeolites 15:247-252, 1995 249  Particulate properties of zeo/ites during ball milling: C Kosanovid et al Figures 4 and 5 in Ref. 5), change of particulate prop- erties of zeolite X during its ball milling is rather dif- ferent than the change of the particulate properties of zeolite A during its milling under the same condi- tions. Although the particulate properties of the sam- ples obtained by milling of zeolite A changed mono- tonically during the milling (see Table 1 , particulate properties changed very little during the first hour of milling of zeolite X q a = 0.98 for t 60 min; see Figure 5 in Ref. 5), and significant changes of the particulate properties were observed during the fur- ther milling of almost amorphous sample (see Table I). At the same time the shape of particle size distri- bution curves of the samples obtained by milling of zeolite X changed considerably (see Figure 4 . Change in the shape of particle size distribution curves (see Figures 3 and 4) and the shifting of maximum fre- quency (e.g., from 2.3 Ixm for t 0 tO 1.3 Ixm for t m = 20 min and to 1.7 p~m for t,, = 45 min, and again to 1.3 ~m for t,, = 75 min in the case of milling of zeolite X) leads to an assumption that a part of smaller particles formed by mechanical breaking of 6 4 2 b; 2 c ~,...., o o 2 4 6 ( m) Figure 3 Particle size distribution by number of srcinal pow- der of zeolite A a) and of the samples obtained by ball milling of the zeolite A for tm = 20 min b); tm = 45 min c); and tm = 75 min e). No is the number percentage of particles having the size between D and D hD. Z 2 2 0 0 ã 2 4 6 8 (ttm) Figure 4 Particle size distribution by number of srcinal pow- der of zeolite X a) and of the samples obtained by ball milling of the zeolite X for tm = 20 min b); tm = 60 rain c); and tm = 75 min e). N D s the number percentage of particles having the size between D and D + AD. srcinal crystals tend to form aggregates (see Figures Id and 2d , as a part of the particulate system which cyclically changes its properties by a series of aggre- gation and deaggregation processes during the mill- ing. Above-mentioned observations lead to an as- sumption that the change of particulate properties is caused by a complex process which includes mechan- ical fragmentation of srcinal zeolite crystals, aggre- gation and deaggregation of smaller particles of crys- talline and amorphous phase, comminution of the particles of fully amorphous phase, their aggregation to larger particles by the compression of material be- tween balls and walls of vessel as well as between balls themselves, and deaggregation of such formed aggre- gates. Based on the same arguments it can be postu- lated that process of amorphization and change of particulate properties are two parallel, but more or less independent processes. Figure 5 shows X-ray diffractograms of srcinal powder of zeolite X (diffractogram a) as well as X-ray diffractograms of the samples obtained by ball milling of the zeolite X for 20 min (b), 40 min (c), 60 min (d), and 90 min (e). In all the presented X-ray diffracto- 250 Zeolites 15:247-252, 1995
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