The Preparation and Characterization of an X-Type Zeolite An Experiment in Solid-state Chemistry

Kenneth J. Balkus, Jr., and Kieu T. Ly University of Texas at Dallas, Richardson, TX 75083-0688

Topics in solid-state chemistry are often neglected in undergraduate laboratories partly because there are rela- tively few experiments that capture the attention and imagination of students. The advent of high-Tc supercon- ductors that provide dramatic yet simple experiments (1) has increased interest in solid-state materials. We have been part of a movement to introduce solid-state chemistry topics in the advanced undergraduate labs. We report an undergraduate experiment based on the syntheiis and charactrrrzat~on o f m X-twe zmlite (21. -.

The synthetic X-type zeolite has the faujasite structure (3) shown below. Faujasite is the naturally occurring, but rare, mineral. The general formula is M,i,(A102),(Si02)~9~.n where n = 77-96 and x = valence of M. The faujasite structure wnsists of ten cages connected by hexagonal prisms or double six-ring (D6R) units. The P cages are oRen called sodalite cages because the structure of the zeolite sodalite (3) contains eight of these truncated octahedra connected through the four rings. The vertices in Figure 1 represent either tetrahedral A1 or Si atoms with the 0 atoms omitted f~r~c la r i ty . This structure transcribes a sphere of about 12 Awhich we designate as the supercage. The 12 ring apertures to the a or supercage are about 7.4 A in diameter. These dimensions allow only certain mole- cules to be adsorbed by the zeolite.

In this experiment we will probe the pore size by moni- toring the adsorption of various molecules. If we view zeolite as a micropourous silicate in which the Si4+ has been partially substitued with A13t then we realize that for every A13+ there must be an equal number of positive charges added for balance. The cations that compensate for the

Figure 1. Structure of zeolite X.

cage

prism

positive trivalent charge on Al can be virtually any electro- positive element, from protons to lanthanides. These cat- ions can he located throughout the structure. In fact, there are more cation sites than cations.

In this experiment we will prepare the sodium form ofan X-tvoezenlite.Thesodium ionscan then brexchanged with othk; metal ions such as cobalt(I1).

We have found the X-type zeolite can be prepared during a typical lab period and later characterized by infrared spectroscopy, ion exchange, and adsorption.

Preparation of NaX Many variables can influence zeolite synthesis: temper-

ature, pH, crystallization time, order of mixing, amount of Si, Al, Na, and HzO. Zeolite NaX is a metastable phase, meaning that other types of zeolites such as P, A, or sodalite may form if this recipe is not followed carehlly. The proce- dure detailed below should produce highly crystalline NaX within a normal lab period (2-4 h) without detectable contamination from other phases.

The first procedure is to prepare sodium silicate and sodium aluminate separately. The sources of silicon and aluminum can vary, but we have found that silica gel (Aldrich) and aluminumisopropoxide (Aldrich) are suitable starting materials. Since this experiment requires working under alkaline conditions, plasticware should be used. I'olypropylene bottles shouldbe used for the rnstallizatiun berausr 1hc.v are generdly autoclavnble. Sote: Polyethyl- ene bottles $11 crick and leak.)

The sodium silicate is prepared by adding 3.0 g of silica gel, 2.4 g of sodium hydroxide, and 6 mL of deionized water to a 250-mL plastic beaker. This mixture is swirled until the solids are completely dissolved. The sodium aluminate solution is prepared simultaneously by adding 6.9 g of aluminum isopropoxide, 2.4 g of sodium hydroxide, and 9 mL of deionized water to a 250-mL plastic beaker. The mixture is stirred with gentle heating (below 80 'C ) in a water bathuntil the solids are dissolved (about 10 min) and a clear gel is formed. A watch glass placed over the beaker should prevent loss ofwntcr. (Note: The isopropanol furmed during ihe hydrolysis of aluminum isopropoxide will evap- orate or form droplets a t the surface. There is no need to separate the alcohol from the gel.) When both solutions are a t room temperature, the aluminate solution is added to the silicate solution. An additional 27 mL of water is added

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. , a,e,<- ?>,,> c . , < e , < - .!" ,~ ,, ,.,:,; have access to this technique. However, ifXRD is available, . .".* ,..... ... *. , I . " .. students should be referred to JCPDS file no. 38, 237 to

I < ,

0 HOURS -.,

2 HOURS

3 HOURS

4 HOURS

obtain a standard pattern for NaX (4). The most reliable alternative is infrared s~ectrosco~v (5).

which we can use to identify the zeolite and estima't;, the crvstallinitv. Fimre 2 shows a series of s~ect ra recorded bv a student durGg the preparation of zeolite X, using KF; oellets. (Note: Excessive minding of samdes should be avoided.) We are examininithe mid-IR region only because the adsorbed water in the zeolite masks the OH reeion. Without an expensive vacuum IR cell, very little informa- tion can be obtained from this region. At 120M00 cn-' there are many bands associated with different Si and A1 tetrahedra vibrational modes.

The spectrum for the initial amorphous aluminosilicate gel (0 h) is a series of broad, featureless bands. There is a correlation between this broadness and crystallinity: As crystallinity increases, the bands become more narrow and better defined. The 4 h spectrum is of a 100% crystalline sample. A comparison with the starting gel reveals several bands and shoulders have grown in. These have been classified as external linkaees or structure-sensitive vibra-

W tions. The appearance of th&e bands coincides withforma- tion of the three-dimensional framework. The location of these bands will shift to higher frequencies as the SiIAl ratio of the product zeolite increases, but students can use these spectra as a guide.

In Figure 2 the main asymmetric stretch is at 982 m-' with a shoulder at 1053 cm-'. The symmetric stretches occur at 748 and 670 m-' with a weak shoulder at 689 cm-'. The band at 560 cm-' is associated with the double 6 rings that connect the sodalite cages. A TO4 bending vibration

2000 1400 1000 BOO so0 400 occurs at 456 m-'. wavmuuems(cm->) If an impurity phase did hystallize, it should be fairly

easy to identify by IR. The key area to monitor is the

Figwe 2 FT-IR speclra of zeol~fe crystal zatlon mlxtJre recordeo as KBr pellets taken alter 0 2, 3 and 4 n.

to the gel and stirred with either a spatula or stir bar until the mixture appears homogenous.

The gel may take on a variety of appearances, but the initial eelatinous mixture will usuallv ouicklv form a sus- - " . pension of white solids. This mixture is quickly transferred to a oolwroovlene screw cao bottle. sealed and laced in . ". ." an oven at about 90 "C.

All students should place their samples in the oven at the same time to minimize the fluctuation in temperature from opening the oven door. The reaction time will depend on the lab period. The best results are obtained at 3 4 h, but reasonably crystalline zeolites can be isolated after only 2 h. Alternatively, the crystallization can be followed by IR spectroscopy to achieve the optimal yield (vide infra).

After 2 4 h the mixture is cooled to room temperature, and the solution is neutralized by washing with much water. This is best accomplished by transferring the mix- ture to a beaker, then diluting with water, followed by suction filtration and further washings. If the high-pH zeolite solution is transferred directlv to a Buchner funnel or frit, contamination may result from dissolution of the oaoer or frit. The white zeolite crvstals mav be air-dried or bvkdried until the next lab period wbkn the yield of hydrated NaX zeolite may be calculated.

Characterization of NaX Probably the best way to identify the zeolite phase and

evaluate the degree of crystallinity is by X-ray powder diffraction. We followed this experiment using XRD and found that highly crystalline NaX can be prepared after only 2 h. More crystalline zeolites were obtained after 4 h. Unfortunately, many undergraduate chemistry labs do not

double-ring region. Common phases that might appear as impurities include zeolites P and sodalite which both lack double-ring structural units (3). Therefore, there should be no IR bands near 560 em-' for these phases. Zeolite P has a characteristic band at 600 cn-'; sodalite, at 660 cm-'. If zeolite A were an imouritv the double-rinevibration would

A - shift to a lower wave number (about 550-cm-') relative to X-tvoe zeolites because it has double four-ring units instead - of D ~ R units.

Ion-Exchange Properties

One of the characteristic properties of zeolites is their ability to ion-exchwe cations. The combination of Si4+ and A13+ results in a deficiency of positive charge which is balanced by exchangeable cations. In a simple test we can determine if the above product has ion-exchange capabili- ties.

In a 250-mL Erlenmeyer flask dissolve 0.1 g of cobalt chloride in about 100 mL of deionized water. Then add 1 g of the product zeolite and stir until the pink solution is decolorized. Times will vary, but heating greatly facilitates this process, so complete exchange can be accomplished in less than anhour. After filtration, wash with water and test the washings for NaCl with a AgN03 solution.

If the zeolite is pink and if the filtrate is colorless but contains NaC1, the product has ion-exchange properties. Ideally two Na+ ions will exchange for every COZ+, as shown in eq 1. In reality a stoichiometric exchange is unlikely because different cobalt species are possible. For example, a Cl- or OH- ligand might be coordinated to the metal ion, with one Na+ exchanged, to maintain electroneutrality.

One can imagine how this ion-exchange property could be exploited commercially to soften water or to remove toxic or radioactive metal ions from water.

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Adsorption Properties If the Co(I1)-exchanged zeolite is allowed to air-dry, i t

remains a pink powder, but if the students heat the zeolite crystals they will eventually turn blueviolet. This change in color results from dehydration of the zeolite and il lustrates the adsorption properties of zeolites. A suprisingly large amount of water can he adsorbed by X-type zeolites: Thermogravimetric measurements indi- cate as much as 25% by weight. This hydrophilicity is related to the large internal surface area and the polarizing ability of the zeolite cages.

Given these strong adsomtion urouerties we can now probe thedimrnsion;bfthe zholite pores by varyingth~size of the adsorbinr! molecule. The ahovo strurture of zeolite X would indicatethat molecules smaller than about 7.4 A should he adsorbed. We can use the kinetic diameter (2) to decide if a molecule will fit through the zeolite pores. For example, water has a kinetic diameter of 2.65 A, benzene, 5.85 A. We already know water is adsorbed, but we can test to see if benzene is adsorbed.

Place about 50 mg of dehydrated zeolite into a 1/2-dram vial or small test tube. Then carefully weigh the vial avoid- ing fingerprints and place it inside a larger vial. Place both vials uncapped into a larger vial or beaker that can be covered tightly. Place a few milliliters of benzene into the largest vial and cover. After an hour or so remove the vial containing the zeolite and weigh.

A weight change indicates that benzene was adsorbed and the pmduct must have pores with diameters of 6 A or more. This experiment can be repeated with other mole- cules provided they have significant vapor pressure. Given the uniform pore distribution of zeolites one can see how these materials wuld be used as molecular sieves to adsorb or exclude molecules by size.

Conclusion The synthesis of an X-type zeolite is a relatively simple

experiment in solid-state chemistry. I t allows the students to prepare a commercially important material and thenuse its physical properties as a probe of molecular structure. The synthesis of this zeolite fmm such simple starting materials is fascinating, and it is fun to realize that ion-ex- change and selective adsorption studies easily relate the synthetic product to the interesting three-dimensional structure of Figure 1.

Acknowledgment We thank the Robert A. Welch Foundation and the donors

of the Pretroleum Research Fund administered by the American Chemical Society for financial support.

Literature Cited 1. Forerample,seeJue~gen~gen,F.H.;EUls.A.B.:DiecLmann,G.H.:Perkins,R.I. JCham.

Edue. 1987.64.851. 2. For an overview of zeolites, see Breck, D. W. &di& Molecuior Siew6; Wiley: New

York, 1974. 3. Meier,W.M.;Olson,D.H.AllasofZ~di~SL~ucfunTyp~s;Butteteorth:London,1988. 4. Pmddd D~ffficfion Pila lhorganjr): JCPDS-International Centre for Diffraction

Data: Swarthmare. PA. 5. Flanken, E. M. in Zeolite Chemistry ond Cafalys&;ACS Monograph No. 171, 1976,

SO.

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The Preparation of Pure Zeolite Nay and Its Conversion to High-Silica Faujasite

An Experiment for Laboratory Courses in Inorganic Chemistry

Fritz Blalier and Emst Schumacher Institute for lnorganic. Analytical and Physical Chemistry, University of Bern, Freiestrasse 3, CH-3012 Bern. Switzerland

Every student of chemistry meets the fascinating proper- ties of molecular sieve zeolites during his or her career. We encounter them as drying agents, selective gas adsorbents, ion exchangers, chromatographic media, catalysts, or cata- lyst supports (I). A large number of interesting experiments can be performed with the many varieties of commercial zeolites, e.g., Linde A, X, and Y (2). However, the prepara- tion of these highly organized porous crystalline systems remains a mystery tomost users. This does not change dras- tically when the synthetic and patent literature is examined (3).

There are many motives for synthesizing zeolites in the laboratory: Commercial zeolites have unknown chemical pu- rity and are often crystallographically not well character- ized. All commercial zeolites are contaminated by heavy metals, mostly iron, which produce all sorts of artifacts if one studies EPR spectra of sorbed free radicals (4). Last but not least: One takes great satisfaction from successfully synthe- sizing one of these enigmatic substances and from proving that i t is monophasic, conforms to a specific type of crystal- lographically well-defined zeolite species, and show all the expected properties even better than the commercial prod- uct. Since the architectural variations for assembly of zeolite structures from the prototype "bricks" (5 ) are not yet ex- hausted by far, it iseven possibleto discover systematically a new phase with unusual adsorptive properties, e.g., built-in chiral discrimination.

The published synthesis procedures are mostly uncom- meuted recipes. Only meager information is given regarding reaction steps, reaction paths or mechanisms. The impor- tant reaction parameters are not clearly described, which creates the reader's impression that the process can hardly be reproducible. However, recent investigations with novel tools have led to a better understanding of the reaction conditions, e.g., MAS (magic angle spinning) NMR of 27Al and 29Si, light scattering and photon correlation spectrosco- py of the phase nucleation steps, and computer simulations. The results allow one to infer what happens and how to control the conditions for a specific synthesis. But predic- tions of how to proceed for creating new zeolites are still unreliable (3).

Plannlng a Synthesis Systematic studies of zeolite preparation involve careful

consideration of the following important areas:

the nature and composition of the reactants and the formation of precursor species, nucleation kinetics and crydtal growth, phase transformations, temperature, and pressure factors.

At least six different zeolites (NaA, NaX, Nay, PI, P2, CHA) and "mixtures" are obtained in hydrothermal pro- cesses using the same set of reactants (SiOa, Al, Al2(SO4)8, NaOH, and HzO) under different reaction conditions (3,6); on the other hand pure Nay can be obtained by several procedures. Because subsequent crystal separation is impos- sible, 100% yield of amonophasicproduct has to be achieved.

Zeolite Nay is a synthetic faujasite with an SilAl ratio of 2.4 f 0.8. We eive a simole. reoroducible method. adanted f rom~asaharae t al. (n, for its preparation from analytically Dure chemicals. The ~rocedure is based on the senaration of nucleation and growth processes. Nucleation of ;he desired seed ia induced in a clear solution with hieh NaOH concen- tration. The dissolution of aluminum and silica in concen- trated solutions of NaOH begins with the following reac- tions:

or 2IAl l t 20H- + 6H,O - 2[AI(OH)J + 3H,

SiO, + NaOH -Na[SiO,OH] dissolved (2)

Condensation leads to the formation of dimeric, trimeric, and finally oligomeric anions, which are already the struc- tural subunits of the zeolite. Equation 3 suggests a first condensation step:

Al(OH),- + Na[SiO,OH] - Na[(OH),A1+SiOOH] + OH-

or Al(OH),- + [BO,OHl- - [(HO),Al-O-SiOOHI- + OH-

(3)

The surrounding cations compensate the charge of the an- ionic network and serve as template agents for the three- dimensional arrangement. All the secondary building units (SBU) of zeolites have been probed by high resolution FT- NMR of 27Al and 29Si in the liquid phase, a method that is powerful enough to discriminate aluminosilicate species havinguo to 10 Sior A1 atoms (8). The formation of colloidal particies-is indicated by the decrease of visible light trans- mittance of the nucleation solution during the aging process. .. .. A simple spectrophotometer is adequatefor these measure. ments. Both methuds combined give strong evidence for the formation of aggregates with about one unit cell dimension from the smaller structwal subunits in the clear nucleation solution.

The clear nucleation solution is mixed with a precipitated eranular sodium-alumina-silica eel in the ratio 15. Mixine Gf the two systems (probably) lea& to a steady state equilib': rium between dissolution of the amor~hous eel and further crystal growth. Crystallization a t 92 * 2 OC needs 24-72 h. The nucleation solution is decisive for the zeolite obtained, and small changes of the composition, aging time, or tem- perature cause remarkable effects on the zeolite crystalliza- tion process.

Zeollte Nay: Experlmenial Procedure For all theswpa w be described below laboratory glassware has to

be avoided. Polyethylene or polypropylene flasks with tight screw caps have to b~ applied. Why?!

Nucleation Solution A (eq 1) is prepared by dissolution of 1.35 g (0.05 mol)

metallic A1 (99.999% obtained from Alusuisse) in a solution of 15.0 g (0.375 mol) best purity NaOH in 35 mL distilled water. Solution B (eq 2) is produced by dissolving 15.0 g (0.25 mol) dry SiOn (Fluka No.

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60780) in 15.6 g NaOH in 35 mL distilled water. Both solutions are mixed in polyethylene flasks in an oil thermostat at 42 * 3 'C and aged for 90 10 min at the same temperature. This is the "nucle- ation solution" wherein the formation of seed structures takes place as has been proved withlight-scattering experiments (7). The nucle- ation solution should he clear after the given time of aging. If some turbidity is left, the concentration of sodium hydroxide has heen too low or sodium carbonate is a contaminant,

The Aiuminosilicete Gel Solution C is 31.5 g (0.05 mol) Alz(S0A (Merck p.a.1 dissolved in

125 mL water, and solution D consists of 30.0 g SiOz and 16.0 g NaOH dissolved in 75 mL HzO. Then D is slowly poured into C under vigorous stirring while the granular sodium-alumina-silicate gel precipitates, which is subsequently washed with cold water. The washed gel is transferred to a polypropylene flask and water is admitted to 180 g total weight.

The Ctystai Growth Process The formation of zeolite crystals from the small snbunita formed

in the nucleation solution occurs in a gel with defined molar compo- sition: 30 g of the nucleation solution (A + B) are added to (C + D), and, after mixing well, the gel is distributed in two flasks, which are kept in a drying oven at (92 r 2 "C). The composition in mole % of the reactant eel is now: HgO: 88.45%. NaOH: 5.70%. SiO?: 5.26%. Al: 0.59%. ~rvst&ization is controlled h;~-rav diffraction after 24 h bv ~ ~~ ~.~~ ~ ~, taking the samples directly from ;he Re:; as urually20-30 h is sufficient for complete reaction, the gel is filtered and washed with boiling water as soon as the X-ray analysis shows a crystalline product. The result is zeolite Nay of high purity with an average crystal diameter of approximately 0.9 pm.

Hlgh-Slllca Zeollte In a second exoeriment the svnthesized zeolite Y (SilAl-

2.5) is converted to high-silica'faujasite with ~ i l ~ l ' r a t i o of -100 or even more. if it is treated with silicon tetrachloride vapor (9) a t 450 OC: The reaction

xSiC1, + Na5,(Al0,),,(SiOz),,, - Na,,(AlO,),,-,(Si0~),36tl + rNaCI+ zAlC13 (4)

is a substitution of the lattice Alnl of the zeolite by SiN with an almost com~le te maintenance of the crvstal structure. .&l3 volatilizes from the zeolite phase and condenses on the elass surface: NaCl or nonvolatile NaA1C14 is leached with water.

Experlrnental SiClr is previously distilled into breakseal tubes; each tube should

contain approx. 5 mL of liquid SEl+ On the basis of the tube content one estimates the stoichiometric quantity of Nay to weigh into the reaction vessel 3 (figure) from eq 4. For complete AlISi exchange a 10-20% excess of SiCln is recommended.

The Pyrex apparatus is connected as indicated in the figure, and the breakseal tube is attached to the cold trap 2. The zeolite is sufficiently dried in a flow of pure Nz(g) (2 bat 450 O C after predry- ing in an oven). Cold trap 1 is cooled with liquid Nz. The breakseal ampule is opened with the iron bar 7 and a magnet. Cold trap 4 might be cooled with liquid nitrogen, or, if not, the gas flow (approx. 1 mL1s) is led into a NaOH solution to remove the unreacted SiCL. The SiCL input is regulated by the gas flow or the ampule aperture. The complek reaction takes appron. 4 h, and then the oven tem. prrature is slowly diminished from 450 'C to 200 ' C in 1 h; the oroduct is washed with0.01 M HCIor NH.CIsolutronand hot water, hried at 110 "C, and investigated with IR spectroscopy (1-3% in KBr) and Debye-Schemer powder X-ray diffraction.

Results and lnterpretatlon The DebyeScherrer diffraction pattern allows one to de-

termine the unit cell parameters of both zeolites N a y and the modified high-silica form. T o every diffraction line Miller indices (h. k. 1 ) can be assiened. Thev are found to be . . . . either odd or even and not of &xed parity, e.g., (331) or (242). but not (321). This moves the presence of a face- . .. centered cubic lktice (spacegroup ~ 3 d k ) . From the diffrac- tion anele B we extract the elementary cell length according

Wex apparaNs tor Hw Mment of zeolltes wlth SlC14 vapor: (I) and (4) cold traps, (2)oold trap with breakseal ampule, (3)reactlon vessel, (5) RoNlex 1919 ccnnenlons, (6) breakseal ampule with SiC14, (7) iron bar.

(I = An(hZ + kZ + 1')'"

2 sin 8

where n = 1, 2, 3,. . . , a = unit cell length, X = X-ray waveleneth. and B = Braze anele. Both elementarv cell oa- rametersare ohtained wiihhigh precisionso that t<eshrink- ape of the unit cell of the Si-exchanged zeolite can be used to estimate the SiIAI ratio with help of literature data (9). The difference of 2% between the two unit cell constants is caused by the different bond lengths dsi.0 = 1.61 Aand d~1.0 = 1.69 A. MID-IR spectroscopy from 300-1400 em-' is also well suited to the orobine of structural alterations in zeolite frameworks. The bands i f both zeolites show a 1:l correla- tion with each other and band assignments should be made (9). The higher ordering of the lattice atoms and the unit cell contraction lead to sharper absorption bands and shifts of approx. 8% to higher frequencies in the modified form. For reproducible X-ray diffraction and (optional) thermogravi- metric analysis standardized humidity conditions are neces- sary, e.g., by keeping the zeolites in a desiccator over a saturated MgClz solution. X-ray diffraction and IR analysis show that the crystal structure is well preserved and that only a small part of the degree of crystallinity is lost during the exchange reaction.

Conclusions

Pedagogically valuable characterizations and interpreta- tions are possible with the zeolite conversion experiment:

Determination of the cubic unit cell constant by powder X-ray diffractometry; a reference substance, e.g., sodium chloride, is to he used for precise determination. . The size of the unit cell is connected with the bond lengths. IR spectroscopy is sensitive for hond lengths in macromolecular systems, and highly symmetric structural subunits are proved.

The zeolites prepared are adequately identified by X-ray diffractometry and solid state IR. Scanning electron micros- copy, determination of adsorption isotherms for different substances, and thermogravimetric analysis are additional tools to reveal the large physicochemical differences be- tween the two zeolites. Most important are the hydrophobic nature. Brdnsted aciditv of the H+ form. adsorotion heats. and therefore catalytic-properties. ore over, the synthe: sized zeolite N a y is free from paramagnetic impurities and therefore adequate for research purposes. EPR measure- ments of small metal clusters in zeolites are possible even if very weak signals result from the metallic particles (4).

All experiments have been checked by the students of the second-year course in inorganic chemistry a t the University of Bern. to ~ r a g g ' s law (9--11):

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Acknowledgment 3. ~echart , . .. . - H. . . stud. -- surf . SC;. cn i . 1~81,24,107-128. ~ar~are~ar, R. M. s l u d surf . sei. cot .

We thank the SNF grant no. 2.273.86 and the Kommission zur F6rderung der Wissenschaftlichen Forschung, grant No. 146111211, for financial support, W. M. Meier, Giline Har- vey, B. Lathy for introduction in the art of zeolite synthesis; R. Giovanoli, M. Faller, R. Steiner, and Beatrice Frey for X- ray service and scanning electron microscopy.

Literature CRed 10. Berry, R. 8.; dice. S. A,: Ross, J. ~hya&iChernistry; Wiley: Nm Yark. 1980. 11. Buerger. M. J.; Azaroff. L. V . The Pouder Method in X-my Cryafdo~raphy:

1. Bmck, D. W . Zeolitr Molecular Siouas: W h y : NelvYork, 1974. McGrsw-Hill: New York, 1958. 2. ~ ~ ~ ~ k ~ i . Y.; r j i rna .~ . : ward,& w.. E~S. N*W Deu.ropmantainzootite seiowe

Technology; Elsener: Amtfcrdam. 19%.

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