UDK 546.212:546.41:537.612 ISSN 1318-0010 Stro kov ni članek KZLTET 33(6)517(1999) B. PLAVŠI] ET AL.: IDENTIFICATION OF CRYSTALLIZATION FORMS OF… IDEN TI FI CA TION OF CRYSTALLIZATION FORMS OF CaCO 3 WITH FTIR SPEC TRO SCOPY IDENTIFIKACIJA KRISTALIZACIJSKIH OB LI K CaCO 3 S FTIR SPEKTROSKOPIJO Barbara Plavši} 1, Spomenka Kobe 1, Boris Orel 2 1Jožef Stefan Institute, Ljubljana, Jamova 39, Slovenia 2National Institute of Chemistry, Ljubljana, Hajdrihova 19, Slovenia Prejem rokopisa - received: 1999-10-06; sprejem za objavo - accepted for publication: 1999-11-16 It has been es tab lished that nu cle ation and crys tal li za tion of cal cium car bon ate in hard wa ter can be in flu enced by mag netic fields. In this study NGIA (Near Grazing In ci dence An gle) reflectance FTIR (Fou rier Trans forme d In fra red) spec tros copy has been used for the iden ti fi ca tion and char ac ter iza tion of the crys tal li za tion forms of c al cium car bon ate in flu enced by mag netic field treat ment. Spec tra ob tained from thin films of cal cium car bon ate crys tals, grown from hard wa ter on dif fer ent sub strates, have been stud ied. The in flu ence of im pu rity ions, which are usu ally pres ent in or di nary t ap wa ter (such as iron, cop per and zinc) and ap pear to fa vor the for ma tion of ar agon ite rather than cal cite crys tals af ter th e mag netic treat ment, was con firmed. The mor pho log i cal dif fer ences be tween mag net i cally treated and un treated sam ples, i.e. crys tals grown from these sam ples, were in ves ti gated by means of scan ning elec tron mi cros copy (SEM). Key words: mag netic wa ter treat ment, FTIR spec tros copy, cal cite, ar agon ite Ugotovljeno je bilo, da je na nukleacijo in kristalizacijo kalcijevega karbonata v vodi mogo če vplivati z delovanjem zunanjega magnetnega pol ja. Za identifikacijo in karakterizacijo kristalizacijskih ob li k kalcijevega karbo nata po tretiranju vode z magnetnim poljem smo uporabljali NGIA (Near Grazing In ci dent An gle) refleksijsko FTIR (Fou rier Trans formed In fra Red) spektroskopijo. Snemali smo spektre na tankih filmih kalcijevega karbonata, ki smo jih dobili s suš enjem trde vode na različnih substratih. Tako smo študirali vpliv elementov v sledovih, kot so železo, baker in cink, ki so nava dno prisotni v vodovodni vodi, na prednostno tvorbo aragonita namesto kalcita ob istočasnem delovanju magnetnega pol ja. Morfološk e razlike med magnetno obdelanimi in neobdelanimi vzorci, to je med kri sta li dobljenimi s kontroliranim sušenjem netreti rane in tretirane modelne vode smo opazovali z vrstičnim elektronskim mikroskopom. Ključne besede: tretiranje trde vode z magnetnim poljem, FTIR spektroskopija, kalcit, aragonit 1 IN TRO DUC TION A number of investigations have been carried out on the effects of magnetic field on hard water 1-5 . It has been established that nucleation and crystallization of calcium carbonate from hard water can be influenced by a magnetic field and it is no longer necessary to always apply chemical methods for water softening. Calcite, the stable crystal modification of calcium carbonate, grows from hard water in clusters, which after a certain time form a solid scale firmly attached to the surface where the nucleation of crystals started. Aragonite, identified in the magnetically treated water, grows in unattached orthorhombic crystals, which are easily removed from the surface. Under normal temperature and pressure conditions, aragonite is an unstable crystal modification which spontaneously transforms into calcite. Another crystal modification of CaCO 3 is vaterite, which is the least stable of the three anhydrous calcium carbonate polymorphs and is gradually transformed into either calcite or aragonite. Different authors have emphasized various parameters (temperature, pH, strength and direction of the applied magnetic field, impurity elements, etc.), which influence the efficiency of the treatment with the magnetic field 6-10 . In our previous work the influence of different parameters on the nucleation and crystallization KOVINE, ZLITINE, TEHNOLOGIJE 33 (1999) 6 of calcium carbonate was studied 11 . For this purpose a special device with permanent magnets based on Sm -Co was developed and constructed 12 . In the present study we have focused on the influence of impurities of different elements on the crystallization form of calcium carbonate in the presence of an applied magnetic field. Herzog and coworkers reported the influence of ferro ions on the inhibition of calcite and promotion of the aragonite crystal form 3. Coetzee and coworkers 13,14 studied the influence of Zn 2+ ions, in ppb quantities, on the preferential formation of aragonite in magnetically treated water. There are other authors too, who have studied the influence of a great number of different trace elements, such as Fe 2+ (3,18) , Fe 3+ (3,18) , Mn 2+ (18) , Mg 2 + (18,19,20,21,22,23) , Zn 2 + (13,14,24) , Cu 2+ (17) as impurities in the water system. Our interest was to find an explanation for the changes in the crystallization form of calcium carbonate (crystals grown from the hard water) in the presence of an applied magnetic field. 2 EX PER I MEN TAL For the experimental work a model system based on bidistilled deionizied water with a maximum resistivity of 18 M ?/cm was used. Solutions of 0.035 M 517 B. PLAVŠI] ET AL.: IDENTIFICATION OF CRYSTALLIZATION FORMS OF… concentration Na 2CO 3 and CaCl 2 were added to the water as precursors for obtaining calcium carbonate (based on the literature data of Higashitani et al. 6). The concentration of Ca was 350 ppm 15 . To study the influence of impurity ions in ppm quantities, we used polished platelets of different metals (5 x 2.5 cm) as substrates for FTIR (Fourier Transformed Infra Red) spectroscopy thin films analyses as well as glass substrates covered by a thin layer of SnO 2:F. The metal platelets were made of Fe, Cu and Zn. These platelets were then covered with a thin film of model water solution and the samples were dried under controlled conditions (70°C and 40% humidity). For every substrate we prepared a treated and untreated sample. Treated water was exposed to a magnetic field of 200 - 280 mT during drying using permanent magnets based on Sm - Co. The crystals obtained by evaporation of water were analyzed by NGIA (Near Grazing Incident Angle) FTIR spectroscopy and scanning electron microscopy (SEM). A Perkin Elmer Spectrometer Model 2000 equipped with Spectra Tech NGIA, which enables measurements at 80° with P-polarized radiation has been used to characterize the thin films of deposited material. For scanning electron microscopy we prepared samples of model water and water with 10 ppm Cu 2+ ions on a graphite substrate. We used a JEOL JSM - 5800 scanning electron microscope and analyzed samples by qualitative and semiquantitative EDS analysis. To follow the differences between the chemical method of water treatment with phosphates and water treatment with magnetic devices we constructed a pilot station with three simultaneously operating lines. In the first line a chemical softener was used, in the second a commercial magnetic device and in the third line a magnetic treatment device based on Sm - Co permanent magnets which was manufactured at our institute. To study the effectiveness of our own magnetic device the heat exchangers from every line were weighed several times during a two year period to check how much calcium carbonate was deposited inside. 3 RESULTS AND DISCUSSION Each vibrational spectrum consists of a set of internal modes for each crystallographically distinct anion, with frequencies perturbed only slightly from the free ion values, and a set of low frequency lattice modes characteristic of the particular crystal structure 16 . The mid-infrared spectra of all carbonate minerals tend to look alike so an IR spectrum is a useful identification tool for this anion. The spectrum obtained from a thin film grown on Cu platelets (Figure 1) shows only the internal modes which appear in the normally accessible region of the infrared. On the spectrum of the untreated sample the fundamental bands of calcite can be seen at: 708 cm -1 ( ?4 - in-plane bend), 883 cm -1 ( ?2 - out-of-plane 518 bend) and at about 1400 - 1500 cm -1 (?3 - asymmetric stretch). The frequency for asymmetric stretching absorption is very broad and intense, so the band assignment is not precise. In contrast, the spectrum of magnetically treated water displays split bands for out-of-plane bending vibration and asymmetric stretching which is characteristic for the aragonite crystal structure. It is hard to say for sure, because of the overlapping of the bands, but it appears that there are also bands of vaterite. Vaterite has a band at ? 750 cm -1 which can be seen in the spectrum of the treated sample only. The bands of aragonite and vaterite can not be seen in the spectrum of calcium carbonate obtained from the untreated model water. Similar results were obtained with iron and zinc substrates but when the spectra of calcium carbonate were obtained from water deposited on the SnO 2: F coated glass (Figure 2) there was no evidence of the influence of the applied magnetic field. Both spectra were almost identical showing only characteristic bands of calcite. The influence of metal impurities from the metal substrates on the crystallization of calcium carbonate is obvious. Those metals are almost always present in tap water too and they impact on the crystallization of calcium carbonate contained in it. It should be noted that small frequency shifts of the observed LO modes in the spectra of the thin films were expected and are attributed to the observed LO modes which systematically appear at wave numbers higher than the corresponding TO modes detected in the IR absorption and/or diffuse reflection spectra. They correspond fairly well to the already known LO modes of calcite and aragonite monocrystals 16 . In addition, their relative intensities conform to observed TO spectra, Fig ure 1: NGIA FTIR spec tra ob tained from a thin film of cal cium car bon ate crys tals grown from treated and un treated wa ter on a cop per platelet Slika 1: NGIA FTIR spektri tankih filmov kalcijevega karbonata dobljenega z sušenjem netretirane modelne vode KOVINE, ZLITINE, TEHNOLOGIJE 33 (1999) 6 B. PLAVŠI] ET AL.: IDENTIFICATION OF CRYSTALLIZATION FORMS OF… Fig ure 2: NGIA FTIR spec tra ob tained from a thin film of cal cium car bon ate crys tals grown from treated and un treated wa ter on a glass platelet Slika 2: NGIA FTIR spektri tankih filmov kalcijevega karbonata dobljenega z sušenjem tretirane modelne vode undoubtedly proving the presence of the aragonite in the spectra of magnetically treated samples. The changes which appear in the model water after magnetic water treatment can also be followed with scanning electron microscopy. In Figure 3 and 4 there are SEM micrographs of calcium carbonate crystals obtained from untreated and treated model water, respectively, and it is clear that the crystals grown from the treated sample are bigger than those which crystallized from the untreated sample which is in accordance with the existing data 2,25 . An increase in the size of particles can have two beneficial effects 2. First, the larger crystals will not coagulate to form scale in the same way that smaller crystals would. This is the Fig ure 3: SEM mi cro graph of cal cium car bon ate crys tals ob tained from un treated model wa ter Slika 3: SEM slika kristalov kalcijevega karbonata dobljenega iz netretirane modelne vode KOVINE, ZLITINE, TEHNOLOGIJE 33 (1999) 6 Fig ure 4 : SEM mi cro graph of cal cium car bon ate crys tals ob tained from treated model wa ter Slika 4: SEM slika kristalov kalcijevega karbonata dobljenega iz tretirane modelne vode purpose of the magnetic water treatment units. Secondly, the presence of the larger crystals disrupts the equilibrium between the fluid and any existing scale. Smaller particles, in general, dissolve more easily so larger particles will reduce the local concentration of calcite in the solution and remove the existing scale. If we add copper ions to the model water (10 ppm Cu 2+ solution) and treat it with a magnetic field, we obtain a lot of spherules (Figure 5) which are due to vaterite formation 14 . The cubes and spherules are much bigger than in the untreated sample, particularly when compared with crystals from pure water. EDS analysis of the cubes reveals just calcium carbonate, while the spherules appear to be composed of calcium carbonate with copper ions accumulated in them (Figure 6). This indicates that trace amounts of copper in hard water Fig ure 5 : SEM mi cro graph of cal cium car bon ate crys tals ob tained from treated model wa ter with cop per im pu ri ties Slika 5: SEM slika kristalov kalcijevega karbonata dobljenega iz tretirane modelne vode z dodatkom 10 ppm Cu 519 B. PLAVŠI] ET AL.: IDENTIFICATION OF CRYSTALLIZATION FORMS OF… Fig ure 6: EDS anal y sis of spheru lites Slika 6: EDS analiza kroglic alters the nucleation and crystallization of calcium carbonate. The results of weighing the calcium carbonate deposits from the heat exchangers are shown in Figure 7. The weight increase of the heat exchanger in the chemical treatment line and the line with the magnetic water treatment device constructed in our laboratory does not differ significantly. In the case of the commercial magnetic treatment device the weight of the heat exchanger increased rapidly and the device had to be removed from the line because it lowered the water pressure. 4 CONCLUSIONS It is already known, and indeed been confirmed several times, that it is no longer necessary to always apply chemical means to prevent the accumulation of calcium carbonate on surfaces exposed to hard water, which is of great importance in reducing the chemical pollution of the environment. The application of a magnetic field to hard water successfully prevents the growth and agglomeration of calcium carbonate as calcite, but to obtain optimal results it is very important that the magnetic field has the proper strength and direction 4,6,15 . The most important aspect of the present work is the new approach of using FTIR spectroscopy as a method for characterizing thin films, which gives the possibility of rapid qualitative analysis of water treated with an external magnetic field. FTIR spectroscopy appears to be a useful method for characterization and identification of different forms of calcium carbonate. 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