Joseph, Cyriac

M A, Ittyachen

Paul, Issac

English

IACS Institutional Repository

liulimi J. Phys. TJX ( I), 37-40 (2003)U P  Aan international journalMicro hardness studies of pure and doped brushite crystalsIssac Paul, Cyriac Jos%>h and M A Ittyachcn*School of Pure and Applied Phj^ics, Mahatma Gandhi University.Kotltayain, K e r^ a  6S6 560, IndiaP A Varghcsc, Jacob Gc^gc and George VargheseCrystal Physics Center J  Si Bcrchmans' College,Changnacherry. K |ra la '6 S 6  101. India4K-inail . ittyac^en@ cusal ac in H e c e i v e d  M a y  2 0 0 2 ,  tU ' i e p t e d  3 S e p t r m h p t  2 0 0 2A b strac t : Vickers micro hardness studies on pure and doped brushite (CaHPOj 2H ,0) crystals are reported The micro hardness value (H j, work h.iidening ctiefficient (n), and first order clastic sliifness coelficient (C,,) are reported for brushite crystals doped with Ni. Cd Mg and Pb It has been ohsened that the micro hardness has a load dependent part and a load independent partK eyw ords . Urinary stones, doped brushite crystals, V ickers micro hardnessPACS Nos. 62 20 Mk, SI 10 I)n, K1 20 Pw1, introductionBio-mincralization in human systems affects a large population woild-widc and the number of cases reported is ever on the increase [ 11. Of the various crystals formed in the human body, de|H>sition of mailer in renal systems has become a common diseases resulting in the wastage of a number of man hours [2). C’alcium phosphates arc the most common crystals m urine. They are often identified at the center of calcium oxalate and calcium phosphate mixed stones 13). A variety of calcium phosphate stones v/z., CaHPO^.lHjO- (Brushites), CaHPO^, Caj^H(PO^).,OH and Ca^CPO^)  ^are found to grow in biological systems of mammals. Of these different stones, crystallization of CaHP0 .^2H20 plays an important role in the formation of metabolic and non-mctabolic urinary stones [4]. Brushites are significant for their role in the nucleation of calcium oxalate cry.slals |5].Investigations made on urinary stones have proved that at least 14 different trace elements are present in these crystalline components of matter [6]. The prominent among these trace elements arc Cd. Ni, Mg and Pb. These trace elements may enter the body through atmospheric pollutants and food. Cadmium Corresponding Authorand lead arc known toxic elements present in the human body and they enter the body along with food particles. Accumulation of cadmium is severe to the body since its presence in liver and kidney leads to renal tubular damage [7J. The incieases in load and nickel content in the body of gout patients results in renal failure due to nephrolithiasis [8|. The presence of an impurity element in crystalline solid changes its elastic properties. The change in hardness of the clement with dopant is very interesting.Fragmentation of stones has become an invasive technique of Slone therapy. The stones can be crushed inside the bladder, ureter or kidney. Hardness of the stones stumbles the process of such bloodless surgery. Extra corporal shockwave lithotripsy (ESWL) has become a primary treatment modality for urinary stone diseases [9]. Becau.se of their differences in chemical composition and structural features the efficacy of stone fragmentation may vary considerably [10]. Hardness of a material is a measure of the resistance it offers to local deformation 111]. A proper knowledge of the hardness of these crystals containing different trace elements will be useful in managing the disease more effectively .^ The variations of hardness on doping the crystal with these dopenls are discussed in this paper. Micro hardness©2003IACS38 Issac Paul et almeasurements have aided the determination of the clastic constants of the crystal. Knowledge of the elastic properties of stones is also essential in optimising the parameters like frequency and intensity required for stone fragmentation by ultrasound lithotripsy.The gel technique was employed to synthesize the brushite crystals. The gel medium has very close resemblance to the mucus medium in which the stones happen to grow in biological systems. In-vitro crystalii.sation m gel medium is popular in the study of cry.slalli/ation of urinary stones 112).2. ExpeninentaiThe crystals were grown in a gel medium of sodium metasilicale gel having density 1.03g cni^ and pH 5 6, by titrating the gel against 1.I8M potassium dihydrogen phosphates. After gelation, I.68M calcium nitrate solution was added as supernatant solution. Liesegang rings were formed within a few days. They arise due to the rhythmic precipitation of the supernatant solution through the gel medium. In a few days, these rings disappear and m that region spherulilic crystals were oKserved. Plaly crystals were also found to grow just below the region where spherulites were found in the medium [ 13). To dope the crystals with ingredients such as lead, nickel, magnesium and cadmium the supernatant solution was mixed with appropriate amounts of lead nitrate, nickel chloride, magnesium chloride and cadmium chloride solutions. Elemental analysis on the doped crystals confirmed the presence of the respective dopents on the doped samples.Crystals with different morphologies were found to grow in each system. Good quality crystals of medium size (5 x 2 x 0.5 mm) were obtained for pH 5.61 and gel density 1.03 gm/cm\ The growth period varied from 60 to 75 days.All the samples were analysed by using X-ray diffraction (XRD) and inductively coupled plasma emission spectroscopy (ICPEAS). The microhardness studies were carried out on pure and doped crystals using Vickers hardness tester.A. X-ray diffraction analysis :Powder XRD pattern lor the pure sample has been recorded using a Rigaku Dmax/2C (Japan) diffractometer fitted with nickel filtered Cu radiation (Figure I). The calculated d values from XRD of the crystals (Table 1) were in good agreement with standard values (14], The following are the lattice parameters of brushite crystals obtained from the XRD data.Ciystal system: Monoclinic,Space group: la,Cell dimensions : a = 5.812 A, /? = 15.180 A, c = 6.239 A, = I16.4P\N o : of molecules in unit ce ll: 4.R  Micro hardness studies :Micro hardness studies on smooth plane surfaces were carried out using Leitez hardness tester type PI 191 fitted with a Vickcr\Tabic 1. Calculated and standard d values of BrushitcsObserved d value (A  ) A S T M  d value (A") hkl plane7,5K4y 7 62 0 2 04 2329 4 .2 7 1213 0452 3 06 1412 9243 2 93 1212 6223 2 63 2 0 02 .5 3 1 5 2 5^ 0 6 02 .4163 2 47 2 2 02 2674 2 27 0 4 22 1702 2 17 1522 0847 2 .0 9 1122 0216 2 03 0712 001 2 01 170pyramidal diamond intendcr. The (100) planes of samples were identified and indentations were made on these faces using the diamond inlender. The indentation time was maintained at 30 seconds. The load was varied from 5g to l(K)g. For each load five indentations were made at a distance greater than 4 times the length of diagonal. The Vicker’s micro-hardness number was calculated loads using the relation.//^,= I.8544(P/d2)kg/mm2,where P is the applied load in kg and d  is the average diagonal length of the Vicker’s impression in mm after unloading. Both pure and doped samples were tested for its hardness.Variations of hardness with load for the pure and doped samples of pure and doped brushites are shown in Figure 2. TheMicro hardness studies on pure and doped hmshite crystals 39samples exhibited practically zero brittleness up to a load of 2(X)g, which is the maximum for the instrument.400350^300*1250*1^ 200 %X 150 100 50 0Figure 2. Hv vs  P curve for pure and doped brushites3. Results and discussionThe hardness and elastic properties of doped crystals show variations from the pure crystals. Figure 2 depicts the variations in microhardness with applied load for the different crystals. All ihc curves show a unique pattern in the low load region. Below a threshold load, the behaviour ol the doped as well as the pure ciystals arc identical. In this region the microhardness dependence with external stress is linear. For higher loads the micro-hardness becomes load independent. This is similar to the proportional resistance model (PSR model) proposed by 115, 16]. In the PSR model micro hardness has two ctintribulions.f !) The indentation load dependent part :Mayer's power law [17] can be applied to this part, which is in the low load region.P=Ad^^ ( 1)A plot of 'log p' versus 'log d' graph provides a straight line (Figure 3), the slope of which gives the work hardening1 8Pure Brushites0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5logd'^Igtirc 3. log p v.T log d curve for pure and doped brushitescoefficient n. The best linear lit ol this curve is taken to evaluate the work hardening coefficient n (Table 2). A is a constant parameter for a given material.Table 2. Mayer's law paramoiers clelei mined for pure and doped brushiic c iv s ta hCrystal Work haidem ng co e lfic ien i-n AHurt* brushites 2 8329 1.3040Nickel doped brushites 7 9135 3 3 120('adm ium  doped brushiie 3 3992 0 .8 1 0 3Magnesiuni doped brushites 3 -4298 1 0210Lead dtiped brushites 4 3883 2 .6192It IS found that the work hardening coefficient is the lowest for pure brushites while it increases for all the doped samples. All the crystals have n > 2, which confirms that they arc soft materials as per the Onslrich concept 118|. Accordingly the lattice is soft if n > 2 and if/? > 2 that lattice is hard. A hard lattice will show brittle characteristics in the high load region. Interestingly no crack lengths were observed when the samples were loaded to diflerent loads, 'fhus all the crystals can be assigned with soft lattices.From clinical experience, it has been concluded that of all urinary stones, brushites come under the middle order in the ea.se to fragment. The toughest ones being calcium oxalate monohydratc and cystine [19, 2()|. The work hardening coefficient n is highest for Ni doped crystals, followed by Cd and Pb doped crystals and interestingly the least for Mg doped. The inhibiting property of Mg in brushiie crystals is well established by Shiv Kumar etal[2\](ii) The indentation load independent p a r t :In the high load region, classical Mayer's law was insufficient as the microhardness tends to be load independent. A polynomial equation represents the experimental data. The indentation test load P is related to indentation size d as :P -  a^d -\raid^ -  a^d +  ! d ^^d ^ , (2)where r/j is the proportionality constant in the load dependent region and a^  ^ that in the load independent region, P. is the critical applied test load above, which micro hardness becomes load independent and d^  ^ is the corresponding diagonal length. The first term m cq. (2) represents the surface energy contribution. Eq. (1) can be rearranged to give(3)Hence, a plot of 'Ptd versus 'd  will give a straight line and the slope of which gives the value of load independent micro hardness when multiplied this by the Vickcr'sconversion factor 1.8S4 gives the load independent micro40 Issue Paul et alhardness. In this region too the micro hardness is the least for the pure samples and high for the doped ones (Table 3). The micro hardness of brushites has considerable variation from there respective pure sam ples. D oping with m agnesium  decreases the //„ values whereas all other dopents like lead, cadmium and nickel increased the //„  value when compared to the pure brushites. Thus the dopents have a considerable inOuence on the hardness of the urinary crystals. As the pollutants like nickel, lead and cadmium increase in the body the liardncss of the formed stones is on the increase making it diflicult for the removal by shock wave lithotripsy.Tabic 3. FKS nuulcl piuamcicrs and load independent rnicrohardness values and lust older elastic constants of pure and doped brushitesCrystal pc/d,; (Pa) II (Pa) C.. (Pa)1 29 2 40 4.62771 14 2 12 3 72462.91 5.41 19 19092.13 3 95 11 06731 44 2 67 5 5769Pure brushites Nickel doped brushites Cadmium doped brushites Majjnesium doped brushilc Lead do|)cd brushiiesThe first order clastic stiffness coefficient C ,, of the samples are calculated using Wooster’s empirical relation 122|.r  -'■II "o  •4. Conclusion(4)Hardness variations in the load dependent and load independent regions for pure and doped brushite crystals are reported for the first time. Elastic properties of pure and doped brushite cry.slals are interestingly related to the impurity addition in crystals. All the crystals show remarkable changes in micro hardness, work hardening coefficient and first order elastic stiffness coefficient. Microhardness studies carried out on the doped crystals shows that the difference in size of the ions constituting the mixed crystal is responsible for internal elastic ion interaction in the lattice and these types of strain gives rise to imperfections affecting the microhardness o f the doped crystal. The pre.sence of the cations of Pb, Ni, Cd, and Mg in place ofC a ions induces strain in the lattice due to the different ionic radius of the dopent resulting in the increase in the work hardening coefficient. In the load independent part too the value of Vicker's microhardness is the least for the pure samples and itincreases for the doped crystals. This study reveals that tlic dopents have a definite influence of brushite crystals and then presence increases the hardness of the crystals making the stone removal harder by way of crushing it inside the body.AcknowledgmentsAuthors (IP, PAV and JG) acknowledge the fellowship under FIl* (IX plan scheme) by UGC, New Delhi.R e fe re n c e s111 W G Roberl.son* M Peacock, A Hodgkinson /  Chronic Diseases 32 469 (1979)[2] J Lapides FumUimentals of (Jrolo}*y (Philadelphia * W. B. SauiidciM P206 (1976)[3J P Dieppe and P Calvert Crystals and Joint Disease (London Chapman & Hall) (1983)[4J SR Khan and P A Glenlon /  Uroi 153 811 (1995)[51 L Clapham, R J C Mclean, J C Nickel and J Downey /  Crysial (Irowih 104 475 (1990)[6] J Hofliancr, I Stelfan, K Hodailh and G Vukicic J Urol 146 (1991)|7) R Scott and C Cunningham Br J. Urol 54 611 (1982)[8] EM Carus and F A Mateos Nephron 75 327 (1997)[9J C G Chaussy and G C Fuchs J Urol 141 782 (1989)[10] D J Sutor Urolithiasis Physical Aspats, (National academy d science, Washington) p43 (1972)[11] B M Mott Mu ronidentalion Hardness Testing (London Butterworths) p206 (1956)[12] Chiller. R Feriiag and H Ridemiller./ Urol 154 1552 (1995)[13] S Nalarajan and N Srinivasan Indian J Phys 70A 563 (1996)[14] ASI'M Pomlei DiHiaciion file No 9-77 ctimpiled by JC PPS (1983)115] H Li and R C Bradi Matei Sci Enf>}i A142 51 (1991)[16] S Mukcrji and T Kar Cry si Res Talinol 34 1323 (1999)[17] E Mayer : PhD Thcsiv (Dreft) (1951)[18] EM Onstrich Microscopic 2 131 (1947)[19] R A Richlcjr, H B Caiter and E D Vaughan J Endourol 137 (1987)[20] S P Dretlei J Urol 139 1124 (1988)[21] G R Shivakuiiiar, S Narayana Kalkura and P Ramaswainy, Main Cheni Phys 57 238 (1999)[22] W A Wooster Rep Pro ,^ Phys 16 62 (1953)

Micro Hardness Studies of Pure and Doped Brushite Crystals

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Micro Hardness Studies of Pure and Doped Brushite Crystals

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