Cerámica y Vidrio A R T I C U L O

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1 B O L E T I N D E L A S O C I E D A D E S P A Ñ O L A D E Cerámica y Vidrio A R T I C U L O A view on organic binder effect on technical propertie of ceramic Rachig ring Y. BEYGI KHOSROWSHAHI, A. SALEM * Mineral Proceing Reearch Center, Chemical Engineering Department, Sahand Univerity of Technology, Tabriz, Iran. Organic binder uch a polyvinyl alcohol, carboxymethyl celluloe and Arabic gum are widely ued to control the technological parameter required for green and intered ceramic bodie. An indutrial ceramic Rachig ring compoed of kaolinite, illite, pyrophillite and quartz mineral wa eparately mixed with different content of above binder and formed by extruion proce in the hape of Rachig ring. The dried pecimen were intered at 1270 C and the phyicalmechanical characteritic of intered bodie were evaluated by meauring bulk denity, total and cloed poroitie and compreive trength. In addition, the effect of binder type and amount on reliability of ceramic Rachig ring wa evaluated by computing Weibull modulu. The obtained data exhibited optimum trength and reliability in preence 0,75 wt.% carboxymethyl celluloe. Keyword: Rachig ring, binder, compreive trength, Weibull modulu Influencia del aglomerante utilizado en el proceamiento de anillo Rachig cerámico obre la propiedade mecánica Lo compueto orgánico tale como el alcohol polivinilico, la carboxilmetil celuloa y la goma Arábica on ampliamente utilizado para coneguir aglomerar lo polvo cerámico en verde. Se han preparado, por el método de extruión, materiale cerámico en forma de anillo Rachig a partir de minerale (caolina, illita, pirofilita y cuarzo) mezclado con diferente contenido de alguno de lo aglomerante mencionado. Lo anillo, una vez eco, fueron interizado a 1270 ºC y caracterizado fíicamente; e midieron la denidad, poroidad total y cerrada y la propiedade mecánica. Aimimo e evaluó el efecto del tipo y cantidad de aglomerante empleado en el proceamiento de lo anillo calculando el módulo de Weibull para lo ditinto anillo. Lo dato obtenido indican que la mayor reitencia mecánica e preenta cuando e ha utilizado 0,75% en peo de carboxilmetil celuloa como ligante. Palabra calve: Anillo Rachig, aglomerante, propiedade mecánica, modulo de Weibull. 1. INTRODUCTION Ceramic Rachig ring are very appealing for high performance application in chemical and oil indutrie due to their thermal and corroion reitance in acidic environment (1). However, improvement and prediction of compreive trength for ceramic Rachig ring i important tep in manufacturing thi group of ceramic (2). A the tre concentrate at defect of ceramic body therefore, the homogeneity increment of ceramic microtructure improve the reliability of ring (3). The all mot of ceramic bodie are brittle material and tre i not relieved by local deformation near the crack tip a it happen in metal and polymeric material. Therefore, it can be expected that crack eaily propagate and decreae the potential of application (4,5). The compreive trength limiting defect often arie during manufacturing of ceramic Rachig ring and perit through the haping proce, o performance of the packed bed may be limited by thi tage of proce (6). For the ceramic bodie prepared by clay baed material, defect can be related to compaction of raw material during haping tep. Extruion i a widely ued fabrication proce for haping of ceramic (7). In thi method the pate of material which are wetted to flow Bol. Soc. Ep. Ceram. V. 49, 5, (2010) through the die by motly water that may contain inorganic or organic additive uch a binder, deflocculant and platicizer were formed. The advantage of extruion method i the production of ring with high reliability compared to other method uch a lip cating and preing (2). A major diadvantage coming from extruion i mall internal defect remaining in tructure of haped body which can coniderably limit the compreive trength of ring after the intering (8). The compreive trength of ceramic Rachig ring,, i related to the geometrical dimenion of ring method by following equation (9): where F i the load for failure of ring, D o, D i and L are out diameter, inide diameter and width of ring repectively. K i the tre contant which i a function of D i /D o ratio and lie in the part of Frocht curve experimentally obtained to be equal 7 for extruded pecimen in D i /D o ratio of [1] 335

2 Y. BEYGI KHOSROWSHAHI, A. SALEM (9). Weibull analyi i widely ued to determine reliability of material. The Weibull modulu i cloely related to defect tatitic remaining in body tructure. Thi method for reliability evaluation of ceramic Rachig ring relate trength to probability of failure uing compreive trength ditribution a follow (4,5): where P n i the probability of failure, V i the ample volume, w i the tre at which the probability of failure i zero, 0 i a characteritic trength and m i Weibull modulu. For brittle material uch a ceramic and gla w i often equal to zero which implifie the equation to the two parameter model a: To apply thi model, the compreive trength a et of ring are ranked in order of acending trength and the probability of failure of each ample i calculated uing the following etimator. Thi equation wa elected according the better fitting of experimental data reported by Salehi and Salem (10). where n i the ample rank and N i the total number of teted ample. The lope of a plot with axe ln[(-ln(1-p n )] and ln() give the Weibull modulu and characteritic trength. Table I: The chemical analyi of ued kaolin L.O.I Na 2 O K 2 O MgO CaO TiO 2 Fe 2 O 3 Al 2 O 3 SiO ±1 58 ± 1 [2] [3] [4] The objective of thi tudy wa to examine the influence polyvinyl alcohol, PVA, carboxymethyl celluloe, CMC, and Arabic gum, AG, on phyical-mechanical propertie of dried and intered ceramic Rachig ring fabricated by extruion proce. In order to better undertand the role of binder type and content on reliability of ring, the Weibull tatitic theory were applied and reult were compared with canning electron microcopy tet. 2. EXPERIMENTAL PROCEDURE Different erie of pecimen were prepared by extruding of indutrial kaolin with different type and amount of binder. Dried denity, poroity and compreive trength were meaured. The influence of binder on characteritic of intered pecimen uch a hrinkage, water aborption, bulk denity, total and cloed poroity, compreive trength and Weibull modulu were evaluated. Indutrial kaolin with mean particle ize of 2.6 mm, pecific urface area of 3.6 m 2 /g and true denity of 2.30 g/ cm 3 wa ued in thi invetigation. The chemical analyi and XRD pattern of raw material are preented in Table I and Figure 1 repectively. The pate were eparately prepared uing different content of PVA, CMC and AG a binder. The mentioned binder with different content firtly were diolved in ditilled water and then were added the kaolin powder. The content of moiture in prepared pate wa conidered 30 wt% per unit of dried powder. Baed on the earlier tudie carried out by Salehi and Salem (6) the obtained pate which contain different binder percentage per unit of dry kaolin were left for 48 hour to achieve the homogenou moiture. The pate were continuouly de-aired uing a laboratory pug mill and extruded uing an extruder, prototype. The extruion rate wa et at 8 mm/min and haped pecimen were cut a Rachig ring with the ame dimenion in length and outer diameter after drying in 100 C. The drying proce wa performed in laboratory oven to remove the moiture of pecimen. Table II: The geometrical dimenion of dry pecimen compoition binder (wt.%) length (cm) internal diameter (cm) external diameter (cm) STD ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.01 STD+AG ± ± ± ± ± ± ± ± ±0.01 Figure 1: The XRD pattern of kaolin ued in experiment I: illite, K: kaolinite, P: pyrophillite and Q: quartz 336 Bol. Soc. Ep. Ceram. V. 49, 5, (2010)

3 A view on organic binder effect on technical propertie of ceramic Rachig ring The geometrical dimenion of ring were preented in Table II Dried denity wa meaured uing weight and geometrical dimenion of ring and total poroity of them were determined from the following equation: In order to tudy the effect of binder on compreive trength of final product, the dried ring were intered in an electrical high temperature furnace (Model EX L, Iran) uing the firing chedule decribed in Table III. The geometrical dimenion of intered ring were reported in Table IV. The following parameter were elected to evaluate the propertie of ceramic Rachig ring according tandard method hrinkage, water aborption, bulk and true denitie and total and open poroity (11,12). The total poroity of intered body wa calculated uing equation 5 and the difference of total and open poroitie how the value of cloed poroity. XRD tet (Model D5000 Siemen, Germany) wa carried out on intered ample to identify the mineral formed in ceramic body. To determine compreive trength of ring, at leat twenty intered pecimen were diametrically compreed between the two plate with cro head peed of 1 mm/min and the trength wa calculated uing equation 1. The Weibull modulu wa evaluated uing the leat-quare method by a two-parameter model. The morphology of the defect and pore were oberved after intering run by canning electron microcopy (Model Eol-4401, England). The SEM tet were performed on cro ection of pecimen. Thermogravimetric analye (Model Perkin Elmer SII, England) were performed on powder containing different Table III: The intering program of furnace heating rate ( C/min) temperature range ( C) time (min) [5] content of binder. The ample were heated from room temperature to 750 C at heating rate of 5 C/min. Fourier tranform infrared pectrometry, FTIR, (Model Unicam Matton 1000, Philip) were obtained to determine chemical group of binder. 3. RESULTS AND DISCUSSION In order to obtain complementary evidence for the chemical band of binder, FTIR pectra were recorded in the region of cm -1. Figure 2 how that FTIR pectrocopy i very enitive to -O- appeared in wave number of 1070 cm -1 in all of binder. There i a group tranmittance peak between cm -1, which i due to band of -CH 2 group and the band at 1700 cm -1 correpond to -C-O that i oberved in PVA. The tranmittance peak related to C-H and C-CO-OH group were alo appeared in FTIR pattern of PVA in wave number of 2250 and 3400 cm -1, repectively. The vibration of C=O and -CO-ONa group can be oberved both in CMC and AG pattern in wave number of 1650 and 3450 cm -1 repectively. Figure 3 depict the TG curve for three binder ued in compoition of ceramic Rachig ring at heating rate of 5 C/ min. The thermogravimetric curve how two weight lo of 1 and 4 wt.% which correpond to burning of binder and dehydroxylation of the kaolinitic-illitic clay. The phyico-mechanical propertie of dried bodie containing different type and amount of binder were reported in Table V. The compoition without binder, denoted by STD, how the lowet bulk denity and highet volume of poroity compared to the ring prepared by addition of binder. The total poroity hould be le to effective control of compreive trength of dried body. The bodie which appear ignificantly change in bulk denity were elected for further tudie of compreive trength tet in each run. From the data of Table V, it i obviouly een that the STD pecimen prepared without binder how the lowet dry trength of 28 kpa. It i alo clearly oberved that the addition of PVA in ceramic body compoition how maximum trength compared to the Table IV: Geometrical dimenion of intered ring compoition binder (wt.%) length (cm) internal diameter (cm) external diameter (cm) STD ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.02 STD+AG ± ± ± ± ± ± ± ± ±0.01 Figure 2: FTIR pattern recorded on PVA, CMC and AG Bol. Soc. Ep. Ceram. V. 49, 5, (2010) 337

4 Y. BEYGI KHOSROWSHAHI, A. SALEM other cae. Among the variou content of PVA ued in thi invetigation the preence 1 wt% PVA in body compoition how maximum improvement in dry compreive trength. The trength of 383 kpa for body prepared with 1 wt% PAV and 28 KPa for STD indicate the increae of 13 time approximately. CMC and AG alo improve the trength of ring but the pecimen how only an increae of 5 and 4 time in preence at 1 wt% CMC and 2.25 wt.% AG repectively. Compared to STD trength, thi increment in dry compreive trength wa obtained in preence 0.5 wt% PVA. Maximum trength ha been oberved in pecimen that prepared with PVA indicating ignificantly improvement over STD compoition. Among all pecimen prepared with binder ued in thi work, AG how lowet degree of improvement in trength. Thi variation in trength indicate coherence between kaolin and PVA when the reult compare to thoe for CMC and AG. The ceramic Rachig ring were fired in 1270 C and the phyical propertie of bodie containing different type of binder were meaured and the reult were reported in Table VI. Figure 3: TG curve of bodie containing different content of PVA, CMC and AG Table V: Phyico-mechanical propertie of dry bodie containing different type and amount of binder compoition binder (wt.%) bulk denity (g/cm 3 ) total poroity (%) dry trength (kpa) STD ± ±0.4 28± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.4 84± ± ± ± ± ± ± ± ± ± ±0.4 - STD+AG ± ± ± ± ± ± ± ±4 Table VI: Phyical propertie of intered bodie containing different type of binder compoition binder (wt.%) hrinkage (%) water aborption (%) bulk denity (g/cm 3 ) total poroity (%) cloed poroity (%) STD ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.2 STD+AG ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Bol. Soc. Ep. Ceram. V. 49, 5, (2010)

5 A view on organic binder effect on technical propertie of ceramic Rachig ring The hrinkage of bodie containing different content of PVA continuouly increae reached a maximum value in preence 1 wt% PVA. It i obviou that the change in hrinkage value i negligible when the ceramic body contain low content of PVA, le than 0.75 wt %. Among the variou content of CMC ued in thi work hrinkage approximately remain contant near to 15.2 %. The variation in hrinkage of bodie contain different amount of AG i imilar to bodie prepared by PVA. Shrinkage remain contant when the amount of AG ued in preparation of body wa le than 1.25%. Therefore, the compoition prepared by 1.75 and 2.25 wt% AG how high value of hrinkage indicating an increment of 1%. Uing the amount of water aborption reported in Table VI, the increae in binder amount i motly accompanied with decreae in water aborption in three group of compoition. Thi decreae in water aborption occur a a reult of compaction of body during extruion proce. Regardle the ome exception, the water aborption le than 0.5% atified the tandard range for production of ceramic packing. Table VI preent the value of bulk denity for kaolin/binder compoition intered at 1270 C. Similarly, the bulk denity of bodie containing 1% PVA and 1.75% AG were higher than that for body prepared by 0.75% CMC. Thee reult follow the fact that the mentioned compoition were compacted relatively better compared to compoition prepared with CMC. The total and cloed poroitie of ceramic Rachig ring hould be compared in order to dicu the denification, becaue the number of pore and poroity ignificantly affect the compreive trength of intered bodie. Table VI report the value of total and cloed poroity of ring prepared with different type of binder. The value of total and cloed poroity of body containing 1% PVA coniderably are low in comparion to the other kaolin/binder compoition, even the preence 2.25% AG in body compoition could not decreae the poroity. For the better undertanding the effect of binder type and content on reliability of ceramic Rachig ring, Weibull tatitic method wa ued. According to ASTMC-1239 tandard (13) method the confidence bound can be contructed for etimated Weibull characteritic trength. The 90% confidence bound on characteritic trength i obtained from the 5 and 95 percentile ditribution. The probability of failure a function of compreive trength were hown correponding to binder Figure 4: The XRD pattern of fired pecimen in 1270 C, M: mullite, Q: quartz type and content in Figure 5. The trength of ceramic Rachig ring prepared with different binder content how good agreement with linear correlation coefficient of 0.95 to 0.98 with Weibull model and good adjutment can be oberved between the experimental data and Weibull ditribution obtained by Equation 2. The lower and upper value of trength and Weibull modulu obtained for kaolin/binder ytem are preented in Table VII The confidence bound of trength vary proportionally with their total poroitie with exception in body containing 0.75% CMC. The trength of thi body wa remarkably improved by uing 0.75% CMC in body compoition. The trength reached a maximum value and then decreaed with a correponding increae in CMC content. On the other hand, the trength of bodie prepared with 1.75% AG i coniderably high which i near to maximum trength of body prepared with 0.75% CMC. The trength of ring eparately prepared with 1% PVA and CMC, are quite equal to average value of 32 MPa. The trength of bodie prepared by 0.5% PVA and CMC tend to behave imilar to STD compoition with value of 21 Table VII: Mechanical propertie of intered bodie containing different type and amount of binder compoition binder (wt.%) characteritic trength (MPa) Weibull modulu compreive trength (MPa) lower bound upper bound lower bound upper bound STD STD+AG a R: Linear regraion cofficint R a Bol. Soc. Ep. Ceram. V. 49, 5, (2010) 339

6 Y. BEYGI KHOSROWSHAHI, A. SALEM Figure 6: The morphology of defect in STD compoition Figure 7: The morphology of defect in body prepared by 0.75% CMC Figure 5: The probability of failure a function of compreive trength Rachig ring prepared with different type and content of binder, (a) PVA, (b) CMC and (c) AG Figure 8: The morphology of defect in body prepared by 1.0% PVA 340 Bol. Soc. Ep. Ceram. V. 49, 5, (2010)

7 A view on organic binder effect on technical propertie of ceramic Rachig ring MPa that how the preence 0.5% of above binder did not affect the trength of body. The poroity dependency of trength for bodie containing 0.75% CMC doe not different ignificantly from the STD body. Epecially, the total poroity of body prepared with 0.75% CMC wa round of 6.0% which i the ame for STD compoition. Generally, pore hould be eliminated becaue the trength of ceramic exponentially decreae with increaing of poroity. It i intereting to note that the body containing 0.75% CMC how a high trength depite it large poroity. It ha been reported that the trength of clay baed ceramic are affected by the mineralogical phae produced during the intering proce. Conequently, the formed phae uch a mullite and reidual crytal uch a quartz influence the trength of ceramic Rachig ring which i found in XRD pattern of fired pecimen in 1270 C a hown in Figure 4. It i clearly een from the data of Table VII that the ue of binder in compoition of ceramic Rachig ring improve the Weibull modulu a reult, the reliability of failure. The value of Weibull modulu are in agreement with cattering found for trength data. Depite, increment of binder content, the Weibull modulu how a general decreae particularly for pecimen containing PVA. Thi trend can be attributed to defect and pore ize ditribution in ceramic body. The defect population play ignificant role in mechanical trength and reliability of ring. They can contribute alo to increae the data cattering. Therefore, the reliability of ring decreae a function of defect ditribution. A dicued before, ince the compoition of clay and heat treatment wa kept contant in thi invetigation, the reult concerning the pecimen trength can be attributed to tructure texture of ring. The ring prepared by 0.5 wt% PVA how coniderably increae Figure 9: The morphology of defect in body prepared by 1.75% AG in reliability compared to STD compoition. The preence 0.5 wt% PVA in initial compoition caue homogenou ditribution of defect on tructure of ring. The total poroity of pecimen alo, i not approximately affected in preence of 0.5 wt% PVA. The SEM photograph of fracture urface how the preence of large defect in STD compoition heterogeneouly ditributed in cro ection of ring a hown in Figure 6. The preence of defect homogeneouly ditributed in tructure of ring prepared by 0.75 wt% CMC i the main reaon for improving reliability of ring a hown Figure 7. In particular, the decreae in dimenion of defect in body prepared by 0.75% CMC can be conidered a reponible for the compreive trength and Weibull modulu of ring compared Figure 10: The SEM photograph of fracture urface of pecimen prepared by (a) with out binder, STD, (b) 1.0% PVA, (c) 0.75% CMC and (d) 1.75% AG Bol. Soc. Ep. Ceram. V. 49, 5, (2010) 341

8 Y. BEYGI KHOSROWSHAHI, A. SALEM to STD tructure. The increment in Weibull modulu of body prepared by AG i the le than that for the ring prepared by PVA and CMC. The reult can be attributed to a low homogenouly ditribution of defect and their dimenion on fracture urface of ring (Figure 8). The inefficient coherence between the clay and AG may be not able to remove the defect of pecimen during extruion a preented in Figure 9. The fracture urface of ring prepared with 1.75wt% AG how rather large defect compared to pecimen prepared with 0.75 wt% CMC. The morphology of pore in ceramic Rachig ring prepared by different type of binder wa compared in Figure 10. The ubtantial difference wa not oberved in ditribution of cloed pore in microtructure of ring. Therefore, from point of view, the defect dimenion and their ditribution can be conidered to be the main reponible for mechanical behavior. Alo, the product containing 0.75 wt% CMC i uggeted a optimum binder content for extruion proce of ceramic Rachig ring. 4. CONCLUSIONS Phyico-mechanical propertie of dried and intered ceramic Rachig ring were tudied in preence different type and content of binder. Compreive trength and Weibull modulu were meaured to evaluate the effect of binder on reliability of ring. The following concluion were drawn from thi invetigation: 1. The addition of 0.5wt.% polyvinyl alcohol improve the mechanical reliability of intered ceramic Rachig ring due to homogeneou ditribution of defect. The increae in binder content yield the defect with elongated dimenion that decreae the Weibull modulu a well a reliability of ring. 2. Carboxymethyl celluloe and Arabic gum did not influence the Weibull modulu of compreive trength compared to polyvinyl alcohol. However, the difference in defect dimenion are affected by carboxymethyl celluloe therefore, the compreive trength i improved in preence of 0.75 wt.% of thi binder. 3. The intered pecimen with high value of trength were fabricated by addition of 1.75 wt.% Arabic gum but the Weibull modulu were 5.2, which i relatively lower than that for pecimen prepared with polyvinyl alcohol and carboxymethyl celluloe. REFERENCES 1. W.L. McCabe, J.C. Smith, P. Harriott, Unit operation of chemical engineering, McGrow-Hill Publihing Co, 6 th, J.M. Villora, P. Calleja, M.F. Barba, C. Baudın, Statitical analyi of the fracture behavior of porou ceramic Rachig ring, J. Eur. Ceram. Soc., 24, , (2004) 3. J.S. Reed, Principle of ceramic proceing, John Wiley & Son, 2 nd, New York, USA, D.W. Richeron, Modern ceramic engineering, Marcel Dekker INC, New York, USA, R. Morrell, Hand Book of Propertie of Technical and engineering ceramic, Her Majety Stationery Office, London, UK, M. Salehi, A. Salem, Effect of moiture content on extruion proce of kaolinitic-illitic clay in manufacturing of ceramic Rachig ring, J. Mater. Proc. Tech., 200, , (2008) 7. J. Benbow, J. Bridgwater, Pate flow and extruion, Oxford Un. Pre Inc., New York, USA, M. Salehi, A. Salem, The effect of intering temperature on reliability of extruded ceramic Rachig ring, Bol. Soc. Ep. Ceram. V., 48, 1, 1-5, (2009) 9. S.A. Bortz, H.H. Lund, The brittle ring tet. In the proceeding of a conference conducted by the chool of engineering and the college extenion diviion, North Carlonina tate college in cooperation with the office and ordinance reearch, ed. Intercience publiher, New York, , M. Salehi, A. Salem, Influence of intering condition on trength reliability of ceramic Rachig ring haped by extruion proce, Material Proceing for propertie and performance conference MP 3, 5, , (2006) 11. ASTM C373, Standard tet method for water aborption, bulk denity, apparent poroity and apparent pecific gravity of fired whiteware product, annual Book of ASTM Standard, PrEN 623-2, Method of teting advanced technical ceramic general and textural propertie, part 2: determination of denity and poroity, European Standard, ASTM C1239, Standard practice for reporting uniaxial trength data etimating Weibull ditribution parameter for advance ceramic, annual Book of ASTM Standard, 2001 Recibido: Aceptado: Bol. Soc. Ep. Ceram. V. 49, 5, (2010)