Crystallization of SiO2–CaO–Na2O Glass Using Sugarcane Bagasse Ashas Silica Source

Silvio Rainho Teixeiraw

Departamento Fısica, Quımica e Biologia, Universidade Estadual Paulista–UNESP, Presidente Prudente,SP 19060-080, Brazil

Maximina Romero and Jesus Ma. Rincon

Department of Building Construction Systems, Eduardo Torroja Institute for Construction Sciences-CSIC,28033 Madrid, Spain

This work reports the feasibility results of recycling sugar canebagasse ash (SCBA) to produce glass–ceramic. The major com-ponent of this solid residue is SiO2 (489%). A 100 g batchcomposition containing ash, CaO and Na2O was melted andafterward, poured into water to produce a glass frit. The crys-tallization kinetic study by nonisothermal method was per-formed on powder samples (o63 lm) at five different heatingrates. Wollastonite is the major phase in crystallization atT49701C, and below this temperature there is a predominanceof rankinite. The crystallization activation energies calculatedby the Kissinger and Ligero methods are equivalent: 374710and 378713 kJ/mol. The growth morphology parameters haveequal values n5m5 1.5 indicating that bulk nucleation isthe dominant mechanism in this crystallization process, wherethere is a three-dimensional growth of crystals with polyhedron-like morphology controlled by diffusion from a constant numberof nuclei. However, differential thermal analysis (DTA) curveson both monolithic and powder glass samples suggest that crys-tallization of the powder glass sample occurs through a surfacemechanism. The divergence in both results suggests that theearly stage of surface crystallization occurs through a three-dimensional growth of crystals, which will then transform toone-dimensional growth.

I. Introduction

INDUSTRIAL processes and energy production always producewaste. Nowadays, there is worldwide consensus that there is a

need to recycle and reutilize these waste residues for an efficientutilization of natural resources. A wide variety of industrial res-idues have been used in the production of glass–ceramics.1–6

Rawlings et al.7 published a review on the re-use of residuescontaining silica for the production of glass–ceramics. The ver-satility of the process of glass–ceramics production is manifestedby the great number of residues that have been used as primarymatter in its production: high furnace slag, fly ash from theburning of charcoal and garbage, sludge from galvanoplastyand alumina production, and remains of disposable glass,among other types. Published works have shown the potentialof transforming silicate-based residues into glass–ceramic prod-ucts of great utility. The general process involves the vitrificationof a silicate (residue), or mixture of various residues, followed bya crystallization process to form the glass–ceramic.

Brazil is the world’s largest producer of alcohol and sugarfrom sugarcane. In view of the strong national demand and thegreat interest shown by industrialized countries for ethyl alco-hol, there is a current race in Brazil for the implementation of asubstantial number of factories for the production of sugar andalcohol. The estimated 2007/2008 sugarcane harvest8 is 528 Mtto produce sugar (49.47%) and alcohol (50.53%). The sug-arcane stalks are crushed to extract their juice and the fibrousresidue remaining is named bagasse. Currently, sugarcane bag-asse is burned in boilers to produce steam, which is utilized inthe factory processes and also to power turbines for the pro-duction of electrical energy, which supplies the factory energyneeds with the excess being commercialized in the region. Thevolume of ash that will be produced in this harvest is approx-imately 3.2 Mt (1000 kg cane-250 kg bagasse-6 kg ash).

The crystallization of glass to make glass–ceramics consists oftwo steps, the nucleation and the growth stages. In the firststage, small stable volumes of product phase (crystalline) areformed, generally at preferential sites (interfaces or on the freesurface) of the glass precursor. Often, internal nucleation orbulk nucleation is required, and the composition of the initialbatch is selected to contain species that increase this form ofnucleation. These species are called nucleating agents and can bemetallic (i.e., Au, Ag, Pt, and Pd) or nonmetallic (i.e., TiO2,P2O5, and fluorides). The rate of nucleation is strongly depen-dent on temperature, and once the stable nuclei are formed, thegrowth of the crystal begins. Growth involves the transport ofmatter, that is, the movement of atoms/molecules of glassthrough the glass/crystal interface and to the inside of thecrystal. The driving force for this process is the difference inthe free energy, DGv, between the vitreous and crystalline states.The transport of atoms/molecules through the interface is ther-mally activated with an associated energy of activation, DGa.Models involving these two energies have been developed forrate of growth as a function of temperature.9,10

Holand and Beall9 discussed the base glasses of the SiO2–Al2O3–CaO system (wollastonite) suitable for producing glass–ceramics according to the mechanism of controlled surface crys-tallization. Conventional heterogeneous nucleating agents, suchas TiO2 and ZrO2 are used in the process. A base glass is pro-duced in the form of granular glass particles measuring 1–7 mmthat are required for controlling surface crystallization. Glass–ceramics with a main wollastonite crystal phase have been madefrom these base glasses according to the above mechanism. Themost significant glass–ceramic for building applications is man-ufactured under the brand name Neoparies, which is producedon a large scale as a building material especially for interior andexterior walls. A basic composition must first be melted to pro-duce a melt that is poured into water to produce a frit. Aftermolding, the glass grains are sintered to a dense monolithic glassby heat treatment. At temperatures above approximately 9501C,

L. Pinckney—contributing editor

wAuthor to whom correspondence should be addressed. e-mail: rainho@fct.unesp.brManuscript No. 25757. Received 26 January 2009; approved 9 September 2009.

Journal

J. Am. Ceram. Soc., 93 [2] 450–455 (2010)

DOI: 10.1111/j.1551-2916.2009.03431.x

r 2009 The American Ceramic Society

450

controlled surface crystallization of b-wollastonite (CaO � SiO2)begins at the boundary of the former glass grains. At 10001C,wollastonite grows in needlelike form from the surface of theglass toward the interior of the glass grain, without crossingboundaries with neighboring glass particles. With heat treat-ment at 11001C for 2 h, controlled surface crystallization of b-wollastonite for the production of finished glass–ceramic sheetsends. During this heat treatment, however, the crystallizedboundaries join together to form large crystal needles withlengths of 1–3 mm. The boundaries of the base glass grainsare virtually indiscernible in the glass–ceramic end product.However, more opaque b-wollastonite of a granular crystallo-graphic morphology is produced if the b-wollastonite glass ce-ramics are heated to 12001C rather than 10001C.

According to Navarro,11 this calcium metasilicate shows twodifferent crystalline modifications: a-wollastonite (or pseudo-wollastonite) and b-wollastonite. The first corresponds to thestable form above 11801C and thus appears in the shape ofspheres or of aggregated large-sized crystals in glass massescooled very slowly. b-Wollastonite is found more frequently atlower temperatures, and appears preferentially in the form ofneedles, prisms, or ribbons. Wollastonite (CaSiO3) is a singlechain silicate (pyroxenoid) with several polytypes. The high-tem-perature stable a-wollastonite occurs at T411251C.12,13

The study of the kinetics of crystallization based on the so-called Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, indifferent materials by differential scanning calorimetry (DSC) anddifferential thermal analysis (DTA), has been widely discussed inthe literature.14–30 Various models have been proposed to deter-mine kinetics parameters for nonisothermal conditions. These in-clude the Ligero,20 Kissinger,21 and Matusita22 methods. Thesemodels have been used in studies on the kinetics of glass crystal-lization for various glass–ceramic systems;23–30 in the developmentof glass–ceramics from residues1,2,5,6,14,31 and to study the crystal-lization of mullite from different materials,16,19,32,33 among others.

For many transformations in the solid state, dependence ofcrystallization in relation to time is the same, that is, a sigmoidalcurve results when the crystallized fraction is plotted as a func-tion of the time. Mathematically, the crystallized fraction at timet, with the velocity of crystallization constant, is expressed by theJMAK equation as follows:

xðtÞ ¼ 1� exp½ð�ktÞn�; (1)

where n is the Avrami exponent, which describes the mechanismof crystallization and provides qualitative information on thenature of the processes of nucleation and growth of the crystals,this parameter varying between 0.5 and 4.

Taking the logarithm of the crystallization rate (dx/dt), anexpression (Eq. (2)) is obtained that establishes a linear rela-tionship between the logarithm of dx/dt and the inverse absolutetemperature,20

lndx

dt

� �¼ ln½kof ðxÞ� �

E

RT(2)

where, ko is the frequency factor, f is a function of the crystal-lized fraction (x) and Avrami exponent (n), E is the activationenergy, R is the ideal gas constant, and T is the isothermal tem-perature in Kelvin. This expression establishes that, for that in-terval of values of the crystallized fraction in which f(x) isconstant, there is a linear relationship between ln(dx/dt) andthe absolute temperature inverse.18

The Kissinger method21 is another kinetic approach used toanalyze DTA data:

lnfT2p

!¼ � E

RTpþ constant; (3)

where Tp is the peak crystallization temperature and f is theDTA heating rate. A modified form of this equation was pro-

posed by Matusita and Sakka22:

lnfT2p

!¼ � mE

RTpþ constant (4)

where m is a numerical factor depending on the dimensionalityof crystal growth. The values of n and m for various crystalli-zation mechanisms obtained by Matusita et al. are shown in thework of Romero et al.19

In the present study, we applied the methods of Ligero, Kiss-inger, and Matusita, to study the kinetics of crystallization ofglasses obtained with sugarcane bagasse ash as the source ofsilica.

II. Experimental Procedure

The bottom ash used in this work was collected in a sugar/alcohol factory from Presidente Prudente, Brazil. Before its use,the ash was hand crushed, sieved (18 mesh, 1 mm) and ground(400 rpm, 10 min) using a planetary steel ball mill (RETSCH,model PM100). Small amounts of powdered ash were sent forchemical analysis (X-ray fluorescence [XRF]) and to identifycrystalline phases (X-ray diffraction [XRD]). CaCO3 andNa2CO3 of reagent grade were used as source of CaO andNa2O, respectively.

A 100 g batch composition containing 49.1 g of ash, 45.8 g ofCaO and 5 g of Na2O was mixed and homogenized. The batchwas heated at 101C/min and melted in an alumina crucible at14501C for 1 h. Afterward, the melt was poured into water toproduce a glass frit. The chemical composition of the frit wasdetermined by XRF analysis. To determine the crystallizationbehavior of the glass, both a powder (o63 mm) and a monolithicglass sample were analyzed by thermal analysis (DTA/TG—SETARAM Labsys, Caluire, France) from room temperature to14001C at a heating rate of 501C/min. The DTA scans were con-ducted in flowing air, platinum crucibles, and calcined Al2O3 asreference. All the DTA curves were normalized with respect tothe sample weight. The kinetic study by nonisothermal methodwas performed on powder samples (o63 mm) from 201 to13001C and heating rates of 51, 101, 201, 301, 401 and 501C/min.

To study the development of the crystalline phases, powdersamples (o63 mm) were crystallized at different temperatures(7501, 8001, 8301, 8601, 9001 and 9701C) at a heating rate of501C/min and held for 15 min. After this time, each sample wastaken out the oven and cooled to room temperature. Phase iden-tification was carried out by XRD (Philips X’PERTMPDAlmelo,the Netherlands) using CuKa radiation and operating at 50 kVand 30 mA. For XRD, powder samples (sieved o60 mm) werescanned in the 51–601 (2y) interval at a scanning speed of 0.51/min.

III. Results and Discussion

(1) Chemical Analysis

Table I shows the chemical analyses by XRF of the sugarcanebagasse ash and derived glass frit. The major component of theash is SiO2, and among the minor components K2O show thehighest concentration. This composition differs from that re-ported in a previous study34 due to differences in the type ofsugarcane and, principally, in the soils where it was harvested.The Al2O3 amount in the glass is incompatible with the ashcomposition, indicating a contamination from the alumina cru-cible. Other chemical elements, such as nucleating agents, arepresent in low amounts. X-ray diffraction of the ash showed thatquartz is the major phase (Fig. 1).

(2) Thermal Analysis (TG/DTA)

The TG curve recorded on sugarcane bagasse ash during heat-ing up to 14001C show a small loss of mass (2%) indicating alow concentration of volatiles (moisture, carbonates, and char-coal).

February 2010 Crystallization of Glass from Sugarcane Ash 451

DTA results for powder (o63 mm) and monolithic sample areshown in Fig. 2. The decrease in particle size leads to both a shiftof the maximum of the exothermic peak to a lower temperatureand an increase in the crystallization peak height. Consideringthat crystallization peak height is proportional to the number ofnuclei formed in the glass, the difference in the results to bothsamples (Fig. 2) implies that surface crystallization plays a majorrole in the crystallization of the glass, in agreement with Li andMitchell35 who observed in calcium aluminate glasses that thecrystallization peak height decreases with increasing particle sizesuggesting that the particles crystallize primarily by surface crys-tallization. Ray et al.36 also have demonstrated this effect indifferent types of glasses when surface crystallization is the dom-inant mechanism.

The endothermic peak at around 10751C indicates the for-mation of a liquid phase or the transition of 1 T to 2M-wol-lastonite.13

(3) XRD

Frit-sintered glass–ceramics crystallized at seven different tem-peratures for 15 and 60 min exhibited different XRD patternsindicating their crystalline phase development during thermaltreatment, as shown in Fig. 3. At 7501C, no XRD peaks areobserved, indicating an amorphous (glass) material. At 8001Csome low intensity peaks indicate the onset of the crystallizationprocess. From 8301 to 9701C, the development of three majorphases is observed: rankinite (Ca3Si2O7), wollastonite (CaSiO3)and a calcium–aluminum silicate (Ca2Al2SiO7). Rankinite showsthe more intense XRD peaks up to 9001C, and after that wol-

lastonite exhibits more intense peaks. At higher temperatures(49001C) the calcium–aluminum silicate disappears, and twonew phases occur: gehlenite (Ca2(Al(AlSi)O7) and sodium–cal-cium silicate (Na2CaSi3O8). The sample heated at 10501C for 1 hshows an increase in the intensity of the XRD peaks and con-firms wollastonite as the major phase. The DTA data did notdetect this phase development and show one exothermic peak,suggesting that the crystallization of these phases is simulta-neous and/or it occurs in a narrow sequential process. Fanet al.37 investigated the crystallization process of CaSiO3 geldoped with Eu31 and, under all conditions, rankinite seems tobe the precursor of wollastonite, as observed in this work.

Mazzucato & Gualtieri13 studied in situ crystallization kinet-ics of wollastonite polytypes in the CaO–SiO2 (1:1 ratio) systemand observed that 1T-wollastonite forms first and progressivelytransforms into an intermediate 1Td-wollastonite disorderedform. Both phases in turn transform into 2M-wollastonite poly-

Table I. Ash and Glass Chemical Compositions by X-Rayfluorescence (wt%)

Oxides Ash Glass

SiO2 89.61 42.38Al2O3 1.62 3.10Fe2O3 1.33 0.93Na2O — 4.72K2O 3.54 0.84CaO 1.01 47.03MgO 0.98 0.43TiO2 0.29 0.11P2O5 1.37 0.20SO2 0.05 0.06Cr2O3 0.08 0.13SrO 0.01 0.02BaO 0.05 0.04Total 99.94 99.99

10 20 30 40 50 60

0

1000

2000

3000

4000Q

Q QQ

Q

Q

Q

Q

QQ

Inte

nsity

(cp

s)

2θ

Q SCBA

Fig. 1. X-ray diffraction pattern of the sugar-cane bagasse ash (Q,Quartz).

600 800 1000 1200 14000.4

0.6

0.8

1.0

1.2

967.47

877.68

Hea

t Flo

w (

μV/m

g)

Temperature °C

< 63 μm

Monolithic

Fig. 2. Differential thermal analysis curves of the glass powder (o63mm) and monolithic sample (501C/min).

Fig. 3. X-ray diffraction patterns of powder glass after heat treatmentat 7501–9701C for 15min and at 10501C for 1 h. (�wollastonite CaSiO3,& rankinite Ca3Si2O7, ~ sodium-calcium silicate Na2CaSi3O8, J ge-hlenite Ca2(Al(AlSi)O7, k calcium-aluminum silicate Ca2Al2SiO7).

452 Journal of the American Ceramic Society—Teixeira et al. Vol. 93, No. 2

type, which is the high-temperature stable wollastonite formedat T411251C. As the sugarcane bagasse ash is not a purematerial the phase peak positions are better adjusted to the2M-wollastonite (75–1395) and para-wollastonite (72–2297).Moreover, the presence of other chemical elements changesthe DTA peak positions and the simultaneous crystallizationof other phases at once with wollastonite change the DTA crys-tallization peak intensity.

(4) Kinetics

Figure 4 depicts part of the DTA curves recorded for powdersamples (o63 mm) at six different heating rates from room tem-perature to 13001C. The glass transition (at around 7101C) isfollowed by a single exothermic crystallization peak. Althoughthe XRD data showed that more than one phase was involved incrystallization, only one crystallization peak was seen here.

The kinetic parameters were calculated using the Ligeromethod20 in which the crystallized fraction interval at whichthe model is constant was taken into account (Eq. (2)). Figure 5shows the plot of ln(dx/dt) with the inverse absolute tempera-ture (1/T) at the same value of crystallized fraction (x) for thedifferent heating rates. It is seen that this plot is linear (r40.99)in the range x5 0.10–0.70 giving an average activation energy of378713 kJ/mol for glass crystallization. The Avrami parameter,n, was obtained by selecting many pairs of x1 and x2 that satisfythe condition ln[kof(x1)]5 ln[kof(x2)]. These pairs of crystalliza-tion fractions x were taken from the data table, to each heating

rate. Each data table was duplicated and the x values were ob-tained comparing them in the two tables, one from the begin-ning to the end with the other from the end to the beginning.The average parameter value using this method is 1.50.

Figure 6 shows the plot of ln[f/Tp2] versus 1/Tp, using the

Kissinger method (Eq. (3)). The activation energy calculatedfrom the slope (r5 0.99) of this plot is 374710 kJ/mol, which isin good agreement with that estimated by the Ligero method(378713 kJ/mol). Using the Matusita equation (Fig. 7), n fromthe Ligero equation, and activation energies (Ea) from Ligeroand Kissinger methods, the numerical factor m obtained was1.51 (for Ligero Ea) and 1.53 (for Kissinger Ea). Both param-eters (n andm) have values close to 1.5, which is an indication ofa three-dimensional growth of crystalline phases with polyhe-dron-like morphology. These results also indicate that bulk nu-cleation is the dominant mechanism and that crystal growth iscontrolled by diffusion from a constant number of nuclei. Thepresence of a mineralizer agent (Na2CO3) or flux and smallcontent of nucleating agents in the glass can favor bulk nucle-ation in the kinetic process.7 However, it is important to pointout that kinetic results are in disagreement with the previousresults taken from DTA curves (Fig. 2), which indicate thatcrystallization of the powder glass sample occurs through a sur-face mechanism. Taken together, these results suggest that theearly stage of surface crystallization occurs through a three-di-mensional growth of crystals, which will then transform to one-dimensional growth. This result has been confirmed by scanningelectron microscopy (SEM). Thus, Fig. 8 shows the microstruc-ture observed by SEM on the glass sintered at 10501C for 1 h. Itis clearly observed a crystallization shell consisted of spheruliticcrystals (three-dimensional), which induce the development oflinear fiber-like crystals aggregations. This result is in agreementwith Karamanov et al.,38 who studying formation of diopsidecrystals via surface crystallization observed that during the ini-tial stage of crystallization a three-dimensional growth takesplace and later on, one-dimensional growth inward the grain ispossible. This modification in the crystallization mechanism willchange the reaction order, n.

Both crystallization mechanisms can occur simultaneouslyand one of them dominates over the other in different stages (ortimes) of the reaction. The broad crystallization peak at 51C/minindicates surface crystallization. The Avrami parameter n asso-ciated to it (using Augis–Bennett equation)39 is 1.64 (close to1.0) indicating surface crystallization. To the others crystalliza-tion peaks obtained at higher heating rates the Avrami param-eter is higher than 2, close to 3, indicating internal or three-dimensional transformation (Table II).36 This change of param-eter n, between 1 and 3, indicates that both mechanisms occursimultaneously. Our data shows that both mechanisms occur,

600 800 1000 1200 14000.2

0.4

0.6

0.8

1.0

1.2

Hea

t Flo

w (

μV/m

g)

Temperature (°C)

05 10

20

30

4050°C/min

Fig. 4. Differential thermal analysis curves for the glass (powder o63mm) at different heating rates (51, 101, 201, 301, 401 and 501C/min).

8.6x10−4 8.8x10−4 9.0x10−4 9.2x10−4 9.4x10−4−7.5

−6.0

−4.5

−3.0 x = 0.1 x = 0.2 x = 0.3 x = 0.4 x = 0.5 x = 0.6 x = 0.7

ln(d

x/dt

)

[1/T] K−1

Fig. 5. Plot of ln(dx/dt) vs. 1/T at the same crystallized fraction (x),using Ligero method.18

8.70x10−4 8.85x10−4 9.00x10−4 9.15x10−4−13

−12

−11

−10

Ln(f

/T2 p)

[1/T] K−1

Activation EnergyKissinger Method

Eat = 374 kJ/mol

Fig. 6. Plot for determination of the activation energy according toKissinger method.19

February 2010 Crystallization of Glass from Sugarcane Ash 453

according to Fig. 2 the surface crystallization is predominantand according to kinetic data the internal crystallization is thedominant mechanism. Then we conclude that the initial stage of

surface crystallization occurs through a three-dimensionalgrowth of crystals.

The ash mineralogical composition makes it difficult to com-pare these kinetic data with other findings about the CaO–SiO2

system with wollastonite formation.9,13,40–42 Heterogeneous nu-cleation occurs due to the minor chemical elements in the ashthat can interfere with the kinetic process shifting the crystalli-zation peaks and the crystal growth rate of the glass.9 Rizkallaet al.40 studied the CaO–SiO2–Na2O–P2O5 system withsix different compositions. The activation energy of crystalliza-tion ranged from 196 to 782 kJ/mol, and one of the composi-tions gave an activation energy of 330 kJ/mol and n5 1.5, veryclose to our results but with surface crystallization. According toMazzucato and Gualtieri,13 it is possible that the use of miner-alizers favored the crystallization of the wollastonite phasein Rizkalla’ work. These authors studied the (1:1) CaO–SiO2

system and obtained activation energy values of 520 and 590 kJ/mol for wollastonite 1T (triclinic structure) and of 430 and 360kJ/mol to 1Td crystallizations. Their data show that in thekinetics of 1T-wollastonite formation the reaction is phaseboundary-controlled with a constant or decelerating nucleationrate and one-dimensional growth at lower temperatures(To8751C). According to them, this is in contrast with earlierpreliminary observations indicating a reaction controlled bydiffusion.12

a

b c

Fig. 8. Microstructure observed by scanning electron microscopy on glass particles after treatment at 10501C/1 h: (a) general aspect, (b) one-dimen-sional growth inward the grain and (c) three-dimensional growth shell at the grain particle.

8.6x10−4 8.8x10−4 9.0x10−4 9.2x10−4−12

−11

−10

−9

−8

−7Ln

(fn /

T2 p)

1/T (K)

Matusita Method

m = 1,5

Fig. 7. Plot for determination of the activation energy according toMatusita method.20

454 Journal of the American Ceramic Society—Teixeira et al. Vol. 93, No. 2

IV. Conclusions

The results obtained in this investigation show that it is possibleto use sugarcane bagasse ash to produce useful glass–ceramicproducts.

For this ash chemical composition and glass formulation, twocalcium silicates (wollastonite and rankinite) and one Na–Ca-silicate are the principal phases formed. Wollastonite is themajor phase in crystallization at T49701C, and below thistemperature there is a predominance of rankinite.

The glass transition temperature is around 7101C. The DTAdata show one exothermic peak (around 8701C), suggesting thatthe crystallization of these phases is simultaneous and/or muchcloser sequential processes.

The crystallization activation energies calculated by the Kiss-inger and Ligero methods are equivalent: 374710 and 378713kJ/mol.

DTA curves suggest that surface crystallization plays a majorrole in the crystallization of the powder sample. However,growth morphology parameters have equal values n5m5 1.5indicating that bulk crystallization is the dominant mechanismin this crystallization process, where there is a three-dimensionalgrowth of crystals with polyhedron-like morphology controlledby diffusion from a constant number of nuclei. Taken together,these results suggest that the initial stage of surface crystalliza-tion occurs through a three dimensional growth of crystals.

Acknowledgments

One of the authors (S. R. Teixeira) is greatly indebted to FAPESP (04368-4/08), to UNESP/PROPE-SANTANDER post-doc program for the scholarshipand to ICCET/CSIC for the laboratories and materials accessibility. We are alsograteful to Dr Ma. S. Hernandez Crespo for assistance in the development of thiswork and to Pilar Dıaz Dıaz for technical support.

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Table II. Calculated Values of Avrami Parameter39

Heating rate Peak temperature (K) Width at half-max n

51C/min 1088 40 1.6410 1103 29 2.3220 1123 33 2.1130 1132 30 2.3640 1141 29 2.4850 1150 30 2.44Mean value 2.22

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