Rearch paper
Novel hybrid organic-geopolymer materials
Claudio Ferone a ,Giuppina Roviello a ,⁎,Francesco Colangelo a ,Raffaele Ciof fia ,Oreste Tarallo b
a Dipartimento per le Tecnologie,Facoltàdi Ingegneria,Universitàdi Napoli ‘Parthenope ’,INSTM Rearch Group Napoli Parthenope,Centro Direzionale Napoli,Isola C4,80143Napoli,Italy b
Dipartimento di Scienze Chimiche,Universitàdegli Studi di Napoli “Federico II ”,Complesso Universitario di Monte S.Angelo,via Cintia,80126Napoli,Italy
a b s t r a c t
a r t i c l e i n f o Article history:
Received 23April 2012
Received in revid form 18October 2012Accepted 2November 2012
Available online 04December 2012Keywords:
Hybrid geopolymer Epoxy resin Metakaolin
Novel hybrid organic –inorganic materials were prepared through an innovative synthetic approach bad on a co-reticulation in mild conditions of epoxy bad organic resins and an MK-bad geopolymer inorganic matrix.A high compatibility between the organic and inorganic phas,even at appreciable concentration of resin,was realized up to micrometric level.A good and homogeneous dispersion (without the formation of agglomerates)of the organic particles was obtained just by hand mixing.The new materials prent signi ficantly enhanced compressive strengths and toughness in respect to the neat geopolymer allowing a wider utilization of the materials for structural applications.
©2012Elvier B.V.All rights rerved.
1.Introduction
Geopolymers reprent an innovative class of ceramic materials 1characterized by advanced technological properties,as well as low manufacturing energy consumption for construction purpos
and engineering applications.Geopolymers are usually obtained through inexpensive and ecofriendly synthetic procedures with low waste gas emission (Duxson et al.,2007;Habert et al.,2011;Komnitsas,2011;Provis et al.,2010).For the reasons they are considered “green materials ”.
In the field of civil engineering,geopolymer-bad materials are also referred to as “alkali-activated cements ”or “chemically-bonded ceramics ”which can be obtained from raw materials with low (or zero)CaO content,such as metakaolin (Ciof fiet al.,2003),clay (Buchwald et al.,2009;Ferone et al.,2012)and other natural silico-aluminates (Xu and van Deventer,2000)as well as industrial process wastes such as coal fly ash (Andini et al.,2008,2010;Ferone et al.,2011),lignite bottom ash (Sathonsaowaphak et al.,2009)and metallurgical slag (Shi et al.,2006).The synthesis of geopolymers can be carried out by mixing reactive silico-aluminate materials with strongly alkaline solutions such as alkali metal (Na,K)hydroxide or silicate.In such reaction environment the silico-aluminate reactive materials are rapidly dissolved.A complex reaction mechanism follows,in which solubilized silica and alumina condensate with the ultimate formation of a three-dimensional geopolymeric network (Davidovits,1991).This pha is crucial in relation to the final product properties
that strongly depend on the degree of cross linking among the different silico-aluminate polymeric ch
胧月多肉图片ains.Geopolymers synthesized at tem-perature lower than 90°C are amorphous,while zeolite-like crystalline products are obtained at 150–200°C (Davidovits,1991).
The materials show excellent mechanical properties,low shrink-age,thermal stability,freeze-thaw,acid and fire resistance,long term durability and recyclability,so the application of geopolymer-bad materials covers many fields.
On the other hand geopolymers are ceramic materials,so they prent a typical brittle mechanical behavior with the conquent low ductility and low fracture toughness.This behavior may repre-nt a great limit in veral structural applications.
This drawback can be overcome by producing geopolymer matrix composites.A great deal of studies (Barbosa and MacKenzie,2003;Dias and Thaumaturgo,2005;Li and Xu,2009;Lin et al.,2008;Menna et al.,2013;Zhang et al.,2006,2008a,2008b,2010a,2010b;Zhao et al.,2007)was produced about this topic and many types of fillers were tested,such as particulate and various kinds of short and continuous fibers.For example,polyvinyl alcohol,polypropylene,basalt and carbon short fibers were employed as additives to improve geopolymeric mechanical performances.In fact fibers provide a control of cracking by a bridging action during both micro and macrocracking of the matrix thus incre
asing the fracture toughness of the brittle matrix (Dias and Thaumaturgo,2005;Li and Xu,2009;Tiesong et al.,2008;Zhang et al.,2006,2008a,2008b,2010a,2010b;Zhao et al.,2007).It is worth pointing out that the composites are usually obtained by a physical blending of the two components,the filler being added as a finely divided powder or as an emulsion,2
Applied Clay Science 73(2013)42–50
⁎Corresponding author.Tel.:+390815476781;fax:+390815476777.E-mail viello@uniparthenope.it (G.Roviello).1
“A ceramic is a nonmetallic,inorganic solid ”(Kingery et al.,Introduction to Ceramics,Wiley &Sons,1976).Geopolymers can be properly considered ceramics since they are a class of synthetic aluminosilicate materials prenting an amorphous three-dimensional structure similar to that of an aluminosilicate
glass.2
Sometimes,to obtain a cloly mix of the two different phas,polymers rather soluble in water,such as sodium polyacrylate (PAANa),polyacrylic acid (PAA),poly-acrylamide (PAm),polyvinyl alcohol (PVA),polyethylene glycol (PEG),were ud (Xu and van Deventer,2000).
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/10.1016/j.clay.2012.11.001
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j ou r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c l a
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sometimes in the prence of compatibilizers(Dias and Thaumaturgo, 2005;Li and Xu,2009;Tiesong et al.,2008;Zhang et al.,2006,2008a, 2008b,2010a,2010b;Zhao et al.,2007).
在水一方简谱Recently,a new class of geopolymeric composites with organic matrix has been developed(Hussain et al.,2004,2005)with the main aim to improve thefire resistance of organic polymers and to reduce the smoke production arising from their burning.The com-posites are also named“hybrid”inorganic–organic a material compod of an intimate mixture of inorganic and organic components,where the components usually interpenetrate on scales of less than1μm.IUPAC,1997).The new class of composites described by Hussain has been obtained by incorporating the geopolymer into the cross-linked polymeric structure,tailoring the chemical composi-tions of the components.In particular,a bi-functional epoxy resin, Diglycidyl Ether of Bisphenol A(DGEBA),was mixed with a small amount of the geopolymer(20%weight fraction)in the p
rence of a curing agent(Hussain et al.,2004,2005).In this way a hybrid material with excellent mechanical properties and improvedfire resistance was obtained.
The development of hybrid materials reprents an extremely interesting and relevant rearchfield for the potentially uful physical properties that could derive from the interfacial interactions of two chemically incompatible phas(De Santis et al.,2007).
By tuning the chemical composition of the components,it is feasi-ble to realize different kinds of materials,with different properties, who applications depend on the ratio between the organic and inor-ganic phas(Kickelbick,2007).
In this paper an innovative strategy for the chemical incorporation of an appreciable amount of organic polymer into an MK-bad geopolymeric matrix,that allows the preparation of novel geopolymer bad hybrid materials,is described.The new propod approach is bad on the mixing of a partly crosslinked epoxy resin of tailored composition to a geopolymeric suspension,when both polymeriza-tion reactions are not yet completed.In this way,an improved com-patibility between the organic and the aqueous inorganic phas is easily realized,affording a homogeneous and stable in time disper-sion of the organic microdomains into the inorganic pha,without addition of external additives,even at appreciable concentration of resin.
By using this new method,novel organic–inorganic hybrid mate-rials have been prepared and characterized through scanning electron microscopy(SEM),thermal analysis(TGA,DSC),FT-IR spectrometry, dynamic mechanical thermal analysis(DMTA)and compressive strength determination.The new materials prent interesting me-chanical properties and,in particular,a considerably reduced brittle-ness in respect to the geopolymeric matrix.For the reasons the hybrid materials could be ud for all the applications in which the u of the pure geopolymer is limited by its brittleness such as the realization of thermo-insulating or thermo-resistant panels with improved tenacity.Moreover,the materials can show more uful rheological(tixotropicity)properties in thefield of restoration and repair of damaged concrete and masonry.
2.Materials and methods
2.1.Materials
N,N-diglycidyl-4-glycidyl-oxyaniline,bis-(2-aminoethyl)amine, 2,4-diamino-toluene and sodium hydroxide were commercially avail-able(Aldrich,Baker).Reagents were of analytical R grade and ud without further purification.Metakaolin,provided by l., has the following composition(%):Al2O341.90,SiO252.90,K2O 0.77,Fe2O31.60,TiO21.80,MgO0.19,CaO0.17.The sodi
um silicate solution was supplied by Prochin l.with the composition of SiO227.40wt.%and Na2O8.15wt.%.2.2.Analytical methods
Thermogravimetric(TGA)and differential scanning calorimetry (DSC)analys were performed by a TA Instrument SDT2960simulta-neous DSC–TGA under airflow at a heating rate of10°C/min using 10–15mg of the powdered specimen stored at room temperature for one week.
DMTA were performed by using a Triton Technology Ltd instrument, Tritec2000DMA.The specimens were clamped in the single cantilever mode.DMTA analys were performed from room temperature to 260°C at2°C/min using a1Hz frequency and having a1%strain.
SEM analysis was carried out by means of a FEI Quanta200FEG microscope.EDS analys were performed by using an Energy Disper-sion Spectrometer Oxford Inca Energy System250equipped with INCAx-act LN2-free detector,working at20kV voltage.
FT-IR measurements were performed using a Thermo Nicolet spectrometer(Mod.Nexus).As far as the geopolymer and hybrids specimens,the experiments were carried out by using KBr discs in which few milligrams of the already cured specimens were disperd. Otherwi,the organic resins were smeared on the surface of a pure KBr disc when they were only partly cured and then kept at r
oom temperature(T=20°C)in dry atmosphere in order to complete the crosslinking process.
The compressive strength of geopolymer and hybrid specimens was determined using a500KN testing machine(MTS mod.810)on 25×50mm(diameter×height)cylindrical specimens prepared into polyethylene molds.The testing was carried out in extension control, with an extension rate of0.5mm min−1.Three specimens for each mixture were tested.However,only one stress–strain curve for each type of specimens is shown in the followingfigures for a better view.
A preliminary LCA study was carried out on the hybrid materials.
2.3.Synthetic procedure
2.3.1.Synthesis of resins
Two different epoxy resins,named resin1and2,were synthesized and employed.
Resin1was obtained by homogeneous mixing at room tempera-ture of N,N-diglycidyl-4-glycidyl-oxyaniline(82.0%w/w)and bis-(2-aminoethyl)amine(18.0%w/w).Resin2was obtained by adding at room temperature N,N-diglycidyl-4-glycidyl-oxyaniline(79.6%w/w) to a mixture of bis-(2-aminoethyl)amine(4.4%w/w)and2,4-diamino-toluene(16.0%w/w).
In both cas,the u of solvents was prevented becau the reaction occurs between liquid reagents(the aromatic amine,solid at room tem-perature,wasfinely disperd into the liquid aliphatic one).3
2.3.2.Synthesis of geopolymer
因为的英语怎么写The alkaline activating solution was prepared by dissolving solid sodium hydroxide into the sodium silicate solution.The solution was then allowed to equilibrate and cool.The composition of the solution can be expresd as Na2O1.4SiO210.5H2O.Then metakaolin was incorporated to the activating solution with a liquid:solid ratio of 1.4:1by weight and manually mixed for15min.The composition of the whole geopolymeric system can be expresd as Al2O33.5SiO2
1.0Na2O10.4H2O,assuming that geopolymerization occurred at100%.
2.3.3.Preparation of hybrid composites
Before being added to the geopolymeric mixture,both resins have been cured for45min at room as soon as they started increasing their viscosity and long before their complete crosslinking and hardening(that takes place in about24h).In the
3The reactions have been carried out on limited amounts of reagents(about20g)in order to avoid possible combustion events due to the strongly exothermic polymeriza-tion reaction.
43
C.Ferone et al./Applied Clay Science73(2013)42–50
conditions,the partly crosslinked polymers obtained were stillfluid materials.A20%w/w of resin was added to the freshly-prepared geopolymeric suspension,and quickly incorporated by a prolonged and accurate mixing by hand in a mortar with a pestle.In this way, hybrid I(geopolymer and resin1)and hybrid II(geopolymer and resin2)were obtained.Both hybrids had a homogeneous aspect and started solidifying in few minutes.
2.3.4.Curing treatments
老虎蛋糕图片
All the specimens of geopolymer,hybrids I and II were cured in 99%relative humidity conditions,at room temperature for7days (the samples ud for the mechanical tests were cured further 21days in air).Moreover,in order to examine the possible effects of different curing conditions on the thermal behavior of the hybrids, specimens of hybrids I and II were cured at60°C for24h and then kept at room temperature for6days.All treatments have been carried out in99%relative humidity conditions.
3.Results and discussion
3.1.Synthetic method
Hybrids I and II have been prepared by mean of the new synthetic approach propod in the prent paper.This method is bad on the incorporation of the resin to the geopolymeric matrix suspension when both polymerization reactions are not yet completed.By following this procedure,a good compatibility between the organic and the aqueous inorganic phas is obtained(e Section3.2.3)thanks to the numerous hydroxyl tails formed during the epoxy ring opening reaction that make the organic pha“temporarily hydrophilic”in-creasing the compatibility with the aqueous inorganic pha.
The pivotal step of this procedure is the mixing of the two phas when both the polymerization reactions(of the organic and inorganic phas)were started but not yet completed:as a matter of fact,an early mixing of the reagents,when the two organic components were not yet reacted,produced the paration of an organic pha made by the triglycidyl compound,while the amine converged in the aqueous one;on the contrary,a tardy mixing of the two compo-nents(the cured organic resin and the geopolymer)strongly reduces their compatibility and the homogeneity of
the dispersion of the two phas.For this reason a careful realization of the synthetic procedure is esntial to produce innovative and interesting materials.
In addition,the choice of the resins has been done in order to obtain an improved compatibility between the organic and inorganic phas.As a matter of fact,instead of the most common commercial diglycidyl(DGEBA,etc.),we have ud a triglycidyl that promotes the crosslinking prenting more reactive sites.蹦床篮球
Moreover,since the ultimate properties(thermal,mechanical, etc.)of thefinal hybrid materials are strongly affected also by the nature of the resin component,in order to improve their thermal sta-bility we have chon to realize a resin containing also an aromatic amine.食品安全教育
Finally,it is worth pointing out that we have experimented differ-ent w/w ratios between the organic and inorganic matrices,ranging from5to30%w/w.Preliminary results indicate that for very low organic resin concentration(5%w/w)the mechanical properties of the hybrid are not significantly affected by the organic resin,since it turned out to be brittle like the neat geopolymer;for the highest resin concentration studied(30%w/w)instead,a significant improve-ment in the mechanical properties of the material but minor pha gregation phenomena have been obrved.In this paper we report o
nly the results obtained in the ca of the hybrids containing80% weight geopolymer and20%weight resin since this composition turned out to be the best compromi between the necessity of keeping a good compatibility of two,at least in principle,dramatically different phas and the need to produce a significant improvement on the mechanical properties of the inorganic matrix.
It is worth pointing out that,in agreement with the expectations of green chemistry,in the propod procedure the u of solvents is completely avoided.Preliminary data obtained using LCA methodology suggest that the new materials can be considered“eco-friendly building materials”.
3.2.Characterization
3.2.1.Thermal analysis(TGA/DSC)
Simultaneous thermo-gravimetric and differential scanning calo-rimetry analys were performed on the geopolymer cured at room temperature and at60°C for24h and then for6days at room tem-perature,on the resins1and2,and on the hybrids I and II.
Fig.1shows the weight loss and the DSC thermograms for the unmodified geopolymers.
In both cas the weight loss starts at about30°C,has a maximum rate around120–130°C and is com
pleted at450°C.This loss can be attributed to the removal of water molecules adsorbed or differently linked to the silicate molecules(Kong et al.,2007).The overall weight loss is28%for the geopolymer cured at room temperature while is24%for the one cured at60°C and a combustion residual of72 and76%respectively remained at800°C.The phenomena are associated with the strong endothermic peaks characterizing the DSC curves centered at123°C and133°C respectively.The geopolymer cured at60°C shows also a broad endothermic peak at about300°C, probably due to zeolitic-like water molecules(Knowlton et al.,1981).
It is worth pointing out that the variation of enthalpyΔH associated to the removal of water is in qualitative agreement with the weight loss of the specimen.
Moreover,by examining the TGA and DSC curves reported in Fig.1 it is clear that the different curing temperatures have the only effect of removing part of the water contained in the specimen and of increasing of few degrees the temperature at which the loss of water has been obrved.
Fig.2shows the weight loss and the thermograms for the unmodified resins1and2cured at room temperature.
Both pure resins showed a two-step degradation mechanism in which the most part of the decompos
ition process is completed below 500°C and implies a weight loss of about70%.The degradation is completed at about700°C and no combustion residual remained.
For resin1,the initial degradation started at around320°C with a high degradation rate.The cond degradation step starts at about 500°C and has a lower degradation rate.As shown by the DSC curve,the two steps are accompanied by two exothermic
peaks
Fig.1.TGA(black curves)and DSC(red curves)of the geopolymer cured at room temperature(continuous lines)and at60°C(dashed lines).
44 C.Ferone et al./Applied Clay Science73(2013)42–50
(the first one centered at 352°C and the cond one centered at 583.5°C)of opposite extent in respect to the corresponding weight loss (ΔH is 295J/g and 1930J/g respectively).
Resin 2showed a very similar behavior,with degradation temper-atures only slightly higher than resin 1(for example,the degradation temperatures at 10%weight loss were found 342°C for resin 1and 349°C for resin 2)possibly due to the prence of the aromatic ring.
A substantially identical behavior (not shown)has been obrved also for the specimen cured at 60°C.
Figs.3and 4show the weight loss of the hybrids I and II after different curing conditions,respectively.
Hybrid I shows a complex degradation mechanism involving three main steps:the first step begins at room temperature and finishes at about 220°C corresponding to a weight loss of 23%;the cond step ends at 406°C and involves a weight loss of about 11%while the third one ends at 750°C with a further weight loss of 14%.The com-bustion residual at 800°C is around 53%.From the comparison of the TGA and DSC curves for the pure geopolymer and resin reported in Figs.1and 2,respectively,the first degradation step can be associ-ated with the loss of water of the geopolymeric matrix while the remaining two correspond to the degradation of the disperd organic phas.It is worth pointing out that in the hybrid the relative extent of the cond and third weight loss steps (around 400°C and 600°C,respectively)is inverted in respect to the corresponding phenomena that have been recorded for the pure resin (e Fig.2).Moreover it is worth noting that the peak temperature of water loss for the hybrid is higher than that of the pure geopolymer (e
Fig.1):probably the polar groups of the resin tend to restrain the water molecules delaying their evaporation.
A very similar behavior has been recorded also in the ca of hybrid II (e Fig.4),the most signi ficant difference being the degra-dation of the resin that takes places in a continuous way up to 600°C.
It is worth pointing out that in both cas the thermal treatment up to 800°C results in a complete removal of the organic pha from the hybrid (e SEM images in Section 3.2.3).
Degradation temperatures and weight loss for all the studied systems are summarized in Table 1.
3.2.2.Dynamic mechanical thermal analysis
Fig.5shows the dynamic-mechanical properties of the pure resin 1and of hybrid I cured at room temperature.DMTA measurements are carried out at very low load,in the elastic deformation field.In the explored temperature range,the cured resin (curve 5a)shows a progressive drop of the storage modulus of one order of magnitude that is likely due to the thermal softening.As a result of the high stiff-ness of the crosslinked resin,the corresponding loss factor (tan δ,curve 5a ′)is very small,being always lower than 8×10−2in all the examined temperature ranges.As far as hybrid I is considered,on account of the geopolymeric matrix,its storage modulus (curve 5b)turns out to be always higher than that of the pure resin and,in the considered temperature range,it decreas less than one order of magnitude.The slight increa of the modulus obrved in the region between 175°C and 225°C could be due to the completion of the curing process of the resin that maybe,at room temperature,was partly inhibited by the prence of the inorganic components.
Moreover,thanks to the higher stiffness of inorganic pha,hybrid I shows a lower drop of the storage modulus in respect to the pure resin.This greater stiffness is the cau also of the lower tan δvalues in respect to tho of the pure resin 1(curve 5b ′
).
Fig.2.TGA (black curves)and DSC (red curves)of the resin 1(continuous lines)and resin 2(dashed lines)cured at room temperature for 7
days.
Fig.3.TGA (black curves)and DSC (red curves)of the hybrid I cured at room tempera-ture (continuous lines)and at 60°C (dashed
lines).
Fig.4.TGA (black curves)and DSC (red curves)of the hybrid II cured at room temperature (continuous lines)and at 60°C (dashed lines).
Table 1
Thermal properties of the geopolymer,resins and hybrids.
Curing
temperature (°C)
Weight loss starting
temperature (°C)
Temperature at 10%weight loss (°C)Weight loss ending
temperature (°C)Combustion residual at 800°C (weight %)Geopolymer 25
301014507260
3012045076Resin 1252603427000Resin 2252903496700Hybrid I 25
301097505360
3014067057Hybrid II 25
微信零钱301126405460
30
154
655
59
45
C.Ferone et al./Applied Clay Science 73(2013)42–50
Finally,it is worth pointing out that,at variance with the pure geopolymer that is very brittle at room te
mperature (Zhao et al.,2007),thanks to the prence of the organic resin,hybrid I is signi fi-cantly less brittle.As a matter of fact,while the neat geopolymer specimen is broken at room temperature during the test (carried out with the same condition of load ud for the hybrid systems and resins),the hybrid specimen is safe up to 220°C.
3.2.3.Microstructural analysis
Fig.6shows micrographs of freshly obtained fracture surfaces of geopolymer and hybrids I and II cured at room temperature.All the specimens show an amorphous structure (few crystals can be en only in the geopolymer specimen,e Fig.6a ′,as con firmed by X-ray diffraction analysis of the starting metakaolin)indicating that the geopolymerization process has been successfully carried out in all cas.Moreover,a compact and homogeneous morphology is clearly obrved for all the specimens.In particular,from the exami-nation of images 6b,b ′and 6c,c ′referring to hybrids I and II ,a very good homogeneity and uniformity of the microdispersion of the organic pha in the inorganic one is evident.The dimension of the resin particles is in the range of 1–20μm.For all the specimens examined,no agglomerations phenomena were obrved.
It is worth pointing out that inorganic –organic hybrids (20%/80%w/w)described in literature (Hussain et al.,2004,2005)are charac-terized by a disperd pha of millimetric dimension.
This result is even more interesting if we consider the fact that this uniform dispersion at micrometric level was obtained just by simple manual mixing.It is likely to be expected that a fine tailoring of the average diameter of the microdisperd organic pha (that reasonably in fluences the mechanical properties of the hybrids)can be obtained simply by mechanically controlling the mixing step.
In addition,in all cas,the strict adhesion between the phas is evident:in particular in the ca of the hybrid II (image 6c and 6c ′),the interaction between the geopolymer matrix and the organic resin microsphere is so good that the particles of resin have been scratched when the specimens were broken to prepare the SEM samples.A more detailed investigation of the interpha region be-tween organic and inorganic phas con firming this clo interaction has been carried out by energy-dispersive X-ray spectroscopy (EDS)analysis on hybrid II and shown in Fig.7and Table 2.In particular,we have recorded EDS spectra on i)the region of a polymeric particle that,up to 5000magni fications,does not prent visible traces or grains of the inorganic pha,but shows traces of Si atoms (region 1of Fig.7,spectrum 1of Table 2);ii)the region around the polymer particle (i.e.the cavity obtained by the removing of the polymer
particle)that,up to 5000magni fications,does not prent visible traces or grains of polymer,but reveals the prence of C atoms (region 2of Fig.7,spectrum 2of Table 2);iii)the area between the pol
ymer particles and the geopolymeric matrix in which the analysis pointed out a signi ficant prence of all the elements revealed (region 3of Fig.7,spectrum 3of Table 3).The obrvations con firm the clo interaction between the different phas.
Moreover,comparing Fig.6a,a ′,b,b ′and c,c ′it can be easily en that the number and the extension of the microcracks that characterize the fracture surface of the geopolymer specimen is strongly reduced by adding the organic resin.Therefore,in agreement with what obrved by DMTA analysis (described in Section 3.2.2)and with the compressive strength determinations (described in Section 3.2.5),the resin ems to prevent the cracking growth and propagation improving the mechanical properties and enhancing the fracture toughness of the brittle inorganic matrix.As a matter of fact,a sort of crack de flection mechanism typical of particle reinforced ceramic matrix composites could be expected to occur (Boccaccini et al.,1997;Monette and Anderson,1993).
Finally,Fig.6d and d ′show the images of a specimen of hybrid I after thermal treatment at 800°C for 1h.It is apparent that,in good agreement with the TGA results shown in Section 3.2.1,the or-ganic pha has been completely removed.In this way a macroporous material characterized by uniformly disperd pores of very similar diameter (e Fig.6d ′)has been obtained.Analogous results (not reported in this paper)have been obtained also for the specimens cured at 60°C.
3.2.
屋顶菜园4.FT-IR analysis
FT-IR spectra of the starting metakaolin,of the geopolymer,the two resins and of the two hybrids are shown in Fig.8.
The FTIR spectrum of the geopolymer (curve 8b)is a typical one,with broad bands at about 3430cm −1and 1635cm −1due to O \H stretching and bending modes of adsorbed molecular water,with a strong Si \O stretching vibration at 1050cm −1,which is lower in wave number than that of the metakaolin (curve 8a),indicating the condensation of Si \O tetrahedra in geopolymer.It is worth pointing out that the characteristic metakaolin Si \O \Al bond at 810cm −1,after the geopolymerization,is replaced by veral weaker bands in the range from 600cm −1to 800cm −1.Finally,the signal at about 460cm −1is due to Si \O bending vibration.(Aronne et al.,2002;Catauro et al.,2003,2004;Clayden et al.,1999;Felahi et al.,2001;Ortego and Barroeta,1991;Wang et al.,2005;Zhang et al.,2008a,2008b ).
The FT-IR spectra of resins 1and 2(curves 8c and 8d respectively)are very similar to each other.For both resins,the prence of some unreacted \NH groups is revealed by the broad peak at around 33
50cm −1(due to the \NH stretching)and at around 1515cm −1(due to \NH bending).This last band,together with that at 830cm −1,can be also attributed to p -disubstituted benzene rings.The signals in the wavenumber range of 2920–2820cm −1and at about 1460cm −1are due to \CH 2\symmetric and asymmetric stretching and bending,respectively.Finally,signals in the region of 1300–1050cm −1can be assigned to C \N,C \C and C \O stretching.In addition,the abnce of bands at 971,917and 775cm −1due to terminal epoxy rings reveals a successful curing process (Felahi et al.,2001;Hummel and Scholl,1971).
As far as the hybrids,their spectra (curve 8e:hybrid I ;curve 8f:hybrid II )are characterized by the main bands of the pure organic and inorganic components.In particular a strong absorption band at about 3430cm −1and 1640cm −1due to water,at about 1050cm −1due to Si \O stretching and at about 450cm −1due to Si \O bending vibration can be obrved.The bands in the region of 800–600cm −1are associated to Si \O \Al vibrations (Barbosa and Mackenzie,2003;Frost et al.,1996;Parker and Frost,1996;Zaharaki et al.,2010
).
Fig.5.Storage moduli (black curves)and mechanical loss tangents (tan δ,circle graphs)of resin 1(cont
inuous black curve and red graph)and of hybrid I (dashed black curve and blue graph)both cured for 7days at room temperature.
46 C.Ferone et al./Applied Clay Science 73(2013)42–50
