Tan YanJin LiuLinfeng DingQingwei Wangand Wan Jiang
(1.State Key Laboratories for Modification of Chemical Fiber and Polymer Materials,Donghua University,Shanghai 201620,China;2.Engineering Research Center of Advanced Glass Manufacturing Technology,Ministry of Education,Donghua University,Shanghai 201620,China;3.Institute of Functional Materials,Donghua University,Shanghai 201620,China)
Abstract:Basalt fiber(BF)is widely applied in the construction industry to improve the mechanical properties of construction materials.Recent studies show that BF has the potential to further enhance its performance via a crystallization approach.In this work,the glass-ceramic basalt fibers(GCBFs)were prepared through nucleation and crystallization treatments according to the crystallization kinetics calculations.Results from XRD and SEM show that GCBFs have main crystalline phases of Diopside and Augite reach crystallinity of around 46%±10%.In particular,the GCBFs sample with the largest mean crystal size maintains the lowest tensile strength of~197 MPa(compared with the pristine BFs of~737 MPa).Moreover,the weight loss and ion dissolution of GCBFs were explored in seawater environments and it was investigated that,GCBFs have better anti-seawater corrosion than the pristine BFs and have the potential to apply in the marine industry.
Keywords:glass-ceramic;basalt fiber;tensile strength;crystallization;seawater environment
Glass-ceramic(GC)fibers have been reported in the literature showing great potential in optical[1-4],bioactive[5],piezoelectrical[6],and refractory[7]systems.However,uncontrollable crystallization can be easily generated during the fiber drawing and heat treatment processes,which will lead to a catastrophic mechanical failure[8].It is of great importance to prepare GC fibers to maintain certain mechanical strength,especially in the construction industry[9].
Basalt fiber(BF)is widely applied in construction industry to improve the mechanical properties of construction materials due to its excellent mechanical strength,corrosion durability[10-11]and high-temperature stability[12-13].BF belongs to ironrich aluminosilicate system which is easily crystallized at high temperatures[9,14].The nature crystallization process starts from the oxidation of Fe2+initiated by a diffusion process of Ca2+and Mg2+and forming nanocrystalline layers on the surface of BF[15-20].Researchers[21-22]have studied the influence of the extra addition of ZrO2and Al2O3on the crystallization behavior of BFs.For example,when the ZrO2content was 7 wt%,pyroxene,hematite,plagioclase,and zirconia were crystalized simultaneously in BF,which will increase the thermal stability[21]of BF.BF with high alumina content tended to have a higher resistance to crystallization with augite as the major crystallization product[22].To the best of our knowledge,few works have aimed to prepare GCBFs to maintain mechanical strength and examined their performance in seawater environments.
Continuous BFs can be prepared directly from natural rocks and have a great advantage in economics.Thus,in this work,the aim is to systematically study the crystallization kinetics of BFs and prepare glassceramic basalt fibers(GCBFs)maintaining tensile strength.Furthermore,the GCBFs will be tested in seawater environments and their application potential in marine industry will be explored.This work will pave the way to a better understanding of the fundamentals of GCBFs as well as benefit the development of the construction industry.
The pristine basalt glass was prepared by melting the basalt rocks(Shandong Province,China)in a quartz crucible at 1550℃for 2 h and quenched in water.The chemical composition of basalt glass,determined by X-ray fluorescence analysis,is 54.9%SiO2,16.4% Al2O3,9.2% Fe2O3,8.1% CaO,5.6%MgO,3.3% Na2O and 2.5% others(wt%).The continuous basalt fibers(BFs)were drawen at temperatures of~1350±10℃from a laboratory monofilament fiber preparation system[23-24]with a platinum crucible.
Glass-ceramic basalt fibers(GCBFs)were prepared by following a two-step(nucleation and crystallization)method based on a thermal analysis(TGA/DSC 3+,Mettler)at a heating rate of 10 K/min.The glass transition temperature(Tg)of BFs is around 670±5℃,and the crystallization peak temperature(Tp)is 883±5℃.The BFs specimens were nucleated at 740℃,760℃,and 780℃(>50℃higher thanTg)for 1,2,and 3 h and crystallized(around crystallization peakTc)at 830℃,880℃,and 930℃for 1,2 and 3 h to obtain GCBFs.The experimental conditions are shown in Table 1.
The crystalline phases of BFs samples were characterized by X-ray diffraction(XRD,Rigaku D/max 2500 PC)at a scan speed of 0.02 °/s.The Crystallinity Index[25](CI%),which represents the volume fraction of the crystalline phases,was calculated by the following equation:
whereAcis the area of the crystalline phases,andAT(AT=amorphous+crystalline)represents the total area.The mean size of the crystallites(D)is calculated via Scherrer’s equation[5,26]:
whereKrepresents a dimensionless shape factor,λis the wavelength,βis the full width at the halfmaximum intensity,andθis the Bragg angle.
The tensile strength of GCBFs was measured via a monofilament dynamometer(YG005A,China).Each sample was measured independently 20 times to get an averaged tensile strength and a standard deviation.The surface morphology of GCBFs samples was characterized by a field emission scanning electron microscope(SEM,JSM-7500F,Japan)and the composition in a local area was measured by energy-dispersive spectroscopy(EDS).
The GCBFs samples were immersed in the seawater solution[9]at 80℃to accelerate the corrosion process in the marine environment.The weights of GCBFs samples were measured by a balance(Precisa,Switzerland,±0.0001 g)before and after the seawater aging for 24 h.Afterwards,1 mL seawater solution was diluted 100 times and analyzed via an inductively coupled plasma spectroscopy(ICP,Prodigy,USA).The ion dissolution rate(IDR)can be calculated as:
wherewseawaterrefers to the weight of each element in seawater solution from ICP tests,andwfiberis the initial weight of each element in pristine BFs or GCBFs.
The crystallization kinetics of BFs was explored by heating the BFs to 1200℃via DSC at different heating rates(e.g.,10℃/min,20℃/min,25℃/min,and 30℃/min).As can be seen in Fig.1(b)that both the glass transition temperature(Tg,which is not the viscosity definition of the glass transition temperature.) and crystallization temperature(Tp)increase with the increase of heating rates.The crystallization activation energy(Ec,J/mol)is calculated by the Kissinger equation[27-28],
whereαrepresents the heating rates(K/s),Rrefers to the gas constant andAis a constant.The value ofEc/Requals the slope of the linear fitting in Fig.1(c),thus,theEcof BFs is 150.4 kJ/mol.To evaluate the crystallization mechanism,the Avrami parameter(n)[28]can be calculated by using the Augis-Bennett equation[29]:
Fig.1 (a)Heat flow curve of basalt fibers at different heating rates;(b)Glass transition temperature(Tg)and crystallization temperature(Tp)of basalt fibers at different heating rates;(c)Linear fitting graph of ln(T2p/α)to 1000/Tp
whereTcorresponds to the temperature interval of the half-width of the crystallization peak.Thenof the BFs sample is equal to 4.3±0.5 at heating rates from 10 K/min to 30 K/min,indicating that the main crystallization mechanism of BFs is three-dimensional crystal growth.
The GCBFs samples were prepared based on the crystallization kinetics research and the XRD patterns of GCBFs are shown in Fig.2.Compared with the amorphous structure of the pristine BFs,GCBFs own main crystalline phases of Diopside(PDF#89-0836)and Augite(PDF#78-1391).The main crystalline phases,as well as the crystallinity,are not changed significantly with different nucleation/crystallization temperatures and times concerning a very high measurement uncertainty of CI around 46%±10%.The mean crystal size shows comparatively more significant change,especially as a function of crystallization time.It can be seen in Table 1,the GCBFs have the largest mean crystal size of 86±10 nm atTn=760℃,tn=2 h,Tc=880℃,andtc=3 h,whereas,the one crystalizing for 1 h(Tn=760℃,tn=2 h,Tc=880℃)has the smallest crystal size of only 45±10 nm.In addition,the SEM morphology of nine different GCBFs samples is shown in Fig.3.From the visual observation,all GCBFs samples show clear crystallization.Some of the samples seem to have very high crystallinities.However,the crystallites are not evenly distributed.The actual crystallinity for all the GCBFs is not changed significantly under different heat treatment conditions.
Fig.2 XRD patterns of GCBFs at different Tn,tn,Tc,tc
Fig.3 SEM images of GCBFs(a)-(i)corresponding to sample ID C1 to C9
Previous studies show that glass fibers will lose tensile strength after crystallization.However,in this work,the GCBFs samples retain up to 50% of tensile strength after heat treatment of up to 930℃(the tensile strength of pristine BFs is~736 MPa).As can be seen in Fig.4(a),the tensile strength of GCBFs first increases from 252 MPa to 300 MPa with an increase in nucleation temperature from 740℃to 760℃and then decreases to 287 MPa when the nucleation temperature reaches 780℃.A similar phenomenon is detected as a function of nucleation time in Fig.4(b),although the minimum tensile strength is 242 MPa at a holding time of 3 h.The influence of crystallization temperature and time is slightly different from the nucleation treatment.As shown in Fig.4(c),the tensile strength of GCBFs continuously decreases from 367 MPa to 214 MPa with an increase in temperature from 830℃to 930℃.Similarly,in Fig.4(d),the tensile strength of GCBFs decreases from 347 MPa to 197 MPa with an increase in holding time from 1 h to 3 h.Overall,the GCBFs reach the highest tensile strength of 367 MPa atTn=760℃,tn=2 h,Tc=830℃,andtc=2 h,and the lowest of 197 MPa atTn=760℃,tn=2 h,Tc=880℃,andtc=3 h.Combing all the results from tensile strength and mean crystal size,it is found that a larger mean crystal size tends to yield a lower tensile strength in GCBFs.It is generally agreed that the glass fracture process must first nucleate cavitation and then percolate through the bulk glass wall to generate a fracture[30].It is perhaps reasonable to conclude that GCBFs with larger crystallites can easily generate cavitation under high tension,which will lead to comparatively lower tensile strength.
Fig.4 Tensile strength of GCBFs at different(a)nucleation temperatures(Tn);(b)nucleation time(tn);(c)crystallization temperatures(Tc);(d)crystallization time(tc).(Note:The error bars represent the standard deviations of tests on 20 samples)
BFs are ideal alternatives to steel bars due to their excellent resistance to seawater corrosion.In this work,it is found that GCBFs have better antiseawater corrosion than the pristine BFs and have the potential to be applied in marine industry.As can be seen in Fig.5,the weight-loss ratio of GCBFs after soaking in seawater solution for 24 h at 80℃.In general,the overall weight-loss rate of GCBFs decreases with the increasing temperature of seawater,and the overall weight-loss rate of BFs increases with the extension of the nucleation and crystallization time.For example,the weight-loss rate of the pristine BFs sample after soaking at 80℃seawater solution for 24 h is~1.3%,but that of the GCBFs(Tn=760℃,tn=2 h,Tc=880℃,andtc=1 h)at the same conditions decreases to~0.5% and it further increases to 0.3% when crystallization time extends to 3 h.A larger mean crystal size will enhance the anticorrosion property of GCBFs due to the increasing probability for crystalline phases to directly contact seawater.It is generally believed that crystalline phases have better anti-corrosion performance than amorphous glass.The results from ICP tests also support this argument.As can be seen in Fig.6,the main dissolution elements of pristine BFs after soaking at 80℃seawater solution for 24 h are glass network formers,e.g.Si and Al,which are different from GCBFs.The breaking of glass network is much slower in GCBFs than in pristine BFs,thus,the ion dissolution rates of Si and Al are much lower in GCBFs than in pristine BFs.Moreover,the overall ion dissolution rates slightly decreases as a function of crystallization time.Therefore,GCBFs with largest mean crystal size has the best anti-corrosion performance in seawater environment.
Fig.5 Weight-loss ratio(weight-loss divided by the initial weight)of pristine BFs and GCBFs after soaking in seawater solution for 24 h at 80℃
Fig.6 Ion dissolution rate of pristine BFs and GCBFs after soaking in seawater solution for 24 h at 80℃
Glass-ceramic basalt fibers were prepared via a two-step(nucleation and crystallization)heattreatment process.The crystallization kinetics calculations prove that the main crystallization mechanism of BFs is three-dimensional crystal growth.Results from XRD and SEM show that,compared with the amorphous structure of the pristine BFs,GCBFs have main crystalline phases of Diopside and Augite.The main crystalline phases as well as the crystallinity are not changed significantly with different nucleation temperatures(740℃to 780℃)and crystallization temperatures(830℃to 930℃),as well as different times(1 h to 3 h),compared with the very high measurement uncertainty crystallinity of around±10%.In particular,the GCBFs sample with the largest mean crystal size maintains the lowest tensile strength of~197 MPa(compared with the pristine BFs of 737 MPa).Moreover,it is found that GCBFs have better antiseawater corrosion performance than the pristine BFs and have the potential to be applied in marine industry.
Journal of Harbin Institute of Technology(New Series)2022年6期