Removal of Pb(II) ions from aqueous solution by adsorption using bael leaves (Aegle marmelos)
Journal of Hazardous Materials 173 (2010) 502–509
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Journal of Hazardous
Materials
j o u 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 /j h a z m a
t
Removal of Pb(II)ions from aqueous solution by adsorption using bael leaves (Aegle marmelos )
S.Chakravarty ?,Ashok Mohanty,T.Nag Sudha,A.K.Upadhyay,J.Konar,J.K.Sircar,A.Madhukar,K.K.Gupta
Analytical Chemistry Centre,National Metallurgical Laboratory,Jamshedpur 831007,Jharkhand,India
a r t i c l e i n f o Article history:
Received 5May 2009
Received in revised form 19August 2009Accepted 24August 2009
Available online 31 August 2009Keywords:Biosorption Aegle marmelos Pb(II)ions
Aqueous solution
a b s t r a c t
Biosorption of Pb(II)on bael leaves (Aegle marmelos )was investigated for the removal of Pb(II)from aqueous solution using different doses of adsorbent,initial pH,and contact time.The maximum Pb loading capacity of the bael leaves was 104mg g ?1at 50mg L ?1initial Pb(II)concentration at pH 5.1.SEM and FT-IR studies indicated that the adsorption of Pb(II)occurs inside the wall of the hollow tubes present in the bael leaves and carboxylic acid,thioester and sulphonamide groups are involved in the process.The sorption process was best described by pseudo second order kinetics.Among Freundlich and Langmuir isotherms,the latter had a better ?t with the experimental data.The activation energy E a con?rmed that the nature of adsorption was physisorption.Bael leaves can selectively remove Pb(II)in the presence of other metal ions.This was demonstrated by removing Pb from the ef?uent of exhausted batteries.
? 2009 Elsevier B.V. All rights reserved.
1.Introduction
Industrial ef?uents are loaded with heavy metals which are haz-ardous to humans and other forms of life.Their toxic nature has a severe environmental impact.This has resulted in the enforcement of stringent laws for the maximum allowable limits of their dis-charge into the open landscapes and water bodies.Lead is used as an industrial raw material for storage battery manufacturing,printing,pigments,fuels,photography material and explosive manufactur-ing [1].Since Pb(II)is a potent neurotoxic metal,its pollution is of major concern.The presence of lead in drinking water,even in low concentrations,may cause diseases such as anemia,hepatitis,nephrite syndrome,etc [2].
A number of processes exist for the removal of metal pollutants from waste water,viz.precipitation,electroplating,ion exchange and membrane separation.These processes have several disadvan-tages such as incomplete metal removal,high reagent and energy requirement and generation of toxic sludge/waste products that require disposal and further treatment.This led to the need to develop an effective,low cost and environment friendly process for wastewater treatment.Adsorption is an ef?cient and econom-ical process used for the removal of heavy metals from industrial wastewater.A number of investigations have been carried out using naturally occurring waste materials for the removal of lead from
?Corresponding author.Tel.:+916572270588;fax:+916572345213.E-mail address:sanchita@https://www.wendangku.net/doc/fa8096367.html, (S.Chakravarty).aqueous systems.Some of the naturally occurring waste materials used for this purpose are ?y ash [3],phosphatic clay [4],clonop-tilolite [5]and sea nodule [6].Many biological materials such as olive stones,fungus Aspergillus niger ,seaweeds have also shown potential for the removal of heavy metal [7].Biosorption of Pb(II)onto a cone biomass of Pinus sylvestris was studied which revealed that the maximum adsorption of Pb onto P.sylvestris was at pH 4.0[8].In another study,ten different seaweed species were com-pared on the basis of lead uptake at different pH conditions [7].The study revealed that the brown seaweed,Turbinarea concoides exhibited the maximum lead uptake of 439.4mg/g at an optimum pH of 4.5and temperature of 30?C.Brown seaweed was extensively used for biosorption and its polysaccharide content was believed to be responsible for its excellent metal binding capacity [9].It was observed that the biological materials could accumulate heavy met-als in their walls,even though the binding sites for chelating were not identi?ed [10].
The objective of the present study is to investigate the utility of various types of locally available biomass to remove Pb(II)from aqueous systems.Dry leaves of bael tree (Aegle marmelos )were tested for the removal of Pb(II)ion from aqueous medium as they are very cheap and easily available biomass.Bael tree is a spiny tree belonging to the family Rutaceae and is abundantly found in India,Myanmar,Pakistan and Bangladesh.Literature reports indi-cate that the leaves of bael tree have medicinal value and are useful for the treatment of ophthalmia,deafness,in?ammations,cataract,diabetes,diarrhoea,dysentery,heart palpitation and asth-matic complications [11].In the present study,leaves of the bael
0304-3894/$–see front matter ? 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.jhazmat.2009.08.113
S.Chakravarty et al./Journal of Hazardous Materials173 (2010) 502–509503
tree were successfully utilized for the removal of Pb(II)ions from aqueous solution.The loading capacity of the bael leaves was opti-mized and the selectivity of the bael leaves towards Pb(II)in the presence of other metal cations was investigated.Attempts have been made to understand the factors responsible for adsorption of Pb(II)to the bael leaves.In an effort to show its practical utility,bael leaves were utilized for the removal of Pb(II)from storage battery ef?uents at the laboratory scale.This paper aims to examine the use of bael leaves as an adsorbent for the contaminated water bodies.
2.Experimental
2.1.Biosorbent
In the present study,bael leaves of the Indian bael tree(Aegle marmelos)were used as a biosorbent for the removal of Pb from aqueous solution.The bael tree is native to northern India but is found widely throughout the Indian peninsula and in Ceylon, Burma,Thailand,Indo-China[12].The bael leaves were?rst washed thoroughly with deionised water.The soluble colored components were then removed by washing repeatedly with hot deionised water(70?C).The bael leaves were then dried at70?C for24h. The dried bael leaves were crushed and sieved through100mesh and stored in polythene bottles.
2.2.Instrumentation
Atomic absorption spectrometer(AAS),GBC,AVANTA equipped with an air acetylene burner was used to determine the concen-tration of all the metal ions in the aqueous solution.The hollow cathode lamp was operated at an analytical wavelength of283.3nm for Pb and the slit was0.2nm for all the experiments.FT-IR spectra of bael leaves samples(before and after adsorption)were obtained using FT-IR spectrometer,Thermo Nicolet,Nexus870.The pro-cessed dry bael leaves in powder form(Section2.1,about0.1g) along with KBr were ground into?ne particles and pressed to make pellets.FT-IR spectrum of the native bael leaves was then recorded using the pellets.For FT-IR spectrum of Pb loaded bael leaves,the native bael leaves were adsorbed with1000mg L?1Pb(II)solution for24h.After adsorption,Pb(II)loaded bael leaves were?ltered, washed with deionised water and air dried.The FT-IR spectrum of Pb loaded bael leaves was then recorded using KBr pellets.A Scanning Electron Microscope,JEOL JSM840,was used to obtain SEM images of the bael leaves before and after Pb adsorption.Metal mapping of the native bael leaves and Pb loaded bael leaves were performed using the same SEM.All pH measurements were made using a digital pH meter.
2.3.Metal solutions
All the chemicals used were AR grade supplied by SRL,Mumbai, India and deionised water was used for preparation of the solu-tion throughout the experiments.The stock solution of Pb(II)was prepared by dissolving Pb(NO3)2in deionised water.Stock solu-tions of Mn2+,Fe2+,Co2+,Ni2+,Cu2+,Ca2+and Mg2+were prepared by dissolving their corresponding nitrate salts in deionised water. The working solutions were prepared by appropriate dilution of the stock solutions with deionised water.
2.4.Batch adsorption studies
Batch adsorption studies were performed in100mL conical ?asks to optimize the operating conditions for Pb(II)adsorption by bael leaves.In a typical experiment,0.2g of processed powder bael leaves(Section2.1)were added to50mL of98mg L?1synthetic Pb(II)solution.The natural pH of the synthetic Pb(II)solutions was measured to be5.1.This pH was maintained throughout for all the experiments except for pH optimization studies.The mixture was shaken for45min at303K using a mechanical shaker at120rpm. The phases were separated by?ltration and the Pb(II)concentration in the?ltrate was determined by Atomic Absorption Spectropho-tometer(AAS).Adsorption parameters,viz.biosorbent dose,initial concentration of Pb(II)and contact time were optimized by con-tinuous variation method.For pH optimization,the initial pH of each Pb(II)solution was adjusted to the required pH by using0.01N HNO3or0.01M NaOH.The concentration of Pb was measured using AAS after the pH adjustment.For desorption studies,Pb(II)was initially adsorbed on the bael leaves at pH5.1.The equilibrium con-centration(C e)of Pb in the solution was measured and the pH was then adjusted to the range of2.0–7.0using0.01M NaOH or0.01N HNO3.The solution after pH adjustment was shaken for half an hour and the equilibrium concentration after desorption(C e)was measured.The percentage of desorption was calculated as follows: %desorption=
C e?C e
C o?C e
×100
where C o is the initial Pb(II)concentration of the solution(mg L?1), C e is the equilibrium Pb(II)concentration(mg L?1)at a particular pH and C e is the equilibrium Pb(II)concentration(mg L?1)at a par-ticular pH after desorption.The kinetic studies were carried out at three different Pb(II)concentrations of48.2,87.8and180.2mg L?1 at temperatures of303,313and323K.
3.Results and discussion
3.1.Removal of Pb(II)from synthetic solutions
Dry bael leaves powder was initially used to remove Pb(II)from synthetic aqueous solutions.Different experimental parameters like contact time,adsorbent dose,and pH were optimized to obtain maximum Pb(II)removal using the bael leaves.For optimization of contact time,a solution of98mg L?1Pb(II)at pH5.1with0.2g of bael leaves was used.The contact time was varied between5 and120min at three different temperatures of303,313,and323K (results not shown here).It was observed that during the?rst 20min there was a rapid uptake of Pb,up to a maximum of65%. The time required for attaining equilibrium was30min.Therefore, a contact time of30min was employed for all other studies.It is to be noted that a contact time of30min was suf?cient for optimum removal of Pb(II)when the initial Pb(II)concentration was raised to180.2g L?1.
3.1.1.Effect of adsorbent dose
Three different solutions having an initial Pb(II)concentration of48.2,87.8and180.2mg L?1,with pH5.1were used to study the effect of the adsorbent dose on the removal of lead.The adsor-bent dose was varied in the range of0.01–0.5g.The result is presented in Fig.1.It was observed that the removal ef?ciency increased with increase of adsorbent dose.It reached a maximum (85%approximately)at around0.2g and then remained almost constant.Therefore,the optimum bael leaves dose was taken as 0.2g and this was used for all further studies.The positive correla-tion between adsorbent dose and metal removal ef?ciency can be related to the increasing surface area of the available binding sites [13].
3.1.2.Effect of pH
pH is a very important parameter that affects any biosorption process.It affects the activity of the functional groups present in the biosorbent that are responsible for metal adsorption and also affects the competition of metallic ions to get adsorbed to the
504S.Chakravarty et al./Journal of Hazardous Materials
173 (2010) 502–509
Fig.1.Effect of adsorbent dose on removal ef?ciency of Pb at three initial Pb con-
centrations.
Fig.2.Effect of pH on adsorption and desorption ef?ciency of Pb;initial Pb concen-tration:10.8mg L ?1,contact time:30min,adsorbent dose:0.2g.
active sites [14].The pH optimization study was carried out for the removal of Pb(II)using bael leaves in the pH range of 2.0–7.0.A solution of 10.8mg L ?1Pb(II)and 0.2g of bael leaves was used for this study.The result is presented in Fig.2.The Pb(II)removal is positively correlated with the pH of up to 4.0and then remains prac-tically constant.Therefore,pH 4.0was considered as the optimum pH for adsorption by bael leaves and the percentage of adsorption was approximately 97%.Similar values of optimum pH for sorp-tion of Pb are reported in the literature using cone biomass of P.sylvestris [8]and pH 5.0using maple sawdust [15]and activated sawdust [16].The decrease of adsorption capacity of bael leaves at lower pH can be attributed to the competition faced by Pb(II)ions with H +ions to get adsorbed on the binding sites of the cells which are responsible for metal adsorption [17].To further investi-gate the reason for pH dependence of adsorption ef?ciency of bael leaves,FT-IR studies were performed for the Pb loaded and Pb free bael leaves (native bael leaves).The results of FT-IR studies will be discussed in the following
sections.
Fig.3.Plot of Loading capacity of Pb vs.initial Pb(II)concentration.
3.2.Regeneration study
Regeneration (by desorption)of the biosorbent is of crucial importance in assessing its potential for commercial application.Desorption study will also help to elucidate the nature of the adsorption process.Desorption experiments were performed by varying the pH in the range of 2.0–7.0.The percentage of desorp-tion of Pb(II)from bael leaves was almost 85%at pH 2.0(Fig.2).It was observed that desorption decreased with increase in pH and beyond a pH of 4.0the percentage of desorption was negli-gible.In order to examine the reusability of the biosorbent,the adsorption–desorption cycle of Pb(II)was repeated twice.A 5%decrease in the adsorption ef?ciency was observed after two cycles.The regeneration of bael leaves showed that adsorption of Pb on to the bael leaves was a reversible process.3.3.Loading capacity
Loading capacity of an adsorbent is de?ned as the amount of adsorbate adsorbed (X )per unit weight (m )of the adsorbent.Load-ing capacity (X /m )of the bael leaves was determined at different initial Pb concentrations by varying the adsorbent dose in a solu-tion of pH 5.1.Fig.3represents the plot of the loading capacity (X /m )versus initial Pb(II)concentration,C o (mg L ?1).The maxi-mum loading capacity was found to be 104mg g ?1at 50mg L ?1of initial Pb(II)concentration.A comparative study of the loading capacity,X /m (mg g ?1)under similar conditions of pH and tempera-ture was carried out with other reported biosorbents (Table 1).The data revealed that bael leaves were a potential biosorbent with sim-ilar or higher loading capacity of Pb compared to some of the other reported biomasses.However,Ulmus tree leaves and Fraxinus tree leaves were better adsorbents with higher loading capacities of Pb.3.4.Mechanism of adsorption
The studies so far indicate that bael leaves can be successfully used for the removal of Pb from aqueous solution.An effort was made to identify the components of the bael leaves that are respon-sible for Pb adsorption.Hence,the FT-IR spectra for native and Pb
Table 1
Comparison of Pb sorption capacity of bael leaves with other reported biosorbents under similar conditions.Biosorbent
Sorption capacity (mg g ?1)pH Temperature (K)Initial concentration (mg L ?1)Ref.
Sago waste
46.6 4.0–5.5298100[29]Cicer arientinum 50.2 5.029810[30]Botrytis cinerea 107.1 4.0298350[31]Fraxinus tree leaves 172.0529850[32]Ulmus tree leaves 201.0529850[32]Spyrogyra Negiecta 116.1 5.029850[33]
Bael leaves
104.0
5.1
298
50
Present study
S.Chakravarty et al./Journal of Hazardous Materials173 (2010) 502–509
505
Fig.4.FT-IR spectra of native bael leaves(a)and Pb(II)loaded bael leaves(b). loaded bael leaves were recorded(Fig.4)to identify the different functional groups of bael leaves responsible for lead removal.An analysis of the FT-IR spectra revealed that the functional groups like carboxylic acids,amides,thioesters,and sulphonamides were present in the native bael leaves.In fact,Sudharameshwari and Radhika,in their study involving medicinal activities of bael leaves had identi?ed that bael leaves contain compounds like alkaloids, carboxylic acids,phenols,sterols and xanthoproteins[18].The complex spectra in Fig.4show several strong absorption bands. The bands were assigned on the basis of the structure and chemical composition of the plant cell wall and cuticle and were facilitated by the available data of FT-IR spectra of cell wall components [19]and plant leaf tissues[20].The broad band positioned around 3430cm?1was assigned the stretching vibration of hydroxyl func-tional groups.The high content of water in the plant leaves and numerous hydroxyl groups in the polysaccharide structure of the plant cell walls explained the presence of the band.The absorption bands located at1631and1565cm?1correspond to the aromatic domains of the cuticle and plant leaves[19].The band frequen-cies at1700–1650cm?1are the characteristic amide-I frequencies of the protein secondary structures.The absorbance at1655cm?1 is due to C O of carboxylic acids[19].The absorbance at around 1550cm?1is usually associated with the amide-II band that is attributable to N–H bending and C–N stretching in protein amide groups.The thioester group corresponds to the band at672cm?1 [20].The band at1382cm?1is assigned to the sulphonamide group.The changes in peak frequency and intensity of FT-IR spec-tra of native and Pb loaded bael leaves suggest that carboxylic acid and thioester groups are involved in the adsorption process.The appearance of a band at1735cm?1in the Pb loaded bael leaves can be assigned to the carboxylate ion(–COO?).At pH greater than4.0, the carboxylic acid group is converted to the carboxylate ion and Pb(II)ion is adsorbed.The involvement of carboxylic acid groups in the adsorption process explains the effect of pH on the adsorp-tion process(Section3.1.2).At pH2.0,majority of the carboxylate ions are converted to carboxylic acid groups(–COOH)and hence the adsorption ef?ciency decreases.This fact is further strength-ened by the regeneration study.As discussed in Section3.2,the Pb loaded bael leaves can be regenerated by decreasing the pH.The band at1382cm?1disappears in the FT-IR spectra of Pb loaded bael leaves.This suggests a strong involvement of the sulphonamide group in the adsorption process.No marked change in frequency in the region of3430cm?1(hydroxyl functional groups)was observed between the native bael leaf and the lead loaded bael leaf.However, the broadening of the peak decreases indicating that the hydro-gen bonding of the hydroxyl groups decreases after Pb loading.All these observations indicate the involvement of functional
groups Fig.5.SEM and metal mapping images of native bael leaves(A and C)and Pb(II)loaded bael leaves(B and D).
506S.Chakravarty et al./Journal of Hazardous Materials173 (2010) 502–509 like carboxylic acid,thioester and sulphonamide in the biosorption
process.
To investigate the adsorption process further,the bael leaves
and Pb loaded bael leaves were observed under the scanning elec-
tron microscope.The SEM images of the native bael leaves and Pb
loaded bael leaves are shown in Fig.5.SEM image of the powdered
bael leaf(Fig.5A)shows a regular symmetry with hollow tubular
structures before adsorption.After Pb adsorption the tubes appear
to be prominently swollen as Pb enters the?bers of the bael leaves
(Fig.5B).This observation indicates that Pb is adsorbed to the func-
tional groups present inside the wall of the tubular structures of the
bael leaf.To visualize the location of the adsorption sites,a metal
mapping was performed using SEM.The metal mapping micro-
graphs of the native and Pb loaded bael leaves are also shown in
Fig.5C and D.The presence of inorganic constituents such as Ca,
Cu,Si,and some amount of Pb in the native bael leaves are repre-
sented by green,red,sea blue and deep blue color,respectively,in
the micrograph(Fig.5C).Fig.5D shows that Pb is heavily loaded
in the bael leaves and adsorption of Pb(II)occurs inside the wall of
the hollow tubes.So,the morphological study of Pb(II)loaded bael
leaves con?rms that the adsorption takes place inside the hollow
tubes of the bael leaves.
3.5.Adsorption isotherm
Two models were used to describe the experimental sorption
isotherm:Langmuir model and Freundlich model.The linear form
of Langmuir equation after rearrangement is
C e q e =1
bV m
+C e
V m
(1)
where C e is the equilibrium concentration of remaining metal in the solution(mg L?1),q e is the amount of metal adsorbed per mass unit of adsorbent at equilibrium(mg g?1),V m is the amount of adsor-bate at complete monolayer coverage(mg g?1),and b(L mg?1)is a constant that relates to the heat of adsorption.
Freundlich adsorption isotherm can be represented as
q e=K f C1/n
e
(2) or in the linear form
log q e=log K f+1
n
log C e(3)
where K f and n are Freundlich constants indicating adsorption capacity and intensity,respectively.K f and n was determined from a linear plot of log q e against log C e.The adsorption capacity(q e) was calculated using the equation
q e=(C o?C e)V
w
(4)
where C o is the initial Pb(II)concentration,C e is the?nal equi-librium concentration of Pb(II),V is the volume of Pb(II)solution (ml),w is the weight of the bael leaves(g).Adsorption equilibrium studies for Pb(II)adsorption on bael leaves were conducted at the optimum conditions using a contact time of30min at pH5.1with ?ve different initial Pb(II)concentrations of8.7,19.0,48.2,87.8and 180.2mg L?1and a?xed adsorbent dose of0.01g.The Langmuir and Freundlich isotherm plots are given in Figs.6and7,respec-tively.It was found that the adsorption of Pb(II)ion onto bael leaves ?ts better with the Langmuir model(R2=0.97)as compared to the Freundlich model(R2=0.8)under the concentration range studied. The calculated results of the Freundlich and Langmuir isotherm constants are given in Table2.The essential feature of the Lang-muir isotherm can be expressed in terms of dimensionless constant separation factor,R L that is used to predict whether an
adsorption
https://www.wendangku.net/doc/fa8096367.html,ngmuir isotherm plot for adsorption of Pb(II)onto bael
leaves.
Fig.7.Freundlich isotherm plot for adsorption of Pb(II)onto bael leaves. system is“favorable”or“unfavorable”[21].The separation factor R L is de?ned as
R L=
1
1+bC e
(5)
where C e(mg L?1)is the equilibrium concentration of Pb(II)and b (mL mg?1)is the Langmuir isotherm constant.The adsorption pro-cess as a function of R L may be described as R L>1;unfavorable, R L=1;Linear,0 3.6.Adsorption kinetics In order to investigate the kinetics of biosorption,two kinetic models,Lagergren’s?rst order rate equation[23]and pseudo sec- Table2 Freundlich and Langmuir model constants for Pb adsorption onto bael leaves. Langmuir model b(L mg?1)0.05 V m(mg g?1)125 R20.97 Freundlich model n 2.04 K(mg g?1)11.4 R20.80 S.Chakravarty et al./Journal of Hazardous Materials173 (2010) 502–509507 Table3 R L values for adsorption of Pb(II)onto bael leaves based on Langmuir model. Initial Pb(II) concentration(mg L?1)Equilibrium concentration(mg L?1) R L 8.7 4.660.8 19.012.420.61 48.228.30.41 87.867.090.22 180.2160.50.11 ond order equation[24]were employed.A solution of98.3mg L?1 Pb(II)(50mL)and0.05g of bael leaves were used for this study. Samples of5mL each were drawn from the solution mixture at time intervals of5,10,15,20,25and30min and analyzed for kinetics https://www.wendangku.net/doc/fa8096367.html,gergren?rst order model is log(q e?q t)=log q e? k1t 2.303 (6) where q e is the amount of adsorbed Pb(II)onto the bael leaves at equilibrium(mg g?1),q t is the amount of Pb(II)adsorbed at time t and k1is the?rst order rate constant.Adsorption data of Pb(II) on bael leaves at three different temperatures(303,313and323K) was?tted to the Lagergren?rst order rate equation.The results obtained are summarized in Table4.The pseudo second order rate equation is represented as dq t dt =k2(q e?q t)2(7) where k2is the second order rate constant of adsorption (g mg?1min?1).Integrating Eq.(7)with boundary conditions t=0 to t=t and q t=0to q t=q t,it becomes 1 q e?q t =1 q e +k2t(8) Eq.(8)can be rearranged to obtain t q t =1 k2q2e +t q e (9) which is the linear form of Ho second order model.The plot of t/q t against t is shown in Fig.8.The?tting of kinetic data in second order rate expression shows excellent linearity with high correlation coef?cient(R2=0.99)over the temperature range of303–323K.The data obtained for pseudo second order kinetic model at three differ-ent temperatures is tabulated in Table4.An analysis of the data in Table4suggests that the kinetics of adsorption of Pb on bael leaves can be explained more accurately by the pseudo second order kinet-ics model.The correlation coef?cients(R2)obtained for the second order kinetic model are better than that of Lagergren?rst order kinetic model.The Lagergren?rst order kinetic model fails to esti-mate the q e values correctly as the estimated values deviate more from the experimental q e values.The calculated q e values in the second order kinetics were found to be quite close to the experi-mental q e values at all the temperatures(303–323K).So,it may be inferred that the adsorption of Pb on bael leaves follows the second order kinetics. Based on the second order kinetic model,the initial adsorp-tion rate and half adsorption time were estimated according to the Fig.8.Plot of pseudo second order kinetics model for adsorption of Pb(II)onto bael leaves. Table5 Kinetic parameters of second order adsorption model for Pb(II)adsorption onto bael leaves. Temperature(K)U(mg g?1min?1)t1/2(min) 30348.79 1.36 31371.37 1.00 323112.30.68 following equation: U=k2q2e(10) t1/2= 1 k2q e (11) where U=initial adsorption rate(mg g?1min?1),t1/2=half adsorp-tion time(min).The estimated values of U and t1/2are presented in Table5.It can be observed from Table5that the initial adsorption rate increases with increase in temperature and the half adsorption time t1/2decreases with increase in temperature. The pseudo second order rate equation of Pb(II)adsorption on bael leaves is expressed as a function of temperature by the Arrhe-nius equation: ln k=ln A? E a RT (12) where E a is the Arrhenius activation energy(kJ mol?1),A is the Arrhenius factor,R is the ideal gas constant(8.314J mol?1K?1), k is the speci?c rate constant and T is the solution temperature (K).The k value of Arrhenius equation was obtained from the rate constant(k2)of pseudo second order equation.To estimate the Arrhenius activation energy,ln k was calculated at three different temperatures of303,313and323K and ln k versus1/T was plotted (Fig.9).The plot gave a straight line with slope?E a/R and intercept of ln A.The Arrhenius activation energy calculated from the slope was found to be22.2kJ mol?1.The results of the activation energy con?rmed that the nature of the adsorption process is physical adsorption on to the bael leaves.The physisorption process usually Table4 Kinetic parameters of Lagergren?rst order and pseudo second order expressions for Pb(II)adsorption onto bael leaves at different temperatures. Temperature(K)Lagergren?rst order kinetic model Experimental value,q e Pseudo second order model q e(mg g?1)k1(min?1)R2q e(mg g?1)q e(mg g?1)k2(mg g?1min?1)R2 303 5.970.0110.806166.60.0110.99 313 6.530.0090.746671.40.014 1.0 323 5.590.0110.6276.076.90.019 1.0 508S.Chakravarty et al./Journal of Hazardous Materials 173 (2010) 502–509 Fig.9.Arrhenius equation plot for adsorption of Pb(II)onto bael leaves. has energies in the range of5–40kJ mol?1while the chemisorp-tions process has higher activation energy(40–800kJ mol?1) [25,26]. 3.7.Selective adsorption of Pb(II)over other metal ions The results obtained from the adsorption studies of synthetic spiked waters(usually distillate water and one or two metals under investigation)can only be applied to real wastewaters to a very limited extent.Waste waters or real samples contain a broad range of different cations as well as other inorganic and organic contami-nants that certainly interfere in the sorption mechanisms,including competitive sorption among metals[27].Therefore,a study was performed to evaluate the effect of the presence of other cationic metal ions on the adsorption process of Pb on bael leaves.Simulta-neous biosorption of Pb(II)ions was studied using a medium that contained10mg L?1of each metal ion Mn2+,Fe2+,Co2+,Ni2+,Cu2+, Ca2+and Mg2+with a common nitrate anion.The pH of the solu-tion was maintained at3.0and0.2g of dry bael leaves were used for the study.The result of this study is presented in Table6.It can be observed from the table that about80%of Pb was removed from the aqueous solution using the bael leaves where as the removal of other metal ions was negligible.Therefore,Pb(II)adsorption on bael leaves is highly selective.The selective adsorption of Pb(II)on bael leaves can be explained by the higher electro-negativity(2.33Paul-ing scale)and lower atomic radius(154pm)compared to the other metal ions[28].Sorption of metals having a smaller ionic radius has been reported as superior to those with larger ionic radius[28]. This result is signi?cant in the sense that Pb(II)can be removed speci?cally in the presence of other cations present in the aqueous system. Table6 Selective removal of Pb(II)by bael leaves in presence of other metal ions. Metal ion Initial concentration (mg L?1)Final concentration (mg L?1) Percentage removal Pb2+9.76 2.1178.3% Mn2+9.259.190.6% Fe2+8.178.06 1.3% Zn2+9.649.16 4.9% Ni2+10.910.78 1.1% Cu2+10.369.8 5.4% Cd2+9.369.23 1.3% Mg2+9.69.540.6%Table7 Removal of Pb from battery ef?uent using bael leaves at different pH. pH Pb concentration(mg L?1) before adsorption Pb concentration(mg L?1) after adsorption %Pb removal 2.211082.425% 4.178.223.270% 6.255.4 6.688% 3.8.Application on battery waste ef?uent In an effort to examine the practical utility of bael leaves for Pb removal from aqueous solution,an experiment was carried out to remove Pb from the ef?uent of waste battery.One of the objectives of the present study was also to examine bael leaves as an adsorbent for the purpose of remediation.The ef?uent of a waste battery was collected by mixing the contents of an exhausted battery in200mL of distilled water.The insoluble portions were?ltered off and the ?ltrate was accepted as the ef?uent.The Pb(II)concentration in the ef?uent was measured to be110mg L?1and the pH of the ef?uent was0.5.For the treatment of this ef?uent by bael leaves,its pH was adjusted to pH2.0,4.0and6.0using0.1(M)NaOH and0.2g of bael leaves were used for the Pb removal purpose.The results of the study are summarized in Table7.It can be observed from Table7 that approximately70%and88%of Pb(II)could be removed from the ef?uent at pH4.1and6.2using1g L?1bael leaves.Since the bael leaves are biodegradable,it can be easily disposed after recovering Pb(II)from the biosorbent by desorption. 4.Conclusion The present investigation showed that bael leaves,Aegle marme-los,are a potential biosorbent for the removal of Pb(II)from an aqueous medium.It was demonstrated that Pb could be removed from the ef?uents of waste batteries.The maximum Pb(II)loading capacity of bael leaves was104mg g?1which was either compa-rable to or better than the Pb loading capacities of other reported biosorbents.The adsorption process was pH dependent and the optimum pH for Pb(II)removal was4.0.Pb was adsorbed inside the tubular structures of the bael leaves and carboxylic acid,sul-phanamide and thioester functional groups were involved in the process.The adsorption process followed pseudo second order kinetic model and the Langmuir model?t better to the adsorp-tion equilibrium data in comparison to the model described by Freundlich.The nature of adsorption of Pb on bael leaves was phys-ical adsorption.The bael leaves could be regenerated using0.1N HNO3but the adsorption ef?ciency decreased by5%after repeated adsorption–desorption process.Bael trees grow widely through-out the Indian peninsula,the leaves have no commercial value, and the present study showed that it could be used as a good and inexpensive source of biomaterial for wastewater treatment. 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[33]A.Singh,D.Kumar,J.P.Gaur,Copper and lead(II)sorption from aqueous solu- tion by non-living Spyrogyra negiecta,Bioresour.Technol.98(2007)3529–3622. 实验一(二) 熔点的测定 一、实验目的： 1、使学生掌握和熟悉显微熔点测定仪的操作步骤； 2、使学生学会利用显微熔点测定仪测定物质的熔点； 3、使学生了解测定物质熔点的意义。 二、实验的装置图 三、实验内容： 1、按照装置：如右图正确安装实验装置仪 器。 2、校正仪器：先用熔点标准药品进行测 量标定（操作参照具体的测量步骤）。求出修正 值（修正值=标准药品的熔点标准值-该药品的熔点测量值），作为测量时的修正值依据。 3、操作步骤： （1）将热台的电源线接入调压测温仪后侧的输出端，并将温度计插入热台孔，将调压测温仪的电源线与AC220V电源相连。 （2）取两片盖玻片，用蘸有乙醚（或乙醚与酒精混合液）的脱脂棉擦拭干净。晾干后，取适量待测物品（不大于0.1mg）放在一片载玻片上并使药品分布薄而均匀，盖上另一片载玻片，轻轻压实，然后放置在热台中心，然后盖上隔热玻璃。 （3）松开显微镜的升降手轮，参与显微镜的工作距离（88mm或33mm）,上下调整显微镜，直到从目镜中能看到熔点热台中央的待测物品轮廓时锁紧该手轮；然后调节调焦手轮，直到能清晰地看到待测物品的像为止。 （4）打开调压测温仪的电源开关。根据被测熔点品的温度值，控制调温手钮1或2（它们表示：1 升温电压宽量调整，2 升温电压窄量调整，其电压变化可参与电压表的显示），以期达到在测物质熔点过程中，前段升温迅速、中断升温渐慢，后段升问平缓。具体方法如下：先将两调温手钮顺时针调到最大位置，使热台快速升温。当温度接近待测物体熔点温度以下40℃左右时（中段），将调温手钮逆时针调节至适当位置，使升温速度减慢。在被测物熔点值以下10℃左右时（后段），调整调温手钮控制升温速度约每分钟1℃左右。（注意：尤其是后段升温的控制对测量精度影响较大，在待测物熔点值以下10℃左右，一定要将升温速度控制在大约每分钟1℃。经过反复调整手钮1或2，方便的无级调整会让用户很快掌握，运用自如。） （5）观察被测物品的熔化过程，记录初熔和全熔时的温度值，用镊子取下隔热玻璃和盖玻片，即完成一次测试。如需重复测试，只需将散热器放在热台上，电压调为零或切断电源，使温度降至熔点值以下40℃即可。 二组分简单共熔体系相图的绘制 ————————————————————————————————作者: ————————————————————————————————日期： 实验七二组分简单共熔体系相图的绘制 -－----Cd～Ｂi二组分金属相图的绘制１实验目的及要求: 1）应用步冷曲线的方法绘制Cd～Bｉ二组分体系的相图。 ２）了解纯物质和混合物步冷曲线的形状有何不同,其相变点的温度应如何确定。 2 实验原理：… 用几何图形来表示多相平衡体系中有哪些相、各相的成分如何,不同相的相对量是多少，以及它们随浓度、温度、压力等变量变化的关系图，叫相图。 绘制相图的方法很多，其中之一叫热分析法。在定压下把体系从高温逐渐冷却,作温度对时间变化曲线，即步冷曲线。体系若有相变，必然伴随有热效应,即在其步冷曲线中会出现转折点。从步冷曲线有无转折点就可以知道有无相变。测定一系列组成不同样品的步冷曲线,从步冷曲线上找出各相应体系发生相变的温度，就可绘制出被测体系的相图，如图Ⅱ一6一l所示。 纯物质的步冷曲线如①⑤所示，从高温冷却，开始降温很快，口６线的斜率决定于体系的散热程度。冷到A的熔点时，固体Ａ开始析出,体系出现两相平衡（溶液和固体Ａ)，此时温度维持不变，步冷曲线出现ｂc的水平段,直到其中液相全部消失，温度才下降。 混合物步冷曲线（如②、④）与纯物质的步冷曲线(如①、⑤)不同。如②起始温度下降很快（如a′b′段），冷却到ｂ′点的温度时，开始有固体析出,这时体系呈两相,因为液相的成分不断改变，所以其平衡温度也不断改变。由于凝固热的不断放出，其温度下降较慢,曲线的斜率较小(b′ｃ′段)。到了低共熔点温度后,体系出现三相，温度不再改变,步冷曲线又出现水平段c′d′,直到液相完全凝固后，温度又迅速下降。 曲线⑧表示其组成恰为最低共熔混合物的步冷曲线，其图形与纯物相似，但它的水平段是三相平衡。 用步冷曲线绘制相图是以横轴表示混合物的成分,在对应的纵轴标出开始出现相变(即步冷曲线上的转折点)的温度,把这些点连接起来即得相图。 ３仪器与药品： 加热电炉１只,热电偶(铜一康铜)1根,不锈纲试管8只，控温测定装置1台，计算机1台，镉（化学纯),铋（化学纯)。 4 实验步骤: 1)配制不同质量百分数的铋、镉混合物各１00g(含量分别为0%,１5%，25％,4０%，55%，75％，90％，100%)，分别放在８个不锈纲试管中。 2）用控温测定装置装置,依次测纯镉、纯铋和含镉质量百分数为9０％,７5％,５5％，40%，25％,15%样品的步冷曲线。将样品管放在加热电炉中加热，让样品熔化,同时将热电偶的热端(连玻璃套管）插入样品管中，待样品熔化后，停止加热。用热电偶玻璃套管轻轻搅 2.熔点测定 固液两相的蒸气压相同而且等于外界大气压时的温度就是该固体物质的熔点。 测熔点时几个概念：始熔、全熔、熔点距、物质纯度与熔点距关系。 混合熔点测定法——鉴定熔点相同或相近的两个试样是否为同一物质？ 测定熔点实验关键是：由于毛细管法是间接测熔点方法，所以加热升温速度是本实验的关键，当接近熔点时升温速度一定要慢，应小于1~2℃/min；密切观察加热和熔化情况，及时记下温度变化。 实验关键 1．样品填装（研碎迅速，填装结实，2~3mm为宜） 2．毛细管安装在温度计精确位置、再固定 3．加热升温测定、注意观察、做好记录 加热升温速度：开始时可快些~5℃/min 将近熔点15℃时，1~2℃/min 接近熔点时0.2~0.3℃/min 每个样品至少填装两支毛细管，平行测定两次。 操作要点和说明 影响毛细管法测熔点的主要因素及措施有： 1、熔点管本身要干净，管壁不能太厚，封口要均匀。初学者容易出现的问题是，封口一端发生弯曲和封口端壁太厚，所以在毛细管封口时，一端在火焰上加热时要尽量让毛细管接近垂直方向，火焰温度不宜太高，最好用酒精灯，断断续续地加热，封口要圆滑，以不漏气为原则。 2、样品一定要干燥，并要研成细粉末，往毛细管内装样品时，一定要反复冲撞夯实，管外样品要用卫生纸擦干净。 3、用橡皮圈将毛细管缚在温度计旁，并使装样部分和温度计水银球处在同一水平位置，同时要使温度计水银球处于b形管两侧管中心部位。 4、升温速度不宜太快，特别是当温度将要接近该样品的熔点时，升温速度更不能快。一般情况是，开始升温时速度可稍快些（5℃／min）但接近该样品熔点时，升温速度要慢（1－2℃／min），对未知物熔点的测定，第一次可快速升温，测定化合物的大概熔点。 5、熔点温度范围（熔程、熔点、熔距）的观察和记录，注意观察时，样品开始萎缩（蹋落）并非熔化开始的指示信号，实际的熔化开始于能看到第一滴液体时，记下此时的温度，到所有晶体完全消失呈透明液体时再记下这时的温度，这两个温度即为该样品的熔点范围。 6、熔点的测定至少要有两次重复的数据，每一次测定都必须用新的熔点管，装新样品。进行第二次测定时，要等浴温冷至其熔点以下约30℃左右再进行。 7、使用硫酸作加热浴液（加热介质）要特别小心，不能让有机物碰到浓硫酸，否则使溶液颜色变深，有碍熔点的观察。若出现这种情况，可加人少许硝酸钾晶体共热后使之脱色。采用浓硫酸作热浴，适用于测熔点在220℃以下的样品。若要测熔点在220℃以上的样品可用其它热浴液。 注释： （1）管壁太厚样品受热不均匀，熔点测不准，熔点数据易偏高，熔程大。 实验 金属相图 [实验目的] 1．学会用热分析法测绘Pb - Sn 二组分金属相图。 2．掌握热分析法的测量技术与有关测量温度的方法。 [基本原理] 热分析法是先将体系加热熔融成一均匀液相，然后让体系缓慢冷却，并每隔一定时间读体系温度一次，将所得温度值对时间作图，所得曲线即为步冷曲线（如下图1）。每一种组成的Pb - Sn 体系均可根据其步冷曲线找出相应的转折点和水平台温度，然后在温度-成分坐标上确定相应成分的转折温度和水平台的温度，最后将转折点和恒温点分别连接起来，即为相图（如下图2）。 图1 步冷曲线 图2 步冷曲线与相图 [仪器结构] 图1 加热装置 图2 测量装置 仪器参数设置法： 最高温度：C 350℃ 加热功率：P1 400W 保温功率：P2 40W 报警时间：E1 30s 报警声音：n 0 按设置键：显示温度时就是退出了设置状态，可以进行实验。 [实验步骤] 1．配制样品。配制含锡量分别为20%，40%，61.9%，80%的铅-锡混合物各100g，装入4个样品管中，然后在样品管内插入玻璃套管(管中应有硅油，增加热传导系数)，并在样品上方盖一层石墨粉； 2．将需加热的样品管放入一炉子中，将加热选择旋钮指向该加热炉（加热炉和选择旋钮上均有数字标号），并将测温传感器置于需加热的样品管中； 3．设定具体需加热的温度，加热功率和保温功率，本实验中这些参数依次设定为350o C，400W, 40W，参数设定完成后, 按下“加热”键，即进入加热状态； 4．当测量装置上的温度示值接近于330 O C时，可停止加热。待样品熔化后，用玻璃套管小心搅拌样品； 5．待温度降到需要记录的温度值时（比如305 C），可点击测量软件中的“开始实验”按钮，降温过程中，若降温速度太慢，可打开风扇；若降温速度太快，则可按“保温”键，适当增加加热量。当温度降到平台以下，停止记录。 按照上述步骤，测定不同组成金属混合物的温度—时间曲线。 [数据处理] 1．依实验数据绘制T-t步冷曲线，6根曲线绘制在同一张图上； 2．依样品的组成和步冷曲线中转折点和平台的温度绘制出Pb-Sn的T-w金属相图； 3．你所测得的Pb, Sn的熔点与教材（东北师大第90面）上的值的相对误差分别为: %, %. [问答题] 金属相图的用途有哪些？ ---------------------------------------------------------------------------------------------------------------- 班级: 姓名: 学号: 实验日期: 分数: 教师: 实验二熔点测定 【实验目的】 1．了解Thiele管法测定熔点的基本原理和熔点测定的意义——识别物质及定性检验物质的相对纯度。 2．掌握Thiele法测定熔点的操作方法。 【实验原理】 纯粹的晶体有机物，在大气压下，固态与液态成平衡状态时（共存）的温度，称为该物质的熔点（melting point，记作 m.p.）。这是晶体有机物的一个十分重要的物理常数。纯净的固体有机物一般都有固定的熔点，熔程不超过0.5-1℃。 由下图可见固相蒸气压随温度的变化速率比相应的液相大，两曲线相交，交点所对应的温度即熔点。交点处固液两相共存，这是纯粹固体有机物有敏锐熔点的原因。 杂质对熔点的影响：熔点下降，熔程变长。根据拉乌尔（Raoult）定律可知，在一定压力和温度下，增加溶质的量导致溶剂蒸汽压的降低（见下图），从而导致熔点下降 【实验的准备】 仪器：Thiele熔点测定管（又称提勒管、b形管）；水银温度计（250℃）；酒精灯；熔点管:内Φ1mm，L=6－7cm 药品：尿素、肉桂酸、混合物。液体石蜡（导热液）。 （苯甲酸、α-萘胺、β-萘酚、水杨酸可供备用）。 【物理常数】 注：A.R.为分析纯； C.P.为化学纯。 【仪器安装要点】 1.装好试料的熔点管用橡皮圈套附在温度计上，试料部分位于温度计水银球的中部。 2.温度计用一个刻有沟槽的单孔塞固定在Thiele管的中心轴线上，水银球的高度位于Thiele管上、下两叉口中间。 导热液的液位略低于Thiele管上叉口。太少不能保证导热液的循环；太多导热液膨胀使橡皮圈浸入溶液中而逐渐溶胀、溶解甚至碳化。 附:导热液的选择参考(导热液的选择视所需温度而定) 1.< 140℃可用液体石蜡或甘油（药用液体石蜡可加热至220℃仍不变色）。 2.>140℃可用浓硫酸(温度超过250℃,浓硫酸发生白烟,防碍温度的读数)。 注意：（1）用浓硫酸作导热液时要戴护目镜。 （2）浓硫酸变黑后可加一些硝酸钾晶体。 3.>250℃可用浓H2SO4和K2SO4的饱和溶液： 浓H2SO4:K2SO4＝7:3（重量）可加热到325℃； 浓H2SO4:K2SO4＝3:2（重量）可加热到365℃； 还可用H3PO4（可加热到300℃）、硅油（可加热到365℃），但硅油价格较贵。 【操作要点】 1.熔点管的准备： 准备3支熔点管，Φ＝1.0 mm，L＝60～70 mm （管壁均匀）。 2.试料及其填充： 试料要研细（受潮的试料应事先干燥），填充装的要均匀、结实。装料高度为2～3 mm。 3.加热速度： 升温速度是测得的熔点数据准确与否的关键。 (1)已知样: 开始升温速度可快些(5－8℃／min)，距熔点约10～15℃时，升温速度1～2℃／min，愈接近熔点，升温速度愈慢，以0.5～1℃／min为宜。 （2）未知样： 至少要测两次。第一次以5℃／min左右的升温速度粗测，可得到一个近似的熔点；第二次开始时升温速度可快些，待达到比近似熔点低10℃时，改用小火，使温度以0.5－1℃／min的速度缓慢而均匀地上升。 4.熔点的记录： 应记录熔点管中刚有小滴液体出现（即初熔温度t1）和试料恰好完全熔融（即全熔温度t2）这两个温度点的读数。以及计算熔程（t2-t1），每个样品测定两次，取平均值。 注意： （1）记录时不能取初熔温度到全熔温度的平均值，即熔程为123℃－125℃，不可记录为124℃。 （2）若物质120℃时开始收缩(坍塌)，121℃开始出现液滴，122℃全部液化，熔程的记录 实验六二组分金属相图的绘制 一、实验目的 1.学会用热分析法测绘Sn—Bi二组分金属相图。 2.了解热电偶测量温度和进行热电偶校正的方法。 二、预习要求 1.了解纯物质的步冷曲线和混合物的步冷曲线的形状有何不同，其相变点的温度应如何确定。 2.掌握热电偶测量温度的原理及校正方法。 三、实验原理 测绘金属相图常用的实验方法是热分析法，其原理是将一种金属或合金熔融后，使之均匀冷却，每隔一定时间记录一次温度，表示温度与时间关系的曲线叫步冷曲线。当熔融体系在均匀冷却过程中无相变化时，其温度将连续均匀下降得到一光滑的冷却曲线;当体系内发生相变时，则因体系产生之相变热与自然冷却时体系放出的热量相抵偿，冷却曲线就会出现转折或水平线段，转折点所对应的温度，即为该组成合金的相变温度。利用冷却曲线所得到的一系列组成和所对应的相变温度数据，以横轴表示混合物的组成，纵轴上标出开始出现相变的温度，把这些点连接起来，就可绘出相图。 二元简单低共熔体系的冷却曲线具有图1所示的形状。 图1根据步冷曲线绘制相图 图2有过冷现象时的步冷曲线 用热分析法测绘相图时，被测体系必须时时处于或接近相平衡状态，因此必须保证冷却速度足够慢才能得到较好的效果。此外，在冷却过程中，一个新的固相出现以前，常常发生过冷现象，轻微过冷则有利于测量相变温度;但严重过冷现象，却会使折点发生起伏，使相变温度的确定产生困难。见图2。遇此情况，可延长dc线与ab线相交，交点e即为转折点。 四、仪器药品 1.仪器 立式加热炉1台；冷却保温炉1台；长图自动平衡记录仪1台；调压器1台；镍铬-镍硅热电偶1副；样品坩埚6个；玻璃套管6只；烧杯(250mL)2个；玻璃棒1只。 熔点、沸点、凝固点与压强的关系原因分析 一、熔点、沸点、凝固点 1、凝固点 凝固点是晶体物质凝固时的温度，不同晶体具有不同的凝固点。在一定压强下，任何晶体的凝固点，与其熔点相同。同一种晶体，凝固点与压强有关。凝固时体积膨胀的晶体，凝固点随压强的增大而降低；凝固时体积缩小的晶体，凝固点随压强的增大而升高。在凝固过程中，液体转变为固体，同时放出热量。所以物质的温度高于熔点时将处于液态；低于熔点时，就处于固态。非晶体物质则无凝固点。 液-固共存温度浓度越高，凝固点越低，液体变为固体的过程叫凝固 2、沸点 饱和蒸汽压：在一定温度下，与液体或固体处于相平衡的蒸汽所具有的压力称为饱和蒸汽压。沸点：在一定压力下，某物质的饱和蒸汽压与此压力相等时对应的温度。沸腾是在一定温度下液体内部和表面同时发生的剧烈汽化现象。 液体沸腾时候的温度被称为沸点。浓度高，沸点高，不同液体的沸点是不同的， 几种不同液体的沸点/摄氏度（在标准大气压下） 液态铁：2750 液态铅：1740 水银（汞）：357 亚麻仁油：287 食用油：约250 萘：218 煤油：150 甲苯：111 水：100 酒精：78 乙醚：35 液态氨：-33 液态氧：-183 液态氮：-196 液态氢：-253 液态氦：-268.9 所谓沸点是针对不同的液态物质沸腾时的温度。 液体开始沸腾时的温度。沸点随外界压力变化而改变，压力低，沸点也低。 沸点:液体发生沸腾时的温度；即物质由液态转变为气态的温度。当液体沸腾时，在其内部所形成的气泡中的饱和蒸汽压必须与外界施予的压强相等，气泡才有可能长大并上升，所以，沸点也就是液体的饱和蒸汽压等于外界压强的温度。液体的沸点跟外部压强有关。当液体所受的压强增大时，它的沸点升高；压强减小时；沸点降低。例如，蒸汽锅炉里的蒸汽压强，约有几十个大气压，锅炉里的水的沸点可在200℃以上。又如，在高山上煮饭，水易沸腾，但饭不易熟。这是由于大气压随地势的升高而降低，水的沸点也随高度的升高而逐浙下降。（在海拔1900米处，大气压约为79800帕（600毫米汞柱），水的沸点是93.5℃）。 在相同的大气压下，液体不同沸点亦不相同。这是因为饱和汽压和液体种类有关。在一定的温度下，各种液体的饱和汽压亦一定。例如，乙醚在20℃时饱和气压为5865.2帕（44 实验五 金属相图 1. 摘要 最早研究Pb-Sn 熔点与组成关系是在19世纪20年代，在这类体系中所发现的 最低共熔组成被误认为是PbSn 3的化合物。直至在Gibbs 推导出相律（1973~1976年间），继1886年Lechatelier Heney L 发现能够正确测量高温的铂-铂铑热电偶以后，奠定了热分析方法的基础。现在，一般采用自动平衡记录仪或者电位差计测量温差电势，通过测定不同金属组成的合金熔融液的步冷曲线（简单热分析方法）绘制简单低共熔体系相图。相律： 关键词：低共熔点 三相线 相区 固熔体 2． 仪器与试剂 暗丝管加热电炉 1只 调压变压器 1只 硬质玻璃样品管 6只 镍铬-镍硅热电偶（铠装） 2支 单笔自动平衡记录仪（或UJ-25型电位差计） 1台 冰水浴 铅（C.P ） 锡（C.P ） 铋（C.P ） （1）配制钝铅、纯锡以及含锡分别为20%、40%、61.9%、80%的样品管（各 管总量100克） （2 3．预习提问 （1）什么叫步冷曲线，纯物和混合物的步冷曲线有何不同？ （2）测定步冷曲线时应自何时开始记录数据或走纸为适宜？如何防止发生过冷现象？如有过冷发生，则相应相变点温度如何推求？ （3）如何由步冷曲线绘制相图？出现固熔体的步冷曲线有何特征？ （4）试述热电偶温度计的简单工作原理。如何进行校正？ （5）试述自动平衡记录仪的简单原理、使用及接线？ 4．操作 5．数据和图象 （1）文献数据 最低共熔点：组成：61.9% 温度：456.9K（据H.穆拉契编著,原重工业部专家工作室译《有色冶金手册》P111） 要求：所测最低共熔温度在455~459K，低共熔组成在61~63% （2）步冷曲线与金属相图 （3）表格 实验二熔点得测定及温度计校正 一．实验目得: 1.了解熔点测定得原理及意义; 2.掌握熔点测定得基本操作方法; 二．实验重点与难点: 1．熔点测定得意义; 2．熔点测定得操作方法； 实验类型:基础性实验学时:4学时 三．实验装置与药品: 主要实验仪器:熔点管；表面皿;玻璃棒;长4０cm得玻管; Thieｌe管(又称b形管）;酒精灯;温度计;液体石蜡； 主要化学试剂:苯甲酸（熔点mp1２2、40Ｃ）；未知样品(或者尿素):水杨酸(mp１５90Ｃ) 或乙酰苯胺(mｐ114、30C） 四．实验装置图： 五．实验原理： 1、熔点熔点就是固体有机化合物固液两态在大气压力下达成平衡得温度,纯净得固体有机化合物一般都有固定得熔点，固液两态之间得变化就是非常敏锐得,自初熔至全熔(称为熔程)温度不超过0、5-１℃。物质受热后,从开始熔化到全部熔完得温度差称作熔点距(或熔程)，纯化合物得熔点距△≤0、５～1℃,据此，可根据熔点测定初步鉴定化合物或判断其纯度。 加热纯有机化合物,当温度接近其熔点范围时,升温速度随时间变化约为恒定值，此时用加热时间对温度作图(如图1)。 图1 相随时间与温度得变化图２物质蒸气压随温度变化曲线 化合物温度不到熔点时以固相存在,加热使温度上升,达到熔点.开始有少量液体出现,而后固液相平衡．继续加热,温度不再变化,此时加热所提供得热量使固相不断转变为液相,两相间仍为平衡，最后得固体熔化后，继续加热则温度线性上升。因此在接近熔点时，加热速度一定要慢,每分钟温度升高不能超过2℃,只有这样,才能使整个熔化过程尽可能接近于两相平衡条件，测得得 熔点也越精确。 当含杂质时(假定两者不形成固溶体),根据拉乌耳定律可知,在一定得压力与温度条件下,在溶剂中增加溶质,导致溶剂蒸气分压降低(图２中M′L′),固液两相交点Ｍ′即代表含有杂质化合物达到熔点时得固液相平衡共存点,TＭ′为含杂质时得熔点，显然，此时得熔点较纯粹者低。 2、混合熔点 在鉴定某未知物时,如测得其熔点与某已知物得熔点相同或相近时，不能认为它们为同一物质。还需把它们混合,测该混合物得熔点，若熔点仍不变，才能认为它们为同一物质。若混合物熔点降低,熔程增大,则说明它们属于不同得物质。故此种混合熔点试验,就是检验两种熔点相同或相近得有机物就是否为同一物质得最简便方法。多数有机物得熔点都在4０0℃以下,较易测定。但也有一些有机物在其熔化以前就发生分解,只能测得分解点。 六．实验內容及步骤： 1、安装测定装置与取样：【参阅教材P42图２、４】 (1)、熔点测定装置包括温度计、毛细管、Thiele管。 (2)、将毛细管一端在酒精灯上转动加热，烧融封闭。取干燥、研细得待测物样品放在表面皿上, 将毛细管开口一端插入样品中,即有少量样品挤入熔点管中。然后取一支长玻璃管，垂直于桌面上,由玻璃管上口将毛细管开口向上放入玻璃管中,使其自由落下，将管中样品敦实。重复操作使所装样品约有２-３mm高时为止。 (3)、向Thiｅlｅ管中加入液体石蜡(作为加热介质)直到支管之上。在温度计上附着一支装好样 品得毛细管,毛细管中样品与温度计水银球处于同一水平。将温度计带毛细管放入Thiｅlｅ管中,使温度计水银球位置在Ｔｈｉｅle管中部。 将少许样品放于干净表面皿上,用玻璃棒将其研细并集成一堆。把毛细管开口一端垂直插人堆集得样品中，使一些样品进入管内,然后,把该毛细管垂宜桌面轻轻上下振动，使样品进人管底,再用力在桌面上下振动，尽量使样品装得紧密。或将装有样品,管口向上得毛细管,放入长约５0一60cm垂直桌面得玻璃管中,管下可垫一表面皿，使之从高处落于表面皿上,如此反复几次后,可把样品装实,样品高度2—３mm。熔点管外得样品粉末要擦干净以免污染热浴液体。装入得样品一定要研细、夯实。否则影响测定结果。 2、熔点得测定: (1)、在Thiｅｌｅ管弯曲部位加热。接近熔点（距熔点十几度)时，减慢加热速度,每分钟升1o C 左右，接近熔点温度时,每分钟约0、2o C观察、记录晶体中形成第一滴液体时得温度（初熔温度开始塌陷并有液相产生)与晶体完全变成澄清液体时得温度(终熔温度)。 (2)、熔点测定应有至少两次平行测定得数据,每一次都必须用新得毛细管另装样品测定，而且必 须等待液体石蜡冷却到低于此样品熔点2０-30o C时，才能进行下一次测定。 (3)、对于未知样品,可用较快得加热速度粗测一次,在很短得时间里测出大概得熔点。实际测定 时，加热到这个熔点以下１0-1５o C,必须缓慢加热,使温度慢慢上升，这样才可测得准确熔点。按图搭好装置,放入加热液(浓硫酸或者液体石蜡),用温度计水银球蘸取少量加热液,小心地将熔点管粘附于水银球壁上,或剪取一小段橡皮圈套在温度计与熔点管得上部（如下图）。将粘附有熔点管得温度计小心地插入加热浴中,以小火在图示部位加热。开始时升温速度可以快些,当传热液温度距离该化合物熔点约10一１5℃时，调整火焰使每分钟上升约1—２℃,愈接近熔点，升温速度应愈缓慢,每分钟约0、2一０、3℃。为了保证有充分时间让热量由管外传至毛细管内使固体熔化，升温速度就是准确测定熔点得关键;另一方面,观察者不可能同时观察温度计所示读数与试祥得变化情况,只有缓慢加热才可使此项误差减小。记下试样开始塌落并有液相产生时(初熔)与固体完全消失时(全熔)得温度读数,即为该化合物得熔距。要注意在加热过程中试祥就是否有萎缩、变色、发泡、升华、碳化等现象,均应如实记录。 3、温度计校正 二组分金属相图的绘制 一．实验目的 1．用热分析法(冷却曲线法)测绘Bi —Sn 二组分金属相图。 2．了解固液相图的特点，进一步学习和巩固相律等有关知识。 二．实验原理 表示多相平衡体系组成、温度、压力等变量之间关系的图形称为相图。 较为简单的二组分金属相图主要有三种：一种是液相完全互溶，凝固后，固相也能完全互溶成固熔体的系统，最典型的为Cu —Ni 系统；另一种是液相完全互溶而固相完全不互溶的系统，最典型的是Bi —Cd 系统；还有一种是液相完全互溶，而固相是部分互溶的系统，如本实验研究的Bi —Sn 系统。在低共熔温度下，Bi 在固相Sn 中最大溶解度为21％(质量百分数)。 图1冷却曲线 图2由冷却曲线绘制相图 热分析法(冷却曲线法)是绘制相图的基本方法之一。它是利用金属及合金在加热和冷却过程中发生相变时，潜热的释出或吸收及热容的突变，来得到金属或合金中相转变温度的方法。通常的做法是先将一定已知组成的金属或合金全部熔化，然后让其在一定的环境中自行冷却，画出冷却温度随时间变化的冷却曲线(见图 1)。当金属混合物加热熔化后再冷却时，开始阶段由于无相变发生，体系的温度随时间变化较大，冷却较快（ab 段）。若冷却过程中发生放热凝固，产生固相，将减小温度随时间的变化，使体系的冷却速度减慢（bc 段）。当融熔液继续冷却到某一点时，如c 点，由于此时液相的组成为低共熔物的组成。在最低共熔混 合物完全凝固以前体系温度保持不变，冷却曲线出现平台，（如图cd 段）。当融熔液完全凝固形成两种固态金属后，体系温度又继续下降（de 段）。 由此可知，对组成一定的二组分低共熔混合物系统，可以根据它的冷却曲线得出有固体析出的温度和低共熔点温度。根据一系列组成不同系统的冷却曲线的各转折点，即可画出二组分系统的相图(T - x 或T - w B 图)。不同组成熔液的冷却曲线对应的相图如图2所示。 图3可控升降温电炉前面板 1.电源开关 2.加热量调节旋钮 3、4.电压表 5.实验坩埚摆放区 6.控温传感器插孔 7.控温区电炉8.测试区电炉 9.冷风量调节 第五节聚合物的结晶热力学 一、结晶聚合物的熔融特点 结晶聚合物的熔融过程与小分子晶体的异同： 相同点：都是一个相转变的过程。 不同点：小分子晶体在熔融过程，体系的热力学函数随温度的变化范围很窄，一般只有℃左右，可名符其实地称之为熔点。结晶聚合物的熔融过程，呈现一个较宽的熔融温度范围，即存在一个“熔限”。一般将其最后完全熔融时的温度称为熔点。 二、分子结构对熔点的影响 聚合物的熔融过程，从热力学上来说，它是一个平衡过程，因而可用以下的热力学函数关系来描述： 在平衡时，，则有 凡是分子结构有利于增加分子间或链段间的相互作用力的，则在熔融过程中增加，而使熔点升高。增加高分子链内旋转的阻力，使高分子链比较僵硬，则在熔融过程中构象变化较小，即较小，也使熔点升高。 (一)分子间作用力 通过在主链或在侧链上引入极性基团或形成氢键，则可使增大，熔点提高。 例如，主链基团可以是酰胺。酰亚胺。氨基甲酸酯。脲，这些基团都易在分子间形成氢键，从而使分子间的作用力大幅度增加，熔点明显提高。 分子链取代基的极性也对分子间的作用力有显著影响。 例如，在聚乙烯(℃)分子链上取代了(等规聚丙烯，℃)、(聚氯乙烯，＝℃)和(聚丙烯晴，℃)，随取代基的极性增加，熔点呈递升的趋势。 (二)分子链的刚性 增加分子链的刚性，可以使分子链的构象在熔融前后变化较小，即变化较小，故使熔点提高。 一般在主链上引入环状结构，共轭双键或在侧链上引入庞大的刚性取代基均能达到提高熔点的追求。 (三)分子链的对称性和规整性 具有分子链对称性和规整性的聚合物，在熔融过程所发生的变化相对地较小，故具有较高的熔点。 例如，聚对苯二甲酸乙二酯的为℃，而聚间苯二甲酸乙二酯的仅为℃。聚对苯二甲酰对苯二胺()的为℃，而聚间苯二甲酰间苯二胺的仅为℃。 通常反式聚合物比相应的顺式聚合物的熔点高一些，如反式聚异戊二烯(杜仲胶)为℃，而顺式聚异戊二烯的为℃。 等规聚丙烯的分子链在晶格中呈螺旋状构象，在熔融状态时仍能保持这种构象，因而熔融熵较小，故熔点较高。 三、结晶条件对熔点的影响 (一)晶片厚度与熔点的关系 晶片厚度对熔点的这种影响，与结晶的表面能有关。高分子晶体表面普遍存在堆砌较不规整的区域，因而在结晶表面上的链将不对熔融热作完全的贡献。 实验六二组分金属相图的绘制 【实验目的】 1. 学会用热分析法测绘Sn—Bi二组分金属相图。 2. 了解纯物质的步冷曲线和混合物的步冷曲线的形状有何不同，其相变点的温度应如何确定。 3. 了解热电偶测量温度和进行热电偶校正的方法。 【基本要求】 （1）学会用热分析法测绘Sn-Bi二组分金属相图。 （2）掌握步冷曲线的绘制和利用。 【实验原理】 测绘金属相图常用的实验方法是热分析法，其原理是将一种金属或两种金属混合物熔融后，使之均匀冷却，每隔一定时间记录一次温度，表示温度与时间关系的曲线称为步冷曲线。当熔融体系在均匀冷却过程中无相变化时，其温度将连续均匀下降得到一平滑的步冷曲线；当体系内发生相变时，则因体系产生的相变热与自然冷却时体系放出的热量相抵消，步冷曲线就会出现转折或水平线段，转折点所对应的温度，即为该组成体系的相变温度。利用步冷曲线所得到的一系列组成和所对应的相变温度数据，以横轴表示混合物的组成，纵轴上标出开始出现相变的温度，把这些点连接起来，就可绘出相图。二元简单低共熔体系的冷却曲线具有图2-5-1所示的形状。 用热分析法测绘相图时，被测体系必须时时处于或接近相平衡状态，因此必须保证冷却速度足够慢才能得到较好的效果。此外，在冷却过程中，一个新的固相出现以前，常常发生过冷现象，轻微过冷则有利于测量相变温度；但严重过冷现象，却会使折点发生起伏，使相变温度的确定产生困难。见图2-5-2。遇此情况，可延长dc线与ab线相交，交点e即为转折点。 图6-1 根据步冷曲线绘制相图 图6-2 有过冷现象时的步冷曲线 【仪器试剂】 立式加热炉1台；保温炉1台；镍铬-镍硅热电偶1副；不锈钢样品管4个；250mL烧杯1个。 Sn(化学纯)；Bi(化学纯)；石腊油；石墨粉。 【实验步骤】 1. 样品配制 用感量0.1g的台称分别称取纯Sn、纯Bi各50g，另配制含锡20%、40%、60%、80%的铋锡混合物各50g，分别置于坩埚中，在样品上方各覆盖一层石墨粉。 2. 绘制步冷曲线 (1) 将热电偶及测量仪器如图2-5-3连接好。 (2) 将盛放样品的坩埚放入加热炉内加热(控制炉温不超过400℃)。待样品熔化后停止加热，用玻璃棒将样品搅拌均匀，并在样品表面撒一层石墨粉，以防止样品氧化。 图6-3 步冷曲线测量装置 1.加热炉； 2.不锈钢管； 3.套管； 4.热电偶 (3) 将坩埚移至保温炉中冷却，此时热电偶的尖端应置于样品中央，以便反映 第 31 讲5.5.3 影响晶态聚合物熔点的因素 熔点是结晶聚合物使用的上限温度，是晶态聚合物材料最重要的耐热性指标。 1）大分子链的化学结构 是决定晶态聚合物熔点高低的最重要因素。 而结晶条件和材料的加工过程也对熔点产生一定影响。 晶态聚合物转变为液态（粘流态）的过程属于热力学相变过程，达到平衡时体系的自由能增量应为： △G ＝ △H m – T m0 △S m ＝ 0 式中：△H m 和△S 分别是晶态聚合物的熔融热和熔融熵； 设聚合物的熔融热和熔融熵分别由不与相对分子质量相关的“基础值”H 0和S 0和大分子链每一个结构单元在晶体熔化前后的增量(△H m) u 和(△S m) u 组成，则： 由此可见，大分子链中结构单元的熔融热增量(△H m) u 愈大，或熔融熵增量(△S m) u 愈小，则晶态聚合物的熔化热也就愈高。 聚合物结构单元的熔融热增量与分子间的作用力强弱有关，而结构单元的熔融熵增量则与晶体熔化以后分子的混乱程度有关。 表5-15 一些结晶聚合物的相关热力学数据 归纳影响晶态聚合物熔点的一般规律： ①刚性分子链的晶态聚合物的熔点高于柔性链聚合物的熔点，如聚苯撑的熔点高达530℃； ②极性分子链的晶态聚合物的熔点高于非极性链聚合物的熔点，如聚丙烯腈熔点高达317℃； ③分子主链含可生成氢键的 O 、N 原子的晶态聚合物的熔点很高，如尼龙的熔点都在260℃以上； ④分子主链上的亚甲基（CH2）数目愈多则大分子的柔顺性愈高，聚合物晶体的熔点愈低，如聚己二 酸己二酯的熔点只有65℃； ⑤凡是能够增加分子链柔顺性的因素都使熔点降低，如天然橡胶和聚氧化乙烯的熔点都很低。 不过需要注意的是：必须综合考虑影响晶态聚合物熔点的各种因素，才能对晶态聚合物的熔点作出正确的判断，有时单从大分子链的结构很难准确判断聚合物的熔点高低。 2)影响熔点的其他因素 ①片晶厚度和结晶缺陷 对所有种类聚合物晶体熔点都有影响。片晶厚度越薄，结晶缺陷越多，熔点越低，如图5-24聚三氟氯乙烯片晶厚度与熔点的关系曲线 所示。 ②结晶温度的影响 由片晶理论厚度与温度的关系公式： 第二：结晶温度越低，则晶体熔化的温度范围即熔限也越宽。右图5-25为天然橡胶的熔化温度与结晶温度的关系。 原因：熔点和熔限对结晶温度的依赖性完全产生于大分子的长链结构。 较低结晶温度下，体系粘度较高，分子链的活动能力较低生成片晶的厚度较小，且晶体内部的缺陷也较多，所以熔点较低，熔限较宽。 反之，在较高的结晶温度下，熔点较高熔限较窄。 在熔点附近温度经长时间的缓慢结晶 ，所得结晶的熔限范围将很小，甚至完全消失。 ③ 添加剂的影响 稀释剂→增塑剂、稳定剂→可溶性物质（助剂） 填充剂→无机颜料、填料→不溶性物质（助剂） 增塑剂的加入可以明显改善聚合物制品的脆性并提高其韧性，但是却使熔点降低。当稀释剂的用量足够低时，可以用下式计算其对熔点降低的程度： 式中T m 0和T m 分别是纯聚合物和加入稀释剂以后的熔点（K ）；x b 是稀释剂的摩尔分率，R 是摩尔气体常数。（上） 图5-26 两种共聚物的熔点与共聚物组成的关系 图5-27增塑和共聚对熔点和玻璃化温度的影响 ()u m b m m H Rx T T ?=-01 1 实验八金属相图 一、实验目的 1、学会用热分析法测绘铅－锡二组分金属相图; 2、掌握热分析法的测量技术； 3、熟悉ZR-HX金属相图控温仪、ZR-08金属相图升温电炉等仪器。 二、基本原理 相图是用以研究体系的状态随浓度、温度、压力等变量的改变而发生变化的图形，它可以表示在指定条件下存在的相数和各相的组成，对蒸汽压较小的二组分凝聚体系，常以温度-组成图来描述。 热分析法是绘制相图常用的基本方法之一。这种方法是通过观察体系在冷却时温度随时间的变化关系，来判断有无相变的发生。通常的做法是先将体系全部融化，然后让其在一定环境中自行冷却，并每隔一定时间记录一次温度，以温度（T）为纵坐标，时间（t）为横坐标，画出步冷曲线。当体系均匀冷却时，如果体系不发生相变，则体系的温度随时间的变化将是均匀的，冷却也较快（如图8-1中ab线段）。若在冷却过程中发生了相变，由于在相变过程中伴随着热效应，所以体系温度的降温速度随时间的变化将发生改变，体系的冷却速度减慢，步冷曲线就出现转折（如图8-1中bc 线段）。当熔液继续冷却到某一点时，由于此时熔液的组成已达到最低共熔混合物的组成，故有最低共熔混合物析出，在最低共熔混合物完全凝固以前，体系温度保持不变，因此步冷曲线出现平台（如图中cd线段）。当熔液完全凝固后，温度才迅速下降（见图中de线段）。 由此可知，对组成一定的二组分低共熔混合物体系来说，可以根据它的步冷曲线，判断有固体析出时的温度和最低共熔点的温度。如果作出一系列组成不同的体系的步冷曲线，从中找出各转折点，即能画出二组分体系最简单的相图（温度-组成图）。不同组成熔液的步冷曲线与对应相图的关系可以从8-2中看出。 图8-2 图8-1 用热分析法测绘相图时，被测体系必须时时处于或接近相平衡状态。因此，体系的冷却速度必须足够慢，才能得到较好的结果。 实验三熔点的测定 一、实验目的： 1、了解熔点测定的意义，掌握测定熔点的操作。 2、了解温度计较正的意义，学习温度计较正的方法。 二、实验原理 熔点：通常晶体物质加热到一定温度时，即可从固态变为液态，此时的温度就是该化合物的熔点。 纯化合物从开始熔化（始熔）至完全熔化（全熔）的温度范围叫做熔点距（熔程），也叫熔点范围。每种纯有机化合物都有自己独特的晶形结构和分子间的力，要熔化它，是需要一定热能的，所以，每种晶体物质都有自己的熔点。同时，当达溶点时，纯化合物晶体几乎同时崩溃，因此熔点距很小，一般为~1℃，但是，不纯品即当有少量杂质存在时，其熔点一般会下降，熔点距增大。因此，从测定固体物质的熔点便可鉴定其纯度。 如测定熔点的样品为两种不同的有机物的混合物，例如，肉桂酸及尿素，尽管它们各自的熔点均为133℃，但把它们等量混合，再测其熔点时，则比133℃低得很多，而且熔点距大。这种现象叫做混合熔点下降，这种试验叫做混合熔点试验，是用来检验两种熔点相同或相近的有机物是否为同一种物质的最简便的物理方法。 三、实验仪器和药品 请学生自已整理罗列 四、实验装置图 五、实验步骤 1、准备熔点管 通常是用直径1~毫米，长约60~70毫米一端封闭的毛细管作为熔点管 2、样品的填装 取 ~ 克样品，研成粉未，聚成小堆。将毛细管开口一端倒插入粉末堆中，样品便被挤入管中，再把开口一端向上，轻轻在桌面上敲击，使粉未落入管底。也可将装有样品的毛细管，反复通过一根长约40厘米直立于玻板上的玻璃管，均匀地落下，重复操作，以免样品受潮。样品中如有空隙，不易传热。 样品：萘，苯甲酸，萘和苯甲酸的混合物 样品一定要研得很细，装样要结实。（每种样品装2根毛细管） 3、仪器的安装 将熔点测定管夹在铁座架上，装入液体石蜡于熔点测定管中至高出上侧管约1厘米为度，熔点测定管中配一缺口单孔软木塞，温度计插入孔中，刻度应向软木塞缺口。毛细管附着在温度计旁，样品正好位于水银球的中间部分。温度计插入熔点测定管中的深度以水银球恰在熔点测定管的中部为准。加热时，火焰须与熔点管的倾斜部分接触。这种装置测定熔点的好处是管内液体因温度差而发生对流作用，省去人工搅拌的麻烦。但常因温度计的位置和加热部位的变化而影响测定的准确度。 影响黏度的因素：1 温度一般来说,温度升高粘度下降 2 时间在玻璃转变区域内,形成的玻璃液体的黏度与时间有关 3 组成硅酸盐材料的黏度总是随着不同改性阳离子的加入而变化粘弹性:在一些特定的情况下,一些非晶体和多晶体在受到比较小的应力作用时可以同时表现出弹性和粘性. 滞弹性:无机固体和金属表现出的这种与时间有关的弹性 影响蠕变的因素:1 温度温度升高,稳态蠕变速率增大2应力稳态蠕变速率随应力增加而增大3显微结构随着气孔率增加,稳态蠕变速率也增大; 晶粒愈小,稳态蠕变速率愈大; 当温度升高时，玻璃相的黏度下降，因而变形速率增大，蠕变速率增大4组成组成不同的材料其蠕变行为不同 5 晶体结构随着共价键结构程度增加，扩散及位错运动降低，蠕变就小材料的理论断裂强度与弹性模量，表面能和晶格常数的有关 影响材料断裂强度的因素：1内在因素材料的物理性能，如弹性模量，热膨胀系，导热性，断裂能等 2 显微结构有相组成，气孔，晶界和微裂纹 3 外界因素温度，应力，气氛及试样的形状大小和表面能 4 工艺原料的纯度粒度形状成型方法等 材料的断裂强度不是取决于裂纹的数量，而是取决于裂纹的大小 防止裂纹扩展的措施：·1 应使作用应力不超过临界应力 2 在材料中设置吸收能量的机构3 人为地在材料中造成大量极微细的裂纹也能吸收能量，阻止裂纹扩展 陶瓷材料显微结构的两个参数是晶粒尺寸和气孔率 提高无机材料强度改进韧性的途径：1 微晶高纯度和高密度（消除缺陷）2提高抗裂能力和预加应力（热韧化技术）3化学强度改变化学组成（大离子换小离子）4相变增韧5弥散增韧6复合材料 影响热容的因素：1温度对热容的影响高于德拜温度时，热容趋于常数；低于时，与(T/θ)3成正比2 化学键弹性模量熔点的影响原子越轻，原子间的作用力越大3无机材料的热容对材料的结构不敏感4相变由于热量不连续变化，热容出现突变 热膨胀系数：物体的体积或长度随温度的升高而增大的现象 影响热导率的因素：1温度的影响声子的自由程随温度升高而降低2显微结构的影响 差热分析法测定Pb-Sn的金属相图 一、实验目的和要求 1.用热分析法测绘Pb-Sn二元金属相图，并掌握应用步冷曲线数据绘制二元体系相图的基本方法； 2.了解步冷曲线及相图中各曲线所代表的物理意义； 二、实验原理 相是指体系内部物理性质和化学性质完全均匀的一部分。相平衡是指多相体系中组分在各相中的量不随时间而改变。研究多相体系的状态如何随组成、温度、压力等变量的改变而发生变化，并用图形来表示体系状态的变化，这种图就叫相图。 将某一物质进行加热或冷却，在这样的过程中，若有物相变化发生，如发生熔化、凝固、晶型转变、分解、脱水等相变时，总伴随着有吸热或放热的现象。两种混合物若发生固相反应，也有热效应产生。因此，在体系的温度——时间曲线上就会发生顿、折，但在许多情况下（例如在试样的来源有限，量很少），体系中发生的热效应相当小，不足以引起体系温度有明显的突变，从而温度——时间曲线的顿、折并不显著，甚至根本显不出来。在这种情况下，常将有物相变化的物质和一个基准物质（或参比物，即在实验温度变化的整个过程中不发生相变、没有任何热效应产生，如Al2O3、MgO等）在相同的条件下进行加热或冷却时，一旦样品发生相变，则在样品和基准物之间产生温度差。测定这种温度差，用于分析物质变化的规律，称为差热分析。。 本实验采用热分析法绘制相图，其基本原理：先将体系加热至熔融成一均匀液相，然后让体系缓慢冷却，①体系内不发生相变，则温度--时间曲线均匀改变； ②体系内发生相变，则温度--时间曲线上会出现转折点或水平段。根据各样品的温度--时间曲线上的转折点或水平段，就可绘制相图。 纯物质的步冷曲线如①、⑤所示，如①从高温冷却，开始降温很快，ab线的斜率决定于体系的散热程度，冷到Ａ的熔点时，固体Ａ开始析出，体系出现两相平衡（液相和固相Ａ），此时温度维持不变，步冷曲线出现水平段，直到其中液相全部消失，温度才下降。 相图由一个单相区和三个两相区组成：即①溶液相区； ②纯A(s)和溶液共存的两相区； ③纯B(s)和溶液共存的两相区； ④纯A(s)和纯B(s)共存的两相区； 水平线段表示：A(s)、B(s)和溶液共存的三相线；水平线段以下表示纯A(s)和纯B(s)共存的两相区；o为低共熔点。 影响差热分析结果的因素很多，主要有： （1）升温速率的选择：升温速率对测定结果影响极大。一般说来速率低时，基线漂移小，可以分辨靠的近的差热峰，因而分辨力高，但测定时间长。速率高时，基线漂移较显著，分辨力下降，测定时间较省，一般选择每分钟2~200C （2）气氛及压力的选择：许多测定受炉中气氛及压力的影响很大。例如NH4ClO4在N2气氛及真空时测得的差热曲线差别很大，而氮气压力不同也有影响。有些物质在空气中易被氧化，所以选择适当的气氛及压力也实验一(二)熔点的测定
二组分简单共熔体系相图的绘制
熔点测定的基本方法及注意事项
金属相图
实验二 熔点测定
实验六 二组分金属相图的绘制
熔点 沸点 凝固点与压强的关系原因分析
金属相图
有机化学实验二熔点的测定
二组分金属相图的绘制
影响熔点的因素(建文)
二组分金属相图的绘制.
第 31 讲5.5.3 影响晶态聚合物熔点的因素
金属相图实验步骤(学生)
实验三熔点的测定
影响黏度的因素
3.差热分析法测定Pb-Sn的金属相图