Adsorption of Pb(II) ions from aqueous solution by native and activated bentonite Kinetic, equilibri
Journal of Hazardous Materials 179 (2010) 332–339
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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
Adsorption of Pb(II)ions from aqueous solution by native and activated bentonite:Kinetic,equilibrium and thermodynamic study
Ali R?za Kul a ,Hülya Koyuncu b ,?
a Yuzuncu Yil University,Faculty of Art and Science,Department of Chemistry,65080Van,Turkey b
Forensic Medicine Foundation,Felek Street No.45,06300Kecioren,Ankara,Turkey
a r t i c l e i n f o Article history:
Received 6November 2009
Received in revised form 27January 2010Accepted 3March 2010
Available online 9 March 2010Keywords:Pb(II)
Adsorption Kinetics Equilibrium
Thermodynamic
a b s t r a c t
In this study,the adsorption kinetics,equilibrium and thermodynamics of Pb(II)ions on native (NB)and acid activated (AAB)bentonites were examined.The speci?c surface areas,pore size and pore-size distri-butions of the samples were fully characterized.The adsorption ef?ciency of Pb(II)onto the NB and AAB was increased with increasing temperature.The kinetics of adsorption of Pb(II)ions was discussed using three kinetic models,the pseudo-?rst-order,the pseudo-second-order and the intra-particle diffusion model.The experimental data ?tted very well the pseudo-second-order kinetic model.The initial sorption rate and the activation energy were also calculated.The activation energy of the sorption was calculated as 16.51and 13.66kJ mol ?1for NB and AAB,respectively.Experimental results were also analysed by the Langmuir,Freundlich and Dubinin–Redushkevich (D–R)isotherm equations at different temperatures.R L separation factor for Langmuir and the n value for Freundlich isotherm show that Pb(II)ions are favorably adsorbed by NB and AAB.Thermodynamic quantities such as Gibbs free energy ( G ),the enthalpy ( H )and the entropy change of sorption ( S )were determined as about ?5.06,10.29and 0.017kJ mol ?1K ?1,respectively for AAB.It was shown that the sorption processes were an endothermic reactions,controlled by physical mechanisms and spontaneously.
? 2010 Elsevier B.V. All rights reserved.
1.Introduction
Among the different heavy metals,lead is one of the common and toxic pollutants released into the natural waters from various industrial activities such as metal plating,oil re?ning,paint and pigment producing and battery manufacturing [1].Lead can enter the human body through inhalation,ingestion or skin contact.As a result when the body is exposed to lead,it can act as a cumula-tive poison.Lead accumulates mainly in bones,brain,kidney and muscles and may cause many serious disorders like anemia,kidney diseases,nervous disorder and sickness even death [2–4].Lead can replace calcium,which is an essential mineral for strong bones and teeth,while play important role in sympathetic actions of nerve and blood vessel for normal functioning of nervous system.It also acts as an enzyme inhibitor in body,e.g.,replaces essential element zinc from heme enzymes.The high level of lead damages cognitive development especially in children [5].Due to toxic effects of lead ions,the removal of them from waters and wastewaters is impor-tant in terms of protection of public health and environment [6].
?Corresponding author at:Forensic Medicine Foundation,Felek street No:45,06300Kecioren,Ankara,Turkey.Tel.:+903123407324;fax:+903123406629.
E-mail address:hkoyuncu@https://www.wendangku.net/doc/ba6933573.html,.tr (H.Koyuncu).The conventional methods for heavy metal removal from water and wastewater include oxidation,reduction,precipitation,reverse osmosis,ion exchange,electrolysis and adsorption.Among all the methods adsorption is highly effective and economical [7].How-ever,the main disadvantage of adsorption treatment is the high price of the adsorbents,which increases the price of wastewater treatment.Thus,adsorbents with low cost and high ef?ciency for Pb(II)adsorption should be developed.Clay minerals have great potential as inexpensive and ef?cient adsorbents due to their large quantities,chemical and mechanical stability,high speci?c surface area,and structural properties.Bentonite is mainly composed of montmorillonite,which is a 2:1-type aluminosilicate.The inner layer is composed of an octahedral sheet situated between two SiO 4tetrahedral sheets.Substitutions within the lattice structure of trivalent aluminium for quadrivalent silicon in the tetrahedral sheet and of ions of lower valence,particularly magnesium,for trivalent aluminium in the octahedral sheet result in a net neg-ative charge on the clay surfaces.The charge imbalance is offset by exchangeable cations such as H +,Na +or Ca 2+on the layer surfaces [8–10].In aqueous solutions,water molecules are inter-calated into the interlamellar space of bentonite,leading to an expansion of the minerals [11].The chemical nature and pore structure of bentonites generally determine their adsorption abil-ity [12,13].Treatment of clay minerals with concentrated inorganic acids usually at high temperature is known as acid activation.
0304-3894/$–see front matter ? 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.jhazmat.2010.03.009
A.R.Kul,H.Koyuncu/Journal of Hazardous Materials179 (2010) 332–339333
Nomenclature
A Frequency factor
c A constant for intra-particle diffusion(mg g?1)
C0Initial concentration of the adsorbate in the solution (mg L?1)
C e Equilibrium concentration of the adsorbate in the
solution(mg L?1)
E Mean adsorption energy(kJ mol?1)
E a Activation energy of sorption(kJ mol?1)
k0Initial sorption rate(mg g?1min?1)
k1Rate constant for pseudo-?rst-order reaction (min?1)
k2Rate constant for pseudo-second-order reaction
(g mg?1min?1)
k i Intra-particle diffusion rate constant (mg g?1min?1/2)
k f Freundlich isotherm constant
K Langmuir isotherm constant(L mg?1)
K Adsorption energy constant(mol2kJ?2)
m Amount of bentonite(g)
n Freundlich isotherm constant
q0Maximum concentration retained by the adsorbent (mg g?1)
q e Amount solute sorbed at equilibrium(mg g?1)
q m Theoretical monolayer saturation capacity (mol g?1)
q t Amount solute sorbed at any time(mg g?1)
R Universal gas constant(J mol?1K?1)
t Time(min)
T Absolute temperature(K)
Acid treatments of clay minerals are an important control over mineral weathering and genesis[14].Such treatments can often replace exchangeable cations with H+ions and release Al and other cations out of both tetrahedral and octahedral sites,but leaving the SiO4groups largely intact.The ion exchange capacity of clay minerals is attributed to structural defects,broken bonds and struc-tural hydroxyl transfers[15].Also,acid treatment of bentonite has been shown to create enhanced mesoporosity with impor-tant textural and structural changes[16,17].The objective of this study is to investigate comparative adsorption characteristics for removal of Pb(II)from aqueous solution by the use of native ben-tonite(NB)and acid activated bentonite(AAB).The effect of several parameters such as contact time,Pb(II)concentration and tem-perature were studied.The adsorption mechanism of Pb(II)ions onto NB and AAB were evaluated in terms of kinetics,equilibrium and thermodynamics.The data obtained from the batch sorption experiments were?tted to pseudo-?rst-order,pseudo-second-order and intra-particle diffusion models.The Langmuir,Freundlich and Dubinin–Radushkevich(D–R)isotherm models were used to describe equilibrium data.
2.Materials and methods
2.1.Materials
The bentonite sample used in this study was obtained from Kütahya region in Turkey.The chemical constituent of the bentonite was analysed by XRF and given in Table1.A stock solution of Pb(II) was prepared by dissolving required amount of Pb(NO3)2(Merck) in double distilled water at room temperature.Other agents used, such as HCl and silver acetate were all of analytical grade.2.1.1.Preparation and characterization of samples
In order to increase the surface area and provide physico-chemical changes in the structure of bentonite,acid activation test was performed.The acid treatment was carried out using a Pyrex glass reactor with re?ux condenser.The reactor was placed onto Chiltern Hotplate Magnetic Stirrer HS31.50g raw bentonite was slowly added to250mL5N HCl solution,stirred and maintained at boiling temperature(approximately378K)during3h.After treat-ment,the reaction products were?ltered and15times washed with distilled water to remove traces of acid.After each washing Cl?ions were detected with silver acetate solution and then the sample was centrifuged with MSE MISTRAL2000at4500rpm for5min.The ?nal sample was centrifuged and kept at333K in an oven(Philip Harris Ltd.)to remove some of the moisture for48h.The sample was milled passing235mesh sieve(61.75?m)to eliminate the for-mation of lumps produced during drying and saved in a desiccator [14–16].Speci?c surface areas(BET)and pore-size distributions of the raw and activated bentonite samples were determined using a Quantachrome NOVA2200series volumetric gas adsorption instru-ment.The determinations were based on measurements of the corresponding nitrogen adsorption isotherms at77K.Before mea-surements,moisture and gases such as nitrogen and oxygen that were adsorbed on the solid surface or held in the open pores were removed under reduced pressure at423K for5h.Cation exchange capacities(CEC)of raw(NB)and activated bentonites(AAB)were determined via methylene blue test(ANSI/ASTM C837-76).
2.2.Methods
Equilibrium and kinetic studies were performed with NB and AAB.Adsorption studies were performed by the batch technique at different temperatures(303K,318K and328K).The batch mode adsorption was selected due to its simplicity and reliability.For that purpose,10mL of Pb(II)solution in the concentration range of5–25mg L?1was transferred into a polyethylene test tube.Then 0.1g of the bentonite sample was added to the solution and the mixture was shaken at300rpm using a thermostatic shaker for each corresponding time intervals.The suspension was centrifuged (Philip Harris Ltd.)at5000rpm for10min.The supernatant was?l-tered and the?ltrate was analysed for Pb level by?ame atomic absorption spectrophotometer(FAAS).The reproducibility during concentration measurements was ensured by repeating the exper-iments two times under identical conditions and calculating the average values.Standard deviations of experiments were found to be within±5.0%.
The adsorption capacity of adsorbent was calculated through the following equation:
q e=(C0
?C e)V
m(1) where q e is the adsorption capacity of Pb(II)on adsorbent(mg g?1), C0is the initial concentration of Pb(II)(mg L?1),C e is the equilibrium Pb(II)concentration in solution(mg L?1),m is the mass of adsorbent used(g)and V is the volume of Pb(II)solution(L).
3.Results and discussion
3.1.Characterization of the samples
Nitrogen adsorption isotherms of NB and AAB samples are shown in Fig.1.The speci?c surface areas of the samples were cal-culated from nitrogen adsorption isotherms by the BET method mainly for comparative purposes.AAB markedly affected N2 adsorption characteristics of the bentonite.However,the general shape of the isotherm stayed at the same,after the activation rela-tively increased the nitrogen uptake as seen in Fig.1.
334
A.R.Kul,H.Koyuncu /Journal of Hazardous Materials 179 (2010) 332–339
Table 1
The chemical composition of Kütahya bentonite.
SiO 2
Al 2O 3Fe 2O 3TiO 2CaO MgO Na 2O K 2O LoI a Others g/100g
71.600
13.150
0.660
0.070
2.230
2.790
0.260
0.360
8.450
0.430
a
Loss of ignition at 1025?C.
The BET surface areas of the samples are also determined.The acid activation causes formation of smaller pores in solid parti-cles resulting higher surface area (109.80m 2/g)relative to than NB (71.95m 2/g).For a textural characterization of any porous solid,the concept of surface area does not give a visual picture of it.Pore size and pore-size distributions are necessary if the material is to be fully characterized.The pore-size distribution in the mesopore region was obtained by applying the method of BJH [18]to the desorption branch of the isotherms of nitrogen at 77K,assuming the pores to be cylindrical in shape.Fig.2compares the change of pore-size distribution for the NB and AAB samples.As seen from the ?gure,the samples have almost mesopores of which diame-ters are between 20and 500?.The NB and AAB
samples exhibited maxima in differential pore volumes at about 39.46and 34.50?in pore diameter respectively.
The cation exchange capacities (CEC)of the NB and AAB were found as 65and 97mequiv./100g,respec-tively.
Fig.1.Adsorption isotherms of nitrogen at 77K of the native and activated bentonite samples.
Fig.2.Pore-size distributions for the native and activated bentonite samples.
3.2.The adsorption ef?ciency
The results showed that 100min was enough to reach the dynamic equilibrium between ?uid phase and solid phase in all studied solution concentration and temperatures.The adsorption ef?ciency of Pb(II)ions was calculated by the difference of initial and ?nal concentration using the equation expressed as follows:
Ads-Eff (%)=
C 0
?C e C 0
×100(2)
The adsorption ef?ciency increases with increasing temperature.
The effect of temperature is fairly common and increasing the tem-perature increase the mobility of the solute.Also,it was explained that the endothermic adsorption enthalpy.Similar results have been reported by [2,17,19].Adsorption ef?ciency for AAB reached at about 78%while it was at about 50.4%for NB at 328K (Fig.3).It was found that the adsorption ef?ciency with the AAB was greater than NB in all studied solution concentration and temperatures.It was
expected,because the acid activation causes formation of smaller pores in solid particles resulting higher surface area relative to NB.Bhattacharyya and Sen Gupta [15]noted that acid activation increased the adsorbent capacity to a good extent.
Fig.3.The adsorption ef?ciency of Pb(II)onto the native (a)and activated bentonites (b)at various temperatures (equilibrium time 100min).
A.R.Kul,H.Koyuncu/Journal of Hazardous Materials179 (2010) 332–339335
Table2
Comparison of the pseudo-?rst-order,pseudo-second-order and intra-particle diffusion models for Pb(II)on the native(NB)and activated(AAB)bentonites(303K and 5mg L?1).
q e,exp(mg g?1)q e,cal(mg g?1)k1(min?1)R2SSE(%)
Pseudo-?rst-order kinetic model
NB0.2010.1190.0550.8980.079 AAB0.3300.2280.0280.9690.104
q e,exp(mg g?1)q e,cal(mg g?1)Deviation(%)k2(g mg?1min?1)k0(g mg?1min?1)R2SSE(%)
Pseudo-second-order kinetic model
NB0.2010.214 6.50.8030.0370.9940.027 AAB0.3300.36911.60.1750.0240.9950.021
q e,exp(mg g?1)q e,cal(mg g?1)k i(mg g?1min?1/2)C(mg g?1)R2SSE(%)
Intra-particle diffusion model
NB0.2010.1920.0170.0560.6720.038 AAB0.3300.2620.0270.0710.9180.026
3.3.Kinetic studies
Kinetic models can be helpful to understand the mechanism of
metal adsorption and evaluate performance of the adsorbents for
metal removal.A number of kinetic models have been developed
to describe the kinetics of heavy metal removal:(a)a pseudo-?rst-
order kinetic model of Lagergren[20,21]based on solid capacity,
(b)a pseudo-second-order kinetic model of Ho[20,22]based on
solid phase sorption,and(c)intra-particle diffusion model of Weber
and Morris[22,23].In this study,batch sorption kinetics of Pb(II)
ions with the bentonites have been studied in terms of pseudo-
?rst-order kinetic,pseudo-second-order kinetic and intra-particle
diffusion models.First,the kinetics of adsorption was analysed by
the pseudo-?rst-order equation given by Lagergren[21]as,
ln(q e?q t)=ln q e?k1t(3)
where q e and q t are the amounts of solute adsorbed(mg g?1)at
equilibrium and at time t(min),respectively,and k1(min?1)is
the rate constant adsorption.Values of k1at303–328K were cal-
culated from the plots of ln(q e?q t)versus t(?gures not shown)
for initial solutions with different concentration of Pb(II).The R2
values obtained were lower than that of the pseudo-second-order
kinetic model and the experimental q e values did not agree with
the calculated values obtained from the linear plots(Table2).This
indicates that the adsorption of Pb(II)NB and AAB does not follow
pseudo-?rst-order kinetics.The similar results were found for the
adsorption of Pb(II)ions on various adsorbents by several authors
[24,25].
Experimental data were also applied to the pseudo-second-
order kinetic model[22]which is given in the following form:
t q t =1
k2q2e
+
t
q e(4)
where k2is the rate constant for pseudo-second-order reaction (g mg?1min?1),q e and q t are the amounts of solute sorbed at equi-librium and any time(mg g?1),respectively.The straight line plots of t/q t versus t are used to obtain the constants for pseudo-second-order reaction.Herein,the initial sorption rate is
k0=k2q2e(5) Fig.4illustrates pseudo-second-order sorption kinetics of adsorp-tion of Pb(II)onto NB and AAB at various temperatures.The values of correlation factor R2,obtained from the plots of pseudo-second-order kinetics given in Fig.4are greater(R2>0.99)than that of the pseudo-?rst-order and intra-particle diffusion models for all studied initial Pb(II)concentration and temperatures(Table2).It also showed a good agreement between the experimental and the calculated q e values(deviations+2.28to+12.40%,Table2).The small deviation might be due to the uncertainty inherent in obtaining the experimental q e values.These results showed that the adsorption of Pb(II)ions onto NB and AAB follows well the pseudo-second-order kinetics.The similar results were reported for the adsorption of Pb(II)on different adsorbents[24,26].The rate constants k2,were found as0.803and0.175g mg?1min?1 for NB and AAB at303K and5mg L?1initial solution concentra-tion(Table2).Kenedy Oubagaranadin
and Murthy[27]reported that the rate of adsorption of Pb(II)on montmorillonite-illite type clay(MIC)followed second order rate mechanism,with decreas-ing rate constant values of0.1097,0.0571and0.0022g mg?1min?1 as the initial Pb(II)concentration was increased in the order of 100,150and200ppm,respectively.Hefne et al.[28]reported that the rate of adsorption of Pb(II)onto natural and treated bentonite followed pseudo-second-order kinetics and rate con-stant value was determined to be0.68g mg?1min?1for natural bentonite.
The metal ions transport from the solution phase to the surface of the clay particles occurs in several steps.The overall adsorption process may be controlled either by one or more steps(e.g.,?lm or external diffusion,pore diffusion,surface diffusion and adsorption on the pore surface)or a combination of more than one step.Besides
Fig.4.Effect of temperature on pseudo-second-order kinetics of Pb(II)onto the native bentonite(a)and activated bentonite(b)(5mg L?1initial solution concen-tration).
336 A.R.Kul,H.Koyuncu/Journal of Hazardous Materials
179 (2010) 332–339
Fig.5.Effect of temperature on intra-particle diffusion kinetics of Pb(II)onto the native bentonite(a)and activated bentonite(b)(5mg L?1initial solution concen-tration).
adsorption at the outer surface of the adsorbent,there is also a possibility of intra-particle diffusion of the metal ion from the bulk of the outer surface into the pores of the adsorbent material,which is usually a slow process.The possibility of intra-particle diffusion studied using the intra-particle diffusion model[2,29,30]:
q t=k i t1/2+c(6) where k i is the intra-particle diffusion rate constant (mg g?1min?1/2)and c is the intercept.In this model,due to the porous nature of adsorbent,pore diffusion is expended to be surface sorption.According to this model,plotting a graphic of q t versus t1/2,if a straight line is obtained passing through the origin,it can be assumed that the mechanism involves the diffusion of the species and the slope of the linear curve is the rate constant of intra-particle transport(k i).In the present study,any plot did not passed through the origin and this deviation from the origin might be due to the difference in the mass transfer rate in the initial and?nal stages of adsorption.The plots present multilinearity,indicating that three steps take place.As can be seen in Fig.5(q t versus t1/2)the?rst,sharper portion may be considered as an external surface adsorption or faster adsorption stage.The second portion describes the gradual adsorption stage, where intra-particle diffusion is rate-controlled.The third portion is attributed to the?nal equilibrium stage,where intra-particle diffusion starts to slow down due to the extremely low adsorbate concentrations in the solution.In the intermediate stage where the adsorption is gradual,the process may be controlled by intra-particle diffusion.The rate of uptake might be limited by the size of the adsorbate molecule,the concentration of the adsorbate and its af?nity to the adsorbent,the diffusion coef?cient of the adsorbate in the bulk phase,the pore-size distribution of the adsorbent,and the degree of mixing[31].The values of R2,obtained from the plots of intra-particle diffusion kinetics are lower than that of the pseudo-second-order model(Table2)but this model indicates that the adsorption of Pb(II)onto the NB and AAB may be followed by an intra-particle diffusion model up to15min.This indicates that although intra-particle diffusion was involved in the adsorption process,it was not the only rate-controlling step.Kenedy Ouba-garanadin and Murthy[27]reported that the adsorption process of Pb(II)on montmorillonite-illite type clay(MIC)was controlled by both intra-particle diffusion and?lm diffusion.
3.4.Validity of kinetic models
The adsorption kinetics of Pb(II)onto NB and AAB was veri?ed at different initial Pb(II)concentration.The validity of each model determined by sum of squared errors(SSE,%)given by,
SSE=
(q e,exp?q e,cal)2
N
1/2
(7)
where N is the number of data points.The lower value of SSE indi-cates the better a?t is.Table2lists the SSE values obtained for the three kinetic models studied.It was found that the pseudo-second-order kinetic model yielded the lowest SSE values.This agrees with the R2values obtained earlier and proves that the adsorption of Pb(II)ions onto NB and AAB can be best described by the pseudo-second-order kinetic model.
As a result,it is clear that the values of correlation coef?cients obtained for the linear plots from the pseudo-second-order equa-tion are greater than those obtained for the pseudo-?rst-order and intra-particle diffusion equation under all conditions studied.Also, the values of SSE obtained for the pseudo-second-order equation are lower than those obtained for the pseudo-?rst-order and intra-particle diffusion equation under all conditions studied.Therefore, it can be said that kinetics of Pb(II)onto NB and AAB complies best with the pseudo-second-order model due to the higher cor-relation coef?cient as reported by Mathialagan and Viraraghavan [30]and lower SSE values as reported Tan et al.[32],and a good agreement between the experimental and the calculated q e values (Table2).Also,the kinetics data derived using the intra-particle diffusion model indicates that intra-particle diffusion rate is one of the rate determining steps.This is also con?rmed by the activation energy values shown below.
3.5.Activation energy
Generally,a rise in temperature of a chemical reaction increases the rate of the reaction,and the temperature dependence results in a change in the rate constant.Activation energy of the sorption for Pb(II)onto NB and AAB can be estimated by Arrhenius equation providing the relationship between rate constant and temperature as shown in the following:
k=A exp
?
E a
RT
(8)
where k is the rate constant for sorption(g mg?1min?1),A is the Arrhenius constant which is a temperature independent factor (g mg?1min?1),E a activation energy(kJ mol?1),R universal gas constant(8.314J mol?1K?1)and T is the solution temperature in Kelvin(K).
In this study,activation energy of sorption process was calculated using the values of the rate constant from a pseudo-second-order kinetic equation at three different temperatures.The values of E a and A from the Arrhenius plots(?gures not shown) for NB and AAB are16.51kJ mol?1and15.62,and13.66kJ mol?1 and 2.26,respectively.Hence,the Arrhenius equation for the Pb(II)/native bentonite sorption system can be written as follows:
k=15.62exp
?16.51×10
3
RT
(9)
A.R.Kul,H.Koyuncu/Journal of Hazardous Materials179 (2010) 332–339
337
Fig.6.The adsorption isotherms of Pb(II)on the native and activated bentonites at various temperatures(equilibrium time100min).
Eq.(8)can be written for the Pb(II)/activated bentonite sorption
system:
k=2.26exp
?13.66×10
3
RT
(10)
The values of E a are low for Pb(II)/native bentonite and Pb(II)/activated bentonite sorption systems.Moreover,the E a obtained is very low for Pb(II)/activated bentonite sorption system, and thus the sorption process may involve not only an activated process but also a physical sorption.
3.6.Equilibrium studies
The analysis of the isotherms data by?tting them into different isotherm models is an important step to?nd the suitable model that can be used for design process.It was found that the adsorp-tion equilibrium time of Pb(II)onto NB and AAB was100min.Fig.6 shows the plots of q e versus of C e for the adsorption isotherms of Pb(II)on the NB and AAB at various temperatures.These curves are convex upward throughout are designated as favorable type [33].The experimental data were applied to the Langmuir,Fre-undlich and D–R,isotherm equations.The constant parameters of the isotherm equations for this adsorption processes were calcu-lated by regression using linear form of isotherm equations.The constant parameters and correlation coef?cients(R2)are summa-rized in Table3.
The Langmuir adsorption isotherm[34]has been successfully applied to many real sorption processes.It predicts the maximum monolayer adsorption capacity of the adsorbent and also deter-mines if the adsorption is favorable or not.The linearized Langmuir isotherm is represented by following equation:
C e
q e
=1
q0K
+
C e
q0(11) where C e is the solute concentration at equilibrium(mg L?1),q e the adsorption capacity in equilibrium(mg g?1),K the Langmuir adsorption constant(L mg?1),and q0is the maximum concentra-tion retained by the adsorbent(mg g?1).The Langmuir(C e/q e versus C e)plots of Pb(II)were found to be linear the whole concentra-tion range studied and the correlation coef?cients were extremely high.The maximum adsorption capacities were determined as 6.49mg g?1for Pb(II)/NB and2.32mg g?1for Pb(II)/AAB systems(at 328K).Mishra and Patel[35]reported that the Langmuir adsorp-tion capacities for Pb(II)onto bentonite,kaolin and active carbon were found as7.56,4.50and6.68mg g?1,respectively.Han et al.
[36]reported that the Langmuir adsorption capacity for Pb(II)on manganese oxide coated sand was found to be1.34mg g?1.Eren [19]reported that the adsorption capacities for Pb(II)on raw,iron-and magnesium-coated bentonite were obtained as16.70,22.20 and31.86mg g?1,respectively.In another study,Kenedy Ouba-garanadin and Murthy[27]reported that the maximum monolayer adsorption capacity of Pb(II)on montmorillonite-illite type clay (MIC)was determined to be52mg g?1.To determine if adsorp-tion process is favorable or unfavorable,for the Langmuir type adsorption process,isotherm can be classi?ed by a term R L,a dimensionless constant separation factor,which is de?ned as below[37]:
R L=1
1+KC0
(12) The R L values are found in the range of0.92–0.98and0.51–0.59for Pb(II)onto NB and AAB at303–328K,showing favorable adsorption and a relatively high metal uptake by the adsorbent is achievable at low concentrations in the solution[27,38].
The Freundlich adsorption isotherm model is based on multi-layer adsorption.In this model,the mechanism and the rate of adsorption are functions of the constants n and k f.The Freundlich adsorption isotherm can be expressed[39]as,
ln q e=ln k f+
1
ln C e(13) where k f and n are isotherm constant which indicate the capac-ity and intensity of the adsorption,respectively.The linear plot of ln q e versus ln C e at each temperature indicates that adsorption of Pb(II)also follows Freundlich isotherm.The Freundlich adsorp-tion isotherm constants and correlation coef?cients were given in Table3.The values of k f and n determined from the Freundlich
Table3
Constant parameters and correlation coef?cients calculated for various adsorption models at different temperatures for Pb(II)on the native(NB)and activated(AAB) bentonites.
Isotherm equation NB AAB
303K313K328K303K313K328K
Langmuir
q0(mg g?1)19.19398.1103 6.4977 1.7349 2.1749 2.3175 K(L mg?1)0.00380.01090.01650.13860.14290.1847 R20.99770.99670.99300.99890.99810.9992 R L0.98110.94820.92360.59060.58330.5198
Freundlich
k f0.81780.84980.8875 1.1372 1.2292 1.3696 n 2.6525 2.5714 2.4492 2.6954 2.2696 1.9984 R20.98910.9960 1.00000.99580.99920.9941
D–R
q m(mol g?1)0.00940.00840.00800.00140.00170.0024 K (mol2kJ?2)0.00710.00630.00550.00350.00330.0032 E(kJ mol?1)8.39188.90879.534611.952312.309112.5000 R20.99770.99620.99170.97120.98790.9997
338 A.R.Kul,H.Koyuncu/Journal of Hazardous Materials179 (2010) 332–339
Table4
Thermodynamic parameters for the sorption processes Pb(II)on the native(NB)and activated(AAB)bentonites.
Adsorbent T(K)K G(kJ mol?1) H(kJ mol?1) S(kJ mol?1K?1)R2
NB 3030.0038?14.0058
47.38650.11090.9904 3130.0109?11.7519
3280.0165?11.1861
AAB 3030.1386?4.9782
10.29610.01690.9902 3130.1429?5.0630
3280.1847?4.6059
model changed with the rise in temperature,k f values increase with temperature.However,n values decrease with increasing temper-ature for Pb(II)onto NB and AAB.The value of n for Freundlich isotherm was found to be greater than1,indicating that Pb(II)ions are favorably adsorbed by NB and AAB at all the temperature stud-ied[40,41].Also,a higher value of n indicates better adsorption and formation of relatively strong bond between the adsorbate and adsorbent[27].
The Dubinin–Radushkevich(D–R)adsorption isotherm model is temperature independent and a more general model than the Fre-undlich and Langmuir models.It predicts the energy of adsorption per unit of adsorbate and a maximum adsorption capacity for the adsorbent.The linear form of the D–R isotherm[24]is,
ln q e=ln q m?K ε2(14) whereε(Polanyi potential)is equal to RT ln(1+1/C e),q e is the amount of the solute adsorbed per unit NB or AAB(mol g?1),q m the theoretical monolayer saturation capacity(mol g?1),C e the equi-librium concentration of the solute(mol L?1),K the constant of the adsorption energy(mol2kJ?2).K is related to mean adsorption energy(E,kJ mol?1)as,
E=1
(2K )1/2
(15)
The constant obtained from the plot of ln q e versusε2at303,313 and328K adsorption temperature are shown in Table3.The differ-ence of q0derived from the Langmuir and q m from D–R models is large.The difference may be attributed to the different de?nition of maximum adsorption capacity in two models.In Langmuir model, q0represents the maximum adsorption of metal ions at mono-layer coverage,whereas q m represents the maximum adsorption of metal ions at the total speci?c micropore volume of the adsorbent in D–R model.The mean adsorption energy(E)gives information about chemical and physical adsorption[42].It was found to be in the range of8.39–12.50kJ mol?1,which is lower than the range of adsorption reaction8–16kJ mol?1.The type of adsorption of Pb(II) onto NB and AAB was de?ned as physical adsorption.
3.7.Thermodynamic studies
The type of sorption may be determined through such thermo-dynamic quantities as Gibbs free energy( G),the enthalpy change ( H)and entropy change( S)for the sorption of Pb(II)onto NB and AAB are given in Table4. G is calculated using the following equation:
G=?RT ln K(16) where K is the adsorption equilibrium constant(from Langmuir model).The relation between K and the thermodynamic parame-ters of H and S can be described by Van’t Hoff correlation in Eq.
(17):
ln K=
S
R
?
H
RT
(17)
H and S were calculated from the slope and intercept of Van’t
Hoff plots,respectively.The negative values for the Gibbs free
energy change, G showed that the adsorption process for the ben-
tonite samples was feasible and spontaneous thermodynamically.
However,the decrease in G values with increase in temperature
showed that the adsorption was not favorable at higher temper-
atures[43].The positive values of H indicate the endothermic
behavior of the adsorption reaction of Pb(II)ions and suggest that
a large amount of heat is consumed to transfer the Pb(II)ions from
aqueous into the solid phase.As was suggested by Nunes and Airoldi
[44],the transition metal ions must give up a larger share of their
hydration water before they could enter the smaller cavities.Such
a release of water from the divalent cations would result in posi-
tive values of S.This mechanism of the adsorption of Pb(II)ions is
also supported by the positive values of S,which show that Pb(II)
ions are less hydrated in the bentonite layers than in the aque-
ous solution.Also,the positive value of S indicates the increased
disorder in the system with changes in the hydration of the adsorb-
ing Pb(II)cations.Hefne et al.[28]noted that positive S value
occurs as a result of redistribution of energy between the adsor-
bate and the adsorbent.Before adsorption occurs,the heavy metal
ions near the surface of the adsorbent will be more ordered than
in the subsequent adsorbed state and the ratio of free heavy metal
ions to ions interacting with the adsorbent will be higher than in the
adsorbed state.As a result,the distribution of rotational and trans-
lational energy among a small number of molecules will increase
with increasing adsorption by producing a positive value of S and
randomness will increase at the solid–solution interface during the
process of adsorption.The values of thermodynamic parameters for
the adsorption of Pb(II)ions onto the clays are consistent with that
given in the literature[39,45,46].
4.Conclusions
The adsorption ef?ciency increases with increasing tempera-
ture.Also,the adsorption ef?ciency with the AAB was greater than
NB in all studied solution concentration and temperatures.The
equilibrium time was100min.The kinetics of sorption processes
were best described by a pseudo-second-order kinetic model and
also?tted well the intra-particle diffusion model up to15min,
but diffusion was not the only rate-controlling step.The activation
energy of sorption was calculated using the pseudo-second-order
rate constant,and it was found to be16.51and13.66kJ mol?1
for the NB and AAB,respectively.From the values of the activa-
tion energy,it was seen that the intra-particle diffusion kinetics
was one of the rate determining steps as well as pseudo-second-
order kinetics for the sorption https://www.wendangku.net/doc/ba6933573.html,ngmuir,Freundlich
and Dubinin–Redushkevich(D–R)isotherm models were used
to represent the experimental data,and the models?tted well.
The adsorption of Pb(II)ions onto NB and AAB was found to be
endothermic according to Langmuir isotherm.R L separation fac-
tor for Langmuir and the n value for Freundlich isotherm show
that Pb(II)ions are favorably adsorbed by NB and AAB.The type
of adsorption of Pb(II)ions onto NB and AAB was de?ned as phys-
ical adsorption.The negative value of G and positive value of S
A.R.Kul,H.Koyuncu/Journal of Hazardous Materials179 (2010) 332–339339
showed that the adsorption of Pb(II)ions onto NB and AAB was feasible and spontaneous.The positive value of H con?rmed the endothermic nature of adsorption.
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实验一(二)熔点的测定
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
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
熔点测定的基本方法及注意事项
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。
金属相图
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
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
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
金属相图
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
有机化学实验二熔点的测定
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
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
影响熔点的因素(建文)
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。
二组分金属相图的绘制.
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
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
金属相图实验步骤(学生)
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
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
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
3.差热分析法测定Pb-Sn的金属相图
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