Biochemical eng J08-Adsorption of copper on rubber (Hevea brasiliensis) leaf powder
Biochemical Engineering Journal39(2008)
521–530
Adsorption of copper on rubber(Hevea brasiliensis)leaf powder:
Kinetic,equilibrium and thermodynamic studies
W.S.Wan Ngah?,M.A.K.M.Hana?ah
School of Chemical Sciences,Universiti Sains Malaysia,11800Penang,Malaysia
Received27April2007;received in revised form24October2007;accepted11November2007
Abstract
The adsorption of Cu(II)ions from aqueous solution by rubber(Hevea brasiliensis)leaf powder(RHBL)was studied in a batch adsorption system. Characteristics of RHBL such as pH of aqueous slurry,pH of zero point charge(pH ZPC),surface area and pore diameter,Fourier transform infrared (FTIR),scanning electron microscopy(SEM)and electron dispersive spectroscopy(EDS)were investigated.Factors in?uencing adsorption such as pH of the solution,adsorbent dosage,particle size,copper concentration and temperature have been studied.The adsorption process was relatively fast and equilibrium was achieved after about60min.Maximum adsorption of Cu(II)ions occurred at around pH4–5.The kinetic data were analyzed using various kinetic models particularly pseudo-?rst-order,pseudo-second-order,Ritchie’s-second-order and intraparticle diffusion.The pseudo-second-order kinetic model was found to agree well with the experimental data.Adsorption equilibrium data could also be described well by Langmuir,Freundlich and Dubinin–Radushkevich isotherm models.Based on the Langmuir isotherm,the monolayer adsorption capacity of Cu(II)ions was8.92mg g?1.Thermodynamic parameters such as enthalpy change( H?),free energy change( G?)and entropy change( S?) were calculated and adsorption process was spontaneous and exothermic.Copper removal by RHBL involved different kinds of mechanisms such as ion-exchange,complexation and physisorption.
?2007Elsevier B.V.All rights reserved.
Keywords:Adsorption;Copper;Rubber leaf powder;Kinetic;Isotherms;Thermodynamic
1.Introduction
Heavy metal ions can be released into wastewater from various industries such as metal?nishing,electroplating,auto-motive,battery manufacturing,steel industries,tannery,paint manufacturing,electronic industries,etc.[1].One of the heavy metals that is toxic to humans and widely studied by many researchers is copper.It has been reported that excessive intake of copper by humans may lead to severe mucosal irritation, hepatic and renal damage,capillary damage,gastrointestinal irritation and central nervous system irritation[2].Copper can be removed by precipitation as copper hydroxide but this method is only ef?cient at high pH value.Other conven-tional methods which have been employed to remove copper in wastewater include ion-exchange,membrane separation,elec-trochemical treatment,reverse osmosis and solvent extraction [3].All these methods are generally expensive;therefore it ?Corresponding author.Tel.:+6046533888;fax:+6046574854.
E-mail address:wsaime@usm.my(W.S.Wan Ngah).is important to search for a low-cost method which is effec-tive and economic.Adsorption technique is much preferred for removal of heavy metals because of its ef?ciency and low cost.Many researchers have been investigating low-cost adsorbents for heavy metal removal such as sawdust[2],rice husk[4],sago waste[5],red pepper seeds[6],barks[7],teak leaves powder[8],saltbush leaves[9],palm kernel?bre[10], groundnut shells[11],tree fern[12],chitosan[13],etc.Rubber leaves are solid wastes largely generated from rubber planta-tions and left unutilized on the?elds,causing a signi?cant disposal problem.No reference to work involving the use of RHBL as an adsorbent for the removal of Cu(II)ions has been found in the literature.However,previous experiments have shown that RHBL was able to adsorb Pb(II)and Cd(II) ions[14,15].The main objective of this study is to assess the effectiveness of RHBL in the removal of copper by determin-ing the maximum adsorption https://www.wendangku.net/doc/318844632.html,ngmuir,Freundlich and Dubinin–Radushkevich adsorption isotherm models were used to?t the equilibrium isotherm.The adsorption kinetic was determined using pseudo-?rst-order,pseudo-second-order, Ritchie’s-second-order and intraparticle diffusion models.
1369-703X/$–see front matter?2007Elsevier B.V.All rights reserved. doi:10.1016/j.bej.2007.11.006
522W.S.Wan Ngah,M.A.K.M.Hana?ah/Biochemical Engineering Journal39(2008)521–530
Thermodynamic of copper adsorption and adsorption mecha-nisms were also discussed.
2.Materials and methods
2.1.Preparation of adsorbent
The yellow coloured rubber leaves,collected from the Uni-versiti Teknologi MARA rubber plantation in Jengka,Malaysia were washed repeatedly with water to remove dust and soluble impurities.The leaves were dried in an oven at80?C overnight, ground and sieved to a constant size of355–500?m.The leaf powder was washed extensively again with distilled water until the washings were free of colour before dried at80?C overnight and stored in a plastic container.The newly prepared leaf pow-der(hereafter called RHBL)was used as adsorbent without any pre-treatment.
2.2.Characterization of adsorbent
The pH of the aqueous slurry was determined by adding1g of RHBL in50mL distilled water,stirred and the?nal pH was measured after24h.The determination of pH ZPC of RHBL was performed according to the solid addition method[16]:50mL of0.01M KNO3solution was placed in conical?asks.The ini-tial pH of the solutions was adjusted to a value between2and 9by adding0.1M HCl or NaOH solutions.Then,1g of RHBL was added to each?ask,strirred and the?nal pH of the solutions was measured after24h.The value of pH ZPC can be determined from the curve that cuts the pH0line of the plot pH versus pH0. The Fourier transform infrared(FTIR)spectrum was recorded by a Perkin Elmer FT-IR System1600Model spectrophotome-ter in the range of400–4000cm?1.The surface structure of RHBL was observed by Leica Cambridge S360scanning elec-tron microscope with energy dispersive spectroscopy(EDS). The surface area and the average pore diameter of RHBL were determined using a Micromeritics ASAP2010gas adsorption surface analyzer.
2.3.Copper solutions
All chemicals used were analytical reagent grade.The stock solution of1000mg L?1Cu(II)was prepared by dissolving1g of copper metal supplied by BDH Chemicals(England)in10mL of concentrated nitric acid in a100mL beaker.After the copper metal dissolved,the solution was transferred to a1L volumet-ric?ask and diluted to the mark.Experimental solutions of the desired copper concentrations were obtained by successive dilutions.
2.4.Batch adsorption studies
In general,the effects of pH,adsorbent dosage,particle size and temperature on adsorption of copper were performed at room temperature(27±1?C)in conical?asks by stirring a mass of 0.1g of RHBL with50mL of5mg L?1copper solutions for1h using adsorbent size of355–500?m(unless otherwise stated).The initial pH of copper solutions was?xed at4(unless oth-erwise stated)by addition of drops of0.1M HCl or NaOH solutions while the stirring speed was?xed at500rpm.The effect of pH on copper adsorption was investigated over a pH range1–5.The effect of adsorbent dosage was studied by vary-ing the amount of adsorbent from0.02to1.0g.Three different particle sizes of RHBL were selected for the study of effect of particle size on copper adsorption:<180?m,180–355?m and 355–500?m.To evaluate the contact time necessary to reach the equilibrium state,kinetic studies were carried out by varying the stirring time(0–90min)using three different concentrations of copper(3,5and10mg L?1).The study on effect of temperature was performed at temperature range300–320K.For isotherm study,0.1g of RHBL was mixed with50mL copper solutions at various concentrations(5–50mg L?1)and the mixtures were stirred for1h at room temperature.The initial pH of the solutions was?xed at4.After adsorption,the adsorbent was?ltered and the amount of Cu(II)ions in the solution was analyzed by atomic absorption spectrometer(Perkin Elmer AAnalyst200Model)at
a wavelength of324.7nm.
2.5.Metal uptake
The amount of copper adsorbed,q e(mg g?1)was computed by using the following expression:
q e=
C0?C e
m
V(1)
where C0and C e are copper concentrations(mg L?1)before and after adsorption,V is the volume of adsorbate(L)and m is the weight of the adsorbent(g).The percent removal of copper is calculated by the following equation:
Removal(%)=
C0?C e
C0
×100(2) 3.Results and discussion
3.1.Characterization of adsorbent
3.1.1.pH ZPC and pH of aqueous slurry
The pH ZPC of an adsorbent is a very important characteris-tic that determines the pH at which the adsorbent surface has net electrical neutrality.At this value,the acidic or basic func-tional groups no longer contribute to the pH of the solution. Cations adsorption will be more favourable at pH value higher than pH ZPC.The value of pH ZPC is close to the value of pH of aqueous slurry which is5.85(Table1).
3.1.2.Pore structure and pore size distribution
The BET surface area,Langmuir surface area and average pore diameter results are presented in Table1.The value of BET surface area of RHBL(0.478m2g?1)is almost similar to the sur-face area of chitosan?akes(0.42m2g?1)[17]but slightly higher than Pinus pinaster bark(0.374m2g?1)[18].The low value of surface area also indicates low porosity.Pore sizes are classi?ed in accordance with the classi?cation adopted by the International
W.S.Wan Ngah,M.A.K.M.Hana?ah/Biochemical Engineering Journal39(2008)521–530523
Table1
Physical characteristics of RHBL
pH of aqueous slurry 5.85
pH ZPC 5.65
S BET a(m2g?1)0.478
S L b(m2g?1)0.728
D p c(′?A)154.6
Particle size(?m)355–500
Colour Yellow
Odour Slight
a BET surface area.
b Langmuir surface area.
c Average pore diameter.
Union of Pure and Applied Chemistry(IUPAC),that is,micro-pores(diameter(d)<20?A),mesopores(20?A
3.1.3.SEM images and EDS spectra
The SEM images at500×and1000×magni?cations reveal the nature of the surface of RHBL as shown in Fig.1.The adsor-bent has irregular structure,thus makes possible the adsorption of Cu(II)ions on different parts of the adsorbent.The EDS spec-tra(Fig.2)indicate that RHBL consists of mainly C and O,and trace amounts of Si and Ca.After adsorption,the copper peak in the spectrum is visible(Fig.2b)while the calcium peaks diminished,thus suggesting ion-exchange might be one of the mechanisms involved in copper removal.The presence of Au peaks in both spectra is due to the gold purposely settled to increase electric conduction and to improve the quality of the images.To prove that ion-exchange mechanism was involved during copper adsorption,the amounts of Ca2+,Mg2+and Na+ released after adsorption were measured.For this experiment, 0.1g of RHBL was mixed with50mL(10mg L?1)of copper solution at pH4.The release of Ca2+,Mg2+and Na+ions from the control(RHBL in deionized water)was also measured.The net release of cations was calculated by subtracting the amount of cations released in the control to the amount of cations measured in the ef?uent after copper adsorption.At equilibrium time,it was found that7.11mg L?1Cu2+ions were adsorbed while the pH of the ef?uent increased by0.6unit.The net release of Ca2+, Mg2+and Na+ions was3.73,1.15and1.33mg L?1,respec-tively.Ion-exchange could be the dominating mechanism if the ratio of cations bound to and released by RHBL is unity.In this work,the ratio of cations bound(Cu2+and1/2H+)to
RHBL Fig.1.SEM images of RHBL at:(a)500×and(b)1000×
.
Fig.2.EDS spectra of RHBL(a)before copper adsorption and(b)after copper adsorption.
524W.S.Wan Ngah,M.A.K.M.Hana?ah /Biochemical Engineering Journal 39(2008)
521–530
Fig.3.FTIR spectra of RHBL.
surface and released (Mg 2++Ca 2++1/2Na +)is 0.85,suggest-ing that ion-exchange might be the dominating mechanism in the copper removal by RHBL.However,other possible mecha-nisms such as complexation and physical adsorption could not be ruled out.
3.1.
4.Fourier transform infrared spectrum
FTIR analysis was carried out in order to identify the func-tional groups in the RHBL that might be involved in the adsorption process.The FTIR spectra of RHBL and that loaded with copper ions are shown in Fig.3.The spectra display a num-ber of absorption peaks,which indicates the complex nature of the adsorbent.The broad and strong band ranging from 3000to 3600cm ?1indicates the presence of OH and NH groups which is consistent with the peak at 1054and 1163cm ?1assigned to alcoholic C O and C N stretching vibration.The peaks observed at 2921and 2851cm ?1can be assigned to asymmetric and symmetric CH 2groups.The peak located at 1723cm ?1is a characteristic of carbonyl group stretching from carboxylic acid or ester group.The peak at 1629cm ?1cor-responds to the carboxylate (COO ?)and C C stretching that can be attributed to the aromatic C C bond [19].The absorp-tion bands around 1400–1600cm ?1are assigned to aromatic skeletal vibration [20,21].The intense band at 1054cm ?1cor-responds to the C O of alcohols and carboxylic acids,while peaks around 1150–1250cm ?1correspond to phenolic hydroxyl groups in lignin [22].The FTIR spectrum for copper loaded adsorbent shows intensity of the peaks were shifted slightly or substantially lower than those in the raw sample,suggesting the participation of these functional groups in the binding of cop-per by RHBL.The wavenumbers of RHBL shifted from 3406and 1630cm ?1to 3395and 1636cm ?1,respectively after cop-per uptake.The intensity of the peak at 1516cm ?1attributed to N–H bending shifts was reduced after copper uptake.A new peak appears at 1384cm ?1which could be assigned to the bind-ing of copper to carboxyl group.In general,hydroxyl,carboxyl
and amino groups are the main functional groups involved in the binding of copper ions,suggesting that the mechanisms of copper adsorption on RHBL could also occur by surface complexation.3.2.Effect of pH
The pH of an aqueous solution is an important controlling parameter in the process of adsorption.Solution pH affects both aqueous chemistry and surface binding sites of the adsorbent.Below pH 5,the dominant species of copper was free Cu 2+and mainly involved in adsorption process.This has been con?rmed by the speciation diagram shown by Wang and Qin [23].Accord-ing to Reddy et al.[7],above pH 5,copper starts to precipitate as Cu(OH)2.Therefore,experiments were performed in the pH range 2–5.The adsorption of Cu(II)ions was found mainly in?u-enced by solution pH.The amounts of copper adsorbed at pH 2,3,4and 5were 0.08,1.64,1.99and 2.19mg g ?1,respec-tively.At very low pH values,copper adsorption was found to be very low due to competition between H 3O +and Cu(II)ions for the adsorption sites.As pH increased,more adsorbent sur-face were exposed and carried negative charges,which results in less repulsion of Cu(II)ions [24].3.3.Effect of adsorbent dosage
The dependence of adsorption of copper on the dosage of RHBL is shown in Table 2.The percent copper removal increased from 45.2to 87.1%for adsorbent dosage of 0.02and 1.0g,respectively.This is due to the availability of more bind-ing sites as the dosage of adsorbent increased.However,the amount of copper adsorbed (mg g ?1)was found to decrease with increasing adsorbent dosage.According to Shukla et al.[25],the decrease in adsorption capacity (mg g ?1)with increase in adsorbent dosage is due to the high number of unsaturated adsorption sites.
W.S.Wan Ngah,M.A.K.M.Hana?ah /Biochemical Engineering Journal 39(2008)521–530
525
Table 2
Amount of Cu(II)ions removed (%)and adsorbed (mg g ?1)at different adsor-bent dosage Adsorbent dosage (g)Removal (%)Copper adsorbed (mg g ?1)0.0245.23 5.650.0561.88 3.090.1078.30 1.960.2079.340.990.5080.040.421.00
87.10
0.22
3.4.Effect of particle size
The amount of Cu(II)ions adsorbed increased as the size of RHBL decreases as shown in Fig.4.The smallest adsorbent size (<180?m)recorded the shortest time to reach equilibrium (20min).The maximum adsorption capacities at equilibrium time were 2.27,2.04and 1.99mg g ?1for adsorbent size of <180,180–355and 355–500?m,respectively.As the size of adsorbent decreases,the surface area will increase and more binding sites are available for Cu(II)ions to be adsorbed.Hence,adsorption capacity will be increased.
3.5.Effect of initial copper concentration and contact time The adsorption data at different initial copper concentrations is shown in Fig.5.The plots show that kinetic of adsorption of copper consisted of two phases;an initial rapid phase where adsorption was fast and a second slower phase where equilib-rium uptake was achieved.The ?rst phase is related to external surface adsorption of copper,which occurs instantaneously.The second phase is the gradual adsorption stage before the copper uptake reaches equilibrium.The time to reach equilibrium is 20min for copper concentration of 3mg L ?1and 60min for 5and 10mg L ?1copper.Based on these results,the contact time was ?xed at 1h for the rest of batch experiments to ensure that the equilibrium was reached.The maximum amounts of copper adsorbed are 1.20,1.99and 3.56mg g ?1for copper
concentra-
Fig.4.Effect of particle size on copper adsorption onto
RHBL.Fig.5.Effect of copper concentration and contact time on adsorption of copper onto RHBL.
tions of 3,5and 10mg L ?1,respectively.The percent removal of Cu(II)are 79.8,79.5and 71.2%for copper concentrations of 3,5and 10mg L ?1,respectively.The initial high rate of copper uptake may be attributed to the existence of the bare surface;however the number of available adsorption sites decreased as the number of copper ions adsorbed increases [26].The increase in adsorption capacity with increasing copper concentration could be due to higher probability of collision between Cu(II)ions and adsorbent surface [27].3.6.Adsorption kinetic studies
The pseudo-?rst-order kinetic equation [28]is given as:log (q e ?q t )=log q e ?
k 1
2.303
t (3)
where q t and q e are the amount of copper adsorbed (mg g ?1)at time t (min)and at equilibrium,and k 1is the rate constant of the pseudo-?rst-order adsorption process (min ?1).Straight-line plots of log (q e ?q t )against t were used to determine the rate constants,k 1and correlation coef?cients,R 2for dif-ferent copper concentrations (Fig.6).The rate constants (k 1)obtained from the slopes of the plots was in the range
of
Fig.6.Pseudo-?rst-order plots of copper adsorption onto RHBL.
526W.S.Wan Ngah,M.A.K.M.Hana?ah /Biochemical Engineering Journal 39(2008)
521–530
Fig.7.Pseudo-second-order plots of copper adsorption onto RHBL.
0.097–0.217min ?1.Although these plots show good linearity,the values of calculated adsorption capacities (q e,cal )are differ-ent from the experimental ones (q e,exp )(Table 3),suggesting that adsorption reaction is not of pseudo-?rst-order.
The pseudo-second-order equation [29]is expressed as:
t q t =1
h +1q e
t (4)
where h =k 2q 2e
can be regarded as the initial sorption rate as t →0,and k 2is the rate constant of pseudo-second-order adsorption (g mg ?1min ?1).The plot t /q t versus t should give a straight line if pseudo-second-order kinetic is applicable and q e ,k 2and h can be determined from the slope and intercept of the plot,respectively.Better linearity was obtained for these plots as shown in Fig.7,with regression coef?cient greater than 0.99and the pseudo-second-order rate constants,k 2having val-ues from 0.094to 3.466g mg ?1min ?1.The values are given in Table 3.The calculated values of adsorption capacities (q e,cal )also agree well with the experimental ones (q e,exp ).Both facts suggest that the adsorption of copper ions by RHBL follows the pseudo-second-order kinetic model.A detail analysis on the pseudo-second-order model also reveals that the values of the initial adsorption rates (h )increases with decrease in the initial copper concentration as given in Table 3.According to Wong et al.[4],the lower the concentration of copper ions in the solution,the lower the probability of collisions among Cu(II)ions,there-fore Cu(II)ions could be bonded to the active sites much faster.Ritchie’s-second-order equation [30]is expressed as:
1q t =1kq e t +1q e
(5)
where k is the rate constant (min ?1)of the second-order adsorp-tion.From Eq.(5),a plot of 1/q t versus 1/t should give a straight line (Fig.8)and the rate constants (k )and adsorption capacity at equilibrium (q e )can be determined from the slope and intercept,respectively.The calculated values of adsorption capacities (q e,cal )obtained from Ritchie’s-second-order plots were found to be slightly lower than those of the experimen-tal values (q e,exp ).The summary of q e and k values determined from Ritchie’s-second-order is given in Table 3.
T a b l e 3C o m p a r i s o n o f t h e p s e u d o -?r s t -o r d e r ,p s e u d o -s e c o n d -o r d e r ,R i t c h i e ’s -s e c o n d -o r d e r a n d i n t r a p a r t i c l e d i f f u s i o n r a t e c o n s t a n t s a n d c a l c u l a t e d a n d e x p e r i m e n t a l q e v a l u e s f o r d i f f e r e n t c o n c e n t r a t i o n s o f C u (I I )i o n s
[C u ]
P s e u d o -?r s t -o r d e r P s e u d o -s e c o n d -o r d e r
R i t c h i e ’s -s e c o n d -o r d e r
I n t r a p a r t i c l e d i f f u s i o n
q e ,e x p (m g g ?1)
(m g L ?1)q e ,c a l (m g g ?1)k 1(m i n ?1)R 2q e ,c a l (m g g ?1)k 2(g m g ?1m i n ?1)h (m g g ?1m i n ?1)R 2q e ,c a l (m g g ?1)k (m i n ?1)R 2
k i d (m g g ?1m i n 1/2)R 2
30.5910.2170.9371
1.1633.4664.6880.99941.1961.1420.97460.1090.94931.19751.0660.1220.9667
2.0340.2801.1600.99971.9070.8120.92150.1690.96781.988102.2580.097
0.9822
3.6870.0941.2760.99933.1170.7960.81090.3060.9977
3.588
W.S.Wan Ngah,M.A.K.M.Hana?ah /Biochemical Engineering Journal 39(2008)521–530
527
Fig.8.Ritchie’s-second-order plots of copper adsorption onto
RHBL.
Fig.9.Intraparticle diffusion plots of copper adsorption onto RHBL.
The intraparticle diffusion equation [31]is given as:q t =k id t 1/2
(6)
where k id (mg g ?1min ?1/2)is the intraparticle rate constant and
can be obtained from the slope of the second portion of the straight line of plot q t versus t 1/2.As can be seen from Fig.9,the adsorption was controlled by three different stages:the ?rst sharper portion being a rapid external surface adsorption,the second linear portion being a gradual adsorption where intra-particle diffusion is the rate limiting factor,and the ?nal portion being ?nal equilibrium stage due to low concentration of copper in solution phase as well as less number of available adsorption sites.It is obvious that intraparticle diffusion is not the sole rate-determining step as the second portions of plots of q t versus t 1/2
Table 5
Comparison of adsorption capacity of Cu(II)with other adsorbents Adsorbent
Maximum adsorption capacity (mg g ?1)Reference Peanut pellets
12[36]
Rubber leaf powder 8.92Present study Pleurotus pulmonarius (fungal biomass) 6.203[37]Rubber wood sawdust 5.729[38]Herbaceous peat 4.84[39]Bagasse ?y ash 2.26[40]Maple sawdust 1.79[41]Turkish coal 1.62[42]Oil shale ash
0.098[43]Mangifera indica sawdust
0.005
[44]
did not have zero intercept [32].The values of k id determined from the plots were 0.109,0.169and 0.306mg g ?1min ?1/2for copper concentrations of 3,5and 10mg L ?1,respectively as shown in Table 3.3.7.Adsorption isotherms
The distribution of metal ions between liquid and solid phases is generally described by using the Langmuir [33],Freundlich [34]and Dubinin–Radushkevich [35]adsorption isotherm models.The Langmuir model assumes uniform energies of adsorption onto the adsorbent surface and no transmigration of adsorbate in the plane of the surface.The Langmuir equation is given as:
C e q e
=1Q max b +
C e
Q max (7)
where C e is the equilibrium copper concentration (mg L ?1),q e the amount of copper adsorbed at equilibrium (mg g ?1),Q max is the maximum adsorption capacity (mg g ?1),b is a constant (L mg ?1)related to energy of adsorption which quantitatively re?ects the af?nity between the adsorbent and adsorbate.The values of maximum adsorption capacity can be obtained from the slope of the plot of C e /q e versus C e .The maximum adsorp-tion capacity of copper by RHBL was 8.92mg g ?1(Table 4).It is also important to compare the value of maximum adsorp-tion capacity obtained from this study with values from other reported adsorbents,since this will suggest the effectiveness of RHBL as a potential adsorbent for treatment of water contain-ing copper.The adsorption capacity for copper using RHBL is comparable with other reported adsorbents as shown in Table 5.The essential feature of Langmuir model can be expressed in terms of a dimensionless constant separation factor (R L )given
Table 4
Langmuir,Freundlich and Dubinin–Radushkevich isotherm constants and correlation coef?cients Langmuir Freundlich Dubinin–Radushkevich q max (mg g ?1)b (L mg ?1)R 2K F (mg g ?1)n R 2q m (mg g ?1)E (kJ mol ?1)R 28.92
0.215
0.9932
2.15
2.54
0.9820
28.67
11.95
0.9909
528W.S.Wan Ngah,M.A.K.M.Hana?ah /Biochemical Engineering Journal 39(2008)521–530
by the following equation [45]:R L =
11+bC 0
(8)
where b is the Langmuir constant (L mg ?1)and C 0is the ini-tial copper concentration (mg L ?1).It has been established that for favourable adsorption,0
The Freundlich isotherm model is derived to model the multi-layer adsorption and applicable to highly heterogeneous surface,and is given as:log q e =log K F +
1
n
log C e (9)
where K F is maximum adsorption capacity (mg g ?1)
and n is related to adsorption intensity.According to Mohanty et al.[46]if the value of n is greater than 1,it indicates favourable adsorp-tion of metal ions on the surface of adsorbent.The value of n determined from Freundlich isotherm was 2.54as shown in Table 4,indicating that Cu(II)ions are favourably adsorbed by RHBL.
The Dubinin–Radushkevich (D–R)equation can be expressed as:ln q e =ln q m ?Kε2
(10)
where ε(Polanyi potential)is equal to RT ln(1+1/C e ),q m is the
maximum adsorption capacity (mg g ?1),K is related to mean adsorption energy (E in kJ mol ?1)as:E =1√
?2K
(11)
The mean adsorption energy (E )gives information about chemical and physical adsorption [47].The E value (11.95kJ mol ?1)lies between 8and 16kJ mol ?1as shown in Table 4,which suggests adsorption occurred by ion-exchange mechanism [48].
3.8.Thermodynamic of copper adsorption
In engineering practice,values of thermodynamic parameters such as enthalpy change ( H ?),entropy change ( S ?)and free energy change ( G ?)must be taken into consideration in order to determine the spontaneity of a process.A spontaneous process will show a decrease in G ?and H ?values with increasing temperature.The experiment was carried out at temperatures of 300,310and 320K.All the thermodynamic parameters such as free energy change ( G ?),enthalpy change ( H ?)and entropy change ( S ?)can be calculated from the following equations:K c =
C Ad C e
(12) G ?=?RT ln
K c
(13)
Fig.10.Van’t Hoff plot of adsorption of copper onto RHBL.
ln K c = S ?R ?
H ?
RT
(14)
where K c is the equilibrium constant,C Ad is the concentration of copper adsorbed on solid at equilibrium (mg L ?1),C e is the equilibrium concentration of copper in the solution (mg L ?1),R is the gas constant (8.314J K ?1mol ?1)and T is the temper-ature in Kelvin.The values of H ?and S ?can be obtained from the slope and intercept of Van’t Hoff plot of ln K c versus 1/T (Fig.10).The negative value of H ?(?31.96kJ mol ?1)as shown in Table 6indicates exothermic nature of adsorp-tion.According to Alkan et al.[49],enthalpy change due to chemisorption takes value between 40and 120kJ mol ?1,which is larger than that due to physisorption.Therefore,the low value of heat of adsorption obtained in this study indicates that adsorption is likely due to physisorption.In the isotherm study,it was reported that adsorption mechanism occurred by ion-exchange according to the calculated value of E obtained from Dubinin–Radushkevich isotherm model.However,it is obvious from the enthalpy of adsorption ( H ?)that physisorption also takes part in adsorption process in which the adsorbate adheres to the surface only through weak intermolecular interactions.The negative value of free energy change ( G ?)is an indica-tion of a spontaneous process whereby no energy input from outside of the system is required.However,the values of G ?decreased with increasing temperature,indicating that adsorp-tion of Cu(II)ions on RHBL became less favourable at higher temperature.The negative value of entropy change ( S ?)shows a decreased disorder at the solid/liquid interface during copper adsorption.As the temperature increases,the mobility of copper ions increases causing the ions to escape from the solid phase to the liquid phase.Therefore,the amount of copper that can be adsorbed will decrease.
Table 6
Thermodynamic parameters of copper adsorption by RHBL Temperature (K) G ?(kJ mol ?1) H ?(kJ mol ?1) S ?(J K ?1mol ?1)300?3.38?31.96
?95.94
310?2.17320
?1.48
W.S.Wan Ngah,M.A.K.M.Hana?ah/Biochemical Engineering Journal39(2008)521–530529
4.Conclusion
This study demonstrated that the dried RHBL biomass could be used as an effective adsorbent for the treatment of wastewater containing Cu(II)ions.The adsorption process is dependent on several factors such as initial metal concentration,solution pH, contact time,adsorbent dosage and temperature.The isotherm study indicates that adsorption data correlated well with Lang-muir,Freundlich and Dubinin–Radushkevich isotherm models. The kinetic data showed that the pseudo-second-order kinetic model was obeyed better than pseudo-?rst-order kinetic model. Adsorption was also more favourable at a much lower temper-ature.The mechanisms of copper removal by RHBL occurred through ion-exchange,complexation and physisorption. Acknowledgment
The authors are grateful to the Universiti Sains Malaysia (Grant No.304/PKIMIA/638056)for?nancial support of this work.
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经典普通话口才练习绕口令
普通话绕口令练习 练习普通话绕口令，要“循序渐进、持之以恒”——既练“嘴劲儿”，又要练“心劲儿”！练习绕口令主要是为了帮助大家训练口齿灵活、语音准确、吐字流畅、颗粒饱满、圆润集中、字正腔圆、助于表达。训练时，大家一定要按照正确的发音部位和发音方法练。一方面要注意纠正自己的发声缺点、弱点、毛病；另一方面还要利用和发挥自己的长处，扬长避短。绕口令练起来有些绕口、难发，但它却是学说好普通话必不可少的练习材料，通过绕口令的练习不仅可以加强咬字器官的力度和提高咬字器官的灵活度，同时也可以有效地锻炼呼吸控制能力。练习时，最初应特别注意字音质量，要把音发准，劲使稳，打开韵腹，利索收音，做到吐字准确、清晰、圆润。然后由慢到快，逐渐加速，可按音、字、词、句、段五步练习法循序渐进。绕口令练习并非只是耍嘴皮子，而是既练“嘴劲”，又要练“心劲”，所以不能一味求快。在训练中，我们还要注意结合气息控制练习。在开口前要注意放松喉部、气息下沉。“运行”当中要补气自如，轻松流畅，字音速度由慢渐快，要做到慢而不断，快而不乱。最后还要注意做到内容清楚、感情充沛。因为气是发声的动力，气息调整不好，字的“运行”就会发生故障，声音的质量也就无法保证。以下是一些有助于普通话发音训练的绕口令，请大家结合自身的发音情况选择自己的发音难点进行练习：一、声母绕口令练习普通话声母的发音过程有三个阶段：成阻、持阻、除阻。声母的
发音部位不同，吐字时的着力点就不一样，比如“b、P、m”，发音时着力点在双唇，“d、t”的着力点在舌尖，靠舌尖的弹力。因此发声母时不要拖长，要咬住、弹开。我们在每段绕绕口令题旁都标有“b、p、m”、“d、t”、“n、l”、“g、k”、“s、sh”等声母字样来说明此段绕口令是专门训练所标声母的绕口令。例如：《八百标兵》一段绕口令题旁标有“b、p”的声母，就说明“b、p”字母在练习过程中是重点训练的内容，训练双唇有力集中。又如：《短刀》一段绕口令题旁标有“d、t”的声母，就说明“d、t”在练习过程中是重点训练的内容，训练舌尖的弹力等等。 ?八百标兵（b、p）八百标兵奔北坡，炮兵并排北边跑，炮兵怕把标兵碰，标兵怕碰炮兵炮。 ?炮兵和步兵（b、p、m）炮兵攻打八面坡，炮兵排排炮弹齐发射。步兵逼近八面坡，歼敌八千八百八十多。 ?一平盆面（b、p）一平盆面，烙一平盆饼，饼碰盆，盆碰饼。?巴老爷芭蕉树（b、p）巴老爷有八十八棵芭蕉树来了八十八个把式要在巴老爷八十八棵芭蕉树下住。巴老爷拔了八十八棵芭蕉树，不让八十八个把式在八十八棵芭蕉树下住，八十八个把式烧了八十八棵芭蕉树，巴老爷在八十八棵树边哭。 ?老六放牛（n，l）
普通话发音训练
普通话发音训练 1、纠正喔鹅音混淆（o,e） 说到唇音双唇碰，喔鹅元音要分清，喔音口形往前撮，不能光是下唇动，鹅音微笑牙打开，声位靠后喉震动。 玻坡摸b,p,m绕口练习： 风雨瓢泼 老婆婆用簸箕来把麦子簸，簸去糠壳磨面再去蒸馍馍，老伯伯把菠萝装进大笸箩，卖了菠萝再去买那香饽饽，忽然一阵风雨雷电似瓢泼，把伯伯婆婆的计划全打破，吹跑了簸箕里的麦子淋湿了磨盘上的面，浇烂了笸箩里的菠萝泡坏了香饽饽。。。。。。老婆婆摸着脖子气得两眼直冒火，老伯伯抡着胳膊急得嗓子赛破锣。 菠萝和萝卜 南面坡过来个老婆婆，俩手托着俩笸箩，北面坡过来个老伯伯，拿着
菠萝和萝卜，老婆婆的俩笸箩装的也是菠萝和萝卜，老伯伯想把菠萝和萝卜也装进老婆婆的俩笸箩。 男民兵女民兵 民兵排民兵多，男女民兵紧急集合奔北坡，男民兵不比女民兵少，女民兵也不比男民兵多。男民兵拉着炮车装填瞄准练习发炮，女民兵挖坑埋药点燃导火索搞爆破。男民兵夸奖女民兵爆破成绩不错，女民兵称赞男民兵射击本领竖起大拇哥。 白平板拜判官 白平板拜判官，城隍庙里为了难。左边拜了王判官，右边又拜了庞判官。也不知是王判官管庞判官呢，还是庞判官管王判官？烧香许愿左顾右盼忙坏了白平板。 板凳和扁担 扁担长，板凳宽，板凳没有扁担长，扁担没有板凳宽，扁担要绑在板凳上，板凳不让扁担绑在板凳上，扁担偏要绑在板凳上。
绑扁担 长扁担比短扁担长半扁担，短扁担比长扁担短半扁担。长扁担和短扁担要绑在板凳上，板凳不能绑比长扁担短半扁担的短扁担，也不能绑比短扁担长半扁担的长扁担。 评标兵 民兵排评标兵，一班的标兵二班的标兵。。。。。。 八班的标兵共评比八名标兵上北京。 以上的绕口令，即纠正喔鹅o,e音的混淆，又是唇音咬字练习的材料。 2、纠正喝佛音混淆（h,f） 唇齿音 h音字例 和好，呵护，合伙，呼唤，互换，互惠，胡混，缓和，欢呼，浩瀚，
链轮参数计算公式
链轮参数计算公式文件管理序列号：[K8UY-K9IO69-O6M243-OL889-F88688]
参数计算公式： :d=p/sin180°/z p=节距可查表 z=齿数 齿顶圆(外径):D=p×(0.54＋cot180°/z) 给你常用链轮节距你自已算算,不明白再问我 3/8=9.525 1/2=12.7 5/8=15.875 3/4=19.05 3分 4分 5分 6分 分度圆直径：d=p/sin（180°/z） ：dmax=d+1.25p-d1 dmin=d+（1-1.6/z）p-d1 ：df=d-d1 注：p 链条节距z 链轮齿数d1 链条滚子直径 链轮型号：包含非标链轮（根据客户图纸定制），（美标和公制）。链轮常用材料：C45 链轮常用加工方法：淬火处理，表面。 链轮齿数选用的一般原则：
19 齿或以上 一般用于中高转速、正常工作条件下运行的主动链轮。 17 齿 只用于小节距主动链轮。 23 齿或多过23齿 推荐用于有冲击的情况。当速比低时，用高齿数链轮可以大大减少i链节的转动量、链条的拉伸负荷和轴承的负荷。 编辑本段链轮的结构设计 1. 链轮的齿形图1 链轮齿形必须保证链节能平稳自如地进入和退出啮合，尽量减少啮合时的链节的冲击和接触应力，而且要易于加工。 常用的链轮端面齿形 1。它是由三段圆弧aa、ab、cd和一段直线bc构成，简称三圆弧-直线齿形。齿形用标准刀具加工，在链轮工作图上不必绘制端面齿形，只需在图上注明"齿形按3RGB1244-85规定制造"即可，但应绘制链轮的轴面齿形，见图2，其尺寸参阅有关设计手册。参数计算前面已经提到，不做重复叙述！ 2. 链轮结构
气息练习与播音主持初级绕口令
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12、陈是陈，程是程，姓陈不能说成姓程，姓程也不能说成姓陈。禾旁是程，耳朵是陈。程陈不分，就会认错人。 13、人寻铃声去找铃，铃声紧跟人不停，到底是人寻铃，还是铃 寻人。 14、风吹灰飞，灰飞花上花堆灰。风吹花灰灰飞去，灰在风里飞 又飞。 15、笼子里有三凤，黄凤红凤粉红凤。忽然黄凤啄红凤，红凤反 嘴啄黄凤，粉红凤帮啄黄凤。你说是红凤啄黄凤，还是黄凤啄红凤。 16、丰丰和芳芳，上街买混纺。红混纺，粉混纺，黄混纺，灰混纺。红花混纺做裙子，粉花混纺做衣裳。穿上衣裳多漂亮，丰丰和芳 芳乐得喜洋洋。 17、河上是坡，坡下是河。坡上立着一只鹅，鹅低头望着一条河，宽宽的河，肥肥的鹅，鹅过河，河渡鹅。河坡飞来丹顶鹤，鹤望河与鹅，小鹤笑呵呵，不知鹅过河还是河渡鹅。来_源：考试大_教师资格 证考试_考试大
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3. 压死边．此种折弯也须用特殊模来完成．（如图４） 4．大Ｒ圆弧折弯。些种折弯如Ｒ在一定围，可用专用Ｒ模压成形，如Ｒ值过大，则须用小Ｒ模多次压制成形。 （如图５） 图５ 这四种折弯的展开计算是不同的。因此在看图时，要根据零件的折弯尺寸来确定使用何种折弯方法。一般使用的ＮＣ数控折弯设备都是日本ＡＭＡＤＡ（天田）公司所生产的。其折弯机所配套的普通通用折弯模具Ｖ形槽宽度通常为适用该折弯模的板厚的５－６倍．如采用一次折一道弯的方法，必须考虑到折弯模的Ｖ形槽的宽度Ｗ１及Ｖ形槽一边到模具外侧的宽度Ｌ１。如图６： 折弯高度Ｈ的经验值根据产品形状有如下三种（以９０度为例，钝角和锐角与直角相近相似）：１．简单的９０度单边折弯。（如图７） 如图７，此种折弯只需考虑下模Ｖ形槽中心到折弯机定位挡块的距离即可确定．通常Ｈ值为Ｈ≥3.5 T+R (R 在１mm 以下) ２．Ｕ形折弯．
钣金展开相关知识及计算方法
钣金展开相关知识及计算方法 一、展开计算原理 板料在弯曲过程中外层受到拉应力，内层受到压应力，理论上内外层之间有一既不受拉也不受压的过渡层------中性层，中性层为一假想层，在弯曲过程中中性层被假想为与弯曲前状态保持一致，即长度始终不变，所以中性层是计算弯曲件长度的基准。中性层位置与变形程度有关，当弯曲半径较大，折弯角度较小时，变形程度较小，中性层位置靠近板料厚度的中心处；当弯曲半径变小，折弯角度增大时，变形程度随之增大。中性层位置逐渐向弯曲中心的内侧移动。中性层到板料内侧的距离用Ａ表示。（图１） 二、折弯方法的确定 折弯方法有单发冲床模具折弯和折弯机模具折弯两种方法。单发冲床模具折弯的方式及精度是由模具来实现的。因此只要做出合格的模具，就能够生产出合格的折弯产品。而采用折弯机折弯不仅需要选用合适的折弯模，还必须调试折弯参数。因此，如采用折弯机折弯，计算展开尺寸时就必须考虑折弯机的折弯方法。 1.一次一道弯。此种折弯由普通通用折弯模来完成。包括折直角，钝角和锐角。（如图２） 2. 一次折两道弯--------压锻差。此种折弯由专用特殊模来完成，但折弯难度比普通折弯大。（如图３）
3. 压死边。此种折弯也须用特殊模来完成。（如图４） 4.大Ｒ圆弧折弯。些种折弯如Ｒ在一定范围内，可用专用Ｒ模压成形，如Ｒ值过大，则须用小Ｒ模多次压制成形。（如图５） 图５ 这四种折弯的展开计算是不同的。因此在看图时，要根据零件的折弯尺寸来确定使用何种折弯方法。一般使用的ＮＣ数控折弯设备都是日本ＡＭＡＤＡ（天田）公司所生产的。其折弯机所配套的普通通用折弯模具Ｖ形槽宽度通常为适用该折弯模的板厚的５－６倍。如采用一次折一道弯的方法，必须考虑到折弯模的Ｖ形槽的宽度Ｗ１及Ｖ形槽一边到模具外侧的宽度Ｌ１。如图６： 折弯高度Ｈ的经验值根据产品形状有如下三种（以９０度为例，钝角和锐角与直角相近相似）：
五金钣金展开计算参数
1. 目的：为完善作业标准，制订本文件。 2. 范围：适用于本公司设计部门之作业。 3. 职责：针对设计计算展开统一计算参数。 4. 内容： 展开计算原理 板料在弯曲过程中外层受到拉应力，内层受到压应力，从拉到压之间有一既不受拉力又不受压力的过渡层一中性层，中性层在弯曲过程中的长度和弯曲前一样，保持不变，所以中性层是计算弯曲件展开长度的基准。中性层位置与变形程度有关，当弯曲半径较大，折弯角度较小时，变形程度较小，中性层位置靠近板料厚度的中心处，当弯曲关径弯小，折弯角度增大时，变形程度随之增大，中性层位置逐渐向弯曲中收的内侧移动，中性层到板料内侧的距离用入表示 展开的基本公式： 展开长度=料内+料内+补偿量 4.1中性层系数 注明：K1适用于有顶底的V形或U形弯曲，K2适用于无顶底的V形弯曲?但通常我们习惯取K2值。 4.2压弯90度角的修正系数a值 注明：此数据可单独用于90度角的折弯修正，也可与中性层系数互相检查核对。 4.3其余图形展开计算方法：
r/t W0.5时，均可按90度清角计算展开长度展开注意事项为了防止产品展开过程中的失误，造成下料模的多次修改，特制定下料模的制作方式. (1) .凡对一些展开存在不确定因素的产品，例如，有拉伸性质的展开，多次折弯，Z折，有拉料现象 等产品的下料模，经工程分析有必要先试模的，其制作方式如下： A. 下料模的模板先不完全加工完毕，先完成机加及热处理部分，线割部分暂缓加工. B. 成型模先做，试模时先镭射(按下料模展开尺寸)试模，产品先做实测，不合格时修正展开尺寸再镭射，一直 修到合格为止，合格样品送客户先承认. C. 样品经客户承认后，按修正展开尺寸整理下料模，进行下料模的线割加工. (2) .对展开较直观的，可基本控制的产品，一般只要经俩人展开核对无误，下料模可按正常方式加工
普通话声母发音要领及训练bpmf
莱芜市莱城区“声之魅”体验之旅 ——声母的魅力 （一）普通话声母发音要领及训练b双唇不送气清塞音 【发音要领】 双唇闭合的同时软腭上声，关闭鼻腔通路，气流到达双唇后蓄气，使气息停留在闭合的双唇后面，凭借积蓄在口腔中的气流突然打开双唇，发出声音。 【发音训练】 单音节： 北(běi)博(bó)包(bāo)背(bèi)办(bàn) 播(bō)班(bān)部(bù)把(bǎ)标(biāo) 双音节： 被捕(bèibǔ)北部(běibù)背部(bèibù)颁布(bānbù) 半部（bànbù）斑驳（bānbó）不变（búbiàn） 必备(bìbèi)辨别(biànbié) 四音节： 不依不饶(bùyībùráo)兵不厌诈(bīngbúyànzhà) 自我标榜(zìwǒbiāobǎng)不言不语(bùyánbùyǔ) 不知不觉(bùzhībùjué)半斤八两(bànjīnbāliǎng) 绕口令： 八百标兵奔北坡，北坡炮兵并排跑。 炮兵怕把标兵碰，标兵怕碰炮兵炮。 p双唇送气清塞音
【发音要领】 p的发音与b的发音基本相同，区别在于p音在最后要发出时，声门开启，从肺部呼出较强气流，用力冲破双唇，发出声音。 【发音训练】 单音节： 评(píng)篇(piān)破(pò)剖(pōu)牌(pái) 胖(pàng)碰(pèng)怕(pà)趴(pā)批(pī) 双音节： 乒乓(pīngpāng)品牌(pǐnpái)批评(pīpíng)匹配(pǐpèi) 翩翩(piānpiān)皮袍(pípáo)枇杷(pípa)噼啪(pīpā) 婆婆(pópo) 四音节： 怕疼怕痒(pàténgpàyǎng)疲于奔命(píyúbēnmìng) 披星戴月(pīxīngdàiyuè)披荆斩棘(pījīngzhǎnjí) 普天同庆(pǔtiāntōngqìng)品头论足(pǐntóulùnzú) 绕口令： 碰碰车，车碰碰，坐着朋朋和平平。 平平开车碰朋朋，朋朋开车碰平平。 不是平平碰朋朋，就是朋朋碰平平。 m双唇浊鼻音 【发音要领】 双唇闭合，软腭上垂，打开鼻腔通路，声带振动，气流同时到达口腔和鼻腔，在口腔的双唇后面受到阻碍，气流由鼻孔出来，发出声音。 【发音训练】
练习发音的绕口令
练习发音的绕口令 想要念好绕口，其实发音是一个非常重要的关键。以下是小编整理的关于练习发音的绕口令，欢迎大家阅读!更多资讯请关注绕口令栏目! 一、韵母部分 (一)十三辙 1、发花辙：韵母包括a、ua、ia。 举例：(1)八百标兵奔北坡，炮兵并排北边跑。标兵怕把标兵碰，标兵怕碰炮兵炮。 (2)打南边来了个喇嘛，手里提拉着五斤鳎犸。打北边来了个哑巴，腰里别着个喇叭。 南边提拉着鳎犸的喇嘛要拿鳎犸换北边别喇叭哑巴的喇叭。 哑巴不愿意拿喇叭换喇嘛的鳎犸，喇嘛非要换别喇叭哑巴的喇叭。 喇嘛抡起鳎犸抽了别喇叭哑巴一鳎犸，哑巴摘下喇叭打了提拉着鳎犸的喇嘛一喇叭。也不知是提拉着鳎犸的喇嘛抽了别喇叭哑巴一鳎犸，还是别喇叭哑巴打了提拉着鳎犸的喇嘛一喇叭。只知道：喇嘛炖鳎犸，哑巴嘀嘀哒哒吹喇叭。 2、梭波辙：韵母包括：e、o、uo。 举例：(1)哥挎瓜筐过宽沟，赶快过沟看怪狗。光看怪瓜筐扣，瓜滚筐空哥怪狗。
(2)瓜棚挂瓜，瓜挂瓜棚。风刮瓜，瓜碰棚。风刮棚，棚碰瓜。 (3)坡上立着一只鹅，坡下就是一条河。宽宽的河，肥肥的鹅，鹅要过河，河要渡鹅，不知是鹅过河，还是河渡鹅。 3、乜斜辙：韵母包括ê、ie、üe。 举例：(1)杰杰和姐姐，花园里面捉蝴蝶。杰杰去捉花中蝶，姐姐去捉叶上蝶。 (2)孩子是孩子，鞋子是鞋子，孩子不是鞋子，鞋子不是孩子。是孩子穿鞋子，不是鞋子穿孩子。谁分不清鞋子和孩子，谁就念不准鞋子和孩子。 4、一七辙：i、ü、er。 举例：(1)闲来没事出城西，瞧见了一个蝈蝈一个蛐蛐吹牛皮。蝈蝈说：在南山我一嘴吃了一只斑斓虎。蛐蛐说：在北山我两嘴吃了两只活叫驴。 (2)王七上街去买席清早起来雨稀稀，王七上街去买席。骑着毛驴跑得急，捎带卖蛋又贩梨。一跑跑到小桥西，毛驴一下跌了蹄。打了蛋，撒了梨，跑了驴，急得王七眼泪滴，又哭鸡蛋又骂驴。 5、姑苏辙：韵母是u。 举例：(1)出南门，走七步，拾块麂皮补皮裤。是麂皮，补皮裤，不是麂皮，不必补皮裤。 (2)胡苏夫和吴夫苏胡庄有个胡苏夫，吴庄有个吴夫苏。胡庄的胡苏夫爱读诗书，吴庄的吴夫苏爱读古书。胡苏夫的书屋里摆满了诗书，吴夫苏的书屋里放满了古书。 6、怀来辙：韵母是ai和uai。
链轮参数计算公式
链轮参数计算公式： 分度圆直径:d=p/sin180°/z p=节距可查表z=齿数 齿顶圆(外径):D=p×(0.54＋cot180°/z) 给你常用链轮节距你自已算算,不明白再问我 3/8=9.525 1/2=12.7 5/8=15.875 3/4=19.05 3分4分5分6分 分度圆直径：d=p/sin（180°/z） 齿顶圆直径：dmax=d+1.25p-d1 dmin=d+（1-1.6/z）p-d1 齿根圆直径：df=d-d1 注：p 链条节距z 链轮齿数d1 链条滚子直径 链轮型号：包含非标链轮（根据客户图纸定制），标准链轮（美标和公制）。 链轮常用材料：C45 链轮常用加工方法：淬火处理，表面发黑处理。 链轮齿数选用的一般原则： 19 齿或以上 一般用于中高转速、正常工作条件下运行的主动链轮。 17 齿 只用于小节距主动链轮。 23 齿或多过23齿 推荐用于有冲击的情况。当速比低时，用高齿数链轮可以大大减少i链节的转动量、链条的拉伸负荷和轴承的负荷。 编辑本段滚子链链轮的结构设计 1. 链轮的齿形图1 链轮齿形必须保证链节能平稳自如地进入和退出啮合，尽量减少啮合时的链节的冲击和接触应力，而且要易于加工。 常用的链轮端面齿形 1。它是由三段圆弧aa、ab、cd和一段直线bc构成，简称三圆弧-直线齿形。齿形用标准刀具加工，在链轮工作图上不必绘制端面齿形，只需在图上注明"齿形按3RGB1244-85规定制造"即可，但应绘制链轮的轴面齿形，见图2，其尺寸参阅有关设计手册。参数计算前面已经提到，不做重复叙述！ 2. 链轮结构 小直径链轮一般做成整体式，中等直径链轮多做成辐板式，为便于搬运、装卡和减重，在辐板上开孔，大直径链轮可做成组合式，此时齿圈与轮芯可用不同材料制造！例如C45，不锈钢等材料。 3. 链轮材料 链轮材料应保证轮齿有足够的强度和耐磨性，故链轮齿面一般都经过热处理，使之达到一定硬度。
钣金件的展开计算---准确计算
钣金中的展开计算 一、钣金的计算方法概论 钣金零件的工程师和钣金材料的销售商为保证最终折弯成型后零件所期望的尺寸，会利用各种不同的算法来计算展开状态下备料的实际长度。其中最常用的方法就是简单的―掐指规则‖，即基于各自经验的算法。通常这些规则要考虑到材料的类型与厚度，折弯的半径和角度，机床的类型和步进速度等等。 总结起来，如今被广泛采纳的较为流行的钣金折弯算法主要有两种，一种是基于折弯补偿的算法，另一种是基于折弯扣除的算法。 为了更好地理解在钣金设计的计算过程中的一些基本概念，先了解以下几点： 1、折弯补偿和折弯扣除两种算法的定义，它们各自与实际钣金几何体的对应关系 2、折弯扣除如何与折弯补偿相对应，采用折弯扣除算法的用户如何方便地将其数据转换到折弯补偿算法 3、K因子的定义，实际中如何利用K因子，包括用于不同材料类型时K因子值的适用范围 二、折弯补偿法
为更好地理解折弯补偿，请参照图1中表示的是在一个钣金零件中的单一折弯。图2是该零件的展开状态。 折弯补偿算法将零件的展开长度(LT)描述为零件展平后每段长度的和再加上展平的折弯区域的长度。展平的折弯区域的长度则被表示为―折弯补偿‖值(BA)。因此整个零件的长度就表示为方程(1)：LT = D1 + D2 + BA (1) 折弯区域（图中表示为淡***的区域）就是理论上在折弯过程中发生变形的区域。简而言之，为确定展开零件的几何尺寸，让我们按以下步骤思考： 1、将折弯区域从折弯零件上切割出来 2、将剩余两段平坦部分平铺到一个桌子上 3、计算出折弯区域在其展平后的长度 4、将展平后的弯曲区域粘接到两段平坦部分之间，结果就是我们需要的展开后的零件
英语发音练习绕口令大全
英语发音练习绕口令大全 导语：现在很多人都用通过绕口令的方式练习英语发音，下面###跟大家分享一些英语绕口令练习，以供参考! 1、A box of biscuits, a batch of mixed biscuits. 一盒饼干，一炉杂饼干。 2、Never trouble about trouble,until troubles troubles you. 从不自找麻烦,直到麻烦来麻烦你。 Can you can a can as a canner can can a can? 你能够像罐头工人一样装罐头吗? 3、bloke's back bike brake block broke. 一个家伙的脚踏车后制动器坏了。 英语发音绕口令练习 4、Knife and a fork, bottle and a cork, that is the way you spell New York. 刀子和叉子，瓶子和木塞，这是你拼写纽约的方法。 5、If you notice this notice you will notice that this notice is not worth noticing. 若你看到这张告示，你会发现这张告示是不直得留意的。 6、I thought a thought. But the thought I thought wasn't the thought I thought I thought.
我思考一个问题。不过，我所思考的问题并不是我认为自己正在思考的问题。 7、A tidy tiger tied a tie tighter to tidy her tiny tail. 一只老虎将领带系紧，清洁它的尾巴。 8、Lily ladles little Letty's lentil soup. 莉莉替小历蒂盛小扁豆汤。 9、A big black bug bit a big black bear, made the big black bear bleed blood. 大黑虫咬大黑熊，大黑熊流血了! 10、Give papa a cup of proper coffee in a copper coffee cup. 给爸爸一杯用铜制咖啡杯盛着的正统咖啡。 11、How much wood would a woodchuck chuck if a woodchuck could chuck wood? He would chuck, he would, as much as he could, and chuck as much wood as a woodchuck would if a woodchuck could chuck wood. 假如一只美洲旱獭能够扔掉木头，它可扔掉多少木头呢?它会扔掉，它会，尽全力把木头扔掉。假如一只美洲旱獭能够扔掉木头，它 会尽全力扔掉一只美洲旱獭能扔的木头。 12、Fred fed Ted bread, and Ted fed Fred bread. 弗雷德喂特德吃面包，特德喂弗雷德吃面包。 13、Flee from fog to fight flu fast. 避开浓雾，感冒会快点痊愈。
折弯展开计算公式
K因子计算方法： K系数是指钣金内边缘之间的距离与钣金厚度之间的比率。通常，金属薄板的外层会受到拉应力的拉伸，而内层会因压应力而缩短。在内层和外层之间有一个纤维层，称为中间层。根据中性层的定义，弯曲部分的毛坯长度应等于中性层的展开长度。因为在弯曲过程中坯料的体积保持不变，所以变形大时中性层将向内移动，这就是为什么不能仅使用横截面的中性层来计算展开长度的原因。如果中性层的位置用P表示（见图1），则可以表示为 其中R为内弯曲半径/ mm；t为材料厚度/ mm；K是中性层位移系数。 图1中性层位置 钣金弯曲的示意图如图2所示。根据中性层展开的原理，毛坯的总长度应等于中性层的直线部分和弧形部分的长度之和。弯曲部分
图2钣金弯曲图 其中，l是零件的总展开长度/ mm；α是弯曲中心角/（°）；L1和L2分别是超出弯曲部分的起点和终点的部分的直线端长度/ mm。 根据以上公式，我们可以计算出确切的弯曲展开长度。可以看出，只要确定参数k，就可以计算出l，并且参数K取决于钣金厚度T和内部弯曲角度R。通常，当R / T为0.1、0.25、0.5时，1、2、3、4、5，≥6，相应的K因子分别为0.23、0.31、0.37、0.41、0.45、0.46、0.47、0.48、0.5-通用零件的R / T值均在1，因此根据上述对应关系计算出的钣金弯曲的展开长度仍然非常准确。对于R / T≥6的情况，金属板在弯曲时不会再次变形，因此中性层等于中心层，并且K因子相应地变为0.5。计算相对容易。唯一的影响是弯曲过程中的回弹问题。这种繁琐的计算最适合计算机完成。下面的三维软件，如AutoCAD，Solidworks，NX，Pro / E，CATIA等也引入了钣金模块，并且K系数已成为这些软件的首选参数，K系数的合理选择大大地减少了流程设计过程中的工作量。
练习发音的绕口令
练习发音的绕口令 本文是关于练习发音的绕口令，仅供参考，希望对您有所帮助，感谢阅读。 一、韵母部分 ( 一) 十三辙 1、发花辙：韵母包括a、ua、ia 。 举例：(1) 八百标兵奔北坡，炮兵并排北边跑。标兵怕把标兵碰，标兵怕碰炮兵炮。 (2) 打南边来了个喇嘛，手里提拉着五斤鳎犸。打北边来了个哑巴，腰里别着个喇叭。 南边提拉着鳎犸的喇嘛要拿鳎犸换北边别喇叭哑巴的喇叭。 哑巴不愿意拿喇叭换喇嘛的鳎犸，喇嘛非要换别喇叭哑巴的喇叭。喇嘛抡起鳎犸抽了别喇叭哑巴一鳎犸，哑巴摘下喇叭打了提拉着鳎犸的喇嘛一喇叭。也不知是提拉着鳎犸的喇嘛抽了别喇叭哑巴一鳎犸，还是别喇叭哑巴打了提拉着鳎犸的喇嘛一喇叭。只知道：喇嘛炖鳎犸，哑巴嘀嘀哒哒吹喇叭。 2、梭波辙：韵母包括：e、o、uo。 举例：(1) 哥挎瓜筐过宽沟，赶快过沟看怪狗。光看怪瓜筐扣，瓜滚筐空哥怪狗。 (2) 瓜棚挂瓜，瓜挂瓜棚。风刮瓜，瓜碰棚。风刮棚，棚碰瓜。 (3) 坡上立着一只鹅，坡下就是一条河。宽宽的河，肥肥的鹅，鹅要过河，河要渡鹅，不知是鹅过河，还是河渡鹅。 3、乜斜辙：韵母包括e、ie、ue。 举例：(1) 杰杰和姐姐，花园里面捉蝴蝶。杰杰去捉花中蝶，姐姐去捉叶上蝶。 (2) 孩子是孩子，鞋子是鞋子，孩子不是鞋子，鞋子不是孩子。是孩子穿鞋子，不是鞋子穿孩子。谁分不清鞋子和孩子，谁就念不准鞋子和孩子。 4、一七辙：i、u、er。 举例：(1) 闲来没事出城西，瞧见了一个蝈蝈一个蛐蛐吹牛皮。蝈蝈说：在南山我一嘴吃了一只斑斓虎。蛐蛐说：在北山我两嘴吃了两只活叫驴。
(2) 王七上街去买席清早起来雨稀稀，王七上街去买席。骑着毛驴跑得急，捎带卖蛋又贩梨。一跑跑到小桥西，毛驴一下跌了蹄。打了蛋，撒了梨，跑了驴，急得王七眼泪滴，又哭鸡蛋又骂驴。 5、姑苏辙：韵母是u。 举例：(1) 出南门，走七步，拾块麂皮补皮裤。是麂皮，补皮裤，不是麂皮，不必补皮裤。 (2) 胡苏夫和吴夫苏胡庄有个胡苏夫，吴庄有个吴夫苏。胡庄的胡苏夫爱读诗书，吴庄的吴夫苏爱读古书。胡苏夫的书屋里摆满了诗书，吴夫苏的书屋里放满了古书。 6、怀来辙：韵母是ai 和uai 。 举例：后来我总算学会了如何去爱，可惜你早已远去消失在人海，后来终于在眼泪中明白，有些人一旦错过就不再。 7、灰堆辙：韵母是ei 和uei(ui) 。举例：贝贝背水杯，水杯贝贝背。贝贝背水杯背背水杯。水杯贝贝背，贝贝背水杯。 8、遥条辙：韵母是ao和iao。 举例：(1) 雕和箫一把雕刀，雕出好箫。刀是小雕刀，箫是“玉屏箫”。好箫出好调，箫靠好刀雕，刀要艺巧高。 (2) 描庙东描庙，西描庙，左描庙，右描庙，调转头来描描庙。前描庙，后描庙。这一描，那一描，描得判官满脸毛。 9、由求辙：韵母是ou 和iu(iou) 。 举例：六十六岁的刘老六，盖了六十六间好高楼，买了六十六篓桂花油，养了六十六头大黄牛，栽了六十六棵垂杨柳。 10、言前辙：韵母是an、ian、uan、uan。举例：搬木板摆木板，摆木板搬木板，摆摆 木板搬木板，搬罢木板摆木板。 先搬木板，后摆木板; 后摆木板，先搬木板。搬木板又摆木板，块块木板搬摆完。 11、人辰辙：韵母有en、in、uen(un)、un。 举例：一平盆面烙一平盆饼，盆平饼，饼平盆
普通话绕口令 声调练习材料
普通话练习绕口令： 声母绕口令 声母的发音部位不同，吐字时的着力点就不一样，比如“b、P、m”，发音时着力点在双唇，“d、t”的着力点在舌尖，靠舌尖的弹力。因此发声母时不要拖长，要咬住、弹开。我们在每段绕绕口令题旁都标有“b、p、m”、“d、t”、“n、l”、“g、k”、“s、sh”等声母字样来说明此段绕口令是专门训练所标声母的绕口令。例如：《八百标兵》一段绕口令题旁标有“b、p”的声母，就说明“b、p”字母在练习过程中是重点训练的内容，训练双唇有力集中。 八百标兵（b、p） 八百标兵奔北坡，炮兵并排北边跑，炮兵怕把标兵碰，标兵怕碰炮兵炮。 炮兵和步兵（b、p、m） 炮兵攻打八面坡，炮兵排排炮弹齐发射。步兵逼近八面坡，歼敌八千八百八十多。 一平盆面（b、p） 一平盆面，烙一平盆饼，饼碰盆，盆碰饼。 巴老爷芭蕉树（b、p） 巴老爷有八十八棵芭蕉树来了八十八个把式要在巴老爷八十八棵芭蕉树下住。巴老爷拔了八十八棵芭蕉树，不让八十八个把式在八十八棵芭蕉树下住，八十八个把式烧了八十八棵芭蕉树，巴老爷在八十八棵树边哭。 老六放牛（n，l） 柳林镇有个六号楼，刘老六住在六号楼。有一天，来了牛老六，牵了六只猴；来了侯老六，拉了六头牛；来了仇老六，提了六篓油；来了尤老六，背了六匹绸。牛老六、侯老六、仇老六、尤老六，住上刘老六的六号楼，半夜里，牛抵猴，猴斗牛，撞倒了仇老六的油，油坏了尤老六的绸。牛老六帮仇老六收起油，侯老六帮尤老六洗掉绸上油，拴好牛，看好猴，一同上楼去喝酒。 颠倒歌（d，t，l） 太阳从西往东落，听我唱个颠倒歌。 天上打雷没有响，地下石头滚上坡; 江里骆驼会下蛋，山里鲤鱼搭成窝; 腊月苦热直流汗，六月暴冷打哆嗦; 姐在房中手梳头，门外口袋把驴驮 白石塔（b，d，t） 白石塔，白石搭，白石搭白塔， 白塔白石搭，搭好白石塔，白塔白又大。 哥挎瓜筐过宽沟（g、k） 哥挎瓜筐过宽沟，赶快过沟看怪狗，光看怪狗瓜筐扣，瓜滚筐空哥怪狗。
金钣金展开计算参数
金钣金展开计算参数 Modified by JACK on the afternoon of December 26, 2020
1.目的：为完善作业标准，制订本文件。 2.范围：适用于本公司设计部门之作业。 3.职责：针对设计计算展开统一计算参数。 4.内容： 展开计算原理 板料在弯曲过程中外层受到拉应力，内层受到压应力，从拉到压之间有一既不受拉力又不受压力的过渡层—中性层，中性层在弯曲过程中的长度和弯曲前一样，保持不变，所以中性层是计算弯曲件展开长度的基准。中性层位置与变形程度有关，当弯曲半径较大，折弯角度较小时，变形程度较小，中性层位置靠近板料厚度的中心处，当弯曲关径弯 小，折弯角度增大时，变形程度随之增大，中性层位置逐渐向弯曲中收的内侧移动，中性层到板料内侧的距离用λ表示. 展开的基本公式： 展开长度=料内+料内+补偿量 4.1中性层系数 注明：K1适用于有顶底的V形或U形弯曲,K2适用于无顶底的V形弯曲.但通常我们习惯取K2值。 4.2压弯90度角的修正系数a值 注明：此数据可单独用于90度角的折弯修正，也可与中性层系数互相检查核对。
4.3其余图形展开计算方法：
4.4当折弯角度为90度，r=0（俗称“90度清角”）时，各材料厚度对应的经验值： r/t≦时，均可按90度清角计算展开长度. 展开注意事项 为了防止产品展开过程中的失误,造成下料模的多次修改, 特制定下料模的制作方式. (1). 凡对一些展开存在不确定因素的产品, 例如, 有拉伸性质的展开, 多次折弯, Z折,有拉料现象 等产品的下料模, 经工程分析有必要先试模的, 其制作方式如下: A.下料模的模板先不完全加工完毕,先完成机加及热处理部分,线割部分暂缓加工.
练口才的绕口令
练口才的绕口令
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练口才的绕口令 练习口齿的伶俐性还是绕口令，不信你试试： 一、扁担宽板凳长 扁担想绑在板凳上 板凳不让扁担绑在板凳上 扁担偏要绑在板凳上 板凳偏偏不让扁担绑在那板凳上 到底扁担宽还是板凳长 二、哥哥弟弟坡前坐 坡上卧著一只鹅 坡下流著一条河 哥哥说宽宽的河 弟弟说白白的鹅 鹅要过河河要渡鹅 不知是那鹅过河 还是河渡鹅 三、有个小孩叫小杜 上街打醋又买布 买了布打了醋 回头看见鹰抓兔 放下布搁下醋 上前去追鹰和兔 飞了鹰跑了兔 洒了醋湿了布 四、嘴说腿腿说嘴 嘴说腿爱跑腿 腿说嘴爱卖嘴 光动嘴不动腿 光动腿不动嘴 不如不长腿和嘴 到底是那嘴说腿还是腿说嘴 怎样用绕口令帮助孩子练习发音 绕口令是一种特殊形式的游戏儿歌，它除了具有语言精炼、有韵律、有节奏、读起来顺口好听、易于熟读背等一般儿歌的特点外，还有意识地使用了一些近似音,读起来不但绕口,而且诙谐、幽默、有趣,对于正处在语言发展关键期的幼儿十分有用。它不但可以帮助孩
子发音,而且还可以丰富孩子的知识，培养良好的品德，活跃生活，增加乐趣。家长或老师如果有意识地每天安排3—5分钟的时间教孩子学说绕口令，就能使孩子说 选择绕口令要根据孩子在发音上的难点及问题。如孩子发不好舌尖前音ｚ、c、s和舌尖后音zh、cｈ、sｈ时可选择《四和十》、《柿子和狮子》等绕口令;如果孩子发不好鼻音“n”与边音“ｌ”时可选择《学捏泥》和《骑鲤鱼》等绕口令。在教孩子学说绕口令时还应注意以下几点: 一、要讲解绕口令的内容，使孩子理解意思。 二、要正确地为孩子做出示范,发音要准,吐字要清。 三、先重点练习发准每一个近似音，使之不但能区分，还会正确运用口形。 四、要鼓励孩子大胆地说，千万不要讥笑和模仿孩子不正确的发音。 五、在一句句领读的基础上，由慢到快，然后逐步提高要求,一直到孩子真正掌握为止。一次掌握不了,可以分2~3次学会、背熟。 六、为了调动幼儿学习绕口令的积极性,父母可以让几个孩子比着说，也可以和爸爸妈妈赛着说,还可以把孩子说的录下来,再放给他们听,让他们自己来总结，哪儿说得好,哪些地方还掌握不准。 附例一: 四和十 四是四,十是十, 十四是十四,四十是四十。 要想说对四和十, 得靠舌头和牙齿。 谁说四十是“戏习”， 谁的舌头没用力； 谁说四十是“事实”， 谁的舌头没伸直。 谁想说对常练习, 四、十、十四和四十。 附例二： 柿子和狮子 树上结了四十四个涩柿子, 树下蹲着四十四只石狮子。
普通话发音训练绕口令小学版
第一关：双唇音b 和p 1. 发音方法 双唇音b 的发音:发音时，双唇紧闭，然后突然打开，气流爆发出来，声带不振动。双唇音p 的发音:发音方法与b 基本相同,不同之处是冲出的气流比b 要强一些。 2. 词语练习 b 奔bēn 波bō 摆bǎi 布bù 八bā拜bài 之zhī交jiāo p 乒pīng 乓 pāng 批pī评píng 旁páng 若ruò无wú人rén b -p 被bèi 迫pò 爆bào 破pò 编biān 排pái 3. 绕口令练习 买mǎi 饽饽 bō bo (b 、p ) 白伯伯bái bó bo ，彭 伯伯péng bó bo ，饽bō饽bo 铺pù里lǐ买mǎi 饽bō饽bo 。 白伯伯bái bó bo 买mǎi 的de 饽饽bō bo 大dà，彭伯伯péng bó bo 买mǎi 的de 大dà饽饽bō bo 。 拿ná到dào 家jiā里lǐ给gěi 婆pó婆po ，婆pó婆po 又yòu 去qù比bǐ饽bō饽bo 。 不bù知zhī白bái 伯bó伯bo 买mǎi 的de 饽bō饽bo 大dà ， 还hái 是shì彭péng 伯bó伯bo 买mǎi 了le 个gè大dà饽bō饽bo 。
第二关：唇齿音f 和舌根音h 1. 发音方法 虽然这两个声母发音时差别比较大，但仍有--些小朋友无法正确区分。最主要的原因是在读字词、短句的过程中,无法立刻转换发音部位而造成的。发f 时是上齿和下唇接触发出,而h 是舌根和软腭接触发出。 2. 词语练习 f 仿fǎn g 佛fú 反fǎn 复fù 发fā人rén 深shēn 省 xǐng h 呼hū唤huàn 黄huáng 昏hūn 海hǎi 纳nà百bǎi 川chuān h -f 话huà费fèi 凤fèng 凰 huáng 发fā挥huī 3. 绕口令练习 买mǎi 混纺 hùn fǎng (h 、f ) 丰fēng 风 fēng 和hé芳fāng 芳 fāng ，上 街shàng jiē买mǎi 混纺 hùn fǎng 。 粉红fěn hóng 混纺 hùn fǎng ，黄huáng 混纺 hùn fǎng ，灰huī混纺hùn fǎng 。 红hóng 花 huā混 hùn 纺 fǎng 做zuò裙子qún zi ，粉fěn 花huā混纺hùn fǎng 做zuò衣裳 yī shang 。 红hóng 、粉fěn 、灰huī、黄huáng 花 huā样 yàng 多 d uō ， 五wǔ颜yán 六liù色sè好hǎo 混hùn 纺fǎng 。