Effect of Pore Structure in Mesoporous Silicas on VOC Dynamic Adsorption Desorption Performance
Effect of Pore Structure in Mesoporous Silicas on VOC Dynamic
Adsorption/Desorption Performance
Katsunori Kosuge,*Shiori Kubo,Nobuyuki Kikukawa,and Makoto Takemori
Research Institute for En V ironmental Management Technology,National Institute of Ad V anced Industrial Science and Technology,16-1Onogawa,Tsukuba,Ibaraki,305-8569Japan
Recei V ed September7,2006
The dynamic adsorption/desorption behavior of volatile organic compounds(VOCs)such as toluene(C7H8)and benzene(C6H6)was evaluated for three kinds of mesoporous silicas of SBA-15,all having almost the same mesopore size of ca.5.7nm,and a MCM-41silica with a smaller pore size of2.1nm using a continuous three-step test.The fiberlike SBA-15silica exhibited exceptionally good breakthrough behavior,a higher VOC capacity,and easier desorption.The fiberlike silica was composed through the catenation of rodlike particles.The rodlike silicas,by comparison,were proven to be less useful in dynamic adsorption processes because of lower dynamic VOC capacities despite having comparative porous parameters with the fiberlike silica.The large dynamic VOC capacity of the fiberlike silica was attributed to the presence of a bimodal pore system consisting of longer,one-dimensional mesopore channels connected by complementary micropores.
Introduction
The removal of volatile organic compounds(VOCs)prior to their emission into the atmosphere is a serious challenge in many industrial processes.1-4Sorption is a proven and reliable chemical engineering method that provides the additional benefit of recovering valuable VOCs for reuse.The most common concentration range for VOCs emitted in most industrial processes is in the low-pressure region below2000ppm,in which microporous adsorbents with a pore size of less than2nm are desirable for their practical dynamic adsorption properties.To these ends,activated carbons are the most widely used materials. However,activated carbons have the drawbacks of added fire risk,pore clogging,hygroscopicity,and a lack of regenerative ability.For these reasons,it is important to investigate the adsorption/desorption performance of other types of microporous adsorbents such as zeolites,2,3,5-7silica gels,8,9and mesoporous silicas.10-20
Mesoporous silicas with high surface areas have attracted a great deal of attention due to their wide range of application as adsorbents for environmentally hazardous chemicals,reaction catalysts,catalyst supports,chemical sensors,and electrical and optical devices.21Mesoporous silicas have great potential for application as adsorbents for the removal of VOCs given their uniform pore size,open pore structure,and in particular,reliable desorption performance.However,studies on the dynamic adsorption/desorption performance of mesoporous silicas in regards to VOCs have been very limited in comparison to those on their adsorption equilibria.14,20Although the saturation adsorption capacity for mesoporous silicas is high,the adsorption capacity is considerably lower in the low-pressure range.
It is well known that mesoporous silicas obtained through triblock copolymer templating such as SBA-15have comple-mentary micropores in the silica walls connecting the primary one-dimensional(1D)mesopore channels to form a well-ordered 2D hexagonal array.22These coexisting pore structures of mesopores and micropores have been called a“bimodal pore system”.22a,23SBA-type mesoporous materials with this bimodal pore system are expected to be ideal as catalysts and adsorbents. Previous work from other research groups has indicated that SBA-15-type mesoporous silicas have a high affinity for various
*To whom correspondence should be addressed.Phone:+81-29-861-8179.Fax:+81-29-861-8459.E-mail:k.kosuge@aist.go.jp.
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10.1021/la062616t CCC:$37.00?xxxx American Chemical Society
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VOCs due to their complementary micropores.Examples have included a high selectivity for benzene 19and a high affinity for light hydrocarbon adsorption.17a Additionally,the presence of strong adsorption sites for toluene 13and for ethylene and ethane in these types of silicas have been observed.17b A plugged hexagonal-templated silica proved to be a better adsorbent for some alkanes than SBA-15on the basis of the larger amount of micropores embedded into the mesopores in this particular silica.24In addition,an investigation into the diffusion process using the zero length column (ZLC)method revealed that the diffusion of n -heptane adsorbed under low pressures occurs entirely through the micropores of SBA-15.25However,most of the previous studies have been confined to an equilibrium state,and any synergetic effect of the bimodal pore system on dynamic adsorption performance has yet to be elucidated.
In the development of practical adsorbents,morphological control at the micrometer level in mesoporous silicas would also be a major factor in helping to avoid the problems associated with low-pressure drops in the reactor.The block copolymer templating method has resulted in a variety of mesoporous SBA-type silicas.26,27Recently,a rodlike SBA-15was shown to play an important role in the immobilization of enzymes in the liquid phase.28Rodlike SBA-15silicas with short mesochannels have attracted attention because they are favorable in mass transfer reactions compared with the conventional fiberlike SBA-15silicas.However,few studies have been conducted on the relationship between macroscopic morphology and dynamic adsorption behavior in the gas phase under low pressures,while means of preparation for various morphological SBA-15silicas and the existence of microporous characteristics in SBA-15silicas have been well established.
The past success our group has had in synthesizing well-defined fiberlike and rodlike SBA-1527has led us to consider attempting to apply these silicas as adsorbents for VOCs.We have observed significant differences in the dynamic VOC adsorption behaviors between the different macroscopic mor-phologies of SBA-15despite nearly the same volumetric porous parameters.In regards to VOC adsorption/desorption behavior,the aim of this study is to determine the synergetic effect between
the macroscopic morphology and bimodal pore system of SBA-15silicas by testing various mesoporous samples with different and/or roughly the same porous parameters.Toluene (C 7H 8)and benzene (C 6H 6)were used as VOCs in this study because both of these compounds are commonly used industrially.It is reported in this study for the first time the remarkably large dynamic adsorption capacity of fiberlike SBA-15under low concentration streams.
Experimental Section
Materials.The samples used in this study were fiberlike and rodlike SBA-15type silicas,which were designated as Fiber A,Rod B,and Rod C,as shown in Table 1.These samples were synthesized using Pluronic P123(EO 20PO 70EO 20)and a sodium silicate solution (SiO 223.6%,Na 2O 7.59%)under acidic conditions.27A sodium silicate solution diluted with deionized water and an acidic mixture of P123dissolved in aqueous HCl were kept separately at 30°C.Fiber A was prepared by the quick mixing of both solutions with continuous magnetic stirring at 600rpm for 6h at a mole composition of SiO 2/P123/HCl/H 2O )1:0.017:5.90:203.For the rodlike silicas,stirring was stopped after 30s of mixing,and the reaction solution was subsequently kept under static conditions for 6h.The corresponding reactant composition for Rod B was SiO 2/P123/HCl/H 2O )1:0.017:7.32:203,in which the amount of HCl was slightly higher,while that for Rod C was almost the same as for that of Fiber A.MCM-41was synthesized according to a procedure described in the literature using sodium silicate and dodecyltrimethylammonium bromide (C 12TMABr),29with a reactant composition of SiO 2/C 12TMABr/H 2SO 4/Na 2O/H 2O )1:0.49:0.14:0.31:70.The resultant MCM-41had small mesopores 2.1nm in size.
Several commercial adsorbents were used for comparison to clarify the unique adsorption/desorption performance of the mesoporous silicas.Sample Q3(CARiACT Q-3,Fuji Silysia Chemical Ltd.)is a spherical silica gel with 75-150μm diameter spheres having both micro-and mesopores.HY (HSZ-320HOA,Toso Co.)is a powdered faujasite-type zeolite with a SiO 2/Al 2O 3molar ratio of 5.7and 3.8wt %Na 2O.AC (LGH006,Takeda Chemical Industries,Ltd.)is a granular activated carbon.HY and AC are typically microporous materials.These commercial samples are also presented in Table 1,according to the abbreviations of the sample names used in this report.
Characterization.The N 2sorption isotherms were measured at -196°C on a BELSORP 28under continuous adsorption conditions.The C 7H 8and C 6H 6sorption isotherms were obtained at 25°C on a BELSORP 18.Prior to measurement,all samples were heated at 200°C for 2h and then outgassed to 10-3Torr at room temperature.Powder X-ray diffraction (XRD)patterns were obtained with a Rigaku Rotaflex diffractometer equipped with a rotating anode using Cu
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Table 1.Porous Properties and VOCs’Adsorption/Desorption Performance of Various Adsorbents a
volumetric adsorption properties
dynamic adsorption properties
porous parameters by N 2sorption isotherms
C 7H 8
C 6H 6
sample name S BET (m 2/g)V total (mL/g)V micro (mL/g)D pore (nm)volumetric C 7H 8capacity (mL/g)volumetric C 6H 6capacity (mL/g)adsorption capacity He (mL/g)amount
desorbed by TPD (mL/g)desorption ratio by purge (%)adsorption capacity He (mL/g)amount desorbed by TPD (mL/g)desorption
ratio by
purge (%)Fiber A 7300.630.12 5.620.540.520.0420.01370.00.0220.000697.4Rod B 7570.650.11 5.840.520.480.0220.00193.60.010<0.000199.5Rod C 4300.460.02 5.460.420.440.0170.00383.40.004<0.000199.4MCM-4111540.750 2.10.700.660.015<0.00199.80.0060
100Q37250.40--0.360.390.0290.01259.00.0140.000596.4HY 7320.360.360.80.330.330.0580.0538.420.0670.04828.0AC
1146
0.47
0.47
1.86
0.45
0.46
0.110
0.065
40.9
0.077
0.072
6.0
a
S BET ,BET surface area;V total ,V micro ,primary total pore and microporous volume evaluated by the t -plot method,respectively;D pore ,BJH mesopore diameter calculated from the adsorption branch.
B Langmuir
Kosuge et al.
K R radiation.Transmission electron microscopy (TEM)images were obtained with a JEOL 2000FX microscope.
Dynamic VOC adsorption/desorption behavior was evaluated by the following three successive steps:The first step was an adsorption step using breakthrough curves for 2h at 25°C in a mixed gas flow of 500ppm (C 7H 8and C 6H 6)/He(balance)at 50mL/min using a fixed-bed reactor.The second step was a continuous purge with He gas for another 2h under vacuum at ca.150Torr,in which the desorption behavior of the sample was investigated without heat treatment.In the third step,the temperature programmed desorption (TPD)spectra were measured under a He flow at a constant heating rate of 10°C/min.The sample weights were 0.055g for the C 7H 8and 0.065g for the C 6H 6experiments,respectively.The VOC concentration at the outlet was monitored by a mass spectrometer.The dynamic adsorption capacities and the amount desorbed with the heat treatment were obtained by numerical integration of the breakthrough curves and the TPD spectra,respectively.The desorption ratio with the He purge under vacuum was calculated by dividing the difference between the dynamic adsorption capacity and the amount desorbed during the TPD by the former value.
Results and Discussions
Macroscopic Morphologies.Figure 1shows scanning electron microscopy (SEM)images of the SBA-15-type silicas Fiber A,Rods B and C,and MCM-41.As can be seen in Figure 1a,Fiber A consists of a large number of fibers several hundred micrometers in length.Each fiber is formed by the coupling of relatively uniform rodlike particles ca.0.5μm in width and 1μm in length.Figure 2a shows a TEM image of Fiber A in which these rodlike constituents can be seen and elucidates the connected structure of these particles.It can be seen in Figure 2a that 1D mesopore channels ca.5.5nm in diameter run through the long axis of these rods and pass through one rodlike unit to the adjacent one.The rodlike particles of Rod B and Rod C have similar dimensions,as can be seen in panels b and c of Figure 1,respectively.In comparison,MCM-41is an agglomerated solid composed of small platelets less than 1μm in size,as shown in Figure 1d.One can see the characteristic hexagonally arrayed mesopores ca.2nm in size in the TEM image shown in Figure
2b.
Figure 1.Scanning electron microscopy (SEM)images of SBA-15-type silicas of (a)Fiber A,(b)Rod B,(c)Rod C,and (d)MCM-41.Scale bars indicate 50(a)and 1μm (b -
d).
Figure 2.Transmission electron microscopy (TEM)images of (a)Fiber A,showing the rodlike constituents and their connecting portions,and (b)MCM-41,showing the primary rounded nanoparticles ca.200nm in size.The arrows indicate that an individual nanoparticle has a hexagonal ordering of the uniform 1D channels ca.2nm in size.Scale bars indicate 50nm.VOC Dynamic Adsorption/Desorption Performance Langmuir C
Figure 3shows the XRD patterns of Fiber A,Rods B and C,and MCM-41.Fiber A and Rods B and C have almost the same XRD patterns,with intense (100)diffraction peaks and two or more well-resolved peaks (100,110,200),which were indexed as 2D hexagonal symmetry.The corresponding XRD peaks of MCM-41were shifted to a higher diffraction angle due to the smaller mesopore size compared with those of Fiber A and Rods B and C.From the TEM images and the XRD patterns,Fiber A,Rods B and C,and MCM-41were typical mesoporous materials that have an ordered array of cylindrical 1D channels irrespective of their macroscopic morphologies.
Pore Structures.The N 2sorption isotherms of the mesoporous samples are shown in Figure 4A.The sorption isotherms of Fiber A and Rods B and C are similar in shape to type IV in IUPAC classification terms.30,31The steep capillary condensation steps for the SBA-15-type samples occur at almost the same position,indicating that Fiber A and Rods B and C have nearly the same BJH mesopore size of 5.5-5.8nm,as summarized in Table 1.MCM-41also has highly uniform mesopores,as no hysteresis loop can be seen in the region of steep capillary condensation
at the relative pressure of ca.0.2.The BJH pore size of MCM-41was ca.2.1nm,which is very small in terms of mesopores that are defined as having a size of 2-50nm.30In addition,the hysterysis loops of Fiber A and Rods B and C exhibit the same shape as clarified in H1,30b which is typical for open 1D-channel pores.The hysterysis loop of MCM-41observed after capillary condensation above a relative pressure of ca.0.45was attributed to interparticle spaces among the agglomerated platelets,as can be seen in the SEM (Figure 1d)and TEM images (Figure 2b).The N 2sorption isotherms of Fiber A and Rod B are almost superimposed upon each other despite the distinct difference in their macroscopic morphologies,while the amount of N 2adsorbed by Rod C was much lower than those for Fiber A and Rod B,as shown in Figure 4A.The corresponding t -plots 30a are shown in Figure 4B.The micropore volumes of the samples are derived from the y -axis intercept of the extrapolated linear region in these plots.Given this,the micropore volumes of Fiber A and Rod B are nearly the same,and have a relatively large number of micropores compared with Rod C.The absence of micropores in MCM-41is confirmed by the fact that the linear region of the t -plot can be extrapolated to the origin.Table 1lists the porous parameters of the samples such as the BET surface area,total pore volume,pore size,and micropore volume in columns 2-5,respectively.
From the analysis of the N 2sorption isotherms along with the XRD patterns and TEM images,it can be concluded that the differences in BET surface areas among Fiber A and Rods B and C are attributable to their micropore volumes.MCM-41has a large BET surface area because of a narrower mesopore size.These data were used for the schematic structure units of Fiber A,Rods B and C,and MCM-41shown in panels a -d of Figure 5,respectively.Each rodlike unit having an ordered array of cylindrical 1D channels is stacked in a well-ordered 2D hexagonal array,drawn as black hexagons.The rodlike units of Fiber A (Figure 5a)and Rod B (Figure 5b)have almost the same number of micropores,which are drawn as small black circles in the white silica walls.The unit structure of Fiber A is formed by the coupling of the unit structures for Rod B.The structural units of Rod C have almost the same dimensions as those of Rod B,although the micropores of Rod C are fewer in number (Figure 5c).MCM-41is composed of smaller hexagons with smaller mesopores and no micropores in the silica walls (Figure 5d).The complementary micropores in the silica walls of Fiber A and Rods B and C are derived from the molecular templating of hydrophilic EO chains.21A higher concentration of HCl increases the hydrophilicity of EO moieties favoring a stronger interlinkage between the hydrophilic EO blocks and the silica species during solidification.This reaction pathway leads to more micropores in the final products and explains the higher number of micropores in Rod B as compared with Rod C.Fiber A and Rod C were synthesized from the same reaction mixture,the only difference being with or without continuous stirring,respectively.Previous work has indicated that shearing flow can cause a larger micropore number,like that in Fiber A,due to easier EO block extension into the silicate framework.27
Volumetric VOC Adsorption.The C 7H 8and C 6H 6sorption isotherms of Fiber A,Rods B and C,and MCM-41are shown in panels A and B of Figure 6,respectively.The corresponding isotherms of commercial samples are presented together with their N 2isotherms in the Supporting Information (Figure S1).Like the N 2isotherms,both of the VOC sorption isotherms of the mesoporous materials were classified into type IV.The region of capillary condensation for the VOCs,however,was
(30)(a)Gregg,S.G.;Sing,K.S.W.Adsorption Surface Area and Porosity ,2nd ed.;Academic Press:New York,1982.(b)Sing,K.S.W.;Everett,D.H.;Haul,R.A.W.;Moscou,L.;Pierotti,R.A.;Rouquerol,J.;Siemienewska,T.Pure.Appl.Chem.1985,57,603.
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2908.
Figure 3.Powder X-ray diffraction patterns of SBA-15-type silicas of (a)Fiber A,(b)Rod B,(c)Rod C,and (d)MCM-41.A part of the pattern for all samples is presented at five
magnifications.
Figure 4.Nitrogen sorption isotherms (A)and the corresponding t -plots (B)of Fiber A (O ),Rod B (3),Rod C (0),and MCM-41(]).The open and closed symbols are for the adsorption and desorption branches,respectively.
D Langmuir Kosuge et al.
shifted to a lower relative pressure with increasing molecular size:nitrogen (0.42nm),benzene (0.73nm),and toluene (0.85nm).31
The volumetric C 7H 8and C 6H 6capacities of the samples are presented in columns 6and 7in Table 1,respectively.Little difference was observed in the VOC capacities for the same adsorbent material,both for the mesoporous silicas and the commercial samples.As can be seen in Figure 7A,a strong correlation exists between the total pore volume and the volumetric VOC capacity.However,the volumetric VOC capacity shares no relationship with the micropore volume,as presented in Figure 7B.This observation indicates that in the case of physical adsorption the volumetric VOC capacity is determined neither by the pore network nor the pore size,but rather by the total pore volume.
Dynamic Adsorption/Desorption Behavior.The actual adsorption processes of VOCs are in many cases associated with adsorption using a fixed bed in which adsorbents are packed,into which fluid with some VOC content at a lower relative
pressure flows.In our study,both VOC concentrations were ca.500ppm and the relative pressures were 3.9×10-3and 11.1×10-3for benzene and toluene,respectively.
A breakthrough measurement is a direct method designed to make clear the dynamic performance of VOC adsorption at low concentrations.Panels A and
B of Figure 8show the
C 7H 8and C 6H 6breakthrough curves of Fiber A,Rods B and C,and MCM-41,respectively.The corresponding curves of the commercial adsorbents,Q3,HY,and AC,are shown in the Supporting Information (Figure S2).
In general,the longer the breakthrough time is,the higher the dynamic adsorption capacity becomes.Additionally,a more rapid increase in the curve after the breakthrough means less resistance in intraparticle mass transfer.Normally,AC has a high dynamic adsorption capacity,as shown in the Supporting Information (Figure S2).However,in this study,the concentration of C 7H 8and C 6H 6increased gradually with time,indicating a very large mass transfer resistance for AC.Figure S2also shows that
the
Figure 5.Schematic drawings of the structural units of Fiber A (a),Rod B (b),Rod C (c),and MCM-41(d).All of the synthetic samples have an ordered array of cylindrical 1D channels stacked in a well-ordered 2D hexagonal array drawn as black hexagons.The mesopore sizes of Fiber A,Rod B,and Rod C are nearly the same,5.7nm.Micropores are drawn as small black circles in the white silica walls.Fiber A was formed through the coupling of the rodlike particles of Rod B,all having a relatively uniform size.Furthermore,Fiber A and Rod B have almost the same porous parameters,indicating that both samples have comparable micropore volumes.The micropores of Fiber A and Rod B penetrate the silica walls into adjacent mesopores or to the exterior of the structure.There are fewer micropores in Rod C.MCM-41has no micropores,although the mesopore size is close to the maximum diameter of micropores,2
nm.
Figure 6.VOC sorption isotherms of (A)C 7H 8and (B)C 6H 6of Fiber A (O ),Rod B (3),Rod C (0),and MCM-41(]).The open and closed symbols are for adsorption and desorption branches,
respectively.
Figure 7.Relationship between (A)the total pore volume and volumetric VOC capacity and (B)the micropore volume and volumetric VOC capacity for all samples including the commercial adsorbents.The circles represent C 7H 8(O )and the triangles represent C 6H 6(4).
VOC Dynamic Adsorption/Desorption Performance Langmuir E
samples Q3and HY exhibited short breakthrough times for both VOCs,while the dynamic VOC capacities of HY,as well as AC,were somewhat larger than those of the mesoporous samples due to the gradual increase in the amount adsorbed after the breakthrough.
The breakthrough curves of Fiber A have an exceptionally good shape,2as shown in Figure 8A for C 7H 8and Figure 8B for C 6H 6,exhibiting a long breakthrough time and a rapid increase after the breakthrough compared with the other mesoporous materials and the samples Q3and HY.However,the VOC capacities of Rod B were lower than those of Fiber A,even though both samples have very similar porous parameters.The breakthrough of Rod C,whose mesopore size is slightly smaller (5.46nm)than that of Rod B (5.84nm),occurred just seconds after the start of C 7H 8exposure,indicating that it has too few micropores and at the same time too large a mesopore size to have a clear breakthrough point.On the other hand,MCM-41shows a clear breakthrough (Figure 8A and B)but has a lower breakthrough capacity in spite of its large volumetric capacity.The dynamic adsorption capacities for C 7H 8and C 6H 6of the samples evaluated here are summarized in columns 7,10,and 12in Table 1.Figure 9A and B depicts the relationships between the respective micropore volumes and total pore numbers and the dynamic VOC capacities for all samples including the commercial adsorbents listed in Table 1.Figure 9B indicates
that adsorbents with a larger volumetric capacity do not necessarily have a larger breakthrough capacity.Figure 9A reveals that the presence of micropores directly lead to an increase in the dynamic capacity for these VOCs and is therefore an essential factor in determining the dynamic capacity of adsorbents.Micropores are primarily responsible for the adsorption of gas molecules at low concentrations due to the overlap of attractive forces from opposing pore walls.30A previous study demonstrated that a decrease in the pore size of MCM-41silicas from mesopores (3nm)to micropores (1.35nm)led to a dramatic increase in the dynamic adsorption performance for low concentrations of benzene.20However,it must be noted that the dynamic VOC adsorption capacities are extremely small with respect to both the total pore volumes and the micropore volumes,as listed in Table 1.
In addition,from Table 1and Figure 8it is clear that the dynamic adsorption capacity of every sample is higher for C 7H 8than for C 6H 6except for HY.This difference may be due to the differences in the relative pressures of 11.1×10-3for C 7H 8and 3.9×10-3for C 6H 6.32Another possibility for this difference may lie in the molecular differences between the two VOCs.33It is well known that,in most cases for silica-based adsorbents,the silanol groups (t Si -O -H)on the pore surfaces act as the adsorption sites for various molecules.9,10The C 7H 8and C 6H 6vapor adsorption by silica occurs through weak π-system hydrogen bonding with silanols on the silica surface.9The attachment of methyl groups to the aromatic nucleus of either C 7H 8or C 6H 6causes an increase in the electron density in the aromatic ring,which consequently leads to a decrease in the ionization potential,8.8eV for C 7H 8and 9.3eV for C 6H 6.31The smaller ionization potential,together with the higher relative pressure,provides more favorable conditions for the adsorption of C 7H 8compared with C 6H 6.Conformational effects may play an important role in explaining the larger dynamic adsorption capacity for C 6H 6than for C 7H 8in the case of https://www.wendangku.net/doc/515007624.html,paring the kinetic diameters of C 6H 6(0.65/0.65nm)and C 7H 8(0.65/0.89nm)with the pore size (0.8nm)of HY,it is possible a molecular sieving effect,which is expected to be found experimentally in the low-pressure region,is the reason for this exception.34
In order to investigate the desorption behavior of the VOCs without heat treatment,the samples were purged with He gas for 2h under vacuum.Panels A and B of Figure 10show the TPD spectra or the samples corresponding to their definitions in panels A and B of Figure 8,respectively.The TPD curves for Q3,HY,and AC are depicted in the Supporting Information (Figure S3).The amounts of C 7H 8and C 6H 6desorbed during the TPD are shown in columns 9and 12along with the corresponding desorption ratio under the He purge only in columns 10and 13in Table 1,respectively.In the case of Fiber A and Rods B and C,over 70%of the total C 7H 8adsorbed was removed during the He purge,and in the case of C 6H 6,this amount increased to as much as over 96%.Almost all of the VOCs adsorbed by MCM-41were eliminated during the He purge before the heat treatment.The TPD results also demonstrate that,for the mesoporous materials used here,the heating temperature of 150°C was sufficient to achieve complete elimination of the VOCs,irrespective of their residual amounts.In comparison,the data in the Supporting Information (Figure S2)indicates that the
(32)Lillo-Ro ′denas,M.A.;Cazorla-Amoro ′s,D.;Linares-Solano,A.Carbon 2005,43,1758.
(33)Pires,J.;Pinto,M.;Carvalho,A.;de Carvalho,M.B.J.Chem.Eng.Data 2003,48,416.
(34)Pinto,M.;Pires,J.;Carvalho,A.;de Carvalho,M.B.J.Phys.Chem.B 2006,110,
250.
Figure 8.The breakthrough curves for (A)C 7H 8and for (B)C 6H 6of Fiber A (O ),Rod B (3),Rod C (0),and MCM-41(b
).
Figure 9.Relationship between (A)the micropore volume and dynamic VOC capacity and (B)the total pore volume and dynamic VOC capacity for all samples including the commercial adsorbents.The circles represent C 7H 8(O )and the triangles represent C 6H 6(4).
F Langmuir Kosuge et al.
amounts of C 7H 8and C 6H 6adsorbed by both AC and HY desorbed more slowly during the He purge.It was eventually required to heat both AC and HY to over 300°C for the complete elimination of residual VOCs (Figure S3).
The desorption behaviors of the silica-based adsorbents described above are very important from the practical point of energy-saving,since VOC-loaded adsorbents that can be regenerated and solvents that can be recovered using mild heat treatment make for superior efficiency.
Effect of Pore Structure and Macroscopic Morphology on Dynamic Performance.Considering the differences among the various adsorbents as evaluated from the adsorption/desorption data,it is concluded that,in addition to superior desorption performance,Fiber A is clearly a good candidate for a VOC adsorbent on the basis of its large,dynamic VOC capacity (Figure 8).Fiber A and Rod B have comparable porous parameters,resulting in little difference in volumetric sorption behavior for both VOCs (Table 1and Figure 6).The exceptional dynamic adsorption performance of Fiber A must then be the result of the differences in the macroscopic morphologies between Fiber A and Rod B,as depicted in Figures 1and 5.
A previous report detailed a large difference in the dynamic adsorption performance of enzymes in the liquid phase between conventional fiberlike SBA-15(20-30μm in length)and rodlike SBA-15(1μm in length),which was formed by cutting the fiberlike SBA-15.28The rodlike particles exhibited a larger dynamic capacity and faster adsorption rate,which were attributed to the higher number of mesochannel openings that were accessible to the enzymes.The slower adsorption behavior of the fiberlike particles was the result of hindered diffusion.Additionally,a rodlike SBA-15100-200nm in length with a larger mesopore size of 8-13nm was recently reported to have exhibited a much faster adsorption rate in a similar reaction.35In contrast,from our experimental results,it was found that VOCs were hardly adsorbed dynamically into mesopores of relatively large size (ca.5.7nm,Figure 8,Rod C)while VOCs were clearly adsorbed into mesopores 2.1nm in size,which is very close to the standard micropore size (ibid,MCM-41).Additionally,the silicas with 1D mesochannels greater than 2.1nm in size exhibited rapid release of the VOCs without any
diffusion resistance (Fiber A,Rod B,and MCM-41).Hence,it is reasonable to assume that the gaseous VOCs used in this study were directly adsorbed into the micropores of Fiber A and Rods B and C.Fiber A has longer 1D-mesopore channels than Rod B as a result of the successive connections of rodlike particles,as shown in Figures 1a and 2a.Therefore,it is concluded that the larger dynamic VOC capacity of Fiber A is derived from a synergetic effect between the macroscopic morphology and intrinsic pore connections between the 1D-mesopore channels and micropores.As shown in the schematic in Figure 11,this bimodal pore system leads to a high accessibility of the interior of the structure for the VOCs through the micropores and at the same time leads to additional,unhindered diffusivity of the adsorbed molecules through the mesopores.Hence,the longer 1D mesochannels of Fiber A afford a larger breakthrough capacity than that for the short 1D mesochannnels of Rod B due to the greater time spent inside the longer 1D mesochannels by the VOCs.
Conclusions
The volumetric and dynamic VOC adsorption/desorption behaviors were evaluated for three kinds of SBA-15silicas and MCM-41,all of which had distinct structural parameters in addition to their respective macroscopic morphologies.These structural characteristics have proven to be important for a better understanding of the factors that affect the dynamic VOC adsorption/desorption properties of silica samples.Both the existence and the overall number of micropores in the silica-based adsorbents are essential contributory factors in achieving a large dynamic capacity.Of key significance,it was revealed in this study that there is a large difference in the dynamic VOC adsorption capacities between fiberlike and rodlike SBA-15silicas having almost the same porous parameters.In a dynamic VOC adsorption/desorption system like the ones described in this report,the synergetic effect between micropores and long 1D-mesopore channels is a key factor in attaining superior performance,indicating that fiberlike SBA-15s will have superior dynamic VOCs adsorption capacities to rodlike SBA-15s.
The results in this study provide some initial information required for understanding the adsorption/desorption behavior in mesoporous materials with 1D mesochannels at low concen-trations of gas molecules.Our fiberlike mesoporous silica appear to be suitable for use in a continuous adsorption-recycling system
(35)Sun,J.;Zhang,H.;Tian,R.;Ma,D.;Bao,X.;Su,D.S.;Zou,https://www.wendangku.net/doc/515007624.html,mun.2006,
1322.
Figure 10.TPD curves for (A)C 7H 8and (B)for C 6H 6of Fiber A (O ),Rod B (3),Rod C (0),and MCM-41(b
).
Figure 11.Schematic representation showing the effect of the bimodal pore system on dynamic VOC adsorption/desorption performance in Fiber A.The large breakthrough capacity of the fiberlike SBA-15is likely derived from the intrinsic pore connections between long 1D-mesopore channels and complementary micropores.A pore network of this nature leads to the strong adsorption of VOCs by the micropores (green arrows)and,moreover,results in additional diffusivity of the adsorbed VOCs through the mesopores (light brown arrows).
VOC Dynamic Adsorption/Desorption Performance Langmuir G
on the basis of both their large dynamic capacity and the ease with which desorption occurs.The advantages stemming from the macroscopic morphology of the fiberlike silicas will make them excellent candidates to be introduced into a composite sheet or film formed by mixing with other materials to then be used in a number of industrial applications.
Supporting Information Available:The sorption isotherms, the breakthrough curves,and the temperature programmed desorption (TPD)curves of commercial adsorbents are depicted as figures. This material is available free of charge via the Internet at https://www.wendangku.net/doc/515007624.html,.
LA062616T
H Langmuir PAGE EST:7.1Kosuge et al.
英语中的比较级与最高级 详解
比较级与最高级 1.as...as 与(not) as(so)...as as...as...句型中，as的词性 第一个as是副词，用在形容词和副词的原级前，常译为“同样地”。第二个as是连词，连接与前面句子结构相同的一个句子(相同部分常省略)，可译为“同..... He is as tall as his brother is (tall) . (后面的as 为连词) 只有在否定句中，第一个as才可换为so 改错: He is so tall as his brother.（X） 2.在比较状语从句中，主句和从句的句式结构一般是相同的 与as...as 句式中第二个as一样，than 也是连词。as和than这两个连词后面的从句的结构与前面的句子大部分情况下结构是相同的，相同部分可以省略。 He picked more apples than she did. 完整的表达为: He picked more apples than she picked apples. 后而的picked apples和前面相同，用did 替代。 He walked as slowly as she did.完整表达为: He walked as slowly as she walked slowly. she后面walked slowly与前面相同，用did替代。
3.谓语的替代 在as和than 引导的比较状语从句中，由于句式同前面 主句相同，为避免重复，常把主句中出现而从句中又出现的动词用do的适当形式来代替。 John speaks German as fluently as Mary does. 4.前后的比较对象应一致 不管后面连词是than 还是as,前后的比较对象应一致。The weather of Beijing is colder than Guangzhou. x than前面比较对象是“天气”，than 后面比较对象是“广州”，不能相比较。应改为: The weather of Bejing is colder than that of Guangzhou. 再如: His handwriting is as good as me. 应改为: His handwriting is as good as mine. 5.可以修饰比较级的词 常用来修饰比较级的词或短语有: Much,even,far,a little,a lot,a bit,by far,rather,any,still,a great deal等。 by far的用法: 用于强调，意为“...得多”“最最...”“显然”等，可修饰形容词或副词的比较级和最高级，通常置于其后，但是若比较级或最高级前有冠词，则可置于其前或其后。
ProE高级曲面建模实例
Pro/E高级曲面建模实例 一、前言 因本人水平有限，理论上没有什么大的建树，现就一些实际的曲面构建题目写出我自己的解法，与大家一起探讨，希望对大家有所帮助，共同进步！ 版权声明：题目来自https://www.wendangku.net/doc/515007624.html,论坛，但解法均为本人原创，如有雷同纯属巧合。 二、知识准备 主要涉及模块： Style（ISDX模块）、高级曲面设计模块 主要涉及概念： 活动平面、曲面相切（G1连续）、曲面曲率连续（G2连续）、Style中的自由曲线/平面曲线/cos曲线、自由曲线端点状态（相切、法向、曲率连续等） 主要涉及命令： 高级曲面命令（边界曲面）、曲线命令及Style中的操作命令 三、实例操作 下面我们结合实际题目来讲述： 1. 题目一：带翅膀的飞梭，完成效果见图1： 图1 飞梭最终效果图
原始架构线如图2所示： 图2 飞梭原始架构线图 首先我们分析一下，先看效果图应该是一个关于通过其中心三个基准面的对称图形，那么从原始架构线出发，我们只要做出八分之一就可以了。很容易想到应该在中心添加于原有曲线垂直面上边界曲线，根据实际情况，我先进入Style中做辅助线，如图3所示： 图3 Style辅助线操作图 图3中标示1处选择绘制曲线为平面曲线（此时绘制的曲线在活动平面上，活动平面为图中网格状显示平面），标示2设置曲线端点处垂直于平面，标示3处设置曲线端点曲率连续。设置方法为，左键点击要设置的端点，出现黄色操纵杆，鼠标放于黄色操纵杆上，按住右键1秒钟以上便会出现菜单，如图4左图所示。
图4 绘制曲线操作图 设置时先选设置属性（相切、曲率连续等），再选相关联的曲面或平面（含基准平面），黄色操纵杆长短可调整，同时可打开曲率图适时注意曲率变化，如图4右图所示。有了图4辅助线后就可以做面了，此处我用高级曲面命令（boundaries），注意线的选取顺序，第一方向选取曲线1，2，第二方向选曲线3（如不能直接利用曲线选项选取，可用链选项，另一个选项也可自己尝试一下），见图5: 图5 构面时线的选取顺序图 如选择完边界直接完成，则生成的曲面并不满足要求，因此我们必须定义边界条件，如图6左图所示。 图6 曲面边界条件定义图
人教版(新目标)初中英语形容词与副词的比较级与最高级
人教版（新目标）初中英语形容词与副词的比较级与最高级 （一）规则变化： 1．绝大多数的单音节和少数双音节词，加词尾-er ，-est tall—taller—tallest 2．以不发音的e结尾的单音节词和少数以-le结尾的双音节词只加-r，-st nice—nicer—nicest , able—abler—ablest 3．以一个辅音字母结尾的重读闭音节词或少数双音节词，双写结尾的辅音字母，再加-er，-est big—bigger—biggest 4．以辅音字母加y结尾的双音节词，改y为i再加-er，-est easy—easier—easiest 5．少数以-er，-ow结尾的双音节词末尾加-er，-est clever—cleverer—cleverest, narrow—narrower—narrowest 6．其他双音节词和多音节词，在前面加more，most来构成比较级和最高级 easily—more easily—most easily （二）不规则变化 常见的有： good / well—better—best ; bad (ly)/ ill—worse—worst ; old—older/elder—oldest/eldest many / much—more—most ; little—less—least ; far—farther/further—farthest/furthest
用法： 1．原级比较：as + adj./adv. +as（否定为not so/as + adj./adv. +as）当as… as中间有名字时，采用as + adj. + a + n.或as + many / much + n. This is as good an example as the other is . I can carry as much paper as you can. 表示倍数的词或其他程度副词做修饰语时放在as的前面 This room is twice as big as that one. 倍数+as+adj.+as = 倍数+the +n.+of Your room is twice as larger as mine. = Your room is twice the size of mine. 2．比较级+ than 比较级前可加程度状语much, still, even, far, a lot, a little, three years. five times,20%等 He is three years older than I (am). 表示“（两个中）较……的那个”时，比较级前常加the（后面有名字时前面才能加冠词） He is the taller of the two brothers. / He is taller than his two brothers. Which is larger, Canada or Australia? / Which is the larger country, Canada or Australia? 可用比较级形式表示最高级概念，关键是要用或或否定词等把一事物（或人）与其他同类事物（或人）相分离 He is taller than any other boy / anybody else.
英语中的比较级和最高级
大多数形容词有三种形式,原级,比较级和最高级, 以表示形容词说明的性质在程度上的不同。 形容词的原级: 形容词的原级形式就是词典中出现的形容词的原形。例如: poor tall great glad bad 形容词的比较级和最高级: 形容词的比较级和最高级形式是在形容词的原级形式的基础上变化的。分为规则变化和不规则变化。 规则变化如下: 1) 单音节形容词的比较级和最高级形式是在词尾加 -er 和 -est 构成。 great (原级) (比较级) (最高级) 2) 以 -e 结尾的单音节形容词的比较级和最高级是在词尾加 -r 和 -st 构成。wide (原级) (比较级) (最高级) 3)少数以-y, -er, -ow, -ble结尾的双音节形容词的比较级和最高级是在词尾加 -er 和 -est 构成。 clever(原级) (比较级) (最高级) 4) 以 -y 结尾,但 -y 前是辅音字母的形容词的比较级和最高级是把 -y 去掉,加上 -ier 和-est 构成. happy (原形) (比较级) (最高级) 5) 以一个辅音字母结尾其前面的元音字母发短元音的形容词的比较级和最高级是双写该辅音字母然后再加 -er和-est。 big (原级) (比较级) (最高级) 6) 双音节和多音节形容词的比较级和最高级需用more 和 most 加在形容词前面来构成。 beautiful (原级) (比较级) (比较级) difficult (原级) (最高级) (最高级) 常用的不规则变化的形容词的比较级和最高级: 原级------比较级------最高级 good------better------best many------more------most much------more------most bad------worse------worst far------farther, further------farthest, furthest 形容词前如加 less 和 least 则表示"较不"和"最不 形容词比较级的用法: 形容词的比较级用于两个人或事物的比较,其结构形式如下: 主语+谓语(系动词)+ 形容词比较级+than+ 对比成分。也就是, 含有形容词比较级的主句+than+从句。注意从句常常省去意义上和主句相同的部分, 而只剩下对比的成分。
proe视频分类-124个实例教程proe族必备!
proe视频分类-124个实例教程proe族必备！ 来看看何为高质量proe视频教程，下面的视频包括了proe安装和配置、proe基础指令、proe曲面造型和逆向造型、proe阵列特征和proe优化设计、proe模具设计和分模、proe 数据管理和二次开发、proe工程图和直接建模、proe机构模拟和动画，总之所有的proe 模块的视频教程你都可以从下面的视频教程中找到。所有视频都进行分类整理，方便各位懒人使用，菜鸟收藏它，早晚成高人！ 1、proe安装配置视频教程 116、Pro/Toolkit二次开发视频教程:Pro/E Wildfire5.0配Microsoft Visual Studio 2008编译安装测试(野火5.0版本)：https://www.wendangku.net/doc/515007624.html,/html/video/2010-03/4178.html 117、proe视频教程之低版本打开高版本模型文件及后续特征更新和操作： https://www.wendangku.net/doc/515007624.html,/html/video/2010-10/4499.html 118、Pro/Engineer精度系统详解和应用： https://www.wendangku.net/doc/515007624.html,/html/video/2008-11/3089.html 119、proe5.0安装方法_终极版视频： https://www.wendangku.net/doc/515007624.html,/html/video/2010-10/4487.html 120、emx4.1安装方法视频教程：https://www.wendangku.net/doc/515007624.html,/html/video/2010-10/4494.html 121、emx5.0安装方法视频教程：https://www.wendangku.net/doc/515007624.html,/html/video/2010-10/4495.html 122、emx6.0安装方法_视频教程：https://www.wendangku.net/doc/515007624.html,/html/video/2010-10/4496.html 123、proe配置文件之config.pro： https://www.wendangku.net/doc/515007624.html,/html/video/2010-10/4542.html 124、proe5.0安装方法视频教程： https://www.wendangku.net/doc/515007624.html,/html/video/2010-10/proe5_sv.html 2、proe基础指令视频教程 88、ProE曲线方程式应用和进化（WildFire）： https://www.wendangku.net/doc/515007624.html,/html/video/2008-11/2965.html 89、ProE实体化曲面造型实例视频教程：手机按键： https://www.wendangku.net/doc/515007624.html,/html/video/2008-11/2966.html 90、ProE螺旋扫描视频教程（WildFire4.0版本）： https://www.wendangku.net/doc/515007624.html,/html/video/2008-11/2975.html 91、ProE可变扫出（vss）的轨迹参数trajpar详解： https://www.wendangku.net/doc/515007624.html,/html/video/2008-11/2976.html 92、ProE扫描混合指令视频教程（WildFire4.0）：
英语比较级和最高级的用法归纳
英语比较级和最高级的用法归纳 在学习英语过程中，会遇到很多的语法问题，比如比较级和最高级的用法，对于 这些语法你能够掌握吗？下面是小编整理的英语比较级和最高级的用法，欢迎阅读！ 英语比较级和最高级的用法 一、形容词、副词的比较级和最高级的构成规则 1.一般单音节词和少数以-er，-ow结尾的双音节词，比较级在后面加-er，最高级 在后面加-est; (1)单音节词 如：small→smaller→smallest short→shorter→shortest tall→taller→tallest great→greater→greatest (2)双音节词 如：clever→cleverer→cleverest narrow→narrower→narrowest 2.以不发音e结尾的单音节词，比较在原级后加-r，最高级在原级后加-st; 如：large→larger→largest nice→nicer→nicest able→abler→ablest 3.在重读闭音节(即：辅音+元音+辅音)中，先双写末尾的辅音字母，比较级加-er，最高级加-est; 如：big→bigger→biggest hot→hotter→hottest fat→fatter→fattest 4.以“辅音字母+y”结尾的双音节词，把y改为i，比较级加-er，最高级加-est; 如：easy→easier→easiest heavy→heavier→heaviest busy→busier→busiest happy→happier→happiest 5.其他双音节词和多音节词，比较级在前面加more，最高级在前面加most; 如：bea utiful→more beautiful→most beautiful different→more different→most different easily→more easily→most easily 注意：(1)形容词最高级前通常必须用定冠词 the，副词最高级前可不用。 例句： The Sahara is the biggest desert in the world. (2) 形容词most前面没有the，不表示最高级的含义，只表示"非常"。 It is a most important problem. =It is a very important problem.
ProE实例训练教程—零件工程图
Pro/E实例训练教程—零件工程图以传动轴工程图的生成为例介绍零件工程图的创建。具体操作步骤如下：（1）单击【新建】按钮，打开【新建】对话框，在“类型”选项中选择“绘图”，输入文件名shaft。 （2）在【新制图】对话框中，单击【浏览…】打开传动轴零件设为“缺省模型”，“指定模板”选择为【空】，“方向”选择为【横向】，“标准大小”选择【A3】，单击【确定】创建工程图。如果选用的模板不合适，可以执行【文件】→【页面设置】命令重新设置模板。 （3）在图纸空白处单击右键并在其快捷菜单中选择【属性】，在【文件属性】菜单管理器中选择【绘图选项】，打开【选项】对话框，更改下列设置，如表2-1所示，并单击【应用】→【关闭】。 表2-1 修改配置值 （4）单击主菜单栏【插入】→【绘图视图】→【一般】，或单击工具栏上的创建一般视图按钮，在图纸中单击绘制视图中心点，弹出【绘图视图】对话框，单击“类型”选项组中的“视图类型”选项，在“视图方向”栏中，选择“查
看来自模型的名称”，在“模型视图名”选项栏中选择“TOP”，单击【应用】。单击“类型”选项组中的“比例”选项，选择“定制比例”并输入比例1，单击【绘图视图】对话框的【应用】→【关闭】，创建的一般视图如图2-所示。 （5）单击主菜单栏【插入】→【绘图视图】→【旋转】，系统打开【绘图视图】对话框，系统提示选取旋转视图的父视图，单击步骤（5）建立的主视图，系统提示选取绘图中心点，单击主视图下方，系统打开【绘图视图】对话框和【剖截面创建】菜单管理器。 图2- （6）在“旋转视图属性”的“属性”栏中选择【创建新…】，在【剖截面创建】菜单管理器中单击【平面】→【单一】→【完成】。在绘图区下方文本框中输入截面名称“A”并回车。系统打开【设置平面】菜单管理器，单击【产生基准】→【偏距】，在主视图中单击左端面或RIGHT,在弹出的【偏距】下拉菜单中单击【输入值】，在下方的文本框中输入50，单击【完成】。 （7）单击【绘图视图】对话框的【应用】→【关闭】，完成旋转视图的创建，如图2-所示。 图2- （8）单击工具栏的打开显示及拭除按钮，系统打开【显示及拭除】对话框，按下【显示】按钮，在“类型”选项中按下驱动尺寸按钮，在“显示方式”栏里选择【特征】选项，并单击【显示全部】按钮，在弹出的【选取】对话框中单击【确定】按钮。在【显示及拭除】对话框里选择轴按钮，在图形区单击零件上的旋转特征，单击【确定】按钮，显示的尺寸和中心线如图2-所
PROE野火版可变截面扫描-指令详细解说
可变截面扫描－指令详细解说 不管版本如何变更，可变扫出始终是我比较偏爱的造型指令。这是因为可变扫出除了可以得到相对规则的曲面外，它丰富的控制属性和可以预见的结果形状让它更能在适当的场合发挥作用。 可变扫出的控制主要有下面的几项：轨迹，截面的定向和截面的形状 1．轨迹 在可变扫出中有两类轨迹，有且只有一条称之为原始轨迹（Origin）也就是你第一条选择的轨迹。原始轨迹必须是一条相切的曲线链（对于轨迹则没有这个要求）。除了原始轨迹外，其它的都是轨迹，一个可变扫出指令可以有多条轨迹。在wildfire以后的版本中，原始轨迹和轨迹的功能性差异除了这点外可以说没有任何差异了；截面的定向依赖于两个方向的确定：Z方向和X方向。 注意看上面的图片你会发现在每条轨迹后面都有三个可选项分别用X，N和T作标题，它们分别代表的是X向量，Normal（垂直方向也就是Z方向）以及T angency切向参考，在对应的方框内打勾就表明采用该选项；显然对于可变扫出只能有一个X向量和一个Z方向，所以你选择了某个轨迹后会自动曲线其它轨迹中对应的选择；对于切向参考，因为一条轨迹很可能是两面链的交线，所以有两个框来供你选择不同的面链。当然你也可以手工选择作为切向参考的面链。在下面的Section Plane Control下拉框中，你可以选择你的截面的定向方法，缺省是Norma To Trajectory是由轨迹来确定截面的定向，但是你也可以用其它两个选项来确定：
最下面就是水平竖直方向的确定，这可以在Horzontal/Vertical Control下拉框中进行选择。 下面就来具体看一下各种组合的截面定向方法的表现形式：
英语比较级和最高级的用法
More than的用法 A. “More than+名词”表示“不仅仅是” 1)Modern science is more than a large amount of information. 2)Jason is more than a lecturer; he is a writer, too. 3) We need more than material wealth to build our country.建设我们国家，不仅仅需要物质财富. B. “More than+数词”含“以上”或“不止”之意，如： 4)I have known David for more than 20 years. 5)Let's carry out the test with more than the sample copy. 6) More than one person has made this suggestion. 不止一人提过这个建议. C. “More than+形容词”等于“很”或“非常”的意思，如： 7)In doing scientific experiments, one must be more than careful with the instruments. 8)I assure you I am more than glad to help you. D. more than + (that)从句，其基本意义是“超过（=over）”，但可译成“简直不”“远非”.难以，完全不能（其后通常连用情态动词can） 9) That is more than I can understand . 那非我所能懂的. 10) That is more than I can tell. 那事我实在不明白。 11) The heat there was more than he could stand. 那儿的炎热程度是他所不能忍受的 此外，“more than”也在一些惯用语中出现，如： more...than 的用法 1. 比……多，比……更 He has more books than me. 他的书比我多。 He is more careful than the others. 他比其他人更仔细。 2. 与其……不如 He is more lucky than clever. 与其说他聪明，不如说他幸运。 He is more （a）scholar than （a）teacher. 与其说他是位教师，不如说他是位学者。 注：该句型主要用于同一个人或物在两个不同性质或特征等方面的比较，其中的比较级必须用加more 的形式，不能用加词尾-er 的形式。 No more than/not more than 1. no more than 的意思是“仅仅”“只有”“最多不超过”，强调少。如： --This test takes no more than thirty minutes. 这个测验只要30分钟。 --The pub was no more than half full. 该酒吧的上座率最多不超过五成。-For thirty years，he had done no more than he （had）needed to. 30年来，他只干了他需要干的工作。 2. not more than 为more than （多于）的否定式，其意为“不多于”“不超过”。如：Not more than 10 guests came to her birthday party. 来参加她的生日宴会的客人不超过十人。 比较： She has no more than three hats. 她只有3顶帽子。（太少了） She has not more than three hats. 她至多有3顶帽子。（也许不到3顶帽子） I have no more than five yuan in my pocket. 我口袋里的钱最多不过5元。（言其少） I have not more than five yuan in my pocket. 我口袋里的钱不多于5元。（也许不到5元） more than, less than 的用法 1. （指数量）不到，不足 It’s less than half an hour’s drive from here. 开车到那里不到半个钟头。 In less than an hour he finished the work. 没要上一个小时，他就完成了工作。 2. 比……（小）少 She eats less than she should. 她吃得比她应该吃的少。 Half the group felt they spent less than average. 半数人觉得他们的花费低于平均水平。 more…than,/no more than/not more than (1)Mr．Li is ________ a professor; he is also a famous scientist． (2)As I had ________ five dollars with me, I couldn’t afford the new jacket then． (3)He had to work at the age of ________ twelve． (4)There were ________ ten chairs in the room．However, the number of the children is twelve． (5)If you tel l your father what you’ve done, he’ll be ________ angry． (6)－What did you think of this novel? －I was disappointed to find it ________ interesting ________ that one． 倍数表达法 1. “倍数+形容词（或副词）的比较级+than+从句”表示“A比B大（长、高、宽等）多少倍” This rope is twice longer than that one.这根绳是那根绳的三倍（比那根绳长两倍）。The car runs twice faster than that truck.这辆小车的速度比那辆卡车快两倍（是那辆卡车的三倍）。 2. “倍数+as+形容词或副词的原级+as+从句”表示“A正好是B的多少倍”。
PROE三维绘图实例
2011-2012年第一学期 《Pro/E三维造型》课程期末综合作业 题目：电脑摄像头的制作 班级：XXXXX 姓名：XXXXX 学号：XXXXX 电话：XXXXXXXX Email： 日期：
设计构思：本次设计实体为立式电脑摄像头，实体绘制过程中主要运用了拉伸、旋转特征，辅助以扫描、螺旋扫描、阵列、圆角、基准点、面等。特征设计中忽略了实体内部的镶嵌结构，以及弹簧、光学透镜镜片、电线、螺钉等结构。从工程实践来讲，该实体并不能用单个的零件来阐述，完成的prt文件只能代表摄像头外形特征，并不具有实际意义。
实物图片
模型截图 制作步骤与说明： 一、绘制头部： 【1】打开程序，先新建一个模型文件：点击系统工具栏里的“新建”图标，在弹出的“新建”对话框中保持默认值，单击“确定”按钮，进入零件设计界面。 【2】单击下拉菜单【插入】、【旋转】命令，或者直接单击特征工具栏中的“旋转工具”
按钮，使用特征面板中的“”图标，单击放置按钮，在弹出的面板中单击其中的“定义”按钮，以绘制旋转截面。 【3】系统弹出“草绘”对话框，选择FRONT面为草绘平面，接收系统默认草绘方向，单击“草绘”按钮，进入草绘工作状态。 【4】如图1所示：先绘制一条旋转轴线（图中竖直虚线），再绘制一个直径100的圆（圆心过旋转轴线），在剪切至图1所示。 图1 【5】单击草绘工具栏下面的按钮，系统回到零件设计模式。此时单击“预览”按钮，模型如图2所示：
图2 【6】接受默认值，单击按钮，完成曲面旋转特征。单击下拉菜单中的【文件】，【保存副本】菜单命令，在新建名称中输入“qiuke”，保存。 【7】在模型树中选中“旋转1”，单击【编辑】、【实体化】，然后点击按钮，将上一步得到的球壳实体化得到球。 二、绘制双耳： 【8】单击特征工具栏里的“基准平面工具”，选择RIGHT平面，偏移距离设置为45，新建一个基准平面；再在RIGHT平面另一边新建一个对称基准平面，名称分别为DTM1和DTM2。 【9】单击特征工具栏中的“拉伸”，选择“拉伸为实体”，以DTM1基准平面为草绘平面，绘制一个直径60的圆，单击完成草绘，拉伸实体参数分别为，单击得到实体局部切槽如图3所示。对切口进行倒圆角处理，圆角半径设为0.5。
初中英语比较级和最高级讲解与练习
初中英语比较级和最高级讲解与练习 形容词比较级和最高级 一．绝大多数形容词有三种形式,原级,比较级和最高级, 以表示形容词说明的性质在程度上的不同。 1. 形容词的原级: 形容词的原级形式就是词典中出现的形容词的原形。例如: poor tall great glad bad 2. 形容词的比较级和最高级: 形容词的比较级和最高级形式是在形容词的原级形式的基 础上变化的。分为规则变化和不规则变化。 二．形容词比较级和最高级规则变化如下: 1) 单音节形容词的比较级和最高级形式是在词尾加-er 和-est 构成。 great (原级) greater(比较级) greatest(最高级) 2) 以-e 结尾的单音节形容词的比较级和最高级是在词尾加-r 和-st 构成。 wide (原级) wider (比较级) widest (最高级) 3) 少数以-y, -er, -ow, -ble结尾的双音节形容词的比较级和最高级是在词尾加 -er 和-est构成。 clever(原级) cleverer(比较级) cleverest(最高级)， slow(原级) slower(比较级) slowest (最高级) 4) 以-y 结尾,但-y 前是辅音字母的形容词的比较级和最高级是把-y 去掉,加上-ier 和-est 构成. happy (原形) happier (比较级) happiest (最高级) 5) 以一个辅音字母结尾其前面的元音字母发短元音的形容词的比较级和最高级是双写该 辅音字母然后再加-er和-est。 原形比较级最高级原形比较级最高级 big bigger biggest hot hotter hottest red redder reddest thin thinner thinnest 6) 双音节和多音节形容词的比较级和最高级需用more 和most 加在形容词前面来构 成。 原形比较级最高级 careful careful more careful most careful difficult more difficult most difficult delicious more delicious most delicious 7)常用的不规则变化的形容词的比较级和最高级: 原级比较级最高级 good better best 好的 well better best 身体好的 bad worse worst 坏的 ill worse worst 病的 many more most 许多 much more most 许多 few less least 少数几个 little less least 少数一点儿 （little littler littlest 小的） far further furthest 远（指更进一步，深度。亦可指更远） far farther farthest 远（指更远，路程）
PROE变截面扫描
可变截面扫描（Variable Section Sweep），单从名字来看我们就知道它的精髓在于一个可变。这是因为可变截面扫描除了可以得到相对规则的曲面外，它丰富的控制属性和可以预见的结果形状让它更能在适当的场合发挥作用。 3.6.1.可变截面扫描（Variable Section Sweep）的构成 可变截面扫描的控制主要有下面的几项：轨迹（Trajectory），截面的定向和截面的形状。 轨迹，在可变截面扫描中有两类轨迹，有且只有一条称之为原始轨迹（Origin）也就是你第一条选择的轨迹，原始轨迹必须是一条相切的曲线链（对于轨迹则没有这个要求），原始轨迹是确定扫描过程中截面的原点的。除了原始轨迹（Origin）外，其它的都是轨迹，一个可变截面扫描指令可以有多条轨迹。在WildFire3.0以后的版本中，原始轨迹和轨迹的功能性差异除了这点外可以说没有任何差异了，截面的定向依赖于两个方向的确定：Z方向和X方向。 注意看上面的图片你会发现在每条轨迹后面都有三个可选项分别用X，N和T作标题，它们分别代表的是X向量，Normal（垂直方向也就是Z方向）以及Tangency切向参考，在对应的方框内打勾就表明采用该选项。 很多用户对X向量的理解都比较迷惑，对于它的具体含义总是无法完全把握，其实它的含义并不复杂，我们知道可变扫描是一定有一条原始轨迹的，这个原始轨迹确定了扫描过程中的截面原点，
而X向量相当于决定了截面坐标的X轴上的另一个点，过这两个点确定的直线就是截面的X轴了。X 轴确定了Y轴也就相当于确定了，这就是X向量的几何意义；而当留空X向量的时候，系统就会自动根据原始轨迹的法向向量来确定截面的X轴了。 显然对于可变截面扫描只能有一个X向量和一个Z方向，所以你选择了某个轨迹后会自动定义曲线为其它轨迹中对应的选择。对于切向参考，因为一条轨迹很可能是两面链的交线，所以有两个框来供你选择不同的面链，当然你也可以手工选择作为切向参考的面链。 图vss.1.05参考（vss/vss-01.prt） 在下面的Section Plane Control（截面平面控制）下拉框中，你可以选择你的截面的定向方法，缺省是Norma To Trajectory是由轨迹来确定截面的定向，但是你也可以用其它两个选项来确定： Normal To Projection（垂直于投影）：可以控制你的截面垂直于轨迹在平面上的投影。Constant Normal Direction（恒定垂直向量）：截面法向始终和给定的方向平行，方向可以用轴，直线或平面法向来确定，如使用平面作参考则在整个扫出过程截面始终和指定平面平行。
英语比较级和最高级
形容词比较级和最高级的形式 一、形容词比较级和最高级的构成 形容词的比较级和最高级变化形式规则如下 构成法原级比较级最高级 ①一般单音节词末尾加 er 和 est strong stronger strongest ②单音节词如果以 e结尾，只加 r 和 st strange stranger strangest ③闭音节单音节词如末尾只有一个辅音字母， 须先双写这个辅音字母，再加 er和 est sad big hot sadder bigger hotter saddest biggest hottest ④少数以 y, er(或 ure), ow, ble结尾的双音节词， 末尾加 er和 est(以 y结尾的词，如 y前是辅音字母， 把y变成i，再加 er和 est，以 e结尾的词仍 只加 r和 st) angry Clever Narrow Noble angrier Cleverer narrower nobler angriest cleverest narrowest noblest ⑤其他双音节和多音节词都在前面加单词more和most different more different most different 1) The most high 〔A〕mountain in 〔B〕the world is Mount Everest，which is situated 〔C〕in Nepal and is twenty nine thousand one hundred and fourty one feet high 〔D〕 . 2) This house is spaciouser 〔A〕than that 〔B〕white 〔C〕one I bought in Rapid City，South Dakota 〔D〕last year. 3) Research in the social 〔A〕sciences often proves difficulter 〔B〕than similar 〔C〕work in the physical 〔D〕sciences. 二、形容词比较级或最高级的特殊形式：
proe参数化建模教程(最新)
proe参数化建模 本教程分两部分，第一部分主要介绍参数化建模的相关概念和方法，包括参数的概念、参数的设置、关系的概念、关系的类型、如何添加关系以及如何使用关系创建简单的参数化零件（以齿轮为例）。 第二部分介绍参数化建模的其他方法：如族表的应用、如何使用UDF(用户自定义特征)、如何使用Pro/Program创建参数化零件。（后一部分要等一段时间了，呵呵） 参数化设计是proe重点强调的设计理念。参数是参数化设计的核心概念，在一个模型中，参数是通过“尺寸”的形式来体现的。参数化设计的突出有点在于可以通过变更参数的方法来方便的修改设计意图，从而修改设计意图。关系式是参数化设计中的另外一项重要内容，它体现了参数之间相互制约的“父子”关系。 所以，首先要了解proe中参数和关系的相关理论。 一、什么是参数？ 参数有两个含义： ●一是提供设计对象的附加信息，是参数化设计的重要要素之一。参数和模型一起存储，参数可以标明不同模型的属性。例如在一个“族表”中创建参数“成本”后，对于该族表的不同实例可以设置不同的值，以示区别。 ●二是配合关系的使用来创建参数化模型，通过变更参数的数值来变更模型的形状和大小。 二、如何设置参数 在零件模式下，单击菜单“工具”——参数，即可打开参数对话框，使用该对话框可添加或编辑一些参数。 1.参数的组成 (1)名称：参数的名称和标识，用于区分不同的参数，是引用参数的依据。注意：用于关系
的参数必须以字母开头，不区分大小写，参数名不能包含如下非法字符：！、”、@和#等。 (2)类型：指定参数的类型 ?a)整数：整型数据 ?b)实数：实数型数据 ?c)字符型：字符型数据 ?d)是否：布尔型数据。 (3)数值：为参数设置一个初始值，该值可以在随后的设计中修改 (4)指定：选中该复选框可以使参数在PDM（Product Data Management，产品数据管理）系统中可见 (5)访问：为参数设置访问权限。 ?a)完全：无限制的访问权，用户可以随意访问参数 ?b)限制：具有限制权限的参数 ?c)锁定：锁定的参数，这些参数不能随意更改，通常由关系式确定。 (6)源：指定参数的来源 ?a)用户定义的：用户定义的参数，其值可以随意修改 ?b)关系：由关系式驱动的参数，其值不能随意修改。 (7)说明：关于参数含义和用途的注释文字 (8)受限制的：创建其值受限制的参数。创建受限制参数后，它们的定义存在于模型中而与参数文件无关。 (9)单位：为参数指定单位，可以从其下的下拉列表框中选择。 2.增删参数的属性项目 可以根据实际需要增加或删除以上9项中除了“名称”之外的其他属性项目
Pro ENGINEER Wildfire5.0钣金设计从入门到精通视频教程素材+pdf
Pro/ENGINEER Wildfire5.0钣金设计从入门到精通视频教程 Pro/ENGINER系统是美国参数技术公司PTC推出的全参数化大型三维CAD/CAM一体化通用软件，是全球CAD/CAE/CAM 领域最具代表性的著名软件。Pro/ENGINEER的单一数据库、参数化、基于特征、全相关及工程数据库再利用等设计概念改变了CAD的传统观念，这种全新的概念已成为当今世界机械CAD/CAE/CAM领域的标准。它能将产品从设计至生产全过程集成到一起，让所有的用户能够同时进行统一产品的设计制造工作。Pro/ENGINEER软件的功能非常强大，有80多个专用模块。 由于钣金成形具有材料利用率高、重量轻，设计和操作方便等特点，因此钣金在我国制造业中应用已很普遍，几乎包含了所有制造行业，例如机械、汽车、电器、食品、仪器仪表行业、航空航天等行业，在市场上，钣金零件占全部金属制品的85%以上。Pro/ENGINEER钣金模块结合钣金产业的设计、加工方法，模拟钣金加工的操作过程，切割、折弯、冲压、冲孔让产品设计过程与加工过程相结合，使设计师与操作人员能更清楚了解整个制造过程，因此Pro/ENGINEER在钣金行业得到广泛的应用。 书本目录【本目录仅供参考，并不是每一节都有视频教程】 前言 第1章钣金设计基础 1.1 钣金加工概述 1.1.1 钣金设计要点 1.1.2 钣金加工方法 1.2 Pro/ENGINEER Wildfire 5.0界面介绍 1.2.1 进入Pro/ENGINEER Wildfire 5.0 1.2.2 Pro/ENGINEER Wildfire 5.0的工作界面 第2章钣金件的基本成型模式 2.1 钣金壁特征 2.2 平整壁特征 2.2.1 平整壁特征命令 2.2.2 创建平整壁特征 2.3 拉伸壁特征 2.3.1 拉伸壁特征命令
高中英语的比较级和最高级用法总结
比较级和最高级 1.在形容词词尾加上―er‖ ―est‖ 构成比较级、最高级： bright（明亮的）—brighter—brightest broad（广阔的）—broader—broadest cheap（便宜的）—cheaper—cheapest clean（干净的）—cleaner—cleanest clever（聪明的）—cleverer—cleverest cold（寒冷的）—colder—coldest cool（凉的）—cooler—coolest dark（黑暗的）—darker—darkest dear（贵的）—dearer—dearest deep（深的）—deeper—deepest fast（迅速的）—faster—fastest few（少的）—fewer—fewest great（伟大的）—greater—greatest hard（困难的,硬的）—harder—hardest high（高的）—higher—highest kind（善良的）—kinder—kindest light（轻的）—lighter—lightest long（长的）—longer—longest loud（响亮的）—louder—loudest low（低的）—lower—lowest near（近的）—nearer—nearest new（新的）—newer—newest poor（穷的）—poorer—poorest quick（快的）—quicker—quickest quiet（安静的）—quieter—quietest rich（富裕的）—richer—richest short（短的）—shorter—shortest slow（慢的）—slower—slowest small（小的）—smaller—smallest smart（聪明的）—smarter—smartest soft（柔软的）—softer—softest strong（强壮的）—stronger—strongest sweet（甜的）—sweeter—sweetest tall（高的）-taller-tallest thick（厚的）—thicker—thickest warm（温暖的）—warmer—warmest weak（弱的）—weaker—weakest young（年轻的）—younger—youngest 2.双写最后一个字母,再加上―er‖ ―est‖构成比较级、最高级： big（大的）—bigger—biggest fat（胖的）—fatter—fattest hot（热的）—hotter—hottest red（红的）—redder—reddest sad（伤心的）—sadder—saddest thin（瘦的）—thinner—thinnest wet（湿的）—wetter—wettest mad（疯的）—madder—maddest 3.以不发音的字母e结尾的形容词,加上―r‖ ―st‖ 构成比较级、最高级：able（能干的）—abler—ablest brave（勇敢的）—braver—bravest close（接近的）—closer—closest fine（好的,完美的）—finer—finest large（巨大的）—larger—largest late（迟的）—later—latest nice（好的）—nicer—nicest ripe（成熟的）—riper—ripest