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Binary solvent mixture for tape casting of TiO2 sheets

Binary solvent mixture for tape casting of TiO2 sheets
Binary solvent mixture for tape casting of TiO2 sheets

Binary solvent mixture for tape casting of TiO 2sheets

Zhang Jingxian a,*,Jiang Dongliang a ,Lars Weisensel b ,Peter Greil b

a

Shanghai Institute of Ceramics,Chinese Academy of Science,Shanghai,Ding-Xi Road,200050,PR China

b

University of Erlangen-Nuremberg,Department of Materials Science,Glass and Ceramics,Martensstr.5,D-91058Erlangen,Germany

Received 4November 2002;received in revised form 12April 2003;accepted 27April 2003

Abstract

Four azeotropic binary solvent mixtures based on ethanol/methyl ethyl ketone,ethanol/toluene,isopropanol/methyl ethyl ketone and isopropanol/toluene were studied for the dispersion of TiO 2powders.Two di?erent polyvinyl butyral polymers (PVB79and PVB98)were selected as dispersant and as binder and dibutyl phthalate (DBP)was used as plasticizer.The dispersability of TiO 2suspensions was characterized by rheological measurements and sedimentation tests.After tape casting,the properties of Green tapes were tested in term of density,surface roughness and strength.Results showed that azeotropic EtOH/MEK mixture is the e?ective solvent system for tape casting of TiO 2sheets.The TiO 2tapes served for multilayer ceramic/metal composite manu-facturing.

#2003Elsevier Ltd.All rights reserved.

Keywords:Rheology;Slurry;Tape casting;TiO 2

1.Introduction

Tape casting is an established method for manu-facturing wide and ?at sheets of ceramic materials.Most applications of tape casting technology refer to the electronic industry,while some authors have also used this technique for obtaining thin ceramic sheets and multilayered structures for di?erent application such as solid oxide fuel cells or laminated composites.1à5A tape casting slurry is a complex system in which each component has a substantial e?ect on the slurry prop-erties.To obtain a reliable processing of high quality products,a homogeneous dispersion of ceramic parti-cles is highly required.5à14Stable suspensions are achieved by polymer steric stabilization or electrostatic repulsion or both according the type of dispersant and solvent used.The powder dispersion is not only depen-dent on the dispersant but also on the type of solvent used.15The major function of solvent is to act as a dis-persing vehicle and to ensure the dissolution of the organic components.Mixture of solvents may be useful to achieve a good compromise between dielectric con-

stant and surface tension (for dispersion)and low boiling point,and an adequate viscosity (for handling and drying).Azeotropic solvent mixtures were reported to have the advantage of improving the organic solubi-lity,and preventing preferential volatilization and poly-meric surface skin formation.8,15However,very few works have appeared in the literature dealing with the e?ect of solvent on the tape casting process.8,15à18Although PVB is well known as binder other than dis-persant due to its high molecule weight,good dis-perserbility is also observed with it as dispersant.17,19In the present work,four binary azeotropic solvent mixtures were studied with respect to the dispersability of TiO 2powders in the presence and absence of dis-persant.PVB79was selected as dispersant.A compar-ison of dispersability of PVB79with polycondensed fatty acid,castor oil,phosphate ester and PVB98was studied,results showed that at low concentration levels (<2wt.%),PVB79can be used as e?ective dis-persant.17,19,20The slurry properties were characterized in terms of sedimentation tests and rheological mea-surements.Green tapes were prepared through tape casting process and the in?uence of solvents on the tape properties was studied.The TiO 2tapes were subse-quently used for manufacturing of multilayer ceramic/metal composites.

0955-2219/03/$-see front matter #2003Elsevier Ltd.All rights reserved.

doi:10.1016/S0955-2219(03)00340-6

Journal of the European Ceramic Society 24(2004)147–155

https://www.doczj.com/doc/5e1180738.html,/locate/jeurceramsoc

*Corresponding author.

E-mail address:jx_zh@https://www.doczj.com/doc/5e1180738.html, (Z.Jingxian).

2.Experimental procedure 2.1.Starting materials

TiO 2powders (Merck Art812,Germany)with a par-ticle size of d =1.5m m and a speci?c surface area of 4.91m 2/g were used for this study.The azeotropic solvent mixtures were prepared from ethyl alcohol (599.8%,Carl Roth GmbHCo,Germany),isopropanol alcohol (599.7%,Carl Roth GmbHCo,Germany),methyl ethyl ketone (599.5%,Carl Roth GmbHCo,Germany)and toluene (599.5,Merck KGaA,Germany).Poly-vinyl butyral (B79,Monsanto,USA)was selected as dispersant.For preparing tape casting slurries,a poly-vinyl butyral of higher molecular weight (B98,Mon-santo,USA)served as a binder and butyl benzyl phthalate (Santicizer 160,Solutia,Inc.,St.Louis,USA)were used as plasticizer.The structure of PVB could be shown as

following:

PVB79and PVB98have the similar average molecue weight,50,000–80,000for PVB79and 40,000–70,000for

PVB98.However,the two polymer are di?ernet in their hydroxyl contents (18–20%for PVB98and 10.5–13%for B79).The properties of the starting materials are shown in Table 1.

2.2.Dispersability studies with binary solvents

Four binary azeotropic mixtures of solvents were selected for the dispersability study,see Table 2.Sus-pensions containing 16vol.%of TiO 2powder were prepared using di?erent solvents in the absence of dis-persant.The slips were ball milled with Al 2O 3balls for 24h.Slightly high concentrated suspension with 18vol.%TiO 2were also prepared with PVB (B79)as dis-persant.The concentration of PVB (B79)was hold as 1wt.%of the solid to assure all the suspensions with dif-ferent solvent mixture are well stabilized.An interval of 24h was allowed by ball milling to achieve equilibrium between the powder surface and the dispersant in the suspension.Then binder and plasticizer were added with the content as 8.56wt.%and 8.32wt.%(of the solid)respectively.The slurries were ball milled for another 48h.Rheological behavior of the suspensions was char-acterized at 25 C using a stress-controlled rheometer (UDS 200,Paar Physica,Austria).Shear dependence behavior of the suspensions under steady shear condi-tions were evaluated by ascending and descending shear rate ramps from 0.01to 1000s à1in 5min,and from 1000to 0.01s à1in 5min,respectively.

Table 1

Properties of raw materials Constituents

Name

Properties Density (g/cm 3)

Dielectric constant Viscosity (mPa s)Solubility

parameter (MPa)Solvent Ethyl alcohol 0.78924 1.226.2Solvent Isopropanol

0.78518.8 2.424.9Solvent Methyl ethyl ketone 0.805180.419.3Solvent Toluene

0.867 2.40.618.3Dispersant Polyvinyl butyral(B79) 1.08 3.1–23.12

Binder Polyvinyl butyral(B98) 1.08––Plasticizer

Butyl benzyl phthalate

1.05

Table 2

Physical properties of four binary azeotropic solvent mixtures Azeotropic solvent

Composition

Properties Density

(g/cm 3)

Dielectric constant Solubility

parameter (MPa)Ethyl alcohol/methyl ethyl ketone 34:660.79920.0721.68Ethyl alcohol /toluene

68:320.81217.5223.83Isopropanol/methyl ethyl ketone 30:700.79918.2421.01Isopropanol/toluene

69:31

0.810

14.06

22.99

148Z.Jingxian et al./Journal of the European Ceramic Society 24(2004)147–155

2.3.Sedimentation tests

Glass cylinders of10ml volume covered with a lid were used to test the sedimentation behavior of18 vol.%TiO2suspensions with PVB(B79).The position of the interface between the clear and supernatant sol-vent was recorded at regular time intervals.A month later,the volume of the sediment was determined before it was removed and the adsorption of dispersant on TiO2powder surface was characterized by TG-DTA, which measured the amount of released de?occulant upon heating in air.

2.4.Tape casting

After milling,the homogenous slurry was transferred to a vacuum chamber where it was de-aired at30kPa for30min.Tape casting was performed on a silicone coated polyethylene substrate foil with a gap height of 500and300m m for18and30vol.%TiO2slurries, respectively.After drying,green sheets were removed and the density was measured using Archimedes method.

3.Results and discussion

3.1.Interaction between solvent and TiO2powder surface The physical properties of the four azeotropic sol-vents are listed in Table2.The rheological properties of 16vol.%TiO2slurries(without dispersant)are char-acterized,see Fig.1.The four azeotropic solvent sys-tems reveal shear thinning behavior with a non-linearity of the viscosity at a shear rate of10sà1.The irregular shape and break points suggest the lack of uniformity of slurries,which can be characterized as an agglomerated/?occulated structure.In non-aqueous solvent systems with low to moderate dielectric constant,the electro-static repulsion between particles might not be high enough to overcome the van Der Waals attraction,so it’s di?cult to e?ciently reduce?occulation/agglomera-tion in the absence of dispersant.

As shown in Fig.1(b),in the0.01–10sà1shear rate range,suspensions show di?erent dropping rate in visc-osity:at low shear rate of0.01sà1,the ETOH/MEK suspension exhibits the highest viscosity of all solvent mixtures;however,with the increasing of shear rate to about10sà1,it drops quickly to the lowest one.This cannot be explained mainly using the surface dissocia-tion phenomena of TiO2particles because suspensions with ETOH/MEK systems show the highest viscosity at low shear rate(0.01sà1).The main reason for the dif-ference in dropping rate of viscosity versus shear rate is the di?erence in polarity of the solvent system.As shown in Tables1and2,EtOH is polar liquid,whereas isopropanol and MEK are weakly polar,so the ethanol has a strong hydrogen bonding and has strong pref-erence to oxide particle surface.22Similar,isopropanol has the second strongest preference to TiO2particle surface.This polarity can be further correlated to the wettability(other than dispersability)of solvent because the surface of oxide particle is also polarized.21,22The di?erence in wettability between solvent and powders lead to the agglomerates with di?erent properties.For ETOH/MEK systems,due to the strong interaction, agglomerates are relatively weak and can be broken easily under shearing.So with the increase of shear rate, the viscosity drops faster than other systems and show the lowest viscosity at about10sà1,see Fig.1(b).This wetting behavior can not be evidenced by viscosity measurement at very low shear rate because di?erent solvent system showed di?erent viscosity level due to hydrogen bonding,see Table1.Based on the rheologi-cal measurement,it can be concluded that EtOH/MEK system shows the best wettability on TiO2powder

surface. Fig.1.Rheological properties of16vol.%TiO2slurries in the absence of dispersant.

Z.Jingxian et al./Journal of the European Ceramic Society24(2004)147–155149

3.2.Interaction between solvent and dispersant

The EtOH/MEK mixture shows a relative dielectric constant of 21.3and e?ective electrostatic stabilization can be achieved when ionic polyelectrolyte surfactants are introduced into the suspension,as is the case for aqueous suspensions.23,24To avoid any in?uence of polarity,PVB79was selected as dispersant.The rheolo-gical properties of 18vol.%TiO 2slurries in the presence of PVB79are shown in Fig.2.A considerable decrease in viscosity is observed for TiO 2suspensions after the addition of dispersant,see Fig.1(b)and 2(b).The curves for EtOH/MEK and isopropanol/toluene sys-tems show a relatively stable character with a near-Newton rheological behavior,where the irregular shape at low shear rate might be due to the formation of weak agglomerates due to the high molecule weight of dispersant.25

The rheological properties of the suspensions can be related to the solubility behavior using the Hansen parameters and Hansen graph of solubility areas,22see

Fig.3.The miscibility between polymer and solvent can be predicated using a three-parameter system,

@2t ?@2d t@2p t@2

h

e1T

where the total Hildebrand value @t (solubility para-meter)is given by three parts:a dispersion force com-ponent @d ,a hydrogen bonding component @h ,and a polar component @p .Hansen also used a three-dimen-sional model to plot polymer solubilities in various sol-vents.He found that,by doubling the dispersion parameter (@d )axis,an approximately spherical volume of solubility would be formed for each polymer,with solvent locations nearest the edge of a solubility area being the least predictable.When a solvent lies within the sphere for a given polymer,a reasonable solubility of the polymer in this solvent is predicated,see Fig.3(a).Hansen’s three dimensional volumes can be similarly illustrated in two dimensions by plotting a cross-section through the center of the solubility sphere on a graph that uses only two of the three parameters for three dif-ferent polymer additives,PVB,PVC and PVA,see Fig.3(b).

As evidenced by Hansen model,isopropanol is loca-ted near the center of PVB while toluene is outside the polymer area of solubility.Therefore,isopropanol is expected to be the most e?ective solvent for PVB,while toluene is the least e?ective one.This corresponds well with the Hildebrand solubility parameter,see Table 1.For isopropanol/toluene systems,the dispersion can be related to the following two possible factors:(1)As isopropanol has the least di?erence in internal energy as PVB,a stretched con?guration of dispersant molecules will be preferred;(2)the di?erence in solubility para-meter between toluene and PVB79will enhance the adsorption of dispersant on powder surface.17There-fore,TiO 2suspensions with isopropanol/toluene as sol-vent show relatively stable state see Fig.2.For EtOH/Toluene system,due to the considerable competition adsorption between solvent and dispersant,a relatively high viscosity is expected though PVB79shows obvious dispersing e?ect (see Figs.1(b)and 2(b)at shear rate 2s à1).For isopropanol/MEK system,the high viscosity may be due to the swelled and well-stretched con?gur-ation of dispersant,which could be evidenced by rheo-logical measurement,Fig.2(a).

Fig.4shows the results of sedimentation and adsorp-tion measurements of the slips.The criteria used for evaluation of the dispersability are the settling rate and the settling density.As shown in Fig.4(a),the iso-propanol/toluene mixture exhibits the best dispersability in the presence of the dispersant represented by the highest supernatant volume and the lowest sediment volume (e.g.highest sediment density).This ?nding is in good agreement with the rheological behavior shown in Fig.2.Fig.4(b)corresponds well with Figs.2and 3

too.

Fig.2.Rheological properties of 18vol.%TiO 2slurries in the

presence of dispersant.

150Z.Jingxian et al./Journal of the European Ceramic Society 24(2004)147–155

Although the adsorption amount is high for iso-propanol/MEK system,due to the well-stretched con-?guration and high molecule weight of PVB79,polymer bridging and agglomeration will be highly possible.25 For EtOH/MEK system,the competition adsorption between solvent and dispersant takes e?ect,therefore,a relatively low adsorption amount is observed.

3.3.Slurry structure in the presence of binder

After the addition of binder and plasticizer,the slur-ries show a near Newton?ow behavior in a wide shear rate range,Fig.5.There is evidence that the binder (PVB98)will compete with dispersant for the adsorp-tion sites on the powder surface.26As the amount of binder is quite large in comparison to that of the dis-persant,the rheological behavior of the suspensions is mainly governed by the binder.The isopropanol/MEK and isopropanol/toluene solvent systems are e?ective for PVB98,so these slurries show high viscosity.On the contrary,in EtOH/toluene system,due to the relatively poor solubility of the solvent,the molecule chain of PVB98is somewhat coiled,and a low viscosity is observed.Therefore,the viscosity level cannot be directly related to the dispersion state of TiO2particles, though it may in?uence the solid content of slurries and the properties of?nal green tapes.

3.4.Processing of green tapes and laminated composites To further characterize the e?ect of solvent on the properties of green sheets,TiO2slurries are cast and dried in controlled conditions.After drying,the four kinds of sheets exhibit a great shrinkage,see Table3. The systems with EtOH/MEK and isopropanol/MEK as solvent show a high density,smooth surface and good strength.For isopropanol/toluene and EtOH/tol-uene systems,rough surface and low strength are observed,though isopropanol/toluene system is on a relative stable state before the addition of binder.

In

combination with Fig.1,it can be concluded that sol-vent systems play an important role on the slurry stabi-lity and?nal properties of green tapes.

Based on the study above,azeotropic EtOH/MEK mixture was selected as e?ective solvent.Further study of di?erent dispersants on the stability of TiO2slurry is reported in another paper.20Finally a formulation for tape casting of TiO2slurries is obtained,see Table4.Green tapes prepared from this formulation are used for the subsequent lamination and in?ltration process.

The concept of laminated composite for improved performance of brittle materials is well established.27à31 Multilayer design is a powerful,?exible approach since the microsturcture of individual layers with di?erent properties(mechanical,thermal or electrical properties) can be well tailored to meet various structural

and

Fig.4.Sediment volume and adsorption of PVB79on powder surface.

152Z.Jingxian et al./Journal of the European Ceramic Society24(2004)147–155

functional requirement such as strength,toughenss,thermol conductivity etc.Based on multilayer disign,a new processing technique is utilized to develop tailored ceramic multilayer blanks using controlled ceramic–metal reaction.This process can be expressed in the following.

The TiO 2green tapes were stacked with aluminum foil (AlMg3,Cochius,Nuremberg,Germany)with a thickness of 300m m.After lamination at 90 C and an applied pressure of 10MPa the organic components of the TiO 2green tape were burned out in air atmosphere and the multiplayer stack was subsequently heated to

1000 C in inert atmosphere.Above the melting tem-perature of Al the metal melt will penetrate into the porous green tape by capillary driven in?ltration and react to form a laminar ceramic/metal composite according to

3=2TiO 2t2tx eTAl !Al 2O 3t3=2TiAl x

e2T

Depending on the excess of Al with respect to the stoi-chiometric reaction a residual metal or intermetallic phase (with x ranging from 1to 3)will be formed.Fig.6shows the green TiO 2/Al-stacks and typical laminar microstructure of the resulting laminar composite.Based on the metal–ceramic reaction,multilayer mate-rials with tailored toughness,anisotropic thermal and electrical behavior are currently under

development.

Fig. 6.Green TiO 2/Al stacks and laminar microstructure of the resulting laminar composite (a)Schematic illustration of the laminar structure of the green TiO 2/Al-stacks (b)SEM micrograph of the resulting Al 2O 3/TiAl 3

structure.

Fig.5.Rheological properties of TiO 2slurries in the presence of dispersant,binder and plasticizer.

Table 3

Green sheet properties Properties

EtOH/MEK EtOH/Toluene Isopropanol/MEK Isopropanol/toluene Average tape thickness (m m)108?9112?2493?11114?13Green density (g/cm 3) 2.34 2.12

2.38 2.19Strength High Very low High Low Flexibility

Good Good Good Good Surface roughness

Smooth

Rough

Smooth

Rough

Z.Jingxian et al./Journal of the European Ceramic Society 24(2004)147–155153

4.Conclusions

The e?ects of solvent composition on the tape casting of TiO2slurries were examined for four di?erent azeo-tropic binary solvent systems.The EtOH/MEK had the highest dielectric constant of the systems investigated and showed the lowest viscosity of the TiO2slips.Green tapes prepared from the EtOH/MEK systems exhibited a high packing density with smooth and defect free sur-face.Results showed that azeotropic EtOH/MEK mix-ture is the e?ective solvent system for tape casting of TiO2sheets.The TiO2tapes can be combined with Al foils to form TiO2/Al stacks which can be converted into a multilayer Al2O3/TiAl x reaction product.The multilayer Al2O3/TiAl x composites o?er an interesting potential for engineering applications. Acknowledgements

The work was a cooperative program between the Chinese Academy of Science and the Max-Planck Foundation.The authors were grateful to the Max-Planck Foundation for providing?nancial support. References

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Dispersant0.880.59

PVB(B98)Binder8.40 5.68

DBP(santicizer)Plasticizer8.40 5.52

EtOH/MEK Solvent57.6328.85

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CAS SSO单点登录实例详细步骤 原创作者:孙俊财

第一步 1、用keytool生成证书: 命令: keytool -genkey -alias sjc -keyalg RSA -keysto re c:/store/mykey 说明: 这里-alias sjc 是表示生成的这个证书的别名叫sjc,-keyalg RSA 指的是采用的RSA算法,-keystore c:/store/mykey是指生成的证书存储的位置。回车后会提示你输入keystore password,这可以自己定(这里输入sunjuncai,下面配tomcat时要用的),然后是一些个人信息及组织信息,可以轻松搞定。 注意:密码输入后,会让你输入其他信息,记得这里第一个姓名必须是服务器的域名这里我输入的是完整计算机名称:gaofeng.nmc.hamcc 这里要注意如果不这样写就会报如下异常: java.io.IOException: HTTPS hostname wrong: should be 实战: C:\Documents and Settings\wangyoushi8>keytool -genkey -alias sjc -keyalg RSA -keystore c:/store/mykey 输入keystore密码:sunjuncai

您的名字与姓氏是什么? [Unknown]:gaofeng.nmc.hamcc 您的组织单位名称是什么? [Unknown]:上海神洲数港 您的组织名称是什么? [Unknown]:网络优化 您所在的城市或区域名称是什么? [Unknown]:郑州 您所在的州或省份名称是什么? [Unknown]:河南 该单位的两字母国家代码是什么 [Unknown]:ZH CN= gaofeng.nmc.hamcc, OU=上海神洲数港, O=网络优化, L=郑州, ST=河南, C=ZH 正确吗? [否]:y 输入的主密码 (如果和keystore 密码相同,按回车): 2、创建证书后,就导出证书: 命令: keytool -export -file c:/store/server.crt -alias sjc -keystore c:/store/mykey 说明: 从c:/store/mykey里取出证书入到c:/store/下,如果没有指定,就是存放在目录下C:\Documents and Settings\用户目录名\ 实战: C:\Documents and Settings\wangyoushi8>keytool -export -file c:/store/server.crt -alias sjc -keystore C:/store/mykey 输入keystore密码:sunjuncai 保存在文件中的认证 3、为客户端的JVM导入密钥: 命令: keytool -import -keystore D:/jdk1.5.0_12/jre/lib/security/cacerts -file c:/store/server.crt -alias sjc 说明: 注意:输入密码时密码为"changeit",这是默认密码. 特别说明:这个D:/jdk1.5.0_12/jre/lib/security/cacerts是指JDK的JRE路径下的lib目录. 至此,第一步完成。 实战: C:\Documents and Settings\wangyoushi8> keytool -import -keystore D:/jdk1.5.0_12/jre/lib/security/cacerts -file c:/store/server.crt -alias sjc 输入keystore密码:changeit

对羟基苯甲酸酯

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一、实现过程 从用到的jar包文件夹的cas-server-3.3.1modules中找出cas.war放到tomcat/webapps下面(cas-server-webapp-3.3.1.war重命名即可)。 现在cas默认的server端已经有了,下面自己写2个客户端测试一下 MyEclipse里面新建web project:sso 新建类HelloWorldExample package servlet; import java.io.IOException; import java.io.PrintWriter; import java.util.Enumeration; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public final class HelloWorldExample extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { response.setContentType("text/html");

PrintWriter writer = response.getWriter(); writer.println(""); writer.println(""); writer.println("Sample Application Servlet Page"); writer.println(""); writer.println(""); writer.println("

"); writer.println(""); writer.println(""); writer.println(""); writer.println(""); writer.println("
"); writer.println(""); writer.println(""); writer.println("

Sample Application Servlet

"); writer.println("This is the output of a servlet that is part of"); writer.println("the Hello, World application."); writer.println("
");

食品中对羟基苯甲酸酯类的检测方法

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