溶 凝 膠 法

簡 介

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溶凝膠法的優缺點 優點：

(1) 均質性與高純度。(2) 節省能源，減少蒸發的損失與空氣的汙染、 較純的樣品、避開相變、結晶的過程。

缺點：(1) 原料昂貴。(2) 凝膠的收縮量大。(3) 孔穴、氫氧基、碳。

溶 凝 膠 法 的 過 程 與 原 理溶凝膠法主要過程 ( 以 SiO2為例 )TMOS+ 水 + 醇

(a) 水解 (hydrolysis) 反應。

(b) 縮合 (condensation) 反應。

Si

OR

OR

OR

RO + H2O Si OR

OR

HO + ROH

OR

Si

OR

O

OR

RO+Si

OR

OH

OH

RO Si

OR

OR

OR

HO Si

OR

OR

OR

+ H2O

(c) 多縮合反應 (polycondensation)

Si

OH

O

OH

HO Si

OH

OH

OH

+ 6(H2O)

+ 6Si(OH)4

Si

O

O

O

O Si

O

O

O

SiHO

OH

OHSi

OH

OHHO

Si OH

OH

HOSiHO OH

OH

Si

OH

OH

OH

Si

OH

OH

HO

聚合反應

單體 (monomer) 顆粒 (particle) 鏈狀結構 (chain)三維網狀結構(3D network)

不同環境下的聚合反應

(1) Far from gel point

(2) Near from gel point

(3) Gel point

(acid-catalyzed)

10nm

(base-catalyzed)

10nm

溶凝膠過程與溫度之關係

Effect of experimental condition on the gelling time

(1) pH value(2) temperature(3) molar ration of H2O:Si

(4) precursor molecules(5) volume ratio of ROH:H2O

(6) solvent and additive solvent gelling time (hrs)

Methanol FormamideDimethyl-formamideAcetonitrileDioxane

86282341

Effect of pH value on the structure of gel

Aging process

Flow Chart of the two methods used to vary the pore characteristics of the gel silica matrices

Drying

Stage 1 CRP

Falling rate period 1 FRP1

Falling rate period 2 FRP2

Densification

Hydrolysis of TEOS with LiNO3 solution and LiOH solution

Example of preparation of lithium containing gel

Infiltration of LiNO3/LiOH in SiO2 gel

a: polymerized/LiNO3 gelb: infiltrated/LiNO3 gelc: polymerized/LiOH geld: infiltrated/LiOH gel

TG curves for the gels

Experimental solidification temperature of LiNO3 gels

Cooling rate (oC/min)

Polymerized T(o

C) InfiltratedT

(oC)0.05 2.06.0

203199191

213208 182

* Melting point of LiNO3 is 254oC

Conductivities ((-cm)-1) of gels at 400oCpolymerized/LiNO3 gel 1.3x10-2

infiltrated/LiNO3 gel 8.0x10-4

polymerized/LiOH gel 1.5x10-5

infiltrated/LiOH gel 4.4x10-6

0.2Li2O-0.8SiO2 glass(350oC)

VO(i-OC3H7)3 or VOCl3

+ C2H5OH+ H2O + dilute HNO3

pH~2 stir 1 day at 65oC dark green color

60oC oven for 4 weeks

Dried gels dark green brown color

Preparation of V2O5 crystals through sol-gel

Heat treated in oxygen atmosphere to varies temperatures

brown color

VOCl3 prepared gel V2O5 crystal forms above 200oC

VO(i-OC3H7)3 prepared gel V2O5 crystal forms above 400oC

VOCl3 prepared gel

200oC

700oC

VO(i-OC3H7)3 prepared gel

400oC

700oC

Alumina gel

HydrolysisThe unhydrolyzed species [Al(OH2)6]+3 exist below pH 3.With increasing pH, [Al(OH2)6]+3 can be hydrolyzed extensively:[Al(OH2)6]+3+hH2O→ [Al(OH)h(OH2)6-h]+3-h+hH3O+ hH3O+ +hOH- →2hH2O

Condensation

Dimer trimer X

Chemical modified Aluminum Alkoxides

Al-tri-sec-butoxide Al(OC4H9)3 modified with -diketonesActeylactone (CH3COCH2COCH3, AcAcH)Benzoylacetone (CH3COCH2COC6H5, BzAcH)Ethyl acetoacetata (CH3COCH2COOC2H5, EAcAcH)

The stabilization of -diketones for Al-tri-sec-butoxide in the order BzAcH < AcAcH < EAcAcH

The Al2O3/BzAc gel film is the most stable in air and have the highest photosensitivity among Al2O3 gel films.

ORMOSILS (Organically Modified Silicates)

Si(OR)4+R2Si(OR)2+YR’Si(OC2H5)3

where R is alkyl group -CH3, R’ is alkylene group -(CH2)n

Y is organofunction group such as -(CH2)3NH2,

-(CH2)3NHCOONH2, -(CH2)3S(CH2)2CHO.

Application:

1. Thin film and coating

2. Monoliths

3. Powders, grains, and spheres

4. Fibers

5. Porous gels and Members

Some Systems have been studied1.SiO2, Al2O3, B2O3, ZrO2, TiO2, Nb2O5, V2O5, Fe2O3, P2O5, ZnO2. Binary : SiO2-Al2O3, Li2O-B2O3, P2O5-SiO2.3. Composite : CdS-SiO2, Pt-SiO2, organic-inorganic hybrids, dye(R6G)-doped hybrids4. Multi-component: BaTiO3, PbZrxTi(1-x)O3, (Pb(1-y)Lay)( ZrxTi(1-x))O3 ( 鐵電 ), YBa2Cu3O7

Some Metal-alkoxidesTEOS (Si(OC2H5)4, 1L, 98%, USD $291), TMOS (Si(OCH3)4), 100g, 98%, USD $100)TPT (Ti(OCH(CH3)2)4, 500ml, 97%, USD $52), TBZ ((Zr(OC4H9)4, 25g, 99%, USD $249),ASB (Al(OC4H9)3, 500g 97% USD $64),

End of Part One