Zishang Ding

The sol-gel process of the yttrium complex from yttrium acetate

Abstract Solid yttrium acetate becomes soluble in methoxyethanol, when diethylenetriamine is introduced and the molar ratio of diethylenetriamine to yttrium acetate is ⩾ 1.5. It is proposed that the mechanism of the dissolution is: (1) free alkoxyl groups are formed due to the reaction of diethylenetriamine with methoxyethanol; (2) the charged alkoxyl groups are coordinated with Y3+ in yttrium acetate to form a soluble species. When water is added to the methoxyethanol solution of yttrium acetate with diethylenetriamine, a gel is formed. The optical transmission of the gels is dependent on the content of H2O. The detailed analysis of the reactions related to dissolution of Y(OAC)3 and its sol-gel process is given.

The drawing behavior of Y-Ba-Cu-O sol from non-aqueous solution by a complexing process

A complexing process is developed to prepare Y-Ba-Cu-O superconducting fibers. The process is not identical to typical sol-gel processes; here the resulting gel network is built up by hydrogen bonding linkage among complexing species in non-aqueous solution. Cu acetate, [Cu(OAC)2], Ba methoxyethoxide [Ba(ORE)2] and Y acetate [Y(OAC)3] are used as precursors for preparing homogeneous gels while α-methacrylic acid (HOAAα) and diethylenetriamine (DETA) as complexing agents, and methoxyethanol (REOH) as solvent. Fibers drawn from a sol obtained through reduced pressure present no or little deformation at 80°MoC via adjusting the amount of DETA and HOAAα. Cu(OAC)2, Ba(ORE)2 and Y(OAC)3 in the complexing process have been demonstrated to form gels without hydrolysis and condensation at ambient atmosphere. The relationships between the drawing behavior of sols and gel structure with different amounts of DETA and HOAAα are suggested. The concentration region of drawing the gel fibers with no or little deformation heated at 80°MoC is also found.

Effect of some process parameters on the deposition mechanism of ASi:H film

Abstract The aSi:H films were deposited through glow discharge decomposition of monosilane-hydrogen gas mixtures. The change of concentration of the SiH and SiH 2 groups in the film with the substrate temperature and rf power, the deposition rate, and the thermal evolution of the hydrogen were determined. They show that the deposition behavior differs with the variation of these parameters. In spite of the complexity of plasma and surface reactions, it is implied that three main surface reactions play an important role in the deposition: the chemisorption of the Si and SiH free radicals, the plasmaasisted hydrogenation, and the plasma-assisted dehydrogenation. Based on these reactions, a general expression of the deposition rate is given. It yields the calculated results in good agreement with the experimental data on the deposition rate.

A complexing approach to inducing sol-gel process of insoluble Cu ethoxide — evolution of local environment of Cu complex species

Abstract A stable gel was obtained from a methoxyethanol solution of Cu ethoxide using glacial acetic acid as a complexing agent with addition of water. Electron spin resonance, infrared and visible spectra of Cu complex species in solutions and gels were measured. The following results can be deduced from these spectra. (1) The structural characteristic of the primary Cu complex species in the methoxyethanol solution of Cu ethoxide with acetic acid (Cu/HOAC = 1:1) is a dimeric species, Cu 2 (OR) 2 (OAC) 2 (HOR) 4 , with small internuclear spacing and the same structure as that in crystalline hydrated copper acetate. (2) The primary Cu complex species transform to a hydrolyzed dimeric species, Cu 2 (OH) 2 (OAC) 2 (H 2 O) 6 , with large internuclear spacing through both hydrolysis and change in its coordination configuration. (3) The olation reaction occurs among the hydrolyzed species and finally results in the formation of a stable transparent gel. (4) The structural form of the hydrolyzed Cu complex species remains in fresh gel, while the structural form of Cu complex species in xerogel is similar to that of the primary Cu complex species.

The gelation behaviour of copper ethoxide

Abstract An alcohol solution of Cu ethoxide can be obtained only by adding a complexing agent. When H2O is added, an ethanol solution of Cu ethoxide with citric acid or diethylenetriamine (DETA) as a complexing agent does not exhibit a sol-gel process. Hard gels can be obtained at 50°C by evaporating the solvents in a solution containing citric acid and a large amount of water, or in a solution containing DETA (DETA/Cu > 2). However, these gels may liquefy when exposed to moisture. An ethanol solution of Cu ethoxide with acetic acid as a complexing agent can turn to a colloidal or polymeric gel, depending on the amount of water added to the solution. A solution prepared by dissolving Cu ethoxide in ethylene glycol monomethyl ether (EGME) with acetic acid has a better gelation behaviour with water. The gels derived from an ethanol or EGME solution of Cu ethoxide with acetic acid are insensitive to moisture.

Structural change of soda lime glass with minor P2O5 addition and heat treatment

Abstract Increasing the P2O5 content or altering the heat treatment conditions of soda-lime glass produces structural changes which have been characterized by Raman, IR and ESR spectra methods. The content of phosphate tetrahedra having double bonds in the glass shows a maximum with increase in P2O5 addition. During heat treatment there appear changes in the structure of phosphate and silicate tetrahedra and in the distribution of sodium cations.

Kinetics on the sol-gel process of the modified Cu ethoxide☆

Abstract Kinetics of the reactions and gelation of modified Cu ethoxide, Cu 2 (OR) 2 (OAC) 2 (HORE) 4 , with H 2 O were measured. When water was added to the methoxyethanol solution of the modified Cu ethoxide, the first reaction was substitution reaction of H 2 O for methoxyethanol ligand in Cu 2 (OR) 2 (OAC) 2 (HORE) 4 . The substitution reactions lead to forming another dimer with larger spacing between Cu atoms, then alkoxy groups were hydrolyzed. Finally, hydrolyzed dimers were formed and polymerized into a transparent gel. With the transformation of a primary dimer, Cu 2 (OR) 2 (OAC) 2 (HORE) 4 , to a hydrated or hydrolyzed dimer, Cu 2 (OX) 2 (OAC) 2 (H 2 O) 2 (HOX) 4 (X = H or R), with large spacing between Cu atoms, a 380 nm absorption band disappeared. Through measurements of changes in absorbance at 380 nm and gelation time with different H 2 O content, kinetic expressions about the reactions and gelation for the sol-gel process of the modified Cu ethoxide were derived. The derived relations are in a good agreement with the experimental results. It is concluded from the kinetic relationships that the effect of H 2 O content is to change the properties of the solvent involved.

Characterization of A-Si : H and A-SiGe : H Films in Liquid Crystal Light Valve

A-Si : H and a-Si : H/a-SiGe : H heterojunctions have been prepared as the photoconductors in the liquid crystal light valves. The impedance matching conditions of the a-Si : H and the heterojunction in the valves have been carefully analysed, which has shown that the adjustment for the capacitance of the photoconductor is the key procedure for the matching, but the low photocapacitance effect in the a-Si : H limits the further improvements on the matching. The formation of the a-Si : H/a-SiGe : H diode promotes the photocapacitance effect in the photoconductor, and the matching behavior in the valve is greatly improved.

Structural characteristics of Gd a-Si(S,O):H films

Abstract The local structure of a-Si(S,O):H films has been characterized by IR, XPS, ESR, and hydrogen evolution method with gas chromatographic analysis. Based on the results, a structural model may be presented.

The effect of different monocarboxylic acids on the gelation behaviour of Cu ethoxide

Cu ethoxide becomes soluble in methoxyethanol when formic, acetic, or acrylic acid is added. For the complete dissolution, the minimum molar ratio of an acid to Cu ethoxide is two for formic acid (HOFA), and one for acetic (HOAC) or acrylic (HOAA) acid. The solutions of Cu ethoxide with any amounts of formic acid are incapable of forming gels. Those with acetic or acrylic acid/Cu ratio of 1 are able to convert to gels. For the range of the water concentration from 1.5 to 10 M, the gelation time is strongly dependent on [H2O] for the solution with HOAC/Cu ratio of 1, while it is almost independent for the solution with HOAA. It is suggested that the differences in the behaviour of soluble Cu species derived from the three acids are attributed to different coordination forms and the bonding strength between ligands and copper ions.