| 1. |
- Vacassy, R., et al.
(författare)
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Synthesis of controlled spherical zinc sulfide particles by precipitation from homogeneous solutions
- 1998
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Ingår i: Journal of The American Ceramic Society. - : American Ceramic Society. - 0002-7820 .- 1551-2916. ; 81:10, s. 2699-2705
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Tidskriftsartikel (refereegranskat)abstract
- Zinc sulfide (ZnS) powders have been obtained by precipitation from homogeneous solutions of various zinc salt compounds with S 2- as precipitating anion, formed by decomposition of thioacetamide. Spherical particles with a very narrow size distribution can be obtained by controlling; the synthesis parameters. The particle sizes are influenced by the nature of the associated anion. For example nanometer-sized ZnS particles are formed using acetate or acetylacetonate anions under acidic pH conditions, controlled by the addition of acetic acid. Although the nucleation is accelerated by the use of acetic acid, limited particle growth occurs because of the formation of complexes with zinc cations that lowers the concentration of free cations in the solution. Also, the complexing-attachment phenomena of the ZnS particles with acetate and acetylacetonate anions lead to the arrest of particle growth processes. The presence of complexed Zn 2+ species in the acidic solution is demonstrated both theoretically, using a model based on the calculations of the solubility isotherms of the soluble species, and by Fourier-transform infrared techniques. The nanostructured ZnS particles may provide a suable semi-conductor nanocluster material for optoelectronic applications as well as a phosphor suitable for application in flat-panel display technology.
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| 2. |
- Vacassy, R., et al.
(författare)
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Tin dioxide nano-powders for gas sensor applications
- 1998
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Ingår i: Materials Research Society Symposium - Proceedings. ; , s. 41-46
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Konferensbidrag (refereegranskat)abstract
- SnO2 nanoparticles are of interest for gas sensor applications because the surface area is much larger compared to conventional powders. Thus, interactions between the material and the gases, which occur on the surface sites of the particles, are increased considerably. The preparation of SnO2 powders has been investigated following two forced precipitation systems: the hydrolysis reaction of SnCl4 in an emulsion media and the hydrolysis reaction of Sn2+ in the presence of a complexing ligand (CH3COO-). Spherical nanoparticles in the 10 to 100 nm range and with a narrow size distribution were synthesized by both precipitating routes. In both cases, it has been demonstrated that the most important parameter which controlled the particle size was the nature of the associated union. When this associated union or ligand is able to form a strong complex with the colloidal subunits, a barrier against Van der Waals attraction is created which results in little growth. This greatly influences the agglomeration/growth kinetics during the precipitation. The effect of acetate chelating ligands which resulted in the SnO2 nano-powders formed of 5-10 nm crystallites will be presented and discussed. Preliminary results on the gas (N2, NO) adsorption studies on pellets formed from these powders are also presented.
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| 3. |
- Hofmann, H., et al.
(författare)
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Potential of nanosized ceramic powder for functional applications
- 1997
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Ingår i: Ceramic Engineering and Science Proceedings. ; , s. 687-694
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Konferensbidrag (refereegranskat)abstract
- Nanophase ceramic particles are building-blocks for the formation of nanostructured ceramics and are important in a composite for functional applications. Different synthesis methods for nanosized ceramics were developed. Depending on the method and chemical composition, powders which are agglomerates of nanosized primary particles exist. These primary particles show very small grain size distribution.
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| 4. |
- Scholz, S. M., et al.
(författare)
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Mie scattering effects from monodispersed ZnS nanospheres
- 1998
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 83:12, s. 7860-7866
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Tidskriftsartikel (refereegranskat)abstract
- Transmission spectra of monodispersed particles exhibit pronounced resonance features from which particle properties can be deduced. ZnS powders were used as model materials since they can be synthesized by homogeneous precipitation with a narrow size distribution. The optical extinction spectra can be simulated using Mie scattering theory, and can be used as an in situ diagnostic tool for following the growth of particles during precipitation reactions. Using results of particle diameter measurements by other methods, information on the refractive index of the particles can be retrieved, indicating a highly porous internal structure of the spheres. Distinct features in the experimental and simulated spectra have been interpreted as to arise from circumference and diameter resonance effects in the particles. The simultaneous observation of these two effects allows one to estimate size and solid volume fraction from simple transmission spectra by application of an effective-medium model for the simulation parameters. The potential of application of Mie resonance effects for selective light screening or as pigments are discussed.
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| 5. |
- Scholz, S. M., et al.
(författare)
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Nanoporous Aggregates of ZnS Nanocrystallites
- 1998
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Ingår i: Applied organometallic chemistry. - : John Wiley & Sons. - 0268-2605 .- 1099-0739. ; 12:5, s. 327-335
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Tidskriftsartikel (refereegranskat)abstract
- During the synthesis of ZnS powders by wet chemical precipitation, the formation of nanoporous spheres is observed. The powders have been investigated using thermogravimetric analysis, X-ray diffraction and optical spectroscopies. Nanopore formation can be explained by several stages of growth. The formation of nanoparticles as primary particles is followed by their agglomeration forming secondary particles. These secondary particles are monodispersed spheres with a considerable porosity, because the agglomeration of the nanoparticles is unlikely to be volume-filling. The voids or nanopores formed by this agglomeration process in the secondary particles is estimated to comprise around 35% of the sphere volume. They are mainly filled with water and the residues of the chemical reagents. Water in the pores partially reacts with ZnS and forms hydrated sulphates. The chemical reagents used for the precipitation reactions are also found to be bound to the nanocrystallite's surfaces as ligands in some cases. Depending on the reaction conditions and reagents, the agglomeration of the nanoparticles can also be modified or hindered by the use of complexing agents acting as a sterically stabilizing surface layer on the nanocrystallites. The agglomeration of nanoparticles to larger units being a general phenomenon, this use of complexing agents to control pore formation and agglomerate size should be applicable to other nanocrystalline systems.
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| 6. |
- Vacassy, R., et al.
(författare)
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Nanostructured zinc sulphide phosphors
- 1998
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Ingår i: Materials Research Society Symposium - Proceedings. ; , s. 369-374
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Konferensbidrag (refereegranskat)abstract
- Zinc sulphide (ZnS) particles are efficient phosphors for application in flat-panel displays. Spherical ZnS particles were prepared by precipitation from a homogeneous solution. Nanoparticles of 20 to 40 nm having a very narrow size distribution could be synthesized by using complexing chelates such as acetate and acetylacetonate. Complexing of the precipitating cation with the anions present in the system lead to a limited concentration of free cations in the solution. This strongly influences the kinetics of the primary particle agglomeration/growth, resulting in nanometer-sized ZnS particles. Nanostructured ZnS synthesized in this way are polycrystalline particles composed of crystallites of 5-10 nm. The synthesis of very small, non-agglomerated, nanocrystalline particles in the 5-10 nm size range was also possible, making use of a strong complexing ligand (thioglycerol) during the synthesis. The synthesis of controlled monosized ZnS particles will be presented and discussed. The photoluminescence characteristics of ZnS make this material a suitable candidate as phosphor for application in low voltage display technology. The effect of Mn2+ doping on the luminescence characteristics of ZnS will also be discussed.
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| 7. |
- Vacassy, R., et al.
(författare)
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Synthesis of zirconia-coated gold nanoparticles
- 1998
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Ingår i: Journal of materials science letters. - : Kluwer Academic Publishers. - 0261-8028 .- 1573-4811. ; 17:19, s. 1665-1667
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Tidskriftsartikel (refereegranskat)
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