PROCESS FOR MAKING SILVER POWDER PARTICLES WITH SMALL SIZE CRYSTALLITES

摘要

The process for making silver powder particles with small size crystallites uses a combination of gum arabic and maleic acid with the reduction of a silver salt with ascorbic acid, Silver thick film paste containing these silver powder particles can be used in electronic applications to form electrodes for semiconductor devices and, in particular, solar cells.

主权项

1. Silver powder particles made by a process comprising:
(a) preparing an acidic aqueous silver salt solution comprising a water soluble silver salt dissolved in deionized water; (b) preparing an acidic aqueous reducing and particle modifier solution comprising:
(i) a reducing agent selected from the group consisting of ascorbic acid, ascorbates and mixtures thereof dissolved in deionized water;(ii) nitric acid;(iii) gum arabic;(iv) maleic acid; and(v) deionized water; (c) maintaining said acidic aqueous silver salt solution and said acidic reducing and particle modifier solution at the same temperature, wherein said temperature is in the range of 10° C. to 65° C., while stirring each said solution during and after preparation; (d) adding said acidic aqueous silver salt solution to said acidic aqueous reducing and particle modifier solution while stirring to make a reaction mixture and maintaining the temperature of said reaction mixture at said temperature of (c), wherein said silver powder particles precipitate and are contained within the resulting final aqueous solution; and (e) increasing the temperature of said final aqueous solution to a temperature in the range of 65° C. to 80° C. while continuing stirring;said silver powder particles comprising crystallites between 30 and 47 nm in size as determined by X-ray diffraction and the Scherrer formula; and said silver powder particles having d50 in the range of 0.5 to 3.5 μm.