CS257153B1 - Process for the preparation of special pancake powders - Google Patents

Abstract

The solution concerns the preparation of palladium black by reduction with sodium phosphate. Unlike other reducing agents, sodium phosphate is stable, highly soluble, can be used in both solid and liquid form, and reduces even concentrated solutions in a strongly acidic environment without the need for prior neutralization of the solution.

Description

The invention relates to a process for the preparation of special palladium powders, in particular very finely divided palladium in the form of palladium black by reduction from a solution of palladium chloride with sodium hypophosphite.

With the development of microelectronics, the requirements for the production of special powder metals with precisely defined physico-chemical properties are increasing. The noble metals platinum, palladium, gold, silver, mixtures thereof and alloys are most suitable for this purpose. For further processing of these materials, eg to conductive plating pastes, it is necessary to maintain the required chemical purity, granulometry, specific surface area, bulk density, moisture, eventually other parameters. To date, powdered metals have been prepared from solutions of their salts with strong reducing agents. Prior to reduction, the solutions of the metal salts of interest are generally neutralized by the addition of a neutralizing agent (ammonium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, calcium hydroxide) to a pH of 4.5 to 6.5. After neutralization, a reducing agent is metered into the reaction mixture. So far, hydroquinone, sodium borohydride, sodium hydrosulfide, phosphoric acid, formic acid, zinc have been used to reduce palladium.

The reduced metal is separated from the mother liquor, washed, filtered and dried.

However, special equipment (atomizer, dispersant, etc.), atypical starting compounds (complex salts) or a complex process scheme with precise reaction conditions are required to prepare the palladium powder in this way to maintain the required particle size. Industrial application is also hindered by the instability of some of the reducing agents used, their form, or their behavior during reduction.

These drawbacks are overcome by the process for preparing the special palladium powders according to the invention, which is based on the use of a sodium hypophosphite reducing agent. The reducing agent is stable, well soluble and can be applied in both solid and liquid form. It also reduces concentrated palladium solutions, especially palladium (II) chloride, even in a strongly acidic environment of 0.5 to 5 M hydrochloric acid, so that the previous neutralization of the solution is eliminated.

The reduction process takes place in a reducing glass flask fitted with a heating element and a stirrer.

Sodium hypophosphite is added to the palladium chloride solution diluted to the desired concentration with deionized water at a given temperature. Palladium black sediments at the bottom of the flask. The end of the reduction is indicated by the formation of a white foam and a colorless liquid phase. Palladium black is washed, avoided and dried.

Example

600 ml of a 20 g.l palladium chloride solution was reduced with sodium hypophosphite at 50 ° C with vigorous stirring. Reduced palladium black settles at the bottom of the flask. After filtration, the palladium content in the liquid phase is less than 0.001 g.l. Consumption was 1.7 g per 1 g of palladium. Mean particle diameter 0.5 µm.

SUBJECT OF THE INVENTION

Claims (1)

SUBJECT OF THE INVENTION Process for the preparation of special palladium powders, characterized in that the palladium chloride solution is reduced with sodium hypophosphite directly from an acid medium having a molarity of hydrochloric acid of 0.5 to 5 M at a temperature of 20 to 70 ° C.