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Physical & Chemical properties

Oxidising properties

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Description of key information

Silver nitrate is marketed in the form of aqueous solutions and in the form of solid crystals with various particle size characteristics. Whereas aqueous solutions do not require classification (United Nations, 2003), solid silver nitrate needs to be classified as an oxidising solid. Depending on the particles size, either classification as oxidising solid category 1 or category 2 is required. As a cut-off size between these categories, a D10 of 250 µm is proposed (see discussion).

Key value for chemical safety assessment

Additional information

According to Annex VI of Regulation (EC) No 1272/2008 of the European Parliament and of the Council on classification, labelling and packaging of substances and mixtures, silver nitrate is classified as an oxidising solid, category 2 (Index No. 047-001-00-2). The Precious Metals and Rhenium consortium has tried to retrieve the underlying test results for the above mentioned classification but unfortunately they were not available to any PMC Members or its experts.

Initial experimental testing (UN O.1 method) then indicated that at least for some specifications of silver nitrate, a classification as Category 1 would be applicable, and is was hypothesised that particle size could have a significant influence, particularly in respect of the content of very fine particulate fraction. Subsequently, the Precious Metals and Rhenium Consortium has conducted a total of seven experimental tests for oxidising properties (UN O.1 method) with silver nitrate. Various commercial samples were tested, either untreated, after worst-case simulated transport (to model abrasion processes which can produce fine attrition particles), or after actual grinding. An overview of these tests is given in the table below. Robust study summaries are available for four studies and are included in the technical dossier.

 

Sample description

D10

D50

D90

Resulting classification category for oxidising solids

Commercial sample from producer 1, untreated

329 µm

491 µm

727 µm

Cat. 2

Commercial sample from producer 1, after worst-case simulation of transport

272 µm

532 µm

958 µm

Cat. 2

Commercial sample from producer 2, untreated

254 µm

421 µm

677 µm

Cat. 1

Commercial sample from producer 2, after worst-case simulation of transport

154 µm

295 µm

498 µm

Cat. 1

Commercial sample, Batch PMC 4, untreated

150 µm

291 µm

457 µm

Cat. 1

Commercial sample, Batch PMC 4, after grinding

134 µm

277 µm

454 µm

Cat. 1

Commercial sample, Batch PMC 2, untreated

< 1 mm (not further specified)

Cat. 1

 

The results of this testing programme show the particles size indeed has an influence on the extent of oxidising properties of silver nitrate. Depending on the particles size, either classification as oxidising solid category 1 or category 2 is required.

As a cut-off size between these categories, a D10 of 250 µm is proposed.

Since fine particles are considered to be the most relevant to oxidising behaviour thresholds in this context, the D10 value (i.e. the particle diameter at which 10% of particle gradation mass is finer than the stated value) has been selected as a categorisation criterion. It is recognised that this threshold has its limitations since it is based on very few data points and there is reliance on only one characteristic. It is therefore used in the absence of a more comprehensive set of influencing parameters. If new and better data become available, the recommended threshold may have to be revised accordingly

 

Justification for classification or non-classification

Silver nitrate is marketed in the form of aqueous solutions and in the form of solid crystals with various particle size characteristics. Whereas aqueous solutions do not require classification (United Nations, 2003), solid silver nitrate needs to be classified as an oxidising solid. Depending on the particles size, either classification as oxidising solid category 1 or category 2 is required. As a cut-off size between these categories, a D10 of 250 µm is proposed (see discussion).