ISO 4491-4:2019

ISO 4491-4:2019 pdf free.Metallic powders-Determination of oxygen content by reduction
methods -Total oxygen by reduction-extraction.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4491-1, Metallic powders — Determination of oxygen content by reduction methods — Part 1: General guidelines
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at
— IEC Electropedia: available at
4 Principle
A test portion of the sample is heated in a graphite crucible at high temperature, either under vacuum or in a flow of an inert carrier gas. Oxygen in the sample is converted to oxides of carbon. These are extracted and transformed completely to either carbon monoxide (CO) or carbon dioxide (C02), which is determined by a suitable gas analysis method.
The methods used in practice to determine the total oxygen content have the following features:
a) Environment in the reaction chamber: — vacuum,or — flow of inert gas (nitrogen, argon, helium).
b) Graphite crucible: — individual, i.e. used only for one test portion, or — cumulative, i.e. the same crucible is used for the analysis of several successive test portions.
c) Reaction medium: — dry, i.e. the test portion alone is poured into the graphite crucible, the reduction being carried out in the solid state if the metal being analysed does not melt, or
— metal bath, i.e. in order to accelerate the reduction of certain metals it is advisable to prepare
first a bath of a fusible metal (for example platinum, tin, iron, nickel) capable of dissolving both
carbon and the metal in the test portion.
d) Heating: — continuous, i.e. the test portion is introduced into the crucible previously heated to the reaction temperature, the reduction taking place over a fixed period of time, of the order of several minutes, or — pulse, i.e. the cold crucible containing the test portion is heated by injecting, over a period of a few seconds, a high-power pulse of energy, reduction taking place very rapidly at the high peak temperature (up to 3 000 °C).
e) Determination of oxygen: Several methods for measuring either CO or CO2 are available. In both cases, a chemical conversion device is used to ensure that the oxygen to be determined is transformed completely into either CO or CO2. The analytical methods commonly used are:
— volumetric (for CO); — chromatography (for CO); — infrared absorption (for CO); — thermal conductivity (for CO and C02); — coulometry (for C02).
5 Apparatus and materials
The main elements of an apparatus suitable for determining the oxygen content of a metallic powder are the following: — crucibles, machined from high purity graphite; — a device to degas the graphite crucible at high temperature; — a device to introduce the test portion and degas it under inert gas or in vacuum at ambient temperature; — a device for gas extraction in accordance with a predetermined temperature cycle;ISO 4491-4 pdf download.

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