ISO 4491-3:1997 pdf download.Metallic powders一Determination of oxygen content by reduction methods
1 Scope
This part of ISO 4491 specifies a method for the determination of the hydrogen-reducible oxygen content of metallic powders containing 0,05 % (rn/rn) to 3 % (rn/rn) oxygen.
The method is applicable to unalloyed, partially alloyed or completely alloyed metal powders and also to mixtures of carbides and binder metal. It is not applicable to powders containing lubricants or organic binders.
The method may be extended to powders containing carbon by the use of a specaI catalytic device.
This part of ISO 4491 shall be read in conjunction with ISO 760 and ISO 4491-1.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part of ISO 4491. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO 4491 are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 760:1978, Determination of water — Karl Fischer method (General method).
ISO 4491-1:1989, Metallic powders — Determination of oxygen content by reduction methods — Part 1; General guidelines.
3 PrincIple
Pre-treatment of a test portion by drying at low temperature (170 °C) In dry nitrogen or argon.
Reduction in a stream of pure dry hydrogen at a given temperature. Absorption in methanol of the water formed by reaction of oxides with hydrogen. Titration with Karl Fischer reagent, the end-point being determined either visually by the colour change or electrometncally with two electrodes (deadstop end-point).
For powders containing carbon, conversion of the carbon monoxide and carbon dioxide formed to methane and water at 380 °C by means of a nickel catalyst.
4 Reagents
During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent punty.
WARNING — Karl Fischer reagent contains four toxic compounds: iodine, sulfur dioxide, pyridine and methanol. It is Important to avoid direct contact and especially Inhalation. Following accidental spillage, rinse with plenty of water
4.1 Methanol, anhydrous.
4.2 Karl Fischer reagent, equivalent to 1 mg of oxygen per millilitre.
Determine the hire of the Karl Fischer reagent by one of the following methods:
a) Add to the hiration flask 20 mg to 30 mg of water, weighed to the nearest 0,1 mg.
b) Add 100 mg to 200 mg, weighed to the nearest 0,1 mg, of sodium tartrate dihydrate (certified material containing theoretically 15,66 % (rn/rn) of water, corresponding to 13,92 % (rn/rn) of oxygenj, previously ground to fine powder and dried at 105°C ± 5 °C to constant mass.
c) Use the method descnbed in clause 7, taking 100 mg to 200 mg of pure sodium tartrate dihydrate, weighed to the nearest 0,1 mg, as the test portion, but limiting the procedure to the drying step at 170 °C and the subsequent titration.
See ISO 760 for detailed procedures of standardization.
4.3 Hydrogen. having a maximum oxygen content of 0,005 % (rn/rn) and a dew point not exceeding 45 °C.
4.4 Nitrogen or argon. having a maximum oxygen content c 0,005 % (rn/rn) and a dew point not exceeding -45°C.
4.5 Desiccant, consisting of granular anhydrous aluminium sodium silicate, activated silica gel or magnesium perchlorate,
5 Apparatus
NOTE — The alternative arrangements of the apparatus are shown m figure 1 (method 1) and figure 2 (method 2) respectivety.
5.1 Hydrogen supply unit (A), fitted with a pressure-regulating valve, a flow control valve and a flow meter.
5.2 Purifier (B), for the hydrogen, containing a catalytic deoxidizer and a dryer.
5.3 NItrogen (or argon) supply unit (C), fitted with a pressure-regulating valve, a flow control valve and a flow meter.ISO 4491-3 pdf download.