GOST 18897-98

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  ГОСТ 18897-98

GOST 18897−98 (ISO 4491−2-97) Powder metal. Determination of oxygen content by methods of recovery. Weight loss while restoring the hydrogen (hydrogen loss) (adjusted)

GOST 18897−98
(ISO 4491−2-97)

Group B59

INTERSTATE STANDARD

POWDER METAL

Determination of oxygen content by methods of recovery.
Weight loss while restoring the hydrogen (hydrogen loss)

Metallic powders. Determination of oxygen content by reduction methods.
Loss of mass on hydrogen reduction (hydrogen loss)

ISS 77.160
AXTU 1790

Date of introduction 2001−07−01

Preface

1 DEVELOPED by the Interstate technical Committee for standardization MTK 150, Institute for problems of materials science I. N. Frantsevich of NAS of Ukraine

SUBMITTED to the State Committee of Ukraine for standardization, Metrology and certification

2 ADOPTED by the Interstate Council for standardization, Metrology and certification (Protocol No. 14 dated November 12, 1998)

The adoption voted:

3. This standard contains the full authentic text of international standard ISO 4491−2-97 «Powder metal. Determination of oxygen content by methods of recovery. Part 2. Mass loss in the process of reduction with hydrogen (combustion loss during annealing in hydrogen)» with additional requirements that reflect the needs of the economy, which in the text are highlighted in italics

4. The decision of the State Committee of the Russian Federation for standardization and Metrology dated December 19, 2000 N 384-St inter-state standard GOST 18897−98 (ISO 4491−2-97) introduced directly as a state standard of the Russian Federation from July 1, 2001

5. REPLACE GOST 18897−73


AMENDED, published in IMS No. 5, 2010

An amendment made by the manufacturer of the database

1 Scope

This standard specifies a method for determining the relative losses of mass of metal powder when heated in a stream of pure dry hydrogen for the evaluation of the chemical properties of the powder.

The method is applicable to unalloyed, partially and fully doped metal powders shown in table 1.


Table 1 — Time and temperature recovery during the test

Method is not applicable to powders containing a lubricant, and mixtures of metal powders.

2 Normative references

The present standard features references to the following standards:

GOST 2184−77 the sulfuric Acid. Specifications

GOST 23148−98 (ISO 3954−77) Powders used in powder metallurgy. Sampling

3 Reagents and materials

3.1 Hydrogen with a maximum oxygen content of 0,005% () and a dew point not higher than minus 45 °C.

3.2 Nitrogen or argon with a maximum oxygen content of 0,005% () and a dew point not higher than minus 45 °C (6.3).

3.3 Askari by ND.

3.4 Phosphorus pentoxide at ND.

3.5 sulfuric Acid according to GOST 2184.

4 Equipment

An example of the most suitable installation scheme for the test is shown in figure 1.

Figure 1 is an Exemplary diagram of an apparatus to test

1 — flow of hydrogen; 2 — flow of nitrogen or argon; 3 — thermocouple; 4 — heating zone; 5 — oven;
6 crew; 7 — quartz tube

Figure 1 is an Exemplary diagram of the setup for the tests (dimensions are given in millimeters)

4.1 Laboratory scales with adequate weighing, ensure weighing to the nearest 0.1 mg.

4.2 Electric heating tube furnace which can continuously operate at these temperatures (table 1) and has a control system for maintaining the temperature within the permissible deviations given in table 1, in the part of tube where there is a porcelain boat (4.5).

Note — When testing the magnetic powders is recommended to perform a winding of an electric furnace heater is non-inductive way.

4.3 gas-tight tube made of quartz (heat-resistant up to 1000 °C) or of refractory material (for example dense alumina). The inner diameter of the tube should be from 25 to 40 mm, and the length should be on each side of the furnace not less than 200 mm.

When you run a large number of tests to determine losses on ignition in hydrogen it is allowed to use the stove, which is more in comparison with described and allows for the simultaneous testing of several of the investigated portions (batches). It is necessary to observe the test conditions given in table 1 and the results obtained should not differ from the results of tests on recommended equipment.

4.4 Fully enclosed thermocouple, e.g. platinum-rhodium, and showing or recording device that provides temperature measurement with an accuracy of 5 °C.

Allowed if it is necessary to measure the temperature on the outer side of the recovery tube. In this case the thermocouple must be pre-calibrated with a second thermocouple inside the tube to ensure that the temperature of the test sample values and tolerances specified in table 1.

4.5 the Boat, preferably of ceramic, with a high content of aluminum oxide and with a polished surface (for example a boat of porcelain or corundum). Can be used for pumps and also other materials, such as quartz, zirconium oxide, molybdenum and Nickel, if conditions permit test. The boat shall be of such size that the thickness of the powder in the boat at a uniform distribution does not exceed 3 mm (e.g. 75 mm long and 12 mm wide).

New boats must be pre-calcined in a stream of hydrogen at test temperature and should be stored in a desiccator. Boats must be calcined to constant weight.

The boat can be used repeatedly, provided that it is always used to test the same metal powder or the like, as well as carefully cleaned by mechanical means after each determination and stored in a desiccator.

4.6 device for feeding the hydrogen and nitrogen or argon with pressure gauges and flow meters to control the flow of gas.

4.7 Desiccator at ND.

4.8 Hook, alloy steel, for loading and unloading the boat from the furnace.

4.9 Scheme of installation, which can be used for pre-purification of hydrogen and nitrogen or argon in accordance with the requirements of 3.1 and 3.2, is shown in figure2.

Figure 2 — Scheme of installation for purification of gases

Figure 2 — Scheme of installation for purification of gases

The installation consists of the following elements: a cylinder with hydrogen and gear 1; a cylinder with nitrogen or argon and the reducer 2, electric tube furnace 3 (the hot zone — not less than 150 mm) with the means of monitoring and control of temperature; quartz pipe 4 with a diameter of 18 and 22mm and a length of about 400 mm, filled with copper shavings, designed for the purification of hydrogen and nitrogen or argon from the oxygen; bottles Tishchenko: Astarita 5, with phosphoric anhydride 6, mixed with calcined asbestos; flask Drexel 9 with concentrated sulphuric acid; glass of tap 8, connecting the cleaning system with a quartz tube 7 of the setup for testing is shown in figure 1.

Askari, phosphoric anhydride and sulfuric acid used to absorb moisture, replace after 1.5−2 months.

For purification of hydrogen from oxygen is also used absorption a bottle of palladianism asbestos to absorb moisture — a jar of silica gel or synthetic zeolite with a grain size from 0.25 to 0.50 mm.

The unit can be used to clean the hydrogen supplied from the main.

Allowed for purification of hydrogen from oxygen to use other settings, providing the requirements of 3.1.

5 Sampling

5.1 the Powder should be tested in the delivery condition.

5.2 mass Loss should be determined on two test portions (batches).

5.3 the Mass of the test portion should be equal to approximately 5 g, with the exception of powders with low bulk density, for which it may be less and must meet the requirements outlined in 4.5 and 6.2.

The selection and preparation of samples for analysis is carried out according to GOST 23148, if they are not specified in the regulations for a specific powder.

Allowed subject to the requirements of 4.5 and 6.2, except the differences in the test results will be used to analyze all sample powders weighing less than 5 g.

6 test procedures

Have two denitions for each test specimen.

6.1 Heat the oven (4.2) with the inserted tube (4.3) to the temperature specified in table 1 for both test metal powder.

6.2 Weigh boat (4.5) with an accuracy of 0.1 mg. Distribute the test portion of the powder along the entire length of the boat with a layer thickness of not more than 3 mm. Weighed the boat with the test portion with an accuracy of 0.1 mg.

6.3 Flow of nitrogen (3.2) through the tube for at least 1 min at flow rate corresponding to a gas velocity (25 mm/s) measured in the cooling zone of the tube. Then insert the boat containing the test portion in the tube and push it until then, until it is in the center of the furnace with uniform temperature. The boat should move slowly enough to prevent the precipitation of powder due to high speed of outgassing. Continue flowing nitrogen for 1 min.

If difficulties arise to prevent precipitation of the powder from the pumps, the powder may be pressed (without the use of lubrication, ligament, moisturizer or other additives) to obtain a pressed powder blanks low density or butoxide wrapped in copper foil, if a powder preparation has a very low strength respecing material. Copper foil can be used only if the test temperature exceeds the melting point of copper.

Extruded powder billet must have a thickness of not more than 2 mm and porosity no less than 30%.

When testing powders that tend to form compounds with nitrogen (for example chromium-containing alloy steel powder), the purging should be performed using argon instead of nitrogen (6.5 and 6.6).

6.4 Let a stream of hydrogen (3.1) and stop flow of nitrogen. Simultaneous switching of gas flows. Establish a steady flow of hydrogen in the tube, corresponding to a gas velocity of 25 mm/s in the zone of its cooling. This corresponds to approximately 50 l/h for tube 25 mm in diameter and approximately 110 l/h, for pipes with a diameter of 40 mm. Support the flow of hydrogen during the period of time specified in table 1. During this time period, maintain temperature of the furnace within a specified range.

6.5 At the end of a specified time again include the nitrogen flow and stop the flow of hydrogen. Simultaneous switching of gas flows. In 2−3 minutes, pushing the boat at the end of the furnace in the cold part of the tube.

6.6 the Boat with the recovered test portion is cooled in a nitrogen atmosphere to a temperature below 35 °C, then transferred her from the tube in a desiccator to cool to ambient temperature.

6.7 Weigh the boat with the recovered portion of the test with an accuracy of 0.1 mg.

Note — Before testing the collected, as indicated in figures 1 and 2, and United into one system installation should be checked for leaks. The gas used to purge the system, must be removed through the exhaust vent.


Throughout the process of working on the installation for purification of gases from oxygen to furnaces 3 (figure 2) must be maintained at a temperature of (450 ±10) °C.

Allowed in 6.3 and 6.5 instead of the flow of nitrogen and argon use a stream of hydrogen.

7 Processing of results

7.1 mass Loss during annealing in hydrogen (mass fraction), %, is calculated by the formula

, (1)

where is the mass of boats with the test portion before the test, g;

 — weight boats with a restored portion of the test after the test, g;

 — the empty weight of the pre-treated boat (4.5),

7.2 the Result of each determination is calculated, rounding to the nearest 0,01% (). The discrepancy between the two definitions should be not more than 0.04% in magnitude, if the mass loss during annealing in hydrogen of less than 0.8% (). If the loss during annealing in hydrogen is equal to or more than 0.8% of (), then the discrepancy should be no more than 5% from the mean value.

7.3 Calculate combustion loss during annealing in hydrogen as the arithmetic average of the two results and write it down, rounding to the nearest 0,02% (), if the losses are less than or equal to 0.8% (), and to the nearest 0,05% (), if the losses of 0.8% ().

Note — If, for example, after you calculate weight loss amount 0,634% 0,677 you have to write with rounding to 0.01%, respectively 0.63% and 0.68% of.

7.4 In interpreting the results of the analysis of the relative loss of mass of metal powder it is necessary to consider the comments set forth in Annex A.

8 test report

The test report shall contain:

— reference to this standard;

all the details (information) required for identification of the test sample;

— the arithmetic average of the two obtained results (7.3);

— all operations not specified in this standard or regarded as optional;

— details of any events that could affect the results.

Annex a (mandatory). Interpretation of results

APPENDIX A
(required)

A. 1 the mass Loss of the powder during recovery of hydrogen (called hydrogen loss) is a characteristic of the powder required for the manufacture of powder metallurgy materials. Originally it was believed that they correspond to the oxygen content in the oxides, the recovered hydrogen, but with the advent of more complex and alloy powders, it was observed that some chemical reactions can influence the measured loss of mass both positively and negatively. Thus, when interpreting the results of the analysis should consider the following factors.

A. 2. Measured mass loss does not include oxygen that is present in the form of oxides such as SiO, AlO, MgO, CaO, BeO, Tiothat if the test conditions are not restored.

A. 3 weight Loss include evaporation of water and/or hydrocarbons present in the powder.

A. 4 weight Loss include gases that are a result of adsorption or absorption is present in the powder and separated when heated. The quantity of such gases is usually negligible.

A. 5 weight Loss include, in addition to oxygen, the elements that are present in the powder and under certain test conditions partially or completely removed due to the volatility or interaction with hydrogen or the oxides, thus forming volatile compounds (e.g. carbon, nitrogen, phosphorus and sulphur).

A. 6 weight Loss include metal impurities in the powder, which, under certain test conditions become volatile and partially or completely removed during the test (for example lead, zinc and cadmium).

A. 7 If the carbon powder is present, loss of mass when tested in the «hydrogen loss» may also include oxygen from oxides which, under certain test conditions are reduced by the carbon, such as oxides of SGOnand IGOs contained in the steel simultaneously with carbon.

A. 8 Powders containing manganese, chromium or elements having a greater affinity to oxygen, can be oxidized when tested under the influence of the external environment or as a result of less recovery of refractory oxides. In exceptional cases, this leads to a negative result for hydrogen loss (i.e. when tested there is an increase in mass).