GOST 23401-90

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  ГОСТ 23401-90

GOST 23401−90 (ST SEV 6746−89) Powder metal. The catalysts and carriers. Determination of specific surface

GOST 23401−90
(ST CMEA 6746−89)

Group B59

STATE STANDARD OF THE USSR

POWDER METAL

The catalysts and carriers. Determination of specific surface

Metal powders. Catalysts and carriers.
Determination of specific area

AXTU 0909

Date of introduction 1992−01−01

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Academy of Sciences of the Ukrainian SSR

DEVELOPERS

V. N. Klimenko, V. V. Skorokhod, A. E. Kushchevsky, I. V. Uvarova, L. D., Bernatsky, T. F. Mozol

2. APPROVED AND put INTO EFFECT by Decision of the USSR State Committee on management of quality and standards from 27.12.90 N 3376

3. The frequency of inspection 5 years

4. The standard fully complies ST SEV 6746−89

5. REPLACE GOST 23401−78

6. REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

This standard specifies a method for determining the specific surface of metal powders, catalysts, and carriers from 0.05 up to 1000 m/g by thermal desorption gas (nitrogen or argon).

The essence of the method consists in determining the volume of gas is first pre-adsorbed on the surface of the sample from the flow of the working gas mixtures (nitrogen-helium or argon-helium) at a temperature of liquid nitrogen is then desorbed from it at higher temperature and subsequent calculation of the specific surface of the sample.

1. SAMPLING METHOD

1.1. A sample selected according to GOST 23148*.
______________
* On the territory of the Russian Federation GOST 23148−98. — Note the manufacturer’s database.

1.2. Sample mass for test definition in accordance with the table.

Samples before measurement is dried in a drying Cabinet to constant weight.

2. EQUIPMENT

Installation (DWG.1, 2) to determine the specific surface consists of 1 tanks of helium; 2 — pressure gauge — according to GOST 2405* (2 PCs); 3 — porous pre-filters (2 PCs); 4 — gas mixing unit; 5 — a model of gauge pressure 0.1 MPa according to GOST 6521; 6 — Dewar vessel NTD with liquid nitrogen according to GOST 9293; 7 — traps silicageles indicator according to GOST 8984; 8 — comparative and the measuring cell of the detector by heat conduction; 9 — potentiometer KSP-4 with a measurement range of 0−10 mV and a time of passing the pointer across the scale no more than 1 according to GOST 7164; 10 — integrator; 11 — shut-off valve (2); 12 — flowmeter, designed to check the rate of gas flow from 0 to 55 cm/min (2); 13 — valve; 14 — adsorbers 6 (Fig.1) and 12 (DWG.2) units; 15 — the thermostat providing temperature up to 400 °C; 16 — a cylinder with nitrogen or argon of grade A according to GOST 10157; 17 — vosmikova crane.
______________
* On the territory of the Russian Federation GOST 2405−88. — Note the manufacturer’s database.

Damn.1. Installation diagram for determining the specific surface of samples with a parallel flow of gas mixture through the cell of the detector

Installation diagram for determining the specific surface of the samples
with a parallel flow of gas mixture through the cell of the detector

Damn.1

Damn.2. Installation diagram for determining the specific surface of the samples during the sequential flow of the gas mixture through the cell of the detector

Installation diagram for determining the specific surface of the samples
the sequential flow of the gas mixture through the cell of the detector

Damn.2

Adsorbers with connecting samples in blocks A and B (Fig.2). In each block depending on the required performance of the installation can be from one to six adsorbers.

The sensitivity of the detector should be between 0.7·100.8·10mV.

Laboratory scales that provide a weighing error of no more than 0,0002 g.

Thermometer 3-A3 according to GOST 8624.

The stopwatch according to GOST 5072.

Drying Cabinet, providing temperature (200±20) °C.

The aneroid.

Medical injection syringe with a capacity of 1 cm.

Helium of high purity according to normative-technical documentation.

3. PREPARATION FOR CONTROL

3.1. Check the installation for leaks

At the gas outlet from the unit close the ball valve 11, in the system creating excess pressure of 4·10PA, as measured by the manometer 5. If the pressure drop within 20 min does not exceed 100 PA, installation, believe to be airtight.

3.2. Preparation of the working gas mixture

3.2.1. As the working gas mixture using argon-helium or nitrogen-helium mixture with a given concentration of the adsorbate. Allowed to be used as a carrier gas dried hydrogen.

3.2.2. The concentration of the adsorbate in the gas mixture regulate the ratio of flow of carrier gas and gas of the adsorbate. The ratio of the speeds of these flows to calculate the partial pressure of the gas adsorbate.

This method of preparation of the gas mixture allows the calculation of the complete isotherms of adsorption and desorption of gas-adsorbate and determination of specific surface area on the complete isotherms of adsorption and desorption (method S. Brunauer, P. X. Emmet and method BETH E. teller).

3.2.3. Allowed advance preparation of gas mixtures in cylinders with the volume fraction:

of the adsorbate from 5 to 10%;

carrier gas from 90 to 95%.

The mixture is prepared in the unit consisting of two cylinders with the carrier gas and adsorbate, the United copper or brass tube with a swivel nut with Teflon gaskets, and standard pressure gauge to the pressure of 16 MPa.

Cylinder with the working gas mixture should be aged for 10 days before putting it to work.

When re-mixing, you should use the existing cylinders with residual pressure of the working gas mixture of 0.5−0.7 MPa.

This method of preparation of a working gas mixture will allow the determination of specific surface area at one point.

3.3. The choice of the optimal amperage

To find the optimal current detector is carried out control experiments, empty connecting the adsorbers 14. Set the speed of the purge installation working mixture (50±5) cm/min after 5 min after purging the supply voltage to the detector by installing the ammeter the amperage of 50 mA.

The temperature and the output signal of the detector is the thermal conductivity stabiliziruemost for 30−40 minutes after switching on to the network and transmission of gas through the cells of katharometer. The process of stabilization modes follow the potentiometer.

After establishing the zero line on the ribbon diagram of the potentiometer of the adsorbers successively immersed in a Dewar of liquid nitrogen and record the fluctuations of the zero line. Upon returning the stylus to starting position at the latest during the canister in the Dewar is replaced by a container of water having a temperature of (20±5) °C to accelerate desorption. This operation is repeated for each canister.

The deviation from the zero line immersion of the adsorbers in the liquid nitrogen and water is recorded every 10−20 mA, changing the strength of the detector from 50 to 100 mA.

The maximum value of current at which the fluctuations of the zero line is not more than 30% of the scale of the potentiometer, is optimal.

The sensitivity of the detector is provided by a supply voltage of 5 V, which must be constant during its operation.

3.4. Calibration of the valve

The installation must have a set of valves dosing with a capacity of 0.1; 0.5 and 2.5 cm.

Calibration of valves dosing allowed by any known methods at least once a year. Pre-emption is a technique of certification of the dosed amounts of adsorption capacities and weight method.

The most simple but less accurate is the pulse chromatographic method using a medical syringe. The flow rate of the working gas mixture or carrier for verification of cranes dispensers must be (50±1) cm/min In the gas stream after heating and setting the zero line on the ribbon potentiometer is administered a medical syringe, the volume of adsorbate corresponding to the calibrated volume of the valve. The potentiometer is fixed and the integrator pravitelya peaks. The operation of the input samples is repeated 10 times.

Next, introduce a sample gas-adsorbate calibrated capacity of the valve. To do this, when the flow of the working gas mixture and gas-adsorbate turn the tap on the dispenser so that the volume of the adsorbate in the tap-dispenser, captured the working gas mixture and fed to the detector. Record indications record the potentiometer and integrator. The operation of the input samples of tap-dispenser, repeat 10 times.

The permissible differences of the parallel measurements shall not exceed 3%.

Calibrated to the capacity of the crane-weigher () in cubic centimeters, reduced to normal conditions, calculated by the formula

, (1)

where  — volume of sample gas-adsorbate, injected cm;

the average floor area provedennogo peak recorded by the integrator with the introduction of gas-adsorbate tap-dispenser, cm;

 — barometric pressure, PA;

the average floor area provedennogo peak recorded with the introduction of gas-adsorbate syringe, cm;

 — temperature of air, °C;

 — normal pressure,

PA.

3.5. Determination of the concentration of gas-adsorbate (nitrogen or argon) working gas mixture

In the absence of a gas mixing unit the gas concentration of the adsorbate in the cylinders with a working gas mixture check or on the testimony of pre-calibrated katharometer frontal method. It should be possible to independently connect the cylinders with a carrier gas and a gas mixture using a three-way tap to the cells of the detector of thermal conductivity.

For analysis and comparative through the measuring cell of the detector by heat conduction flow the flow of carrier gas to stabilize the readings of the detector. After establishing the zero baseline flow of the carrier gas in the measurement cell of the potentiometer is replaced by a flow of the working gas mixture. The pen of the recorder deviates from the zero position to a distance and write a line parallel to the zero.

The volume fraction of gas-adsorbate (a) in percent is calculated by the formula

, (2)

where is the calibration factor of the detector, cm, calculated by the formula

, (3)

 — the distance between the front and the zero lines on the chart tape recorder, cm;

 — speed chart paper, cm/min;

 — the flow rate of the working gas mixture, cm/min;

 — calibrated the volume of the valve, cm;

the average floor area provedennogo peak recorded by the integrator with the introduction of gas-adsorbate tap-dispenser, see

.

3.6. Preparation of adsorbers

The vessels thoroughly washed and dried in a drying Cabinet at a temperature of (200±20) °C. and Then weighed with an error not exceeding 0.0002 g, download the sample and re-weighed to determine the mass of the sample. Adsorbers choose this capacity, to over the breakout was minimal space for the passage of the gas mixture. For determining the specific surfaces up to 1 m/g gas mixture is recommended to omit from the adsorbers through a layer of granules of powder. In order to avoid entrainment of the powder include swabs of cotton wool.

3.7. Preparation of the detector to the measurement and degassing of the sample

3.7.1. Preparation of detector and degassing the samples are at the same time.

For the preparation of the detector, the working gas mixture from the gas mixing unit flow at a speed of (50±1) cm/min through the trap 7 (Fig.1, 2), cooled with liquid nitrogen, the six adsorbers in the comparative and the measuring cell of the detector 8.

5 min after start of purge, the voltage applied to the detector, setting of the optimal amperage or voltage. The detector is heated in the working gas mixture for 30 min. For 15 min before the end of warm-up include a potentiometer and an integrator.

The readiness of the detector to work check on the stability of the zero line recorded by the stylus potentiometer on the ribbon diagram.

3.7.2. Degassing of samples was carried out at a blowdown of adsorbers 14 of the working gas mixture for 40−50 min. flow Rate controlled by a flow meter 12. Under the adsorbers 15 substitute the thermostat and set the temperature taking into account thermal stability of the powder but not higher than 400 °C. after degassing the pen of the recorder goes to the zero line and the sample is cooled to a temperature of (20±5) °C.

4. MEASUREMENTS

4.1. The adsorbers alternately, starting with the first along the gas, is immersed in the Dewar vessels with liquid nitrogen. In order to avoid air suction via the exhaust line gas in the absence of automatic devices for lifting vessels should be immersed in liquid nitrogen at such a rate that the film is in the flow meter 12 can only move up. In the adsorption pen of the recorder of the potentiometer deviates from the zero line. Adsorbers kept in liquid nitrogen until the return of the stylus potentiometer to the zero line, i.e. before the establishment of the adsorption equilibrium (15−30 min depending on the gas-adsorbent).

4.2. Last along the gas adsorber is taken out from the Dewar vessel with liquid nitrogen and immerse in a container of water. The water temperature in the vessel should be (20±5) °C.

During desorption, the stylus writes on the ribbon diagram of the potentiometer of the desorption peak, and the integrator of the figure is proportional to the area of this peak.

Desorption measurements were carried out successively for all the remaining samples.

4.3. A sample of gas-adsorbate introduced into the system with tap-dispenser. In this ribbon diagram of the potentiometer are recorded and appear on the integrator corresponding figures provedennogo peak area depending on the capacity of the calibrated valve (). When calculating the specific surface take into account that the calibrated capacity, which area is closer to square captured when the gas desorption of the adsorbate from the surface of the measured powder samples.

4.4. To determine the specific surface of the material by BET method should be the measurement for the PP.4.1 and 4.2 to repeat at three to five different concentrations of gas-adsorbate in the working gas mixture within: 3−5; 5−7; 7−10; 10−17; 17−25%. The concentration of the adsorbate in the working gas mixture is controlled by the unit of mixing ratio of volumetric feed rates of gas-adsorbate and carrier gas.

4.5. The volume of gas adsorbed on the surface of the sample with subsequent calculation of its specific surface area may be determined by other experimental methods of ensuring the accuracy of determining the specific surface area of not more than 5%.

5. PROCESSING OF THE RESULTS

5.1. Specific surface area () square meters per gram determined by the formula

, (4)

where 4,73 — the area which is occupied under normal conditions, 1 cmof argon or nitrogen, respectively, of adsorbed monomolecular layer, m/cm;

 — calibrated capacity of the valve, in normal conditions, cm;

 — the area of the desorption peak, cm;

square provedennogo peak recorded with the introduction of gas-adsorbate tap-dispenser, cm;

 — weight of sample, g;

 — partial pressure of a gas-adsorbate defined by the formula

, (5)

where  — volume fraction of gas-adsorbate in the mixture, %;

 — barometric pressure, PA;

 — elasticity of saturated steam gas of the adsorbate at the temperature of liquid nitrogen super-cooled liquid (3·10PA for argon and 11·10PA for nitrogen);

 — constant characterizing the energy of adsorption interaction of adsorbent-adsorbate, equal to 50.

When building the complete isotherms of adsorption and desorption volume adsorbed and desorbed gases lead to normal conditions and build dependency , which sets the amount of substance adsorbed in monoszló

E.

5.2. The results of measurement of gas volume and specific surface area with an absolute error of determining the amounts of no more than 5% of the designated volume of gas for the detector and integrator (within their physical capabilities) must meet the following.

5.2.1. The limits determine the amount of adsorbed and desorbed gas:

the capabilities of the computational algorithm and display the results of from 0.005 to 99.999 cm;

according to the physical capabilities of the analyzer from 0.025 to 10 cm.

5.2.2. The detection limits of the specific surface calculated according to the volume of desorbed gas:

the capabilities of the computational algorithm and display of results from 0.02 to 500 m;

according to the physical capabilities of the analyzer from 0.1 to 50 m.

5.3. The results of measurements of specific surface are entered into the Protocol, which must include:

the name (brand) of powder;

batch number;

the name of the manufacturer (consumer);

information on the conditions of drying powder;

the results of parallel measurements and average the result;

the designation of this standard;

date of the test.