HG/T 2347.8-1992 γ. Determination of specific surface area of Fe2O3 magnetic powder
Some standard content:
Chemical Industry Standard of the People's Republic of China
Determination of specific surface area of Y·Fe,O3 magnetic powder
Subject content and scope of application
This standard specifies the determination method of specific surface area of Fe,O, magnetic powder for magnetic recording HG/T 2347.8-
This standard is applicable to the determination of specific surface area of Fe,O, magnetic powder for magnetic recording, and is also applicable to the determination of specific surface area of modified Fe,O, magnetic powder.
Cited standards
GB4962
GB6679
3 Summary of methods
Safety technical regulations for the use of hydrogen
General rules for sampling of solid chemical products
This method is based on the BET gas multilayer adsorption principle and adopts flow gas chromatography to adsorb nitrogen molecules on the surface of Y·Fe,O, magnetic powder particles. Several points that meet the BET linear relationship were measured experimentally. The specific surface area of Fe,O, magnetic powder can be calculated from the amount of adsorbed nitrogen by applying the BET formula.
4 Instrument
The schematic diagram of the gas path for determining the specific surface area is as follows: HHe
-Pressure regulator valve: 2-Three-way valve; 3-Mixer; 4-Cold cake; 5-Sample tube;www.bzxz.net
7-Soap foam flowmeter: 8-Dewar flask
6-Thermal conductivity detector;
The instruments applicable to this method should meet the following requirements: 4.1 Pressure regulator valve
During the experimental operation, the gas flow fluctuation through the pressure regulator valve shall not exceed "%. 4.2 Thermal conductivity detector
4.2.1 Baseline stability
Approved by the Ministry of Chemical Industry of the People's Republic of China on June 1, 199220
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1993-03-01 implementation
HG/T2347.8-92
Use hydrogen or hydrogen as carrier gas, bridge current is 200mA, without attenuation, baseline drift is not greater than 0.1mV after 30min, noise is not greater than 0.05mV,
4.2.2 Insulation layer
Thermal conductivity detector should be insulated with asbestos layer,
4.3 Integration Instrument
The precision of the integrator is 10μV·s.
4.4 Balance
Analytical balance with a sensitivity of 1mg.
5 Reagents and materials
5.1 Carrier gas: nitrogen (He) or hydrogen (H,), purity not less than 99.9%. Adsorbed gas: nitrogen (N), purity not less than 99.9%.5.2 Liquid nitrogen: temperature between -197 and -194℃. 6 Measurement conditions||t t||The saturated vapor pressure of liquid nitrogen is obtained by measuring the temperature of liquid nitrogen, and the temperature measurement is accurate to 0.1C. 6.1
6.2 The ratio of nitrogen equilibrium pressure to nitrogen saturated vapor pressure (PN2/p) is suitable for BET equation in the range of 0.05-0.3, and the experimental point must be within this range.
6.3 During adsorption at each relative pressure, the distance between the sample and the liquid nitrogen surface is greater than 5cm. During desorption, room temperature water is used to control the desorption rate, and the distance between the sample and the water surface is greater than 5cm. 6.4
The determination conditions of the instrument constant K value must be consistent with the experimental conditions. 6.5
6.6 During the measurement, the bridge current is controlled at 140mA.6.7
During the entire test process, the cold trap tube must be immersed in liquid nitrogen. The instrument use environment shall be carried out in accordance with the instrument instruction manual. 6.8
The use of hydrogen shall comply with the provisions of GB4962. 7 Sample
7.1 Sampling
Sampling should comply with the provisions of GB6679.
7.2 Sample treatment
Take 0.2~0.5g of FeO2 magnetic powder that has passed the 160um sample sieve, and then use a small funnel to put it into a clean sample tube of known mass. Do not fill any section of the sample tube. Treat it at 120±5℃ for 2h, move it into a dryer, and after cooling to room temperature, weigh it with a balance to constant weight, accurate to 0.001g, calculate the mass of FeO2 magnetic powder, and then plug a little glass wool at both ends of the sample tube, pass nitrogen, and treat it at 120±5℃ for another 1h. 8 Determination
8.1 Preparation of the instrument
Connect the sample tube containing the sample treated in 7.2 to the gas line, turn on N2 and H2 (He), and adjust the flow rate to the selected value, turn on the instrument, and adjust it until the baseline is stable.
8.2 Adsorption
Adjust PN2/p to the required value, and put the Dewar flask filled with liquid nitrogen on the sample tube. At this time, an adsorption peak appears on the recorder. After the recorder returns to the baseline position, the adsorption reaches equilibrium. 8.3 Desorption
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Remove the liquid nitrogen Dewar flask and quickly put on a beaker filled with room temperature water. A desorption peak will appear on the recorder. The desorption peak area is used as the basis for calculation.
Relative pressure PN2/P, within the range of 0.05 to 0.3, select more than 4 points for adsorption and desorption experiments, read the desorption peak area by the integrator, and do it twice in parallel for each point, and calculate the average value. 8.4 Determination of adsorption amount
The determination of adsorption amount is divided into two types: external standard method and instrument constant method. 84.1 Instrument constant method
When the circuit conditions of the instrument remain unchanged, there is a constant relationship between the peak area and the corresponding gas volume and carrier gas flow rate. The calculation formula is (1):
Where: K
-Instrument constant, min/uV·s;
-Ratio of the partial pressure of nitrogen in the mixed gas to the atmospheric pressure; VThe volume of the sample tube, mL:
-The volume of the sample tube Y, corresponding to the peak area Area, uV·s; A
R Carrier gas flow rate, mL/min;
Atmospheric pressure under experimental conditions, kPa;
Room temperature under experimental conditions, K,
Use three sample tubes with different volumes, calculate their K values respectively, and then use the average value of K as the instrument constant value of the instrument. The adsorption amount is calculated according to formula (2):
Where: V
-adsorption amount under standard conditions, mL;
Total flow speed, mL/min;
desorption peak area, μV·s.
8.4.2 External standard method
The external standard method is to add a known volume of pure nitrogen to the sample after the desorption peak value of the sample is measured by the above method. The peak value that appears on the recorder at this time is the standard peak. The adsorption amount V is calculated according to formula (3): V
Where:
-adsorption amount in standard state, mL;
-known volume of pure nitrogen, mL;
|A and V, corresponding to the peak area of pure nitrogen, uVs; A—desorption peak area, μV·s;
—atmospheric pressure under experimental conditions, kPa;
—room temperature under experimental conditions, K
9 Calculation of specific surface area
9.1 Calculation of the saturated adsorption capacity of nitrogen monolayer BET formula is:
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HG/T 2347.8-92
—equilibrium pressure of nitrogen, P;
Wherein: PW
P—saturated vapor pressure of nitrogen, P:
—nitrogen adsorption capacity under standard conditions, mL; Vn
—saturated adsorption capacity of nitrogen monolayer, mL; constant of BET equation.
/P is plotted to obtain a straight line, whose slope is proportional to P
. The saturated adsorption capacity of nitrogen monolayer V can be obtained from the slope and the intercept according to formula (5). V
9.2 Calculation of the specific surface area of Fe,o, magnetic powder The saturated adsorption capacity of nitrogen monolayer V. is calculated according to formula (6). The specific surface area of Fe,O, magnetic powder: S.-4.36V./m
Where: S.—specific surface area, m2/g;
—mass of sample, g
4.36—--the area occupied by 1 mL of nitrogen monolayer under standard conditions, m2/mL10 Precision
The precision of this method is within 5%.
The experimental report should include:
Sample name and weight;
Analysis date;
Experimental temperature;
Laboratory atmospheric pressure;
Saturated vapor pressure of liquid nitrogen;
Analysis results (take 3 significant figures)
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(4)
HG/T2347.8
Appendix A
Single-point method for measuring the specific surface area of Fe,O, magnetic powder (reference part)
In the production of Fe,O, magnetic powder, in order to achieve the purpose of quality control, the single-point method can be used to measure the specific surface area of Fc,O, magnetic powder. For Fe,For Y·Fe,O magnetic powder samples, the BET straight line intercept is very small. If it is ignored, only one point needs to be measured to measure the specific surface area of Y·Fe,O, magnetic powder.
Pn,/p, take a point between 0.2 and 0.3, carry out adsorption and desorption experiments, read the desorption peak area to obtain V. The single-point method for measuring specific surface area BET formula is simplified to: PN
V.=1/a=V(1-
Pn,/p)
The specific surface area of FezO, magnetic powder can be obtained from this. The specific surface area of Y·Fe,O, magnetic powder measured by the single-point method is compared with the multi-point method, and the difference is within 5%. Appendix B
Determination of the specific surface area of iron yellow (FcOOH)
(reference)
The measurement method of the specific surface area of iron yellow (FeOOH) is the same as that of the specific surface area of Y·Fe2O, magnetic powder, except that the sample processing temperature in 7.2 is changed from 120C to 105℃.
Additional instructions:
This standard is proposed by the Science and Technology Department of the Ministry of Chemical Industry of the People's Republic of China. This standard was drafted and managed by the First Film Factory of the Ministry of Chemical Industry. The main drafters of this standard are Su Guangru and Xiao Zhenlong.
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