GB/T 2596-1981 Tungsten powder, tungsten carbide powder specific surface area (average particle size) determination simplified nitrogen adsorption method
Some standard content:
Silver
National Standard of the People's Republic of China
Specific Surface Area
(Average Particle Size) Determination of Tungsten Powder and Tungsten Carbide Powder (Simplified Nitrogen Adsorption Method) GB 259681
This method is applicable to the determination of the specific surface area (average particle size) of tungsten powder and tungsten carbide powder, and the measurement range is 0.01-4 microns. Note: Changing the volume of Vc and Vs can appropriately expand the measurement range. 、Original
When nitrogen is adsorbed on the surface of a substance, the pressure in the measurement system drops until the adsorption equilibrium is reached. Measure the pressure before and after adsorption, calculate the volume of the adsorbed gas at the equilibrium pressure (under standard conditions), and calculate the sample monolayer adsorption amount according to the B·E·T isothermal adsorption formula, thereby calculating the sample's specific surface area. By measuring the nitrogen adsorption volume Vo under a series of relative pressures P2/P:, the following B·E·7 equation is used to calculate the monolayer adsorption amount Vm of the sample.
When P2/Ps=0.05～0.35
Vo (Ps- P2)
,C-1×P2
-VC+VC
In the formula: Pz—
Nitrogen pressure at adsorption equilibrium;
Ps-saturated vapor pressure of nitrogen at adsorption temperature T;Ps
C——-constant related to the type of adsorbate and adsorbent and adsorption temperature;Vo
adsorbed nitrogen volume (STP);
monolayer adsorption, the adsorbate is nitrogen, the volume of gas released as a monolayer completely covering the surface of the powder sample (STP).
P,/V. (Ps-P2) is plotted against Pz/Ps, and a straight line with a slope of C-1/V and a C intercept of 1/VnC is obtained. C and Vm can be calculated from the figure. In fact, the C value obtained for most powders is very large, that is, the intercept is very small (the experimental results of tungsten powder and tungsten carbide powder meet this situation), so formula (1) can be simplified to a single-point B·E·T formula. V
Using a single-point adsorption (P2, Vo), the specific surface area (Sw) of Vmc powder can be calculated using the following formula: Sw
Where: N-Avogadro constant (6.023×1023); VmoN
V. -——The molar volume of an ideal gas under standard conditions (22410 cm3); W-——The weight of the powder sample (g);
The cross-sectional area of a nitrogen molecule (16.2×10-20 m2). Sw
National Standards Administration
The Ministry of Metallurgical Industry of the People's Republic of China proposed 136
March 1, 1982
Zhuzhou Cemented Carbide Factory
GB 2596-—81
Or the volume specific surface area Sv (in m2/cm3) of the powder is calculated by the following formula: Sy-Swp
Where: 0—-density of the powder (g/cm3). II. Instrument
1. Instrument structure (see Figure 1).
This instrument is a complete set of glass devices, with piston 6 as the boundary, the left side is the measuring part, the right side is the nitrogen part, and it is equipped with a mechanical vacuum pump.
Connected to mechanical vacuum pump
Diagram of instrument
1, 3, 4, 6, 7—two-way pistons; 2, 5, 8—three-way pistons; A—sample bottle, detachable (volume is 22ml, 40ml), with vacuum ground joint, each sample bottle is marked with a clear number; B—mercury pressure gauge, the scale unit is 1mm, equipped with a reading magnifying glass; C—nitrogen storage bottle (volume is about 5000ml); D—trap, used to purify impurities such as carbon dioxide and water vapor in nitrogen; E—gas bottle (volume is about 80ml). 2. Instrument accessories (see Figure 2).
Used to measure the temperature of the low-temperature bath.
3. Instrument calibration:
GB2596—81
Figure 2 Oxygen vapor thermometer
Instrument calibration refers to the accurate determination of the volumes of several important components in the instrument so that these data can be used when measuring the specific surface area. (1) Use the mercury weighing method to determine the volumes of the sample bottle, piston 2, and capillary tube (from piston 2 to the ground mouth of the sample bottle), i.e., Vbottle t
(2) Calculate the relationship between the volume Vx from the mercury surface to the zero point of the scale in the pressure measuring tube and the position of the mercury surface (i.e., the reading) × 2 (given by the instrument manufacturer"\the inner diameter d of the pressure gauge glass tube), and calculate: Vx-dzxi. 4
(3) Nitrogen filling steps:
Close pistons 2, 3, and 8, open pistons 1, 4, 6, and 7, start the vacuum pump, open piston 5, and evacuate the entire system to a vacuum. Put the cryogenic bath on the trap D, close piston 5, open piston 8, and allow pure nitrogen to slowly enter the gas storage bottle C. At the same time, pay attention to the mercury pressure gauge B. When the pressure shown is about a negative pressure of 10 cm column, immediately close pistons 8, 7, and 4, open piston 5, remove the cryogenic bath outside the trap, and allow the impurities deposited in the trap to be completely removed by the vacuum pump. The pure nitrogen stored in the gas storage bottle is ready for measurement. 4. Use an oxygen vapor thermometer (see Figure 2) to measure the temperature of the cryogenic bath, read the height difference 4H, and find out the absolute temperature T of the cryogenic bath and its saturated vapor pressure P.° from Appendix 1.
5. Volume V. The calibration of the volume (referring to the entire volume of pistons 1, 2 and the mercury pressure gauge above the zero point including the gas bottle E) is carried out in full accordance with the operating procedures for determining the specific surface area of the sample (see Articles 6 to 12, except that no sample is placed in the sample bottle). Read xo, x1, X2, T, T, and calculate using the following formula:
Wherein:
P = XI -xo;
P2 =X2 Xo;
Ve =P (V, yk+aAVs) -PiVel
Xo—the reading of the pressure gauge after vacuuming;
xi-the reading of the pressure gauge after nitrogen filling
x2-—the reading of the positive force gauge after adsorption:
Vx=Vyu
GB 2596- 81
Vx, V×2--is the volume between the zero point of the pressure gauge and the scale ×, 2; 273.2+r
1 = room temperature ℃;
T—absolute temperature K of low temperature bath,
一-correction factor of the deviation of adsorbed nitrogen from ideal gas at absolute temperature T and adsorption equilibrium pressure P2, according to the formula: 0.06-0.00164(T-77.4)], generally take α=1.01. α=1
Vc is measured at least 10 times with different P, and the abnormal value is selected according to Appendix 2. The result is taken as the average value, accurate to two decimal places. 3. Sample preparation
The sample should be dried at 100-110℃ for 1 hour (vacuum oven should be used for easily oxidized powder), placed in a dryer, and cooled to room temperature. Weigh the sample accurately to 0.01 grams. The weight of the sample should be weighed to ensure that the amount of nitrogen adsorbed (volume) is greater than 10 cm3. IV. Determination of the sample
6. Carefully put the weighed sample into the sample bottle through the funnel, and apply vacuum grease to the ground end of the capillary tube, and cover the sample bottle with 7. Start the vacuum pump. Open pistons 5, 4, 1, 3, and 2 in order, and the action should be slow to avoid pumping powder into the system. 8. Vacuum desorption for 30 minutes, use a high-frequency spark leak detector to check that the vacuum degree meets the requirements, and record ×o (estimated to 0.02 cm Hg, and ×2 are the same).
9. Turn piston 5 to connect the vacuum pump to the atmosphere, while the measuring part is isolated from the outside world, stop the pump, and then close pistons 3, 4, 2, 1, and 10 in order. Open pistons 6, 4, and 1 in order to allow nitrogen to slowly fill the gas bottle E. After the mercury column of the pressure gauge drops to an appropriate position, close 1, 4, and 6, and record x1.
11. Put the low temperature bath on the ground mouth of the sample bottle, open piston 2 (turn right to form), let the nitrogen expand into the sample bottle, and the powder begins to adsorb. After the adsorption equilibrium (about 10-15 minutes), lift the low temperature bath so that the liquid level is outside the 1/2 capillary. When the position of mercury does not change, record x2.
12. Close piston 2, remove the low temperature bath, measure the temperature of the low temperature bath with an oxygen vapor thermometer, record 4H, find out T and Ps, and record the room temperature ℃. The measurement is now complete.
V. Calculation
13. Calculate V:
Pi(Vc+Vxt)
Where:
273.2 +V's
-(Vc +V×2+Vk）
-The volume of nitrogen adsorbed by the sample at t, P; (7)
VsVm——--The dense volume of the sample V
The result is rounded to two decimal places.
14. Calculate Vo!
15. Calculate Vm, see formula (2).
GB 2596-81
16. Calculate Sw, Sy, see formula (4) (5), and the result is rounded to three significant figures. 17.Calculate d:
d is rounded to three significant figures.
Formula (9) is only applicable to powders with smooth and nearly spherical surfaces. Otherwise, for the same type of powder, only the relative size of the powder particle size is meaningful.
18. Determination of results:
×1=×2×100% shall not exceed ±10%. If it exceeds the tolerance, weigh a sample, measure it twice, and take the average value as the result, but re-measure the original Www.bzxZ.net
. If it still exceeds the tolerance, check whether the instrument and operation are wrong. VI. Operation precautions
19. The entire operation process must be slow and careful. Do not open or close the piston quickly. 20 When checking the vacuum degree with a high-frequency spark detector, do not hit it on mercury, piston and powder sample. 21. The application of vacuum grease requires uniformity and transparency without filaments. 22. The instrument and sample bottle must be very clean. When cleaning the sample bottle, the brush core must not touch the ground mouth. 23 The samples should be properly preserved to prevent oxidation. Generally, the samples should be placed in ground-mouth bottles, and the oxygen content of the samples should not exceed the requirements of the technical conditions.
Appendix—
GB 2596--81
T and 4H relationship table
117.2 35.8
87.5216.1
Appendix II
GB2596-81
Selection limit table (Grubbs)
Value reliability
Appendix III
Calculation of Ve value
GB 2596--81
0n =0.743
On - 1 =0.758
82.85 is suspected to be an abnormal value
Using Grubbs method
84.19 - 82.85
Check Appendix 2
a(25.5%)=2.82
So 82.85 is not an abnormal value and should be included in the average value. Then measure V. The relative standard deviation
×100%=
× 100% =0.9%
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