JPS5834342A - Measuring apparatus of specific surface area - Google Patents

Abstract

PURPOSE:To improve measuring accuracy of powdered body having >=500m<2>/g specific surface area, by constuting a sample tube with anhydrous quartz containing <=1ppm volatile components in a measuring apparatus of the specific surface area performing by an adsorption method. CONSTITUTION:A gaseous N2 11 adsorbed to a sample and a gaseous He 12 not adsorbed to the sample are mixed in a proportional mixing tank 13 and gaseous mixture is flowed at a constant flowing speed and is cooled in a cold trap. Then, said gas is passed through a TC detector 15 and the gaseous N2 11 is adsorbed to the sample in a sample tube 16. The tube 16 is made of anhydrous quartz containing <=1ppm volatile components. After reached adsorption equilibrium, the gaseous N2 is released because of heating the tube 16 at a normal temperature again and a peak of released gas is recorded on a recorder 18 after passing through the detector 15. A known volume N2 calibration gas 19 is introduced into the tube 16 for carrying out calibration and the peak is recorded and then, the quantity of the gaseous N2 adsorbed to the sample is found by comparing each peak. A specific surface area is measured by changing mixing composition of gaseous N2 and He and repeating the same process.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a specific surface area measuring device, and improves the accuracy of measuring powders having a specific surface area of 500 m''/g or more.

Methods for measuring the specific surface area of powders can be roughly divided into adsorption methods, wetting methods, permeation methods, and reaction rate methods.However, for powders with a large specific surface area, in addition to the external surface area, the internal surface area, that is, the pores and The gas phase adsorption method is the most suitable method for measuring powders where the internal surface area of particles, such as cracks, is largely involved, and therefore the m1 area of the specific table is large. This is a method of measuring and calculating based on the BET formula. This BET equation is an equation derived based on multimolecular adsorption, and it is assumed that @ heat deposition E in the first layer is equal to the liquefaction heat El of the adsorbed gas in the second layer and below, and further, The thickness of the adsorption layer is assumed to become infinite as the pressure of the adsorbed gas approaches the saturated vapor pressure at that temperature.

In addition, the point that there is no interaction between adsorbed molecules in the same layer is based on the Langmuir equation (Q
Same as in case. From the above assumptions, the following formula (1): [where Po: saturated vapor pressure, P: gas pressure, ym:
The so-called BET equation is derived, where the volume of gas required to cover the entire surface with one molecular layer, ■=adsorption amount, C: constant].

Therefore, if P/v (Po-P) is plotted against P/P, and a linear relationship holds, then for measuring the surface area,
It can be seen that this BET formula can be applied. In addition, the above E,
-Ee is equal to uWf'C1e-H in formula (]), where R
is the gas constant, and T is the feed temperature. In general, the actual measured value that satisfies equation (1) is 0,05 (P/Po
<0.35.

Below, a method for measuring specific surface area by a conventional gas phase adsorption method using this BET equation will be described in detail.

Generally, a flow-through gas adsorption method is used as a simple and rapid method, and the principle diagram of the device is shown in the drawing. As the adsorbed gas, N is mainly used in normal BET surface area measurements because (a) it does not chemically adsorb to the sample, (m) liquefied gas can be easily obtained, and (C) gas with good purity can be obtained. ing. The feature of this method is that gas adsorption is measured by changing the partial pressure of the adsorbed gas using an inert carrier gas (usually He is selected) as a diluent that does not substantially adhere to the sample under all measurement conditions. There is a particular thing. Usually P/P
.

Select 3 points in the range of 0.05 to 0.35 and select BE'l'
Perform calculations using the law. Here P is 7131. The partial pressure of N in the combined gas (fiH,!i') is the saturated vapor pressure of the adsorbed gas (vR) at the boiling point of the liquid nitrogen used.
Hg).

The measurement method is N! A mixed gas of He and He flows at a constant flow rate. A sample cooled with liquid nitrogen adsorbs N in the mixed gas at the humidity of the liquid nitrogen, and adsorption equilibrium is reached with respect to the N7 partial pressure of the mixed gas.

The sample tube is then rapidly heated. This heating is usually sufficient to return the material to room temperature. N2 adsorbed on the sample
is desorbed and passes through the TC detector as a pulse,
The peak of the desorbed gas is recorded on the recording paper. Separately, for calibration purposes, pump a known volume of N and record the peaks. By measuring the peak area of the desorbed gas and comparing it with the area of the calibration peak, the amount of N adsorbed on the sample can be determined. In this way, one point on the attraction crosstalk is obtained. Similarly, N.

Repeat the above procedure three or more times by changing the composition of the mixed gas of
Find the specific surface area (m/, !i') using the formula.

In this way, the flow gas adsorption method measures the specific surface area of powder, but the inventors have found that powders with a large specific surface area cause problems in the sample sampling stage. In this method, the data is not reliable unless the peak area of the desorption gas and the peak area of the calibration gas are within a range of ±30%. Ke, 10100O/
,! In the case of the powder sample i', a sample of 2 to 31v must be accurately weighed and collected, and furthermore, there was a drawback that weight fluctuations of the glass sample tube greatly affected the measurement of the specific surface area.

It is an object of the present invention to provide a specific surface area measuring device which improves on the points set out in the present invention and has extremely few errors.

Namely, a proportional mixing tank that mixes adsorbed gas and carrier gas, a cold trap that cools the mixed gas, and a TC that introduces the gas that has passed through the cold trap.
A detector, a sample tube into which the gas that has passed through the TC detector is introduced and has a powder sample inside, a cold drag that cools the calibration gas and mixed gas mixed in the sample tube, and a mixed gas that has passed through the cold trap. A specific surface area measurement comprising a TC detector for detecting the combined gas again and a recorder for recording the detected value, wherein the sample tube is made of anhydrous quartz having a volatile component of 1 ppm or less. It is related to the device.

The present invention will be explained below with reference to examples. In the figure, N and F gas 11, which are adsorbed to the sample, and He gas 12, which is an inert carrier gas that is not adsorbed to the sample, are mixed in a proportional mixing tank 13 at a constant flow rate. The sample was cooled in a cold trap, passed through a TC detector 15, and then placed in a sample tube 16 with N.

Adsorbs gas. After reaching adsorption equilibrium, sample tube 16
The passed gas passes through the cold trap 17, and the sample tube is heated to room temperature again, so that the N,
The gas is desorbed and passes through the TO detector 15 in the form of a gas, and the peak of the desorbed gas is recorded on the recording paper of the recorder 18. Separately, for the purpose of calibration, N2 calibration gas 19 with a known volume was introduced into the sample Ii1'+' 16 and the peak was recorded. By comparing with the area, the amount of Nt that has not been adsorbed to the sample can be determined.

In the same way, change the mixture composition of N, gas and l (e gas) and repeat the above procedure three or more times.
f (m'/g) can be found.

That is, the sample was dried by heating at 300° C. for 2 hours, allowed to cool in a desiccator, and then accurately measured for gravity.

Approximately 2 to 3 samples of activated carbon powder were collected into an anhydrous quartz sample tube of the present invention containing volatile components of less than ippm and a conventional glass sample tube containing about 1000 ppm of volatile components. Then, the sample tube was dried by heating at 300° C. for 2 hours while supplying nitrogen and gas, and then allowed to cool in a desiccator, followed by accurate weight measurement. At 300℃, 21F
The reason for heating and drying for 8 hours is, as mentioned earlier, that for powders with a large surface area, the internal surface area, that is, the surface area inside the particles such as pores and cracks, has a larger specific gravity than the surface area of the rows. The adsorbed water closes the pores and cracks, so the surface area of the material is not reduced.

Therefore, an operation is performed to remove that water. The table shows the results of determining the specific surface area by the flow-through gas adsorption method for the sample whose amount was measured in this manner.

As shown in the table above, the specific surface measuring device according to the present invention can perform measurements with extremely high accuracy and has few errors.

[Brief explanation of the drawing]

The figure is a conceptual diagram of the specific surface measuring device of the present invention. 11... Adsorption gas, 12... Carrier gas, 13
River proportional mixing tank, 14.17...cold trap, 15...TC detector, 16...sample tube, 18...
・Recorder, 19... Calibration gas.

Claims (1)

[Claims] A proportional mixing tank that mixes adsorbed gas and carrier gas, a cold trap that cools the mixed gas, a TC detector that introduces the gas that has passed through the cold trap, and a tank that introduces the gas that has passed through the TC detector and enters the interior. A sample tube containing a powder sample, a cold trap that cools the calibration gas and mixed gas mixed in the sample tube, a TC detector that again detects the mixed gas that has passed through the cold drag, and a record that records the detected values. 1. A specific surface area measuring device, characterized in that the sample tube is made of anhydrous quartz having a volatile component of 1 ppm or less.