How to choose high-precision dynamic specific surface area tester - Database & Sql Blog Articles

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High-precision specific surface meters should have the following ten characteristics:

<1>Whether it has a program-controlled wind-heat assist system

When the sample is heated and desorbed after being saturated at a liquid nitrogen temperature of -195.8 ° C, the temperature needs to be rapidly increased, so that the nitrogen adsorbed on the surface of the powder is quickly desorbed and enters the detector; high-speed desorption can concentrate the signal. Obtaining sharp and sharp desorption peaks is beneficial to improve the sensitivity and resolution of the instrument. In addition, sharp and sharp desorption peaks can reduce the influence of background noise and improve the accuracy of instrument testing. Sharp desorption peaks are pursued by chromatographers. Ideal peak shape. In the previous semi-automated instruments, the liquid nitrogen cup was usually replaced with a water cup, and the temperature of the water was used to quickly raise the temperature of the sample to normal temperature. However, in the fully automated instrument, if the heating was automated, the auxiliary heating was abandoned. Attached, the natural temperature rise and desorption in the air, because the thermal conductivity of the glass is very low, the temperature rise is slow, the desorption peak is short and wide, the background noise is increased, the sensitivity and resolution are reduced, and the test accuracy is lost. Program-controlled wind-heat assisting device, fully automatic program-controlled start-stop, wind-heat time can be set according to the sample desorption speed, ensuring sharp and rapid desorption peak, shortening peak time, de-peak peak sharpening and reducing background error .

<2> Does the nitrogen partial pressure detection control pass the flow sensor method or the concentration chromatographic detector method?

In the BET multi-point test, the nitrogen concentration needs to be adjusted from 5% to 30% according to the BET theory. The nitrogen concentration detection is the key link of the accuracy of the test results. In the nitrogen concentration test, the flow sensor method measures the nitrogen gas and the carrier gas flow rate separately to determine the nitrogen concentration. The nominal limit accuracy of the imported Hollinger flow sensor is 0.1ml/min, and the highest accuracy for a nitrogen flow rate of 5ml/min can only reach 2%. The chromatographic concentration sensor tests the nitrogen concentration with an accuracy of 0.1% or more and is not affected by the flow rate range;

<3> Is there a programmable six-way valve calibration system; whether the quantitative tube volume can be programmed to switch

The six-way valve is the main calibration device for the calibration of the chromatograph. It has the manual six-way valve and the electric six-way valve. The program-controlled electric six-way valve calibration system, the calibration process software is fully automatic control; the quantitative tube volume program control optional function; for different The sample may be thousands of times different from the surface, and the amount of nitrogen adsorbed is also very different. It is not possible to calibrate the adsorption amount of all samples by a volumetric tube. Therefore, for the calibration system, different volumetric tubes should be connected to achieve higher accuracy. Manual replacement of different volumetric tubes is complicated and even the case is replaced. The program-controlled quantitative tube switching only needs to set the access number in the software and switch it electrically.

<4>Is there an integrated in-situ purge?

In the form of a purge in the form of a split purge, the sample purge process needs to be installed on a purge furnace that is separated from the main unit. After the treatment is completed, it is disassembled and reinstalled on the instrument mainframe for testing. The integrated purging treatment system has two advantages over the split purging furnace: one is easy to operate and only needs to be installed once; the other is that the treatment effect is better, and the sample is prevented from coming into contact with the air again when the sample tube is disassembled; For organic and biological powder materials, the mass percentage of water may be relatively large. If it exceeds 1%, it needs to be oven dried before purging, otherwise it needs to be re-weighed after purging treatment;

<5> Is there a purge timing function?

When the purge program is timed, the heating is stopped at the time, and the sound prompts, this function makes the purge processing conditions uniform, and also makes the operator more comfortable with other work, without having to worry about the inconsistent processing conditions caused by the purge timeout;

<6> Is there a gas purification cold trap device?

The purity of high-purity nitrogen and high-purity helium used in the surface test is generally 99.99% to 99.999%, and 0.001%-0.01% of impurity gases (mainly high-boiling, easily adsorbable gases such as moisture) are firstly adsorbed at low temperature. Adsorption, which affects the amount of nitrogen adsorbed; since the gas is continuously flowing through the sample to be tested in the surface test, the gas impurities such as moisture on the surface of the sample will gradually accumulate; see the influence of water on the adsorption process. 》. Cold traps are an effective way to eliminate high-boiling gas impurities. They are usually equipped in high-demand equipment. The cold traps provided by the surface meters allow the high-boiling impurities such as water absorbed by the sample to be trapped by the cold trap in advance. The moisture content in the purified high-purity nitrogen and high-purity neon gas is lower than 10-17Pa, and the ultra-high purity gas state is achieved;

<7> Is there a detector thermostat system?

The chromatographic surface analyzer uses a thermal conductivity cell as the detector; the temperature drift is the main error cause of the thermal conductivity cell detector. The detectors of the high-precision chromatograph generally have a complex thermostat system and a temperature drift suppression elimination system, but at the same time The cost of the instrument increases; before and after the detector thermostat, the zero drift can be reduced from 1% to 0.1%. The device is particularly effective for testing small specific surface area samples (<10m2/g);

<8> Is there a real-time monitoring function for liquid nitrogen temperature?

The liquid nitrogen used in the surface test is purchased by the nearest unit. It is generally a by-product of oxygen production in gas plants. The purity instability is quite different, which makes the liquid nitrogen temperature change by about ±1 °C. The change of nitrogen temperature is very sensitive; in addition, the liquid nitrogen surface of the liquid nitrogen Dewar cup also affects the adsorption amount; the liquid nitrogen temperature monitoring sensor can monitor the liquid nitrogen temperature and the liquid nitrogen content in the Dewar cup.

<9>Is there a gas source switch indication and protection device?

Chromatographs generally require the operator not to turn on the power when there is no air, that is, "turn on the gas after turning on the gas first, then turn off the gas after turning off the power first", otherwise the detector may be burnt out without being energized. Danger; and the source indication and protection device removes this hazard.

<10> Whether the instrument parameters are displayed at the same time

The main parameters of the specific surface instrument include main detector voltage, current, concentration detector voltage, current, main detector output voltage signal, concentration detector output signal, signal amplification factor, liquid nitrogen temperature, and the like. If the instrument has not only the software to detect the display, but also the hardware display function on the LCD screen of the instrument, even if the computer is not turned on or the communication is abnormal, the instrument state can be clearly grasped, which makes the instrument more reliable; The mechanical parts, such as the motor, the detached fan, the purge timing, the air source switch status, etc., all have a hardware indicator to indicate the working state, and the various parts of the complex device work normally or not, while being displayed by the software, Hardware indication is necessary; the gas flow is displayed in addition to the electronic sensor, and then displayed by the mechanical rotameter, which will make the flow at a glance, the size is clear, more stable and reliable, the modern analytical instrument can have only one control button, but the display The operating status indications of the screens, indicators, etc. cannot be saved;

2. The selection of high-precision specific surface meters should have the following five points:

<1> Select products from classic manufacturers.

Performance evaluation of analytical instruments includes accuracy, repeatability, and stability. Accuracy and Reproducibility Purchasing parties generally achieve the purpose of inspection through actual sample testing and multiple batches or single groupings. The stability is also the long-term stable operation of the instrument, the adaptability to the environment, etc., compared with the surface analyzer as a comprehensive analytical instrument for chemical, mechanical, electronic, software, etc., without long-term actual customer site practical experience accumulation and information feedback, It is difficult to have a reliable quality stability guarantee, and the accuracy of the experimental results and the stability of the instrument cannot be guaranteed. Therefore, the first choice factor is to choose a product with a long-term research and development history and a long-term use of customers. The 3H-2000 series surface surface meter has a 9-year production history and customer use in China.

<2> Excellent value for money.

It is not necessary to spend money for features that are not needed. In the case that the product quality is guaranteed and the performance is basically the same, a more favorable price can guarantee the efficiency of the use of funds by the unit or individual. Welcome to the economic brands of classic manufacturers.

<3> Annual average usage fee.

Includes natural wear and maintenance costs. For example: A product purchase price of 80,000 yuan, B product purchase price of 100,000 yuan. If the A product has a service life of 5 years, the B product has a service life of 10 years. In fact, the B product is cheaper than the average annual usage fee. The above does not include the loss and maintenance cost caused by the interruption of the experiment due to the frequent repair of the A product.

<4> Product after-sales service

Avoid quality problems as much as possible, and if there are quality problems, classic manufacturers can provide timely and thoughtful service. The market is fiercely competitive, and companies with viability and basic profit can provide long-term and thoughtful service and technical support.

<5> Humanized design.

The user-friendly design avoids accidental operation errors and damages the instrument. At the same time, the user's use process is light, comfortable and pleasing to the eye. Such as 3H-2000BET-M type in-situ purge treatment, gas source switch indication and automatic gas shutoff protection, operation instructions of various hardware, quantitative tube program control switching, important parts sound prompts, etc.