1. The high-precision specific surface analyzer shall have the following ten characteristics:
<1> Whether it has a program-controlled wind-heat removal system
When the sample is heated to desorption after being saturated at the liquid nitrogen temperature of -195.8 ° C, the temperature needs to be rapidly increased to rapidly desorb the nitrogen adsorbed on the powder surface into the detector; high-speed desorption can concentrate the signal, Obtaining sharp and sharp desorption peaks is helpful 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 test accuracy of the instrument. The sharp desorption peaks are pursued by chromatographers Ideal peak shape. In the previous semi-automated instruments, artificially replacing the liquid nitrogen cup with a water cup was used, and the temperature of the sample was rapidly increased to normal temperature by using the characteristic of the large specific heat of water; but in the fully automated instrument, if auxiliary heating is removed for automation Attached, for natural temperature desorption in the air, due to the low thermal conductivity of the glass and slow temperature rise, the desorption peak will be short and wide, which will increase the influence of background noise, reduce sensitivity and resolution, and lose test accuracy. Programmable wind-heat assisted desorption device, fully automatic program-controlled start and stop, wind-heat time can be set according to the sample desorption speed, to ensure sharp and fast desorption peak, shorten the peak out time, sharp and sharp desorption peak, reduce background error .
<2> Whether the nitrogen partial pressure detection control is by flow sensor method or concentration chromatography detector method
In the BET multi-point method test, the nitrogen concentration needs to be adjusted from 5% to 30% according to the BET theory. Nitrogen concentration detection is the key link in the accuracy of the test results. In the nitrogen concentration test, the flow sensor method is to measure the nitrogen and carrier gas flow to determine the nitrogen concentration. The nominal limit accuracy of the imported Hollingwell flow sensor is 0.1ml / min, and the highest accuracy for the nitrogen flow rate test of 5ml / min can only reach 2%. The chromatographic concentration sensor measures the nitrogen concentration, the accuracy can reach more than 0.1%, and it is not affected by the flow rate range;
<3> Whether it has a program-controlled six-way valve calibration system; whether the volume of the quantitative tube can be switched by program control
Six-port valve is the main calibration device for quantification of chromatograph. There are manual six-port valve and electric six-port valve. Programmable electric six-port valve calibration system, fully automatic control of the calibration process software; optional function of quantitative tube volume program control; for different The sample may differ from the surface by thousands of times, and the amount of nitrogen absorbed is also very different. It is impossible to calibrate the adsorption amount of all samples with one volume of quantitative tube. Therefore, the calibration system should be connected to quantitative tubes of different volumes to achieve higher accuracy. It is more complicated to manually replace the quantitative tubes of different volumes, and even open the case for replacement. Program-controlled quantitative tube switching only needs to set the access number in the software, electric switching.
<4> Whether it has an integrated in-situ purge device
The purge method in the form of a separate purge furnace requires the sample to be installed on a purge furnace that is separate from the main unit during purge processing. After processing, the sample is removed and reinstalled on the main unit of the instrument for testing. The integrated purge processing system has two advantages over the split purge furnace: first, it is easy to operate and only needs to be installed once; second, the processing effect is better, avoiding the sample coming into contact with the air again when disassembling the sample tube; (for some For organic and biological powder materials, the mass percentage of moisture 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;)
<5> Whether it has a purge timer function
Purge program timing, stop heating at the time, and sound prompt, this function makes the purge processing conditions uniform, and also makes the operator more at ease in other work, without having to worry about the inconsistent processing conditions caused by the purge timeout;
<6> Whether there is a gas purification cold trap device
The purity of high-purity nitrogen and high-purity helium used in the specific surface test is generally 99.99% to 99.999%, of which 0.001% -0.01% of impurity gases (mainly high-boiling easily adsorbable gases such as moisture) will be firstly adsorbed at low temperature Adsorption, which affects the amount of nitrogen adsorbed; gas is continuously flowing through the sample to be measured in the specific surface test of chromatography, so gas impurities such as moisture on the surface of the sample will gradually accumulate; for specific effects, see "The Effect of Moisture on the Adsorption Process" ". The cold trap is an effective way to eliminate high-boiling gas impurities. Generally, this device will be equipped in high-demand equipment; the cold trap equipped with a surface analyzer allows high-boiling impurities such as water that will be adsorbed by the sample to be captured by the cold trap in advance. The water content in the purified high-purity nitrogen and high-purity helium gas is lower than 10-17Pa, and the ultra-high purity gas state is achieved;
<7> Whether it has a constant temperature detector system
The chromatographic surface analyzer uses a thermal conductivity cell as the detector; temperature drift is the main cause of error in the thermal conductivity cell detector. Generally, the detectors of high-precision chromatographs have complex constant temperature systems and temperature drift suppression and elimination systems, but at the same time The cost of the instrument increases; before and after the constant temperature device of the detector, the zero drift can be reduced from 1% to 0.1%. This device is particularly effective for testing samples with small specific surface area (<10m2 / g);
<8> Whether it has real-time monitoring function of liquid nitrogen temperature
The liquid nitrogen used in the specific surface test is purchased by the nearest unit, and is generally a by-product of oxygen production in a gas plant. Its purity instability varies greatly, so that the temperature of the liquid nitrogen varies by about 1 ° C; the amount of nitrogen adsorption on the liquid The change of nitrogen temperature is very sensitive; in addition, the level of the liquid nitrogen surface in the liquid nitrogen Dewar also affects the amount of adsorption; the liquid nitrogen temperature monitoring sensor can monitor the liquid nitrogen temperature and the amount of liquid nitrogen in the Dewar.
<9> Is there a gas source switch indication and protection device
The chromatograph generally requires the operator not to turn on the power when the gas is not turned on, that is, "turn on the gas first and then turn on the power, then turn off the power and then turn off the air." Otherwise, it may happen that the detector is powered on and burned out without ventilation. Danger; the gas source indication and protection device makes this danger removed.
<10> Whether the instrument parameters are displayed simultaneously in software and hardware
The main parameters of specific surface instruments include main detector voltage, current, concentration detector voltage, current, main detector output voltage signal, concentration detector output signal, signal amplification factor, liquid nitrogen temperature, etc. If the instrument has not only the detection and display on the software, but also the hardware display function on the LCD display of the instrument, even if the computer is not turned on or the communication is abnormal, the instrument status can be clearly grasped, making the instrument more reliable; The mechanical parts of the machine, such as motor, desorption fan, purge timing, air source switch status, etc., all have hardware indicator lights to indicate the working status. The status of each part of the complex equipment is working normally or not. Hardware indication is necessary; the display of the gas flow rate is in addition to the electronic sensor, and then displayed by the mechanical rotor flowmeter, which will make the flow rate and size clear at a glance. More stable and reliable modern analytical instruments can have only one control button, but the display The operation status indication of each part such as screen and indicator light cannot be saved;
2. The purchase of high-precision specific surface analyzer should have the following five points:
<1> Choose products from classic manufacturers.
The performance evaluation of analytical instruments includes accuracy, repeatability, and stability. The accuracy and repeatability of the purchaser can generally achieve the purpose of the inspection through actual measurement and multiple batches or single grouping. Stability is whether the instrument can run stably for a long period of time, adaptability to the environment, etc. As a comprehensive analysis instrument for chemistry, machinery, electronics, software, etc. It is difficult to have reliable quality stability guarantees, and it is impossible to guarantee the accuracy of later experimental results and instrument stability. Therefore, one of the selection factors is to choose the products of classic manufacturers with long-term R & D and production history and long-term customers. 3H-2000 series surface analyzer has 9 years of production history and customers in China.
<2> Excellent cost performance.
No need to spend money on features that are not needed. In the case of guaranteed product quality and basically consistent performance, a more favorable price can guarantee the efficiency of the use of funds by units or individuals. Welcome to use the economic brands of classic manufacturers.
<3> Average annual usage fee.
Including natural loss and maintenance costs. For example: the purchase price of product A is 80,000 yuan, and the purchase price of product B is 100,000 yuan. If product A has a service life of 5 years, product B has a service life of 10 years. In fact, the average annual cost of using product B is cheaper. The above does not include the loss and maintenance costs caused by the interruption of the experiment of the A product due to frequent repairs.
<4> After-sales service of products
As far as possible to avoid quality problems, if quality problems occur, classic manufacturers can provide timely and thoughtful services. Market competition is fierce, and only companies with survivability and basic profits can provide long-term and thoughtful service and technical support.
<5> Humanized design.
The humanized design can avoid the damage of the instrument caused by occasional operation errors. At the same time, it guarantees that the user is light, comfortable and pleasing to use. Such as 3H-2000BET-M type in-situ purge processing, gas source switch indication and automatic gas shut-off protection, operation instructions of various hardware, quantitative tube program control switching, and sound prompts for important links.
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