For small specific surface area samples, such as battery materials, organic compounds, biological substances, metal powders, and abrasives with low porosity, the static method of testing often encounters significant challenges. Due to the minimal amount of gas adsorption, the results from static tests can be less accurate compared to those obtained using a wind-heat assist device and a detector thermostat. In contrast, the high-precision dynamic method may introduce larger instrument errors. The difficulty in ensuring accuracy for small surface area samples using the static method stems from several factors.
Take, for example, a sample with a specific surface area of 1 m²/g. When 0.5 g of nitrogen is adsorbed onto this sample under BET partial pressure conditions, the adsorption volume is approximately 0.1 ml. However, during the test, the volume of the adsorption environment at liquid nitrogen temperature is only about 0.03 ml. Meanwhile, the background volume of the sample tube itself is around 3–5 ml. To accurately quantify the 0.03 ml of adsorption within a 3–5 ml sample tube and ensure an accuracy of less than 3%, the pressure sensor must have an accuracy of over 0.03%. Unfortunately, even the best imported pressure sensors typically have an accuracy of only 0.1%, while standard sensors used in surface and pore analyzers usually range between 0.15% and 0.2%.
This means that even with ideal temperature control and stable liquid nitrogen conditions, the uncertainty in adsorption volume could reach up to 10%, making it extremely difficult to achieve reliable results. Additionally, when dealing with samples that have low density or require large sample loads, the accuracy becomes even more challenging to maintain.
On the other hand, for medium-to-large surface area samples, the static method can easily achieve an accuracy of 2% or even 1%, as the adsorption amounts are significantly larger. Therefore, in testing small surface area samples, the static method can only reduce errors by increasing the sample mass. Many static instruments are equipped with large-capacity sample tubes for such cases, but this also increases the background volume, which limits overall accuracy. Some manufacturers claim their static methods can measure surfaces as small as 0.0001 m²/g, which is misleading and not scientifically valid.
In contrast, high-precision dynamic methods that incorporate wind-heat assist, detector constant temperature control, and low-temperature cold traps significantly improve measurement accuracy. These instruments enhance signal-to-noise ratios by improving signal strength, suppressing background noise, and reducing external interference. Increasing the sample weight or detector current can boost signal strength, but it also increases noise, so there is an optimal balance to strike. Temperature drift and signal sharpness are key sources of error in these systems. Detector thermostats help suppress temperature drift, while wind-heat assist improves signal clarity.
For a sample with a surface area of 1 m²/g and an adsorption amount of 0.5 g of nitrogen at a partial pressure of ~0.2, the peak area and background can be controlled within 2%, demonstrating the effectiveness of the dynamic method.
Thus, for small surface area samples, the advantages of sensitivity and resolution provided by dynamic instrumentation with wind-heat assist, detector thermostat, and low-temperature cold trap become evident. However, for medium-to-large surface area samples, both static and dynamic methods can provide comparable accuracy. The dynamic method has the advantage of faster testing due to its solid standard reference method, while the static method uses the BET point method, which may save on liquid nitrogen consumption.
When measuring both surface area and pore size distribution, the static volumetric method of a surface and pore analyzer is generally recommended.
In summary:
1. For small surface area samples (below 10 m²/g), the dynamic chromatography specific surface instrument with wind-heat assistance and detector thermostat is preferred, as it offers better resolution and sensitivity.
2. For medium-to-large surface area samples, both dynamic and static methods are viable. The dynamic method is faster and more efficient, while the static method may be more cost-effective in terms of liquid nitrogen usage.
3. If pore size distribution analysis is required, the static volumetric method is typically the most suitable approach.
Water Heater Breaker
Leakage protector, also known as leakage switch, is a new type of electrical safety device, mainly used for:
(1) Prevent electric shock accidents caused by electrical equipment and electrical circuit leakage;
(2) Preventing single-phase electric shock accidents during electricity use
(3) Timely cut off single-phase grounding faults in the operation of electrical equipment to prevent fire accidents caused by leakage
(4) With the improvement of people's living standards and the continuous increase of household appliances, personal electric shock and fire accidents caused by defects, improper use, and inadequate safety measures of electrical equipment in the process of using electricity have brought undue damage to people's lives and property. The emergence of leakage protectors provides reliable and effective technical means for preventing various accidents, timely cutting off power, and protecting equipment and personal safety.
The leakage protector should meet the following technical requirements
(1) The sensitivity of electric shock protection should be correct and reasonable, and the starting current should generally be within the range of 15-30 milliamperes
(2) The action time of electric shock protection should generally not exceed 0.1 seconds
(3) The protector should be equipped with necessary monitoring equipment to prevent it from losing its protective effect when the operating state changes. For example, for voltage type electric shock protectors, a neutral grounding device should be installed.
ZHEJIANG QIANNA ELECTRIC CO.,LTD , https://www.traner-elec.com