For small specific surface area samples, such as battery materials, organic compounds, biological substances, metal powders, and abrasives with low porosity, the static method often struggles to deliver accurate results. This is because the amount of adsorption is minimal, leading to higher relative errors when compared to the wind-heat assist device and detector thermostat. Additionally, the high-precision dynamic method may introduce larger instrument errors due to its sensitivity to external factors.
The difficulty in ensuring accuracy for small surface area samples using the static method can be illustrated through an example. Consider a sample with a specific surface area of 1 m²/g. When 0.5 g of nitrogen is adsorbed under the BET partial pressure range, the adsorption volume is approximately 0.1 ml. Under liquid nitrogen temperature, the adsorption volume is about 0.03 ml, while the background volume in the sample tube is around 3–5 ml. To accurately measure this small adsorption volume within a large background volume, the pressure sensor must have an accuracy of at least 0.03%. However, even the best imported pressure sensors only offer 0.1% accuracy, and typical surface and pore analyzers operate at 0.15% accuracy. Even with ideal conditions—such as perfect temperature control and stable liquid nitrogen levels—the uncertainty in adsorption volume can still reach 10%, making it challenging to achieve reliable results.
Moreover, small or low-density samples require larger quantities to be loaded, further complicating the measurement process. In contrast, for medium-to-large surface area samples, the static method can easily maintain an accuracy of 2% or even 1%, as the adsorption volumes are significantly larger.
Therefore, for small specific surface area samples, the static method can reduce error by increasing the sample weight, but this also increases the background volume, which limits overall accuracy. Some manufacturers claim their static methods can test samples below 0.0001 m²/g, which is misleading and not scientifically supported.
On the other hand, high-precision dynamic methods equipped with wind-heat assistance, detector thermostats, and low-temperature cold traps offer significant improvements in accuracy. These instruments rely on signal-to-noise ratio, where enhancing signal strength, suppressing noise, and eliminating external interference are crucial. Increasing the sample weight or detector current can boost signal strength, but it also increases noise. Thus, the optimal balance between signal and noise is essential. The use of a detector thermostat helps reduce temperature drift, while wind-heat assistance improves signal sharpness. For a 1 m²/g sample with 0.5 g of nitrogen adsorption, the peak area and background can be controlled within 2%.
In summary:
1. For small surface area samples (below 10 m²/g), dynamic chromatography instruments with wind-heat assistance and detector thermostats are preferred due to their superior sensitivity and resolution.
2. For medium-to-large surface area samples, both dynamic and static methods can provide comparable accuracy. The dynamic method offers faster testing with a solid standard reference, while the static method may save liquid nitrogen consumption.
3. If measuring both surface area and pore size distribution is required, the static volumetric method from a specific surface and pore analyzer is recommended.
These considerations highlight the importance of selecting the appropriate method based on the sample type and desired level of precision.
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