Surface effect details - Database & Sql Blog Articles

Concept: The surface area of ​​a spherical particle is proportional to the square of the diameter, and its volume is proportional to the cube of the diameter, so its specific surface area (surface area/volume) is inversely proportional to the diameter. As the diameter of the particles becomes smaller, the specific surface area will increase remarkably, and the number of atoms on the surface of the particles will increase relatively, so that these surface atoms are highly active and extremely unstable, causing the particles to exhibit different characteristics, which is the surface. effect. Principle: The surface area of ​​a spherical particle is proportional to the square of the diameter, and its volume is proportional to the cube of the diameter, so its specific surface area (surface area/volume) is inversely proportional to the diameter. As the particle diameter becomes smaller, the specific surface area will increase significantly, indicating that the percentage of surface atoms will increase significantly. The surface effect of particles larger than 0.1 micron in diameter is negligible. When the size is less than 0.1 micron, the surface atomic percentage increases sharply, and even the sum of the surface area of ​​1 gram of ultrafine particles can be as high as 100 m2. The surface effect at this time cannot be ignored. . The specific surface area of ​​ultrafine particles is also very important. In the ultrafine particle specific surface area research and related data reports, only the results detected by the BET method are true and reliable, because the specific surface area measurement standards developed at home and abroad are The BET test method is based. A method for determining the specific surface area of ​​a solid material by the gas adsorption BET principle. The specific surface area tester is the only fully automated and intelligent specific surface area inspection equipment in China. The test results are highly consistent with international standards and stability, and reduce human error and improve the accuracy of test results. As the particle size of the nanomaterial decreases, the number of surface atoms increases rapidly. For example, when the particle diameter is 10 nm, the number of surface atoms is 20% of the total number of complete crystal atoms; and when the particle diameter is 1 nm, the surface atomic percentage is increased to 99%; at this time, all about 30 of the nanocrystal grains are composed. Almost all of the atoms are distributed on the surface. Due to the lack of adjacent atoms around the surface atoms: there are many dangling bonds, which have unsaturation and are easily combined with other atoms to stabilize, thus exhibiting high chemical activity. As the particle size decreases, the surface area, surface energy and surface binding energy of the nanomaterials increase rapidly. The surface of ultrafine particles is very different from the surface of large objects. If high-magnification electron microscopy is used to image the gold ultrafine particles, real-time observation shows that these particles have no fixed shape and will automatically form each time with time. The shape (such as cubic octahedron, decahedron, icosahedron, etc.), which is different from ordinary solids and liquid, is a quasi-solid. Under the electron beam irradiation of the electron microscope, the surface atoms seem to enter the "boiling" state, and the instability of the particle structure is not seen after the size is larger than 10 nm. At this time, the microparticles have a stable structural state preservation: ultrafine The surface of the particles is highly active, and the metal particles are rapidly oxidized and burned in the air. To prevent spontaneous combustion, surface coating or conscious control of the oxidation rate can be used to slowly oxidize to form a very thin and dense oxide layer to ensure surface stabilization. With surface activity, metal ultrafine particles are expected to be a new generation of highly efficient catalysts and gas storage materials as well as low melting point materials. The surface effect of condensed matter: a large number of atoms, atoms and ions of the atomic world are aggregated into various solid, liquid and gaseous substances, which become the basis of the macroscopic world. When a substance forms a phase, in general, each part of the substance has uniform physicochemical properties. However, this is only true for the inside of the material. The components on the surface of the material, the environment and interactions are different from those in the material, which causes the properties of the surface part and the inner part to be different. For gases, the components are not dense and the surface effect is not large. For liquids and solids, it will show surface effects. The surface effect is expressed on a layer of components on the surface of the material. For a general macroscopic object, the components of the surface layer occupy only a small proportion of the total number of components, and the surface effect is often completely negligible. However, for small condensed particles, the surface effect is sometimes very important. The ratio of the number of components on the surface to the total number of components can be used as a coefficient to describe the degree of surface effect. When the particles are large, the coefficient is close to zero; as the particles continue to decrease, the coefficient increases; when the particles are small to the nanometer range, the coefficient increases significantly. Application: Artificial rainfall in a system composed of many phases, sometimes surface The existence of the phase will become very important, it will affect the balance between the various phases. A typical example of surface effects that we can usually encounter is the formation of water droplets. Water droplets in saturated or supersaturated steam, if its radius is large enough, the surrounding water vapor will gradually condense on the water droplets, and the water droplets will gradually become larger. If the water droplets are small, then, due to the influence of the surface effect, in order to maintain the existence of water droplets, the outside world must have a high vapor pressure, so that under normal vapor pressure conditions, the water droplets will not increase, and Will gradually evaporate. The clouds floating in the sky are made up of many such tiny water droplets. On the eve of the rain, the external steam pressure is increased. These miniature water droplets gradually combine into larger and larger water droplets by colliding with each other. Finally, when the buoyancy and motion resistance of the air can no longer bear their weight, they will It fell to the ground and became a raindrop. It can also be seen that if some impurity particles such as dust or the like are doped into the supersaturated steam, it will contribute to the formation of water droplets. If there is already a very thick cloud in the sky, then using the aircraft to spread some impurity particles in the clouds will speed up the formation of raindrops, thus achieving the purpose of rainfall, which is artificial rainfall. Application: boiling water, the tap water used in our usual boiling water contains many gases, they exist in the form of small bubbles. When the temperature of the water gradually rises to nearly 100 degrees Celsius, the water vapor continuously enters the interior of the small bubbles, causing the small bubbles to gradually increase, and the bubbles gradually rise due to the buoyancy of the water, reaching The water surface breaks and releases water vapor inside it into the air. When such bubbles are produced in large quantities, the water boils. However, if the small bubble is very small, the bubble may not increase due to the presence of the surface phase. When this happens, the water will not boil even if it is added to a very hot level. This is a superheated liquid. Surface-effect anti-submarine frigates: With the advent of nuclear submarines, the speed of surface anti-submarine warships has become a major obstacle to the implementation of anti-submarine warfare. To this end, the US Navy began to develop a high-speed anti-submarine frigate with a displacement of 2000-3000 tons in the early 1980s. The number of the ship was set to 3KSES. Because this high-speed anti-submarine frigate is designed according to the surface effect, it is called "surface effect type anti-submarine frigate". This type of frigate is actually a side-walled hovercraft that relies on an air cushion to make the hull surface, and uses a supercavitating propeller or water jet propulsion device to drive the hull. The speed can reach 80-100 knots. In order to ensure that the ship has good stability during high-speed navigation, two steel sidewalls are installed on the ship to extend into the water. The surface effect type anti-submarine frigate has the ability to sail at high speed in the open sea and can undertake a wide range of anti-submarine missions. Some experts predict that surface effect anti-submarine frigates and small waterplane double-body frigates will become the new frigates of the 21st century. Recommended Products:

High Precision

Three- station side-by-side automatic mesoporous micropore analyzer

JW-BK300 series high-precision three-station parallel-type fully automatic mesoporous microporous analyzer (), a new generation of high-end microporous analyzer independently developed on the basis of JW series aperture analyzer. The core hardware of this instrument adopts international advanced brand, equipped with "turbomolecular pump" and pressure sensors of different ranges such as 1000Torr, 10Torr and 1torr. Through the full modular design and accurate application of microporous analysis model, it realizes micro Accurate analysis of the hole, the minimum aperture can be measured up to 0.35nm, the accuracy, accuracy and stability of the test results reach the level of imported similar instruments, the cost performance is very high, very suitable for activated carbon, activated alumina, molecular sieve, zeolite, MOF materials, etc. Research and application of pore nano-powder materials.

Performance parameters:

Instrument model: JW-BK300 Three-station automatic mesoporous microporous analyzer

Principle method: static capacity method, low temperature nitrogen adsorption;

Test function: isothermal adsorption desorption curve; single point, multi-point BET specific surface area; Langmuir specific surface area; external surface area (STSA); total pore volume, average pore size; BJH mesoporous pore volume and pore size distribution analysis; Plot method, as-plot method, DR method, MP method micro-well conventional analysis; HK method, SF method micro-hole accurate analysis; NLDFT method pore size distribution analysis; true density test; gas adsorption amount, adsorption heat test; mass input method test ;

Test gas: nitrogen, oxygen, hydrogen, argon, helium, carbon dioxide, methane, etc.;

Test range: specific surface 0.0005m2 / g to no upper limit, aperture 3.5 ?-5000 ?;

Repeatability: specific surface area ≤ ± 1.0%, pore size ≤ 0.2 ?;

Test efficiency: average surface area per 10 min; mesoporous, macroporous analysis average 1-1.5 hours; microporous analysis average 10-16 hours per sample;

Analytical station: 3 completely independent sample analysis stations, which can be degassed in the same position;

P0 position: 3 completely independent P0 stations, real-time monitoring;

Lifting system: 3 sample analysis stations are equipped with 2 sets of independent lifting systems in situ, electric control, automatic control, and no interference with each other;

Vacuum system: multi-channel parallel vacuum system, cartridge type modular design, patented technology of vacuum pumping speed adjustment valve system, can be automatically adjusted within the range of 2-200ml/s;

Vacuum pump: external imported two-stage rotary vane mechanical vacuum pump (automatic anti-return oil) + built-in imported turbomolecular pump, ultimate vacuum degree up to 10-6Pa;

Degassing system: 3 sample analysis stations are equipped with 3 in-situ and in-situ degassing stations: 3 independent heating packages, 3 independent temperature control systems, programmable temperature control, and programmable temperature steps up to 10 steps. Simultaneous configuration of external ectopic 4-station vacuum degassing pretreatment system

Degassing temperature: room temperature - 400 ° C, accuracy ± 1 ° C;

Pressure sensing: original imported capacitive film multi-pressure sensor, 1000 torr (133.3KPa), 10torr (1.333KPa), 1torr (0.1333KPa) or 0.1torr (0.01333KPa), accuracy ≤ ± 0.15%;

Partition range: P/P0 10-4-0.998;

Pressure control: Balanced pressure intelligent control method, pressure controllable interval <0.1KPa, the highest pressure point can be automatically controlled;

Data acquisition: Ethernet data acquisition, fast acquisition speed, high precision, compatible with Windows 7/XP 32/64 bit system;

Mesoporous Microporous Analyzer Features:

● Completely independent three stations for side-by-side analysis, which can be degassed in the same position and has high test efficiency;

● External 4 degassing station, special mechanical vacuum pump, the highest degassing temperature is 400 °C;

● Multi-point BET specific surface test of three samples, which can be completed automatically within 30 minutes;

● Adopt liquid nitrogen surface control integrated system and software compensation technology to ensure that the non-uniform temperature field of the sample chamber is relatively constant during the whole test process to ensure the accuracy of analysis, suitable for various cold baths such as liquid nitrogen, liquid argon and ice water;

● Introduce foreign advanced thermostat clamp technology, equipped with 3L large-capacity vacuum glass liner dewar and anti-liquid nitrogen volatilization unit to ensure the experiment can last for 72 hours;

● Self-control adjustable multi-channel parallel vacuum system, built-in anti-splash unit, and "stepped" anti-splash program to effectively prevent ultra-fine powder from flying and avoid contamination inside the instrument;

●The original imported turbo molecular pump and mechanical pump are used together. The ultimate pressure of the analytical station is up to 10-8, which can fully satisfy the ultra-microporous analysis of 0.35nm-0.7nm.

●Imported 1000torr, 10torr, 1torr (upgradable to 0.1torr) pressure sensors of different ranges, combined without interruption, high pressure data acquisition accuracy, small error, fully meet the precise analysis of micro-holes;

● During the mesoporous micropore experiment, the nitrogen saturated vapor pressure P0 is completely tested in real time, and is carried out in parallel with the analysis station; the P0 value can also be determined by the atmospheric pressure input method;

●The instrument control panel is equipped with a valve position control indicator. The experimenter can visually and clearly see the working state of the control valve, and the user-friendly design;

● Non-localized density function theory NLDFT analysis model standard configuration, reaching the international advanced level;

● HK, SF model micro-hole analysis technology has passed the measurement certification of China Metrology Institute;

● Balanced pressure intelligent control technology, sample suction/desorption equilibrium pressure automatic judgment and data acquisition, and the control precision of isothermal suction and desorption curve measurement reaches the international advanced level;

● Ethernet data acquisition and processing software, guided operation, a set of software can control multiple instruments at the same time, can achieve remote control;

● The instrument can be expanded to 3 stations of completely independent micropore analysis;

Mesoporous micropore analyzer application areas:

● Catalyst material: activated alumina, molecular sieve, zeolite, etc.;
●Environmental protection field: adsorbent such as activated carbon;
● Nanomaterials: nano ceramic powder (alumina, zirconia, yttria, silicon nitride, silicon carbide, etc.), nano metal powder (silver powder, iron powder, copper powder, tungsten powder, nickel powder, etc.), nano high Molecular materials, carbon nanotubes, etc.;
● Coal mining industry: coal, ore, rock, shale gas, coalbed methane, etc.;
● Other materials: microfiber, porous fabric, composite materials, etc.
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