The surface area per unit mass of a powder or porous body, in m²/g. For spherical particles S = 6/(ρd), increasing in inverse proportion to particle size.
Japanese name: 比表面積
Specific surface area appears in 6 practice questions across 3 topics, including Nanomaterials, Thin films, surfaces and nanomaterials, Ceramics and glasses.
Field: Nanomaterials
Answer: B. 100 times
A sphere has a surface area of 4πr² and a volume of (4/3)πr³, so the surface area per unit volume is 3/r, inversely proportional to the radius (diameter). When the diameter falls to 1/100, from 1 µm = 1000 nm to 10 nm, the specific surface area increases 100 times. Ten times takes the square root of the ratio, and 10,000 times confuses this with the ratio of the surface areas of single particles (the square of the diameter ratio). In particles about 10 nm in diameter, roughly a tenth of all atoms are at the surface, and the properties of the surface atoms strongly influence those of the particle as a whole. Nanoparticles are used as catalysts because of their large specific surface area.
Answer: B. About 75 m²/g
Dividing the surface area of one sphere, πd², by its mass, ρπd³/6, gives a specific surface area per mass of S = 6/(ρd). Substituting ρ = 4.0 g/cm³ = 4.0×10⁶ g/m³ and d = 20×10⁻⁹ m gives S = 6/(4.0×10⁶ × 20×10⁻⁹) = 6/0.080 = 75 m²/g. About 150 m²/g puts the radius, 10 nm, in place of d, and about 37.5 m²/g puts the diameter, 20 nm, in place of r in the radius form S = 3/(ρr). The specific surface area is inversely proportional to particle size, so halving the size doubles it. In real powders the particles touch and agglomerate, so measured values are usually smaller than this calculated value.
When the diameter falls to 1/100, from 1 µm = 1000 nm to 10 nm, the specific surface area increases 100 times.
When the diameter of spherical particles is reduced from 1 …Dividing the surface area of one sphere, πd², by its mass, ρπd³/6, gives a specific surface area per mass of S = 6/(ρd).
Spherical TiO₂ nanoparticles 20 nm in diameter (density 4.0…Finer particles have a larger specific surface area and shorter diffusion distances, so sintering proceeds at lower temperatures.
Which statement about sintering of ceramic powders is corre…Nanoparticles have a large specific surface area and readily stick together and agglomerate through van der Waals attraction.
Which is an appropriate way to keep oxide nanoparticles dis…BET method XRD (X-ray diffraction) Scherrer equation Sintering Zeta potential Bottom-up synthesis Carbon nanotube Graphene Melting point depression of nanoparticles Quantum dot