Lecture 1 Flashcards
What are the Highly Porous Materials?
Substances characterized by having a large number of pores or void spaces within their surface area.
Mention characteristics of the pores
These pores can vary in size, shape and distribution; but they are typically small relative to the overall size of the material.
Where can be found porous materials?
Porous materials can be found in various forms, including:
- Solids
- Liquids
- Gases
Areas of application of highly porous materials
- Catalysis
- Adsorption
- Gas storage
- Sensor technology
- Cromatography
SOLIDS
Porous solids
Materials like carbon, silica gel, zeolites and metal-organic frameworks (MOFs).
They have a network of interconnected pores that provide a large surface area, making them useful as:
- Adsorption
- Filtration
- Catalysis
SOLIDS
Porous Ceramics
Ceramics engineered to have high porosity, often used for their lightweight, insulating filtering properties.
- Alumina: with controlled porosity are used in: thermal insulation, membrane support and catalyst support.
- Silicon carbide: used in applications requiring high thermal conductivity, chemical resistance and mechanical strength, such as: filters for hot gas filtration.
LIQUIDS
Aerogels
Lightweight materials derived from gels where the liquid component has been replaced with gas, resulting in a highly porous structure.
GAS
Foams
Materials consisting of gas bubbles trapped within a solid or liquid matrix, resulting in a porous structure.
Highly materials common feature
Interaction between: molecule <———> Solid surface
Solid material should have a large specific surface area:
- Textural porosity: breaking up of a particle into smaller pieces
- Structural porosity: Drilling in the particle
How can be porosity classified?
Textural
Structural
Motivation for the use of Porous Materials
- Field of application: insulation material for thermal insulation
- Principal property: supression of heat conduction by discontinuities (ex: pores in the solid matrix)
- Ideal case: Closed cavities without gas exchange with the environment and thus without heat transport by convection
Name 3 commercial known (or examples) of porous materials
Z.b:
Zeolite
Activated carbon
Silica gel
PORE SYSTEMS:
How is divided the Structural Porosity?
Pores in particles, specific surface area stems from the surface area of the pore walls.
It is divided into: open porosity and closed porosity
According to the width: how can be classified the porous?
One value: Zeolite
Narrow range: Activated carbon
Width range: Silica gel
PORES SYSTEMS - Structural porosity
What is the classification of Open Porosity?
- Micropores: <2 nm width ; very high surface area ; strong interaction with molecules ; poor mass transport
- Mesopores: 2 - 50 nm width (Silica gel)
- Macropores: > 50 nm width ; small surface area ; very good mass transport
Mentioned the 2 ways that porosity can be generated?
- Breaking up of a particle into
smaller pieces
(textural porosity). - Drilling in the particle
(structural porosity).
Name the 3 principles of synthesis of P.M
Aggregation
Substraction
Recrystallisation
What is sintering?
Sinterizar: Producir piezas de gran resistencia y dureza, calentando, sin fundir, conglomerados de polvo modelador por presión
Which two processes reinforce the “aggregation”?
Drying and Sintering
Explain Aggregation as a principle of the synthesis of PM
- Starting with finely dispersed,
non-porous particles. - Agglomeration.
- Drying and sintering that produces solidification of the
microstructure.
Name two types/procedures of substraction in PM
Dissolving
Oxidising
Name a moment when the “Recrystallisation” is used:
In the Zeolite synthesis through an Amorphous precipitation
Are micropores, when compared to macropores, suitable for mass transport?
No, micropores are characterized for having poor mass transport characteristics
Explain Substraction as a principle of the synthesis of PM
Removal of components from non-porous or porous macroscopic particles of inhomogeneous
composition by dissolving, oxidising and other processes.
Explain Recrystallisation as a principle of the synthesis of PM
Precipitation of amorphous precipitates, through post-treatment (e.g. hydrothermal ) formation of
complete or partially crystalline products.
Which is the common feature of all the applications of HPM?
The focus is always on the interaction between molecules and the surface of a solid
5 g of Zeolite may have an internal surface area of
Almost a football field: 5000- 6000 m2
Particles of nanometre range are difficult to handle. What can be done to tackle this issue, regarding to HPM?
Create the pores in the material itself. Structural porosity.
HPM are used as insulating thermal materials. BUT, what does it mean?
Supress heat conduction by discontinuities
Closed porosity, which belongs to structural porosity, should we take it into account? Why?
No, ´cause the pdf, AI voice and script says so
Is Activated carbon usually: Micro, meso or macro porous? Unique, narrow or wide pore distribution?
Microporous.
Distribution is wider than Zeolite.
Pore width is narrower than Zeolite
Is Silica gel: Micro, meso or macro porous? Unique, narrow or wide pore distribution?
Mesoporous and broad pore width distribution
How is tipcally presented the silica gel? Powder, granulate, liquid, gas…?
Powder or Granulate
