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.
