HS2440 Week 1_Asyn_Agencies of Decay

Question 1

What are the agencies of decay? (8)

Answer 1

• water (the agent of a lot of these)
• oxygen
• Dissolved Salts
• Gases and vapours
• Temperature
• Mechanical damage
• Biological agencies
• Light

Question 2

Describe how Oxygen is an agent of decay

Answer 2

• Oxidising power, needs two electrons to fill outer ring, the removal of electrons is oxidation.

Question 3

How is water an agent of decay?

Answer 3

Water is the media for chemical reactions. can contain acids or alkalis. can damage when absorbed. often with the crystallisation of salts within porous materials. also biodeterriation.

Question 4

Salts as an agent of decay

Answer 4

Question 5

Acids as an agent of decay

Answer 5

Question 6

RH and water based chemical reactions

Answer 6

• RH controlled the absorption of moisture onto surfaces
• High RH, strong absorption of moisture.

Question 7

Describe temperature as an influence on decay

Answer 7

• crystallisation of salts
• reaction rates (kinetics)
• Can make polymers flow (Tg)
• Expansion and contraction of material
• in organic material, aids with bond scission

Question 8

Biodeteriation as a decay factor for inorganic materials?

Answer 8

• The byproducts of lichen or algae hold water on surfaces, which gases could dissolve in= acid
• also acidic byproducts through metabolism
• and moisture for microbial activity

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Question 9

What is relative humidity?

Answer 9

• The concentration of water in a given volume of air
• the amount of water as a mass in a volume of air/ the amount of water vapour (mass) needed for total saturation.
• related to temperature

Question 10

1. describe how some salts are more soluble than others. 2. what are electrolytes.

Answer 10

• Sodium Chloride. The attraction between sodium and chloride is not as strong as the attraction of water to the chloride ion.
• if the ionic bond is stronger than the attraction to water eg. calcium carbonate, it is not soluble, and a non- electrolyte.
• an electrolyte is salts dissolved in water

Question 11

Describe hygroscopic salts, and why they are problematic

Answer 11

• are a problem, they attract moisture to themselves, absorb from the atmosphere
• dissolve in their own water (deliquesent)
• once they have attracted enough moisture, at a particular humidity, they dissolve
• can act as electrolytes on metals