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Fixed Final > Investing Materials (2) > Flashcards

Investing Materials (2) Flashcards

1
Q

What is the starting mineral for Gypsum?

A

Calcium Sulfate Dihydrate

CaSO4:2H2O

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2
Q

What is the product form calcining?

A

Calcium Sulfate Hemihydrate

CaSO4:1/2H2O

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3
Q

What is the calcining procedure for Plaster?

A

Open container to air

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4
Q

What is the calcining procedure for Stone?

A

Closed autoclave under steam pressure

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5
Q

Setting reaction for Gypsum products

A

Exothermic reaction
Reverse of calcining process
End product is gypsum
Same for all gypsum products

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6
Q

What is a common accelerator for Gypsum products?

A

Potassium Sulfate

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7
Q

What is a common retarder for Gypsum products?

A

Borax

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8
Q

What happens to plaster when it sets?

A

It expands

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9
Q

What causes porosity in dry Gypsum?

A

Loss of excess water beyond that required for balanced setting reaction

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10
Q

What does porosity do to Gypsum?

A

Acts to concentrate stress, leading to material fracture

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11
Q

What is the binder in Gypsum?

A

Calcium sulfate hemihydrate

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12
Q

T/F - Refractory component of Gypsum participates in the setting reaction

A

False - it does not

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13
Q

What is the most important role in the refractory component of Gypsum?

A

Provide thermal expansion during heating in burnout furnace

Also provides strength of investment at temperatures above 100 C

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14
Q

Is the relative amount of expansion greater for Cristobalite or Quartz?

A

Cristobalite

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15
Q

What do manufacturers offer for thermal expansion investments?

A

Quartz

Cristobalite

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16
Q

Changes in crystal structure cause…

A

Large thermal expansion over a narrow temperature range

17
Q

An increase in the P/W ratio causes…

A

An increase in strength and expansion

18
Q

What causes increased in expansion and strength in greater P/W ratio

A

It’s due to a more dense gypsum framework

19
Q

Why do companies include in heating investments? Why?

A

Insoluble raw starch

It provides expansion by water absorption and swelling. The starch burns out along with patterns during burnout process

Fixed Final (8 decks)

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