Gypsum Products

gypsum is the dihydrate form of what?

once gypsum is heated it loses 1.5 of its 2 g mol of H2O and is converted to

True/False: When water is added to calcium sulfate hemihydrate the reverse reaction happens and calcium sulfate dihydrate is formed
True False

the process in which gypsum is heated and part of the water of crystallization is driven of

2CaSO4 . 2H2O with open kettle heating creates

2CaSO4 . 2H2O with high-pressure steam creates

2CaSO4 . 2H2O with Boil and CaCl2 creates

T/F: excess amount of measured water above the theoretically correct amount required for hydration is always necessary
True False

amount of gauging water from most to least

water to powder ratio for:

plaster:
stone:
improved stone:

the working time is the length of time from the start of the mix until he setting mass reaches a

the length of time from the start of the mix until the setting mass becomes rigid and can be separated from the impressions

Surface penetration test using glimmer needles

initial setting time when:
final setting time when:

In clinical setting what can be used to determine the working time 

average working time?

what can be used to determine relative rigidity and hardness that could be used to indicate final set

average, subjective setting time for final set

4 ways to increase setting time (a slower-setting product)

4 ways to decrease setting time (a faster-setting product)

the first indication of moisture contamination is ___ ___ of the product and if the contamination continues, ____ ____ occurs

expanding percentages of

plaster:
stone:
high strength stone:

2 things increase setting expansion

2 things decrease setting expansion

increase in setting expansion that occurs when gypsum materials are immersed in or come in contact with water during the setting process

hygroscopic expansion is ___ as great as the normal setting expansion

strength of gypsum product is usually measured in terms of ____ or _____ strength

the strength that is measured when the sample contains some or all of the water in excess of the theoretical amount required for hydration; typical condition after setting; material feels well for several hours

the strength that is measured when the excess water is not present in the sample

the dry strength may be ___ or ___ times the wet strength

T/F: cast must sit in a dry environment overnight to approach dry weight values
True False

thicker mixes will ___ strength whereas thinner mixes will ____ strength

related to compressive strength but reaches it maximum value more rapidly because the surface is the first to dry

when does the greatest surface hardness occur?

if gypsum must be soaked in water for a lab procedure, the water should be saturated with ____ to prevent surface erosion

1 g of water roughly equals

mixing to get a smooth, homogenous mix should be obtained in how much time?

provides a gypsum mix free of air bubbles and is homogenous in consistency; used when elimination of voids and surface bubbles is critical