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Ceramics exam 2 > Glazes > Flashcards

Glazes Flashcards

1
Q

What is frit?

A

Water-insoluble source of PbO and B2O3

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2
Q

What is whiting?

A

CaCO3

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3
Q

What is white lead?

A

2PbCO3 * Pb(OH)2

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4
Q

What are glazes made of?

A

frits (PbO and Ba2O3), white lead (2PbCO3 * Pb(OH)2), whiting (CaCO3), quartz, clay, water, sometimes organic binder

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5
Q

What substitution is being made in glazes and why?

A

B2O3 for PbO as there are health risks associated with PbO ingestion

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6
Q

What fine crystals are devitrified during the formation of matte glazes?

A

> anorthite: CaAl2Si2O8
wollastonite CaSiO3

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7
Q

What’s a fritted glaze?

A

Used in semivitirious wares and hotel china

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8
Q

What are qualities of lead containing glazes?

A

high brilliance and flow well during firing

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9
Q

How are fritted glazes, including lead containing, fired?

A

They are first bisque fired: without glaze, then glost fired: with glaze

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10
Q

What is a crystalline glaze?

A

> specialty glaze that fosters devitrification of large spherulitic willemite (2ZnO*SiO2) crystals

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11
Q

How are crystalline glazes formed?

A

By overheating and then cooling to a low temperature soak

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12
Q

Why do glazes need opacity?

A

to hide body defects

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13
Q

What is opacity caused from?

A

scattering of light from fine crystalline particles dipersed within the glassy matrix, particularly if they have a high index of refraction difference with the glass

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14
Q

What is the most effective opacifying particle?

A

Zircon (ZrSiO4)

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15
Q

What causes cracking in glazes?

A

too much clay or glaze particles that are too fine = excessive water adsorption

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16
Q

What is whiting?

A

washed powdered chalk

17
Q

What are frits and why are they used?

A

pre-melted, quenched in water to form a glass, used as a water-insoluble form of PbO and Ba2O3

18
Q

What happens as the silica content of the glaze increases during highest firing temps of glaze?

A

The liquid viscosity increases, preventing gravitational movement of the glaze

19
Q

What effect do bubbles have on firing glazes?

A

–> porosity is trapped as bubbles in the viscous liquid.
–> decomp of CaCO3 (carbonates) further forms bubbles
–> at maturing/soaking temp, liquid viscosity is low enough for most bubbles to escape from surface

20
Q

What reactions between the glaze and body improve adherence?

A

–> different phases on the surface of the body have different solubilities, forming ROUGH INTERFACE
–> MULLITE NEEDLES from SiO2 and Al2O3 grow from the body into the glaze

21
Q

What happens to bubbles in glazes while cooling?

A

Remaining bubbles shrink, causing minor dimples in glaze surface, which slightly degrades surface reflectance

22
Q

What CTE do you want for the glass and glaze?

A

You want the glass/glaze to have a lower coefficient of thermal expansion than the body so at room temp the glaze is in compression

23
Q

What is crawling?

A

If glaze has high surface tension and/or doesn’t wet the body due to high interfacial energy; it will bead up rather than spread

24
Q

How do you increase the CTE of a glaze? (which you don’t want to do)

A

increase the alkali content of the glaze

25
Q

What are pinholes?

A

a pore close to the surface that provides a source of gas due to slow evolution of gases from organics into the clay batch

26
Q

What is crazing?

A

–> happens if the glaze is in TENSION
–> can be purposefully made for aesthetics through a high CTE content

27
Q

What is orange peel?

A

droplets in sprayed-on glaze that do not consolodate

28
Q

What is waviness?

A

uneven application in which large variations in coating thickness don’t even out during firing

29
Q

What are the qualities of glaze particles?

A

–> insoluble in the liquifying glaze during heat treatment
–> most typical are spinels

30
Q

Why are spinels the most common glaze color particle? How are colors produced?

A

–> because it accomodates a wide range of cation substitution
–> colors are produced by replacements of transition metal or rare earth cations

31
Q

What is the structure of typical ceramic stains/pigments?

A

like spinel; close-packed FCC array of oxygen anions, with chemical formula AB2O4

Ceramics exam 2 (17 decks)

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