Inorganic Materials

Question 1

What is electrical conduction?

Answer 1

When charges are free to move throughout the material. It involves dissipation of energy as heat.

Its differences in magnitude is what distinguishes metals, semiconductors, and insulators.

Compare with electric polarization.

Question 2

What is electric polarization?

Answer 2

Of a material, a state of positive/negative charge separation due to charges that are moving only limited distances being halted by opposing binding forces. Its measurement is its dielectric constant. It involves storage of potential energy in the material.

Compare with electrical conduction.

Question 3

What is silicate?

Answer 3

A class of minerals fomed on the basis of the strong and ionic Si-O. It makes up the bulk of rocks, clays, sand, and soils in earth’s crust. It provides the ingredients for building materials such as bricks, cement, concrete, and glass. Its physical properties correlate closely w/ its structures.

Question 4

What is an orthosilicate?

Answer 4

A group of individual SiO₄^4- anions w/ cations arranged around them on a regular crystalline lattice. These are the simplest silicates.

Question 5

List and characterize all the types of silicate structures.

Answer 5

Question 6

What is an olivine?

Answer 6

[Mg,Fe]₂SiO₄

A class of minerals containing forsterite (Mg₂SiO₄) and fayalite (Fe₂SiO₄), which are the extreme members of the class and are orthosilicates.

Question 7

What is a disilicate?

Answer 7

The simplest silicate structure in which 2+ SiO₄^4- tetrahedra link and share oxygen vertices. Of all the silicate structures, it is 2^nd in simplicity to tetrahedral.

Question 8

What is asbestos?

Answer 8

A generic term for a group of naturally occurring, hydrated silicates that can be processed mechanically into long fibers.

They are fibrous because the bonds along the strandlike tubes are stronger than those that hold different tubes together

It is an excellent thermal insulator, does not burn, resists acids, and is strong. For many years, it was used in cement for pipes and ducts and woven into fabric to make fire-resistant roofing paper and floor tiles, but now it’s used much less because inhalation of its small fibers can cause asbestosis.

Question 9

What is an aluminosilicate?

Answer 9

A class of minerals derived by substituting some of the Si atoms in silicates w/ Al atoms. Since Al can only contribute 3e^-, not 4e^-, the additional required e^- is supplied by the ionization of a (alkali) metal atom.

Ex.: feldspar: Si/Al silicate tetrahedral network like quartz, accompanied by other cations such as Na+, K+, or Ca2+. Temperature inversely proportional to order in structure.

Ex.: mica: Si/Al silicate infinite sheet network like talc, accompanied by cations between the sheets, augmenting the van der Waals interactions holding sheets together.

Question 10

What is clay?

Answer 10

Mineral of variable composition produced by the weathering action of water and heat on primary minerals. They are microcrystalline or powdered in form and are usually hydrated.

Often used as supports for catalysts, fillers in paint, and ion-exchange vehicles. The ones that readily absorb water and swell (by forming hydration shells) are used as lubricants and bore-hold sealers in drilling oil wells.

Question 11

What is zeolite?

Answer 11

A class of 3-D aluminosilicates that carry a (-) charge compensated by neighboring alkali-metal/alkaline-earth cations, like a feldspar. However, zeolites have much more open structures than feldspars.

These open structures consist of polyhedral cavities connected by tunels. Though many are natural, they can be synthesized under conditions controlled to favor cavities of uniform size/shape.

Question 12

What is the “hardness” of water?

Answer 12

The concentration of Ca and Mg salts such as Ca(HCO3)2 and Mg(HCO3)2, which when heated become insoluble carbonates (boiler scale).

Question 13

How does zeolite soften water?

Answer 13

Its 3-D open structure consists of polyhedral cavities connected by tunnels. Most zeolites accommodate H₂O in their cavities, providing a mobile phase for migrating charge-compensating cations, and thus enabling them to serve as ion-exchange materials (cation swap).

When hard H₂O is passed through a column packed w/ zeolite w/ Na⁺, the Ca²⁺ and Mg²⁺ ions exchange w/ Na⁺ ions and are removed from the water phase. This reaction can be reversed by passing concentrated NaCl_(aq) through the zeolite to regenerate its Na form.

Question 14

How are zeolites used as “molecular sieves”?

Answer 14

They can easily adsorb small molecules.

Their spongelike affinity for H₂O: useful drying agents. For example, they are put between panes of double-pane glass windows to prevent moisture from condensing on inner surfaces.

The pore size of zeolites can be selected to filter molecules pasing through by size, like letting O₂ through while repressing N₂.

Question 15

How can zeolite be used as a catalyst?

Answer 15

It “selects” which molecules diffuse through, which become trapped, and which cannot enter its structure. Some are also “shape-selective.”

Question 16

What is a ceramic?

Answer 16

A synthetic material that has as its essential components inorganic, nonmetallic materials.

Its density can differ greatly despite same chemical composition due to its porosity. It can have small openings into which fluids (air/water) can infiltrate, or have no channels of this sort.

Question 17

What are the pros/cons of using ceramics?

Answer 17

They offer stiffness, hardness, resistance to wear, and resistance to corrosion. They are less dense than most metals, good electrical insulators at ordinary temperatures, and retain their strength well at high temperatures.

Several important structural metals soften/melt at temperatures 103 ℃ below their melting points of their chemical compounds in ceramics.

However, ceramics are generally brittle and low in tensile strength. They tend to have high thermal expansion but low thermal conductivity (subject to thermal shock). Their strengths tend to unpredictably fail. As they age, some lose mechanical strength.

Question 18

What are silicate ceramics?

Answer 18

Made from aluminosilicate clay minerals, all contaiing tetrahedral SiO₄ grouping.

These include commonplace pots, dishes, and bricks.

Question 19

What are oxide ceramics?

Answer 19

Made from a number of metals combined w/ oxygen to give compounds such as alumina (Al₂O₃), magnesia (MgO), or yttria (Y₂O₃), and hardly any, if existent, silicon.

Question 20

What are nonoxide ceramics?

Answer 20

Made of compounds free of oxygen as principal components. Common compounds include silicon nitride (Si₃N₄), silicon carbide (SiC), and boron carbide (≈B₄C).

Question 21

What is a ceramic phase?

Answer 21

Any portion of the whole ceramic body that is physically homogeneous and bounded by a surface that separates it from other parts. Often visible at a glance in coarse-grained ceramic pieces, or through a microscope in fine-grained pieces.

Question 22

What is the microstructure?

Answer 22

The structural aspects of a solid on a length scale smaller than macroscopic but larger than nanoscopic/atomic. It includes sizes and shapes of crystalline grains and voids, and the presence of mechanical stresses.

Question 23

What is the microstructure of a ceramic body? What does it suggest about its quality as structural material?

Answer 23

It depends markedly on details of its fabrication: the techniques of forming/firing a ceramic piece are as important as its chemical composition in determining ultimate behavior because