Page 442 - Carrahers_Polymer_Chemistry,_Eighth_Edition

12 Inorganic Polymers

12.1 INTRODUCTION
Just as polymers abound in the world of organics, they also abound in the world of inorganics.
Inorganic polymers are the major components of soil, mountains, and sand. Inorganic polymers are
also extensively employed as abrasives and cutting materials (diamond, boron carbide, silicon carbide
(carborundum), aluminum oxide), coatings, flame retardants, building and construction materials

(window glass, stone, Portland cement, brick, tiles), and lubricants and catalysts (zinc oxide, nickel
oxide, carbon black, graphite, silica gel, alumina, aluminum silicate, chromium oxides, clays).

The first somewhat man made, semisynthetic polymer was probably inorganic in nature. Alkaline
silicate glass was used in the Badarian period in Egypt (about 12,000 bc) as a glaze, which was
applied to steatite after it had been carved into various animal, and so forth, shapes. Frience, a
composite containing powered quarts or steatite core covered with a layer of opaque glass, was
employed from about 9,000 bc to make decorative objects. The earliest known piece of regular
(modern day type) glass, dated to 3,000 bc, is a lion’s amulet found at Thebes and now housed in the
British Museum. This is a blue opaque glass partially covered with a dark green glass. Transparent

glass appeared about 1,500 bc. Several fine pieces of glass jewelry were found in Tutankhamen’s
tomb (ca 1,300 bc), including two bird heads of light blue glass incorporated into the gold pectoral
worn by the Pharaoh.
Because of the wide variety and great number of inorganic polymers, this chapter will focus on
only a few of the more well-known inorganic polymers. Table 12.1 contains a partial listing of com-
mon inorganic polymers.
Along with the silicates that will be dealt within other sections, there are many other inorganic
polymers based on other units. One of these is the hydroxylapatite or hydroxyapatite materials that
have general formula of Ca (PO ) (OH), which is a member of the apatite group. Seventy percent
5
4 3
of bone is composed of hydroxyapatite. Dental enamel is made from carbonated-calcium defi cient
hydroxylapatite nanotubes. It is believed that the initial step is the production of composite nano-
spheres of nanocrystallite apatite and amelogenin. These then aggregate forming nanorods about
50 nm in diameter and 250 nm long. These nanorods further assemble forming elongated crystals
that compose our dental enamel.

12.2 PORTLAND CEMENT
Portland cement is the least expensive, most widely used synthetic inorganic polymer. It is employed
as the basic nonmetallic, nonwoody material of construction. Concrete highways and streets span
our country side and concrete skyscrapers silhouette the urban skyline. Less spectacular uses are
found in everyday life as sidewalks, fence posts, and parking bumpers.
The name “Portland” is derived from the cement having the same color as the natural stone quar-
ried on the Isle of Portland, a peninsula on the south of Great Britain. The word cement comes from
the Latin word caementum, which means “pieces of rough, uncut stone.” Concrete comes from the
Latin word concretus, meaning “to grow together.”
Common (dry) cement consists of anhydrous crystalline calcium silicates (the major ones being
tricalcium silicate, Ca SiO , and β-dicalcium silicate, Ca SiO ), lime (CaO, 60%), and alumina
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2
3
5
(a complex aluminum silicate, 5%). While cement is widely used and has been studied in good
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