Category Materials and the Environment: Eco-Informed Material Choice

Borosilicate glass (Pyrex)

The material. Borosilicate glass is soda lime glass with most of the lime replaced by borax, B203. It has a higher melting point than soda-lime glass and is harder to work, but it has a lower expansion coefficient and a high resistance to thermal shock, so it is used for glassware and laboratory equipment.

Composition

74% SiO2/1% Al2O3/15% B2O3/4% Na2O/6% PbO General properties

Density

2200

– 2300

kg/m3

Price

*4.15

– 6.22

USD/kg

Mechanical properties

Young’s modulus

61

– 64

GPa

Yield strength (elastic limit)

*22

– 32

MPa

Tensile strength

22

– 32

MPa

Compressive strength

*264

– 384

MPa

Elongation

0

%

Hardness—Vickers

*83.7

– 92.5

HV

Fatigue strength at 107 cycles

*26.5

– 29.3

MPa

Fracture tough...

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Soda-lime glass

The material. Soda-lime glass is the glass of windows, bottles, and light bulbs, used in vast quantities, the commonest of them all. The name sug­gests its composition: 13-17% NaO (the "soda"), 5-10% CaO (the "lime") and 70-75% SiO2 (the "glass"). It has a low melting point, is easy to blow and mold, and it is cheap. It is optically clear unless impure, when it is typ­ically green or brown. Windows today have to be flat and until 1950 that was not easy to do; now the float-glass process, solidifying glass on a bed of liquid tin, makes "plate" glass cheaply and quickly.

Composition

73% SiO2/1% Al2O3/17% Na2O/4% MgO/5% CaO

General properties

Density

Price

Mechanical properties

Young’s modulus

Yield strength (elastic limit)

Tensile strength

Elongation

Hardness—Vickers

Fatigue strength at ...

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Alumina

The material. Alumina (Al2O3) is to technical ceramics what mild steel is to metals—cheap, easy to process, the workhorse of the industry. It is the material of spark plugs, electrical insulators, and ceramic substrates for microcircuits. In single crystal form, it is sapphire, used for watch faces and cockpit windows of high-speed aircraft. More usually it is made by pressing and sintering powder, giving grades ranging from 80-99.9% alumina; the rest is porosity, glassy impurities, or deliberately added components. Pure aluminas are white; impurities make them pink or green. The maximum operating temperature increases with increasing alumina content...

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Concrete

The material. Concrete is a composite, and a complex one. The matrix is cement; the reinforcement, a mixture of sand and gravel ("aggregate") occu­pying 60-80% of the volume. The aggregate increases the stiffness and strength and reduces the cost (aggregate is cheap). Concrete is strong in compression but cracks easily in tension. This is countered by adding steel reinforcement in the form of wire, mesh, or bars ("rebar"), often with sur­face contours to key it into the concrete; reinforced concrete can carry useful loads even when the concrete is cracked. Still higher performance is gained by using steel wire reinforcement that is pretensioned before the concrete sets. On relaxing the tension, the wires pull the concrete into compression.

Composition

6:1:2:4 Water:Portland cement:Fine a...

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Stone

The material. Stone is the most durable of all building material. The Pyramids (before 3000 BC), the Parthenon (5th century BC), and the cathe­drals of Europe (1000-1600 AD) testify to the resistance of stone to attack of every sort. It remained the principal material of construction for impor­tant buildings until the early 20th century; the railroads of the world, for example, could not have been built without stone for the viaducts and sup­port structures. As the cost of stone increased and brick became cheaper, stone was increasingly used for the outer structure only; today it is largely used as a veneer on a concrete or breezeblock inner structure. Carefully selected samples of fully dense, defect-free stone can have very large com­pressive strengths—up to 1000MPa...

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Brick

The material. Brick is as old as Babylon (4000 BC) and as durable. It is the most ancient of all manmade building materials. The regularity and pro­portions of bricks make them easy to lay in a variety of patterns, and their durability makes them an ideal material for building construction. Clay, the raw material from which bricks are made, is available almost everywhere; finding the energy to fire them can be more of a problem. Pure clay is gray – white in color; the red color of most bricks comes from impurities of iron oxide.

Composition

Bricks are fired clays, fine particulate alumino-silicates that derive from the weathering of rocks.

The proportions and regularity of brick make it fast to assemble. Brick weathers well, and the texture and color make it visually attractive.

Eco...

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Ceramics and glasses

Ceramics are materials of both the past and the future. They are the most durable of all materials—ceramic pots and ornaments survive from 5000 BC; Roman cement still bonds the walls of villas. It is ceramics ‘ durabil­ity, particularly at high temperatures, that generates interest in them today. They are exceptionally hard (diamond, a ceramic, is the hardest of them all) and can tolerate higher temperatures than any metal. Ceramics are crystalline (or partly crystalline) inorganic compounds. They include high-performance technical ceramics such as alumina (used for elec­tronic substrates, nozzles, and cutting tools), traditional, pottery-based ceramics (including brick and whiteware for baths, sinks, and toilets), and hydrated ceramics (cements and concretes) used for construction...

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Polychloroprene (Neoprene, CR)

The material. Polychloroprenes (Neoprene, CR), the materials of wetsuits, are the leading nontire synthetic rubbers. First synthesized in 1930, they are made by a condensation polymerization of the monomer 2-chloro-1,3 butadiene. The properties can by modified by copolymerization with sulfur, with other chloro-butadienes and by blending with other polymers to give a wide range of properties. Polychloroprenes are characterized by high chemi­cal stability and resistance to water, oil, gasoline, and UV radiation.

Composition

(CH2-CCl-CH2-CH2)n

General properties

Density

1230

– 1250

kg/m3

Price

*5.33

– 5.86

USD/kg

Mechanical properties

Young’s modulus

7e-4

– 0.002

GPa

Yield strength (elastic limit)

3.4

– 24

MPa

Tensile strength

3.4

– 24

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EVA

The material. Ethylene-Vinyl-Acetate elastomers (EVA) are built around polyethylene. They are soft, flexible, and tough and retain these properties down to -60°C and have good barrier properties as well as FDA approval for direct food contact. EVA can be processed by most normal thermoplas­tic processes: co-extrusion for films, blow molding, rotational molding, injection molding, and transfer molding.

Composition

(CH2)n-(CH2-CHR)m

General properties

Density

945

– 955

kg/m3

Price

*2.1

– 2.31

USD/kg

Mechanical properties

Young’s modulus

0.01

– 0.04

GPa

Yield strength (elastic limit)

12

– 18

MPa

Tensile strength

16

– 20

MPa

Compressive strength

13.2

– 19.8

MPa

Elongation

730

– 770

%

Fatigue strength at 107 cycle...

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Butyl rubber

The material. Butyl rubbers (BRs) are synthetics that resemble natural rubber in properties. They have good resistance to abrasion, tearing, and flexing, with exceptionally low gas permeability and useful properties up to 150°C. They have low dielectric constant and loss, making them attractive for electrical applications.

Composition

(CH2-C(CH3)-CH-(CH2)2-C(CH3)2)n

General properties

Density

900

– 920

kg/m3

Price

*3.93

– 4.32

USD/kg

Mechanical properties

Young’s modulus

0.001

– 0.002

GPa

Yield strength (elastic limit)

2

– 3

MPa

Tensile strength

5

– 10

MPa

Compressive strength

2.2

– 3.3

MPa

Elongation

400

– 500

%

Fatigue strength at 107 cycles

*0.9

– 1.35

MPa

Fracture toughness

0.07

– 0.1

MPa...

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