Borosilicate glass is the oldest type of glass to have

appreciable adj. 可評(píng)估的；可感知的；相當(dāng)可觀的resistance to thermal impact vt. 影響；撞擊；沖突；壓緊vi. 沖擊；產(chǎn)生影響n. 影響；效果；碰撞；沖擊力

 and higher temperatures, also has excellent resistance to

chemical attack.

In this glass structure, the first to carry the Pyrex trademark, some of the SiO² is replaced by boric oxide.

Borosilicate glass has a low coefficient of thermal expansion

and is, thus, suited for telescope mirrors and other precision

parts. Also, because this glass can withstand thermal shock, it is used for oven and laboratory ware, headlamp ['hedlæmp] n. 桅燈；照明燈；車前燈lenses, and boiler gage glasses. Most borosilicate glasses have better resistance to acids than do soda-lime堿石灰 glasses, but poor resistance to alkalis'ælkəlai] n. 堿；可溶性無機(jī)鹽adj. 堿性的. Glass fibers used in reinforcing plastic compounds ['kɔmpaund, kəm'paund] n. 化合物；混合物；復(fù)合詞are a modified borosilicate glass.

Chemical Composition
SiO2 = 80%
B2O3 = 13%
Na2O +K2O= 4.3%
Al2O3 = 2.4%

·         Physical Properties
Coefficient of expansion (20°C–300°C) 3.3 x 10-6 K-1
Density 2.23g/cm3
Refractive index折射率： (Sodium D line) 1.474
Dielectric [,daii'lektrik] adj. 非傳導(dǎo)性的；誘電性的n. 電介質(zhì)；絕緣體constant 電容率(1MHz, 20°C) 4.6
Specific heat比熱 (20°C) 750J/kg°C
導(dǎo)熱系數(shù) (20°C) 1.14W/m°C
Poisson’s Ratio['reiʃiəu, -ʃəu] n. 比率，比例地基應(yīng)力和變形泊松比(25°C – 400°C) 0.2
Young’s Modulus['mɔdjuləs, -dʒu-]n. 模數(shù)；系數(shù)

彈性模量，楊氏系數(shù) (25°C) 6400 kg/mm2
Optical Information
Refractive index (Sodium D line) = 1.474
Visible light transmission, 透光率2mm thick glass = 92%
Visible light transmission, 可見光穿透率5mm thick glass = 91%
Critical Temperatures
150°C - When working above this temperature care should be taken to heat and cool Borosilicate glass in a slow and

uniform manner.
500°C - The maximum temperature that Borosilicate glass

should be subjected to and then only for short period of no

longer than a few minutes.
510°C - Temperature at which thermal stress can be

introduced to Borosilicate glassware.
565°C - Annealing [ə'ni:l] vt. 使退火，韌煉；鍛煉n. 退火；鍛煉，磨練temperature. When uniformly heated in controlled conditions, such as a

kiln or oven thermal stress’s can be removed.
820°C - Softening point at which Borosilicate may deform [di'fɔ:m] vt. 使變形；使成畸形vi. 變形；變畸形adj. 畸形的；丑陋的.
1252°C - Working point, the temperature that glassblowers need to attain in order to work Borosilicate glass.
Working Temperatures
Borosilicate glass retains its mechanical strength and will

deform only at temperatures which approach its strain point應(yīng)變點(diǎn).

The practical upper limit for operating temperatures is much

lower   and is controlled by the temperature ditterentials  in

the glass, which depend on the relative temperatures of the

contents of the equipment and the external surroundings.
Provided borosilicate glass is not subjected to rapid change in temperature, creating undue adj. 過度的，過分的；不適當(dāng)?shù)模晃吹狡诘?/span>thermal shock, it can be operated safely at temperatures up to 450°F (232°C). The normal limiting factor is actually the gasket ['ɡæskit] n. 墊圈；襯墊；束帆索material. The degree of

thermal shock (usually defined as sudden chilling ['tʃiliŋ] adj. 寒冷的；冷漠的；使人恐懼的；令人寒心的；[俚]呱呱叫的n. 寒冷；冷卻) which it can withstand depends on many factors, for example: stresses

due to operating conditions; stresses imposed in supporting

the equipment; the wall thickness of the glass, etc. It is

therefore undesirable adj. 不良的；不受歡迎的；不合需要的to give an overall figure but, as a

general guide, sudden temperature changes of up to about

 216°F (120°C) can be accommodated .

At sub-zero adj. 零下的；嚴(yán)寒的temperatures, the tensile adj. [物]拉力的；可伸長(zhǎng)的；可拉長(zhǎng)的strength of borosilicate

glass tends to increase and equipment can be used with

safety at cryogenic [,kraiə'dʒenik] temperatures.

Further development in glassmaking continues to create new

glass-ceramics n.【材料學(xué)】微晶玻璃，玻璃陶瓷that outperform vt. 勝過；做得比……好borosilicate glass in various

ways.