It is less prone to chemical attack, and the coefficient of expansion is lower, so that it is more resistant to thermal shock. Borosilicate for beadmaking comes in thin, pencil-like rods. This is done by heating the end of the tube or rod in a roaring bunsen flame until the sharp edges of the glass become red hot. Because it is more shock-resistant and stronger than soft glass, borosilicate is particularly suited for pipe making, as well as sculpting figures and creating large beads. Glass Alchemy, Trautman Art Glass, and Northstar are popular manufacturers, although there are other brands available. Borosilicate glass contains substantial amounts of silica (SiO2) and boron oxide (B 2 O 3 >8%) as glass network formers, and are typically composed of 70–80 wt% SiO 2, 7–13 wt% of B 2 O 3 4–8 wt% Na 2 O or K 2 O, and 2–8 wt% of Al 2 O 3 (Bauccio, 1994; Pfaender, 1996). Carbon–carbon composites have excellent resistance to hydrohalic acids and found application for internal components, particularly in HF acid duties. Such joints will fail during cooling. If a sample is heated in a bunsen flame, soda glass will quickly become white hot and soften, whereas borosilicate glass will merely become red hot, and unless the sample is very thin, it will not easily bend or collapse.Whenever glass tubing or rod are used, it is very important to flame-polish the ends in order to remove the sharp edges. Soda glass rod should not be placed directly into a roaring bunsen flame, because the high coefficient of expansion will probably result in shattering; it should be cautiously introduced into a non-roaring flame, and the air supply gradually increased to raise the temperature.Borosilicate glass can only be worked satisfactorily with the use of an oxygen–coal gas flame provided by a blowlamp or torch; an ordinary air–coal gas flame, such as provided by a bunsen burner, is not enough for more than simple bending.ScienceDirect ® is a registered trademark of Elsevier B.V.The United States has, in the past few years, continued the construction of very large Joule-heated glass melters having throughputs of several tonnes of glass per day at the Hanford reservation in Washington State.Silicon carbide is composed of tetrahedra of carbon and silicon atoms with strong bonds in the crystal lattice. The high thermal conductivity coupled with low thermal expansion and high strength gives this material exceptional thermal shock resistant qualities. It is sometimes possible to distinguish the two types of glass by visual inspection; the cut end of a piece of soda glass has a white or greyish-green appearance, while borosilicate has a distinct yellowish tint. Excessive heating may cause collapse or distortion of the glass.
When the glass has become very soft, it is removed from the flame and the ends slowly pulled apart about 10 cm to give a thick–walled capillary between the unheated portions; it is then held by one end so that it hangs down vertically. The common type of borosilicate glass used for laboratory glassware has a very low thermal expansion coefficient (3.3 × 10 K ), about one-third that of ordinary soda-lime glass. It is used in abrasives, refractories, ceramics, and numerous high-performance applications.
In this way, the capillary does not sag, and remains in the same axis as the undrawn portion. Related sites: Glass Properties on GlobalSpec, GlassOnWeb, MatWeb, Glass Global A general overview about glass art, history, science, literature, social studies, and technology is available at the Corning Museum of Glass (view as PDF, 1.8 MB). Most of the modern beakers, flasks, and other glass receptacles designed for laboratory use are made of borosilicate glass. Chemical Resistance Borosilicate glass 3.3 is resistant to chemical attack by almost any product, which makes its resistance much more comprehensive than that of other well-known materials. For preparing capillary tubes for the determination of melting points, ordinary narrow-bore glass tubing is treated in a similar way.Borosilicate glass has several advantages over soda glass. Chemical purity, resistance to chemical attack at temperature, and strength retention at high temperatures has made this material very popular as wafer tray supports and paddles in semiconductor furnaces. While borosilicate glass requires a roaring bunsen flame fitted with a bat's-wing spreader, soda glass may be softened excessively under similar conditions. The glass should be rotated between the finger and thumb while being heated. Carbon bricks find occasional use in very hot, concentrated acid duties.It is not possible to make satisfactory fused joints between borosilicate and soda glasses because of the differences in thermal expansion properties. The structure of glass 1 1.2. According to glass supplier Pulles and Hannique, borosilicate Pyrex is made of Corning 7740 glass and is equivalent in formulation to Schott Glass 8330 glass sold under the "Duran" brand name. The process is then repeated, heating the centre portion of the capillary, and drawing out to give a very fine thread of glass. Borosilicate glasses .