Laboratory Glass-Working for Scientists - Sciencemadness Dot Org

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PHYSICAL AND CHEMICAL PROPERTIES OF GLASS a complex glass object is cooled rapidly there will finally be a complex distribution of permanent strain, and this can be great enough to cause fracture of the glass. The drops of glass produced by Prince Rupert of Bavaria by dropping molten glass into oil become rigid when there is a great temperature gradient and the surface is consequently in strong compression. This makes the drops very strong, but they disintegrate violently as soon as the tail of the drop is cut off, when the internal stresses are no longer balanced. Annealing of Glass The object of this process is to prevent permanent strain arising from the cooling of glass. The glass must be cooled slowly through the critical temperature range in which it becomes rigid and ceases to relieve internal stresses by viscous flow. The rate at which these stresses are relieved in the annealing range of temperatures (A to B in FIGURE 2) depends on temperature; when this is such that the viscosity is 10 13 * 4 poises, the glass will become practically stress-free in 15 minutes (A. E. DALE and J. E. STANWORTH, 1945). Below the lower annealing temperature the glass can be cooled quickly without introduction of permanent strain, but the temporary strain could become great enough to fracture the article. Annealing is carried out most satisfactorily in an oven (p. 45). Complex articles of Pyrex glass can be annealed at 560°C for 30 minutes, followed by slow cooling with the oven door shut. Articles of Firmasil glass should be annealed at 575°C, but even at 475°C strain is very slowly removed. For Phoenix, the upper annealing temperature is 600°C and the lower annealing temperature is 520°C. Annealing at 560-5 80°C is therefore satisfactory for this glass. The annealing temperatures of these borosilicate glasses are not at all critical. The article must not, of course, be made too hot, or it will deform. Annealing is of great importance for articles made of a soda-lime-silica glass. Wembley X.8. soda glass should be annealed in the range 520-400°C, and the General Electric Company, which makes this glass, recommends annealing at a high temperature of 520°C for 5-10 minutes, followed by cooling to an intermediate temperature of 460°C at a rate dependent upon the glass tubing thickness. These rates are:— 3°C per minute for J mm wall thickness 2°C per minute for 1 mm wall thickness 1°C per minute for 3 mm wall thickness. The glass should be cooled from the intermediate temperature of 460°C tc a low temperature of 400°C at double the above rates. The 20
ANNEALING OF GLASS Article can then be cooled to room temperature at any rate possible Without cracking it by temporary thermal strain. The corresponding hl|ht intermediate and low temperatures for Wembley L.L lead glass Iff 430°Ct 390°C, and 340°C. The same annealing schedule can be mid. For Wembley M.6. 'white neutral' glass the temperature range || $I0"45O O C. Again the same schedule should be used. Complex apparatus assembled on the bench must be annealed by lame, and this method must also be used when no oven is available (Mt p. 170). In our experience, very complex apparatus of Pyrex glass tail be flame-annealed satisfactorily. Usually with Pyrex the apparatus either cracks in a day or two after making, or else not at all. Complex apparatus of soda-Kme-silica glass can be annealed by flame, but we do not find this satisfactory. For research apparatus it Ift beet to avoid this kind of glass. With a complex vacuum apparatus Of boroiilicate glass a fracture can often lead to unfortunate consequancet, especially when there are many mercury cut-offs present; iDd in such cases it is well, before evacuating, to wait for a few days altar a repair or alteration has been made in a position where flame a&nealing is difficult. •J-BI IS Some Types of Glass for General Use Many different kinds of glass are made. In this Section and the Mowing Sections we mention only a few of these which are useful |S the laboratory. Wmbley X.8. fllis is a soda-Hme-silica glass, containing magnesia and boric oxide than 1 per cent), made by the General Electric Co. It is often bed as GEC X.8. or simply as X.8. The linear coefficient of al expansion between 20 and 350°C is 9-65 ±0-10 x 10~ 6 . This is available as tubing and rod in a wide range of sizes. &£< •irir. by the British Thomson-Houston Co., this is a soda-lime Jass. The linear expansion coefficient is 9*5 x 10 8 f50~400°C*. alass fiftaox Ibis is a borosilicate glass, free from arsenic, antimony and lead, lada by John MoncriefF Ltd. The coefficient of linear expansion is M *I(H/°C The glass is available as tubing and rod of various pin; in addition many standard pieces of laboratory glass-ware iBBStructed in Monax are available. L\". 21
Page 1 and 2: FOREWORD ACKNOWLEDGEM ENTS PREFACE
Page 3 and 4: CONTENTS Grinding glass Releasing f
Page 5: ACKNOWLEDGEMENTS We thank the follo
Page 8 and 9: PREFACE scattered in the literature
Page 10 and 11: INTRODUCTION ready outgassing on ba
Page 12 and 13: INTRODUCTION in succession broke th
Page 14 and 15: INTRODUCTION MOREY, G. W., 1938, Th
Page 16 and 17: PHYSICAL AND CHEMICAL PROPERTIES OF
Page 30 and 31: Pyrex PHYSICAL AND CHEMICAL PROPERT
Page 36 and 37: GLASS-WORKING EQUIPMENT 3 The Glass
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BASIC GLASS-WORKING OPERATIONS but
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BASIC GLASS-WORKING OPERATIONS to t
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Chapter 5 THE MANIPULATION OF LARG
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THE MANIPULATION OF LARGE TUBING th
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THE MANIPULATION OF LARGE TUBING ro
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THE MANIPULATION OF LARGE TUBING jo
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SOME OPERATIONS WITH A GLASS-WORKIN
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SOME OPERATIONS WITH A GLASS-WORKIN
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Chapter 7 METAL-TO-GLASS SEALS ALTH
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METAL-TO-GLASS SEALS The finished b
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METAL-TO-GLASS SEALS Multiple Wire
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METAL-TO-GLASS SEALS will not be le
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METAL-TO-GLASS SEALS but in either
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METAL-TO-GLASS SEALS 29 per cent Ni
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METAL-TO-GLASS SEALS hard glasses i
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METAL-TO-GLASS SEALS Glass tubing m
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SOME TYPICAL SINGLE PIECES OF EQUIP
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Chapter 9 THE ASSEMBLY OF COMPLEX A
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THE ASSEMBLY OF COMPLEX APPARATUS d
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THE ASSEMBLY OF COMPLEX APPARATUS d
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THE ASSEMBLY OF COMPLEX APPARATUS u
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THE MANIPULATION OF SILICA with a f
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THE MANIPULATION OF SILICA surface
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Anhorn, V. J., 5, 28, 41, 47, 123,
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Abrasives, 39 Alkaline attack on gl
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Lead glass, 23,108 Lead glass compo
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