# Glass Formula Options: ## Alkaline Earth Aluminosilicate Glass [Schott technical glass - 8253: data on Matweb](http://www.matweb.com/search/datasheet.aspx?matguid=863cb3ed7395450bb6fcc86680ff63f9&ckck=1) [Schott Technical Glass manual](http://www.schott.com/d/epackaging/2fbc7180-e37c-4209-9eec-617ad9208e51/1.0/18.11.15_final_schott_technical_glasses_row.pdf) From page 6 of the above manual: > **Alkaline earth aluminosilicate glasses** > Characteristically, these glasses are free of alkali oxides and > contain 15–25% Al2O3, 52–60% SiO2, and about 15% alkaline > earths. Very high transformation temperatures and > softening points are typical features. Main fields of application > are glass bulbs for halogen lamps, high-temperature > thermometers, thermally and electrically highly loadable > film resistors and combustion tubes. > Examples: Halogen lamp glass types 8252 and 8253. Alkaline earths contain the elements from the 2nd column of the periodic table, combined with oxygen. In this case, the ones that count are calcium oxide (CaO) and magnesium oxide (MgO). Barium oxide would also qualify, but does not exist on the Moon. From page 15 of the same manual: ![chart of viscosity to temperature including glass of interest - working point 1300 C, annealing point 800 C](https://www.moonwards.com/img/GlassViscositySchott8252-8253.png) # Quotes from reference material: ## [Chemistry Explained](http://www.chemistryexplained.com/Ge-Hy/Glass.html) > The making of glass involves three basic types of ingredients: formers, fluxes, and stabilizers. The glass former is the key component in the structure of a glassy material. The former used in most glasses is silica (SiO 2 ). Pure silica is difficult to melt because of its extremely high melting point (1,723 o C, or 3,133 o F), but fluxes can be added to lower the melting temperature. Other glass formers with much lower melting points (400 o C–600 o C, or 752–1,112 o F) are boric oxide (B 2 O 3 ) and phosphorus pentoxide (P 2 O 5 ). These are easily melted, but because their glass products dissolve in water, they have limited usefulness. > Most silica glasses contain an added flux, so that the silica can be melted at a much lower temperature (800 o C–900 o C, or 1,472–1,652 o F). Standard fluxes include soda (Na 2 O), potash (K 2 O), and lithia (Li 2 O). Frequently the flux is added as a carbonate substance (e.g., Na 2 CO 3 ), the CO 2 being driven off during heating. Glasses containing only silica and a flux, however, have poor durability and are often water-soluble. > To make glasses stronger and more durable, stabilizers are added. The most common stabilizer is lime (CaO), but others are magnesia (MgO), baria (BaO), and litharge (PbO). The most common glass, made in largest amounts by both ancient and modern glassmakers, is based on silica as the glass former, soda as the flux, and lime as the stabilizer. It is the glass used to make windows, bottles, jars, and lightbulbs. Read more: http://www.chemistryexplained.com/Ge-Hy/Glass.html#ixzz4fZF3ve8N ## Glass Manufacture ### Walter Rosenhain - [Public Domain copy at Project Gutenberg](https://www.gutenberg.org/ebooks/52724) * The dissolved substances have, however, natural freezing-points of their own, and if the molten mass be kept for any length of time at a temperature a little below one of these freezing-points, that particular substance will begin to solidify separately in the form of crystals... In some cases this devitrification sets in so readily that it can scarcely be prevented at all, while in other cases the glass must be maintained at the proper temperature for hours before crystallisation can be induced to set in. * There is thus for every glass a certain critical range of temperature during which the greatest tendency exists for the crystallising forces to overcome the internal resistance; through this range the glass must be cooled at a relatively rapid rate if devitrification is to be avoided; at lower temperatures the crystallising forces require increasingly longer periods of time to produce any sensible effect, until, as the ordinary temperature is approached, the forces of internal resistance entirely prevent all tendency to crystallisation an increased alkali content reduces the chemical resistance of glass, while at the same time such an increase of alkali is the readiest means whereby the glass-maker can improve his glass in other respects by making it more fusible and easier to work in every way. _( alkali metals are the first group in the periodic table and Alkali Earth are the second group)_ * Leaving aside the inferior glasses, containing, generally, more than 15 per cent. of alkali, the behaviour of glass surfaces to the principal chemical agents may be summed up in the following statements. Pure water attacks all glass to a greater or lesser extent; in the best glasses the prolonged action of cold water merely extracts a minute trace of alkalies, but in less perfect kinds the extraction of alkali is considerable on prolonged exposure even in the cold, and becomes rapidly more serious if the temperature is raised. Superheated water, i.e. , water under steam pressure, becomes an active corroding agent, and the best glasses can only resist its action for a limited time. * dilute acid—on the other hand acts upon most varieties of glass decidedly less energetically than even pure water, and much less vigorously than alkaline solutions; this peculiar behaviour probably depends upon the tendency of acids to prevent the hydration of silica, this substance being thereby enabled to act as a barrier to the solvent action of the water upon the alkaline constituents of the glass. * quantity of moisture contained in a ton of sand appreciably affects the resulting composition of the glass, and if the sand cannot be obtained perfectly dry, it should at least contain a constant proportion of moisture, otherwise it becomes necessary to determine, by chemical tests, the percentage of moisture in the sand that is used from day to day, and to adjust the quantity used in accordance with the results of these tests * In another direction the expansive properties of glass are of importance wherever glass is rigidly attached to metal. At the present time this is done in several industrial products, such as incandescent electric lamps and “wired” plate glass. In certain varieties of incandescent lamps, metallic wires are sealed into the glass bulbs, and the only metal available for this purpose, at all events until recently, has been platinum, whose coefficient of expansion is low as compared with most metals, and whose freedom from oxidation when heated to the necessary temperature makes it easy to produce a clean joint between glass and metal. More recently the use of certain varieties of nickel steel has been patented for this purpose, since it is possible to obtain nickel steel alloys of almost any desired coefficient of expansion from that of the alloy known as “invar,” having a negligibly small expansion compared with that of ordinary steel. By choosing a suitable member of this series a metal could be obtained whose coefficient of expansion corresponds exactly with that of the glass to which it is to be united. The oxidation of the nickel steel when heated to the temperature necessary for effecting its union with the glass presented serious difficulties to the production of a tight joint, and several devices for avoiding this oxidation have been patented. * The thermal conductivity of glass, except in so far as it affects the thermal endurance, is not a matter of any great direct practical importance, although the fact that glass is always a comparatively poor conductor of heat is utilised in many of its applications, as, for example, the construction of conservatories and hot-houses, although even in that case the opacity of glass to thermal radiations of long wave-lengths is of more importance than its low thermal conductivity. * The insulating properties of glass, as well as the property known as the specific inductive capacity, vary greatly according to the chemical composition of the material. Generally speaking, the harder glasses, i.e. , those richest in silica and lime, are the best insulators, while soft glasses, rich in lead or alkali, are much poorer in this respect.