lab Glassware use and properties
Glassware is one of the most frequently used instruments in the laboratory, and no material can predict it. However, in order to better use glassware, in addition to the basic operating skills, it is also important to understand the material properties of glassware, which will give you a deeper understanding of glassware.
General properties of glass
The main raw materials of glass are silica sand (SiO2), boric acid (H3BO3) or borax (Na2B4O7 10H2O), lime (CaO), glass shavings (cullet), phosphoric acid (P2O5), alkali (Ha2O, supplied by NaNO3, Na2B4O7, etc.) and Other raw materials containing oxides such as potassium, magnesium, zinc and aluminum.
Glass products have good chemical resistance to water, salt solutions, acids, bases and organic solvents, and in this respect exceed most plastic products. Only hydrofluoric acid and strong base or concentrated phosphoric acid at elevated temperatures attack the glass. Another feature of glassware is the stability of the shape (even under elevated temperatures) and its high degree of transparency.
Special properties of a particular glass
In laboratory applications, there are many different types of glass that can be selected.
Sodium-calcium glass
Sodium-calcium glass (such as AR-Glas) has good chemical and physical properties. Suitable for short-term exposure to chemical reagents and limited thermal shock applications.
Borosilicate glass (BORO3.3, BORO 5.4)
Borosilicate glass has excellent chemical and physical properties. As described in the international standard DIN ISO 3585, the primary hydrolyzed glass has a linear expansion coefficient of 3.3 and is suitable for applications requiring excellent chemical and thermal resistance (including thermal shock resistance) and high mechanical stability. It is a typical glass for chemical instruments, such as round bottom flasks and beakers and metering products.
Use of glass products
When using glass, it is necessary to consider resistance to thermal shock and mechanical force. Strict safety measures must be followed:
Do not hot mix the heating volume meter, measuring cylinder or reagent bottle.
When performing an exothermic reaction, such as diluting sulfuric acid or dissolving sodium hydroxide, be sure to continue stirring and cooling the reagents, and select a suitable container, such as a conical flask, never use a graduated cylinder or volumetric flask.
Glass instruments must never be exposed to sudden, intense temperature changes. When removing the glass instrument from the hot drying oven, do not place it on a cold or wet surface immediately.
For pressure-bearing applications, only glass instruments designed for this purpose can be used. For example, the filter bottle and the dryer can only be used after vacuuming.
Chemical resistance
The chemical interaction of water or acid with glass is negligibly small; only very small amounts, mainly monovalent cations, are dissolved from the glass. A very thin, almost void-free layer of silica gel is formed on the surface of the glass to prevent further erosion. The exception is hydrofluoric acid and hot phosphoric acid because these two acids inhibit the formation of a protective layer.
Chemical interaction between alkali and glass
The base will look down on the glass and will increase with increasing concentration and temperature. The borosilicate glass 3.3 limits the surface to a level of μm. Of course, as the contact time increases, volume changes and/or scale damage can still occur.
Hydrolysis resistance of glass
The first stage hydrolyzed glass can reach the first stage of 5 hydrolysis resistance levels according to DIN ISO 719 (98 ° C). This means that the glass having a particle size of 300-500 μm is exposed to water at 98 ° C for 1 hour, and less than 31 μg Na 2 O / gram glass of water is dissolved. In addition, the primary hydrolysis glass also reached the first stage of the three hydrolysis levels of DIN ISO 720 (121 ° C). This means that exposure to water at 121 ° C for 1 hour, less than 62 ug Na 2 O / gram of glass is hydrolyzed.
Tolerance to acid
The primary hydrolyzed glass meets the first level of four levels of DIN 12 116 standard tolerance. The primary hydrolysis glass, also known as acid-resistant borosilicate glass, is boiled in 6N HCL for 6 hours with a surface flank of less than 0.7 mg/100 cm 2 ; More DIN ISO 1776 Na2O loss is less than 100ug Na2O/100cm2.
Resistance to alkali
The primary hydrolysis glass meets the second grade of the three alkali-resistant grades of the DIN ISO 695 standard. The erosion caused by boiling of the same volume of sodium hydroxide (1 mol/L) and sodium carbonate (0.5 mol/L) for 3 hours was about 134 mg/100 cm2.
Mechanical resistance
Thermal Stress
Harmful thermal stresses may be introduced during the production and processing of the glass. During the cooling of the molten glass, the transition from the plastic state to the hard state occurs between the high and low annealing temperature points. At this stage, existing thermal stresses must be eliminated through a carefully controlled return process. Once the low annealing point has passed, the glass can accelerate cooling without any significant new stress.
The glass reheating reaction is similar, for example, by directly heating it with its own flame, to a point above the grounding temperature, uncontrolled cooling or causing “freezing into” heat, and severely reducing the resistance of the glass to breakage. Ability and mechanical stability. In order to remove the inherent stresses, the glass must be heated to a temperature between the high and low annealing temperatures for about 30 minutes and then cooled at a specified rate of temperature reduction.
Resistance to temperature changes
When the glass is heated to a temperature below the low push-fire temperature, poor thermal conductivity and poor thermal conductivity can cause tension and pressure. If, due to an improper heating or cooling rate, the glass is broken, beyond the mechanical force that can be withstood. In addition to the coefficient of expansion, the value varies with the type of glass, the wall thickness, and the shape of the glass. Any scratches present on the glass need to be considered. Therefore, it is very difficult to specify an exact value against thermal shock. Of course, the coefficient of thermal expansion is worth comparing to the fact that the first-class hydrolyzed glass is more resistant to temperature changes than AR-Glas glass.
Mechanical stress
From a technical point of view, the elastic properties of the glass are very good, that is to say, when the tolerance is exceeded, the tension and pressure do not cause deformation, but cause cracking. The tension that the glass can withstand is relatively small and further decreases as there is a scratch or gap in the glass. For safety reasons, the primary hydrolysis glass used in mechanical and industrial designs can withstand a tension of 6 N/MM2.
If you’re in need of information or have any questions, please contact WUBOLAB, the laboratory glassware manufacturer.
