| Coefficient of Thermal Expansion | Approximately 3.3 × 10−6 K−1 from 20–300 °C | Review the material certificate and test method, typically based on dilatometry such as ISO 7991 or ASTM E228. | Choose a low-expansion grade when the sheet will experience repeated heating and cooling or must be joined to metals, ceramics, or other glass. |
| Strain Point | Approximately 510–525 °C | Confirm the reported strain point on the technical data sheet; it is determined from viscosity–temperature behavior. | The sheet should remain below its strain point during normal service to reduce the risk of permanent thermal stress. |
| Annealing Point | Approximately 555–570 °C | Check the grade specification and whether the sheet was properly annealed after forming or cutting. | Proper annealing is important for large sheets, drilled sheets, and parts exposed to temperature gradients. |
| Softening Point | Approximately 815–830 °C | Verify the softening point from the supplier’s technical documentation; do not use it as the normal operating temperature. | Use this value to understand forming limits, not as a continuous-use rating. Actual service temperature must also consider load, time, and thermal gradients. |
| Recommended Continuous Temperature | Often about 450–500 °C for an uncoated, properly designed sheet; application-specific limits apply | Evaluate the complete temperature cycle, sheet size, thickness, edge condition, mounting method, and thermal gradient. | For rapid temperature changes or localized heating, perform a thermal-stress calculation or practical qualification test instead of relying only on a single temperature value. |
| Thermal Shock Resistance | Commonly rated around 160–180 K for suitable borosilicate articles; sheet geometry and edge quality strongly affect the result | Use a controlled heating–cooling test with the actual thickness, dimensions, support, and edge finish. Inspect for cracks after cycling. | Select finer edges, polished edges, and adequate thickness for severe thermal cycling. Avoid sharp notches, chips, and rigid point mounting. |
| Thermal Conductivity | Approximately 1.1–1.2 W/(m·K) near room temperature | Check the declared value at the relevant temperature because thermal conductivity changes with temperature. | Borosilicate glass has relatively low thermal conductivity; design for temperature uniformity when fast heat transfer is required. |
| Visible Light Transmittance | Typically about 90–92% for clear, polished thin sheet; thickness, iron content, surface condition, and wavelength affect the result | Request spectral transmission data for the actual thickness and measure with a spectrophotometer when optical performance is critical. | For optical or display applications, specify thickness, wavelength range, surface quality, haze, and allowable inclusions separately. |
| Refractive Index | Approximately 1.47 at the sodium D line near 589 nm; exact value depends on composition and wavelength | Check the refractive-index value at the operating wavelength and temperature. | Use wavelength-specific data for lenses, sensors, imaging windows, and optical assemblies. |
| Hydrolytic Resistance | Typically Hydrolytic Resistance Class 1 under ISO 719 for borosilicate glass 3.3 | Request an ISO 719 test result or equivalent water-resistance report for the exact formulation. | Class 1 is appropriate for contact with water and many aqueous solutions, but it does not guarantee resistance to every chemical or cleaning process. |
| Acid Resistance | Generally high against many mineral acids, excluding hydrofluoric acid and hot concentrated phosphoric acid; alkali-containing chemicals may attack the surface | Test the actual chemical at its concentration, temperature, exposure time, and flow condition. Examine weight loss, haze, and surface roughness. | Never specify borosilicate glass for hydrofluoric-acid service. Consider a coating or an alternative material for aggressive acid or alkaline environments. |
| Alkali Resistance | Good compared with ordinary soda-lime glass, but prolonged exposure to strong hot alkalis can cause surface corrosion | Use a chemical compatibility test based on the real alkaline solution and temperature rather than relying on a generic resistance label. | For hot caustic cleaning, specify exposure limits, cleaning frequency, and allowable surface change. |
| Density | Approximately 2.23 g/cm³ at room temperature | Verify the value in the material certificate; calculate mass using actual dimensions and thickness tolerance. | Use density to estimate handling loads, frame loads, shipping weight, and the mass of large panels. |
| Young’s Modulus | Approximately 63–65 GPa | Check the modulus used in the design calculation and confirm the supported-span and loading assumptions. | Glass is stiff but brittle. Deflection, support spacing, edge contact, and local stress must be considered together. |
| Poisson’s Ratio | Approximately 0.18–0.22 | Use a verified material value in finite-element or plate-bending calculations. | Include this value when calculating bending stress, deflection, or thermal stress in restrained sheet assemblies. |
| Flexural Strength | Commonly about 30–70 MPa for annealed glass, depending strongly on surface and edge condition | Use a standardized four-point or three-point bending test, such as ASTM C158 or EN 1288, with the intended edge finish. | Do not treat flexural strength as a fixed material constant. Scratches, chips, drilled holes, and handling damage can reduce strength substantially. |
| Compressive Strength | Typically about 700–1,000 MPa in idealized material data; practical design values must be much lower | Assess the actual contact area, loading alignment, surface damage, and restraint. Avoid concentrated point loading. | Glass tolerates compression better than tension, but uneven supports can create tensile stresses and cause sudden fracture. |
| Vickers Hardness | Approximately 4.5–6 GPa, depending on test load and composition | Compare Vickers hardness data using the same test load and method; inspect the surface for scratches after handling. | Hardness does not equal scratch-proof performance. Use protective films, clean handling, and suitable packaging for finished sheets. |
| Surface Quality | Should be specified by allowable scratches, digs, haze, pits, bubbles, stones, and inclusions rather than by the word “clear” alone | Inspect under controlled illumination and compare with an agreed visual standard or optical-quality specification. | Optical windows require tighter surface and inclusion limits than furnace covers, laboratory panels, or general protective shields. |
| Thickness and Dimensional Tolerance | Must be defined according to the intended use; thickness uniformity affects optical distortion, mass, and thermal stress | Measure multiple points with a calibrated thickness gauge and verify length, width, squareness, flatness, and edge condition. | For large or precision panels, request thickness mapping and flatness data instead of checking only one point. |
| Edge and Hole Quality | Ground, fine-ground, or polished edges are safer than sharp cut edges; drilled holes require rounded transitions and adequate edge distance | Inspect for chips, vents, checks, star cracks, and grinding marks. Confirm hole diameter, position, chamfer, and edge distance. | Edge finishing is one of the most effective ways to improve practical mechanical reliability and reduce crack initiation. |
| Thermal Tempering Option | Heat-treated borosilicate sheet can have higher bending strength and better thermal-shock performance, but it is not unbreakable | Request the heat-treatment classification, surface compression value if applicable, flatness, optical distortion, and fragmentation requirements. | Use heat-treated glass where impact or thermal loading is significant, while remembering that cutting and drilling generally must be completed before tempering. |
| Recommended Documentation for Purchase | Composition or grade designation, thickness tolerance, thermal data, chemical compatibility, mechanical data, surface quality, edge finish, and inspection records | Compare the supplier’s certificate with the purchase specification and test reports for the actual batch when qualification is critical. | A complete specification is more reliable than selecting only by the words “heat-resistant” or “chemical-resistant.” |
