Is borosilicate glass more fragile?

Tendency of matter to change volume in response to a change in temperature

Expansion joint in a road bridge used to avoid damage from thermal expansion.

Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.[1]

Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves. Substances which contract with increasing temperature are unusual, and only occur within limited temperature ranges (see examples below).

The relative expansion (also called strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion and generally varies with temperature. As energy in particles increases, they start moving faster and faster, weakening the intermolecular forces between them and therefore expanding the substance.

Prediction

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If an equation of state is available, it can be used to predict the values of the thermal expansion at all the required temperatures and pressures, along with many other state functions.

Contraction effects (negative expansion)

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A number of materials contract on heating within certain temperature ranges; this is usually called negative thermal expansion, rather than "thermal contraction". For example, the coefficient of thermal expansion of water drops to zero as it is cooled to 3.983 °C and then becomes negative below this temperature; this means that water has a maximum density at this temperature, and this leads to bodies of water maintaining this temperature at their lower depths during extended periods of sub-zero weather.

Other materials are also known to exhibit negative thermal expansion. Fairly pure silicon has a negative coefficient of thermal expansion for temperatures between about 18 and 120 kelvin.[2] ALLVAR Alloy 30, a titanium alloy, exhibits anisotropic negative thermal expansion across a wide range of temperatures.[3]

Factors

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Unlike gases or liquids, solid materials tend to keep their shape when undergoing thermal expansion.

Thermal expansion generally decreases with increasing bond energy, which also has an effect on the melting point of solids, so high melting point materials are more likely to have lower thermal expansion. In general, liquids expand slightly more than solids. The thermal expansion of glasses is slightly higher compared to that of crystals.[4] At the glass transition temperature, rearrangements that occur in an amorphous material lead to characteristic discontinuities of coefficient of thermal expansion and specific heat. These discontinuities allow detection of the glass transition temperature where a supercooled liquid transforms to a glass.[5]

Absorption or desorption of water (or other solvents) can change the size of many common materials; many organic materials change size much more due to this effect than due to thermal expansion. Common plastics exposed to water can, in the long term, expand by many percent.

Effect on density

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Thermal expansion changes the space between particles of a substance, which changes the volume of the substance while negligibly changing its mass (the negligible amount comes from mass–energy equivalence), thus changing its density, which has an effect on any buoyant forces acting on it. This plays a crucial role in convection of unevenly heated fluid masses, notably making thermal expansion partly responsible for wind and ocean currents.

Coefficients

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The coefficient of thermal expansion describes how the size of an object changes with a change in temperature. Specifically, it measures the fractional change in size per degree change in temperature at a constant pressure, such that lower coefficients describe lower propensity for change in size. Several types of coefficients have been developed: volumetric, area, and linear. The choice of coefficient depends on the particular application and which dimensions are considered important. For solids, one might only be concerned with the change along a length, or over some area.

The volumetric thermal expansion coefficient is the most basic thermal expansion coefficient, and the most relevant for fluids. In general, substances expand or contract when their temperature changes, with expansion or contraction occurring in all directions. Substances that expand at the same rate in every direction are called isotropic. For isotropic materials, the area and volumetric thermal expansion coefficient are, respectively, approximately twice and three times larger than the linear thermal expansion coefficient.

In the general case of a gas, liquid, or solid, the volumetric coefficient of thermal expansion is given by

α = α V = 1 V ( ∂ V ∂ T ) p {\displaystyle \alpha =\alpha _{\text{V}}={\frac {1}{V}}\,\left({\frac {\partial V}{\partial T}}\right)_{p}}

The subscript "p" to the derivative indicates that the pressure is held constant during the expansion, and the subscript V stresses that it is the volumetric (not linear) expansion that enters this general definition. In the case of a gas, the fact that the pressure is held constant is important, because the volume of a gas will vary appreciably with pressure as well as temperature. For a gas of low density this can be seen from the ideal gas law.

For various materials

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Volumetric thermal expansion coefficient for a semicrystalline polypropylene. Linear thermal expansion coefficient for some steel grades.

This section summarizes the coefficients for some common materials.

For isotropic materials the coefficients linear thermal expansion α and volumetric thermal expansion αV are related by αV = 3α. For liquids usually the coefficient of volumetric expansion is listed and linear expansion is calculated here for comparison.

For common materials like many metals and compounds, the thermal expansion coefficient is inversely proportional to the melting point.[6] In particular, for metals the relation is:

α ≈ 0.020 T m {\displaystyle \alpha \approx {\frac {0.020}{T_{m}}}}

α ≈ 0.038 T m − 7.0 ⋅ 10 − 6 K − 1 {\displaystyle \alpha \approx {\frac {0.038}{T_{m}}}-7.0\cdot 10^{-6}\,\mathrm {K} ^{-1}}

for halides and oxides

In the table below, the range for α is from 10−7 K−1 for hard solids to 10−3 K−1 for organic liquids. The coefficient α varies with the temperature and some materials have a very high variation; see for example the variation vs. temperature of the volumetric coefficient for a semicrystalline polypropylene (PP) at different pressure, and the variation of the linear coefficient vs. temperature for some steel grades (from bottom to top: ferritic stainless steel, martensitic stainless steel, carbon steel, duplex stainless steel, austenitic steel). The highest linear coefficient in a solid has been reported for a Ti-Nb alloy.[7]

(The formula αV ≈ 3α is usually used for solids.)[8]

In solids

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When calculating thermal expansion it is necessary to consider whether the body is free to expand or is constrained. If the body is free to expand, the expansion or strain resulting from an increase in temperature can be simply calculated by using the applicable coefficient of thermal expansion.

If the body is constrained so that it cannot expand, then internal stress will be caused (or changed) by a change in temperature. This stress can be calculated by considering the strain that would occur if the body were free to expand and the stress required to reduce that strain to zero, through the stress/strain relationship characterised by the elastic or Young's modulus. In the special case of solid materials, external ambient pressure does not usually appreciably affect the size of an object and so it is not usually necessary to consider the effect of pressure changes.

Common engineering solids usually have coefficients of thermal expansion that do not vary significantly over the range of temperatures where they are designed to be used, so where extremely high accuracy is not required, practical calculations can be based on a constant, average, value of the coefficient of expansion.

Length

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Change in length of a rod due to thermal expansion.

Linear expansion means change in one dimension (length) as opposed to change in volume (volumetric expansion). To a first approximation, the change in length measurements of an object due to thermal expansion is related to temperature change by a coefficient of linear thermal expansion (CLTE). It is the fractional change in length per degree of temperature change. Assuming negligible effect of pressure, one may write:

α L = 1 L d L d T {\displaystyle \alpha _{L}={\frac {1}{L}}\,{\frac {\mathrm {d} L}{\mathrm {d} T}}}

L {\displaystyle L}

d L / d T {\displaystyle \mathrm {d} L/\mathrm {d} T}

whereis a particular length measurement andis the rate of change of that linear dimension per unit change in temperature.

The change in the linear dimension can be estimated to be:

Δ L L = α L Δ T {\displaystyle {\frac {\Delta L}{L}}=\alpha _{L}\Delta T}

This estimation works well as long as the linear-expansion coefficient does not change much over the change in temperature Δ T {\displaystyle \Delta T} , and the fractional change in length is small Δ L / L ≪ 1 {\displaystyle \Delta L/L\ll 1} . If either of these conditions does not hold, the exact differential equation (using d L / d T {\displaystyle \mathrm {d} L/\mathrm {d} T} ) must be integrated.

Effects on strain

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For solid materials with a significant length, like rods or cables, an estimate of the amount of thermal expansion can be described by the material strain, given by ε t h e r m a l {\displaystyle \varepsilon _{\mathrm {thermal} }} and defined as:

ε t h e r m a l = ( L f i n a l − L i n i t i a l ) L i n i t i a l {\displaystyle \varepsilon _{\mathrm {thermal} }={\frac {(L_{\mathrm {final} }-L_{\mathrm {initial} })}{L_{\mathrm {initial} }}}}

where L i n i t i a l {\displaystyle L_{\mathrm {initial} }} is the length before the change of temperature and L f i n a l {\displaystyle L_{\mathrm {final} }} is the length after the change of temperature.

For most solids, thermal expansion is proportional to the change in temperature:

ε t h e r m a l ∝ Δ T {\displaystyle \varepsilon _{\mathrm {thermal} }\propto \Delta T}

ε t h e r m a l = α L Δ T {\displaystyle \varepsilon _{\mathrm {thermal} }=\alpha _{L}\Delta T}

Δ T = ( T f i n a l − T i n i t i a l ) {\displaystyle \Delta T=(T_{\mathrm {final} }-T_{\mathrm {initial} })}

degrees Rankine,

α L {\displaystyle \alpha _{L}}

°F−1

,

°R−1

,

°C−1

, or

K−1

, respectively. In the field of

Area

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Thus, the change in either the strain or temperature can be estimated by:whereis the difference of the temperature between the two recorded strains, measured in degrees Fahrenheit degrees Celsius , or kelvin , andis the linear coefficient of thermal expansion in "per degree Fahrenheit", "per degree Rankine", "per degree Celsius", or "per kelvin", denoted by, or, respectively. In the field of continuum mechanics , thermal expansion and its effects are treated as eigenstrain and eigenstress.

The area thermal expansion coefficient relates the change in a material's area dimensions to a change in temperature. It is the fractional change in area per degree of temperature change. Ignoring pressure, one may write:

α A = 1 A d A d T {\displaystyle \alpha _{A}={\frac {1}{A}}\,{\frac {\mathrm {d} A}{\mathrm {d} T}}}

A {\displaystyle A}

d A / d T {\displaystyle dA/dT}

whereis some area of interest on the object, andis the rate of change of that area per unit change in temperature.

The change in the area can be estimated as:

Δ A A = α A Δ T {\displaystyle {\frac {\Delta A}{A}}=\alpha _{A}\Delta T}

This equation works well as long as the area expansion coefficient does not change much over the change in temperature Δ T {\displaystyle \Delta T} , and the fractional change in area is small Δ A / A ≪ 1 {\displaystyle \Delta A/A\ll 1} . If either of these conditions does not hold, the equation must be integrated.

Volume

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For a solid, one can ignore the effects of pressure on the material, and the volumetric (or cubical) thermal expansion coefficient can be written:[27]

α V = 1 V d V d T {\displaystyle \alpha _{V}={\frac {1}{V}}\,{\frac {\mathrm {d} V}{\mathrm {d} T}}}

V {\displaystyle V}

d V / d T {\displaystyle \mathrm {d} V/\mathrm {d} T}

whereis the volume of the material, andis the rate of change of that volume with temperature.

This means that the volume of a material changes by some fixed fractional amount. For example, a steel block with a volume of 1 cubic meter might expand to 1.002 cubic meters when the temperature is raised by 50 K. This is an expansion of 0.2%. If a block of steel has a volume of 2 cubic meters, then under the same conditions, it would expand to 2.004 cubic meters, again an expansion of 0.2%. The volumetric expansion coefficient would be 0.2% for 50 K, or 0.004% K−1.

If the expansion coefficient is known, the change in volume can be calculated

Δ V V = α V Δ T {\displaystyle {\frac {\Delta V}{V}}=\alpha _{V}\Delta T}

Δ V / V {\displaystyle \Delta V/V}

Δ T {\displaystyle \Delta T}

whereis the fractional change in volume (e.g., 0.002) andis the change in temperature (50 °C).

The above example assumes that the expansion coefficient did not change as the temperature changed and the increase in volume is small compared to the original volume. This is not always true, but for small changes in temperature, it is a good approximation. If the volumetric expansion coefficient does change appreciably with temperature, or the increase in volume is significant, then the above equation will have to be integrated:

ln ⁡ ( V + Δ V V ) = ∫ T i T f α V ( T ) d T {\displaystyle \ln \left({\frac {V+\Delta V}{V}}\right)=\int _{T_{i}}^{T_{f}}\alpha _{V}(T)\,\mathrm {d} T}

Δ V V = exp ⁡ ( ∫ T i T f α V ( T ) d T ) − 1 {\displaystyle {\frac {\Delta V}{V}}=\exp \left(\int _{T_{i}}^{T_{f}}\alpha _{V}(T)\,\mathrm {d} T\right)-1}

α V ( T ) {\displaystyle \alpha _{V}(T)}

T, and

T i {\displaystyle T_{i}}

T f {\displaystyle T_{f}}

Isotropic materials

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whereis the volumetric expansion coefficient as a function of temperature, andandare the initial and final temperatures respectively.

For isotropic materials the volumetric thermal expansion coefficient is three times the linear coefficient:

α V = 3 α L {\displaystyle \alpha _{V}=3\alpha _{L}}

This ratio arises because volume is composed of three mutually orthogonal directions. Thus, in an isotropic material, for small differential changes, one-third of the volumetric expansion is in a single axis. As an example, take a cube of steel that has sides of length L. The original volume will be V = L 3 {\displaystyle V=L^{3}} and the new volume, after a temperature increase, will be

V + Δ V = ( L + Δ L ) 3 = L 3 + 3 L 2 Δ L + 3 L Δ L 2 + Δ L 3 ≈ L 3 + 3 L 2 Δ L = V + 3 V Δ L L . {\displaystyle V+\Delta V=\left(L+\Delta L\right)^{3}=L^{3}+3L^{2}\Delta L+3L\Delta L^{2}+\Delta L^{3}\approx L^{3}+3L^{2}\Delta L=V+3V{\frac {\Delta L}{L}}.}

We can easily ignore the terms as ΔL is a small quantity which on squaring gets much smaller and on cubing gets smaller still.

So

Δ V V = 3 Δ L L = 3 α L Δ T . {\displaystyle {\frac {\Delta V}{V}}=3{\Delta L \over L}=3\alpha _{L}\Delta T.}

The above approximation holds for small temperature and dimensional changes (that is, when Δ T {\displaystyle \Delta T} and Δ L {\displaystyle \Delta L} are small), but it does not hold if trying to go back and forth between volumetric and linear coefficients using larger values of Δ T {\displaystyle \Delta T} . In this case, the third term (and sometimes even the fourth term) in the expression above must be taken into account.

Similarly, the area thermal expansion coefficient is two times the linear coefficient:

α A = 2 α L {\displaystyle \alpha _{A}=2\alpha _{L}}

This ratio can be found in a way similar to that in the linear example above, noting that the area of a face on the cube is just L 2 {\displaystyle L^{2}} . Also, the same considerations must be made when dealing with large values of Δ T {\displaystyle \Delta T} .

Put more simply, if the length of a cubic solid expands from 1.00 m to 1.01 m, then the area of one of its sides expands from 1.00 m2 to 1.02 m2 and its volume expands from 1.00 m3 to 1.03 m3.

Anisotropic materials

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Materials with anisotropic structures, such as crystals (with less than cubic symmetry, for example martensitic phases) and many composites, will generally have different linear expansion coefficients α L {\displaystyle \alpha _{L}} in different directions. As a result, the total volumetric expansion is distributed unequally among the three axes. If the crystal symmetry is monoclinic or triclinic, even the angles between these axes are subject to thermal changes. In such cases it is necessary to treat the coefficient of thermal expansion as a tensor with up to six independent elements. A good way to determine the elements of the tensor is to study the expansion by x-ray powder diffraction. The thermal expansion coefficient tensor for the materials possessing cubic symmetry (for e.g. FCC, BCC) is isotropic.[28]

Temperature dependence

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Thermal expansion coefficients of solids usually show little dependence on temperature (except at very low temperatures) whereas liquids can expand at different rates at different temperatures. There are some exceptions: for example, cubic boron nitride exhibits significant variation of its thermal expansion coefficient over a broad range of temperatures.[29] Another example is paraffin which in its solid form has a thermal expansion coefficient that is dependent on temperature.[30]

In gases

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Since gases fill the entirety of the container which they occupy, the volumetric thermal expansion coefficient at constant pressure, α V {\displaystyle \alpha _{V}} , is the only one of interest.

For an ideal gas, a formula can be readily obtained by differentiation of the ideal gas law, p V m = R T {\displaystyle pV_{m}=RT} . This yields

p d V m + V m d p = R d T {\displaystyle p\mathrm {d} V_{m}+V_{m}\mathrm {d} p=R\mathrm {d} T}

p {\displaystyle p}

V m {\displaystyle V_{m}}

V m = V / n {\displaystyle V_{m}=V/n}

n {\displaystyle n}

T {\displaystyle T}

R {\displaystyle R}

whereis the pressure,is the molar volume , withthe total number of moles of gas),is the absolute temperature andis equal to the gas constant

For an isobaric thermal expansion, d p = 0 {\displaystyle \mathrm {d} p=0} , so that p d V m = R d T {\displaystyle p\mathrm {d} V_{m}=R\mathrm {d} T} and the isobaric thermal expansion coefficient is:

α V ≡ 1 V ( ∂ V ∂ T ) p = 1 V m ( ∂ V m ∂ T ) p = 1 V m ( R p ) = R p V m = 1 T {\displaystyle \alpha _{V}\equiv {\frac {1}{V}}\left({\frac {\partial V}{\partial T}}\right)_{p}={\frac {1}{V_{m}}}\left({\frac {\partial V_{m}}{\partial T}}\right)_{p}={\frac {1}{V_{m}}}\left({\frac {R}{p}}\right)={\frac {R}{pV_{m}}}={\frac {1}{T}}}

Absolute zero computation

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Lord Kelvin, the namesake of the unit of measure

which is a strong function of temperature; doubling the temperature will halve the thermal expansion coefficient.

From 1787 to 1802, it was determined by Jacques Charles (unpublished), John Dalton,[31] and Joseph Louis Gay-Lussac[32] that, at constant pressure, ideal gases expanded or contracted their volume linearly (Charles's law) by about 1/273 parts per degree Celsius of temperature's change up or down, between 0° and 100 °C. This suggested that the volume of a gas cooled at about −273 °C would reach zero.

In October 1848, William Thomson, a 24 year old professor of Natural Philosophy at the University of Glasgow, published the paper On an Absolute Thermometric Scale.[33][34][35]

In a footnote Thomson calculated that "infinite cold" (absolute zero) was equivalent to −273 °C (he called the temperature in °C as the "temperature of the air thermometers" of the time). This value of "−273" was considered to be the temperature at which the ideal gas volume reaches zero. By considering a thermal expansion linear with temperature (i.e. a constant coefficient of thermal expansion), the value of absolute zero was linearly extrapolated as the negative reciprocal of 0.366/100 °C – the accepted average coefficient of thermal expansion of an ideal gas in the temperature interval 0–100 °C, giving a remarkable consistency to the currently accepted value of −273.15 °C.

In liquids

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The thermal expansion of liquids is usually higher than in solids because the intermolecular forces present in liquids are relatively weak and its constituent molecules are more mobile.[36][37] Unlike solids, liquids have no definite shape and they take the shape of the container. Consequently, liquids have no definite length and area, so linear and areal expansions of liquids only have significance in that they may be applied to topics such as thermometry and estimates of sea level rising due to global climate change.[38] Sometimes, αL is still calculated from the experimental value of αV.

In general, liquids expand on heating, except cold water; below 4 °C it contracts, leading to a negative thermal expansion coefficient. At higher temperatures it shows more typical behavior, with a positive thermal expansion coefficient.[39]

Apparent and absolute

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The expansion of liquids is usually measured in a container. When a liquid expands in a vessel, the vessel expands along with the liquid. Hence the observed increase in volume (as measured by the liquid level) is not the actual increase in its volume. The expansion of the liquid relative to the container is called its apparent expansion, while the actual expansion of the liquid is called real expansion or absolute expansion. The ratio of apparent increase in volume of the liquid per unit rise of temperature to the original volume is called its coefficient of apparent expansion. The absolute expansion can be measured by a variety of techniques, including ultrasonic methods.[40]

Historically, this phenomenon complicated the experimental determination of thermal expansion coefficients of liquids, since a direct measurement of the change in height of a liquid column generated by thermal expansion is a measurement of the apparent expansion of the liquid. Thus the experiment simultaneously measures two coefficients of expansion and measurement of the expansion of a liquid must account for the expansion of the container as well. For example, when a flask with a long narrow stem, containing enough liquid to partially fill the stem itself, is placed in a heat bath, the height of the liquid column in the stem will initially drop, followed immediately by a rise of that height until the whole system of flask, liquid and heat bath has warmed through. The initial drop in the height of the liquid column is not due to an initial contraction of the liquid, but rather to the expansion of the flask as it contacts the heat bath first.

Soon after, the liquid in the flask is heated by the flask itself and begins to expand. Since liquids typically have a greater percent expansion than solids for the same temperature change, the expansion of the liquid in the flask eventually exceeds that of the flask, causing the level of liquid in the flask to rise. For small and equal rises in temperature, the increase in volume (real expansion) of a liquid is equal to the sum of the apparent increase in volume (apparent expansion) of the liquid and the increase in volume of the containing vessel. The absolute expansion of the liquid is the apparent expansion corrected for the expansion of the containing vessel.[41]

Examples and applications

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Thermal expansion of long continuous sections of rail tracks is the driving force for rail buckling. This phenomenon resulted in 190 train derailments during 1998–2002 in the US alone.[42]

The expansion and contraction of the materials must be considered when designing large structures, when using tape or chain to measure distances for land surveys, when designing molds for casting hot material, and in other engineering applications when large changes in dimension due to temperature are expected.

Thermal expansion is also used in mechanical applications to fit parts over one another, e.g. a bushing can be fitted over a shaft by making its inner diameter slightly smaller than the diameter of the shaft, then heating it until it fits over the shaft, and allowing it to cool after it has been pushed over the shaft, thus achieving a 'shrink fit'. Induction shrink fitting is a common industrial method to pre-heat metal components between 150 °C and 300 °C thereby causing them to expand and allow for the insertion or removal of another component.

There exist some alloys with a very small linear expansion coefficient, used in applications that demand very small changes in physical dimension over a range of temperatures. One of these is Invar 36, with expansion approximately equal to 0.6×10−6 K−1. These alloys are useful in aerospace applications where wide temperature swings may occur.

Pullinger's apparatus is used to determine the linear expansion of a metallic rod in the laboratory. The apparatus consists of a metal cylinder closed at both ends (called a steam jacket). It is provided with an inlet and outlet for the steam. The steam for heating the rod is supplied by a boiler which is connected by a rubber tube to the inlet. The center of the cylinder contains a hole to insert a thermometer. The rod under investigation is enclosed in a steam jacket. One of its ends is free, but the other end is pressed against a fixed screw. The position of the rod is determined by a micrometer screw gauge or spherometer.

To determine the coefficient of linear thermal expansion of a metal, a pipe made of that metal is heated by passing steam through it. One end of the pipe is fixed securely and the other rests on a rotating shaft, the motion of which is indicated by a pointer. A suitable thermometer records the pipe's temperature. This enables calculation of the relative change in length per degree temperature change.

Drinking glass with fracture due to uneven thermal expansion after pouring of hot liquid into the otherwise cool glass

The control of thermal expansion in brittle materials is a key concern for a wide range of reasons. For example, both glass and ceramics are brittle and uneven temperature causes uneven expansion which again causes thermal stress and this might lead to fracture. Ceramics need to be joined or work in concert with a wide range of materials and therefore their expansion must be matched to the application. Because glazes need to be firmly attached to the underlying porcelain (or other body type) their thermal expansion must be tuned to 'fit' the body so that crazing or shivering do not occur. Good example of products whose thermal expansion is the key to their success are CorningWare and the spark plug. The thermal expansion of ceramic bodies can be controlled by firing to create crystalline species that will influence the overall expansion of the material in the desired direction. In addition or instead the formulation of the body can employ materials delivering particles of the desired expansion to the matrix. The thermal expansion of glazes is controlled by their chemical composition and the firing schedule to which they were subjected. In most cases there are complex issues involved in controlling body and glaze expansion, so that adjusting for thermal expansion must be done with an eye to other properties that will be affected, and generally trade-offs are necessary.

Thermal expansion can have a noticeable effect on gasoline stored in above-ground storage tanks, which can cause gasoline pumps to dispense gasoline which may be more compressed than gasoline held in underground storage tanks in winter, or less compressed than gasoline held in underground storage tanks in summer.[43]

Expansion loop on heating pipeline

Heat-induced expansion has to be taken into account in most areas of engineering. A few examples are:

• Metal-framed windows need rubber spacers.
• Rubber tires need to perform well over a range of temperatures, being passively heated or cooled by road surfaces and weather, and actively heated by mechanical flexing and friction.
• Metal hot water heating pipes should not be used in long straight lengths.
• Large structures such as railways and bridges need expansion joints in the structures to avoid sun kink.
• A gridiron pendulum uses an arrangement of different metals to maintain a more temperature stable pendulum length.
• A power line on a hot day is droopy, but on a cold day it is tight. This is because the metals expand under heat.
• Expansion joints absorb the thermal expansion in a piping system.[44]
• Precision engineering nearly always requires the engineer to pay attention to the thermal expansion of the product. For example, when using a scanning electron microscope small changes in temperature such as 1 degree can cause a sample to change its position relative to the focus point.
• Liquid thermometers contain a liquid (usually mercury or alcohol) in a tube, which constrains it to flow in only one direction when its volume expands due to changes in temperature.
• A bi-metal mechanical thermometer uses a bimetallic strip and bends due to the differing thermal expansion of the two metals.

See also

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References

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Borosilicate glass might sound like something out of a science lab but you probably have something made of it sitting in your kitchen right now. It’s commonly used by some of the biggest names in kitchenware for its non-toxic composition and durable design. But what exactly is borosilicate glass and how is it used?

Borosilicate glass is made by melting sand with boron trioxide to limit the material’s ability to expand when exposed to heat. This makes it the ideal material for making glass cookware, containers, and even scientific tools. You’ve likely used it before without even realizing it.

In this overview, we’ll explain everything you need to know about borosilicate glass. Get ready to learn how it’s made, what sets it apart from standard glass, where you’ve likely seen it before, and how safe it is for your family and friends.

What is Borosilicate Glass?

Borosilicate glass is a special type of glass made by mixing 70-80% silica sand with boron trioxide. At first glance, you likely wouldn’t be able to tell the two-component materials apart but, when heated, boron trioxide absorbs massive amounts of heat before crystallizing into a glass. Once the two fuses into the glass, boron trioxide slows the annealing process, producing a harder, more durable material.

Thanks to its ability to absorb such high temperatures, boron trioxide also makes the glass less susceptible to thermal exposure, thus guaranteeing that the final product can withstand a lot of heat without melting, warping, or cracking. For this reason, borosilicate glass is a popular choice for chefs and scientists alike.

What is Borosilicate Glass Used For?

Just about everyone who’s gone through the public school system has used borosilicate glass at least once in their life. Since it’s able to withstand incredibly high temperatures without melting or cracking, borosilicate glass is the material de jour for making scientific equipment such as test tubes, beakers, and stirring rods. If you’ve ever heated a beaker over a Bunsen burner, you’ve used borosilicate glass.

What is the Difference Between Regular Glass and Borosilicate Glass?

Besides the added boron trioxides, borosilicate glass stands out from regular glass for a few important reasons:

1) Durability – First and foremost, borosilicate glass is more durable than standard glass. Most objects made from borosilicate glass can survive a knock or two without chipping, cracking, or shattering.

2) Heat Resistance – As we’ve mentioned above, borosilicate glass is prized for its ability to withstand incredibly high temperatures without cracking or melting.

3) Stability – Borosilicate glass is highly stable, meaning it won’t leach chemicals or toxins. In fact, it’s so stable that it’s used in nuclear reactors to transport nuclear waste without leaching radiation.

Of course, just looking at it, you might not be able to tell the difference between borosilicate glass and regular glass. In the next section, we’ll spill the beans and fill you in on how to tell the difference.

How Can You Tell if Glass is Borosilicate?

Before we explain exactly how to tell the two apart, we need to get a little more specific. Most glass kitchenware is made from one of two materials—soda-lime glass or borosilicate glass. Soda-lime glass is made from a combination of silica sand, sodium oxide, and calcium oxide. It’s able to withstand high temperatures but at a lower coefficient than borosilicate glass.

If you’re unsure which material your glass kitchenware is made from, you can try eyeballing it to make a rough estimation. Take a close look at the edge of your baking dish, container, or bowl and try to find a bluish-green tinge. If it’s there, you’ve got soda-lime glass. If not, you’ve got borosilicate glass. However, this test isn’t exactly accurate.

If you want to know which material you’ve got, you’ll have to contact your nearest scientist. They can heat the material to extreme temperatures, scratch it with diamonds, or use a special optical lens to gauge which type of glass you have. If this sounds like too much effort, there’s one other option.

Simply check with the manufacturer! All glass kitchenware brands should publicly disclose which type of glass they used to manufacture their products. If it’s not easily available on the object itself, check the company’s website or send them an email to enquire.

Is Borosilicate Glass Safe for Health?

Remember when we said that borosilicate glass is made from boron trioxide?

In its raw form, boron is unsafe for human or animal consumption. It’s such a powerful toxin that it’s commonly used as a pesticide. In dry seasons, it sometimes washes into drinking water supplies, leading to widespread boron poisoning. So, if it’s so dangerous, why are we making glass from boron?

The trick is to bind boron with silica glass. When boron trioxide is melted and fused with silica sands, it becomes inert and highly stable. Even if exposed to chemical reactants, the boron cannot escape its glassy prison, keeping you safe from its toxicity. It’s so stable that borosilicate glass is even used in nuclear reactors to prevent radiation from leaching from waste.

Is Borosilicate Glass Safe in the Kitchen?

The boron in borosilicate glass is safe because it stays trapped inside the glass.

Remember, borosilicate glass can withstand incredibly high temperatures. It has a melting point of around 3,000 degrees Fahrenheit. Unless you currently own a smelting furnace, you’re unlikely to ever reach those temperatures in your home kitchen. Therefore, you can safely cook with borosilicate glass.

Is Borosilicate Glass More Durable?

Compared to standard glass, borosilicate glass is definitely more durable. Thanks to the addition of boron trioxide, the material takes a long time to cool during the manufacturing process. Slower cooling helps harden the glass and prevents it from becoming brittle. Once it finally cools into a baking dish or storage container, it’s strong enough to survive a trip through the dishwasher or a few bumps and drops.

That being said, there are a few things you should avoid doing to your borosilicate glass cookware:

➔ Sudden temperature changes – Avoid shocking borosilicate glass with sudden and drastic temperature changes. Moving borosilicate glass directly from a freezer into an oven can shock the material and cause it to crack.
➔ High drops – Just because it can survive a few bumps and knocks without cracking or chipping doesn’t mean you can drop a borosilicate dish from the top of your counter onto a hard stone floor.
➔ Physical trauma – Borosilicate glass is still glass. Don’t think that just because it’s more durable it can stand up to a hefty smack. It will break if you throw it or hit it with something hard or heavy.

As long as you use your borosilicate glass kitchenware as it’s intended, you shouldn’t have to worry about it breaking. It’s oven, microwave, and dishwasher safe and can withstand everyday bumps and knocks.

Is Borosilicate Glass Better for the Environment?

Stop to consider your daily habits. Do you buy a plastic water bottle every day? Do you use plastic containers at home? If so, you’re actively contributing to the ongoing plastic crisis affecting the world’s oceans and waste management systems. Every year, it’s estimated that 91% of the world’s plastic production goes unrecycled, left to be thrown in landfills and onto garbage barges.

Switching to borosilicate glass can help reduce your dependency on plastics by eliminating your daily use of plastic bottles and replacing your warped plastic food containers. Borosilicate glass lasts far longer than plastics and can be reused every day for years on end. Best of all, a borosilicate thermos or water bottle can keep your beverages hot or cold far longer than a standard plastic bottle.

Consider switching from plastic to borosilicate glass and do your part to save the planet. It’s stylish, durable, and cheaper in the long run than buying plastic bottle after plastic bottle.

Is Borosilicate Glass More Expensive than Normal Glass?

If we compare two glass baking dishes—one made from soda-lime glass and the other made from borosilicate glass—the borosilicate product will most likely be more expensive. This comes down to the manufacturing process needed to produce the material:

➔ Composite materials – Boron trioxide is far less common than sodium and calcium. It makes up just 0.001% of the Earth’s crust and is, therefore, more expensive to use than other elements.
➔ Energy consumption – Borosilicate glass only melts at extremely high temperatures. It, therefore, requires a massive amount of energy to transform the composite materials into a sheet of malleable glass. More energy consumption drives up the cost of production.
➔ Higher quality – After going through an intense production process, finalized borosilicate glass objects are considered high-quality glassware and therefore cost more than standard annealed glass.

As far as we are concerned, though, borosilicate kitchen and glassware are well worth the added price. Thanks to its higher durability and heat resistance, borosilicate glass containers will last far longer than traditional glass kitchenware, saving you the cost of replacing your broken or damaged objects in the future.

Where to Buy the Best Borosilicate Glass Cookware

Crystalia is an American brand based out of California that manufactures high-quality glass and kitchenware. Our products are all non-toxic, as well as lead and BPA-free, and are manufactured following strict European guidelines. When you purchase from Crystalia, you can guarantee that you’re getting both luxury and superior quality.

Crystalia currently has 15 unique borosilicate glass items for sale, including:

➔  and Square and rectangular baking dishes

Every item is designed and produced by Crystalia’s team of expert glassmakers to the highest standards. They guarantee 100% customer satisfaction.

Crystalia glassware is both beautiful and affordable, costing well within most people’s budgets. We highly recommend checking out their line of borosilicate kitchenware and investing in high-quality glass today.

Borosilicate glass is a highly durable glass material made from silica sands and boron trioxide used to withstand incredibly high temperatures. Yet it’s also a common household item used to make glass baking dishes, coffee pots, mugs, and other heated glassware. Check your kitchen and you probably have some already.

If not, we highly recommend investing in new borosilicate glass kitchenware. It’s more durable and will last longer in your oven, dishwasher, or microwave than any other glass material. Check out Crystalia’s line of opulent borosilicate items and make your purchase today. We guarantee you’ll be satisfied with the quality.

Stop relying on low-quality, environmentally hazardous plastics when you could experience the benefits of superior, non-toxic borosilicate glass kitchenware. Make the change today and experience the luxury.