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PHYS 691 Glass Science

Dr. Biprodas Dutta

Fall 2020

Homework #1

Luis P. Aguinaga

Structures and Properties of B2O3, SiO2, GeO2 and P2O5 Glasses Boron trioxide (B2O3)

Figure 1. Glassy structure of B 2O3 (left) and its crystal structure (right)

In its structure a B atom is surrounded by 3 O atoms. In its glassy configuration the B2O3 forms rings of 3 atoms of B as shown in the left of the figure 1. In nature B2O3 Is mostly found in its glassy state, because its 2 crystal forms requires high pressure to form, along with an slowing cooling to form; nevertheless to an annealing process it can be turn into a crystal form. Figure 2 shows the phase diagram of the B2O3.

Figure 2. Phase diagram of B2O3 𝛼 and 𝛽 crystal forms are show

Borate glasses are almost no commercial used because they react with atmospheric water under the exothermically reaction: B O + 3H O ⟶ 2H BO Nevertheless, it can be uses as starting material to synthesizing other compounds. Doping semiconductors or as a ceramic flux (a material used in glazes and ceramic to lower the high melting point). In combination with other materials can be form other glasses like Borosilicate glass ( SiO + (0.08 ↔ 0.13)B O ): This type or glasses have a very low coefficient of thermal expansion (≈ 3𝑥10 𝐾  at 20 𝐶) this crystal are able to resist high temperatures ( 165 𝐶 ) without fracture. One common commercial trademark of the borosilicate is Pyrex. These properties can be improved with the addition of smaller amounts of alkalis and Al2O3. These components have low thermal expansion and low softening

points. Borosilicate glasses can be also use in the manufacturing of optic fiber to reduce the optical refractive index of the fiber. Barium diborate (BaO ∙ 2B O ) barium diborate usually is found as a mixture of its 2 crystal phases and its glass phase as shown in the figure 3.

Figure 3. Thermal dependences of density for barium diborate glass, α-crystal and β-crystal obtained by dilatometry (solid lines) and X ray power difraction (dash line).

The common uses of barium diborate are glazes for dishes, ceramic color pastes for automobile windows, and electronic parts. Lead diborate (PbO ∙ 2B O ) Lead oxide is added to the glass in order to increase the glass density, refractive index, dielectric constant, X and Gamma ray absorption. At the same time hardness, chemical stability and, viscosity decreased. Due its radiation absorption properties this glasses are use in the medical field as shield. Also due the lead toxicity this glass cannot be use to make kitchen appliances. Boron trioxide can be study using its x-ray diffraction, as its show in figure 4. Other properties of the boron trioxide are listed in table 2.

Figure 4. X- ray diffraction pattern of crystalline boron oxide.

Silicon dioxide (SiO2 ) (Silica, Quartz, Q Sand)

Figure 5. Glassy structure of B2O3 (left) and its crystal structure (right)

The Si atoms in the compound are a surrounded by 4 atoms of O. In figure 5 we can see a 2D cut of the crystal and glass structture. The silicon dioxide is the most used glass, because of its properties and the fact that silicon can be found in sand making ita cheap andd wide spread material. It is commonly found as quartz (one of its crystalline forms) and in various plants like rice husk, the skeleton of maany sponges and more The principal use of silicon dioxide is in the construction industry as one of the main components of the concrete in a combination with water (H2O) and quicklime (CaO). In the mix sand and gravel are about 60-80% 6 of the mix. The sand acts as filler reduccing the air in the mixture, and incrementing its strength. Silica is the primary ingredient in the production of most glass. Many of these glasses are used as optical fibers for telecommunications, earthenware, stoneware and porcelain. Silica can also be use to produce pure Si. S Hydrophobic silica is use as a thermal protection fabric Silica, colloidal, precipitated, or pyrogenic fumed, is a common additive in foood production. It is used primarily as a flow or anti-caking agent in powdered foods such as sp pices and nondairy coffee creamer, or powderss to be formed into pharmaceutical tablets Silica doping with B or P atoms form the p, n type semiconductors, which are thhe base of the modern electronic technology. Silica can be found in many diffeerent solid phases which are listed in table 1 Crystalline forms of SiO2 Form

α-quartz

Crystal symmetry ρ Pearson symbol, group g/cm 3 No.

Notes

Helical chains making individual single rhombohedral (trigonall) 2.648 crystals optically active; α-quartz converts [66] hP9, P31 21 No.152 to β-quartz at 846 K

Structure

β-quartz

Closely related to α-quartz (with an Si-O- Si hexagonal [67] 2.533 angle of 155°) and optically active; βhP18, P62 22, No. 180 quartz converts to β-tridymite at 1140 K

α-tridymite

orthorhombic oS24, C2221 , No.20[68]

β-tridymite

hexagonal hP12, P63 /mmc, No. 194[68]

α-cristobalite

tetragonal [69 ] tP12, P4 12 12, No. 92

β-cristobalite

cubic cF104, Fd3m, No.227 [770]

keatite

tetragonal tP36, P4 12 12, No. 92 [71]

moganite

monoclinic mS46, C2/c, No.15[72]

2.265 Metastable form under normal pressure

Closely related to α-tridymite; β-tridymite converts to β-cristobalite at 2010 K

2.334 Metastable form under normal pressure

Closely related to α-cristobalite; melts at 1978 K

Si5O10, Si 4O8 , Si8 O16 rings; synthesised 3.011 from glassy silica and alkali at 600–900 K and 40–400 MPa

Si4O8 and Si6 O12 rings

coesite

monoclinic mS48, C2/c, No.15[73]

stishovite

One of the densest (together with seifertite) tetragonal [74] 4.287 polymorphs of silica; rutile-like with 6- fold tP6, P42/mnm, No.136 coordinated Si; 7.5–8.5 GPa

seifertite

orthorhombic oP, Pbcn[75]

2.911

Si4O8 and Si8 O16 rings; 900 K and 3–3.5 GPa

One of the densest (together with 4.294 stishovite) polymorphs of silica; is produced at pressures above 40 GPa.

[76]

cubic (cP*, P4 232, melanophlogite No.208)[8] or tetragonall (P42/nbc)[77]

Si5O10, Si 6O12 rings; mineral always found 2.04 with hydrocarbons in interstitial spaces - a clathrasil [78]

fibrous W-silica [10]

orthorhombic oI12, Ibam, No.72 [79]

1.97

2D silica[80]

hexagonal

Like SiS 2 consisting of edge sharing chains, melts at ~1700 K

Sheet-like bilayer structure

Table 1. SiO22 many crystalline forms are called polymorphs .

A simplified version of a silica phase diagram is show in figure 6 and its x-ray distraction in figure 7.

Figure 6. Simplified phase diagram of pure SiO 2

Figure 7. X-Ray Diffraction of nano Silicon dioxide powder

Germanium dioxide (GeO2) Germanium and silicon are in the same group of the periodic table they share similar chemical and physical properties. Its crystal and glass structure is the same as in Si. Figure 5 is a good representation of its structure we only need to switch the Si atoms for Ge ones. Because of its optical refractive index (1.7) is large use in wideangle lenses, optical microscope objective lenses and as core of fiber optic lines. Due its transparence to the infrared is use for night vision and thermographic cameras especially in military applications due its strength.

Germanium glasses have lower thermal properties than its silicon equivalents, because of this heat can damage the glass make this materials hardly use in thermal resistant hardware or semiconductor applications. Also Si is much more abundant material making its commercial price much lower than Ge, this makes ornamental glasses application unviable. Nevertheless its optical properties are better than the Si glasses this makes the Ge a better candidate in the production of optic fibers. Ge optic fiber can have a lower attenuation than the Si ones making the Ge fibers more economical and reliable even do the fact that the material use in its manufacturing are more expensive. GeO2 phases are similar to the SiO2. Figure 8 shows some of the phases of a system GeO2SiO2

Figure 8. Pressure-composition phase diagram for the system GeO2–SiO2. Solid lines: phase relations at 200°C. Dotted lines: selected phase relations at 1500°C.

The X-ray diffraction patter is fundamentally the same in the case of system GeO2 and SiO 2 the only practically notice difference is phase in the angle of diffraction as it is show in figure 9.

Figure 9. Comparison of the x-ray diffraction pattern of silicon, germanium and the Si80Ge20 alloy synthesized from a mixture of 80% silane and 20% germane. Due to handling in air, the diffraction pattern of germanium shows an additional peak around 26° originating from crystalline germanium oxide.

Phosphorus pentoxide (P2O5)

Figure 10. Unitary cell of P2O5.

As shows in figure 10 each P atom is surrounded by 4 O atoms and one of this atoms has a double enlace with P. Phosphorus is an element of VA family in contras Boron is part of the IIIA family. The fundamental difference between P and B are that P has one electron more than Si or C in its last orbital and B has one less. This little change makes that P and B acting in many cases as opposites. For example B impurities in a semiconductor make it a p-type or acceptor make it more likely to trap an electron. In the other hand P impurities make it a n-type o donor and it is more likely to expel an electron. This makes that around P there is a + Electric field, and around B a – one. As borosilicate glasses can be also use in the manufacturing of optic fiber to reduce the optical refractive index of the fiber, the phosphosilicate glasses are use to increase the optical refractive index. Like Borate glasses phosphate glasses are almost no commercial used because they react with atmospheric water under the exothermically reaction: P O + 3H O ⟶ 2H PO This property are make the P O commercially use as a potent dehydrating agent. This fact made it a hazard substance that can cause burs in eyes; skin, mucous membrane and

respiratory tract do its exothermic reaction with water. P O can be combine with silica and form phosphosilicate glasses mostly use in semiconductors and optic fiber Phosphosilicate glasses (SiO + (0.25 ↔ 0.5)P O ): these families of glasses are usually form by mixing SiO and P O in different proportions this system lead to the following phase diagram

Figure 11. SiO 2–P2O5 binary system:Tienand Hummel (right )and Mal'shikov Bondar(b).

Also the x-ray diffraction is

Figure 12. XRD after firing at 800 0C of 75S–25P and 50S–50P samples

Finally here are some properties of these materials

Molar mass

B2O3 69.6182 g/mol

SiO2 60.08 g/mol

GeO 2 104.6388 g/mol

P 2O5 283.9 g mol

−1

Appearance

white, glassy solid

Density

2 .460 g/cm3, liquid; 2.55 g/cm3, trigonal; 3.11–3.146 g/cm3, monoclinic 450 °C (trigonal); 510 °C (tetrahedral) 1,860 °C sublimes at 1500 °C 66.9 J/mol K

Melting point

Boiling point

Heat capacity (C)

Transparent solid (Amorphous) White/Whitish Yellow (Powder/Sand) 2.648 (αquartz), 2.196 (amorphous) g·cm−3

white powder or colorless crystals

white powder very deliquescent odorless

4.228 g/cm 3

2.39 g/cm

1,713 °C (amorphous) [

1,115 °C

340 °C

2,950 °C

Std molar entropy (So298)

80.8 J/mol K

42 J·mol − 1·K −1

Std enthalpy of formation (ΔfH⦵298)

-1254 kJ/mol

−911 kJ·mol −1

Gibbs free energy (ΔfG˚)

-832 kJ/mol

3

360 °C (sublimes)

Table 2. Properties of different materials

Boron Oxide Anomaly Pure boron in an oxide has a valence of +3 (B O ) that is usually its natural and stable state. In this configuration B is able to share its 3 electrons and form a bond. The boron configuration is [He]2s22p1 the last 3 electrons joins with the outer O electron and form hybrid sp3 orbital. Now if we start to add an alkali oxide to the mixture (R  O) there will a probability that the O from de alkali be close to a B molecule, alkali oxides are form from an ionic bond, this means that we have a R+ atom attracted by a coulomb force to an O -2 atom in its proximity. But this oxygen are deprived of 2 electrons, therefore if they are close to the B O this ionized will be try to make a bond with B. The boron will feel the pressure from this O to form a bond that will be still a close electron from the R+ atom and form hybrid sp4

orbital looking as if we haveB ⟶ B . As more alkali we put in the mixture more B will convert into B in figure 1 we can see this process

Figure 1. B  ⟶ B  conversion

The amount of B will be increasing until reach a maximum of 50% when the alkali mole fraction is 0.33. B is an unstable configuration therefore as soon as the alkali atoms and the oxygen move away the B will be expel the additional electron a returning back to its stable configuration B . This conversion reconversion process will be reach an equilibrium point base on the alkali concentration. If we increase the concentration of the alkali beyond the 0.33 concentration the equilibrium point will be reach in a B fraction lower than 50%. It is true than at more concentration the probability of having a R  O close to a B O will be higher, but also the probability of have a R  O close to another R  O the proximity with the 2nd alkali oxide makes less like to have the B  ⟶ B conversion. This is due the fact that the 2nd alkali atom will attract the capture electron breaking the conversion. Figure 2 shows this new boron bonds and Figure 3 shows the fraction of B as a function of the alkali concentration

Figure 2. Configuration of B after the conversion on the right

Figure 3. The fraction of B  atoms in alkali borate glasses for different alkali oxides

Several characteristics of the glass change base on the Na O concentration as can be show in figure 4.

Figure 4. Concentration of bridging oxygen (Ob),coefficient of thermal expansion (α) and the softening temperature (SP)as functions of alkali-oxide in a binary B203 glass

Other compound that calls the attention is Bi O − B O bismuth is a metal that can make metal bond given the B the opportunity of catch one of the electrons in the cloud form around the metal nucleus. Glasses containing high Bi2O3 content are characterized with marked high density, refractive index and second and third harmonic generation coefficients. Such glasses have applications in high energy physics as host for rare earth scintillators and are used as Pbfree sealing glasses, materials for sensors, solar cells and electronics. Figure 5 show the fraction of B as function of the concentration of Bi.

Figure 5. N4(B ) concentration Heavy lines are extensions of the plot in the regions lacking experimental data

Several properties of the compound are show in the figures 6, 7 and 8.

Figure 6. Density of Bi O − B O as function of B O content

Figure 7. Concentration of constituents as a function of Bi2O3 content in Bi2O3–B2O3 glasses. CB3s is the concentration of symmetric BO3 triangles, CB4 is the concentration of BO4 tetrahedra, CBif is the concentration of BiO6 distorted octahedral former units, CB3as is the concentration of asymmetric BO 3 triangles and CBi4 represents the concentration of Bi2O3 incorporated in BO4 units. The concentration CBi3as (mol%) of Bi2O3 linked to asymmetric BO3 units is not presented for the sake of clarity. Lines are fitting plots of the presented data.

Figure 8. Change with the Bi2O3 content of the volume of structural units per glass mole of Bi2O3–B2O3 glasses. The symbol (+) refers to calculated molar volume. Lines are fitting plots of the presented data.

Alumina and Alkali Oxides in Ternary Al2O3-Na2O-SiO2 Glasses The Al2O3 content of alkali aluminosilicate glasses is typically 10-25% and the alkali content over 10%. The high alkali content prepares the glass for ion exchange with bigger alkali ions in order to improve the surface compressive strength. Due to this particular feature, this glass type is especially suitable for the use in touch displays, solar cells cover glass and laminated safety glass. High transformation temperatures and outstanding mechanical properties, e.g. hardness and scratch behavior, are characteristic of this glass type. This ternary system is an important system in geology as part of many volcanic rocks and has therefore been mainly studied in the region of interest for this field (relatively high silica content). However various experimental challenges, such as high vapor pressures at high Na2O content, high viscosity values for melts at high SiO 2 content and high liquidus temperatures at high Al 2O3 content. The Al2O3 are mixed in between the SiO2 grid. But the Al has only 3 O atoms surrender it; therefore it needs to trap another O in order to replace the Si in the grid. The Al impurity has and effective charge of -1 and the form AlO2- grid in order to keep the charge balance the Na+ atoms move near to the Al in a process show in figure 1.

Figure 1. Acting as a glass former alongside SiO2, Al2O3 assumes tetrahedral coordination of oxygen ions.

The Al atoms act as doping in the Si grid and the Na atoms help to stabilize the system. Some of the effects of this system are increase in viscosity and elastic modulus, decrease in the coefficient of thermal expansion, and others. The balance occurred when [Al O ] = [Na O] more Al or Na will not create more of these connections but they still change the properties of the mix, this is mostly for the tri-coordinated oxygen formation. The face diagram of this ternary system is show in figure 2; the diagram is base on the concentration take at a constant preassure and temperature.

Figure 2. Calculated isothermal section at 1873 K in the (Al2O3 + Na2O + SiO2) system. Experimental data: (α-Al2O3 + liquid),  (α-Al2O3 + β-Al2O3 + liquid),  (β-Al2O3 + Liquid); calculated phase equilibria: A = αAl2O3, B = β-Al2O3, L = liquid, M = mullite, NA = sodium aluminate (solid solution), S = SiO 2(highcristobalite).

Figures 3, 4, and 5 show some of the physical properties of the (Al2O3 + Na2O + SiO2) system.

Figure 3. Calculated liquidus curves for ((Na2O)x(SiO2)1_x + Al2O3) isoplethal sections. Experimental data: (Na2O)0.068(SiO2)0.932, (Na2O)0.092(SiO2)0.908, (Na2O)0.117(SiO2)0.883, (Na2O)0.129(SiO2)0.871, . (Na2O)0.143(SiO2)0.857, (Na2O)0.171(SiO2)0.829, (Na2O)0.200(SiO2)0.800, (Na2O)0.225(SiO2)0.775.

Figure 4. Calculated liquidus curves for ((Na2O)x(SiO2)1_x + Al2O3) isoplethal sections. Experimental data: *(Na2O)0.244(SiO2)0.756, (Na2O)0.269(SiO2)0.731, (Na2O)0.294(SiO2)0.706,  (Na2O)0.313(SiO2)0.687, (Na2O)0.333(SiO2)0.667, (Na2O)0.394(SiO2)0.606.

Figure 5. Calculated activity of Na2O (liquid reference state) at 1400 K in the (Al2O3 + Na2O + SiO2) system. Experimental data 0.05mole fraction Al2O3, 0.10mole fraction Al2O3, 0.15mole fraction Al2O3....