Pyrex Borosilicate Glass Research Articles

SIZING A PARABOLIC TROUGH COLLECTOR FOR A MICRO SOLAR ORGANIC RANKINE CYCLE

There are many remote villages in Malaysia that are not connected to an electric grid, and are dependent on expensive diesel generator sets (gensets) in their daily activities. Malaysia, a tropical country, has the potential to promote solar power generation in these isolated areas. The organic Rankine cycle (ORC) using solar thermal energy as the heat source could be an attractive approach to off-grid power generation. In this study, a 1 kWe solar ORC with a parabolic trough collector (PTC) is proposed. The ORC utilizes R245fa as the working fluid and Therminol VP1 as the heat transfer medium between the PTC and ORC. Thermodynamic analysis of the ORC is performed, predicting the performance of the ORC and the operating conditions of the PTC. Based on the design requirements of the PTC from the power cycle analysis, process of sizing the PTC is conducted via a numerical model. Seven sets of heat collector elements (HCE) are examined. The effects of absorber tube material, selective coating on the outer surface of the absorber tube, and the absorber tube diameter on the PTC performance are presented. Simulation results show that HCE with 6 mm of SS316L absorber tube, enclosed with 11 mm of Pyrex borosilicate glass tube, has the highest collector efficiency of 62.25%. The receiver length required is 8.05 m and the aperture width of the collector is 3.54 m. Further study is recommended to select a thermal storage system for night-time operation of the ORC.

Second-order optical nonlinearity in thermally poled Pyrex borosilicate glass

The thermal poling method was utilized to create second-order optical nonlinearity in Pyrex borosilicate glass. The distribution and amplitude of the induced nonlinearity were characterized with second harmonic microscopy. The induced optical nonlinearity was found in a thin layer around 1.9μm under the anode surface with a magnitude as high as 0.24pm/V, comparable to that observed in fused silica samples. SEM observation of the cross-section of the poled glass region, after it had been etched in diluted hydrofluoric acid for several minutes, revealed an etched trench, ∼1.8μm under the anode edge and ∼0.3μm in width; while in post-annealed samples, no such etched trench could be observed. The effect of poling voltage on the magnitude of the induced nonlinearity was also studied, where the results showed that higher poling voltage resulted in higher nonlinearity with a threshold of ∼0.9kV.

Improvement of Young's modulus and tensile strength of polymer impregnation and pyrolysis processed SiC/SiC composite by improved continuity of matrix

Influences of the continuity of the matrix on Young's modulus and tensile strength of unidirectional SiC/SiC mini-composite prepared by the polymer impregnation and pyrolysis method were studied experimentally by observation of appearance of matrix and tensile test and analytically by a shear lag–Monte Carlo simulation. The continuity of the matrix was improved by the addition of particles such as ZrSiO4, barium magnesium aluminosilicate, and Pyrex (borosilicate glass) into the matrix. The improved continuity of the matrix led to the increase in stress carrying capacity of the matrix and therefore to the increase in Young's modulus and tensile strength of the composite. Such a correlation between the continuity of the matrix and the property of the composite was verified numerically by the shear lag–Monte Carlo simulation.

Effect of alumina addition on properties of glass/ceramic composite

A series of glass/ceramic composites were prepared from pyrex borosilicate glass with silica. The effects of 15 vol.-% alumina addition on cristobalite formation in this system have been studied. Cristobalite formation in the composites has been found to decrease with addition of alumina, which may be attributed to a strong coupling reaction between Al3+ from alumina and K+ from pyrex borosilicate glass. The resulting glass/ceramic composites containing alumina have low thermal expansion coefficient owing to the presence of a lower amount of cristobalite in the glass matrix. The formation of cristobalite limits the efficiency of the ceramic substrate when used in circuit boards.

Crystallization behavior and origin of c-axis orientation in sol–gel-derived ZnO:Li thin films on glass substrates

Preferentially, c-axis-oriented lithium-doped zinc oxide (ZnO:Li) thin films were prepared on Pyrex borosilicate glass substrates by a sol–gel method starting from zinc acetate dihydrate, lithium chloride, 2-methoxyethanol and monoethanolamine. Decomposition and crystallization behavior of dip-coated amorphous precursor films during post-annealing treatments were investigated by thermogravimetry–differential thermal analysis (TG–DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), optical transmittance measurements, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). It was revealed that the films contained the organic compounds at temperatures up to 300°C, which was the key to the transformation from the amorphous to the crystalline state. Thermodynamical consideration of nucleation and crystal growth was made taking account of surface energies of the film and the glass substrate and an interfacial energy between them. Mechanisms underlying the c-axis orientation were proposed based upon the initial orientation due to nucleation and final growth orientation.

Devitrification kinetics and mechanism of Pyrex borosilicate glass

Cristobalite is formed when initially amorphous Pyrex borosilicate glass (Corning 7740) is fired at temperatures ranging from 700 to 1000 °C. The sigmoidal devitrification kinetics of cristobalite obeys Avrami-like three-dimensional diffusion-controlled kinetics. Activation energy analysis indicates that the diffusion of Na+ in the glass is the rate-limiting step during phase transformation. The above conclusion is further confirmed by calculated and measured results of linear growth rates.

Solid-gas hydrogenation of hex-3-yne and 1,4-cyclohexadiene in the presence of the clusters Ru3(CO)12, H4Ru4(CO)12, H2Ru4(CO)13 and H2FeRu3(CO)13 supported on inorganic materials. Infrared evidence for surface organometallic reactions

The clusters Ru3(CO)12 (1), H4Ru4(CO)12 (2), H2Ru4(CO)13 (3), and H2FeRu3(CO)13 (4) supported on pyrex borosilicate glass behave as catalysts for solid–gas hydrogenation reactions of hex-3-yne and 1,4-cyclohexadiene. Their activity and selectivity are discussed. Ru3(CO)12 (1) was also supported on inorganic oxides, normally used as chromatographic materials or supports for heterogeneous catalysis and characterized by different acidities and surface areas. The observed activities depend on the nature of the inorganic supports; the presence of water also has some influence. Some of these materials were characterized by HRTEM microscopy. Organometallic products have been collected after the catalytic runs both when pyrex and inorganic oxides were used as supports. In particular, the “surface organometallic reactions” of Ru3(CO)12 and H4Ru4(CO)12 supported on silica have been followed by IR spectroscopy. The nature and role of the arising organometallic compounds are discussed. Our solid–gas results are in good agreement with the mechanisms previously proposed for the hydrogenation of comparable substrates under homogeneous conditions.

Effect of alumina particle size on prevention of crystal growth in low- k silica dielectric composite

The effect of alumina particle size on cristobalite formation in binary borosilicate glass composite, containing a low-softening Pyrex borosilicate glass and a high-softening high silica glass, has been studied. With an added alumina content greater than a critical value, however, cristobalite formation in the glass composite is completely inhibited. The critical alumina content is found to decrease with decreasing alumina particle size, from 10–15 vol.% for 3 μm to 1–2.5 vol.% for 0.02 μm at 950 °C. The above result is attributed to a strong coupling reaction between Al 3+ from alumina and Na + from Pyrex borosilicate glass. The resulting cristobalite-free glass composite has a dielectric constant of 4.5–5.5 at 1 MHz and a thermal expansion coefficient of 2.5–5.5 ppm °C −1 in the temperature range 25–200 °C.

Crystallization and Properties of a Low k Glass Composite

The effect of gallium oxide on crystallization, thermal expansion and dielectric behaviors of a binary glass composite which contains a low-softening Pyrex borosilicate glass and a high-softening high silica glass has been studied. It is found that on sintering, cristobalite precipitates out of the initial amorphous binary glass mixture; however, the addition of gallium oxide prevents this. The above result is further supported by microstructural observation, thermal expansion and dielectric constant measurements.

Crystallization inhibitors during sintering of Pyrex borosilicate glass

Oxides with a trivalent metal ion, such as Al 2 O 3 , Ga 2 O 3 , Y 2 O 3 , La 2 O 3 and Sc 2 O 3 , were added to prevent cristobalite formation in the initially amorphous Pyrex borosilicate glass during sintering

Cristobalite growth inhibitor in Pyrex borosilicate glass—gallium oxide

The effect of gallium oxide on cristobalite formation in Pyrex borosilicate glass has been studied. XRD results show that with 20 vol.% gallium oxide, the precipitation of cristobalite at 800 °C is completely prevented. This result is further evidenced by the linear thermal expansion measurement, in which, in contrast to the system without a sufficient amount of gallium oxide (0–10 vol.%), the thermal expansion coefficient of the composite with 20 vol.% gallium oxide remains unchanged with sintering time at the temperature investigated and, moreover, is very close to the theoretically calculated value.

Dissolution Rates of Commercial Soda–Lime and Pyrex Borosilicate Glasses: Influence of Solution pH

Dissolution rates of two commercial soda—lime silicate glasses and Pyrex borosilicate glass (Corning 7740) have been measured as a function of pH. The dissolution rate was constant with time and increased with increase in pH from 4 to 9. The activation energy for dissolution was nearly constant with pH for the Pyrex borosilicate glass, and decreased somewhat as pH increased for the soda—lime glasses. The openness of the glass surface influences strongly the rate of dissolution. The solubility of silica as a function of pH increases at pH above 8 but does not seem to be quantitatively related to dissolution rate. Other possible influences on this rate are briefly considered.

Dissolution Rates of Silicate Glasses in Water at pH 7

Dissolution rates of different glasses in buffered solutions of constant pH of 7 were measured by weight change, profilometry, and ion implantation with Rutherford backscattering. Rates with different techniques agreed within experimental error. Natural obsidian glass dissolved most slowly, at a rate comparable with those of quartz and crystalline aluminosilicate minerals. Commercial soda–lime glass containing alumina dissolved slowly, at about the same rate as vitreous silica; soda–lime silicate glasses both commercial and laboratory without alumina dissolved much more rapidly. Pyrex borosilicate glass dissolved at a rate intermediate between those of soda–lime silicate glasses with and without alumina; at room temperature Pyrex borosilicate glass dissolved about 100 times faster than a commercial soda–lime glass containing alumina. We suggest that surface structure is the main factor determining the relative dissolution rates of silicate glasses. Glasses with transformed surface layers caused by hydration dissolve most rapidly; phase separation and openness of the glass structure are also important factors.

Thermal diffusivity and conductivity of a carbon fibre-reinforced borosilicate glass

A study was conducted of the thermal diffusivity, thermal conductivity and specific heat of hot-pressed Pyrex borosilicate glass reinforced with randomly oriented carbon fibres perpendicular to the hot-pressing direction. The thermal diffusivity and conductivity of the composite perpendicular to the plane of the fibres was only slightly higher than the corresponding value for the matrix, attributed to the low thermal conductivity of the carbon fibres perpendicular to their axis. Within the plane of the fibres the thermal diffusivity and conductivity were approximately twice those of the matrix. The specific heats of the matrix and composite were nearly identical. The temperature dependence of the thermal diffusivity of the matrix and composite was minor only. The corresponding positive temperature dependence of the thermal conductivity of the matrix and composite was attributable primarily to the positive temperature dependence of the specific heat. Heating the composite to temperatures above ~ 600 ° C resulted in a permanent decrease in thermal diffusivity at a rate which depended strongly on temperature. This change was attributed to the relaxation of the elastically bent fibres by the thermally activated viscous flow of the surrounding matrix, which as shown by electron microscopy resulted in interfacial separation and crack formation within the composite. These effects, in turn, caused the observed decrease in thermal diffusivity.

Static fatigue of glass: functional dependence of failure time on stress

Static fatigue of as-received Pyrex borosilicate glass was examined over a wide range of stress and failure time under constant temperature, relative humidity, and surface treatment. It was necessary to calculate the load on the sample from strain guage measurements. The mean log failure time was related to the reciprocal of stress or the reciprocal of stress squared; power law and direct proportionality to stress gave poorer fits.

Initial crack paths in glass: influence of temperature and composition

Fracture initiation sites in soda-lime glass are similar for fracture at room temperature and at −196° C, where slow crack propagation should be absent. For most samples the measured depths of these sites were greater than the actual depths of the fracture initiating flaws. Micrographs of fracture initiation sites in Pyrex borosilicate glass and a lithium aluminosilicate glass-ceramic are also shown.