Fused Silica Rod Research Articles

The onset of grain refinement temperature in undercooled Ge

When an undercooled specimen crystallizes, its microstructure depends on the initial bulk undercooling, {Delta}T = T{sub m} {minus} T where T{sub m} is its thermodynamic melting temperature. At {Delta}T near but smaller than 200 K, a typical undercooled Ge specimen exhibits an ordered and connected structure, in which the various dendrites are arranged side by side in a very orderly way. Indeed, the entire surface of this specimen is covered with this regular dendritic pattern. Another undercooled specimen with {Delta}T = 206 K, on the other hand, illustrates a small region inside which the grains are more or less randomly oriented. It appears that these grains are fragments of dendrites scattered all over the region where contact had been made with the fused silica rod. Furthermore, the size of the grains near this region is smaller than those further away indicating grain refinement has just occurred in this region. Summing up, it can therefore be concluded that the onset of grain refinement in undercooled Ge lies between {Delta}T = 201 and 206 K which is substantially smaller than the previous value, 230 K. For simplicity, the onset of grain refinement temperature is chosen to be 203 K.

Simultaneous acquisition of photoacoustic and fluorescence spectra at high sensitivity from powdered samples at variable temperature

An apparatus has been built for simultaneous high-sensitivity photoacoustic and fluorescence studies at temperatures from 4 to 295 K that uses a pulsed tunable dye laser as the excitation light source. A powdered sample, pressed into the pellet, is attached to a coiled fused-silica rod that provides thermal isolation from and good acoustic contact to an ambient temperature acoustic detector. The surface of the rod is roughened, thereby eliminating acoustic interference arising from scattered excitation light. As a test of the apparatus, the absorption spectrum of the (4)F(9/2) state of Nd(3+) in A-phase Nd(2)O(3) powder, dispersed in a KBr pellet, was recorded simultaneously by means of photoacoustic and fluorescence excitation spectroscopies.

A New Apparatus for Simultaneous Measurement of Acoustic Emission and Differential Thermal Analysis and Its Application to Dehydration, Phase Transition, and Decomposition Studies of Several Inorganic Salts

Abstract A new apparatus for simultaneous measurements of acoustic emission (AE) and differential thermal analysis (DTA) is described. Two fused silica cells are used as the sample and reference holders and a fused silica rod, fixed at the bottom of the sample holder, acts as the waveguide for AE signals emitted in the sample. A 140 KHz resonance frequency sensor is attached at the end of the rod to detect the AE signals which are converted by an AE tester to three parameters, the wave form, the event count rate, and the cumulative count. The technique has been successfully utilized to study the dehydration, phase transition, and decomposition of NaN3, KNO3, KClO4, CaCrO4·0.1H2O, and MgCl2· 6H2O, for which the interesting results are reported.

Corrosion of Refractories by Vanadium Pentoxide

The nature of attack of V2O5 melts on polycrystalline alumina and fused silica rods was studied under conditions of forced convection dissolution at several temperatures in the range 800°–1000°C. The rate of corrosion as a function of the square root of angular velocity of rotation at various temperatures was found to be linear. This was in agreement with the theoretical model of forced convection dissolution. Using the experimental data, the effective diffusivities were calculated for both silica and alumina. Throughout the temperature range of the present investigation, alumina was found to have greater diffusivity. As the dissolution was diffusion-controlled, it was concluded that silica would act as a better refractory than alumina in vanadium-rich environments.

A technique for making low-loss fused silica core-borosilicate clad fiber optical waveguides

A technique for producing low-loss fused silica core-borosilicate clad fiber optical waveguides is described. The method consists of depositing radially oriented needles of borosilica on the outside surface of a fire-polished fused silica rod. This deposition is accomplished by a flame reaction of boron and silicon hydrides with oxygen. The deposit is subsequently sintered at approximately 1000°C to form a bubble free glass cladding. A thin fused silica outer jacket is then developed on this cladding to enhance the strength and the composite structure is drawn down to a fiber.

Borosilicate clad fused silica core fiber optical waveguide with low transmission loss prepared by a high-efficiency process

A method for making fused silica core-borosilicate clad optical fiber waveguides is described. The process involves the growth of a needlelike layer of borosilicate glass onto the surface of a commercially available high-purity fused silica rod by an efficient flame reaction of boron and silicon hydrides with oxygen. The needlelike layer is subsequently heat treated at relatively low temperature to form a homogeneous bubble-free glass with a smooth surface. It is then covered with a thin protective jacket of silica and drawn into a fiber. These fibers have attenuation coefficients only slightly greater than the bulk loss of the fused silica core materials. Over the Al1−xGaxAs injection laser wavelength range, 0.82–0.88 μm, the loss is 5 dB/km, while at the YAG : Nd laser wavelength, 1.06 μm, it is 3 dB/km. The process appears to be attractive for the economical manufacture of low-loss fibers due to its simplicity and high chemical conversion efficiency.

Influence of Environment on Brittle Fracture of Silica

The fracture strength of fused silica rods was determined in vacuum and in the saturated vapors of water, ethyl alcohol, n-butyl alcohol, n-propyl alcohol, acetone, ethyl acetate, undried benzene with “less than 0.02% water,” and dried benzene. The relation between the lowering of the fracture strength of the fused silica caused by the vapor and the corresponding decrease in surface free energy of quartz was found to be consistent with the Griffith theory of brittle fracture.

Measurement of Dynamic Shear Impedance of Liquids at High Ultrasonic Frequencies

Further development of a shear reflectance technique reported on previously is here described [Phys. Rev. 75, 936 (1949)]. Shear waves at 30 mcps are reflected at a low grazing angle from a polished surface on a fused silica rod. Simultaneously waves are transmitted through a second path designed to provide a precisely matched reference channel with high relative stability. The specimen liquid when placed on the polished surface produces a change of amplitude and phase for the reflected wave from which the complex shear impedance can be calculated. Illustrative data is presented for a series of Dow Corning DC-200 silicone fluids having steady flow viscosities from 1.5 to 200 000 centistokes. At 39 mcps and 25°C relaxation effects are present for viscosity grades as low as 5 centistokes. The limiting stiffness (Voigt) is ∼2×107 dynes/cm2—in the range for rubber-like materials.

Measurement of Elastic Constants at Low Temperatures by Means of Ultrasonic Waves–Data for Silicon and Germanium Single Crystals, and for Fused Silica

Ultrasonic waves (shear or longitudinal) in the 10–30 mc range are transmitted down a fused silica rod, through a polystyrene or silicone one-quarter wavelength seal, and into the solid specimen. Measurement of reflections within the specimen yields values for velocities of propagation and elastic constants. Data obtained over a temperature range of 78° to 300°K for silicon and germanium single crystals, and 1.6° to 300°K for fused silica are listed. For the latter, a high loss is noted, with an indicated maximum near 30°K.

Measurement of Elastic Constants at Low Temperatures by Means of High Frequency Ultrasonic Waves

Pulse-modulated ultrasonic waves (shear or longitudinal) in the 10–30 Mc range are transmitted down a fused silica rod, through a polystyrene or silicone one-quarter wavelength seal, and into the solid specimen. Phase comparison of waves reflected back and forth within the specimen yields values for velocities of propagation and elastic constants. Advantages of the method are: (1) the specimen need not be large to insure a fair degree of accuracy—a thickness of one-quarter inch is usually sufficient; and (2) the quartz crystal transducer initiating the waves is maintained near room temperature, thus insuring well-defined wave trains. Illustrative data obtained over a temperature range of 78° to 300°K for silicon and germanium single crystals and 1.6° to 300°K for fused silica are given. For the latter, a high loss is noted, with an indicated maximum near 30 degrees Kelvin.