Showing papers on "Devitrification published in 1973"

Laser‐beam writing on amorphous chalcogenide films: crystallization kinetics and analysis of amorphizing energy

Abstract: By using laser pulses, the kinetics of crystallization of Te‐rich films were studied as a function of light intensity and pulse duration. The initial devitrification was found to be temperature activated (ΔE≃1–1.6 eV), and no evidence for photocrystallization was found. Amorphizing energies for 100‐nsec pulses ranged from 0.13 to 0.55 nJ/μ2, depending on the degree of crystallization. Part of this increase is due to heat‐of‐fusion effects, but most of it is due to increased thermal conductivity with increased crystallization.

The crystallization of cordierite glass

Abstract: The results of a study of the crystallization characteristics of a glass near the cordierite composition are discussed. The devitrification of the base glass was studied by the method of DTA and the development of this technique is described. The effects of additions of vanadium pentoxide and tungstic oxide on the behaviour of the base glass were also determined and are discussed.

Crystallizable glass suitable for fiber production

Abstract: The manufacture of fibrous insulating products which will devitrify or crystallize when exposed to fire. Such insulating products will withstand relatively high fire temperatures without deformation. The compositions have comprised by weight the following constituents. The disclosure also contains a method of preparing glass-ceramic compositions of high softening point and having the constituents in proportions as recited above, and which after solidification are capable of rapid devitrification when reheated which comprises compounding conventional glass making raw materials in proportions suitable for yielding the foregoing glass compositions and melting said mixture of raw materials in a neutral or oxidizing environment to obtain a homogeneous glass mass. The melting will preferably be effected in an oxidizing atmosphere at temperatures in the range of 1200* to 1500*C.

Process for making transparent silica glass

Abstract: A crucible formed from pulverized particles of fused quartz is fired and vacuum dried to remove all water and is thereafter placed on a heated graphite form or susceptor shaped to conform to the surface of said article and rapidly heated in an induction furnace to a high temperature, in the range of about 3000*F. to about 3150*F. The crucible is maintained at a temperature in such range in a vacuum or in a helium atmosphere for a period of at least one minute sufficient to obtain full density while avoiding substantial devitrification. The vacuum drying preferably provides the glass of the crucible with an infrared absorption beta OH factor below .01 at a wavelength of 3.5 microns. A unique apparatus is provided to carry out the process rapidly and efficiently without forming significant amounts of cristobalite and to cause gases trapped in the crucible to move radially outwardly. The process minimizes devitrification and can be employed for mass production of precision transparent amorphous quartz glass products having excellent resistance to thermal shock.

Sintering and hot pressing of Fra Mauro composition glass and the lithification of lunar breccias

Abstract: It is proposed that Apollo 14 type breccias lithify by sintering of particles of matrix glass under stress-free conditions. Meteorite impacts generate the heat necessary for sintering. Compacted angular particles of glass with the composition of an Apollo 14 rock were sintered experimentally. Loose clods of sub 37 micron grains form in several days at 700 C. Synthetic rocks, which texturally resemble the breccias, were produced at 795 C and above in 7.5 hours. Glass devitrified with increasing temperature. At 850 C, devitrification prevents much further densification of the synthetic breccias after 2 hours. Experiments compressing glass at 500 bars at 600 C produced dense vitreous masses which did not resemble lunar breccias. Confining pressure does not play a major role in lithifying the breccias. It is concluded that Apollo 14 type lunar breccias form at shallow depths at 800 C+ in a period of minutes to days.

Laser glasses with high damage threshold and method of making such glasses

Abstract: Laser glasses having high resistance to self-damage during operation are formed in all ceramic melting units, in the presence of a fining agent to eliminate the formation of metallic inclusions and semi-conductive inclusions and using base glass compositions with reduced tendency toward microphase separation and devitrification. The major ingredients of the glass batches include silicon dioxide, alkali and alkaline earth nitrates, carbonates and fluorides. The method involves introducing oxidizing compounds into the reaction mixture in a sufficient amount that during the reaction and fining phase, oxidizing conditions are maintained throughout the entire volume of the glass melt.

Electrical Conductivity of Coal Slag

Abstract: The electrical conductivity of natural and synthetic slags (containing 14 to 36 wt% Fe) was measured from 1200 to 1700 K at O2 pressures from 1 to 2×10−6 atm. The conductivity is relatively high (∼10−2Ω−1 cm−1 at 1700 K) and stems from the transfer of electrons between Fe2+ and Fe3+ ions. Anomalies in the conductivity around 1600 K are the result of devitrification of the glass samples.

Crystallization of phosphate glasses

Abstract: A microscopical technique has been used to determine rates of crystallization (devitrification) of some lead phosphate and potash lead phosphate glasses. The devitrification rate is viscosity dependent, and compositional effects were resolved from viscosity effects by the use of isoviscous rate plots, which were obtained by plotting the half-time of crystallization against ΔT, where ΔT is the difference between the crystallization temperature and the transformation temperature of the glass.