William C. LaCourse

Laboratory preparation of highly pure As2Se3 glass

Abstract Arsenic selenide glass samples have been prepared using a combination of heat treatment and distillation techniques to remove impurities. Transmission spectra of the samples in the infrared region (2.5–20 μm) were measured. The spectra indicate that the majority of absorbing oxide species can be removed by a simple heat treatment. Chemical analysis shows that distilled samples contain less silicon impurity, indicating that Si is most likely incorporated during tube sealing procedures. Increased transmission for the purified samples in the 10–11 μm range shows the necessity of purification to obtain glasses with good transparency for CO 2 laser applications. The highest transmission values at 10.6 μm are greater than those suggested by simple theoretical relations. The high refractive index at this wavelength results in additional contributions to the transmitted intensity, most probably due to sample lensing effects arising from non-parallel sample faces or misalignment of the sample in the spectrophotometer beam.

The Strength of Glass

The search for new high strength materials has always been one of the more active areas in the materials sciences, and while glass is not normally catagorized with high strength metallic alloys and crystalline ceramics, it does have particular properties which will warrant, or necessitate, its use in many new applications.

Impurity effects on the structure and electrical properties of non-crystalline selenium

Abstract The structure and electrical properties of pure and impurity doped non-crystalline selenium have been investigated. Contrary to existing theories certain impurities (O, Cl, K) decrease the resistivity of the glass by up to 8 orders of magnitude with additions on the order of ppm. While effects of metallic impurities such as K may be explained on the basis of impurity induced structural changes, it appears that other impurities studied may introduce active donor or acceptor sites.

Development of bioabsorbable glass fibres

Calcium-iron phosphate glasses with an iron oxide content ranging from 5 wt.% to 22 wt.% were prepared to investigate the effect of iron oxide on the properties of the glass. It was found that the dissolution rate, the fibre strength and the glass transition temperature were strongly affected by iron oxide. The glass dissolution rate exhibited a 50-fold reduction while the fibre strength doubled when the iron oxide content was increased from 5 wt.% to 22 wt.%. The phosphate glass containing 22 wt.% of iron oxide had a dissolution rate of about 5 micrograms/(cm2 day). The fibres drawn from this glass also exhibited the highest tensile strength over 1000 MPa. A cortical bone plug method was used to assess the biocompatibility of the glasses with the hard and soft tissues. The tissues surrounding the samples showed no inflammation at 9 wk.

Experimental survey of the chemical durability of commercial soda-lime-silicate glasses

Abstract We present the results of durability experiments on commercial and experimental soda-lime-silica glasses. Glasses were subjected to a simple, short-duration alkali leaching experiment after which the K and Na concentrations in the leachate were measured. Our results show that Na is preferentially leached over K from the glass. A multiple variable linear regression was applied to the data to produce a predictive durability model based on glass composition. The model shows that, within the range of the tested compositions, only Al 2 O 3 significantly increases durability while Na 2 O and K 2 O decrease durability, with Na 2 O apparently having a greater effect. Our model, together with a previously published model for chemical strengthening, and composition/viscosity models can be used to formulate a durable glass optimized for rapid Na-K ion exchange strengthening. Specifically, our observations indicate that the replacement of K 2 O for Na 2 O in the glass will increase the exchange rate and increase durability.

Stress measurements in sol-gel films

Thin solid films of a wide variety of materials have received increased attention during the past decade. These films have been instrumental in the growth of numerous technologies. Until recently, “thin films” have primarily described layers of metallic or dielectric materials deposited onto substrates by evaporation, electron beam or ion beam techniques. Advances in sol-gel technology have extended film research to include “glassy” materials of either crystalline, or amorphous nature. Sol-gel films can be tailor-made to accommodate a diverse range of applications due primarily to flexibility in chemical make up which determines the respective films structure. One important characteristic of such films is their inherent residual stress. This inherent stress, and the stress the film introduces to the substrate as it is deposited, can result in a complex stress profile. While “thin” in the case of sol-gel films generally means <1 μm in thickness, large (10–100s of nm of retardance) inherent stress per unit thickness can severely limit a films performance and subsequent application. We describe our efforts to quantify the residual stress in silica-based sol-gel films as a function of several processing parameters.

Density and microhardness of As–Se glasses and glass fibers

Abstract The density and Vickers microhardness of bulk glasses and glass fibers in the As–Se system have been determined for up to 50% As. Arsenic selenide glasses were batched in an argon atmosphere using high purity arsenic and selenium to produce samples that contained between 5 and 50% As, the balance being Se. The density and hardness of both fibers and bulk glasses increase up to the stoichiometric As 2 Se 3 composition, with the hardness exhibiting a maximum at this composition, in accordance with the average coordination number (〈 r 〉) approach. The microhardness of aged fibers of all compositions is found to be higher than the corresponding bulk glass, indicating different structures. Both the density and microhardness of AsSe 4 are found to increase rapidly with time after drawing. Density and microhardness results are discussed in terms of quench induced stresses which result from the fiber drawing process, and stress relaxation in arsenic selenide glasses.

Variations in K+–Na+ ion exchange depth in commercial and experimental float glass compositions

Abstract We report the results of ion-exchange experiments conducted on 17 commercial soda–lime–silicate (SLS) float glass and 8 experimental SLS glass compositions. A significant variation in the depth of K + penetration with relatively small changes in composition was observed. The data were fit to a multiple regression model in which the major oxides are the independent variables and depth of K + is the dependent variable. The model indicates that increased depth of exchange (increased interdiffusion coefficient) correlates predominantly with increased K 2 O and/or Na 2 O content of the glass, with a decreased total alkaline earth content and with the ratio of CaO/MgO.

A defect model for the mixed alkali effect

The mixed alkali effect is postulated to be due to the existence of distinct sites for specific alkali ions. The sites begin to form in the liquid state and are frozen in as the glass cools below the strain point. Long range diffusion of the alkali ions requires formation of more mobile “mixed alkali defects” in which ions of one type exist and diffuse on sites of the opposite ion. The concentration of defects increases with temperature and with decreasing difference between the field strengths of ions. Defect formation at temperatures above the strain point causes the decreased viscosity of mixed alkali compositions.

Structure-hardness relation for high-temperature SO2-dealkalized float glass

Abstract Changes in the surface mechanical properties of float glass that had been heat treated in atmospheres containing SO2 gas were measured. An analysis combining dynamic microhardness and structure investigations indicates that a relation exists between the hardness and surface structure. This relation is used in establishing an understanding of the microhardness variations and the corresponding surface mechanical properties. The treatment parameters, temperature, time and treatment atmosphere conditions, are shown to have an effect on these properties. Their extent is suggested to depend on the formation of a thermal expansion coefficient difference between a dealkalized surface and the interior dealkalization properties and structure alterations. The changes in the mechanical properties are described which connect these effects. The structure-hardness relation of the air side differs from the tin side of float glass.