Lucalox

Hollomon s ethos, combined with his ferocious energy and determination, and his sustained determination to recruit only the best researchers to join his group, over the next 15 years led to a sequence of remarkable innovations related to materials, including man-made diamond, high-quality thermal insulation, a vacuum circuit-breaker, products based on etched particle tracks in irradiated solids, polycarbonate plastic and, particularly, the Lucalox alumina envelope for a metal-vapour lamp. (Of course many managers besides Hollomon were involved.) A brilliant, detailed account of these innovations and the arrangements that made them possible was later written by Guy Suits and his successor as director, Arthur Bueche (Suits and Bueche 1967). Some of these specific episodes will feature later in this book, but it helps to reinforce the points made here about Hollomon s coneeption of broad research on materials if I point out that the invention of translucent alumina tubes for lamps was... 

The Lucalox story is a prime specimen of a valuable practical application of a parepistemic study begun for curiosity s sake. 

Burke, J.E. (1996) Lucalox Alumina The Ceramic That Revolutionized Outdoor Lighting, MRS Bull. 21/6, 61. 

Fig. 4. High-pressure/high-temperature cavity for in-situ EPR measurements (1) pressure vessel body (2) pressure vessel lid (3) nut (4) thrust washer (5) cavity top (6) cavity (7) high-pressure gas fitting (8) PTFE tuning wedge (9) tapered waveguide (10) water jacket (11) Lucalox plug (12) heater lead feedthrough (13) modulation coil feedthrough (14) thermocouple feedthrough and (15) heater assembly. Reprinted from Reference 44).

P-ALUMINA y-ALUMINA ALUMINUM OXIDE o-ALUMINUM OXIDE P-ALUMNUM OXIDE y-ALUAHNUM OXIDE ALUMINUM SESQUIOXIDE ALUMTE ALUNDUM BROCKMANN, ALUMINUM OXIDE CAB-O-GRIP COMPALOX DIALUMINUM TRIOXIDE DISPAL DOTMENT 324 FASERTON G 2 (OXIDE) KHP 2 LUCALOX MICROGRIT WCA... 

FIGURE 17.18 (a) Cavity-size distribution as a function of creep strain in alumina without a glassy phase (Lucalox). (b) Cavity-size distribution as a function of creep strain in alumina with a glassy phase (AD99). 

Coble, Robert (Bob) L. (1928-1992) was best known for showing that small additions of MgO made it possible to form polycrystalline translucent alumina (Lucalox). This occurred while he was at the General Electric Research Laboratory in Schenectady, New York. He joined MIT in 1960. [More about this appears in the special alumina issue of J. Am. Ceram. Soc. 77(2), 1994.] He is also known for Coble creep. 

Coble, R.L. (Bob) (1928-1992) developed Lucalox , a transparent polycrystalline alumina (AI2O3) ceramic, at the GE laboratory in Schenectady in 1961 GE is still a major supplier of lamp envelopes but Silvania, Osram and others also manufacture the envelopes now. 

Fig. 6.76 Comparison of the predicted (-) and experimentally observed conditions for zero cavity growth (white square) Lucalox, 1600 °C (black square) AD99, 1300 °C, and for cavity growth (white circle) Lucalox, 1600 °C (black circle) AD99,...

When steps are taken during fabrication to substantially reduce the amount of residual porosity, the ceramic undergoes a transformation from opaque to translucent or even to nearly transparent. Such a transition can be observed in special polycrystalline alumina ceramics. Normally, sintered alumina bodies are observed to be opaque to somewhat translucent. However, an alumina material is produced under the trade name of Lucalox (General Electric Co.) in which there is low residual porosity. The ceramic is almost transparent to light and is used in the production of lamp envelopes for exterior lighting. 

Sheaths for high-voltage sodium vapor lamps (Lucalox )... 

The second material used was Lucalox alumina from General Electric Corporation. The material was purchased as disks - in, thick by in. diameter. One face was polished for thermal etching. 

The third material used was Triangle RR alumina from Morganite, Inc. This is the material used in the previously reported work ( ). It was purchased as disks in. thick by about 1 in. diameter. Pieces in. in. X in. were cut from the disks for use as samples. The Lucalox and the Morganite aluminas were sintered materials with moderately fine grain size. The Linde and Lucalox were polished to smooth, pit-free surfaces using a diamond abrasive. Because of considerable porosity, the best polished surfaces of Morganite still contained numerous pits and holes. 

Linde alumina Lucalox alumina Morganite alumina... 

It can be seen that the groove widths at a given temperature are narrower for the Linde and Lucalox materials than for the Morganite alumina. The data for the three materials at 1600°C are compared in Fig. 2. At lower temperatures the difference becomes greater. 

For the Linde alumina the point at 1400°C was not included in the above line, though it is evident that it falls close to the calculated lines. The values of Dq and obtained from the least squares fits are given in Table II. The Morganite alumina had an activation energy for surface diffusion of 75 kcal/mole, while that for the Lucalox and Linde aluminas is 50-60 kcal/mole larger. 

The most notable effect that this work demonstrates is that there is a marked difference in the thermal grooving behavior of different aluminas under similar experimental conditions. Hence we must look for differences in the materials to be able to understand the differences in behavior. The composition of the materials is the obvious place to look for differences, and here we immediately run into problems of interpretation. The total impurity content for the two sintered materials are about equal and about twice that of the Linde alumina. Hence the total impurity content does not rationalize the fact that the Linde and Lucalox behave similarly while the Morganite grooves more rapidly. We must then look for differences in the particular impurities present in order to rationalize the observed behavior. 

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