Reactions Between Silicon and Graphite Substrates at High Temperature: In Situ Observations

Graphite as a refractory material has found wide application in many process steps to produce photovoltaic silicon. In the current study, the melting behavior of silicon in contact with different grades of graphite was investigated. The infiltration of silicon into graphite was found to be highly dependent on the internal structure of the graphite substrate. It was confirmed that the heating history of silicon in contact with a graphite substrate strongly influences the melting behavior, which is likely attributed to a gas–solid reaction that forms SiC at less than the liquidus temperature of silicon and alters the surface properties of the graphite. It was also observed that a concentration of CO greater than 5 pct in the inlet gas leads to SiC formation on the surface of the silicon and severely hinders melting.     

Characterization of Elastic Properties in Porous Silicon Carbide Preforms Fabricated Using Polymer Waxes as Pore Formers

Thorough elastic analysis of porous silicon carbide preforms fabricated using two different polymer waxes as pore formers is carried out. Both the amount and the mixture ratio of the waxes were varied to fabricate preforms with different pore morphologies and porosities in the range of 27–67 vol%. Results show that both the longitudinal and the shear elastic constants decrease with increasing porosity. The rate of decrease in the elastic constants follows a model based on minimum solid area up to an intermediate porosity level. Uniaxial pressure applied prior to cold isostatic pressing and sintering significantly reduces the stiffness along the press direction. For the same initial powder mixture type, the elastic anisotropy of the preforms increases with an increase in the applied uniaxial pressure. The extent of anisotropy is strongly dependent on both the SiC/wax ratio as well as the mixture ratio between the two wax types. At low pore volume fractions a higher volume content of the smaller diameter wax and at high pore volume fractions a higher volume content of larger diameter wax lead to preforms with lowest anisotropy. A map is finally proposed to describe the dependence of the preform elastic properties on the type of initial powder mixture used.     

JOHANN FRIEDRICH EULER (1741–1800): MATHEMATICIAN AND CRYPTOLOGIST AT THE COURT OF THE DUTCH STADHOLDER WILLIAM V

During the latter part of the 18th century, some mathematicians started to turn their interest to cryptology. Their attitude differed in many ways from the approach of the professional crypt analysts, of their time, but their interest was far from being merely academical. Johann Priedrich Euler, mathematician and cryptologist at the Court of the Dutch Stadholder William V, showed a marked ability to put into practice some of the new principles and insights, forwarded in scholarly journals of the time.     

Multiple platinum printing

Abstract

In the development of platinum printing as an art, one of the most encouraging signs of its individuality and virility has been the latitude of the hand-coated platinum print.     

Synthesis and characterization of polyelectrolyte hydrogels with controlled swelling behaviour

Copolymerization of sulfopropyl methacrylate potassium salt (K‐SPMA) and 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) has been studied in the range 10–90% K‐SPMA in the feedstock. The reactivity ratios have been determined for K‐SPMA/AMPS copolymers. The copolymer compositions, utilized for determining the reactivity ratio, have been determined from nitrogen content. Crosslinked poly(AMPS) and K‐SPMA/AMPS copolymers were prepared in water in the presence of potassium persulfate as initiator and N,N‐methylene bisacrylamide (MBA) as tetrafunctional crosslinker. Irradiation of K‐SPMA and AMPS with an electron‐beam was carried out at 50 wt% aqueous solution with low pH and irradiation dose 40–120 kGy. The swelling behaviour of highly crosslinked K‐SPMA/AMPS copolymer polyelectrolyte gels in aqueous medium was studied in the presence of different types of salts. The crosslink density, the average molecular weight between the crosslinks and the dissociation constant (pK_a) of the crosslinked polymer were determined from stress–strain measurements. © 2001 Society of Chemical Industry     

Psychometric properties of the Posttraumatic Cognitions Inventory (PTCI) in a German sample of individuals with a history of trauma.

In this study, we examined the psychometric properties of the 33-item Posttraumatic Cognitions Inventory (Foa, Ehlers, Clark, Tolin, & Orsillo, 1999) in 213 individuals with accident-related trauma and 190 individuals with interpersonal trauma. Confirmatory factor analyses generally supported the scale's original three-factor structure—Negative Cognitions About Self (SELF), Negative Cognitions About World (WORLD), and Self-Blame (BLAME)—after four redundant items were excluded. However, in line with previous findings, results for BLAME remained inconclusive because the scale performed poorly with the individuals with accident-related trauma, whereas its fit with those with interpersonal trauma was acceptable. BLAME might possibly relate to trauma type. Our results indicate that the proposed 29-item version shows acceptable psychometric properties and that the role of BLAME should be further investigated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structural Basis for Intumescence – Part III – Thermal Degradation Study of Intumescent Polymers Containing Spirophosphorus Moiety in the Backbone

3,9-Dichloro-2,4,8,10-tetraoxo-3,9-disphosphaspiro-[5.5]-undecane-3,9-dioxide (spiro) was melt condensed with structurally different dihydric phenols to form poly aromatic spirophosphates. The thermal volatilization analysis showed eruptive release of gases above 300°C and the temperature region of release depends on the nature of the aromatic units incorporated in the polymer backbone. The thermal degradation in nitrogen atmosphere indicated the formation of phenol, substituted phenols, aromatics, alkyl and alkenyl substituted aromatics and condensed aromatics like azulenes, indanes and fluorenes. The source for the formation of these products is the spiropentadiene released from the spiro unit during degradation.