Some recent new applications of glass technology

Currently, at Corning Glass Works we are involved in several new, interesting applications of glass technology, which have the potential of impacting a wide diversity of applications. Three such areas presently under investigation will be reviewed, viz., molded optics, dental restorative materials, and inorganic paper. The common denominator relating these three examples is the fact that each relies on a unique glass composition as the starting material.

The first development is a special area of glass composition capable of being molded directly into optical elements without grinding and polishing. The second involves a new castable micaceous ceramic dental material derived from special glass compositions for application in several phases of restorative dentistry. Finally, the third development relates to a ceramic paper based upon a mica-like crystal, which is precipitated from glass.

The current status of the technology will be discussed for each in the context of the potential applications.     

X-ray diffraction from ideal mosaic crystals in external fields of certain types, part III: Changes in space symmetry and symmetry of diffraction pattern

The change in the space symmetry and the symmetry of the corresponding diffraction pattern occurring under the effect of uniform electric and magnetic fields applied to a crystal have been analyzed. The tables of point symmetry groups for various directions of applied magnetic fields are constructed. It is shown that in the absence of an external field, the diffraction patterns are described by nine possible point groups; in an electric field, they are described by eleven point groups; and in a magnetic field, by only five point groups. The theoretically calculated diffraction parameters are compared with the corresponding experimental values.     

Symmetry and topological analysis of the OD nenadkevichite-labuntsovite-zorite family

The symmetry and topology of the structures of nenadkevichite, labuntsovite, and zorite minerals are analyzed within the Dornberger-Schiff OD theory. The common “layers,” their symmetry, and the symmetry variants of their stacking determining their diversity and close structural characteristics are considered, which allowed us to relate these minerals to one family. According to the fundamental theorem of the OD theory, the number Z of possible combinations of aperiodic blocks inserted between the layers in zorite equals two simultaneously along two axes of the structure, which explains the structural disorder. Some hypothetical structures are also considered.     

Some geometric characteristics of four-dimensional crystallographic point symmetry groups and their subgroups

Using three-dimensional point and tablet antisymmetry groups and also rosette and zero-dimensional groups of generalized antisymmetry that model all possible subgroups of four-dimensional crystallographic point groups, we determined the number of various symmetry groups forming the four-dimensional crystallographic classes for each category of such subgroups. These results allowed us to establish (without the use of the complete catalogue of the groups themselves) that 168 four-dimensional crystallographic classes preserve not only the point but also some other geometrical objects. The remaining 103 classes preserve only one invariant point of the four-dimensional Euclidean space.     

X-ray diffraction analysis of modulated crystals: Review

The state of the art of X-ray diffraction analysis of modulated crystals is reviewed. The review begins with a brief historical overview followed by the consideration of the main concepts and notations used in this field. Then, methods of structural analysis of modulated crystals are considered with emphasis on recent achievements. The most interesting objects are listed, and the directions of investigation are outlined. Examples of analysis of both individual structures and families of modulated and incommensurate composite structures are given in terms of superspace symmetry.     

Some results of microscopic and X-ray investigations of calcium carbide

The structure of calcium carbide is investigated using thin sections and ground sections. Depending on chemical and other factors, calcium carbide occurs in three types of structure, which are interpreted as conversion products resulting from a high-temperature structure. The pavement-like structure containing CaC₂-I is present in industrial carbide with a low content of nitrogen. With increasing fraction of lignite high-temperature coke used for carbon supply as a substitute for coal coke in the production of carbide, the particle size decreases, and the micro hardness increases. The interlocked structure with CaC₂-II and higher contents of nitrogen, which has been detected in carbide produced in the laboratory, is extremely dense. No grain sizes can be given. This kind of carbide produced in the laboratory has a lower micro hardness than industrial carbide. The mixed crystal structure is typical of carbide with a high content of sulphur. CaC₂—CaS-I is present as a phase. In all three types, the respective carbide phases have a marked lamellar structure. No typical shapes of crystals can be detected. In consequence of poor crystal formation, the information obtained with a microscope about the phases contained in the material investigated is complemented by X-ray diffraction methods.     

X-ray structures of fifty year old crystals of cholesterol iodide forms I and II

  The molecular framework of steroids was firmly established from the successful X-ray analysis of cholesteryl iodide crystals over fifty years ago. At the time, this was a triumph for the rapidly developing technique of X-ray crystallography. We describe here new analyses of cholesteryl iodide using crystals of forms I and II^(A) which are at least 50 years old. Comparison of these two structures reveals subtle differences in the geometry of the steroid skeleton, the attached side chain and the covalently bound iodine. The crystals of both forms occur in the same monoclinic space group, P2₁, with similar but nevertheless different unit cells, particularly in the b-axis length. As a consequence, there are subtle differences in the packing mechanisms of the two polymorphs. The two forms were originally classified by Bernal and Crowfoot, on the basis of their studies of more than 60 crystals of sterols and sterol derivatives, as “normal, type A - the common form” (corresponding to form II) and “reverse or type B” (corresponding to form I), respectively. Those crystals of form I which have survived for almost 55 years are poor X-ray diffractors at room temperature and have been analysed at liquid N temperature, diffracting well under these conditions. Form II crystals diffract well at room temperature and for this reason the crystals were not cooled. The main differences in geometry occur in the side-chain which is disordered in the room temperature form II crystals, whilst the individual ring conformations in the steroid skeleton are similar, ring A being a strained chair, ring B a 7α/8β half-chair, ring C a symmetrical chair and D a 13β/14α half-chair. (A) Originally denoted Forms B and A respectively. See Additional Note (A) for explanation.

Nontrivial role of the resolution function in the formation of double-crystal X-ray rocking curves

A theoretical analysis of the shape of the resolution function of an X-ray diffractometer in the double-crystal nondispersive scheme for measuring rocking curves has been performed. It is shown that this function, along with the strong narrow central line (corresponding to the characteristic line to which the collimator crystal and slits in the experimental scheme are tuned) always contains an additional weak satellite, corresponding to the neighboring characteristic line. This feature manifests itself in experimental curves as an additional pseudopeak, whose intensity is comparable with the corresponding diffraction scattering intensity from a sample in the fundamental characteristic line, and whose shape and exact position are set by the resolution function in a specific experimental scheme. It is shown that the exact allowance for the angular and spectral distribution of incident radiation in the double-crystal scheme makes it possible to precisely determine the parameters of the structures studied.     

Some new bis-1,4 pentazadienes: synthesis and photochemical properties

Abstract

The synthesis of some new bis-1,4-pentazadienes and their photolytic decomposition are described. The uniformity of photolysis reactions is studied by the AD-diagram method. It was found that the photolysis on the later stages does not proceed by the first-order reaction kinetics.     

Syntheses and X-ray structures of new phenoxy imino compounds

Four new phenoxy imino compounds were synthesized, and the solid-state structures of 1–3 were determined by single-crystal X-ray diffraction study, giving crystallographic data as follows. 2-Acetyl-6-[1-(2,6-diisopropylphenylimino)ethyl]-4-methylphenol (1): a = 13.5893(5) Å, b = 10.5781(4) Å, c = 15.6778(4) Å, = 113.1804(18), P2₁/c. 2,6-[1-(2,6-Diisopropylphenylimino)ethyl]-4-methylphenol (2): a = 12.1909(5) Å, b = 16.3324(6) Å, c = 15.9456(7) Å, = 96.990(2), P2₁/c. 2-Acetyl-6-[1-(4-bromine-2,6-dimethylphenylimino)ethyl]-4-methylphenol (3): a = 7.5337(4) Å, b = 10.0457(5) Å, c = 12.6163(4) Å, = 90.139(3), = 104.003(3), = 106.485(2), P–1. Their molecular structures show that the 2,6-substituted phenyl ring is located approximately orthogonal to the hydroxyphenyl ring with the dihedral angle varying from 85.2 to 101.4.for X-ray Diffraction     

Study of the diffraction contrast of dislocations in X-ray topo-tomography: A computer simulation and image analysis

Oblique X-ray diffraction images of individual dislocations in the symmetric Laue geometry from a plane-parallel silicon plate have been calculated based on the Takagi-Taupin equations and analyzed. Computer simulation is used to develop a general mathematical model of the formation of oblique images which correspond to sample rotation around the diffraction vector h in X-ray topo-tomography. The results of numerical calculations and analysis of different oblique images of straight-line dislocations, where the dislocation line vector τ lies in a plane parallel to input surface of {111}Si plate with a diffraction vector h 〈220〉, are presented.     

Algorithms,software, and examples of pseudotranslational sublattice analysis for crystal structures

Software for analyzing pseudotranslational sublattices (PTSs) in crystal structures is described. This software makes it possible to enumerate triads of reflections, sort them out with respect to different characteristics, calculate linear and angular subcell parameters, and express the sublattice vectors in terms of the initial lattice vectors. The solution to the most widespread problems is illustrated by the example of the well-known [Ru(NH₃)₆]Cl₃ and [CuL](NO₃)(ReO₄) crystal structures (L is 4,6,6-trimethyl-1,9-diamino-3,7-diazanon-3-en) and the structure of mineral iltisite, which is still unknown. In all cases we observed a tendency of crystal structures to have a higher symmetry, which was noted by Academician Belov in his time. “A material that in fact crystallizes in a lower system is nevertheless rather close (in its crystalline form) to numerical relations characteristic of a higher system.” (Belov [1, p. 227])     

Synthesis and powder X-ray diffraction of new Schiff-base liquid crystal

Liquid crystals (LCs) are soft materials that combine the fluidity of disordered liquids and the long-range orientational or positional order of crystalline solids, along one or two directions of space. A search for better stationary phases, including highly selective ones, is an important trend in chromatography development. Among the stationary phases under investigation are LC stationary phases that have been recently generated much interest. A variety of isomeric molecules were separated with high accuracy. Successfully, X-ray scattering is widely used to investigate and characterise the microscopic structure of most LCs. In this paper, a new liquid crystalline material that can be used potentially as stationary phase in gas chromatography was synthesised and characterised by means of nuclear magnetic resonance (NMR), infrared (IR) spectra, elemental analysis and X-ray diffraction.     

State-of-the-art and problems of X-ray diffraction analysis of biomacromolecules

The state-of-the-art of X-ray diffraction studies of biomacromolecules is briefly characterized, and the challenge imposed by science is discussed. These studies are characterized by a wide scope and extensive use. This field of science is of great interest and is developed in many countries. The main purpose is to solve practical problems in medicine consisting in the design of drugs against various diseases. X-ray diffraction analysis of enzymes brought the pharmaceutical industry to a new level, thus allowing the rational design of drugs against formerly untreatable diseases. Modern X-ray diffraction studies of biomacromolecules laid the basis for a new science called structural biology. This method allows one to solve fundamental problems of physical chemistry for a new state of matter existing in living systems. Here, science poses numerous problems in analysis of X-ray diffraction data on biological macromolecules. Many of theses problems are in their infancy.     

Comparison of the data of X-ray microtomography and fluorescence analysis in the study of bone-tissue structure

The possibility of localizing clusters of heavy atoms is substantiated by comparing the data of X-ray microtomography at different wavelengths, scanning electron microscopy, and X-ray fluorescence analysis. The proximal tail vertebrae of Turner??s thick-toed gecko (Chondrodactylus turneri) have been investigated for the first time by both histological and physical methods, including X-ray microtomography at different wavelengths and elemental analysis. This complex methodology of study made it possible to reveal the regions of accumulation of heavy elements in the aforementioned bones of Turner??s thick-toed gecko.     

Synthesis and X-ray structure analysis of 2-acetylamino-benzoic acid

The title compound crystallizes in the orthorhombic space group Fdd2 with unit cell parameters a = 10.848(1) Å, b = 30.264(1) Å and c = 10.577(1) Å, V = 3472.47(2) ų, and Z = 4. The final reliability index is 0.030 for 700 observed reflections. Nitrogen of the amide group and carbon atom of the acid group deviate significantly below and above the plane of the phenyl ring. The crystal cohesion is accentuated by N—HO and O—HO hydrogen bonds.     

X-ray diffraction phase analysis of the crystalline phase of polytetrafluoroethylene

Samples of ultradispersed polytetrafluoroethylene, which were prepared with the use of different technological approaches, were studied by X-ray diffraction. The samples were found to belong to the monoclinic system. For some samples, basal reflections, which can be related to paraffins, were found for the first time. This indicates that polymer chains can form yet another type of monoclinic structure.     

Crystal structure of a new Mn, Na-ordered analogue of eudialyte with the symmetry R3

The crystal structure of a new representative of the eudialyte family was studied. This mineral is characterized by a low calcium content and by ordering the elements that isomorphically replace calcium, which lowers the symmetry from R3m to R3. The structure of the sample under study consists of the six-membered rings with two octahedra of substantially different volumes, one occupied mainly by manganese and the other, mainly by sodium and characterized by the average distances of 2.22 and 2.45 Å, respectively. The formation of such octahedra is the most characteristic structural feature of the third low-symmetry mineral of the eudialyte family.