Chemical structure of a protostellar core: B68
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Structural and chemical complexity of minerals: An update
The complexities of chemical composition and crystal structure are fundamental characteristics of minerals that have high relevance to the understanding of their stability, occurrence and evolution. This review summarises recent developments in the field of mineral complexity and outlines possible directions for its future elaboration. The database of structural and chemical complexity parameters of minerals is updated by H-correction of structures with unknown H positions and the inclusion of new data. The revised average complexity values (arithmetic means) for all minerals are 3.54(2) bits/atom and 345(10) bits/cell (based upon 4443 structure reports). The distributions of atomic information amounts, chemIG and strIG, versus the number of mineral species fit the normal modes, whereas the distributions of total complexities, chemIG,total and strIG,total, along with numbers of atoms per formula and per unit cell are log normal. The three most complex mineral species known today are ewingite, morrisonite and ilmajokite, all either discovered or structurally characterised within the last five years. The most important complexity-generating mechanisms in minerals are: (1) the presence of isolated large clusters; (2) the presence of large clusters linked together to form three-dimensional frameworks; (3) formation of complex three-dimensional modular frameworks; (4) formation of complex modular layers; (5) high hydration state in salts with complex heteropolyhedral units; and (6) formation of ordered superstructures of relatively simple structure types. The relations between symmetry and complexity are considered. The analysis of temporal dynamics of mineralogical discoveries since 1875 with the step of 25 years show the increasing chemical and structural complexities of human knowledge of the mineral kingdom in the history of mineralogy. In the Earth’s history, both diversity and complexity of minerals experience dramatic increases associated with the formation of Earth’s continental crust, initiation of plate tectonics and the Great Oxidation event.
complexity↗
JUPITER- CHEMICAL COMPOSITION, STRUCTURE AND ORIGIN OF A GIANT PLANET
Chemical composition and structure of jupiter as test case of origin of giant planets
JUPITER /PLANET/↗
Electrical, structural, and chemical characterization of silicon sheet materials
Progress on the electrical, structural, and chemical characterization of silicon sheet material is reported. In the study on high temperature deformation of dendritic web ribbon, experimental creep tests were performed in four point bending under constant load conditions, and unusual behavior was observed. Also, measurements of oxygen content in web ribbon were made. Two conclusions reached are creep behavior of web which is very different from any seen for single crystal silicon and oxygen level in web silicon which is near the saturation level at the melting point of silicon.
Ast, D. G.↗
Analysis of plasma-nitrided steels
The analysis of plasma nitrided steels can be divided to two main categories - structural and chemical. Structural analysis can provide information not only on the hardening mechanisms but also on the fundamental processes involved. Chemical analysis can be used to study the kinetics for the nitriding process and its mechanisms. In this paper preliminary results obtained by several techniques of both categories are presented and the applicability of those techniques to the analysis of plasma-nitrided steels is discussed.
Salik, J.↗
Analysis of plasma nitrided steels
The analysis of plasma nitrided steels can be divided to two main categories - structural and chemical. Structural analysis can provide information not only on the hardening mechanisms but also on the fundamental processes involved. Chemical analysis can be used to study the kinetics for the nitriding process and its mechanisms. In this paper preliminary results obtained by several techniques of both categories are presented and the applicability of those techniques to the analysis of plasma-nitrided steels is discussed.
Salik, J.↗
X-ray diffraction studies of model compounds of thermoplastic polyimides
Several model compounds which represent aspects of the chemical structure of the Langley Research Center thermoplastic (LARC-TPI) have been synthesized for comparison studies using wide angle X-ray scattering (WAXS) as the discriminatory tool. The model compounds included N-phenylphthalimide, 3,3',4,4'-benzophenonetetracarboxylic diphthalimide, and N,N'-diphenyl-3,3',4,4'-benzophenonetetracarboxylic diphthalimide. X-ray diffraction studies of appropriate model compounds can yield information to aid in the understanding of polymeric crystallographic structure. Crystallinity and physical property changes can thus be induced into materials having complicated structures by chemical and thermal processes.
Wakelyn, N. T.↗
Relation between microhardness and microbrittleness of refractory compounds with their electron structure
Chemical and X-ray phase determinations of relationship of microhardness and microbrittleness of powdered refractory compounds with electron structure
REFRACTORY METAL↗
Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit
A predictive tool was developed to estimate the low Earth orbit (LEO) atomic oxygen erosion yield of polymers based on the results of the Polymer Erosion and Contamination Experiment (PEACE) Polymers experiment flown as part of the Materials International Space Station Experiment 2 (MISSE 2). The MISSE 2 PEACE experiment accurately measured the erosion yield of a wide variety of polymers and pyrolytic graphite. The 40 different materials tested were selected specifically to represent a variety of polymers used in space as well as a wide variety of polymer chemical structures. The resulting erosion yield data was used to develop a predictive tool which utilizes chemical structure and physical properties of polymers that can be measured in ground laboratory testing to predict the in-space atomic oxygen erosion yield of a polymer. The properties include chemical structure, bonding information, density and ash content. The resulting predictive tool has a correlation coefficient of 0.914 when compared with actual MISSE 2 space data for 38 polymers and pyrolytic graphite. The intent of the predictive tool is to be able to make estimates of atomic oxygen erosion yields for new polymers without requiring expensive and time consumptive in-space testing.
Bank, Bruce A.↗
Crystal Structure and Chemical Composition of a Presolar Silicate from the Queen Elizabeth Range 99177 Meteorite
Mineral characterization of presolar silicate grains, the most abundant stardust phase, has provided valuable information about the formation conditions in circumstellar environments and in super-nova (SN) outflows. Spectroscopic observations of dust around evolved stars suggest a majority of amor-phous, Mg-rich olivine grains, but crystalline silicates, most of which are pyroxene, have also been observed [1]. The chemical compositions of hundreds of presolar silicates have been determined by Auger spectroscopy and reveal high Fe contents and nonstoichiometric compositions intermediate to olivine and pyroxene [2-6]. The unexpectedly high Fe contents can partly be attributed to secondary alteration on the meteorite parent bodies, as some grains have Fe isotopic anomalies from their parent stellar source [7]. Only about 35 presolar silicates have been studied for their mineral structures and chemical compositions by transmission electron microscopy (TEM). These grains display a wide range of compositions and structures, including crystalline forsterite, crystalline pyroxene, nanocrystalline grains, and a majority of amorphous nonstoichiometric grains. Most of these grains were identified in the primitive Acfer 094 meteorite. Presolar silicates from this meteorite show a wide range of Fe-contents, suggestive of secondary processing on the meteorite parent body. The CR chondrite QUE 99177 has not suffered as much alteration [8] and displays the highest presolar silicate abundance to date among carbonaceous chondrites [3, 6]. However, no mineralogical studies of presolar silicates from this meteorite have been performed. Here we examine the mineralogy of a presolar silicate from QUE 99177.
Nguyen, A. N.↗
Polyimidazoles via aromatic nucleophilic displacement
Polyimidazoles (PI) are prepared by the aromatic nucleophilic displacement reaction of di(hydroxyphenyl) imidazole monomers with activated aromatic dihalides or activated aromatic dinitro compounds. The reactions are carried out in polar aprotic solvents such as N,N-dimethyl acetamide, sulfolane, N-methylpyrrolidinone, dimethylsulfoxide, or diphenylsulfone using alkali metal bases such as potassium carbonate at elevated temperatures under nitrogen. The di(hydroxyphenyl) imidazole monomers are prepared by reacting an aromatic aldehyde with a dimethoxybenzil or by reacting an aromatic dialdehyde with a methoxybenzil in the presence of ammonium acetate. The di(methoxyphenyl) imidazole is subsequently treated with aqueous hydrobromic acid to give the di(hydroxphenyl) imidazole monomer. This synthetic route has provided high molecular weight PI of new chemical structure, is economically and synthetically more favorable than other routes, and allows for facile chemical structure variation due to the availability of a large variety of activated aromatic dihalides and dinitro compounds.
Connell, John W.↗
Poly(1,3,4-oxadiazoles) via aromatic nucleophilic displacement
Poly(1,3,4-oxadiazoles) (POX) are prepared by the aromatic nucleophilic displacement reaction of di(hydroxyphenyl) 1,3,4-oxadiazole monomers with activated aromatic dihalides or activated aromatic dinitro compounds. The polymerizations are carried out in polar aprotic solvents such as sulfolane or diphenylsulfone using alkali metal bases such as potassium carbonate at elevated temperatures under nitrogen. The di(hydroxyphenyl) 1,3,4-oxadiazole monomers are synthesized by reacting 4-hydroxybenzoic hydrazide with phenyl 4-hydrobenzoate in the melt and also by reacting aromatic dihydrazides with two moles of phenyl 4-hydroxybenzoate in the melt. This synthetic route has provided high molecular weight POX of new chemical structure, is economically and synthetically more favorable than other routes, and allows for facile chemical structure variation due to the large variety of activated aromatic dihalides which are available.
Connell, John W.↗
Di(hydroxyphenyl)- 1,2,4-triazole monomers
The di(hydroxyphenyl)- 1,2,4-triazole monomers were first synthesized by reacting bis (4-hydroxyphenyl) hydrazide with aniline hydrochloride at 250 C in the melt and also by reacting 1,3 or 1,4-bis- (4-hydroxyphenyl)- phenylene- dihydrazide with 2 moles of aniline hydrochloride in the melt. Purification of the di(hydroxyphenyl)- 1,2,4-triazole monomers was accomplished by recrystallization. Poly (1,2,4-triazoles) (PT) were prepared by the aromatic nucleophilic displacement reaction of di(hydroxyphenyl)- 1,2,4-triazole monomers with activated aromatic dihalides or activated aromatic dinitro compounds. The reactions were carried out in polar aprotic solvents such as sulfolane or diphenylsulfone using alkali metal bases such as potassium carbonate at elevated temperatures under nitrogen. This synthetic route has provided high molecular weight PT of new chemical structure, is economically and synthetically more favorable than other routes, and allows for facile chemical structure variation due to the availability of a large variety of activated aromatic dihalides.
Connell, John W.↗
Polyimidazoles via aromatic nucleophilic displacement
Polyimidazoles (Pl) are prepared by the aromatic nucleophilic displacement reaction of di(hydroxyphenyl)imidazole monomers with activated aromatic dihalides or activated aromatic dinitro compounds. The reactions are carried out in polar aprotic solvents such as N,N-dimethylacetamide, sulfolane, N-methylpyrroldinone, dimethylsulfoxide, or diphenylsulfone using alkali metal bases such as potassium carbonate at elevated temperature under nitrogen. The di(hydroxyphenyl)imidazole monomers are prepared by reacting an aromatic aldehyde with a dimethoxybenzil or by reacting an aromatic dialdehyde with a methoxybenzil in the presence of ammonium acetate. The di(methoxyphenyl)imidazole is subsequently treated with aqueous hydrobromic acid to give the di(hydroxyphenyl)imidazole monomer. This synthetic route has provided high molecular weight Pl of new chemical structure, is economically and synthetically more favorable than other routes, and allows for facile chemical structure variation due to the availability of a large variety of activated aromatic dihalides and dinitro compounds.
Connell, John W.↗
New Synthesis Of Poly(1,3,4-Oxadiazoles)
Synthesis via aromatic nucleophilic displacement yields new high-molecular-weight polymers. Polymers exhibited good mechanical and thermal properties. Synthetic route provided high-molecular-weight POX of new chemical structure, potentially more economical. Availability of large variety of activated aromatic dihalides, facilitates variation of chemical structures. Exhibit properties making them useful as films. Also useful in coatings, adhesives, moldings, and composites.
Connell, John W.↗
Highlights of 10th plasma chemistry meeting
The chemical structure is given of a film formed by plasma polymerization from pyridine monomers. The film has a hydrophilic chemical structure, its molecular weight is 900, and the molecular system is C55H50N10O3. The electrical characteristics of a plasma polymerized film are described. The film has good insulating properties and was successfully applied as video disc coating. Etching resistance properties make it possible to use the film as a resist in etching. The characteristics of plasma polymer formed from monomers containing tetramethyltin are discussed. The polymer is in film form, displays good adhesiveness, is similar to UV film UV 35 in light absorption and is highly insulating.
Kitamura, K.↗
New developments in thermally stable polymers
Advances in high-temperature polymers since 1985 are discussed with the emphasis on the chemistry. High-temperature polymers refer to materials that exhibit glass-transition temperatures greater than 200 C and have the chemical structure expected to provide high thermooxidative stability. Specific polymers or series of polymers were selected to show how the chemical structure influences certain properties. Poly(arylene ethers) and polyimides are the two principal families of polymers discussed. Recent work on poly(arylene ethers) has concentrated on incorporating heterocyclic units within the polymer backbone. Recent polyimide work has centered on the synthesis of new polymers from novel monomers, several containing the trifluoromethyl group strategically located on the molecule. Various members in each of these polymer families display a unique combination of properties, heretofore unattainable. Other families of polymers are also briefly discussed with a polymer from an AB maleimidobenzocyclobutene exhibiting an especially attractive combination of properties.
Hergenrother, Paul M.↗
Poly(1,2,4-Triazoles) Via Aromatic Nucleophilic Displacement
Synthesis involves nucleophilic displacement of monomers with activated aromatic dihalides. Polymers exhibited desirable physical and thermal properties. Synthesis of polymers provides high-molecular-weight PT of new chemical structures, potentially more economically favorable than other routes, and, because of availability of large variety of activated aromatic dihalides, provides for facile variation of chemical structure. Useful for producing films, moldings, adhesives, and composites.
Connell, John W.↗