Fabrication and properties of highly transparent Tm3Al5O12 (TmAG) ceramics

Highly transparent Tm₃Al₅O₁₂ (TmAG) ceramics were fabricated by solid-state reaction and vacuum sintering. Densification, microstructure evolution, mechanical, thermal, and optical properties of the TmAG ceramics were investigated. Fully dense TmAG ceramic with average grain size of 15 μm was obtained by sintering at 1780 °C for 20 h. The in-line transmittance was 80.5% at 2000 nm. The absorption coefficients at 682 nm and 785 nm were 8.03 cm⁻¹ and 8.33 cm⁻¹, respectively. The Vickers hardness, the Young modulus, the bending strength, and the fracture toughness values were 15.14 GPa, 343 GPa, 230 MPa, and 2.35 MPa m^1/2, respectively. The thermal conductivity at room temperature was 3.3 W/m K and the average linear thermal expansion coefficient from 20 °C to 1000 °C was 8.915 × 10⁻⁶ K.     

Bending and compressive behaviours of a new cement composite

The Laboratoire Central des Ponts et Chaussées (LCPC) has recently developed and patented a new cement composite, the CEMTEC_multiscale, which is stress hardening in tension and has a very high uniaxial tensile strength, more than 20 MPa. This paper is about the determination of the compressive and bending behaviors of the CEMTEC_multiscale used in the frame of ribbed slabs.The principal results obtained are the following:

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the characteristic modulus of rupture is equal to 42 MPa for the “slab” function;

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the characteristic modulus of rupture is equal to 48 MPa for the “rib” function;

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the ultimate tensile strain is around 5 10⁻³;

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the characteristic strength and ultimate strain in compression are equal to 205 MPa and 4 10⁻³, respectively; and

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the Young modulus is equal to 55 GPa and the Poisson coefficient is equal to .21.

     

Crosslinking of ultra-high strength polyethylene fibers by means of γ-radiation

Summary Ultra-high strength polyethylene fibers, with a tensile strength at break varying from 1.6 up to 3.5 GPa, were irradiated, at room temperature under vacuum by means of ⁶⁰Co -radiation. Sol-gel analysis showed a ratio of crosslinking to main-chain scissioning of about 1. The tensile strength at break decreased upon irradiation. The decrease of tensile strength at break depended on initial fiber strength and could be attributed to main-chain scissioning. It was concluded that stressed chains break preferentially upon irradiation. Fiber networks exhibited a deformation ratio of 16 during stress-strain measurements.     

The model of polymer orientation strengthening and production of ultra-high strength fibers

Summary A model of junction network that is deformed upon drawing has been used to calculate maximum attainable draw ratios (X) and corresponding values of tensile strength (F) for different conditions of polymer film and fiber forming. Experimental data for melt-spun samples of polyethylene (PE), polycaproamide and polyoxymethylene and solution-cast films of polyvinylalcohol appeared to be in good agreement with calculated values. Considered also are methods for the increase of X and F due to polymer molecular weight enhancement in samples forming from poor solvent with subsequent orientation drawing under optimal conditions. Values of X=130–230 and those of F = 7 GPa with a Young's modulus E=144 and sonic modulus E_s=200 GPa, approximating theoretical, have been obtained for monofilaments of PE with m.w. 2.10⁶.     

Properties of massive Ag/YBCO contacts obtained by explosive compaction with subsequent heat treatment

Axisymmetric explosive compaction with a shock-wave pressure of 2 GPa was used to obtain low-resistance Ag/YBCO (YBa₂Cu₃O_7–x) contacts. Measurements were made of compressive strength at 300 K and microhardness and electrical resistivity within the temperature interval 300–77 K for annealed specimens of Ag/YBCO. Ultimate compressive strength was 0.12 GPa. The microhardness of the ceramic near the Ag/YBCO interface was 3.1 GPa. Contact resistance at the temperature of liquid nitrogen <1·10^–8 ·cm² (contact area 1.0 cm²).IGiL, Siberian Branch of the Russian Academy of Sciences, 630090, Novosibirsk. Translated from Fizika Goreniya i Vzryva, No. 1, pp. 130–134, January–February, 1995.     

Ultradrawing of amorphous polymers by coextrusion illustrated with atactic polystyrene

Films of pure and high-impact atactic polystyrene were prepared by the recently developed technique of solid-state coextrusion. The films were produced at extrusion rates ≥4 cm/min at 126°C with a maximum extrusion draw ratio (EDR) of 11.6. These ultradrawn films are fibrous, have a high birefringence of ?2.24 × 10^?2, and exhibit a 72% elastic recovery. The material has a tensile modulus of ～4–5 GPa and a tensile strength to break of 85 MPa. Thermal analysis suggests a constant T_g.     

Densification,Mass Loss,and Mechanical Properties of Low-Temperature Pressureless-Sintered Si3N4 with LiYO2 Additive: The Effects of Additive Content and Annealing

The effects of annealing on the residual Li content, microstructure, and mechanical properties of pressureless-sintered LiYO₂–Si₃N₄ were investigated. The bending strength and fracture toughness of the as-fabricated specimens were fair (∼640 MPa, ), in spite of the sintering at a low temperature (1600°C). The strength, Young's modulus, and hardness were improved up to 697 MPa, 284 GPa, and 13.9 GPa, respectively, by annealing treatments. Residual Li could be reduced to 0.008 wt% by annealing at 1650°C in Ar. Si₃N₄ could be sintered at a low temperature to give materials with a relatively low elastic modulus but reasonable strength values.     

Instrumented impact testing of glass reinforced polypropylene

The impact response of a glass fiber reinforced polypropylene was studied in a 3-point drop-weight impact test between ?15 and 85°C and at a constant impact velocity of 2.2 m/s (5 mph). The response is a combination of tension and shear and can be expressed in terms of an apparent modulus, E_A: 1 . Where E₁₁ is the tensile modulus, G₁₂: shear modulus, d: specimen thickness, and l: specimen length. For a 40 weight-percent glass reinforced polypropylene, E₁₁ was found to have a room temperature value of 5.8 GPa, and shear modulus of 0.43 GPa. Both decreased with temperature increase, with the shear modulus showing greater sensitivity to a temperature change. The fracture initiation and propagation energies were relatively independent of temperature. The fracture initiation energy per unit deformed volume was of the order of 1 MJ/m³. The total fracture energy was found to be sensitive to l/d: about 7 MJ/m³ at l/d of 5.3 and about 1.7 MJ/ m³ at l/d of 16.     

Multifunctional carbon nanofiber-reinforced Ge25Sb10S65 chalcogenide glassy composites

Carbon nanomaterials have wide applications in sensors, batteries, electromagnetic shielding, and mechanical reinforcement. Here, carbon nanofiber (CNF)-reinforced Ge₂₅Sb₁₀S₆₅ chalcogenide glassy composites with excellent mechanical and electrical properties were obtained. These glassy composites maintained the amorphous properties of glass. Thermodynamic parameters, microscopic morphology, and structural characteristics were further studied. Benefiting from the remarkable high strength and conductivity of CNFs, as well as the great interface connection between CNFs and glass, the electrical and mechanical properties of glassy composites were greatly enhanced. The Vickers hardness improved by 36% (from 200 kg/mm² to 272 kg/mm²), the tensile modulus increased from 45.9 GPa to 57 GPa, and the shear modulus increased from 22.2 GPa to 23.7 GPa when the CNF concentration increased from 0 wt% to 3.0 wt%. Furthermore, DC conductivity was raised by several orders of magnitude compared with bulk glass at 293 K (from 4.55 × 10⁻¹⁰ S/cm to 3.15 × 10⁻⁴ S/cm) owing to the formation of a continuous conductive network. Thus, these CNF-reinforced glassy composites provide a new way for realizing multifunctional composites.     

Polyimide Fibers Obtained by Spinning Lyotropic Solutions of Rigid‐Rod Aromatic Poly(amic ethyl ester)s

Summary: Fibers were spun from a lyotropic solution of a high‐molecular‐weight (η = 5.89 g · dL^?1), rigid‐rod, fully aromatic polyimide precursor polymer in a dry‐jet, wet‐spinning process in NMP. Acetone was identified as the coagulant of choice since fibers could be drawn extensively in this solvent, resulting in improved mechanical properties (tensile modulus: E = 17 GPa, strength at break: σ_break = 400 MPa, elongation at break: ε_break = 5.3%) and orientation, which was shown by WAXS patterns. SEM images showed a layered, skin‐core morphology without any visible fibrillation. Additional processing of these fibers by step‐wise hot‐drawing up to 400 °C under tension rendered oriented polyimide fibers with excellent mechanical properties. (E = 68 GPa, σ_break = 700 MPa, ε_break = 1%). An analysis of the WAXS diffraction patterns showed an improved orientation of the fibers in the axial and lateral directions; however, probably due to the CF₃ side groups, the lateral distance was still too large for crystallization. SEM images of these imidized fibers showed, for the first time, a fibrillar morphology in addition to the typical, skin‐core, sheet‐like morphology.

SEM image of the hot‐drawn fiber PI 4 (12). The image shows a skin‐core morphology which was delaminating into ribbons during preparation.     

Strength of Some Grades of Steel and Armco Iron under Shock Compression and Rarefaction at Pressures of 2 – 200 GPa

This paper reports results from a comparative experimental study of the dynamic strength of St. 20 and 09G2S steels (which are of interest as structural materials for the loadbearing casings of explosionproof chambers) under shock compression and tension (spalling) at shockfront pressures of 1–5 GPa and strain rates of 10³ – 10⁴ sec^-1. A comparative analysis is performed of the obtained and available data on the dynamic yield point and spall strength of St. 3, St. 20, 09G2S, 12Kh18N10T, ÉI712, 30KhGSA, 36NKhTYu, KhVG, and 35Kh3NM steels and armco iron, whose strengths and ductilities under static loading conditions differ by a factor of up to five. Experiments are described in which spheres of St. 3, St. 20, 12Kh18N10T, and 30KhGSA steels with markedly different strengths and ductilities are loaded by a convergent quasispherical shock wave with a pressure at the center of 200 GPa and a strain rate of 10⁵sec^-1.     

Synthesis and Properties of Soluble and Light-Colored Poly(amide-imide-imide)s Based on Tetraimide-Dicarboxylic Acid Condensed from 4,4'-Oxydiphthalic Anhydride, 2,2-Bis[4-(4-aminophenoxy)phenyl]sulfone, and m-Aminobenzoic Acid, and Various Aromatic Diamines

A new-type of tetraimide-dicarboxylic acid (I) was synthesized starting from the ring-opening addition of m-aminobenzoic acid (m-ABA), 4,4'-oxydiphthalic anhydride (ODPA), and 2,2-bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS) at a 2:2:1 molar ratio in N-methyl-2-pyrrolidone (NMP), followed by cyclodehydration to the diacid I. A series of soluble and light-colored poly(amide-imide-imide)s (III _a-j) was prepared by triphenyl phosphite-activated polycondensation from the tetraimide-diacid I with various aromatic diamines (II _a-j). All films cast from DMAc had cutoff wavelengths shorter than 390 nm (379–390 nm) and had b ^* values between 24.17–35.50; these polymers were much lighter in color than those of the alternating trimellitimide series. All of the polymers were readily soluble in a variety of organic solvents such as NMP, N,N-dimethyl acetamide, N,N-dimethylformamide, dimethyl sulfoxide, and even in less polar m-cresol and pyridine. Polymers III _a-j afforded tough, transparent, and flexible films, which had a strength at break ranging from 93 to 118 MPa, elongation at break from 8 to 11%, and initial modulus from 2.2 to 2.8 GPa, and some films showed yield points in the range of 95–111 MPa at stress–strain curves. The glass transition temperature of the polymers was recorded at 240–268°C. They had 10% weight loss at a temperature above 540°C and left more than 55% residue even at 800°C in nitrogen.     

Zirconia crystals with yttrium and cerium oxides

Results obtained for a new material, namely, zirconia crystals stabilized by Y₂O₃ and CeO₂ and containing a technological addition of neodymium oxide, tested at room temperature are described. Special features of the surfaces of the crystal blocks grown and the distribution of the additions introduced into the charge over their height are investigated. The dependences of the amounts of the stabilizing components and the fracture properties of the investigated material on its strength are determined. Certification results for the mechanical characteristics of the material are presented (mean four-point bending strength 1250 MPa, crack resistance in bending of a notched bar 11.43 MPa·m^1/2 at an elasticity modulus of 366 GPa for the crystallographic direction 100). The crystals are investigated in the crystallographic plane {100} by applying Vickers and Knoop indenters, and their hardness at different loads (beginning with 0.1 N) is determined. It is established that zones of phase transformations are formed near the indentations in addition to radial and lateral cracks. Problems of change in the specific features of the mechanical behavior of the crystals with change in the valence of cerium (most experiments were conducted for Ce₂O₃), with the heat treatment, etc. are considered. The results are analyzed using data of fractographic investigations and the new data obtained in tests of similar crystals partially stabilized by yttrium and terbium oxides.Translated from Ogneupory, No. 7, pp. 2–10, July, 1995.     

Role of cold isostatic pressing in the formation of the properties of ZrO2-base ceramics obtained from ultradisperse powders

The physicomechanical properties of ceramics obtained from plasmachemical and sol-gel powders of partially stabilized (3% Y₂O₃) zirconia (PSZ) and its compositions with 20% Al₂O₃ by cold isostatic pressing (CIP) at a pressure of at most 2 GPa and sintering at 1300–1650°C are investigated. It is established that plasmachemical PSZ exhibits its best properties (K _lc=7.8 MPa · m^1/2, a strength of 650 MPa) only after complete disintegration at a CIP of 0.1 GPa and a sintering temperature of 1650°C, when the material is sintered to a density of 5.5 g/cm³. After partial stabilization and CIP at 0.1 GPa the plasmachemical composition of PSZ+20% Al₂O₃ is sintered at 1650°C to a density of 4.7 g/cm³, but hasK _lc=8.5 MPa · m^1/2 and a strength of 700 MPa. The deagglomerated sol-gel powder exhibits properties at a level ofK _lc=12.4 MPa · m^1/2 and a strength of 950 MPa at a density above 6.0 g/cm³ after CIP at 0.3 GPa and sintering at 1450°C. The latter obviously has the best mechanical properties of all the investigated materials.Translated from Ogneupory, No. 2, pp. 12 – 19, February, 1995.     

A new class of high Tg and organosoluble polynaphthalimides

A new class of soluble six-membered ring polynaphthalimides (PNIs) was synthesized from asymmetrical fluorinated naphthalene-substituted monomers. All the resulting PNIs were easily soluble in many organic solvents, such as N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and chloroform. They also showed good thermal stability with glass transition temperature of 340-386 °C, 10% weight loss temperature in excess of 529 °C. Polyimide 3c could be solution-cast into tough and flexible film. The film had a tensile strength, elongation at break, and Young's modulus of about 117.6 MPa, 23.6%, and 1.77 GPa, respectively. The gas permeation property of the film of 3c was investigated with oxygen permeability coefficient (PO₂=3.99) and permeability selectivity coefficient of oxygen to nitrogen (PO₂/PN₂=5.27). Therefore, these materials are expected to be a good alternative to PIs based on five-membered rings with applications in gas separation membranes.     

Synthesis and properties of novel soluble polyimides having a spirobisindane-linked dianhydride unit

A new synthetic procedure was elaborated allowing the preparation of semiaromatic dianhydride. N-Methyl protected 4-chlorophthalic anhydride was nitrated with HNO₃ to produce N-methyl-4-chloro-5-nitrophthalimide (1). The aromatic nucleophilic substitution reaction between 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1-spirobisindane and 1 afforded spirobisindane-linked bis(N-methylphthalimide) (2), which was hydrolyzed and subsequently dehydrated to give the corresponding dianhydride (3). The latter was polymerized with five different aromatic diamines to afford a series of aromatic polyimides. The properties of polyimides such as inherent viscosity, solubility, UV transparency and thermal stability were investigated to illustrate the contribution of the introduction of spirobisindane groups into the polyimide backbone. The resulting polyimides were readily soluble in polar solvents such as chloroform, THF and N-methyl-2-pyrrolidone. The glass-transition temperatures of these polyimides were in the range of 254-292 °C. The tensile strength, elongation at break, and Young's modulus of the polyimide film were 68.8-106.6 MPa, 5.9-9.8%, 1.7-2.0 GPa, respectively. The polymer films were colorless and transparent with the absorption cutoff wavelength at 286-308 nm.     

Crosslinking of ultra-high strength polyethylene fibers by means of γ-radiation

Summary An ultra-high strength polyethylene fiber with an initial tensile strength at break of 3.0 GPa, was irradiated at room temperature under vacuum by means of ⁶⁰Co -radiation.Gelcontent and equilibrium volume degree of swelling of the gelfraction, were determined as a function of dose. From a plot of the effective network chain density versus dose, it was concluded that the fiber contained about 2 entanglements per number average molecule. Furthermore, a crosslinking efficiency of 0.33 crosslink per 100 eV of absorbed energy was found.Part 1 : cf⁵ It is a pleasure to acknowledge the support by the Netherlands Foundation for Chemical Research (S.O.N.) with financial aid from the Netherlands Organization for the Advancement of Pure Research (Z.W.O.).     

Proton-conducting ceramics as electrode/electrolyte materials for SOFC's—part I: preparation,mechanical and thermal properties of sintered bodies

The aim of these investigations was to prepare and to examine compounds of a high temperature solid oxide fuel cell with a proton conducting electrolyte in view of the mechanical and thermal properties. The powders were made by the conventional solid reaction of carbonates and oxides. The stoichiometry of the electrolyte Ba,Ca niobate (BCN) was varied with x=0, x=0.12 and x=0.18. As potential cathode material SrCeO₃ and SrZrO₃ stabilised with 5% Yb was prepared, and as anode material cermet of BCN and Ni with 50:50 wt.% was synthesised. The mechanical properties like bending strength (room and high temperature), Young modulus (E), modulus of rigidity (G), Poison's ratio, micro hardness and fracture toughness were measured on sintered samples. The highest values for bending strength, E and G could be found for BCN12 (156 MPa, 160 GPa, 63 GPa) and the cerate (175 MPa, 145 GPa, 56 GPa), the lowest for the cermet BCN/Ni (72 MPa, 68 GPa, 29 GPa). The investigation of the thermal properties of the bulk material showed a thermal stability to a temperature of 1400 °C. The thermal expansion coefficient measured at 1000 °C was found to be in the range of 10–12×10⁻⁶/K. Further investigations with respect to the mechanical and thermal properties have to be made for the whole system of cathode–electrolyte–anode.     

Mechanical properties of reactively processed W/Ta2C-based composites

The mechanical properties of reactively processed W/Ta₂C cermet composites were studied. Dense W/Ta₂C cermets with a nominal composition of 40.4 vol% W(Ta)ss, 48.9 vol% Ta₂C and 10.6 vol% Ta₂WO₈ were fabricated using a pressureless reactive processing method. Four-point bend strength, fracture toughness, elastic modulus, and microhardness were measured at room temperature. The average flexure strength was 584 MPa which is lower than for pure W; however the strength of pure Ta₂C is unknown. The fracture toughness was 8.3 MPa m^1/2 which fits a rule of mixtures between literature values for the fracture toughness of the W and Ta₂C phases. The elastic modulus was 476 GPa, and the microhardness was 13.4 GPa. Both Young's modulus and hardness were higher than values reported for other W-based cermets.     

Influence of alkali fiber treatment and fiber processing on the mechanical properties of hemp/epoxy composites

Industrial hemp fibers were treated with a 5 wt % NaOH, 2 wt % Na₂SO₃ solution at 120°C for 60 min to remove noncellulosic fiber components. Analysis of fibers by lignin analysis, scanning electron microscopy (SEM), zeta potential, Fourier transform infrared (FTIR) spectroscopy, wide angle X‐ray diffraction (WAXRD) and differential thermal/thermogravimetric analysis (DTA/TGA), supported that alkali treatment had (i) removed lignin, (ii) separated fibers from their fiber bundles, (iii) exposed cellulose hydroxyl groups, (iv) made the fiber surface cleaner, and (v) enhanced thermal stability of the fibers by increasing cellulose crystallinity through better packing of cellulose chains. Untreated and alkali treated short (random and aligned) and long (aligned) hemp fiber/epoxy composites were produced with fiber contents between 40 and 65 wt %. Although alkali treatment generally improved composite strength, better strength at high fiber contents for long fiber composites was achieved with untreated fiber, which appeared to be due to less fiber/fiber contact between alkali treated fibers. Composites with 65 wt % untreated, long aligned fiber were the strongest with a tensile strength (TS) of 165 MPa, Young's modulus (YM) of 17 GPa, flexural strength of 180 MPa, flexural modulus of 9 GPa, impact energy (IE) of 14.5 kJ/m², and fracture toughness (K_Ic) of 5 MPa m^1/2. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011