Ultra‐High Temperature Mechanical Properties of a Zirconium Diboride–Zirconium Carbide Ceramic

The mechanical properties of a ZrB₂‐10 vol% ZrC ceramic were measured up to 2300°C in an argon atmosphere. Dense billets of ZrB₂‐9.5 vol% ZrC‐0.1 vol% C were produced by hot‐pressing at 1900°C. The ZrB₂ grain size was 4.9 μm and ZrC cluster size was 1.8 μm. Flexure strength was 695 MPa at ambient, decreasing to 300 MPa at 1600°C, increasing to 345 MPa at 1800°C and 2000°C, and then decreasing to 290 MPa at 2200°C and 2300°C. Fracture toughness was 4.8 MPa·m^½ at room temperature, decreasing to 3.4 MPa·m^½ at 1400°C, increasing to 4.5 MPa·m^½ at 1800°C, and decreasing to 3.6 MPa·m^½ at 2300°C. Elastic modulus calculated from the crosshead displacement was estimated to be 505 GPa at ambient, relatively unchanging to 1200°C, then decreasing linearly to 385 GPa at 1600°C, more slowly to 345 GPa at 2000°C, and then more rapidly to 260 GPa at 2300°C. Surface flaws resulting from machining damage were the critical flaw up to 1400°C. Above 1400°C, plasticity reduced the stress at the crack tip and the surface flaws experienced subcritical crack growth. Above 2000°C, microvoid coalescence ahead of the crack tip caused failure.     

Grain Boundary Space Charge Effect and Proton Dynamics in Chemically Stable Perovskite‐Type Ba0.5Sr0.5Ce0.6Zr0.2Gd0.1Y0.1O3−δ (BSCZGY): A Case Study on Effect of Sintering Temperature

The present study reports the effect of sintering temperature on the proton dynamics of perovskite‐type Ba_0.5Sr_0.5Ce_0.6Zr_0.2Gd_0.1Y_0.1O_3?δ (BSCZGY) by establishing a co‐relation between the grain‐boundary (GB) space charge effect, electrical conductivity and dielectric loss of the BSCZGY samples sintered at 1300°C, 1400°C, and 1550°C for 20 h in air. Although, the GBs are the main source of resistance in BaZrO₃ based ceramic proton conductors, we show that the GB impedance disappeared above 450°C and 300°C, respectively, for BSCZGY samples sintered at 1300°C and 1400°C. Interestingly, the BSCZGY sample sintered at 1550°C showed absence of GB contribution to total conductivity even at 200°C. The GB electrostatic potential [?(0)] was found to vary between 0.35–0.38 V and 0.4–0.45 V, respectively, for the samples sintered at 1300°C and 1400°C at 200°C–300°C. The migration energy (E_m) of the protons was found to be 0.71, 0.65 and 0.58 eV for the sample sintered at 1300°C, 1400°C and 1550°C, respectively.     

The effect of temperature on the properties of calcined red iron oxide pigments

The effect of calcination temperature on the properties of red iron oxide pigments obtained from FeSO₄, 7H₂O by calcination at constant temperatures over the range from 700 to 900 °C, has been investigated. It was found that the particle diameter increased from 0.065 μm at 700 °C to 0.25 μm at 900 °C; the increase was gradual up to 800 °C and abrupt at 850 and 900 °C. The colour changed from red with decreasing yellowish hue between 700 and 750 °C, to red with increasing bluish hue between 750 and 900 °C; the dominant wavelength increased from 599 nm at 700 °C to 610 nm at 900 °C. The tinting strength was found to vary irregularly with temperature, and to pass through a maximum at 750 °C. The oil absorption was found to decrease with temperature and to be a linear function of the specific surface area.     

Effects of alkaline conditioning and temperature on the properties of glass fiber polymer composite rebar

This article investigated long term alkaline conditioning and temperature on the physical and mechanical properties of glass fiber‐reinforced polymer (GFRP) composite rebar for structural applications. The GFRP rebar was immersed in alkaline solution (pH ≈ 13) for 23 months at 23°C, and for 24 months at 60°C. The moisture absorption was found to be 0.34% at 23°C after 23 months, and 0.76% at 60°C after 24 months. At both temperatures, moisture absorption did not reach equilibrium which was attributed to two stages non‐Fickian behavior. Glass transition temperature (T_g) of the polymer matrix of rebar that conditioned at 23°C was found to be decreased because of plasticization, whereas T_g of the rebar that conditioned at 60°C was remained greater than the T_g of control rebar due to nonplasticization effect. Shear strength was retained by 83.5% at 23°C and 80.5% at 60°C, flexural strength was retained by 81% at 23°C and 69% at 60°C, and tensile strength was retained by 91.2% at 23°C and 74.3% at 60°C. It was revealed that durability of GFRP rebar in alkaline environment was controlled by the absorbed moisture; this was because the load transfer efficiency of fiber/matrix interface is vulnerable to moisture. POLYM. COMPOS., 37:3181–3190, 2016. © 2015 Society of Plastics Engineers     

Physical properties and structure of silk: 4. Spherulites grown from aqueous solution of silk fibroin

Spherulite formation in silk fibroin films cast from aqueous solution has been studied for crystallization conditions such as drying temperature, drying rate and pretreatment (freezing). Negatively birefringent spherulites in the α-form are observed in films cast between 0° and 40°C, and with a high drying rate at 20°C; positive β-form spherulites appear at higher temperatures up to 80°C and with a low drying rate at 20°C. Positive β-form spherulites are also obtained by freezing fibroin solution at ?2° to ?18°C and then drying at 20°C. It is found that positive β-form spherulites grow at 20°C on the surface of well-oriented β-form silk fibroin filaments (degummed silk) immersed in fibroin solution.     

Microstructure evolution and bonding mechanisms of silica sol bonded coating at elevated temperatures

High emissivity coating plays a critical role in thermal protective system, which can radiate a large amount of aero-convective heat. Silica sol bonded MoSi₂-SiC-Al₂O₃ (S-MSA) coating was proved to be promising for mullite fibrous insulation. However, the bonding mechanisms of the coating at elevated temperatures are not clear. In this work, the S-MSA coatings were heat-treated at temperatures from 600 °C to 1500 °C to reveal the bonding mechanisms at elevated temperatures. The S-MSA coatings go through a relatively stable stage (600 °C–1000 °C), a crystallization stage (1100 °C–1200 °C), and a densification stage (1300 °C–1500 °C) at ever increasing temperatures. Results show that both the contact damage resistance and the bonding strength of the calcined coatings exhibit a decrease followed by an increase at elevated calcination temperatures, with the inflection point at 1200 °C, corresponding to the transition temperature of the bonding mechanisms from 600 °C to 1500 °C.     

Effect of thermal aging on electrical conductivity of the 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid‐doped polyaniline fiber

The thermal characteristics of inherently conductive polyaniline (PANi) fiber have been studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Fibers show five major weight losses at ∼100°C, 165°C, 215°C, 315°C, and 465°C, which are associated with the removal of moisture, residual solvent, decompositions of the sulfonic acid and degradation of PANi fiber, respectively. The 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPSA) that dopes the PANi (in fiber form) performs two‐stage decompositions. The conductivity of the drawn fibers aged at 50°C, 100°C, 150°C, and 190°C under vacuum for various periods of time decreases, particularly at temperatures higher than 100°C. The reduction in conductivity of the fiber aged at temperatures lower than 100°C is mainly due to the evaporation of the residual solvent (15–20% in the as‐spun fiber). Further decrease in conductivity of the fiber aged at temperatures higher than 100°C is caused by the decomposition of the dopant AMPSA. The temperature‐dependent conductivity of the fiber was measured at 15 K (−258.5°C) to 295 K (21.5°C). The conductivity of both aged and un‐aged fibers is all temperature activated, however, the conductivity of the un‐aged fibers is higher than that of the aged fibers. Although a negative temperature coefficient was observed in the temperature range from 240 K (–24.5°C) to 270 K (–3.5°C) for the un‐aged fibers, it was disappeared when the fibers were thermal aged at 100°C for 24 h in vacuum oven. These results indicate that the residual solvent trapped inside the fiber enhanced the electrical conductivity of the fibers and its “metallic” electrical conductivity at temperatures ∼263 K (–10°C). © 2001 John Wiley & Sons, Inc. † J Appl Polym Sci 79: 2503–2508, 2001     

Properties of syndiotactic-rich poly(vinyl alcohol) thin film in water. III. Contraction and extension of drawn and annealed thin film in water

Contraction and extension behaviors in water for drawn (four times original length) and annealed (at 60–215°C) thin films of poly(vinyl alcohol) (PVA_VTFA) derived from vinyl trifluoroacetate have been examined. At a constant temperature of 25°C, drawn films annealed at 60–190°C contracted after a certain standing time. Length of films annealed at 200°C did not change after standing of 20 min and film annealed at 215°C extended very little. As the temperature was raised, the drawn films annealed at 60–190°C contracted further until a certain temperature and then extended. The drawn film annealed at 200°C first started contraction at 70°C. The drawn film annealed at 215°C extended further very little until 75°C and then contracted very little until 99°C (in boiling water). In standing at 99°C, it contracted very little with standing and resisted without breaking for 300 min.     

Elevated Temperature Strength Enhancement of ZrB2–30 vol% SiC Ceramics by Postsintering Thermal Annealing

The mechanical properties of dense, hot‐pressed ZrB₂–30 vol% SiC ceramics were characterized from room temperature up to 1600°C in air. Specimens were tested as hot‐pressed or after hot‐pressing followed by heat treatment at 1400°C, 1500°C, 1600°C, or 1800°C for 10 h. Annealing at 1400°C resulted in the largest increases in flexure strengths at the highest test temperatures, with strengths of 470 MPa at 1400°C, 385 MPa at 1500°C, and 425 MPa at 1600°C, corresponding to increases of 7%, 8%, and 12% compared to as hot‐pressed ZrB₂–SiC tested at the same temperatures. Thermal treatment at 1500°C resulted in the largest increase in elastic modulus, with values of 270 GPa at 1400°C, 240 GPa at 1500°C, and 120 GPa at 1600°C, which were increases of 6%, 12%, and 18% compared to as hot‐pressed ZrB₂–SiC. Neither ZrB₂ grain size nor SiC cluster size changed for these heat‐treatment temperatures. Microstructural analysis suggested additional phases may have formed during heat treatment and/or dislocation density may have changed. This study demonstrated that thermal annealing may be a useful method for improving the elevated temperature mechanical properties of ZrB₂‐based ceramics.     

Phase changes in mineral matter of North Dakota lignites caused by heating to 1200 °C

Changes in structures of minerals taking place in lignitic coals during combustion were investigated by first concentrating the mineral matter in the coal by low-temperature ashing and then heating the mineral matter at 100 °C intervals from 200 °C–1200 °C and analysing the major mineral phases by X-ray powder diffraction. Samples of high and low sodium contents were analysed to determine differences in mineral phases with varying sodium contents. Quartz and bassanite were identified as major phases in the low-temperature mineral matter of all ten lignite samples, and pyrite and calcite were identified in eight of the ten samples. Kaolinite was the only clay mineral identified and appeared in nine of the ten samples. Those samples with a sodium oxide content of 8.56 wt % or greater, showed sodium nitrate as a major mineral phase in the low-temperature mineral matter. When the mineral matter was heated to higher temperatures, quartz was a major phase at 1200 °C in five of the samples, and was stable to 1000 °C in all of the samples. Anhydrite was a major mineral phase in all samples from 600 °C–800 °C, appearing in some of the samples as low as 200 °C, and persisting to 1100 °C in some samples. Hematite was found to be a major phase in seven of the ten samples, having an overall temperature range from 300 °C–1000 °C. Magnetite was detected in the range from 800 °C–1200 °C with hercynite forming as a major mineral phase, after magnetite, in two of the samples at 1200 °C. The solid solution series gehlenite-akermanite was found in all ten samples from 1100 °C–1200 °C although they appeared in some samples at 900 °C. Samples of high sodium content formed sodium sulphates at intermediate temperatures and sodium silicates at higher temperatures. Low Sodium samples formed bredigite, a calcium silicate, at higher temperatures.     

The Fractional Extraction of Lipids and Cholesterol from Dried Egg Yolk Using Supercritical Carbon Dioxide

Results from extraction of cholesterol and other lipid components from dried egg yolk using supercritical carbon dioxide at the range of temperature from 40°C to 60°C and pressure between 150 bar und 350 bar for 2.5 hours and 2.7 kg CO₂ consumption is described in this paper. The solubility of lipids and cholesterol increased with the increase of pressure at a constant temperature of 50°C, while at a constant pressure, more cholesterol was removed at 45°C than that at other temperatures. Nearly 60 percent cholesterol was removed at 45°C and 250 bar. Lipids were more efficiently extracted at 60°C than at 40°C at 250 and 350 bar, however, a decrease in the total extracted lipids was observed with the increase in temperature at 150 bar. The removed total lipids from dried egg yolk at 250 bar/55°C was over 80 %.     

Transitions of polytetrafluoroethylene at about 90 and 130°C. studied by x-ray diffraction and infrared spectra

By means of x-ray diffraction, the lattice spacing of the (100) plane for molded polytetrafluoroethylene was measured at different temperatures from 25 to 190°C. In the crystalline region, the linear expansion coefficient, in the direction perpendicular to the molecular chain axis, was obtained as 1.1 × 10^?4°C.^?1 below 60°C., as 1.2 × 10^?4°C.^?1 above 90°C., and as a minimum value of some 0.2 × 10^?4°C.^?1 at about 80°C. As the linear expansion coefficient of the crystalline region in bulk was observed as some 0.6 × 10^?4°C.^?1, the expansion coefficient in the direction of molecular chain axis must be negative except in the transition region near 80°C. The variation of molecular chain axis separation with temperature showed an irregularity at about 80°C. but none near 130°C. in the crystalline region. Infrared absorbance of film samples of PTFE was measured at different temperatures of 25 to 150°C. range for 518, 627, and 639 cm.^?1 bands. On absorbance–temperature curves for those b?ands, irregularities were observed near 30, 50, 90, and 130°C. Particularly with 518 cm.^?1 band, a more crystalline sample gave more distinct irregularities near 50 and 90°C. than a less crystalline sample. The change at about 90°C. in infrared spectra may correspond to that obtained by x-ray measurements near 80°C., which was thought to occur in the crystalline region. The results obtained by x-ray and infrared measurements support the previous results by thermal, rheological, and dielectric methods: there exist first-order transitions in the crystalline region at about 90°C. and second-order transitions in the amorphous region at about 130°C.     

Prooxidative and antioxidative effects of phospholipids on milk fat

The effects of dipalmitoylphosphatidylethanolamine (DPE) and dipalmitoylphosphatidylcholine (DPC) on milk fat oxidation was examined at 50°C and 95°C under various conditions by monitoring oxygen uptake and fatty acid composition. DPE strongly inhibited milk fat oxidation both at 50°C and 95°C in the absence of water. DPC was less effective than DPE. In aqueous systems, the reverse was observed. DPE accelerated milk fat oxidation at both 50°C and 95°C. DPC accelerated the oxidation at 50°C, but inhibited it at 95°C. The free amino group in DPE may be responsible for its inhibiting effect in the dry system. The accelerating activity of DPE in the aqueous system is probably due to the formation of a more dispersed structure with better oxygen accessibility.     

Effect of hydrogen bond formation on dynamic mechanical properties of amorphous cellulose

The temperature dependence of the dynamic modulus (E′) and the mechanical loss tangent (tanδ) of amorphous cellulose prepared from cellulose triacetate by saponification was measured and compared with that of cellophane, recrystallized cellulose obtained by immersing amorphous cellulose in water, and cellulose triacetate. The E′ of amorphous cellulose decreased initially with increasing temperature and then began to increase at about 70°C with a maximum at 80°C, decreasing again at about 100°C. Another decrease in E′ was observed at 220°C accompanied by a discontinuity at 155°C. In the tan δ-versus-temperature curve, a medium peak at 60°C a shoulder peak at 146°C, and a broad peak at 200°C were observed. It was found that the transition at about 60°C was related to hydrogen bond formation by free OH groups. The transition at about 150°C was attributed to a recrystallization process by heating, and the relaxation at 200°C, to the glass transition of the polymer. The decrement in E′ observed at about 100°C was attributed to the cooperative motion of an individual pyranose ring in amorphous cellulose, juding from the E′ and tan δ assignment of other cellulose materials. The change in E′ was also measured isothermally as a function of time in the temperature range between 40°C and 80°C, where a maximum in tan δ and an increment in E′ were observed as the temperature dependence of the dynamic viscoelasticity. The change in E′ with elapsed time was analyzed kinetically, and an activation energy of 2.6 kcal/mole was calculated. This value is the expected activation energy of hydrogen bond formation.     

Formation of porous α-alumina from ammonium aluminum carbonate hydroxide whiskers

Ammonium aluminum carbonate hydroxide (AACH) whiskers prepared by hydrothermal technique were employed as precursor material for development of porous alumina. After compaction of AACH whiskers at 8 bars, calcination was performed at 650?°C followed by sintering at different temperatures. The sintered samples were characterized by XRD, FTIR, SEM and mercury intrusion porosimetry. Mechanical strength was determined by compression testing. At sintering temperatures of 1200?°C to 1400?°C, the % age porosity was around 80%. At 1500?°C, the percentage porosity decreased to 71%. The as-prepared AACH consisted of bundles of whiskers with diameters as thick as 0.7?µm, while an individual whisker had a diameter of about 100?nm with an aspect ratio of about 33. A two-phase mixture consisting of θ- and α-alumina was obtained at 1100?°C, while at 1200?°C and above, single phase α-alumina was formed. θ-alumina retained the bundle-like morphology. However, transformation to α-alumina was accompanied by formation of bead-like morphology. These beads were joined together through necks/stems within the whiskers as well as across the parallel-lying whiskers. These necks grew at 1300?°C to form aggregates with smooth surfaces. At 1400?°C, these aggregates started joining with each other by neck formation and at 1500?°C, a three-dimensional network was formed. For sintering temperatures of up to 1400?°C, pores with sizes around 260?nm were very stable. At 1500?°C, significant pore growth took place along with an overall densification. Therefore, number of pores with sizes of around 260?nm decreased and those with sizes around 10?µm, 1?µm and 5?nm increased. The compression strength of samples sintered at 1100?°C to 1300?°C was in the range of 3.4–4.3?MPa. At 1400?°C, the strength increased to 5.2?MPa, while at 1500?°C, it jumped to 10.8?MPa due to the formation of three-dimensional network.     

Synthesis and evaluation of mechanical and thermal properties of segmented condensation polyurethanes

Abstract

Condensation polyurethanes with different hard segment (HS) content were prepared by condensation reaction of urea, phenol sulphonic acid and formaldehyde and tested for their mechanical, physical and thermal properties. Obtained polyurethane (PUR) films were first heated at 50°C for 120 min and then treated at 135°C for 15 min or 160°C for 10 min. The tensile strength of samples thermally treated at 50°C then at 135°C was 120% higher than for samples treated only at 50°C. The obtained polyurethanes exhibited segmented structures with phase separation between HSs and soft segments (SSs). Films containing 19 and 21%HSs heated at 50°C then 135°C exhibited acceptable mechanical properties and water resistance. The lower and higher end use temperatures of PUR films were affected mainly by the polymer composition. Moreover, the polyurethane samples containing 19 and 21%HSs have shown the highest decomposition temperature (i.e. >165°C), compared to 80°C for polymers with 32%HSs.     

A STUDY OF THE HEATING AND COOLING CURVES OF JAPANESE KAOLINITE

Effect of heating Japanese kaolinite at 100° to 1400° C for 3 to 4 hours.—Ignition loss of weight Was found to occur chiefly between 400° and 600°C, the rate of increase per degree reaching a maximum at about 460 °C. Changes of microstructure were observed at 600°, 900–1000°, 1250–1300° and at 1400 °C, when sillimanite began to develop. Heating and cooling curves for Japanese kaolinite, to 1400°C.—A differential method was used with quartz sand as the comparison substance. In addition to the known reactions: (1) an endothermic from 450° to 700°, and (2) an exothermic near 950°, (3) an exothermic change between 1200° and 1300° was discovered, and it was observed that the endothermic reaction seems to include two periods of heat absorption, (1a) 450° to 650° and (1b) 650° to 700°. In explanation , the author suggests that 1a is due to dehydration, 1b to dissociation of kaolinite into free alumina and free silica, 2 to a polymerization of the alumia and 3 to the formation of amorphous sillimanite. In the discussion, E. W. Washburn calls attention to the fact that the author has neglected the endothermic reaction of quartz at 575 °C and suggests that some of his conclusions are therefore erroneous. Heating and cooling curves for alumina obtained from the nitrate, hydroxide and sulfate by calcination are given in figure 6. Exothermic reactions which are ascribed by the author to polymerization of alumia occur at 800° to 900° and at 1100° to 1200° instead of at 950° and at 1250° as in the case of kaolinite.     

Preparation of diamine-POSS/Ag hybrid microspheres and its application in epoxy resin

Carbon nanowires having different functionality has been synthesized through the template assisted approach using poly(vinyl alcohol) (PVA) as precursor polymer at 400?°C, 600?°C, 700?°C and 800?°C in the absence of any catalyst. Carbon nanowires with a diameter range of about 90?C120?nm have been obtained. Scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy are been adopted to characterize the morphology, thermal properties and chemical configuration of the synthesized samples. Raman spectroscopy indicates carbonization of the samples upto 600?°C. Above that carbon-cluster formation is observed at 700?°C and 800?°C. SEM images show the formation of nanowires in alumite template by infiltration of PVA into the pores at 400?°C. The nanowires produced are very flexible at about 700?°C, above which the nanowires tended to retain their rigidity due to the formation of graphite clusters / crystallites.     

Diameter Effect and Failure Diameter of a TATB-Based Explosive

The detonation velocity of PBX-9502, an explosive consisting of 95 wt% TATB and 5 wt% Kel-F 800, was measured precisely over a range of charge diameters at 75°C, 24°C, and −55 °C. The diameter-effect curves obtained by plotting detonation velocity versus the reciprocal of charge radius were found to differ from those reported in the literature for other solid and liquid explosives, being concave upward at large diameters. The curve at 75°C was found to be a straight line at small diameters and thus simulates the behavior of a homogeneous explosive. At intermediate charge diameters, the effect of varying the temperature by 130°C was quite small. The failure diameter varied from 5.85 ± 0.15 mm at 75°C to 10.5 mm at −55 °C.     

Tribological behavior of graphene reinforced chemically bonded ceramic coatings

To investigate tribological behavior of graphene reinforced chemically bonded ceramic coatings at different temperatures, tribological tests at room temperature, 200 °C and 500 °C were carried out. Results show that the fracture toughness and the hardness of the coating are improved with the introduction of graphene. Besides, the friction coefficient of the coating decreases with the addition of graphene at the room temperature and 200 °C. The coating without graphene achieves the similar friction coefficient at all temperatures. However, the coating with graphene achieves the lowest friction coefficient at 200 °C, and achieves the highest at 500 °C. In addition, the wear rate of the coating decreases with the increase of graphene. Besides, the wear rate at 200 °C is almost similar with that at room temperature. In contrast, the wear rate at 500 °C is much larger than those at room temperature and 200 °C. The mechanisms for graphene to decrease the friction coefficient and improve the wear resistance of chemically bonded ceramic coatings at evaluated temperatures are clarified.