Experimental study on the reactivity of aggregate in concrete

The specimens mixed with cement and various crushed minerals (149–74 μm) were cured at 80°C in saturated steam for 28–180 days as the basic study for cement-aggregate reactions. Quartz and feldspars (microcline, albite and anorthite) reacted with the cement paste, whereas hornblende, augite and olivine did not react. Anorthite was the most reactive and the reactivity of quartz, microcline and albite were almost the same as each other. Jennite was formed by cement-quartz reaction and 11 Å tobermorite, CSH (II) and hydrogarnet were formed by cement-anorthite reaction. The compressive strength of the specimens in which aggregates reacted to cement paste increased as the curing time was prolonged.     

CHEMICAL ABSORPTION OF CO2 AND SO2 INTO Ca(OH) 2 SLURRY

Chemical absorption of CO₂ and SO₂2 as single gases and as a mixture into slurries of Ca(OH) ₂ was studied in a stirred vessel with a flat gas-liquid interface. In the case of CO₂, the reaction product interrupted the subsequent gas absorption in the absence of a surface active agent. With single gases, the enhancement factor for SO₂ was much larger than that for CO₂, though both were larger than that into saturated solution. With the mixed gases, the enhancement factor for S02 was almost equal to that for the single gas absorption, but for CO₂ it was only slightly larger than that into the saturated solution     

Phase formation and diffusion path of SiC/Ta/SiC joint

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis and properties of platinum-dispersed carbon by pressure pyrolysis of organoplatinum copolymer

Platinum-dispersed carbon was synthesized by pressure pyrolysis of divinylbenzenebis (2-allylphenyl)platinum (APPt) and phenylacetylene-APPt at 550 °C and 125 MPa. The crystallinity of platinum dispersed in the carbon matrix synthesized from phenylacetylene(PA)-APPt was higher than that from divinylbenzene(DVB)-APPt. Platinum particles less than 60 nm were dispersed in the carbon matrix synthesized from DVB-APPt at 550 °C and 125 MPa. The carbon matrix formed from PA-APPt contained platinum particles of about 120 nm. The specific area of platinum-dispersed carbon synthesized at 550 °C and 125 MPa increased on subsequent heat treatments in argon, and reached 90 m² g^–1 after heat treatment at 800 °C for 1 h. The activity of platinum-dispersed carbon for the hydrogenation of cyclohexene increased with increasing specific area. Platinum-dispersed carbon formed from DVBAPPt was more active for hydrogenation reaction than that from PA-APPt. The highly active platinum-dispersed carbon could be synthesized from DVB-APPt at 520 °C. The surface area reached 154 m² g^–1 after heat treatment at 800 °C.     

Polymer-metal chelate precursor reduced its firing temperature and time for preparing yttrium barium cuprate powder

Bulk YBa₂Cu₃O _x was prepared by a polymer chelate precursor method using poly[(N,Ndicarboxymethyl)allylamine] as a chelating polymer of which molecular weights were 3 × 10⁴ (PDAA-L) and 3 × 10⁵ (PDAA-H), respectively. X-ray diffraction (XRD) analysis of the precursor from PDAA-H shows that YBa₂Cu₃O _x (Y123) phase appeared after being calcined at 750 °C for 5 h and the mixture was completely converted to tetragonal Y123 phase after being calcined at 800 °C for 5 h. The phase evolution of the precursor from PDAA-H during isothermal experiment at 800 °C showed that pure tetragonal Y123 was produced even after the polymer chelate precursor was heated for 2 h in air, although a very small amount of BaCO₃ was recognized. This BaCO₃ phase was hardly recognized after 4 h calcination. The precursor prepared from PDAA-L was fully converted to pure tetragonal Y123 after 3 h calcining at 800 °C. On the other hand, the sample prepared from metal nitrate solution without PDAA was not fully transferred to Y123 phase after heating at 800 °C for 10 h. Large amounts of Y₂O₃, BaCO₃ and CuO were observed. These results indicated that the greater homogeneity in the polymer chelate precursor leads to reduced firing times and temperature compared with the metal nitrate precursor.     

Structure and strength of AlN/V bonding interfaces

AlN ceramics are bonded using vanadium metal foils at high temperatures in vacuum. Different bonding temperatures were used in the range 1373–1773 K with bonding times of 0.3–21.6 ks. The AlN/V interfaces of the bonded joints were investigated using SEM, electron probe microanalysis and X-ray diffraction. A bonding temperature of 1573 K was found to be suitable to activate both parts to initiate a phase reaction at the interface, because a thin V(Al) solid solution layer formed adjacent to the ceramic at 1573 K just after 0.9 ks, and a small flake-shaped V₂N reaction product formed inside the vanadium central layer. The formation of V(Al) and V₂N controls the interfacial joining of the AlN/V system at 1573 K up to 5.4 ks bonding time. The pure vanadium layer quickly changed to vanadium-containing V₂N. The diffusion path could be predicted for the AlN/V joints up to 0.9 ks at 1573 K following the sequence AlN/V(Al)/V₂N/V, while after 0.9 ks, the interface structure changed to AlN/V(Al)/V₂N + V by the growth Of V₂N into the vanadium. The AlN/V joints shovyed no ternary compounds at the interface. A maximum bond strength could be obtained for a joint bonded at 1573 K after 5.4 ks having a structure of AlN/V(Al)/V₂N + V. At 7.2 ks, nitrogen, resulting from AlN decomposition, escaped and the remaining aluminium reacted with V(Al) to form V₅Al₈ intermetallic, which is attributable to the decrease in bond strength.     

A Mathematical Model of Perception with Reference to Peripheral Vision and its Application to the Hermann Grid Illusion

Central vision and peripheral vision are two of main components of visual perception. The functional differences between the two visions are considered with two points of view: the physiological receptive field and the psychological perceptive field.

The authors propose a retinal model of lateral inhibition. The output is discrete summation of ganglion cell responses through the Difference of Gaussian (DOG) function of the coupling width. The coupling width is given by the size of receptive field, according to Fisher’s findings that the distribution of the ganglion cell density decreases from the fovea to the peripheral area. Sampling points of the summation correspond to the positions of the ganglion cells, so that a number of points in all the same in each receptive field. The coupling width was determined by the data of Jung and Spillmann’s (1970) psychological experiment. As an application of this model, the Hermann grid illusion is quantitatively explained.