Initial sintering

Densification during liquid-phase sintering occurs in tliree stages. Initially, liquid fonns at particle intersections and redistributes tliroughout the particulate mass under the influence of the capillary action. Shear stresses due to the... 

The values of m given above conform to Hemng s scaling law (1950) which states that since the driving force for sintering, the transport length, the area over which uansport occurs and the volume of matter to be transported are proportional to a, and respectively, the times for equivalent change in two powder samples of initial particle size ai q and 2,0 are... 

Synthesis of bicuculline and nitroadlumine. Groenewoud and Robinson synthesised bicuculline by the general method devised by Hope and Robinson, the initial products in this case being 6-nitro-3 4-methylene-dioxyphthalide (IV) prepared by a new method from normeconin, and hydrastinine (V). The condensation produet, called nitro-a -bicuculline (the X indicating that the dZ-product eannot yet be allocated to the a- or )3-stereoisomeric series cf. synthesis of hydrastine, p. 167), forms minute yellow needles, sinters at 176° and decomposes at 179°. It was reduced to amino-a -bicuculline (I R = NHj), yellow prisms, m.p. 208—4°, the latter... 

Both molybdenum and tungsten are obtained initially in the form of powders and, since fusion is impracticable because of their high mps, they are converted to the massive state by compression and sintering under H2 at high temperatures. 

The cold solution was then allowed to stand overnight and all crystalline material filtered through a sintered glass filter. The filtrate was treated with an additional 300 ml of concentrated hydrochloric acid to yield a heavy white precipitate. The precipitate was filtered, dried and combined with the Initial precipitate obtained as described above. The combined precipitated product, 3A-dihydroxy-N-[3-(4-hydroxyphenyl)-1-methyl-n-propyl-/ henethylamine hydrochloride, had a melting point of about 184°Cto 186°C after recrystallization from boiling 4N hydrochloric acid. 

If the phases present can be unambiguously identified, microscopy can be used to determine the geometry of interface initiation and advance, and to provide information about particle sizes of components of mixed reactants in a powder. Problems of interpretation arise where materials are poorly crystallized and where crystallites are small, opaque, porous or form solid solutions. With the hot-stage microscope, the progress of reactions can be followed in some instances and the occurrence of sintering and/or melting detected. 

These salts decompose [39] to the carbonates in the temperature intervals Li, 811-826 K Na, 737-814 K and K, 754-798 K (from DTA measurements, 5 K min-1). The reaction of lithium oxalate [98] (742— 765 K) obeyed the contracting volume equation [eqn. (7), n = 3] with E = 223 13 kJ mole-1. A marked increase in surface area during the initial stages of decomposition was later followed by extensive sintering. 

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