Clays termed thixotropic are those that reveal this property by weakening
when they are remolded and by increasing in strength when allowed to stand
undisturbed. See also:remolding
oil-well drilling fluids. Hammond
a. The property of certain colloidal substances, such as a thixotropic
clay, to weaken or change from a gel to a sol when shaken, but to increase
in strength upon standing. AGI
b. The property of a material that enables it to stiffen in a relatively
short time on standing, but upon agitation or manipulation to change to a
very soft consistency or to a fluid of high velocity, the process being
completely reversible. Used in muds for drilling deep oil wells since, if
the drill stops, rock chips on the way to the surface are held in
suspension instead of settling to the bottom where they might jam the
drilling bit. See also:gel; plastic deformation. ASCE
A silica-oversaturated (quartz-normative) basalt, characterized by the
presence of low-calcium pyroxenes (orthopyroxene and/or pigeonite) in
addition to clinopyroxene and calcic plagioclase. Olivine may be present
in the mode, but neither olivine nor nepheline appear in the norm.
CF:basalt
A variety of siderite that is found massive and in pyramidal crystals.
Standard, 2
A bottom-blown basic pneumatic converter having a basic bottom and lining,
usually dolomite, and employing a basic slag. ASM, 1
Conversion of iron to steel in basic-lined Bessemer converter. Phosphorus
combines with dolomite in this lining to produce basic slag.
Pryor, 3
The finely powdered basic slag obtained in the Thomas-Gilchrist process.
It consists of phosphates and is used as a fertilizer. Hackh
Steel made in a Bessemer converter using a basic refractory lining. The
process was developed by Thomas and Gilchrist. In Europe such steel is
known as Thomas steel; in Great Britain, Thomas-Gilchrist steel; and in
the United States, basic Bessemer steel. Henderson
See:arc cutter
An orthorhombic mineral, Na4 Ca8 [Al20 Si20 O
80 ].24H2 O ; zeolite group; pseudotetragonal; occurs in
amydules and crevices in basalts and tuffs; also an alteration of
anorthite. Also called ozarkite.
Thompson pilot shoulder reamer
A reaming or coring bit with an articulated steel pilot protruding about
36 in (91 cm) beyond the face of the bit. The diameter of the pilot is
slightly smaller than the set inside diameter of the bit; its upper end is
a piston fitted tightly inside a single-tube barrel with its attached
coring bit. When lowered into a borehole in which a deflection wedge has
been set, the pilot section forces the coring bit to ream out the first
part of the deflected hole at a point about 20 in (51 cm) above the tip of
the wedge. Reaming is continued to about 6 in (15 cm) below the wedge tip,
at which point the pilot shoulder reamer is withdrawn and replaced by a
bullnose or deflection bit. Long
A retrievable type of deflecting wedge. See also:deflecting wedge
Long
A monoclinic mineral, NaCaAlF6 .H2 O ; dimorphous with
pachnolite; forms small, white prismatic crystals on cryolite.
A monoclinic mineral, SnTa2 O6 ; forms a series with
foordite; brown; in pegmatite at Katanga, Congo.
A rare refractory oxide, ThO2 .
See:thorogummite
An isometric mineral, ThO2 ; commonly contains lanthanides; has
fluorite structure; forms a series with uraninite; highly radioactive and
metamict; sp gr, 9.7; in pegmatites; in placers associated with zircon,
ilmenite, geikielite, thorite, and other heavy minerals; an important
source of uranium and thorium. Also called isometric thorium.
A variety of uraninite containing thorium in partial substitution for
uranium. Crosby
Two borides are known: ThB4 (gray) and ThB6 (deep red). More
attention has been paid to the tetraboride, the properties of which are
melting point, >2,200 degrees C (but oxidizes slowly above 1,000 degrees
C); thermal expansion, 5.9X10-6 (20 to 1,000 degrees C); sp gr,
8.45 g/mL; modulus of rupture (20 degrees C), 20,000 psi (138 MPa) . Some
properties of ThB6 are melting point, 2,200 degrees C; sp gr, 7.1.
Dodd
Two carbides are known: ThC, melting point, 2,625 degrees C; ThC2 ,
melting point, 2,655 degrees C. These special carbides are of potential
interest in nuclear engineering. Dodd
The series of radioactive elements produced as successive intermediate
products when the element thorium (thorium 232) undergoes its spontaneous
natural radioactive disintegration into stable lead (lead 208).
CCD, 2