KINETICS OF WETTING IN WASHOUT OF DUST
293
Experiments were next conducted with ball-bearing steel. This
material gave rapid wetting after pickling it in 12N HNO. Hencethe
passivation of the surface by the concentrated HNO; is not decisive to
the wetting. It was then attempted to study the effect of dissolved hydrogen in the steel. To this end the two steels mentioned (steels A and
B) and also stainless steel 440 (steel C) were given various pickling
treatments and cleaned by tumbling them in silica sand. The analyses
of the three steels are given in Table 3. The results obtained after
various treatments are summarized in Table 4.
Table 3—-ANALYSES OF THREE STEELS
Mild steel
Ball-bearing
Stainless steel
0.10
0.45
0.80
0.20
0.10
0.25
1.3
0.40
0.01
{A), %
Carbon
Manganese
0.10
Silicon
Chromium
Nickel
Molybdenum
steel (B), %
440 (C), &
0.30
1*
1*
17*
0.75*
*Nominal analysis (steel was analyzed for carbon only).
Table 4——TIME DELAYS FOR STEEL AFTER VARIOUS TREATMENTS, MSEC
‘Mild steel (A)
Treatment
+
=
Pickling in 2N H,SO,
0.2
0.3
Pickling in 2N HNO;;
for steel A followed by
0.15 to
0.40
0.25 to
1.5
tumbling in sand
Pickling in 12N HNO,
Tumbling in sand
Ball-bearing steel (B)
(erratic)
No wetting
+
0.5
tv? =6
tV=3
i= 1.5
+O.17 V
-
0.4
tV? = 66
tV=3
Stainless steel
440 (C)
+
~
No wetting
No wetting
tV=3
= 2.80
tV=3
+ 0,09 V
+ = 3.30
+ 0.17 V
The results are discussed in detail later in this paper. Mild steel
holds hydrogen in interstitial solid solution. The hydrogen moves rapidly within the metal. Its rate of exchange with the environmentis determined by surface reactions. This subject has been studied in pre-
vious investigations.''~'* High-carbon steels, particularly hardened
ones, contain a hydrogen-rich carbide, known as e carbide. This car-
bide!‘ probably has the composition Fe,HC. The hydrogen is comparatively strongly held in this carbide but is released in the transformation of € carbide into cementite, Fe;C. The € carbide is known to be
stabilized by chromium. Therefore steels B and C may be expected to