Identification of Compound Impurities and Cubic Phase in Titanium Diboride by Wet Chemical Analysis JOSEPH W. TERESHKO, VERNON J. ROLLAND, and JACOB WEINARD Union Carbide Corp., Carbon Products Division, Fostoria Developmenf laboratory, P .
b Separation and identification of compound impurities in titanium diboride are described. The method is based on the solubility and decomposition of these compounds by various solvents. Previous work based on x-ray diffraction analysis has shown evidence that some of the impurities are in the form of a cubic phase with characteristic diffraction lines at d values of 2.44 to 2.48 A. and 2.03 to 2.17 A. The line displacement indicates that the cubic phase exists in a solid solution. The identification of possible compounds in the phase was not possible by x-ray diffraction or standard chemical methods. has been done on TiB2 and related compounds, especially in determining the impurities in the cubic phase (14, df, 2 3 ) . A11 of the analytical data presently available for compound impurities in TiB, have been made by x-ray diffraction and the analyses indicate the impurities are in the form of a cubic phase. This phase exists in a solid solution and the individual compounds cannot be readily identified. The characteristic diffraction lines appear a t d values of 2.44 to 2.48 A. and 2.13 to 2.17 A. (Figure 1). The possible constituents of this phase include Tin, Tic, and T i s . Many authors have tried various ways to synthesize and identify the reaction plus the components of the cubic phase. To verify the existence of these impurities, which exist in the cubic phase, these authors devised and studied a number of systems allowing them to predict the compounds which would eo-exist in a controlled environment. Because this paper attempts to identify completely the compound impurities in T i n z , it might be well to review briefly what has previously been attempted and the conclusions drawn by other workers in the field. The binary system TiC-E4C has been studied extensively by Greenhouse, Akcountivs, and Sisler (9), who found that these two compounds react to form titanium diboride and carbon a t temperatures between 1920" and 2150°C. Glaser ( 8 ) and Selson, Willmore, and Ronieldorph (13) verified UCH WORK
558
ANALYTICAL CHEMISTRY
this reaction, but a t the lower temperatures of 1200" and 1650" C., respectively. Although there are many compounds possible in the cubic phase, titanium carbide is one of the most probable constituents. Steinitz (23) demonstrated that titanium diboride and titanium carbide are the end products when the preparation of titanium diboride takes place in a graphite capsule, because the carbide phase is predominant over the monoboride. Portnoj, Sainsonov, and Frolova (16) and Geach and Jones (7') found that the react'ion of titanium diboride with titanium carbide does not occur. Geach noted t'hat it is difficult to avoid contamination by air or carbon, and the presence of air provides the origin for the formation of cubic titanium nit'ride. Brewer and Haraldsen (2) investigated the stability of these borides with respect to nitrogen and carbon. Like Glaser (8),they observed that titanium diboride does not react with carbon but is readily attacked by nitrogen on the cooling cycle. Roche
N
m i=
-8
DEGREES I
22 t
I
(19) introduced nitrogen between 1400" and 1900" C., and observed that titanium diboride picks up more nitrogen at the lower temperatures. Titanium monoboride, a third possibility for the cubic phase, has been definitely established by Decker and Kasper (4). Erhlich (5) previously had identified a titanium monoboride phase, but Brewer et al. ( 3 ) doubted the correctness of this identification and believed that this phase was actually titanium nitride. Noivotny et al. (14) identified titanium monoboride, but doubted the presence of TisBa or Ti2B, which they were unable to prepare. They concluded that the amount of titanium monoboride present depends on sample preparation. Post and Glaser (17 ) prepared the rare titanium borides TiB, Ti2B, and TizBb, but Palty, Margonline, and Nielson (15) observed that TiJ3 decomposed to TiB in the presence of Tin, at 1800°C. illthough these rare borides have been synthesized, they are not stable in the presence of carbon, but react to form titanium diboride and titanium carbide. Thus, none of these borides is formed as a side reaction when the production of titanium diboride is carried out in a carbothermic system.
I
N
m .c
24
0.Box 7 9 7, Fosforia, Ohio
I
8 18
20 n
t
EXPERIMENTAL
I
16 i
J
Figure 1 . X-ray tracing of TiBz and its cubic phase
Analysis of Titanium Diboride for Elemental Constituents. Apparatus. The determination of carbon was conducted with a gasometric carbon analyzer, Leco (Laboratory Equipment Corp.) Model KO. 4000 CPS, which was used in conjunction with a Leco Model No. 523 induction furnace. h Leco Model S o . 534-300 oxygen analyzer was used for the determination of oxygen. The glass t r a p for the determination of nitrogen is shown in Figure 2 . Procedure. T I T A N I U (26). ~ ~ .I sample containing 0.12 to 0.15 gram of titanium is dissolved in 10 grams of KHSOa and 10 ml. each of H2S04 and H N 0 3 . After the sample is in solution, the nitrates are decomposed by conventional means. The reduction of titanium is accomplished by the addition of 200 nil. of 1 to 3 H2S04 and, after adjusting the temperature to approximately 40' C., 15 ml. of HCI and 4 grams of aluminum wire (c.P. 20 gauge). The titanium is titrated with standard ferric
chloride using potassium thiocyanate as the indicator. NITROGEN.A 1- to 2-gram sample is placed in a 38- X 200-mm. borosilicate glass test tube containing 10 grams of Ascarite and thoroughly mixed. This mixture is then covered with 25 grams of S a O H and 10 grams of Ascarite, and a trap (Figure 2) is connected. The sample is heated slowly with a burner and after the lower Ascarite layer is molten, the heating is gradually increased with a gentle fanning action. The heating is continued until the molten mass reaches a dull red heat (approximately 500" C.) and then for an additional 3 minutes or until the reaction is complete. After the system is flushed and the dispersion tube is rinsed the excess acid is titrated with a standard base. (Suitable shielding must be provided when this determination is performed. Severe burns may be incurred from the molten caustic should a hole develop in the reaction tube.) BORON. Follow the procedure of Blumenthal ( I ) , Frank (6),or Tereshko (24)' CARBON.Determine as per instrument manufacturer's instructions (12). Use a Leco No. 528-15 combustion crucible with 1.0 gram of iron and 0.25 gram of tin as accelerators. OXYGEN. Determine as per instrument manufacturer's instructions (1I ) . Analysis of Titanium Diboride for Compound Impurities. Procedure. The analysis is accomplished by making four determinations, one each on four leaches. From these data all of the compound impurities may then be calculated. OXYGENAS Tr02 A N D B&. A 1gram sample is refluxed with 100 ml. of ethanol for 4 hours. A weight loss is obtained and the determination of oxygen in the residue is corrected to the original sample weight. The difference in oxygen from the elemental value is attributed to boric oxide and the remaining oxygen as titanium dioxide. BOROKAS BN AND B4C. A 1-gram sample is mixed with 30 grams of KHS04 and 30 ml. each of H N 0 3 and H2S04. The mixture is heated until copious fumes of SO,appear. After it cools, 250 ml. of H 2 0 are added to the mixture and the solution is filtered through a KO. 40 Whatman paper. The residue is then ashed a t 500' to 600" C. in a platinum crucible and treated as described by Tereshko (24) with the exception of adding EDTA and substitution of 0.05,V for 0.2-VNaOH. The boron found in the residue is present as BN and B4C. NITROGENAS BN A N D T I N . The sample is treated in the same manner as above through the filtering step, After the filter paper is dried, the nitrogen is determined as previously described in the elemental analysis. Thr nitrogen in this residue is attributed to 13K and the difference is calculated to TiN. CARBONA B B&, TIC, AND FREE CARBOX(CJ. The sample is placed
T1B2 A N D TIB. The quantity of titaiium monoboride and diboride is calculated from the titanium to boron ratio of the remaining titanium and boron not combined as any other compound. By applying this value to a graph representing the ratio of titanium to boron for all percentages of a TiB2, TiB mixture, the percentage of TiB2, and TiB can be obtained DISCUSSION
The particle size of the samples has no effect on the results. Generally, the samples had an average particle size of 50 weight yo less than 8 microns. Samples of TiB2 which were analyzed by the described method were prepared from approximately the same amount of Ti02, C, and B 2 0 3 and fired to a temperature in excess of 1800" C. As is shown in typical results (Table I), the carbide phase is the main constituent of the cubic phase. To understand the reaction mechanism in the formation of Ti&, a series of firings were made a t temperatures ranging from 1000' C. to a maximum temperature in excess of 1950' C. Samples were analyzed for the cubic phase, and the results are shown in Table 11, which indicates that an intermediate phase of T i c is present in the formation of Ti&. As the temperature is increased, this carbide phase reacts with B203to form the end product TiB2. These reactions may be summarized as follows.
Figure 2. Custom-made glass trap used in nitrogen analysis
in solution with H F and H S 0 3 as described by Touhey and Redmond (25) or Kriege (10) with 25 ml. of an aqueous 5% solution being added before filtering. The insoluble material is collected in a Leco disposable filtering crucible (No. 528-30), washed well with a 5% aqueous HC1 solution and hot distilled water, and dried before being analyzed for carbon as previously mentioned (12). The difference in carbon from the elemental value is the amount present in T i c . The carbon in the residue is corrected for B4C (20) and this corrected value represents free carbon.
Table I.
+ 3C + Bz03 + 2C TiOz + Bz03 + 5C -+ TiOz
-+
Tic
+ 2CO + 3CO TiBz + 5CO Tic
+ TiBz
X-ray diffraction data on this series indicated that crystalline BzO3 was not present a t 1500" C. However, by. chemical analysis, an appreciable weight
High Temperature Material Fired to 1950"
C., Compound Analysis
Sample
Tica
Ti02
BN
B2Oj
TiN4
B&
Ct
TiBa
TiBz
A B C D E F G H
4.45 2.90 1.75 3.55 1.20 230 362 200
0.37 2.87 1.23 1.50 2.12 075 315 130
0.25 0.94 0.57 0.62 0.30
0.20 1.42 1.09 3.63 0.80
0.71
0.1
0.48 0.64 0.25 0.29
1.16 0.0 0.0 3.67
90.46 89.4 92.51 85.29
0 0
020
596 054
107 070
014 021 013
0 0 0 0 0 0
9485 7669 9208
TiB
TiBz
0.0 0.0 0.6 6.16 3.81 1.6
0.0 0.0
a
1
1.28
1.11 0.66
n
71
ii6
768 184
0.0 0.0 0.0
nn
n_ ifi - -
00 0 0
0 0
n 1
3 -
44
I-
-
F,
Cubic structure. Table II.
Temperature Series
Temp., a C.
TIC
Ti02
BN
B203
TiN
1000 1300 1400 1500 1700 1950
2.4 7.0 29.4 8.70 3.26 4.80
35.3 32.5 8.53 3.50 1.73 1.8
0.0
36.1 35.5 36.1 9.12
0.0 0.0 0.0
3.98
1.81
Cr 25.7 24.7 14.1 2.56
