Papers by Keyword: Metal Hydride

Abstract: Synthesis of TiFebased metal hydride-forming alloy from mixed titanium iron oxide (ilmenite, FeTiO₃) was carried out by a two-stage reduction of the latter using H₂ and CaH₂ as reducing agents. The reversible hydrogen absorption capacity of the TiFe based material was about 0.5 wt. % H, that is significantly lower than the corresponding values (~1.8 wt. % H) reported in the literature. The main reason for that was in too high amount of oxygen present in the as-prepared TiFe alloy. Thus in order to improve the hydrogen absorption of the raw TiFe, the material was further alloyed together with Zr, Cr, Mn, Ni and Cu to yield an AB₂ alloy. For the as-prepared AB₂ alloy, the reversible hydrogen sorption capacity was about 1.3 wt. % H at P = 40 bar and >1.8 wt. % at P = 150 bar, which is acceptable for stationary applications. Finally, the material was found to be superior when compared to known AB₂-type alloys, with regard to their activation and poisoning tolerance.

Abstract: This paper presents a neuro-fuzzy proportional integral derivative (PID) control technique for improving thermodynamic performance of a metal hydride (MH) reactor via heating/cooling effects generated by a thermoelectric module. The thermal behavior of the MH reactor coupled with a thermoelectric module is numerically studied by mathematical representations of genuine practical applications. It is found that the integrated system has strong nonlinearity owing to thermal characteristics. To obtain the desired performances of the MH reactor, a neuro-fuzzy PID control is used in real-time implementation. A non-linear optimization of a back-propagation technique is applied for fine-tuning the parameters of the neuro-fuzzy PID controller. The simulated results show the effectiveness of the proposed technique compared to conventional PID control.

Abstract: The charge/discharge properties of commercial metal hydride alloy powder (MmNi_3.81Mn_0.41Al_0.19Co_0.76) is improved and modified by electroless plating nickel. The effect of concentration of reducing agent (Cr), concentration of complex agent (C_c), reaction temperature (T), reaction time (t), and the amounts of MH powder per volume (CMH) on the utilization of the modified MH alloy used as the negative electrode of Ni/MH battery is systematically studied. The utilization of modified MH alloy is mainly affected by Cr, Cc and t. The utilizations of MH alloys modified with condtions of T = 70 oC, t = 90 min, Cr = 20 g l^-1, Cc = 20 g l^-1 and CMH = 20 g l^-1, respectively, are obtained to be 92.3, 64.7 and 23.6% at discharging rate of 1, 4, and 10 C. The utilizations of modified MH alloy are increased by 15.5, 45.6 and 19.8% compared with the pristine MH alloy for discharging rates of 1, 4 and 10 C, respectively.

Abstract: It Has Been Reported that the Metal Hydride, Ymn2hy (y ≤ 4.5), Wherein the Hydrogen Atoms Are Located into the Interstitial Sites, Transformed into a Complex Hydride, YMn₂H₆, Containing Complex Anions, [MnH₆]^5-. We Investigated the Possibility of Synthesizing the Complex Hydride, Y(Mn_1-xFe_x)²H₆ (x ≤ 0.3), where Mn Atoms Were Partially Substituted by Fe. As a Result, the Transformation into the Complex Hydride, Y(Mn1-Xfex)2H6, Was Successfully Realized for x ≤ 0.10 upon the Hydrogenation of the Metal Hydride, Y(Mn_1-xFe_x)₂H_y (y = 4.4 and 4.5), under 50 Mpa H₂, much Lower than the Previously Reported Value of 1 GPa. Our Structural Investigation Suggested that the Fe Substitution in Y(Mn_1-xFe_x)₂H₆ (x ≤ 0.10) Resulted in the Form of Complex Anions, I.e., [MnH₆]^5- Were Partially Substituted by [FeH₆]^4-.

Abstract: The effect of charging current, temperature, concentrations of KOH and LiOH, soaking time and temperature on the utilization of metal hydride (MH) electrode in the formation of Ni/MH battery is investigated by the conventional experimental design. The experimental results indicate that the optimal charging conditions are the charging time ratio of 9/1 with 0.1 and 1.0 C-rates. The other optimal conditions for the formation of MH electrode re 25°C, 8.02 M KOH and 0.48 M LiOH aqueous solution. The steady utilization of MH electrode is 83.52% for the soaking temperature of 45°C and the soaking time greater than 24 h, respectively. According to the Taguchi's orthogonal arrays, the relationship between the utilization of metal hydride electrode (y) and the formation factors is obtained to be y = 75.52 - 6.58A + 3.98C + 5.09E + 6.71F - 1.32AC + 2.57BC + 5.62E² - 10.67F² where A, B, C, E and F are the charging current, the charging temperature, the concentration of KOH in the electrolyte, the soaking time and temperature, respectively. Under the optimal formation conditions, the utilization of MH electrode is increased from 87.25% to the steady value of 98.50% by increasing the charging/discharging cycle from 1 to 4.

Abstract: The synthesis and characterizations of Fe-Ti and Mg-Ti-Fe alloys with the atomic ratio of Fe:Ti = 2:1 and Mg:Ti:Fe = 2:5:6 prepared by mechanical alloying technique in toluene solution and measurement the hydrogen absorption properties of the yields have been performed. The Fe-Ti and Mg-Ti-Fe elemental powders are milled with the milling time of 30 h, in a Mixer Mill, type PW 700i high energy ball mill. The milled specimens are analyzed with an X-ray diffractometer, Philip, type PW 1710, using Cu as the anode tube and l = 1.5406 Å. Qualitative and quantitative analyses are determined using Rietveld method developed by Fuji Izumi. The microstructure of the specimens after milling and hydriding are identified with a scanning electron microscope, Philip type 550. The refinement analysis of the x-ray diffractions results for Fe-Ti alloy shows that before milling the specimen consists of Ti and Fe phases, and after 30 h of milling new phases identified as FeTi and Fe₂Ti are formed. In case of Mg-Ti-Fe alloy after 30 h of milling new phases identified as Fe₂Ti and FeTi compounds are formed with the absence of Mg-Ti and Mg-Fe. Quantitative analysis of the milled powders shows that the mass fractions of FeTi and Fe₂Ti phases are correspondingly 22.5 wt% and is 21.1 wt%, and the rest is Fe. The disappearance of Mg peaks after milling is suggested from the transformation of the crystallite into amorphous state. On hydriding at room temperature, the milled Fe-Ti and Mg-Fe-Ti powders are transformed into b-Ti₄FeH_8.5, Fe and TiH₂. Considering the high hydrogen capacity and the low hydriding temperature of the Mg-Ti-Fe alloy compared to those of Fe-Ti alloy, the Mg-Ti-Fe alloy could be promoted as a new hydrogen storage material.

Abstract: Mg-based nanostructured materials with a composition of Mg₈₅Ni_15-xM_x (M=Y, La, or Pd) have been fabricated by proper alloying additions and controlling the crystallization process of melt spun metallic glass ribbon. XRD suggests that the average crystallite sizes range from 100 nm in the binary materials to <30 nm in the ternary alloys. Hydrogen absorption/desorption measurements show improved properties compared to nanocrystalline alloys fabricated using other processing strategies. Surface treatment of the binary and Pd-containing ribbons by ball milling or submersion in aqueous NH₄⁺ allows the materials to be activated at 473 K, significantly lower than conventional Mg-based hydrogen storage materials. Y and La additions improve the maximum storage capacity. Absorption kinetics are also improved the materials is alloyed with La, while Y slows the reaction kinetics. Some degradation in storage capacity is observed when the materials are exposed to a cyclic absorption/desorption process, likely due to microstructural coarsening. The Mg₈₅Ni₁₀Pd₅ composition fully absorbs and desorbs ≈5 wt. % H at 473 K, while other bulk Mg-based materials require temperatures in excess of 573 K.

Abstract: Ti45Zr30Ni25RE3 (Y, La) alloys were prepared by melt-spun at wheel velocities of 20 m s–1. Ti45Zr30Ni25 and Ti45Zr30Ni25La3 were composed of I-phase, amorphous and Laves phases. Ti45Zr30Ni25Y3 consisted of amorphous phase and I-phase. The addition of La and Y caused the decrease of maximum discharge capacity and the increase of cycling stability, which should be ascribed to the change of various phase abundant. The high-rate dischargeability of Ti45Zr30Ni25 alloy electrode was better than that of Ti45Zr30Ni25Y3 and Ti45Zr30Ni25La3 alloy electrode, which was attributed to the better electrochemical kinetics.

Abstract: Perturbed Angular Correlation (PAC) measurements were performed at room temperature on samples of Hf7Ni10 and of Hf7Ni10 combined with TiV0.8Cr1.2, and at temperatures in the range from 17 K to 350 K in a concentrated hydride of the combined alloy. The PAC results show that the Hf7Ni10 intergranular phase becomes amorphous in the combination process. The results for the hydride composite show in the Hf7Ni10 phase the formation of a stable interstitial hydrogen state below 100 K and a smooth rearrangement of the hydrogen atoms position above 100 K,corresponding to a slow diffusion movemnet of a short-range nature. A second phase transition is observed at around 300 K, presumably to aphase precursor of the hydrogen desorption of the hydride.