Ten years ago, Donald Sawdouil, a professor of materials chemistry at the Massachusetts Institute of Technology, invented high-capacity liquid metal batteries with his students. His team has now discovered the new chemical ingredient, calcium, which makes the technology cheaper and more usable, opening the way for large-scale applications of liquid metal cells.
Their latest research, published in the journal Nature Communications, shows that calcium, a rich and inexpensive chemical, can be an important starting point for three-layer liquid metal cells.
Multi-dimensional representation, this discovery is unexpected, because the properties of calcium make it seem almost impossible to become a liquid metal battery raw materials. On the one hand, calcium dissolves easily in salt solutions. However, one of the main features of liquid metal cells is that three of its key components form separate layers; on the other hand, calcium has a high melting point and, if it is used Raw materials, liquid metal batteries have to work at 900 degrees Celsius temperature.
However, this seemingly the most playful material has aroused the interest of researchers. Because cheap calcium can greatly reduce the cost of liquid metal batteries, and its inherent high pressure performance makes it a good "candidate" for liquid metal battery negative electrode layers.
To solve the problem of calcium melting point, researchers have alloyed calcium with magnesium, which is inexpensive and has a melting point well below calcium. The combination of the two reduces the original melting point by 300 degrees Celsius while still maintaining the high pressure performance of calcium.
Another innovation is in the liquid metal battery that is the middle layer of the electrolyte design. When the battery is in use, the ions move through the electrolyte, and as they move, the current passes through the wires that connect the poles of the liquid metal cell.
The newly designed electrolyte contains a mixture of lithium chloride and calcium chloride, and the calcium-magnesium alloy as the negative electrode layer is hardly dissolved in this electrolyte. This design also brings a new surprise. In general, in powered batteries, swimming ion is acting alone. For example, in lithium-ion batteries, only lithium ions swim, and only sodium ions swim in sodium-sulfur batteries. But researchers found that in the latest design, many kinds of ions move in the electrolyte, increasing the overall energy output of the battery.
Sadow said that this fortuitous discovery will open a new path for battery design. "As time goes on, you can explore more elements of the chemical's periodic table to find better battery formulations," he said.
Tungsten carbide roller has characteristics of good wear resistance, high temperature red hardness, thermal fatigue resistance and thermal conductivity and high strength , have been widely used in high-speed wire rod, bar, rebar, seamless steel tubes, etc. Domestic production of tungsten carbide roller materials mostly WC- Co, WC- Co- Ni- Cr two series, and the content of Co, Co- Ni - Cr is in the range of 6wt% ~ 30wt%. From the use of perspective, tungsten carbide rollers has good mechanical properties, its flexural strength up to 2200 MPa or more, shock toughness up (4 ~ 6) × 10^6 J/ m^2, Rockwell hardness (HRA) is up to 78 to 90, widely in the high-speed wire rod rolling process, which is much higher than single-slot chilled cast steel or high speed steel rolls.Tungsten carbide is made of Tungsten Carbide Powder and binder phase (such as drilling, nickel, etc.), and then pressing and sintering, regardless of the conditions under cold rolled or hot rolled has excellent wear resistance, tungsten carbide rollers has been widely used in pre-finishing mill and finishing of high-speed wire rod currently. On the performance of tungsten carbide roller in hot-rolling wire rod , the material must meet the following requirements:
1. Sufficient anti-fracture strength;
2. Good abrasion resistance;
3. The smooth surface finish;
4. Excellent corrosion resistance, thermal fatigue, thermal cracking performance.
Tungsten carbide roller rings can working in bad conditions , small profile rolling (especially rebar rolling) process conditions is harsher than the high-speed wire rod, and therefore corresponds to the profile rolling ,tungsten carbide rollers recommend using high binder phase carbide.
Tungsten carbide roller material design
Pre-finishing all vehicles roller should ensure its high toughness, strength, rigidity and thermal conductivity, followed before considering its wear resistance. When designing each vehicles roller, pre-finishing materials should choose carbide grades of Co, Co- Ni- Cr binder content is high (greater than or equal to 25wt%) , requiring an average WC grain size of coarse (5μm ~ 6μm), to obtain a higher shock toughness, proper strength and hardness. For the finishing of the roller movements, particularly the last two rollers of the finish rolling, which suffered load is small, and high relative velocity of the material to be pressed (80 m / min ~ 120 m / min). In this case, the wear resistance of the roller to be the most important requirements, and must ensure the strength , timpact toughness and hardness of a reasonable match, so the binder of Co / Ni content ratio and the average grain WC control of particle size and other factors must have greater control in front of different pre-finishing rolling roll.
Tungsten carbide roller category
According to the structure of tungsten carbide rollers, it can be divided into solid tungsten carbide roller and composite tungsten carbide roller. Solid tungsten carbide rollers have been widely used in pre-finishing and finishing stands high speed wire rod mill (including fixed reducing the rack, pinch roller rack). Composite tungsten carbide roller is made of cemented carbide and other materials, and it can be divided into tungsten carbide composite roll rings and solid tungsten carbide composite roller. Tungsten carbide composite roll rings mounted on the roller shaft; solid tungsten carbide composite roller will be directly cast in the roll axis to form a whole, a large load is applied to the rolling mill.
Tungsten carbide roller production process control
Tungsten carbide rollers produced by powder metallurgy method, the key to its process control is the chemical composition of the material and the mixture was prepared, pressed molding, sintering and deep processing and other preparation process parameters.
1. Preparation of starting material (WC focus quality): As the WC raw material and quality control of the use of different levels of quality may fluctuate, resulting in adverse effects on microstructure.
2. Preparation of the mixture: Mixture preparation is the key to the production process of the roller, the roller of failure modes - trachoma, mainly generated by this procedure.
3. Pressing: roller pressing is an important process of the roller mill.
4. Sintering: roller sintering is to determine the final quality of the roller production processes, use of advanced low-pressure sintering technology, HIP sintering technology can greatly improve the performance of roller.
5. Deep processing: deep processing rollers have a greater impact on the quality and accuracy of the roller surface.
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