Main application background and overview of lithium tetraborate
Lithium tetraborate white crystal. Melting point 930℃. Slightly soluble in water, insoluble in ethanol and other organic solvents. Usually pentahydrate. Lithium pentaborate (Li2B10O16) is usually octahydrate, white powder, relative density 1.72, at 300-350℃ All crystallization water is lost. Both can be produced by the melting reaction of lithium hydroxide and boric acid. Used as enamel. .
Main applications of lithium tetraborate
Lithium tetraborate, also known as lithium pyroborate, has a molecular formula of Li2B4O7 and a molecular weight of 169.12. High-purity, high-density lithium tetraborate is a new type of temperature-compensated surface wave substrate chip and piezoelectric single crystal substrate material. It is widely used in microelectronics, digital technology, optoelectronic technology, new computers, video communication, military technology, aerospace , satellite communications, national defense technology and many other fields have extensive and important applications. For example, a lithium tetraborate piezoelectric crystal can be prepared, particularly a method for preparing a large-size lithium tetraborate piezoelectric crystal based on tri-tert-butylphosphine tetrafluoroborate. It includes pressing the previously synthesized lithium tetraborate polycrystalline material into a dense round nitropyridine columnar block, loading the block into a Pt crucible with seed crystals placed in advance, and incorporating it into the furnace. The furnace temperature is controlled at 950~1000°C, and the crucible is The descent rate is 0.1~0.6mm/h, and high-quality large single crystals with a thickness of 30~80mm, a width greater than 120mm, and a length of more than 150mm can be grown. Then through lateral processing, the larger side is used as the axis of the crystal ingot, and the smaller One side is processed in the thickness direction of the crystal rod, and a large-size lithium tetraborate piezoelectric crystal profile can be obtained. Compared with the traditional descent method, the above method overcomes the technical bottlenecks encountered when growing large-size lithium tetraborate crystals by the traditional descent method, such as difficult inoculation, easy crucible leakage, and easy crystal cracking. It adopts lateral growth and flat crucible design, which can improve The crystal growth rate thereby reduces the difficulty of crystal growth and is conducive to the industrial growth of large-sized lithium tetraborate crystals.
As early as the early 20th century, people had produced lithium tetraborate. However, due to the weak application of chemical technology at that time, lithium tetraborate was not widely used in various industries. It was not until the 1980s that it gradually began to be used in enamel. As a component of industrial glazes and greases, with the promotion of material chemistry in the later period, lithium tetraborate was gradually used as a buffer and preservative, and was also used in the development of new materials. Until the 21st century, with the advancement of steel smelting technology Innovation, lithium tetraborate is used in wavelength dispersive XRF fluorescence spectrometer, AA atomic absorption and ICP sample preparation to detect steel components. This officially announces the arrival of the new year of lithium tetraborate. However, with the continuous advancement of technology, traditional methods The produced high-purity lithium tetraborate (density is about 0.7g/㎝3) can no longer meet the needs of the testing industry. Various high-purity and high-density lithium tetraborate are becoming more and more popular.
In addition, lithium tetraborate can also be used in the field of analysis, such as detecting the main content of industrial barium carbonate. The method includes: using analytically pure lithium tetraborate as a solvent in a platinum crucible at high temperature to melt it into a sample required for a fluorometer, as a sample to be prepared. Before testing the sample, use analytically pure lithium tetraborate as the solvent and add high-grade pure barium carbonate to melt a series of standard samples to establish a standard working curve. Finally, use the working curve to detect and analyze the barium carbonate content of the sample to be tested. (1) The present invention uses analytically pure lithium tetraborate to melt the standard sample and the sample to be tested, and utilizes the stable and fast characteristics of the fluorescence meter for detection. The entire process of a sample is sample melting (automatic), detection (instrument detection), time Within 25 minutes, errors thought to be caused by chemical titration can be eliminated, while labor is liberated and scientific and technological content is improved. (2) Using analytically pure lithium tetraborate as the solvent, the melted sample is uniform and stable, and the detection results are true and reliable; (3) The elements of analytically pure lithium tetraborate are all light elements, with almost no matrix interference, and the detection results are more reliable than traditional methods high.
Main application preparation of lithium tetraborate
Method 1: A method for preparing high-purity, high-density lithium tetraborate with simplified process, low process condition requirements, low cost, easy operation, quality indicators that can reach the international advanced level, and little environmental pollution and easy control. The technical concept is as follows: Purify industrial-grade lithium hydroxide through low-temperature dissolution, filtration, evaporation concentration, cooling crystallization, centrifugal separation and other steps. The purified lithium hydroxide is dissolved in boiled pure water at a solid-liquid mass ratio of 1:2. , according to the content of lithium hydroxide in the solution, add industrial grade boric acid to the neutralization reaction (that is, add an excess of 5 to 20% of boric acid) at 105% to 120% of the stoichiometric ratio of the reaction (hereinafter referred to as “stoichiometric ratio”) ), and then through evaporation and concentration, primary drying, crushing, secondary drying, high-temperature melting, water quenching and cooling to obtain high-purity and high-density lithium tetraborate. The main reaction principle is:
The steps are as follows:
A. Purify lithium hydroxide: Dissolve the raw material industrial-grade lithium hydroxide monohydrate into pure water at a solid-liquid mass ratio of 1:5; add impurity removal reagents and filter to remove insoluble matter; the filtrate is evaporated and concentrated until visible Crystal; cool to room temperature and centrifuge to obtain recrystallized lithium hydroxide monohydrate; the impurity-removing reagent is mixed with ethylenediaminetetraacetic acid and ammonium bicarbonate in a mass ratio of 1:0.54; the ethyl alcohol in the impurity-removing reagent is The amount of diamine tetraacetic acid is the total amount of impurity metals Ca, Mg, Fe, and Pb in the raw material industrial grade lithium hydroxide monohydrate.Twice of �;
B. Neutralization ingredients: Dissolve recrystallized lithium hydroxide monohydrate in boiling pure water at a solid-liquid mass ratio of 1:2, and then add boric acid to neutralize it according to the stoichiometric ratio of 105% to 120% to obtain neutralization Mix liquid;
C. Evaporate and concentrate the neutralized solution in a stainless steel bucket until the solution turns white;
D. One-time drying: Pour the lithium tetraborate solution that has evaporated until it turns white into a stainless steel baking pan while it is hot, dry it at 100-150℃ for 3-4 hours, and then dry it at 200-240℃ 8-10h;
E. Secondary drying: crush the once-dried material until the particle size is between 10 and 60 mesh, and then dry it for a second time at -450°C for 4-5 hours;
F. Melt the twice-dried lithium tetraborate powder in an electric furnace at a melting temperature of 930-950°C and a time of 4-5 hours;
G. The molten material is poured into circulating pure water for water quenching, cooling and crystallization, and centrifugal separation to obtain high-density lithium tetraborate crystals;
H. Dry the crystals obtained in step G at 60-80°C for 1-2 hours to remove moisture from the crystal surface.
Method 2: A hydrothermal purification method of lithium tetraborate. The method includes the following steps: 1) Mix commercial anhydrous lithium tetraborate and deionized water in proportion; 2) Put the mixed sample into water In the thermal reaction kettle, seal it at a constant temperature of 90~200°C for 1~12 hours; 3) Natural cooling, solid-liquid separation, the solid phase is washed and dried to obtain purified lithium tetraborate, and the liquid phase is returned to the hydrothermal reaction kettle for circulation Use, or discharge based on purity requirements. The invention eliminates the dissolution of lithium tetraborate and the preparation process of the supersaturated solution, and does not require stirring and condensation reflux. It simplifies the process flow, the equipment is simple and easy to operate, and can be produced in batches. It effectively solves the complex process and problems of the existing purification methods. Technical problems such as high costs and unsatisfactory purification effects can greatly reduce production costs and have good industrialization prospects.
