Study On The Mineralogical Characteristics And Modification As Well As Application Of The Tibet Hydromagnesite

Hydromagnesite?Mg₅?CO₃?₄?OH?₂ · 4H₂O?is a naturally produced carbonate mineral with a wide range of distribution in the world,but the large sedimentary water magnesite deposits which has industrial exploitation value are very rare.In the late 1950 s,Zheng Mianping discovered the minerals for the first time in the Bangor Lake area in northern Tibet,and the study shows that the hydromagnesite in this area belongs to the lake sedimentary chemical formation.At the same time,because of its wide distribution,large reserves,and often directly exposed to the surface,suitable for direct open-air mining use.However,in China,the relevant theoretical and applied research of this rich mineral resources is not much enough.In the mineralogy research,in addition to Zheng,who had researched its mineral external morphology,chemical composition,nature,crystal development characteristics of mineralogical characteristics of a certain study in the late 1980 s,the current domestic has not yet seen other scholars for the mine carries out public reports on related mineralogy studies.In addition,in recent years,some countries abroad with their own hydromagnesite thermal decomposition process of deepening understanding of the natural hydromagnesite has been a substitute for aluminum hydroxide,magnesium hydroxide minerals flame retardant filler used in the field of polymer flame retardant.However,due to the current lack of research on the nature and mechanism of thermal decomposition of the mine,it is rarely seen in the field of inorganic flame retardant materials with close relationship with its thermal decomposition properties.And with the future application development is closely related to the surface of the powder work.Therefore,in view of the above research situation,this paper has carried on the detailed mineralogical study,the thermal decomposition characteristic and the heat treatment research to the hydromagnesite in the Bangor Lake area in Tibet,the surface modification of the powder and the hydromagnesite/EVA flame retardant composite materials research,made the following research results :.The chemical composition and mineral composition,mineral assemblage and typical characteristics of natural magnesite in Tibet were studied by using polarizing microscope,scanning electron microscope,transmission electron microscopy,electron probe and MLA mineral analysis and detection system.The results show that:?1?The crystal particles of the magnesite are very small,mainly in mud crystal-micro-muddy crystal,and most of the observed particles are between 4 and 20?m.Patchy,lenticular dense aggregates,and at the edge of the pores,common aragonite distribution.?2?The observed form of mud crystals observed under polarized microscope is actually a cluster of clusters of magnesite developed into lamellar structures.The monomer is in the form of a single plate,and the plane is?001?.The crystal face with characteristic oblique stripes is?001?.?3?The magnesite is mainly composed of carbonate magnesite,aragonite,dolomite and other carbonate minerals,silicate minerals?muscovite,biotite,chlorite,talc,plagioclase?and Oxide minerals?quartz,goethite,titanium magnetite?and other associated minerals are few.?4?In hydromagnesite,the most important symbiotic relationship is the hydromagnesite-aragonite-dolomite symbiosis.The above three minerals are disseminated symbiotic relationship,hydromagnesite particles the most coarse,dolomite particles the smallest,the use of physical processing methods to remove the aragonite,dolomite more difficultThe thermal decomposition process,gas product and solid product of water magnesite in Bangao Lake area,Tibet,were carried out by means of thermogravimetry-differential scanning calorimetry,thermogravimetry-mass spectrometry and in-situ X-ray diffraction.The results show that the total endotherm of water magnesite is about 889.8 J/g in the temperature range of 150⁶50?,and the crystal water is removed at 350 ? to produce carbonate-containing amorphous magnesium And then remove the structural water and remove the carbonate at 350 550? to release the CO₂-generated periclase.The H₂O and CO₂ escape peaks of the water magnesite at different temperature intervals may be present in the crystal structure Complex hydrogen bonding systems and different carbonate structures.?1?With the increase of calcination temperature,the phase is mainly composed of water magnesite?<200??,amorphous magnesium?MgO?,and the calcined temperature will be affected by the calcination temperature.The compounds?200 to 300??were converted to magnesite?>400??.Accompanied by the escape of gas,the appearance has also undergone significant changes.?2?When the calcination temperature reaches 400?,due to the destruction of crystal structure and the formation of nano-scale activated magnesia,with a typical mesoporous structure,the specific surface area of the largest?132.445 m²/g?,balanced moisture up to 14.05%,and the development of green environment-friendly humidity-functional materials.The surface modification formula and process of the water magnesite ore powder were studied by using a single surface modifier and composite surface modifier.The water magnesite / EVA composites prepared by modified magnesite.The results show that?1?The silane coupling agent SCA-1113 has a good effect in the modification of the single modifier,and the tensile strength of the water magnesite / EVA composite material can be improved to 11.00 Mpa,elongation at break increased to 224.90%,oxygen index unchanged at 28%,UL-94 level increased to V-0 level.?2?The modifier SCA-1113 / F-2,SCA-1113 / SCA-1613 could increase the tensile strength of the composites to 11.60 Mpa and 11.80 Mpa when the mass ratio was 2: 1,the elongation at break increased to 193.80% and 226.10%.?3?The single modifier and composite modifier have little effect on the oxygen index of magnesite / EVA composites.When the stearic acid is modified or used in a large amount,the flame retardant effect of the composite material is reduced.?4?The SEM images of the flame-retardant composites show that the dispersibility of the magnesite powder in the EVA matrix is improved when the composite modifiers SCA-1113 / SCA-1613 and SCA-1113 / F-2 are used,and reduce the defects in the composite material.?5?Under the condition of dry surface modification,when the composite modifier SCA-1113 / SCA-1613 is used,the modifier dosage and modifier ratio will significantly affect the mechanical properties of the composites.?6?Considering the mechanical properties and flame retardancy of water magnesite / EVA composites,the optimum conditions for the dry surface modification of water magnesite powder using SCA-1113 / SCA-1613 composite modifier are : The amount of modifier is 2.10 wt.%,SCA-1113: SCA-1613?wt%?= 2: 1,the modification temperature is 100?,the modification time is 30 min.The tensile strength of modified EVA composite flame retardant material reached 11.9 MPa 12.1 MPa,the elongation at break reached 232.0% 250.8%,and the oxygen index reached 28%.?7?Composite modifier SCA1613 / SCA1113 modified water magnesite powder used in EVA cable material expansion test results: EVA cable flame retardant insulation material tensile strength of 11.2MPa,elongation at break 274.9%,oxygen index of 30 %,Flame retardant?vertical combustion?close to UL-94 standard V-0 level,volume resistivity 4.03 × 10¹²? · cm,excellent aging resistance.The tensile strength is similar to that of the flame retardancy test,and the elongation at break is better than that of the laboratory test.?8?Modified water magnesite powder compared with the active magnesium hydroxide,filled with EVA cable material mechanical and processing performance test results are similar,and flame retardant?oxygen index,vertical combustion?better.Compared with the activated aluminum hydroxide,the decomposition temperature of the two is close.In the same formula,the flame resistance and insulation properties of the modified magnesite powder and the tensile strength of the filled EVA cable are better than that of aluminum hydroxide.In addition,the modified water magnesium powder filled EVA flame retardant sheath material anti-aging performance is better than aluminum hydroxide and magnesium hydroxide.