The Improvement Effects of NaH_(2)PO_(4) and KH_(2)PO_(4) on the Properties of Magnesium Oxysulfate Cement

Sodium dihydrogen phosphate (NaH_(2)PO_(4)) and potassium dihydrogen phosphate (KH_(2)PO_(4)) were selected as additives for magnesium oxysulfate (MOS) cement.The phase composition and the microstructure of MOS cement were characterized using X-ray diffraction (XRD),thermogravimetric analysis (TG-DSC),Flourier transform infrared spectroscopy (FT-IR),mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM).It is found that both NaH_(2)PO_(4) and KH_(2)PO_(4) lead to an increase in the compressive strength and an improvement in the volume stability of MOS cement.The XRD,MIP and SEM results show that the addition of NaH_(2)PO_(4) or KH_(2)PO_(4) does not change the phase composition of MOS cement but promotes the formation of strength phase of 5Mg(OH)_(2)·MgSO_(4)·7H_(2)O (5·1·7 phase).This phase brings a considerable improvement in the microstructure of MOS cement,which has a positive effect on the properties of MOS cement.

Preparation and properties of magnesium oxysulfate cement and its application as lost circulation materials

Loss of drilling fluids in large porous and fractured zones inevitably up-regulates the overall cost of drilling.As a type of acid-soluble cement,magnesium oxysulfate(MOS)cement is arousing huge attention for the less hygroscopic nature and less damaging to steel casings compared with magnesium oxychloride(MOC)cement.The present study developed MOS cement as a fast setting,high strength and acid-soluble lost circulation material to reduce the problem of losses.As suggested in this study,a higher strength of MOS cement at 70℃could be achieved by elevating M_(g)O/MgSO_(4)·7 H_(2)O molar ratio or downregulating H_(2)O/MgSO_(4)·7 H_(2)O molar ratio.Boric acid and borax could act as effective retarders.Plugging slurry based on MOS cement could effectively block the simulated porous loss zones exhibiting a diameter from 1.24 mm to 1.55 mm,as well as the fractured loss zones with a width from 2 mm to 5 mm and bearing a pressure difference up to 8 MPa.Permeability recovery test demonstrated that it facilitated future oil and gas production.The successful field application in the Junggar Basin,Xinjiang,China verified the significant plugging effect of MOS cement for severe loss problems.

Effects of the properties of Mg(OH)_(2)precursor on the hydrothermal synthesis of magnesium oxysulfate whiskers

Magnesium oxysulfate(MOS)whiskers are commonly synthesized through a dissolution-precipitation mechanism,wherein Mg(OH)_(2)dissolves to form Mg(OH)_(6)^(4−),followed by reactions with SO_(4)^(2−)and H_(2)O to yield MOS whiskers.However,the impact of Mg(OH)_(2)precursor properties on the formation process of MOS whiskers has been insufficiently explored,and sector-like and needle-like morphologies were both observed in previous studies.In this study,we systematically investigated how the properties of Mg(OH)_(2)precursors influenced the crystalline structure and morphology of MOS whiskers.Under various experimental conditions,MgSO_(4)·5Mg(OH)_(2)·2H_(2)O(152MOS)whiskers were consistently obtained,regardless of Mg(OH)_(2)morphology and size.The size of Mg(OH)_(2)emerged as a critical factor in shaping the morphology of 152MOS whiskers.Smaller-sized Mg(OH)_(2)(≤106±37 nm)favored the formation of sector-like whiskers,while larger-sized Mg(OH)_(2)(≥206±98 nm)encouraged the development of needle-like whiskers.This distinction was attributed to the slower dissolution rate exhibited by larger-sized Mg(OH)_(2),maintaining a smaller number of 152MOS nuclei and promoting the growth of needle-like whiskers instead of the aggregation of 152MOS nuclei into sector-like structures.In addition,the effects of the molar ratio of Mg^(2+)to SO_(4)^(2−)and hydrothermal temperature were also studied.The average length and diameter of the needle-like whiskers prepared with Mg(OH)_(2)of 331±145 nm under optimized conditions were 77±32 and 0.39±0.10μm,respectively.This study presented an effective strategy for controlling the morphology of 152MOS whiskers.

Mechanical properties and flame retardancy of surface modified magnesium oxysulfate(5Mg(OH)_(2)·MgSO_(4)·3H_(2)O)whisker for polypropylene composites

Magnesium oxysulfate(MOS)whisker is considered as a promising inorganic material recently attracting a great attention for being used as a reinforcing filler for polymer composites due to high aspect ratio and extremely-low bulk density.In this study,the MOS was treated with 3-methacryloyloxypropyl-trimethoxy silane(MPS)via sol-gel condensation reactions,which successfully allowed melt mixing with polypropylene(PP)up to 30 wt%of MOS.The tensile strength at yield and modulus of the MOS/PP composites were substantially increased by 50.8%and 362%,respectively,when compared with the pristine PP.As a novel finding,the flame retardancy of MOS was proved by identifying water evolution at elevated temperatures giving out 9 wt%of water in 250-320℃and 14 wt%in 350-420℃in two steps.This work demonstrated that the MOS could be an excellent filler for PP not only increasing the mechanical properties in a great extent but also imposing flame retarding capability.

Surface modification mechanism of magnesium oxysulfate whiskers via wet chemical method

Magnesium oxysulfate whisker（MOSW） was produced using magnesite and sulfuric acid as raw materials by hydrothermal method and further modified by taking zinc stearate as modifier via wet chemical method.The infiuences of the amount of modifier, slurry concentration, modification duration, modification temperature and the stirring rate on the surface modification were investigated. The effects of surface modification in functional groups, morphology and electron binding energies of surface elements of MOSW were characterized by Fourier transform infrared spectroscopy（FT-IR）, scanning electron microscopy（SEM） and X-ray photoelectron spectroscopy（XPS）. The mechanism of modification was analyzed by studying the microstructure model of the surface of MOSW, which was modified by zinc stearate. The results show that the coordination is generated by the Mg element and O in carboxylic ion of modifier, and the chemical bond could be obtained by modification. Moreover, the surface of MOSW bonds the molecules of zinc stearate, and it becomes rough. Then, the hydrophobicity of MOSW is also improved significantly. In addition, the 1s electron binding energies of Mg and O on the surface of MOSW decrease by1.2 and 0.2 eV, respectively.

Growth Habit of the Basic Oxysulfate Magnesium Whisker

The growth habit of the basic magnesium oxysulfate whisker was investigated based on the theoreticalmodelof anion coordination polyhedron growth units.It is found that typicalbasic magnesium oxysulfate whisker growth is consistent with anion tetrahedralcoordination incorporation rules.The growth units of basic magnesium oxysulfate whiskers are [Mg-（OH）_4]^（2-） and HSO_4^-.[Mg-（OH）_4]^（2-） is the favorable growth unit and whisker growth is in the direction of the [Mg-（OH）_4]^（2-） combination.A plurality of [Mg-（OH）_4]^（2-） s combine and become a larger dimensionalgrowth unit in a one-dimensionaldirection.Then HSO_4^- and larger dimensionalgrowth units connect as basic magnesium sulfate whiskers,according to the structuralcharacteristics of the basic magnesium sulfate whisker,which can guide the synthesis of magnesium hydroxide whisker.

Synthesis and characterization of superhydrophobic magnesium oxysulfate whiskers

Superhydrophobic materials have attracted much attention for their special wettability.In this study.magnesium oxysulfate(MOS)whiskers were surface modified by vinyltrimethoxysilane(VTMS)and prepared as superhydrophobic materials,which are expected to be widely used in self-cleaning,corro-sion prevention,and oil-water separation.The factors of silane concentration,hydrolysis time,reaction temperature,and reaction time were investigated.The superhydrophobic Mos whiskers were synthe-sized.SEM and XRD turned out that there were no apparent changes in the morphology and crystalli-zation behavior of whiskers before and after modification,while the surface was uniformly coated with a layer of non-crystal material,and the surface of the whiskers employed a chemical bond Si-O-Mg covalently connected.The thermogravimetric analysis ultimately demonstrated that surface modification was beneficial to the improvement of the thermal stability of MoS whiskers.Superhydrophobic MoS whiskers showed good compatibility with organic solvents through oil-water separation experiments,and demonstrated excellent self-cleaning performance.The methodology for the surface treatment of Mos whiskers to prepare superhydrophobic whiskers in this work may be extended for other whiskers or fillers,which may be promising for the preparation of superhydrophobic materials.

Synthesis and characterization of MgSO_4·5Mg(OH)_2·2H_2O flake powders

Magnesium oxysulfate （MgSO4·5Mg（OH）2·2H2O） flake powders with an average diameter of 2 ~tm and a thickness of 0.052 μm were prepared using magnesium sulfate and sodium hydroxide as raw materials by hydrothermal synthesis process. The composition, morphology and structural features of the hydrothermal products were examined with X-ray powder diffraction （XRD）, scanning electron microscopy （SEM） and Fourier transform infrared spectroscopy （FTIR）. The experimental results indicate that in the conditions of n（NaOH）/n（MgSO4） of 1.25, the dosage of w（Na3PO4） crystal additives of 1.0% w（MgSO4）, stirring for 5 h at 180 ℃, the morphology of MgSO4·5Mg（OH）2·2H2O products is flaky and laminar, which is a kind of complex magnesium singlecrystal. The recycling of MgSO4 mother liquor was also investigated to make a full use of the materials and reduce disposal. The results prove that there is no adverse effect on the yield and purity of the products.

Carbon-negative cement-bonded biochar particleboards

Biochar from bio-waste pyrolysis presents excellent CO_(2) sequestration capacity.This study innovated the design of cement-bonded particleboards utilizing a substantial amount of 50-70 wt.%pre-soaked biochar to render the products carbon-negative.We investigated the roles of biochar in magnesium oxysulfate cement(MOSC)system and demonstrated good mechanical and functional properties of biochar cement particleboards.In the presence of biochar,the amounts of hydration products were enriched in the cement systems as illustrated by the thermogravi-metric analyses(TGA)and X-ray diffraction(XRD).We further incorporated supplementary cementitious materials(SCMs)and generated 5 Mg(OH)_(2)⋅MgSO_(4)·7H_(2)O(5-1-7)phase in the MOSC system.As a result,our designs of biochar particleboards satisfied the standard requirements for flexural strength(>5.5 MPa)and thickness swelling(<2%).Moreover,our biochar particleboards presented a low thermal conductivity as the biochar pores disrupted thermal bridging within particleboards.We illustrated that the high dosage ratio of biochar could significantly offset the CO_(2) emissions of the particleboards(i.e.,carbon-negative)via life cycle assessment.Noticeable economic profits could also be accomplished for the biochar particleboards.For instance,the 50BC-MOSC bonded particleboard(with 50 wt.%pre-soaked biochar as aggregate,50 wt.%MOSC as binder)with promising mechanical properties could store 137 kg CO_(2) tonne^(−1) and yield an overall economic profit of 92 to 116 USD m^(−3) depending on the carbon prices in different countries.In summary,our new designs of carbon-negative biochar particleboards could curtail carbon emissions in the construction materials and promote the realization of carbon neutrality and circular economy.